KOLOID TANAH & MINERAL LIAT Foto:smno.kampus.ub.sept2012

Penyusun Tanah Mineral Mineral Primer: Kuarsa Mineral Sekunder: Liat silikat Udara: Mineral: 20-30% 45% Air: 20-30% Organik 5% Pori: 50% Padatan: 50%

MINERAL Mineralogi: cabang ilmu geologi yg mempelajari kerak bumi dari sudut pandang MINERAL MINERAL = “minera” , yang artinya “BIJIH” “Mineral” adalah komponen batuan yg mempunyai komposisi kimiawi tertentu dengan sifat-sifat fisik yg khas (warna, kekerasan, kilap, dll). Mineral ini merupakan produk alami dari proses kimia-fisika di dalam kerak bumi. AMORF dan KRISTALIN Amorf: bahan padatan yg dicirikan oleh tidak adanya struktur yg tegas, mempunyai sifat fisik seragam pd semua arah (isotropik) Kristalin = kristaloid: bahan padatan yg mempunyai struktur kristal tertentu, sifat-sifatnya ditentukan oleh (1) jumlah unit struktural (atom , ion, atau molekul) yg diikat bersama oleh gaya elektrostatika dlm suatu pola tertentu, (2) perbandingan ukuran unit-unit strukturalnya, dan (3) ikatan kimia antara atom-atom. KOLOID : “COLLA” = perekat, lem adalah sistim dispersi yg heterogen terdiri atas fase terdispersi dan medium dispersi. Fase terdispersi merupakan partikel halus ( 1 - 100 mU) tersebar merata dlm medium dispersinya. Koloid ada dua macam, yaitu GEL (partikel terdispersi dominan) dan SOL (medium dispersinya dominan)

KLASIFIKASI MINERAL Divisi I : Unsur-unsur alami dan senyawa inter-metalik Divisi II : Karbida, Nitrida, dan Fosfida Divisi III : Sulfida, Garam Sulfon, dan senyawa turunannya Divisi IV : Halida (Fluorida; Klorida, Bromida, dan Iodida) Divisi V : Oksida (Oksida sederhana, Hidroksida) Divisi VI : Garam oksigen (Iodat, Nitrat, Karbonat, Sulfat, Kromat, Molibdat, Fosfat, Arsenat, Borat, dan Silikat) Klasifikasi Silikat: 1. Neso-Silikat : Tetrahedra SiO4 berdiri sendiri-sendiri 2. Soro-silikat : dua SiO4 berpolimerisasi 3. Siklo-silikat : Tetrahedra SiO4 membentuk rantai siklis 4. Ino-silikat : Tetrahedra SiO4 membentuk lembaran kontinyu 5. Filo-silikat : Polimerisasi SiO4 membentuk struktur tiga dimensi 6. Tekto-silikat : Tetrahedra SiO4 berpolimerisasi membentuk struktur tiga dimensi yang kompleks.

KELOMPOK OKSIDA 1. Dalam pembentukannya diperlukan oksigen dari udara 2. Ikatan ionik di antara unit-unit strukturalnya 3. Struktur kristal mengandung O (oksida) dan OH- (hidroksida) 4. Dlm struktur kristalnya, kation inti dikelilingi oleh anion oksigen dan hidroksil HEMATIT : Fe2O3 Komposisi kimia : mengandung 70% Fe, campurannya Ti dan Mg Struktur kristal : Agak kompleks Habit : Pipih, Rhombohedral Warna : Hitam besi hingga kelabu baja Kekerasan : 5.5 - 6.0; Rapuh Berat jenis : 5.0 - 5.2 Sifat diagnostik : Warna goresannya merah, sangat keras, tidak magnetik Genesis : Dibentuk dalam suasana oksidasi dlm endapan dan batuan MAGNETIT : FeFe2O4 Komposisi kimia : FeO 70%, Fe2O3 69%, kadar Fe 72.4% Sistem : Kubik, simetrik, heksoktahedral Habit : Oktahedral Warna : Hitam besi Kekerasan : 5.5 - 6.0; Rapuh Berat jenis : 4.9 - 5.2 Sifat diagnostik : Magnetik kuat, Warna goresannya hitam Genesis : Dibentuk dalam suasana reduksi dlm endapan bijih dan batuan

KELOMPOK OKSIDA KUARSA: SiO4 1. Ada tiga polimorfiknya: Kuarsa, Tridimit, Kristobalit 2. Modifikasinya diberi awalan alfa, beta 3. Ion inti Si4+ dikelilingi oleh empat anion oksigen O= yg menempati titik sudut tetrahedron KUARSA : SiO2 Komposisi kimia : Sesuai dg formulanya Struktur kristal : Agak sederhana . Habit : Heksagonal Warna : Tidak berwarna, putih susu, kelabu Kekerasan : 7.0 Berat jenis : 2.5 - 2.8 Sifat diagnostik : Bentuknya yg khas, keras, tdk mempunyai belahan Genesis : Bentuk kristal Kuarsa

1. Senyawa logam dengan OH- : Hidrat atau hidroksida KELOMPOK HIDROKSIDA 1. Senyawa logam dengan OH- : Hidrat atau hidroksida 2. Struktur kristalnya berlapis 3. Heksagonal BRUSIT : Mg(OH)2 Komposisi kimia : MgO 69%; H2O 31%; campurannya Fe dan Mn Struktur kristal : Berlapis Habit : Tabuler tebal Warna : Putih, kadangkala kehijauan Kekerasan : 2.5 Berat jenis : 2.3 - 2.4 Sifat diagnostik : Mudah larut dlm HCl HIDRARGILIT : Al(OH)3 Komposisi kimia : Al2O3 65.4%, H2O 34.6% Sistem : Monoklin, Simetri prismatik Struktur kristal : Berlapis, lembaran Al dijepit oleh dua lembaran hidroksil Habit : Tabuler-heksagonal Warna : Putih, sedikit kekelabuan Kekerasan : 2.5 - 3.5 Berat jenis : 2.43 Sifat diagnostik : Belahan sgt baik, kilap kaca, ringan

KELOMPOK KARBONAT KALSIT : CaCO3 MAGNESIT : Mg(CO3 ) Komposisi kimia : CaO 56%; CO2 44%; campurannya Mg, Fe dan Mn sampai 8% Struktur kristal : spt NaCl Habit : Skalenohedral Agregat : Kalsit yg kompak disebut “Marble”, Sdg Batukapur bersifat kriptokristalin kompak Warna : umuknya tdk berwarna, atau Putih susu Kekerasan : 3.0; Rapuh Berat jenis : 2.6 - 2.8 Sifat diagnostik : Bereaksi dg keras bila diberi HCl MAGNESIT : Mg(CO3 ) Komposisi kimia : MgO 47.6, CO2 52.4% Sistem : Trigonal, Simetri , ditrigonal skalenohedral Struktur kristal : Analog dg kalsit Habit : Umumnya rhombohedral Warna : Putih dg becak kekuningan atau kekelabuan Kekerasan : 4.0 - 4.5 ; Rapuh Berat jenis : 2.9 - 3.1 Sifat diagnostik : Larut asam bila dipanaskan, kondisi dingin tdk bereaksi dg HCl DOLOMIT : CaMg(CO3)2 Komposisi kimia : MgO 21.7%, CaO 30.4%, CO2 47.9% Sistem : Trigonal, Simetri rhombohedral Warna : Putih kelabu Kekerasan : 3.5 - 4.0 ; Rapuh Berat jenis : 1.8 - 2.9 Sifat diagnostik : Kondisi dingin lambat bereaksi dg HCl

KELOMPOK FOSFAT VIVIANIT : Fe3(PO4)2 . 8H2O APATIT : Ca5(PO4)3Cl,OH,F Sistem : Monoklinik Habit : Kristal prismatik Warna : tidak berwarna Kekerasan : 1.5 - 2.0 Berat jenis : 2.68 Sifat diagnostik : Biasanya berubah menjadi biru atau hijau , belahan jelas, larut asam nitrat menghasilkan endapan fosfat yg kuning APATIT : Ca5(PO4)3Cl,OH,F Sistem : Heksagonal Habit : Kristal dlm batu kapur prismatik Belahan : Tidak jelas Kekerasan : 5.0 ; Rapuh Berat jenis : 3.1 - 3.2 Warna : Hijau, hijau kebiruan, hijau kelabu, biru, violet Sifat diagnostik : Bentuk kristalnya, warnanya , lareut dlm asam TURQUOIS : CuAl6(PO4)4(OH)8. 4H2O Sistem : Triklinik Habit : Kristal jarang ditemukan, biasanya masif Warna : Putih kelabu Kekerasan : 5 - 6.0 Berat jenis : 2.6 - 2.8 Warna : Biru langit, Hijau kebiruan Sifat diagnostik : Warna biru yang khas

KELOMPOK FELDSPAR SANIDIN= ORTOKLAS : KAlSi3O8 MIKROKLIN : KAlSi3O8 Sistem : Monoklinik Habit : Kristal prismatik pndek, agak pipih atau memanjang Warna : umumnya tidak berwarna Kekerasan : 6.0 Berat jenis : 2.56 Sifat diagnostik : Kilap kaca MIKROKLIN : KAlSi3O8 Sistem : Triklinik Habit : Serupa dg Ortoklas Belahan : Sempurna, baik Kekerasan : 6.0 Berat jenis : 2.56 Warna : Putih, cream, merah muda Sifat diagnostik : Sifat optik PLAGIOKLAS : (Ca,Na)(Al,Si) AlSi2O8 Sistem : Triklinik Habit : Kristal biasanya berbentuk batang Warna : Putih atau kelabu Kekerasan : 6.0 Berat jenis : 2.62 - 2.76 Sifat diagnostik : bentuk kembar

FILOSILIKAT 1. Ciri khusus: Adanya tetrahedron SiO4 dimana tiga atom oksigen pd titik sudutnya mengikat tetrahedra lainnya shg membentuk lembaran tetrahedra 2. Lembaran tetrahedra ini dapat bergabung dg lembaran oktahedra membentuk lapisan majemuk tetrahedra-oktahedra KAOLINIT : Al4Si4O10(OH)8 Sistem : Triklinik Habit : Kristal pseudoheksagonal pipih Belahan : Sempurna Kekerasan : 2.0 Berat jenis : 2.6 Warna : Putih, seringkali berbintik coklat atau kelabu Kimiawi : Komposisi sesuai formula, substitusi jarang terjadi. Polimorfiknya adalah Dikrit, Nakrit, dan Haloisit. MONTMORILONIT : Al2Si4O10(OH)2. xH2O Sistem : Monoklinik Habit : Kristal sukar dilihat Warna : Biasanya kelabu atau kelabu kehijauan Kekerasan : 2 - 2.5 Berat jenis : 2.0 - 2.7, menurun dengan kadar air Sifat diagnostik : Komposisinya selalu menyimpang dari formula ideal, sering terjadi substitusi atom dlm struktur kristal, misalnya Mg mengganti Al, Al mengganti Si. Substitusi ini mengakibatkan munculnya muatan negatif pd struktur.

FILO-SILIKAT VERMIKULIT : Mg3Si4O10(OH)2 . xH2O Sistem : Monoklinik Habit : Biasanya pseudomorf Belahan : Sempurna Kekerasan : 1.5 Berat jenis : 2.4 Warna : Kuning sampai coklat Kimiawi : Selalu ada sejumlah Al yg menggantikan Si, Mg oleh feri

KELOMPOK MIKA MUSKIVIT : KAl2(AlSi3O10) (OH)2 Sistem : Monoklinik Habit : Biasanya masanya berlapis Warna : Tidak berwarna atau pucat Kekerasan : 2.5 Goresan : Putih Komposisi kimia : Komposisinya beragam akibat substitusi atom. Sejumlah Na menggantikan K. Sebagian Al (koordinasi enam) digantikan oleh Mg dan Fe. BIOTIT : K(Mg,Fe)3 (AlSi3O10)(OH)2 Sistem : Monoklinik Habit : Kristalnya prisma pseudo-heksagonal, seringkali pipih berlapis Belahan : Sempurna Kekerasan : 2.5 Berat jenis : 2.8 - 3.4 Warna : Kuning pucat hingga coklat Komposisi kimia : Komposisinya beragam. Sebagian K diganti oleh Na, Ca, Rb, Cs. Mg dapat diganti oleh fero dan feri; sebagian OH dapat diganti oleh F KHLORIT : (Mg, Fe,Al)6 (Al,Si)4O10 (OH)8 Sistem : Monoklinik Habit : Kristal pseudo-heksagonal Warna : Hijau khas Kekerasan : 2.5 Berat jenis : 2.6 - 3.3 Warna : Hijau khas Komposisi kimia : Mg dan Fe dapat saling menggantikan

Diagram ttg Kondisi umum pembentukan liat silikat dan oksida Fe & Al Alumino silikat Kaya Mg, Ca, Na, Fe Kaya K Feldspar; Augit; Hornblende Muskovit; Mika; Biotit Mikroklin; Ortoklas -Mg -K Klorit Hidrous mika -K -Mg -Mg -K Derajat Pelapukan Meningkat Vermikulit +K Pengusiran basa lambat Montmorilonit Kaya Mg dlm zone pelapukan Pengusiran basa cepat Kaolinit Pengusiran basa cepat Oksida Fe dan Al Iklim panas basah (-Si) Iklim panas basah (-Si) Diagram ttg Kondisi umum pembentukan liat silikat dan oksida Fe & Al

TETRAHEDRA SILIKA OKTAHEDRA ALUMINA OH

KAOLINIT MINERALOGI LIAT 3 O O-OH-O 2 Al Okta- 3 OH 1. Paket lapisan mineral tersusun atas lempeng aluminium-hidroksida yg bergabung dg lempeng silika 2. Salah satu ion oksigen menjadi mata rantai (jembatan) di antara kedua lempengan 3. Seluruh kristal merupakan tumpukan dari paket-paket lapisan seperti di atas O Si Al OH 3 O tetra- 2 Si hedra O-OH-O 2 Al Okta- 3 OH Pd kondisi kemasaman alamiah (pH 4 - 8), kaolinit tdk begitu aktif. Hidroksil permukaan yang terikat pada Al, bersifat asidoid pd pH > 8.1, bersifat basidoid pd pH < 8.1. Shg pd kondisi pH tinggi, permukaan liat ini akan bermuatan negatif, KTK nya tinggi

Kisi kristal tidak tahan terhadap pemanasan MINERALOGI LIAT HALOISIT 1. Seringkali mengiringi kaolinit, formulanya Al2O3.2SiO2.4H2O 2. Lempeng-lempeng Si dan Al tidak diikat oleh ion-ion oksigen milik bersama 3. Seluruh kristal terdiri atas lempeng Si2O5H2 bergantian dg lempeng Al2(OH)6 O Si Al OH 3 O tetra- 2 Si hedra 2 OH 3 OH 2 Al Oktahedra Kisi kristal tidak tahan terhadap pemanasan Pada suhu 40oC air telah lenyap dan lambat laun terbentuk suatu persenyawaan meta-haloisit

PIROFILIT MINERALOGI LIAT 1. Rumus umumnya Al2O3.4SiO2.H2O 2. 3 O tetra- 2 Si hedra O-OH-O 2 Al okta- O-OH-O hedra hedra 3 O Permukaan kristal tersusun atas atom oksigen dari lempengan Si2O5, bersifat inert

MINERALOGI LIAT MONTMORILONIT 1. Kisi kristalnya bersifat dapat membengkak 2. Ruang antara Lempeng-lempeng dapat dimasuki air, shg jarak antar lempengan melebar 3. Rumus umum Al2O3.4SiO2.H2O.nH2O n H2O n H2O n H2O n H2O ……….. n H2O ………... 3 O tetra- 2 Si hedra O-OH-O 2 Al /Fe/Mg oktahedra O-OH-O tetra- hedra 2 Si ………..n H2O ……..

SERISIT MINERALOGI LIAT 1. Adalah Muskovit yg bersisik halus dg formulanya K2O. 3Al2O3. 6SiO2. 2H2O atau KAl2(AlSi3)O10(OH)2 2. Mg menggantikan sebagian Al (Substitusi isomorfik) 3. Paket-paket Al2(AlSi3)O10(OH)2 dirangkaikan bersama oleh ion kalium K Si OH Al O 6 O …………. K ………... tetra- Al, 3Si hedra 2O-2OH-2O 4 Al oktahedra Al, 3Si tetrahedra …………. K ……….

MINERAL LIAT Liat Fe dan Al-hidrous-oksida: Ukuran liat  2 mikron Ukuran partikel koloid  1 mikron Tidak semua liat bersifat koloidal LIAT SILIKAT: Berbentuk pipih-laminer, lapisan lempengan Berstruktur kristal = kristalin Umumnya bersifat koloidal Luas permukaannya sangat besar Permukaannya bermuatan elektronegatif shg mampu menjerap kation-kation Liat Fe dan Al-hidrous-oksida: Tidak mempunyai struktur kristal, amorf Banyak dijumpai di daerah tropika ALOFAN: Si dan Al seskui-oksida Al2O3.2SiO2.H2O

STRUKTUR LIAT SILIKAT Ukuran kecil , KRISTALIN Tersusun atas unit-unit kristal Susunan mineralogik dari unit kristal ini tgt pada tipe liat Struktur Dasar LIAT SILIKAT: Silikat-alumina = alumino-silikat: Lempengan tetrahedra-silika bertumpukan dg lempengan oktahedra alumina Tetrahedra silika Oktahedra alumina Kedua lempengan ini berikatan satu-sama lain dalam kristal liat melalui atom oksigen …….. “Jembatan oksigen” Tetrahedra Oktahedra SiO4

Mineralogi Liat Silikat Berdasar susunan lempeng dlm unit kristal: 1. Tipe mineral 1:1 (Silika : Alumina) 2. Tipe mineral 2:1 yg unit kristalnya memuai 3. Tipe mineral 2:1 yg unit kristalnya tdk memuai 4. Tipe mineral 2:2 Tipe Mineral 1:1 Kaolinit, Haloisit, Anauksit, Dikit Unit kristal terdiri atas satu lempeng silika & satu alumina Kisi kristalnya 1:1 Kedua kisi dlm unit kristal diikat oleh atom oksigen yg dipegang bersamaan oleh atom Si dan Al dlm masing-masing kisi Unit-unit kristal diikat bersama secara kuat oleh ikatan hidrogen sehingga tidak dapat memuai (mengembang-mengkerut) Permukaan efektif terbatas di permukaan luar saja Hampir tidak ada substitusi isomorfik Nilai KTK-nya rendah Kristal Kaolinit berbentuk heksagonal, diameternya 0.1 - 5 mikron Sifat plastisitas dan kohesinya rendah Sifat koloidalnya tidak terlalu intensif

Mineralogi Liat Silikat Tipe mineral Memuai 2:1 Unit kristalnya tersusun atas lempeng alumina yang dijepit oleh dua lempeng silika Dua Kelompok yang terkenal: 1. Montmorilonit : Montmorilonit, Beidelit, Nontronit, Saponit 2. Vermikulit MONTMORILONIT Unit-UNIT kristal diikat bersama melalui ikatan oksigen yang lemah, sehingga kisi kristal mudah mengembang bila basah Diameter montmorilonit 0.01 - 1 mikron Permukaannya sangat luas: Permukaan luar dan permukaan dalam Muatan listrik negatif pada permuakaannya sangat besar, terdiri atas muatan permanen dan muatan yang tergantung pH. Muatan permanen terbentuk melalui proses substitusi isomorfik Mg menggantikan sebagian Al dalam lempeng Oktahedron Al menggantikan sebagian Si dalam lempeng Tetrahedron Sifat plastisitas dan kohesinya tinggi, mengembang & mengkerut Sifat koloidalnya sangat intensif

Mineralogi Liat Silikat VERMIKULIT Ciri-ciri strukturalnya serupa dengan Montmorilonit Pd bbrp Vermikulit ternyata Mg dominan, menggantikan Al dalam lempeng alumina. Pd lempeng silika sebagian Si digantikan oleh Al, inilah yang Menimbulkan MUATAN NEGATIF yg sangat besar Kapasitas jerapan (KTK) sangat besar. Molekul air bersama dg kation Mg dijerap kuat di antara unit kristal, sehingga derajat memuainya tidak terlalu intensif (MEMUAI TERBATAS) Tipe mineral 2:1 Tidak Memuai (ILLIT) Ukurannya berada di antara montmorilonit dan kaolinit Muatan negatifnya terutama pd lempeng silika tetrahedra, karena sekitar 15% dari Si digantikan oleh Al. Kalium diikat kuat di antara unit-unit kristal, sehingga tidak mudah mengembang

Mineralogi Liat Silikat KLORIT: Tipe mineral 2:2 Mineral liat Magnesium-silikat yg mengandung Fe dan Al. Satu unit kristal tersusun atas LAPISAN TALK (spt montmorilonit) dan LAPISAN BRUSIT [ Mg(OH)2 ] Atom Mg mendominasi lempeng oktahedron lapisan TALK. Sehingga unit kristal terusun atas dua lempeng tetrahedron silika dan dua lempeng oktahedron magnesium (Tipe 2:2) Mineral liat ini bersifat mudah memuai CAMPURAN LIAT SILIKAT Susunan unit kristalnya berbeda-beda, spt misalnya: 1. Klorit - Illit 2. Ilit-Montmorilonit

KOMPARATIF TIGA LIAT SILIKAT Ciri-ciri Tipe Liat Montmorilonit Ilit Kaolinit Ukuran (mikron) 0.01 - 1 0.1 - 2 0.1 - 5 Bentuk Serpih tak menentu Serpih tak menentu Heksagonal Permukaan jenis (m2/g) 700-800 100-200 5 - 20 Permukaan luar Luas Sedang Sempit Permukaan dalam Sgt luas Sedang Tdk ada Kohesi / Plastisitas Tinggi Sedang Rendah Kapasitas Memuai Tinggi Sedang Rendah KTK (me/100 g) 80-100 15 - 40 3 - 15 Sumber: Sifat dan Ciri Tanah (G. Soepardi, 1983)

Mineral Koloidal selain Silikat HIDRUS OKSIDA BESI & ALUMINIUM Liat ini penting karena Sangat dominan di daerah tropika Molekul air berasosiasi dengan oksida : Fe2O3.xH2O : Limonit dan Goetit Al2O3.xH2O : Gibsit Muatan negatifnya sedikit Sifat plastisitas, lengket, dan kohesinya rendah Tanah yg kaya minerla liat ini biasanya sifat isiknya baik ALOFAN & MINERAL AMORF Bersifat koloidal non-kristalin Alofan: Gabungan antara silikon dan aluminium seskuioksida Susunannya mendekati Al2O3.2SiO2.H2O Banyak ditemukan pada tanah-tanah Abu volkan

SIFAT Koloidal MINERAL LIAT Karakteristik bahan koloid: penyebaran cahaya, osmotik dan muatan listrik Koloid tanah bersifat amfotir, diduga ada kaitannya dg gel-gel besi, aluminium, dan mangan yang menyelimuti inti kristalin. Berbagai jenis kation dijerap oleh koloid tanah dengan kekuatan yang berbeda-beda, tergantung pada ukuran, muatan (valensi) dan hidratasi kation. Penjerapan kation oleh mineral liat berhubungan erat dengan tipe mineral liat Kaolinit dan Haloisit: muatan listrik terdapat pd ikatan yg patah di tepi kristal, dan disosiasi H dari gugusan OH permukaan Ilit dan Khlorit; muatan listrik pd ikatan yg patah di tepi kristal, dan muatan permanen akibat substitusi atom inti kristal Montmorilonit dan Vermikulit: muatan listriknya terutama akibat dari substitusi atom inti kristal. PENJERAPAN DAN PERTUKARAN ION Penjerapan kation dipengaruhi oleh: 1. Jenis kation 2. Konsentrasi ion-ion 3. Sifat anion yang berhubungan dg kation 4. Sifat partikel koloid

Sumber muatan negatif liat Silikat PINGGIRAN KRISTAL YANG TERBUKA Ada dua mekanisme, yaitu: 1. Adanya valensi dari atom inti (Si atau Al) yg tidak dijenuhi yg terdapat pd pinggiran patahan lempeng silika dan alumina 2. Permukaan luar yg datar (pd Kaolinit) mempunyai gugusan oksigen dan hidroksil (OH-) yg tersembul dan merupakan titik-titik yg bermuatan negatif. Muatan ini sifat dan besarannya tergantung pH SUBSTITUSI ISOMORFIK = Penggantian atom inti kristal O = Si = O O = Al - O - (tidak bermuatan) (bermuatan negatif satu) OH OH OH OH OH OH - 1 Al Al Mg Al O O OH O O OH

KARAKTERISTIK MUATAN MINERAL LIAT Material KTK (meq/100g) KTA Permanen Variabel Total Montmorilonit 112 6 118 1 Vermikulit 85 0 85 0 Illit 11 8 19 3 Halloisit 6 12 18 15 Kaolinit 1 3 4 2 Gibsit 0 5 5 5 Goetit 0 4 4 4 Alofan 10 41 51 17 Peat 38 98 136 6 Sumber: Mehlich & Theisen (Sanchez, 1976).

LAYER SILICATE SYSTEMS R - C = O R - C = O O O R - C Al + 3OH- R - C + Al(OH)3 R - C R - C O O Peningkatan muatan negatif gugusan karboksil terjadi kalau ion kompleks aluminium diendapkan; ini terjadi kalau pH tanah meningkat (ada OH-)

OXIDE SYSTEMS Fe Fe Fe Fe POSITIF ZERO NEGATIF O OH HO O O OH HO O O OH H+ + HO O O OH + OH- O O + H2O H+ Fe Fe Fe Fe O OH HO O O OH HO O POSITIF ZERO NEGATIF

PERUBAHAN MUATAN PERMUKAAN dgn pH Andept Humult Hor A Hor A - + - + Hor B pH(H2O) = 5.8 pH(H2O) = 6.5 Net surface charge me/100g Orthox Udalf Hor A - + - + Hor A Hor B Hor B pH(H2O) = 6.8 pH(H2O) = 6 pH dlm 0.01 N NaCl

 pH & ZERO POINT of CHARGE 1. Status muatan dari sistem liat-oksida dpt dg mudah ditentukan dg mengukur pH-nya dalam air dan dalam larutan garam netral seperti 1 N KCl 2.  pH = pH (1 N KCl ) - pH ( H2O) = positif : koloid liat bermuatan positif (KTA) = negatif : koloid liat bermuatan negatif (KTK) 3. Dalam sistem liat silikat berlapis,  pH selalu negatif : [Liat]-H+ + H2O ===== [ Liat ]-H+ + H2O [Liat]-H+ + KCl ===== [ Liat ]-K+ + Cl- + H+ sehingga pH dalam air lebih tinggi dp pH dalam lrt KCl

 pH & ZERO POINT of CHARGE 4. Dalam sistem liat oksida,  pH dpt positif atau negatif tgt pada pH tanah aktual: [Liat+]OH- + H2O ===== [ Liat +]OH- + H2O [Liat+]OH- + KCl ===== [ Liat+]Cl- + OH- + K+ 5. Nilai  pH negatif, bukan berarti seluruh permukaan liat bermuatan negatif, ada sedikit muatan positif pada titik-titik yang terisolir dari muatan negatif. Ultisol, Oxisol, Alfisol: KTA = < 1 meq/100g Andepts : KTA = 6.8 meq/100g ------------------- pd kondisi pH tanah lapangan

FAKTOR HUBUNGAN pH vs MUATAN LISTRIK Pada sistem liat-oksida hubungan tsb adalah: kDRT pHo  = --------- . -------- 4  F pH dimana:  : muatan permukaan (m.eq./ 100 g) k : reciprocal tebal lapisan rangkap (tgt konsentrasi lrt tanah) D : konstante dielektrik R : konstante gas T : temperatur absolut F : konstante Faraday pH : pH tanah pHo : pH tanah pd titik isoelektrik, yaitu pH pd ZPC

PERTUKARAN KATION Contoh sederhana: Ca-[MISEL] + 2H+ H-[MISEL]-H + Ca++ PERTUKARAN KATION DI ALAM 40Ca 38Ca + 2 Ca(HCO3)2 20Al + 5 H2CO3 20Al 20H 25H L(HCO3) 20L 19L tercuci MISEL MISEL KEHILANGAN KATION LOGAM: Dengan mekanisme reaksi seperti di atas, kation logam Ca, Mg, K, dan Na dapat hilang tercuci dari tanah, dan tanah menjadi semakin masam PENGARUH PEMUPUKAN: 40Ca 7K 20Al 38Ca + 2 CaCl2 40H + 7 KCl 20Al 20L 39H HCl 18L 2 LCl MISEL MISEL

KAPASITAS TUKAR KATION [ KTK ] Koloid tanah bermuatan negatif, sehingga mampu menjerap (mengikat) kation. Kation-kation yg dijerap ini dapat ditukar dengan ammonium atau barium, kemudian ammonium atau barium itu ditentukan jumlahnya. ………… ………..Kapasitas jerapan dapat diketahui besarnya PENGARUH pH TANAH Sebagian dari muatan negatif pd koloid tanah tergantung pd pH, sehingga kapasitas jerapan juga dipengauhi pH Biasanya KTK ditetapkan pd pH 7.0 atau lebih, ini berarti meliputi muatan permanen dan sebagian besar muatan yg tergantung pH CARA MENYATAKAN Satuan untuk kapasitas tukar kation (KTK): mili-ekuivalen (meq atau me) 1 meq = 1 mg hidrogen atau sejumlah ion lain yg dapat bergabung atau menggantikan ion hidrogen tsb. KTK liat = 1 me/100 g : setiap 100 gram liat dapat menjerap 1 mg hidrogen

Koloid Organik Montmorilonit Muatan tgt pH Muatan permanen KTK, me/100 g) Koloid Organik Montmorilonit Muatan tgt pH Muatan permanen 200 160 120 80 40 4.0 5.0 6.0 7.0 8.0 pH tanah

KTK TANAH Tanah asal KTK (me/100g) Kelas tekstur Ciletuh, Jabar 8.1 Lempung Berdebu Way Seputih, Lampung 16.0 Lempung Liat Berdebu Pengubuan, Lampug 22.9 Lempung Liat Berdebu Tj.Kresik, Krawang 28.7 Liat Berdebu Rentang Barat 38.8 Liat Berdebu FAKTOR YG MEMPENGARUHI 1. Tekstur tanah: semakin halus teksturnya semakin tinggi KTKnya 2. Kandungan humus dan liat koloidal menentukan KTK tanah 3. Macam liat koloidal juga mempengaruhi besarnya KTK tanah

PERSENTASE KEJENUHAN BASA TANAH H+ dan Al+++ : sumber kemasaman tanah Al+++ + H2O Al(OH)++ + H+ Al(OH)++ + H2O Al(OH)2+ + H+ Kation basa: Ca++, Mg++, K+, dan Na++ CaO + H2O Ca(OH)2 Ca++ + OH- KB dan pH Proporsi KTK yang ditempati oleh kation-kation basa disebut PERSENTASE KEJENUHAN BASA Penurunan %KB mengakibatkan menurunnya pH Tanah di daerah iklim kering biasanya mempunyai KB yang tinggi Tanah di daerah iklim humid biasanya mempunyai KB yang rendah

PERTUKARAN KATION & KETERSEDIAAN HARA Kation terjerap mudah tersedia bagi tanaman & jasad renik Penyerapan kation oleh akar: 1. Penyerapan melalui larutan tanah 2. Pertukaran ion antara akar dg koloid tanah Kejenuhan kation dan serapan hara Faktor pelepasan kation jerapan: 1. Rasio / proporsi jenis-jenis kation pd kompleks jerapan 2. Kejenuhan Ca yg tinggi ------- Ca++ mudah diserap tanaman 3. Pengaruh jenis kation lain: Afinitas dan aktivitas kation PENGARUH TIPE KOLOID Berbagai koloid mempunyai daya ikat kation yg berbeda Kalsium diikat oleh montmorilonit lebih kuat daripada oleh kaolinit

Pertukaran ion dengan akar tanaman Plants obtain some mineral nutrients through ion exchange between the soil solution and the surface of clay particles. Diunduh dari sumber: http://bcs.whfreeman.com/thelifewire8e/pages/bcs-main_body.asp?v=chapter&s=36000&n=00010&i=36010.01&o=|36000|&ns=0 ……. 27/10/2012

MINERAL LIAT MUATAN LISTRIK PADA Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Visual comparison of common silicate clays Strongly held “2:1:1” illite montmorillonite Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

= Layer bond type = Location of charge imbalance H-H = Layer bond type = Location of charge imbalance octa octahedral octahedral & tetrahedral octahedral & tetrahedral H-H tetrahedral more strongly held than in smectite H-H O-O O-Cation tetrahedral Ionic NONE octahedral & tetrahedral octahedral & tetrahedral octahedral illite “2:1:1” montmorillonite Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Organization of tetrahedral and octahedral sheets in common soil clays NONE Octahedral & Tetrahedral Octahedral & Tetrahedral Octahedral Montmorillonite Illite Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Ciri-ciri Umum Liat Silikat Kaolinit Smektit / Vermiculit Illit (fine-grained micas) Kelas Umum 1:1 (TetraOcta) 2:1 (TOT) Pengembangan Ikatan lapisan ionic > H-bonding > van der Waals Muatan negatif neto (KTK) Fertility Lokasi muatan Low Low, none High/Moderate Hydrogen (strong) O-O & O-Cation van der Waals (weak) Potassium ions (strong) http://en.wikipedia.org/wiki/Van_der_Waals_force: “the name van der Waals force is sometimes used as a synonym for the totality of non-covalent forces (also known as intermolecular forces). These forces, which act between stable molecules, are weak compared to those appearing in chemical bonding. To explain this, we refer to the article on intermolecular forces, where it is discussed that an intermolecular force has four major contributions. In general an intermolecular potential has a repulsive part, prohibiting the collapse of molecular complexes, and an attractive part. The attractive part, in turn, consists of three distinct contributions (i) The electrostatic interactions between charges (in the case of molecular ions), dipoles (in the case of molecules without inversion center), quadrupoles (all molecules with symmetry lower than cubic), and in general between permanent multipoles. The electrostatic interaction is sometimes called Keesom interaction or Keesom force after Willem Hendrik Keesom. (ii) The second source of attraction is induction (also known as polarization), which is the interaction between a permanent multipole on one molecule with an induced multipole on another. This interaction is sometimes measured in debyes after Peter J.W. Debye. [this is distinct from H-bonding: “The typical hydrogen bond is stronger than van der Waals forces, but weaker than covalent, ionic and metallic bonds.” - http://en.wikipedia.org/wiki/Hydrogen_bond] (iii) The third attraction is usually named after London who himself called it dispersion. This is the only attraction experienced by noble gas atoms, but it is operative between any pair of molecules, irrespective of their symmetry. “ Low High / Highest Moderate Edges only – No isomorphic substitution Octahedral / Octa+Tetra Tetra(~balanced by K+’s) so: Edges Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Tipe-Tipe Muatan Permanen (due to isomorphous substitution) pH-dependent = Tergantung pH (due to isomorphous substitution) (variabel, disebabkan oleh patahan – patahan pada kristal mineral liat) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

doesn’t change rapidly Substitusi Isomorfik Sama Bentuk/Ukuran Penggantian satu ion oleh satu ion lainnya yang ukurannya hampir sama di dalam struktur kristalin dari mineral liat takes eons – doesn’t change rapidly Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Octahedral sheet neutral Muatan Permanen Octahedral sheet neutral Net negative charge Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Muatan tergantung-pH : tepi kristal H+ bound tightly, so the lower the pH, the less exchange there is (i.e., lower nutrient availability) Especially important in kaolinite, humus, where no internal charge imbalance Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Muatan tergantung-pH : tepi kristal Variable or pH-dependent charge Dissociation of exposed OH groups ]-OH ]-O- + H+ uncharged negative charge <-----------(+ H+) ------------------ ----------------- (- H+) --------------> Diunduh dari sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm……. 27/10/2012

Muatan tergantung-pH : tepi kristal Occurs with humus, hydrous oxides, and Broken edges of silicate clays Diunduh dari sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm……. 27/10/2012

Muatan tergantung-pH : Increased pH values = more negative charge acid = less negative charge Protonation of O and OH groups ]-O- + H+ ]-OH + H+ ]-OH2+ Negative-charge no-charge positive-charge high pH intermediate pH low pH Diunduh dari sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm……. 27/10/2012

Muatan tergantung-pH : Depends on soil colloids present Colloid Negative charge Positive charge % constant % variable Humus 200 10 90 Vermiculite 120 95 5 Smectite 100 Illite 40 80 20 Kaolinite 12 4 Fe & Al Oxides Diunduh dari sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm……. 27/10/2012

Muatan tergantung-pH : Positive charge << negative charge in most temperate zone soils Acid tropical soils = net + charge Diunduh dari sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm……. 27/10/2012

Pertukaran Ion The substitution of one ion for another on the surface or in the interstitial spaces of a crystal Cation exchange (e.g., Ca2+ for K+) Anion exchange (e.g., H2PO4- for NO3-) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

What’s so great about ion exchange? Retards the release of pollutants to groundwater Affects permeability, with implications for landfills, ponds, etc. Affects nutrient availability to plants (constant supply, protection vs. leaching) “Next to photosynthesis and respiration, probably no process in nature is as vital to plant and animal life as the exchange of ions between soil particles and growing plant roots.” Nyle C. Brady Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Definitions cation: An ion that carries a positive charge cation exchange: A process - cations in solution exchanged with cations on exchange sites of minerals and OM cation exchange capacity (CEC): The total amount of exchangeable cations that a particular material or soil can adsorb at a given pH Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Controls on ion exchange Strength of adsorption Related to hydrated ionic radius and valence The smaller the radius and greater the valence, the more closely and strongly the ion is adsorbed. Strength  valence/radius Relative concentration in soil solution Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Kapasitas Tukar Kation= KTK Jumlah total semua kation tukar yang dapat dijerap oleh tanah Dinyatakan dalam “muatan positif” yang dapat dijerap oleh satu satuan massa Kalau KTK =10 cmolc/kg  tanah mnejerap 10 cmol H+  dapat menukarnya dengan 10 cmol K+, atau 5 cmol Ca2+ jumlah muatan, bukan jumlah ion, cmolc = centimole muatan yang tidak dinetralkan (diseimbangkan) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Strength of adsorption proportional to valence ÷ hydrated radius Afinitas Pertukaran Held more weakly Held more strongly H+  Al3+ > Ca2+ > Mg2+ > NH4+ = K+ > Na+ This is referred to as the “Lyotropic series” Strength of adsorption proportional to valence ÷ hydrated radius Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

How many charges are there to fill??? Pertukaran Ion vs. KTK How many charges are there to fill??? VERY acidic soil Sandy loam NH4+ Ca2+ H+ Mg2+ K+ NO3- Cl- H+ NO3- HSO4- NO3- H+ H+ NO3- Crystal edge H+ HCO3- CEC = 7; AEC = 2 Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Jumlah liat dan bahan organik Tipe mineral liat KTK tergantung pada Jumlah liat dan bahan organik Tipe mineral liat Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012 Diunduh dari sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm……. 27/10/2012

The reactions are reversible, unless… Petukaran Kation + 2K+ Ca2+ K+ Al3+ + 3K+  + Ca2+  K+ + Al3+ The interchange between a cation in solution and one on a colloid must be CHARGE balanced. The reactions are reversible, unless… Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Muatan Listrik pada Koloid Tanah Tipe Koloid Muatan Negatif Muayan Positif Humus (O.M.) Liat Silikat Oksida Al dan Fe 200 cmolc/kg 0 cmolc/kg 100 cmolc/kg 0 cmolc/kg 4 cmolc/kg 5 cmolc/kg Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Sumber Muatan pda Liat Tipe 1:1 Broken edge of a kaolinite crystal showing oxygen atoms as the source of NEGATIVE charge ALL clay minerals have edge charges. Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Sumber muatan pada liat Smectite Isomorphous substitution here, in the octahedral sheet means a net NEGATIVE charge Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Sumber muatan pada Liat Mica K+ 1. Isomorphous substitution is in the tetrahedral sheets 2. K+ comes into the interlayer space to satisfy the charge and “locks up” the structure 3. Charge imbalance now mostly on edges Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Muatan Negatif pada Humus ENORMOUS external surface area! (but no internal surface – all edges) Central unit of a humus colloid (mostly C and H) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Perbandingan Muatan Permukaan 13 out of 18 “sites” are negative (72%) 3 out of 9 “sites” are negative ( 33%) (a) 13 negative charges and 5 positive charges; (b) 3 negative charges and 6 positive charges both low CEC relative to 2:1 clays & OM Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Kation dijerap oleh Ordo-Tanah “Kation asam” (H+, Al3+) “Kation Basa” (misalnya Ca2+, NH4+, K+, etc.) Ultisol Alfisol Mollisol 65 35 45 55 30 70 Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Common %OC for A horizons in productive areas ~4%  Bahan Organik dan KTK (cmolcl/kg) Common %OC for A horizons in productive areas ~4%  So: y = (4.9 * 4%) + 2.4; or CEC = 22 cmolc/kg Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Kation Tukar : Area Tanah di daerah iklim Arid Tanah di daerah iklim Humid K+ Ca2+ Mg2+ H+ NH4+ H+ Al3+ K+ Low pH (acidic) High pH (basic) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

KTK dan pH high Na+ binds loosely, exchanges readily CEC H+ binds tightly, doesn’t exchange low 3 8 Soil pH Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Pengaruh pH terhadap KTK liat Smectit dan Humus Edge charge = Internal charge Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Permanent vs. pH-dependent Karakteristik Muatan Tipe Koloid Total Muatan Konstan (%) Variable (%) Bahan Organik 200 Smectite Kaolinite 8 10 90 95 5 5 95 Permanent vs. pH-dependent Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

OM has highest CEC 2:1 clays 1:1 clays Non-clayey soils Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

KTK dan Intensitas Pelapukan Alfisols, Vertisols, Argiudolls* Ultisols Oxisols Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012 *remember nomenclature structure = “argi-ud-oll”

Rule of thumb for estimation of a soil’s CEC CEC = (% O.M. x 200) + (% clay x 50) But the CEC of clay minerals ranges from 3 to 150! KTK tanah: (a) Related to components Humus » 200 cmolc/kg Smectites » 100 cmolc/kg Illite » 25 cmolc/kg Kaolinite » 10 cmolc/kg Fe and Al oxides » 4 cmolc/kg Estimate soil cation exchange capacity from composition: 5 % O.M. & 20 % smectite clay 200 x 0.05 = 10 100 x 0.20 = 20 Total = 30 cmolc/kg Sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

KTK Ordo -Tanah (cmolc/kg) Oxisols Low Ultisols Alfisols 9.0 Mollisols 18.7 Vertisols 35.6 Histosols Key factor High Al/Fe oxides low high 3.5 1:1 clays Low pH 2:1 clays 128.0 O.M. Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

KEJENUHAN BASA A measure of the proportion of basic cations occupying the exchange sites Base cations are those that do not form acids Ca2+, Mg2+, K+, Na+, NH4+ .……..., Ion-ion selain H+ and Al3+ Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Kejenuhan Basa beberapa Ordo Tanah Oxisols Low Ultisols Alfisols Medium-High Mollisols High >50% low high <35% Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

1:1 Clay Minerals CEC ~ 7 meq/100 g non-expanding Kaolinit Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al 0.72 nm Si Al Si Al Si Al Si Al Si Al Si Al Si Al Colored image of kaolinite to replace B&W Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al Si Al Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Kaolinite Kaolinite is the most common soil mineral in many parts of the world. Kaolinite and halloysite generally form through the weathering of primary aluminosilicates under earth surface conditions under moderately acidic to acidic conditions. Kaolinite is commonly associated with acidic parent materials that have low buffering capacities, such as granitic rock. Alternatively, long term weathering can gradually acidify even relatively basic parent materials. Over time, the base status of these materials declines and the buffering capacity is diminished. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

tropics and subtropics, Kaolinite Where do you expect to find regions with high kaolinite in the world? tropics and subtropics, where stable landforms and intense weathering conditions have resulted in the removal of almost all weatherable bases from the soil materials. Other areas include those with acidic parent materials or very stable landscapes. Minerals commonly associated with kaolinite are quartz and feldspars, especially microcline and orthoclase. Clay minerals associated with kaolinite include aluminum oxides (especially gibbsite), iron oxides (hematite, goethite, or amorphous iron oxides), and titanium oxides (anatase and rutile), in large part due to their resistance to weathering Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Mineral Liat Tipe 2:1 Expansive Non expansive Like a sandwich with two slices of bread Two silica tetrahedrons (bread) One aluminum octahedron (filling) The 2:1 clays can be broken into 2 groups Expansive Non expansive 2:1 clays are like a sandwich with two slices of bread. Two silica tetrahedrons (bread) to one aluminum octahedron (filling). The 2:1 clays can be broken into 2 groups; Expansive, and Non expansive Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

2:1 Clay Minerals CEC ~ 40 meq/100 g non-expanding T O Layer T Colored image - mica Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Mineral Liat Tipe 2:1 Classification of the 2:1 phyllosilicates is based on the total number of permanent charges per half unit cell layer. Muatan Lapisan Kelompok Spesies yang Umum < 0.2 Talc-Pyrophyllite Talc, Pyrophyllite 0.2 - 0.6 Smectite Montmorillonite, Beidellite 0.6 - 0.9 Vermiculite > 0.9 Micas Muscovite, Biotite approx. 2.0 Brittle Micas Margarite Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Liat Tipe 2:1 Tidak Mengembang the sheets or layers are held together strongly neither water nor a change in the interlayer cations causes them to swell Illites are one group of non-expandable clays In the non-expansive 2:1 clays the sheets or layers are held together strongly so that neither water nor a change in the interlayer cations causes them to swell. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

MICA - Liat Tipe 2:1 Micas are 2:1 phyllosilicates of high charge (> 0.9 charges per half unit cell layer). The vast majority are formed from magma, and are generally present as macroscopic crystals. Micas in soil are almost always inherited from the parent material A common mica is biotite, which has K+ ions held tightly between the 2:1 layers to balance negative charges in the layers themselves resulting from isomorphous substitutions. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

This non-exchangeable K+ can become important for plant uptake. MICA - Liat Tipe 2:1 Mica typically have K+ interlayer to balance the negative charges due to isomorphous substitutions. This non-exchangeable K+ can become important for plant uptake. HOW? Through weathering. Weathering occurs through the loss of interlayer cations, in particular K+ interlayer, and their exchange for cations present in the soil solution Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Micas Diagrammatic sketch of the structure of Muscovite. Micas are a 2:1 lattice type mineral. ion substitution is mainly in the tetrahedral layer where Si is replaced with Al the charge deficiency is ballanced by potassium ions - successive sheets are strongly bound together - non expanding structure Different types of micas are Muscovite, Biotite and Illite The micas found in sedimentary shale sections is normally classed as Illite Diagrammatic sketch of the structure of Muscovite. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012 96

Mineral Liat Tipe 2:1 Mengembang Bound together by very weak hydrogen bounds (easily broken) Will swell upon wetting Smectites (montmorillonite) are one group of expandable clays The expansive 2:1 clays are bound together by very weak hydrogen bounds (easily broken). These minerals will swell upon wetting. Smectites are one group of expandable clays. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Mineral Liat Smectite Smectites are 2:1 phyllosilicates with total layer charge between 0.2 to 0.6 negative charges per half unit cell layer. This group was formerly called the Montmorillonite group, but the name was changed in the 1970s to avoid confusion because the name montmorillonite also refers to an individual species of smectite. Smectites characteristics: 2:1 phyllosilicates total layer charge 0.2 to 0.6 hydrated Because smectites have permanent negative charge, interlayers always contain cations to provide electroneutrality. These cations typically participate to cation exchange reactions Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

2:1 Clay Minerals (expanding) KTK: 100 – 200 meq/100 g (vermiculite) 70 – 120 meq/100 g (smectite) Colored image – vermiculite and smecite (partially and fully expanding minerals) Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

The quantity of water present between the layers depends on several factors, including: The nature of the cations present in the interlayer (specifically related to hydration characteristics, including their energies of hydration). The total or specific charge of the smectite. The distribution of total charge between the tetrahedral and octahedral sheets. The ionic strength of the soil solution external to the interlayer space. The relative humidity of the external space (for those samples not in aqueous suspension). Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

The quantity of water present between the layers depends on several factors, including: The nature of the cations present in the interlayer (specifically related to hydration characteristics, including their energies of hydration). In the presence of Ca2+ or Mg2+, two layers of water (the thickness of the first hydration shell for Ca2+ or Mg2+) are generally present between smectite layers, which provides an interlayer spacing of approximately 4Å and a total layer spacing of 14Å (the layers themselves are approximately 10Å thick). Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Mineral Liat Montmorillonit These clay silicates form by crystallization from solution high in soluble silica and magnesium. Montmorillonite has a 2 : 1 layer structure. All tetrahedra in the sheets contain Si4+ ions. Aluminium is the normal ion in the central sheet, but about one-eight of the octahedra contain Mg2+ as a substituting ion for Al3+. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Mineral Liat Montmorillonit The force of bonding between cations and the sheets is not very strong and depends on the amount of water present. In dry montmorillonites the bonding force is relatively strong. When wet conditions occur, water is drawn into the interlayer space between sheets and causes the clay to swell dramatically (expanding clay). A characteristic feature of montmorillonite is the extensive surface for the adsorption of water and ions, therefore the cation exchange capacity of montmorillonite is very high. Layers of the smectite group range in thickness from 0.98 to 1.8 nm or more. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Mineral Liat Montmorillonit also called smectite; expands on contact with water Si Al Si Al 0.96 nm easily separated by water joined by weak van der Waal’s bond Si Al Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Mineral Liat Montmorillonit A highly reactive (expansive) clay swells on contact with water (OH)4Al4Si8O20.nH2O high affinity to water Bentonite montmorillonite family used as drilling mud, in slurry trench walls, stopping leaks Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

fit into the hexagonal holes in Si-sheet Mineral Liat Illite Si Al joined by K+ ions 0.96 nm Si Al fit into the hexagonal holes in Si-sheet Si Al Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Diagrammatic sketch of the structure of Chlorite. Clorite are a 2:1:1 lattice type mineral the charge deficiencies in mica layer is ballanced by kations - successive sheets are strongly bound together - non expanding structure Chlorite tends to be associated with old sediments Diagrammatic sketch of the structure of Chlorite. Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012 107

Chlorite : Mineral liat Tipe 2:1:1 Chlorite structure is similar to that of vermiculites except that an organized octahedral sheet replaces the double water layer between mica layers There is Al3+ for Si4+ substitution in the tetrahedral sheet (net negative charge) There is Al3+ for Mg2+ substitution in the interlayer (net positive charge) Both dioctahedral and trioctahedral occupancies can exist in chlorites. Chlorite CEC 10-40 cmol Kg-1 Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Karakteristik Mineral Liat dalam Tanah Secondary mineral Type Interlayer condition / Bonding CEC [cmol/kg] Swelling potential Specific surface area [m2/g] Basal spacing [nm] Kaolinite 1 : 1 (non-expanding) lack of interlayer surface, strong bonding 3 - 15 almost none 5 - 20 0.72 Montmorillonite 2 : 1 (expanding) very weak bonding, great expansion 80 - 150 high 700 - 800 0.98 - 1.8 + Vermiculite weak bonding, great expansion 100 -150 500 - 700 1.0 - 1.5 + Hydrous Mica 2 : 1 (non-expanding) partial loss of K, strong bonding 10 - 40 low 50 - 200 1.0 Chlorite 2 : 1 : 1 (non-expanding) moderate to strong bonding, non-expanding none 1.4 Allophane - 10 - 50 Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Substitusi Isomorfik pada Kristel Mineral Liat Tipe 2:1 No substitution sheet charges sheet charges 5 + -1 With isomorphic substitution Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Sumber muatan tergantung pH pada Kaolinit More acid More acid -3 - 1 +1 Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

REAKSI PERMUKAAN MUATAN Dan Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Luas Permukaan Partikel Koloid Selected mineral groups often occur as colloids / nanoparticles: FeOOH  SA up to 500 m2/g, site density 2-20/nm2 Al(OH)3  SA up to 150 m2/g, site density 2-12/nm2 MnOOH  SA hundreds m2/g, site density 2-20/nm2 SiO2  SA 0.1 – 300 m2/g, site density 4-12/nm2 Clays  SA 10-1000 m2/g, site density 1-5/nm2 Organics  SA up 1300 m2/g, site density 2/nm2 Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

DEFINISI SORPSI : removal of solutes from solution onto mineral surfaces. Sorbate - the species removed from solution. Sorbent - the solid onto which solution species are sorbed. Tiga macam SORPSI : Adsorption - solutes held at the mineral surface as a hydrated species. Absorption - solute incorporated into the mineral structure at the surface. Ion exchange - when an ion becomes sorbed to a surface by changing places with a similarly charged ion previously residing on the sorbent. The three different types of sorption processes defined above cannot always be distinguished clearly in practice. However, it is useful to make these distinctions in theory. When it is not clear exactly which of these processes is occurring, the general term sorption should be used. It should also be kept in mind that not all authors define these processes in exactly the same way as Kehew (2001). Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Permukaan Mineral Minerals which are precipitated can also interact with other molecules and ions at the surface Attraction between a particular mineral surface and an ion or molecule due to: Electrostatic interaction (unlike charges attract) Hydrophobic/hydrophilic interactions Specific bonding reactions at the surface Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Orbit Dalam dan Orbit Luar Inner Sphere and Outer Sphere Outer Sphere surface complex  ion remains bounded to the hydration shell so it does not bind directly to the surface, attraction is purely electrostatic Inner Sphere surface complex  ion bonds to a specific site on the surface, this ignores overall electrostatic interaction with bulk surface (i.e. a cation could bind to a mineral below the mineral pHzpc) Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Permukaan Koloid yang Bermuatan Mineral surface has exposed ions that have an unsatisfied bond  in water, they bond to H2O, many of which rearrange and shed a H+ ≡S- + H2O  ≡S—H2O  ≡S-OH + H+ OH OH OH2 H+ OH OH OH H+ OH Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Permukaan Koloid sebagai Reaktan Asam-Basa The surface ‘SITE’ acts as an amphoteric substance  it can take on an extra H+ or lose the one it has to develop charge ≡S-O- + H+ ↔ ≡S-OH ↔ ≡S-OH2+ The # of sites on a surface that are +, -, or 0 charge is a function of pH pHzpc is the pH where the + sites = - sites = 0 sites and the surface charge is nil OH OH2+ O- OH O- OH OH2+ Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Building Blocks for Silicate Clays Silicon Tetrahedron Aluminum octahedron hydroxide (OH-) oxygen Aluminum (Al3+) silicon (Si4+) Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Tetrahedra and Octahedra Sharing the Oxygens Linkage of thousands of silica tetrahedra and aluminum octahedra O { Tetrahedra Si O, OH { octahedra Al OH 1:1 Mineral Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

{ { { Mineral tipe 2:1 Tetrahedra octahedra Tetrahedra Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Diunduh dari sumber: soillab. ifas. ufl. edu/. /Lecture%2010%20Catio

Mineral Tipe 2:1 Mineral Tipe 1:1 Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

KESEIMBANGAN MUATAN Si4+ O2- Al3+ OH- = Positive charge Negative charge Al3+ Si4+ OH- O2- Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Substitusi Isomorfik Substitution of lower-charge cations for higher charge cations during mineral formation. Al3+ for Si4+ in tetrahedra Mg2+ for Al3+ in octahedra The result is a deficit of positive charge or a surplus of negative charge in the mineral structure. Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Substitusi Tetrahedra: Al menggantikan Si Al3+ for Si4+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Substitusi Octahedra: Mg menggantikan Al Mg2+ for Al3+ Substitusi Octahedra: Zn menggantikan Al Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Al3+ for Si4+ Mg2+ for Al3+ Tetrahedral Substitution Octahedral Substitution Mg2+ for Al3+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Muatan listrik Na+ Na+ Na+ Na+ Na+ Na+ Na+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Permukaan yg bermuatan Ambient solution concentration Kerapatan awan kation Permukaan yg bermuatan High cation concentration Ambient solution concentration - - - - - - - - - - - - - - - Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

The cations and anions are liberated from the diffuse double layer. Zeta Potential The zeta potential (electrokinetic potential) decreases with increasing concentration of the ions of opposite charge from the soil solution. The cations and anions are liberated from the diffuse double layer. Diunduh dari sumber: http://www.ch-non-food.com/science.htm ……. 27/10/2012

What is zeta potential? Most particles dispersed in an aqueous system will acquire a surface charge, principally either by ionization of surface groups, or adsorption of charged species. These surface charges modify the distribution of the surrounding ions, resulting in a layer around the particle that is different to the bulk solution. The zeta potential is the potential at the point in this layer where it moves past the bulk solution. This is usually called the slipping plane. The charge at this plane will be very sensitive to the concentration and type of ions in solution. Diunduh dari sumber: http://www.malvern.com/labeng/technology/zeta_potential/zeta_potential_lde.htm ……. 27/10/2012

Helmholtz Double Layer . Electric Double Layer The double layer model is used to visualize the ionic environment in the vicinity of a charged surface. Helmholtz Double Layer This theory is a simplest approximation that the surface charge is neutralized by opposite sign counterions placed at an increment of d away from the surface. The surface charge potential is linearly dissipated from the surface to the contertions satisfying the charge. The distance, d, will be that to the center of the countertions, i.e. their radius.  The Helmholtz theoretical treatment does not adequately explain all the features, since it hypothesizes rigid layers of opposite charges.  This does not occur in nature.  Diunduh dari sumber: http://web.nmsu.edu/~snsm/classes/chem435/Lab14/double_layer.html ……. 27/10/2012

Gouy-Chapman Double Layer  Gouy suggested that interfacial potential at the charged surface could be attributed to the presence of a number of ions of given sign attached to its surface, and to an equal number of ions of opposite charge in the solution.  The counter ions are not rigidly held, but tend to diffuse into the liquid phase until the counter potential set up by their departure restricts this tendency.  The kinetic energy of the counter ions will, in part, affect the thickness of the resulting diffuse double layer.  Gouy and Chapman developed theories of this so called diffuse double layer in which the change in concentration of the counter ions near a charged surface follows the Boltzman distribution  n = noexp(-zeY/kT)   where no  = bulk concentration            z = charge on the ion             e = charge on a proton             k = boltzman constant Diunduh dari sumber: http://www.ch-non-food.com/science.htm ……. 27/10/2012

Stern Modification of the Diffuse double Layer …. Electric Double Layer Stern Modification of the Diffuse double Layer Stern theory states that ions do have finite size, so cannot approach the surface closer than a few nm.  Stern assumed that it is possible that some of the ions are specifically adsorbed by the surface in the plane d, and this layer has become known as the Stern Layer.  Therefore, the potential will drop by Yo - Yd over the "molecular condenser" (ie. the Helmholtz Plane) and by Yd over the diffuse layer.  Yd has become known as the zeta (z) potential. Diunduh dari sumber: http://web.nmsu.edu/~snsm/classes/chem435/Lab14/double_layer.html ……. 27/10/2012

Kation mana yang lebih disukai? Pertukaran Kation K+ Na+ K+ Na+ K+ K+ K+ Na+ Na+ Na+ Na+ Na+ Kation mana yang lebih disukai? Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Faktor yang menentukan preferensi kation Konsentrasi kation Muatan (+1, +2,+3) Ukuran (diameter atau radius) In hydration, cations (positive, metallic) like Na+ and K+ will be surrounded by water molecules presenting their negative poles Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012 Diunduh dari sumber: http://www.boostdam.net/stories/tonic.html……. 27/10/2012

Kation Tukar The charge of the cation and the size of the hydrated cation essentially govern the preferences of cation exchange equilibria. In summary, highly charged cations tend to be held more tightly than cations with less charge and secondly, cations with a small hydrated radius are bound more tightly and are less likely to be removed from the exchange complex. The combined influence of these two criteria can be summarized generally by the lysotrpoic series. Radius Unit Na+ K+ Mg2+ Ca2+ Al3+ Non-hydrated nm 0.095 0.133 0.066 0.099 0.050 Hydrated 0.360 0.330 0.430 0.410 0.480 aluminium > calcium > magnesium > potassium, ammonium-NH4+ > sodium > hydrogen Diunduh dari sumber: http://nelspeterson1.wordpress.com/agrn-2124-chapter-8-notes/ ……. 27/10/2012

Konsentrasi Kation Larutan tanah K+ K+ K+ Na+ K+ Na+ K+ K+ K+ K+ K+ K+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Muatan listrik Larutan tanah Ca+2 Ca+2 Ca+2 Ca+2 Ca+2 K+ K+ K+ K+ Ca+2 Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Hydration energy also depends on the electronegativity of the element. Ukuran Kation Larutan tanah Na+ As expected from Coulomb's Law , the hydration energy of a cation depends on the charge and radius of the cation. Hydration energy also depends on the electronegativity of the element. Stronger bond (H+ preferred) H+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012 Diunduh dari sumber: http://www.wou.edu/las/physci/ch412/hydrolysis.htm ……. 27/10/2012

Pertukaran Kation Diunduh dari sumber: http://nelspeterson1.wordpress.com/agrn-2124-chapter-8-notes/ ……. 27/10/2012

Kation Dapat Ditukar The surface of an individual clay particle or organic colloid is negatively (-) charged. As a consequence their surfaces attract and adsorb positively charged ions called cations. When water is added to soil, cations can move into solution, however, they are still attracted to the clay particle or organic colloid surface and as a result swarm around them. Positively charged ions capable of being readily substituted from the soil solution and onto the surface of a negatively charged soil particle, and vice-a-versa, are termed exchangeable cations. Diunduh dari sumber: http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_exchangeable_cations.html ……. 27/10/2012

[M(H2O)n]z+ + H2O [M(H2O)n-1(OH)](z-1)+ + H3O+ Kation Tyukar Hydrolysis Metal ions in aqueous solution behave as Lewis acids. The positive charge on the metal ion draws electron density from the O-H bond in the water. This increases the bond's polarity making it easier to break. When the O-H bond breaks, an aqueous proton is released producing an acidic solution. [M(H2O)n]z+ + H2O [M(H2O)n-1(OH)](z-1)+ + H3O+ Diunduh dari sumber: http://www.wou.edu/las/physci/ch412/hydrolysis.htm ……. 27/10/2012

The total quantity of cations a clay can adsorb. KTK Mineral The total quantity of cations a clay can adsorb. Related directly to the amount of Isomorphous substitution Equal to the amount of charge Units are cmolc/kg soil Range: 0 - 180 cmolc/kg Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

1/100 of a mole 1mole = 6.02 x 1023 charges What is a Centimole? 1/100 of a mole 1mole = 6.02 x 1023 charges 1cmol = 6.02 x 1021 charges 1 cmol = 6,020,000,000,000,000,000,000 Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Konsentrasi sangat tinggi NH4+ NH4+ - - - - - - - - - - - - - - - - - - - - - - Na+ Mg2+ H+ NH4+ K+ Ca2+ Al3+ Mg+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

NH4+ Soil beaker K+ Ca2+ Na+ Mg2+ NH4+ K+ Ca2+ Na+ Mg2+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

The number of ammonium ions = number of charges Ba+2 NH4+ Soil Ba2+ NH4+ beaker The number of ammonium ions = number of charges Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

The displaced cations are collected in a Beaker. 1 kg of clay whose negative sites are saturated with NH4+. High concentrations of Ba2+ are used to displace them The displaced cations are collected in a Beaker. The volume of solution in the beaker is 1L. The concentration of NH4+ cations in the beaker is equal to 10 cmol/L 10 cmol NH4+ 1 Liter X 1 L of solution = 10 cmol NH4+ 10 cmolc/kg clay = CEC Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Ukuran bola hidrasi ion sangat beragam + H O Na H O - H O Cl H O H O H O Ukuran bola hidrasi ion sangat beragam Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

H O + H O Na H O H O Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Hydroxide (OH-) O - H “Electron greedy” + Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Kaolinite 1:1 Na+ CEC = 2 – 5 cmolc O - kg Limited isomorphous substitution in octahedra (Al3+ for Si4+ ) CEC = 2 – 5 cmolc kg O H + - Layers are H-bonded Non-expansible Adsorption is on external surfaces and edges Slightly Negative Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Layers weakly held together by cations Mineral Tipe 2:1 Smectites: montmorillonite Significant substitution in the octahedra (Al3+ for Si4+) Ca2+ Mg2+ Na+ CEC = 80-120 cmolc kg Cations satisfying charge Layers weakly held together by cations Highly expansible Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Smectite Air berlebihan H H O Ca Ca Ca Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Smectite Air terbatas H H O Ca Ca Ca Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Moderately expansible Vermiculite Significant substitution in tetrahedra CEC = 100-180 cmolc kg Mg2+ Mg2+ Source of negative charge Is very close to the adsorbed cations Layers tightly bound Moderately expansible Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Illite CEC = 20-40 cmolc kg Significant substitution in tetrahedra K+ Source of negative charge Is very close to the adsorbed Cations Potassium fits into cavities on Clay surfaces clamping them shut. K+ K+ Non-expansible CEC = 20-40 cmolc kg Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Tetrahedra Side View Octahedra Tetrahedra Tetrahedra Top View K+ K Clay Layer Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

{ Mineral-mineral Kaolinite Smectite Vermiculite illite Mineral Expansion CEC (cmol/kg) 1:1 None 2 – 5 2:1 High 80 - 120 2:1 Limited 100 – 160 2:1 None 20-40 { tetrahedral substitution Octahedral substitution tetrahedral substitution Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Where do the minerals occur? Illites Vermiculites Smectites Kaolinite Fe, Al oxides Increased weathering 2:1 1:1 Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

pHzpc Zero Point of Charge, A.k.a: Zero Point of Net Proton Charge (pHZPNPC) or the Isoelectric Point (IEP) Measured by titration curves (pHzpc similar to pKa…) or electrophoretic mobility (tendency of the solids to migrate towards a positively charged plate) Below pHzpc  more sites are protonated  net + charge Above pHzpc  more sites are unprotonated  net - charge Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

POINT OF ZERO CHARGE (PZC) yang disebabkan oleh pengikatan atau disosiasi Proton As can be seen here, the pHpznpc of oxides and silicates varies over a wide range (at least from 2 to > 10). For minerals with very low pHpznpc values (e.g., quartz, feldspars), anion sorption is not likely to be very strong in most natural waters. This is because the pHpznpc value of about 2 is less than the common pH range of natural waters (5.5-8.5), so the surfaces of quartz and feldspars will be negatively charged in most natural waters. On the other hand, minerals with high pHpznpc values (e.g., corundum, Fe-oxides and chrysotile) will generally be more efficient sorbents for anions than for cations, because their surfaces will be positively charged over the pH range of most natural waters. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

From Stumm and Morgan, Aquatic Chemistry Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

REAKSI PERTUKARAN ION Ions adsorbed by outer-sphere complexation and diffuse-ion adsorption are readily exchangeable with similar ions in solution. Cation exchange capacity: The concentration of ions, in meq/100 g soil, that can be displaced from the soil by ions in solution. Also anion exchange capacity for positively charged surfaces Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

REAKSI PERTUKARAN ION Exchange reactions involving common, major cations are treated as equilibrium processes. The general form of a cation exchange reaction is: nAm+ + mBX  mBn+ + nAX The equilibrium constant for this reaction is given by: In the ion-exchange reaction given above, the X represents the solid surface on which ion exchange occurs. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

KTK MINERAL DAN TANAH Note that cation exchange capacities are greatest for 2:1 clay minerals (montmorillonite and vermiculite) and soil organic matter. Oxides, hydroxides and silica sand have the lowest CEC values. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

SORPSI ISOTHERMIK The capacity for a soil or mineral to adsorb a solute from solution can be determined by an experiment called a batch test. In a batch test, a known mass of solid (S m) is mixed and allowed to equilibrate with a known volume of solution (V ) containing a known initial concentration of a solute (C i). The solid and solution are then separated and the concentration (C ) of the solute remaining is measured. The difference C i - C is the concentration of solute adsorbed. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Kd Descriptions of how solutes stick to the surface What would the ‘real’ behavior be you think?? Kd Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

SORPSI ISOTHERMIK The mass of solute adsorbed per mass of dry solid is given by where S m is the mass of the solid. The test is repeated at constant temperature but varying values of C i. A relationship between C and S can be graphed. Such a graph is known as an isotherm and is usually non-linear. Two common equations describing isotherms are the Freundlich and Langmuir isotherms. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

FREUNDLICH ISOTHERM The Freundlich isotherm is described by where K is the partition coefficient and n  1. When n < 1, the plot is concave with respect to the C axis. When n = 1, the plot is linear. In this case, K is called the distribution coefficient (Kd ). The partition coefficient K is a measure of the degree to which a sorbate partitions between the surface and the solution. The higher the value of K, the greater affinity the sorbate has for the surface. The graph above shows how K and n affect the shape of the Freundlich isotherm. The higher K, the steeper the initial slope of the isotherm. The smaller the value of n, the greater the deviation from linearity (the more concave the isotherm becomes with respect to the C axis. The case where n = 1 does not fit the adsorption of most inorganic solutes. However, a Freundlich isotherm with n = 1 is often used successfully to describe the sorption of hydrophobic organic compounds (e.g., carbon tetrachloride). Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

The governing equation for Langmuir isotherms is: The Langmuir isotherm describes the situation where the number of sorption sites is limited, so a maximum sorptive capacity (S max) is reached. The governing equation for Langmuir isotherms is: . The Langmuir isotherm describes cases in which there are a limited number of sites available for sorption, so the sorption sites become saturated. Note that the Langmuir isotherm has a form very similar to the Michaelis-Menton equation used to describe the kinetics of enzyme-mediated reactions (hyperbolic kinetics). Recall that the Michaelis-Menton equation results from the possibility that saturation of the enzyme may limit the rate of reaction. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Sorpsi Kontaminan Organik Organic contaminants in water are often sorbed to the solid organic fractions present in soils and sediments Natural dissolved organics (primarily humic and fulvic acids) are ionic and have a Koc close to zero Solubility is correlated to Koc for most organics Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Mengukur Ciri-ciri Sorpsi Organik Kow, the octanol-water partition coefficient is measured in batches with ½ water and ½ octanol – measures proportion of added organic which partitions to the hydrophobic organic material Empirical relation back to Koc: log Koc = 1.377 + 0.544 log Kow Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

ADSORPSI KATION LOGAM In a natural solution, many metal cations compete for the available sorption sites. Experiments show some metals have greater adsorption affinities than others. What factors determine this selectivity? Ionic potential: defined as the charge over the radius (Z/r). Cations with low Z/r release their waters of hydration more easily and can form inner-sphere surface complexes. Cations with low charge to radius ratios (ionic potentials) are not strongly hydrated. These cations can easily shed their waters of hydration to participate in inner-sphere surface complexes. Cations with high ionic potentials are strongly hydrated; they do not surrender their waters of hydration easily, and so are more likely to form outer-sphere surface complexes. Because inner-sphere complexes are stronger than outer-sphere complexes, we would expect that cations with low ionic potentials would sorb more strongly to surfaces than cations with high ionic potentials. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

ADSORPSI KATION LOGAM Experimental results confirm our suspicions: for series of cations with the same oxidation state (isovalent series), larger cations have greater sorption affinities than smaller cations. Because the charge is constant, larger cations have lower ionic potentials than smaller cations. Thus, as expected, lower ionic potentials correlate with higher sorption affinities. For transition metals, there are additional complications. Transition metals, by definition, differ in the number of d-electrons in their valence shells. These different electronic configurations give rise to something called ligand field effects. Ligand field effects are more important than ionic size in determining sorption affinities, resulting in the order given above. Many isovalent series cations exhibit decreasing sorption affinity with decreasing ionic radius: Cs+ > Rb+ > K+ > Na+ > Li+ Ba2+ > Sr2+ > Ca2+ > Mg2+ Hg2+ > Cd2+ > Zn2+ For transition metals, electron configuration becomes more important than ionic radius: Cu2+ > Ni2+ > Co2+ > Fe2+ > Mn2+ Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

ADSORPSI KATION LOGAM For variable-charge sorbents, the fraction of cations sorbed increases with increasing pH. For each individual ion, the degree of sorption increases rapidly over a narrow pH range (the adsorption edge). For minerals whose surface charge is determined by variable charge, we find experimentally that the percentage of cations sorbed increases with increasing pH. This is a result of the fact that, at low pH, the mineral surface is positively charged, and tends to repel cations, but at high pH, the surface is negatively charged and tends to attract cations. Each cation exhibits a relatively narrow range of pH (about 2 units) over which its sorption increases from near 0% to near 100%. This is referred to as the adsorption or sorption edge. Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

Reaksi Pertukaran dan Kompetisi Tapak For a reaction: A + BX = B + AX Plot of log[B]/[A] vs. log[BX]/[AX] yield n and K When n and K=1  Donnan exchange, exhange only dependent on valence, bonding strictly electrostatic When n=1 and K≠1  Simple ion exchange, dependent on valence AND size, bonding strictly electrostatic When n≠1 and K≠1 Power exchange, no physical description (complicated beyond the model) and unbalanced stoichiometry Diunduh dari sumber: www.uvm.edu/.../Lecture%20... - Amerika Serikat ……. 26/10/2012

KTK Tanah – Rapat muatan permukaan Cation Exchange Capacity of Soils Clay soil particles and organic matter carry a negative charge on their surfaces. Cations are attracted to the negatively-charged particles by electrostatic forces. The net charge of the soil is, therefore, zero. Diunduh dari sumber:   http://www.smart-fertilizer.com/articles/Cation-Exchange-Capacity ……. 27/10/2012

KTK TANAH…. . Larger CEC values indicate that a soil has a greater capacity to hold cations. Therefore, it requires higher rates of fertilizer or lime to change a high CEC soil. When a high CEC soil has good test levels, it offers a large nutrient reserve. However, when it is poor, it can take a large amount of fertilizer or lime to correct that soil test. A high CEC soil requires a higher soil cation level, or soil test, to provide adequate crop nutrition. Low CEC soils hold fewer nutrients, and will likely be subject to leaching of mobile "anion" nutrients. Diunduh dari sumber: http://www.spectrumanalytic.com/support/library/ff/CEC_BpH_and_percent_sat.htm...  ……. 26/10/2012

PERTUKARAN ION Ions adsorbed to soil surfaces can be exchanged with ions in soil solution. Cations and anions CONTOH: Ca+2-colloid + 2 H+ ¬ ¾® 2 H+-colloid + Ca+2 = H+ replaces Ca+2 adsorbed to soil colloids Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

PERTUKARAN ION Organic colloids and inorganic micelles (clays) are sites of ion exchange Where do ions in soil come from? Release from organic matter Rain Weathering of parent material Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Reaksi Pertukaran kation PERTUKARAN ION Exchangeable cations (on soil surfaces) cannot be removed by leaching. Soluble cations (in solution) can be removed by leaching. Reaksi Pertukaran kation Ions with a positive (+) charge are referred to as "cations," while those with a negative (-) charge are referred to as "anions." The interaction of potassium and other cations, such as calcium and magnesium, with the soil colloids is referred to as "cation exchange." Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012 Diunduh dari sumber: http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm……. 27/10/2012

Muatan di Permukaan: Stern Theory The Stern model of the double layer: Ions do have finite size, so cannot approach the surface closer than a few nanometers. Through a distance known as the Stern Layer, ions can be adsorbed onto the surface up to a point referred to as the slipping plane, where the ions adsorbed meet the bulk liquid. At the slipping plane the potential, Ψ, has decreased to what is known as the zeta potential. Diunduh dari sumber: http://en.wikipedia.org/wiki/Surface_charge   ……. 27/10/2012

On soil surfaces, there are: Exchangeable and Nonexchangeable Ions: Exchangeable: weakly held, in contact with soil solution, ready for quick replacement. “outer sphere complex” Nonexchangeable: “inner sphere complex” adsorbed by strong bonds or held in inaccessible places (e.g., the K+ between layers of illite) not part of ion exchange ! Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

KAPASITAS TUKAR KATION (KTK) Sum total of exchangeable cations that a soil can adsorb. ( prevents nutrients from leaching away from roots) Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

KTK = Kapasitas Tukar Kation Dinyatakan dalam satuan: milliequivalents per 100 g (meq/100g). Clay particles and organic matter have negatively charged sites that hold positively charged ions on their surfaces. These cations are rapidly exchangeable with other soluble ions, so when root uptake depletes the nutrient supply they replenish plant-available cations in the soil solution. KTK = Kapasitas Tukar Kation Diunduh dari sumber: http://www.extension.umn.edu/distribution/horticulture/m1193.html   ……. 2/10/2012

KEJENUHAN BASA % of exchange sites occupied by basic cations Basic cations are cations other than H+ and Al+3 The relationship between nutrients attached to the soil clay and organic matter and nutrients in the soil solution. Diunduh dari sumber: http://agsource.crinet.com/page2573/BaseSaturation   ……. 27/10/2012

KEJENUHAN BASA Base saturation is defined as the percentage of the soil exchange sites (CEC) occupied by basic cations, such as potassium (K), magnesium (Mg), calcium (Ca), and sodium (Na). The base saturation percentages are calculated for each cation then added up to determine base saturation. Elements Hypothetical Soil Test Ppm    Divide ppm by     this factor to     calculate meq/100 g   Meq/100 g   % of CEC K+ Mg++ Ca++ Na+ Base (sum) Acidity (H+) Total 75 150 1800 30 390 120 200 230 0.19 1.25 9.0 0.13 10.57 2.0 12.57 1.5 % 9.9 % 71.6 % 1.0 % 84.1% 15.9 % 100.0 % CEC = K ppm/390 + Mg ppm/120 + Ca ppm/200 + Na ppm/230 + H (buffer pH) CEC = Acid (meq/100g) + Base (meq/100g) Base Saturation = Base (meq/100g)/CEC X 100 Diunduh dari sumber: http://agsource.crinet.com/page2573/BaseSaturation   ……. 27/10/2012

Kejenuhan Hidrogen dan pH Tanah Notice neutral pH (7.0) requires a base sat of 80%. (neutral pH is not 50% because most base cations have a + charge of 2) Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

KESETIMBANGAN Strive for equivalent proportions of solution and exchangeable ions. Upset equilibrium by: removal by plants leaching fertilization weathering Initiate ion exchange Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

PERTUKARAN ION: Penambahan ion H+ ke tanah : Ca+ Ca+ Ca+ Ca+ H+ Ca+ Ca+ soil H+ Ca+ + + H+ Ca+ Ca+ H+ H+ Ca+ H+ Ca+ Ca+ Ca+ solution Ca+ Ca+ Ca+ exchangeable solution exchangeable solution Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Diunduh dari: http://www3.ul.ie/~childsp/CinA/Issue41/HomePage.html PERTUKARAN ION The double layer system associated with a negatively charged clay surface Process is Reversible Charge by charge basis Ratio Law: ratio of exchangeable cations will be same as ratio of solution cations Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012 Diunduh dari: http://www3.ul.ie/~childsp/CinA/Issue41/HomePage.html

Menambah pupuk K …..… K+ Ca+2 Ca+2 K+ Ca+2 + K+ + K+ K+ Ca+2 K+ K+ K+ Same ratio Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Energi Adsorpsi Kuat -------------------------------------- Lemah Al+3 > Ca+2 > Mg+2 > [K+ = NH4+ ] > Na+ > H+ (Berdasarkan atas muatan dan radius ion hidrat) Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Pentingnya pH Tanah Determines solubility of nutrients Before plants can get nutrients, they must be dissolved in soil solution Microbial activity also depends on pH Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Soil pH is pH of solution, NOT exchange complex Logaritma negarif dari konsentrasi ion H+ (juga menjadi ukuran konsentrasi ion OH-) If H+ concentration > OH- : acidic If OH- > H+ : basic Soil pH is pH of solution, NOT exchange complex Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Kondisi Umum pH Tanah “Slightly acid” 6.0 – 6.6 “Moderately acid” 5.0 – 6.0 “Strongly acid” < 5.0 “Slightly basic” 7.4 – 8.0 “Moderately basic” 8.0 – 9.0 “Strongly basic” > 9.0 Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Kondisi Umum pH Tanah In soil, both H+ and Al+3 ions produce acidity Al+3 produces H+ ions when it reacts with water. (when pH below 6: Al+3 is the cause of acidity) Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012 Illustration of the Equilibrium Relationship among Residual, Exchangeable, and Active Acidity in a Soil with Organic and Mineral colloids. Diunduh dari sumber: http://www.landfood.ubc.ca/soil200/interaction/acidity.htm ……. 27/10/2012

Sebab-sebab Ke-basa-an Tanah Hydrolysis of basic cations Hydrolysis of carbonates Liming materials consist of calcium and magnesium carbonates. When applied, the carbonates slowly dissolve in the acid soil solutions and replace the hydrogen ions with the calcium and magnesium ions. As the hydrogen ions are replaced by the calcium and magnesium ions, the pH of the soil rises. Diunduh dari sumber:   http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilising-dairy-pastures/chapter-4 ……. 27/10/2012

Hidrolisis kation basa : (especially Ca+2, Mg+2, K+, NH4+, Na+) (also called exchangeable bases) Extent to which exchangeable bases will hydrolyze depends on ability to compete with H+ ions for exchange sites. Na Na Na Na + H2O + OH- Na H Na + Na Na Na Na Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Hidrolisis kation basa : (especially Ca+2, Mg+2, K+, NH4+, Na+) K+ and Na+ are weakly held compared to Ca+2 and Mg+2. Recall energy of adsorption So, K+ and Na+ are hydrolyzed easily and yield higher pHs . Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Hidrolisis Karbonat (especially CaCO3, MgCO3, Na2CO3) As long as there are carbonates in the soil, carbonate hydrolysis controls pH. Calcareous soils remain alkaline because H+ ions combine with OH- to form H2O. For those soils to become acid, all carbonates must be leached. Basic cations replaced by Al+3 and H+ CaCO3 + H2O Ca+2 + HCO3- + OH- Na2CO3 + H2O Na + HCO3- + OH- (higher pH because Na more soluble) Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012

Sebab-sebab Kemasaman Tanah Accumulation of soluble acids Exchangeable acids (Al+3, H+) The pH of the soil is dependent on the quantity of hydrogen ions in the soil solution. If we want to raise soil pH, we need to increase the quantity of OH- ions in solution. However, when more H+ ions are removed from the solution, they are replaced by hydrogen ions that were held on the cation exchange sites. This ability of the soil to withstand rapid changes in pH is important for plant growth. However, it means that the total amount of bases needed to raise the pH is dependent on the total amount of hydrogen ions held on the reserve. This is referred to as buffering capacity. Diunduh dari sumber: http://www.swac.umn.edu/classes/soil2125/doc/s12ch6.htm……. 27/10/2012

Precipitation increases Accumulation of soluble acids at faster rate than they can be neutralized or removed Carbonic acid (respiration and atmospheric CO2) b. Mineralization of organic matter (produces organic, nitric, sulfuric acids) Precipitation increases both a and b Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012 Diunduh dari sumber:  http://hubcap.clemson.edu/~blpprt/acid1.html……. 27/10/2012

Asam Dapat-ditukar: Exchangeable acids Exch. H+ or Al+3 dissociate Al+3 ties up OH- from water, releases an equivalent amount of H+ ions. Al+3 + H2O AlOH+2 + H+ Diunduh dari sumber:   http://hubcap.clemson.edu/~blpprt/acid1.html ……. 27/10/2012

KTK dan pH Only 2:1 silicate clays do not have pH-dependent CECs. Others are pH-dependent: 1:1 kaolinite: low pH: low CEC high pH: high CEC Oxidic clays The relationships between the soil pH and the normalized CEC. The base data were obtained from Saigusa et al. (1992). Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2...  ……. 26/10/2012 Diunduh dari sumber: http://www.sciencedirect.com/science/article/pii/S0167880911000326 ……. 26/10/2012