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Foto:smno.kampus.ub.sept2012. Penyusun Tanah Mineral Udara: Mineral: 20-30% 45% Air: 20-30% Organik 5% Padatan: 50% Pori: 50% Mineral Primer: Kuarsa.

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Presentasi berjudul: "Foto:smno.kampus.ub.sept2012. Penyusun Tanah Mineral Udara: Mineral: 20-30% 45% Air: 20-30% Organik 5% Padatan: 50% Pori: 50% Mineral Primer: Kuarsa."— Transcript presentasi:

1 Foto:smno.kampus.ub.sept2012

2

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

4 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. 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. 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 ( mU) tersebar merata dlm medium dispersinya. Koloid ada dua macam, yaitu GEL (partikel terdispersi dominan) dan SOL (medium dispersinya dominan)

5 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.

6 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 : Fe 2 O 3 Komposisi kimia: mengandung 70% Fe, campurannya Ti dan Mg Struktur kristal: Agak kompleks Habit: Pipih, Rhombohedral Warna: Hitam besi hingga kelabu baja Kekerasan: ; Rapuh Berat jenis: Sifat diagnostik: Warna goresannya merah, sangat keras, tidak magnetik Genesis: Dibentuk dalam suasana oksidasi dlm endapan dan batuan MAGNETIT : FeFe 2 O 4 Komposisi kimia: FeO 70%, Fe2O3 69%, kadar Fe 72.4% Sistem: Kubik, simetrik, heksoktahedral Habit: Oktahedral Warna: Hitam besi Kekerasan: ; Rapuh Berat jenis: Sifat diagnostik: Magnetik kuat, Warna goresannya hitam Genesis: Dibentuk dalam suasana reduksi dlm endapan bijih dan batuan

7 KELOMPOK OKSIDA KUARSA: SiO4 1. Ada tiga polimorfiknya: Kuarsa, Tridimit, Kristobalit 2. Modifikasinya diberi awalan alfa, beta 3. Ion inti Si 4+ dikelilingi oleh empat anion oksigen O = yg menempati titik sudut tetrahedron KUARSA : SiO 2 Komposisi kimia: Sesuai dg formulanya Struktur kristal: Agak sederhana. Habit: Heksagonal Warna: Tidak berwarna, putih susu, kelabu Kekerasan: 7.0 Berat jenis: Sifat diagnostik: Bentuknya yg khas, keras, tdk mempunyai belahan Genesis: Bentuk kristal Kuarsa

8 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: 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: Berat jenis: 2.43 Sifat diagnostik: Belahan sgt baik, kilap kaca, ringan

9 KELOMPOK KARBONAT KALSIT : CaCO 3 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: Sifat diagnostik: Bereaksi dg keras bila diberi HCl MAGNESIT : Mg(CO 3 ) 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: ; Rapuh Berat jenis: Sifat diagnostik: Larut asam bila dipanaskan, kondisi dingin tdk bereaksi dg HCl DOLOMIT : CaMg(CO 3 ) 2 Komposisi kimia: MgO 21.7%, CaO 30.4%, CO2 47.9% Sistem: Trigonal, Simetri rhombohedral Warna: Putih kelabu Kekerasan: ; Rapuh Berat jenis: Sifat diagnostik: Kondisi dingin lambat bereaksi dg HCl

10 KELOMPOK FOSFAT VIVIANIT : Fe 3 (PO 4 ) 2. 8H 2 O Sistem: Monoklinik Habit: Kristal prismatik Warna: tidak berwarna Kekerasan: Berat jenis: 2.68 Sifat diagnostik: Biasanya berubah menjadi biru atau hijau, belahan jelas, larut asam nitrat menghasilkan endapan fosfat yg kuning APATIT : Ca 5 (PO 4 ) 3 Cl,OH,F Sistem: Heksagonal Habit: Kristal dlm batu kapur prismatik Belahan: Tidak jelas Kekerasan: 5.0 ; Rapuh Berat jenis: 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: Berat jenis: Warna: Biru langit, Hijau kebiruan Sifat diagnostik: Warna biru yang khas

11 KELOMPOK FELDSPAR SANIDIN= ORTOKLAS : KAlSi 3 O 8 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 : KAlSi 3 O 8 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) AlSi 2 O 8 Sistem: Triklinik Habit: Kristal biasanya berbentuk batang Warna: Putih atau kelabu Kekerasan: 6.0 Berat jenis: Warna: Putih atau kelabu Sifat diagnostik: bentuk kembar

12 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 : Al 4 Si 4 O 10 (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 : Al 2 Si 4 O 10 (OH) 2. xH2O Sistem: Monoklinik Habit: Kristal sukar dilihat Warna: Biasanya kelabu atau kelabu kehijauan Kekerasan: Berat jenis: , 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.

13 FILO- SILIKAT VERMIKULIT : Mg 3 Si 4 O 10 (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

14 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: 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: Warna: Hijau khas Komposisi kimia: Mg dan Fe dapat saling menggantikan

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

16 TETRAHEDRA SILIKA OKTAHEDRA ALUMINA Si O Al OH

17 MINERALOGI LIAT KAOLINIT 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- hedra 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

18 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 3 OH Kisi kristal tidak tahan terhadap pemanasan Pada suhu 40oC air telah lenyap dan lambat laun terbentuk suatu persenyawaan meta-haloisit

19 MINERALOGI LIAT PIROFILIT 1. Rumus umumnya Al2O3.4SiO2.H2O 2. O Si Al OH 3 O tetra- 2 Si hedra O-OH-O 2 Al okta- O-OH-O hedra tetra- 2 Si hedra 3 O Permukaan kristal tersusun atas atom oksigen dari lempengan Si 2 O 5, bersifat inert

20 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 ………... 3 O tetra- 2 Si hedra O-OH-O 2 Al /Fe/Mg oktahedra O-OH-O tetra- hedra 2 Si 3 O ……….. n H2O ……..

21 MINERALOGI LIAT SERISIT 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 ………... 6 O tetra- Al, 3Si hedra 2O-2OH-2O 4 Al oktahedra 2O-2OH-2O Al, 3Si tetrahedra 6 O …………. K ……….

22 MINERAL LIAT 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 Al 2 O 3.2SiO 2.H 2 O

23 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

24 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 mikron Sifat plastisitas dan kohesinya rendah Sifat koloidalnya tidak terlalu intensif

25 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 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

26 Mineralogi Liat Silikat 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 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)

27 Mineralogi Liat Silikat CAMPURAN LIAT SILIKAT Susunan unit kristalnya berbeda-beda, spt misalnya: 1. Klorit - Illit 2. Ilit-Montmorilonit 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

28 Ciri-ciri Tipe Liat Montmorilonit Ilit Kaolinit Ukuran (mikron) BentukSerpih tak menentu Serpih tak menentu Heksagonal Permukaan jenis (m 2 /g) Permukaan luarLuasSedangSempit Permukaan dalamSgt luasSedangTdk ada Kohesi / PlastisitasTinggiSedangRendah Kapasitas MemuaiTinggiSedangRendah KTK (me/100 g) Sumber: Sifat dan Ciri Tanah (G. Soepardi, 1983)

29 Mineral Koloidal selain Silikat ALOFAN & MINERAL AMORF Bersifat koloidal non-kristalin Alofan: Gabungan antara silikon dan aluminium seskuioksida Susunannya mendekati Al 2 O 3.2SiO 2.H 2 O Banyak ditemukan pada tanah-tanah Abu volkan 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

30 SIFAT Koloidal MINERAL LIAT 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 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.

31 Sumber muatan negatif liat Silikat 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 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

32 Material KTK (meq/100g)KTA Permanen Variabel Total Montmorilonit Vermikulit Illit Halloisit Kaolinit Gibsit Goetit Alofan Peat Sumber: Mehlich & Theisen (Sanchez, 1976).

33 R - C = O R - C = O O O R - C Al + 3OH - R - C + Al(OH) 3 O O 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 - )

34 Fe Fe Fe Fe O OH HO O O OH HO O Fe Fe Fe Fe O OH H + + HO O O OH + OH - O O + H2O H + Fe Fe Fe Fe O OH HO O O OH HO O Fe Fe Fe Fe POSITIF ZERO NEGATIF

35 Net surface charge me/100g AndeptHumult Udalf Orthox pH dlm 0.01 N NaCl Hor A Hor B pH(H2O) = 6 pH(H2O) = 6.8 Hor A Hor B pH(H2O) = 6.5 Hor A pH(H2O) = 5.8 Hor A Hor B

36  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

37  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

38 FAKTOR HUBUNGAN pH vs MUATAN LISTRIK Pada sistem liat-oksida hubungan tsb adalah: kDRT pHo  =  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

39 PERTUKARAN KATION Contoh sederhana: Ca-[MISEL] + 2H + H-[MISEL]-H + Ca ++ PERTUKARAN KATION DI ALAM 40Ca 38Ca + 2 Ca(HCO 3 ) 2 20Al + 5 H 2 CO 3 20Al 20H 25H L(HCO 3 ) 20L 19L tercuci 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: 40Ca7K 20Al 38Ca + 2 CaCl 2 40H + 7 KCl 20Al 20L 39H HCl 18L 2 LCl MISEL

40 KAPASITAS TUKAR KATION [ KTK ] 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 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 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

41 Koloid Organik Montmorilonit Muatan tgt pH Muatan permanen pH tanah KTK, me/100 g)

42 KTK TANAH 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 Tanah asal KTK (me/100g) Kelas tekstur Ciletuh, Jabar8.1Lempung Berdebu Way Seputih, Lampung16.0Lempung Liat Berdebu Pengubuan, Lampug22.9Lempung Liat Berdebu Tj.Kresik, Krawang28.7Liat Berdebu Rentang Barat38.8Liat Berdebu

43 PERSENTASE KEJENUHAN BASA TANAH 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 H + dan Al +++ : sumber kemasaman tanah Al H2O Al(OH) ++ + H + Al(OH) ++ + H2O Al(OH) H + Kation basa: Ca ++, Mg ++, K +, dan Na ++ CaO + H2O Ca(OH) 2 Ca ++ + OH -

44 PERTUKARAN KATION & KETERSEDIAAN HARA 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 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 PENGARUH TIPE KOLOID Berbagai koloid mempunyai daya ikat kation yg berbeda Kalsium diikat oleh montmorilonit lebih kuat daripada oleh kaolinit

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

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

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

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

49 Organization of tetrahedral and octahedral sheets in common soil clays Octahedral Octahedral & Tetrahedral Octahedral & Tetrahedral NONE Tetrahedral Octahedral & Tetrahedral Octahedral & Tetrahedral Illite Montmorillonite Diunduh dari sumber: ……. 25/10/2012

50 Ciri-ciri Umum Liat Silikat Ciri-ciriKaolinit Smektit / Vermiculit Illit (fine-grained micas) Kelas Umum1:1 (TetraOcta)2:1 (TOT) Pengembangan Ikatan lapisan ionic > H-bonding > van der Waals Muatan negatif neto (KTK)  Fertility Lokasi muatan LowLow, noneHigh/Moderate Hydrogen (strong) O-O & O-Cation van der Waals (weak) Potassium ions (strong) 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

51 Tipe-Tipe Muatan Permanen 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

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

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

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

55 Muatan tergantung-pH : tepi kristal Diunduh dari sumber: 27/10/2012 Variable or pH-dependent charge Dissociation of exposed OH groups ]-OH ]-O - + H + uncharged negative charge < (+ H + ) (- H + ) >

56 Muatan tergantung-pH : tepi kristal Diunduh dari sumber: 27/10/2012 Occurs with humus, hydrous oxides, and Broken edges of silicate clays

57 Muatan tergantung-pH : Diunduh dari sumber: 27/10/2012 Increased pH values = more negative charge acid = less negative charge Protonation of O and OH groups ]-O - + H + ]-OH + H + ]-OH 2 + Negative-charge no-charge positive-charge high pH intermediate pH low pH

58 Muatan tergantung-pH : Diunduh dari sumber: 27/10/2012 Depends on soil colloids present Colloid Negative charge Positive charge % constant% variable Humus Vermiculite Smectite Illite Kaolinite Fe & Al Oxides550100

59 Muatan tergantung-pH : Diunduh dari sumber: 27/10/2012 Positive charge << negative charge in most temperate zone soils Acid tropical soils = net + charge

60 Pertukaran Ion The substitution of one ion for another on the surface or in the interstitial spaces of a crystal Cation exchange (e.g., Ca 2+ for K + ) Anion exchange (e.g., H 2 PO 4 - for NO 3 - ) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

61 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

62 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

63 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

64 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 cmol c /kg  tanah mnejerap 10 cmol H +  dapat menukarnya dengan 10 cmol K +, atau 5 cmol Ca 2+ jumlah muatan, bukan jumlah ion, cmol c = centimole muatan yang tidak dinetralkan (diseimbangkan) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

65 Afinitas Pertukaran Held more strongly Held more weakly This is referred to as the “Lyotropic series” H +  Al 3+ > Ca 2+ > Mg 2+ > NH 4 + = K + > Na + Strength of adsorption proportional to valence ÷ hydrated radius Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

66 Pertukaran Ion vs. KTK Sandy loam VERY acidic soil How many charges are there to fill??? NH 4 + Ca 2+ H+H+ Mg 2+ K+K+ NO 3 - Cl - H+H+ H+H+ NO 3 - H+H+ HSO 4 - H+H+ HCO 3 - Crystal edge CEC = 7; AEC = 2 Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

67 KTK tergantung pada Jumlah liat dan bahan organik Tipe mineral liat Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.p pt -……. 25/10/2012 Diunduh dari sumber: 90/Lecture%209/index.htm……. 27/10/2012

68 Petukaran Kation + 2K + Ca 2+ + Ca 2+  K+K+ K+K+ Al K +  K+K+ K+K+ K+K+ + Al 3+ 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

69 Muatan Listrik pada Koloid Tanah Tipe KoloidMuatan NegatifMuayan Positif Humus (O.M.) Liat Silikat Oksida Al dan Fe 200 cmol c /kg0 cmol c /kg 100 cmol c /kg 0 cmol c /kg 4 cmol c /kg5 cmol c /kg Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

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

71 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

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

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

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

75 Kation dijerap oleh Ordo-Tanah Ordo Tanah “Kation asam” (H +, Al 3+ ) “Kation Basa” (misalnya Ca 2+, NH 4 +, K +, etc.) Ultisol Alfisol Mollisol Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

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

77 Kation Tukar : Area Tanah di daerah iklim Humid Tanah di daerah iklim Arid H+H+ H+H+ H+H+ Al 3+ K+K+ K+K+ Ca 2+ Mg 2+ H+H+ NH 4 + Low pH (acidic) High pH (basic) Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

78 CEC low high 38 Soil pH KTK dan pH H + binds tightly, doesn’t exchange Na + binds loosely, exchanges readily Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

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

80 Karakteristik Muatan Tipe KoloidTotal Muatan Konstan (%)Variable (%) Bahan Organik 200 Smectite200 Kaolinite Permanent vs. pH-dependent Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

81 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

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

83 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! Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012 KTK tanah: (a) Related to components Humus » 200 cmol c /kg Smectites » 100 cmol c /kg Illite » 25 cmol c /kg Kaolinite » 10 cmol c /kg Fe and Al oxides » 4 cmol c /kg Estimate soil cation exchange capacity from composition: 5 % O.M. & 20 % smectite clay 200 x 0.05 = x 0.20 = 20 Total = 30 cmol c /kg Sumber: 90/Lecture%209/index.htm

84 KTK Ordo -Tanah (cmol c /kg) Ordo Tanah KTK Oxisols Low Ultisols Alfisols9.0 Mollisols18.7 Vertisols35.6 Histosols low high 1:1 clays 2:1 clays O.M. Low pH High Al/Fe oxides Key factor Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

85 KEJENUHAN BASA A measure of the proportion of basic cations occupying the exchange sites Base cations are those that do not form acids Ca 2+, Mg 2+, K +, Na +, NH 4 +.……..., Ion-ion selain H + and Al 3+ Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

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

87 1:1 Clay Minerals CEC ~ 7 meq/100 g non-expanding Kaolinit 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 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 Si Al Si Al Si Al Si Al Si Al Diunduh dari sumber: ……. 25/10/2012

88 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: ……. 25/10/2012

89 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: ……. 25/10/2012 Kaolinite

90 Mineral Liat Tipe 2:1 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 Diunduh dari sumber: ……. 25/10/2012

91 2:1 Clay Minerals CEC ~ 40 meq/100 g non-expanding Layer T O T Diunduh dari sumber: ……. 25/10/2012

92 Classification of the 2:1 phyllosilicates is based on the total number of permanent charges per half unit cell layer. Muatan LapisanKelompokSpesies yang Umum < 0.2Talc-PyrophylliteTalc, Pyrophyllite SmectiteMontmorillonite, Beidellite Vermiculite > 0.9MicasMuscovite, Biotite approx. 2.0Brittle Micas Margarite Diunduh dari sumber: ……. 25/10/2012 Mineral Liat Tipe 2:1

93 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 Diunduh dari sumber: ……. 25/10/2012

94 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 MICA - Liat Tipe 2:1 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: ……. 25/10/2012

95 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: ……. 25/10/2012 MICA - Liat Tipe 2:1

96 Micas 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: ……. 25/10/2012

97 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 Diunduh dari sumber: ……. 25/10/2012

98 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 Mineral Liat Smectite Diunduh dari sumber: ……. 25/10/2012

99 2:1 Clay Minerals (expanding) KTK: 100 – 200 meq/100 g (vermiculite) 70 – 120 meq/100 g (smectite) Diunduh dari sumber: ……. 25/10/2012

100 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: ……. 25/10/2012

101 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 Ca 2+ or Mg 2+, two layers of water (the thickness of the first hydration shell for Ca 2+ or Mg 2+ ) 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: ……. 25/10/2012

102 1. These clay silicates form by crystallization from solution high in soluble silica and magnesium. 2. Montmorillonite has a 2 : 1 layer structure. 3. All tetrahedra in the sheets contain Si 4+ ions. 4. Aluminium is the normal ion in the central sheet, but about one- eight of the octahedra contain Mg 2+ as a substituting ion for Al 3+. Mineral Liat Montmorillonit Diunduh dari sumber: ……. 25/10/2012

103 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: ……. 25/10/2012 Mineral Liat Montmorillonit

104 Si Al Si Al Si Al Si 0.96 nm joined by weak van der Waal’s bond  easily separated by water  also called smectite; expands on contact with water Diunduh dari sumber: ……. 25/10/2012 Mineral Liat Montmorillonit

105  A highly reactive (expansive) clay  montmorillonite family  used as drilling mud, in slurry trench walls, stopping leaks Bentonite swells on contact with water  (OH) 4 Al 4 Si 8 O 20.nH 2 O high affinity to water Diunduh dari sumber: ……. 25/10/2012 Mineral Liat Montmorillonit

106 Mineral Liat Illite Si Al Si Al Si Al Si 0.96 nm joined by K + ions fit into the hexagonal holes in Si-sheet Diunduh dari sumber: ……. 25/10/2012

107 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: ……. 25/10/2012

108 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 Al 3+ for Si 4+ substitution in the tetrahedral sheet (net negative charge) There is Al 3+ for Mg 2+ substitution in the interlayer (net positive charge) Both dioctahedral and trioctahedral occupancies can exist in chlorites. Chlorite CEC cmol Kg -1 Diunduh dari sumber: ……. 25/10/2012

109 Secondary mineral Type Interlayer condition / Bonding CEC [cmol/kg] Swelling potential Specific surface area [m 2 /g] Basal spacing [nm] Kaolinite 1 : 1 (non- expanding) lack of interlayer surface, strong bonding almost none Montmorillonite 2 : 1 (expanding) very weak bonding, great expansion high Vermiculite 2 : 1 (expanding) weak bonding, great expansion high Hydrous Mica 2 : 1 (non- expanding) partial loss of K, strong bonding low Chlorite 2 : 1 : 1 (non- expanding) moderate to strong bonding, non-expanding none1.4 Allophane Karakteristik Mineral Liat dalam Tanah Diunduh dari sumber: ……. 25/10/2012

110 Substitusi Isomorfik pada Kristel Mineral Liat Tipe 2:1 No substitution With isomorphic substitution sheet charges 5 + Diunduh dari sumber: ……. 25/10/2012

111 Sumber muatan tergantung pH pada Kaolinit More acid Diunduh dari sumber: ……. 25/10/2012

112 Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 MUATAN Dan REAKSI PERMUKAAN

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

114 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. Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 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).

115 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: - Amerika Serikat ……. 26/10/2012

116 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 pH zpc ) Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

117 Permukaan Koloid yang Bermuatan Mineral surface has exposed ions that have an unsatisfied bond  in water, they bond to H 2 O, many of which rearrange and shed a H + ≡S- + H 2 O  ≡S—H 2 O  ≡S-OH + H + H+H+ OH H+H+ OH2 OH Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

118 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-OH 2 + The # of sites on a surface that are +, -, or 0 charge is a function of pH pH zpc is the pH where the + sites = - sites = 0 sites and the surface charge is nil OH2 + OH O- O-O- OH2 + Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

119 oxygen silicon (Si 4+ ) hydroxide (OH - ) Aluminum (Al 3+ ) Silicon Tetrahedron Aluminum octahedron Building Blocks for Silicate Clays Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

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

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

122

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

124 Positive charge Al 3+ Si 4+ Negative charge OH - O 2- KESEIMBANGAN MUATAN Al 3+ Si 4+ OH - O 2- = Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

125 Substitusi Isomorfik Substitution of lower-charge cations for higher charge cations during mineral formation. Al 3+ for Si 4+ in tetrahedra Mg 2+ for Al 3+ 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

126 Substitusi Tetrahedra: Al menggantikan Si Al 3+ for Si 4+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

127 Substitusi Octahedra: Mg menggantikan Al Mg 2+ for Al 3+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012 Substitusi Octahedra: Zn menggantikan Al

128 Tetrahedral Substitution Octahedral Substitution Al 3+ for Si 4+ Mg 2+ for Al 3+ Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

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

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

131 Diunduh dari sumber: ……. 27/10/2012 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.

132 Diunduh dari sumber: ……. 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.

133 Diunduh dari sumber: ……. 27/10/2012 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..

134 Diunduh dari sumber: ……. 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. 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 = n o exp(-zeY/kT) where n o = bulk concentration z = charge on the ion e = charge on a proton k = boltzman constant 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.

135 …. 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 Y o - Y d over the "molecular condenser" (ie. the Helmholtz Plane) and by Y d over the diffuse layer. Y d has become known as the zeta (z) potential. Diunduh dari sumber: ……. 27/10/2012

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

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

138 Diunduh dari sumber: ……. 27/10/2012 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. Kation Tukar RadiusUnitNa + K+K+ Mg 2+ Ca 2+ Al 3+ Non- hydrated nm Hydratednm aluminium > calcium > magnesium > potassium, ammonium-NH 4+ > sodium > hydrogen

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

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

141 Na + H+H+ Stronger bond (H + preferred) Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... … …. 26/10/2012 Larutan tanah Ukuran Kation 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. Diunduh dari sumber: ……. 27/10/2012

142 Diunduh dari sumber: ……. 27/10/2012 Pertukaran Kation

143 Diunduh dari sumber: ……. 27/10/2012 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. Kation Dapat Ditukar

144 Diunduh dari sumber: ……. 27/10/2012 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. Kation Tyukar [M(H 2 O) n ] z+ + H 2 O [M(H 2 O) n-1 (OH)] (z-1)+ + H 3 O +

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

146 What is a Centimole? 1/100 of a mole1mole = 6.02 x charges 1cmol = 6.02 x charges 6,020,000,000,000,000,000,000 1 cmol = Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

147 Na+ Mg2+ H+ NH 4 + K+ Ca2+Na+ Al3+ K+ Na+ Ca2+ Mg+ K+ NH 4 + Al3+ NH 4 + Konsentrasi sangat tinggi Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

148 Soil NH 4 + K+K+ Ca 2+ Na + Mg 2+ K+K+ Ca 2+ Na + Mg 2+ beaker NH 4 + Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

149 Soil Ba +2 beaker NH 4 + Ba 2+ The number of ammonium ions = number of charges Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

150 1 kg of clay whose negative sites are saturated with NH 4 +. High concentrations of Ba 2+ are used to displace them The displaced cations are collected in a Beaker. The concentration of NH 4 + cations in the beaker is equal to 10 cmol/L The volume of solution in the beaker is 1L. 10 cmol NH Liter X 1 L of solution = 10 cmol NH cmol c /kg clay = CEC Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

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

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

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

154 CEC = 2 – 5 cmol c kg Limited isomorphous substitution in octahedra (Al 3+ for Si 4+ ) Kaolinite 1:1 Layers are H-bonded Non-expansible Adsorption is on external surfaces and edges Na + O H + - Slightly Negative Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

155 Mineral Tipe 2:1 Smectites: montmorillonite Significant substitution in the octahedra (Al 3+ for Si 4+ ) Ca 2+ Mg 2+ Na + Cations satisfying charge CEC = cmol c kg Layers weakly held together by cations Highly expansible Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

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

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

158 Mg 2+ Source of negative charge Is very close to the adsorbed cations Layers tightly bound Moderately expansible Significant substitution in tetrahedra CEC = cmol c kg Diunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012 Vermiculite

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

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

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

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

163 pH zpc Zero Point of Charge, A.k.a: Zero Point of Net Proton Charge (pH ZPNPC ) or the Isoelectric Point (IEP) Measured by titration curves (pH zpc similar to pK a …) or electrophoretic mobility (tendency of the solids to migrate towards a positively charged plate) Below pH zpc  more sites are protonated  net + charge Above pH zpc  more sites are unprotonated  net - charge Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

164 POINT OF ZERO CHARGE (PZC) yang disebabkan oleh pengikatan atau disosiasi Proton Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 As can be seen here, the pH pznpc of oxides and silicates varies over a wide range (at least from 2 to > 10). For minerals with very low pH pznpc values (e.g., quartz, feldspars), anion sorption is not likely to be very strong in most natural waters. This is because the pH pznpc value of about 2 is less than the common pH range of natural waters ( ), so the surfaces of quartz and feldspars will be negatively charged in most natural waters. On the other hand, minerals with high pH pznpc 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.

165 From Stumm and Morgan, Aquatic Chemistry Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

166 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: - Amerika Serikat ……. 26/10/2012

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

168 KTK MINERAL DAN TANAH Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 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.

169 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: - Amerika Serikat ……. 26/10/2012

170 KdKd Descriptions of how solutes stick to the surface What would the ‘real’ behavior be you think?? KdKd Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

171 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: - Amerika Serikat ……. 26/10/2012

172 FREUNDLICH ISOTHERM 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 ). Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 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). The Freundlich isotherm is described by where K is the partition coefficient and n  1.

173 LANGMUIR ISOTHERM 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: Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012. 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.

174 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 K oc close to zero Solubility is correlated to K oc for most organics Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

175 Mengukur Ciri-ciri Sorpsi Organik K ow, 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 K oc : log K oc = log K ow Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012

176 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. Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 ADSORPSI KATION LOGAM 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.

177 ADSORPSI KATION LOGAM Many isovalent series cations exhibit decreasing sorption affinity with decreasing ionic radius: Cs + > Rb + > K + > Na + > Li + Ba 2+ > Sr 2+ > Ca 2+ > Mg 2+ Hg 2+ > Cd 2+ > Zn 2+ For transition metals, electron configuration becomes more important than ionic radius: Cu 2+ > Ni 2+ > Co 2+ > Fe 2+ > Mn 2+ Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 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.

178 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). Diunduh dari sumber: - Amerika Serikat ……. 26/10/2012 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.

179 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: - Amerika Serikat ……. 26/10/2012

180 KTK Tanah – Rapat muatan permukaan Diunduh dari sumber: ……. 27/10/2012 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.

181 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: ……. 26/10/2012

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

183 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: ……. 26/10/2012 PERTUKARAN ION

184 Exchangeable cations cannot be removed Exchangeable cations (on soil surfaces) cannot be removed by leaching. Soluble cations leaching. Soluble cations (in solution) can be removed by leaching. Diunduh dari sumber: nts/Soil%2... ……. 26/10/2012 PERTUKARAN ION 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: 27/10/2012 Reaksi Pertukaran kation

185 Diunduh dari sumber: ……. 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.

186 On soil surfaces, there are: Exchangeable and Nonexchangeable Ions : Exchangeable Exchangeable: weakly held, in contact with soil solution, ready for quick replacement. “outer sphere complex “outer sphere complex” Nonexchangeable 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: ……. 26/10/2012

187 KAPASITAS TUKAR KATION (KTK) Sum total of exchangeable cations that a soil can adsorb. ( prevents nutrients from leaching away from roots) Diunduh dari sumber: ……. 26/10/2012

188 KTK 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. Diunduh dari sumber: ……. 2/10/2012 KTK = Kapasitas Tukar Kation

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

190 KEJENUHAN BASA Diunduh dari sumber: ……. 27/10/2012 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 % 9.9 % 71.6 % 1.0 % 84.1% 15.9 % % 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

191 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: ……. 26/10/2012

192 KESETIMBANGAN Strive for equivalent proportions of solution and exchangeable ions. Upset equilibrium by: removal by plants leachingfertilizationweathering Initiate ion exchange Diunduh dari sumber: ……. 26/10/2012

193 PERTUKARAN ION: Penambahan ion H + ke tanah : soil Ca+ + H+H+ H+ solution exchangeablesolution + H+ Ca+ exchangeablesolution Diunduh dari sumber: ……. 26/10/2012

194 PERTUKARAN ION Reversible Process is Reversible Charge by charge Charge by charge basis Ratio Law Ratio Law: – ratio of exchangeable cations will be same as ratio of solution cations Diunduh dari sumber: oints/Soil%2... ……. 26/10/2012 The double layer system associated with a negatively charged clay surface Diunduh dari:

195 Menambah pupuk K …..… Ca +2 K+K+ + K+ + 1 Ca : 2 K Same ratio Diunduh dari sumber: ……. 26/10/2012

196 Energi Adsorpsi Kuat Lemah Al +3 > Ca +2 > Mg +2 > [K + = NH 4 + ] > Na + > H + (Berdasarkan atas muatan dan radius ion hidrat) Diunduh dari sumber: ……. 26/10/2012

197 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: ……. 26/10/2012

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

199 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: ……. 26/10/2012

200 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: ……. 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: ……. 27/10/2012

201 Sebab-sebab Ke-basa-an Tanah 1.Hydrolysis of basic cations 2.Hydrolysis of carbonates Diunduh dari sumber: pastures/chapter-4 ……. 27/10/2012 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.

202 Hidrolisis kation basa : (especially Ca +2, Mg +2, K +, NH 4 +, Na + ) exchangeable bases ( also called exchangeable bases ) Extent to which exchangeable bases will hydrolyze depends on ability to compete with H+ ions for exchange sites. Na + H2OH2O H + + OH - Diunduh dari sumber: ……. 26/10/2012

203 Hidrolisis kation basa : (especially Ca +2, Mg +2, K +, NH 4 +, 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: ……. 26/10/2012

204 Hidrolisis Karbonat (especially CaCO 3, MgCO 3, Na 2 CO 3 ) 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 H 2 O. For those soils to become acid, all carbonates must be leached. Basic cations replaced by Al +3 and H + CaCO 3 + H 2 O Ca +2 + HCO OH - Na 2 CO 3 + H 2 O Na + HCO OH - (higher pH because Na more soluble) Diunduh dari sumber: ……. 26/10/2012

205 Sebab-sebab Kemasaman Tanah 1.Accumulation of soluble acids 2.Exchangeable acids (Al +3, H + ) Diunduh dari sumber: 27/10/2012 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.

206 Accumulation of soluble acids at faster rate than they can be neutralized or removed a.Carbonic acid (respiration and atmospheric CO 2 ) b. Mineralization of organic matter (produces organic, nitric, sulfuric acids) Precipitation increases both a and b Diunduh dari sumber: oil%2... ……. 26/10/2012 Diunduh dari sumber: …. 27/10/2012

207 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 + H 2 O AlOH +2 + H+ Diunduh dari sumber: ……. 27/10/2012

208 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 Diunduh dari sumber: %2... ……. 26/10/2012 The relationships between the soil pH and the normalized CEC. The base data were obtained from Saigusa et al. (1992). Diunduh dari sumber: ……. 26/10/2012


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