KOLOID TANAH & MINERAL LIAT

KOLOID TANAH&MINERAL LIAT

Foto:smno.kampus.ub.sept2012

Penyusun Tanah Mineral

Udara: Mineral:

20-30% 45%

Air:

20-30%

Organik

5%

Padatan: 50%

Pori: 50%

Mineral Primer: KuarsaMineral Sekunder: Liat silikat

MINERAL Mineralogi: cabang ilmu geologi yg mempelajari kerak bumi dari sudut pandang MINERALMINERAL = “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, lemadalah 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)

Divisi I : Unsur-unsur alami dan senyawa inter-metalikDivisi II : Karbida, Nitrida, dan FosfidaDivisi III : Sulfida, Garam Sulfon, dan senyawa turunannyaDivisi 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-sendiri2. Soro-silikat : dua SiO4 berpolimerisasi3. Siklo-silikat : Tetrahedra SiO4 membentuk rantai siklis4. Ino-silikat : Tetrahedra SiO4 membentuk lembaran kontinyu5. Filo-silikat : Polimerisasi SiO4 membentuk struktur tiga dimensi6. Tekto-silikat : Tetrahedra SiO4 berpolimerisasi membentuk struktur tiga

dimensi yang kompleks.

KELOMPOK OKSIDA

1. Dalam pembentukannya diperlukan oksigen dari udara2. Ikatan ionik di antara unit-unit strukturalnya3. Struktur kristal mengandung O (oksida) dan OH- (hidroksida)4. Dlm struktur kristalnya, kation inti dikelilingi oleh anion oksigen dan hidroksil

HEMATIT : Fe2O3Komposisi kimia : mengandung 70% Fe, campurannya Ti dan MgStruktur kristal : Agak kompleksHabit : Pipih, RhombohedralWarna : Hitam besi hingga kelabu bajaKekerasan : 5.5 - 6.0; RapuhBerat jenis : 5.0 - 5.2Sifat diagnostik : Warna goresannya merah, sangat keras, tidak magnetikGenesis : Dibentuk dalam suasana oksidasi dlm endapan dan batuan

MAGNETIT : FeFe2O4Komposisi kimia : FeO 70%, Fe2O3 69%, kadar Fe 72.4%Sistem : Kubik, simetrik, heksoktahedralHabit : OktahedralWarna : Hitam besi Kekerasan : 5.5 - 6.0; RapuhBerat jenis : 4.9 - 5.2Sifat diagnostik : Magnetik kuat, Warna goresannya hitam Genesis : Dibentuk dalam suasana reduksi dlm endapan bijih dan batuan

KELOMPOK OKSIDA

KUARSA: SiO41. Ada tiga polimorfiknya: Kuarsa, Tridimit, Kristobalit2. Modifikasinya diberi awalan alfa, beta3. Ion inti Si4+ dikelilingi oleh empat anion oksigen O= yg menempati titik sudut tetrahedron

KUARSA : SiO2Komposisi kimia : Sesuai dg formulanya Struktur kristal : Agak sederhana . Habit : HeksagonalWarna : Tidak berwarna, putih susu, kelabuKekerasan : 7.0Berat jenis : 2.5 - 2.8Sifat diagnostik : Bentuknya yg khas, keras, tdk mempunyai belahanGenesis :

Bentuk kristal Kuarsa

KELOMPOK HIDROKSIDA

1. Senyawa logam dengan OH- : Hidrat atau hidroksida2. Struktur kristalnya berlapis 3. Heksagonal

BRUSIT : Mg(OH)2Komposisi kimia : MgO 69%; H2O 31%; campurannya Fe dan MnStruktur kristal : BerlapisHabit : Tabuler tebalWarna : Putih, kadangkala kehijauan Kekerasan : 2.5 Berat jenis : 2.3 - 2.4 Sifat diagnostik : Mudah larut dlm HCl

HIDRARGILIT : Al(OH)3Komposisi kimia : Al2O3 65.4%, H2O 34.6%Sistem : Monoklin, Simetri prismatikStruktur kristal : Berlapis, lembaran Al dijepit oleh dua lembaran hidroksilHabit : Tabuler-heksagonalWarna : Putih, sedikit kekelabuan Kekerasan : 2.5 - 3.5Berat jenis : 2.43Sifat diagnostik : Belahan sgt baik, kilap kaca, ringan

KELOMPOK KARBONAT

KALSIT : CaCO3Komposisi kimia : CaO 56%; CO2 44%; campurannya Mg, Fe dan

Mn sampai 8%Struktur kristal : spt NaClHabit : SkalenohedralAgregat : Kalsit yg kompak disebut “Marble”, Sdg

Batukapur bersifat kriptokristalin kompakWarna : 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 skalenohedralStruktur kristal : Analog dg kalsit Habit : Umumnya rhombohedralWarna : Putih dg becak kekuningan atau kekelabuan Kekerasan : 4.0 - 4.5 ; RapuhBerat jenis : 2.9 - 3.1Sifat diagnostik : Larut asam bila dipanaskan, kondisi dingin tdk bereaksi dg HCl

DOLOMIT : CaMg(CO3)2Komposisi kimia : MgO 21.7%, CaO 30.4%, CO2 47.9%Sistem : Trigonal, Simetri rhombohedral Warna : Putih kelabu Kekerasan : 3.5 - 4.0 ; RapuhBerat jenis : 1.8 - 2.9 Sifat diagnostik : Kondisi dingin lambat bereaksi dg HCl

KELOMPOK FOSFAT

VIVIANIT : Fe3(PO4)2 . 8H2OSistem : MonoklinikHabit : Kristal prismatikWarna : 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,FSistem : Heksagonal Habit : Kristal dlm batu kapur prismatikBelahan : Tidak jelas Kekerasan : 5.0 ; RapuhBerat jenis : 3.1 - 3.2Warna : Hijau, hijau kebiruan, hijau kelabu, biru, violetSifat diagnostik : Bentuk kristalnya, warnanya , lareut dlm asam

TURQUOIS : CuAl6(PO4)4(OH)8. 4H2OSistem : Triklinik Habit : Kristal jarang ditemukan, biasanya masif Warna : Putih kelabu Kekerasan : 5 - 6.0 Berat jenis : 2.6 - 2.8Warna : Biru langit, Hijau kebiruan Sifat diagnostik : Warna biru yang khas

KELOMPOK FELDSPAR

SANIDIN= ORTOKLAS : KAlSi3O8Sistem : MonoklinikHabit : Kristal prismatik pndek, agak pipih atau memanjangWarna : umumnya tidak berwarna Kekerasan : 6.0 Berat jenis : 2.56 Sifat diagnostik : Kilap kaca

MIKROKLIN : KAlSi3O8Sistem : Triklinik Habit : Serupa dg OrtoklasBelahan : Sempurna, baik Kekerasan : 6.0 Berat jenis : 2.56Warna : Putih, cream, merah mudaSifat 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 - 2.76Warna : Putih atau kelabu 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 pipihBelahan : Sempurna Kekerasan : 2.0 Berat jenis : 2.6Warna : Putih, seringkali berbintik coklat atau kelabu Kimiawi : Komposisi sesuai formula, substitusi jarang terjadi.

Polimorfiknya adalah Dikrit, Nakrit, dan Haloisit.

MONTMORILONIT : Al2Si4O10(OH)2. xH2OSistem : Monoklinik Habit : Kristal sukar dilihat Warna : Biasanya kelabu atau kelabu kehijauanKekerasan : 2 - 2.5 Berat jenis : 2.0 - 2.7, menurun dengan kadar airSifat 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 . xH2OSistem : Monoklinik Habit : Biasanya pseudomorfBelahan : Sempurna Kekerasan : 1.5 Berat jenis : 2.4Warna : Kuning sampai coklat Kimiawi : Selalu ada sejumlah Al yg menggantikan Si,

Mg oleh feri

KELOMPOK MIKA

MUSKIVIT : KAl2(AlSi3O10) (OH)2Sistem : MonoklinikHabit : Biasanya masanya berlapisWarna : Tidak berwarna atau pucatKekerasan : 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)2Sistem : Monoklinik Habit : Kristalnya prisma pseudo-heksagonal, seringkali pipih berlapisBelahan : Sempurna Kekerasan : 2.5Berat jenis : 2.8 - 3.4Warna : 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)8Sistem : Monoklinik Habit : Kristal pseudo-heksagonal Warna : Hijau khas Kekerasan : 2.5 Berat jenis : 2.6 - 3.3Warna : Hijau khas Komposisi kimia : Mg dan Fe dapat saling menggantikan

Alumino silikatKaya 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

-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

TETRAHEDRA SILIKA OKTAHEDRA ALUMINA

Si

O

Al

OH

MINERALOGI LIATKAOLINIT

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 Otetra- 2 Sihedra

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

MINERALOGI LIATHALOISIT

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 Otetra- 2 Sihedra 2 OH

3 OH2 Al Oktahedra

3 OH

Kisi kristal tidak tahan terhadap pemanasanPada suhu 40oC air telah lenyap dan lambat laun terbentuk suatu

persenyawaan meta-haloisit

MINERALOGI LIATPIROFILIT 1. Rumus umumnya

Al2O3.4SiO2.H2O2.

O

Si

Al

OH

3 Otetra- 2 Sihedra O-OH-O 2 Al okta-

O-OH-O hedra

tetra- 2 Sihedra 3 O

Permukaan kristal tersusun atas atom oksigen dari lempengan Si2O5, bersifat inert

MINERALOGI LIATMONTMORILONIT

1. Kisi kristalnya bersifat dapat membengkak2. Ruang antara Lempeng-lempeng dapat dimasuki air, shg

jarak antar lempengan melebar3. Rumus umum Al2O3.4SiO2.H2O.nH2O

n H2O n H2O

n H2O n H2O

……….. n H2O ………...

3 Otetra- 2 Sihedra O-OH-O

2 Al /Fe/Mg oktahedraO-OH-O

tetra-hedra 2 Si

3 O

………..n H2O ……..

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 Otetra- Al, 3Sihedra 2O-2OH-2O

4 Al oktahedra

2O-2OH-2O

Al, 3Si tetrahedra6 O

…………. K ……….

MINERAL LIAT Ukuran liat 2 mikron

Ukuran partikel koloid 1 mikronTidak semua liat bersifat koloidal

LIAT SILIKAT:Berbentuk pipih-laminer, lapisan lempenganBerstruktur kristal = kristalinUmumnya bersifat koloidalLuas permukaannya sangat besarPermukaannya bermuatan elektronegatif shg mampu menjerap kation-kation

Liat Fe dan Al-hidrous-oksida:Tidak mempunyai struktur kristal, amorfBanyak dijumpai di daerah tropika

ALOFAN: Si dan Al seskui-oksida Al2O3.2SiO2.H2O

STRUKTUR LIAT

SILIKAT

Ukuran kecil , KRISTALINTersusun atas unit-unit kristalSusunan 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 silikaOktahedra alumina

Kedua lempengan ini berikatan satu-sama lain dalam kristal liat melalui atom oksigen …….. “Jembatan oksigen”

Tetrahedra OktahedraSiO4

Mineralogi Liat Silikat Berdasar susunan lempeng dlm unit kristal:

1. Tipe mineral 1:1 (Silika : Alumina)2. Tipe mineral 2:1 yg unit kristalnya memuai3. Tipe mineral 2:1 yg unit kristalnya tdk memuai4. Tipe mineral 2:2

Tipe Mineral 1:1Kaolinit, Haloisit, Anauksit, DikitUnit kristal terdiri atas satu lempeng silika & satu aluminaKisi kristalnya 1:1Kedua 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 hidrogensehingga tidak dapat memuai (mengembang-mengkerut)Permukaan efektif terbatas di permukaan luar sajaHampir tidak ada substitusi isomorfikNilai KTK-nya rendahKristal Kaolinit berbentuk heksagonal, diameternya 0.1 - 5 mikronSifat plastisitas dan kohesinya rendahSifat koloidalnya tidak terlalu intensif

Mineralogi Liat Silikat

Tipe mineral Memuai 2:1 Unit kristalnya tersusun atas lempeng alumina yang dijepit oleh dua lempeng silikaDua Kelompok yang terkenal:1. Montmorilonit : Montmorilonit, Beidelit, Nontronit, Saponit2. Vermikulit

MONTMORILONIT

Unit-UNIT kristal diikat bersama melalui ikatan oksigen yang lemah, sehingga kisi kristal mudah mengembang bila basahDiameter montmorilonit 0.01 - 1 mikronPermukaannya 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 OktahedronAl menggantikan sebagian Si dalam lempeng Tetrahedron

Sifat plastisitas dan kohesinya tinggi, mengembang & mengkerutSifat koloidalnya sangat intensif


Tipe mineral 2:1 Tidak Memuai (ILLIT) Ukurannya berada di antara montmorilonit dan kaolinitMuatan 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 MontmorilonitPd 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 besarKapasitas jerapan (KTK) sangat besar.

Molekul air bersama dg kation Mg dijerap kuat di antara unit kristal, sehingga derajat memuainya tidak terlalu intensif (MEMUAI TERBATAS)


CAMPURAN LIAT SILIKAT Susunan unit kristalnya berbeda-beda, spt misalnya:

1. Klorit - Illit2. 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

Ciri-ciri Tipe Liat Montmorilonit Ilit Kaolinit

Ukuran (mikron) 0.01 - 1 0.1 - 2 0.1 - 5Bentuk Serpih tak menentu Serpih tak menentu HeksagonalPermukaan jenis (m2/g) 700-800 100-200 5 - 20Permukaan luar Luas Sedang SempitPermukaan dalam Sgt luas Sedang Tdk adaKohesi / Plastisitas Tinggi Sedang RendahKapasitas Memuai Tinggi Sedang RendahKTK (me/100 g) 80-100 15 - 40 3 - 15

Sumber: Sifat dan Ciri Tanah (G. Soepardi, 1983)

Mineral Koloidal

selain Silikat

ALOFAN & MINERAL AMORF Bersifat koloidal non-kristalin Alofan: Gabungan antara silikon dan aluminium seskuioksida

Susunannya mendekati Al2O3.2SiO2.H2OBanyak ditemukan pada tanah-tanah Abu volkan

HIDRUS OKSIDA BESI & ALUMINIUM

Liat ini penting karena Sangat dominan di daerah tropikaMolekul air berasosiasi dengan oksida :

Fe2O3.xH2O : Limonit dan GoetitAl2O3.xH2O : Gibsit

Muatan negatifnya sedikitSifat plastisitas, lengket, dan kohesinya rendahTanah yg kaya minerla liat ini biasanya sifat isiknya baik

SIFAT Koloidal

MINERAL LIAT

PENJERAPAN DAN PERTUKARAN ION Penjerapan kation dipengaruhi oleh:

1. Jenis kation2. Konsentrasi ion-ion3. Sifat anion yang berhubungan dg kation4. 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.

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 alumina2. 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

Material KTK (meq/100g) KTAPermanen Variabel Total

Montmorilonit 112 6 118 1Vermikulit 85 0 85 0Illit 11 8 19 3Halloisit 6 12 18 15Kaolinit 1 3 4 2Gibsit 0 5 5 5Goetit 0 4 4 4Alofan 10 41 51 17Peat 38 98 136 6

Sumber: Mehlich & Theisen (Sanchez, 1976).

R - C = O R - C = O

O O O O

R - C Al + 3OH- R - C + Al(OH)3

O O 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-)

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

Net surface chargeme/100g

Andept Humult

UdalfOrthox

-

0

+

-

0

+

-

0

+

-

0

+

pH dlm 0.01 N NaCl

Hor A

Hor B

pH(H2O) = 6pH(H2O) = 6.8

Hor AHor B

pH(H2O) = 6.5

Hor A

pH(H2O) = 5.8

Hor AHor B

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/100gAndepts : 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 pHdimana: : muatan permukaan (m.eq./ 100 g)k : reciprocal tebal lapisan rangkap (tgt konsentrasi lrt tanah)D : konstante dielektrikR : konstante gasT : temperatur absolutF : konstante FaradaypH : pH tanahpHo : 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

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

MISEL MISEL

KAPASITAS TUKAR KATION

[ KTK ]

PENGARUH pH TANAHSebagian 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 MENYATAKANSatuan 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

4.0 5.0 6.0 7.0 8.0 pH tanah

200

160

120

80

40

KTK, me/100 g)

KTK TANAH

FAKTOR YG MEMPENGARUHI1. Tekstur tanah: semakin halus teksturnya semakin tinggi KTKnya2. Kandungan humus dan liat koloidal menentukan KTK tanah3. Macam liat koloidal juga mempengaruhi besarnya KTK tanah

Tanah asal KTK (me/100g) Kelas tekstur

Ciletuh, Jabar 8.1 Lempung BerdebuWay Seputih, Lampung 16.0 Lempung Liat BerdebuPengubuan, Lampug 22.9 Lempung Liat BerdebuTj.Kresik, Krawang 28.7 Liat BerdebuRentang Barat 38.8 Liat Berdebu

PERSENTASE KEJENUHAN BASA TANAH

KB dan pHProporsi KTK yang ditempati oleh kation-kation basa disebut PERSENTASE KEJENUHAN BASAPenurunan %KB mengakibatkan menurunnya pHTanah di daerah iklim kering biasanya mempunyai KB yang tinggiTanah 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)2+ + H+

Kation basa: Ca++, Mg++, K+, dan Na++

CaO + H2O Ca(OH)2 Ca++ + OH-

PERTUKARAN KATION &

KETERSEDIAAN HARA

Kejenuhan kation dan serapan haraFaktor pelepasan kation jerapan:1. Rasio / proporsi jenis-jenis kation pd kompleks jerapan2. Kejenuhan Ca yg tinggi ------- Ca++ mudah diserap tanaman3. Pengaruh jenis kation lain: Afinitas dan aktivitas kation

Kation terjerap mudah tersedia bagi tanaman & jasad renikPenyerapan kation oleh akar:

1. Penyerapan melalui larutan tanah2. Pertukaran ion antara akar dg koloid tanah

PENGARUH TIPE KOLOIDBerbagai koloid mempunyai daya ikat kation yg berbedaKalsium diikat oleh montmorilonit lebih kuat daripada oleh kaolinit

Pertukaran ion dengan akar tanaman

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

Plants obtain some mineral nutrients

through ion exchange between the soil solution and the surface of clay

particles.

MUATAN LISTRIKPADA

MINERAL LIAT

Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Visual comparison of common silicate clays

illitemontmorillonite“2:1:1”

Strongly held


illitemontmorillonite

“2:1:1”

H-H

= Layer bond type = Location of charge imbalance

NONE

octahedral

octahedral & tetrahedral

tetrahedral


octahedral octahedral & tetrahedral tetrahedral


O-OO-Cation

Ionic

H-H

octaH-H

more strongly heldthan in smectite


Organization of tetrahedral and octahedral sheets in common soil clays

Octahedral

Octahedral

Octahedral & Tetrahedral


NONE

Tetrahedral

Tetrahedral



IlliteMontmorillonite

Diunduh dari sumber: www.univsul.org/.../Clay%20Chemistry%20(P... ……. 25/10/2012

Ciri-ciri Umum Liat Silikat

Ciri-ciri Kaolinit Smektit /Vermiculit

Illit(fine-grained micas)

Kelas Umum 1:1 (TetraOcta) 2:1 (TOT) 2:1 (TOT)

Pengembangan

Ikatan lapisanionic > H-bonding > van der Waals

Muatan negatif neto (KTK)

Fertility

Lokasi muatan

Low Low, 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


Tipe-Tipe Muatan

• Permanen

• pH-dependent = Tergantung pH

(due to isomorphous substitution)

(variabel, disebabkan oleh patahan – patahan pada kristal mineral liat)


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


Muatan Permanen

Octahedral sheet neutral Net negative charge


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: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm……. 27/10/2012

Variable or pH-dependent charge

Dissociation of exposed OH groups

]-OH ]-O- + H+

uncharged negative charge

<-----------(+ H+) ------------------

----------------- (- H+) -------------->



Occurs with humus, hydrous oxides,

and Broken edges of

silicate clays

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



Depends on soil colloids present

Colloid Negativecharge

Positivecharge % constant % variable

Humus 200 0 10 90

Vermiculite 120 0 95 5

Smectite 100 0 95 5

Illite 40 0 80 20

Kaolinite 12 4 5 95

Fe & Al Oxides 5 5 0 100



Positive charge << negative charge in most temperate zone

soils

Acid tropical soils = net + charge

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-)


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


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


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


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)


Afinitas Pertukaran

Held more strongly Held more weakly

This is referred to as the “Lyotropic series”

H+ Al3+ > Ca2+ > Mg2+ > NH4+ = K+ > Na+

Strength of adsorption proportional to valence ÷ hydrated radius


Pertukaran Ion vs. KTK

Sandy loamVERY

acidic soil

How many charges are there to fill???

NH4+

Ca2+

H+

Mg2+

K+

NO3-

Cl-

H+

H+

NO3-

NO3-

NO3-

H+

HSO4-

H+ HCO3-

Crystal edge

CEC = 7; AEC = 2


KTK tergantung pada

• Jumlah liat dan bahan organik

• Tipe mineral liatDiunduh dari sumber:

culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Diunduh dari sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/i

ndex.htm……. 27/10/2012

Petukaran Kation

+ 2K+

Ca2+

+ Ca2+ K+

K+

Al3++ 3K+

K+

K+

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




Broken edge of a kaolinite crystal showing oxygen atoms as the source of

NEGATIVE charge

Sumber Muatan pda Liat Tipe 1:1


Sumber muatan pada liat Smectite

Isomorphous substitution here, in the octahedral sheet

means a net NEGATIVE charge


Sumber muatan pada Liat Mica

3. Charge imbalance now mostly on edges

K+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


Muatan Negatif pada Humus

Central unit of a humus colloid

(mostly C and H)

ENORMOUS external surface area! (but no internal surface – all edges)


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


Kation dijerap oleh Ordo-Tanah

Ordo Tanah

“Kation asam”(H+, Al3+)

“Kation Basa”(misalnya Ca2+, NH4

+, K+, etc.)

Ultisol

Alfisol

Mollisol

45 55

65 35

30 70


Bahan Organik dan KTK(c

mol

cl/kg

)

Common %OC for A horizons in productive areas ~4%

So: y = (4.9 * 4%) + 2.4; or CEC = 22 cmolc/kg


Kation Tukar : Area

Tanah di daerah iklim Humid

Tanah di daerah iklim Arid

H+

H+

H+

Al3+

K+

K+

Ca2+

Mg2+

H+

Mg2+

NH4+

Low pH (acidic)High pH (basic)


CEC

low

high

3 8Soil pH

KTK dan pH

H+ binds tightly, doesn’t exchange

Na+ binds loosely, exchanges readily


Karakteristik Muatan

Tipe Koloid Total Muatan

Konstan (%) Variable (%)

Bahan Organik

200

Smectite 200

Kaolinite 8

10 90

5 95

95 5

Permanent vs. pH-dependent


OM has highest CEC

2:1 clays

1:1 clays

Non-clayey soils


KTK dan Intensitas Pelapukan

Alfisols, Vertisols,

Argiudolls*Ultisols Oxisols

*remember nomenclature structure = “argi-ud-oll”Diunduh dari sumber: culter.colorado.edu/.../Slides15_25Oc07.ppt -……. 25/10/2012

Rule of thumbfor 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 componentsHumus » 200 cmolc/kgSmectites » 100 cmolc/kgIllite » 25 cmolc/kgKaolinite » 10 cmolc/kgFe and Al oxides » 4 cmolc/kg

Estimate soil cation exchange capacity from composition:

5 % O.M. & 20 % smectite clay

200 x 0.05 = 10100 x 0.20 = 20Total = 30 cmolc/kg

Sumber: http://soils.cals.uidaho.edu/soil205-90/Lecture%209/index.htm

KTK Ordo -Tanah (cmolc/kg)

Ordo Tanah KTK

Oxisols Low

Ultisols

Alfisols 9.0

Mollisols 18.7

Vertisols 35.6Histosols

low

high

1:1 clays

2:1 clays

O.M.

Low pH

128.0

3.5

High Al/Fe oxides

Key factor


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+


Kejenuhan Basa beberapa Ordo Tanah

Ordo Tanah Kejenuhan Basa

Oxisols Low

Ultisols

Alfisols Medium-High

Mollisols High >50%

low

high

<35%


1:1 Clay Minerals CEC ~ 7 meq/100 gnon-expandingKaolinit

SiAl

SiAl

SiAl

SiAl

0.72 nm

SiAl

SiAl

SiAl

SiAl

SiAl

SiAl

SiAl

SiAl

SiAl

SiAl

SiAlSiAl

SiAl

SiAl

SiAlSiAl

SiAl

SiAlSiAl

SiAl

SiAl

SiAlSiAl

SiAlSi

Al


KaoliniteKaolinite 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.


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


Kaolinite

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


2:1 Clay MineralsCEC ~ 40 meq/100 g

non-expanding

Layer

T

O

T


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 Vermiculite

> 0.9 Micas Muscovite, Biotite

approx. 2.0 Brittle MicasMargarite


Mineral Liat Tipe 2:1

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


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.


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


MICA - Liat Tipe 2:1

Micas•Micas are a 2:1 lattice type mineral. ion substitution is mainly in the tetrahedral layer where Si is replaced with Althe 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.


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


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

hydratedBecause smectites have permanent negative charge, interlayers always contain

cations to provide electroneutrality.These cations typically participate to cation exchange reactions

Mineral Liat Smectite


2:1 Clay Minerals (expanding)

KTK:

100 – 200 meq/100 g

(vermiculite)

70 – 120 meq/100 g (smectite)


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).


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).


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 Si4+ ions.

4. Aluminium is the normal ion in the central sheet, but about one-eight of the octahedra contain Mg2+ as a substituting ion for Al3+.

Mineral Liat Montmorillonit


http://www.wwnorton.com/college/chemistry/chemconnections/Rain/moviepages/montmorillonite_layers.htm

• 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.



SiAlSi

SiAlSi

SiAlSi

0.96 nm

joined by weakvan der Waal’s bond

easily separated by water

also called smectite; expands on contact with water



A highly reactive (expansive) clay

montmorillonite family

used as drilling mud, in slurry trench walls, stopping leaks

Bentonite

swells on contact with water (OH)4Al4Si8O20.nH2O

high affinity to water



Mineral Liat Illite

SiAlSi

SiAlSi

SiAlSi

0.96 nm

joined by K+ ions

fit into the hexagonal holes in Si-sheet


Chlorite•Clorite are a 2:1:1 lattice type mineralthe 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

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


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 2 : 1 (expanding)

weak bonding, great expansion 100 -150 high 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 10 - 40 none 1.4

Allophane - - 10 - 50 - -

Karakteristik Mineral Liat dalam Tanah


Substitusi Isomorfik pada Kristel Mineral Liat Tipe 2:1

No substitution

With isomorphic substitution

sheet charges

sheet charges

5 +

-1


Sumber muatan tergantung pH pada Kaolinit

More acid More acid

-3 - 1 +1


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

MUATANDan

REAKSI PERMUKAAN

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


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).

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


Orbit Dalam dan Orbit LuarInner 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)


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+

H+

OH

OH

OH

OH

H+OH2

OH

OH


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

OH2+

OH

OH

OH

O-

O-

OH2+


oxygen

silicon (Si4+)

hydroxide (OH-)

Aluminum (Al3+)

Silicon Tetrahedron Aluminum octahedron

Building Blocks for Silicate Clays

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

Tetrahedra and OctahedraSharing the Oxygens

Linkage of thousands of silica tetrahedra and aluminum octahedra

OSiO, OHAlOH

Tetrahedra

octahedra

{{

1:1 MineralDiunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Tetrahedra

octahedra

{{

Tetrahedra {

Mineral tipe 2:1



Mineral Tipe 1:1Mineral Tipe 2:1


Positive charge

Al3+ Si4+

Negative charge

OH- O2-

KESEIMBANGAN MUATAN

Al3+

Si4+

OH-

O2-

=


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.


Substitusi Tetrahedra: Al menggantikan Si

Al3+ for Si4+


Substitusi Octahedra: Mg menggantikan Al

Mg2+ for Al3+


Substitusi Octahedra: Zn menggantikan Al

Tetrahedral Substitution

Octahedral Substitution

Al3+ for Si4+

Mg2+ for Al3+


Na+

Na+

Na+Na+

Na+Na+

Na+Muatan listrik


- - -

- - -

- - -

- - -

- - -

Hig

h ca

tion

conc

entr

atio

n

Am

bien

t sol

utio

n co

ncen

trat

ion

Permukaan yg

bermuatan

Kerapatan awan kation


Diunduh dari sumber: http://www.ch-non-food.com/science.htm ……. 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.

Diunduh dari sumber: http://www.malvern.com/labeng/technology/zeta_potential/zeta_potential_lde.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://web.nmsu.edu/~snsm/classes/chem435/Lab14/double_layer.html ……. 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 LayerThis 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://www.ch-non-food.com/science.htm ……. 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 = noexp(-zeY/kT)

where no = 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.

…. Electric Double LayerStern Modification of the

Diffuse double LayerStern 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

Na+

K+

K+Na+

K+K+

K+Pertukaran Kation

Na+ Na+ Na+

Na+ Na+

Kation mana yang lebih disukai?


Faktor yang menentukan preferensi kation

1. Konsentrasi kation2. Muatan (+1, +2,+3)3. Ukuran (diameter atau

radius)Diunduh dari sumber:

soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 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: http://www.boostdam.net/stories/tonic.html……. 27/10/2012

Diunduh dari sumber: http://nelspeterson1.wordpress.com/agrn-2124-chapter-8-notes/ ……. 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

Radius Unit Na+ K+ Mg2+ Ca2+ Al3+

Non-hydrated nm 0.095 0.133 0.066 0.099 0.050

Hydrated nm 0.360 0.330 0.430 0.410 0.480

aluminium > calcium > magnesium > potassium, ammonium-NH4+ > sodium > hydrogen

Konsentrasi Kation

Na+

K+

K+Na+

K+K+

K+

Na+

K+

K+Na+

K+K+

K+

K+

K+K+

K+

K+

K+

K+

K+

K+

K+

Larutan tanah


Ca+2

K+

K+K+

Ca+2

K+

K+

K+K+

K+

K+

K+K+

Ca+2

Ca+2

Ca+2

Ca+2

K+

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2

Ca+2


Muatan listrikLarutan tanah

Na+

H+

Stronger bond(H+ preferred)


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:

http://www.wou.edu/las/physci/ch412/hydrolysis.htm ……. 27/10/2012

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

Pertukaran Kation

Diunduh dari sumber: http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_exchangeable_cations.html ……. 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

Diunduh dari sumber: http://www.wou.edu/las/physci/ch412/hydrolysis.htm ……. 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(H2O)n]z+ + H2O [M(H2O)n-1(OH)](z-1)+ + H3O+

The total quantity of cations a clay can adsorb.

Equal to the amount of charge

Units are cmolc/kg soil

Range: 0 - 180 cmolc/kg

Related directly to the amount of Isomorphous substitution


KTK Mineral

What is a Centimole?

1/100 of a mole 1mole = 6.02 x 1023 charges1cmol = 6.02 x 1021 charges

6,020,000,000,000,000,000,000

1 cmol =


- - - - - - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - - - - - -

- - - - - - - - - - - - - - - - - - - - - -

Na+

Mg2+

H+ NH4+K+ Ca2+Na+ Al3+

K+ Na+ Ca2+ Mg+ K+ NH4+ Al3+

NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+

NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+ NH4+

Konsentrasi sangat tinggi


Soil

NH4+

K+

Ca2+

Na+

Mg2+

K+

Ca2+

Na+

Mg2+

beaker

NH4+


Soil

Ba+2

beaker

NH4+

NH4+

NH4+

NH4+

NH4+

Ba2+

The number of ammonium ions = number of chargesDiunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

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 concentration of NH4+ cations in the beaker is equal to

10 cmol/L

The volume of solution in the beaker is 1L.

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

Na

HH

O

HH

O

HH

O

H H

O

+

HIDRASI ION

ClH H

O

HH

O

HH

O

HH

O

-

Ukuran bola hidrasi ion sangat beragam


Na

HH

O

HH

O

HH

O

H H

O

+


Hydroxide (OH-)

O

H

“Electron greedy”

+

-


CEC = 2 – 5 cmolc

kg

Limited isomorphous substitutionin octahedra (Al3+ for Si4+ )

Kaolinite 1:1

Layers are H-bonded

Non-expansible

Adsorption is on external surfaces and edges

Na+

OH

+

-

Slightly Negative


Mineral Tipe 2:1

Smectites: montmorillonite

Significant substitution in the octahedra

(Al3+ for Si4+)Ca2+ Mg2+ Na+

Cations satisfying charge

CEC = 80-120 cmolc

kg

Layers weakly held together by cationsHighly expansible


H

O

Air berlebihan

H

Ca Ca Ca


Smectite

Smectite

CaH

O

Air terbatas

H Ca Ca


Mg2+Mg2+

Source of negative charge Is very close to the adsorbedcations

Layers tightly boundModerately expansible

Significant substitution in tetrahedra

CEC = 100-180 cmolc

kg


Vermiculite

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 = 20-40 cmolc

kgDiunduh dari sumber: soillab.ifas.ufl.edu/.../Lecture%2010%20Catio... ……. 26/10/2012

Illite

Side ViewTetrahedra

Octahedra

Tetrahedra

Top ViewTetrahedra

K+

K K KClay Layer

Clay Layer


Mineral-mineral

Kaolinite Smectite Vermiculite illite

1:1None2 – 5

2:1 High80 - 120

2:1 Limited100 – 160

2:1None 20-40

MineralExpansionCEC (cmol/kg)

Octahedralsubstitution

tetrahedralsubstitution

{tetrahedralsubstitution


Increasedweathering

Illites

Vermiculites

Smectites

Kaolinite

Fe, Al oxides

2:1

1:1

Where do the minerals occur?


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


POINT OF ZERO CHARGE (PZC)yang disebabkan oleh pengikatan atau disosiasi Proton

Material pHpznpc Material pHpznpc Material pHpznpc-Al2O3 9.1 -Fe2O3 8.5 ZrSiO4 5-Al(OH)3 5.0 Fe(OH)3 8.5 Feldspars 2-2.4-AlOOH 8.2 MgO 12.4 Kaolinite 4.6CuO 9.5 -MnO2 2.8 Montmorillonite 2.5Fe3O4 6.5 -MnO2 7.2 Albite 2-FeOOH 7.8 SiO2 2 Chrysotile >10


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.

From Stumm and Morgan, Aquatic Chemistry


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


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:

mB

nA

nA

mB

NN

aaK


In the ion-exchange reaction given above, the X represents the solid surface on which ion exchange occurs.

KTK MINERAL DAN TANAHMineral CEC

(meq/100 g)Mineral CEC

(meq/100 g)Chlorite 10-40 Soil organic

matter>200

Illite 10-40 Sand 2-7Kaolinite 3-15 Sandy loam 2-18Montmorillonite 80-150 Loam 8-22Vermiculite 100-150 Silt loam 9-27Oxides andhydroxides

2-6 Clay loam 4-32

Clay 5-60


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.

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.


Kd

• Descriptions of how solutes stick to the surface

• What would the ‘real’ behavior be you think??

Kd


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.

m

i

SVCCS


FREUNDLICH ISOTHERM

nKCS 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 ).

C (mg L-1)0 10 20 30 40

S (m

g g-1

)

0

10

20

30

40

50

60

S = 1.5C1.0

S = 5.0C0.5

FREUNDLICH ISOTHERMS


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.

LANGMUIR ISOTHERMThe Langmuir isotherm describes the situation where the number of sorption

sites is limited, so a maximum sorptive capacity (S max) is reached.

C (mg L-1)0 10 20 30 40

S (m

g g-1

)

0

10

20

30

40 LANGMUIR ISOTHERMS

CCS

1.011.030

CCS

5.115.130

The governing equation for Langmuir isotherms is:

KCKCSS

1max


. 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.

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

solutionin g/mlC organic solidadsorbed/g gKoc


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


• 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.


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.

ADSORPSI KATION LOGAM• 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+


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.

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.

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

][][loglog

][][log

BXAXnK

AB

ex

n

ex BXAX

ABK

][][

][][


KTK Tanah – Rapat muatan permukaan

Diunduh dari sumber: http://www.smart-fertilizer.com/articles/Cation-Exchange-Capacity ……. 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.

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 IONIons adsorbed to soil surfaces can be exchanged with ions in soil solution.Cations and anions

Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil%2... ……. 26/10/2012

CONTOH:

Ca+2-colloid + 2 H+ ¬ ¾® 2 H+-colloid + Ca+2

= H+ replaces Ca+2 adsorbed to soil colloids

• 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


PERTUKARAN ION

• Exchangeable cations (on soil surfaces) cannot be removed by leaching.

• Soluble cations (in solution) can be removed by leaching.


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: http://www.ca.uky.edu/agc/pubs/agr/agr11/agr11.htm…….

27/10/2012

Reaksi Pertukaran kation

Diunduh dari sumber: http://en.wikipedia.org/wiki/Surface_charge ……. 27/10/2012

Muatan di Permukaan: Stern TheoryThe 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.

http://upload.wikimedia.org/wikipedia/commons/3/31/Stern_Layer.png

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 !


KAPASITAS TUKAR KATION (KTK)Sum total of exchangeable cations that a soil can adsorb.

( prevents nutrients from leaching away from roots)


KTKDinyatakan 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: http://www.extension.umn.edu/distribution/horticulture/m1193.html ……. 2/10/2012

KTK = Kapasitas Tukar Kation

KEJENUHAN BASA% of exchange sites occupied by basic cations

Basic cations are cations other than H+ and Al+3

Diunduh dari sumber: http://agsource.crinet.com/page2573/BaseSaturation ……. 27/10/2012

The relationship between nutrients

attached to the soil clay and

organic matter and nutrients in the

soil solution.

KEJENUHAN BASA

Diunduh dari sumber: http://agsource.crinet.com/page2573/BaseSaturation ……. 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

75150

180030

390120200230

0.191.259.0

0.1310.57

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

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)


KESETIMBANGAN

Strive for equivalent proportions of solution and exchangeable ions.

Upset equilibrium by:removal by plantsleachingfertilizationweathering

Initiate ion exchange


PERTUKARAN ION:Penambahan ion H+ ke tanah :

soil

Ca+

Ca+

Ca+Ca+

Ca+

Ca+ Ca+

Ca+

Ca+Ca+

Ca+ Ca+

Ca+

Ca+

+

H+

H+

H+H+

H+H+

solution

exchangeable solution

+

H+H+Ca+

Ca+

exchangeable solution


PERTUKARAN ION

• 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/powerp

oints/Soil%2... ……. 26/10/2012

The double layer system associated with a negatively charged clay surface

Diunduh dari: http://www3.ul.ie/~childsp/CinA/Issue41/HomePage.html

Menambah pupuk K …..…

Ca+2

K+

Ca+2

+ Ca+2 Ca+2K+K+

K+ K+ K+K+

K++

1 Ca : 2 K 1 Ca : 2 K

Same ratioDiunduh 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)


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


pHLogaritma negarif dari konsentrasi ion H+

(juga menjadi ukuran konsentrasi ion OH-)

If H+ concentration > OH- : acidicIf OH- > H+ : basic

Soil pH is pH of solution, NOT exchange complexDiunduh 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


Kondisi Umum pH TanahIn soil, both H+ and Al+3 ions produce

acidityAl+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

1. Hydrolysis of basic cations

2. Hydrolysis of carbonates

Diunduh dari sumber: http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilising-dairy-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.

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.

NaNa

Na NaNa

Na

Na Na

NaNa+

H2O H + + OH-


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 .


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)


Sebab-sebab Kemasaman Tanah1. Accumulation of soluble acids2. Exchangeable acids (Al+3, H+)

Diunduh dari sumber: http://www.swac.umn.edu/classes/soil2125/doc/s12ch6.htm……. 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.

Accumulation of soluble acidsat faster rate than they can be neutralized or removed

a. 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/S

oil%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

http://hubcap.clemson.edu/~blpprt/acid_photos/Buffering2.jpg

KTK dan pHOnly 2:1 silicate clays do not

have pH-dependent CECs.

Others are pH-dependent:

1:1 kaolinite:low pH: low CEChigh pH: high CEC

Oxidic clays

Diunduh dari sumber: www.d.umn.edu/.../Soils/powerpoints/Soil

%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: http://www.sciencedirect.com/science/article/pii/S0167

880911000326 ……. 26/10/2012

Documents

KOLOID TANAH & MINERAL LIAT