The Effect of Species and Concentration of Cations and Anions for The Phosphate Adsorption Behaviour onto Allophane

TANDADITYA A. A., Dr. Ir. Eko Hanudin, M.S; Prof. Dr. Naoto Matsue

2019 | Tesis | MAGISTER ILMU TANAH

Alofan adalah mineral liat tanah dengan kapasitas adsorpsi fosfat yang tinggi melalui mekanisme pertukaran ligan. Penelitian ini bertujuan untuk membandingkan karakteristik adsorpsi fosfat oleh Alofan dari Gunung Merapi dan Gunung Lawu dalam kaitannya dengan sifat kimia dan mineralogi dan untuk mengetahui pengaruh spesies dan konsentrasi kation dan anion untuk perilaku adsorpsi posphate. Hasil X-Ray Flourescence menunjukkan bahwa sampel Merapi dan Lawu memiliki rasio Si / Al yang rendah (2,0; Merapi) dan (1,9; Lawu). Karakteristik spektral inframerah dari alofan menunjukkan bahwa pita adsorpsi utama muncul pada kisaran 2700-3700 cm-1 (karena getaran semua kelompok hidroksil (OH)), 1400-1800 cm-1 (getaran deformasi HOH) , 650-1200 cm-1 (getaran antara Si-O-Al). Eksperimen adsorpsi fosfat pada alofan dilakukan pada konsentrasi adsorbat awal hingga 2,0 mM dan pada pH 4,0 dan 8,0. Adsorpsi fosfat pada Alofan menunjukkan bahwa Merapi dan Lawu dikategorikan sangat tinggi dalam mengadsorpsi fosfat dan sesuai dengan persamaan adsorpsi langmuir. Adsorpsi fosfat meningkat dengan penurunan pH karena situs muatan positif seperti Al-OH2 + dalam struktur alofan meningkat, alasan lain adalah muatan negatif fosfat secara bertahap menurun dari -2 ke -1 dengan penurunan pH, dan gaya tolak antara Si-O- bermuatan negatif dalam struktur alofan dan anion fosfat berkurang. Adsorpsi fosfat pada sampel Merapi dan Lawu lebih tinggi dalam larutan kation (Ca (NO3) 2 dan KNO3) daripada dalam larutan anion (NaNO3, NaCl, dan Na2SO4) ini disebabkan oleh efek jembatan kation antara alofan dan fosfat, sehingga adsorpsi fosfat pada alofan dalam larutan latar belakang kation meningkat.

Allophane is a known clay mineral with high capacity phosphate adsorption via ligand-exchange mechanism. This study aims to understand the mechanism of phosphate adsorption on allophane from Mt. Merapi and Mt. Lawu in relation to its chemical and mineralogical properties and to know the effect of species and concentration of cations and anions for the posphate adsorption behaviour. X-Ray Flourescence result shows that both merapi and lawu sample have low Si/Al ratio (2,0; Merapi) and (1,9; Lawu). Infrared spectral characteristic of the allophane material indicated that the main adsorption bands appeared at a range of 2700-3700 cm-1 (due to stretching vibration of all hydroxyl (OH) groups), 1400 � 1800 cm-1 (vibration of HOH deformation), 650 - 1200 cm-1 (vibration between the Si-O-Al). Adsorption experiment of phosphate on allophane samples were conducted at initial adsorbate concentration of up to 2,0 mM and at pH 4,0 and 8,0. Phosphate adsorption on allophane shows that both Merapi and Lawu were categorized as very high in adsorbing phosphate and fit with the langmuir adsorption equation. Phosphate adsorption increase with decreasing pH due to positive charge sites such as Al-OH2+ in the allophane structure increase, the other reason is the negative charge of phosphate gradually decrease from -2 to -1 with decreasing pH, and the repulsive force between negatively charged Si-O- in the allophane structure and phosphate anions decrease. Phosphate adsorption in Merapi and Lawu sample is higher in cation background solution ( Ca(NO3)2 and KNO3 ) than in anions background solution ( NaNO3, NaCl, and Na2SO4 ) this is due to bridging effect of cations between allophane and phosphate, resulting in increase of phosphate adsorption on allophane in cations background solutions

Kata Kunci : Allophane, Merapi, Lawu, Langmuir Equation