Studies on Ion Adsorption/Fixation by Synthetic Amorphous Aluminosilicates and their Organic Complexes of varying Si/Al Molar Ratio

Phosphate, potassium and ammonium adsorption/fixation by synthetic amorphous aluminosilicates of varying Si/Al molar ratio and their organic complexes with humic and fulvic acids was studied under laboratory condition. Phosphate adsorption increased with decreasing pH. Adsorption of phosphate by synthetic amorphous aluminosilicates and their organic complexes conformed to Langmuir adsorption isotherm. Langmuir adsorption maxima per unit specific surface area decreased with increasing Si/Al molar ratio while synthetic amorphous aluminosilicates of lower and higher Si/Al molar ratio showed high P fixation capacity per unit specific surface area indicating that P was fixed by more than one mechanisms. Potassium and NH₄ fixation capacity increased with increasing Si/Al molar ratio. Phosphorus adsorption maxima and fixation of P, K and NH₄ decreased in the order: Allophane > allophane-HA complex> allophane-FA complex. The decrease in P adsorption maxima was positively correlated with organic carbon content. Fixation of P, K and NH₄ by organo-mineral complexes initally increased and then decreased with decreasing organic carbon content indicating the presence of multiple fixation sites in organo-mineral complexes.