Adsorptive removal of silica onto ‘waste’ Fe(III)/Cr(III) hydroxide: Kinetics and isotherms

Removal of silica from aqueous solution by industrial solid ‘waste’ Fe(III)/Cr(III) hydroxide was investigated. Initial pH has no effect on the adsorption of silica in the pH range 4.0–10.0 studied. First, second order and Elovich kinetic models were used to study the adsorption process. The adsorption system followed second order and Elovich kinetics. Langmuir and Freundlich isotherms have been employed to analyze the adsorption equilibrium data. Adsorption process followed Langmuir isotherm. The Langmuir adsorption capacity (Q0) was found to be 12.25 mg g−1. Freundlich constants kf and n were found to be 2.44 and 2.74, respectively. Silica adsorption in the presence of vanadate, phosphate and selenite was decreased whereas molybdate, thiocyanate, chloride, nitrate and sulfate have shown negligible effect.