Recycling Fe(III)/Cr(III) hydroxide, an industrial solid waste for the removal of phosphate from water.

Industrial solid waste, Fe(III)/Cr(III) hydroxide, was investigated to assess the capacity for the removal of phosphate from aqueous solution. Langmuir and Freundlich isotherms were used to model the adsorption equilibrium data. The system follows both isotherms. Adsorption capacity was found to be 6.5 mg/g. Kinetic studies show that the adsorption obeyed second order kinetics. Thermodynamic parameters were evaluated. Overall adsorption process was endothermic and spontaneous. Optimum pH for phosphate adsorption was found to be 4.0. Effect of coexisting anions has also been examined.