ADSORPTION BEHAVIOR OF ORTHOPHOSPHATE ONTO ACTIVATED CARBON LOADED WITH MOLYBDENUM(VI) OR IRON(III)

Abstract

The study on the adsorption behavior of orthophosphate onto activated carbon loaded with molybdenum(VI) (Mo(VI)-AC) or iron(III) (Fe(III)-AC) was carried out by a column method. Orthophosphate adsorbed increases with increasing the amount of molybdenum(VI) loaded onto activated carbon. The optimum pH for the adsorption of orthophosphate onto Mo(VI)-AC was 2.0. As much as 7.7 × 10^-4 mol of orthophosphate was adsorbed onto 5.0 g of activated carbon loaded with 1.1 g of molybdenum(VI) at pH 2.0. The molar ratio of orthophosphate adsorbed onto Mo(VI)-AC to molybdenum(VI) adsorbed onto activated carbon was found to be 1 : 12. Orthophosphate may be adsorbed in the form of phosphomolybdenic acid (H_3-nPO₄Mo₁₂O₃₆^n-) onto Mo(VI)-AC. Orthophosphate adsorbed onto Fe(III)-AC decreases on both sides of the optimum pH 6.0. As much as 3.0 × 10^-4 mol orthophosphate was adsorbed onto 5.0 g of activated carbon with 23.5 mg of Fe(III). The amount of orthophosphate adsorbed increases with increasing Fe(III) loaded onto activated carbon; the molar ratio of orthophosphate adsorbed to Fe(III) adsorbed was less than unity in the pH range over 2.5 to 10.4. Orthophosphate may be adsorbed onto Fe(III)-AC by the coordination of orthophosphate to Fe(III).