A comparative study on different metal loaded soybean milk by-product 'okara' for biosorption of phosphorus from aqueous solution.

Cationization of agricultural by-products using metal salts is widely used to activate their phosphorous capture ability. This study developed three kinds of new metal loaded soybean milk by-product 'okara' for phosphorus biosorption. A comparative study among these biosorbents was carried out with respect to their performances in terms of affinity, stability and reusability. Zirconium loaded okara (ZLO) was found to have the highest affinity towards PO(4)(3-) anions (47.88 mg/g), followed by iron/zirconium loaded okara--IZLO (40.96 mg/g) and iron loaded okara--ILO (16.39 mg/g). ZLO was successfully desorbed with 0.2M NaOH and activated with 0.1 HCl prior to the next cycle. After five consecutive cycles, the efficiency of both adsorption and desorption of ZLO remained about 85% whilst no Zr(IV) leakage was observed. Conversely, IZLO and ILO suffered from vital short comings such as high metal release and/or sharp reduction in PO4(3-) sequestering capability after multi operation cycles.