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

• ZLO was superior to IZLO and ILO, especially in terms of affinity and reusability.
• ZLO could remove 97% P at the initial concentration of 50 mg/L, dose of 10 g/L.
• 0.2 M NaOH was suitable for elution of P from ZLO with the efficiency of 94.25%.
• No Zr(IV) leakage was observed during adsorption and desorption tests using ZLO.
• Activation of desorbed ZLO with 0.1 M HCl was necessary for ZLO to be recycled.

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 PO43− 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 0.2 M 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 PO43− sequestering capability after multi operation cycles.