Comparison of gold adsorption by Chlorella vulgaris, rice husk and activated carbon

Chlorella vulgaris and rice husk were selected from microorganisms and agricultural waste, respectively, to create new gold-eluteable adsorbents for adsorption of gold–thiourea complex, and compared with activated carbon. The maximum gold adsorption of heated-immobilised C. vulgaris, heated rice husk, and activated carbon was 10.34, 28.22 and 35.88 mg Au/g adsorbent, respectively. FTIR spectrum, thermodynamic study and elution tests indicated that heated-immobilised C. vulgaris and heated rice husk adsorbed gold by chemical adsorption: co-ordinate covalent bond. The active functional groups of heated-immobilised C. vulgaris were ketone, carboxylate and ester, while the groups of heated rice husk were ketone, carboxylate and siloxane. Activated carbon mainly adsorbed gold by physical adsorption. Gold adsorbed onto heated-immobilised C. vulgaris, heated rice husk, and activated carbon was able to be eluted by 0.5 M Na2S2O3 to 100, 87 and 41%, respectively. Although heated-immobilised C. vulgaris had the highest eluteability, it adsorbed less gold. Therefore, heated rice husk could be used as an alternative adsorbent for gold–thiourea pre-concentration.