Recovery of gold from industrial wastewater by immobilized gold-binding proteins on porous silica carriers grafted with amino group

Our recent work demonstrated excellent gold biosorption potential of extracellular proteins obtained from a thermophilic bacterium Tepidimonas fonticaldi AT-A2. In this study, the gold-binding proteins were immobilized on amino-grafted porous silica carriers to further enhance the feasibility of using them for Au recovery from real industrial wastewater. The maximum protein immobilization capacity on the amino-grafted porous silica reached the highest level of 13.83 mg protein/g carrier when the protein loading concentration was 400 mg/L and the amino groups content on the silica carrier was 16%. The mechanical strength of the amino-grafted porous silica could be improved to 19.47 kg by converting the silica powder into pellet form using a calcination temperature of 700 °C. Continuous biosorption of Au (III) from prepared Au solution and from real industrial wastewater was carried out using fixed beds packed with the protein-loaded amino-grafted porous silica pellets. The maximum Au adsorption capacity of the fixed beds with a feeding rate of 0.12 ml/min was 1259 and 448 mg Au/mg protein from the prepared Au solution and an electroplating wastewater (Au concentration was approximately 40 mg/L), respectively. The maximum Au adsorption rate of the fixed beds when using the real wastewater was 33.4 mg/g/h, which is similar to the results of using the prepared Au solution.