Recovery of gold from industrial wastewater by extracellular proteins obtained from a thermophilic bacterium Tepidimonas fonticaldi AT-A2

•Extracellular proteins from T. fonticaldi AT-A2 adsorb gold in aqueous solution.•The optimal pH and temperature for gold adsorption was 4-5 and 50 °C, respectively.•Maximum adsorption capacity of the protein biosorbent is 9.7 mg Au/mg protein.•Both Langmuir and Freundrich models could describe the adsorption equilibrium.•Nearly 71% gold removal efficiency from industrial wastewater was obtained.

Biosorption has emerged as a promising alternative approach for treating wastewater with dilute metal contents in a green and cost effective way. In this study, extracellular proteins of an isolated thermophilic bacterium (Tepidimonas fonticaldi AT-A2) were used as biosorbent to recover precious metal (i.e., Au) from wastewater. The Au (III) adsorption capacity on the T. fonticaldi AT-A2 proteins was the highest when the pH was set at about 4.0-5.0. The adsorption capacity increased with increasing temperature from 15 to 70 °C. Adsorption isotherm studies show that both Langmuir and Freundrich models could describe the adsorption equilibrium. The maximum adsorption capacity of Au (III) at 50 °C and pH 5 could reach 9.7 mg Au/mg protein. The protein-based biosorbent was also used for the recovery of Au from a wastewater containing 15 mg/L of Au, achieving a high adsorption capacity of 1.45 mg Au/mg protein and a removal efficiency of 71%.