Efficient and selective gold recovery from practical e-waste and electroplating wastewater using protein crystals

Gold recovery from wastes is becoming increasingly important in gold production. However, satisfactory recovery technologies are lacking. Here we show that protein (hemoglobin) crystals exhibit outstanding performance in gold recovery. We prepared crosslinked hemoglobin crystals (CLHCs) from discarded bovine blood. The CLHCs demonstrated combined advantages in gold recovery: high recovery efficiency (100 %), high selectivity (recovery efficiency 95.14 % for Au³⁺ versus 0 % for ions like Cu²⁺), ultra-trace gold recovery (residual Au³⁺ 0.19 ppb), rapid equilibrium (2 min), and low cost (25.25 CNY/kg). We tested their recovery performance on e-waste and electroplating wastewater, proving that they are indeed practically applicable. Mechanism studies have shown that the performance is attributed to the combined effects of the physical adsorption of Au³⁺ by the crystals and the chemical reduction of Au³⁺ by the amino acids. Our approach is a typical sustainable technology, as it utilizes waste (animal blood) to recycle waste (e-waste and electroplating wastewater).