Diatom Biochar Recovered Au(III) Efficiently from Both Synthetic and Real Electroplating Wastewaters

To face the current critical challenges of gold recovery and beneficial utilization of solid waste, this study synthesized diatom biochar from the anoxic pyrolysis of diatoms and proved the superiority of the diatom biochar as a novel adsorbent for Au(III) in both synthetic and real electroplating wastewaters. The diatom biochar was found to have a high adsorption capacity of 443.0 mg/g and a superior recovery efficiency of up to 92.1%. The Au(III) adsorption kinetics followed the pseudo-second-order and intraparticle diffusion models. Electrostatic attraction and reduction were detected as the major adsorption mechanisms. An exceptional selectivity was also observed for the diatom biochar toward Au(III) with other coexisting heavy metals. Even in the presence of CN– in the solution, the diatom biochar still exhibited superiority in Au(III) adsorption. Owing to its high affinity to Au(III), the diatom biochar was successfully applied in real electroplating wastewater containing trace Au(III), with an adsorption efficiency as high as 96.7%. These findings sufficiently demonstrate the excellent performance and economic feasibility of diatoms for Au(III) recovery from electroplating wastewater, which also promoted solid waste minimization of diatom biorefineries.