The first is analytical. Portable X-ray fluorescence, combined with oxidation–reduction potential, gives the Fe(III) concentration in real time and allows the end of a culture to be determined; its integration into a microfluidic chip is a proof of concept for online monitoring. Optical density and sulfate quantification by ATR-FTIR proved unsuitable.
The second concerns the process. Two 24-hour leaching steps delaminate 95.8 % of the surface gold, allowing to recover gold at a purity of 97.9 %. Cementation with Fe(s) followed by oxalic precipitation removes all Cu(II) without solvent extraction, and the purified leachate supports a new culture with no loss of performance: the loop is closed.
The third is environmental. Life cycle assessment places the process above a pyrometallurgical benchmark, but the gap arises from the purification reagents, not from the biological step. Prior enrichment by sorting is the decisive lever.