Biorecovery of Platinum Nanoparticles by Anaerobic Sludge

Abstract

The future supply of platinum (Pt) and the platinum group metals (PGM) is at risk because of their scarcity and their high demand. Therefore, recovery of Pt and PGM is an alternative worth of study to help solving possible future supply problems. This research explored a new alternative for the microbial recovery of Pt. The ability of an anaerobic granular sludge to reduce Pt(IV) and Pt(II) ions to elemental Pt(0) nanoparticles under different physiological conditions was studied. Results demonstrated the ability of a methanogenic consortium (anaerobic granular sludge) to reduce Pt(IV) and Pt(II) ions to elemental Pt(0) nanoparticles under different physiological conditions. X-Ray diffraction (XRD) and transmission electron microscope (TEM) analyses confirmed the formation of nanoparticles that were deposited on the cell surface as well as in the periplasmic space. Ethanol supported the biologically catalyzed Pt(IV) reduction in both cases, Pt(IV) and Pt(II), meanwhile hydrogen (H2) and formate promoted the chemical reduction of Pt(IV) and Pt(II) with some additional biological stimulation in the case of H2. A hypothesis is proposed in which H2 formed from the acetogenesis of ethanol is implicated in subsequent abiotic reduction of Pt(IV) indicating an integrated bio-chemical process. Endogenous controls lacking exogenous electron donor also resulted in slow Pt(IV) removal from aqueous solution. However, the rate of Pt(II) reduction was much faster compared to that of Pt(IV) indicating that Pt(II) should not be expected to accumulate as an intermediate in the reduction of Pt(IV). Finally, both Pt(IV) and Pt(II) were found to cause severe inhibitory effects in the methanogenic activity of anaerobic granular sludge, both having a similar IC50 (concentration causing a 50% of inhibition) at about 3 mg L-1. This Master’s thesis presents a new green and environmental-friendly method for the recovery of Pt from wastewater that could contribute to fight future problems in Pt and PGM supply.