A novel electrobiotechnology for the recovery of precious metals from spent automotive catalysts

Abstract

Platinum group metals are routinely used in automotive catalysts but recycle technology lags behind demand. There is no available 'dean technology' and leach solutions (e.g. aqua regia) to solubilise the metals from scrap are highly aggressive. A microwave-assisted leaching method was developed which gave 80% metals recovery, with the leach time reduced from 2 h to 15 min using 50% (aq.) diluted aqua regia to give potentially a more biocompatible leachate. Desulfovibrio desulfuricans reduces soluble platinum group metals to cell-bound insoluble base metals (e.g. Pd(II) --> Pd(0)). For use, biofilm was immobilised on a Pd-23% Ag solid alloy membrane which delivered H. to the cells via an electrochemical chamber at the back-side. The biomass-coated Pd-Ag alloy electrode was used in a flow-through reactor for recovery of Pd, Pt and Rh from aqua regia leachates (pH 2.5) of spent automotive catalysts with up to 90% efficiency at a flow residence time of 15 minutes. Free cells did not reduce platinum group metals from the leachates but the electrobioreactor did so using biofilm-cells pre-loaded with Pd(0). Reactors lacking biomass or reactors with heat-killed biofilm removed less platinum group metals, via electrochemically-synthesised H. reductant alone. The use of an active biofilm layer in a flow-through electrobioreactor provides a simple, dean and rapid potential recycle technology.

From bio-mineralisation to fuel cells: biomanufacture of Pt and Pd nanocrystals for fuel cell electrode catalyst

“…Previous studies have demonstrated that sulphate-reducing bacteria can recover Pd and Pt from liquid wastes (Yong et al 2002(Yong et al , 2003. This was achieved by using hydrogenase to split H 2 and coupling this oxidation to the reduction of soluble Pd(II) and Pt(IV) ions to form metallic deposits of Pd(0) and Pt(0), which are scaffolded onto to the biomass surface.…”

Cr(VI) reduction by bio and bioinorganic catalysis via use of bio‐H2: a sustainable approach for remediation of wastes

“…18 Automotive catalyst leachates, electronic scrap and industrial processing wastes contain Pd and other precious metals. Previous studies have shown that D. desulfuricans can be used to biorecover palladium from industrial wastes and leachates produced from scrap 18,21 (and also from leachates produced from bio-Pd(0) when recycling of the Pd(0) into a fresh series of experiments is desired). The catalytic activity of the bio-Pd(0) made from Pd(II) in 'industrial waste' leachates was similar to that obtained using a 'pure' source of Pd(II).…”

“…8,10,19 Bio-Pd(0) also reduced Cr(VI) continuously in a flow-through column, 17,19,20 with Cr(III) recovered in the outflow solution. 17,18 Reduction of Cr(VI) by resting and palladized SRB cells used H 2 as the electron donor, supplied from a cylinder or generated electrochemically, and delivered through a H-transfer membrane, 21 or from formate, which is split to give H 2 enzymatically via the formate hydrogenlyase (FHL) complex (see below), a vestigial form of which is thought to operate in the SRB. 22 Alternatively, Pd(0) itself catalyses the breakdown of formate to give highly reactive H…”

Bionanocomposites Assembled by “From Bottom to Top” Method

“…To the early works in this field belong bioutilization of Pd(II) from solutions in form of Pd(0) [88] with usage of sulfate-reducing bacteria. D. Desulfuricans demonstrates bioreducing activity with respect to ions of the considered metals in the medium of liquid wastes and in sewage in spent car catalysts [65,89]. Processes of reduction are implemented in electrobioreactors, containing bacterial cells immobilized on external surface of Pd-Ag electrode.…”