The bioreduction and biorecovery of critical metals by Geobacter sulfurreducens

Abstract

Much attention has been focused on the influence of biogeochemical processes on the fate of metals and metallic minerals in the environment, and potential use of microorganisms to reduce and recovery critical metals from wastes. This thesis presents research into the bioreduction processes of Ce bearing ferrihydrite and Sb adsorbed ferrihydrite by the dissimilatory metal-reducing bacterium Geobacter sulfurreducens. The characterization of post reduction solid materials were performed by XRD, XPS, XMCD, XAS and TEM. Low contents of Ce and Sb had a neglectable impact on the bioreduction of ferrihydrite to biomagnetite. With increasing contents of Ce and Sb, the proportion of magnetite in secondary formed Fe minerals gradually decreased (and was not detected at 2% Ce/Sb or above), while goethite, an intermediate product of the bioreduction of ferrihydrite, became the primary Fe mineral type detected. During Fe(III) bioreduction process, no Ce or Sb was released, suggesting the fixation of Ce and Sb by Fe minerals during biological redox cycling in the natural environment. Applications of the biominerals formed were also explored, and the 0.5% Ce bearing magnetite nanoparticles were incorporated into carbon black supported Pt catalysts, which improved the duration of the catalyst, and can therefore reduce the use of platinum in this application. Finally experiments were also conducted which quantified the feasibility of using Geobacter sulfurreducens for PGM reduction and nanoparticle formation. Soluble Pd(II), Pt(IV), Rh(III) and Ru(III), and also mixes of Pd(II)-Pt(IV), Pd(II)-Rh(III) and Pd(II)-Ru(III), were all tested to determine if zero valent metallic nanoparticles could be formed. Nano-scale Pd(0), Pt(0) and Rh(0) particles were formed via bioreduction, but Ru(III) was not reduced, but still precipitated on the surface of bacterial cells. The sizes, morphology, distributions and crystal structures of nanoparticles were all characterised using a range of imaging and spectroscopy techniques. The location of most of the PGM nanoparticles was on the surface of G. sulfurreducens and sizes ranged from 2.6-3.8nm. Compared to the monometallic PGMs, the size of the bimetallic PdPt and PdRh alloys was smaller and were also more evenly distributed on the surface of the cell. Monometallic Pd(0) and bimetallic PdPt alloy nanoparticles showed the highest catalytic performances for the reduction of 4- NP, which were 3-30 times better than other nanoparticles. These results in this studies highlight the abilities of G. sulfurreducens to bioreduce and biorecover a wide range of metal and metalloid nanoparticles, often making potentially useful functional nanomaterials as end products.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jonathan Lloyd (Supervisor), Victoria Coker (Supervisor) & Brian O'Driscoll (Supervisor)