The demand for critical metals is increasing at an exponential rate. In order to limit the environmental and societal impact of resource extraction and to meet net-zero targets for CO2 reduction, the recycling of metals from spent lithium ion batteries is vital. Recycling solutions need to be both adaptive and flexible to meet the needs of the competitive and constantly evolving cathode chemistry market.

Our group has previously outlined the first steps for the separation and recovery of the most abundant and valuable metals present in a wide range of lithium ion battery (LIB) cathode chemistries. This being the recovery of Mn, Co and Ni from vehicular LIBs by the biosynthesis of metallic nanoparticles from battery leachates. Our method supports the principles of green chemistry since the reactions take place in aqueous solutions using bacteria that are both renewable and scalable. Furthermore, they take place at temperatures below 30 degrees Celsius without the addition of hazardous solvents. The synthesis of specific metallic nanoparticles, as a result of this bacterial recycling process, provides an added incentive for the recycling industry and offers up novel materials for future green technology developments.

The aim of this research proposal is to optimise the bioprocess by (i) adapting S. oneidensis MR-1, the bacterium responsible for the separation of Mn in the first step of our bioprocess, to ensure 100% Mn removal from LIB leachates (ii) developing a bioseparation process for Co and Ni using engineered strains of the bacterium Desulfovibrio alaskensis G20, and (iii) demonstrating scale up of the bioprocess to 5L scale. The nanoparticles produced will be characterised and their potential for remanufacture into LIB electrodes assessed, with life cycle analysis completed to determine the environmental impact of this engineered bioprocess.

Technical Abstract:
The aim of this research proposal is to optimise a bioprocess for recycling metals contained in spent lithium ion batteries (LIBs) by (i) adapting Shewanella oneidensis MR-1, the bacterium responsible for the separation of Mn in the first step of our bioprocess, to ensure 100% Mn removal from LIB leachates (ii) developing a bioseparation process for Co and Ni using engineered strains of the bacterium Desulfovibrio alaskensis G20, and (iii) demonstrating scale-up of the Co and Ni separation using the most efficient engineered strain in terms of metal selectivity and metal recovery yield.

S. oneidensis MR-1 will be engineered to optimise Mn removal through the synthesis of carbonates. The construction of a mutant library followed by high-throughput screening will identify the genes responsible for raising the pH via NH3 production (e.g. deaminases) and hydration of CO2 to carbonic acid (carbonic anhydrases) leading to the carbonate synthesis.

For enabling a Co/Ni bioseparation process the sulphate reduction pathway in D. alaskensis G20 will be deleted. The screening for the mechanism responsible for Ni and Co nanoparticle (NP) synthesis will be performed using the plasmid libraries created based on our Co and Ni proteomics datasets.

The capabilities of the engineered strains for metal separation through NPs synthesis will be investigated with real LIB leachates. Metal removal and NPs physicochemical properties will be analysed using a set of complementary techniques that will involve electron microscopy, spectroscopy (TEM, SEM, EDX, XRPD, ICP-OES) and electrochemical tests to assess the potential of the NPs for remanufacture into LIB electrodes.

High-throughput screening using micro fermenters will speed up the process optimisation and scale-up to 5L. The NPs characterisation and scale-up work will provide the data needed for the implementation of an LCA to assess the environmental impact of this bioprocess.