Heterotrophic Bioleaching of Rare Earth Elements and Base Metals from Spent Nickel-Metal-Hydride Batteries

Tutkimustuotos: VäitöskirjaCollection of Articles


To overcome the environmental and supply challenges related to extracting rare earth elements (REEs) from virgin ores, recycling end-of-life products is of great importance. The main goal of this study was to develop an efficient heterotrophic bioleaching process for REE and base metal extraction from spent NiMH batteries. Therefore, the impacts of phosphorus source on organic acid production and metal leaching steps were evaluated and accordingly an optimized medium composition was developed. In addition, the effects of bio-oxidation of gluconic acid to its keto-derivatives on REEs and base metals leaching was investigated. Finally, a non-aseptically operated Gluconobacter oxydans-amended fluidized bed reactor (FBR) process was developed for high-rate and -yield continuous production of gluconic acid to further enhance metals leaching.

The optimal addition of phosphorus sources such as K2HPO4, positively affected gluconic acid production by G. oxydans, while precipitation of the leached metals with residual dissolved phosphate in the medium led to significant metal loss during the leaching stage. REEs were proportionally more affected by precipitation than the base metals. Use of optimal ratio of yeast extract to glucose in the bioleaching medium instead of K2HPO4 resulted in leaching of 1.5- and -11.0-fold higher concentrations of total base metals and REEs, respectively. Comparison of the leaching potential of gluconate with its bio-oxidation products revealed that under all studied pH conditions, gluconate leached more REEs, while 5-ketogluconate at target pH ≥6 leached more base metals. The highest overall leaching yields for both base metal and REEs were obtained using gluconate at target pH of 3.0. Using the developed G. oxydans-amended FBR, high gluconic acid production rate of 390 g/l∙d with corresponding glucose-to-gluconic acid conversion yield of 94% was achieved at hydraulic retention time of 6.3 h and 380 g/l∙d glucose loading rate. Using the FBR effluents as leaching agents total REEs and base metals leaching yields of up to 55% and 82%, respectively, were obtained with 1% (w/v) spent battery pulp density within 7 days. The high-rate and -yield glucose-to-gluconic acid bioconversion in a non-aseptic FBR system with an ecological engineering-based strategy indicated the industrial feasibility of gluconic acid production and therefore, applicability of heterotrophic bioleaching.
ISBN (elektroninen)978-952-03-3047-7
TilaJulkaistu - 2023
OKM-julkaisutyyppiG5 Artikkeliväitöskirja


NimiTampere University Dissertations - Tampereen yliopiston väitöskirjat
ISSN (painettu)2489-9860
ISSN (elektroninen)2490-0028


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