# Circular economy approaches to microbially-induced carbonate precipitation for bioprocessing of geothermal brine for lithium recovery

## TL;DR

This study uses microbes to remove harmful metals from geothermal brine, keeping lithium intact, and repurposes waste products to make the process sustainable.

## Contribution

The study introduces a circular economy approach using waste substrates for MICP to treat geothermal brine and selectively retain lithium.

## Key findings

- MICP removed 96% of Ca, 46% of Mg, 88% of Mn, and 91% of Sr while retaining over 96% of Li in solution.
- S. pasteurii grew effectively on spent yeast extract and cow urine, achieving similar carbonate precipitation rates as commercial media.
- The slurry waste from MICP improved acidic soil and enhanced microbial activity, demonstrating its value as a soil amendment.

## Abstract

Microbial Induced Carbonate Precipitation (MICP) is a biogeochemical process that drives the formation of carbonate minerals. This study employed MICP, using the urease-overproducing bacterium Sporosarcina pasteurii to remove cationic metals from geothermal Li-bearing brines. MICP successfully removed 96% of Ca, 46% of Mg, 88% of Mn, and 91% of Sr from a natural brine solution. Over 96% of Li remained in the solution following the treatment process. Circular economy approaches were applied by using waste products to stimulate ureolysis and testing the slurry waste generated from bioprocessing of the brine for use as a soil amendment. S. pasteurii grew on 62.5 g L−1 of spent yeast extract and precipitated metal carbonates from natural brine at rates similar to those observed when cultivated in commercial media (TSB plus 30 g L−1 urea). S. pasteurii was also able to utilize urea from cow urine and precipitate an equivalent amount of calcium to commercial urea. The slurry was able to neutralize acidic soils and enhance the microbial activity of the soil. This study highlights the use of waste products (cow urine and spent yeast from the brewery industry) as cost-effective alternatives for the biomass production of S. pasteurii. The novelty of this study lies in the application of MICP using waste substrates, in the treatment of Li-bearing geothermal brines, and in demonstrating selective removal of scaling metals while retaining Li in solution, a significant step toward enabling efficient Li recovery.

Graphical representation of microbially induced carbonate precipitation by Sporosarcina pasteurii selectively removes divalent cations from geothermal brine, enabling sustainable lithium retention through a circular bioeconomy route.