Bioprocessing of lithium brines

Lead Research Organisation: UNIVERSITY OF EXETER
Department Name: Camborne School of Mines


Global heating due to greenhouse gas emissions is already disrupting the natural world and human society. We must reduce and eliminate our greenhouse gas emissions to prevent catastrophic climate change. This means generating electricity from renewable sources such as solar, wind and geothermal and using vehicles powered by electricity. As renewable energy sources can be intermittent (e.g. the wind doesn't blow all the time), we need to be able to store the energy generated using batteries. Electric vehicles also need lightweight batteries. Making lots of batteries will therefore be a key part of our transition to a society with low greenhouse gas emissions.

Most modern batteries use the chemical element lithium as a main component. Movement of the positively charged lithium through the battery structure stores and releases the electrical energy, meaning that to make many more batteries, we need a lot more lithium. At present we get lithium from two main sources: mining rocks rich in lithium (mostly in Australia) and extracting lithium from salty water (called brine) stored in rocks (mostly in South America). Lithium-rich brines can also be found in rocks in the UK, including in Cornwall, which could be used to give the UK a reliable lithium supply for battery manufacture. These Cornish brines are hot when they are pumped out - as well as containing lithium they are a source of geothermal heat and power from which electricity can be generated.

This project will use biotechnology to help recover lithium from geothermal brines. Although technology exists to extract lithium from brine, other chemical elements in the brine can cause scaling (much like in a kettle) in the pipes and clog up the system, which then requires expensive cleaning with toxic chemicals. In this research we will use bacteria that can make chalk-like minerals from the elements in the brine to remove problematic elements at the beginning of the lithium extraction process. After this we will use algae called diatoms to remove silica from the brine to prevent another cause of scaling. We will work with an industrial partner, Cornish Lithium, to build a pilot-scale extraction system of up to 1000 litres to test whether these processes could be used in commercial lithium extraction.

This project aims to find new ways in which this biotechnology can contribute to the circular economy. Firstly, we will investigate if we can use waste products (cow urine) to feed the bacteria that make the chalk-like minerals. Secondly, we will test whether the waste materials from the bacteria and diatom treatment tanks can be used to improve local agricultural soils which are nutrient poor and acidic. Finally, we will perform a life cycle assessment to find out how the carbon footprint, environmental impacts, costs and benefits of the system compared with other technologies.

Technical Summary

Energy storage capacity both at grid scale and in transport will be key to achieving Net Zero. Lithium-ion batteries are currently the dominant battery technology, so demand for Li is projected to increase by around 5-fold by 2050, and a secure supply of Li will be essential for achieving Net Zero. Around 1/3 of Li is sourced from salar brines in South America, but geothermal brines in the UK are also rich in Li, which could provide the UK with a secure Li supply. A key challenge in Li extraction from brines is avoiding scaling caused by the precipitation of silicates, iron and manganese oxides or gypsum - these can limit plant lifetime and necessitate expensive cleaning with caustic chemicals. We aim to address this issue with novel, low emission and low environmental impact bioprocessing methods with waste streams used as inputs and generating useful waste outputs.

The two novel biotechnology approaches we will use are 1) microbially induced carbonate precipitation (MICP) and 2) diatom-based silica stripping. In preliminary work we have found that MICP driven by ureolysis can remove problematic metals from complex brines. We will optimise this process to rapidly remove Ca, Fe, Mn and Mg from geothermal brine samples while minimising losses of lithium. We will also test whether waste sources of urea can reduce the carbon footprint of the process. Diatoms make silica cell walls and are known for stripping silica out of ocean waters. We will test both marine diatoms from culture collections and diatoms isolated from brackish Cornish waters for their silica uptake capacity in brines. After optimising these technologies in the laboratory, we will work with Cornish Lithium (project partner) to scale-up the system to a pilot plant capable of processing 1000 L of brine. We will measure the efficacy of the process and perform an LCA Hotspot analysis of the performance of the pilot in terms of carbon efficiency and adherence to circular economy principles.


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