Ionic liquid-based metal recovery from aqueous industrial process and waste streams

One of the EU’s strategies to combat climate change is the transition toward low-carbon energy technologies such as the transition to electric vehicles (EV’s). The accelerated introduction of EVs increases the demand for lithium-ion batteries (LIBs), where Cobalt (Co) supply is expected to be the bottleneck in their production. Co is one of the most critical raw materials on earth due to its rare existence and its near-monopolistic supply structure. Therefore, there is a growing incentive, if not critical need. for recycling Co from different waste sources such as industrial wastewater streams and spent LIB’s leachate. Although the process of Co retrieval plays an important role in replenishing Co stockpiles, it also contributes to reducing the environmental impact of industrial Co use and reducing the reliance on Co mining, during which the miners are exposed to highly hazardous conditions.
Liquid-liquid extraction (LLX) is one of the most widely applied hydrometallurgical techniques for metal separation and recovery. This technology allows efficient processing of large volumes of aqueous solution in a continuous mode with relatively low capital and operational costs. At the beginning of the 21st century, a new type of solvents, known as ionic liquids (ILs), found their way to scientists as alternatives to the conventional volatile organic compounds (VOCs). These liquids, defined as salts which is in the liquid state at ambient temperatures or below 100 oC, have interesting properties such as a negligible vapor pressure, high thermal stability and a wide liquidus temperature range.
In this PhD thesis, several aspects of process upscaling of an IL-based LLX system are considered. The goal is to investigate the application of an IL-based LLX process for the extraction and recovery of different transition metals (notably Co) from different process streams. In order to achieve this, fundamental research, experiments, modelling and a preliminary economic analysis are all included. It is decided to use tetraoctylphosphonium oleate [P8888][Oleate] as the solvent due to its unique selectivity towards transition metals. This makes it a good candidate for the extraction of Co from industrial wastewater and spent synthetic LIB leachate.