A guide for ion exchange resins used in lithium concentrate purification

Traditionally, selective chelating Ion Exchange resins possessing either iminodiacetic acid (IDA) or aminomethylphosphonic acid (AMPA) functional groups have been used for more than three decades in the chloralkali industry. Their superior selectivity characteristics facilitate the removal of trace impurities such as calcium, magnesium and other multivalent cations from a 300 g/L saturated sodium chloride brine solution. Thus, it became obvious to transfer this established technology to a related technical challenge in hydrometallurgical processes: the hardness from lithium brines. Driven by the surge in demand for high purity battery grade lithium compounds, purification of lithium concentrates to meet the stringent specifications for typical contaminants is a critical step in the production of these chemicals. There is evidence that conventional purification methods such as precipitation might be insufficient in many cases. Selective chelating ion exchange resins have proven to be a viable and reliable option when it comes to removal of trace levels of earth alkaline metals and other impurities from Li concentrates. This paper gives a comprehensive overview about the use ion exchange resins in the purification of lithium brines, in particular the removal of residual quantities of contaminants such as calcium, magnesium, boron and other metals. Key aspects of ion exchange resins such as selection criteria, their physical and chemical characteristics, and the process and operating parameters which have an influence on the overall performance of the Ion Exchange resin purification systems shall be discussed.