Lithium is typically obtained from brines, pegmatites «hard rock», and sedimentary deposits. Due to low cost of processing, lithium-based chemicals have been produced from salar or salt lake brines. However, the lithium from these brines is low grade and therefore the lithium extraction process needs to be thoroughly optimized.

Additionally, each individual salar has properties that can influence the overall lithium yield (e.g., different lithium concentrations, ambient temperature, rainfall, and impurities), thus they have to be monitored continuously to pick up any changes in process conditions.

Lithium processing (Figure 1) consists of multiple steps. First, lithium brine is extracted from the ground and pumped to the evaporation ponds. Here, most of the liquid water content is removed through solar evaporation. Once the brine in the evaporation ponds reaches an ideal concentration, then the recovery and purification stages begin.

In the second step, the lithium brine is transported to the chemical treatment section. This step consists of dosing chemicals to isolate the lithium ions from other impurities. This process can vary depending on the nature of the lithium source, but generally involves a purification step to remove any other contaminants (e.g., magnesium and calcium) from the brine by filtration or ion exchanger.

Next, the treated sample stream continues to the filtration step to separate the brine from precipitated solids. Finally, the lithum rich sample stream is sent to the reaction tank to produce different forms of lithium for the market. Depending on the product, different chemicals are applied, e.g., sodium carbonate (soda ash) to form lithium carbonate.

Optimizing the purification step is crucial to obtain high quality lithium. This step removes any unwanted constituents from the stream and thus significantly affects the final yield of the lithium produced. Typically, lithium in brine could be determined by potentiometric titration which requires a variety of reagents with diverse shelf lives and hazards. In order to optimally measure very low concentrations of lithium, a tight control of the chemical composition is necessary. With ion chromatography (IC), it is possible to determine various inorganic and organic anions and cations in parallel and over a wide concentration range.

The 2060 IC Process Analyzer from Metrohm Process Analytics is able to continuously measure and monitor multiple cationic impurities in brine in a robust housing suitable for such a corrosive environment. This robust analyzer for online process monitoring and control can be connected to multiple sampling points covering multiple measurement points inside a plant. Thus a sequential analysis at multiple areas inside of a production plant is possible. 

This application is also valid for other lithium extraction processes like: pegmatites «hard rock», and sedimentary deposit excavations. After mining extraction, samples go through purification and crystallization steps, where online monitoring of multiple cationic impurities is necessary.