In a previous article in Innovation News Network (INN), we discussed the environmental issues in Chile and Argentina and the compelling case for effective and environmentally sustainable Direct Lithium Extraction (DLE). On 18 April 2023, the Chilean government announced a broad restructuring of its lithium industry, in which the government will establish state control of the industry. In essence, private companies must adopt DLE-based processes to partner with the Chilean government. While some may consider this action to be driven by governmental desire to control industry, it is clear that environmental concerns play a very large role in this decision. In the previous INN article, we highlighted the environmental issues related to solar evaporation processes that are currently practiced in Chile. These issues include depletion of brine within the Salar Atacama, massive depletion of fresh water around the salar, and pollution from massive salt piles that are stacked around the salar. Each of these issues are very important. However, the loss of potable water has seriously impacted Indigenous people who live around the Atacama. To counter these issues, the Boric administration has set a process in motion that will move lithium production from solar evaporation to DLE processes. To meet the Chilean government’s goals of preserving salar ecosystems, preserving freshwater, and continuing to be a global leader in lithium production, an entirely new paradigm must be put in place that focuses on minimal impact on brine and water ecosystems. Direct Lithium Extraction connotes a methodology in which lithium is selectively removed from brine. In fact, several companies are working to develop a variety of DLE technologies. Unfortunately, most of these processes have a poor track-record in terms of water consumption and brine disposal. DLE, as noted above, is not one specific technology. It is a group of technologies and concepts that are designed to extract a lithium salt from brine and prepare it for product production. The most commonly reported DLE technologies are listed below. It must be noted that the process of inventing and developing new process technologies, such as Direct Lithium Extraction, is quite challenging. Most attempts will fail. In the case of lithium extraction from brine, the problem is quite complicated due to the chemical characteristics of lithium, brine composition, and environmental requirements that the industry must adopt. Chile’s environmental requirements will probably be too onerous for most DLE processes due to issues mentioned above. However, these objectives are necessary for Chile to achieve its humanitarian and environmental necessities. Many DLE processes have been proposed, and some have been piloted. As stated above, one is commercial. The most common DLE processes are based on ion exchange mechanisms. These processes are inherently disadvantaged with respect to water conservation, product quality and extraction efficiencies due to the nature of natural lithium-bearing brines and specific ion exchange extraction mechanisms. Ion-exchange-based DLE utilises materials that are either organic polymeric compounds or inorganic materials. Organic exchangers typically contain negatively charged functionalities such as carboxylates or sulfonates that are distributed through a polymer matrix. Some of these exchangers may have additional complexing moieties, such as polyethers. The inorganic ion exchangers are based on crystalline metal oxide solids that demonstrate ion exchange capabilities. Some of these exchangers contain manganese, titanium, cobalt, or other heavy metals. They may be ‘freestanding’ or supported by another material such as a polymer or an inorganic support structure. Regardless of the ion exchanging Direct Lithium Extraction composition, the mechanism is the same. The exchange substrate, polymer or inorganic, will have specific negative sites within the compound. Each of these sites must contain a positive ion, cation, to balance a structural negative charge. When brine containing lithium is passed through an ion exchanger, some fraction of lithium in the brine will replace ions associated with negative sites in the exchanger, such as sodium (Na+). When the exchanger has reached a state of ionic equilibrium with the brine, the process of ion exchange is finished. The next step is a four-step process known as ‘regeneration’. During this operation, a mineral acid such as hydrochloric acid is pumped through the exchange bed. Protons displace the exchanged ions which enter the bulk solution. The exchanger is then rinsed with water to remove residual extraction products. It is then neutralised with a base such as sodium hydroxide, and rinsed with water to prepare the exchanger for lithium extraction from brine. When one considers lithium extraction from a natural brine via ion exchange, it is important to note that lithium is not the only cation that will be exchanged by the material. The distribution of cations on exchange sites is governed by selectivity coefficients, ionic charge, and concentrations of the relative cations in solution. For example, lithium chloride in a clean sodium chloride (NaCl) brine may be easily and economically extracted. However, extraction of the same lithium concentration in a complex natural brine that contains high concentrations of calcium and magnesium will likely be much less efficacious. This is due to the Donnan Effect, which describes the impact of ion electrostatics. It states that ion selectivities are a function of ionic charge. Thus, divalent cations such as calcium and magnesium will be more strongly preferred than monovalent ions such as lithium and sodium. Since calcium and magnesium concentrations are typically significant in natural brines, these ions can dominate the extraction process, significantly reducing the lithium extraction capacity. Furthermore, upon regeneration, the resulting product solution will contain very high concentrations of calcium and magnesium. Another issue that challenges most extraction mechanisms is ‘mass action’. Even the highest quality Chilean brines actually contain relatively low concentrations of lithium. Thus, the odds are stacked against selective lithium extraction. The law of mass action will dominate the extraction process. Ultimately, the quantity of extracted lithium from one pass through an ion exchange bed will most likely be low. The resulting regeneration solution must be recycled through another ion exchange bed to produce a higher percentage of lithium chloride. The process may require numerous cycles to achieve a reasonable lithium concentration. Each regeneration cycle consumes acid and base to extract the cations and neutralise the exchanger in order for it to extract ions from the brine. An unavoidable consequence of this type of process is the production of copious volumes of waste salt water during each cycle. To recap, there are typically six steps in the lithium extraction steps for the ion exchange system: Acid and base regeneration produces significant quantities of waste salt water during each cycle of the process. Since the water is now contaminated with salt, it cannot be reused as is. Either water must be removed from the solution, or the salty wastewater must be released. The Chilean regulators are not likely to support the latter practice. Furthermore, the amount of produced NaCl is quite significant. Assuming 100% efficient lithium extraction, a plant that is designed to produce 20,000 MT/yr of lithium carbonate will also produce approximately 31,350 MT/yr of NaCl in an aqueous solution. Since ion exchange systems have not demonstrated high lithium extraction selectivities, one would expect a significantly higher ratio of waste salt to lithium carbonate. This level of waste salt solution is not consistent with the new Chilean requirements. Lithium selectivity coefficients of most ion exchange processes are typically poor. Notably, some of the inorganic exchangers appear to show a higher selectivity than organic-based ion exchange. However, these materials also tend to degrade after a small number of process cycles. Other types of Direct Lithium Extraction include solvent extraction, membrane processes, adsorbent processes, and absorbent processes. Solvent extraction is a process in which a non-miscible liquid, such as kerosine containing an organic moiety that can strongly associate with lithium, is emulsified with a target brine. The combined solution is then pumped through a phase separator to recover the brine and the organic phase. If the chemistry is correct, lithium will be extracted into the organic phase. This solution is then mixed with an aqueous solution that may contain a ‘release agent’, such as an acid, to recover the lithium. Some amount of organic phase will dissolve into the brine phase, creating an unwanted contaminant in the waste brine. The Chilean government will probably not allow this contaminated brine to re-enter the salar system. Therefore, a significant purification process will be required. To our knowledge, this type of lithium extraction has never been successfully demonstrated at scale with naturally occurring brines. The likely problem is that cations such as calcium and magnesium, which are ubiquitous in natural brines, are much more strongly associated with solvent extractants than lithium. During the extraction step, these ions saturate organic phase co-ordination sites. Lithium, having a much lower selectivity coefficient for these types of extractants, is left in the brine solutions. Reverse osmosis (RO) utilises a very tight membrane to generate clean water salt water. An example of commercial RO systems is fresh water from seawater processes around the world. Sea water is injected into the RO membrane systems under considerable pressure. Clean water leaks through the membrane and a more concentrated salt solution is retained. This salty solution is returned to the ocean. Nanofiltration is similar to reverse osmosis. In these operations, the membrane has a significantly higher porosity than RO membranes. This allows ions to leak through. Nanofiltration is often employed when one desires to remove ions such as calcium and magnesium from a dilute aqueous stream. When the membrane is under pressure, a water stream containing the target salts will leak through. The bulk solution is retained by the membrane system. This becomes the product stream. It will contain lower concentrations of the target impurities. Several problems exist in efforts to extract lithium through membranes. The first is that membrane separation only works in low concentrations. As the salt concentration increases, the permeate flow decreases. Essentially, the amount of water that is available for basic ion hydration decreases. Ultimately, there is no ‘free’ water. So much of the water is involved in solvation of the salts that the RO pressure exceeds the pressure limit of the membrane. At this point, beneficial operations stop and membranes often rupture. Unfortunately, the total salt concentrations that limit RO are much lower than the concentration of natural brines. Some internet postings refer to routes that run natural brine on one side of the membrane and some other, high total dissolved solids (TDS) solution on the other. I have found no credible evidence for productive lithium extraction from natural occurring brines. Some review articles have listed ‘adsorptive’ processes for lithium extraction. I am not aware of any functional adsorption-based processes for extraction of lithium from aqueous solutions. An absorption process is one in which lithium is reversibly transported to specific sites within a solid substrate. A caveat to this statement is that the absorption site is not negatively charged. A negatively charged site would connote an ion exchange mechanism. Absorption does not rely on ionic charges to attract lithium to a specific site. Absorption occurs when a lithium ion moves into a site that has characteristics that provide a lower energy environment for lithium ions. These characteristics may attract other ions as well. Furthermore, since we cannot separate charges, there must also be an opportunity for counter ions, such as sulfate or chloride, to reside close to the absorbed lithium ion(s) to maintain charge balance. Several Direct Lithium Extraction processes utilise manganese oxide, titanium oxide, or aluminum oxide as absorbents. Some of these systems require special regeneration steps. Some also tend to dissolve slowly during operations and must be periodically treated. International Battery Metals utilises a proprietary absorbent that operates on a brine/water cycle. This extraction process does not require chemicals. Furthermore, our absorbent demonstrates a double selectivity. Thus, it absorbs lithium and chloride ions, and rejects other brine constituents. Upon water regeneration, very pure lithium chloride solution can be produced. International Battery Metals (IBAT) has developed a patented modular plant that is capable of meeting all of these criteria, with highlights including: Not only is this patented technology ready for Chile, but it is also suitable for broad application in lithium-bearing brines around the world.
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