Dr John L Burba, CEO of International Battery Metals Inc (IBAT), details the various methods to extract lithium, highlighting IBAT’s direct lithium extraction technology, which demonstrates superior performance over other methods.
With the global focus on environmentalism and global warming, lithium production to support batteries for electric vehicles has been a global hot topic. Correspondingly, the lithium industry’s meagre ability to supply the industry needs has become evident. Thus, with estimates of a 52% global lithium production shortfall by 2030, much focus has been placed on our industry.
Currently, there are only two commercial lithium production sources, spodumene and naturally occurring lithium-containing brine. The details of these resources, including the advantages and disadvantages of each, have been discussed in previous articles.
This article will focus on brine resources and a particular type of lithium extraction, commonly referred to as direct lithium extraction or DLE. Several promoters and pundits have recently suggested that DLE is a new technology, and they have the solution to lithium extraction. In fact, the origins of DLE go back to the Advanced Separations Laboratory at the Dow Chemical Company in the 1970s. This lab was founded and headed by Dr William C. Bauman, the inventor of ion exchange resin.
Upon graduating with my PhD in physical chemistry in 1979, I was fortunate to become Dr Bauman’s understudy at Dow. While our charter was the development of efficient, new extraction technologies, Bill’s primary focus was lithium. He chose lithium because he saw value for Dow and loved challenging problems. Thus, over the next five years, we developed a very selective composite ion exchange resin that demonstrated dual selectivity for lithium and chloride ions. We constructed and operated a pilot plant in Arkansas in 1984.
We demonstrated that the direct lithium extraction technology could extract lithium from natural brines and produce high purity lithium chloride. However, while the composite resin could successfully extract lithium chloride from brine, it had some serious efficiency issues. The plant did not demonstrate the necessary economics to support commercial development, and the project ended.
In 1992, Bill and I filed two patent applications for selective absorbents that were not dependent on ion exchange or chelation. Later, I joined the Food Machinery Corporation (FMC). In early 1994 FMC chose to license our patents and initiated a DLE project focused on extracting lithium from saturated salt brine at Salar Hombre Muerto in Argentina. I led the absorbent development programme and designed the basic plant. FMC had an excellent team of engineers that did the detailed engineering. FMC’s lithium extraction plant at Salar Hombre Muerto started up in 1998. Thus, direct lithium extraction technology was invented and piloted in the 1980s and commercialised in 1998.
Intricacies of direct lithium extraction technology
Direct lithium extraction technology removes lithium and associated anions from a brine solution and transfers it into a different medium, such as water, for further processing to final products.
Conceptually, DLE is straightforward. One utilises an extractant that will selectively remove lithium ions from a complex solution. The extractant is exposed to a lithium-bearing brine until a state of equilibrium is achieved. At this point, the extractant is ‘saturated’ and additional lithium will not be taken up. This does not suggest that all sites in the extractant will necessarily have lithium associated with them. Brine solutions typically contain multiple positive ions, ‘cations’, that will compete with lithium for specific sites on the extractant.
Thus, when an extractant is contacted with a complex brine solution, a state of equilibrium will be established with all ions in the solution. Depending on the ion uptake mechanism associated with a specific extractant, multiple competing ions can be found on the same extractant particle. It is important to understand that competition for extraction sites is based on fundamental thermodynamics. Essentially, the ion ‘mix’ on exchange sites of a particular extractant represents the lowest enthalpy that can exist at a specific temperature, with a particular extractant and a particular solution composition.
DLE’s obvious goal is to extract lithium and leave the other cations behind. However, thermodynamics will rule. For economic lithium extraction to occur, the chosen extractant must present a situation where the lithium association with extraction sites is thermodynamically strongly preferred over other cations in the solution. The ultimate test is straightforward. After reaching ionic equilibrium, the exchange sites are regenerated. However, what will the lithium to non-lithium cation ratio, [Li]/[Na, K, Ca, Mg, Zn, Mn, etc.] be? This relationship defines the extraction efficiency and the lithium product purity of the process.
Thus far, our focus has been on specific ion association sites in the extractant. An equal party in this interaction is the brine. Naturally occurring brines have several characteristics that seriously complicate ion extraction, as detailed here:
1) Natural brines vary from resource to resource and even within the same resource. In addition to lithium, oilfield brines in North America can contain very high levels of calcium, magnesium, iron, and silica. Geothermal brines in Southern California contain sodium, potassium, manganese, zinc, magnesium, calcium, iron, and silica.
Salar Atacama in Chile supports two commercial lithium solar evaporation plants. This brine contains lithium, sodium, potassium, calcium, magnesium, sulfate, and borate. The Atacama is an extensive resource, and elemental concentrations change dramatically across the salar. This is a problem for solar evaporation processes because the various salt solubilities, such as magnesium chloride, are seriously impacted by sulfate and borate ions. If these anion concentrations are too high, magnesium solubility is significantly increased. Thus, clean removal of magnesium chloride and potassium magnesium chloride salts does not occur. Instead, the magnesium tracks with lithium through the rest of the process and becomes a considerable impurity in the final lithium pond, seriously impacting lithium recovery rates.
2) Location is another issue. Andean brines are often in very remote locations with limited access to critical support systems such as labour, electricity, natural gas, or fresh water. In fact, most resource locations will typically have one or more adverse issues.
3) Total salt concentrations are typically very high, but lithium concentrations are low. In some cases, such as Chilean, Argentine, or oilfield brines in the United States, total salt concentrations can exceed 350,000 mg/kg (parts per million), or 35%wt. In these brines, sodium concentrations can exceed 100,000 mg/kg.
Correspondingly, target ion concentrations are very low. For instance, a commercial brine from the Salar Atacama typically presents lithium concentrations that range from 1000 to 2000 mg/kg. Some oilfield brines in Alberta may contain only 50 mg/kg to about 90 mg/kg.
If we are considering a brine that has a sodium concentration of 125,000 mg/kg and a lithium concentration of 2,000 mg/kg, the [Li]/[Na] ratio is 0.016. Correspondingly, if the lithium concentration is only 50 mg/kg, the [Li]/[Na] ratio is 0.0004. Assuming constant extraction efficiency, we will need to pump 40 times as much 50 mg/kg brine as we would pump with 2,000 mg/kg brine to achieve our production goals.
Furthermore, extraction efficiency is higher with greater lithium concentrations. Thus, with a 50 mg/kg brine, we will likely see lower lithium recovery even with the very high flow rates. Thus, lithium concentration matters.
4) Generally, lithium extractants are quite sensitive to competing ions that are found in the brine. This is a particularly thorny problem with ion-exchange-based extractants.
Why do so many direct lithium extraction processes fail?
Numerous companies have proposed and are working on various schemes designed to extract lithium from brines. Except for MGX’s failed efforts to thermally evaporate diluted Alberta brine using crystallisers to recover pure lithium chloride and millions of tons per year of unusable waste salt, DLE start-ups are focused on identifying and developing processes for the selective removal of lithium from a source brine.
In their quests, these companies have employed numerous materials to selectively recover lithium, including solvent extraction, membrane separations, polymeric- and inorganic-based ion exchange, chelation and coordination schemes, combination exchangers, adsorption and absorption materials.
Our intent is not to drill into each concept in detail. Instead, we are more interested in demonstrating the daunting challenges associated with direct lithium extraction technology. We hope to explain the general concepts and ultimately describe an approach that demonstrates superior performance.
The ion exchange concept
The most common class of commercial extractants is ion exchange resin. These materials are employed predominantly in water purification applications. They are also utilised to perform various tasks in the chemical industry. They are polymer beads produced as polymer ‘gel’ resin or open networked polymer resin, called macro reticular resin. Polymer ion exchange resins are typically called IX Resin. Ion exchangers can also be based on inorganic materials such as zeolites or insoluble metal salts that have specific functionalities allowing charge-based association with ions.
The term ion exchange is quite literal. When IX resin is placed in a solution containing salts, it will quickly achieve a distribution of ions in the resin that will be different from the composition of either the original salt solution or the final solution. The factor that determines the ion distribution in the resin is the relative affinity of it to the various ions in solution, typically referred to as the ion exchange selectivity. It is defined by selectivity coefficients for each exchangeable ion in the solution.
In a simple two salt system, such as lithium chloride and sodium chloride, the selectivity coefficient for lithium vs sodium can be defined as Ratio{Li/Na}resin/{Li/Na}solution. Ion exchange selectivities are typically driven by valence and ionic radius. Polyvalent cations such as calcium are generally more strongly attracted to the resin than monovalent cations such as sodium or lithium. Ions with large ionic radii are more strongly attracted to exchange sites than ions with smaller radii.
Thus, in natural brine systems, the association of lithium with a cation exchanger will be weaker than all other cations on the periodic table because it is monovalent and has the smallest mass of all cations in the periodic table. Note that only magnesium and beryllium have smaller ionic radii than lithium. However, they are both divalent cations. Beryllium is not typically found in the brines of interest. However, magnesium is often present in significant concentrations. Thus, ion exchangers will preferentially exchange magnesium over lithium.
Once the resin is at equilibrium with the source brine, it must be regenerated with strong acid. This step is followed by a strong base to restore the resin to its initial state. The total molar amount of acid and base will be equivalent to the number of ions exchanged onto the resin plus any waste in the operation. This regeneration step creates significant quantities of waste salt solution. Additionally, the resulting regeneration product solution containing lithium will be acidic, and it must also be neutralised, creating even more waste salt solution.
Thus, each ion exchange cycle is burdened by the cost of large quantities of acid and base plus correspondingly large amounts of water. Additionally, process engineers must remember that all of this waste salt must go somewhere. Therefore, there is a significant environmental challenge associated with this regeneration operation.
Unfortunately, for ion exchange processes, unless there is a ‘magical’ ion exchange material that can recover very high percentages of lithium in one pass, the story is worse. The next step is to run the regeneration solution from the previous step through another ion exchange column to enhance the lithium concentration on the resin.
This multistep process must be repeated numerous times to reach a reasonable lithium concentration in the working solution. The bottom line is that, unless the IX system demonstrates stunning selectivity for lithium, the entire process becomes a giant Rube Goldberg nightmare that will demonstrate poor economics with serious environmental issues.
The chelation and coordination method
Other DLE groups are working with chelation and coordination systems. Most of these approaches are associated with IX, described above. Therefore, they are also wedded to acid-base regeneration cycles. Most of these processes have essentially the same problems as straight IX. A frustrating truth associated with chelation and coordination systems is that they work very well on transition metal ions such as cobalt, copper, nickel, and the like. However, these ions are enormous when compared with a lithium ion. These transition metals have large, expanded electron orbitals that easily associate with coordinating functionalities. The cobalt cation, Co++ has 25 electrons while lithium, Li+ has only two electrons. Again, without some type of special situation, lithium ions are unreachable.
The liquid extraction method
Liquid extraction materials are typically immiscible with water or brine. They function by chelation or ion exchange that takes place at the organic/aqueous interface. When we were doing fundamental extractive research at Dow, one of the excellent chemists that I worked with, John Lee, studied the use of certain complex ethers to extract Li via an association mechanism. His systems worked remarkably well in simple NaCl-LiCl systems. However, when adding Ca, Mg, Zn, or Mn to the system, the Li consistently demonstrated very low selectivity. John’s process was impractical since natural brines will contain at least some of these ions in high concentrations.
The selective absorption method
After working with these materials at Dow, we concluded that direct lithium recovery would only work if we could find an ion ‘discriminator’ specific to only Li and could function effectively in a lithium extraction process. Fortunately, Bill and I found one in the early 1990s. The material has a unique crystal structure that allows absorption of lithium ions into its crystal lattice. Other cations cannot enter the crystal lattice.
This characteristic of exclusive lithium uptake into the lattice leads to a selectivity coefficient for lithium over all other cations that is essentially unmeasurable. We have conducted numerous experiments with various brine compositions. We have never observed lattice absorption of any cation other than lithium in each case. For example, we have conducted multiple experiments with a South American brine containing 1200 mg/kg of lithium. The brine was saturated and contained concentrations of calcium, magnesium, sulfate, and borate typical of the Atacama brine.
We can routinely reduce the brine lithium concentration in the brine to less than 0.1 mg/kg. Furthermore, upon regeneration of the absorbent, we produced a lithium chloride solution that contains approximately 99% lithium chloride in water. In these operations, regeneration is done with water. No acid or base is necessary. Furthermore, unlike ion exchange systems, the absorbent reached saturation with lithium in one cycle. Thus, the industrial process will cycle between brine for lithium chloride uptake and water for regeneration.
IBAT’s direct lithium extraction technology
Over the last four years, we have worked to integrate this selective absorbent with a highly efficient modular and mobile extraction plant. First, IBAT’s direct lithium extraction technology takes advantage of an improved version of the ‘selective absorbent’ invented by Dr John Burba and Dr Bill Bauman in the early 1990s. As stated above, this absorbent will extract lithium and chloride ions selectively from high salinity brines.
The sorbent rejects other salt components such as sodium, potassium, calcium, magnesium, sulfate, and borate. IBAT’s process operates on a brine-water cycle, unlike virtually all other DLE systems. Lithium chloride is absorbed from the brine and released into the water. Unlike other DLE processes, acid and base are not necessary. Thus, the corresponding waste salts do not exist in the IBAT process. This inherently creates a cleaner operation.
Several other key distinctions exist between IBAT’s patented process and other proposed DLE processes.
1) IBAT’s plant is modular and mobile. This means we can build our entire plant in a fabrication shop in months. Conventional lithium extraction plants require between five and 12 years to construct and start-up. Correspondingly, IBAT’s plants will cost much less than traditional plants.
Furthermore, IBAT’s modules can be transported and assembled at the resource. The benefits are not limited to time and capital cost. There is also a huge environmental advantage. Conventional plants have large buildings on large concrete foundations that will remain in place long after the operation is finished. When IBAT reaches the end of an operation, the equipment will be moved to another location. We will leave a clean site.
2) IBAT’s plant is designed to produce minimal environmental damage during lithium extraction. We have incorporated several novel technologies that are very environmentally protective.
a) IBAT has developed novel water recovery technology that recycles approximately 98% of the plant’s process water. Solar evaporation projects require enormous quantities of fresh groundwater to support their operations. This has been a significant problem in areas where indigenous peoples farm and ranch. IBAT will not compete with local people for precious water resources. Due to our water recovery innovations, we will not need local water.
b) With the concurrence of country regulators, IBAT prefers to inject lithium depleted brine back into salars in Chile and Argentina. A great deal of history in the US suggests that this process can be done safely. The advantage is that we will not be polluting vast resource areas with huge quantities of salt waste.
c) Our process is designed to minimise our carbon footprint. We plan to incorporate renewable energy into our plants. We will utilise solar energy. We are also investigating other novel and exciting renewable energy systems that can provide thermal and electrical energy.
IBAT’s novel patented direct lithium extraction technology is based on proven selective absorbent technology and innovative engineering. Our goal is to significantly advance the lithium extraction and production industry ethically.
Please note, this article will also appear in the tenth edition of our quarterly publication.
