Sustainable Lithium Extraction: A Novel DEHEHP-Based System for High Mg/Li Brines

Lithium plays a huge role in today’s technology, fueling everything from electric cars to renewable energy storage solutions. As the world shifts toward cleaner energy, the need for lithium keeps growing, mainly because it is so important for making lithium-ion batteries. These batteries are the backbone of energy storage in electric vehicles, portable gadgets, and renewable energy systems. It is no surprise that lithium is now one of the most in-demand materials of the century. But even though it is found in abundance, extracting it efficiently, sustainably, and at a reasonable cost is still a big hurdle—especially when dealing with tricky sources like salt lake brines. Salt lake brines are a major source of lithium, making up more than 60% of the global reserves. Compared to hard rock lithium ores, brines are cheaper and friendlier to the environment to process. They require less energy and produce much less waste. However, they come with their own set of problems. The main issue is the high magnesium-to-lithium ratio (Mg/Li) in these brines, espeically the ones located in Qinghai-Tibet plateau in China. Magnesium ions, which have similar chemical properties to lithium ions, make it very hard to isolate lithium efficiently. Most current extraction methods struggle with poor selectivity, environmental damage, and operational challenges. Traditionally, lithium has been recovered using solvent extraction systems, such as those that rely on tributyl phosphate (TBP) paired with ferric chloride (FeCl₃). These methods, while somewhat effective, are far from perfect. They lose too much organic solvent, harm the environment, and sometimes create a problematic third phase that disrupts the process. To make things worse, TBP’s high solubility in water raises red flags for both ecological impact and large-scale economic viability.

Faced with these ongoing issues, new research paper published in Separation and Purification Technology and conducted by graduate student Hemin Li, associate professor Yuefeng Deng, and led by Professor Ji Chen from the Changchun Institute of Applied Chemistry at Chinese Academy of Sciences designed a new extraction system. Their approach replaces TBP with di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP), used together with FeCl₃. DEHEHP stands out for its lower water solubility, strong resistance to breaking down, and smaller environmental footprint. This research aimed to create a system that is more efficient, selective, and sustainable, solving the challenges posed by high Mg/Li ratio brines. The researchers came up with and fine-tuned a fresh approach to extracting lithium from salt lake brines, which are notoriously tricky to work with because of their high Mg/Li ratios. They started by testing a low-dissolution-loss system using DEHEHP as the main extractant, paired with FeCl₃ as a co-extractant. For the tests, they used concentrated brine from Da Qaidam Lake—a challenging yet realistic choice due to its complex mix of ions. To figure out the best setup, the team tinkered with key variables. They discovered that a 70% DEHEHP concentration in kerosene struck the perfect balance between efficiency and practicality. Using less DEHEHP lowered viscosity but wasn’t strong enough to extract lithium effectively. On the flip side, higher concentrations boosted performance but created new problems, like longer phase separation times. They also pinpointed the ideal preloaded amount of Fe³⁺ at 14 g/L. Adding more improved lithium extraction but caused too much ferric ion to escape into the aqueous phase, cutting into overall efficiency. Another important tweak was finding the right ratio of aqueous-to-organic (A/O) phases. A 1.5:1 ratio worked best, delivering strong lithium recovery while keeping magnesium in check. Going higher didn’t add much value, while lower ratios weakened the extraction. The real game-changer was the multi-stage countercurrent process they designed where they ran an eight-stage extraction followed by two stages of scrubbing and three of stripping, they managed to recover 99.4% of the lithium. The final stripped solution had 20 times more lithium than the original brine, and the Mg/Li ratio dropped by an incredible factor of 3,900. The end product was over 98.5% pure lithium carbonate, perfect for industrial needs like battery manufacturing. Moreover, sustainability was another win. DEHEHP’s dissolution loss in water was just 22.5 ppm, a major improvement over older systems. This not only reduced environmental harm but also cut costs by minimizing the need for replenishing the organic phase. Furthermore, the authors investigated in the detail the chemistry of the process using spectroscopic tools showed that FeCl₄⁻ played a key role as the co-extractant, forming a stable complex (LiFeCl₄·2DEHEHP) that helped move lithium into the organic phase. Plus, the reaction was found to release heat, meaning cooler temperatures would make the process even more efficient.

To wrap things up, the work led by Professor Ji Chen and his team marks a big step forward in making lithium extraction more sustainable. Their innovative DEHEHP-based solvent extraction system directly tackles one of the toughest challenges in this field—getting lithium out of brines with very high Mg/Li ratios. This issue has been a persistent roadblock, but the researchers’ approach offers a fresh solution. Their system stands out for its efficiency, precision, and scalability, making it an ideal option for industries heavily dependent on lithium, especially as the electric vehicle and renewable energy markets continue to grow. We believe one of the most impressive aspects of this research is how it boosts lithium recovery while keeping environmental damage to a minimum. The system’s low dissolution loss of DEHEHP—just 22.5 ppm—significantly reduces its ecological footprint compared to older methods that relied on TBP. This advancement helps cut down on organic waste in surrounding ecosystems and supports a move toward greener and more sustainable resource management practices, aligning well with global environmental goals. This makes it a great fit for use in areas with complex salt lake brine compositions, such as those found in China and South America.

Economically, the work of Professor Ji Chen and colleagues opens up exciting possibilities for more cost-effective lithium extraction. Eliminating problems like third-phase formation and efficient use of chemicals, means lower operational costs and greater feasibility for scaling up. This is especially valuable in today’s market, where demand for lithium outpaces supply, causing price swings and uncertainty. The system developed here offers a reliable way to stabilize production while keeping costs in check. The study also lays the groundwork for future innovations. By uncovering the role of FeCl₄⁻ as a co-extractant and revealing the stable LiFeCl₄·2DEHEHP complex, it provides valuable insights into solvent extraction chemistry. These findings could inspire similar approaches for extracting other critical minerals, addressing resource challenges in various industries.