Core Technology Analysis of Lithium Extraction from Salt Lakes (Part 2)

(2) In salt lakes with high sulfate levels in Argentina, such as Olaroz Salt Lake under Orocobres and Cauchari Olaroz Salt Lake controlled by Ganfeng Lithium, not only are they evaporated through salt fields, but a large amount of quicklime is also directly added to the salt fields to reduce sulfate and magnesium levels. The enriched old brine is then transported through pipelines to the mining area's factories for extraction, boron removal, and finally lithium deposition. Overall, the principle of salt field precipitation method is simple, the process is relatively mature, and the direct production cost is low. However, the overall lithium recovery rate is relatively low (from salt fields to lithium salt plants), less than 30% and less than 50%. There is still significant room for improvement in optimizing yield and promoting refined mining in the future.

02

Adsorption method

The promising and rapidly increasing number of industrial cases is hindered by high freshwater consumption and the need for lithium in adsorbent preparation.

The adsorption method has mature applications in water treatment, medicine, food, hydrometallurgy and other fields, but lithium extraction from salt lakes is still a blue ocean. After long-term industrial trials, adsorption has become one of the most widely used and promising processes in lithium extraction from salt lakes, with a rapid increase in industrial project cases. In the development process of adsorption method, the Fenix facility of Liment (FMC Lithium) in Hombre Muerto Salt Lake, Argentina, and the Blue Science Lithium Industry controlled by Salt Lake Corporation are two iconic projects that must be mentioned. In China, adsorption technology has also undergone a transformation from introducing first and second generation technologies from Russia to self-developed. We believe that:

(1) The adsorption method is particularly suitable for salt lakes with low lithium ion concentrations in the original brine. Given the explosive demand, the global development of suboptimal salt lake resources has been put on the agenda, so adsorption has great potential for promotion;

(2) For high-quality salt lakes, adsorption can also form a blessing. On the one hand, it can improve yield, and on the other hand, it can significantly reduce the area of salt fields, in line with the increasingly stringent environmental and ESG requirements worldwide.

(3) The biggest constraint of adsorption is the high consumption of fresh water during the desorption process, but by developing adsorbents with larger adsorption capacity and adding water circulation devices, a solution can be formed; In addition, the adsorbent needs to consume a certain amount of lithium hydroxide or lithium chloride to form an intercalation structure during the preparation process, which will increase the cost.

(4) The core of adsorption method lies in developing adsorbents with large adsorption capacity, strong separation performance, and long cycle life for specific types and components of salt lake brine, as well as devices for continuous adsorption, to solve the drawbacks of poor recyclability, severe solution loss, and weak selectivity.

(5) In industrial practice, the adsorption method requires special attention to the design of the reinjection of the desorption solution. If not considered carefully, it can easily lead to significant dilution of the original brine concentration in the brine mining area.

The principle of adsorption method is that it can achieve functions such as separation, purification, concentration, and enrichment of substances through ion exchange and adsorption of the exchanged substances. Therefore, it can be applied to many solid-liquid separation processes and has a wide range of potential applications. It was first used in wastewater treatment in the late 1960s and later expanded to traditional fields such as industrial water treatment, food and drinking water, as well as wet metallurgy, biomedicine, environmental protection, electronics, etc Emerging fields such as nuclear energy. However, due to the wide range of application fields, there are significant differences in the selection, production, and technology of resin materials in specific sub fields. In addition, different customers have different application conditions, and in emerging fields, customized research and development of special adsorption resins are usually required. This has created the core competitiveness of adsorption technology enterprises.

The barriers to adsorption resins and lithium adsorbents in lithium extraction from salt lakes are relatively high. At present, aluminum based molecular sieve adsorbents are the most widely commercialized and applicable types of brine (chloride type, magnesium sulfate subtype, etc.), and the next generation of manganese based ion sieve adsorbents and titanium based ion sieve adsorbents are also expected to be commercialized in specific salt lake brine. Among them, aluminum based molecular sieve adsorbent, as the only industrialized and mature adsorption material currently, was first applied by Atomic Energy Corporation of Russia and Dow Resin Company of the United States. The former's technology was sold to Foshan Lighting and became the foundation of Lanke Lithium's lithium extraction process; The latter is traded with Livent (formerly FMC Lithium) and improved for use in lithium extraction from its Argentine salt lakes. In the development of adsorbents, professional technical service providers such as Lanxiao Technology and Jiuwu High Tech have formed rich practical experience in industrialization cases and have a first mover advantage. In addition, owners such as Lanke Lithium also have skilled proprietary technology, but professional technical service providers have faster technological iteration and optimization upgrades.

We believe that the core advantage of adsorption method for lithium extraction lies in:

(1) Significantly reduced the marginal selection grade of the original brine, currently capable of processing brine with lithium ion concentrations as low as 50ppm;

(2) Improved recovery rate, shortened production cycle of lithium products, and higher production efficiency;

(3) Due to the increase in yield, production capacity can be significantly increased while resource endowment and brine extraction intensity remain unchanged;

(4) Although the adsorbent has dissolution loss, it does not introduce new chemical elements or organic matter, making it relatively green and environmentally friendly;

(5) The cost remains attractive, but this is not its main advantage over other lithium extraction paths. The main disadvantage of adsorption method is that it consumes a large amount of fresh water, and salt lake mining areas either have scarce fresh water or strictly limited water usage quotas. However, from a development perspective, in the future, MVR and other devices can be added at the back end of the production line for the recycling of fresh water.

Looking ahead, we believe that efficient adsorption technology will be more widely applied in the development of lithium resources in suboptimal salt lakes worldwide (with lower lithium content and longer evaporation cycles in salt fields).

Even for salt lake brine with high lithium ion concentration on the global front line, although the application of adsorption is not urgent, the recovery rate can still be improved. In the longer term, the development of adsorption technology will strive to be applicable to continuously lower concentrations of raw materials, and the ultimate goal may be the commercialization of lithium extraction from seawater.

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03

Membrane separation

The limitation of achieving low-cost lithium ion separation through high-pressure filtration of old brine lies in the limited flux of the nanofiltration membrane.

Membrane separation method is one of the most active industrial applications currently. The essence of membrane separation method is to use the selective separation function of the membrane to separate different components of the feed liquid through pressure, and the core is the selection of membrane materials. Usually, membrane separation for lithium extraction requires gradient coupling of multiple membrane materials to achieve the extraction of low-priced lithium ions, separation of divalent and multivalent ions (such as magnesium ions, sulfate ions, lithium ions, etc.), and has the advantages of environmental protection and relatively low capital expenditure.

In the past, membrane separation was mainly used in industrial wastewater treatment, food and other fields. Currently, commercial cases of lithium extraction in salt lakes include Hengxinrong and Wukuang Yiliping Salt Lakes. However, issues such as high power consumption, membrane loss, membrane fouling, stability, and optimization of high and low price ion retention rates still need to be optimized.

Among them, we believe that the biggest obstacle to lithium extraction by membrane method is the limited flux of nanofiltration membranes, especially in high magnesium lithium ratio salt lakes. The old brine enriched in salt fields needs to be greatly diluted before it can enter the membrane system, resulting in a large process system, excessive investment intensity, and large freshwater consumption. In the field of membrane materials, especially in high-pressure operating environments, overseas suppliers still have leading advantages. However, with the introduction and digestion of teams and technologies, domestic enterprises are rapidly iterating and upgrading, and the progress of domestic substitution is accelerating.

The selection of membrane materials for lithium extraction from salt lakes is based on organic membranes. The range of intercepted substances is determined by the pore size of the microporous structure of membrane materials. Therefore, the key to the separation accuracy and efficiency of membrane materials lies in the pore size distribution and porosity. In practical applications, membrane separation methods are often applied in different process steps based on the characteristics of different membranes. The membrane materials of salt lakes are mainly divided into:

(1) Ultrafiltration membrane (UF): mostly used in qualified solutions that have completed adsorption and analysis, to reduce the possibility of subsequent nanofiltration membrane fouling and loss by filtering suspended particles, etc;

(2) Nanofiltration membrane (NF): It can achieve the separation of divalent and divalent ions (such as magnesium ions and lithium ions), and the nanofiltration membrane is an charged membrane that can selectively purify different substances. However, the nanofiltration membrane used for lithium extraction from old brine needs to be diluted before passing through due to its low flux, resulting in a decrease in concentration significance;

(3) Reverse Osmosis Membrane (RO): It can be used in the lithium extraction process of salt lakes to concentrate lithium solutions at the backend of the process.

China's organic membranes are in the stage of gradually realizing import substitution, and membrane material loss still needs to be optimized. At present, China's ultrafiltration membranes have basically reached the level of foreign countries through independent innovation, but nanofiltration and reverse osmosis membranes still mostly rely on foreign imports. The former's key focus is on improving permeability, anti pollution, oxidation resistance, and cost reduction, while the latter includes not only cost optimization but also aspects such as water production, energy consumption reduction, and stable operation.

In addition, in practical applications, membrane materials are generally consumed quickly, and how to reduce loss rate, improve membrane material strength, or resist pollution is still the research and development direction.

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04

Electrodialysis

Utilizing a direct current electric field to achieve directional migration of charged ions, producing stable and low water consumption. But there are applicable prerequisites.

Electrodialysis is also a type of membrane separation, and ion exchange membranes (IEMS) are the core consumables. The separation principle is mainly to allow brine to enter the desalination chamber of the electrodialysis device under the action of an external DC electric field, and to selectively migrate charged ions to the electrode through monovalent ion selectivity. Ion enrichment forms a concentration chamber to obtain a concentrated lithium rich brine solution, while magnesium, borate, and sulfate ions remain in the desalination chamber, Basically removing impurities such as sulfate ions, borate ions, and magnesium ions, the lithium recovery rate is high and can reach over 80%, resulting in a purity of 99.6% of lithium carbonate products. In addition, in recent years, continuous process improvement and power consumption issues have been gradually optimized.

According to the electrodialysis patent, this process can form a lithium rich concentrate by electrodialysis with an initial lithium ion concentration of 0.02-20g/L and a magnesium lithium ratio of 300:1-1:1 in the brine. The lithium ion concentration can reach 200g/L and the magnesium lithium ratio can be reduced to 10-0.1. It is suitable for salt lake brine with high magnesium lithium ratios, and the removal rate of magnesium ions, boron ions, and sulfate ions is above 95% -99%.

05

Solvent extraction method

Efficient, short process, and low-cost lithium extraction technology with environmental disputes.

The solvent extraction method is widely used in industries such as petrochemicals, hydrometallurgy, pharmaceuticals, and nuclear fuel extraction. It is also an efficient concentration and separation process in the field of lithium extraction from salt lakes, but it is also an environmentally controversial process path.

In the future, with the development of new extraction systems and the standardization of environmental treatment, the industry will have a more comprehensive understanding of lithium extraction through extraction methods. In commercial cases, the extraction method has been validated and continuously upgraded in the Dachaidan Salt Lake in Qinghai.

In principle, the extraction method uses organic solvent extractants with high selectivity for lithium. Lithium is extracted from the old brine into the organic phase, and then eluted. Therefore, the development of suitable extractants (efficient, environmentally friendly, safe, and affordable) and extraction devices (such as box extraction tanks) is the key to the process. According to our tracking, the current main lithium extraction systems include neutral phosphate and amide extraction systems (lithium magnesium separation), diketone neutral phosphate oxygen co extraction systems (lithium alkali metal separation), crown ether extraction systems (lithium isotope separation, lithium alkali metal separation), and ionic liquid extraction systems (solvents, co extractants, co extractants, etc.).

Extractants are often not used alone, but in combination with co extractants and solvents to form a mixed extraction system. As of now, neutral phosphorus extractants are the most extensively studied and more suitable reagents for high magnesium lithium ratio salt lakes. Among them, the extraction effect of tributyl phosphate (TBP) system is more recognized and has become the main extractant currently used. However, there are also situations such as high water solubility, easy degradation under strong acid-base conditions, and short continuous operation life.

Overall, we believe that the extraction and extraction process for lithium has advantages such as short process flow (resulting in low capital investment and operating costs), high magnesium lithium separation efficiency, short time, and high lithium recovery rate (ideal to reach over 90%), which can produce high-quality lithium chloride. Under the same conditions, the capital investment is significantly lower than that of the adsorption method.

But the core constraint is that although the emissions of the latest extraction system can be reduced to ppm level (by adding treatment devices), far below the emission standards in mainland China, it will still add non-existent organic matter to the salt lake ecosystem and participate in the circulation of the salt lake. If adsorption pre concentration and back-end integrated extraction are adopted in the future, without participating in salt lake circulation, it may be one of the solutions.

Meanwhile, in the case of continuous processing of large volume solutions, the economy of extraction will face challenges, with certain requirements for the lithium ion concentration in brine. In addition, in industrial practice, there have been challenges such as difficulty in long-term operation of production lines, high consumption of extractants, and easy corrosion of equipment (requiring acid addition to inhibit the hydrolysis reaction of FeCl3).

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06

Calcination leaching method

The earliest generation of industrialized high magnesium lithium ratio salt lake lithium extraction process in Qinghai has clever ideas but many engineering constraints.

The calcination leaching method is one of the earliest industrially applied high magnesium lithium ratio salt lake lithium extraction processes in Qinghai. It was independently developed by Qinghai CITIC Guoan in 2005 based on the characteristics of Xitai Salt Lake brine. As its name suggests, its process flow is somewhat similar to the ore method.

Firstly, a solid mixed salt of bischofite and lithium chloride is obtained by evaporating the deboronized brine, followed by high-temperature calcination (450-900 ℃), water immersion decomposition of magnesium oxide, and precipitation separation with soda ash to obtain lithium carbonate. The calcination method overcomes the problem of magnesium lithium separation. The clever principle lies in converting magnesium dissolved in water and lithium chloride into insoluble compounds, thereby achieving magnesium lithium separation. It also achieves simultaneous production of lithium, boron, and magnesium products on the production line. In addition, the quality consistency of lithium carbonate products produced by the calcination method is relatively ideal, and in recent years, it has reached the national standard battery level. However, the calcination method faces significant challenges in engineering practice.

Due to the high magnesium lithium ratio in brine, the natural gas consumption in the roasting process is high, and it is difficult to avoid lithium entrainment in the process, which will produce a large amount of hydrochloric acid. At the same time, there are also drawbacks such as complex processes, high water consumption, corrosive equipment requiring a large amount of dilute hydrochloric acid for calcination, and incomplete decomposition of MgCl2 · 6H2O. The previous exhaust emissions have been technically improved to meet the standards. Regarding the shortcomings of the calcination leaching method, improvement measures have been proposed one after another. For example, before high-temperature calcination, a precipitant is added to the de boronized brine to precipitate magnesium lithium in various forms such as hydroxide, and then calcination can avoid the production of hydrogen chloride gas. Given the maturity of the new generation of salt lake lithium extraction technology, which can significantly improve lithium recovery rate, save energy and reduce consumption, the calcination method will fade out of the stage. Currently, the membrane production line of Xitai Jiner Salt Lake in Qinghai has also started construction.