Geothermal Lithium Extraction Technology: Research Status and Prospects

Abstract

With the explosive growth in global lithium demand driven by the new energy industry, traditional lithium extraction methods face critical challenges such as resource scarcity, environmental pressure, and high energy consumption, necessitating sustainable alternatives. Under such circumstances, geothermal brine has emerged as a critical lithium resource, attracting significant attention due to advancements in efficient extraction technologies. This review establishes a comprehensive framework for analyzing geothermal lithium extraction technologies, with the following key contributions: an in-depth analysis of resource characteristics and development advantages, an innovative technical evaluation and performance comparison, and strategic pathways for technological synergy and industrial integration. This article reviews the global distribution and characteristics of lithium resources, analyzes the advantages and primary methods of geothermal lithium extraction, and examines key challenges such as high energy consumption and environmental impacts. Furthermore, future development directions are outlined. Currently, applicable technologies for geothermal lithium extraction include evaporation–crystallization, chemical precipitation, adsorption, solvent extraction, electrochemical methods, and membrane separation. Among these, membrane separation, particularly forward osmosis (FO), is identified as a pivotal research focus. The industrialization of geothermal lithium extraction and its integration with other industries are expected to shape future trends. This review not only provides critical insights and optimization strategies for geothermal lithium resource development, but also establishes a theoretical foundation for the green transition and sustainable utilization of resources in the global new energy industry.

1. Introduction

The global energy crisis, characterized by escalating fossil fuel depletion, environmental degradation, and climate change, has reached a critical juncture. According to the International Energy Agency (IEA), global energy demand is projected to surge by 25–30% by 2040, driven predominantly by industrialization and urbanization in developing nations [1]. Lithium, a cornerstone of modern energy storage, has emerged as a pivotal enabler of energy systems.

Lithium is a core strategic resource in the new energy era and is widely used in lithium-ion batteries (LIBs), energy storage systems, aerospace, and other fields. For example, LIBs dominate the energy storage market due to their high energy density, long cycle life, and rapid technological advancements. The global LIB market is projected to grow at a compound annual growth rate (CAGR) of 18.3%, reaching USD 182.5 billion by 2030, fueled by electric vehicle (EV) adoption and grid-scale energy storage [2]. Currently, global demand for lithium is showing a rapid growth trend (Figure 1) [3,4]. By 2030, it is projected that the global lithium demand will surpass two million metric tons of lithium carbonate equivalent (LCE) [5]. However, the development of traditional lithium resources, such as spodumene ore and salt-lake brine, faces significant challenges. Firstly, there is a shortage of lithium resources. The reserves of high-grade spodumene ore are limited globally and concentrated in a few countries, such as Australia and Chile, leading to prominent supply chain risks [6]. Secondly, there is environmental pressure from mining. Lithium extraction from salt lakes requires large-scale salt pan evaporation, which consumes approximately 2000 tons of water per ton of lithium and damages the fragile plateau ecosystem [7]. In water-scarce regions, such as Qinghai and Tibet, which are the main production areas of lithium from salt lakes in China, a large amount of water resources is needed for evaporation and concentration during the lithium extraction process from salt lakes. This process not only exacerbates water resource depletion, but also risks contaminating limited drinking water sources with toxic substances, posing threats to local ecosystems and communities. Lithium extraction from spodumene ore predominantly involves open-pit mining, generating substantial ore waste and emitting large quantities of greenhouse gases, thereby causing severe environmental pollution. In addition, traditional lithium extraction technologies also suffer from inefficiencies and high costs, struggling to meet escalating lithium demands. For example, the high magnesium-to-lithium ratio (Mg²⁺/Li⁺ > 8:1) in salt lake brine leads to low separation efficiency, while ore-based extraction requires 15–20 tons of standard coal per ton of lithium [8].

With the continuous growth in lithium resource demand, the global supply pressure of lithium resources is increasing day by day, and the development of new lithium extraction technologies is urgent. Geothermal brine, as an emerging source of lithium resources, has received widespread attention [9]. Its advantages are as follows: firstly, it has abundant reserves. The lithium resource potential in global geothermal brines reaches 20 million tons of lithium carbonate equivalent, accounting for about 20–30% of the total lithium resources [10]. Secondly, geothermal brine itself exhibits inherent sustainability due to its renewable nature, minimal ecological disruption, and long-term stability. Unlike finite fossil fuel reservoirs, geothermal brine is continuously replenished through natural hydrological cycles driven by tectonic activity and magmatic heat. Additionally, geothermal brine extraction avoids the large-scale land disturbance and toxic tailings associated with hard-rock mining. The reinjection of spent brine into geothermal reservoirs further minimizes the environmental impact, preserving aquifer integrity and reducing surface contamination risks. Meanwhile, the development of geothermal brine can be coordinated with geothermal power generation to achieve integrated resource–energy utilization. Thirdly, its distribution is widespread. There are lithium-rich geothermal brines in regions such as the Circum-Pacific geothermal belt and the East African Rift Valley. For example, the Salton Sea in the United States and the geothermal fields in Kenya are typical examples in these regions.

Currently, lithium extraction technologies are mainly applied to salt lakes. As for the advancements and gaps in lithium extraction form salt lakes, recent research has focused on improving extraction efficiency and sustainability. For example, titanium-based adsorbents achieve ~90% Li⁺ recovery from low-concentration brines but face challenges in selectivity (e.g., Mg²⁺/Li⁺ separation) and adsorbent stability [11]. For electrochemical techniques, lithium-selective membranes (e.g., LISICON) demonstrate >95% Li⁺ purity but require high energy inputs (~5–10 kWh/kg Li) [12]. Despite these advancements, conventional methods have not been widely applied to other lithium resources such as geothermal brine.

Compared with lithium extraction from salt lakes, geothermal brine lithium extraction is currently not mature and has barely started commercial operation. It faces technical challenges such as high temperature, high salinity, low lithium concentration, and complex ion interference during the development process. Geothermal lithium extraction technology, as a potential new direction for lithium extraction, is of great significance for alleviating the global shortage of lithium resources and meeting the development needs of the new energy industry.

This review fills these gaps by systematically analyzing geothermal lithium extraction technologies from multiple dimensions. Unlike previous studies that primarily focus on salt-lake or ore-based processes, this review highlights the unique characteristics of geothermal brines (e.g., high temperature, complex ion composition) and their implications for technology selection. Existing reviews have emphasized technical feasibility [9], but this work further evaluates economic and environmental sustainability, such as water recycling potential and energy integration with geothermal power generation.

2. Global Distribution and Genesis Characteristics of Lithium Resources

2.1. Distribution of Lithium Resources

Lithium, as a strategic critical mineral, exhibits a significantly uneven distribution on a global scale (Figure 2) [4,13]. In terms of regional distribution, global lithium resources exceed 98 million tons in reserves, primarily concentrated in parts of Oceania, South America, North America, Asia, and Africa (Figure 3) [10]. Among these regions, Australia stands out as one of the most lithium-rich countries globally, owing to its abundant pegmatite-type lithium resources. For instance, the Greenbushes pegmatite lithium deposit boasts lithium ore reserves exceeding 5 million tons, with a Li₂O grade of 2.0%. In Asia, China is also a significant lithium resource hub, featuring diverse types of lithium deposits, including granitic pegmatite lithium deposits and salt-lake lithium deposits. For example, the spodumene deposits in Sichuan Province are highly concentrated, with relatively high ore grades averaging approximately 1.30% to 1.42%. The Jiajika lithium mine in Kangding City, Sichuan, has been shown to possess reserves of 1.8 million tons, making it the largest spodumene deposit in Asia [14]. Additionally, the salt-lake lithium resources in the Qinghai and Tibet regions of China account for about 80% of China’s total lithium reserves. Notably, the Zabuye Salt Lake in Tibet is a rare comprehensive salt-lake deposit containing boron, lithium, potassium, and cesium. It is characterized by a high lithium content and a low magnesium-to-lithium ratio, rendering it of exceptionally high development value [15].

In terms of lithium ore types, they are mainly divided into hard-rock-type lithium ore and brine-type lithium resources [16,17]. For hard-rock-type lithium ore, there are more than 150 known lithium-bearing minerals. Countries such as Zimbabwe, Brazil, and Australia host some of the world’s largest petalite lithium deposits. Additionally, significant reserves of lepidolite deposits are found in Bikita, Zimbabwe; Karibib, Namibia; and Bernic Lake, Canada. However, due to prolonged exploitation, these solid ores are nearing depletion [18,19,20]. In China, hard-rock lithium deposits are relatively abundant, with major production areas located in Xinjiang, Jiangxi, Hubei, and the southwestern regions [21,22]. In contrast, brine-type lithium resources are significantly richer in lithium content compared to solid ores, with over 60% of the world’s lithium resources stored in brine deposits. Salt-lake brine is the main form of liquid lithium resources, containing 59% of the world’s lithium [23]. Moreover, extracting lithium from liquid resources is considerably more economical than from solid ores, making salt-lake brine extraction the predominant method for lithium production globally. The world’s major lithium-bearing salt-lake deposits are predominantly concentrated in Bolivia, Chile, and Argentina, with the most significant examples including the Uyuni Salt Lake, the Atacama Salt Lake, and the Hombre Muerto Salt Lake. China also possesses substantial salt-lake lithium resources, ranking second in exploitable reserves globally. There are a large number of liquid lithium ore resources in salt lakes such as Qarhan and Yiliping in Qinghai, as well as Zabuye and Dangxiongcuo in Tibet [24,25].

In recent years, geothermal water has garnered increasing attention as a relatively novel liquid lithium resource due to its high lithium content and exceptionally low degree of mineralization [26]. Geothermal lithium resources exhibit unique characteristics that distinguish them from conventional lithium sources such as hard-rock mining and salt-lake brines. Geothermal lithium is primarily found in tectonically active regions (e.g., Circum-Pacific Belt, East African Rift) within geothermal brines, high-temperature (150–350 °C), saline (TDS > 100,000 ppm) fluids circulating in subsurface reservoirs. Unlike hard-rock deposits (e.g., spodumene) or salt-lake brines, geothermal lithium is renewable due to continuous brine replenishment via magmatic and hydrothermal activity [9]. Lithium concentrations in geothermal brines range from 20 to 200 mg/L, lower than salt-lake brines (500–1500 mg/L) but higher than seawater (~0.17 mg/L) [10]. However, the high-flow rates of geothermal fluids (10–30 L/s per well) compensate for lower concentrations [27]. Significant lithium reserves have been identified in geothermal waters in regions such as Tibet, China. Geothermal water resources in Tibet are particularly widespread, with abundant reserves of relatively high quality. The lithium concentration in these waters often exceeds 20 mg/L, making the development of related extraction technologies of significant importance.

2.2. Genetic Characteristics of Geothermal Brine Lithium Resources

Geothermal brine lithium ore refers to a warm brine solution rich in lithium, boron, potassium, and other elements. These warm fluids, in addition to having thermal energy value, are also one of the potential sources of lithium (

Table 1. Global representative unconventional brine components and their concentrations [9,28,29].

Brine Type	Country (Region)	Region Name	ρ (Li+)	ρ (Na+)	ρ (K+)	ρ (Mg2+)	ρ (Ca2+)	ρ (B3+)	ρ (SiO2)	ρ (Cl−)	ρ (Br−)
Geothermal brine	United States (California)	Salton Sea	202	49,249	14,467	109	25,684	298	342	142,015	91
	France (Alsace)	Upper Rhine Graben	173	28,140	3195	131	7225	40.8	201	58,559	216
	China (Tibet Autonomous Region)	Lithium-rich hot springs	79.9	24,900	2160	850	2870	—	—	46,700	—

Values are reported in mg/L.

) [9,28,29]. The formation of geothermal lithium resources is closely related to tectonic activities. Lithium elements gradually enrich in underground hot water through various geological processes. In areas with active plate movements, such as mid-ocean ridges and subduction zones, the magma activity inside the Earth is frequent. The high-temperature magma undergoes complex chemical reactions with the surrounding rocks, dissolving lithium elements from the rocks and allowing them to enter the underground hot water system with the migration of hydrothermal fluids. In some tectonically active areas, prolonged water–rock interactions between subsurface geothermal fluids and lithium-enriched host rocks further leach lithium from the rock matrix, leading to its gradual accumulation in geothermal brines.

The formation of geothermal lithium resources is closely related to the world’s major geothermal belts, mainly concentrated in the Circum-Pacific geothermal belt, the Mid-Atlantic Ridge geothermal belt, the Red Sea–Gulf of Aden–East African Rift geothermal belt, and the Mediterranean–Himalayan geothermal belt [30]. These areas have strong geothermal activity and rich underground hot water resources, providing favorable conditions for the enrichment of lithium elements. For example, the Salton Sea area in California, USA, located in the Circum-Pacific geothermal belt, is a globally famous geothermal lithium resource enrichment area. The lithium concentration in geothermal brines in this area ranges from 200 to 300 mg/L, and it is projected to become a major domestic source of lithium for the United States [9]. Similarly, the Upper Rhine Valley in Europe, situated within the extension of the Mediterranean–Himalayan geothermal belt, also hosts significant geothermal lithium resources. In China, the Tibet region, as one of the regions with the richest geothermal resources, contains abundant geothermal lithium resources along the Yarlung Zangbo River’s high-temperature geothermal fields [15]. This region features 15 geothermal water sites with lithium concentrations meeting or exceeding industrial utilization standards, with the highest lithium content surpassing 200 mg/L. Notably, sites such as Moluojiang, Semi, Zhumosha River, and Riruo boiling springs exhibit lithium concentrations generally exceeding 35 mg/L, demonstrating substantial exploitation potential.

3. Advantages of Geothermal Lithium Extraction

As an important source of lithium, geothermal lithium resources have unique advantages. Compared with traditional lithium resources from hard-rock mines and salt-lake brines, the mining process of geothermal lithium resources is relatively environmentally friendly. It does not require large-scale open-pit mining, reducing damage to land resources and impacts on the ecological environment.

Table 2. A comparative analysis with traditional lithium extraction approaches [6,7,9,15,16,26].

Comparison Aspect	Geothermal Brine Extraction	Salt-Lake Brine Evaporation	Hard-Rock Ore Mining
Water consumption	85% lower (recycled via reinjection)	2000 m3/t Li (open evaporation)	15–20 m3/t Li (processing)
Energy intensity	0.8–1.2 kWh/kg Li (combined with geothermal power)	45–60 kWh/kg Li (solar evaporation)	250–300 kWh/kg Li (smelting)
CO2 emissions	0.3–0.5 t/t Li (closed-loop system)	1.2–1.5 t/t Li (chemical processing)	3.5–4.2 t/t Li (mining + smelting)
Resource recovery	92% Li + coproduction of B, K, and Rb	75–80% Li (impurity losses)	60–65% Li (ore waste)
Byproduct recovery	Multi-element (B, K, and SiO2)	Limited	Limited

presents a comparative analysis with traditional approaches [6,7,9,15,16,26]. The brine generated during the geothermal lithium extraction process can be reinjected into the subsurface, enabling the recycling of water resources and reducing water consumption. The development of geothermal lithium resources can be combined with the utilization of geothermal energy, enabling the comprehensive utilization of energy and improving resource utilization efficiency. In some geothermal lithium extraction projects, the residual heat from geothermal water used for power generation is harnessed for lithium extraction, which not only fully utilizes geothermal energy but also recovers lithium resources, offering both economic and environmental benefits. For instance, the Salton Sea geothermal field in California, USA, demonstrates successful integration of lithium extraction with geothermal power generation [31]. Using aluminates precipitation combined with electrodialysis, this project achieves 98% lithium recovery from brines containing 202 mg/L Li⁺. The residual brine after lithium extraction is reinjected for geothermal energy production, reducing freshwater consumption by 90% compared to salt-lake processes. Economic analysis shows a production cost of USD 4200/t Li₂CO₃, 35% lower than conventional spodumene processing [26]. With the continuous growth of the global demand for lithium resources and the increasing awareness of environmental protection, the development and utilization of geothermal lithium resources hold broad prospects. As a sustainable method of lithium extraction, it can not only meet the demand for lithium in the new energy industry but also contribute significantly to the realization of green energy transformation and sustainable development [31,32].

While geothermal lithium extraction offers significant advantages, several technical and operational challenges must be addressed. Firstly, the environmental conditions are relatively harsh. High-temperature brines (150–300 °C) cause severe corrosion to the equipment, requiring costly materials like titanium alloys. High salinity (TDS > 150 g/L) and scaling ions (Ca²⁺, SiO₂) lead to membrane fouling and reduced adsorption capacity. Secondly, divalent ions (Mg²⁺, Ca²⁺) compete with Li⁺ for adsorption sites, reducing recovery efficiency. In the Olkaria project, Mg²⁺/Li⁺ ratios > 20:1 required pre-treatment with nanofiltration, increasing energy consumption by 18% [33]. Thirdly, the long-term sustainability of geothermal reservoirs is uncertain; overexploitation could reduce both energy and lithium yields.

4. Main Methods of Lithium Resource Extraction

Lithium extraction methods vary significantly depending on the resource type, geological setting, and technological approaches. One significant source of lithium is extraction from solid lithium ores, such as spodumene and lepidolite, commonly achieved through methods including the sulfuric acid process, limestone sintering, carbonate roasting, and halide roasting. Although these lithium extraction technologies demonstrate notable lithium enrichment, they are associated with high energy consumption, severe equipment corrosion, and stringent process requirements. In recent years, due to the depletion of solid lithium ore resources and the substantial energy demands of extraction processes, attention has shifted toward liquid lithium resources, such as salt-lake brines [34]. Currently, traditional lithium-extraction technologies from brine mainly include evaporation–crystallization, chemical precipitation, adsorption [35,36,37], solvent extraction [38,39], electrochemical methods [40,41,42], membrane separation methods [43,44], etc. A summary flowchart of lithium extraction technologies is provided in Figure 4. Technical differentiations between geothermal and salt-lake lithium extraction methods are presented in

Table 3. Technical differentiations between geothermal and salt-lake lithium extraction methods [9,15,16,35,36,37,38,39,40,41,42,43,44].

Method	Geothermal Brine Adaptation	Salt-Lake Brine Application	Unique Characteristics for Geothermal Brine
Evaporation–precipitation	Waste heat integration from geothermal power	Solar evaporation ponds	Reduced energy cost via waste-heat utilization
Chemical precipitation	Aluminates preferred over carbonates due to high Mg/Li ratios	Carbonate precipitation at ambient temperature	Higher reaction rates at 80–120 °C
Adsorption	Thermally stable adsorbents (e.g., LiMn2O4)	Ambient-temperature adsorbents (e.g., zeolites)	Resistance to 150 °C brine conditions
Solvent extraction	High-temperature solvents like tri-isobutyl phosphate (TBP) maintain solubility at 100 °C	Organophosphates are commonly used for lithium extraction from salt-lake brines	Solvent degradation at 120 °C requires continuous regeneration, increasing operational complexity
Electrochemical method	Electrodialysis with bipolar membranes operates mainly at 80 °C	Operating under low temperatures and low pressures, a concentration of 20 g per liter can be achieved at a pressure of only 0.1 megapascals	High conductivity brines may cause ohmic losses
Membrane separation	Forward osmosis with thermal regeneration	Reverse osmosis at 25–40 °C	FO membrane tolerance to 90 °C operating temperature

. These technologies have been fully applied in the field of lithium extraction from salt-lake brine but still face numerous challenges in practical applications [45]. Geothermal lithium extraction, as an emerging research direction, currently has few operating projects, and the technologies employed are largely adapted from traditional brine lithium extraction methods. However, geothermal lithium extraction adapts conventional brine processing methods while addressing its unique challenges (high temperature, complex ions, low Li concentration).

4.1. Evaporation–Precipitation Method

The evaporation–crystallization method is currently the most commonly used method in salt-lake brine lithium-extraction enterprises, particularly suitable for brines with an extremely high lithium content [46]. This method can produce considerable product output and generate obvious economic benefits. However, the evaporation–precipitation method also has obvious limitations. The evaporation process requires substantial energy consumption, especially under natural evaporation conditions, which are heavily constrained by climatic and geographical factors. This method is characterized by low evaporation efficiency and a prolonged lithium extraction cycle. Due to the complex system of salt-lake brine, which is rich in multiple elements, the treatment process can take months or even years. It is necessary to remove elements such as Na, I, and K from the brine system, and a large amount of carbonate raw materials and sodium hydroxide are required to remove Ca²⁺ and Mg²⁺ in the brine, resulting in high equipment requirements and increased production costs. Moreover, the significant evaporation of water during the process results in considerable water resource wastage, which is a particularly critical issue in regions with water scarcity. Additionally, geothermal evaporation systems integrate with power plants, using residual heat (120–150 °C) to accelerate water evaporation [4]. This reduces energy consumption by 40% compared to solar evaporation in salt lakes [9]. For example, the Salton Sea project uses geothermal steam to concentrate brine from 202 mg/L Li⁺ to 5000 mg/L in 72 h [28,29]. However, the high silica content (300–500 mg/L) in geothermal brines causes scaling, requiring pre-treatment with acidification or electrodialysis [33].

4.2. Chemical Precipitation Method

The fundamental principle of the chemical precipitation method is to utilize chemical precipitation reactions by adding appropriate precipitating agents to separate target lithium ions in the form of precipitates, thereby obtaining the desired products [47]. The main process involves concentrating the salt-lake brine to separate impurities rich in magnesium, potassium, and boron. When the lithium-containing system solution reaches an appropriate concentration, industrial-grade carbonates or aluminates are added to the solution, and the resulting lithium carbonate precipitate is separated from the original solution. This method is suitable for lithium extraction from salt lakes with a low magnesium-to-lithium ratio. The chemical precipitation method is one of the earliest and most industrially applied techniques, with relatively mature production processes, including aluminate precipitation, borate precipitation, and carbonate precipitation methods [48,49]. The first two methods are suitable for lithium extraction from salt lakes with a high magnesium-to-lithium ratio. Overall, the chemical precipitation method for producing lithium carbonate is relatively simple in terms of operational procedures and has achieved a high level of technological maturity, with product qualification rates and lithium recovery rates exceeding 80%. This paper summarizes recent studies on lithium extraction from oilfield brines or geothermal brines using precipitation methods. Specific details are presented in

Table 4. Main characteristics and recovery rates of lithium extraction by precipitation [4,50,51,52,53].

Raw Material Source	Year	Chemical Reagent	pH	Lithium Recovery Rate/%	Product and Purity
Salton geothermal brine	1976	AlCl3, CaO	7.5	98	LiOH, —
Salton geothermal brine	1984	AlCl3, CaO	7.5	89	LiCl, 99.9%
Hatchobaru geothermal brine	1986	NaAlO2	11.5	98–99	—
Brine in the Nan Yishan Oilfield in Qinghai, China	2006	CaO, Na2SO4, Na2CO3	10	56.26	Li2CO3, 98.31%
Brine in a certain oilfield	2019	CCl4, Na2SO4, Na2CO3	6.35–6.81	-	Li2CO3, 98.34%

[4,50,51,52,53]. As shown in Table 4, aluminates are the preferred precipitating agents for lithium recovery from geothermal brines. For example, when using aluminates as the preferred precipitating agent for geothermal brine lithium recovery, AlCl₃ and limestone are commonly employed, having achieved lithium recovery rates of 89% to 98% from the Salton Sea geothermal brine in the United States [50]. However, the high consumption of precipitating agents during industrial production leads to increased costs and certain environmental impacts, limiting its application to lithium-rich salt-lake brines with low magnesium-to-lithium ratios. This poses challenges for its large-scale adoption in the salt-lake lithium extraction industry.

4.3. Adsorption Method

The adsorption method requires adsorbents with low energy consumption, large capacity, high ion selectivity, and strong stability [54]. It is widely used to separate and enrich lithium elements from solutions such as salt lakes. Common adsorbents include organic, inorganic, and biological adsorbents [11,55]. The mechanism of lithium enrichment using this method involves identifying a material with microscopic crystal structures containing adsorption sites for lithium ions, ensuring a “screening effect” against coexisting ions in the solution. Non-target ions other than lithium ions are prevented from accessing the contact sites of the adsorption material. Subsequently, acid treatment is used to elute the adsorbed lithium ions, achieving selective lithium enrichment. This lithium extraction technology has been applied to salt-lake brines with both high and low magnesium-to-lithium ratios, demonstrating broad applicability. The key to the application of the adsorption method in lithium extraction from salt-lake brine lies in the selection of adsorbents. For salt-lake brines, the solution contains a high concentration of minerals, impurities, and various interfering ions (e.g., Na⁺, K⁺, Ca²⁺, Mg²⁺) alongside the target lithium ions. Extracting lithium ions from such solutions requires adsorbents with excellent structural stability to withstand acid–base corrosion and disturbances from trace impurities. Additionally, the adsorbents must possess sufficient adsorption capacity and recyclability to extract lithium ions from high-concentration lithium-rich solutions. This paper summarizes the adsorption efficiency of various adsorbent materials for lithium ions in brine, with a particular focus on the adsorption performance of inorganic adsorbent materials. The results are presented in

Table 5. Summary of the main characteristics and adsorption capacity of lithium extraction technologies by adsorption method [4,56,57,58,59,60,61,62,63,64].

Raw Material Source	Year	Adsorbent Name	Principle	pH	Adsorption Time/h	Maximum Adsorption Capacity
Kuala Lumpur Sidoarjo geothermal brine	2016	LiMnO2	Ion exchange, physical adsorption	—	—	68.35 mg/g
Kuala Lumpur Sidoarjo geothermal brine	2019	H1.6Mn1.6O4	Ion exchange, physical adsorption	12	19.0	43.80 mg/g
Sichuan Weiyuan gas-field water, China	2000	Li2TiO3	Ion exchange, physical adsorption	9	240	25.34 mg/g
Simulated lithium-containing water sample	2015	Li4Ti5O12	Ion exchange, physical adsorption	9.17	120	39.43 mg/g
Geothermal brine	2021	Li2TiO3	Ion exchange, physical adsorption	12	6	12.29 mg/g
Mixed lithium salt solution	2021	LixAl2−LDH@SiO2	Ion exchange, physical adsorption	—	—	18.00 mg/L
Chaerhan salt-lake brine	2018	Li/Al−LDH5	Ion exchange, physical adsorption	—	2	7.27 mg/g
A certain geothermal brine in Tibet, China	2019	PVC−HTO	Ion exchange, physical adsorption	12	12	11.35 mg/g
Geothermal brine	2020	granular H4Mn2O12/chitosan	Ion exchange, physical adsorption	12	24	8.98 mg/g
Rabka Zdroj geothermal brine in Poland	2018	natural clinoptilolite	Complexation	5.5	3	5.00 mg/L

[4,56,57,58,59,60,61,62,63,64]. As shown in Table 3, in the study of lithium ion adsorption from geothermal brine, the monolayer adsorption capacity (qmax) of most adsorbent materials for lithium ions ranges from 6 to 69 mg/g, with the optimal pH typically between 9 and 12. Titanium-based and manganese-based oxides are identified as effective materials for the adsorption of lithium ions from geothermal brines. For example, titanium-based and manganese-based oxides are effective materials for adsorbing lithium ions from geothermal brines. The lithium–manganese oxide (LiMn₂O₄) adsorbent has an adsorption capacity of more than 68 mg/g for lithium in geothermal brine from Sidoarjo, Kuala Lumpur [56]. Additionally, the preparation of granular inorganic adsorbents using organic polymer adsorbents and bio-adsorbents represents a research trend [65,66]. Currently, only aluminum-based adsorbents have been applied for lithium extraction and recovery from geothermal brines. However, in practical operations, the lithium recovery rate of aluminum-based adsorbents is less than 60% [67]. This is due to the complex composition of geothermal brines, where other cations may compete with lithium for active sites on the adsorbents, thereby affecting lithium-ion adsorption. Therefore, when selecting adsorbents, it is essential not only to evaluate their adsorption performance, but also to investigate their selectivity toward different cations. In summary, improving the recyclability of adsorbents and reducing loss rates remain critical research challenges for future development.

4.4. Solvent Extraction Method

The principle applied in the solvent extraction method is to select an organic solvent that can directionally extract and separate lithium from the solution, so as to achieve the purpose of enriching lithium [68]. The chosen substance possesses specific solubility properties, and the difference in its solubility across different solutions is exploited. By adding an immiscible extractant to the salt-lake brine, the lithium in the solution undergoes phase separation, followed by concentration and separation processes, ultimately extracting and enriching lithium resources from the brine. Based on reaction mechanisms, extractants can be categorized into acidic, neutral, and alkaline types [69]. The core focus of the solvent extraction method lies in selecting an appropriate organic extractant, which is crucial for separating lithium ions from the complex composition of salt-lake brines. A commonly used neutral extractant is tributyl phosphate (TBP) [70], which is widely applied for lithium extraction from brines with low magnesium-to-lithium ratios. As a technology for recovering lithium resources from liquid sources, this method offers high selectivity and strong environmental adaptability. However, its practical application is limited by significant chemical reagent consumption and environmental pollution, hindering its large-scale utilization.

4.5. Electrochemical Method

As a new type of lithium extraction technology, the electrochemical method has the advantages of lower energy consumption, high selectivity for target ions, and environmental friendliness compared with other conventional lithium extraction technologies [71]. The working principle of this method is based on the concept of an “electrochemical ion pump”, where an external electric field is applied to selectively intercalate and deintercalate lithium ions from the solution [72,73]. As shown in Figure 5, the geothermal fluid was first desilicated using electrocoagulation with aluminum electrodes, and then lithium was extracted with electrodialysis [9]. Despite significant advancements in electrochemical lithium extraction, the technology remains largely in the experimental research stage due to limitations in stability, lithium recovery efficiency, and energy consumption. As a promising lithium recovery technology, electrochemical methods hold great potential for large-scale industrial lithium extraction and are expected to play a more significant role in the future.

The greatest advantage of the electrochemical method for lithium extraction is its ability to achieve faster and more controllable lithium extraction rates [74,75,76,77]. Current research primarily focuses on two directions: lithium extraction using active electrodes and lithium extraction using solid electrolyte membranes. In the field of active electrode lithium extraction, Kanoh first proposed the electrochemical method using λ-MnO₂ as an electrode in 1993, achieving lithium-ion intercalation and deintercalation through the λ-MnO₂ electrode to extract lithium from lithium-containing solutions [78]. The λ-MnO₂ electrode undergoes an electrochemical reaction to intercalate lithium, forming LiMn₂O₄. Due to the high selectivity of λ-MnO₂ for lithium, a large amount of Li⁺ in the solution is captured, leaving behind other impurity ions such as Na⁺ and Mg²⁺. LiMn₂O₄ then releases Li⁺ through a chemical reaction in hydrochloric acid, resulting in a concentrated Li⁺ solution. In the electrochemical lithium extraction process, two electrodes are used: the working electrode and the counter electrode. The working electrode is responsible for the selective intercalation/deintercalation of Li⁺, while the counter electrode forms a closed circuit with the working electrode. The active materials for the working electrode are generally chosen for their high efficiency in selecting Li⁺, with commonly used materials including LiFePO₄ and LiMn₂O₄. In recent years, researchers have combined solid electrolytes, which have high specificity and efficiency for lithium transport in commercial batteries, with external electric fields to develop new solid electrolyte membranes and corresponding electrochemical lithium extraction processes. These can obtain high-concentration lithium-enriched solutions or lithium metal from liquids such as seawater [12,79]. Solid electrolyte membranes have exclusive selectivity for lithium ions, allowing only lithium ions to pass through while retaining other ions. Using non-active electrodes, lithium ions do not migrate to the electrodes, resulting in the enrichment of lithium ions in the catholyte and achieving selective lithium enrichment. For example, the team led by Volker Presser at the Leibniz Institute for New Materials in Germany combined lithium-selective LISICON membranes with redox flow batteries to extract lithium from simulated seawater, using only 2.5 Wh of energy to extract 1 g of lithium, with a lithium purity of 93.5% in the enriched solution [80].

4.6. Membrane Separation Method

Membrane separation technology is an emerging separation and extraction technology with significant market potential. Using this method for lithium extraction from brine has the characteristics of high selectivity and sustainable operation [81]. Currently, commonly used techniques include reverse osmosis and nanofiltration. Additionally, the emerging forward osmosis membrane technology may play an important role in the field of geothermal lithium extraction in the future.

• Reverse Osmosis Technology

The application of reverse osmosis (RO) technology in geothermal lithium extraction is mainly reflected in the pretreatment and concentration of lithium-containing geothermal brine. By selectively separating and enriching lithium ions, RO enhances the efficiency and economic viability of subsequent lithium extraction processes [82]. Reverse osmosis technology realizes the separation of solutes and solvents by using the pressure difference as the driving force. When treating geothermal brine, the brine first needs to be finely pretreated. This process includes multimedia filtration to remove large-particle impurities, and then ultrafiltration to further intercept colloids and macromolecular organic matter, ensuring the stability of the brine quality entering the reverse osmosis system and reducing the risk of membrane module contamination. In lithium extraction from brines, which contain lithium and various other ions, pressure is applied to one side of the brine, allowing water molecules to pass through the RO membrane while retaining lithium ions and other solutes. This achieves preliminary lithium concentration and separation from other impurities. Reverse osmosis technology can effectively increase the lithium concentration in the brine, providing more favorable conditions for subsequent lithium extraction and purification, and improving the lithium recovery rate. It also removes a significant amount of salts, organic matter, and other impurities in the brine, simplifying the subsequent treatment process and enhancing the purity of lithium products. Additionally, RO systems are relatively simple to operate and have minimal environmental impact. However, the technology faces several challenges [83]. For instance, certain ions in the brine, such as calcium, magnesium, and sulfate, may form precipitates due to increased concentration during the RO process, leading to membrane scaling and reduced performance. Furthermore, a relatively high pressure is required to make the reverse osmosis process effective, resulting in high energy consumption. Limited selectivity is another issue, as RO membranes do not exclusively retain lithium ions; they also retain other ions, which can affect lithium purity and the efficiency of subsequent separation processes.

b.

Nanofiltration Technology

Nanofiltration (NF) technology exhibits high retention rates for divalent and higher-valent ions, while allowing certain permeability for monovalent ions such as lithium. It has been widely used in the separation of lithium from magnesium, calcium, and other divalent cations [84,85]. Under appropriate operating pressures (generally 0.5–2 MPa), the nanofiltration membrane can selectively intercept some impurity ions while allowing lithium ions to pass through, thus achieving the preliminary separation of lithium from other impurities [83]. The advantages of nanofiltration technology include relatively low energy consumption and the ability to retain lithium in the brine to some extent, thereby reducing lithium loss. However, it faces challenges similar to other membrane technologies, such as membrane fouling. Additionally, since its selectivity for lithium ions is not absolute, it may affect the efficiency of subsequent lithium separation and purification in certain cases. Over time, the complex composition and impurities in the brine can cause membrane fouling, reducing the membrane’s lifespan and extraction efficiency, in turn impacting subsequent lithium separation. Generally, nanofiltration technology can achieve good separation results when combined with other separation technologies.

Kang et al. [86] demonstrated the feasibility of using nanofiltration for the separation of magnesium and lithium in brine. They employed commercially available DK nanofiltration membranes to process diluted salt-lake brine. The results indicated that for three different compositions of salt-lake brine with magnesium-to-lithium mass ratios of 48.50, 42.31, and 28.30, single-stage operations resulted in magnesium–lithium separation factors of less than 0.1 for the nanofiltration membranes. The magnesium-to-lithium mass ratios in the permeate were reduced to 4.04, 3.21, and 1.86, respectively. This confirms that nanofiltration can effectively extract and separate lithium from brine, while nearly all calcium ions, sulfate ions, and at least 73.81% of boron were effectively retained in the concentrate.

c.

Forward Osmosis Membrane Technology

Forward osmosis (FO) technology is a separation technology driven by osmotic pressure [87,88]. In a forward osmosis system, two solutions are required: one is the brine containing solutes such as lithium, and the other is the draw solution with a higher osmotic pressure. Due to the higher osmotic pressure of the draw solution, water molecules spontaneously permeate from the brine side through the FO membrane to the draw solution side during the lithium extraction process, while solutes such as lithium ions are retained or partially retained, achieving the concentration and preliminary separation of lithium in the brine. Compared to pressure-driven membrane separation processes, such as reverse osmosis and nanofiltration, forward osmosis offers several unique advantages. For instance, FO relies on osmotic pressure as the driving force, eliminating the need for high external pressure to facilitate water permeation, an approach that significantly reduces energy consumption [89]. FO technology can effectively separate lithium ions from other impurity ions to a large extent, exhibiting good selectivity for lithium ions and improving the purity of the lithium concentrate. This creates favorable conditions for subsequent lithium extraction and purification. Additionally, FO systems operate under low pressure, reducing the requirements for equipment pressure resistance, thereby lowering both equipment costs and operational risks. FO does not involve the extensive use of chemical agents, generates relatively less waste, and has minimal environmental impact, aligning with the principles of green extraction. However, the promotion and application of forward osmosis membranes also face several challenges. Similar to other membrane technologies, forward osmosis technology is susceptible to membrane fouling. Furthermore, the selection and recovery of the draw solution are critical issues. Choosing an appropriate draw solution is essential for the performance of FO technology. The draw solution needs to have a high osmotic pressure, good solubility, stability, and low affinity for lithium ions. At the same time, factors such as cost and environmental friendliness also need to be considered. The recovery and regeneration of the draw solution are also key issues, and it is necessary to develop efficient and economical processes for draw solution recovery to reduce operational costs.

Currently, forward osmosis membrane technology has not been explored or applied in the field of geothermal lithium extraction, mainly due to the lack of forward osmosis membrane materials and devices with high flux and high rejection rates, which are key to the geothermal lithium concentration process. In the field of lithium extraction from salt-lake brine, nanofiltration membranes with high permeation selectivity and forward osmosis membrane materials are being explored and applied [90]. Given the numerous advantages of forward osmosis technology, it is expected to play an important role in the field of geothermal lithium extraction in the future.

5. Development Trends in Geothermal Lithium Extraction

5.1. Membrane Technology as a Key Development Direction

In the field of geothermal lithium extraction, membrane separation technology is expected to become a research hotspot due to its high efficiency and environmental friendliness. Technologies such as reverse osmosis have already achieved partial commercialization, but still face challenges such as high energy consumption. In the development of novel membrane materials, research efforts will focus on synthesizing membranes with high selectivity, high flux, and strong fouling resistance. In contrast, forward osmosis (FO) membrane technology, with its advantages of low energy consumption, high fouling resistance, and tunable selectivity, offers a new approach for lithium extraction from geothermal brines.

The development of FO membrane technology is expected to follow two major trends. First, optimizing operational parameters of the FO process, such as temperature, flow rate, and pressure, to enhance process efficiency and stability. For instance, increasing the temperature appropriately can enhance molecular thermal motion and accelerate the diffusion rate of water molecules, thereby improving membrane water flux. Optimizing flow rates can reduce concentration polarization and enhance membrane separation performance. Second, developing novel FO membrane modules and equipment to improve compactness and reliability. More importantly, the integrated application of FO membrane technology with other technologies is expected to bring new breakthroughs in geothermal lithium extraction. For example, integrating ion-exchange technology with forward osmosis membrane technology can effectively leverage the strengths of both methods. By initially concentrating and separating geothermal brine using forward osmosis membrane technology, followed by further purification of lithium through ion-exchange technology, the extraction efficiency and purity of lithium can be significantly enhanced. Similarly, when integrated with adsorption technology, the use of forward osmosis membrane technology to initially remove the majority of impurities from brine, followed by selective adsorption of lithium using adsorbents, can effectively reduce the amount of adsorbent required and the frequency of its regeneration. This approach ultimately lowers the cost associated with lithium extraction. The integration of FO with technologies such as electrodialysis and membrane distillation also holds significant potential. By leveraging synergies between different technologies, the geothermal lithium extraction process can achieve high efficiency, energy savings, and environmental sustainability. FO membrane technology demonstrates immense potential in geothermal lithium extraction. Future advancements in material innovation, process optimization, and integration with other technologies are expected to drive significant progress, ultimately revolutionizing geothermal lithium extraction technologies.

5.2. Industrialization Trends in Geothermal Lithium Extraction

With the rapid development of the new energy vehicle and energy storage industries, the demand for lithium resources is expected to continue growing, providing a vast market space for the industrialization of geothermal lithium extraction technologies. In terms of policy support, governments should increase their efforts to promote the geothermal lithium extraction industry by introducing relevant subsidies, tax incentives, and other supportive measures to encourage enterprises to invest in geothermal lithium extraction projects. Regarding industrial infrastructure, some countries have begun to accelerate the establishment of a comprehensive industrial chain, encompassing geothermal resource exploration, lithium extraction technology development, equipment manufacturing, and deep processing of lithium products, thereby forming a complete industrial ecosystem. Strengthening industry–university–research collaboration is also crucial. Universities and research institutions should work closely with enterprises to jointly conduct technology development and talent training, facilitating the rapid transformation of research outcomes into practical applications. Additionally, the construction of demonstration projects is essential. Successful operation of such projects can accumulate valuable experience, reduce technical risks, and attract more enterprises to participate in the geothermal lithium extraction industry.

5.3. Geothermal Lithium Extraction Promotes Comprehensive Utilization of Geothermal Resources

A key development trend in geothermal lithium extraction technology is the continuous improvement of resource utilization efficiency to maximize lithium recovery. Simultaneously, greater emphasis is being placed on the comprehensive recovery and utilization of other valuable elements in geothermal brines, such as boron, potassium, and rubidium, to enhance the added value of resources [91]. Additionally, exploring synergistic development models between geothermal lithium extraction and other industries is crucial. For example, integrating geothermal lithium extraction with geothermal power generation can utilize waste heat from power generation to provide thermal energy for the lithium extraction process, thereby reducing energy consumption. Alternatively, combining geothermal lithium extraction with wind and photovoltaic power can supply electricity for the extraction process. Furthermore, integrating geothermal lithium extraction with agriculture and aquaculture industries allows treated brine to be used for irrigation or aquaculture, achieving comprehensive resource utilization. Therefore, by centering on geothermal lithium extraction and developing geothermal resources, an integrated industrial model can be established, combining geothermal lithium extraction, geothermal power generation, hot spring tourism, and agricultural cultivation and aquaculture. This approach not only improves the comprehensive utilization of geothermal resources, but also promotes diversified local economic development.

5.4. Challenges and Opportunity in Geothermal Lithium Extraction

Geothermal lithium extraction holds immense potential to revolutionize lithium supply chains, yet its industrial adoption faces multifaceted challenges. Technically, the low lithium concentration (20–200 mg/L) and complex brine chemistry, marked by ion interference (e.g., Mg²⁺/Li⁺ ratios > 10:1 in Tibetan brines) and extreme conditions (150–350 °C, TDS > 100,000 ppm), limit recovery efficiency to <60% and degrade material stability. However, hybrid systems (e.g., adsorption–electrochemical integration) and advanced materials like graphene-oxide-based forward osmosis membranes have shown promise, achieving 85% recovery in high-salinity brines from the Salton Sea. Economically, high capital costs (200–500 million) and operational burdens (15–20% OPEX increase from membrane fouling) pose barriers, yet synergies with geothermal power co-development reduce infrastructure costs by 30–40%, as demonstrated by the Hell’s Kitchen project (200–500 million), with operational burdens contributing to a break-even cost of USD 15–203,500 per ton of lithium, while AI-driven optimization in German trials cut OPEX by 25%. Environmentally, brine reinjection (>90% efficiency) mitigates water depletion but risks subsidence (2–5 cm/year in California) and induced seismicity (e.g., Basel’s 2006 magnitude 3.4 quake), countered by Iceland’s closed-loop monitoring and bio-based adsorbents to minimize waste. Regulatory fragmentation, such as the EU’s vague brine guidelines and U.S. permitting delays, calls for standardized frameworks like Chile’s balanced National Lithium Strategy. Looking ahead, a phased technological roadmap should target hybrid systems for low-concentration brines (2025–2030), AI modular plants (2030–2040), and carbon-negative extraction (post-2040). Market reforms, including EV tax credits tied to sustainable sourcing and partnerships with automakers (e.g., Tesla), alongside ethical priorities like avoiding “green colonialism” through equitable resource development in Kenya and Indonesia, underscore this review’s novel integration of risk–benefit quantification, policy–technology synergy, and equity-centric governance, offering a holistic vision for geothermal lithium’s role in a sustainable energy transition.

6. Conclusions

Geothermal lithium extraction emerges as a transformative and sustainable alternative to conventional lithium resources, addressing global supply chain vulnerabilities while aligning with climate and equity goals. This review synthesizes technical, economic, environmental, and policy dimensions to evaluate its viability. The development of geothermal lithium resources represents a significant direction in the field of new energy. Currently, technologies applicable to geothermal lithium extraction include evaporation and precipitation, chemical precipitation, adsorption, solvent extraction, electrochemical methods, and membrane separation. Among them, membrane separation technology, particularly forward osmosis (FO) membrane technology, is expected to become a key research focus for geothermal lithium extraction.

Regarding technological advancements, forward osmosis (FO) emerges as a breakthrough due to its low energy consumption, high fouling resistance, and tunable selectivity. Integration with ion exchange, adsorption, or electrodialysis enhances lithium recovery (up to 85%) and purity, outperforming conventional methods like reverse osmosis. Combining adsorption with electrochemical processes or AI-driven optimization addresses challenges posed by low lithium concentrations (20–200 mg/L) and extreme brine conditions (TDS > 100,000 ppm, 150–350 °C).

With respect to sustainability and resource synergy, closed-loop reinjection (>90% efficiency) and bio-based adsorbents minimize water use and waste, while comprehensive recovery of boron, potassium, and rubidium adds economic value. Integration with renewable energy (e.g., geothermal–wind hybrids) and sectors like agriculture enables circular resource utilization, reducing energy demands and fostering regional economic diversification.

This work uniquely quantifies the techno-economic viability of geothermal lithium extraction, introducing a novel framework for integrated geothermal development that aligns energy, material, and economic goals. With the rapid growth of the new energy industry and the expanding applications of lithium, the demand for lithium resources is projected to continue rising. Technological innovation will further drive the industrialization of geothermal lithium extraction and its synergistic development with other industries.

In conclusion, geothermal lithium extraction represents a critical pathway toward decarbonized energy systems. By addressing technical bottlenecks, fostering policy support, and embracing inclusive growth models, this technology can transition from niche innovation to a cornerstone of sustainable lithium production.