Global Business, BICHEM Group
I.Background and Industry Status
Driven by China’s dual carbon targets, global demand for lithium is growing exponentially at an annual rate exceeding 30%. Lithium resources mainly originate from minerals and brines, among which brine resources (including salt lake brines, geothermal brines, and oilfield brines) are thousands of times greater in reserves than minerals. Owing to their environmental and cost advantages, brines have become the core focus of lithium industry development.
Current mainstream lithium extraction technologies, including traditional evaporation and direct lithium extraction (DLE), still face significant limitations. First, there is inadequate adaptability to feedstocks. Existing technologies primarily process high-quality brines with lithium concentrations above 260 mg/L and magnesium-to-lithium ratios (MLR) below 6.15, while more than 99% of global brine reserves fall below this standard as low-grade brines, which remain largely undeveloped. Second, the processes entail high energy consumption and environmental costs. Traditional evaporation requires large land areas and long cycles ranging from months to years, with over 60% of lithium lost through entrainment, while also disrupting groundwater resources and local ecosystems. Third, the contradiction in water use is acute. Existing DLE technologies consume more than 500 m3 of freshwater for every ton of lithium carbonate produced, yet brine deposits are mostly located in deserts, plateaus, and other freshwater-scarce regions, creating the “water-intensive extraction” dilemma. Finally, technical bottlenecks are evident: adsorption suffers from low mass transfer efficiency and slow kinetics at low lithium concentrations; membrane separation must overcome concentration polarization effects; electrochemical methods require external power input and are further constrained by low temperatures (e.g., the average annual temperature of western China’s salt lakes is only 5.2 °C).
II. Concept and Innovation of SDLE Technology
To overcome these traditional bottlenecks, the Solar-Driven Direct Lithium Extraction (SDLE) system has emerged. This system integrates Solar Interface Evaporation (SIE) with DLE, harnessing clean and renewable solar energy to overcome the challenges of extracting lithium from low-grade brines while simultaneously producing freshwater, achieving synergistic utilization of resources, energy, and water.
The core breakthroughs of SDLE technology can be summarized in three aspects:
1. Revolution in energy supply: from high consumption to zero carbon
The SDLE system uses solar energy as the sole or primary energy input, driving the extraction process through photothermal or photoelectric effects, without dependence on the power grid or fossil fuels. Photothermal SDLE systems achieve localized interfacial heating (heating only the brine at the evaporation interface), improving energy utilization efficiency by 3 to 5 times compared with traditional evaporation. Photoelectric SDLE systems use photovoltaic effects to directly drive electrochemical lithium extraction, achieving “zero external power supply”.
2. Breakthrough in feedstock range: from high-quality to all grades
By gradient driving (temperature, concentration, and pressure gradients generated by photothermal effects) or field driving (internal electric fields generated by photoelectric effects), SDLE systems significantly enhance the diffusion and enrichment of Li+. In photothermal systems, temperature gradients accelerate Li+ migration toward the extraction layer while suppressing diffusion of competing ions such as Mg2+. In photoelectric systems, internal electric fields direct Li+ transport across selective membranes, enabling efficient Li+ enrichment even from seawater (where lithium concentration is only 0.2 mg/L).
3. Synergistic resource utilization: from single lithium extraction to lithium-water co-production
While extracting lithium, SDLE also condenses evaporated water vapor into freshwater, realizing “one energy input with dual outputs”. For example, SDLE adsorption systems can achieve freshwater recovery rates exceeding 90% while extracting lithium, effectively addressing the “water-intensive extraction” in brine mining regions.
III. Photothermal and Photoelectric SDLE Systems
Depending on the form of solar energy conversion, SDLE systems can be classified into photothermal and photoelectric types.
1. Photothermal SDLE systems: gradient-driven “natural extraction”
Photothermal SDLE systems rely on gradient-driven natural extraction mechanisms and consist of a solar absorption layer and a lithium extraction layer. Their working mechanism includes three stages: thermal gradient formation, where localized interfacial heating generates the driving force for water evaporation; concentration gradient enrichment, where water evaporation concentrates lithium ions in the extraction layer and forms a diffusion gradient; and pressure-gradient mass transfer, where the evaporation-induced pressure gradient accelerates transport of water and lithium ions while suppressing salt scaling and concentration polarization.
Key materials include carbon-based materials with high light absorption, high-temperature and acid–alkali resistance; plasmonic metals; and semiconductor materials. The lithium extraction layer employs adsorbents, selective membranes, and crystallization layers for fast and selective lithium recovery.
2. Photoelectric SDLE systems: field-driven “precise extraction”
Photoelectric SDLE systems are driven by photovoltaic effects for electrochemical separation, composed of semiconductor solar absorption units, electrode units, and lithium-ion selective membranes. Photogenerated carriers form internal electric fields between electrodes, directing Li+ across the membrane to enrich at the cathode, while competing ions are retained, enabling high selectivity.
The breakthrough of auxiliary-free photoelectric systems lies in their ability to drive lithium extraction without external bias voltage. They exhibit stable continuous operation and high efficiency, significantly enriching lithium ions even from extremely dilute solutions, thereby completely eliminating dependence on external power sources.
IV. Technological Implications and Development Prospects
SDLE technology is not merely a novel lithium extraction method, but also an innovative paradigm for synergistic utilization of “resources–energy–water”. Through fundamental innovation, it achieves three goals: extraction from low-grade brines, zero-carbon energy supply, and freshwater recovery, offering new pathways for global energy transition, water conservation, and sustainable mineral development.
The important insight from SDLE exploration is that it represents more than a technological breakthrough in lithium extraction; it exemplifies a paradigm of synergistic resource, energy, and water utilization. By harnessing solar energy to convert low-grade brines into co-production of lithium and freshwater, it provides a new approach for global energy transition, water resource protection, and green mineral development. Its core principle is to innovate from the fundamental level, breaking away from the conventional single-target mindset to achieve multi-objective optimization, offering a transferable framework for the green development of other mineral resources.