Subverting Traditional Salt Production! Professor Wang Peng's Team from Sun Yat-sen University Develops One-Step Evaporation Method to Directly Extract 99.36% High-Purity Salt from Seawater
The efficient extraction of high-purity salt is a core technological demand in the fields of salt production, resource recovery, and specialty chemical engineering. However, when traditional processes extract high-purity salt from mixed brines (such as seawater and salt lake brine), they often face bottlenecks of complex procedures, high energy consumption, and poor environmental sustainability. These processes not only require multiple steps of pretreatment, separation, and post-purification operations but also frequently rely on chemical reagents or high-energy-consuming equipment, making it difficult to balance efficiency and environmental protection needs.
To address this key scientific and engineering issue, a research project led by Professor Wang Peng's team from Sun Yat-sen University and Professor Zhang Hanchao's team from The Hong Kong Polytechnic University has published relevant research results in the international top journal Nature Water. The study proposes the "Diffusion-driven Selective Crystallization (DiSC)" strategy, which for the first time enables the direct preparation of high-purity salt from mixed brines through a single-step evaporation process, providing a revolutionary technical solution for this field.
The core innovation of the DiSC strategy lies in the precise regulation of ion migration and crystallization processes, and its scientific logic breaks through the inherent paradigm of traditional ion separation. First, the strategy actively inhibits non-ion-selective transfer processes (such as convection and disordered capillary flow) through system design. These processes are key causes of low ion separation efficiency and insufficient salt purity in traditional processes, as they lead to undifferentiated migration of target ions and impurity ions to the crystallization interface, undermining the effect of selective separation.
On this basis, the DiSC strategy fully leverages the inherent differences in diffusion coefficients of different ions in solutions (e.g., differences in diffusion rates between Na⁺ and K⁺, Mg²⁺ and Li⁺) to construct a "diffusion-dominated" mass transfer environment. This allows target ions (such as Na⁺ required for table salt production and Li⁺ in resource recovery) to diffuse preferentially to the crystallization surface, while impurity ions are "delayed" in the bulk solution due to their slower diffusion rates. Ultimately, this achieves the selective crystallization of target salts and fundamentally solves the core pain points of traditional processes.
To translate the DiSC strategy from theory to practical application, the research team has designed a floating porous membrane evaporator. This device serves as the key carrier for implementing the strategy, with its structure and functions highly adapted to the separation requirements driven by diffusion.The evaporator adopts a floating design, allowing it to float directly on the surface of brine without the need for complex liquid delivery systems, which simplifies the operation process. Its core component is a ceramic-based porous membrane: the membrane’s pore structure can precisely control the capillary flow rate to further suppress convective interference, while providing directional channels for ion diffusion—ensuring that the mass transfer process is dominated by diffusion. More importantly, the device requires no additional auxiliary reagents such as chemical precipitants or ion exchange resins, nor does it need subsequent purification steps. It can be directly connected to raw brine, fundamentally reducing process complexity and environmental burden.
A series of experiments were conducted to systematically verify the effectiveness, universality, and practical application potential of the DiSC strategy. In the treatment of mixed-ion brines, targeting three typical mixed salt systems—Na⁺/K⁺, Ba²⁺/K⁺, and Mg²⁺/Li⁺ (simulating salt lake brine or industrial brine)—the floating porous membrane evaporator consistently achieved stable production of high-purity salts:
For the NaCl-KCl mixed brine, the purity of NaCl obtained through selective crystallization exceeded 99.10%;
In the Ba²⁺/K⁺ system, the content of impurity K⁺ in the BaCl₂ crystallization product was less than 0.9%;
In the Mg²⁺/Li⁺ system, LiCl with a purity of over 99.10% was successfully separated from the MgCl₂-LiCl mixture, effectively solving the technical problem of Mg²⁺ interference in traditional lithium extraction.
To further evaluate its practical application value, the research directly used real seawater (with complex components including NaCl, MgCl₂, KCl, and other impurities) as raw material. Without any pretreatment or post-treatment, high-purity NaCl crystals with a purity of 99.36% were successfully prepared through a single evaporation step using this evaporator—this purity fully meets the standards for food-grade and industrial-grade high-purity salt.Additionally, via COMSOL multiphysics simulation, the study quantified the effects of capillary flow control and ion diffusion on the crystallization process. The results showed that when the membrane pore size was controlled within a specific range (e.g., 3 mm), the capillary flow rate could be suppressed to a level where convection was negligible; at this point, ion migration was completely dominated by diffusion. This highly aligned with the experimental result of "selective crystallization of target salts," confirming the mechanistic rationality of the DiSC strategy from a theoretical perspective.This research not only expands the theoretical framework of precise ion separation at the academic level but also provides a green and efficient technical pathway for high-purity salt production at the application level.
Theoretically: The DiSC strategy breaks through the traditional ion separation paradigms of "pore size-based sieving" or "chemical adsorption-based separation." For the first time, it takes "diffusion difference" as the core separation driving force, offering a new scientific perspective for research on low-energy-consumption and high-selectivity ion separation.
Technologically: The one-step evaporation process significantly shortens the production chain. According to Dr. Liu Yang, the first author, the energy consumption calculation for seawater salt production shows that compared with traditional processes, this new method can reduce energy consumption by 30%-50%. Moreover, it avoids chemical reagent pollution, which is in line with the demand for green production under China’s "dual carbon" goals (carbon peaking and carbon neutrality).
Application extension: The strategy is not only applicable to salt production but can also be extended to fields such as salt lake lithium extraction and valuable metal recovery from industrial wastewater (e.g., separation of Ba²⁺ and Sr²⁺), providing a new tool for the efficient recovery of scarce resources.
In summary, through a complete logical chain of "principle innovation - device design - experimental verification," this study systematically confirms the feasibility and superiority of diffusion-driven selective crystallization in high-purity salt preparation. It not only provides key technical support for the efficient and sustainable utilization of mixed brine resources but also opens up a new direction for ion separation research in related fields.
Link：https://www.nature.com/articles/s44221-025-00474-z
