Diffusion-driven selective crystallization of high-purity salt through simple and sustainable one-step evaporation

Abstract

High-purity salt extraction from saline water through conventional processes is complex and environmentally unsustainable. Here we propose a diffusion-driven selective crystallization strategy for high-purity salt production directly from source water with mixed salts. The essence of the strategy lies in purposefully suppressing non-ion-selective transfer processes (for example, convection) to harness differences in ion diffusion, thereby directing the targeted ion to selectively move to the crystallization surface. As a proof of concept, a floating porous membrane evaporator was designed, which universally achieved high-purity salt production (>99.10%) from saline water of mixed ions such as Na+/K+, Ba2+/K+ and Mg2+/Li+. Furthermore, the practical application potential of the strategy was demonstrated by the evaporator, which, in the absence of any pre- and posttreatment, successfully produced high-purity NaCl crystals (99.36%) out of real seawater in just one step. This strategy opens a new horizon for precise ion separation and enriches the toolbox of high-purity salt production. Extracting high-purity salt from saline water through conventional processes is complex and environmentally unsustainable. A diffusion-driven selective crystallization strategy that uses a precisely designed floating porous membrane to suppress non-ion-selective transfer enables simple and precise ion separation and high-purity salt production from mixed source solutions such as Na+/K+, Ba2+/K+ and Mg2+/Li+.