Inclined Multilayer Solar Evaporator for Directional and Refined Salt Crystallization from Practical Industrial Wastewater

Interfacial solar evaporation with directional salt crystallization offers a sustainable approach for the mineral recovery. However, its application to real industrial wastewater is hindered by co-precipitate of organic pollutants, leading to crystal contamination. In this study, we present a rationally designed solar evaporator featuring dual functionality of directional crystallization and organic contaminants adsorption. The innovation lies in the coupling of an inclined evaporation surface with multilayer functional structures: a top hydrophobic layer for efficient solar energy harvesting, a middle hydrophilic layer for organic contaminants interception and bottom water transport layers for controlled water delivery. By tuning the inclination angle and water transport layers to regulate the mass transport, the evaporator achieves directional salt crystallization and maintains a stable evaporation rate of 1.42 kg m⁻² h⁻¹ during long-term evaluation. Moreover, the integrated adsorption layer effectively retained organic pollutions and purified the crystal. Compared to salts obtained through conventional thermal crystallization, the organic pollution content of the recovered crystals was reduced by 60.4%. The system’s scalability and outdoor applicability were further validated through a scaled-up rooftop test. This integrated interfacial evaporation strategy offers a new avenue for refined crystal recovery and advanced industrial wastewater treatment beyond the capabilities of conventional evaporators.