Dual-ion permeation Janus membrane-assisted element reconstitution system enables fluorosilicate-oriented recovery from fluoride-rich and silica-rich wastewaters

Abstract

Rapid development of semiconductor manufacturing and photovoltaic industry leads to significant generation of fluoride-rich and silica-rich wastewaters. Due to the emphasis on circular economy and resource recovery, there is a shift from regarding wastewater as waste to a recoverable resource. In this study, we present a uniquely designed dual-ion permeation Janus membrane (DPM)-assisted element reconstitution system (MERS) for selective recovery of high-value fluorosilicates from fluoride-rich and silica-rich wastewaters. The MERS with a configuration of cation-exchange membrane/bipolar membrane/DPM/anion-exchange membrane/cation-exchange membrane achieved HF formation in silica chamber and further SiF₆^2- generation from the reaction of HF with SiO₂. Driven by the electric field, SiF₆^2- was then transported through DPM into acid chamber for fluorosilicates selective recovery. The DPM with positively-charged nanoporous substrate/negatively charged active layer enhanced electrostatic interaction for SiF₆^2-/H⁺ transport and steric exclusion for coexisting foulants rejection. Ion transport mechanism analysis demonstrated DPM enhanced SiF₆^2- migration while inhibiting back diffusion by electrostatic interaction and steric exclusion. Through the application of DPM, MERS showed rejections over 99% for nanoparticles and over 90% for organics. Thus, MERS stably selectively recovered SiF₆^2- with recovery rate over 85% and fluorosilicates purity over 99.5%. Compared to traditional technologies, MERS achieved valuable resource recovery with the advantages of simple operation, small footprint and no secondary pollutant generation. Overall, this study provides a new strategy for simultaneous recovery of fluoride and silica from different waste streams, enabling a more sustainable strategy for semiconductor and photovoltaic industries development.