Fast-selective electro-driven membrane reactor in fluoride/silica crystallization for microelectronic wastewaters recycling

Abstract

Rapid growth of the microelectronic industry leads to a significant increase in the generation of microelectronic wastewaters containing complex pollutants. Resource recovery technologies offer promising solutions for effective wastewater reuse in the microelectronics sector. However, how to simultaneously achieve high-efficiency crystallization and high crystal purity of ionic resources from complex wastewater remains a challenge. Here, for the first time, we propose an electro-driven membrane reactor (EMR) for the ex-situ crystallization of fluoride/silica from microelectronic wastewaters as high-purity fluorosilicates. This EMR with independent chambers combines a bipolar membrane to produce protons for SiF₆^2- generation from the reaction between fluoride and silica. An internal ultrafiltration membrane is used to reject nanoparticles/organics while providing ion channels for protons and SiF₆^2- migration. Selective recovery of Na₂SiF₆ from the coexisting ions (Cl^-, SO₄^2-, NO₃^- and PO₄^3-)/nanoparticles (SiO₂, Al₂O₃ and CeO₂)/organics (tetramethylammonium hydroxide, isopropyl alcohol, bovine serum albumin, sodium alginate and humic acid) is demonstrated. Over 99.5% Na₂SiF₆ purity and 64.5% crystallization rate are verified under the optimal conditions (voltage of 8 V, UH050 membrane, operation mode Ⅰ, and forward permeate flux of 1 mL min^-1). This EMR with the advantages of accurate capture capability may be an innovative strategy for enlarging the scale of pollutant elimination, ionic resources and fresh water recovery from micro-electronic wastewaters.