Co-sintering of ceramic ultrafiltration membrane with gradient pore structures for separation of dye/salt wastewater

Robust ceramic membranes with low fabrication cost and high separation performance are particularly suitable for the separation of dye wastewater containing high salinity. In this work, a co-sintering process was employed to fabricate alumina tight ultrafiltration (UF) membranes with gradient pore structures on the alumina supports that could decrease the sintering consumption and improve the separation efficiency simultaneously. It was revealed that the phase compositions of the alumina support, alumina intermediate layer, and separation layer were all α phase, demonstrating a high acid/alkali resistance. The resulting alumina membranes produced from the co-sintering process exhibited a mean pore size of ∼5 nm and water permeance of 72 L m⁻¹ h⁻¹ bar⁻¹. As a result, the membranes reject nearly 99% of dyes and allow most salts (above 99%) to pass through the membranes in treating the single dye solution, single salt solution, and mixed dye/salt solution. Finally, a concentration-diafiltration process was designed and conducted to separate and recover the saltwater and dyes from the dye/salt mixture. The results showed that Na₂SO₄ content in the retentate decreased from 21 g/L to 0.5 g/L while maintaining the dye concentration above 980 mg/L. This work provided a cost-effective method to prepare high-performance ceramic UF membranes for the separation of dye/salt solution.