Diffusion dialysis-nanofiltration separation process to reclam the acidic desulfurization wastewater from steel enterprises

Abstract

The treatment of acidic desulphurization wastewater is challenging due to its high acidity and complex composition. Typically, acidic desulphurization wastewater is treated as high-salt wastewater after alkali neutralization, leading to issues such as high treatment costs and secondary pollution. To achieve resource utilization and reduce pollutant discharge, diffusion dialysis was employed for heavy metal removal and acid recovery (comprising hydrochloric acid and sulfuric acid). Subsequently, the separating property of hydrochloric acid and sulfuric acid between monovalent selective electrodialysis and acid-resistant nanofiltration was compared to determine the optimal process, the parameters were optimized through experiments. The results indicated that optimal performance was achieved at membrane surface flow rate of 2.86×10-6 cm/s, with acid recovery rate of 87.5% and metal ion removal rate of >93%. The monovalent selective coefficient PSO42-Cl- reached its peak at 7.5 MPa, significantly surpassing that of monovalent selective electrodialysis. Through the combined treatment of diffusion dialysis and acid-resistant nanofiltration, hydrochloric acid with a mass fraction of 3.34% and purity of 99.65% could be obtained. The treatment water volume was 30 m3/d, total project investment was 3.96 million yuan, and operating cost was estimated at 1.27 million yuan/a. Compared to traditional treatment processes, annual savings was approximately 1.06 million yuan with the investment payback period of about 3.8 years, which had significant environmental and economic benefits.

Keywords

• desulfurization wastewater
• diffusion dialysis
• monovalent selective electrodialysis
• acid-resistant nanofiltration
• resource utilization