Ceramic micro/ultra-filtration of low-concentration ultrafine sulfur in desulfurization wastewater

BACKGROUND: A low concentration of ultrafine suspended sulfur (SS) in the wastewater produced from the coking gas desulfurization process is a serious problem. In this study, ceramic microfiltration and ultrafiltration membranes were used to remove ultrafine SS for further recovery. RESULTS: Results showed that membrane with a pore size of 0.05 µm at the operating conditions 0.15 MPa, 40 °C and 4.0 m s⁻¹ experienced the lowest flux decline and degree of fouling in comparison with other conditions. All membranes exhibited good rejections of sulfur (>99.9%) and tar oil (>98.0%). The SS ranged from 1.5 to 34.0 g L⁻¹ had no influence on the permeate turbidity (<1 NTU) but resulted in an increase in the tar oil content and a decrease in the permeate flux. SEM/EDX results indicated that the membrane surface was fouled by the sulfur particles and ammonium salts, while the tar oil entered the membrane pores. An effective cleaning method with high flux recovery (>98%) was applied to remove the foulants using mixed solutions of 1% (w/w) NaOH and 0.5% (w/w) NaClO. CONCLUSION: The results showed that the ceramic membranes are effective in ultrafine sulfur removal from the wastewater.