Combined ultrafiltration and suspended pellets for lead removal

A novel process combining an outside-in ultrafiltration membrane and suspended pellets in a stirred tank reactor for removing lead (Pb) from aqueous solutions was investigated. The incorporation of the membrane avoids breakthrough of fine particulate matter, which can plague conventional fluidized pellet reactors. The Pb removal efficiency increased with increasing solution pH and pellet surface area. At pH 7, increasing the total carbonate-to-lead molar ratio increased lead removal efficiency. However, increasing pH is more effective than increasing total carbonate-to-lead molar ratio for improving treatment efficiency. Using XRD, SEM and EDX, we concluded that the surface of the pellets was approximately 15% covered by Pb3(CO3)2(OH)2 at pH 9.0 after 5 days of operation with a feed containing 50 mg L−1 Pb.