Removal of silver from aqueous solutions by complexation–ultrafiltration using anionic polyacrylamide

Abstract

Wastewaters containing silver ions are produced by several sources like metal finishing, electroplating, electronics, hazardous waste disposal sites, galvanic industries, etc. Complexation–ultrafiltration (CUF) is a developing hybrid process for the removal and recovery of heavy metals, even at trace level concentrations, which uses the selectivity of complexing agent and filtration ability of ultrafiltration (UF) membrane. In the present work, separation of silver ions from aqueous solutions by CUF using a novel complexation agent, namely anionic polyacrylamide (average molecular weight >50kDa) and a polyethersulfone UF membrane (molecular weight cut-off: 10kDa) was studied along with the effects of operating parameters on metal ions rejection including fouling behavior of the UF membrane used and decomplexation of silver ions for recovery. The UF experiments were performed on Perma®-pilot plant using synthetic aqueous solutions of metal salt at different applied pressures (4, 5, 6atm), initial metal ions concentration in feed (5, 10, 15, 20, 50ppm), feed pH (4, 5, 6, 7, 8, 9) and polymer-to-metal ions ratio (0.5, 1, 1.5) at a constant feed flow rate of 15L/min. Maximum rejection, close to 100%, of silver ions has been obtained at optimum operating parameters. Kinetics of complexation reaction of metal ions with anionic polyacrylamide (aPAM) was studied in a separate experiment which suggested that about 24min is required for silver ions to reach complexation equilibrium.