Membrane filtration is increasingly used to separate dissolved metal ions from dispersed particles, often using ultrafiltration membranes such as polyethersulfone (PES) membranes with a molecular weight cutoff of 3 kDa. The disadvantage of this technique is that the retention of ions is not ideal, which is caused by the interaction of coulombs with the sulfonic acid groups of the membrane.
Thus, this membrane acts like a cation exchange column. We address this shortcoming by pretreating PES membranes with other cations. Using CuSO4 as a model compound, we compared the effectiveness of five cations using their salt solutions (Ca2+, Mg2+, Fe2+, Ag+, Ba2+) as pretreatment agents and identified the most effective pretreatment components to achieve high copper ion recovery.
After unpretreated membrane filtration, only 52 ± 10%, 64 ± 5%, 75 ± 8% and 89 ± 7% of nominal Cu concentrations were obtained when the initial concentrations were 0.2, 0.5, 1.0 and 4.0 mg L-1, respectively. The efficiency of the studied cations increases in the order Fe < Ag < Mg < Ca < Ba. In addition, we analyzed the most effective concentration of the preconditioning agent. The best performance is obtained using 0.1 mol L-1 CaCl2, which improves copper recovery to just under 100%, even at the lowest test Cu concentration (93 ± 10% recovery at 0.2 mg L-1). In the environmentally relevant Cu concentration range of 0.2 mg L-1, 0.1 mol L-1 BaCl2 was determined to be the most effective pretreatment (103 ± 11%).