Recovery of copper from process waters by nanofiltration and reverse osmosis

Copper rejections of a nanofiltration (NF) and a reverse osmosis (RO) membrane are investigated with coppersulfate and copper-nitrate solutions as test wastewaters. The copper content of the solutions represents the typical copper ion concentration of process waters from a textile coating plant, i.e. 2 kg/m3.Experiments are performed with the test solutions on a bench-scale cross-flow membrane filtration apparatus with acid resistant flat sheet membranes. The active membrane area is 28 cm2. Isotherm experiments at 25°C are carried out. The applied conditions (e.g. pressure or pH) are in the applicable range of parameters. Permeate flux, conductivity, pH, and copper concentration of the permeate are measured to determine the membrane characteristic and rejection. The transport through the membrane is modeled in the function of time with the solution–diffusion model and in the function of yield with the modified osmotic pressure model. Modeled data is then compared to the experimental data. This comparison shows a good agreement between the measured and the modeled fluxes. Finally, the effect of anion composition on permeate flux is also studied using copper-sulfate and -nitrate at a constant copper content of 2 kg/m3. However, no influence of the anions on the permeate flux and copper rejection can be observed.