Influence of operating conditions on the removal of metals and sulfate from copper acid mine drainage by nanofiltration

The primary objective of this investigation was to evaluate the ability of two commercial spiral-wound membranes (NF90 and NF270) to remove metals and sulfate from acid mine drainage from an active copper mine. The structural and surface properties of the membranes, hydrodynamic conditions, polarization, and filtration resistance had a significant influence on the effectiveness of the treatment. The obtained results demonstrated a good removal capacity in both membranes (> 94%) at a low operating pressure (15 bar). The increase in pressure had a strong impact on permeate flux, concentration polarization, and contaminant removal rate; however, the increase in the value of the Reynolds number exhibited had no significant effects. The NF270 membrane was selected to perform concentration and long-term tests as it demonstrated a high treatment capacity, high rejections, low resistance, and low polarization at moderate pressures. The permeate flux in the concentration and continuous operation tests decreased by similar to 45% and similar to 12%, respectively, due to the increases in resistance of similar to 63% and similar to 13%, respectively, while rejection exhibited a slight increase in both tests. The model parameters successfully identified the convective and diffusive contributions to ions transport in all experiments.