Nanofiltration and reverse osmosis applied to gold mining effluent treatment and reuse

Abstract

Gold mining and ore processing are activities of great economic importance. However, they are related to generation of extremely polluted effluents containing high concentrations of heavy metals and low pH. This study aims to evaluate the optimal conditions for gold mining effluent treatment by crossflow membrane filtration regarding the following variables: nanofiltration (NF) and reverse osmosis (RO) membrane types, feed pH and permeate recovery rate. It was observed that retention efficiencies of NF90 were similar to those of RO membranes though permeate fluxes obtained were 7-fold higher. The optimum pH value was found to be 5.0, which resulted in higher permeate flux and lower fouling formation. At a recovery rate above 40% there was a significant decrease in permeate quality, so this was chosen as the maximum recovery rate for the proposed system. We conclude that NF is a suitable treatment for gold mining effluent at an estimated cost of US$ 0.83/m3.