Nanofiltration of Mine Water: Impact of Feed pH and Membrane Charge on Resource Recovery and Water Discharge

This study investigates the retention capabilities of two nanofiltration membranes, Dow NF 270 and TriSep TS 80, when filtering mine influenced water streams across varying acidic pH values. The objective was to evaluate how feed pH and membrane charge affect resource recovery and discharge compliance. Methodologically, the membranes were tested against sodium sulphate solutions to determine their functional iso-electric points, revealing significant changes in retention at pH 3 and indicative of a zero net charge. Further experiments with copper mine drainage and synthetic solutions, characterized by pH levels between 2 and 5, demonstrated that optimal cation retention occurred when the feed solution's pH was below the iso-electric point, resulting in a net positive charge of the membrane. Results indicated that under these conditions, cation transmission was minimized, enhancing the potential for metal recovery while meeting mine water discharge criteria. Hence, the nanofiltration process emerged as a viable option for improving metal recovery from mining waste streams and ensuring regulatory compliance for filtrate disposal.