Gold acid mine drainage treatment by membrane separation processes: An evaluation of the main operational conditions

• Evaluation of gold acid mine drainage treatment by nanofiltration and reverse osmosis.
• Process evaluation in terms of: membrane type selection, effluent feed pH, and water recovery rate.
• Preliminary capital and operational costs estimate.

Acid mine drainage (AMD) is an effluent characterized by low pH and high concentrations of sulfate, metals, and metalloids. AMD treatment by membrane separation processes (MSP), specifically nanofiltration (NF) and reverse osmosis (RO) is particularly interesting; as these processes can retain divalent ions efficiently to produce high quality permeate for industrial reuse. This study aimed to evaluate the main operational conditions of the gold AMD treatment by MSP, and conduct a preliminary capital and operational cost evaluation. The results showed that the NF had a higher potential to treat the AMD than the RO, as the NF had higher permeate flux and satisfactory solutes retention efficiency. The NF90 membrane had the highest retention efficiency among the NF membranes, while the NF270 membrane had the highest permeate flux. Effluent pH affected both the solutes retention efficiency and the membrane-fouling tendency. The best combination of membrane type and feed pH was the NF270 at pH 5.5. The maximum water recovery rate at this condition was 60%, when a sharper decrease in the retention efficiency and the permeate flux was observed. The estimated capital cost of the UF-NF unit considering an effluent volumetric flow rate of 15 m3/h was US$ 131,250.00, and the operational cost was 0.263 US$/m3 of effluent.