Technology selection and process development for enhancing water recovery from mine tailing water: A case study

A mining operation uses mechanical vapor recompression to treat mine tailings water for discharge to the environment. To maintain the mine’s operations, the removal of an additional 1 MLD of water is required. The water has a high TDS, is supersaturated, and a low pH. A range of water treatment technologies were reviewed and assessed. It was determined that a membrane system was the best option to deploy, and an NF/RO system was recommended for further evaluation. However, because the tailings water pH is in the vicinity of most membrane isoelectric points (~3-4), electrostatic rejection would be greatly affected, allowing excessive ion transmission to the permeate. It was hypothesized that a membrane with an isoelectric point >4 would provide enhanced rejection. Two acid resistant NF polymeric membranes with isoelectric points at approximately pH 5 were tested at laboratory scale. The volume recovery was restricted due to supersaturation chemistry limitations, not osmotic pressure or the operating pressure of the selected membranes. An overall system recovery of ~50% was achievable. An integrated flowsheet was developed for a system that required significantly less capital and energy that an additional thermal evaporation process.