The recovery of silver from mining wastewaters using hybrid cyanidation and high-pressure membrane process

The main objective of this work was to investigate the recovery of silver from mining wastewaters using a hybrid cyanidation and high-pressure membrane process. The tested hybrid process in lab-scale experiments includes the concentration and recovery of silver by nanofiltration (NF) or reverse osmosis (RO) after the silver is taken into solution as AgCN employing re-cyanidation and subsequent sedimentation and/or pre-filtration of wastewaters. Synthetic water experiments were conducted in this work. In synthetic water experiments (in distilled and deionized water), the soluble AgCN complex was formed after cyanidation of low-soluble AgCl particles which were added to the leach tank. Two different NF membranes and one RO membrane were tested in a lab-scale flat-sheet configuration test unit. The results indicated that although a significant amount of silver was lost on the RO membrane due to irreversible sorption, RO membrane performed better than NF membranes based on higher silver rejections, thus higher mass recoveries. Therefore, RO membrane was found to be more effective in terms of precious metal recovery and production of high quality permeate that can be reused in the leaching process. The tested hybrid cyanidation (leaching) and high-pressure membrane process in this work may be an effective approach in recovering precious metals and producing reusable water from wastes or wastewaters of mining industry.