Integrated UF-NF-RO route for gold mining effluent treatment: From bench-scale to pilot-scale

This study focused on the performance of an UF-NF-RO integrated system treating a gold mining effluent from the pressure-oxidation stage in order to concentrate metals, and recover acid and water. Aspects such as the most suitable cross-flow velocity, cleaning procedure, and water recovery fraction were evaluated. For cross-flow velocities, a threshold value of 1.5 × 10−2 m/s was found for NF and RO stages. Besides, the system had its best performance while operating at recovery fractions of 90%, 40-50%, and 50% for UF, NF, and RO, respectively. Concentration factors of 2.0 and 2.7 were found in metals from the NF retentate and sulfuric acid from the RO retentate respectively. For cleaning purposes, hydrochloric and oxalic acid demonstrated the best cost-benefit. A long-term operation inside the mining company was assessed and the results confirmed that NF and RO association allowed for the recovery of a purified acid stream, which may be reused in the ore processing; the production of a metal enriched stream, that can be transferred to a subsequent metal recovery stage; and the generation of high quality reuse water. The total cost of the proposed route was US$ 1.137/m3 of effluent, including UF and NF concentrate neutralisation.