Integration of layer-by-layer hollow-fibre nanofiltration membranes and crystallization for water reclamation and resource recovery from acidic mine waters

Abstract

Water pollution remains a critical issue in the global mining industry. Moreover, the access to a reliable source of raw materials such as Cu, Zn, Mg and Rare Earth Elements has become a challenge for the European Union. In this context, the treatment of Acidic Mine Waters (AMW) with a circular perspective can be a solution to both challenges. This study focused on the integration of crystallization processes and nanofiltration (NF) to selectively recover Mg(OH)2(s) and reclaim AMW for irrigation purposes from the Aznalcóllar open-pit (1629 mg/L Mg2+, 360 mg/L Ca2+ and 10,962 mg/L SO42−). The pre-treatment, involving selective precipitation, attained removals higher than 95 % of transitions elements. Different concentrations of NaOH (0.16 M, 0.25 M, 0.5 M) were used for the crystallization of Mg(OH)2(s), affecting the morphology and content of the final product. The removal of Ca2+ was performed by the addition of NaHCO3 at constant pH, achieving Ca removals of 99 %. The remaining salinity removal was achieved using a layer-by-layer hollow-fibre NF membrane, resulting to rejections higher than 80 % for Ca2+, SO42−, and Na+. The obtained results demonstrate that the combined crystallization and NF stages is a feasible approach for the efficient treatment and water reclamation of AMW.