Arsenic impact on the valorisation schemes of acidic mine waters of the Iberian Pyrite Belt: Integration of selective precipitation and spiral-wound nanofiltration processes

Abstract

Arsenic and selenium presence in acid mine waters (AMWs) limits their disposal due to environmental regulations. The focus to solve the economic infeasibility is directed to sustainable solutions, promoting resource recovery. In fact, rare earth elements (REEs) recovery is proposed in most of the Iberian Pyrite Belt AMWs. However, the presence of arsenic and selenium may impact in the REEs recovery. Among different alternatives, nanofiltration (NF) provides a concentration stage on REEs recovery, reduces the nominal flow and removes hazardous species. In this work, Iberian Pyrite Belt AMWs with up to 10 mg/L REEs, containing arsenic (2 mg/L), were treated with a NF membrane. Firstly, AMWs were pre-treated with H2O2/NaOH, to oxidise Fe(II) to Fe(II) and As(III) to As(V), promoting their removal and avoiding their potential precipitation at the membrane. Subsequently, NF pressure effect (6–20 bar) was studied, removing metals (>95 %), whereas arsenic rejections ranged from 60 to 71 %. Then, water recovery potential was evaluated at 10, 15 and 22 bar by reproducing a 10-stages NF plant. Results showed that the proposed treatment could be an alternative for arsenic and selenium removal (70 µg/L and 0.5 µg/L permeate concentrations, respectively) to achieve mining discharge limits according to regulations.