The removal of Zn from complex circumneutral pH mine waters using magnetic nanoparticles (MNPs)

Mine water discharges pose a significant environmental challenge due to elevated metal concentrations, which can be detrimental to aquatic ecosystems and water quality. In this study, four circumneutral-pH mine water samples were treated with different magnetic nanoparticle (MNP) concentrations (0.1 g L^-1, 1 g L^-1, and 5 g L^-1) to assess their efficacy for Zn removal. Sorption of Zn to all MNP systems tested, occurred within 48 hours. At 5 g L^-1, MNPs removed Zn from all mine waters tested, reducing concentrations to 0.09, 0.66, 0.0 and 0.0 mg L^-1 for the River Ystwyth, Cwmystwyth adit, River Nent and Haggs adit respectively. A clear positive correlation was recorded for Zn removal as a function of MNP dose, with MNP concentrations >1 g L^-1 required for Zn removal to below trace concentrations. Analysis of competing ions (<i>e.g.</i>, Ca²⁺, Mg²⁺, Na⁺) showed that a decrease in concentration followed the order Zn > Na⁺> Ca²⁺ > Mg²⁺. These findings confirm that MNPs are effective for the removal of Zn from real mine water samples even when applied at low dosages, suggesting that they are a highly promising water treatment technology for such applications.