The Removal of Dissolved Metals by Hydroxysulphate Precipitates during Oxidation and Neutralization of Acid Mine Waters, Iberian Pyrite Belt

This study examines the removal of dissolved metals during the oxidation and neutralization of five acid mine drainage (AMD) waters from La Zarza, Lomero, Esperanza, Corta Atalaya, and Poderosa mines in the Iberian Pyrite Belt, Huelva, Spain. The objective is to understand the geochemical processes that lead to metal removal and attenuation in these acidic environments. To achieve this, laboratory experiments were conducted to simulate the geochemical evolution of these waters, covering various pH levels (2.2–3.5) and chemical compositions (e.g., 319–2,103 mg/L Fe; 2.85–33.3 g/L SO₄²⁻). The research identifies two main stages: the oxidation of dissolved Fe(II) and the subsequent precipitation of Fe(III), followed by an increase in pH during mixing with fresh waters, leading to the formation of precipitates such as schwertmannite and other hydroxysulphates. The results show that trace elements are removed at varying rates based on pH and sulfate activity, with significant removal rates for cationic metals at higher pH levels. As and V are scavenged at lower pH, showcasing the effectiveness of these natural processes in reducing metal concentrations in acidic mining regions.