Cu(II) incorporation to schwertmannite: Effect on stability and reactivity under AMD conditions

• Published in: Geochimica et cosmochimica acta Vol. 119; pp. 149 - 163
• Main Authors: Antelo, Juan, Fiol, Sarah, Gondar, Dora, Pérez, Claudio, López, Rocío, Arce, Florencio
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.10.2013
• Subjects: acid mine drainage; adsorption; Contaminants; Copper; Coprecipitation; goethite; iron; Iron oxides; mining; oxides; Sulfates; Surface chemistry; Surface water; Transformations
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2013.05.029

The formation, transformation and surface chemistry of iron oxides is geologically important in surface waters polluted by acid mine drainage (AMD). The geochemical behaviour of these oxides controls the availability and mobility of contaminants in such highly polluted systems. The low pH values, together with the presence of large amounts of sulphate, favour the formation of schwertmannite, which is a metastable iron oxide that is transformed to goethite under oxic conditions. However, in copper mining environments, co-precipitation of iron and copper ions is expected and therefore the surface chemistry of the iron oxides present in these systems may be different. Several schwertmannite samples were prepared in the presence of high concentrations of sulphate and different concentrations of copper to simulate copper-rich mining environments. Long-term transformation experiments were conducted to study the mineral oxide stability and variations in surface chemistry produced over a period of 15months. Schwertmannite-like particles were initially formed, but sulphate release and the dissolution and re-precipitation of iron and copper ions occurred under more acidic conditions throughout the experiment, which led to the formation of goethite-like particles. The capacity for arsenate adsorption was highest in the initial schwertmannite-like particles, and arsenate mobility increased in the presence of more stable iron mineral phases that were formed throughout the transformation experiment.