Immobilization of neodymium by coprecipitation of iron and aluminum oxides

Mining exploration plays an important role in the state of Minas Gerais, but the generation of effluents when processing metals can release high concentrations of trace elements into water, such as rare earth elements, like neodymium. In areas affected by the generation of acid mine drainage, the problem becomes more critical due to the production of potentially polluting acidic waters because ores containing sulfides undergo oxidation when exposed to atmospheric conditions. The present paper aims to investigate the efficiency of iron and aluminum oxides as geochemical barriers to control the mobility of neodymium and to unravel the stability of precipitates. The removal of soluble neodymium was evaluated through the coprecipitation of this element with iron and aluminum (hydr)oxides. The concentration of soluble neodymium was evaluated in the supernatant by optical emission spectroscopy. The mineralogical phases in the precipitates were determined by X Rays diffraction. Stability was evaluated through chemical extractions. Overall, iron and aluminum precipitates provided a highly efficient removal of soluble neodymium (> 99%), showing that they can be promising alternatives for the treatment of acid drainage. Gibbsite, goethite, lepidocrocite and magnetite were detected in the precipitated phases, and only magnetite and lepidocrocite were identified in treatments with lower aluminum content. The greater presence of aluminum decreases neodymium removal and increases its recovery. Neodymium in iron and aluminum precipitates seems to be more stable under circumneutral conditions and, therefore, constant monitoring is needed to prevent neodymium loss.