Assessment of iron oxide paint pigments recovered from acid mine drainage through selective precipitation

Abstract Acid mine drainage (AMD) and its elevated concentrations of heavy metals are a widespread source of water pollution throughout Pennsylvania. Current AMD treatment methods are costly to operate and maintain due to the large volumes of waste sludge produced as a byproduct of treatment. The sludge requires regular removal and disposal yet has no practical use or commercial value. New resource recovery methods of AMD treatment aim to reduce waste by extracting metal contaminants in alternate usable forms which can be marketed and sold to recoup treatment costs. In particular, the iron loadings characteristic of AMD hold potential as vast untapped sources of iron oxides, commonly used in inorganic paints and pigments. Following a series of proof-of-concept experiments, a variety of iron oxide powders were successfully prepared from natural and synthetic AMD samples through the selective precipitation of iron along with drying and milling processes. Variables such as pH, temperature, alkaline addition rate and drying duration were controlled and varied, and their effects on oxide morphology and composition were observed using x-ray diffraction and scanning electron microscope technology. Powders were mixed with binder and successfully used as paint, and were evaluated based on color, tinting strength, and phases of iron oxide present. Treated natural AMD samples were found to meet NPDES limits. Further exploration into the kinetics of the selective precipitation process and its effects on iron oxide morphology is currently underway, in an effort to produce improved pigments at cheaper costs.