Recovery of Iron from Acid Mine Drainage in the Form of Oxides

Acid mine drainage (AMD) typical by low pH, high concentration of sulphates and different heavy metals is one of the major sources of environmental damage in mining industry. Treatment methods to address AMD are focused on neutralizing, stabilizing and removing pollutants through various physical, chemical and biological processes. However this type of mining influenced water should be considered not only as serious environmental problem, but also as an important resource due to the universal high metal demand and ambition of potential reuse of metals recovered from AMD. The aim of this work was to recovery of iron in the form of oxides from AMD drained from enclosed and flooded Smolnik sulphidic deposit (Slovakia). The iron was removed from AMD in two steps to very low levels that meet required water quality criteria. The ferrous iron present in AMD was oxidized using hydrogen peroxide. In this stage decreasing of pH value and partial iron precipitation were observed. The follow neutralization using sodium hydroxide resulted in total iron removing by precipitation. The obtained solids were identified as a schwetmannite. The iron oxides were produced by thermal decomposition of precipitates. The morphology of acquired intermediates was studied by cryo-scanning electron microscopy (cryo-SEM) and the Fourier transform infrared spectroscopy (FTIR) was applied to characterization of their composition. Energy dispersive X-ray spectroscopy (EDX) was used for qualitative and quantitative analysis of intermediates and products. The X-ray powder diffraction (XRPD) was performed for the mineralogical analysis of the iron precipitates before and after the differential (DTA) and thermogravimetric (DTG) experiment.