The fate and impact of contaminants in a biological iron oxidation and jarosite precipitation process

Abstract Biological iron oxidation results in both soluble and precipitated ferric iron, dependent on pH conditions, ionic strength and solution chemistry. Soluble ferric iron plays a well-documented role in hydrometallurgical processing. Ferric iron precipitation, however, plays a vital role in the removal of various soluble elements from solution via co-precipitation. This removal process reduces the soluble concentration of elements that may otherwise inhibit bioleaching microorganisms. Hydrometallurgical process solutions often contain various contaminant elements due to the dissolution of gangue minerals during ore processing. In this work, the effect of a combination of often-encountered potentially inhibitory contaminants (5 g L −1 Mg, 2 g L −1 Al, 0.4 g L −1 Mn, 0.2 g L −1 Co, 0.05 g L −1 F and 0.05 g L −1 As) on ferrous iron oxidation activity at room temperature as well as the fate of these contaminants was evaluated using a synthetic pregnant leach liquor that contained 1.5 g L −1 Cu and Ni and 15 g L −1 Fe 2+ . The solution analysis results showed notable removal of F (54%) and As (17%), the two main elements with known severe inhibitory effects on bioleaching bacteria growth and activity. Other contaminant elements were removed to a lesser extent; 12% of Mg and −1  h −1 ) and extent (from 99 to 98%) and increased the extent of iron precipitation (from 16 to 23%) at an influent Fe 2+ concentration of 13–14 g L −1 and a hydraulic retention time of 13–15 h.