Ferrous iron biooxidation in a flooded packed-bed bioreactor at extreme conditions of iron concentration and acidity

Abstract

The utility of ferrous iron biooxidation is to regenerate Fe(III) at required rates and conditions in specific hydrometallurgical contexts, such as metal extraction from ores/concentrates and mining and electronic waste. In these applications, considerable kinetics improvements can be achieved by increasing [Fe(III)], but pH must be decreased to avoid precipitation of this oxidant. Information about continuous biooxidation operation is limited to [Fe] < 20 g/L and 2.3 > pH > 1, therefore, it is interesting to test wider ranges for these parameters.A 1L flooded packed-bed bioreactor (30 cm in height), inoculated with Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, was operated 60 days in continuous mode without interruptions at [Fe] up to 57 g/L and pH up to 0.44.Total Fe(II) conversion was achieved when operating at [Fe] = 57 g/L and pH = 1.2. The maximum biooxidation rate reached was 3.5 g/L·h for [Fe] = 40 g/L and 1 h of hydraulic retention time. Biooxidation rate decreases by 32 % when pH decreases from 1.2 to 0.44. Nevertheless, the biofilm remained stable at this low pH and steady state was achieved. When comparing the relative decreases in biooxidation rate and oxygen solubility, the drop of efficiency can be explained by aeration limitations and salting out effect.