Iron dissolution and speciation from combustion particles under environmentally relevant conditions

Abstract

Environmental context Iron-containing combustion particles are likely to contribute to environmental iron deposition, while atmospheric acidic processing of such particles can promote their dissolution. Here we report the surface-mediated dissolution of iron from ashes generated by biomass burning power plants and kilns. Examination of the dissolution process at several environmentally relevant pHs, suggests that pH has little impact on the fraction of bioavailable Fe(II) that dissolves into the aqueous phase, although Fe(III) is heavily pH dependent. Rationale Anthropogenic combustion particles, such as ash produced in power plants or kilns, are byproducts with limited use that accumulate in large deposits and become materials of environmental concern. While stored, these particles can be carried by winds into the atmosphere or into soil or near water bodies. Recent studies suggest that a fraction of metals present in the environment come from combustion particles. Methodology In this study, we carry out a comparative study of iron dissolution and speciation from two different combustion particles: bottom ash from a biomass-fired power plant (BA) and lime kiln dust (LKD). Samples were fully characterised and their iron leaching was investigated in aqueous suspensions under environmentally relevant acidic conditions. Iron analysis and speciation was carried out calorimetrically. Results For the combustion particles examined, the fraction of bioavailable Fe2+ is lower than Fe3+. The solubility of Fe3+ is highly dependent on pH, dropping significantly at pHs higher than 3. On the other hand, the solubility of Fe2+ from both BA and LKD was found to be relatively constant over the range of pH investigated. Discussion Iron availability from combustion particles with similar mineralogy is driven by the particle’s surface properties. While iron from LKD dissolves faster than that from BA, the initial rate of dissolution of iron remains statistically constant at pHs relevant for the atmospheric aerosol deliquescent layer, decreasing at pHs above 3. This work provides insight into the ability of combustion particles to provide iron micronutrients under different environmentally relevant acidic conditions.