Comparative evaluation of iron leach from different sources of fly ash under atmospherically relevant conditions

Abstract

Environmental contextIron, a limiting nutrient of plankton in the ocean, is deposited to the sea from atmospheric aerosols. In particular, atmospheric acidic conditions promote dissolution of iron from fly ash, a by-product of coal-fired power plants. Here, we report that the iron leached from fly ash depends on its source region, and that the type of combustion process may influence the iron species mobilized. AbstractFly ash, an iron-containing by-product of coal-fired power plants, has been observed in atmospheric aerosol plumes. Under the acidic atmospheric conditions resulting from the uptake of atmospheric gases, iron leached from fly ash can impact global biogeochemical cycles. However, the fly ash source region, as well as its generating power plant, plays an important role in the amount, speciation and lability of iron. Yet no comparative studies have been made on iron leached from fly ash from different sources. This study reports the iron mobilisation by proton-promoted dissolution from well-characterised fly ash samples from three distinctive locations: the USA Midwest, north-east India and Europe. In addition, pH dependency was also investigated. Proton-promoted dissolution showed a variability between source regions with a relative iron leach in the order USA Midwestern>north-east Indian>European ash. In addition, the initial rate of iron leach suggests that source region is indeed a determining factor in the iron leaching capacity of fly ash, because dissolution from Midwestern fly ash is also faster than both European and Indian ash. Finally, the combustion process of fly ash proved to be significant for the iron speciation, given that well-combusted fly ash samples leached mostly Fe3+ rather than bioavailable Fe2+. The role of fly ash should therefore be taken into account in order to better understand the effects of combustion particles in atmospheric iron deposition.