Areas in the vicinity of metal smelters are inevitably exposed to metal(loid)-bearing particulates, which are emitted and dispersed in the environmental compartments. Especially surrounding soils represent an important sink for the most of these anthropogenic emissions.
1. Dust emitted from the copper smelter
The main objective of our study is to identify the fate of smelter dusts when deposited in soils as well as to clarify subsequent dynamics of smelter-related contaminants in the soil systems, which can interact with water and biota. We use a long-term in situ experimental approach, where polyamide bags filled with smelter dusts are placed for incubation into different depths of soil profiles. Our current 4-year in situ experiment has been initiated in October 2013 in four contrasting soil types and under different vegetation covers using the methodology described by Ettler et al. (2012). We have compared the weathering rates of smelter dusts in the following soils: neutral-to-alkaline Chernozem developed on loess (grass cover), neutral-to-slightly acidic Cambisol (grass cover), and acidic Cambisols developed under the beech and spruce forests. Our study materials are (i) arsenic rich fly ash (composed mostly of arsenolite, As2O3, galena, PbS and gypsum, CaSO4·2H2O) and (ii) copper slag (enriched in Cu, Zn and Pb). We collect experimental bags each 6 months and soil columns are vertically sampled (each 5 cm of depth) using physical rings and when possible, soil pore water is collected using Rhizon samplers. We perform mineralogical analysis on smelter dusts (to identify changes in phase composition), supplemented with bulk chemistry of dusts and soil samples coupled to As speciation analysis in soil pore waters and extracts.
2. Soil sampling after the smelter dust incubation using physical rings
Despite the fact that our field experiment is just in the middle and data collection is still in progress, we find that fly ash particles are highly reactive in soil systems and their dissolution is increasing over time. Arsenic leaching associated with the highest fly ash dissolution was the most significant in soil developed under the beech forest mainly due to specific seepage conditions leading to more rapid flush regime (higher moisture than for other soil types). Observation under the scanning electron microscopy (SEM) indicated that the fly ash incubated in soil under the beech was the most weathered with etched arsenolite surfaces and secondary formation of a complex metal-bearing arsenate phase.
Field experimental studies are always more difficult than laboratory investigations, because a number of parameters cannot be fully controlled. However, they are more suitable for understanding complex processes in real-life scenarios. We are looking forward to the next sampling campaign in October 2016 J
PhD candidate at Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University in Prague, Czech Republic
Ettler, V., Mihaljevič, M., Šebek, O., Grygar, T., Klementová, M., 2012. Experimental in situ transformation of Pb smelter fly ash in acidic soils. Environ. Sci. Technol. 46, 10539-10548.