Article pubs.acs.org/est
Experimental in Situ Transformation of Pb Smelter Fly Ash in Acidic Soils Vojtěch Ettler,†,* Martin Mihaljevič,† Ondřej Šebek,‡ Tomás ̌ Matys Grygar,§ and Mariana Klementov᧠†
Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University in Prague, Faculty of Science, Albertov 6, 128 43 Praha 2, Czech Republic ‡ Laboratories of the Geological Institutes, Charles University in Prague, Faculty of Science, Albertov 6, 128 43, Praha 2, Czech Republic § Institute of Inorganic Chemistry of the AS CR, v.v.i., 250 68 Husinec-Ř ež, Czech Republic S Supporting Information *
ABSTRACT: Soils in the vicinity of nonferrous metal smelters are often highly polluted by inorganic contaminants released from particulate emissions. We used a technique with double polyamide experimental bags (1-μm mesh) to study the in situ transformation of fly ash (FA) from a secondary Pb smelter in acidic soil profiles. Between 62 and 66% of the FA dissolved after one year’s exposure in the soils, leading to complete dissolution of primary caracolite (Na3Pb2(SO4)3Cl) and KPb2Cl5, with formation of secondary anglesite (PbSO4), minor PbSO3, and trace carbonates. Release of Pb was pHdependent, whereas not for Cd and Zn. Significant amounts of metals (mainly Cd and Zn) partitioned into labile soil fractions. The field data agreed with laboratory pH-static leaching tests performed on FA, which was washed before the experiment to remove soluble salts. This indicates that appropriate laboratory leaching can accurately predict FA behavior in real-life scenarios (e.g., exposure in soil).
■
points of view.15−19 Recently, Birkefeld et al. 20 proposed a new in situ method for analyzing mineral particle reactions in soils, where the particles were fixed to a polymer support with a thin film of epoxy resin. However, this technique is only suitable for particles larger than 20 μm and the fly ash from smelters generally contain particles smaller than 5 μm.5 For this reason, the bag technique used by numerous authors for in situ weathering studies (e.g., refs 15 and 16), with the application of testing bags of appropriate mesh size, is definitely more suitable for such types of solid materials. However, some disadvantages have been mentioned in the literature,18 related to limited contact with the soil matrix, and the disturbing of the soil structure during application of the sample. After the decline of primary Pb smelting activities in the past decades, secondary Pb smelters extracting metals from recycled acid-lead batteries have become a potential pollution source in Europe.4,8 Our previous studies of Pb smelter impacted soils using a combination of chemical, mineralogical, and isotopic approaches indicated that secondary Pb smelter contamination is more mobile in soil systems than that related to ore smelting/processing.1,6 Investigation of secondary Pb smelter fly ashes (air-pollution-control residues) demonstrated that
INTRODUCTION Nonferrous metal smelting has long been recognized as one of the most important local sources of metallic pollution of both soils and vegetation. Extremely high concentrations of metals (e.g., Cd, Pb, Zn) have been found in forest and agricultural soils in the vicinity of Pb smelters.1−3 At a Pb smelter-affected site in the Czech Republic, Ettler et al. 1 found up to 3.5% Pb in the organic horizons of forest soils. Such high contaminant concentrations in these soils are related to the long-term deposition of smelter fly ash particles. Although flue-gas cleaning technology in the smelters is generally highly efficient (>99.5%),4,5 periods of filtering inefficiency can occur during e.g. furnace turn-on or toward the end of the lifetime of the fabric filters, which are mainly used for dust abatement in the baghouse facilities (Z. Kunický, technical director of the Přı ́bram Pb smelter, personal communication). It has also been demonstrated that the metal contamination originating from smelters can migrate vertically in soil profiles, often accelerated by bioturbation, leading to the possible risk of groundwater contamination.1,2,6,7 Another issue is related to the bioavailability/bioaccessibility of smelter-derived metals from contaminated soils for plants,8−10 contaminated watersheds for fish,11 and from soils and particulate matter for humans.12,13 Soils represent an important sink for metals emitted into the environment by anthropogenic activities.14 Numerous in situ studies have indicated that solid materials can rapidly evolve when deposited in soils, from the chemical and mineralogical © 2012 American Chemical Society
Received: Revised: Accepted: Published: 10539
April 13, 2012 August 9, 2012 August 31, 2012 August 31, 2012 dx.doi.org/10.1021/es301474v | Environ. Sci. Technol. 2012, 46, 10539−10548
nd nd 27.3 52.7 nd 58 66.5
nd 10YR 2/1 7.5YR 3/4 7.5YR 4/6
10YR 3/2 7.5YR 4/2 7.5YR 4/6
nd 26.9 28.8
nd nd 50.8 43.4
nd nd 40.3 25
31.8
silt
nd 15.1 4.7
nd nd 21.9 3.9
nd nd 6.1 3.2
2.7
clay
5.61 4.38 4.6
3.58 3.55 3.46 3.98
3.50 3.40 3.56 4.25
4.2
std units
pH
28.58 9.82 6.26
23.14 22.1 12.3 8.1
27.81 14.41 9.46 4.271
98.5 34.2 21.8
74.7 32.1 20.2 9.4
38.3 23.8 16.3 11.9
26.2
%
cmol+ kg−1 1.71
BS
CEC
13.2 8.2 5.7
45 40.5 9.2 3.8
42.8 15.6 4.6 2.5
1.52
%
Corg
0.09 0.06 0.04
0.24 0.28 0.06 0.04
0.25 0.11 0.03 0.04
0.06
%
Stot
7.06 6.69 5.85
3.97 3.59 8.31 7.97
5.18 5.85 8.15 6.33
5.44
g kg−1
Feoxa
4.90 6.40 7.98
1.63 1.20 1.86 3.85
1.72 1.82 1.89 4.34
4.95
g kg−1
Aloxb
