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Buffering from Secondary Minerals as a migration limiting factor in lead polluted soils at historical smelting sites
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posted on 2023-06-08, 09:43 authored by Clare Gee, Michael H Ramsey, Iain ThorntonExamination of calcareous slags from several historical smelting sites has indicated that the specific soil environment, in particular the soil pH, may have a very significant effect on the rate of weathering and metal release. A series of acid titration experiments were used to investigate whether the weathering of the calcareous slags could be increasing the buffering effect of the soils through accumulating CaCO3 in the slag-rich horizons. Such a buffering mechanism would maintain high pH levels and so limit the migration of Pb through the soil profile. Three sites were chosen; one with high levels of Ca in the soil, one with relatively low Ca levels and one with intermediate Ca levels. Analysis of metal concentrations was determined using ICP-AES. The results support the hypothesis that, while the soil pH remains between 8 and 5, the CaCO3 provides an effective buffer against the mobilisation of Pb. Between soil pH 5 and 4 it is suggested that both CaCO3 and PbCO3 participate in the buffering reaction, which slows down with a further drop in pH. However, this reaction ultimately releases Pb into the soil solution, although at a much slower rate than would be the case in an unbuffered soil. An important implication of these findings is that migration rates of metals in soils cannot be assumed to be constant over time, if such buffering mechanisms are operational.
History
Publication status
- Published
Journal
Applied GeochemistryISSN
0883-2927External DOI
Issue
9-10Volume
16Page range
1193-1199Pages
7.0Department affiliated with
- Evolution, Behaviour and Environment Publications
Full text available
- No
Peer reviewed?
- Yes
Legacy Posted Date
2012-02-06Usage metrics
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