Heavy metals in contaminated ore processing areas present a risk of contamination of waters and life. Therefore, the most mobile fractions of metals, which can be evaluated by chemical extraction, require a special research attention. Classical reports using batchwise extraction methods are debatable in terms of real metal availability because naturally occurring processes are always dynamic. Therefore, here we used dynamic extraction in a rotating coiled column in order to mimic natural conditions. We studied Cu, Pb, Zn, and Cd in soils and sand wastes from a tungsten–molybdenum plant. Soils had been buried under tailing dumps during 70 years. Exchangeable and acid-soluble fractions were separated using 0.05 M Ca(NO3)2 and 0.43 M CH3COOH, respectively. Results show that mobility, availability, and vertical transport of metals are surprisingly different. Specifically, there is nearly no mobile exchangeable Zn in wastes, whereas all studied soil horizons are characterized by elevated Zn concentrations, up to 0.6 g/kg. Cd behaves like Zn. The concentration and mobility of Cu vary with depth. The upper humus horizon contains up to 2.1 g/kg of exchangeable Cu. The behavior of Pb is quite particular: soils are nearly free from lead, though its total concentration in wastes may reach 3.9 g/kg. To the best of our knowledge, such unusual variations in the behavior of heavy metals have not been reported before.
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The work was supported by the Russian Science Foundation, project No. 16-13-10417 (dynamic extraction, exposure assessment of heavy metals) and the Russian Foundation for Basic Research, Projects No. 16-05-01041 (sampling and morphological description of collected samples) and No. 17-03-00207 (characterization and analysis of bulk samples). The equipment was purchased and maintained with the support of the Ministry of Education and Science of the Russian Federation (Program of Increasing Competitiveness of NUST “MISiS,” Projects No. К1-2014-026, No. К2-2016-070). The authors are indebted to Dr. Natalia Fedyunina (NUST “MISiS”) for her kind assistance in ICP-MS analysis of extractable fractions.
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