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MIGRATION ABILITY AND FORMS OF ELUATED METAL POLLUTANTS FROM SOIL AND DUMPS (PB - ZN SMELTER SITE)

E. N., BENDEREV, A., ATANASSOVA, R. Pentcheva

Abstract

Experimental modeling investigations in heavy metal polluted site of KCM (Pb-Zn smelter) are carried out in two aspects: 1) Determination of the migration ability of the metal (+As) pollutants during water-soil and water-clinker interactions effecting of water and MgCl2 lixiviation and 2) Establishment of the chemical speciation of the pollutants in the eluated liquid phase and of the mineral phases, controlling the water migration, in juxtaposition with the data for ground and surface polluted waters in the site. The concentrations of Pb, Zn, Cu, Cd, Cr, Ni, Co and Mn in soils are determined in exchangeable (MgCl2 extraction) and water soluble fraction (water leaching). Among all elements the highest part of the total Cd content (up to 50\%) is presented in exchangeable form – thus Cd is found to be the most mobile pollutant. In minor extent this is reported to Zn, Cu and Mn. In contrast in water soluble fraction only up to 1\% of the total and 2,7\% of the exchangeable Cd is comprised, the other metals also in relatively low concentrations. A good correlation is proved between total exchangeable and water soluble Cd, Pb and Zn. Original results are obtained by the speciation researches accomplished, elucidating the active metal mobile forms, endangering the site studied. The eluation from clinker material (old and new dump) gives very different data: exceptional active extraction of metals and As (by pH <5,7) especially in the case of the chemical active material in the new dump (pH=3,7). The composed 3D presentation of the metal distribution in the eluated phase from clinker is confirming the metal remobilization activity in result of the water interaction with metallurgical waste. In soil eluates PbCO3 form is prevailing in the vicinity of the smelter – similar results to the species distribution in the most polluted ground waters. In the clinker PbSO4>Pb2+>Pb(SO4)2 2-. The sulphate species are absent in the recent waste material, not yet metamorphized. The carbonate species of Zn are prevailing in soil eluates, the sulphates and the metal forms - in clinker extracts. The species differentiation of Cd in soils eluates, like in waters, is the most expressed: CdCO3>Cd2+>CdHCO3>CdSO4, and in clinker extracts CdSO4≈Cd2+>Cd(SO4)2 2-. Cu(OH)2>CuCO3 is predominating in soils eluates and surface waters, clinker lixiviation gives the result: CuSO4>Cu>CuHCO3. In soils extracts and in waters the HAsO4 2- form is the most important. The observation of the data obtained, concerning the mineral phases, controlling the pollutants migration shows, that for Cd and As a significant undersaturation exists, the similar is the conclusion concerning Pb and Cu, suggesting supplement leaching possibilities and metal remobilization. Only the Zn mineral phases manifest saturation indexes near the equilibrium. The undersaturation is most characteristic for dumps eluates. The results obtained are elucidating the evidence for a secondary contamination of the environment in consequence of the remobilization of accumulated and metamorphized mineral and chemical forms in the solid phase heavy metals + As. The investigations are financed by the Bulgarian budget of the NATO Science for Peace Program Project NATO SfP 973 739 “WATMETAPOL”.

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