Speciation of metals in soils of steppe landscapes affected by mining (Southern Urals)

Abstract

Speciation of ore and accompanying elements (Cu, Zn, Fe, Ni, Pb, Cd, Cr, V, Ba, Sr) in steppe soils of the Transurals (vicinity of city of Sibay, Bashkortostan) was studied with sequential extraction method. Attention was given to change of elements’ speciation in area affected by mining (Cu-Zn deposit). The results are supplemented by chemical analysis of humic acids (isolated by alkaline extraction) and granulometric fractions. It was revealed that the soils of background areas are characterized by low mobility of studied elements and a relatively uniform distribution over soil profile. Residual fraction percentage (fraction’s share in element’s total content) is the highest. Percentage of exchangeable and carbonate fractions is insignificant (Sr and Ba are exceptions). Percentage of fraction of crystalline Fe hydroxides, reduceable and oxidizable fractions varies from shares of a percent to 15%. Cd stands out for a high percentage of oxidizable fraction (up to 30% of Cd total content) and relatively low percentage of residual fraction (up to 50%). Comparison of obtained results allows us to suggest that near objects of mining industry dust enriched with Cu, Zn, Cd, Pb and Sb comes to the surface. This leads to shard increase of Cu, Zn, Cd content in the upper layer of chernic horizon, change of these elements’ speciation and distribution among granulometric fractions. Increase of elements content is not only due to prevailing residual fraction; Cu, Zn, Cd of oxidizable fraction, reducible fraction and Fe hydroxides fraction significantly increase. Sharp increase of oxidizable fraction percentage (largely due to sulfides) is noted.