Physicochemical Features of Soil-Forming Processes in Conditions of Technogenic Load

Abstract

The investigations were made in the zone of influence of the Irkutsk UC RUSAL aluminum smelter. Soil cover on this territory is represented by gray medium and light loamy soils, with a small thickness of the humus profile. The stoichiometric formulas of solid mineral solutions, humic substances and components of soil solutions formed under the influence of technogenic load are calculated by thermodynamic modeling methods using the Selector software package. The readily soluble forms of existence of the components of gas and dust emissions and solid phases accumulating in soils were determined. The most common condensed components are fluorapatite and fluorite (CaF2 and A1F3). Complex ions (Al(OH)2F0, A1F2+ and A1F4–) are dominant in the aqueous solution, a high concentration of which is due to the presence of readily soluble compounds (NaF, KF and NH4F) in emissions. In terms of physicochemical models it was determined that 70–90% of the total amount of F and Na arriving at the day surface can be fixed in soils exposed to the Irkutsk aluminum smelter. Therefore, in spite of high solubility, these pollutants are sorbed by soil. Technogenic transformation is accompanied by a slight increase in pH (from 5.6 to 5.75), an increase of the amount of mixed-layer aluminosilicates: smectites and chlorites (from 43 to 51%), and by a decrease in muscovite content (from 14 to 12%) and humus (from 3.42 to 3.32%). Simulation modeling was used to assess changes in the phase-component composition of soils under the influence of gas and dust emissions from aluminum production. It was found that in gray soils experiencing the anthropogenic impact, the composition of the soil mineral matrix as well as of organic matter changes. A dominant main role is played by the process of acid hydrolysis of alumosilicates whose agents are represented by decomposition products of amorphized fluorine-containing pollutants. The most important feature of this process is a change in composition of clay minerals and humus. An increase in fluorine and chlorine contents in soils leads to an increase of the amount of methane in the gas phase, rather than increasing solubility of organic substances.