The soil assessment was carried out in the technogenically-affected area of Irkutsk Oblast with the geochemical approach as a key geoecological method using physical and chemical techniques of analysis and ecodiagnostics. Diagnostic signs of the disturbed natural properties of the soil were revealed up to a depth of 40 cm in the profile based on macro- and micromorphometric parameters. The content of heavy metals (HM) – Pb, Zn, Hg, and Cu with an excess of standards was determined, and empirical HM – pH correlations were obtained by statistical clustering of the data array. The contributions of additional factors affecting the chemical element distribution in the soil layer were investigated. Significant soil contamination with sulfates and the possibility of implementing the ion-exchange of HM andfor element immobilization were revealed. It was shown that reactions with sulfates and the influence of pH, HM exchange processes involving mobile K and P can determine the nature of the described chemical element distribution in the multi-factor-contaminated technogenic soil. However, the effectiveness of such types of interaction is different for each metal and also depends on the quantitative ratio of substances and soil characteristics, even under a minor change in pH. Two-parameter correlations of HM distribution in sulfate-contaminated soils confirmed the different degrees of involvement of chemical elements in these types of interactions. The results obtained and the identified factors are of applied significance and can be used as the basis for geoecological differentiation of the contaminated soil, as well as for determining local geochemical fields in the technogenesis zone. Areas of advanced research are related to three-dimensional modeling for a more complete study of the cause-and-effect relationships of geochemical parameters.
Levels of contamination of three mining industrial zones in Irkutsk Oblast and Zabaykalsky Krai were revealed by means of geoecological and geochemical monitoring. Bulk contents and mobile forms of As in soils, stubs, bricks, and dumps of the mining and processing industry were defined. This allowed revealing features of chemical composition of technogenic substrates for the purpose of a choice of a way of their neutralization. The possibility of chemical immobilization of mobile ionic forms of As in natural and man-made objects by treatment with alkaline reagents was studied. X-ray diffraction (XRD) analysis revealed pharmacolite CaHAsO 4 ·2H 2 O, calcium arsenate Ca 3 (AsO 4 ) 2 , and segnititePb(Fe 3+ ) 3 AsO 4 (AsO 3 OH)(OH) 6 that are formed in the obtained solid insoluble precipitates. Formation of new solid insoluble compounds indicates the chemical binding (immobilization) of arsenic-containing compounds and the irreversibility of the process. This allows us to offer an effective way of fixing toxic agents to reduce migration in the environment by stabilizing immobilized forms. Experiments with the use of lignin sludge ash (accumulated waste of the closed Baikal pulp and paper mill) for the neutralization of arsenic-containing waste of mining and metallurgical industries were carried out. Application of modified coal sorbing agents for the sorption of residual mobile forms of As (after treating with an alkaline reagent) allows achieving a decrease in its concentrations to the TLV standard for a hazardous substance. NoritRO 3520 is the most effective sorbing agent. The results are of high applied importance for the implementation of the method of chemical immobilization of mobile ion forms of As in technogenesiszones.
The purpose of this study was to obtain diagnostic features and criteria for the distribution of heavy metals in technogenically altered soils in the area of industrial facilities, depending on their altered geochemical properties, which make it possible to fix chemical elements in landscapes (the formation of geochemical barriers). On the basis of the geoecological assessment, disturbance of the soil buffer properties, which is reflected in the ionic composition change, alkalization, pH increase, and sulfate-chloride salinization have been revealed. This forms the heavy metals alkaline barrier. For example, in case of Cu, Pb, Zn, and N, it contributes to their accumulation and subsequent concentration in the soil layer due to the exchange interactions between chemical elements and Na + , K + , Ca 2+ cations. Soil saturation with sulphates also increases the probability of metals demobilization in the soil layer. It has been shown that intra-sectional soil migration of oil products (one of the most common pollutants of industrial areas) and chemical elements occurs at a depth of 30-50 cm, where the oil products based on a clay sorption layer form a technogenic barrier. The direct correlation between the oil content in the soil and the amount of toxic sulphate and chloride salts was found. The set of identified factors forms technogenic geochemical barriers in the industrial production area, on which pollutants and chemical elements, including heavy metals, are demobilized. The revealed effects are the rationale for creating artificial geochemical barriers on the migration path of both pollutants and valuable components with the aim of their subsequent extraction from the soil when developing an appropriate extraction method.
