Technogenic Influence of the Composition of Ash Waste of the Zmiiv Power Plant on the Pedosphere

Abstract

Purpose. The aim of the study is to analyze the geochemical composition of ash and slag waste at the Zmiiv  Thermal Power Plant (TPP) and to identify the features of migration of heavy metals (HM) from the place of storage of ash and slag waste into the ecosystem. To achieve this goal, the following tasks were solved: geochemical analysis of ash and slag waste at Zmiiv TPP; study of the reliability of HM migration into the soil in the places of ash and slag waste storage.

Methods. The content of heavy metals in ash, slag and soil were investigated using atomic absorption analysis (AAA) on a spectrophotometer S-115. X-ray diffraction analysis was used to determine the solid inorganic part of ash and slag.

Results.  Ash and slag of Zmiiv TPP contain Cu, Cr, As, Cd, Ni, Pb in quantities that are several times higher than the maximum permissible concentration (MPC). For ash and slag waste, the total pollution index is Zc = 43, which corresponds to a high level. That is, this artificially created horizon is dangerous. HM migrate into groundwater and into the soil near the ash dump due to the infiltration of atmospheric precipitation, emissions from water pipelines, filtration of water through the base of the ash dump of the Zmiiv TPP. To determine soil contamination near the ash dump, soil analyzes were performed at a distance of 0 ... 100 meters. At a distance of up to 100 meters from the dump, there is an excess of MPC in the soil for the content of Ni, Cu, As, Cr. At a distance of up to 100 meters from the dump, an excess of the MPC in the content of Ni, Cu, As, Cr is observed. Concentration factor exceeds unity for Cr, As, Cu, Cd, Ni. The content of Pb and Zn reaches background values only at a distance of more than 100 meters. The calculation of the total soil pollution indicator allows us to classify these soils as moderately hazardous and permissible. However, there are several significant disadvantages of the Zc indicator. First of all, it does not take into account the differences in the potential hazard of chemical elements, and, most importantly, the synergistic effects of polymetallic pollution. The coefficient of the synergistic effect of heavy metals is 26.64 (in the soil of the ash dump), then it decreases, but even at a distance of 100 meters it is 11.23, that is, at a distance of 0 ... 100 m from the ash dumps, the condition of the coefficient of synergistic effect is less than one. It has been established that Cu, Ni, Zn and Cr are characterized by low mobility in the soil near the ash dump, therefore they accumulate in the ecosystem near the ash dump, which is explained by the neutral and slightly alkaline soil pH values (pH = 8.0 ... 8.5). The ratio of mineral phases to glass is unstable; however, it should be noted that aluminosilicates, calcium silicates and glass predominate in ash and slag. Сompounds with HM are confined mainly to amorphous clay aggregates and sooty-carbon formations of ash, to a lesser extent to slag glass and even less to grains of quartz sand.

Conclusions. Since the ash contains such fractions that can be easily carried by wind, it should be assumed that the HM entry into the ecosystem is also by air, which also contributes to air pollution. The solution to the problem of ash and slag waste disposal should be found in the production of building materials, in road construction, but it is necessary to study the composition of ash and slag and the probability of HM migration depending on the conditions of use.