Geoecological Analysis of Threats of Using Phosphogypsum in Construction of Roads

Abstract

The problem of recycling and storage of phosphogypsum is relevant for many coun- tries of the world, as it is associated with environmental problems such as pollution of water bodies, soil and atmosphere. This study analyzes the possibility of using phosphogypsum for the construction of roads. The objective was a geoecological analysis of the danger of phos- phogypsum stockpiles and a study of the possibility of using phosphogypsum in road construction to solve the problem of its accumu- lation in the environment. The chemical composition of phosphogypsum samples of the Sumyhimprom and Rivneazot companies was studied using the method of X-ray diffractometry. The content of heavy metals (HM) was analyzed using atomic absorption spectros- copy. An extremely high level of chromium was determined, accounting for more than 20-33 Maximum Concentration Values (MCV). The content of cuprum in the phosphogypsum samples of Rivneazot was 2 MCVs. The contents of other heavy metals did not exceed the MCVs, the synergistic effect should be taken into account. Migration of heavy metals is one of the main problems associated with phosphogypsum stockpiles. The increased acidity of phosphogypsum promotes the formation of soluble HM compounds. Depending on the solubility of toxicants, they accumulate in the ecosystem or migrate, dissolve, and enter plants. The traditional methods of storing phosphogypsum, both from an environmental and economic points of view, are less acceptable than the methods of its recycling and reuse in various sectors of the national economy. The paper theoretically substantiates that the reuse of accumulated phosphogypsum and the implementation of new technological solutions in road construction would reduce the level of technogenic loading that phos- phogypsum imposes on the environment. Based on the analysis of the content of heavy metals and the development of concentration logarithmic diagrams, mobile forms of metals were studied and the harmful effect of metals leaching from phosphogypsum was considered. We determined the positions of toxic substances in the engineering road construction – environment. We recommended dividing hydroxides and hydroxocomplexes of heavy and toxic metals into three groups according to their solubility, having the ability to migrate in acidic, neutral and alkaline environments, respectively. Strict regulations are needed to protect soil cover in areas with acidic soils. We grouped soils on which it is not recommended to use engineered road structures with phosphohypsum due to increased migration of HMs into the ecosystem: sandy; soils rich in humus components, acidic soils (sod-podzolic) or in case of existing proba- bility of an increase in soil acidity (unorganized ingress of industrial waste, acid rain, etc.); acidic soils salinized with chlorides; soils containing ammonia; soils containing sulfates.