MINERAL COMPOSITION, GEOCHEMICAL FEATURES AND ENVIRONMENTAL IMPACT OF THE PHOSPHOGYPSUM DUMP (NOVOROZDILSKYI PLANT OF COMPLEX MINERAL FERTILIZERS, LVIV REGION)

Abstract

Phosphogypsum of Novorozdilsky Plant of Complex Mineral Fertilizers (Lviv region) is a typical artificial neogenic mineral formation, solid waste by-product generated when sulphuric acid reacts with the phosphorus-containing ores (apatite or phosphorite concentrates) during manufacturing of phosphoric acid. The raw materials for fertilizer production at the plant were sulphuric acid, which was obtained from the sulphur ores of Rozdilske SMCE “Sirka”, apatite concentrate from the Khibiny deposit (Kola Peninsula) and, to a lesser extent, phosphorite concentrate from sedimentary phosphorites. The plant has not been operating since 1995, but 4.5 million tons of phosphogypsum and also acidic mineralized water in the settling lake have accumulated on its territory since then. Gypsum (85–95 %) and bassanite (5–10 %) dominate in the mineral composition of phosphogypsum, there are also undissolved apatite (up to 2–3 %) and trace amounts of minerals that were originally in apatite concentrate (quartz, nepheline, pyroxene, aegirine, feldspar, biotite, etc.). The surface of the phosphogypsum heap is a phytophilous man-made substrate that is actively overgrown with woody vegetation. This is due to the filtration properties of phosphogypsum (they promote water accumulation and leaching of phytotoxic compounds from the zone of active water exchange) and the presence of a significant amount of phosphates. Currently, a dense aspen-sea buckthorn forest grows on the slopes of the dump. Acidic infiltrates are formed in the process of infiltration of precipitation through the thickness of the phosphogypsum dump, they are accumulated in the settling lake (Central/Acid Lake). In terms of chemical composition, it is sulphate-phosphate sodium-magnesium-calcium water with high fluorine content and mineralization of 2931.6 mg/dm3. The cessation of the use of the lake (as a settling tank for the plant's circulating waters) and the constant accumulation of infiltrate have led to a number of environmental problems. Acidic infiltrates flow into the mine canal and significantly impair the quality of water in it. Only due to the dilution of infiltrates with clean water of the drainage channel (with a flow rate of three to four times higher) before flowing into the transboundary Dniester River hydrochemical composition of water meets the normative values of salt composition and content of major pollutants. Deterioration of the water quality of the mine canal and, as a consequence, pollution of the Dniester in case of prolonged drought or reduction of the debit of the drainage canal are envisaged. To minimize the negative impact of the phosphogypsum dump on the environment, a project to build a cascade of filter dams from local carbonate materials has been proposed. Limestones have the ability to neutralize acidic waters; they are highly permeable and contain sulphur, which causes the binding of heavy metals to insoluble compounds. Due to the interaction of carbonates with acidic infiltrates, water-insoluble calcium phosphates and calcium fluoride (fluorite) are formed, which helps to purify water from F and P, and newly formed hydrates reduce the moisture content of the phosphogypsum mixture with flotation tails. The proposed approach will make it possible to control a constant source of pollution and restore the ecological balance disturbed by economic activities.