The Level of Snow Cover Contamination with Fluoride Compounds in the Emission Zone of a Primary Aluminum Smelter

Abstract

Background: Fluoride compounds are one of the main components of industrial emissions from aluminum production. Natural deposition of fluorides with precipitation leads to their accumulation in soil and surface waters. In winter, the snow cover enables an assessment of industrial pollution with fluoride compounds. The objective of our work was to study fluoride levels in the snow cover in the emission zone of the primary aluminum smelter in the town of Shelekhov, Irkutsk Region. Materials and methods: Snow sampling was performed at nine points at different distances from the plant and fluoride concentrations were then measured in the aqueous fraction and solid precipitate by a potentiometric method with ion-selective electrode. Results: The aqueous fraction was a solution of hydrofluoride and sodium fluoride. Insoluble fluorides were found as a mixture of aluminum fluoride, calcium fluoride, cryolite, and aluminum tetrafluoride. We established that the soluble fraction exceeded 90 % in all snow samples. Within the urban agglomeration, snow pollution was distributed differentially. The total fluoride level in residential areas of Shelekhov was 14 to 21 times higher than that at the reference point. At the same time, in the area of a suburban rural settlement located downwind of the smelter, it reached a 33-fold excess. Conclusion: The main source of environmental pollution in the Shelekhovsky district of the Irkutsk Region is the processing of cryolite and fluoride salts in the primary aluminum production technological cycle generating fluorine-containing gaseous emissions and solid wastes. Concentrations of industrial pollutants in snow correlated with the distance from the source of emissions and the prevailing wind directions. Contribution of a heat power engineering enterprise to the industrial pollution of the local environment with fluorides was also revealed.