FEATURES OF CHEMICAL ELEMENT BEHAVIOR IN THE WATER–ROCK SYSTEM OF THE RUBBLE STONE QUARRY IN PITKÄRANTA DISTRICT (KARELIA)

Abstract

The relevance. The study of the chemical element distribution in the water–rock system in areas of active development of mineral deposits is relevant because of the potential impact of these processes on environmental conditions. It changes the geochemical conditions of the natural environment. It is particularly important for the area under study, which is a part of the catchment of the largest natural fresh water reservoir in Europe – Lake Ladoga. The research aimed to study the aqueous removal of chemical elements from granitoid rocks opened-up by the quarry and the behavior of these elements in natural waters and bottom sediments of the region. The study objects are the natural waters and bottom sediments of the rubble stone quarry area (Pitkäranta ore district, Karelia). The authors traced the changes in the chemical composition of natural waters and associated bottom sediments as the water moves from its discharge from the quarry to inflow into the river network. Methods. The analysis of the chemical composition of natural waters and bottom sediments was carried out by standard methods: potentiometry, titrimetry, ICP-AES, ICP-MS. The study of the mineral composition of the quarry rocks was carried out using LA-ICP-MS. The chemical composition of the rocks was studied by XRF, ICP-MS, and ICP-AES. Thermodynamic modeling of metal speciation in natural waters and secondary mineral precipitation was conducted by the HydroGeo software package. The model was verified based on the analysis of the chemical composition of bottom sediments. Results. In the studied water bodies, an excess of the maximum permissible concentration of Fe, Mn, Cu, Zn, Mo, V at some points was found. The value of total dissolved solids and the content of the main components and Sr, U, V, Mo, Zn, Cd decrease with the increase of distance from the rubble stone quarry. The concentration of Fe increases due to the growth in the content of organic matter in the water. In bottom sediments, the maximum concentrations of many elements (Fe, Mn, Co, Cu, Zn, Cs, Ce, La, Y) is detected at the point of water discharge from the quarry. The maximum U content is observed slightly downstream from the mentioned point. It is consistent with the data on the composition of bottom sediments and modeling data, which indicate the possibility of uraninite precipitation from an aqueous solution in the point of water discharge from the quarry and the stream source originating in the discharge point. The role of organic matter is essential for Fe accumulation in water due to the formation of a stable hydroxo-fulvate complex of Fe and rare earth elements due to the formation of complexes with humic acids. Analysis of the metal distribution and speciation and secondary mineral precipitation allowed us to conclude that the exploitation of the rubble stone quarry affects the redistribution of chemical elements in the study area significantly.

Keywords

• water–rock system
• leaching
• metal speciation
• mineral precipitation
• fulvic acids
• humic acids
• dissolved organic matter
• thermodynamic calculation
• uranium
• complexation