Hydrogeochemistry and aragonite scaling in the Sijarinska spa (Serbia)

Abstract

This paper presents the results of the inorganic carbon species hydrogeochemistry in order to explain aragonite precipitation in the mineral geothermal waters of Sijarinska spa, where the deep B-4 borehole represents the most important geothermal water discharge. Hydrogeochemistry of ions in B-4 water showed domination of Na-HCO₃-type. The detailed hydrogeochemical analysis of the major carbon species gave reasons for CaCO₃ precipitation. The main reason is CO₂ partial pressure reduction, which led to the increase of the pH value from the aquifer value of 5.88–6.39 to 7.1–7.8, measured in surface discharge. These changes led to the increase of the concentration of ${\text{CO}}_{3}^{2 - }$ ions which with Ca²⁺ ions form poorly soluble aragonite. The Ryznar’s index of solubility values, 4.2-4.7, indicates that the examined water has the prominent tendency to carbonate scaling. This tendency was confirmed by the mineralogical analysis of precipitated solids, which are dominated by aragonite (>95 %) accompanied by small amounts of calcite (<5 %) with minor amount vaterite. Monitoring saturation index values for the examining period (1995–2015) exhibited that B-4 geothermal water showed constant tendency toward CaCO₃ deposit formation.