Conditions and processes of precipitation of iron compounds upon discharge of high-mineralized artesian water from artesian borehole R-30, Staro Oryahovo, Bulgaria
2022
Benderev, Aleksey | Trayanova, Mila | Tarassov, Mihail | Tarassova, Eugenia
The artesian borehole R-30–Staro Oryahovo with total depth of 1740 m gives waters of chlorine–sodium type with a mineralization of 31 g/L from formations of Paleogene age. These waters contain high concentrations of iron and because of this, intense precipitation of iron compounds takes place at and around the wellhead. To clarify the ongoing processes, samples of precipitates and overflow water were taken. It was shown that the predominant form of iron in the water before reaching the surface is Fe²⁺–85–90% and FeCl⁺–4–11%. The calculated saturation index for a number of Fe²⁺-containing minerals showed that hydroxides and sulfates of Fe²⁺ are the possible candidates for sources of iron in the water. The reductive dissolution of wide spread Fe³⁺-containing minerals (hematite, goethite) was assumed as a possible alternative process releasing Fe²⁺ into water. At the surface, due to the contacts with the atmospheric oxygen, the environment is sharply changed to oxidizing one thus forming a geochemical barrier and causing mass precipitation of Fe³⁺ oxides. Simultaneous Fe²⁺ oxidation, hydrolysis of Fe³⁺ and co-precipitation with silica and other components are assumed as the major processes causing the formation of low-crystalline Si-containing ferrihydrite or ferrihydrite-like phase. After formation, the precipitated gels due to the processes of aging and continued interaction with the outflowing water have suffered the further change including the formation of goethite. It was shown that due to the intensive precipitation processes, the iron migration to the surface is limited to a very small area and does not affect adjacent agricultural territories with Fe.
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