Email: ftagt@uaf.edu

The purpose of proposed study is to understand the predominant factors that control the mobility and potential bioavailability of toxic elements during the utilizing of hydrothermal resources for electricity production. Hydrothermal systems are often enriched in the toxic elements such as As, Sb and B. Preliminary results from the Dachny area in Kamchatka Russia - a high capacity hydrothermal field - show that fluid extracted from the depth of 800-2,000 m used for the electricity production contains concentration of As, Sb and B in excess of drinking water standards. Water from natural hot springs in the vicinity show concentrations of these elements ~3 orders of magnitude lower than the deep well waters (2 ppm compared to 0.5 ppb as average numbers for the well fluid and hot spring water). In its current state of operation the Dachny geothermal fields retain the majority of spent hydrothermal fluids in settling ponds, ultimately these fluids are released into local groundwater and surface water system. The potential for downstream transport of these metals has raised concerns about pollution of local water resources. The objective of this study is (1) determine the extent of trace element transport in surface waters and sediments surrounding the Dachny area to asses which if any elements are highly mobile in the surface environment, (2) provide a detailed analysis of the speciation of these elements in the near surface aquatic and sediment environment to correlate chemical form with transport characteristics, (3) use laboratory based experimental work coupled to geochemical simulations to develop a model for predicting trace element speciation in this and similar systems.

Mutnovsky volcano

Geothermal plant at Dachny area

Based on the current preliminary results and previous studies of metal transport and speciation in aquatic systems it is hypothesized that the partitioning (sorption) of As, Sb and B to high surface area secondary hydroxide and clay minerals in the sediments and soils is the key process removing these elements from the water and hence controlling aqueous phase concentrations. The extent of partitioning is likely a strong function of the pH (and buffering capacity), redox state and temperature among other physicochemical factors. Therefore, a major aim of my project is to identify the key pathways controlling the aqueous concentrations in order to develop a (semi-)quantitative model for predicting trace element speciation and transport. At the present state of knowledge, mobility and transport of antimony and the extent of its adsorption onto mineral surfaces are not well understood, as well as the stability of adsorbed As, Sb and B ions with the changing physicochemical parameters. The change in pH, redox potential and ionic strength (e.g. during sediment accumulation and transport to marine environment), as well as presence of competing ions can potentially cause mobilization of adsorbed species. There is a need for a detailed understanding of the physicochemical factors that control the fate and transport of As, Sb and B after deep well hydrothermal fluid release at the surface. This work will contribute to better understanding of toxic trace (semi-)metal mobility and transport in the system of interest as well as in the similar hydrothermal systems in different geographic locations. The practical use of the results of the work will be the assessment of environmental impact of operating a geothermal power plant, and recommendations for options of the fluid treatment prior to its release.

Kotyol stream with hydrothermal features

Ghydrothermal field at Dachny area