Arsenic speciation and transport associated with the release of spent geothermal fluids in Mutnovsky field (Kamchatka, Russia)

作者：Ilgen Anastasia G^*; Rychagov Sergey N; Trainor Thomas P

来源：Chemical Geology, 2011, 288(3-4): 115-132.

DOI：10.1016/j.chemgeo.2411.07.010

• Geothermal arsenic
• Speciation
• Adsorption
• Oxidation
• Transport
• Mutnovsky power plant

The use of geothermal fluids for the production of electricity poses a risk of contaminating surface waters when spent fluids are discharged into (near) surface environments. Arsenic (As) in particular is a common component in geothermal fluids and leads to a degradation of water quality when present in mobile and bioavailable forms. We have examined changes in arsenic speciation caused by quick transition from high temperature reducing conditions to surface conditions, retention mechanisms, and the extent of transport associated with the release of spent geothermal fluids at the Dachny geothermal fields (Mutnovsky geothermal region), Kamchatka, Russia - a high temperature field used for electricity production. In the spent fluids, the arsenic concentration reaches 9 ppm, while in natural hot springs expressed in the vicinity of the field, the As concentration is typically below 10 ppb. The aqueous phase arsenic speciation was determined using Liquid Chromatography (LC) coupled to an Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The arsenic speciation in the bottom sediments (<65 mu m fraction) of the local surface waters was analyzed using X-ray Absorption Spectroscopy (XAS). Arsenic in the geothermal source fluids is predominantly found as As(III), while a mixture of As(III)/As(V) is found in the water and sediment of the Falshivaia River downstream from the power plant. The extent of elevated arsenic concentrations in water is limited by adsorption to the bottom sediment and dilution, as determined using CI(-) from the deep well fluids as a tracer. Analysis of the Extended X-ray Absorption Fine Structure (EXAFS) spectra shows that sediment phase arsenic is associated with both Al- and Fe-rich phases with a bi-dentate corner sharing local geometry. The geothermal waste fluids released in the surface water create a localized area of arsenic contamination. The extent of transport of dissolved As is limited to similar to 7 km downstream from the source, while As associated with bottom sediment travels similar to 3 km farther.

• 出版日期2011-9-25