Chemical assessment of Icelandic geothermal fluids for direct applications

Abstract

This research deals with the chemical assessment of geothermal fluids for direct applications from low-temperature geothermal fields in Iceland. In addition, geothermal brine, geothermally heated groundwater, cold spring water, seawater or a mixture of two of these different fluids were evaluated for direct use or for use via a heat exchanger for space heating, balneotherapy, agriculture, aquaculture, and industrial applications. In order to fulfil the objectives, all the water samples were analysed and compared with the standards and guidelines for physicochemical parameters as well as for trace elements. The results revealed that, in some cases, there is the possibility of scaling and corrosion from low-temperature geothermal waters, brine and heated groundwater. The risk of amorphous silica scaling was observed only for brine water and the risk of magnesium silicate scaling was observed both for low-temperature geothermal water and heated groundwater.

No scaling is likely to occur due to the mixing of brine water from Svartsengi and cold groundwater from Lágar at 40°C and 15°C, which are the ideal temperatures for balneotherapy and agriculture. Geothermal brine is effective for balneotherapeutic applications. A mixture of 37% brine and 63% cold groundwater at a temperature of 40°C also appears to be effective for this purpose as is sea water if it is heated to a temperature of 40°C. Some geothermal waters are permissible for agricultural application with respect to EC, TDS, sodium percent, SAR, boron toxicity and trace elements. Brine and sea water should not be used for this purpose. Dissolved H2S gas in geothermal fluids was identified as a major limiting factor for aquaculture applications, even after mixing with 90% cold groundwater. Geothermal fluids that contain H2S are not suitable for food processing industries because of their taste and odour and sometimes because of high concentrations of trace elements such as fluoride and boron. Cold spring waters are suitable for this purpose.