Energy-dispersive x-ray fluorescence analysis of geothermal fluids, plant and soil samples from Olkaria, Eburru, Bogoria and Magadi areas

Abstract

Energy- dispersive X-ray fluorescence technique (EDXRF) utilizing experimentally determined fundamental parameters was employed for quantitative analysis of elements in various samples from geothermal areas in the Rift Valley~ Kenya. The procedure involves preparing thin-film and transparent specimens and analysing them using the energy-dispersive X-ray spectrometer with Cd-l09 as the excitation source. At Olkaria geothermal area~ the wide variety of samples analysed included water, steam condensates, soil and plant leaves from eight different wells. The heavy elements found in these samples were Mn, Fe, Cu, Zn, Pb, and Hg. In some few cases As was detected in the thermal fluids, in as high concentration as 0.5 mg/L. Other elements included Ti, Cr, Mo, Br, and Zr. The well thermal waters from five wells under exploration at Eburru geothermal field, sampled at different depths below the earth's surface show maximum concentrations (mg/L) of the trace elements as 4:Mn, 18:Fe, 10:Cu, 3.2:Zn, 10:Pb and 0.3:Mo.

Hotsprings from Bogoria and Magadi geothermal fields had a similar chemical composition of a few heavy metals Mn~ Fe, Cu, Zn, Pb and Ti existing in low concentrations, below 1 mg/L with exception of Fe in a few hotsprings. Lakes Magadi and Bogoria, being fed by these springs and other suspected underneath sources, are highly saline lakes. From the elemental data, the cause of environmental pollution resulting into poor vegetation and scarcity of animals at the environs of the developed Olkaria Geothermal Power Plant, producing about MWe, has been deduced as due to toxic and heavy trace elements. Other applications of the trace data in geothermal research such as deducing the nature of geological setting and cold/hot water mixing plus the general geochemistry of the thermal fluids in above mentioned areas are discussed.