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Silica, Boron and Lithium Concentrations In Olkaria Geothermal Brines: Theoretical Considerations For Extraction
Many of the chemical constituents in geothermal fluids are a potential source of valuable minerals and metals. Mineral recovery has been made at Larderello, Italy, as early as the turn of the last century where boric acid was extracted from geothermal steam. Some geothermal fields such as the Salton Sea, in the United States, Milos in Greece, Assal in Djibouti Cheleken in Russia and Reykjanes in Iceland to mention only a few, contain significantly rich mineral brines to make them potentially economically viable sources of some minerals.
In various sectors of Olkaria the estimated separated brines from the Olkaria East, Olkaria Northeast and Olkaria Domes is ~ 5000 t/hr. There is a relatively large amount of brine available from the production fields in Olkaria obtained from the separated water at various re-injection points. Silica (SiO2), Boron (B) and Lithium (Li) content of brines from the different sectors between 650 to 800 ppm, 3-4 ppm and 1.32 – 1.7 mg/kg respectively. These could be of interest for mineral recovery. Other metal elements found in the separated geothermal water in are Manganese (Mn), Cadmium (Cd), Chromium (Cr), Nickel (Ni), Cobalt (Co), Zinc (Zn), Mercury (Hg) at trace levels. Despite the low concentration of the metal elements in the separated waters the amount of recoverable minerals could be large given the large volumes of separated water that is re- injected. Silica, Boron and Lithium find use in various industries eg the manufacture, glass, soaps, toothpaste, pharmaceuticals, pesticide, as filler material, rechargeable nickel lithium batteries and battery storage. World market prices for some of these elements make it attractive for economic mineral recovery from geothermal brines. Recoverable minerals and metals from the geothermal brines at Olkaria can offer sources of alternative revenue stream. The choice of technology can be done after conducting initial pilot studies.