Technology review of mineral extraction from separated geothermal water

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Mroczek, E.K.; Carey, B.S.; Climo, M.; Li, Y. 2015 Technology review of mineral extraction from separated geothermal water. Lower Hutt, N.Z.: GNS Science. GNS Science report 2015/25 iii, 27 p.

Abstract: The possibility of extracting minerals from geothermal fluids was recognised many years ago. In Parliament in 1949 the Hansard records in the Supply Debate (p2511) the Hon Mr Broadfoot, MP for Waitomo, identifying “Thermal activity had been used for power purposes successfully in Italy, and if it were used in New Zealand there might be mineral by-products associated with it.” The ideas are not new. This technology review is a component of a broader inquiry and update into the potential for the extraction of minerals from New Zealand separated geothermal water (SGW). The work is a part of a small Ministry of Business, Innovation and Employment funded research programme “From Waste to Wealth” (Contract No. C05X1307). This report is a summary of the mineral extraction work undertaken in New Zealand, adding material from relevant overseas studies and the authors’ catalogue of techniques. A complementary technology review, which was not just limited to processing geothermal fluids, was undertaken in 2014 by Shirley Li at the University of Auckland in partial fulfilment for a Masters of Engineering. This review identifies technologies and processes for removal of silica, lithium, boron and rubidium and cesium from New Zealand SGW. The implicit assumption is that none of these extraction processes would be viable without ready access to the SGW and easy integration into an energy production process, as the cost for stand-alone production and disposal of fluid for the express purpose of minerals extraction is unlikely to be economically viable in the next few decades. Whether this could be achieved with existing infrastructure is a crucial point of discussion. The most important mineral to extract is silica, as its removal holds the potential to improve energy generation efficiencies, which might encourage adoption by the energy companies and resource owners. Once removed, the geothermal fluid is in a condition where other dissolved minerals should be able to be extracted with less interference. (auth)