Selective Silica Removal in Geothermal Fluids : Implications for Applications for Geothermal Power Plant Operation and Mineral Extraction

Raw material extraction from geothermal fluids often comprises concentrating and cooling steps, which increases the risk of silica scaling formation. However, existing silica removal strategies do not consider the impact on raw material extraction. In this study, the applicability and element-selectivity of three silica removal techniques (seed-induced, lime and caustic precipitation) were tested in batch experiments using synthetic and natural geothermal fluid samples. Increasing the pH-value to 10.5 and the Ca/Si ratio > 1.25 was found to mitigate silica scaling effectively via formation of calcium-silicate-hydrate phases (C-S-H phases). The developed silica removal process does not affect the raw materials and is therefore suitable for brine mining purposes.