Abstract
In an enhanced geothermal system (EGS), geothermal energy in rocks with insufficient permeability or fluid saturation can be used by creating artificial geothermal reservoirs. Generally, EGS geothermal fluid contains high concentrations of total dissolved solids that originated from various geochemical reactions between the fluid in the reservoir and the minerals in the rock. For example, the concentration of lithium ions are measured approximately 150 mg/L, and several researchers have focused on the recovery of lithium in the geothermal fluid using various methods, one of which is liquid extraction. Solvent extraction has been used to recover lithium from various sources, and successful recovery efficiency have been attained. However, the geothermal fluid in EGS reservoirs contains high concentrations of SiO2, which might inhibit the selective recovery of lithium. Thus, in this study, two consecutive stages of solvent extraction were used to separate the lithium from the geothermal fluid that contained different concentrations of SiO2 ions. The divalent ions were removed in the first stage, and the lithium ions were extracted effectively in the second stage. The SiO2 inhibits the selective recovery of lithium in the first stage to a greater extent than it does in the second stage. The spectroscopy data shows a decrease of the organic solvents main functional group (P=O & P-O-H) absorbance that reacts with the metal ions of the geothermal water after extraction however the intensity difference was reduced as the SiO2 concentrations increases. Silicate ions can be problematic due to the formation of scaling in EGSs, so controlling its concentration in the geothermal reservoir would be beneficial for the long-term operation of EGSs and for the successful recovery of valuable metal resources from EGS reservoirs.
Highlights
Geothermal energy is known to be thermal energy that is contained inside the Earth (Barbier, 2002), and geothermal systems use this geothermal energy to generate electricity (Olasolo et al, 2016)
The influence of different dissolved SiO2 concentrations (0, 150, 350 mg/L) in geothermal water was observed during the solvent extraction process of metal ions
During the two step solvent extraction process, the total lithium recovery efficiency decreased from 6.8 % to 4.5% as the
Summary
Geothermal energy is known to be thermal energy that is contained inside the Earth (Barbier, 2002), and geothermal systems use this geothermal energy to generate electricity (Olasolo et al, 2016). Enhanced geothermal systems (EGSs) are one of the geothermal systems used to extract thermal energy from hot dry rock (HDR) (Lei et al, 2019). EGSs apply hydraulic stimulation at depths deeper than 3 km of HDR to create an artificial geothermal reservoir for a sustainable geothermal system (Hofmann et al, 2014; Kim et al, 2018). Water is injected through an injection well where the thermal energy is stored in the Effect of Silicate During Extraction deep fractured network, and it comes out through the pumping well with thermal energy (Caulk et al, 2016; Hofmann et al, 2019; Lee and Chung., 2020a). The heated water passes through a geothermal heat exchanger where the heat is used to generate electricity
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