The CRM-geothermal project recently achieved a major milestone, with significant progress in testing adsorption materials for lithium and strontium extraction. Trials were conducted using manganese dioxide and zeolite-based materials at GFZ and IzTech laboratories, alongside a field test at the Tuzla geothermal power plant in Türkiye.
For the adsorptive extraction of Critical Raw Materials using ion sieves, suitable adsorbents must be identified and tested. Batch tests in high-pressure, high-temperature environments are performed to investigate the influence of various parameters, record adsorption isotherms, and determine adsorption/desorption kinetics. The goal is to find adsorbents that perform well under the expected geothermal conditions of model brines, including high-salinity brines from sedimentary reservoirs and low-salinity brines from crystalline reservoirs.
In lithium extraction, adsorption tests at GFZ involved static batch experiments with synthetic lithium solutions (LiCl solutions with pH buffers) and dynamic flow-through experiments using synthetic fluids simulating natural geothermal fluids from the British Cornwall site and the German Groß Schönebeck site.
Image: Decantation solution containing high concenrtation of Li+ and Na+ at low pH.
The batch experiments recorded adsorption isotherms at room temperature, 50°C, and 75°C, with estimated maximum adsorption capacities between 16 and 28 mg/g. The flow-through experiments used synthetic fluids containing NaCl, KCl, CaCl2, MgCl2, SrCl2, and LiCl in concentrations identical to natural fluids and with matching pH values. Over approximately three hours, lithium was successfully removed selectively.
At the Tuzla geothermal power plant, the commercial spinel-type λ-MnO2 was used for less than 1 hour at a reinjection temperature of 90°C using a mini-reactor system. The brine-treated λ-MnO2 powder was collected and dried for the desorption process, conducted in a 1 M HCl solution at room temperature. The desorption solution was rich in Li+, Mn2+, and Na+. Na2CO3 powder was added to the solution to precipitate Mn2CO3 in three consecutive steps. After water evaporation, a white powder was obtained, containing both Li+ and Na+ carbonates. The initial Li+/Na+ ratio of 1/1.4 in terms of moles was increased to 3/1.
For strontium extraction, experiments were performed in the lab using synthetic Sr solutions. The effects of particle size, pH, temperature, and initial concentration were examined during the sorption process, which achieved a capacity ranging between 6 and 12 mg/g. A flame photometer was used to measure the concentration in the water solution.
Lead researchers:
Jörg Zotzmann (GFZ) and Mustafa Demir (IzTech)
