Lithium extraction from geothermal brine by granulated HTO titanium-based adsorbent with block-co-polymer poly (ethylene-co-vinyl alcohol) (EVAL) as binder

This study reports a novel highly selective H2TiO3 lithium-ion sieve (LIS) based adsorbent spheres using a block-co-polymer poly (ethylene-co-vinyl alcohol) (EVAL) as the binder for selective extraction of lithium from geothermal brine. Combination of the intrinsic hydrophobic/hydrophilic characters of EVAL satisfies the requirement for adsorbent's robust mechanical strength and access by aqueous brine. Via adjustment of EVAL concentration and the pore former polyethylene glycol (PEG), porous structure as well as the pore connectivity of the spherical EVAL-HTO were well controlled. The adsorption equilibrium, kinetic characteristics, and cycle performance were investigated using a simulated brine with pH adjustment and the real Tibet geothermal brine. The equilibrium adsorption behavior of Li+ on EVAL-HTO showed Langmuir adsorption and the adsorption kinetics conformed to the pseudo-second-order kinetic model. Kinetic analysis using the intra-particular diffusion model confirmed the open porous structure in EVAL-HTO spheres. In real geothermal brine with no pH adjustment, the EVAL-HTO showed adsorption capacity of 11.8 mg/g, slightly below 13.5 mg/g in the simulated brine at pH = 12, but with more stable cycle performance and cost advantage. Excellent selectivity between Li+ and other contaminant ions, except Ca2+, indicated great potential to obtained purified lithium chemicals. Options to remove Ca2+ ions were proposed for future investigation. The results indicate great promise to use EVAL-HTO in lithium adsorption from real geothermal brine.