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 blockco-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.

Automated summary

This study introduces a new type of highly selective H2TiO3 lithium-ion sieve (LIS) based adsorbent spheres using a block co-polymer poly (ethylene-co-vinyl alcohol) (EVAL). The spherical EVAL-HTO has a controlled porous structure and pore connectivity, providing robust mechanical strength and access by aqueous brine. The EVAL-HTO showed great potential as a lithium adsorbent, with adsorption equilibrium following Langmuir adsorption and adsorption kinetics conforming to the pseudo-second-order kinetic model. The excellent selectivity of EVAL-HTO between Li+ and other contaminant ions, except Ca2+, indicates the possibility of obtaining purified lithium chemicals.