Highly selective granulation adsorbents for lithium recovery from gas field brine: Selectivity, kinetics and mechanism

Abstract

Polyvinyl chloride (PVC)-based granulated adsorbents with high mechanical stability have proven effective for extracting lithium from salt lake brine on a commercial scale. However, granular materials with high adsorption selectivity for Na+/Li+ separation and long service life still remain a great challenge. Here, we prepared granulated spherical adsorbents by a phase conversion method using PVC as a binder; PEG, PMMA, PAN, and PAA as hydrophilic co-binders; and Li1.33Mn1.67O4 (LMO) as a powder adsorbent. Among these materials, P-PAA exhibited excellent hydrophilicity and excellent binder compatibility, facilitating the dispersion of LMO powders and ensuring high adsorption. Moreover, the mechanism of action of the PVC/PAA binders was first explored via experiments and simulations, which revealed that Li+ migration was promoted and occurred primarily on LMO rather than on binders, so nonselective adsorption decreased. Therefore, P-PAA demonstrated exceptional Li+ adsorption capacity (12.9 mg/g) and selectivity for Li+ (distribution factor of 1391.3 mL/g) over other coexisting cations and a separation factor of αNaLi= 718, which are greater than those of other adsorbents reported in the literature. Furthermore, the unique structure of P-PAA, which was obtained by interconnecting larger core pores (5–10 μm) and abundant smaller pores (0.5–1 μm), accelerated the water/ion transfer kinetics without causing powder leakage. Hence, the lifespan of these materials has been extended, as salt crystals or internal cracks did not form during long-term cyclic use, unlike in the case of other granules. All of the above factors made P-PAA effectively recover Li+ from Puguang gas brine, which contains a high sodium salt content and organic pollutants, with an efficiency of 98.4 %. All these properties demonstrate that P-PAA could be used in an appealing and competitive manner for industrial processes.