Efficient recovery of rubidium from high-salinity brine using dual crosslinked hydrogel beads encapsulating ammonium phosphotungstate

Extracting rubidium from brine is critical for addressing the rubidium supply challenge. Ion exchange is an effective method for rubidium recovery, but practically, it faces the challenge that the adsorbent powder is too fine for column operation. Herein, hydrogel beads (AWP@AlG&PVA) were innovatively synthesized through dual crosslinking between sodium alginate and CaCl₂, as well as polyvinyl alcohol and boric acid, incorporating ammonium phosphotungstate (AWP) as the active component, and were employed as adsorbents for rubidium extraction from high-salinity brine. The mercury intrusion pore measurement confirmed that the prepared AWP@AlG&PVA is a porous material, with the majority of pores being large pores. Through systematic adsorption experiments, over 90 % of rubidium was adsorbed from the simulated solution under optimal conditions. The coexisting K⁺ interfered with rubidium adsorption, while Na⁺, Ca²⁺, and Mg²⁺ had no apparent influence. Adsorption kinetic study revealed that Rb adsorption adhered to the pseudo-first-order kinetic model. The adsorption isotherms of AWP@AlG&PVA on Rb⁺ accord with the Freundlich model. XPS and SEM-EDS analyses indicated that the adsorption mechanism was ascribe to ion exchange between NH₄⁺ and Rb⁺. Remarkably, the adsorbent exhibited excellent regeneration performance, retaining over 71.3 % of its adsorption ability after undergoing six sequential adsorption-desorption cycles in actual brine. This research suggested that the AWP@AlG&PVA beads address the challenges posed by fine powder and high solubility and are a feasible material for Rb adsorption from high-salinity brine.