Solid phase extraction of uranium (VI) from phosphoric acid medium using macroporous silica-based D2EHPA-TOPO impregnated polymeric adsorbent

This paper describes uranium extraction from aqueous phosphoric acid medium using a silica/polymer based D2EHPA-TOPO adsorbent. The mixture of di-2-ethyl-hexylphosphoric acid (D2EHPA) and tri-n-octylphosphine oxide (TOPO) was impregnated and immobilized into the pores of SiO2-P particles. The various experimental parameters such as the synergistic mixture ratio of extractants, phosphoric acid concentration, the contact time and the temperature were investigated. The results showed that 95% uranium extraction was achieved after 10 min contacting time using D2EHPA-TOPO/SiO2-P (mass ratio = 3:1 w/w) adsorbent from 1 M phosphoric acid solution containing 165 ppm U (VI), 5000 ppm Fe (III), 1000 ppm Ca (II) and 1000 ppm Al(III) at 25 °C. Also, the obtained results displayed the high adsorption capacity for Uranium as high as 48 mg g− 1 at the mentioned conditions. The rate constant (1.62 g mg− 1 min− 1) was calculated by the pseudo-second order equation and it shows that reaction rate was controlled by the chemical adsorption of uranium. Furthermore, D2EHPA-TOPO (3:1)/SiO2-P has a good selectivity for U(VI) among the co-existing elements (Fe, Al and Ca). The adsorption isotherms were well described by the Redlich-Peterson equation, closely followed by the Langmuir equation which confirms the mechanism is chemical monolayer adsorption. Obtained thermodynamic parameters (∆ H° . ∆ S° and ∆ G°) reveal that the U(VI) adsorption to be an exothermic and spontaneous process.