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

Abstract

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 10min contacting time using D2EHPA-TOPO/SiO2-P (mass ratio=3:1 w/w) adsorbent from 1M phosphoric acid solution containing 165ppmU (VI), 5000ppm Fe (III), 1000ppm Ca (II) and 1000ppm Al(III) at 25°C. Also, the obtained results displayed the high adsorption capacity for Uranium as high as 48mgg−1 at the mentioned conditions. The rate constant (1.62gmg−1min−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.