Preparation of p-carboxyphenyl azo calix[4]arene phosphate derivative and its extraction properties toward uranium(VI)

P -carboxyphenyl azo calix[4]arene phosphate derivative (P-CACPD) was successfully synthesized using calix[4]arene as raw material. The P-CACPD was characterized by FT-IR and 1 H-NMR. The effects of pH, extraction time and temperature on the extraction of U(VI) by P-CACPD were investigated. The results show that pH value, extraction time and temperature have an effect on the extraction of U(VI) by P-CACPD. When the initial pH is 5, temperature is 25 °C, extraction time is 2 h, the extraction rate of U(VI) by P-CACPD reaches the maximum. Both kinetics parameters and thermodynamic parameters of the extraction process were calculated. The calculated data indicate that the extraction process of uranium by P-CACPD is an exothermic spontaneous process, which well fits with the pseudo-second-order kinetic model.