Effect of pH, fulvic acid and temperature on the sorption of uranyl on ZrP2O7

The sorption of UO ₂ ²⁺ onto ZrP₂O₇ was studied using the batch technique and the point of zero charge of ZrP₂O₇ was obtained through mass titration. The results indicated that sorption of UO ₂ ²⁺ onto ZrP₂O₇ was strongly affected by pH, solid-to-liquid ratio (m/V), the species of electrolyte in solution and fulvic acid (FA), but was insensitive to ionic strength. The sorption of UO ₂ ²⁺ increased with increasing pH and m/V. The presence of FA enhanced UO ₂ ²⁺ sorption onto ZrP₂O₇ at low pH. The presence of phosphate or sulfate caused opposite effects on the sorption of UO ₂ ²⁺ onto ZrP₂O₇. Addition of citrate also significantly affected UO ₂ ²⁺ sorption. The sorption of UO ₂ ²⁺ increased as the temperature of the system increased. The Langmuir and Freundlich models were used to simulate the sorption isotherms of UO ₂ ²⁺ onto ZrP₂O₇ at different temperatures. The results indicated that the Freundlich model described UO ₂ ²⁺ sorption better than the Langmuir model. Thermodynamic parameters for the sorption process were calculated from the temperature dependent sorption isotherms. The results suggested that the sorption process of UO ₂ ²⁺ onto ZrP₂O₇ is spontaneous and endothermic. The desorption process of UO ₂ ²⁺ from ZrP₂O₇ was also investigated and it was found that sorption onto ZrP₂O₇ was irreversible.