Enhanced sorption capacities for lead and uranium using titanium phosphates; sorption, kinetics, equilibrium studies and mechanism implication

The application of new synthesized titanium phosphates to the lead and uranium removal from acidic aqueous solutions (pH(2)) was explored. Batch sorption experiments were carried out using lead-and uranyl solutions of concentration range 50-6000 and 50-4000 mg.L-1 respectively. The effect of pH, concentration, competing cations, temperature and reaction time on the adsorption equilibrium was investigated. The sorbents were examined by FTIR, XRD, XPS and SEM-EDS and characterized as mix salts while the formation of precipitates chloropyromorphite (Pb-5(PO4)(3)Cl) and sodium-autunite (NaUO2PO4) after sorption was demonstrated. Typical sorption isotherms were constructed and modelled by the Langmuir, Freundlich and Temkin equations. The highest sorption capacity values (q(max): 2000 mg.g(-1) Pb and 1250 mg.g(-1) U) were observed for TiP3 which contains sodium in its structure. The kinetic data, obtained at 298, 308 and 323 K, obeyed a pseudo-second order equation and thermodynamic parameters were calculated. EPA Toxicity Characteristic Leaching Procedure and desorption experiments were performed in order to test the environmental compatibility of the sorbents. The results indicated that the sorption of Pb and U on titanium phosphates can be interpreted by a model combining adsorption and surface complexation toward surface precipitation.