高含氯废酸中铀的萃取动力学及机理研究OA

To address the critical challenges of intense uranium/iron extraction competition and low mass transfer efficiency caused by the high chloride and high acidity characteristics of zirconium smelting waste acid,this study established a binary extraction system of N235-TBP-kerosene using the constant interfacial area cell method.The mass transfer kinetics and thermodynamic behavior of uranium under extreme Cl--H+synergistic conditions were systematically elucidated.By investigating interfacial area and temperature,the extraction control mechanism was determined,and the location of the chemical reaction was identified.The effects of uranium concentration,hydrochloric acid concentration,N235 volume fraction,and TBP volume fraction on the extraction rate were examined,leading to the derivation of the uranium extraction kinetic equation.Results indicate that the uranium extraction process follows a kinetic pattern of diffusion control coupled with in-phase reaction.The apparent extraction rate equation is given by r=37.68 c1.27U c0.37HCl c0.81N235,with reaction orders of 1.27,0.37,and 0.81 for uranium,hydrochloric acid,and N235,respectively.This demonstrates that the initial uranium concentration exerts the most significant influence on the rate.The apparent activation energy Ea=11.29 kJ/mol further confirms that the mass transfer process is dominated by the diffusion step.Combined with the slope method and charge balance analysis,the formation mechanism of a 1∶1 ion-association complex,UO2Cl3·R3NH,is clarified,wherein uranium in the form of the[UO2Cl3]-complex anion combines with the protonated tertiary amine extractant R3NH+.Thermodynamic parameter calculations yielded a standard Gibbs free energy change ΔG⊖U=-2.231 kJ/mol,indicating the spontaneity of the extraction reaction under experimental conditions.The positive values of the standard enthalpy change ΔH⊖U=26.26 kJ/mol and standard entropy change ΔS⊖U=95.62 J/(mol·K)confirm that the process is endothermic and entropy-driven.Elevated temperature not only promotes uranium migration by reducing the coordination energy barrier,but also enhances the thermodynamic driving force of the reaction due to the increased contribution of the TΔS term,which is favorable for the selective separation and recovery of uranium.This study clarifies the efficient uranium extraction mechanism in high-chloride and high-acidity media from both kinetic and thermodynamic perspectives,providing an important theoretical basis for the optimization and scale-up of uranium recovery processes from zirconium smelting waste acid.