Study On Cerium(Ⅳ) And Thorium Extraction Kinetics In Fluorine-containing Sulfuric Acid System

As a kind of function material, rare earths are widely used in magnetic, optical and electronic fields, and thus of much strategic significance to national economy and defense industry. Bastnaesite is a kind of important light rare earths resouce, and usually treated with oxidation roasting-hydrochloride acid leaching process which was featured by simplicity and low cost. However, fluorine and thorium were left in alkaline waste water and iron-Thorium slag, respectively, therefore could not be recovered effectively, causing environmental pollution and waste of resources. General Research Institute for Nonferrous Metals has developed a new process named Bastnaesite Oxidation roasting-Sulfuric acid leaching-Extraction separation of Cerium, Thorium and Fluorine. In this process, Cerium, Thorium and Fluorine can be extracted by HEH/EHP from sulfuric acid leaching solution in a single step. Characterized by simplicity and low cost, it can effectively recover the Fluorine and Thorium resources and eliminate environmental pollution. But the system containing many elements such as Cerium, Thorium and Fluorine, the sulfuric acid leaching solution is relatively sophisticated and deserve further research on thermodynamic and kinetic mechanism of the extraction process to build a solid basis for improvement.The work was funded by the National Key Natural Science Foundation Project. Based on the process developed by GRINM and choosing the complicated sulfuric acid solution containing Cerium(Ⅳ), Thorium(Ⅳ) and Fluorine as research object, The extraction kinetics of Cerium(Ⅳ) and Thorium(Ⅳ) with HEH/EHP by using a constant interfacial cell with laminar flow were studied and therefore provided the theoretical basis and technical support for further optimizing process conditions and controlling the extraction speed. Detailed research content are:(1) Judging the order of the interphase mass transfer reaction.(2) Determining the controlling mode of the kinetics of extraction reaction, i.e, the controlling step of the extraction reaction.(3) Calculating the apparent activation energy of the extraction reaction.(4) Deducing the extraction rate equation and build the mode of extraction kintics.(5) Exploring the mechanism of the extraction reaction. Based on experiment, we can get the following conclusions:(1) The extraction of Cerium(IV) from Fluorine-contained sulfuric acid medium by HEH/EHP is a one-order reaction. The apparent activation energy of the extraction reaction is50.8kJ·mol-1, and the reaction is controlled by chemical reaction. The kinetic equation of the extraction reaction is R=k[CeF2(HSO4)x2-x][H2A2]2[H+]-2, and the apparent rate constant of the extraction reaction is k=9.30×10-4mol-1·L·s-1.(2) The extraction of Thorium(IV) from Fluorine-contained sulfuric acid medium by HEH/EHP is a one-order reaction. The apparent activation energy of the extraction reaction is45.8kJ·mol-1, and the reaction is controlled by chemical reaction. The kinetic equation of the extraction reaction is R=k[ThF3+][H2A2][H+]-1, and the apparent rate constant of the extraction reaction is k=5.37×10-3mol-1·L·s-1.(3) By comparing the variance laws of extraction rates of Cerium(ⅣV), Thorium(Ⅳ) and Fluorine in experiments of influence factors on extraction rate, we validate that Cerium(Ⅳ), Thorium(Ⅳ) and Fluorine enter organic phase through coordination extraction.(4) Discussing the extraction mechanism of Cerium(Ⅳ) and Thorium(Ⅳ) from Fluorine-contained sulfuric acid medium by HEH/EHP. The extraction rate equation deduced with steady method is consistent with the one obtained from experiment.