Physicochemical Study On Separation Of Fluorine And Earths From Sulfuric Acid Rare Solution

The existence of large amount of fluoride with strong coordination ability in bastnaesite makes it difficult to separate fluorine and rare earths, and it is the origin of the high consumption and high cost in rare earths hydrometallurgy. Currently, the "oxidizing roasting-sulfuric acid leaching-solvent extraction" process has a higher degree of comprehensive utilization, but the formation of third phase caused by fluoride limits its application. In this study, using fluoride-bearing rare earths solution to simulate the bastnaesite leaching solution, physicochemical properties of fluoride elements were studied to explore the existing state and reaction mechanism of fluoride, and provide theoretical basis for the efficient utilization of rare earth resources. The study is divided into three parts:Firstly, the extraction and stripping conditions were researched. The optimum extraction condition by P204is that:n(F-)/n(Ce4+)=2, c(H+)=0.2mol·L-1. With the larger initial Ce4+concentration and higher hydrochloric acid acidity, the stripping effect is better.Secondly, the optimal conditions of separation of F-Ce binary system and F-Ce-RE3+ternary system with the adding of fluoride-coordination agent were studied. The results show that:aluminum salts are the most suitable fluoride-coordination agent for F-Ce separation, and aluminum nitrate is best for fluoride complexation. The optimum conditions of F-Ce separation are as follows:c(H+)=0.2mol·L-1, the more aluminum nitrate is added, the higher temperature is, the better separation effect of F-Ce is obtained. The F-Ce orthogonal experiments show that c(P204) is main factor for F-earth separation in Ce-F-Nd system, pH of rare earths sulfuric acid solution is main factor for F-earth separation in Ce-F-La system, and extraction time is main factor for F-earth separation in Ce-F-Pr system.Finally, the adsorption of fluoride from fluoride-bearing rare earths solution by activated alumina and hydrous zirconium oxide was studied. The results show that:using activated alumina as adsorbent, F-Ce separation can be achieved when c(H+)>0.6mol·L-1, adsorbent dosage>30g·L-1, and the adsorption process is accord with pseudo second order kinetic model equation:dqt/dt=k2(qe-qt)2with k2=322. Using hydrous zirconium oxide as adsorbent, F-Ce separation can be achieved when0.1mol·L-1<c(H+)<1.0mol·L-1, adsorbent dosage≥20g·L-1, and the adsorption process is accord with pseudo second order kinetic model equation: dqt/dt=k2(qe-qt)2with k2=0.024. The optimal conditions for adsorping fluoride of zirconium-based composite adsorbent also studied.The above results prove that the fluorine-rare earth can be separated effectively, and the high efficient utilization of rare earth resources can also be achieved.