Study On Reaction Mechanism Of The Process Involving Oxidation Roasting And Hydrochloric Acid Leaching Of Bastnaesite

Process involving oxidation roasting and hydrochloric acid leaching is the main process of bastnaesite treatment.Because of the existence of fluorine,the process becomes longer.What's more,the F-bearing wastewater,produced by alkaline digestion-water washing,is difficult to be treated,and it poses serious threat to the eco-environment.In recent years,against the above problems,the relevant researchers have been committed to the development of green metallurgical process of bastnaesite treatment.The main ideas of these processes are to fix fluorine in the hydrochloric acid leaching residue or be distraged by vaporizeing or washing after converting it into a kind of soluable salt.Howerever,the two problems above still exist in these new processes.So,they can not take place of the existing process.Therefore,based on the existing process,this paper conducts deep study on the oxidation roasting process of bastnaesite concentrate and hydrochloric acid leaching process of bastnaesite roasted,and it was expected to provide new ideas for new process development.The main research contents and test results are as follows:?1?Analysis of kinetics of bastnaesite calcination in different atmosphere was conducted by thermal analysis.The experimental results show that the calcination in air and argon atmosphere respectively belongs to two-dimensional diffusion control and three-dimensional diffusion control.The roasting test of bastnaesite concentrates was carried out under the condition of different atmosphere and different temperature.The testing result shows that mineral decomposition and cerium oxidation is carried out simultaneously during bastnaesite roasting.The temperature,at which the bastnaesite concentrates begins to decompose when roasted in oxygen,is 150 ? lower than in argon,indicating that the oxidation of cerium can accelerate the decomposition.The law of phase change is REFCO₃?REOF,Ce₇O₁₁+REF₃.A part of fluorine was escaped,and the higher the temperature is,the more of fluorine would be escaped.?2?M-?Cl?-?F?-H₂O system Eh-pH diagrams were plotted with HSC6.0 software.The mechanism of hydrochloric acid leaching process of roasted bastnaesite was investigated.The results are as follows:Adjusting the pH of hydrochloric acid in the range of?0?6?,the initial separation of cerium and non-cerium rare earth can be achieved.However,some of the tetravalent cerium will be reduced to trivalent cerium transferred into the leaching solution.Trivalent rare earth ions and fluoride ions will be combined to generate rare earth fluoride entering into the slag,which reduce the efficiency of cerium and non-cerium rare earth separation seriously.On the other hand,controlling the pH of hydrochloric acid below 0,the tetravalent cerium and fluoride could be leached in the form of[CeF3]+.Therefore it can avoid the generation of rare earth fluoride,and when the solution pH is in the range of?-1?0?,[CeF₃]+ could be reduced to be CeF₃ transferred into the slag.?3?Optimization test of leaching conditions was conducted,and the optimization conditions of leaching conditions were selected:acid content was 110%,acid concentration was 1.0 mol/L,leaching time was 3 h,leaching temperature was 25 ?.Rare earth leaching rate was up to 90%,but the rare earth concentration is low and acid consumption is relatively large.?4?In order to reduce the amount of acid in the leaching solution,the coordination ion species and addition test were carried out.The results show that the addition of sulfate ion reduce acid consumption and increase the concentration of rare earth within a certain range.