Research On Roasting Defluorization Process Of Bastnaesite

Bastnaesite is the second largest resource of rare earth in china, which is important to the development of rare earth industry. At present, the technology of oxidative roasting is generally employed in roasting decomposition mainly applied of bastnaesite. The trend of fluorine in the roasting course of bastnaesite is the important problem of the technique. In the producing process, one part of fluorine with off-gases release into the atmosphere, and the other remained in roasting product can react to form solid-phase of rare earth fluorides in extracting phase, which have a bad effect on the extraction and increase the cost of production. In this, paper, in order to provided a theoretical basis to the recycling in the fluorine producing process and the development in bastnaesite clean smelting methods, a new process in the roasting process of bastnaesite under the saturated water vapor atmosphere were researched innovatively. And the optimal industrial process conditions and the regular pattern of fluorine behaviors in the defluorinating were determined. The research details are as following:(1) By researching the DSC-TG curves of bastnaesite roasting in the static air, the roasting conditions were determined:the optimal roasting temperature was600℃～1000℃. The influences of other single factors on the bastnaesite roasting defluorization under saturated water vapor atmosphere were studied, which gave the results that the Bastnaesite defluorization rate would decrease when the roasting temperature and time increased or the particle size decreased. Finally the optimized conditions for the defluorization of bastnaesite were obtained by orthogonal experiments as follows:roasting temperature of1000℃, roasting time of3hours, particle size of-200mesh and these parameters lead to a more than99.7%defluorization rate.(2) In this part, the roasting decomposition process of bastnaesite, the reaction mechanism and trend of fluorine were studied. Firstly, roasting decomposition process of fluoride (LaF3) and oxyfluoride (LaOF) under the saturated water vapor atmosphere were studied, we obtained a conclusion that the production of bastnaesite thermal decomposition process was REF3and RE2O3.Secondly, further research on the XRD patterns of the bastnaesite roasting productions under different atmospheres and the micro-zone analysis of the production roasted under the saturated water vapor atmosphere was executed. And thermal decomposition process of bastnaesite and the behavior of fluorine in the roasting process were further confirmed.(3) By using H2O and NaOH solution to absorb the fluorine-containing off-gas after the roasting process, studies on absorbent type (H2O or NaOH solution), the density of absorbent, absorption series. We could conclude the optimal absorption conditions:the gas flow rate was100L/min, NaOH liquor density was0.02mol/L, absorption series was3. Under this circumstance, we obtained an absorption rate of99.87%.