Study On The Effect Of Decomposition Of Baotou Rare Earth Concentrate On Fluoride By Roasting Of Different Aluminum Salts

In the decomposition process of Baotou mixed rare earth concentrate,due to the oxidation roasting of bastnaesite in the air,fluorine will be discharged into the air in the form of HF gas to pollute the environment.In this paper,the mechanism of aluminum ions immobilizing fluorine ions in the roasted ore was studied by using the complex characteristics of fluorine ions and aluminum ions and the experimental method of mixed roasting of rare earth concentrate and aluminum salt.In this paper,aluminum chloride,aluminum sulfate and aluminum oxide are mixed with Baotou mixed rare earth concentrate,and TG-DTA analysis experiment,XRD analysis experiment and influencing factors experiment are carried out respectively.The main research contents are as follows:Firstly,according to the differential thermal analysis experiment of rare earth ores,the temperature range of thermal decomposition is determined as the basis for the subsequent analysis of the reaction temperature range of mixed aluminum salt ores.The results of differential thermal analysis show that the thermal decomposition of bastnaesite occurs at360?⁵08?,and fluorine mainly escapes at this stage.After adding aluminum chloride,the reaction stage of aluminum salt and rare earth ore is 450?⁵00?;after adding aluminum sulfate,440?⁵40?is the reaction stage of aluminum salt and rare earth ore;after adding aluminum oxide,250?⁵50?is the reaction stage of aluminum salt and rare earth ore.Secondly,X-ray diffraction analysis experiment was carried out on the roasted ore in each reflection stage,and the phase of the roasted product in the roasted ore was measured,which confirmed the conclusion of TG-DTA curve analysis.The calcination products of these three kinds of aluminum salts are mainly in the form of AlF₃ and[AlF₄]^-compounds.At last,the influencing factors of fluorine fixation efficiency were studied.The effects of the ratio of ore to agent,the roasting temperature and the roasting time on fluorine emission were studied.The results showed that when the ratio of ore to agent is 1:1,the roasting temperature is 500?,the roasting time is 120 min,the maximum fluorine fixation efficiency is 66.9%;when the ratio of ore to agent is 1:0.7,the roasting temperature is500?,the roasting time is 120 min,the maximum fluorine fixation efficiency is 1:1 The ratio of alumina to rare earth concentrate is 77.1%.When the ratio of ore to agent is 1:1,the roasting temperature is 400?,the roasting time is 120 min,and the maximum fluorine fixation efficiency is 68.4%.According to the calculation of thermal decomposition kinetics,the order of activation energy is aluminum chloride?78 kJ/mol?,aluminum sulfate?65 kJ/mol?,aluminum oxide?38 kJ/mol?.Therefore,aluminum oxide is more likely to react than the other two aluminum salts,and the energy consumption is relatively small,and the reaction order of the three aluminum salts is similar.