| Bastnaesite is one of raw material used to produce rare earth.After the discovery of bastnaesite,there have been many different methods to produce rare earth from bastnaesite since last century.However,there are still some defects in the current metallurgy process of bastnaesite in industry,so how to make the development of rare earth reasonable and better production come true is vital important for rare earth industry.This study mainly focus on the decomposition process and mechanism of bastnaesite by acid-base combination method,aiming to explore the efficient and green process of bastnaesite decomposition of rare earth.The contents and results of this study are as follows:(1)The removal of impurity in bastnaesite was carried out.The optimal conditions of the impurity removal process were as follows: p H was maintained at about 3,liquidsolid ratio was 10,bastnaesite reacted with hydrochloric acid at room temperature and atmospheric pressure for 20 min,stirring rate was 250 r/min.After the reaction,85% impurities were leached,and the grade of bastnaesite pickling ore was 95%.After removing impurities,the acid pickling ore of bastnaesite was obtained and the acidbase decomposition experiment was carried out next.(2)The Eh-pH diagram of bastnaesite in aqueous solution was drawn by software to reveal the mechanism of the reaction.Then,the law of the decomposition of bastnaesite by acid-base combination method was studied by experiments.It is found that the experimental factors of hydrochloric acid concentration,reaction temperature and time,alkali dosage,liquid-solid ratio and decomposition time are positively related to the leaching rate of rare earth.Besides,the reaction of hydrochloric acid leaching process is calculated theoretically,and conditions of this research process are optimized.The acid leaching conditions are as follows: 3 mol/L hydrochloric acid is used to leach bastnaesite acid washing ore for 3 hours at 95 ?,the liquid-solid ratio is 6:1,and the leaching rate of rare earth is about 50%.The experimental conditions of alkali decomposition: when the liquid-solid ratio is 2:1,60% sodium hydroxide solution is used to decompose at 140 ? for 120 min,and then the leaching rate reaches 93% after leaching with hydrochloric acid.(3)In this paper,the kinetics of the decomposition of bastnaesite by acid and alkali is studied.The results show that the process of hydrochloric acid leaching and alkali decomposition of bastnaesite is controlled by the chemical reaction of the phase interface.The relationship between reaction rate and hydrochloric acid concentration is calculated as r1 = 1.732 × [HCl]2.06,and the relationship between reaction rate and alkali concentration is r2 = 0.046·e-1380/T·[Na OH]1.65.The apparent activation energies of acid decomposition and alkali decomposition were 11.94 k J/mol and 11.47 k J/mol,respectively.(4)Through the experiment under the optimized conditions of decomposing bastnaesite,the total extraction rate of rare earth is 94.67%,and the purity of rare earth in the leaching solution is high.In addition,the X-ray diffraction analysis of the final reaction slag shows that there are still little amount rare earth in the form of bastnaesite and some barium sulfate in the slag.It can be concluded that this part of barium sulfate is the main insoluble impurity in the concentrate,which is the main reason why the grade of rare earth pickling ore can not reach a higher level in the process of dilute hydrochloric acid impurity removal. |
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