Study On The Extraction Of Rare Earth From Calcium Smelting Rare Earth Smelting Slag

Rare earth smelting slag?referred to as reductive slag?of calciothermy is produced during rare metals smelting,it contains rich rare earth,which is very worthy of reuse.In view of the low extraction yield of rare earth,this paper carried out a series of technology and theory researches,which aimed at efficient extraction of rare earth,the main contents are as follows:?1?Explore the direct acid leaching and alkaline-heating-acid leaching method to deal with the smelting slag,the results show that: the two methods aren't effective in extraction of rare earth from smelting slag.?2?using sodium hydroxide,sodium carbonate and calcium oxide as additives,through the reduction of slag and roasting additive thermodynamic calculation,roasting the g.theta ?G_T^?-T map is established,analyzes the in the roasting process,additives and reduction reaction of each component in the slag.The thermodynamic analysis shows that all the selected additives can be converted to rare earth oxide.Through the acid leaching experiments of the calcined products,the leaching rates of rare earth were 92.3%,93.4% and 93.9%,respectively,with the addition of sodium hydroxide roasting acid leaching,roasting with sodium carbonate,and calcium oxide roasting acid leaching.Finally combined with the roasting thermodynamics and experimental analysis,the use of sodium carbonate as an additive is better.?3?The acid leaching slag process to extract rare earth with sodium carbonate roasting was studied.Under the conditions: ratio of reduced slag to sodium carbonate1:1 ?calcination temperature 700? ?roasting time 1h? the concentration of hydrochloric acid 3mol·L^-1?acid leaching temperature 50??acid leaching time 40min?liquid-solid ratio 6:1,the leaching rate reachs 94.09%,but the extraction effect can also continue to be optimized.CaF₂ in the slag has effect on the leaching of rare earth through thermal analysis.It need to be built on the foundations of rare earth fluoride converting into rare earth oxide by adding additive to optimize the leaching rate.Based on the previous research findings,fluorite and sodium carbonate and silcon dioxide can be used to change the fluoride into the soluble fluoride.Method for roasting with sodium silicate was proposed through this thought.The fluoride in the slag is changed to be soluble in water,separation of rare earth and fluorine was achieved.?4?The rare earth extraction process was studied by adding sodium silicate roasting and water washing and acid leaching reduction slag.The results of the study showed that the leaching rate reachs 99.05% under the experimental conditions of ratio of reduced slag to sodium carbonate1:1?alcination temperature 850??roasting time 2h?the concentration of hydrochloric acid 3mol·L^-1?acid leaching temperature 60??acid leaching time 1.5h?liquid-solid ratio 11:1.?5?In order to validate the research ideas of the new process,which is sodium silicate roasting-washing-acid leaching,the mechanism of the extraction of rare earth by the new process was studied.The results show that the new process is not completely consistent with the original idea.The roasted product are CaF₂,Ca₄Si₂O₇F₂,RE₂O₃,Na F and CaCO₃.Then wash the roasted product with water to remove Na F.Although CaF₂ will dissociate F^-,but the massive of silicate,decomposed by Ca₄Si₂O₇F₂,is effective absorption of F^-.That makes the low concentration of F^-in the solution,so as to ensure the high extraction rate of the rare earth.