The Process And Mechanism Of Recovering Rare Earth From Rare Earth Waste Powder By Alkali Roasting-acid Leaching Method

As the rising number of rare earth phosphor,under the situation of steady growth in market demand,recycling effectively from the waste containing rare earth phosphor of rare earth elements has important application prospect and practical significance.Aimming on the problem of low direct leaching recovery from mixed type of phosphor powder,this article adopts process,such as alkali roasting pretreatment-washing-hydrochloric acid leaching,and studies phase change and leaching thermodynamics of the alkali roasting process.The main work and research results are as follows:Firstly,after analyzing the roasting results of rare earth phosphor roasting process with adding different roasting additives,we determine that result of adding sodium hydroxide roasting is optimal.For the alkali roasting process,using the three factors,four levels L9?34?orthogonal experiment research,it is concluded that order of affecting rare earth leaching rate is,sodium hydroxide amount,roasting temperature and roasting time.After analyzing thermal-thermogravimetric of the raw material which adding sodium hydroxide,we conclude roasting process can be roughly divided into three phases.The phases analysis in different roasting factors shows that the product under optimal roasting condition is mainly for the high rare earth oxide,such as?CeO₂?Tb₄O₇?Y₂O₃?Eu₂O₃??NaAlO₂?NaYO₂?MgO and BaCO₃.We calculating the thermodynamic data,kinetic parameters through simulation of the green powder and blue powder roasting reaction.The reaction activation energy is 212.31 k J?mol-1,and the reaction rate constant is 0.56 min^-1,former factor is 1.76×10¹⁶ min^-1.Under the optimal conditions of roasting: sodium hydroxide content75%,calcination temperature 850 ? and roasting time 1.5 h,the rare earth leaching rate is 99.64%,and the aluminum leaching rate is 1.74%.Through calculating gibbs free energy of acid reaction of Ce,Tb oxide in the process of leaching and analyzing Ce-H₂O,Tb-H₂O E-pH diagram,the result shows that Ce suboxide is easy to react with acid,but Ce high pricedoes not react with acid.CeO₂ can only existstable in strong acid system,low or high price oxide of Tb are easy to react with acid.Therefore,in the process of leaching,adding a certain reduction additives make the high price of rare earth oxides reduce into a low state in order to increase rare earth leaching rate.Through acid leaching for the optimal roasting product,we determined the most optimum leaching process is: the hydrochloric acid concentration: 2 mol·L^-1,liquid-solid ratio: 11:1,hydrogen peroxide volume fraction: 10%,leaching temperature: 75 ?,leaching time 1.5 h.At the same time the rare earth leaching rate can reach 99.98%.Based on microscope analysis of raw material,washing slag and the leaching residue of electron,we determines raw material structure has been destroyed,and further leaching effect is very good.