Study On Extraction Of Rare Earth From Molten Salt Electrolysis Slag Based On Mineral Phase Reconstruction

The production of rare earth metals is mostly used by molten salt electrolysis.A lot of rare earth molten salt electrolysis slag is produced while obtaining rare earth metals.The content of rare earth elements?rare earth oxides?in the slag is between 20%⁸0%,becoming an important secondary resource of rare earth.The importance of recycling and reusing rare earth elements is self-evident.The rare earth molten salt electrolysis slag can be divided into two categories:chlorine salt system rare earth molten salt electrolysis slag and fluorine salt system rare earth molten salt electrolysis slag.Because the latter is difficult to be directly decomposed by inorganic acids,it is necessary to separate the rare earth from the fluorine by other methods in order to effectively recover the rare earth.In this context,a high efficiency green recovery fluorine salt system of rare earth in the rare earth molten salt electrolysis slag is proposed.The specific contents are as follows:?1?Inspired by metallogenic process and decomposition process of ytterbite,a novel method of extraction of rare earth elements from fluoride molten salt electrolytic slag by mineral phase reconstruction is proposed.The effects of various factors on the leaching rate of rare earth in the process of roasting,washing and acid leaching were investigated.The reaction mechanism in the process of roasting and acid leaching is explored by means of X ray diffraction analysis and energy spectrum analysis.Under the following conditions:roasting time 1.5 h,roasting temperature 850?,the mass ratio 1.5:1,leaching time 2 h,the concentration of hydrochloric acid was 4 mol·L^-1,the leaching temperature 80?and L/S12:1,the leaching efficiency of rare earth can reach as high as 98.96%.When a proper amount of sodium silicate is added,La₁₀?SiO₄?₆O₃,which is difficult to dissolve in water but easily decomposed by hydrochloric acid,and NaF are produced.When sodium silicate is overdose,NaLa₄?SiO₄?₃F is also produced during the roasting process.The substance is also difficult to dissolve in water but is easily decomposed by hydrochloric acid.In the process of washing,the separation of the rare earth elements La and F elements can not be completely realized,and the rare earth ion La³⁺is combined into LaF₃.The results show that the leaching rate is reduced by a small amount of LaF₃ in the acid leaching residue.?2?The use of oxalic acid to precipitate the rare earth in the acid extract.The La₂O₃,which can be returned to the molten salt electrolysis process,was finally obtained.The influence of the amount of oxalic acid,the time of precipitation and the aging time on the rare-earth precipitation rate were investigated.The results are as follows:the precipitation rate of rare earth is up to 98.59%when the dosage of oxalic acid is 0.35 g,the precipitation temperature is 35?,the precipitation time is 10 min,the aging time is 60 min and the stirring rate is 100 r·min^-1.After the X ray diffraction analysis,the sediment was determined to be La₂?C₂O₄?₃ 10H₂O.After calcining,La₂O₃ can be obtained with a purity of 99.40%,which can be directly returned to the electrolysis process.?3?The acid wastewater after oxalic acid precipitation is used to regulate the pH value of alkaline wastewater.This creates favorable acidic conditions for the defluorination of hydroxyapatite?HAP?.The effects of HAP dosage,conversion time and initial pH value on the effect of curing and defluorination were investigated.The results are as follows:under the optimum conditions of HAP dosage of 1.5 g,initial pH value of 1,conversion time 30 min,reaction temperature 35?,and stirring rate 400 r·min^-1,the residual fluorine concentration in the waste water is as low as 9.78 ppm.It is in conformity with the discharge standard of national industrial wastewater.