Enrichment And Recovery Of Rare Earth From Low Concentration Leaching Solution Of Ion-Adsorption Rare Earth Ores By Non-Saponification And Non-Equilibrium Extraction

Ion-adsorption rare earth(RE)ores are strategic resources for they are rich in high valued middle-heavy rare earth elements.RE elements basically absorb to clay mineral in the form of ionic states,which results in failure to enrich by mineral processing.The current process for recovering ion-adsorption RE is using salt leaching and ammonium bicarbonate or oxalic acid precipitation.However,there still exists some problems,such as ammonia nitrogen wastewater pollution,long process flow(including impurity,precipitation,aging,filtration,roasting),low RE recovery rate(process of purification and precipitation loss more than 10%),as well as hard disposal of radioactive residue.In order to solve the above problems from the source,Professor Xiaowei Huang group proposes the method using Mg/Ca salts as the leaching reagent and then recovery of rare earth through solvent extraction.As part of the new technology,the basic research on the enrichment process of low concentration rare earth leaching solution is carried out,this paper focuses on the fast accurate test of extractant content in the raffinate,extraction thermodynamic behavior and regularity of RE by HEH(EHP)and HDEHP,extraction kinetics regularity,model and behavior trends of RE and iron,aluminum impurities,RE enrichment and distribution rule in the process of HEH(EHP)one-step extraction and HEH(EHP)/HDEHP stepwise extraction.Finally,the industrial tests are carried out to verify the above basic research results.The main conclusions are as follows:1.Nitric-perchloric mixed acid are performed to decompose the extractants in the raffinate for content fast test.Organic phosphorus is digested to inorganic orthophosphate for Inductively Coupled Plasma Atomic Emission Spectrometry(ICP-AES)testing.The detection limit of phosphorus can reach 0.06 mg/L when the sample acidity<5%,RE concentration<30 mg/L.The sample standard addition recovery rate is founded to be 97.5-103%.The standard deviations<5%.The above results offer a new,fast and accurate method to analysis organic phosphorus content in the raffinate and also other waste water.2.The relationship between RE concentration and equilibrium acidity was obtained through the RE extraction thermodynamic behavior and regularity by RE HEH(EHP)and HDEHP.Based on the cascade extraction theory,the MESH equation was used to fit the multi-stage countercurrent extraction process.The quantitative relationship between the REO,the extraction stage and the extraction rate was obtained.Furthermore,limited concentration of one-step extraction by HEH(EHP)have been obtained by calculation fitting for different stage numbers(1-4 stages),which can offer theoretical direction for HEH(EHP)or HEH(EHP)/HDEHP stepwise extraction process.3.HEH(EHP)/HDEHP stepwise extraction of high concentration RE solution is studied based on the features of acidic phosphorus-containing extractants and leaching solution.The influences of extractant concentration,phase ratio,and stages have been systematically summarized.The extraction and stripping process McCabe-Thiele isotherm are plotted.Total extraction rate reaches more than 99%by multi-stage cascade simulation tests,and the stripping efficiency is high.200 g/L chlorinated light RE and 240 g/L chlorinated medium-heavy RE are obtained by stepwise extraction and stripping.Foreordain grouping is realized for light and middle-heavy RE.The problems of low light RE extraction rate by HEH(EHP)and stripping difficulty of middle-heavy RE by HDEHP are both solved,which achieves efficient enrichment and recovery of RE.4.The difference of RE and impurities extraction kinetics can be designed to realize "non-equilibrium separation",of impurities during the extraction process.The transfer quality control step of Nd and A1 extraction is diffusion in the constant interface pool,and corresponding apparent activation energies are 6.32 kJ/mol and 13.88 kJ/mol,respectively.Extraction reaction prefers to carry out on the two-phase interface.Al extraction behavior is affected by interfacial chemical reaction and mass transfer rate is much lower than Nd under the condition of high speed centrifugation to eliminate diffusion influence.Nd(H2O)8SO4+ and Al(H2O)5SO4+ are the main forms for the two elements in the sulfuric system.The extraction rate of Al is limited by the inner layer coordination.When both Nd and Al elements exist,the steric hindrance of HEH(EHP)-Nd complex is large,the dissociation rate is slow which increases the separation factor of Nd/Al β>50 when mixing 50 s.Al extraction rate<1.5%and Fe extraction rate reduces from 100%to 20%for mixing time of 50 s by practical leaching solution extraction,however,RE extraction rate has not been affected.This method can realize RE directly separation with impurities during the extraction process.5.The hydrodynamic characteristics and mass transfer characteristics of RE are studied by centrifugal extractor using 0.43 g/L low concentration leaching solution.RE in the loading organic phase can be up to 17 g/L,the extraction rate of middle-heavy RE is higher than 99.5%and total RE extraction rate is higher than 98%.The extraction procedure of RE is positive sequence extraction,which shows tetrad effect:La/Ce/Pr/Nd,Sm/Eu/Gd/Tb,Dy/Ho/Er,Tm/Yb/Lu.At 278-313 K,△Gθ<0,△Hθ>0,△Sθ>0,centrifugal extraction reaction is a endothermic entropy increasing process.Increasing temperature can lead to positive going of extraction reactions.The mixing time and phase ratio are the main factors which influence the stripping efficiency.By reducing the flow rate and aqueous phase reflowing,RE single-stage strpping rate can be higher than 77%.Through 3 stages stripping,the RE extraction rate is 96.7%,the residual acid is 0.4 mol/L and the obtained RE chloride concentration is up to 237 g/L.Blank organic phase after stripping can be washed and recycle,raffinate can be used for cyclic leaching and does not reduce the leaching efficiency,which realizes recycling of the whole process.6.Industrial centrifugal extraction tests with HEH(EHP)as the extractant are carried by low concentration RE leaching solution(0.2-0.5 g/L).The mixture and separation results can be realized under the conditions of phase ratio A/O =20/1-50/1 and flow rate 42-50 m3/h.After 3 stages counter-current extraction and 3 stages counter-current stripping,RE yield is higher than 98%,the stripping chlorinated RE solution concentration gradually reaches 230 g/L or more,while the content of impurities Fe2O3,Al2O3 and SO42-are reduced to 0.01%,0.5%and 0.05%.The quality meets the requirement of RE separation plant.