Preparing Rare Earth Chloride Solution With High Purity And High Concentration From The Leachate Of Ion Adsorption Rare Earth

Techniques of ammonium sulfate leaching and ammonium bicarbonate precipitation are widely used to produce ion adsorption rare earth（IARE）due to their characterizations of high leaching efficiency,excellent precipitation crystallization effect and low cost.However,the excessive use of leaching agent and precipitating agent has led to serious ammonia nitrogen pollution.As an inexpensive ammonium-free leaching agent,calcium chloride has great application potential.However,its leaching capacity needs to be further improved.Novel techniques are also be proposed to recover rare earth from its leachate of IARE and prepare high purity and high concentration of rare earth chloride solution for the further separation of rare earths.In this study,lime was employed to precipitate rare earths from their chloride and sulfate medium respectively.It was proved that the product obtained from the sulfate medium was basic rare earth sulfate,and the purity of the calcined oxide was less than83%.In contrast,the products obtained from the chloride medium were rare earth hydroxides（REHO）with higher purity and better crystallinity,the purity of calcined oxides can reach more than 98%,and the crystallinity and product quality of rare earth hydroxides can be further improved by increasing the precipitation temperature and decreasing the feeding speed.However,the presence of aluminum can be precipitated together and reduces the purity of final product.Therefore,two basic methods were proposed to prepare rare earth chloride feed solution with high purity and high-concentration.One method is to precipitate all rare earth and aluminum with lime,and then dissolve the REHO after filtration and dry in hydrochloric acid only controlling the final p H value between 4-5.The rare earth and aluminum in the acid-insoluble slag were dissolved in the leachate of aluminum sulfate.After extracting rare earth by N1923,the aluminum sulfate in raffate was reused as leaching agent,which can realize the efficient separation and recovery of both rare earth and aluminum.The other method is a stages process,first is to separate impurities by adjusting the p H value at about 6,and then to precipitate all rare earths with lime bycontrolling p H between 9.3-9.5 and to obtain high-purity rare earth hydroxide.Then,rare earth chloride solution with high purity and high-concentration can be prepared by directly dissolve the dry REHO with hydrochloric acid.The obtained REHO can also be subjected to a multi-stage continuous saponification in the presence of rare earth chloride to obtain a qualified saponified organic phase without discharge of saponification wastewater.With this method,the problems of environmental pollution and high cost caused by the organic phase loss in the integrated technology of leaching and extraction could be overcome,and the subsequent extraction and separation processes would not produce waste water and radioactive waste residues.In addition,the separation work of the saponification process could be introduced into the rare earth extraction and separation process through a dual feed mode of both organic phase and aqueous phase by using the obtained saponified organic phase and high-concentration rare earth chloride solution.Which can further optimize the separation process and improve the separation efficiency.The leaching of IARE by inorganic electrolytes can be strengthen with the addition of citric acid.It was demonstrated that when the concentration of citrate acid is 0.6 times and above that of rare earth,lime or Na OH can not completely precipitate the rare earth because of the formation of soluble complexes of citrate.However,the addition of aluminum can increase the precipitation rate of rare earth due to its competition coordination toward rare earth with citrate.Therefore,the rare earth can be completely precipitated by reducing the concentration of citric acid and increasing the concentration of aluminum,and then enriched by extraction after acid dissolution of the precipitates.The effects of citric acid（ca）on the extraction separation of rare earth from aluminum were studied in sulfate and chloride medium respectively.It was found that in case of n_ca/n _RE≤3,the extraction separation coefficient between RE and Al(β_RE/Al)by a saponified P507-kerosene organic phase in HCl medium showed a downward trend with the increase of acid acid concentration.However,the separation coefficientβ_RE/Alin a single-stage extraction or a three-stage countercurrent extraction were still above 1×10^3.04and 1×10^5.4respectively.Meanwhile,the extraction separation coefficient between RE and Al(β_RE/Al)by a N1923-kerosene organic phase in sulfate medium increased with the increase of citric acid concentration,and can be kept above 1×10^2.9.Based on the large extraction separation coefficient between RE and Al by N1923,a method to determine the content of rare earth and aluminum in the leachate of sulfate was established.When the concentration of rare earth concentration is lower than 0.01 mol/L and phase ration of organic/water is employed 1,the rare earth extraction rate can be kept above 98%.After scrubbing the Al from organic phase with a 2wt%（NH₄）₂SO₄solution at p H=1,the efficient separation of rare earth from aluminum can be realized.This method is not only simple to operate,but also has high accuracy with low requirements for laboratory equipment,which is applicable to most laboratories.