High Efficient And Green Leaching Of Rare Earth Resources Coupled With Technologies Of Reducing Emission And Consumption During Their Extraction Separation

Green exploitation of rare earth resources requires new advanced technologies.In the development of ion adsorption rare earth resources in the South and mineral rare earth resources in the North,varieties leaching and extraction separation processes of rare earth elements have been developed.However,with the improvement of environmental protection requirements,the original leaching reagents and processes as well as the extraction separation methods of rare earth elements cannot meet the new requirements.In this paper,the ion adsorption rare earth was leached by calcium chloride and aluminum sulfate in stages,and the acid organic phase of P507 was saponified with rare earth hydroxide to optimize the extraction separation process of rare earths both in south and north of China by coupling with the technologies of reducing consumption and reducing emission during extraction separation.In order to solve the problems of ammonia nitrogen pollution,low efficiency and soil erosion of tailings,a stages leaching technology of ion adsorption rare earth successively using calcium chloride and aluminum sulfate was proposed.Therefore,the effects of different leaching agents and their concentrations as well as the limewater neutralization for tailing protection on rare earth leaching efficiency(RELE)and the zeta potential of clay mineral particles(ZPCMP)in tailing were studied.The results show that the RELE by calcium chloride is lower than that of by ammonium sulfate,magnesium sulfate and aluminum sulfate,but it can be partially compensated by increasing the concentration.However,when the concentration is greater than 0.256 N,the increase of RELE tends to be gentle.By introducing a second stage of leaching with aluminum sulfate,RELE can be greatly improved,and the absolute value of ZPCMP in tailing can be reduced to ensure the stability of tailing.When the ratio of liquid to solid is 1:1,the RELE can be improved to 96%by using 20%aluminum sulfate and 80%calcium chloride to leaching in stages.The rare earth in the leaching solution of calcium chloride can be precipitated with limewater to form crystalline rare earth hydroxide(REHO).This REHO can be used to saponify P507 organic phase.Therefore,the influences of the initial concentration of rare earth in aqueous phase(ICREAP),the phase ratio of organic phase to aqueous phase(R=O/A)and the stage number(SN)of countercurrent extraction were determined on the basis of the loaded concentration of rare earth in organic phase(LCREOP).It is proved that the LCREOP can be adjusted within 0.16-0.24 mol/L by changing the CREAP,the R and the SN.The raffinate from saponification was recycled to dissolve REHO for preparing high concentration of rare earth solution.The insoluble residue was combined with the leaching solution of aluminum sulfate,and the rare earth was enriched and separated from the aluminum by N1923 extraction.Based on this,a new extraction process of ion adsorption rare earth was proposed,which consists of leaching,precipitation,extraction,enrichment,and recycling etc.Meanwhile,REHO obtained from the alkali conversion of rare earth phosphate and fluorocarbon minerals was used to replace the original basic compounds such as ammonium,sodium,calcium,magnesium,etc.to saponify the organic phase of P507-kerosine and prepare rare earth chloride solution.Therefore,the dependence of the LCREOP and the acidity of raffinate(pHR)on ICREAP,the R=O/A and the SN of countercurrent extraction were studied in this paper.With the mode of continuous countercurrent extraction,the outlet of LCREOP can be easily controlled by adjusting R,ICREAP and SN,and qualified organic phases with LCREOP ranging from 0.16 to 0.24 mol/L can be obtained.Moreover,through the adjustment of the pH of the aqueous phase of the final stage of the solvent and the first stage of extraction,the concentration of Th4+and Al3+ entering the organic phase is controlled at about 1 mg/L.Based on these,a new process consisting of a countercurrent saponification unit(CSU)for producing required P507-kerosine organic phase and an acidic raffinate recycling unit(ARRU)for dissolving REHO and obtaining required aqueous phase was developed.The process overcomes the influence of the small size of the REHO and co-existing impurities on the saponification process,which not only saves the consumption of raw materials,but also does not produce saponification waste water.