Studies On The And Separation Of Ce/La In The P507-LA-HCl System

As a kind of non-renewable strategic resources,rare earths are playing an indispensible role in the high-technology fields.Among them,lanthanum and cerium are most widely used with largest contents in the crust and most industrial reserves and productions.The current main industrial process of separating the two elements is solvent extraction with saponification P507 as major extraction agent.Saponification wastewater containing ammonia and nitrogen,high acid and alkali consumption and emulsification result in high production cost and serious environmental pollution.Therefore,it is extremely essential to develop a new environmentally friendly process of high efficiency and energy saving to replace the traditional technology.The P507-LA-HC1 system was used in this paper to completely eradicate the production of saponification wastewater from the source.Then TBP was employed to recycle the lactic acid,which was regarded as complex agent in the extraction.The performance of P507-LA-HC1 system on the extraction separation of La and Ce was studied at first.The distribution ratio of La and Ce showed a decreasing tendency with acidity rising while became lager at higher lactic acid concentration.Following the laws of positive sequence extraction,it was significantly higher than that of P507-HCl system.The extraction capacity was also greatly superior to P507-HCl system and presented the same change rule with water phase acidity and lactic acid concentration as distribution ratio.Maximum extraction capacity of La and Ce are respectively 28.85g/L and 44.88g/L,higher than that in P507 saponification system.These indicated that P507-LA-HCl system had better extraction performance of La and Ce.Separation factor increased with the rise of balanced acidity while showed a decreasing tendency with the concentration of lactic acid rising.The factor of P507-LA-HCl system was is about 7.45 to 12.92,significantly better than 6.6 in the P507-HCl system.The extraction mechanisms of the two systems were determined as cation exchange by slope analysis method and lactic acid was proved to retain in the aqueous phase at the same time.The equilibrium constant of lactic acid system was greater than that of hydrochloric acid system and the equilibrium constant of Ce was larger than that of La.RE3+had replacement function hydrogen on phosphorus hydroxyl and coordinated with the oxygen on phosphoryl,demonstrated by FT-IR.Extraction separation process of P507-LA-HCl system was then studied.Separation factors under different components were measured by single stage extraction.Based on this,mathematical model of the relationship between separation factor and composition was established and recursive model with constant mixed extraction ratio can be further set up.The optimal processing conditions were obtained:LA:RE=1:1,pH=2.5.Lanthanum with purity of 99.995%and cerium with purity of 99.991%can be got after fourteen level extraction and seven steps of water washing.Finally,the experiments of recovery of complexing agent in this system are studied and the results are listed as follows.The orthogonal experiments and variance analysis of extracting lactic acid with TBP show that lanthanum chloride concentration and the concentration of the TBP and the acidity of material liquid have a significant impact on the extraction rate of lactic acid,and the temperature have certain effect on the extraction rate.The results of the multistage extraction experimental of TBP extracting lactic acid are listed as follow.The recovery rates of lactic acid can reach 99.98%and the COD value of 11.57mg/L can meet the emission standards of industry by 10-stage cross-current-extraction at a phase ratio O/A=1:1,t=20?,pH=1.0,[LaCl3]=0.2mol/L,75 vol.%TBP in kerosene.The recovery rates of lactic acid reach 99.97%and lactic acid concentration in the extraction residue low to 54 mg/L,and the COD value of 57.6mg/L can meet the emission standards of pollutants from rare earths industry by 13-stages counter-current extraction at the material liquid with exporting water phase of the separation of lanthanum cerium.The extraction equations of TBP extracting lactic acid is listed as follows:TBP +LA=TBP · LA,it is exothermically driven.The lactic acid was extracted by TBP through intermolecular hydrogen bond with lactic acid molecular.The experiment of stripping lactic acid show that phase ratio have an obvious impact and temperature have an Certain impact on the stripping ratio.The values of stripping ratio for complexing agents reach 100%with an O/A volume ratio(1:1)through 6-stage extraction,with a phase ratio O/A=1.5:1 through 8-stage extraction,with a phase ratio O/A=2:1 through10-stage extraction and with a phase ratio O/A=2:1 through 12-stage extraction using the deionized water.The values of stripping ratio for complexing agents reach 99.5%at an O/A volume ratio(1:1)through 11-stage counter-current extraction by graphical method of McCabe-Thiele and through 14-stage counter-current extraction in practice.lactic acid can be recycled through further concentration by evaporation.In general,the P507-LA-HCl system has realized the non-saponifiable complexing extraction of La and Ce and can be further developed to a high efficient,energy saving and environmentally friendly separation process.