Study On The Process Of Deacidification And Iron Removal From The Unsaponifiable Extractant For Rare Earth Separation

In industry,P507and P204are widely used as the extractions for the separation of therare earth.However,these processes find many complaints because of the seriousenvironmental problems which come from the generated large amounts of ammonia-nitrogencontaining wastewater.In order to reduce the environmental problems,we had developed anovel green process by using the P507-N235binary extractions.Unfortunately,this process hashigh acidity in the mixed organic phase and a difficulty to strip the Fe3+.To understand andsolve these problems,the rare earth was leached by the acid together with P507-N235.theeffects of feed concentrations、phase ratio、leaching time on the extraction capacity and theproperty of the phase separation were studied in this work.Meanwhile,the process with P507extracting rare earth and N235extracting acid separately was also presented.Finally theproperties of the extraction and stripping of Fe3+in P507-N235process were also discussed inthis work.The optimal process parameters were determined by the experiment of neodymiumcarbonate decomposition with acid-containing organic phase： the feed concentration is72.5g/L、 the leaching time is30min、 the phase ratio is1:1,under these conditions,theextraction capacity of Nd is0.1185mol/L and this process has a good phase separation.For theneodymium hydroxide decomposition with acid-containing organic phase,under the optimalprocess such as the feed concentration is73.3g/L、leaching time is50min、phase ratio is1:1,the extraction capacity of Nd is0.1288mol/L.Experiments demonstrated the feasibility of thisscheme,the acid-containing organic phase can realize recycle and the effect of acid utilizationis better.The extraction capacity of La is only about0.025mol/L under the un-saponifiableP507-kerosene system.Using the composite organic extractant of N235-kerosene-A1416toextract acid in raffinate,97.7%of hydrochloric acid can be removed with favorable phaseseparation,and the extracting conditions are as follows:phase ratio is1:1、ratio of total acid inwater phase to amount of N235in organic phase is0.96、volume fraction of A1416is15%.After acidification,we used N235-kerosene-A1416to decompose neodymium hydroxideunder the following conditions: phase ratio is2:1、reaction time is90min、T=25℃、stirringspeed is350r/min,and95.8%of decomposition rate toward neodymium hydroxide wasachieved. P507-N235has a strong capability of extracting Fe3+,when phase ratio is1:1、oscillationtime is3min、pH of the feed is2.2、Fe3+concentration in feed is2.374g/L, and the single stageextraction rate of iron reached about99.2%.The effect of extracting Fe3+from P507-N235wasnot good by oxalic acid,however,Fe3+was easily back-extracted in P507-N235system byEDTA,the single stage extracting rate of iron(Ⅲ) was over97%when phase ratio is1:1、back-extraction time is14min、concentration of EDTAis0.0394mol/L.Concentration of Fe3+was decreased from2.207g/L to0.007g/L after4-stage of cross-flow back-extraction and theextraction rate reached99.77%.