Extraction And Separation Of Yttrium In Naphthenic Acid System

Naphthenic acid is widely used for the extraction of rare earth elements.But it needs to be saponified with ammonia before extraction,leading to the production of large amounts of waste water containing ammonia-nitrogen.This greatly restricts the development of rare earth industry.Additionally,the saponification naphthenic acid system has the disadvantages of slow time of phase separation,poor flowability,malodorous mixed alcohol.In this article,we will purify industrial-grade crude naphthenic acid,and explore the composition of the saponification naphthenic acid system and naphthenic acid-N235 system applicable for naphthenic acid with different acid values,and study the process conditions of extraction of yttrium with naphthenic acid-N235 system and industrial production simulation.The organic phases before and after extraction were also determined by spectrum analysis.The main contents and results of this paper are as follows:(1)There are different ingredients from different manufacturers for the crude naphthenic acid.The purity of naphthenic acid has some influences on the extraction of rare earths.The refined naphthenic acid which has less non-naphthenic ingredients can be obtained by vacuum distillation method,but its initial fraction contains more neutral oil that is needed to be removed for further use.Ammonia-alcohol solvent purification method can purify naphthenic acid,but the effect is not better compared to vacuum distillation and can not reduce the odor of the crude naphthenic acid.Non-naphthenic acid ingredient may interact with oxygen,deepening the color of naphthenic acid.(2)20%naphthenic acid+20%n-butanol+60%n-hexane saponified-naphthenic acid system has a better applicability for the naphthenic acid with different acid values.Usually,the naphthenic acid with higher acid value(>160 mg KOH/g)is more suitable for saponification system.The amount of ammonia has a significant impact on the process of saponification of naphthenic acid and extraction of yttrium and the raffinate pH value,too high amount of ammonia will lead to emulsification during saponification and extraction.(3)Suitable composition of non-saponification naphthenic acid system is 20%naphthenic acid+10%octanol+25%isopropyl alcohol+40%N235+5%n-hexane.The feed pH value has little effect on the extraction of yttrium,the extraction rate increases with increasing the phase volume ratio,the amount of N235 and acid value of naphthenic acid.When the phase volume ratio is 3:1,phase separation time is shorter and extraction rate is more than 55%.When the phase volume ratio is greater than 3:1,the phase separation time increases.The naphthenic acid with acid values of 100-200 mg KOH/g can be used to extract yttrium in naphthenic acid-N235 system,and there is no the third phase during the extraction process.In naphthenic-N235 system,isopropyl alcohol,N235 and octanol have synergistic extraction effect,among which isopropyl alcohol has the strongest synergetic effect,followed by N235 and octanol.(4)In naphthenic-N235 system,the addition of isopropyl alcohol can significantly improve the extraction rate,but too high amount of isopropanol alcohol(>30%)can cause the yellow raffinate and an increase in volume of the raffinate because of part of isopropanol and naphthenic acid entering into the aqueous phase.In saponification naphthenic acid system and naphthenic acid-N235 system,n-hexane can short the phase separation time,but the increase of n-hexane will decrease the extraction rate of yttrium.(5)The organic phase obtained before and after saponification,extraction and stripping and recycling were determined by spectrum analysis.After saponification,C=O peak of naphthenic acid at 1710 cm-1 disappeared,and the antisymmetric and symmetric characteristic peak of COOappears at 1554 cm-1 and 1406 cm-1.After extraction of rare earth ions,the antisymmetric and symmetric absorption peak of COO-shifts,indicating that a complex between naphthenic acid and rare earth ions is fromed and the extraction of yttrium is a typical reaction of cation exchange.It is not observed this phenomenon in the naphthenic acid-N235 system,indicating the difference between naphthenic acid-N235 extraction system and saponified-naphthenic acid system.(6)The extraction and separation of yttrium from liquors containing 15 kinds of rare earth elements requires two steps.Firstly,the liquid is separated by YLaCePrNd/Sm-Lu grouping.Sm-Lu elements are the easily extracted components and are obtained at the exit of the organic phase,and Y,La,Ce,Pr,Nd belong to the hardly extracted component,and are obtained at the exit of the aqueous phase.Secondly,Y,La,Ce,Pr,Nd obtained from the first step were performed Y/LaCePrNd grouping to finally obtain the pure Y,Y is easy to extract,and obtained at the exit of the organic phase.The cascade theory is used to calculate and simulate the extraction process of yttrium.For the separation of Y,La,Ce,Pr,Nd from the middle and heavy rare earth elements,the separation factor between the easily extracted component and difficultly extracted component is quite high,and the separation process belongs to the extraction section control;To obtain the product with purity of 0.9999,the stages of the extraction section and scrubbing section are 11 and 9,respectively.For the separation of Y from La,Ce,Pr,Nd,of which belongs to the scrubbing section control,to obtain the product with purity of 0.9999,the required stages of the extraction section and scrubbing section are 19 and 21,respectively.Due to the smaller separation factor,Y separation from La,Ce,Pr,Nd requires more stages of extraction section and scrubbing section and larger flow of organic and aqueous phases.Compared with the saponified-naphthenic acid system,naphthenic acid-N235 system is more suitable for the naphthenic acid with different acid values.Additionally,naphthenic acid-N235 system has the advantages of no ammonia saponification,no ammonia emissions,easily phase separation and no third phase generation.Yttrium can be separated from rare earth liquids by two-step separation.