The Extraction And Separation Of Zirconium And Hafnium With Organic Phosphoric Acid Extractants

Zirconium and hafnium mainly exist in the state of ore in nature.There is no separate zirconium and hafnium.They are in the same period,have similar atomic radii,ion radii and physicochemical properties,making them difficult to separate.Due to their excellent mechanical properties,strong corrosion resistance,high hardness and high melting points,zirconium and hafnium have been widely used in the fields of atomic energy industry,aerospace,weapon manufacturing and petrochemical industry.The thermal neutron absorption cross section of zirconium is more than 600 times that of hafnium,and they play completely different and indispensable roles in the nuclear industry.To ensure the safe and stable operation of nuclear power plants,nuclear grade zirconium and hafnium have extremely strict requirements for purity.Therefore,the separation of zirconium and hafnium is of profound significance for the advancement of the atomic energy industry.Solvent extraction is the most common method for the separation of zirconium and hafnium,but in the industry there are problems such as environmental pollution,equipment corrosion,emulsification.It is a general trend to develop a new extraction and separation system of zirconium and hafnium.Organic phosphoric acid extractants,such as di?2-ethylhexyl?phosphoric acid?D2EHPA?,have been widely used in the extraction and separation of metals due to their low cost and high efficiency.In this paper,a variety of organic phosphoric acid extractants with P?O?OH group were used to compare the properties,optimize the reaction conditions,and improve the extraction rates and separation factor of zirconium and hafnium.The anti-synergistic effect of organic acids on organic phosphoric acid extractants was studied,and a separation method of zirconium and hafnium with preferential extraction of hafnium was obtained.The diphosphonic acid extractant with extremely strong extraction ability was designed and synthesized.The changes of extraction mechanisms and complex structures under different acidities were mainly studied.The effect of the structure of organic phosphoric acid extractants on the extraction and separation performance of zirconium and hafnium in different acidic solutions was systematically analyzed.The main research contents are as follows:1.The specific working principles,advantages,disadvantages as well as operating procedures of spectrophotometric method and inductively coupled plasma method were compared.According to research,the inductively coupled plasma method is more suitable for detecting the concentrations of zirconium and hafnium.2.Using D2EHPA as extractant,we investigated the anti-synergistic effect of organic acids on zirconium and hafnium under the hydrochloric acid system and the influence of acidity on the extraction and separation of zirconium and hafnium in sulfuric acid.Infrared spectroscopy showed that the complexation capacity of organic acid and zirconium was stronger than that of hafnium.The addition of organic acid in the aqueous phase inhibited the extraction of zirconium and gave priority to the extraction of hafnium.In sulfuric acid system,D2EHPA had the best separation effect on zirconium and hafnium,with the separation factor of 73.62.3.Taking 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester?PC88A?as extractant,we studied the effects of diluent type,extractant concentration,hydrochloric acid concentration,and organic acid concentration on the extraction and separation of zirconium and hafnium.The co-extraction system composed of PC88A and organic acid was less effective in the extraction and separation of zirconium and hafnium than the co-extraction system composed of D2EHPA and organic acid.4.The new diphosphonic acid extractant,N,N-n-octylamine di?methylene phenylphosphinic acid??OADMPPA?,was synthesized,and the influence of diluent type,time,temperature,hydrochloric acid concentration,extractant concentration on the extraction and separation of zirconium and hafnium was investigated.In 0.5,3 and 6 mol/dm³ hydrochloric acid,the extraction mechanisms were converted from cation exchange mechanism to solvation mechanism,and the complex compositions were ZrOA,Zr?HA?₂Cl₂ and ZrCl₄·H₂A,respectively.Compared with bis?2,4,4-trimethylpentyl?phosphinic acid?Cyanex272?and tri-n-octylamine?TOA?,the extraction rates of OADMPPA for zirconium and hafnium were 8and 14 times of Cyanex272 system but the separation factor did not change.5.Di?2-ethylhexyl?dithiophosphoric acid?D2EHDTPA?was synthesized.Under the same experimental conditions,the extraction and separation performance of D2EHPA,PC88A,Cyanex272 and D2EHDTPA was compared under hydrochloric acid,sulfuric acid and nitric acid systems.The extraction capacity of the four extractants was ranked as follows:D2EHPA>PC88A>Cyanex272>D2EHDTPA,which was related to the number of P-O bonds.With the increased number of P-O bonds,the pKa value of the extractant decreased and the activity of the functional group P?O?OH increased.The separation ability sequencings in hydrochloric acid,sulfuric acid and nitric acid systems were D2EHDTPA>Cyanex272>PC88A>D2EHPA,D2EHPA>PC88A>Cyanex272,D2EHPA>Cyanex272 and PC88A,respectively.D2EHDTPA had a low extraction rates and poor selectivity for zirconium and hafnium,which might be related to the radii and electronegativity of sulfur and oxygen atoms.