A calixarene derivative, 5,11,17,23-tetra（diethoxyphosphoryl）-25,26,27,28-tetraacetoxycalix[4]arene （L）, was studied for the extraction and separation of thorium and rare earths in nitrate medium. Thorium was extracted into the organic phase by a complex of Th（NO3）4·L with the logarithm of the equilibrium constant of 2.77. Thermodynamic functions, AH, AG and AS were calculated to be -2.49, -15.55 kJ/mol and 44.53 J/（mol·K）, respectively. The results indicated that this calixarene derivative might be used to separate thorium from rare earths and the separation factors were larger than 26. However, the salting-out agents affected the separation.
In the present work, a novel α-aminophosphonate extractant（Cextrant 230） was synthesized for the extraction and recovery of cerium and thorium from sulphate medium. The introduction of amine group into the phosphate molecule would enhance the extraction of Ce（Ⅳ） and Th（Ⅳ）. The effects of extractant concentration, H2SO4 concentration and temperature on the metal extraction were investigated in detail. It was found that the extraction of Ce（Ⅳ）, Th（Ⅳ） and REs（La, Gd, Yb） in sulphate medium decreased in the following order： Ce（Ⅳ）〉Th（Ⅳ）〉REs（Ⅲ）. A solvent extraction process to extract and recover cerium and thorium from bastnasite leaching was proposed, in which the purities of cerium and thorium products reached 99.9% and 99% with yield of 92% and 98%, respectively.
Rare earths(REs) play a key role in high-tech fields and the associated thorium is a vital element for nuclear energy. However, to be used in high-tech industry or nuclear energy, these elements must first be recovered from the deposits and purified. As solvent extraction is the main technology for the recovery and purification of the metals, the review mainly presents our recent works on the extraction and separation of tetravalent cerium cation by neutral α-aminophosphonates, the individual rare earth separation by α-aminophosphonic acids, and the continuous preparation of high-purity thorium. The extraction and separation of some other metals are also discussed.
Synergistic solvent extraction of rare earth elements （REEs） from nitrate medium was investigated with mixtures of 8-hydroxyquinoline （HQ） and acidic organophosphorus extractants, bis（2,4,4-trimethylpentyl） dithiophosphinic acid （Cyanex 301） and bis（2,4,4-trimethylpentyl） monothiophosphinic acid （Cyanex 302）. The extraction behavior of Cyanex 301/Cyanex 302 and their binary mixtures with HQ towards several lanthanoids （La, Nd, Sm, Tb, Ho, Tm） and yttrium （Y） was investigated. The separation ability of REEs was studied according to the various extraction effects. The extraction mechanisms for yttrium were studied with the methods of slope analysis and constant moles in the synergistic systems. The extracted compounds, the equilibrium constants, and thermodynamic functions were also determined.
The extraction and separation of heavy rare earths（REs） using newly synthesized a-aminophosphonic acid extractant 2-ethylhexyl-3-（2-ethylhexylamino）pentan-3-yl phosphonic acid（HEHAPP, HA） in nheptane were investigated from chloride medium. The extraction stoichiometries of lanthanum, gadolinium, yttrium and lutetium are determined to be REA3 by the slope analysis method. The favorable separation factors of adjacent heavy REs（Ⅲ）,i.e. β（Y/Ho）, β（Er/Y）,β（Tm/Er）,β（Yb/Tm） and β（Lu/Yb）, are determined to be1.87,1.36, 3.21,3.22 and 1.93, respectively, when extracted from a binary system at proper condition. The loading capacities of HA for Ho, Er, Yb and Lu increase in the order Ho 〈 Er 〈 Yb 〈 Lu with the values being 0.201, 0.205, 0.216 and 0.229 mol/L, respectively. So HA would be a potential extractant for the separation of heavy REs（Ⅲ）. Among inorganic acids such as H2 SO4, HNO3 and HCl, HCl is tested to be the most effective stripping agent.
Three 4.8 nm isostructural{M_(72)}(M=Co^(Ⅱ) for CIAC-128,Ni^(Ⅱ) for CIAC-129,Fe^(Ⅱ) for CIAC-130) metal-organic polyhedra(MOPs) are constructed by eighteen M_(4)-p-tert-butylthiacalix[4]arene (M_(4)-TC4A) units bridged via sixteen four-connected 5,5′-(1H-1,2,4-triazole-3,5-diyl) diisophthalic acid (H_(4)TADIPA) linkers.These MOPs are featured with a rarely reported concave coordination cage,which can be simplified as a squeezed double-decker hexagonal prism pressed from the top and bottom hexagonal faces.Furthermore,CIAC-128,CIAC-129 and CIAC-130 are the highest nuclearity discrete clusters of Co,Ni and Fe reported so far.CIAC-128 has higher separation selectivity of C_(3)H_(8) than CH_(4) under ambient conditions,and also exhibits separation selectivity for C_(2)H_(6)/CH_(4),C_(2)H_(2)/CH_(4),and C_(2)H_(4)/CH_(4).In addition,CIAC-128 can provide the cavity for the confined synthesis of noble metal nanoclusters such as Pd nanoclusters and the resulting Pd@CIAC-128 hybrids show higher electrocatalytic activity than commercial Pt/C towards hydrogen evolution reaction (HER).
Synergistic extraction of heavy rare earths(REs) were investigated in chloride media by the mixture of(2-ethylhexylamino)methyl phosphonic acid mono-2-ethylhexyl ester(HEHAMP) and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester(HEHEHP). The maximum synergistic enhancement coefficients(R) of Lu, Yb, Tm, Er, Y and Ho are 2.89, 2.76, 2.54, 2.14, 2.14 and 2.06, respectively, when the mole fraction X_(HEHAMP) is 0.5. The synergistic separation factors of the heavy REs are obtained(β_(Y/Ho)=1.31,β_(Er/Y)= 1.61,β_(Tm/Er)= 1.78, β_(Yb/Tm)= 1.76, β_(Lu/Yb) = 1.20). The extracted complex is determined to be RE[H(EHAMP)_2][H(EHEHP)_2]_2 by the slope analysis method. The loading capacities of the mixtures consisting of 15% HEHAMP and 15% HEHEHP for Y and Lu are about 26.59 g/L(Yb_2 O_3) and 27.25 g/L(Lu_2 O_3),respectively.
