As a relatively new extractant, di-（2,3-dimethylbutyl）-phosphinic acid （HYY-2） is more efficient to separate heavy rare earths Tm/Yb/Lu than Cyanex 272 and P507. In this paper, HYY-2 was synthesized in our lab, and the extraction equilibrium, thermodynamics and stripping acidity for La, Gd and Y, which stood for light rare earth elements （REE）, middle REE and heavy REE respectively, from nitrate media with this extractant were investigated. Meanwhile, extraction ability, capacity and stripping acidity of HYY-2 were investigated and compared with those of Cyanex 272 and P507. The separation performance for rare earth element couples Gd/Eu and Er/Y were also studied. Compared to Cyanex 272, it possessed higher extraction capacity; while compared with P507, it has lower stripping acidity. The maximum βGD/Eu 1.46 occurred at PHequilibrium=2.78 and the maximumβEr/Y was 1.47 when pHequilibrium= 2.01.
Fine face-centered cubic (FCC) nickel powders were synthesized by liquid phase reduction with different surfactants. The products were investigated by scanning electron microscopy (SEM), laser particle size analyzer and X-ray powder diffraction (XRD). The results indicate that the type, dosage and relative molecular mass of surfactants significantly impact the purity, dispersion property, particle size, size distribution and morphology of the products. The nonionic surfactants poly ethylene glycol (PEG) and polyethylene glycol sorbitan monostearate (Tween) showed better dispersing ability in the reaction system than the others. The optimal mass ratios of surfactant to Ni are 100 mg/g and 150 mg/g for PEG-600 and Tween-40, respectively. The products obtained in the optimal conditions have ideal morphology and narrow size distribution. Moreover, study on the relative molecular mass effect revealed that with the increase of the relative molecular mass of Tween, the morphology of nickel powders changed from sphere to spiny ball.
The Li Ni1/3Co1/3Mn1/3O2 is first obtained by the controlled crystallization method and then coated with Ni3(PO4)2particles. The effects of the coating on rate capability and cycle life at high cut-off voltage are investigated by electrochemical impedance spectroscopy and galvanostatic measurements. The element ratio of Ni:Mn:Co is tested by inductively-coupled plasma spectrometer(ICP) analysis and it testified to be 1:1:1. It is indicated that Ni3(PO4)2-coated Li Ni1/3Co1/3Mn1/3O2 has an outstanding capacity retention, where 99% capacity retention is maintained after 10 cycles at 5C discharge rate between 2.7 V and 4.6 V. The electrochemical impedance spectroscopy(EIS) results show that the current exchange density i0 of the coated sample is higher than that of Li Ni1/3Co1/3Mn1/3O2, which is beneficial to its electrochemical performances. All the conclusions show that the Ni3(PO4)2coating can prominently enhance the high rate performance of the Li Ni1/3Co1/3Mn1/3O2, especially at high cut-off voltage.
Kinetics of Co（II） extraction from sulfate aqueous solution by the sodium salt of di-decylphosphinic acid （Na-DDPA） was studied using a modified Lewis cell to disclose the mechanism of extraction. Parameters affecting the extraction rate, such as stirring speed, temperature, interfacial area, Na-DDPA concentration and Co（II） concentration, were investigated, respectively. The effect of diffusion resistance on extraction rate was negligible when the stirring operation was conducted in a plateau region of 95-110 r/min. Extraction rate increased with the increase in the temperature or specific interfacial area. The activation energy E was calculated to be 32.75 kJ/mol. These suggested that rate controlling mechanism of Co（II） extraction by Na-DDPA was chemical reaction regime and the rate-determining step of Co（II） extraction was chemical reaction at the interface. The initial extraction rate also increased with the increase in the concentrations of Na-DDPA and Co（II）. The extraction rate equation and mechanism of Co（II） extraction by Na-DDPA were proposed.
