查看更多>>摘要：Weathered crust elution-deposited rare earth ores(WREOs)in China are the main source of medium and heavy rare earths in the world.In order to improve the seepage and the mass transfer of traditional ammonium salt leaching process of WREOs,surfactants were added in the ammonium sulfate leaching solution and the ammonium chloride leaching solution.The leaching kinetics,the mass transfer process,and the adhesion work reduction factor calculated from the interfacial properties were studied to reveal the strengthening mechanism of surfactant.In the presence of the tested five surfactants,cetyl trimethyl ammonium bromide(CTAB),dodecyl trimethyl ammonium bromide(DTAB),sodium dodecyl sulfate(SDS),sodium oleate and oleic acid,the permeability of WREOs is improved,the rare earth(RE)leaching efficiency increase and the impurity aluminum(Al)leaching efficiency decrease,indicating its promo-tional effect on the leaching process of WREOs.Furthermore,CTAB shows a better leaching enhance-ment,and the optimal addition dosage is 0.4 g/L for the two ammonium salt leaching agent systems.The kinetics analysis shows the internal diffusion controls model of RE and Al leaching process,and the leaching kinetics equations of RE and Al related to CTAB concentration were obtained for the two ammonium salt leaching systems.According to the chromatographic plate theory,the mass transfer efficiency of RE increases with the CTAB concentration increasing until 0.4 g/L,which confirms that the optimal CTAB addition is 0.4 g/L.Smaller adhesion work and adhesion work reduction factor indicate more favorable permeation as well as the leaching process.
查看更多>>摘要：The relationship between dialkylphosphinic acid structure and their loading capacity for HREEs and emulsification phenomena has rarely been studied.In this paper,we took Lu extraction as an example to study the effect of β,γ,δ-substituents of dialkylphosphinic acids on their loading capacity and anti-emulsification performance for HREEs.To discuss conveniently,the dialkylphosphinic acids were clas-sified into two groups:β-substituent group(P208,INET-1,P218,USTB-1 and P227)and γ,δ-substituent group(P218,P2132 and Cyanex 272).For β-substituent group extractants,their loading capacities are in the order P208(299.7 mg/L)≈ INET-1(299.5 mg/L)＞P218(270.8 mg/L)＞＞USTB-1(163.1 mg/L)＞P227(151.4 mg/L),while their anti-emulsification/gelation performances are just in the opposite order P227＞USTB-1＞P218＞P208 ≈ INET-1 under the studied conditions.For γ,δ-substituent group extractants,their loading capacities are in the order P218(270.8 mg/L)＞P2132(192.3 mg/L)＞Cyanex 272(131.7 mg/L),while the anti-emulsification performance of P218 is better than those of P2132 and Cyanex 272.The loading capacity data given in the parentheses are obtained through repeatedly extracting Lu from～4 × 10-4 mol/L of Lu aqueous feed solution with initial pH of 2.40 by 0.01 mol/L extractant at phase ratio A/O of 1∶1.
查看更多>>摘要：It is difficult to achieve selective separation and enrichment of different rare earths from high abundance yttrium ores efficiently only dependent on their discrepancy in thermodynamic properties.The present work suggests a new strategy based on non-equilibrium kinetic separation of Er and Tm on the surface of freely rising oil droplets to control the separation order of Y.It is revealed that the mutual separation of Er/Tm is significantly promoted with the separation coefficient of 2.89 during the non-equilibrium extraction with the addition of diethylenetriaminepentaacetic acid(DTPA).The extraction sequence of Tm,Er and Y can be controlled as Tm＞Y＞Er,thus Y can be selectively enriched during the process of separation of Er and Tm.Such a sequence is subject to the controllable dissociation rates of RE(Ⅲ)-DTPA complexes and extraction abilities of P507 with the three RE(Ⅲ)ions.The dissociation rate is dependent on the stabilities of RE(Ⅲ)—DTPA complexes and follows the sequence of Y(Ⅲ)-DTPA＜Tm(Ⅲ)—DTPA＜Er(Ⅲ)-DTPA.However,the extraction abilities of the three RE(Ⅲ)ions follow the sequence of Y(Ⅲ)-P507＜Er(Ⅲ)-P507＜Tm(Ⅲ)—P507.The competition complexation of DTPA and P507 at the interface of oil droplets results in an obvious change in the separation order of Y from Tm＞Er＞Y toTm＞Y＞Er.
查看更多>>摘要：With the development of the economy and the increasing demand for environmental protection,the efficient and selective recovery of Gd(Ⅲ)from actual wastewater is of critical importance.In this work,lanthanum-based metal-organic framework(LaBDC)materials were prepared by a hydrothermal method,and then polyethyleneimine(PEI)and LaBDC were combined by an impregnation method to form a novel LaBDC@xPEI composite.The prepared materials were characterized using Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDX),Brunauer-Emmett-Teller(BET),thermogravimetric analysis(TGA)and X-ray photoelectron spectroscopy(XPS).Experiments show that LaBDC@50％PEI has the highest adsorption capacity(181.77 mg/g)among lanthanum-based MOFs with different PEI loadings at pH=5.5,which is about 5.1 times that of bare LaBDC.The adsorption isotherm analysis shows that LaBDC@50％PEI follows the Langmuir model.In addition,the adsorption kinetics of LaBDC@50％PEI fol-lows a pseudo-second-order kinetic model,indicating that the adsorption process is chemical adsorp-tion.It is worth noting that LaBDC@50％PEI maintains good adsorption performance and stability after three recycling tests,and exhibits excellent selectivity in cation interference experiments.Overall,the LaBDC@50％PEI composites possess good stability and hold great promises in rapid recovery of Gd(Ⅲ)from practical aqueous environments.
查看更多>>摘要：The effects of Ce addition(310 ppm and 1500 ppm)on the microstructure,texture and properties of ultrahigh-purity copper(99.99999％)were systematically studied using scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electron backscattered diffraction(EBSD)analyses,combined with the microhardness and conductivity tests.Regarding the microstructure of the as-cast and as-extruded samples,the addition of Ce refines the grain size of the ultrahigh-purity copper and the refinement effect of 310Ce alloy is greater than that of 1500Ce alloy.This is due to the stronger component supercooling and the accelerated recrystallization caused by lower Ce content.In addition,Ce can react with Cu to form the Cu-Ce eutectic phases,which are deformable during the hot deformation.Furthermore,the added Ce can weaken the texture,showing a variation of brass recrystallization(BR),rotated cube,copper and S texture components,which depends on the recrystallization,the particle stimulated nucleation(PSN)as well as the stacking fault energy(SFE).Most remarkably,the introduction of Ce enhances the hardness of the ultrahigh-purity copper without obviously reducing its conductivity.The major {111} orientations and the stress distributions are responsible for such a superior conductivity of the Ce-containing alloys.
查看更多>>摘要：In order to reduce or eliminate the adverse effects of calcium impurity,the interaction of Ca and rare earth Y co-doping on the preparation of WC-Co cemented carbides was investigated.X-ray diffraction,scanning electron microscopy and transmission electron microscopy were employed to analyze the phase compositions,particle sizes and morphologies of them,respectively.The results show that the second type of"yttrium barrier effect"is observed and the adverse influence of Ca-rich phase on tungsten powder can be eliminated by it.The flexural strength and fracture toughness of YG6-0.01％Ca+0.09％Y alloy are 2199.5 MPa and 11.49 MPa·m1/2,showing improvement of 6.5％and 2.7％compared to YG6 alloy,respectively.The evolutions of Ca-rich phase and Y-rich phase at the every alloy preparation stage of WO3,W,WC and cemented carbides are obtained.Furthermore,the strengthening mechanism of WC-Co cemented carbide with co-addition of Ca and Y is proposed.
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