Round Top Mountain rhyolite(Texas, USA), a massive, unique Y-bearing-fluorite-hosted heavy rare earth element(HREE) deposit

Round Top Mountain in Hudspeth County, west Texas, USA is a surface-exposed rhyolite intrusion enriched in Y and heavy rare earth elements （HREEs）, as well as Nb, Ta, Be, Li, F, Sn, Rb, Th, and U. The massive tonnage, estimated at well over 1 billion tons, of the deposit makes it a target for recovery of valuable yttrium and HREEs （YHREEs）, and possibly other scarce ele-ments. Because of the extremely fine grain size of the mineralized rhyolite matrix, it has not been clear which minerals host the YHREEs and in what proportions. REE-bearing minerals reported in the deposit included bastn？site-Ce, Y-bearing fluorite, xeno-time-Y, zircon, aeschynite-Ce, a Ca-Th-Pb fluoride, and possibly ancylite-La and cerianite-Ce. Extended X-ray absorption fine struc-ture （EXAFS） indicated that virtually all of the yttrium, a proxy for the HREEs, resided in a coordination in the fluorite-type crystal structure, rather than those in the structures of bastn？site-Ce and xenotime-Y. The YREE grade of the Round Top deposit was just over 0.05%, with 72%of this consisting of YHREEs. This grade was in the range of the South China ionic clay deposits that supply essentially all of the world’s YHREEs. Because the host Y-bearing fluorite is soluble in dilute sulfuric acid at room temperature, a heap leaching of the deposit appeared feasible, aided by the fact that 90%-95%of the rock consists of unreactive and insoluble feld-spars and quartz. The absence of overburden, remarkable consistency of mineralization grade throughout the massive rhyolite, prox-imity （a few km） to a US interstate highway, major rail systems and gas and electricity, temperate climate, and stable political location in the world’s largest economy all enhanced the potential economic appeal of Round Top.

Local concentration of middle and heavy rare earth elements in the col on the weathered crust elution-deposited rare earth ores

This present study focused on investigating the content and relative enrichment multiple of rare earth elements（REEs） in different terrain of weathered ore body, and the value of light rare earth elements/middle and heavy rare earth elements（LREEs/HREEs）, in order to understand the mobilization and redistribution of HREEs, Furthermore, the abrasion pH was investigated as well, The results show that the average contents of HREEs in the knap, ridge and col are 37.26, 61.71, and 271.3 μg/g, respectively. The value of LREEs/HREEs is decreased from 16.78 to 7.914 between knap and col and the relative enrichment multiple of HREEs is as follows： CCol-HREEs 〉 CRidge-HREEs 〉 0. It is indicated the HREEs is concentrated in the col and the enrichment degree of HREEs is stronger than the ridge and the knap. Rare earth elements fractionation is exhibited in the different terrain of weathered ore body. Based on this study, the finding that HREEs concentrate in the lower terrain of weathered crust elution-deposited rare earth ores, such as in the col, would become a marker or indicator to search for middle and heavy rare earth enriched zone.

Tb doping induced enhancement of anomalous Hall effect in NiFe films

Tbx（Ni0.8Fe0.2）1-x films with x ≤ 0.14 are fabricated and the anomalous Hall effect is studied. The intrinsic anomalous Hall conductivity and the extrinsic one from the impurity and phonon induced scattering both increase with increasing x. The enhancement of the intrinsic anomalous Hall conductivity is ascribed to both the weak spin–orbit coupling enhancement and the Fermi level shift. The enhancement of the extrinsic term comes from the changes of both Fermi level and impurity distribution. In contrast, the in-plane and the out-of-plane uniaxial anisotropies in the Tb Ni Fe films change little with x. The enhancement of the Hall angle by Tb doping is helpful for practical applications of the Hall devices.

Loading capacity and emulsification phenomena of HREE extraction by dialkylphosphinic acids with different β,γ,δ-substituents

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 classified 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)>Cyanex272(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.

Effect of grain boundary diffusion of terbium on mode of mechanical fracture of sintered NdFeB magnets

Grain boundary diffusion process(GBDP)is a widely used method of increasing the coercivity of sintered NdFeB magnets.In this study,the effects of the GBDP on the bending strength and microhardness of sintered NdFeB magnets and the fracture mode were investigated.Results show that the bending strength of magnets is reduced by pickling and heat treatment and greatly recove rs after heavy rare earth element(Tb)grain boundary diffusion.The pickling and the heat treatment cause a slight decrease in microhardness.Compared with the recovery of the bending strength,the hardness decreases after the GBDP.The fracture mode of bended magnets changes from intergranular to transgranular.This study helps in further improving the mechanical and magnetic properties of sintered NdFeB magnets.

The role ofβ,γ,δ-substituent of dialkylphosphinic acids in HREE extraction and separation behaviors

Heavy rare earth element(HREE)separation has always been a great challenge.The kind of dialkylphosphinic acids is recognized as the third generation of organophosphorous acid extractants.However,detailed relationship betweenβ-substituent(especially when it changes from H to methyl,and further to ethyl)and their extraction behaviors and selectivity for HREEs have rarely been reported.Besides,there are also few reports on effect ofγ,δ-substituent on HREE extraction and separation.In this paper,we synthesized five and collected two dialkylphosphinic acids with differentβ,γ,δ-substituents(from H to ethyl).These extractants were divided into two groups to discuss their extraction behaviors and selectivity for HREEs:β-substituent group(P208,INET-1,P218,USTB-1 and P227)andγ,δ-substituent group(P218,P2132 and Cyanex 272).To evaluate and compare their extractabilities,P507 was used as a reference and Tm,Yb,Lu were extracted with 0.01 mol/L of these extractants from single Tm,Yb and Lu solutions(~4×10^(-4)mol/L)at different initial pH.Besides,pH_(0.5)(Tm),pH_(0.5)^(Yb)and pH_(0.5)^(Lu)values and their differences(ΔpH_(0.5)^(Tm-Yb),ΔpH_(0.5)^(Yb-Lu),ΔpH_(0.5)^(Tm-Lu))for each extractant were given to roughly evaluate their separation performance for Tm,Yb and Lu.To further investigate the selectivity of these extractants for HREEs,Tb,Dy,Ho,Er,Tm,Yb and Lu were extracted from their mixed solution with initial pH of 4.00 at phase ratio A/O of 2:1,1:1 or 1:2.Their HREE separation performance is mainly discussed based on the adjacent HREE separation factors(β_(N+1/N))and their average value(β_(Tb-Lu)).

Effect of aluminum on microstructure and magnetic properties of sintered Nd-Fe-B magnets processed by grain boundary diffusion of Tb-Al

The grain boundary diffusion process(GBDP)of Tb can improve the coercivity of sintered Nd-Fe-B magnets.In this study,the effect of AI on the diffusion of Tb in the GBDP was investigated.The content of diffused Tb-Al was precisely controlled by adjusting the magnetron sputtering process.The Tb equivalent of Al was also studied.Results show that AI promotes the diffusion of Tb deeper into the magnet,reducing the thickness of the shell in the core-shell structure.This study is helpful for further developing the process,reducing the consumption of heavy rare earth elements(Tb),and improving the coercivity of sintered Nd-Fe-B magnets.