SOLID STATE PROPERTIES AND LEACHING OF MECHANICALLY ACTIVATED TETRAHEDRITE

The mechanical activation of tetrahedrite Cu_(12)Sb_(4)S_(13) was carried out in a planetary mill. The changes in the surface and bulk properties produced in mineral by mechanical activation were detected by infrared, photoelectron and Mossbauer spectroscopy. The rate and selectivity of tetrahedrite acid leaching depends on conditions of mechanical activation.

Synthesis-temperature-dependent phase composition manipulation toward high thermoelectric performance in tetrahedrites

Tetrahedrite,an Earth-abundant natural mineral,has attracted extensive research interest because of its excellent thermoelectric performance.Herein,tetrahedrite samples comprising Cu-poor Cu_(12)Sb_(4)S_(13)and Cu-rich Cu_(14)Sb_(4)S_(13)phases have been synthesized using a colloidal method,in which the ratio of two phases is manipulated by controlling the synthesis temperature to improve the thermoelectric perfor-mance.It is found that an ultralow total thermal conductivity of∼0.3 W m^(−1)K^(−1)at 723 K is realized in the sample with a Cu-rich phase fraction of∼50%,which can be attributed to maximized phonon scattering by phase boundaries.As a result,combined with a decent power factor,this sample obtains an optimal zT of 1.15,which is about 85%higher than that of the sample with a Cu-rich phase fraction of∼64%and comparable to zT values of other eco-friendly,abundant Cu-based thermoelectric materials.This work demonstrates an effective synthesis-temperature-dependent phase composition manipulation strategy toward enhanced thermoelectric performance in tetrahedrites.

Enhanced thermoelectric performance of Cu_(12)Sb_4S_(13-δ) tetrahedrite via nickel doping

Cu12Sb4S13 tetrahedrite has received great attention as an earth-abundant and environmental-friendly thermoelectric material. This work aims to uncover the thermoelectric performance-enhancing effect and the mechanism of nickel doping on tetrahedrite. A series of Cu12-xNixSb4S13-δ（x = 0.5, 0.7, 1.0, 1.5 and 2.0） compounds were synthesized by mechanical alloying combined with spark plasma sintering. It is found that the thermal conductivity sharply reduces with increasing Ni content over the entire temperature range,0.9 W m^-1K^-1, accompanied with an enhanced thermoelectric power factor. The model predicted that the reduced lattice thermal conductivity is attributed to mid-frequency phonon scattering, caused by precipitates and dislocations resulting from Ni doping. Consequently, a high ZT value up to 0.95 at 723 K was achieved for Cu11NiSb4S13-δ, corresponding to a ~46% increase over non-doped Cu12Sb4S13-δ. Furthermore,the cyclic measurement showed that the Ni-doped tetrahedrites displayed high chemical stability.

Resistive-switching tunability with size-dependent all-inorganic zero-dimensional tetrahedrite quantum dots

All-inorganic zero-dimensional(0D)tetrahedrite(Cu12Sb4S13,CAS)quantum dots(QDs)have attracted extensive attention due to their excellent optical properties,bandgap tunability,and carrier mobility.In this paper,various sized CAS QDs(5.1,6.7,and 7.9 nm)are applied as a switching layer with the structure F:Sn O2(FTO)/CAS QDs/Au,and in doing so,the nonvolatile resistive-switching behavior of electronics based on CAS QDs is reported.The SET/RESET voltage tunability with size dependency is observed for memory devices based on CAS QDs for the first time.Results suggest that differently sized CAS QDs result in different band structures and the regulation of the SET/RESET voltage occurs simply and effectively due to the uniform size of the CAS QDs.Moreover,the presented memory devices have reliable bipolar resistive-switching properties,a resistance(ON/OFF)ratio larger than 104,high reproducibility,and good data retention ability.After 1.4×10^6s of stability testing and 104cycles of quick read tests,the change rate of the ON/OFF ratio is smaller than 0.1%.Furthermore,resistiveswitching stability can be improved by ensuring a uniform particle size for the CAS QDs.The theoretical calculations suggest that the space-charge-limited currents(SCLCs),which are functioned by Cu 3d,Cu 3p and S 3p to act as electron selftrapping centers due to their quantum confinement and form conduction pathways under an electric field,are responsible for the resistive-switching effect.This paper demonstrates that CAS QDs are promising as a novel resistive-switching material in memory devices and can be used to facilitate the application of next-generation nonvolatile memory.

An investigation of oxygen pressure acid leaching of Gacun complex Cu-Pb bulk concentrate

The treatment of the Gacun complex Cu-Pb bulk concentrate with high Zn,Ag,etc.,by oxygen pressure acid leaching was studied.The pri-mary copper and leadminerals in the concentrate are tetrahedrite and galena.The treatment of tetrahedrite was rarely studied,and most of silver occurred in themineral too.The optimum operating parameters of oxygen pressure acid leaching were established by conditional tests.Under these parameters,the result of pilot scale test showed that the leaching percentages of copper and zinc were separately as high as 98.9 wt.% and 94.9 wt.%,while lead and silver were transformed into sulfate and sulfide precipitations,respectively.The copper and zinc in lixivium were reclaimed by extraction-electrowinning and purification-electrowinning,respectively,and the lead and silver in the residue were reclaimed separately by carbonate transformation-silicofluoric acid leaching and thiourea leaching.

Distribution Patterns of Ag in Hydrothermal Precipitates from the Okinawa Trough

The Okinawa Trough is characterized by enrichment of Ag in hydrothermal precipitates;however, the distribution of this enrichment remains poorly constrained. This study presents the results of a field-emission scanning electron microscopy and electron-microprobe analysis based mineralogical and geochemical investigation of the spatial distribution of Ag within Ag-rich sulfide samples from the Okinawa Trough. The tetrahedrite, covellite, and galena in these samples contain high concentrations of Ag(average values of 1.60, 0.78, and 0.23 wt%, respectively) and also various Ag sulfosalts. Examination of the Ag budget of these samples indicates that most of the Ag is hosted by tetrahedrite followed by galena. The Ag within tetrahedrite is incorporated by substitution into the Cu site, whereas galena becomes Ag-enriched by the coupled incorporation of monovalent Ag, Tl, and Cu, and trivalent Sb and Bi into Pb lattice sites. Tetrahedrite and galena containing higher concentrations of Sb favor increased Ag substitution. Four sets of Ag host minerals are identified with distinct ore formation temperatures. Tetrahedrite and galena concentrate the majority of Ag at medium temperatures(150–300°C). Other Ag host minerals concentrate only minor or trace amounts of Ag, including massive sphalerite, chalcopyrite, and pyrite at high temperatures(>300°C), colloform pyrite and sphalerite at low temperatures(<150°C), and Ag-sulfosalts at even lower temperatures(<100°C).

Modelling and process optimisation of antimony removal from a complex copper concentrate

The modelling and optimization for the alkaline sulphide leaching of a complex copper concentrate containing 1.69% Sb and 0.14% Sn were studied.Response surface methodology,in combination with central composite face-centred design（RSM-CCF）,was used to optimise the operating parameters.The leaching temperature,sulphide ion concentration and solid concentration were chosen as the variables,and the response parameters were antimony and tin recovery,and the time required to achieve 90% Sb dissolution.It was confirmed that the leaching process was strongly dependent on the reaction temperature as well as the sulphide ion concentration without any significant dependence on the solid concentration.Furthermore,a mathematical model was constructed to characterise the leaching behaviour.The results from the model allow identification of the most favourable leaching conditions.The model was validated experimentally,and the results show that the model is reliable and accurate in predicting the leaching process.

Oxygen pressure acid leaching of Gacun complex Cu concentrates

The treatment of the Gacun complex Cu concentrate with high contents of Pb,Zn,Ag,etc by oxygen pressure acid leaching was studied.It is unusual that tetrahedrite,whose treatment was rarely studied,is the primary copper mineral of the concentrates.Most of silver also occurs in the mineral.The optimum operating parameters of oxygen pressure acid leaching were established by conditional tests.Pilot scale test was carried out under the parameters,and the leaching rates of copper and zinc are as high as 97.10% and 89.83% while lead and silver are transformed into sulfate and sulfide respectively and stay in leaching residue.The copper and zinc in lixivium were reclaimed by extraction-electrowinning and purification-electrowinning,respectively,and the lead and silver in the residue were reclaimed separately by chloride leaching and thiourea leaching.The extraction rate of copper achieves 96%,and the leaching rates of lead and silver reach 90% and 95%,respectively.