Ultrasound-assisted cyanide extraction of gold from gold concentrate at low temperature

A sonochemical reactor was developed to study the ultrasound-assisted cyanide extraction of gold from gold ore at low temperature. The effects of ultrasound on gold leaching in low temperature and conventional conditions were investigated. At the low temperature of 10 °C, ultrasound-assisted extraction increased extraction rate of gold by 0.6%–0.8% and reduced the gold content of cyanide tailings to 0.28 g/t in the leaching of gold concentrate and cyanide tailings, respectively. At the conventional temperature of 25 °C, ultrasound-assisted extraction obtained a 0.1% higher extraction rate of gold compared with conventional extraction, with the unit consumption of NaCN reduction of 15%. The analysis of kinetic model also demonstrated that sonication indeed improved the reaction of gold leaching greatly. The mineralogy and morphology of ore were further analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and particle size analyzer to explore the strengthening mechanism of gold leaching. The results showed that the ore particles were smashed, the ore particle surface was peeled, the passive film was destroyed and the reaction resistance decreased under ultrasonic processing. Therefore, the extraction rate of gold was improved and the extraction time was shortened significantly in ultrasound-assisted cyanide extraction.     

Effects of hydrogen transitions in niobium at very low temperature

The presence of hydrogen in Nb containing O and N interstitial impurities gives rise to a relaxation process at liquid helium temperature. The effect, studied by exciting two vibration modes of the specimen (20 and 75 kHz), can be described by a single Debye curve and is characterized by an apparent activation energy of 1.8 meV and by the rise of the relaxation strength with increase of peak temperature.     

Excited level lifetime measurements following very low energy nuclear recoils

Using high resolution gamma spectroscopy it is possible to observe Doppler broadening of gamma transitions from excited states which have themselves been populated after emission of gamma photons or other low energy nuclear radiation. This allows the determination of the lifetimes of these intermediate states, providing the time dependence of the recoil velocities is known. Conversely, if the lifetime is well known, this technique may be used to study the recoil process itself (and hence the atomic interaction) at energies of only a few times the lattice binding energy.     

Specific heat measurements in small samples at low temperature

We describe a calorimeter which has been used to measure the heat capacity of small samples weighing 50 to 200 mg in the temperature range of 1.5 K to 20 K. We have used the thermal relaxation method as well the heat pulse method for our measurements with the same experimental set-up. An accuracy of better than 5% is obtained with this system.     

Variable range hopping in Si:P at very low temperature

The resistivity of doped semiconductor Si: P in the intermidiate concentration range was measured in low temperature region down to 10 mK. In the lowest temperatures Mott's formula for the variable range hopping is shown to be not applicable and T^-n-like temperature dependence of resistivity is confirmed. The Importance of the level correlation in the random system is discussed.     

Study of molecular line parameters down to very low temperature

The impact of precise spectroscopic measurements on the P(9) multiplet in the ν₃ band of ¹²CH₄, obtained using a newly developed cold Herriott cell coupled with a tunable diode laser spectrometer, is examined in the context of remote sensing of methane in the atmosphere. More specifically, the influence of the air-broadening temperature dependence, of line narrowing and of line-mixing effects is assessed when fitting high resolution atmospheric spectra recorded from a balloon in the solar occultation mode. This is achieved by considering residuals and retrieved methane volume mixing ratio profiles. By combining data from previous studies together with new measurements, the expression for the temperature dependence of the broadening coefficient has been revisited. It is shown that a correcting factor applied to the usual law gives better results, when considering all the available measurements from room temperature down to about 10–20 K, as compared to the usual expression of the width versus temperature. These results clearly demonstrate that collision broadening is more sensitive to long-range attractive forces when the temperature is decreased. PACS 33.70.Jg; 34.20.-b     

Anomalous temperature dependence of paraelectric relaxation at very low temperatures

Hydroxyl doped KCl crystals were subjected to two dimensional stress in a (001)-plane so that the paraelectric hydroxyl dipoles can be described by a double-well system with a small tunneling splitting. In the temperature range from 0.025 to 0.3 K this system exhibits a dielectric relaxation rate that increases with decreasing temperature.     

Optical measurements of stress distributions in GaAs at low temperature

We have measured the stress distribution at He temperature on two epitaxial GaAs wafers which were compressed along one edge. The stress was determined non-destructively at different points on the wafer surface by using the line-splitting and the lineshifts of the photoluminescence spectra of the acceptor-bound excitons in comparison with calibration spectra at known uniaxial stress.     

Spectral-line width measurements in Ar II from a laser-heated gas-puff plasma

Stark profiles for certain non-blended spectral lines radiating in the visible spectral region from Ar II multiplets were measured at the University of Maryland in a plasma created by the laser heating of a puff of gas at high pressure. The resulting line widths are found to agree within a ±30% experimental precision with previous ±25% measurements obtained at lower densities and temperatures in long-burning arcs, as well as with semi-classical calculations.     

Magnetization measurements of polycrystal ZnMn alloys at very low temperatures

The magnetization of ZnMn alloys with Mn concentration ranging from 68 to 1 ppm has been measured from 2 K down to 10 mK. The results show large departures from free spin behavior due to impurity-impurity interactions and some concentration independent effects.     

Field ion microscope studies of very low coverage low temperature oxygen adsorption on tungsten

The field ion microscope has been used to study very low coverage oxygen adsorption on tungsten at 78°K. Adsorbed oxygen cannot be directly observed on the surface using helium ion imaging, but its presence may be inferred from resultant corrosion damage which occurs during the imaging process. Atom for atom comparison before and after an adsorption-desorption sequence allows the crystallographic position and extent of the damage to be precisely determined. Preferential damage along certain zones in the {111} and {411} regions can be correlated with the degree of unsaturation of surface metal bonds. The nature of the adsorbed species and its relationship with the adsorption site are discussed.     

Hydrogen adsorption on thin low temperature deposited unsintered gold films

It has been found that molecular hydrogen does adsorb at 78 K on unsintered thin gold films deposited at low temperature, while sintering of these films at 420 K precludes H₂ chemisorption. The adsorbate is characterized by a single TD peak with a maximum placed at 125 K. The rate of desorption fits neither the first nor the second order kinetic equations exactly.     

Evidence for stress-induced decoupling of valence bands in GaSb from galvanomagnetic measurements

The behavior of p-GaSb has been examined using uniaxial compressional stresses up to $\text{10}{}^{10}\text{dyn}\text{cm}{}^2$ in the temperature range 50–300°K. Hall effect and resistivity results are interpreted in terms of decoupling of the valence bands, and reduction of the impurity activation energies.     

Magnetic ordering versus lattice distortion in very narrow bands

A simple criterion for antiferromagnetic ordering versus lattice distortion in very narrow band materials is obtained. The model describing these narrow band materials contains the Hubbard Hamiltonian, short ranged interatomic Coulomb and exchange interactions, and the electron-phonon interaction.     

Rotational bands and particle-hole excitations at very high spin

A method of calculating high-spin states of nuclei within the cranked Nilsson-Strutinsky framework is presented and discussed in some detail. With this method, various high-spin features of nuclei are studied, such as shape coexistence, shape changes, band crossings and band terminations. Nuclei with different mass numbers such as ¹⁰⁶Pd, ¹¹⁸Te, ¹⁵⁸Yb and ¹⁸⁷Au are used to exemplify the formalism. Comparisons are made with observed discrete high-spin states in ^{160, 165, 168}Yb, ¹⁶⁸Hf, ¹⁷¹Ta and ¹³⁰Ce.     

Enhancement of the room temperature oxidation of silicon by very thin predeposited gold layers

The oxidation of Si(111) surfaces covered with very thin layers of gold is studied by Auger and electron energy loss spectroscopies under ultra high vacuum conditions. It is found that by exposing the Au covered surface to an oxidizing atmosphere, formation of silicon dioxide occurs at room temperature on top of the substrate and the presence of SiO₄ tetrahedra is clearly seen on electron energy loss spectra. In contrast, oxidation under the same conditions of a clean Si(111) surface leads to the formation of an oxygen monolayer and no structure corresponding to Si-O bonds in SiO₄ tetrahedra are observed. This enhancement of the oxidation is attributed to a change in the hybridization state of Si atoms in a gold environment.     

Intensity measurements in freon bands of atmospheric interest

The absolute intensities of the i.r. absorption bands, which are located in the atmospheric window region, of CFCl₃ (“Freon-11”) and CF₂Cl₂ (“Freon-12”) have been measured at 300°K. Our best estimates for these parameters are: for CFCl₃ (“Freon-11”), S_v = 635±36 cm^-2atm^-1 (9.2μ band), S_v = 1536±45 cm^-2atm^-1 (11.8μ band); for CF₂Cl₂ (“Freon-12”), S_v = 718±14 cm^-2atm^-1 (8.7μ band), S_v = 1136±22 cm^-2atm^-1 (9.1μ band), and S_v = 1302±40 cm^-2atm^-1 (10.9μ band).