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1.
Using a levitation technique, molten nickel sulfide droplets were oxidized at temperatures above 1500°C under oxygen potentials
varying from 5 to 40 pct in He gas. To analyze the results, the oxidation process was divided into two stages. The first stage
corresponded to the desulfurization of Ni3S2 by oxidation of the dissolved sulfur. In the second stage, a small amount of desulfurization, oxidation of nickel vapor and
absorption of oxygen gas into the droplet occurred. Both stages were found to be controlled by mass transfer of oxygen within
the gas boundary layer. Under conditions of high oxygen potential, a halo appeared around the levitated droplet during the
initial period. This halo disappeared during desulfurization, but reappeared towards the end of the oxidation period.
Formerly Post-Doctoral Fellow, Department of Metallurgy and Materials Science, University of Toronto. 相似文献
2.
The vaporization of Ni3S2 was investigated at high temperatures by a levitation technique. Vaporization was controlled by a mass transfer process within
a gas boundary layer around the Ni3S2 droplet. The vaporized S2(g) and Ni(g) recombine within the gas boundary layer, and this recombination along with the condensation of Ni(g) was found to enhance the vaporization rate. A model has been developed to account for the experimentally-obtained mass transfer
coefficients.
Y. FUKUNAKA, formerly Research Associate, Department of Metallurgy and Materials Science, University of Toronto 相似文献
3.
Shalabh Singhania Qiankun Wang Dimitrios Filippou George P. Demopoulos 《Metallurgical and Materials Transactions B》2005,36(3):327-333
Arsenic is a major contaminant in the nonferrous extractive metallurgy. In the past 20 years, many studies have shown that
it can be precipitated as relatively stable crystalline scorodite (FeAsO4·2H2O) by precipitation under ambient or elevated pressures. In the present study, an extensive program of scorodite precipitation
tests under ambient pressure has shown that the rate of scorodite formation increases dramatically by a small increase in
temperature from 85 °C to 100 °C. The beneficial effects of temperature are attributed to the higher thermodynamic stability
of scorodite at elevated temperatures, but also to higher rates of secondary nuclei formation and crystal growth. In any case,
irrespective of the precipitation temperature, the leachability of all scorodite precipitates observed in toxicity characterization
leaching procedure (TCLP) tests is below 5 mg/L As. Another parameter examined in this study was seeding. It was observed
that the higher the initial concentration of seed, the faster the precipitation. Precipitation of well-crystallized scorodite
can be effected equally well on heterogeneous seed such as hematite (Fe2O3) or gypsum (CaSO4·2H2O) added externally or formed in situ. 相似文献
4.
5.
D. M. Vanderwalker 《Metallurgical and Materials Transactions A》1987,18(7):1191-1194
TEM, microdiffraction, and X-ray microanalysis were used to study the precipitation processes in Co-free maraging steel. Austenite
crystals were found to nucleate in the martensite matrix as the first step in the precipitation sequence of Ni3Ti. The austenite reversion is a result of Ni segregation. Ni3Ti nucleates in the austenite. The shape and orientation of Ni3Ti is determined by the austenite precursor. The same sequence occurs for heterogeneous nucleation on dislocations and grain
boundaries. At the later stages of growth Mo is incorporated in the Ni3Ti lattice. 相似文献
6.
The age hardening of a Ni?Fe?Cr?Nb alloy containing 4.85 wt pct Nb has been studied using transmission electron microscopy. The major hardening phase in this alloy isγ*, DO22-ordered Ni3Nb, which precipitates as a fine dispersion of square plates. It is shown that nucleation ofγ* plates may be dependent upon matrix excess vacancy concentration, but nucleation ofγ* plates is also observed at dislocations and extrinsic stacking faults. Theγ* phase is metastable with respect to the orthorhombic Ni3Nb phase, β, which precipitates by either a cellular or an intragranular reaction, depending upon the aging temperature. It is proposed that the intragranular nucleation of β laths proceeds by the growth of stacking faults from withinγ* plates; theγ* plates subsequently dissolve in favor of the β laths. Room temperature deformation of theγ* dispersion is shown to produce faults within theγ* plates; possible dislocation reactions occurring during this deformation are discussed. 相似文献
7.
Shalabh Singhania Qiankun Wang Dimitrios Filippou George P. Demopoulos 《Metallurgical and Materials Transactions B》2006,37(2):189-197
The present study is focused on the precipitation of scorodite from mixed sulfate media at 95 °C under atmospheric pressure.
In particular, this study explores the effects of acidity (pH), valency [Fe(II)/Fe(III), As(III)/As(V)], and solution composition
(third cation/anion) on the yield, crystallinity, and stability (leachability) of scorodite precipitates. Thus, it was found
that the precipitation of crystalline scorodite can be achieved without stringent pH control once the precipitation has started.
Nonetheless, the selection of the initial pH is critical to avoid the formation of an amorphous precipitate. A leachability
as low as 0.5 mg/L As at pH 5 and 22 °C (TCLP-like test) is obtained when the initial molar ratio Fe(III):As(V) is increased
to 3:1, but the precipitation yield is very low. When Fe(II) is used as excess iron, the precipitate solubility drops to 0.2
mg/L As with a yield exceeding 80 pct in 2.5 hours. The stability of the product is not measurably affected by the presence
of Cu2+, Zn2+, Ni2+, Co2+, Mn2+, SO
4
2−
, and NO
3
−
. The presence of PO
4
3−
, however, leads to the formation of crystalline phosphate-containing scorodite precipitates of somewhat reduced stability.
In most cases, the TCLP leachability of the precipitate was found to be between 1 and 3 mg/L As, and never exceeded the regulatory
limit of 5 mg/L As. 相似文献
8.
9.
10.
《Canadian Metallurgical Quarterly》2013,52(4):432-438
A microfluidic solvent extraction method is put forward to solve the problems existing in the conventional solvent extraction of indium, such as large waste of extractant, fire hazards, etc. Experiments were performed in a series of microreactors to separate In3+ and Fe3+ from sulfate solutions using D2EHPA as the extractant. The effect of main parameters such as different contact times, microchannel sizes, interface to volume ratios and pH values on the indium extraction efficiency was investigated. The results show that the smaller the channel size, the more the beneficial diffusion and mass transfer. Specifically, in a microchannel, with a size of 100?μm?×?50?μm?×?120?mm, almost 100% extraction efficiency was reached with contact time about 0·5?s. The mean mass transfer rate can be as high as 0·291?g?m??2?s??1, and the ratio of mean mass transfer rate of In3+ to that of Fe3+ can be as high as 29·76. 相似文献
11.
Author E. Burkhart is deceased. 相似文献
12.
13.
A detailed study has been carried out to investigate the possibility of recovering vanadium by resin ion exchange from acid sulfate solutions containing 10 mg/l vanadium. In particular the recovery of vanadium by an anion exchange resin, Dowex 21K, has been investigated. Batch loading tests have been carried out to elucidate the role of Eh and pH on vanadium loading. An Eh-pH diagram has been constructed to determine the most stable vanadium species in solution at different Eh and pH conditions, and this information has been used to explain and predict the loading of vanadium onto the anion exchange resin. Kinetic data have been obtained for the loading of vanadium at different pH values. A film diffusion model has been found to fit the experimental data gathered at pH 4.0, while a particle diffusion model seems to offer a better fit to the experimental data at pH 2.0. 相似文献
14.
Michelle L. Caetano Virginia S.T. Ciminelli Sonia D.F. Rocha Matheus C. Spitale Claudia L. Caldeira 《Hydrometallurgy》2009,95(1-2):44-52
Enriched arsenic precipitates were obtained from dilute industrial As(III) solutions (1.1–0.1 g As/L) at 95 °C in batch and continuous reactor operations. A complete and fast oxidation of As(III) was obtained at room temperature with 20% excess of hydrogen peroxide. Arsenic removal varied from 80.5 to 94.6% and increased with the total surface area (SSA) of the seed. SSA higher than 270 m2/g was required to promote an arsenic removal of approximately 85%. Recycling of solids was necessary to achieve high yields of arsenic removal in continuous operation. Approximately 75 to 85% As was removed in 1 h of residence time in the MSMPRR (Mixed Suspension Mixed Product Removal with Solids Recycle) reactor; the rate of crystal growth was calculated as 10? 12 m/s. Arsenic removal was not favored by the excess of iron in the solution. TCLP (Toxicity Characterization Leaching Procedure) testing indicated that ageing plays an important role in the leachability of scorodite, which decreased from 13.6 mg As/L to 0.1 mg As/L after 8 h in a batch reactor. The decrease in As leachability was related to the decrease in the SSA (14 m2/g to 0.9 m2/g after 62 h in the MSMPRR) as a combination of crystal growth (1.6 μm to 5.3 μm) and densification. Scorodite was the only arsenic phase identified by X-ray diffraction and micro-Raman analyses of the precipitates. 相似文献
15.
U. S. Mohanty B. C. Tripathy S. C. Das V. N. Misra 《Metallurgical and Materials Transactions B》2005,36(6):737-741
The effect of thiourea on the cathodic current efficiency (CE), deposit quality, crystallographic orientations, surface morphology,
and polarization behavior of the cathode was investigated during nickel electrodeposition from acidic sulfate solutions for
2 hours at 60 °C. A slight decrease of 3 to 4 pct in the CE was observed, when the concentration of thiourea was increased
from 2 to 40 mg dm−3. The nickel deposit quality deteriorated significantly at higher thiourea concentrations; the surface morphology deteriorated
and the contamination of the nickel deposits increased. The presence of thiourea affected the peak intensities of the crystal
planes. Cyclic voltammetric studies on nickel deposition at 25 °C revealed depolarization behavior of the cathode at lower
thiourea concentrations, ≤10 mg dm−3; however, a mixed behavior is observed at higher thiourea concentrations. These changes were also observed in the exchange
current density (i
0) values. 相似文献
16.
Chemical precipitation of copper by hydrogen sulphide at three values of pH (3.0; 5.0; 7.0) did not result in complete elimination of the metal from a solution. If sulphate reducing bacteria and a source of organic substance, for instance, disintegrated reed, are introduced into the medium, the microorganisms begin to grow, the redox potential decreases, hydrogen sulphide is formed, and copper is completely eliminated from a solution within 10--15 days in model experiments. 相似文献
17.
W.A. Rickelton 《Hydrometallurgy》1998,50(3):339-344
Cadmium sometimes occurs as a minor impurity in cobalt–nickel solutions which are to be processed by solvent extraction for the recovery of cobalt. However, the organophosphorus reagents used for this purpose extract cadmium in preference to cobalt. Consequently, the feed solutions must be pretreated for the removal of cadmium in order to avoid contamination of the final product. This note describes a selective method of removing cadmium by precipitation as its diisobutyldithiophosphinate complex. 相似文献
18.
The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_4~(2-)1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_4~(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_3)_2 as a precipitant.The results indicate that the contents of SO_4~(2+) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La2(CO_3)_(2.15)(-SO_4)_(0.85)·4 H_2 O and Ce2(CO_3)_(2.15)(SO_4)_(0.85)·3 H_2 O,while those of the Pr and Nd precipitates are 4 wt%-5 wt%since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_4~(2-) enclosed in the precipitation.The content of SO_4~(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_4~(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_4~(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO_3)_2 precipitation method. 相似文献
19.
The effect of additions of aluminum and iron on the formation of transitional phases has been examined for alloys of the Ni-Nb system. It has been established that metastable phases of approximate composition Ni3Nb will not form in binary Ni-Nb alloys under normal conditions of quenching and aging, but that iron or iron and aluminum additions promote their formation when certain size and electronic factors are satisfied. In Ni-Nb-Fe alloys containing more than ≈ 12 at. pct Nb, iron promotes the formation of a bct (DO22) Ni3Nb precipitate. Aluminum additions to these Ni-Nb-Fe alloys promote the precipitation of fcc (L12) Ni3Nb γ’, initially together with the bct phase, but at higher aluminum concentrations the tetragonal phase disappears. The appearance of both precipitates followed the Hagel-Beattie requirement for interfacial mismatch of < or ~ 1 pct between the matrix and the precipitate. The presence of both precipitating phases can be predicted on the basis of the Engel-Brewer correlations. The preferrede/a ratio for the stability of the bct (DO22) phase is 2.50 to 2.62. In the present investigation this phase precipitates only in the presence of iron (bcce/a ratio = 1.5), and only when the lattice constant of the matrix is greater than 3.600Å. The preferrede/a ratio for the stability of the γ’ having a fcc L12 structure is between ~2.75 and 3.0. Precipitation of this phase occurred only when aluminum(e/a) ratio = 3.0) was present, and when the matrix lattice constant was greater than 3.589Å. 相似文献
20.
S. Nourbakhsh H. Margolin F. L. Liang 《Metallurgical and Materials Transactions A》1989,20(10):2159-2166
Pressure castings of Ni3Al(IC218)/Al2O3 and Ni/Al2O3 composites, made with continuous DuPont FP α-Al2O3 and DuPont PRD166 α-Al2O3+20 wt pct partially stabilized ZrO2 20 μm diameter fibers, were examined by optical, scanning electron microscope (SEM), and transmission electron microscope
(TEM) techniques. According to optical magnifications, excellent infiltration took place. However, in SEM and TEM magnifications,
small gaps were found adjacent to regions where bonding had taken place between fibers. On the basis of available evidence,
the gap formation was attributed to trapped gases and microshrinkage. Titanium was added to the metal to promote infiltration.
Diffusion of Ti into the fibers of the Ni/Al2O3 composites occurred, but similar diffusion into the fibers of the IC218/Al2O3 composites did not take place. The qualitatively higher bond strength of the interfaces of the Ni/Al2O3 composites was ascribed to the diffusion of Ti into Al2O3. No interface reaction layer was found in any of the composites. Very little grain growth was found to take place in either
the FP or PRD 166 fibers after casting and after a subsequent ten day anneal at 1150 °C. 相似文献