The oxidation of liquid Ni3S2

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.     

The vaporization kinetics of Ni3S2

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     

Temperature and seeding effects on the precipitation of scorodite from sulfate solutions under atmospheric-pressure conditions

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.     

Ni3S2-FeS-Cu2S冰镍体系的表面张力

运用几何模型 (Kohler及Toop模型 )和通用溶液模型 (Chou模型 ) ,由Ni3S2 FeS、FeS Cu2 S和Cu2 S Ni3S2 三个二元边界体系的表面张力计算了Ni3S2 FeS Cu2 S三元系表面张力。计算结果与实验值 (实验误差为± 2 5 % )十分吻合 ,1 4 73K下Ni3S2 FeS Cu2 S冰镍体系的等表面张力曲线有较高的可信度 ,对分析研究镍的闪速熔炼和转炉吹炼过程有重要意义。     

The precipitation sequence of Ni3Ti in Co-free maraging steel

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.     

The precipitation of Ni3Nb phases in a Ni−Fe−Cr−Nb alloy

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.     

Acidity, valency and third-ion effects on the precipitation of scorodite from mixed sulfate solutions under atmospheric-pressure conditions

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.     

Separation of In3+ and Fe3+ from sulfate solutions using D2EHPA in a laminar microreactor

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.     

Continuous precipitation of uranium peroxide from high-vanadium mill solutions

Author E. Burkhart is deceased.     

针铁矿吸附水中硫酸根离子的试验研究

利用合成的针铁矿对水中硫酸根离子进行吸附试验。试验表明，吸附量主要受pH值和硫酸根离子浓度影响。通过配位体交换理论，很好地解释了吸附量随pH下降而增加，随硫酸根离子浓度的下降而减少。     

Batch and continuous precipitation of scorodite from dilute industrial solutions

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.     

The recovery of vanadium from dilute acid sulfate solutions by resin ion exchange

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 E_h and pH on vanadium loading. An E_h-pH diagram has been constructed to determine the most stable vanadium species in solution at different E_h 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.     

Effect of thiourea during nickel electrodeposition from acidic sulfate solutions

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.     

Participation of sulfate reducing bacteria in copper precipitation

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.     

The removal of cadmium impurities from cobalt–nickel solutions by precipitation with sodium diisobutyldithiophosphinate

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.     

Behavior of sulfate in preparation of single light rare earth carbonate by Mg(HCO_3)_2 precipitation method

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.     

The influence of iron and aluminum on the precipitation of metastable Ni3Nb phases in the Ni-Nb system

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.     

Microstructural observations of pressure cast Ni3Al/Al2O3 and Ni/Al2O3 composites

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.