Corrosion of Mo,Nb, Cr,and Y in molten aluminum

The corrosion (dissolution) kinetics of solid molybdenum, niobium, chromium, and yttrium in molten aluminum were investigated at temperatures between 700 °C and 915 °C under hydrodynamic conditions using the rotating disc method. Dissolution was governed by diffusion under laminar flow conditions (in the angular velocity range of 10 to 32 rad/s) regardless of the number of intermetallic compound layers formed at the solid-liquid interface. The solubility limit (C _S ), dissolutíon rate constant(K), and diffusion coefficient(D) were determined. It was found that temperature dependencies of the solubility, dissolution rate, and diffusion coefficient for each system obeyed Arrhenius-type relationships; from these, the activation energies were calculated. The single or multiphase intermetallic layer growth occurring at the solid-liquid interface during dissolution in an unsaturated melt between 700 °C and 915 °C was characterized.     

The ferric fluosilicate leaching of lead concentrates: Part I. Kinetic Studies

A new hydrometallurgical leaching process, which dissolves lead concentrates with acidified ferric fluosilicate solution, has been investigated for the selective extraction of lead and zinc from lead concentrates containing galena. The leaching of the Pine Point lead concentrate by ferric fluosilicate solutions was studied under various experimental conditions in the temperature range 20 °C to 95 °C. Temperature had a pronounced effect on the dissolution of the concentrates. The rates of lead leaching are very rapid over the temperature range 38 °C to 95 °C. The kinetics of zinc extraction are much lower than those of lead extraction. The reaction rates for the dissolution of galena were found to be controlled by surface chemical reaction. The apparent activation energy of the leaching reaction was calculated to be 62.1 kJ/mol. The initial concentrations of Pb²⁺, H⁺, and Fe³⁺ in the lixiviant do not have a significant effect on the rate or extent of lead extraction under the experimental conditions in this study.     

Dissolution of zinc ferrite samples in acids

The dissolution of rotating discs of synthetic zinc ferrite — the principal constituent of the ‘Moore Cake’ residue in zinc extraction plants — was studied in mineral acids, particularly in 1–5 N H₂SO₄ at 70–99°C. This dissolution was found to be directly proportional to the surface area, and the order of the zinc ferrite-sulphuric acid reaction with respect to proton activity, [H⁺], to be 0.6. The apparent energy of activation was established as 15 kcal/mole, and the chemical reaction on the solid surface as the rate-controlling step.What appeared to be ‘non-stoichiometric’ or preferential dissolution of zinc (over iron) from zinc ferrite was observed during the initial stages of reaction. This was attributed to the existence of trace amounts (undetectable by X-ray methods) of unreacted zinc oxide grains in the zinc ferrite matrix. This is, to our knowledge, the first time that electron microprobe analysis has been used to identify and analyse these grains. Prolonged sintering at 1200°C for 48 hours eliminated the ZnO phase.Dissolution of zinc ferrite in acid is stoichiometric. A typical dissolution rate is ～ 10^?8 mol cm^?2 sec^?1, which corresponds to almost complete extraction of zinc from ‘Moore Cake’ particles in 2–5 N H₂SO₄ solution at 95°C in 1–2 hours.     

The Dissolution of Sphalerite in Ferric Chloride Solutions

The kinetics of dissolution of both sintered sphalerite disks and untreated sphalerite particles in ferric chloride-hydrochloric acid solutions have been investigated. Over the temperature interval 25 to 100°C, the dissolution occurred according to a linear rate law and with an associated apparent activation energy of about 10 kcal/mole. Most of the oxidized sulfide ion reported as elemental sulfur in the leach residues. The leaching rate was independent of the disk rotation speed and this fact, together with various hydrodynamic calculations, indicated that the reaction was chemically controlled. The dissolution rate increased as the 0.36 power of the ferric chloride concentration and it also increased substantially in the presence of dissolved CuCl₂. The accumulation of the ferrous chloride reaction product severely retarded the leaching reaction, but the presence of dissolved zinc chloride only slightly impeded it. The leaching rate was relatively insensitive to low levels of HC1 (>1 M), but increased dramatically at higher acid concentrations because of direct acid attack of the ZnS.     

The production of nickel-zinc alloys by powder injection

Alloys of nickel and zinc are used for the hot dip galvanizing of reactive steels containing around 0.1 pct Si. The production of these alloys is hindered by the low solubility of nickel in molten zinc at normal zinc alloying temperatures (450 °C to 550 °C). The kinetics of the dissolution of nickel in molten zinc were investigated in the temperature range 450 °C to 550 °C to show that the dissolution rate is controlled by mass transfer in the liquid boundary layer. The experiments involved dipping nickel plates into a crucible of zinc, which could be rotated to provide controlled convection around the stationary nickel plates. The dissolution rate of nickel plates immersed vertically in a static zinc melt was measured to determine the diffusion coefficient of nickel in zinc as a function of temperature and the activation energy of diffusion. A mathematical model was formulated to predict the dissolution time of nickel particles suspended in molten zinc. The dissolution times observed during plant-scale alloying tests to produce 0.15 wt pct Ni alloys using powder injection to introduce the nickel into the zinc melt agreed with the predictions of the mathematical model. The plant tests demonstrated that alloying times of less than 10 minutes can be achieved at normal alloying temperatures if the nickel is added as a powder.     

Rates of dissolution of rotating iron cylinders in liquid copper and cu-fe alloys

Iron cylinders with molybdenum capped ends are rotated at speeds of 260, 570, and 835 rpm in liquid copper and Cu-Fe alloys maintained at 1220°, 1300°C, and 1370°C under argon at 1 atm pressure. The dependence of the dissolution rate of the cylinders on the concentration of iron in the bulk liquid is observed. The solution-rate constants defined by an approximate form of the Berthoud equation vary from 7 × 10^-3 to 30 × 10^-3 cm.s^-1. There is a linear relation between the logarithm of the rate constant and the reciprocal of absolute temperature for each rotational speed. The rate constant is found to vary with the 0.85 to the 0.96 power of the Reynolds number in the range 6500 〈 Re 〈 22000. This suggests that the dissolution process is diffusion controlled. The dependence of the dissolution rate on the activity of iron in the bulk liquid is observed. Oxygen increases markedly the dissolution rate, whereas sulfur does not.     

Kinetics of dissolution of sulfur in tetrachloroethylene

The kinetic regularities of the dissolution of sulfur in tetrachloroethylene (TCE), which depend on the temperature, hydrodynamic conditions, and TCE concentration, are presented. Using the rotating disc method, it is revealed that this process occurs in a mixed mode; its diffusion and kinetic components are revealed. The reaction order of the kinetic component of the dissolution rate of sulfur by TCE is 1.5, while the experimental activation energy of the process is 39.2 ± 2.0 kJ/mol. The activation energy of the diffusion component of the convective mass transfer during the dissolution of sulfur in TCE is 28.0 ± 2 kJ/mol.     

Extraction of lead into a metallic phase from natural sulfide compounds in an alkaline medium

Reduction of lead from concentrates of Gorevskii, Dal’negorskii, and Dukatskii lead depositions in alkaline medium in the fusion and agitation modes is investigated. The formation of metal lead from the Dukatskii concentrate is completed at t = 450–470°C, from Dal’negorskii at 500–520°C, and from Gorevskii at 600–620°C. An increase in the alkali: concentrate ratio promotes a certain enhancement of coalescence of reduced metal particles. It is found that under conditions of intense stirring of a mixture of molten alkali with concentrate, the problems of defoaming and coalescence of a metallic phase are solved. A criterion of hydrodynamic similarity in the formation process of a continuous metallized lead phase is suggested. The specific consumption of alkali during zinc reduction from industrial sulfides is determined to be 0.42–0.43 g/g.     

Enhanced carbon solubility in solvent for SiC rapid solution growth:Thermodynamic evaluation of Cr-Ce-Si-C system

The carbon dissolution in solvent plays a key role in the process of solution growth route for SiC single crystal,which could determine the growth rate and quality of the products.However,the carbon dissolving ability of binary alloy solvent still needs to be improved.Here,we demonstrate the improved carbon dissolution and enlarged carbon supersaturation in Cr-Ce-Si ternary solvent,showing great potential for SiC solution growth.The phase relations of Cr-Ce-Si-C system were determined by using C...     

Effects of additives and temperature on dissolution rate and diffusivity of lime in Al2O3-CaO-SiO2 based slags

The dissolution rate of dense lime specimens in calcium aluminosilicate based melts was measured at 1430 °C to 1600 °C in air, using a rotating disk/cylinder technique. The measured dissolution rates were strongly dependent on the rotation speed with the results indicating mass transfer in the slag phase to be a rate-limiting step. At a given rotation speed, the slag chemistry and temperature had strong effects on the dissolution rate. The diffusivity of CaO in the slag was calculated from the dissolution rate and solubility data, using known mass-transfer correlations. Addition of CaF₂ MnO _x , FeO _x , and TiO₂ to the slag increased the CaO diffusivity, while SiO₂ had an opposite effect. Addition of CaF₂ had the strongest effect and increased the diffusivity by a factor of 3 to 5 in the temperature range of 1500 °C to 1600 °C. The deduced activation energy for diffusion of CaO in these slags ranged from about 53 to 246 kJ/mole, depending on the concentration of additives used.     

Thermodynamics Calculation and Experimental Study on Separation of Bismuth from a Bismuth Glance Concentrate Through a Low-Temperature Molten Salt Smelting Process

The main purpose of this study is to characterize and separate bismuth from a bismuth glance concentrate through a low-temperature, sulfur-fixing smelting process. This article reports on a study conducted on the optimization of process parameters, such as Na₂CO₃ and zinc oxide wt pct in charging, smelting temperature, smelting duration on the bismuth yield, resultant crude bismuth grade, and sulfur-fixing rate. A maximum bismuth recovery of 97.31 pct, crude bismuth grade of 96.93 pct, and 98.23 pct sulfur-fixing rate are obtained when a charge (containing 63.50 wt pct of Na₂CO₃ and 22.50 wt pct of bismuth glance, as well as 5 pct in excess of the stoichiometric requirement of zinc oxide dosage) is smelted at 1000 K (727 °C) for 150 minutes. This smelting operation is free from atmospheric pollution because zinc oxide is used as the sulfur-fixing agent, which can capture sulfur from bismuth sulfide and form the more thermodynamic-stable compound, zinc sulfide. The solid residue is subjected to a mineral dressing operation to obtain suspension, which is filtered to produce a cake, representing the solid particles of zinc sulfide. Based on the results of the chemical content analysis of the as-resultant zinc sulfide, more than 93 pct zinc sulfide can be recovered, and the recovered zinc sulfide grade can reach 60.20 pct. This material can be sold as zinc sulfide concentrate or roasted to be regenerated as zinc oxide.     

Kinetics of Ammonia Leaching of Multimetal Sulphides

This paper briefly describes the studies carried out on oxidative ammonia leaching of Cu-Zn-Pb multimetal sulphides. Kinetics of zinc and copper dissolution were studied with ? 200 + 300 mesh BSS fraction and 1% solids in the slurry. It is observed that the dissolution of sphalerite proceeds by a phase boundary reaction model and that of copper via diffusion through product layer in the temperature range of 70-100°C. The rate equations for zinc and copper dissolution are given by:

1 ? (1 ? α)^1/3 = k _Zn[NH₃][pO₂]^1/2

1 ? 2/3α ? (1 2/3α )^2/3 = k^Cu[NH₃]²[pO₂]^1/2

where the symbols have the usual meanings.

Activation energies for zinc and copper dissolution reactions are estimated to be 66.5 and 55.4 kJ/mole, respectively. Activation energy values thus obtained are also comparable to those obtained using a differential approach.

The leaching results obtained with 10% solids using a wide range of particle size (? 140 + 500 mesh) indicate that copper dissolution is chemically controlled in ammonia as well as ammonia-ammonium sulphate medium in the temperature range of 115-135°C. However, at lower temperature (?55°C). the leaching reaction follows a diffusion model. Zinc dissolution data show deviations from the shrinking core model due to high extractions in the initial stages.     

Rates of dissolution of a vertical nickel cylinder in liquid aluminum under free convection

The rate of dissolution of a vertical nickel cylinder, completely immersed in liquid aluminum in the absence of any forced convection at 675°C, was found to be at steady-state and controlled by the rate of mass transfer in the fluid boundary layer under free convection arising from the mass transfer process itself. The value of the diffusion coefficient of nickel in liquid aluminum at 675°C has been caclulated as 1.79×10^?5 sq cm per sec. Atx<0.5 cm, wherex is the distance downwards from the upper end of the cylinder, the local rate of dissolution was found to vary asx ^?1/4, as expected in free convection. However, the rate decreased more rapidly at larger values ofx, possibly due to the interference in fluid flow caused by the proximity of the crucible bottom.     

Kinetic investigations of two processes for zinc recovery from zinc plant residue

Abstract

This paper presents a kinetic study of hydrometallurgical and pyrometallurgical processes employed for the recovery of zinc from a zinc plant residue (ZPR). The hydrometallurgical process investigated involved zinc leaching from the ZPR with sulphuric acid solution, while the pyrometallurgical process was based on zinc oxide reduction from the ZPR using activated carbon as the reducting agent. At the optimum leaching conditions, the zinc recovery was 89·5% at 95°C after 60?min. The data obtained for the leaching kinetics indicated that the dissolution of ZPR is a diffusion controlled process and the activation energy is equal to 21±2?kJ?mol^?1. The maximum zinc recovery, obtained during pyrometallurgical treatment was 72% at 1300°C after 60?min. Kinetic investigations revealed that the zinc oxide reduction is carried out in the transient kinetic area, where both diffusion and the chemical reaction control the overall process rate, with an activation energy of 38±5?kJ?mol^?1.

Cet article présente une étude cinétique d'un procédé hydrométallurgique et d'un procédé pyrométallurgique utilisés pour la récupération du zinc du résidu d'une usine de zinc (ZPR). Le procédé hydrométallurgique investigué impliquait la lixiviation du zinc du résidu de l'usine de zinc avec une solution d'acide sulfurique, alors que le procédé pyrométallurgique était basé sur la réduction de l'oxyde de zinc du résidu de l'usine de zinc en utilisant du charbon activé comme agent de réduction. Aux conditions optimales de lixiviation, la récupération du zinc était de 89·5% à 95°C après 60?min. Les données obtenues pour la cinétique de lixiviation ont indiqué que la dissolution du résidu de l'usine de zinc était un procédé contrôlé par la diffusion et l'énergie d'activation est égale à 21±2?kJ?mol^?1. La récupération maximale de zinc, obtenue lors du traitement pyrométallurgique, était de 72% à 1300°C après 60?min. Les investigations de la cinétique ont révélé que la réduction de l'oxyde de zinc était effectuée dans la zone de cinétique transitoire, où tant la diffusion que la réaction chimique contrôlent la vitesse globale du procédé, avec une activation d'énergie de 38±5?kJ?mol^?1.     

Growth of aluminum antimonide in solid aluminum-liquid antimony diffusion couples

An investigation was made of the isothermal growth of the intermediate alloy phase aluminum antimonide AlSb, at the interfaces of diffusion couples consisting either of solid aluminum and liquid antimony or of solid aluminum and of an Sb−Al alloy slightly supersaturated in AlSb. The diffusion anneals were carried out in the temperature range 635° to 655°C and for times up to 48 hr. In the solid aluminum vs liquid antimony couples, it was found that considerable dissolution of solid aluminum occurred at the solid-liquid interface before the first crystals of AlSb appeared. Subsequently, a two-phase region, consisting of AlSb crystals of greatly varying sizes interspersed throughout the liquid antimony developed between the instantaneous solid-liquid interface and the original solid-liquid interface. The results suggest that the dominant mechanism influencing the growth of AlSb in these diffusion couples is diffusional mass transport of aluminum in liquid antimony. The rapid diffusion of aluminum leads first to the dissolution of solid aluminum and saturation of the liquid antimony, and next to the growth of large discrete crystals of AlSb presumably via an Ostwald-ripening mechanism. N. GRADO, formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, Brooklyn, N.Y.     

Aluminum Leaching from Calcined Coal Waste Using Hydrochloric Acid Solution

Coal waste is the largest industrial solid waste generated from coal preparation plants during the processing and cleaning of coal for electric power generation. Aluminum oxide (Al₂O₃, 16–36%), silicon dioxide (SiO₂, 45–58%), and carbon (4–25%) account for more than 90% of the coal waste. In this paper the results of aluminum leaching from calcined coal waste are reported. Techniques including XRD, SEM, and FTIR were used to characterize the coal waste before and after calcination. Three additives were evaluated during the calcination process to improve the extraction of Al₂O₃ by hydrochloric acid dissolution. The results from the leaching experiments show that coal waste is activated after calcination at a temperature between 650°C and 750°C. With addition of sodium fluoride effective aluminum dissolution of 90% was achieved under certain conditions. The extent of leaching was found to be 20% higher than that achieved without sodium fluoride addition.     

The evolution of microstructure in Al-2 Pct Cu thin films: Precipitation,dissolution, and reprecipitation

The precipitation, dissolution, and reprecipitation processes of Al₂Cu (θ phase) in Al-2 wt pct Cu thin films were studied. The films were characterized in the as-deposited condition, after annealing at 425 °C for 35 minutes, and after rapid thermal annealing (RTA) at 345 °C, 405 °C, and 472 °C. In the as-deposited samples, the precipitates had a fine even distribution throughout the thin film both at aluminum grain boundaries and within the aluminum grains. Annealing below the solvus temperature caused the grain boundary precipitates to grow and precipitates within the center of aluminum grains to diminish. Annealing above 425 °C caused the θ-phase precipitates to dissolve. Upon cooldown, the θ phase nucleated at aluminum grain boundaries and triple points in the form of plates.In situ heating and cooling experiments documented this process in real time. Analytical microscopy revealed that there is a depletion of copper at the aluminum grain boundaries in regions free of precipitates. The θ-phase precipitates nucleated and grew at the grain boundariesvia a collector plate mechanism and drew copper from the areas adjacent to the aluminum grain boundaries. This paper is based on a presentation made in the symposium “Interface Science and Engineering” presented during the 1988 World Materials Congress and the TMS Fall Meeting, Chicago, IL, September 26–29, 1988, under the auspices of the ASM-MSD Surfaces and Interfaces Committee and the TMS Electronic Device Materials Committee.     

Thixoforging of Wrought Aluminum Thin Plates with Microchannels

A direct die-filling thixoforging method is designed to fabricate aluminum thin plates with a pattern of microchannels in a single forming operation. Extruded AA2024 and AA7075 wrought aluminum billets are used. A recrystallization and partial remelting process is used to prepare the semisolid slurries required for the forming process. Under a thixoforging pressure of 70 MPa, AA7075 thin plates are successfully thixoforged in a temperature range of 883 K to 893 K (610 °C to 620 °C), corresponding to liquid fractions of ~30 to 50 pct in the semisolid slurry. AA2024 thin plate requires a thixoforging temperature range of 888 K to 898 K (615 °C to 625 °C), corresponding to the liquid fractions of ~45 to 60 pct. Final microstructures of the thin plates comprise primary α-Al equiaxed globular grains in a matrix of a solidified liquid phase. With increasing thixoforging temperature, the yield strength values continuously decrease. The ultimate tensile strength (UTS) values of the thin plates initially decrease with increasing thixoforging temperature from 883 K to 888 K (610 °C to 615 °C) and from 888 K to 893 K (615 °C to 620 °C) for the AA7075 and AA2024 thin plates, respectively. The UTS values stabilize and slightly enhance when the thixoforging temperatures are further increased to 893 K and 898 K (620 °C and 625 °C) for the AA7075 and AA2024 thin plates, respectively. Very brittle behavior (elongation value of ~1 pct) is observed for the AA7075 thin plates thixoforged at 883 K and 888 K (610 °C and 615 °C). The elongation value increases to 3 pct with increasing the thixoforging temperature to 893 K (620 °C). In contrast, larger elongation values (between 4 and 6 pct) are achieved for the AA2024 thin plates. Increasing the thixoforging pressures from 70 to 100 MPa and then to 150 MPa improves the tensile properties of the thin plates. The tensile properties of the thixoforged thin plates are linked to their microstructural characteristics and processing conditions and are discussed here in detail.     

Phase equilibria in the system Al-Rh

Methods of differential thermal analysis, x-ray diffraction, microstructural analysis and electron probe microanalysis are used to study alloys of the Al-Rh system over the whole concentration range. It is established that the phase of equiatomic composition AlRh melts congruently at 2060°C and it has an extended range of homogeneity (45.1–54.2 at.% Rh). The solubility of aluminum in rhodium reaches 9 at.%, decreasing to 6 at.% at 850°C. Coordinates are determined for the eutectic point l ⇆ AlRh + 〈Rh〉 as 70 at.% Rh and 1715°C. The existence of intermediate phases, their crystal structure, and also the method of forming phases in the field of composition rich in aluminum given in publications are confirmed. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 48–56, May–June, 2006.     

Kinetics of Carbon Dissolution of Coke in Molten Iron

The effect of temperature on the dissolution rate of carbon from coke in molten iron was investigated using a sampling technique in the temperature range of 1723?K to 1923?K (1450?°C to 1650?°C). The dissolution rate of carbon from coke in molten iron increased as the temperature increased. At 1923?K (1650?°C), the rate-determining step was the mass transfer of carbon in the boundary layer adjacent to the metal-carbon interface. At 1723?K (1450?°C), the rate-determining step changed from the mass transfer to the interfacial chemical reaction as the reaction proceeded. At 1823?K (1550?°C), both reaction steps affected the apparent reaction rates. Sulfur dissolution did not affect the carbon dissolution rates in molten iron, so it was considered that the sulfur adsorption at the metal/coke interface was not so significant. The apparent activation energy of the carbon dissolution of coke in molten iron was estimated to be 442?kJ/mol.