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Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1983"


Journal ArticleDOI
TL;DR: In this article, the effect of variables such as rotational speed, bed depth, cylinder diameter, particle size, and particle shape on bed motion has been determined, and the scaling of bed behavior with respect to particle size and cylinder diameter requires similarity of Froude number modified by(D/d p)1/2, and pct fill.
Abstract: Slumping and rolling beds have been studied extensively in a continuous pilot kiln and batch rotary cylinders. Solids investigated include nickel oxide pellets, limestone, sand, and gravel. The effect of variables such as rotational speed, bed depth, cylinder diameter, particle size, and particle shape on bed motion has been determined. For a given material, the different modes of bed motion can be delineated conveniently on a Bed Behavior Diagram which is a plot of bed depthvs rotational speed. The scaling of bed behavior with respect to particle size and cylinder diameter requires similarity of Froude number modified by(D/d p)1/2, and pct fill. Measurements of key variables characterizing slumping and rolling beds have also been made.

372 citations


Journal ArticleDOI
TL;DR: Several factors affecting the precipitation of the alkali jarosites (sodium jarosite, potassium, ammonium, rubidium, and ammonium jarosite) have been studied systematically using sodium jarosite as the model.
Abstract: Several factors affecting the precipitation of the alkali jarosites (sodium jarosite, potassium jarosite, rubidium jarosite, and ammonium jarosite) have been studied systematically using sodium jarosite as the model The pH of the reacting solution exercises a major influence on the amount of jarosite formed, but has little effect on the composition of the washed product Higher temperatures significantly increase the yield and slightly raise the alkali content of the jarosites The yield and alkali content both increase greatly with the alkali concentration to about twice the stoichiometric requirement but, thereafter, remain nearly constant At 97 °C, the amount of product increases with longer retention times to about 15 hours, but more prolonged reaction times are without significant effect on the amount or composition of the jarosite Factors such as the presence of seed or ionic strength have little effect on the yield or jarosite composition The amount of precipitate augments directly as the iron concentration of the solution increases, but the product composition is nearly independent of this variable A significant degree of agitation is necessary to suspend the product and to prevent the jarosite from coating the apparatus with correspondingly small yields Once the product is adequately suspended, however, further agitation is without significant effect The partitioning of alkali ions during jarosite precipitation was ascertained for K:Na, Na:NH4, K:NH4, and K:Rb Potassium jarosite is the most stable of the alkali jarosites and the stability falls systematically for lighter or heavier congeners; ammonium jarosite is slightly more stable than the sodium analogue Complete solid solubility among the various alkali jarosite-type compounds was established

150 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a model to predict the conditions giving rise to the different forms of transverse bed motion in a rotary cylinder: slumping, rolling, slipping, cascading, cataracting, and centrifuging.
Abstract: Mathematical models have been developed to predict the conditions giving rise to the different forms of transverse bed motion in a rotary cylinder: slumping, rolling, slipping, cascading, cataracting, and centrifuging. Model predictions of the boundaries between these modes of bed motion compare well with previously reported measurements, and can be represented conveniently on a Bed Behavior Diagram which is a plot of pct fill against Froude number (or bed depthvs rotational speed). The location of the boundaries is shown to depend on material variables which characterize frictional conditions in the bed. For the slumping/rolling boundary these are primarily the shear angle and the limiting wedge angle which defines the solids involved in a slump. For the slipping/slumping and slipping/rolling boundaries the governing material variables are the bed/wall friction angle and the upper angle of repose and dynamic angle of repose, respectively. Similarly, the location of the other boundaries related to cascading and cataracting is determined by the dynamic angle of repose. Complete Bed Behavior Diagrams have been calculated for solids having different particle size and particle shape rotated in cylinders having different diameters.

142 citations


Journal ArticleDOI
TL;DR: A process for preparing Al-alloy castings containing dispersions of zircon particles is described in this article, where composites were prepared by stirring Zircon particle (40 to 200 µm size) in commercially pure Al (99.5 pct)* and Al-11.8 pct Si melts and subsequently casting these melts in permanent molds.
Abstract: A process for preparing Al-alloy castings containing dispersions of zircon particles is described. Composites were prepared by stirring zircon particles (40 to 200 µm size) in commercially pure Al (99.5 pct)* and Al-11.8 pct Si melts and subsequently casting these melts in permanent molds. It was found to be necessary to alloy the above two melts with 3 pct Mg to disperse substantial amounts of zircon particles (25 to 30 pct). Further, it was possible to disperse up to 60 wt pct zircon by adding up to 5 pct Mg; however, the melts containing above 30 wt pct zircon showed insufficient fluidity for gravity diecasting and had to be pressure diecast. Microstructural studies of cast composites indicated the presence of a reaction zone at the periphery of zircon particles, and electron probe microanalysis showed concentrations of Mg and Si at the particle-matrix interface. Hardness, abrasive wear resistance, elastic modulus, 0.2 pct proof stress, and tensile strength of cast Al-3 pct Mg alloy were found to improve with the dispersions of zircon particles. Scanning electron micrographs of abraded and fractured surfaces did not show any evidence of particle pull-outs or voids at the particle matrix interface, indicating strong continuous bonding.

86 citations


Journal ArticleDOI
TL;DR: An extension of the associated solution model is developed and applied to the Cu-O liquid phase in this paper, where associated species "Cu2O" in the liquid solution are assumed, which interact with the surrounding free Cu and O atoms.
Abstract: An extension of the associated solution model is developed and applied to the Cu-O liquid phase Associated species “Cu2O” in the liquid solution are assumed, which interact with the surrounding free Cu and O atoms All thermodynamic properties and the phase diagram calculated from this model are in good agreement with the experimental information The success of this mathematical description is, of course, no proof for the physical existence of associated species A consistent set of thermodynamic data of the various solid, liquid, and gaseous phases is given by this comprehensive evaluation In addition, linear approximations for the Gibbs energies of reaction of formation and the interaction coefficients are offered A metastable liquidus of the compound CuO at elevated pressure is predicted, the congruent melting point being 1228 °C at δC atP O 2 = 244 atm (247 MPa)

83 citations


Journal ArticleDOI
TL;DR: In this article, a mathematical representation for the electromagnetic force field, flow field, temperature field and for transport controlled kinetics, in a levitation melted metal droplet, was developed for the mutual inductances.
Abstract: A mathematical representation was developed for the electromagnetic force field, the flow field, the temperature field (and for transport controlled kinetics), in a levitation melted metal droplet. The technique of mutual inductances was employed for the calculation of the electromagnetic force field, while the turbulent Navier - Stokes equations and the turbulent convective transport equations were used to represent the fluid flow field, the temperature field and the concentration field. The governing differential equations, written in spherical coordinates, were solved numerically. The computed results were in good agreement with measurements, regarding the lifting force, and the average temperature of the specimen and carburization rates, which were transport controlled.

76 citations


Journal ArticleDOI
TL;DR: In this paper, the axial temperature profiles of the flame and wall and axial profiles of heat flux to the solids bed and refractory wall were modeled mathematically.
Abstract: Heat flow in the flame zone of a direct-fired rotary kiln has been modeled mathematically. The flame has been assumed to be cylindrical in shape, backmixed radially, and moving axially in plug flow. The length of the flame and the rate of entrainment of secondary air have been characterized by empirical equations reported in the literature. It has been shown that the axial component of radiation can be reasonably neglected since it is relatively small compared to the radial component. The resulting one-dimensional model is capable of predicting the axial temperature profiles of the flame and wall and the axial profiles of heat flux to the solids bed and refractory wall. The model has been employed to study the influence on heat flow to the bed of the following variables: fuel type (fuel oil, natural gas, producer gas), firing rate, temperature of secondary air, pct primary air, and oxygen enrichment. Of the three fuels, combustion of fuel oil gives the longest flame and the greatest heat input to the solids in the flame zone. Raising the secondary-air temperature increases the flame length significantly but has a small effect on the maximum flame temperature and heat flux to the solids. Increasing percent primary air decreases the flame length and increases the peak values of flame temperature and solids heat flux but reduces the quantity of heat received by the solids in the flame zone. Oxygen enrichment results in a shorter flame, higher maximum flame temperature, and increase in the heat transferred to the solids in the flame zone.

62 citations


Journal ArticleDOI
TL;DR: In this article, the influence of temperature, pH, acid type, and surface area on the acid dissolution of natural and synthetic willemites and natural hemimorphites has been investigated.
Abstract: The influence of temperature, pH, acid type, and surface area on the kinetics of the acid dissolution of natural and synthetic willemites and natural hemimorphites has been investigated. Specific rate constants, based upon areas determined by krypton adsorption measurements, were estimated from the experimental data obtained. For both willemite and hemimorphite, the rates of dissolution in different acids are shown to be related to the relative strengths of zinc-acid anion complexes. The reactivity of willemite toward acids increases with increasing replacement of zinc by manganese. Mixed chemical/diffusion control is responsible for the observed rates of willemite dissolution under the conditions studied (HNO3, HCl, HClO4, H3PO4, H2SO4, pH 0.31 to 3.00,T 21 to 94 °C). Estimates of the relative contributions of chemical and diffusional resistances to the overall rate have been made for the dissolution of manganese-free willemite in sulfuric acid solutions. The experimentally measured rates have been demonstrated to be in reasonable agreement with predicted overall dissolution rates. Proposals are made regarding the nature of the diffusion and chemical steps involved in the dissolution process. Hemimorphite was found to be considerably more reactive than willemite and its dissolution is primarily diffusion controlled under the conditions studied (T 20 to 76 °C, pH 2 to 3.5).

58 citations


Journal ArticleDOI
TL;DR: In this paper, the diffusivity and solubility of oxygen in solid copper have been determined in the temperature range 700 to 1030 °C using potentiostatic and potentiometric techniques.
Abstract: The diffusivity and solubility of oxygen in solid copper have been determined in the temperature range 700 to 1030 °C using potentiostatic and potentiometric techniques. The results are summarized by the following equations: Do Cu = 1.16-0.31 +0.42 × 10−2 exp(−67300 ± 3000/RT) cm2 per second; No s = 154 exp(−149600/RT)atom fraction of oxygen where R is in joules/degree/mole. The experimentally determined value of the pre-exponential factor in the diffusivity equation is found to be consistent with Zener’s model for an interstitial diffusion mechanism.

55 citations


Journal ArticleDOI
TL;DR: In this paper, the results of an initial systematic study of laser surface alloying nickel onto AISI 1020 steel substrates using a statistical experimental design technique were reported, where processing conditions were related to dimensions, solute content, and microstructural refinement of the laser alloyed zones.
Abstract: Laser surface alloying, a process of growing interest for local surface modification, relies upon a suitable composition and microstructure for satisfactory on-the-job performance. This paper reports the results of an initial systematic study of laser surface alloying nickel onto AISI 1020 steel substrates using a statistical experimental design technique. The objective was to relate processing conditions to dimensions, solute content, and microstructural refinement of the laser alloyed zones. Solute content was of principal concern as it is the single most important factor affecting the properties of laser surface alloys. The effects of varying the laser power, beam diameter, and speed on the width, depth, nickel content, and fluctuations in nickel content are reported. Interactions between process parameters are discussed, the reproducibility assessed, contour plots for solute content drawn. Dimensionless plots are developed that relate average solute content and microstructural refinement to process parameters. Previously published data for alloying chromium into 1018 steels are shown to contain similar trends. It is felt that such an approach would facilitate selection of processing conditions to obtain reproducibly the compositions and microstructures necessary for gainful utilization of laser surface alloys.

51 citations


Journal ArticleDOI
TL;DR: In this article, experimental measurements were reported on the rate at which commercial grade, low silica hematite pellets react with a gas mixture consisting of CO, H2, and N2 over the temperature range 500 °C to 1200 °C.
Abstract: Experimental measurements are reported on the rate at which commercial grade, low silica hematite pellets react with a gas mixture consisting of CO, H2, and N2 over the temperature range 500 °C to 1200 °C. Systems of this type are of considerable practical interest, both regarding the operation of direct reduction processes and ironmaking in the blast furnace. The results of the work may be summarized as follows: No carbon deposition was found when operating the system above 900 °C and in the absence of CO gas. When operating the system below 900 °C carbon deposition occurred, which in effect prevented the normal conversion from reaching completion. The maximum rate of carbon deposition was found to occur between 500 °C and 600 °C. In general hydrogen (in the presence of CO) tended to promote carbon deposition, while the presence of nitrogen appeared to retard the deposition process. When the reaction process was being carried out below 900 °C with CO + H2 gas mixtures, the reduction process occurred simultaneously with carbon deposition. At lower temperatures, say around 500° to 600 °C, the deposition process dominated, while at the higher temperatures, and particularly at a high hydrogen content of the reactant gas, the reduction process was dominant. The structural examination of the partially reacted specimens has shown that the carbon deposited was found primarily in the form of elemental carbon rather than cementite. Furthermore, X-ray analysis of the free pellet surface has indicated that iron was present in the carbon deposit phase. The practical industrial implications of these findings are discussed in the paper.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluate the results of roasting both natural and synthetic arsenopyrite (FeAsS) in inert, reducing, and oxidizing atmospheres at 798 and 873 K.
Abstract: Existing thermodynamic data for the Fe-As-S-0 system were evaluted and predominance area diagrams for that system were constructed at 798 and 973 K. Isopleths for the As/S and As/O atomic ratios in the vapor phase have been added to the diagrams by solving the complex equilibria. These modified diagrams were used to evaluate the results of roasting both natural and synthetic arsenopyrite (FeAsS) in inert, reducing, and oxidizing atmospheres at 798 and 873 K. Conditions leading to the retention of As as As2O5(s) and FeAsO4(s) were also reviewed. The experimental results indicate that both reducing and oxidizing atmospheres are more effective in the removal of As than an inert atmosphere. In a reducing atmosphere arsenic sulfides are evolved and the percentage of As removal increases with decreasing PO 2The greatest percent of As removal occurred with highly oxidizing atmospheres which generated As4O6 vapor.

Journal ArticleDOI
TL;DR: In this paper, an emf technique is reported using porous alumina tubes to contain reference metals and alloys in a molten salt electrolyte. But this technique is not suitable for the reduction of magnesium oxide.
Abstract: An emf technique is reported using porous alumina tubes to contain reference metals and alloys in a molten salt electrolyte. Data are reported for the activity of magnesium and its temperature derivative in several liquid metal solvents. These include lead (650 °C), tin (800 °C), bismuth (850 °C), antimony (850 °C), and mixtures of tin and antimony (800 °). In all cases, the solvents show strong negative deviations from ideal thermodynamic behavior, due to the effects of strong solvation caused by the formation of intermetallic compounds. The extent of this effect is Pb < Sn < Bi < Sb. The data reported are useful in evaluating solvents for the possible carbothermic reduction of magnesium oxide.

Journal ArticleDOI
TL;DR: In this article, the rate of dissociation of high purity liquid iron and iron-sulfur alloys between 1550 and 1650 °C has been studied by means of the 15N-14N exchange reaction.
Abstract: The rate of dissociation of N2 on high purity liquid iron and iron-sulfur alloys between 1550 and 1650 °C has been studied by means of the15N-14N exchange reaction. It is shown that the rate constants at given sulfur concentrations are consistent with those for the absorption of nitrogen into iron-sulfur alloys, indicating a common rate determining step. The rate constant for high purity liquid iron, in units of mol cm−2 s−1 aim−1, is given by: logk f = −340/T − 1.38. The rate constant is found to be independent of carbon concentration up to about 4.3 wt pct and to be closely consistent with ideal chemisorption kinetics. The results are combined with those of previously published studies to give rational equations for the apparent rate constants for Fe-S and Fe-O alloys. Consistent values for the adsorption coefficients at 1600 °C for sulfur and oxygen are deduced to be about 130 and 220, respectively, for a standard state of the 1 wt pct ideal solution.

Journal ArticleDOI
TL;DR: In this paper, the effects of germanium, antimony, arsenic, cobalt, glue, and free acid concentration on both commercial and synthetic electrolytes were studied on both synthetic and real world.
Abstract: The effects of germanium, antimony, arsenic, cobalt, glue, and free acid concentration were studied on both commercial and synthetic electrolytes. The effects of a single factor and the combined effects of multiple factors were elucidated. The temperature, zinc concentration, and current density were varied for some of the tests. It was found that the acid content was the most critical factor when impurity levels were at normal plant solution concentrations. The ranges where the effect of the impurity became apparent were: greater than 20 ppb (parts per billion) for antimony; 40 ppb for germanium; 120 ppb for arsenic; and 7 to 8 mg/1 for cobalt for a solution containing 65 g/1 zinc and 100 g/1 free sulfuric acid. At higher levels of acid, the acceptable level of impurity declined markedly. Glue additions were found to counteract the effects of antimony and germanium, but did little to counteract the effects of cobalt and arsenic. The level of acid was found to be especially critical when cobalt and arsenic were in the electrolyte. Cobalt and arsenic exhibited synergism, and lower current efficiencies were obtained for arsenic-cobalt combinations than expected. A factorially designed experiment was conducted to quantify the effects observed by one-factor-at-a-time testing. The structures and morphologies of the deposits were examined using X-ray diffraction and scanning electron microscopy.

Journal ArticleDOI
TL;DR: In this paper, a geometric equation for leaching of malachite with ammonium carbonate was developed based on the kinetic data (activation energy and entropy), particle size and concentration dependence, residue morphology, and general leaching behavior evident from microscopic monitoring during leaching.
Abstract: Leaching of malachite was conducted with ammonium carbonate as lixiviant and with temperature, lixiviant concentration, and particle size as variables. Two stages of reaction were found. In Stage I, the initial dissolution of malachite proceeds rapidly, but after about 10 pct reaction the rate is reduced by surface blockage due to the presence of a needle-structured intermediate, presumably Cu(OH)2. Subsequently, malachite and the intermediate dissolve concurrently. In Stage II, after 90 pct reaction, essentially all of the malachite has dissolved and only the intermediate remains. It dissolves in Stage II. The activation energy is 64 kJ/mole (15.3 kcal/mole) for Stage I and 75 kJ/mole (18 kcal/mole) for Stage II. The rate of reaction in Stage I is proportional to the reciprocal of particle size and is 0.8 order with respect to the concentration of ammonium carbonate. The structures of leaching residues were studied using a scanning electron microscope. The kinetic data (activation energy and entropy), particle size and concentration dependence, residue morphology, and general leaching behavior evident from microscopic monitoring during leaching were used to develop the geometric equation for leaching in Stage I. The equation, based on a heterogeneous reaction with geometric rate control, is: 1 - (1 - α1/3 = K01/r0/[(NH4)2C03]0.8 exp(-64,000/RT)t. It was deduced that initial steps in reaction were: (1) release of Cu2+ from malachite; (2) initial complexing with ammonia to form Cu(NH3)2+; and (3) subsequent complexing to produce Cu(NH3) 4 2+ which is stable in solution at pH 8.8, the buffered pH of reaction. Stage II appears to be a similar reaction except that the reaction obeys cylindrical geometry instead of spherical geometry as in Stage I.

Journal ArticleDOI
TL;DR: In this paper, the dissolution kinetics of UO/sub 2/ were investigated under acid in situ leaching of sandstone uranium deposits and a simple kinetic model that considered dissolution and precipitation to be independent processes was proposed.
Abstract: Laboratory experiments have been carried out to determine the dissolution kinetics of UO/sub 2/ in the UO/sub 2/-H/sub 2/O/sub 2/-SO/sub 4/-H/sub 2/O system under conditions similar to those which occur during acid in situ leaching of sandstone uranium deposits. UO/sub 2/ dissolution proceeds by an electrochemical reaction at the UO/sub 2/ surface. Sulfate ions adsorb onto the UO/sub 2/ surface and reduce the rate of UO/sub 2/ dissolution by blocking sites of potential oxidation. UO/sup 2 +//sub 2/ precipitates as insoluble uranium peroxide hydrate (UO/sub 4/ X XH/sub 2/O), and under even moderate pH conditions can greatly reduce the UO/sub 2/ dissolution rate. The overall UO/sub 2/ dissolution (including UO/sub 4/ X XH/sub 2/O precipitation) can be usefully described by a simple kinetic model that considers dissolution and precipitation to be independent processes. The model has the advantage that the dissolution rate at a given temperature is a function only of solution composition and UO/sub 2/ surface area. The chemical model can thus be easily combined with fluid flow models to obtain a full chemical-physical model of the leaching of uranium ore in a column experiment or in situ.

Journal ArticleDOI
TL;DR: The construction of a sodium beta alumina probe for the determination of the sodium activity in molten aluminum alloys is described in this paper, where it was found that the emf at a given sodium concentration was a strong function of the silicon content.
Abstract: The construction of a sodium beta alumina probe for the determination of the sodium activity in molten aluminum alloys is described. It was found that the emf at a given sodium concentration was a strong function of the silicon content. Henry’s law was obeyed in super purity aluminum and the activity coefficient of 350 at 998 K agrees with other determinations.

Journal ArticleDOI
TL;DR: In this paper, the ternary oxide phases of the Fe-Al-0 system were determined at temperatures in the range 1123 to 1423 K using solid state electrochemical cells.
Abstract: Equilibrium oxygen pressures of the univariant ternary coexistences hematite + spinel + alumina, alloy + wustite + spinel, and alloy + spinel + alumina were determined at temperatures in the range 1123 to 1423 K using solid state electrochemical cells. The compositions of alloys and oxide phases of this Fe-Al-0 system that equilibrated with one another at 1273, 1423, and 1573 K were determined. These results and those from the literature are used to determine stabilities of the ternary oxide phases as a function of oxygen pressure and composition by constructing equilibrium oxygen pressure diagrams at 1073, 1173, and 1273 K.

Journal ArticleDOI
TL;DR: In this article, the authors identify the basic features of burden movement in a rotary kiln and determine the influence of length to diameter ratio (L/D) on the filling degree, hold-up, and residence time of the charge.
Abstract: The present work identifies the basic features of burden movement in a rotary kiln The cold model study was conducted with iron ore as the feed material to determine the influence of length to diameter ratio (L/D) of a rotary kiln on the filling degree, hold-up, and residence time of the charge An empirical equation correlating different operating variables has been derived on the basis of the experimental results The influence of individual parameters under different conditions on the residence time and back spillage has also been evaluated

Journal ArticleDOI
TL;DR: In this article, the authors investigated the reasons of the significant slowing down observed between 700 °C and 900 °C in many experimental investigations of iron ore (or oxide) reductions with hydrogen and attributed to very different reasons.
Abstract: Many economic studies have shown that iron ore reduction could be an important use of hydrogen, provided that its price was low enough. With this in mind, it was important to clarify the reasons of the significant slowing down, observed between 700 °C and 900 °C, in many experimental investigations of iron ore (or oxide) reductions with hydrogen and attributed to very different reasons. The experiments reported here have been designed with wustite single crystals so that safer conclusions may be derived than with the more complex situation encountered with iron ores. TGA, coupled with microstructure investigations, has shown conclusively that the slowing down is connected with the iron texture evolution toward a layer more impermeable to diffusion in the pores. Such a behavior is still increased in wet hydrogen by the blocking of active sites on wustite by water vapor. Another result is worth stressing: the very irregular shape of the reaction interface, quite different from the classical topochemical model.

Journal ArticleDOI
TL;DR: Carol Lake hematite particles were reduced to magnetite at 600 and 1000 °C using CO + CO2 mixtures as discussed by the authors, and the porosity was constant at a porosity level of 8.8 pct, but the average pore size depended on the rate of oxygen removal.
Abstract: Carol Lake hematite particles were reduced to magnetite at 600 and 1000 °C using CO + CO2 mixtures. The rate of reduction was measured in gravimetric tests and structural changes followed by optical microscopy, BET surface area, and mercury porosimetry. At 600 °C, the reduction of each grain approximately followed the shrinking core model, and fine pores were created in the magnetite produced. The volume of pores was constant at a porosity level of 8.8 pct, but the average pore size depended on the rate of oxygen removal, and finer pores were obtained under conditions of fast reduction. The reaction followed a different path at 1000 °C and proceeded by sideway thickening of a finite number of magnetite lamellae formed parallel to each other in each grain. Reduced particles showed reentrant surface depressions and cracks, but no porosity. Reaction mechanisms were postulated to relate these structural features to the progress of the reaction. Examination of the reaction steps indicated that the separation of oxygen from solid surfaces was likely to be the rate determining step at both temperatures. This was reflected in rate measurements by a strong dependence on CO pressure while the influence of oxygen activity (as represented by CO2/CO ratio) was of secondary importance at 1000 °C and negligible at 600 °C. A detailed analysis of reaction rates could not be made, however, because the particles were of a wide range of sizes and their structure changed during reduction.

Journal ArticleDOI
TL;DR: In this article, the first stage dissolution reaction is electrochemical and is mixed kinetics-controlled; ferric-ion transfer through the solution boundary layer and reduction on the surface to release Cu2+ into solution are both important in controlling the rate.
Abstract: In an acidified ferric chloride solution, bornite leaches in two stages of reaction with the first being relatively much more rapid than the second; the first terminates at 28 pct copper dissolution. The first-stage dissolution reaction is electrochemical and is mixed kinetics-controlled; ferric-ion transfer through the solution boundary layer and reduction on the surface to release Cu2+ into solution are both important in controlling the rate. The concentration of labile Cu+ in the bornite lattice governs the potential of the surface reaction, and, once Cu+ is depleted from the original bornite, stage-I reaction ceases. The solid reaction intermediate formed is Cu3FeS4. Minute subcrystallites formed at the latter part of stage I leach topochemically in stage II. This reaction which commences at 28 pct Cu dissolution is characterized by a change in mechanism at about 40 pct copper dissolution, though the overall chemical equation for reaction is unchanged in stage II; cupric and ferrous ions and sulfur as a solid residue are products of reaction. The region 28 to about 40 pct Cu dissolution is designated as a transition period to stage-II reaction. Reaction rate in this period is interpreted as being controlled by reduction of Fe3+ on active product sulfur surface sites, and hence the reaction rate is controlled by the rate of nucleation and growth of sulfur on the Cu3FeS4 intermediate surfaces. Strain in the Cu3FeS4 crystal lattice is released during this period by diffusion from the lattice of Cu+ remaining from the labile copper initially present in the bornite. After about 40 pct Cu dissolution the rate of reaction is controlled by diffusion through the fully formed sulfur layer in an equiaxial geometrically controlled reaction.

Journal ArticleDOI
TL;DR: In this paper, the rate of oxidation of liquid aluminum and its alloys under conditions similar to those found industrially, carbon dioxide was bubbled through the melt and the change in gas composition monitored using a mass spectrometer.
Abstract: In order to investigate the rate of oxidation of liquid aluminum and its alloys under conditions similar to those found industrially, carbon dioxide was bubbled through the melt and the change in gas composition monitored using a mass spectrometer. It was found that the dynamic oxidation of aluminum was a function of the carbon dioxide partial pressure and was considerably faster than oxidation under quiescent conditions. For alloys containing an appreciable amount of magnesium, the magnesium oxidized in two stages. The carbon dioxide was first reduced to carbon monoxide and then to carbon. At lower magnesium levels, aluminum is preferentially oxidized, but the reduction of the carbon dioxide proceeds only as far as carbon monoxide.

Journal ArticleDOI
TL;DR: In this paper, the dissolution behavior of iron and cobalt in ammoniacal ammonium carbonate solution has been investigated with the aid of Eh-pH diagrams for the Fe-NH3-H2O-CO3 and Co-NH 3-H 2O- CO3 systems, and electrochemical techniques such as open circuit potential measurements and potentiostatic and potentodynamic polarization experiments.
Abstract: The dissolution behavior of iron and cobalt in ammoniacal ammonium carbonate solution has been investigated with the aid of Eh-pH diagrams for the Fe-NH3-H2O-CO3 and Co-NH3-H2O-CO3 systems, and electrochemical techniques such as open circuit potential measurements and potentiostatic and potentiodynamic polarization experiments. The polarization measurements indicate that both Fe and Co electrodes show active and passive behavior, and that Co dissolves at a more oxidizing potential than does Fe(e.g., E = −0.34 V (SHE) for Co andE = −0.52 V for Fe at a dissolution rate of 1 mA cm−2). The active and passive current densities for Co are both greater than for Fe. In sintered Fe-Co mixtures, the presence of Fe shifts the potential of the maximum current to less noble values and also lowers the magnitude of this current. In addition there is practically no cobalt dissolution when the potential exceeds 0.6 V (SHE). It is suggested that the well-known poor recovery of cobalt from reductive-roasted ferruginous oxide ores may be partly related to the dissolution behavior of a metallic alloy phase containing both iron and cobalt.

Journal ArticleDOI
TL;DR: In this paper, the free energies of formation of ZnO-SiO2 melts are significantly more negative than published estimated values and this, together with the behavior observed in the system CaO-Al2O3, SiO2, CaO−14.7, and A12O3 in the range 1400° to 1550 °C were analyzed.
Abstract: The activity of ZnO in ZnO-SiO2 and CaO-ZnO-SiO2 melts has been measured at 1560 °C using a transpiration technique with CO-CO2 mixtures as the carrier gas. The activities of ZnO in dilute solution in 42 wt pct SiO2−38 wt pct CaO-20 wt pct A12O3 in the range 1400° to 1550 °C and in 62 wt pct SiO2−23.3 wt pct CaO−14.7 wt pct A12O3 at 1550 °C have also been measured. The measured free energies of formation of ZnO-SiO2 melts are significantly more negative than published estimated values and this, together with the behavior observed in the system CaO-Al2O3-SiO2, indicate that ZnO is a relatively basic oxide. The results are discussed in terms of the polymerization model of binary silicate melts and ideal silicate mixing in ternary silicate melts. The behavior of ZnO in dilute solution in CaO-Al2O3-SiO2 melts is discussed in terms of the possibility of the fluxing of ZnO by iron blast furnace slags.

Journal ArticleDOI
TL;DR: In this article, a rotary kiln-based direct reduction pilot plant for sponge iron production in India is investigated. But the work was divided into two parts: first, a study of the influence of several operating parameters, i.e., rotational speed, inclination of the kiln, effect of circular dams at the feed and the exit ends of the Kiln, etc., and second, an investigation of the extent of segregation of a mixture of solids in a rotating kiln.
Abstract: Looking forward to the need of developing coal-based sponge iron technology in India, a country having no significant resources of either coking coal or natural gas, the Research and Development Division of the Tata Iron and Steel Company Limited (TISCO) set up a rotary kiln based direct reduction pilot plant in 1975. In this pilot plant, a totally indigenous technology for production of sponge iron has been developed in which non-coking coal is essentially used as the reductant. For easy scaling up of the TISCO Direct Reduction (TDR) process to units of 300 to 400 tpd capacity, it was thought necessary to explore some of the fundamental aspects of material flow in a rotary kiln. This was carried out by studying the flow of materials in room temperature models. The work was divided into two parts: first, a study of the influence of several operating parameters,viz., rotational speed, inclination of the kiln, effect of circular dams at the feed and the exit ends of the kiln,etc., and second, an investigation of the extent of segregation of a mixture of solids in a rotating kiln. The highlights of the experimental results dealing mainly with the effect of various kiln operating variables on the filling degree profile of the charge in the kiln are presented.

Journal ArticleDOI
TL;DR: In this paper, a Teflon filter membrane with xylene solution of di-2-ethylhexyl phosphoric acid (HDEHP) as a mobile carrier held within the pores by capillary forces is presented.
Abstract: The mechanism of europium transport through a supported liquid membrane is presented. The membrane consisted of a Teflon filter membrane with xylene solution of di-2-ethylhexyl phosphoric acid (HDEHP) as a mobile carrier held within the pores by capillary forces. Interposing the liquid membrane between two aqueous solutions of different pH, europium was transported and concentrated from the high pH solution to the low pH solution across the liquid membrane. The experiments were carried out to investigate the effects of the concentration of europium in the aqueous phase and HDEHP concentration in the membrane solution on the permeation rates of europium. The experimental results have been compared with a transport model for concentrating europium across the liquid membrane. The permeation rates of europium can be explained approximately by the diffusion process of the complex formed between europium ion and HDEHP at the membrane interface through the membrane in addition to the diffusion process of europium in the aqueous film adjacent to the membrane interface.

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TL;DR: In this paper, an optimization technique based upon least squares regression is presented to permit the simultaneous analysis of diverse experimental binary thermodynamic and phase diagram data, which can subsequently be used to calculate the thermodynamic properties or the phase diagram.
Abstract: An optimization technique based upon least squares regression is presented to permit the simultaneous analysis of diverse experimental binary thermodynamic and phase diagram data. Coefficients of polynomial expansions for the enthalpy and excess entropy of binary solutions are obtained which can subsequently be used to calculate the thermodynamic properties or the phase diagram. In an interactive computer-assisted analysis employing this technique, one can critically analyze a large number of diverse data in a binary system rapidly, in a manner which is fully self-consistent thermodynamically. Examples of applications to the Bi-Zn, Cd-Pb, PbCl2-KCl, LiCl-FeCl2, and Au-Ni binary systems are given.

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TL;DR: In this paper, the authors investigated the kinetics of hydrogen reduction of thin, dense strips of hematite in the range 245 °C to 482 °C, where pure hydrogen gas at 1 atm was used as reducing agent.
Abstract: The kinetics of hydrogen reduction of thin, dense strips of hematite were investigated in the range 245 °C to 482 °C. Pure hydrogen gas at 1 atm was used as the reducing agent. Because of the relative thinness (only 136 /μm thick) of the specimens used, the pore-diffusion of gases offered no significant resistance to the reduction process. The interfacial-reaction-rate constantk s * , which has been corrected for film-mass-transfer effects, is found to be given by logk s * = −1.032 (±0.138) -[7860 (±200)]/2.303r where k s * is in g · atom O · cm−2 · s−1 · atm−1. The activation energy for the reduction process is found to be 65,325 (±1650) J · mol−1; the rate-controlling step appears to be the Fe3O4 → Fe conversion step.