Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1986"

Thermodynamic analysis of ordered liquid solutions by a modified quasichemical approach—Application to silicate slags

Abstract: A system of semi-empirical equations has been developed for the analysis of the thermodynamic properties of ordered liquid solutions such as slags. The equations, which are based upon modifications of the quasichemical theory, take into account the concentration and temperature dependence of the solution properties of ordered systems and thus enhance the reliability of interpolations and extrapolations of data. For binary systems, these equations have been coupled with an optimization computer program to analyze simultaneously all available thermodynamic data including phase diagrams, Gibbs energies and enthalpies of formation of compounds, activities, enthalpies of mixing, entropies of fusion, miscibility gaps,etc. In this manner, data for several binary slag systems have been analyzed. In the present article, analyses for the CaO-SiO2, FeO-SiO2, and CaO-FeO systems are presented. The resulting equations represent all the binary data, including the phase diagrams, essentially within experimental error limits. The calculations have been extended to ternary systems, thereby permitting ternary thermodynamic properties to be approximated solely from data from the subsidiary binary systems. Results for the SiO2-CaO-FeO system are in excellent agreement with measured ternary data.

Computer modeling of heat flow in welds

Abstract: This paper summarizes progress in the development of methods, models, and software for analyzing or simulating the flow of heat in welds as realistically and accurately as possible. First the fundamental equations for heat transfer are presented and then a formulation for a nonlinear transient finite element analysis (FEA) to solve them is described. Next the magnetohydrodynamics of the arc and the fluid mechanics of the weld pool are approximated by a flux or power density distribution selected to predict the temperature field as accurately as possible. To assess the accuracy of a model, the computed and experimentally determined fusion zone boundaries are compared. For arc welds, accurate results are obtained with a power density distribution in which surfaces of constant power density are ellipsoids and on radial lines the power density obeys a Gaussian distribution. Three dimensional, in-plane and cross-sectional kinematic models for heat flow are defined. Guidelines for spatial and time discretization are discussed. The FEA computed and experimentally measured temperature field,T(x, y, z, t), for several welding situations is used to demonstrate the effect of temperature dependent thermal properties, radiation, convection, and the distribution of energy in the arc.

Analysis of solute distribution in dendrites of carbon steel with δ/γ transformation during solidification

Abstract: Solute distribution in dendrites during solidification of carbon steel was analyzed by unidirectional solidification experiments and mathematical analysis. The characteristic of the mathematical analysis is that diffusion of solutes in solid and redistribution of solutes at solid/liquid andδ/γ interfaces are taken into consideration. Based on the observed and calculated results, it was found that phosphorus was redistributed fromγ-phase toδ-phase, and that manganese was slightly redistributed fromδ-phase toγ-phase. Therefore the concentrated region of phosphorus can be separated from that of manganese duringδ/γ transformation in the case of slow cooling. Moreover, it was concluded that rapid diffusion inδ-phase and the redistribution duringδ/γ transformation played an important role in the variation of the interdendritic concentrations of solutes with lower carbon concentration.

The air-gap formation process at the casting-mold interface and the heat transfer mechanism through the gap

Abstract: The formation process of the air gap at the casting-mold interface and the heat transfer mechanism through the gap were investigated by measuring the displacement of, and the temperature in casting and mold for cylindrical and flat castings of aluminum alloys The thickness of the air gap was measured as the difference between the location of the casting surface and that of the mold inner surface For cylindrical castings, the mold began to move outward immediately after pouring, while the casting stayed until solidification progressed to a great extent For flat castings, the mold began to move greatly toward the casting pushing the casting immediately after pouring and moved reversely after a maximum appeared It was possible to calculate the displacement of the mold by thermal expansion It was found that when the thickness of the air gap was not large, the heat through the gap was transferred mainly by heat conduction

The composition and temperature dependence of the sulfide capacity of metallurgical slags

Abstract: The concept of optical basicity and its applicability as a means of correlating the available data on the sulfide capacity of metallurgical slags has been reviewed. An excellent correlation based on very extensive data at 1500 °C, which was discussed in a previous paper, is combined with good correlations based on considerably less data at 1550 °C and 1650 °C to quantify the effect of temperature on the sulfide capacity of slags. The combined effects of slag composition and temperature have been expressed in the equation, logC s = [(22690 – 54640A)/7] + 43.6A − 25.2. Use of this equation permits the calculation of the sulfide capacity of a slag at any temperature between 1400 °C and 1700 °C simply from a knowledge of its chemical composition, and can be employed for virtually any oxide slag of interest in the field of iron and steelmaking. This, in turn, permits calculation of the equilibrium distribution of sulfur between this slag and iron or steel, provided that the oxygen potential is known or can be calculated from the degree of deoxidation applied.

Pressures produced by gas tungsten arcs

Abstract: The pressure of gas tungsten welding arcs has been measured for currents from 300 to 600 amperes using argon and helium gases. Although the measurements are generally consistent with previous results at lower currents, the present work shows that the pressure exerted by helium is a strong function of arc length. Several different scaling laws for the maximum pressure as a function of arc current and electrode tip angle are discussed.

Rotational electromagnetic stirring in continuous casting of round strands

Abstract: A model is presented to compute the three-dimensional flow field in rotational electromagnetic stirring of round strands. The model involves the solution of the Maxwell equations, the Navier-Stokes equations, and the transport equations for the turbulence characteristicsk ande. For the limiting case of one-dimensional stirring, the computations were checked with experiments using mercury as the fluid. Several sets of computations were carried out to determine the influence of stirrer position, stirrer length, and electromagnetic parameters on the flow field in continuous casting of steel strands.

The temperature coefficient of the surface tension of pure liquid metals

Abstract: The surface tensions of liquid Fe, Co, Ni, Cu, Ag, Zn, Pb, Cd, and Sn have been measured by the sessile droplet method and/or the levitated droplet method over wide ranges of temperature. The values of surface tension obtained by the levitated droplet method have always been found to be higher than those measured by the sessile droplet method, a result which is attributed to decreased droplet contamination with the containerless levitation method. Negative temperature coefficients of surface tension have been obtained for all of the metals investigated in this work. Based on a literature survey of the available experimental data, it is shown that the values of both surface tension and the temperature coefficient are influenced in a systematic manner by the presence of surface active impurities. On this basis, positive values of the temperature coefficient of surface tension for liquid Zn and Cd found in the literature may be explained in terms of impurity effects which tend to be particularly pronounced in volatile metals.

Thermodynamics of the Si-C-O system for the production of silicon carbide and metallic silicon

Abstract: The predominance diagrams of the Si-C-O system for 1350 to 2200 °C have been constructed thermodynamically by taking into account the presence of liquid silicon monoxide. The high-temperature behavior of various feeds, such as the SiO2-C and SiO2-SiC systems, have been calculated as functions of mixing ratio and reaction temperature by using the method of equilibrium mass-balance. For an efficient SiC-making, a charge having a C/Si ratio of 2.91 should be heated between 2035 and 2045 °C, where SiC crystals can be grown mainlyvia gas-phase reactions of SiO(g). Metallic silicon cannot be produced unless a charge of the Si-C-O system is heated above 2037 °C. In Si-making, liquid SiO plays an important role in that the yield can be improved substantially by enhancing the condensation of SiO gas in the upper cooler part of the furnace. This work also lends thermodynamic proof and support to the double-reactor model, in which a greater fixation of ascending SiO gas on carbon as SiC is considered essential for obtaining a higher silicon yield in industrial furnaces. Some fundamental strategies useful to the improvements of commercial Si- and SiC-making operations have been described quantitatively.

An analysis of radial segregation for different sized spherical solids in rotary cylinders

Abstract: Rotary reactors such as ball mills, driers, mixers, blenders, and kilns are extensively used in chemical and metallurgical industries to process billions of tons/year of granular solids. Longitudinal and radial segregation of the feed and/or product due to size, shape, and density differences of the feed or product are often encountered in these unit operations. This paper presents some observations of radial segregation due to size differences of spherical solids for slumping, rolling, cascading, cataracting, and centrifuging beds. The mechanism by which spherical beads segregate radially is a combination of percolation and flow. The kinetics of radial segregation for rolling beds is observed and quantified using high speed photography. The rate of segregation is shown to be a function of the cylinder rpm but is independent of bed depth. Furthermore, the larger the size ratio of coarse to fines, the faster the rate of segregation. The scale-up of the segregation process is investigated using two cylinders, 0.2 m ID × 0.2 m L and 0.4 m ID × 0.4 m L. Both the size ratio of the solids and the Froude number are the scale-up criteria for the rate of radial segregation. The former is related to the packing characteristics of loosely packed beds when rolling and to the effective radius of rotation of particles when cataracting or centrifuging.

The leaching of chalcopyrite with cupric chloride

Abstract: A comparative study of electrochemical leaching and chemical leaching of chalcopyrite was performed mainly at 343 K to elucidate the leaching mechanism of chalcopyrite with CuCl2. Also, the morphology of the leached chalcopyrite surface was studied by using a single chalcopyrite crystal. The leaching with CuCl2 produced a porous elemental sulfur layer on the chalcopyrite surface, showing a similar morphology to that produced during leaching with FeCl3. The leaching kinetics were found to be linear over an extended period, followed by an acceleration stage, as a result of an increase in the reaction surface area. The leaching rate of chalcopyrite was proportional to C(CuCl2)0.5, whereas it was inversely proportional to C(CuCl)0.5. The mixed potential of chalcopyrite exhibited a 66 mV decade−1 dependency upon C(CuCl2), and—69 mV decade−1 upon C(CuCl). Based on these observations together with other findings, an electrochemical mechanism involving the oxidation of chalcopyrite and CuCl − 2 and the reduction of CuCl+ was proposed. The Tafel plot between the mixed potential and the current density obtained by converting the rate of chemical leaching gave a straight line whose slope was in good agreement with that of the electrochemical leaching. These findings strongly support the electrochemical mechanism of chalcopyrite leaching with cupric chloride.

Mixing models for gas stirred metallurgical reactors

Abstract: The mixing of liquids in ladles, (0.5 ≦L/D ≦ 2.0), agitated by a centrally rising bubble plume, has been analyzed both theoretically and experimentally. An exhaustive review of previous metallurgical literature on mixing in ladles and furnaces demonstrates that the majority of previous investigators in the field consider mixing to be brought about primarily by turbulent diffusion phenomena. The present study clearly shows that mixing is a combination of both convection and eddy diffusion processes, neither of which can be disregarded for gas stirred systems. For predicting mixing times during such gas injection procedures, a simple empirical equation is proposed for axisymmetric systems:τ mαem −1/3L−1R5/3. Hereτ m is the 95 pct mixing time,e m is the specific energy input rate,R is the vessel radius, andL is the depth of liquid. On the basis of physical and mathematical modeling, the rate of liquid mixing in conventional gas injection ladle metallurgy operations is compared with those observed in C.A.S. (composition adjustment by sealed argon bubbling) systems. It was found that mixing in C.A.S. operations is relatively slow and highly insensitive to gas flowrates(i.e., specific energy input rates).

Mathematical modeling of flows in large tundish systems in steelmaking

Abstract: Numerical solutions of the three-dimensional turbulent Navier-Stokes equations, incorporating thek-e turbulence model, are presented for the turbulent flow of liquid within a tundish of high aspect ratio. Experimental results, obtainedvia Laser-Doppler anemometry and flow visualization techniques, are also reported. Calculated flow fields were shown to be similar to corresponding experimental flow fields. Such results can provide useful technological information regarding the design of tundishes in the steel industry for optimization of steel cleanliness.

Resistance spot welding of galvanized steel: Part II. Mechanisms of spot weld nugget formation

Abstract: Dynamic inspection monitoring of the weld current, voltage, resistance, electrode displacement, and force was performed in conjunction with a detailed study of the effects of material variations and weld process parameter modifications on resistance spot welding of coated and uncoated steels. In order to determine the mechanisms of weld nugget formation and growth, scanning electron microscopy photos were taken of the developing nugget. These physical changes were then related to the dynamic inspection curves and the welding current lobe. The effects of material variations and weld process modifications, the results of which were presented in Part I, can be explained through an understanding of these mechanisms.

Comparison of surface tension measurements using the levitated droplet method

Abstract: Measurements of the surface tension of some metals by the levitating drop technique have been carried out by two independent laboratories in order to establish the levels of agreement. Results obtained for pure iron, cobalt, and copper showed reasonable agreement, but in the case of stainless steel, significant differences were apparent, which were shown to be a consequence of the different hydrogen concentrations in the respective environmental gases. Surface tension values for pure gold obtained by this method showed good agreement with the data obtained by established methods and show that the levitating drop technique is capable of yielding reliable results.

The dissolution of galena in ferric chloride media

Abstract: The dissolution of galena (PbS) in ferric chloride-hydrochloric acid media has been investigated over the temperature range 28 to 95 °C and for alkali chloride concentrations from 0 to 4.0 M. Rapid parabolic kinetics were observed under all conditions, together with predominantly (>95 pet) elemental sulfur formation. The leaching rate decreased slightly with increasing FeCl3 concentrations in the range 0.1 to 2.0 M, and was essentially independent of the concentration of the FeCl2 reaction product. The rate was relatively insensitive to HCl concentrations <3.0 M, but increased systematically with increasing concentrations of alkali or alkaline earth chlorides. Most significantly, the leaching rate decreased sharply and linearly with increasing initial concentrations of PbCl2 in the ferric chloride leaching media containing either 0.0 or 3.0 M NaCl. Although the apparent activation energy was in the range 40 to 45 kJ/mol (∼10 kcal/mol), this value was reduced to 16 kJ/mol (3.5 kcal/mol) when the influence of the solubility of lead chloride on the reaction rate was taken into consideration. The experimental results are consistent with rate control by the outward diffusion of the PbCl2 reaction product through the solution trapped in pores in the constantly thickening elemental sulfur layer formed on the surface of the galena.

Calorimetric and emf studies on liquid Li-Sn alloys

Abstract: By means of high temperature calorimetry the mixing enthalpies ΔH of liquid Li-Sn alloys have been measured; however, due to experimental problems they were determined only forx Li = 0.01 to 0.5 andx Li = 0.87 to 0.99. The range of temperatures studied was 691 to 938 K. High compound forming tendency in Li-Sn is reflected by a triangular-shaped relation for ΔH vs x Li. The extrapolated maximum of this plot is about −40 kJ mol−1 close to Li4Sn. Using the concentration cell Bi(l)Li3Bi(s)¦ LiF-LiCl¦Li-Sn(l) the emf was measured as function of temperature (775 to 906 K) atx Li = 0.1 to 0.603 enabling calculations of partial thermodynamic data for lithium in liquid Li-Sn solutions. Integral enthalpies calculated from partial enthalpies of lithium correspond well to the calorimetrically obtained integral mixing enthalpies in the concentration range where both emf and calorimetric data were obtained. The extrapolated maximum of ΔH from calorimetric studies and minimum of integral excess entropies from emf measurements correlate well with results of structure measurements and of other structure sensitive properties. All this experimental information indicates a maximum chemical short range order close to the composition Li4Sn.

Kinetics of galena dissolution in ferric chloride solutions

Abstract: A leaching investigation of galena with ferric chloride has been carried out as a function of concentration of ferric chloride and sodium chloride, temperature, and particle size. Three size fractions were considered in this investigation, namely, 48 × 65, 35 × 48, and 28 × 35 mesh. The concentration ranges of ferric chloride and sodium chloride used in this investigation were 0 to 0.25 M and 0 to 3 M, respectively. The reaction rate mechanism has been discussed in terms of a shrinking core model developed for cubic systems. Mass transport of ferric chlorocomplex through the product sulfur layer appears to be responsible for establishing the overall leaching rate under most of the conditions used in this investigation. The apparent activation energy for the leaching of 28 × 35 mesh galena with 0.1 M FeCl3, 1 M HC1, and 3.0 M NaCl was found to be about 8.05 kcal/mol (33.7 kJ/mol), which was partially contributed by diffusion and partially by the heat of reaction of the formation of ferric chlorocomplexes. Rate of dissolution at both 50° and 90 °C is greatly affected by ferric chloride concentration up to 0.2 M and is essentially constant with ferric chloride concentration above this value.

Interfacial rates of reaction of CO2 with liquid iron silicates, silica-saturated manganese silicates, and some calcium iron silicates

Abstract: Measurements of the rates of dissociation of CO2 have been made by the14CO2-CO isotope exchange technique on liquid iron silicates, calcium iron silicates, and silica-saturated manganese silicates as functions of temperature and imposed equilibrium CO2/CO ratio. It is shown that the rates of reduction of the liquid iron silicates and an iron oxide-rich slag in CO-CO2 atmospheres are consistent with the rates of isotope exchange, indicating a common rate determining step. The dependences of the apparent first order rate constant on the oxygen activity for the dissociation of CO2 on silica-saturated iron silicates and an equimolar “FeO”-CaO-SiO2 melt are found to be closely consistent with the ability to transfer two charges to the adsorbing or dissociating CO2 molecule, as was previously found for liquid iron oxide and lime-saturated calcium ferrites. Apparent rate constants at fixed oxygen activity are found to increase generally with the basicities of the melts.

Intrinsic kinetics of the oxidation of chalcopyrite particles under isothermal and nonisothermal conditions

Abstract: The overall kinetics of oxidation of chalcopyrite in the absence of heat- and mass-transfer effects were studied for temperatures up to 1150 K. Experiments were conducted using a nonisothermal technique. Below 873 K, the pore-blocking model was applicable with an activation energy of 71 kJ/mol in the temperature range 754 to 873 K and 215 kJ/mol below 754 K. Above 873 K, the rate of sulfur vaporization dominates the kinetics of oxidation in the initial stage. The oxidation of the decomposition product above 873 K is described by power-law kinetics. The kinetics of sulfur vaporization were found to follow the power-law kinetics with an activation energy of 208 kJ/mol. The results indicate that the oxidation rate is first order with respect to oxygen concentration and inversely proportional to the square of the particle size over the entire range of temperatures studied. Predominance area diagrams were constructed at various temperatures and used in conjunction with X-ray analyses of partially oxidized samples to determine the intermediate phases formed during the reaction. This analysis also provides a justification for the kinetic models used.

A kinetic model for the vacuum refining of inductively stirred copper melts

Abstract: An experimental investigation into the removal of impurities (bismuth, lead, arsenic, and antimony) from baths of molten copper (blister, anode and cathode type copper) under vacuum was carried out. A pilot scale vacuum induction melting facility was used for these tests. The effects of (1) vacuum levels of 8.0 to 40.0 Pascals, (2) melt temperatures of 1150 to 1350 °C, (3) melt surface area to volume ratios of 6 to 10 m−1, (4) a water cooled condenser placed within a distance of two centimeters above the melt surface, and finally, (5) different levels of dissolved oxygen and/or sulfur contained in the melt, were studied. Kinetic data were obtained for evaluating the potential of a full scale vacuum melting facility. A mathematical model was also developed for the proper interpretation of the experimental results and for making projections for lower pressure and higher temperature levels. The rate of removal of bismuth and lead increased as the chamber pressure was lowered and the melt temperature increased, while removal of arsenic and antimony was negligible. Neither the melt surface area to volume ratio nor the distance of the condenser to melt surface had any significant effects on the rate constants governing the rate of removal of impurities. The rate of elimination of bismuth and lead over the range of 1150 to 1350 °C and 40.0 to 8.0 Pa followed first order kinetics. Removal rates were largely controlled by mass transport in the gas phase.

Studies on role of oxygen in the adsorption of Au(CN) 2 − and Ag(CN) 2 − onto activated carbon

Abstract: Comparative studies of the adsorption of Au(CN) 2 − , Ag(CN) 2 − , and Hg(CN) 2 − onto activated carbon (Norit R2020) have suggested that oxygen and oxygen containing surface functional groups play a role in the adsorption process of Au(CN) 2 − and Ag(CN) 2 − but not in the adsorption of Hg(CN) 2 − . Adsorption of Au(CN) 2 − and Ag(CN) 2 − on carbon degassed at 950 °C under 10−5 torr (1.33 × 10−3 P) vacuum is decreased by 50 pct compared with the adsorption on normal activated carbon. However, in the presence of oxygen in solution, the degassed carbon adsorbs Au(CCN) 2 − to the same extent as normal carbon. The effect of organic solvents and the variation in the potential of the two types of carbon upon adsorption of Au(CN) 2 − were also investigated. These results indicate that activated carbon behaves like an ion-exchange resin but is capable of oxidizing cyanide and cyanide complexes by chemisorbed oxygen. A dual mechanism for the adsorption of Au(CN) 2 − and Ag(CN) 2 − onto activated carbon is therefore proposed, in which cyanide complexes adsorb on carbon by anion exchange with OH− followed by partial oxidative decomposition of Au(CN) 2 − or Ag(CN) 2 − to insoluble AuCN or AgCN.

Resistance spot welding of galvanized steel: Part I. Material variations and process modifications

Abstract: Material variations and process modifications have been studied to determine their effects on the acceptable range of resistance spot welding conditions for galvanized steel sheet. The material variations studied include zinc coating integrity, structure, composition, thickness, roughness, oil, and the amount and type of Fe-Zn intermetallics. Process modifications studied include upsloping and downsloping of the weld current, preheat current, postheat current, electrode tip geometry, and applied force. It was found that hot-dipped galvanized materials with coatings which have a very thin Fe-Zn alloy layer have a wider range of acceptable welding conditions than the commercial galvannealed products, which have a fully alloyed Fe-Zn coating. The decreased lobe width of the galvannealed material is due to the discontinuous Fe-Zn coating structure and morphology. Small variations in the thickness of the coatings studied have no significant effect on the welding current range. Surface roughness of the coating has no effect on lobe width. Upsloping and downsloping of the weld current increase the welding range of hot-dipped products when using truncated cone electrodes, whereas sloped current has no advantage for galvannealed or uncoated materials. Radiused electrodes can increase the lobe width of hot-dipped products but are not beneficial when using sloped current or when welding galvannealed or uncoated materials.

Potentiometric studies on the adsorption of Au(CN) 2 and Ag(CN) 2 onto activated carbon

Abstract: The adsorption of Au(CN) 2 − and Ag(CN) 2 − onto activated carbon has been correlated with potential measurements of carbon. It is proposed that Au(CN) 2 − , Ag(CN) 2 − , and CN− are adsorbed on carbon by both an ion exchange mechanism and an oxidative reaction which leads to a decrease in carbon potential. The potential of carbon decreased according to the degree of anion adsorption in the order Au(CN) 2 − > Ag(CN) 2 − > CN− > I− > Cl−. Adsorption of anions is accompanied by release of OH− ion which raises the solution pH and decreases the carbon potential. The potential of carbon in contact with solutions containing KAu(CN)2, KAg(CN)2, or KCN is much more negative than that in contact with chloride solution at the same pH. The results indicate that cyanide is oxidized on the carbon surface by oxygen or by reducible functional groups such as quinone.

Model study of mixing and mass transfer rates of slag-metal in top and bottom blown converters

Abstract: Water model experiments have been conducted to clarify mixing rates of molten steel and mass transfer rates between slag and metal in LD and Q-BOP furnaces using six different circular tuyere arrangements. Splashing and ‘spitting’ were also examined with a view to finding a quiet bath with minimum mixing time and maximum mass transfer rate. Froude’s similarity criterion was fulfilled to determine gas flow rate and bath depth. Complete mixing time of water determined by tracer technique had been 0.9 second to 1.8 seconds for Q-BOP as compared to 6 seconds to 13 seconds for LD. This shows that the stirring intensity in Q-BOP is remarkably larger than that of LD. A simple relationship τ = 5.9(Q/N) −0.49 was obtained with gas flow rateQ and number of tuyereN. This indicates that flow rate of gas per tuyere should be intensified to realize better mixing. Mass transfer coefficient KBa for bottom blowing was found to be almost double that for top blowing. Of all the tuyere configurations studied for Q-BOP’s, a half circular tuyere arrangement was found to be the best considering all aspects of mixing, mass transfer, and bath agitation.

A mathematical model of the planar flow melt spinning process

Abstract: The Planar Flow Melt Spinning Process for the Rapid Solidification of metallic materials is analyzed using a mathematical model based on the principles of capillary fluid dynamics and solidification heat transfer. The results suggest the existence of a region of slowly recirculating flow inside the melt puddle which acts as a lubricant between the nozzle and the wheel. Markedly different thermal conditions across the ribbon thickness are also predicted by the model, as are the resultant microstructural variations across such thickness. The results of the model compare well with the available experimental evidence. The model is sufficiently general as to be immediately applicable to the study of other meniscus controlled continuous casting processes.

An Investigation of the Thermodynamics and Kinetics of the Ferric Chloride Brine Leaching of Galena Concentrate

Abstract: The solution thermodynamics of acidified ferric chloride brine lixiviants and the dissolution kinetics of a galena concentrate in such solutions have been investigated. The distribution of the various metal chloro complexes calculated from available thermodynamic data shows that the distribution is shifted to the higher complexes, predominantly FeCl3o, FeCl2o, and PbCl4=, as the total Cl− concentration increases, and that the distribution is unaffected by the extent of reaction. The dissolution of PbS concentrate is presented as a competition between a nonoxidative reaction with H+ and the oxidative reaction with ferric ion. Acid dissolution of PbS predominates when the activity ratio of hydrogen ion to ferric ion is high. Under these conditions H2S is produced. When the activity ratio of hydrogen ion to ferric ion is low, and especially when the concentration of Fe3+ is greater than 0.15 M, oxidative dissolution of PbS becomes the controlling reaction. The dissolution can be represented by a shrinking core model with a surface chemical reaction as the rate controlling step. This is supported by the activation energy of 72.1 kJ/mole and the dependence of the rate on the inverse of the particle radius. The following rate equation was found to be in excellent agreement with the experimentally observed leaching behavior for 0.15 to 0.6 M [Fe+3]T up to approximately 90 to 95 pet extraction: $$1 - \left( {1 - \alpha } \right)^{1/3} = \left[ {\frac{{2.3 x 10^{12} }}{{r_0 }}\left[ {{\text{Fe}}^{{\text{ + 3}}} } \right]_T^{0.21} \exp \left( {\frac{{ - 72100}}{{{\text{R}}T}}} \right)} \right]t$$ The rate deviates from the 0.21 order for Fe+3 concentrations greater than 0.6 M. The deviation from the surface model at higher values of PbS conversion is due to the presence of solid PbCl2 in the pores of the reacting particles.

A solid-state emf study of ternary Ni-S-O, Fe-S-O, and quaternary Fe-Ni-S-O

Abstract: Four two-phase equilibria in Ni-S-O, three two-phase equilibria in Fe-S-O, and one two-phase equilibrium and four three-phase equilibria in Fe-Ni-S-0 atPSO2 ≃ 1 atm were studied using the following emf cell: $$Pt, O_2 (air) \left| {\begin{array}{*{20}c} {ZrO_2 \cdot CaO or} \\ {ZrO_2 \cdot Y_2 O_3 } \\ \end{array} } \right|\begin{array}{*{20}c} {mixture of phases, Au} \\ {SO_2 , S_2 , O_2 , SO_3 with P_T \simeq 1 atm} \\ \end{array} $$ The seven two-phase equilibria in Ni-S-O and Fe-S-O are NiS/Ni3S2, Ni3S2/Ni0, NiS/NiO, NiO/NiSO4, Fe2O3/Fe2(SO4)3, Fe2O3/FeSO4, and FeSO4/Fe2(SO4)3, and the four three-phase equilibria and the one two-phase equilibrium in Fe-Ni-S-0 are sp + (Fe, Ni)S + (Fe, Ni)4S3, sp + (Fe,Ni)4S3 + (Fe, Ni)O, sp + (Fe, Ni)O + (Fe, Ni)SO4, and Fe2O3 + sp + (Fe, Ni)SO4 and sp + (Fe,Ni)S. The sp + (Fe, Ni)S two-phase equilibrium was measured by using mixtures containing a major portion of one phase and a minor portion of the other. The results are presented in terms of oxygen potential as a function of metal ratio,yNi =xNi/(xFe +xNi) at constant temperatures andPSO2 = 1 atm. The calculated stability diagrams atPSO2 = 1 atm from thermodynamic models are in agreement with experimental results. Several of the stability diagrams atPSO2 = 0.1 and 0.01 are also calculated and presented.

Soda slag system for hot metal dephosphorization

Abstract: Phosphorus partition ratios between Na2O-SiO2-PO2.5 slags and carbon saturated iron have been measured as a function of slag composition at 1200 °C. To avoid excessive Na2O loss by reaction with carbon, the initial slag-metal interfacial area was increased by using a powder mixture of slag and metal to reduce the time for the equilibrium. The results indicate that phosphorus partition ratios, Lp, are relatively high, about 20 for an equimolar slag (XNa2O/XS1O2 = 1) and are independent of P level in the slag. The phosphate capacity and the activity coefficients of PO2.5 and FeO for these slags are calculated from the experimental results using available thermodynamic data. The oxygen potential at the slag-metal interface was found not to be controlled by Si in metal under an Ar atmosphere or by CO partial pressures in CO-Ar mixtures. Experimental results and thermodynamic calculations show thatPO2 at the interface between Na2O-SiO2 slags and carbon saturated iron is controlled by the C-CO equilibrium where the CO pressure is determined by C-Na2O equilibrium for which the CO pressure is close to 1 atmosphere in all cases.