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By W. J. Kroll

Jan 1, 1960

By E. W. Dewing

The nature of solid solutions of sodium in non-paphitic carbon at temperatures near 1000°C has been investigated by an electrolytic technique. The activity coefficient is found to vary strongly with the heat-treatment temperature of the carbon, and an analysis of the energy terms involved suggests that this is due to variations in the Fermi level. The diffusion coefficient for sodium is in the range implying that the sodium atoms (or ions) are not bound to specific sites on the carbon, in agreement with lack of evidence for specific compounds in the activity -composition curves. In the light of These results phenomena occurring in aluminum reduction cell linings are dis-cussed. It is concluded that sodium migrates by diffusion through the carbon lallice and not the pores, and that A14C9 is formed within the lining hy The excess of NaF invariably found in used linings is formed by this reaction and by air oxidation: There has recently been much interest in the swelling of carbon which occurs when it is made cathodic in an aluminum electrolysis cell, and there is general agreement that the phenomenon is due to the penetration of sodium atoms, derived from the reaction on the carbon lattice. (NaF and AlF3 are constituents of the fused-salt electrolyte.) The low-temperature lamellar compounds of potassium with graphite are well-known, and one compound between sodium and graphite has been reported.4 There is, however, virtually no information on the basic chemistry of the interaction of sodium with nongraphitic carbon at high temperatures, although Dell3 has made some fundamental studies of rates of penetration. At the time the present work was carried out these were not available. Rapoport and samoilenkol had measured rates of physical expansion in a dilatometer, using the fractional increase in length of a carbon specimen after electrolysis in a cryolite bath for 2 hr as an index of susceptibility to cathodic swelling. Work here with a similar apparatus showed that expansion (of a 1.5-in.-diam cylindrical specimen) ceased in less than 20 hr, and that the final expansion was much more reproducible than the value at some intermediate time. This suggested that an equilibrium was being set up, and that a thermodynamic approach was required. The results obtained are not as accurate as had been hoped, but they are the only ones of their type available and have enabled useful conclusions to be drawn. The experimental work was divided into two parts: an investigation of the activity-concentration diagram for sodium in carbon, and a rough determination of the diffusion rate. For the former, most of the experiments were made with petroleum coke even though this is not a form of carbon used in cell linings. It has the advantages, however, that it is a homogeneous material, that it is low in ash, and that its structure is reasonably well understood. Anthracites and coal cokes gave results of the same type as obtained with petroleum coke, but the reprodu-cibility from specimen to specimen was extremely poor. EXPERIMENTAL 1) The Activity-Composition Diagram for Sodium in Carbon. The petroleum coke was ground, pressed at 40,000 psi into plates 19 by 9 by 2 mm without added binder, and heat-treated. The sodium activities were established by an electrolytic technique. The carbon was made anodic in a cryolite bath with an aluminum cathode, and a controlled potential, E, applied so that the sodium activity at the anode was given by ln Na = 1n asa - EF/RT [21 where as, is the sodium activity generated by Reaction [I]. The relative activity is sufficient for many purposes and is simply given by The value of Na not at present known, but when the thermodynamics of the Na-A1 system have been worked out it can be derived from the equilibrium

Jan 1, 1963

By C. Pin, J. Bruce Wagner

In order to demonstrate the role of defect chemistry in the solid state to a process-metallurgy reaction, laboratory experiments were carried aut to remove copper from liquid lead using lead sulfide which had been doped to provide definite concentrations of cation vacancies. The removal of copper decreases in the order: bismuth- or antimony-doped PbS, undoped PbS or tin-doped PbS, and silver-doped PbS. The data are explained using the simple mass -action law and in terms of the exceedingly rapid interstitial diffusion of coppw in PbS to vacant cation sites. Results are in agree-ment with thermodynamic predictions and certain industrial practices that copper may be removed from lead below the limit of its coexistence with pure Cu,S and pure PbS. The role of defects in solids has been exploited in semiconductors and many device applications, in explaining tarnish formation, dissolution rates, and mechanical properties. The application of these principles to many process-metallurgical problems has not received as much attention. It was the purpose of this study to illustrate the role of defect structures of solids in a process-metallurgical application. When lead is refined, the ore, galena (PbS), is reduced by a series of operations to liquid lead (lead bullion) containing impurities such as copper, bismuth, antimony, arsenic, and silver depending on the original composition, the fluxes added, and the particular type of operation, see Fig. 1. In order to produce a pure lead, a series of refining operations are carried out. A typical lead-bullion analysis before drossing is shown in Table I. Copper is removed first as its presence increases the zinc consumption during the desilverizing process. For preliminary copper removal the lead bullion is brought to a temperature of 440°C in a kettle of 60 metric tons capacity. Some tar (or sawdust or resins) is usually added and the kettle is cooled slowly to 400°C while the liquid is stirred. A solid phase, called a dross, floats on top of the liquid and the particles of the solid phase adhere to the tar. This "hot dross" is collected. It contains mostly lead and copper which are partly oxidized and/or sulfurized if the lead bullion contains some sulfur.*

Jan 1, 1963

By J. W. Powell, F. H. Spedding

A complete review of the use of chelating agents in the sepa ration of rare earths by ion-exchange is given as well as a concise description of the recent pilot-plant operations of the Ames Laboratory. The two chelating agents which show the greatest promise are ethylenediamine-N,N,N',N'-tetraacetic acid and N'-(2-hydroxyethyl)ethylenediarnine-N,N,N '-triacetic acid. The first successful separations of rare earths by ion exchange were reported in a collection of papers which appeared in the November, 1947, issue of the Journal of the American Chemical Society.1'9 Some of this work was performed at the Ames Laboratory of the A.E.C., the remainder at the Oak Ridge National Laboratory. The processes developed at Oak Ridge, as well as some of the early Arnes methods, employed 5 pct citric acid-ammonium citrate eluant at low pH and were carried out on either H+-state or NH:-state resin beds. These techniques were successful for the separation of small quantities of either naturally occurring or radioactive rare earths and are still used for the isolation of rare-earth activities from fission products. Concentrated citrate is not economical, however, for use in moderate or large-scale rare-earth separations. For this reason, the Ames Laboratory turned its attention to lower concentrations and higher pH's in order to make more effective use of the eluting agent.10-14 Although elutions have been performed successfully over a wide range of conditions, 0.1 pct citrate at a pH of 8.0 is highly recommended for use on H+-state resin beds.15,16 Elu-tion with 0.1 pct citrate in the pH range from 5 to 9 brings about the separation of the constituent rare earths into a series of flat-topped elution bands which progress down the resin bed, head to tail, without actually pulling apart as do the rare-earth peaks which develop when trace quantities are eluted with 0.25M (5 pct) citrate at low pH's. Because of this, elution with 0.1 pct citrate at pH 8.0 do not produce pure rare earths unless sufficient quantities are present to provide developed bands which are at least several inches long on the columns. Although other eluting agents have proved more effective than citrate solutions, articles concerning the use of citric acid for separating rare earths still appear in the literature occasionally. For example, Ketelle and Boyd17 reported some further studies on the separation of rare earths with 5 pct citrate in 1951. They used 270 to 325 mesh Dowex-50 columns at 100°C and a pH of 3.28. vickery18 compared the effectiveness of a number of eluants for the separation of rare earths on NH+4 state Dowex-50 in 1952. He found that citric acid was more efficient than acetic, malic, tartaric, and aminoacetic acids. In 1953, Mayer and Freiling18 reported that citrate was inferior to malate, glycolate, lactate, and EDTA for the resolution of Sm-Eu and Y-Tb mixtures on 250 to 500 mesh, NH+4-state, Dowex-50 at 87°C. pinta20 used 5 pct citrate in the pH range 2.8 to 3.4 to obtain some rare earths for analytical work the same year. Trombe and Loriers21 reported the use of citric acid in their laboratory to separate rare earths in kilogram quantities. Lariers and Quesney22 reported some separations with citrate in 1954. They used 5 pct citrate at pH 2.8 to separate yttrium and the yttrium-group rare earths from the cerium-group rare earths. briers23 used 5 pct citrate at pH 3.2 and 90°C as late as 1956 to isolate thulium in fair purity. For the separation of tracer quantities of rare earths, Mayer and Freiling19 have recommended pH 5.00, 0.24M lactate at 87 °C on 250 to 500 mesh, NH+4-form Dowex-50. Freiling and Bunney24 have also employed lactic acid for the separation of fission-product rare earths. Cunninghame, Size-land, Willis, Eakins, and Mercer25 have reported a 4-hr separation of Y, Eu, Sm, Pm, Nd, and Pr with 1M lactic acid at pH 3.25 on Zeokarb-225 at 87°C. Stewart, et al.,26 reported separation factors for rare earths distributing between Dowex-50 and 0.25M glycolic acid. stewart27 also reported a 30-61 separation of Y, Tm, Er, Tb, and Lu tracers with buffered, 0.25M glycolic acid containing 0.05 pct Aerosol OT. The resin bed was 400-mesh Dowex-50 (X12). The pH of the ammonia-buffered eluant was 3.5. Various aminopolyacetic acids have also been used to obtain varying degrees of separation of the rare earths. In 1951, Fitch and Russell28 investigated iminodiacetic acid (IDA) and nitrilotriacetic

Jan 1, 1960

By Frank E. Woolley, Robert D. Pehlke

Jan 1, 1965

By Charles Law McCabe, Lyndon H. Everett, Edna A. Dancy

It has been found that the carbide phase present at equilibrium in the system M-H2-CH4, at about 600°C, is MC for the rare-earth metals Ce and Pr. X-ray diffraction analysis showed that the monocarbides have fcc structures with lattice constants of 5.036 + 0.009Å and 5.131 + 0.001Å for CeC and PrC respectively. Gaseous equilibrium measurements were used to calculate the standard free energy of formation of the monocarbides from the elements. for the formation of (+ 1300) for the formation of PrC. THE rare-earthdicarbides, and their crystal structures, have been known for some years,l but only more recently were the carbides CeC,2,3 Ce2C3 2 and CeCS3 reported. In 1958 to 1959, Spedding et al. published work on the lanthanum-carbon system4 and other rare-earth metal-carbon systems,5 proving the existence of M2C3 and MC2, and measuring the lattice constants. They also demonstrated that tri-rare earth carbides, M3C, exist for the rare-earth metals samarium through ytterbium. However, they concluded that the cerium monocarbide reported by Brewer and Krikorian2 and by Warf,3 and given a fcc structure with a lattice constant of 5.130Å bythe former workers, was, in fact, cerium metal with carbon dissolved in it. They were also unable to find any evidence for the existence of Warf's CeC3, for which no structural details had been given. Even more recently, Palenik22 reported the existence of only M2C3 and MC2, having been unable to find any evidence for the existence of any other rare-earth carbides. There are no published experimentally derived thermodynamic data for the formation of any of these carbides, although Brewer and Krikorian6 have estimated values of for CeC, Ce2C3 and CeC2. The objective of the present investigation was; to determine experimentally the free energy of formation of any of the reported carbides of cerium and praseodymium, through a study of the rare-earth metal-hydrogen equilibrium. EXPERIMENTAL A methane-hydrogen mixture was circulated, in a closed system over previously prepared cerium or praseodymium hydride, and when equilibrium had been attained, the gas mixture was analyzed by selectively oxidizing the hydrogen and condensing out the water formed. The metal hydrides were used as starting material for convenience because, otherwise, the hydrogen in the gas mixture would immediately dissolve in the metals; in addition, the metals would not react with methane alone at the experimental temperature (around 600°C). The circulating system was based on that used by Browning, DeWitt, and Emmett7 for similar studies on iron carbides. It consisted of a quartz reaction vessel, all-glass circulating pump, analysis tube containing copper oxide that could be heated to 300" C by means of a small furnace, a solid CO2-methanol trap, and a double limb absolute manometer, Fig. 1. A cathetometer, capable of reading to 0.005 cm, was used to measure the difference in height between the two columns of mercury. In its final form, the reaction vessel was enclosed in an outer jacket, containing approximately the same pressure of hydrogen as that within, to reduce errors due to diffusion of hydrogen out through the fused silica of the reaction vessel., The circulating system was supplied with

Jan 1, 1962

By D. A. Belforti, M. P. Lepie

Spectroscopically pure copper was melted on sapphire plaques in a zydrogen atmosphere. The surface tension of the liquid metal was determined using the sessile drop technique. Measurements were made by direct observation with the aid of a specially const,mcted telescope. The value obtained, 1268 dynes per cm, is compared to that found in the literature. THERE is at this time considerable interest in the use of ceramics for vacuum tubes. The crystalline material is superior to the more conventional glass in mechanical strength, chemical inertness, dielectric properties, ability to withstand high temperatures, and so forth. However, ceramics are much more difficult to seal hermetically with metals than are the glasses. For this reason an investigation was undertaken to determine the wetting and adhesion of metals to ceramics. The sessile drop technique offers a convenient means at elevated temperatures for measuring liquid surface tension, wetting angle, density, spread- ing coefficient, and work of adhesion. Thus, from the contour of a drop of liquid at rest on a solid surface one can obtain a quantitative evaluation of the degree to which the two substances will bond. To this end a special apparatus was constructed so that various molten metals could be observed. Standardization of the apparatus was done initially by measuring the surface tension of copper since this is well documented in the metallurgy literature. Although there are many methods available for the measurement of surface energy,'+ the sessile drop technique has been used most extensively for molten metals and ceramics.5"' Fig. 1 illustrates the dimensions to be measured. From these values, the surface tension of the liquid can be obtained using the Bashforth and bdams' equation and tables.

Jan 1, 1963

By E. S. Tankins, G. R. Belton

A simple solution model, based upon the formation of molecular species, is developed for strongly electronegative dilute solutes in liquid binary-metallic solvents. Two approximations are considered for the relative concentrations of the species: the random and the quasi-chemical. Equations are presented for the partial molar free energy, enthalpy, and entropy of mixing of the solute. An experimental study has been made of equilibrium in the reaction H2 6) +0 (dissolved) = H2O(g))for the liquid Cu-Co alloys. The standard free energy of solution of oxygen is presented as a function of composition for the alloys at 1550°C and as a function of temperature for five of the alloys. The experimental results for these alloys and also for Cu-Ni alloys are shown to be in reasonable agreernent with the theory in the random approximation. A knowledge of the thermodynamic behavior of dilute solutes in liquid metals and alloys is of importance in understanding and designing refining and alloy-making processes. Accordingly, several attempts have been made to derive suitable solution models to forecast the effect of a third component on the activity coefficient of such a solute in a metal. Alcock and Richardson' reviewed the literature prior to 1958 and also showed that a regular solution model gave a reasonable description in the case of metallic solutes but failed to account for the behavior of the more electronegative solutes sulfur and oxygen. These same authors2 later modified their model by using the quasi-chemical approximation3 to calculate the average composition of the first coordination shell surrounding each solute atom. This modified model was shown to lead to a better qualitative description of the behavior of the electronegative solutes; however, quantitative agreement with experimental data for oxygen in alloys could only be achieved by assuming a very small coordination number. The authors concluded that the major source of error in the model was the assumption that pairwise interaction energies were independent of composition. Substitutional and interstitial random solution models by Wada and saito4 are essentially similar to the first model except that the required interchange energies were derived from the modified solubility parameter equation of Mott, instead of from experimental binary data. Most recently Hoch5 has presented a statistical model for interstitial solutions and has applied the model to the Fe-C-O system. However, as the various interaction energies needed in the model had to be derived from the ternary data, the model does not promise well as a means of forecasting ternary behavior. Each of the above models carries the assumption that the strongly electronegative solutes have the same configurational environment as metallic solutes; i.e., the solute can be treated as a substitutional or interstitial atom in a quasi-crystalline lattice and is surrounded by a normal coordination shell of solvent atoms. There are, however, a number of facts which suggest that this is unlikely. First, the heats of solution are large, being more typical of molecule formation rather than alloying. For example, the heats of solution of monatomic oxygen and sulfur in liquid iron are -90 kea16,8 and -74 kea1,7, 8 respectively. These are to be compared with maximum heats of solution of metallic solutes in liquid iron of about -13 keal (silicon is an exception with -28.5 kea17). The large depression of the surface tension of liquid iron by trace amounts of the electronegative solutes oxygen, sulfur, and selenium9 suggests, by analogy with aqueous systems, the possible existence of polar molecules in the liquid. The effect of these solutes is at least three orders of magnitude greater than normal metal solutes.10 As has been pointed out by Richardson,11 the electron affinities and ionization potentials of oxygen and sulfur are such that it is likely that they exist in metallic solution as negatively charged ions. If this is so, and it is assumed that electrostatic forces play an important role in determining the configuration, it is unlikely that the stable configuration will be that of an isolated ion surrounded by a symmetrical coordination shell of solvent ions. It is more likely that the energy of the system would be lowered by the formation of solute-solvent screened dipoles. The above arguments suggest the formation of "molecular species" between solute and solvent atoms. The idea of the existence of molecular species in such solutions is not new, however', for Marshall and chipman12 have explained in a semi-quantitative manner the C-O equilibrium in liquid iron by postulating the species CO. Chen and Chip-man13 interpreted their measurements on the Cr-O equilibrium in iron in terms of the species CrO. Zapffe and sims14 have also postulated the existence of such species in liquid-iron alloys.

Jan 1, 1965

By J. W. Matousek, C. S. Samis

me thermodynamic properties of the components in the Cu-Ni-S ternary system have been studied by measuring the H2S/H2 ratios in a gas phase equilibrated with the molten matte at 1200°C. The measured sulficr potentials have been extended by extrapolation and combtned with previously published data to permit the thermodynamic analysis of the ternary system by integration techniques. A simplifying assumption of ideality in the Ni3Sz-CuS pseudobinary has been made. SINCE copper and nickel metals were first extracted from their sulfide ores the interaction between the two metals and sulfur has been of industrial and theoretical interest. The processes developed to extract copper and nickel have been reported periodically in the literature. The theoretical studies on the Cu-Ni-S ternary have been restricted to problems directly associated with production. It is only within recent years that the binary systems related to this ternary have been analyzed thermodynamically and mathematical devices developed to permit a corresponding treatment of the ternary system. In 1910 an investigation of the role of nickel in Cu-Ni-Fe-S mattes was reported,' It was concluded from this work that nickel is not an element replacing iron in mattes, but rather that Cu-Ni alloys behave as a single metal during the matte converting operation. The laws which govern the converting of Cu-Ni alloys were found to be the same laws as those that govern the conventional converting of copper alone. Although considerable information has been reported on the theoretical aspects of copper smelting, little data is available on the smelting of Cu-Ni ores except for phase diagrams and process descriptions. The available information on the Cu-Fe-S ternary and related systems prior to 1953 has been summarized by Ruddle.2 Since Ruddle's publication, Rosenqvist and coworkers have completed phase equilibria investigations of the Fe-S, Co-S, and Ni-S binaries,3 the Fe-S-O ternary,4 and the Cu-Fe-S-O quaternary.4 An extensive investigation of the Cu-Fe-S ternary system at smelting temperatures has been made by Krivsky and Schuhmann.5 At these temperatures, the Cu-Fe-S system is very similar to the Cu-Ni-S ternary with respect to the location of the single-phase and two-phase liquid matte regions. In the former, however, the area of immiscibility is more extensive and the region of liquid matte-liquid metal-solid metal equilibria is much more extensive. Krivsky and Schumann observed that the Cu2S-FeS pseudobinary system is, for practical purposes, an ideal mixture. This investigation has served as a valuable guide in analyzing the Cu-Ni-S ternary. EXPERIMENTAL The experimental procedure employed in this investigation was the conventional technique of equilibration of the sulfide matte with gaseous mixtures of hydrogen and hydrogen sulfide at 1200°C. The thermodynamic properties of sulfur (S2) in the gas phase are determined by means of Eq. [I] and the activity of sulfur in the matte by Eq. [2].

Jan 1, 1963

By Thomas C. Wilder

Jan 1, 1965

By Monte J. Pool, Rudolph Speiser, George R. St. Pierre, William T. Ebihara

Standard free energies of formation of WO,, W O W20058 and WO3from oxygen and the lower oxide or tungsten have been determined in the tempel-ature range of 700° to 1220°C. A tentative W-O phase diagmm is presented based on the evidence that the oxide phases, "W18O49" and "W20058", are unstable at l~atm total pressure, below 585° and 485°C:, respectively. A HE need for a complete quantitative treatment of the phase equilibria of the W-O system has been establishedby metallurgists during the past few years. In an attempt to improve the endurance of tungsten exposed to oxidizing atmospheres at high temperatures, many research groups have studied the kinetics of tungsten oxidation. The reverse process, the reduction of the tungsten oxides to metal, has also been investigated to some extent. Regardless of the particular interest, metal to oxide or oxide to metal, a knowledge of the phase equilibria of the W-O system is required to properly interpret all of the kinetic observations. It should be possible to state the stable phases of the W-O system at any given values of the chemical potential of oxygen and the temperature.

Jan 1, 1962

By T. H. Weldon, L. V. Whiton, R. R. McNaughton, J. H. Hargrave

Oxygen enriched air is being used quite extensively in the metallurgical plants of The Consolidated Mining and Smelting Co. of Canada, Limited, at Trail, B.C. The oxygen used for this purpose is a by-product from the Company's chemical plants located in the area. Most of the ore treated in the Trail metallurgical plants comes from Com-inco's Sullivan Mine at Kimberley, B.C. At Kimberley the ore is milled to produce lead and zinc concentrates which are shipped to Trail for further treatment to metal. One section of this paper deals with the use of oxygen enriched air in the suspension roasting of the zinc concentrates. In this process the concentrate is calcined for leaching preparatory to electrolytic recovery of the zinc. A second section of the paper describes the use of oxygen enriched air in operations at the lead smelter. There oxygen enriched air is used in the blast to the lead blast furnaces and in the slag fuming furnace which recovers the lead and zinc contained in lead blast furnace slag. The final section of the paper outlines the precautions necessary for the safe use of oxygen enriched air in any plant operation. The Use of Oxygen Enriched Air in the Suspension Zinc Roasters The suspension roasting of zinc concentrate developed at Trail, B.C., has been described in AIME Vol. 121, "The Electrolytic Zinc Plant of The Consolidated Mining and Smelting Company of Canada, Limited" by B. A. Stimmel, W. 11. Hannay and K. D. McBean. Since the publication of that paper, the use of oxygen enriched air in suspension roasting has been introduced as regular practice with marked advantage. The relative importance of a specific advantage may vary with changing conditions, but, in general, it may be stated that improved operation has been achieved at increased capacities. Suspension roasting is carried out at Trail in converted standard 25 ft diam Wedge roasters. The 2nd, 3rd, 4th and 5th roasting hearths have been removed and the drying hearth covered over. Drying of the concentrate is done on the drying hearth and the 1st roasting hearth. The dried concentrate, after any lump's have been broken up in a ball mill, is fed to a single burner located in the upper part of the combustion chamber. Oxygen is introduced at the burner fan along with the gases from drying, returned combustion gases from the waste heat boiler outlet and the required amount of new air. Up to 60 pct of the concentrate settles out on the 6th roasting hearth, the rest passilig out of the roaster. The product collected in the waste heat boiler is finished calcine, but the dust collected in the cyclones after the boilers is returned to the base of the combustion chamber where the sulphate is decomposed. Gases from the c'yclones go to a Cottrell precipitator. The discharges from the 7th roasting hearth and the waste heat boiler are combined with the Cottrell dust to give the finished calcine. Following small scale tests started in 1933, oxygen enriched air has been used continuously in the suspension roasting of zinc concentrate in Trail, beginning in 1937. A significant factor in promoting its use in this operation was the availability of by-product oxygen from the Company's near-by Chemical and Fertilizer Division. To-day it is standard practice at Trail to use oxygen enriched air for zinc concentrate roasting. The most important requirement in roasting a zinc concentrate for an electrolytic plant is that the zinc in the calcine should have maximum solubility. It is also desirable at Trail that the gas produced for the manufacture of suhhuric acid should have a ~naximum concentration of SO2 and that a substantial recovery of waste heat from the gas be achieved. High solubility of zinc requires that the sulphide sulphur and zinc ferrite in the calcine be kept low. These are both functions of temperature and time, with formation of zinc ferrite also dependent on contact between the iron and zinc particles. One of the inherent advantages of suspension roasting is that minimum time and contact are achieved. The limit on temperature is imposed by the fusion point of the concentrate and not by the need to control zinc ferrite formation. Operating temperatures are normally maintained within the limits of 1725" and 1850°F. A relatively low zinc sulphate in the calcine is required at Trail, and this results from discharging the calcine from the high sulphur dioxide atmosphere at a temperature above 1600°F.

Jan 1, 1950

By N. A. Gokcen

THE data of Chaudron,1 Tonosaki,2 and Collins³ on the thermodynamic properties of MOO, disagree widely. These authors, by using essentially similar methods, studied the following reaction: 1/2MoO2(s) + H2(g) == i/2Mo(s) + Ph,o H2O(g),K = —----- [1] Ph2 Tonosaki used a vacuum system consisting of a furnace containing MOO, and a water saturator whose temperature was kept at 25 °C with a thermostat. After repeated evacuation, hydrogen was admitted slowly into the system. The experiments were based upon the fact that at a constant furnace temperature and constant partial pressure of water, the total pressure of gas mixture over MOO? + Mo is constant. Any attempt to vary the pressure by external forces would vary only the amounts of MoO2, and Mo, after which the pressure should return to the equilibrium value in accordance with the equilibrium constant of reaction 1. The actual value of K was determined from the total equilibrium pressure (sum of Ph2o + Ph2) at each temperature. The total pressure of gas was varied within the range of 80.2 to 125.4 mm Hg, within a temperature range of 645" to 823 °C. The results were summarized as log K = 0.9413 — 1444.6/T for reaction 1. The ratio of H2O/H2 was considered to be uniform in spite of the presence of a thermal gradient across the static gas phase. It was shown by Rosenqvist and Cox,' however, that in somewhat similar circumstances the error resulting from thermal diffusion may be large. Collins³ improved Tonosaki's method by attempting to avoid thermal diffusion errors. His equilibrium data were obtained at 700°, 800°, and 900° C, and the result for reaction 1 was expressed as log K = 1.258 — 1822/T. The purpose of this investigation was to study reaction 1, avoiding the thermal diffusion errors, and to obtain equilibrium data in a considerably wide temperature range for the reliable extrapolation of the resulting thermodynamic functions. Experimental Procedure The diagram of the apparatus is shown in Fig. 1. Tank hydrogen was passed through a tube containing platinized asbestos at 425 °C in order to convert a trace of oxygen into water vapor. The flow rate was carefully controlled with a capillary-type flow-meter B and a bubbling column D. The gas was then presaturated sufficiently at P and led into a condenser system immersed in a thermostat, controlled to within ±0.002C. The temperature of the thermostat was measured with a thermometer calibrated against a certified standard. The temperature of P was adjusted to avoid the condensation of unduly large amounts of water as judged from the rate of flow out of the capillary tube M. Argon was purified by passing it through magnesium chips kept at 630°C. After passing through the flowmeter B', it was mixed with moist hydrogen emerging from the thermostat. The resulting gas mixture was then led into the hot zone of the furnace through the heated glass tubing and the silica tube S, thus insuring the same ratio of PII2o/Ph2 from the condenser to the reaction chamber, thus avoiding thermal diffusion. The entire gas system was of all-glass construction, except at the magnesium train. The furnace comprised a glazed alumina tube over which a 15-in. platinum coil was wound. The lower end of the alumina tube was tightly closed with a brass bottom and a silicone rubber gasket, and the upper end with two glass disks, each with a hole of 1/16 in. in diameter, through which the gas mixture escaped into the atmosphere. A back-up coil of kanthal wire facilitated the temperature control of the furnace. A coil of annealed molybdenum strip of 99.99 pct purity, 0.005 in. thick and 0.050 in. wide, and weighing 17 g was hung in the furnace with a 0.010-in. platinum wire attached to one end of a sensitive analytical balance. The temperature of the furnace was measured with a Pt-Pt-10 pct Rh thermocouple checked against a standard. The experimental procedure consisted of heating the gas purification trains, adjusting the gas flow rates, attaining a constant thermostatic temperature, flushing the entire system for 2 hr while heating the furnace to well above the expected equilibrium temperature and then cooling it at a rate of 0.3°C per min during which time the change in the weight of molybdenum was observed on the balance. For a given thermostatic temperature, i.e., a constant Prr,o/Px,, molybdenum oxidized upon cooling slightly below the equilibrium temperature. The procedure was then repeated by heating the furnace and thus reaching a temperature slightly above the equilibrium value. The average of the two temperatures, differing by 2" to 3"C, was considered to be the true equilibrium temperature. In order to determine the stoichiometric composition of the oxide phase present in this investigation,

Jan 1, 1954

By H. H. Kellogg, T. R. Ingraham

Three anhydrous zinc sulfates have been identified. They are: ZnSO,(a), stable below 1007°K; ZnS04(/3), stable above 1007OK; and ZnO.ZZnSO,. The decomposition pressure of each sulfate has been measured and the following relations calculated from the results: The measured data have been combined with the known themzodynamic properties of ZnS, ZnO, Zn, SO,, and SO, to yield univariant and bivariant phase diagrams for the system Zn-S-0. The application of these diagrams to problems of roasting zinc concentrates is discussed. PRESENT knowledge of the equilibrium chemistry of the system Zn-S:O, so essential to scientific control of zinc-blende roasting, is deficient in several respects. A basic sulfate of zinc has been reported by many investigators, but its composition is in doubt and its thermodynamic properties have not been measured. Our scanty knowledge of the properties of the normal sulfate at roasting temperatures is based on old and inexact studies. A crystal transformation in the normal sulfate, involving a sizable heat effect, has been noted by several investigators but has never been quantified. The studies reported herein were designed to fill these gaps in knowledge and to make possible a reasonably complete thermodynamic description of the system Zn-S-0 at roasting temperatures. The results make possible a far more exact understanding of zinc roasting chemistry than was hitherto possible. EXPERIMENTAL The principal experimental technique employed was the measurement of the total gas pressure developed from decomposition of either ZnSO, or ZnO2ZnS0, in a closed system. The apparatus employed was essentially the same as that described by Warner and lngrahaml and Flengas and tngraham.' The unusual feature is a flexible Pyrex bellows used to separate the reaction gas mixture (S03, SOz, and 02) from the mercury in the manometer and thus prevent corrosion of the mercury by SO3. The bellows operates without evidence of hysteresis and, barring accidents, may be used for several months. The response of the bellows varies from manometer to manometer, but is generally of the order of 0.6-cm displacement for a l-cm change in pressure. The response for all manometers has been linear over the range 0 to 1 atm. To prevent condensation and polymerization of sulfur trioxide, the bellows-manometer was maintained at 100.0" * 0.5" by a circulating bath of silicone oil. The connecting tubing between the manometer and the furnace was maintained at 100.0" * 0.2"* also, with a stirred air bath. The open end of the manometer was connected with a chamber which was maintained at a known pressure. The pressure could be varied so that readings of the height of the mercury column, measured with a cathetometer, could be made with both rising and falling mercury column. By using the average of the readings, any error due to sticking of the mercury column was minimized. The sample was placed in a 2-in.-long platinum boat formed into the shape of a half-cylinder. The sample was prepared as a fine powder and pressed against the inner wall of the platinum boat. A silica thermocouple well, covered with a platinum sleeve, was placed lengthwise along the center of the boat. The temperature of the sample was read on a calibrated Pt-10 pct Rh theirnocouple. The temperature profile of the furnace was constant within ± 0.2 C over the length of furnace occupied by the sample. The horizontal furnace used to contain the sample and the quartz reaction tube was electrically heated, with the control thermocouple placed 1/4 in. from the windings. A Brown Pyro-O-Vane temperature controller with a 3-sec response time was used to maintain the furnace temperature. Before beginning a run, the apparatus, including the bellows manometer, was thoroughly washed in sib with acid and distilled water to remove any

Jan 1, 1963

By R. Schuhmann Jr., P. J. Ensio

As a first step in a study of the physical chemistry of copper-smelting slags, experimental measurements were made of the oxygen pressure of simple iron-silicate slags in equilibrium with solid iron. The experiments consisted in bubbling CO2-CO mixtures through the slags in iron crucibles and in finding the equilibrium ratios of CO2 to CO. From the data, activities and partial molal heats of solution FeO and SiO2 in the slags were calculated. THE ternary system FeO-Fe,O,-SiO, is the simplest system which can represent adequately the important chemical properties of the slags formed in matte smelting and converting. Accordingly, the experimental study of slags in this system was started as the first step in a general research program on the thermodynamics of copper smelting. A recent paper by one of the authors' outlines this general research program and shows in some detail how information on thermodynamic properties of iron-silicate slags, especially information on oxygen activities, is essential to a full understanding of the chemistry of copper smelting. The FeO-Fe,O,-SiO, system also is the basis of slags produced in other processes, such as acid steelmak-ing processes, and is important in relation to the behavior of silicious refractories. In addition, data on the physicochemical properties of iron-silicate slags should contribute to a general understanding of the nature of slags, since at present such data for all kinds of slags are relatively meager. The principal quantitative information already available on iron-silicate slags consists in Bowen and Schairer's constitution diagram for slags in equilibrium with metallic iron,' Darken and Gurry's complete and precise thermodynamic study of the Fe-0 system,",' and Darken's study of the phase equilibria in the Fe-Si-o system. From the results of this previous work, it was clear that a complete thermodynamic study of ternary iron-silicate melts was a major undertaking which would have to be broken down into parts, including the working out of the ternary equilibrium diagram as well as extensive activity measurements on slags. The experimental measurement of oxygen activity, using CO-CO, and other gas mixtures as yardsticks of oxygen activity, was the basis of Darken and Gurry's study of the Fe-0 system. From the experimental measurements of oxygen activities over a large range of temperatures and compositions, they were able to calculate the activities of other species such as Fe, FeO, Fe,O,, etc., and also the other important thermodynamic properties in the Fe-0 system. At the start of the present investigation, it appeared that the same approach would be fruitful for the study of iron-silicate melts. Also, the experimental measurement of oxygen activities seemed particularly attractive because oxygen activity itself is a quantitative measure of oxidizing or reducing power, which is an important variable in copper-smelting slags. The slag compositions in equilibrium with yFe appeared most suitable for the first investigation of this kind, for the following reasons: 1—Good constitution data2 were available. 2—An iron crucible could be used, thus affording a simple solution to the refractory problem without introducing contarnination. 3—With Fe activity fixed, at unity with respect to a standard state of solid Fe, measurements of 0 activity could be followed by simple calculations of activities of FeO and other Fe-0 complexes and of SiO,. 4—This starting point afforded several possibilities for cross-checking with previous work,

Jan 1, 1952

By R. Schuhmann, E. J. Michal

Experimental measurements are reported for the oxygen pressures of iron-silicate slags in equilibrium with solid silica. CO2-CO mixtures were bubbled through the slags in silica crucibles to find equilibrium values of p co2/p co over the entire composition range of silica-saturated slags at 1250°, 1300°, and 1350°C. From the data, the activity vs. composition relationships were calculated for O, FeO, and Fe. SLAGS composed primarily of silica and iron oxides have particular practical importance in copper smelting,' in acid steelmaking, and in accounting for the service behavior of silica refractories. These slags all contain both ferrous and ferric iron, so that, strictly speaking, they are ternary or three-component liquid solutions. For convenience, the components may be taken as the three oxides, FeO, Fe2O3, and SiO2. The constitution of the FeO-Fe,O,-SiO, system at slagmaking temperatures has been studied in a recent investigation described in a separate paper.' This work showed the compositional ranges of iron-silicate melts at temperatures up to 1450°C and also the temperature-composition relationships for melts in equilibrium with various solid phases, including iron, wüstite, magnetite, and silica. Broadly speaking, the compositions of iron-silicate melts at a given temperature should be thought of as varying over a two-dimensional field. In the first place, the silica/total iron oxide relationship varies from maximum silica for silica-saturated melts to minimum silica for wüstite-saturated melts or, at higher temperatures, to zero silica for straight iron oxide melts. In copper smelting, for example, the converter slags approach the low silica limits while the reverberatory-furnace slags have intermediate silica contents, perhaps approaching silica saturation in some circumstances. Liquids formed in the pores of silica refractories presumably are close to silica saturation. The second type of composition variation is in the ferric/ferrous relationship, which depends on how oxidizing or how reducing the process conditions are. Relatively reducing slags, such as acid-steelmaking slags, are lower in ferric oxide and ap- proach saturation with metallic iron. Oxidized slags, such as copper-smelting slags, contain larger percentages of ferric oxides and approach or reach saturation with magnetite. Since these two kinds of compositional variations are closely related to two general properties of interest for all metallurgical slags, basicity, and oxidizing power, it is hoped that the thermodynamic study of iron-silicate slags eventually will throw further light on the significance and nature of these long-recognized but as yet poorly understood slag properties. Measurements of oxygen activity as a function of slag composition, using CO-CO2 gas mixture to fix oxygen activities, afford an experimentally convenient approach to the study of the thermodynamic properties of iron-silicate slags. In a preceding investigation,³ his approach was used in a systematic study of iron-silicate slags in equilibrium with solid iron. The present paper gives the results of a similar study of the iron-silicate slags in equilibrium with solid silica. The experimental work consisted in the determination of CO2: CO ratios in gas mixtures at equilibrium in the system: gas: liquid slag: silica Determinations were made at temperatures from 1250° to 1350°C for slags ranging in composition from iron saturation to magnetite saturation. Also, equilibrium CO,: CO ratios and slag compositions were determined for the univariant systems: gas: liquid slag: silica: iron gas: liquid slag: silica: magnetite Experimental Methods The experimental procedure was essentially the same as that used in the previous study of iron-silicate slags saturated with solid iron," but in order to work with the silica-saturated slags an all-silica crucible assembly was used. A liquid slag was prepared from pure prefused stock materials and brought to equilibrium with the silica crucible at the desired temperature. Then a mixture of CO2 and CO was continuously bubbled through the melt

Jan 1, 1953

By Malcolm T. Hepworth

RECENT interest in thermoelectric devices has been directed toward studies of the properties of thermoelectric materials of semiconducting solid compounds with little attention given to ionic and semiconducting liquids such as aqueous solutions, fused salts, and mattes. One type of thermoelectric system is the thermocell: a nonisothermal galvanic cell with two identical electrodes at different temperatures connected by an electrolyte bridge. An electromotive force, v, is generated which is a function of the electrode reactions and the properties of the electrolyte according to the Eastman' equation: where S* is the entropy change of the system arising from the electrode reactions and by heat transferred by ion migration and by thermal conduction. The quantity nF is the product of equivalents passed and Faraday's constant. A value of S* of 23.06 cal per "C is equivalent to 1 mv-Faraday per "C. The symbol, a, is used for dV/dT in analog to the See-beck coefficient of solid-state thermoelements. de Bethune2 has calculated the temperature coefficients of the electromotive force of a large number of nonisothermal aqueous cells from measurements on the nonisothermal temperature coefficients of the standard hydrogen electrode, combined with data on the isothermal temperature coefficients of half-cells tabulated in the literature. Values of these coefficients (a) in de Bethune's compilation ranged up to 3 mv per C. In particular he reported a value of +2.059 mv per "C at 25'C for the cell: Fe (aqueous, unit activity) (aqueous, unit activity) written for the hot-electrode reaction. The positive sign indicates that the hot electrode is positive (an "n-type thermocell"). In analog to a solid-state p-n system, it would be possible to couple two thermocells together to form a system in which the figure of merit could be calculated by adding the temperature coefficients according to the relationship described by offee:' where a is the Seebeck coefficient in volts per "C, p is the specific resistivity in ohm-cm, and K is the thermal conductivity in watts per cm "C. Even though ionic systems have rather high electrical resistivities compared with semiconducting and metallic systems, it was felt that a preliminary study of one ionic system should be made to establish some basis for evaluating the possibility of a p-n thermocell for energy conversion. Accordingly the Fe", Fe"' system was studied as a possible component for a p-n system. A glass system was constructed consisting of two vertical water-jacketed tubes connected by a horizontal tube, Fig. 1. Platinum-black electrodes 1 cm by 1 cm in dimension were inserted in each vertical tube with thermometers to register the electrode-compartment temperatures. The temperature of the electrode compartments was controlled by circulating water from thermostatted baths around the electrode compartments. The electromotive force of the cell was then read by a potentiometer for zero current as a function of the temperature of the hotter electrode. Current output of the cell for varying external loads was also measured. The cell resistance was measured by means of a bridge circuit with 10,000 cps signal and oscilloscope. Resistance measurements were converted to specific resistivity by calibrating the cell with a solution of known conductivity.

Jan 1, 1965

By R. J. Hopkins, L. B. Haney

On the basis of limited experimental work conducted at the Port Pirie smelter, it would appear that, by increasing the specific surface of sinter, and possibly that of coke as well, a marked increase in the rate and degree of sinter reduction in the furnace shaft can be achieved. Fusion-point tests have shown that this increased reduction means a much higher sinter fusion point and narrower plastic zone, while the more efficient utilization of coke in the furnace is inherent in the intensification of reduction by the provision of a more reactive sinter surface. Investigations aimed at increasing the ability to operate the blast furnace with a higher lead tenor of sinter reducing fuel cost proportionately, and at eliminating the loss in reduction potential in coke entering the furnace, as shown by the presence of appreciable proportions of CO in the top gases, are reported. Several lines for future investigations that could result in improved smelting methods are proposed. A SOMEWHAT informal presentation of ideas on lead blast-furnace smelting will be given in this paper. These ideas have been developed during observations of furnace behavior at Port Pirie and earlier at Mt. Isa, and have been guided by the results of laboratory experiments at Port Pirie. The authors do not intend to propound any particularly new theories, but present their ideas as a basis for discussion which may help toward a better understanding and improved control of blast-furnace operation. Performance variations of considerable magnitude occur from time to time at most lead blast-furnace plants. While Port Pirie is fortunate in having a very regular supply of high grade concentrates, it is no exception in this respect. Such irregularities are of considerable economic importance and they constitute a challenge to present-day metallurgists in their efforts to obtain an ever greater degree of control over furnace operation. In operating as Port Pirie does with a relatively high lead charge, it has been recognized for a long time that shaft conditions are ,of the greatest importance. A practical, or engineering, attack on the problem of accretions consisted of changes in furnace design, e.g., by widening the shaft to 10 ft above the bottom row of tuyeres, and by the provision of curved ends and vertical walls.' That this attack has had a great measure of success is shown by the fact that barring down of these wide furnaces is rarely necessary, shaft conditions have greatly improved, and sensitivity to charge variations has been markedly reduced. These modifications, followed by some metallurgical changes (chiefly the incorporation of pig iron into the furnace charge in 1948), have brought furnace operation to a point where some variables which were previously masked can now be studied. Accordingly, over different periods of time during the last five years, such variables as could be given numerical values have been recorded and subjected to statistical examination. The objectives of this work were: 1—to reveal the true importance of the different variables and 2—to show the proportion of total furnace variation which is unexplained and therefore referable to causes not measured at present? e.g., shaft accretions, sinter structure, coke structure, and others. Statistical Study of Variables In this work factors relating to furnace speed and lead reduction have been examined: 1—slag com-

Jan 1, 1955

By H. H. Podgurski

Above 200°C the observed increase in the apparent solubility of hydrogen in low alloy steels caused by cold work is attributed to the formation of methane in microvoids. This methane can be isolated quantitatively, and furthermore, the amount of methane is in accord with the equilibrium 2H2 + Fe3C = CH4 + 3Fe. The micro-void volume, calculated from the methane content via the equation of state for methane, corresponds approximately to that calculated from the measured density decrement produced by cold work. THIS investigation was undertaken with the intent of employing the hydrogen atom as a probe in detecting specific crystallographic defects in cold worked steel. It was expected that different degrees of chemical interaction of hydrogen with the various types of defects could be utilized. The original aim was to assign concentration values to defect sites. The success of this approach requires that experimental conditions can be attained under which lattice-dissolved hydrogen equilibrates primarily with only one type of defect. A set of experiments which appeared potentially to embody these requirements was described several years ago by Keeler and Davis.1 They noted in the case of a mild steel (low carbon) that the solubility of hydrogen between 200° and 400°C near atmospheric pressure was notably increased by cold working the steel. The observed solubility was an order of magnitude greater than the normal lattice solubility. * Although the Keeler and Davis studies suggested that the density decrement effected by their cold-working operation might be related to the anomalous solubility of hydrogen, they offered no explanation of the relationship between the two effects. Prior to this work, Darken and smith3 had noted a similar effect of cold work upon enhanced sorption of hydrogen by steel when charged by acid pickling. In the light of present-day concepts, interaction between lattice-dissolved hydrogen and dislocations was strongly suggested. More recently, Hill and Johnson,4 working with a

Jan 1, 1962

By E. M. Elkin, J. H. Schloen

All known methods of treating and recovering the various components of copper refinery slimes are discussed. The slimes treatment processes presently used by five copper refineries are described and flowsheets are given. A bibliography is appended. THE recent increase in anode copper production at the Noranda smelter placed an additional load on the Montreal East plant of Canadian Copper Refiners Limited. The consequent increase in the amount of anode slimes led to a careful consideration of the various methods of slimes treatment. A critical review of these methods is presented here in the belief that it would be of interest to copper refiners. No such review has yet been published, although a number of individual flowsheets have been described. To make the information of greater value, a questionnaire was sent to all copper refineries. While the overall response to the questionnaire was not entirely satisfactory, the foreign refiners gave much detail in their answers and expressed willingness to cooperate further if needed. Although the data below do not cover all refineries, it is thought that examples of all flowsheets currently in use are included. A comparison of these flowsheets should prove of interest. The paper is divided into two parts. One part deals with a discussion of all known methods of treating and recovering the various components of the slimes. The second describes the processes now in use at various copper refineries for the treatment of raw slimes up to the production of Doré bullion. A brief description of the two main electrolytic methods of parting Doré bullion is appended. Since the first commercial application of electrolytic refining of copper by J. B. Elkington in 1865, the treatment of anode mud or slimes has undergone many changes. The object of treating slimes has always been the recovery and separation of precious metals. With the passage of time, increasing attention has been paid to improvement in recovery and quality of byproducts, mainly selenium and tellurium. The original methods of treatment were crude, although relatively direct. For example," the slimes were fused on a dolomitic clay bed in a reverbera-tory furnace; the slag was removed and the resulting metal cupelled to silver and gold. In another process, the dried slimes were oxidized and scorified on the lead bath of a cupelling furnace. Later, these pyrometallurgical methods were modified by sulphuric acid leaching, followed by fusion with niter in a reverb eratory furnace. A preliminary oxidizing roast improved the leaching step. Straight hydro-metallurgy has not found practical application. No matter what method is employed, the result is Dorb metal—a silver-gold alloy, with or without the metals of the platinum group. Characteristics of the Slimes Anode slimes are made up of those components of the anodes which are not soluble in the electrolyte. They contain varying quantities of copper, silver, gold, sulphur, selenium, tellurium, lead, arsenic, antimony, nickel, iron, silica, etc. The color of raw slimes is grayish black and the particle size is —200 mesh. However, Baraboshkin and Gaev (Ref. 1, p. 37), describe light gray colored slimes from the electrolysis of secondary copper which are composed predominantly of sulphates and of basic salts. In anode furnace practice primary and secondary metals are not usually segregated and such slimes do not commonly occur. Copper in the slimes originates to a large extent in the cuprous oxide of the anodes and is therefore dependent on the oxygen content of the latter: Cu2O + H2SO4 + CuSO4 + H2O + Cu [I] Opinions have been expressed that some of the copper is formed by decomposition of cuprous to cupric sulphate Cu2SO4 ? CuSO4 + Cu PI The product of either reaction is very finely divided. Depending on the slimes composition, much of the copper is combined with sulphur, selenium, tellurium, etc. The balance of the copper is in the free metallic state.

Jan 1, 1951