Search Documents

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

John Chipman (Massachusetts Institute of Technology, Cambridge, Mass.)—The activity of FeO in silica-saturated slags shown in Table V is about 0.40 in the temperature range 1260" to 1350°C. Recent measurements by N. A. Gokeen at 1600" lead to about the same value. He finds the oxygen content of liquid iron in equilibrium with silica and ferrous silicate slags to be 0.088 pct. Under pure iron oxide slags at the same temperature, it is 0.225 pct. The ratio places the activity at 0.39.

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 Leo Brewer, Gerd M. Rosenblatt

Thermodynamic calculations predict the species vaporizing from metal-oxide mixtures when reliable free energy functions, enthalpies of formation, and dissociation energies are available for the possible gaseous and condensed oxide components. Calculations of the oxygen to metal ratio in the vapor phase compared with the oxygen to metal ratio in a liquid metal saturated with oxide impurity are presented The possibility of purifying metals contaminated with oxide by vacuum melting or by distillation is discussed. Kinetic considerations affecting rates are neglected. IN recent years extensive information has been obtained on the thermodynamic stability of gaseous oxides of metals due to a variety of new types of measurement. Perhaps the greatest amount of information has come from the application of mass spec-trometry to the study of high-temperature vapors.' In many instances oxides of quite unusual oxidation states are found to be important in the high-temperature vapors. At low temperatures the standard free energy change for a reaction as given by the equation ?F° = ?H° - T?S° is determined primarily by the AH" value. However, at higher temperatures where the value of T in the T?S° term is large, the entropy term becomes equal to or greater than the AH term. At low temperatures only reactions for which AH is negative or only slightly endothermic are of importance. This restricts the main equilibrium species largely to those with completed octets or those with the principle oxidation number of the element. At

Jan 1, 1962

By T. R. Ingraham

The thermal decomposition of cupric sulfate and of cupric oxysulfate has been examined by deter-mining the equilibrium gas pressure generated over each pure compound. The equilibrium data have been used to calculate the thermodynamic properties of both compounds, and the results have been combined with previously published data to establish a predominance-volume diagram for the Cu-S-O system over the normal range of roasting temperature and gas composition used in the treatment of copper minerals. Copper oxysulfate recrystal-lizes at 1100°K with an apparently irreversible en-dothermic heat requirement of 2.9 * 0.3 kcal per mole. WHEN mixed sulfide minerals containing copper are roasted, either of two procedures may be followed, depending on the nature of the other metals. In the first procedure, the roasting is controlled to produce a maximum amount of water-soluble copper sulfate which may be removed selectively from the water-insoluble compounds of the other metals. In the second, control is directed toward the production of water-soluble sulfates of the other metals and an insoluble salt of copper. Effective control of either of these processes would be enhanced by knowledge of the thermal stability of cupric sulfate and of cupric oxysulfate. In this paper, established data for the thermal stability of cuprous and cupric sulfide and of cuprous and cupric oxide will be combined with new data for the therma1 stability of cupric sulfate and cupric oxysulfate, to designate the volumes of stability of the significant compounds in the Cu-S-O system in the temperature range 750° to 950°K. EXPERIMENTAL Materials, Apparatus, and Procedure. The copper source material used in all experiments was Fisher Certified Reagent Grade "anhydrous" cupric sulfate, for which the following analysis was supplied by the manufacturer: chloride, 0.002 pct; alkalies and earths, 0.2 pct; insoluble, 0.002 pct; iron, 0.020 pct. Cupric oxysulfate was prepared from the normal sulfate by two procedures. In the first, equimolar quantities of cupric oxide (prepared by decomposition of the sulfate) and cupric sulfate were ground together and heated under vacuum in a sealed silica vessel at 800°C. This procedure was subject to failure because of explosion of the silica vessels due to the pressure of the final traces of water released from the sulfate on the initiation of its decomposition. The second procedure involved roasting the cupric sulfate, with frequent rabbling, in a muffle furnace at 725°C for a period of 48 hr. This produced an excellent product, which was confirmed as copper oxysulfate by X-ray and chemical analyses. The experimental technique used was that of measuring the total pressure exerted by the sulfur trioxide, sulfur dioxide, and oxygen produced by the following reactions: 2 CuS04 = cuo • CuSO4 + SO3 [1] cuo . CuSO4 = 2 cuo + SO3 [2] SO3= SO2 + 1/2 O2 [3] The apparatus used in the experiments has been described previously.1-3 Its main feature of a U-tube mercury manometer in which the mercury is protected from corrosion by enclosure in a flexible Pyrex bellows. Before beginning a run, the interior of the apparatus, including the bellows-manometer and all connecting tubing, was thoroughly washed with hydrochloric acid and distilled water to remove any

Jan 1, 1965

By Harold M. Feder, Irving Johnson

Tkermodynamic functions for dilute solutions of uranium in liquid cadmium were obtained from galvanic cell measurements. Deviations from Henvy's law were observed at concentvations down to 2 x 10-3 atom fraction. Unusually large negative values of the pavtial molal relative enthalpy and excess entvopy of uranium, suggestive of the occu,vvenctwe of partial ovdering of cadmium around uranium in these solutions, were found. The negative relative partial molal enthalpy of uranium at the liquidus accounts for the observed retrogvade solubility of metallic uranium between 473" and about 630°C. The standard free enevgy of formation of UCd,, from a-uranium and liquid cadmium is given by F,° THE constitutional diagram of the U-Cd system,' Fig. 1, is unusual in several respects. The near equality of the Goldschmidt atomic radii2 (Cd, 1.52A U, 1.56A) might be expected to give rise to extensive mutual solubility of the elements except for the restrictions imposed by differences in valence and electronegativity.3 The latter factors must be strongly influential because mutual solubilities in the terminal solid phases are probably negligible, and the solubility of uranium in liquid cadmium in the readily accessible range is only about 1 at. pct. Interestingly, the solubility of uranium in liquid cadmium actually decveases slightly with increasing temperature from 473" to about 630°C. Such a retrograde solubility in a liquid phase is a rare phenomenon in metallic systems; no other authenticated examples were found among the nearly 700 binary phase diagrams compiled by Hansen and Anderko.2 These observations suggested the existence of some unusual interaction between uranium and cadmium. Greater insight into the nature of this interaction was sought by measurement of the thermodynamic properties of the system. EXPERIMENTAL PROCEDURE The emf of cells denoted by the scheme was measured. Each cell consisted of two uranium and two alloy electrodes immersed in a molten lithium chloride-potassium chloride eutectic mixture containing uranium trichloride. The physical arrangement is shown in Fig. 2. The potential between any pair of electrodes could be measured with a Leeds and Northrup Type K-3 potentiometer. The measurements were made at points marked in Fig. 1. It should be noted that points on the phase boundaries represent the concentrations of uranium in the saturated liquid phases of heterogeneous alloys. Uranium Electrodes. Uranium, which is not a particularly soft metal, is capable of retaining residual stresses, and its potential may depend upon its physical condition. Electrodes were prepared from 3-mm diam rods of hot-rolled high-purity4

Jan 1, 1962

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 D. F. Stoneburner

The thermoelectric power and electrical conductivity of a series of liquid alloys of thallium were determined in order to study the relation of chemical bonding to semiconduction in liquids. The results indicate metallic behavior for the alloys of thallium with arsenic, antimony, and bismuth, while the sulfides, selenides, and tellurides indicate semiconduction. The results are compared with the Properties of the same alloys in the solid state. This work supports the observation that long-range order is not a necessary requirement for semiconduction. PREVIOUS work1,5 has shown that some sulfides and oxides behave as semiconductors in the liquid state. Although the band theory has been of great help in understanding the properties of solid semiconductors, its quantitative application to liquids is difficult. The very existence of liquid electronic semiconductors shows that ascribing the discrete structure of the energy spectrum to strict lattice periodicity, or long-range order, is not always satisfactory. Rather, the short-range order determines the structure of energy levels and the width of the forbidden gap and, consequently, the concentration of free holes and electrons. This is borne out by the analysis of data accumulated by Regel and coworkers.6 The similarity of electronic structure of liquid and solid phases of certain liquid metals was pointed out by Knight et a1.,7 who examined nuclear resonance in solid and liquid Li, Na, Rb, Cs, Mg, Al, Ga, Sn, and Bi. They found noticeable changes in the electronic structure upon melting only in the cases of bismuth and gallium. They concluded that "a liquid metal possesses a band structure which is very like that of the solid, provided the short-range structure is not altered during melting." In semiconductors in which the near-neighbor arrangement remains the same on fusion, the material would be expected to retain its semiconducting properties. The quantum theory of semiconductors, with its band structure of energy levels, is linked exclusively to long-range order. Furthermore, it has limited usefulness in predicting new semiconductors. Many sulfide8-12 have made comparisons of properties on the basis of crystal structure or the position in the periodic table, both methods involving the same factors as chemical bonding. Mooser and Pearson8"10 have pointed out that crystal structure depends on chemical bonding, and that this bonding is a property of the atoms themselves. As the periodic arrangement of the atoms offers an easy comparison of such factors as atomic weight and number of valence electrons it provides clues to expected similarities of bonding for various elements or groups of elements. This approach has led Mooser and Pearson to formulate their valence-bond theory of semiconduction, in which they define a semiconducting bond. These authors state that "semiconductivity is the result of the presence in a solid of predominantly covalent bonds. These lead, through the process of electron sharing, to completely filled s and p orbi-tals in the valence shells of all atoms of elemental semiconductors while in semiconducting compounds only one atom of any two bonded together need acquire closed s and p orbitals. The presence of empty 'metallic' orbitals in some atoms of a compound does not destroy the semiconductivity provided that these atoms are not bonded together; it may, however, give rise to pivoting resonance in

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 R. G. Knickerbocker, A. G. Starliper, H. Kenworthy, C. H. Gorski

This report describes the progress made in the research work on the development of a new method for preparing lower-cost titanium tetrachloride and preparing titanium oxide pigment. One of the requirements for the commercial production of ductile titanium in the process used by the Bureau of Mines is a source of lower-cost titanium tetrachloride. The production of ductile titanium by a modification of the Kroll1 process, recently developed by the Bureau of Mines, requires such a source of lower-cost titanium tetrachloride to make it commercially feasible. This report describes the progress of work done at the Mississippi Valley Experiment Station at Rolla, Missouri, on the development of a new method for preparing titanium tetrachloride. During the course of this research a new method for preparing pigment-grade titanium oxide was developed. At present, the price of technical-grade titanium tetrachloride is $0.32 a pound, which makes the price of the contained titanium $1.28 a pound.2 In addition, the titanium tetrachloride must be purified further before it is suitable for processing into metal, thus making its cost still higher.3 There were 8,562 tons of rutile produced in the United States in 1947, which was 900 tons in excess of that consumed. In addition there were 13,937 tons in various stocks, exclusive of the stocks in the Government strategic stock pile. No estimates of the domestic production of rutile are given for any of the prewar years. However, in 1939, 442 tons of rutile were imported as compared to 14,307 tons in 1947. One of the reasons for the large increase in the production of rutile is the working of the Florida beach sands for ilmenite, during which a considerable amount of rutile is produced as a by-product. It would be of value to determine methods for utilizing the excess production of rutile. The Arkansas titanium deposits in Hot Spring County produced commercial-grade rutile concentrates from 1933 to 1942. These were sold mainly to England, Germany, and Russia.

Jan 1, 1950

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

By R. T. C. Rasmussen, L. H. Banning, W. E. Anable

In the rapidly growing industry of elemental-phosphorus production from western phosphates, most of the vanadium and chromium contained in the phosphate rock collect in the byproduct ferro-phosphorus. Results are presented of a completed laboratory project, which developed a tristage crystallization and hydrolysis process for recovering strategic vanadium and chromium, as well as a valuable phosphorus product, after extracting these elements from the ferro-phosphorus by roasting and leaching. THE Phosphoria formation in Idaho, Montana, Wyoming, and Utah contains the Nation's largest reserve of phosphate rock. A unique feature of the Phosphoria beds is their content of a fraction of a percentage each of vanadium, chromium, nickel, and molybdenum. Vanadium is the most important as to quantity and value. Small-scale tests by the Bureau of Mines at Albany, Oregon, in 1947, indicated that most of the vanadium in the phosphate rock collects in the ferrophosphorus product of smelting. Subsequent electric smelting operations to produce elemental phosphorus from western phosphate rock (experimentally by TVA and industrially at Pocatello, Idaho) have shown that the vanadium and other metals in the rock are to a large extent recovered in concentrated form in the ferrophosphorus byproduct. This paper reports the results of completed laboratory research on the recovery of vanadium from ferrophosphorus, which was undertaken by the Bureau of Mines at Albany in 1948 as the first phase of a project entitled, "Vanadium and Fluorine from Western Phosphates." The various vanadium-recovery methods investigated, including the roast-leach method that showed most promise and was studied in greatest detail, are discussed in an earlier publication.' Subsequent systematic study of the roast-leach method of extracting vanadium from western ferrophosphorus developed the more effi- cient tristage crystallization process, which is the subject of this paper. Process Development The investigations were made on ferrophosphorus produced in the electric smelting of elemental phosphorus from western phosphate rock. The TVA provided two sample lots of ferrophosphorus produced in pilot plant smelting of phosphatic shale from the Fort Hall Indian Reservation in Idaho. The Westvaco Chemical Div. of the Food Machinery & Chemical Corp. supplied two sample lots of ferrophosphorus produced by its phosphorus smelter at Pocatello, Idaho. The analyses of all four lots are shown in Table I. Westvaco lot B was the starting material for the more recent tests. The roast-leach process for recovering vanadium from western ferrophosphorus, as originally developed, employed the following principal steps: Roasting of a mixture of pulverized ferrophosphorus, soda ash, and salt; extraction of the water-soluble vanadium, phosphorus, and chromium compounds from the calcine by leaching, settling, and decanta-tion of the pregnant solution; primary crystallization of trisodium phosphate from the pregnant solution; purification of the trisodium phosphate crystals by dissolution in water and secondary crystallization; purification of the pregnant vanadium solution from the primary crystallization step by adding calcium chloride to precipitate calcium phosphate; and hydrolysis of vanadium red cake from the puri-

Jan 1, 1954

By R. M. Caves

High-purity dense tungsten coating is obtained by means of a modified de Boer-van Arkel iodide process using tungsten bromides. The all-glass reaction system is pumped, baked, and sealed (pinched-off) at about 10-7 mm Hg pressure. The bromides then formed in situ are decomposed, depositing tungsten on heated tungsten surfaces. Heating of the specimen is done inductively in a novel arrangement that avoids electrodes of glass-to-metal seals. The tungsten, deposited at specimen temperatures from 2000° to 2800°F and bulb (halide) temperatures of 225" to 725°F, was adherent and uniform, and ranged in thickness to 1/8-in. REFRACTORY metals are of interest at NASA for use in hypersonic aircraft, in rocket engines, and in other thrust devices where very high temperatures are encountered. Tungsten, with a melting point about 6100° F, is potentially very useful for some of these applications. Considerable research on tungsten and its alloys is currently being conducted at the NASA Lewis Research Center. In this tungsten research program, there is need for a method of depositing high-purity, nonporous tungsten coatirlgs. Metallurgical bonding of the coating both to itself and to the substrate is required. In addition, it is necessary to be able to deposit thin, uniform coatings on substrates of a variety of shapes and sizes for laboratory test purposes. A survey of the methods previously used for depositing tungsten coatings indicated that none would likely meet these requirements for high purity, good uniformity, and high density except thermal decomposition of the halides. The method for coating that was selected for investigation was the thermal decomposition of tungsten bromide. This is a variation of the van Arkel and de Boer iodide process established years ago and recently reviewed.1,2 This process is applicable to the transition metals in general. More recently, the application and techniques were extended with chlorine3 and fluorine,4 and included the coating of tungsten. This is believed to be the first report on the use of the bromide for tungsten coating. Bromine was chosen over the other halogens because it promised a lower temperature for tungsten

Jan 1, 1962

By R. E. Steiner, A. F. Weinberg, R. J. Van Thyne

Uranium solubility in molten bismuth was determined in the temperature range 350" to 600°C, varying from 0.09 wt pct to near 2 wl pct, respectively. Zirconium and magnesium, simulated fission products, and sodium were found to increase or decrease uranium solubility in bismuth in the temperature range 370° to 420°C, depending upon the addition or temperature. Data were obtained by both chemical analysis of samples obtained by filtration from saturated melts and by measurement of the variation of electrical resistance with temperature. IN a study for the United States Atomic Energy Commission, a Liquid Metal Fuel Reactor Experiment (LMFRE) was proposed in which a solution of uranium dissolved in molten bismuth served as both the fuel solution and the primary coolant. It was proven necessary to add other elements to this solution for certain desirable properties: 1) zirconium acts to prevent reaction of the fuel solution with the graphite core (which would result in the formation of uranium carbide) and also to inhibit mass transfer of iron and chromium from the walls of the reactor tubing to cold spots resulting in blockage; and 2) magnesium acts as a deoxidant and prevents loss of uranium. In addition to these intentional additives, other elements entering the solution are: 1) fission products which are a by-productof reactor operation, 2) sodium (the secondary coolant) through possible small leaks in the heat exchange system, and 3) iron and chromium from the container walls. Each of these elements may affect the solubility of uranium in the fuel solution. Since the concept of this reactor is based upon a liquid solution, the relatively low solubility of uranium in bismuth will dictate the minimum temperature at which the reactor heat exchanger can be operated. The solubility of uranium in liquid bismuth and the effect of some additives on this solubility have pre- viously been investigated1-' (more recent results6" became avaliable after initiation of this investigation). However, some discrepancies between the various results have been noted, and also the cumulative effect of the several additions or impurities was not known. This investigation was commenced to obtain definitive results. MATERIALS Analyses of the materials used are presented in Table I. Although ostensibly of extreme purity (99.999 wt pct), the bismuth was found to contain a significant amount of impurities, probably oxides. Except for determination of the binary system, Bi-U, prior to use all bismuth was hydrogen-refined and

Jan 1, 1962

By R. W. Mancantelli, J. R. Woodward

IN 1947 a large low grade deposit of uranium was located in the northwest corner of Saskatchewan, in the Beaverlodge property of Eldorado Mining & Refining Ltd. Most of the values occur as thin seams and as coatings on other minerals, and the ore, which is light and friable, is not amenable to the usual gravity methods of concentration. The acid leaching process developed to retreat the company's Port Radium tailings was also impractical, as the percentage of carbonates is high and the percentage of sulphides relatively low. Construction of the mill building and installation of equipment, both scheduled for 1952, awaited selection of a satisfactory ore dressing process on or before Oct. 1, 1951. An extensive research program on dressing of ores from the Ace mine therefore was undertaken by the Mines Branch in Ottawa, a research team at the University of British Columbia, and an ore dressing group at the company's Port Hope refinery. Pilot plant operations were conducted at the Ottawa plant of Sherritt Gordon Mines Ltd. under the general direction of C. S. Parsons, consultant on metallurgy and ore dressing for Eldorado. In mid-September, having compared results of the several research programs, Dr. Parsons recommended a process employing a carbonate or basic leach. He reported that, while the chemistry of the process had been proved, engineering of the flowsheet was incomplete, and he suggested that under normal conditions further pilot plant work at the Ace mine might be profitable. However, since this would involve a delay of 12 to 18 months in bringing the property into operation, he recommended that design of the concentrator proceed immediately. Concentrator capacity was determined by two considerations: 1) the amount of ore then available and 2) the expectation that continued improvements would be made in the ore dressing process as a result of the intensive research being carried out by the Mines Branch of the Department of Mines and Technical Surveys. As these improvements could affect both the chemistry and the en-

Jan 1, 1956

By T. R. A. Gokcen

THE possibilities of separating and purifying metals by high vacuum distillation were examined by Kroll.1 He suggested vacuum treatment for the removal of zinc from the lead produced after Parkes desilverizing. The St. Joseph Lead Co. developed the first commercial vacuum dezincing process at their Herculaneum refinery, as described by Isbell.² The Broken Hill Associated Smelters at Port Pirie, Australia, has, after several years of pilot plant operations and fundamental investigations, developed a continuous process, which will be described briefly in a forthcoming publication." As the full-scale continuous vacuum dezincing plant at Port Pirie is still experimental, publication of full practical details of the plant will be deferred until the unit is operating as a normal part of the continuous refinery. This paper deals only with theoretical aspects of vacuum distillation processes, with particular reference to vacuum dezincing. The method of mathematical analysis is of general interest as it may be applicable to other metallurgical separations which have been investigated recently.4-6 Evaporation Processes At about atmospheric pressure, or higher, most liquids possess a boiling point—a temperature at which any heat put into the liquid is absorbed only as latent heat, not as specific heat. If a steady heat input is supplied, the liquid's temperature rises to this value, then remains constant while bubbles of vapor form beneath the surface. The rate of evaporation is determined solely by the rate of heat transfer to the liquid; the temperature of boiling is determined by the partial pressures of the volatile constituents in the liquid, and the total pressure above the surface. If the rate of heat transfer to the liquid is increased, the temperature remains constant, and the rate of boiling increases. When evaporating metals under vacuum, however, the partial pressures concerned are generally so small that boiling does not occur, because at even a fraction of a millimeter below the surface the hydrostatic pressure is usually too great to permit the formation of a pocket of vapor. In addition, the high thermal conductivity of metals tends to prevent the local superheating which is necessary for bubble formation.' Although this effect is doubtless also exerted when boiling metals at higher pressures, the magnitude will be less because the degree of superheat required to form bubbles is very much less at the higher temperatures involved. Under vacuum, therefore, evaporation of volatile constituents takes place only from the exposed surface, and the rate of evaporation depends upon the surface area, the surface concentration of volatile constituents, the surface temperature, and the partial pressures of volatile constituents immediately above the surface. If the heat input is raised above a certain level, the effect is not to increase the evaporation rate at constant temperature, but to raise the temperature of the liquid until at some higher level an increased rate of evaporation (and thus of latent heat absorption) again balances the heat input rate.? Many substances (including metals) have a very large intrinsic evaporation rate at quite low temperatures—far below their normal boiling points. However, at atmospheric pressure, the large numbers of atoms evaporated are almost completely deflected back into the liquid (or solid) surface by air molecules. Thus the back condensation rate is practically equal to the gross evaporation rate, and the net evaporation rate is practically zero. It can therefore be seen that an overall distillation rate depends not only upon the intrinsic evaporation rate, but also upon the ability of the volatile atoms to move away from the evaporating surface. This movement is facilitated by the provision of a condensing surface close by. Vacuum Distillation: The function of the vacuum above the evaporating surface is to remove foreign molecules, so that the chances of deflection of an evaporated atom back into its source are reduced. When the residual gas pressure is reduced so far that the evaporated atoms have a high probability of reaching a nearby condensing surface without suffering collision with a foreign molecule, the state of affairs is termed "molecular distillation." This process is practiced commercially today for the purification of numerous organic chemical products of high unit value, but not, to the writer's knowledge, for any metallurgical separation. When the degree of vacuum produced in a still is not sufficient to promote molecular distillation, then the evaporated molecules must diffuse through the

Jan 1, 1954

By A. W. Schlechten, R. F. Doelling

Parkes' process crusts were vacuum distilled using a shortened Pidgeon retort. Zinc was effectively removed below 800°C and recovered as a zinc sheet easily stripped from the furnace liner. Lead dasdistillationazinc required about 950°C and the resulting lead condensate tillationtended to stick to the thin metal liner. Final purity of residue is limited only by nonvolatile metals such as copper. THE successful commercial application of vacuum distillation for the removal of zinc from lead, as described by W. T. Isbell,' raises the question of whether or not a similar method can be used for other metal separations. Preliminary laboratory experiments on the vacuum distillation of Parkes' crusts by one of the authors' gave such encouraging results that it was decided to make a series of tests with large scale equipment to determine the results that might be expected in plant operation. The pilot-plant test results are reported in this paper. The great advantages of vacuum dezincing are its simplicity, the relatively low temperature of operation, and the fact that the zinc is recovered in the metallic state ready for use again in the desilveriza-tion of lead bullion. These same advantages and others would be realized from the vacuum distillation of the zinc-lead-silver crusts made in the Parkes' process. Zinc readily will distill over at temperatures of 800" to 900 °C as contrasted with the 1200°C or more used in the Faber du Faur furnace. Furthermore, the recovery of zinc as metal is practically perfect since there is no loss by oxidation or fuming. If the vacuum distillation is continued and hastened by raising the temperature to around 1000°C, the lead will distill over at an appreciable rate and deposit in a warmer zone of the condenser. This lead will contain a small amount of silver, but it can be returned to the desilverizing kettles and there is not the chance of loss that there is in disposing of the rich litharge from cupelling. The lower temperatures required will mean a saving of fuel and less wear on the equipment. One further point is that the vacuum distillation could be run on a small scale practically continuously, so as to avoid the accumulation of large amounts of silver-rich material and the need of assembling a large crew for special cupellation runs. It should be pointed out here that the final purity of the silver residue will depend on the copper or iron content of the crusts, as these and other metals with low vapor pressure will not be eliminated. The idea of treating the silver-zinc-lead crusts from the desilverization of lead bullion by vacuum distillation is not a new one, but such experiments have not been reported, as far as can be determined. In 1912, T. Turner presented a paper3 before the Institute of Metals on the vacuum distillation of brass, and a member of the audience suggested that he try his method on Parkes' crusts. In 1935, W. J. Kroll, noted for his discovery of debismuthiz-ing lead by calcium additions, published a paper' on vacuum distillation of metals and pointed out possible applications in the lead industry. Principles of Separation The successful separation of two or more metals by distillation depends upon an appreciable difference in the effective vapor pressures of the metals in the alloy to be treated. The vapor pressures of the common metals have been determined with considerable accuracy; for example, at 800°C the vapor pressures of the individual metals which are of particular interest in this paper are about .as follows: Zn, 241 mm; Pb, 0.0553 mm; and Ag, 0.0000276 mm. Unfortunately,, data are not available on the activities of the components in the ternary system Zn-Pb-Ag, but it can be estimated that on the basis of the vapor pressures of the individual metals a good separation can be made by distillation. The preliminary laboratory tests previously mentioned' supported this assumption. The pilot-plant size vacuum distilling furnace is shown in Fig. 1. It consisted of an abbreviated Pidgeon retort, 5 ft long with an ID of 8 in., heated by six silicon carbide elements placed symmetrically

Jan 1, 1952

By A. W. Bethune, L. M. Pidgeon

The equilibrium vapor pressure of zinc has been determined over the systems: ZnS(s) + Fe(s) = FeS(s) + Zn (vapor) and ZnS(s) + 2Cu(s) = Cu2S(s) + Zn (vapor) by reacting the components in an evacuated tube containing a thin copper fiber, and allowing equilibrium to be established with respect to the brass formed and the zinc in the vapor phase. The composition of the brass formed was determined and equilibrium vapor pressure values obtained from existing data. Between 850' and 1000°C, values for the first reaction ranged from 8 to 58 mm Hg; for the second reaction from 1.8 to 22 mm Hg. THE direct reduction of metallic sulphides may be indicated by an equation of the form MS + X = XS + M [1] where X is some suitable reducing agent. In the case where M is a metal of relatively high volatility, the use of vacuum will displace the equilibrium to the right at comparatively low temperatures in the face of the usually unfavorable thermochemistry. For this technique to be feasible, MS, X, and XS, must of course be nonvolatile compared to M. In this regard, zinc becomes an obvious metal both from the point of view of its volatility and the fact that most commercial ore deposits of this metal occur as the sulphide, and its direct reduction would avoid the expensive roasting process necessary prior to present day reduction methods. Two reducing agents are of interest, namely copper and iron, with the former having the added attraction of being relatively easily regenerated by oxidation in the copper converter. The possibility of these reactions has been considered before. Imbert1 patented a process whereby zinc sulphide was reduced by either copper or iron. The process as described took place at atmospheric pressure and, at the high temperatures required, the system was molten, resulting in the formation of a matte with the consequent reduction in the activities of the reactants. Peterson2 did further experimental work on these reactions and, although promising results were obtained on a small scale, attempts to increase the size of the furnace led to excessive "blue powder" formation. The early workers failed to realize the large reduction in temperature afforded by the use of vacuum and its desirable results. More recently, the direct reduction of zinc sulphide by iron has been the subject of a thermody-namic investigation by Kelley,3 and Gross and War-rington' have studied the kinetics of the reaction in the temperature range 900" to 1000°C, their experiments being conducted using vacuum and indicating that the reaction would proceed practically to completion in 1 to 3 hr, depending on the temperature. A qualitative examination of the system ZnS-Cu carried out at this University indicated that 98 pct of the theoretical zinc in the charge could be recovered in 1 hr at 1000°C when operating under reduced pressure. The purpose of this research program was to study the equilibrium of the two reactions. During the investigation, reference to the experimental work of Schenk5 was found but, due to lack of detail in the report, it was felt that it would be desirable to continue the equilibrium measurements. Selection of Method The measurement of vapor pressure of metals presents obvious problems resulting from the high temperatures which must be employed. In the present case, the production of the "reaction pressure" introduces a further difficulty since a chemical reaction must proceed before any metal vapor pressure is produced, resulting in depletion of the re-

Jan 1, 1954

By Donald Ofte, L. J. Wittenberg

The absolute viscosity coefficients and activation energies for viscous flow of bismuth, lead, and zinc are reported. The viscosities were measured in an oscillating cup viscosimeter from nearly 1000°C to within 1 deg of the melting point of zinc; 2 deg of the melting point of lead; and in the supercooled condition of bismuth, 9 deg below the melting point. Two methods of relating the change in the viscosity coeflicient with temperature were compared. From the plot of the logarithm of viscosity (77) as a function of reciprocal absolute temperature (1/T), the equations of the lines which fit the data are: AS a part of the Reactor Fuels and Materials Research program at Mound Laboratory, precise measurements of the physical properties of liquid metals are of interest because the desirability for a low vapor pressure liquid coolant in high-temperature nuclear power plants has focused attention on the properties of the liquid metals.' Also, a clearer understanding of the liquid metal state can be achieved when better measurements are available. For these reasons, the viscosity values of certain liquid metals have been determined. The viscosities of the liquid metals, bismuth, lead, and zinc are measured in an oscillating cup viscosi-meter. In this apparatus the liquid is sealed in a right-circular cylindrical cup which is attached to a torsion fiber so that the system forms a torsion pendulum. The damping effect of the molten metal upon the normal oscillations of the torsion pendulum is a function of the viscosity of the liquid. This method is advantageous because of the small amount of sample required (8 to 10 cc), the ease of remote operation of the apparatus in a vacuum system, and the containment of the liquid metal in a hermetically sealed, nonreactive, tantalum crucible. With the liquid metal sealed in the crucible, loss of liquid by vaporization and chemical reactions with atmospheric gases are prevented. Additionally, an absolute viscosity determination is obtained which avoids the sources of possible error in a relative measurement. The difficulties in a relative method include the repetitious cup calibrations, and the uncertainty inherent in the practice of calibration of the apparatus at room temperature and extrapolation to the high temperatures necessary for the investigation of most liquid metals. The oscillating cup viscosimeter was first described by Meyer in 1891.2 The first complete mathematical treatment offering an absolute measurement of viscosity with this type of apparatus was proposed by Andrade and chiong3 in 1936 for an oscillating sphere filled with a liquid. This solution was modified to include a right circular cylinder by Hopkins and Toye4 in 1950, and R. Roscoe5 in 1958. Roscoe's treatment for the calculation of the viscosity of a liquid at a particular temperature from the logarithmic decrement and period of oscillation of the torsion pendulum was used in this investigation. A detailed description of the method of calculating the viscosity from these measurements has been reported earlier.' This calculation has been programmed for the IBM 704 and IBM 1620 computers for expedition of the otherwise laborious calculations. APPARATUS The cutaway view of the apparatus in Fig. 1 shows the suspension system within the high vacuum enclosure. The low residual gas pressure. maintained between 1 x 10-4 and 5 X 10-6 mm Hg during a determination, avoided both air drag on the pendulum and

Jan 1, 1963

By A. W. Schlechten, C. M. Hsiao

The apparent vapor pressures of a number of metal sulphides were determined by measuring their rate of weight loss when they were heated under vacuum. The calculated pressures are due in some instances to the volatility of the sulphide and in others to the decomposition pressure. FIE direct reduction of metallic sulphides, as in the precipitation method for lead or antimony, is not a widely used process today. However, it might be employed for the production of a number of metals if the operation were carried out under reduced pressures. Two general procedures are possible; the reducing agent could form a stable nonvolatile sulphide from which the valuable metal could be removed by volatilization or liquation. The other approach would be to choose a reducing agent which would form a sulphide that could be volatilized away from the valuable metal. A vacuum operation would serve to protect the sulphides and metals from oxidation and would increase the evaporation rates. A related process is the separation of metallic sulphides by selective volatilization either at atmospheric pressure or under vacuum. This procedure is already used commercially for the elimination of lead and cadmium as PbS and CdS from zinc calcines; it might well have other applications. To predict such processes it is necessary to know the relative volatilities of the metallic sulphides and to know whether they volatilize as sulphides or whether the predominant weight loss is due to decomposition. Such data would also be of value in studying problems such as the use of sulphides for refractories, as described by Brewer,] or in the evaluation of the theory of ore deposition from the vapor state, as proposed by Brown.' Qualitative statements concerning the volatility of metallic sulphides can be found frequently in the literature and are well summarized by Mellor, but accurate determinations of rates of evaporation or vapor pressures are very scarce. Kelly" lists vapor pressure data only for PbS; his reference being to the work of Schenck and Albers,4 who measured the vapor pressure of PbS by a dynamic method between 850" and 995°C. More recently Veselovskii5 has determined the vapor pressures of the sulphides of antimony, lead, cadmium, and zinc at temperatures ranging from 360" to 1000°C using Knudsen's method. A second Russian worker, Pogorelyi,6 determined the vapor pressures of CdS and ZnS at temperatures from 900" to 1250°C. The results obtained by these workers are shown in subsequent graphs in comparison with the data of this paper. Brewer and coworkers1 have studied some of the metallic sulphides to determine their suitability as refractories in vacuum. Veselovskii's determinations on PbS checked well with those of Schenck and Albers, and his determinations of CdS check almost exactly with Pogo-relyi. For the vapor pressure of ZnS the data of Veselovskii and that of Pogorelyi are in fair agreement, as shown in Fig. 1, but it should be pointed out that Lumsden7 has discovered that the equation given by Veselovskii for the vapor pressure of ZnS: - 14,200 log P9.495 is in error by a factor of ten when compared to the experimental data. In contrast with the scarcity of data on vapor pressures, the decomposition pressures of many metal sulphides have been determined and are summarized by Smithells.8 Theoretical Considerations The experiments described in this paper consisted of determinations of the rate of weight loss of certain metallic sulphides under very low pressures at different temperatures. These data plus observation and analyses of the products reveal the mechanism of the weight loss and also provide a basis for the calculation of the vapor pressure or apparent vapor pressures of the sulphides.

Jan 1, 1953