1056
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 9, No.
11
METALLURGICAL SYMPOSIUM
I
I.
I
Four papers read at the 55th Meeting of the American Chemical Society, Boston, September 10 to 13, 1917
PHYSICO-CHEMICAL DATA NEEDED BY METALLURGISTS B y J. W. RICHARDS
Metallurgical chemists are vitally concerned with the energy involved in the chemical reactions useful in metallurgical operations. These energies are based primarily on thermochemical data, and raise the question of the sufficiency of these data for metallurgical purposes. They are woefully insufficient, and this from two standpoints: ( I ) thermochemical data a t ordinary temperatures and (2) data permitting their evaluation a t higher temperatures. THERMOCHEMICAL DATA AT ORDINARY TEMPERATURES
These are the figures of the thermochemical tables. They give the heats or energies of formation of compounds as determined in the laboratory, starting and ending a t or about room temperature. They enable us t o figure out easily the energy of a chemical reaction beginning and ending a t ordinary temperatures, when the heats of formation of all the substances concerned are contained in the tables. They give us no exact information a t all about the energy of the chemical reaction at temperatures other than the ordinary room temperature. Even so, the tabulated data are often lacking. Thermochemists active in the past, such as Thomsen and Berthelot, gave us the energy of formation of most common compounds, but chemists have been increasing rapidly the list of known compounds and the thermochemical laboratories have not kept pace with them, but have fallen far behind. Let us mention a few directions in which thermochemical data of the ordinary kind are sadly deficient or lacking: Combinations of metallic oxides with silica, forming silicate slags; combinations of metallic sulfides with each other, forming mattes; combinations of metallic arsenides with each other, forming speisses ; combinations of metals with each other, forming alloys; heat of formation of iron pyrites, F e S ; heats of formation of metallic arsenides, antimonides, nitrides, phosphides, silicides, carbides; heats of formation of metallic arsenates, antimonates, phosphates, tungstates, borates, molybdates, titanates, vanadates, chromates, manganates, aluminates. There are enough of these lacking data, needed now in metallurgical chemistry, t o keep a dozen thermochemical laboratories busy for ten years. For every one which is being published (and this applies t o antebellum conditions), a dozen or a score are urgently needed. Here is a wide field in which the thermochemist can be of immediate assistance t o the scientific metallurgist. THERMOCHEMICAL DATA AT HIGHER TEMPERATURES
The larger part of metallurgical reactions are carried on at temperatures above the ordinary, running up t o 3000' C. in electric furnaces. But, for any temperature above the ordinary, the thermochemical data are not exact, and the energy involved in the reaction is different from what it is beginning and ending a t room temperature. A s an example: If we are reducing liquid silica in an electric furnace, at 1800' C., to liquid silicon and CO gas, the energy calculated for the equation Si02
+ zC = Si + 2 C 0 ,
taking the tabulated heats of formation of Si02 and C O , applies only t o 15-20' C., and not to the actual conditions under which the reaction is taking place. Moreover, it applies only to solid
Si02 being reduced to solid Si, and not to the reaction when both these are in the liquid state. A S a further example: Distilling off zinc vapor from a mixture of ZnO and C, a t a working temperature of 1 0 5 0 ~C., the energy absorbed is far from being the difference between the tabulated values used in the equation
ZnO
+ C = Zn + CO,
because this involves the formation of solid zinc, while as the operation is actually performed, zinc vapor is produced. For such a reaction, the tabulated thermochemical heats of formation are only the starting point from which to evaluate the heat of the reaction a t any temperature and for any physical state of the reacting substances and products. A concise statement of the method of evaluating what is needed metallurgically from what is given by the ordinary tabulated thermochemical data, is as follows: The heat absorbed in a reaction a t any temperature t is equal to the heat absorbed a t ordinary temperature, as given by using the tabulated thermochemical data, increased numerically by the heat necessary t o raise the reacting substances from ordinary temperature to t (including heat absorbed in any change of state-fusion or vaporization), and diminished by the heat which would be given out by the products of the reaction in cooling from t to room temperature (including likewise heat evolved in any change of state-condensation or solidification). For these calculations, it is seen that we must, therefore, have some or all of the following data: Specific heats of all the substances involved in the reaction, in the physical state they possess a t ordinary temperature; their latent heats of fusion (solidification) ; specific heats in the liquid state; latent heats of vaporization (condensation) ; specific heats in the gaseous state. The physical chemist must be looked to for these data. There is no longer occasion t o say that this work is the function of the physicist; three-fourths of the work of the physical chemist is physics and physical measurements, and the metallurgical chemist needs these data so badly that the physical chemist must make it his business t o provide them for him. And they need providing, badly. Not one-tenth of the data which scientific metallurgists need and should have, is known and tabulated. We will briefly review what is needed. SPECIFIC HEATS
These have been well worked at, but mostly only for temperatures between 1 0 0 and 0' C., or room temperature. Such an average value for a short range is of little use t o the metallurgist. He needs the specific heat curve, from its actual value at 0 ' to its actual value a t the melting point, then its values in the liquid state to the boiling point, then its value for the gas or vapor. He wants a whole range of values, for all temperatures, while the tables usually give him only one. Or, putting it in another way, he wants the total heat content from any temperature down to zero. Such heat content curves are known for some of the elements and for a few compounds, but not for many. Most of the determinations concern the substance only in the solid state, while i t is needed also for the liquid and gaseous states. Out of forty metals, the specific heats of perhaps ten are known in the liquid state, and of only two as gases; of metallic compounds, which are much more numerous, the above statement may be repeated, with approximate accuracy, There are a t least a hundred important metallic compounds which need t o be studied in these respects.
Nov., 1917
T H E J O U R N A L OF I N D U S T R I A L A N D . E N G I N E E R I N G C H E M I S T R Y LATENT HEAT OF FUSION
One has only t o look in the best book of physicochemical tables published, t o realize the paucity of information on this topic. For every one known there are a dozen important ones unknown. It would well repay any large metallurgical firm to hire an investigator to determine such of these faFtors as it is interested in. For instance, there are a t least a dozen typical kinds of cast-iron, and there exists only a doubtful value for one kind. No reliable determinations have been made on steel, of any kind. No determinations are published for any kind of brass or bronze. The recent enlarged use of the electric furnace for melting metals has accentuated this deplorable lack of data on which t o base metallurgical engineering calculations. LATENT HEAT O F VAPORIZATION
What has just been said regarding latent heat of fusion applies with much greater urgency to the heat of vaporization. It has been experimentally determined for only three metals, and six metallic compounds, so that it is almost an unknown quantity. Yet we need it for all metals which are distilled, and for all metals and substances which are vaporized (at great expenditure of power) a t the high temperatures in electric furnaces. The latent heat of vaporization of zinc, for instance, represents probably 25 per cent of the net thermal work done in a zinc retort, yet it is experimentally unknown. Metallurgists are looking expectantly to physical chemists for these experimental values, so necessary for correctly interpreting and studying chemical reactions a t high temperatures. VAPOR TENSION
One more topic of very similar nature which is pressing for investigation is the vapor tension of the metals and metallic compounds a t various temperatures. For a few elements we have their vapor tension curves through a large range for the liquid element. For the solid element these are lacking, except for arsenic, selenium, iodine, phosphorus and sulfur. Yet the vapor tension of zinc below its melting point is the working force in the sherardizing process. Almost all metals lose weight in being melted, both before they melt and after melting, yet the data on which properly to study this phenomenon quantitatively are almost entirely lacking. I n producing silicon, 2 5 per cent of the product is lost by vaporization; silver evaporates before it melts, like blocks of ice in a current of cold, dry air. Important consequences could be multiplied; the need of further accurate data is urgent. EXAMPLE
As an example of what is needed in the way of physicochemical data, we will instance zinc. Heat content solid, to 0’ C.: 0.09061 4- 0.000044P. Heut i n solid at melting point: 45.2 calories. Lutent hrat of fusion: 22.6 calories. Heat i n liquid al melting point: 67.8 calories. Specific heat liquid: 0.179 (not determined for all temperatures). Heat in liquid at boiling point: 159 calories (estimated). Latent heat of uaporizalion: 446 calories (calculated from the vapor tension curve). Heat in vapor at boiling point: 605 calories, Specific heat of gas. PCY kilogram: 0.077 (estimated on theoretical grounds). 8.17 (deduced from Vapor tension. liquid: log p (mm.) = -6365/T Barur‘ observations). Vapor tension a t the melting point: 0.093 mm. of mercury. 8.63. Vapor tension. solid: log p (mm.) = -6685/T Vapor tension a t O o C.: 1 X 10-18 mm. of mercury.
+
+
The completeness of the data for zinc will emphasize, by comparison, the poverty of our data for other important metals, alloys and compounds. For brass and bronze, for instance, the most important alloys next to steel, we know only their specific heat from 1 0 0 t o o o , and the total heat content at the melting point, f o r only one variety of each.
I057
If any properly equipped chemists are looking for experimental work which will be of immediate assistance t o the metallurgical industries, we urge them t o look a t this field, with its great opportunities for service, and “ d o their bit” in this direction. LEEHIGH UNIVERSITY SOUTH
BETHLEHEM, PA.
RECENT DEVELOPMENTS IN CONNECTION WITH THE USE OF SULFUR DIOXIDE IN HYDROMETALLURGY By EDWARD R. WBIDLBIN
The researches on the metallurgy of copper conducted under the auspices of the Mellon Institute of Industrial Research since 1913 have aroused considerable interest but only preliminary announcements of the results of the experimental work have been made up t o the present time. This contribution reports briefly upon the present status of the investigations and the results presented show the industrial value of the author’s method for treating low-grade copper deposits. The increasing adaptation of flotation t o the treatment of low-grade copper ores has somewhat discouraged theuse of leaching methods and accordingly these processes have not made the progress expected; but the field is still open for oxidized ore where flotation has not thus far been successfully applicable. Successful flotation assumes that the copper content of the ore is in the form of disseminated mineral. I n the case of ores wherein the copper compound is diffused throughout the mass of gangue, such as is undoubtedly true of the copper silicate ores found a t Inspiration, it is certain that flotation is out of the question and that some leaching process must be used. With the exception of the ammonia leaching process, all the hydrometallurgical processes in use are based upon the employment of sulfuric acid as the leaching agent and the copper is then precipitated by one of three methods: viz., electrolytic, gas or iron. Of these methods, the electrolytic has received the preference, although in a few instances the iron process has been installed. The experimental plant a t Thompson, Nevada, was erected under the author’s supervision and placed in operation by him on the first of April, 1916. The process employed therein is based upon the precipitation of copper by means of sulfur dioxide. Prior t o its development, the use of sulfur dioxide for precipitating copper had been frequently suggested but was evidently not followed up on a sufficiently large scale t o make apparent the defects and merits of the process. The application of this process to large scale experimentation has developed several new features, as described in United States Patents issued t o the author. These have so materially reduced the cost of operction in the experimental plant that it is now clear that the process possesses many advantages over its chief competitor, the electrolytic process. The various innovations rendered imperative the elaboration of a process perfect in mechanical detail for dealing with low-grade oxidized and sulfide copper ores. I n fact, the various chemical problems involved in the investigation had been satisfactorily solved and were available for use three years prior t o the perfection of the necessary mechanical equipment of the plant. Of especial interest are the method of precipitating the copper from the solution and the process for the concentration of sulfur dioxide from smelter fumes or other sulfurous gases. The method of treatment is applicable to either carbonate or “sweet” roasted sulfide copper ores. Ore that readily yields to treatment is leached by percolation in large tanks, but for finer materials a 6-step Dorr classifier has been used with countercurrent flow of solution. I n precipitation, the solution is neutralized with lime and treated with sulfur dioxide until it has dissolved a percentage of gas equal to that of the contained copper. The precipitation of metallic copper ensues instantly when this solution
