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). Vapor tension. liquid: log p (mm.) = -6365/T 8.17 (deduced from Barur‘ observations). Vapor tension a t the melting point: 0.093 mm. of mercury. Vapor tension. solid: log p (mm.) = -6685/T 8.63. Vapor tension a t O o C.: 1 X 10-18 mm. of mercury.
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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.
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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
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
is brought to a temperature of 160’ C., under a pressure of 100Ibs.
The results of the first year’s operation, based upon, the treatment of 5 tons of ore per day, show conclusively that the author’s sulfur dioxide process can be operated continuously without interference from accumulated impurities in the solution. During this time various ores were treated, some containing a very high iron content, while others were high in lime, and in every case a satisfactory recovery of the copper content was 0btained.l Theoretically, only twice the quantity of sulfuric acid originally present in combination with the copper is regenerated. In actual practice, however, the amount of sulfuric acid regenerated is above this amount. In fact, during the operation of the process it has been necessary to neutralize sulfuric acid with lime, in order to keep down the volume of the solution on hand. The copper assays, when melted, over 99 per cent pure and contains oxygen as the sole impurity. This copper is disposed of without further purification. The chief advantage of the process over other metallurgical procedures consists in its simplicity of construction and operation; no skilled labor is necessary and fewer men are required per ton of ore treated. The actual recovery of metallic copper approximates 90 per cent. The mechanical arrangements are such that the processes of dissolution and precipitation are continuous. Heat is conserved by returning the hot precipitated solution through a heat exchanger in countercurrent to the flow of fresh solution to the precipitator. The latter is a lead-line cylinder through which the solution flows from bottom to top. The necessary temperature is obtained by circulating oil of high flash-point from a heater through the jacket surrounding the lead lining. Precipitated copper is discharged through a bottom gate into a receptacle, from which it is periodically removed, washed and melted. An interesting phase of this research work and one of prospective economic importance is a process of concentrating the sulfur dioxide fumes or other gases weak in that constituent, which has been developed by Mr. G. A. Bragg. The plant was in continuous operation for one year, when it was decided to close down in order to increase the daily capacity and t o install this method of concentrating sulfur dioxide. MELLONINSTITUTE O F INDUSTRIAL RESEARCH PITTSBURGH. PA.
THE IMPORTANCE OF T Z E FLOTATION PROCESS IN THE METALLURGY OF COPPER By E. P. MATHEWSON The flotation process has revolutionized the metallurgy. of copper. Recently constructed plants, costing millions of dollars, have been discarded or scrapped and the flotation process introduced. Notable examples of this are the Washoe Reduction Works a t Anaconda and the plants of the Utah Copper Company a t Garfield, Utah. It took considerable time t o convince the copper metallurgists of the country that the flotation process was a success, but as soon as a satisfactory demonstration of the process was made, which occurred after numerous failures, these metallurgists took up the new process with avidity, scrapped their old plants and rebuilt t o adopt this modern system of concentration. The Mining and Scienti$c Press of San Francisco, under the able direction of T. A. Rickard, has published an immense amount of information about flotation and has given out the following figures, which are astounding when one considers 1 Among
the ores treated were silicious ores containing approximately
70 per cent of Si02 and high-lime ores running about 25 per cent of CaO. The excess acid resulting in the treatment of silicious ores was used in the extraction of copper from ore high in lime.
Vol. 9 , No.
II
that the application of the process on anything more than an experimental scale is only a few years old: FLOTATION-THELE.4DISG PROCESS I N THE METALLURGICAL FIELD TREATMENT Tons per Annum F1,OTATION. ....................... 30,000,000 Copper smelting. 26,000,000 Gravity concentration. 25.000.000 Gold and Silver milling. 13,000,000 Lead smelting. ........................ 5.500.000 Copper leaching.. ..................... ?.000.000 1,000,000 Zinc smelting. ........................
...................... ................ ...............
Of the figures given above, that for copper leaching is, perhaps, a little low, but it is so much smaller than the figure for flotation that it does not signify. Prior to the adoption of the flotation process in copper concentration the losses were seldom less than The 20 per cent, whereas now they are seldom over 8 per cent. figures published by the Anaconda Copper Mining Company indicate that the concentration loss in the most modern gravity concentration plant in existence was 17 per cent; now, with flotation, the loss is given a t a trifle over 4 per cent. Other large establishments can show equally amazing results. The savings are now so great and the economies so extensive, due to the introduction of the process, that the so-called hold-up by owners of patents on the process cannot possibly cripple the users of the process, even if exemplary damages be allowed by the Courts. The slime problem, the bugbear of copper metallurgists for a generation, has been solved by flotation. Many copper metallurgists will recall the numerous experiments conducted with a view to recovering the values from slime and the enormous sums of money expended in putting up plants that recovered only 60 per cent of the values from these slimes and which were considered marvels in their day. These plants, like the concentrators, have gone into the discard and now from the most pernicious slimes, savings of 90 per cent of the values by means of the flotation process are quite common. Strange to say, the process is a rule-of-thumb development. The practical application of the process was first made on an extensive scale with zinc. Copper metallurgists never imagined in those days that the process would ever be applied in their specialty, but to-day the tonnage treated by the process is largely made up of copper ores, zinc long ago taking a secondary position. Each particular ore seems to require a special treatment. This is because no satisfactory theory has as yet been evolved regarding the process. Many students are working on the problem with some promise of success, but a t this writing we know less about flotation itself than we do about the true nature of electricity, while the results of the flotation process are as well known as the effects of electricity, Naturally, a process creating such enormous profits and handling such large tonnages has produced a great amount of litigation. We have had cases involving millions of dollars tried in various courts and the end is not yet. However, as indicated above, there is money enough in the process t o pay for all the litigation and still leave a good return on the investments. BRITISH AXERICANICKEL CORPORATION, LTD. TORONTO, CAKADA
CHEMICALS USED IN ORE FLOTATION’ By OLIVGRC. R A L S T O NA ~ N D L. D. Y U N D T ~
The flotation of minerals from ore-pulps, as practiced a t present, involves the use of a small amount of a flotation “oil” which so modifies the water in the pulp that a froth is formed and that certain valuable minerals are gathered in the froth. The froth must have sufficient persistence t o allow time for Published by permission of the Director, U. S. Bureau of Mines. Metallurgist, U. S. Bureau of Mines. Salt Lake City Station. 8 Metallurgical Research Fellow, University of Utah, 1916. Now Metallurgist, Stimpson Equipment Co., Salt Lake City. 1 2
