WORK OF OTHER INVESTIGATORS. The first patent covering sulphide-filming of oxidized minerals, followed by flotation of the artificial sulphides, was probably that of Schwarz, issued in 1905. Schwarz mentions recovery of the artificial sulphide by use of his own method of "bulk oil" flotation with a hydrocarbon, such as paraffin, which is solid at ordinary temperatures, the separation being made in hot solutions and the pulp permitted to cool in order to congeal the paraffin with the entrapped sulphides of lead. He mentions the use of any "soluble sulphide," and states that he generally uses more than the theoretical quantity of sulphur needed to convert the oxide, carbonate, or chloride completely to a sulphide. He claims any method of separating the artificial sulphide which employs concentration by the use of a hydrocarbon, by which one might infer that he can claim the use of froth flotation as at present day developed. The next mention of artificial sulphidizing and flotation of oxidized minerals is made by Sulman and Pickard in British patent 26019, of 1909. In this patent more different methods of sulphidizing the oxidized ore are mentioned and greater familiarity with actual testing of the ores by the proposed processes is shown than in any other sulphidizing patent. Besides oxidized copper ores, oxidized lead ores are mentioned as being adaptable to the process. Hydrogen sulphide and soluble alkaline sulphides are mentioned as possible sulphidizing agents; also a method of sulphidizing by the use of sulphur vapor is described. One variation of the latter method is to heat the powdered ore with FeS, in a neutral or reducing atmosphere, distilling one atom of sulphur from the FeS2, the freed sulphur combining with the oxidized ore. Terry describes a process for sulphidizing oxidized ores of copper (and other metals) by the use of hydrogen sulphide gas in flowing pulp, with suitable apparatus for recovery of any excess hydrogen sulphide gas after sulphidizing the pulp. A method for the use of sodium sulphide is also described, and of adding copper sulphate to aid the formation of nuclei of copper sulphide around which the formation of sulphide granules and coagulations can take place. Hovland and Frankforter,d in their process, use hydrogen sulphide gas on the dry ore to sulphidize the oxidized material previous to flotation. The advantage claimed is the greater rapidity of reaction. From the properties of gases as compared to solutions this claim • Schwarz, Alfred, Process of concentrating ores: U. S. patent 807501, Apr. 19, 1905. Sulman, H. L., and Pickard, H. F. K., Improvements in concentration of oxidized ores: British patent 26019, Nov. 10, 1909. C Terry, J. T., jr., Process for recovering metalliferous constituents of ores: United States patent 1094760, Sept. 8, 1913. & Hovland, H. B., and Frankforter, C. B., Art of treating metalliferous materials: United States patent 1098668, Dec. 12, 1913. seems justified, because the rate of diffusion of gas in the dry state is thousands of times that of the same gas dissolved in a solution. They state that 10 to 20 minutes' contact of the dry ore with hydrogen sulphide gas is sufficient before flotation. They even claim that the gas might be applied to the ore before mining. The gas, they state, will penetrate the oxidized capping of a body of copper ore, sulphidizing the oxidized forms of copper and disintegrating the mass so that it can be mined easily. a Bacon, in 1914, describes a process for using hydrogen sulphide and sulphur dioxide in pulp to aid flotation by means of the colloidal sulphur resulting from the reaction of the two chemicals on each other. The colloidal sulphur acts as a substitute for flotation oil. By introducing the hydrogen sulphide first, oxidized minerals can receive a sulphide coating before the excess of hydrogen sulphide is neutralized by the introduction of sulphur dioxide. This feature is described by Bacon in another patent in connection with some tests said to have been made on an oxidized copper ore. A few months later, Hovland took out another patent for the sulphidizing of minerals. A method for the flotation of oxidized copper ore is described. Sulphuric acid is first applied to the pulp to form a solution of copper sulphate. On the addition of calcium sulphide and ferric sulphate to the pulp, copper sulphide forms, which can be recovered by flotation. It is claimed that the reaction is greatly promoted by the ferric sulphate. Without the presence of the ferric sulphate, it is difficult to make the calcium sulphide react. Bacon has also patented a process for the use of hydrogen sulphide under pressure for sulphidizing. As stated before, practically all of the patents had reference to the oxidized ores of copper and little had been said regarding lead ores, except that various patentees claimed the application to lead carbonates and sulphates. Sulman and Pickard are the only ones that definitely describe the application of these processes to various lead ores. Hence it was decided to test the application of sulphide filming to the oxidized ores of lead, followed by flotation, as a method of ore concentration. SCOPE OF EXPERIMENTS. A rather extensive series of tests was outlined in testing various methods of sulphidizing, although a number of the methods were soon found to be impracticable. An outline of the different proposed methods follows: a Bacon, R. F., Flotation of minerals: United States patent 1140865, Aug. 14, 1914. d Bacon, R. F., Flotation of minerals: U. S. patent 1180816, Aug. 14, 1914. 1. Sulphidizing by treating the dry crushed ore with hydrogen sulphide gas. 2. Sulphidizing by leaching the crushed ore in a solution of hydrogen sulphide or by bubbling hydrogen sulphide through the suspended pulp. 3. Sulphidizing with solutions of the various sulphides of sodium. 4. Sulphidizing with solutions of the various sulphides of calcium. 5. Sulphidizing by passing sulphur vapor through the dry crushed ore. 6. Sulphidizing by flotation with a flotation oil containing loosely combined sulphur in the oil molecule. Such oils may be called "sulphureted" oils. 7. Sulphidizing with colloidal sulphur solutions. For each of these methods many tests would be necessary to determine the best length of time to apply the sulphidizing agent, whether the mineral formed needed to be floated in neutral, alkaline, or acid solutions, whether certain flotation oils would be better. than others in flotation of the filmed sulphides, and other problems. The complete testing of all these variables would be an immense undertaking, and therefore many "short cuts" to results that were worth while had to be used. This called for a great deal of the "cut and try" type of research work, and the results are hence difficult of tabulation. It is almost necessary that a flotation test man be an opportunist and when he sees a test yielding poor results to change the flotation or other conditions immediately, in order to save a test that might otherwise prove to bo only the waste of an hour's time. SULPHIDIZING WITH DRY HYDROGEN SULPHIDE. Hydrogen sulphide, as a metallurgical reagent, was used as a precipitant in the old chlorination processes of extracting gold from its ores, but since the displacement of chlorination by cyanidation it has fallen into disuse. The development of the hydrometallurgy of copper gave some promise of reviving its use, but both electrolytic and scrap-iron cementation methods of precipitation of copper permit the direct production of metallic copper, so hydrogen sulphide was again discarded. FORMER ATTEMPTS TO USE HYDROGEN SULPHIDE. In spite of the fact that the use of hydrogen sulphide has been repeatedly introduced and discarded by the metallurgical profession, this reagent is still of good repute among chemical engineers, because it can be produced cheaply. The chief reason for not using hydrogen sulphide has not been the cost of production, but rather the fact that better metallurgical methods made its use unnecessary. The best-known method of making hydrogen sulphide gas is to treat ferrous sulphide (iron matte) with a dilute solution of sulphuric acid. Iron matte can be made in almost any smelter, by distilling half the sulphur from pyrite, at a cost not to exceed $5 per ton of matte. Sulphuric acid is available in most mining districts at $5 to $25 per ton, so that the ultimate cost of hydrogen sulphide per ton of gas, everything considered, will be $30 to $60. Another old method of making hydrogen sulphide is by the ClausChance process, in which calcium sulphide is treated with carbon dioxide gas in one form or another, according to the reaction: CaS+H2O+CO2=CaCO3+H2S Still another method of making hydrogen sulphide is by passing sulphur vapor and hydrogen or hydrocarbon gases through a heated vessel in the presence of the proper catalytic agents, such as charcoal. About 450° C. is said to be the most favorable temperature. During 1914 and 1915 a number of attempts were made to use hydrogen sulphide in some of the concentration mills of the Southwest where sulphide ores of copper carrying some oxidized minerals were being concentrated. The gas was usually introduced directly into the flotation machines and the atmosphere of the mills, as a result, became unbearable. Hydrogen sulphide gas acts like a narcotic poison and the men working in it finally suffered from nervous demoralization. Any use of such a chemical in a mill must be made in machines that will not permit it to escape into the atmosphere of the mill. Successful machinery for this use is described by Callow.a RESULTS OF TESTS AND DISCUSSION OF RESULTS. The results of applying dry hydrogen sulphide gas to dry crushed ore, for three different Utah ores, are given in tables 36 and 38. The tests in Table 36, on material from the May Day mine, were made to investigate a number of points. Tests 1 to 5 and tests 6 to 10 were made respectively by dry sulphidizing followed by flotation in neutral and acid solutions, with the idea of determining what length of treatment of the ore with the hydrogen sulphide gas was necessary. The results of the first five tests show that treatment of the ore with hydrogen sulphide gas in the dry state, followed by flotation in neutral solutions, did not give satisfactory extractions. The best results in these tests were with prolonged treatment with hydrogen sulphide. Considerable heat was generated by the reaction and the ore was quickly blackened by the action of the gas. A well sulphidized sample of ore could be poured through the air after sulphidizing with the result that it as quickly reoxidized. The iron analyses show that some of the iron was also sulphidized and accompanied the lead. a Callow, J. M., Notes on flotation, 1916: Bull. Am. Inst. Min. Eng., 1917, pp. 245-275. |