About three years ago John Hays Hammond took over the control of the Eureka Metallurgical Co., at Salt Lake City, Utah. Funds were advanced for investigating the process invented by R. V. Smith, for concentrating oxidized lead ores. A great deal of laboratory work was done and a reagent was developed by C. M. Nokes of Salt Lake, which was found to be particularly suitable for oxidized copper ores, refractory manganese silver ores, and oxidized gold ores. After sufficient laboratory work had been
performed to demonstrate the fundamental principles of these inventions, a test mill, having a capacity, of 20 tons of ore daily, was erected at Murray, Utah.
In this test mill approximately 1200 tons of various types of ores have been concentrated by means of the above-mentioned process and reagents, and this large-scale work as well, as laboratory work is being continued at present. Details of these mill tests are given in Table 1, and a representative group of laboratory tests are shown in Table 2.
The process requires no special machinery or apparatus. Its success depends entirely on the method of preparing the pulp and its subsequent flotation in clean water, as outlined in the Smith patent. The reasons for the success of the Nokes special reagent are not definitely known. The outstanding feature, which seems to be of extreme importance, is that when the concentrates are examined under the microscope, each particle of mineral appears to have a particle of paraffin attached to it. This paraffin-mineral combination seems to be particularly suitable for flotation and it follows that any coating oils readily attach themselves to the paraffin-mineral combination.
The costs for this process are the usual milling and flotation costs, with an additional charge due to the use of sodium sulfide and larger quantities of oils. This additional charge will vary from 30 to 75 c. per ton of ore treated. If paraffin-sodium sulfide combination is used, a large amount of paraffin is subsequently recovered for re-use by merely heating the concentrate, suspended in water, whereupon the paraffin rises to the top and can be skimmed.
Extracts from the patent specifications of the two above-mentioned inventions will possibly be interesting.
Charles M. Nokes Patent (U. S. No. 1,444,552; issued Feb. 6, 1923)
In a typical instance of the use of my process, I employ in the preparation stage, a solid hydrocarbon, such as paraffin, and an alkaline sulfide, such as sodium-sulfide, the ore under treatment being a non-sulfide ore, or a mixture of sulfide and non-sulfide ores. The paraffin and the sodium-sulfide are fused or mixed together at a temperature sufficiently high to permit of the liquefaction of the hydrocarbon. To effect this I may pulverize the sodium-sulfide to say 100 to 250 mesh. I next melt the paraffin, and then make a paste by mixing the paraffin and the pulverized sodium-sulfide. This paste, as it cools, solidifies into an apparently homogeneous mass. If this be allowed to solidify without stirring, it becomes hard and flinty and must be pulverized before addition to the tube mill. But stirring seems to give it a more or less granular condition, somewhat lumpy, and suitable, when broken into fragments, for the tube mill. It is introduced into the tube mill along with the ore, to be ground into pulp, or it may be introduced into the pulp after the ore has been ground and passed to emulsifiers.
It should be understood that this mixture is not a froth or scum maker, or “lifter,” and therefore other oils are added, such as pine oils, to expedite the formation of a certain amount of froth or scum wherein the particles of the mixture collect and with which they may be removed from the flotation cell. The function of the paraffin-sodium-sulfide mixture is one of preparation, and not one of flotation or frothing. It acts upon non-sulfide or oxidized ores so that in the flotation stage they float, while the gangue remains submerged. Certain lifting oils, like Yaryan pine, which will not lift oxidized ores direct, will do so after the
addition of the paraffin mixture. If the lifting oils were omitted, the paraffin-sodium-sulfide mixture alone would give flotation in the flotation stage, but the scum would be too sparse to remove with sufficient rapidity; it would be very sparse and very rich, made up of a vast number of particles of paraffin of minutest size, each one solid and with the mineral particles or values clinging to it.
The amounts of the mixture employed, and the ratios between paraffin and sodium-sulfide vary. On oxidized copper ores I have used six to ten pounds, per ton of ore, of sodium sulfide, and the same amount of paraffin. On other ore I have used ten pounds of the sodium sulfide and seven and one-half pounds of paraffin. In this case I used thirteen pounds per ton of ore of the lifting oils, etc.
Reinold V. Smith Patent (U. S. No. 1,459,167; issued June 19, 1923)
The ore to be treated is prepared as usual, that is to say, it is broken up and crushed to the desired condition of fineness, and if desired the disintegrated material may be separated into granular and slimes portions, these being subjected to substantially the same treatment, thereafter, but separately.
One of the important features of the process is in the fact that the finely divided ore, in a thick water pulp, is treated with an oil or other substance, such as petroleum sludge, for instance, in the presence of a soluble sulfide, with the object of preparing the pulp so that the particles that it is desired to concentrate may be floated in the subsequent steps of the process. Where oil is used it may be added to the thick pulp in a suitable apparatus.
After the pulp has been treated as described in the preceding paragraph, the water, including such preparation substances as remain with it, is separated, the thoroughly mixed dewatered pulp is diluted with several times its volume of new water which is not effectively contaminated by the preparation substances, and is then discharged into a flotation cell, wherein concentration is accomplished in the usual way.
It will be understood that the process divides itself naturally into two parts, i.e., preparation of the finely divided ore in a thick pulp, and flotation of mineral-particle components thereof in a dilute pulp. Further, instead of removing the water of preparation I may form the thin flotation pulp by dilution with quantities of new water, sufficient to substantially eliminate the deterrent effect of remanent sulfidizing agents.
The granular portions of the ore, and the slimes, may be treated separately by the steps above described, and the preparation water from the sands pulp be re-used in the preparation of a fresh supply of slimes, while that from the slimes pulp, is re-used in the preparation of fresh supplies of sands.
The test mill of the company is equipped with a 4-ft. Hardinge tube mill; drag classifier; ball-mill classifier; small tube mill; two Janney flotation machines; a Fahrenwald flotation machine, and a small American filter. There are also two Dorr thickeners. Preliminary crushing for all test work is done at the local ore testing plant. The mill is so equipped that the flowsheet can be varied to every possible combination. Work up to date has clearly demonstrated that all laboratory results can be duplicated in the test mill and that the quantities of oils and chemicals required in the laboratory machine can be reduced about 40 per cent, when the same ore is put through the mill. In nearly all cases the concentrate produced in the mill is of higher grade than that in the laboratory tests.