TABLE 42.-Average results of sulphidizing miscellaneous materials.

DISCUSSION OF RESULTS.

The tables show that the extractions of silver, when present, were usually lower than the extractions of the lead. This result was unexpected, as the writers had been led to believe that the silver in such materials was intimately associated with the lead. Grinding the sample to the fineness necessary for flotation (passing 60 mesh) evidently freed the silver to a large extent, as far as these results are concerned.

The crushed ore could probably be treated with sodium sulphide solution in Dorr thickeners by adding solution to the inflow. The overflow of clear solution, containing some sodium sulphide, could be brought to the proper strength by adding strong sodium sulphide solution from a drip, and returned to join the inflow. If the solution should become too alkaline, it would have to be either thrown away or neutralized and oxidized. Tests to determine the maximum alkalinity permissible showed that solutions containing proportions ranging up to 0.3 per cent of sodium hydroxide could be successfully used in flotation of many ores, but that with more than 0.3 per cent the froth was often too tough and leathery and the flotation was not selective. When a longer time of contact with the sodium sulphide solution than that necessary to pass through the Dorr thickener was required, some form of agitator that does not utilize a jet of air would be necessary. Tests of agitating a pulp with air while sulphidizing showed serious oxidation of the sodium sulphide and of the artificial lead sulphide, so that practically no blackening of the particles took place. A series of Dorr classifiers or a tube mill containing no grinding balls are machines that could meet the requirements of nonaeration combined with agitation of the pulp.

The interfering elements that prevent successful sulphide filming of lead carbonate ores were gradually isolated during the course of this investigation. In a number of instances materials were tested that would give no extraction of lead by sulphide filming and flotation. From the flotation tailing a streak of white lead carbonate could be separated on a gravity concentration table. This carbonate had seemingly not been sulphidized, some constituent in the ore combining with the sodium sulphide before it had time to act on the lead. A number of the minerals that caused trouble were identified. In the ore from the Chief Consolidated mine of Eureka, Utah, it was possible to identify a large amount of basic sulphates of iron, such as utahite and jarosite. These combine vigorously with sodium sulphide and become black, but are nonfloating. Manganese dioxide minerals also combine vigorously with sodium sulphide, oxidizing it to thionates and thiosulphate, and hence cause trouble. Enough sodium sulphide to satisfy these compounds must be added before

the lead minerals can be sulphidized. In the Michigan-Utah mine in Alta, Utah, is a lead carbonate ore containing both manganese dioxide and basic sulphates of iron. Attempts to remove these compounds have thus far been unusccessful, because the basic sulphate of iron is insoluble in water, as is also the manganese dioxide. The use of acids to remove them is not practicable, owing to the high percentage of lime and other acid-consuming elements usually present in these ores. Sulphur dioxide will "bleach" the manganese dioxide, but it forms di-thionates, which are deleterious to flotation. The presence of these minerals, which are fairly common, owing to the fact that they have their origin in oxidation of sulphide ores, probably explains the difficulty of floating certain carbonate ores of lead. Where an ore is not refractory to sulphidizing and flotation, this method is a useful one.

CONCLUSIONS AS TO RESULTS OF TESTS WITH SODIUM SULPHIDE.

The conclusions reached from the tests with sodium sulphide as a sulphidizer previous to flotation are as follows:

1. Small quantities of sodium sulphide, varying from 2 to 40 pounds per ton of ore, will convert the lead carbonate of ordinary low-grade oxidized lead ores to a condition amenable to flotation.

2. The amount of sodium sulphide consumed is so small that evidently only a lead sulphide film is formed over the surfaces of the particles of lead carbonate.

3. The time of contact of the sodium sulphide with the ore should be varied according to the strength of the solution used and the properties of the ore. With a 1 per cent solution usually about two hours is required, although with some ores a much shorter period of contact suffices. Much better results are obtained when the sulphidized ore stands for a considerable length of time before flotation.

4. Air agitation during sulphidizing is to be avoided on account of oxidation of the sodium sulphide and of the lead sulphide.

5. Ores containing large amounts of colloidal alumina or iron, or basic sulphates of iron or alumina, or manganese dioxide minerals, are difficult to sulphidize and more difficult to treat by flotation. So far they have not been treated successfully by this method. Most oxidized ores contain one or the other of these deleterious constituents.

6. When silver minerals are present in the ore, the extraction of silver is usually 5 to 15 per cent lower than the extraction of lead.

7. Commercial sodium sulphide can be bought at a reasonable price, and the quantity required to sulphidize a ton of ore is small,

hence this phase of sulphidizing and flotation is distinctly promising from a commercial standpoint.

8. The polysulphides of sodium and the sulphydrate are acceptable substitutes for the normal sulphide, although they are usually not for sale on the market. The sulphydrate seems to be the most. active sulphidizing agent of all the sulphur compounds of sodium tested.

CALCIUM POLYSULPHIDE FOR SULPHIDIZING.

COMPOUNDS AVAILABLE FOR COMMERCIAL USE.

The sulphidizing compounds available for commercial use that have calcium as a base are the normal sulphide, CaS, the polysulphides, CaS and CaS, and the sulphydrate, Ca (SH),. They are prepared in exactly the same way as the sodium compounds, and, similarly, the sulphydrate has been found to be the most active. The normal sulphide of calcium is a by-product in the Le Blank process of soda manufacture, but unfortunately is only slightly soluble. It can also be produced by the reduction of gypsum with carbon. The polysulphides of calcium can be prepared from quicklime and powdered sulphur and have the further advantage of being extremely soluble. The materials for the manufacture of calcium polysulphide are easily available; also it is on the market in both solutions and in powdered form, being used in agriculture as an animal dip and a fungicide. For these reasons more work was done with this reagent than with the others. The sulphydrate is likewise extremely soluble and better adapted for use than the normal sulphide.

RESULTS OF TESTS AND CONCLUSION FROM RESULTS.

The results of three tests with calcium polysulphide on the ore from the May Day mine of the Tintic district, in Utah, are shown in Table 43. At least 16 pounds per ton of ore seem to be necessary to get a satisfactory extraction of the lead, and recovery of the silver is very difficult. This latter point was observed in the tests with sodium sulphide on this ore, hence the inability to extract the silver in a satisfactory manner from this ore is not a peculiarity of calcium polysulphide.

TABLE 43.-Results of sulphidizing ore from May Day mine with calcium polysulphide. [Assay of heading: Lead, 4.5 per cent; silver, 2.8 ounces per ton.]

Calcium polysulphide, although somewhat more sluggish, is otherwise as satisfactory as sodium sulphide for sulphidizing and flotation.

OTHER METHODS OF SULPHIDIZING.

SULPHUR VAPOR.

Oxidized lead ores can be sulphidized by treating the heated, pulverized ore with sulphur vapor, but the mechanical difficulties of applying the sulphur vapor caused the writers to discard this method as impracticable. Sulphur boils at 445° C., and in order to apply the vapor to the ore a temperature above this point must be maintained. Lead carbonate begins to break up into lead oxide and carbon dioxide at about 200° C. and is very easily reduced to metallic lead, so that there is little need of using sulphur vapor on such an ore at the temperatures that are required to prevent the sulphur vapor from condensing. The application to copper ores would not be attended with the same objections, as the various copper compounds have much higher melting points than lead sulphide and lead oxide. Elemental sulphur can be bought at coastal points in normal times for $20 to $25 per ton. It can also be cheaply distilled from pyrite at smelters or reduced from roaster gases by using an excess of reducing agent at a high temperature. Its commercial preparation for use in such a process need not be considered here.

SULPHURETED FLOTATION OIL.

The use of a sulphureted flotation oil is also possible theoretically. Much petroleum containing loosely combined sulphur is being refined by the use of copper oxide, which forms copper sulphide and leaves