On the Reduction of Sulphuretted Lead Ores in Utah and Nevada.
TO THE EDITOR : Sir—The smelting of lead ores in Utah and Nevada has, so far, been almost exclusively confined to oxidized, or so-called carbonate, ores. We must expect, however, that, as soon as the mines have reached a greater depth, sulphurets will take the place of oxidized ores. In some mines this change has already taken place before reaching the water-level. As a prominent example, I mention the Winamuck mine, in Bingham Cañon, Utah. The sul-phurets in this mine are composed of pyrites of iron, galena, zinc blende, and pyrites of copper, which occur in part massive and in part enclosed in a very hard quartz. All these sulphurets carry silver and some gold. I estimate their relative proportion to be about as follows, viz.: 72 per cent, pyrites of iron, 22 per cent, galena, 4 ½ per cent. zinc blende, 1 ½ per cent, pyrites of copper, with from 7 oz. to 100 oz silver per ton. The proportion of gold to diver is about 1 oz. of gold for every 320 oz. of silver.
My ideas in regard to the treatment of such ores are as follows:
In the first place, the ore is to be sorted into three classes:
1st. Ore with galena predominant.
2d. Ore with pyrites of iron predominant.
3d. Ore with quartz predominant.
Each class, separately, is to be subjected to a process of concentration, in order to get rid of the worthless and refractory gangue, and to separate the different sulphurets from each other. The concentration of such ores is not an easy task. I have reason to believe that a large percentage of the silver is not chemically combined with the sulphurets, but occurs as silver-glance, which per-meates and incrustates the whole mass. Consequently, concentration by water would undoubtedly cause a heavy loss in silver by floating off the fine silver- glance in slimes. I, therefore, propose KROM'S system of dry-air concentration, which seems admirably adapted for this esptcial case. This mode would have another advantage, because it furnishes all products in a dry state, which is very desirable, as all ores must be subjected to a process of roasting.
After concentration, I propose to treat the ore by the following processes:
1st. Roasting and sintering the galena with so much pyrites of iron, and quar-tzy ore, as is necessary for the formation of an easily fusible slag.
The roasting of galena is done in Europe, where the roast-reduction process is in vogue, in reverberatory furnaces. But here, reverberatory furnace roasting is altogether too expensive and out of the question. I believe that the Stete'eldt furnace, generally used for chloridizing or roasting of silver ores, could also be successfully introduced for roasting gahna, if some slight changes were made in its construction. I estimate the cost of roasting in this furnace to be from $2 to $3 per ton.
2d. Reduction of the roasted ore in the blast furnace with the addition of old slags.
The smelting of roasted ore in the blast furnace would be much easier and cheaper than at present with refractory carbonate ores. The expensive iron ore as flux would be entirely discarded, the capacity of the furnace increased and consequently much labor and coal saved. I believe that the cost of smelting would be reduced 30 per cent, compared with present figures.
3d. Roasting of the surplus pyrites of iron, quartz ore, zinc blende, and dust from Krom's concentration with salt in the Stetefeldt furnace to chloridize the silver.
4th. Amalgamation of the roasted ore to extract gold and silver.
By this system we may not only expect a cheapening in the cost of reduction, but also much better results in regard to the percentange of lead and the precious metals as compared with present methods C. A. STETEFELDT.
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