As representative of wet-dressing practice, the Anaconda scheme may be noted, as summarised below.
There are eight mills, each treating 1,000 tons of ore per day, and conducting the—
- Coarse crushing in Blake crushers.
- Coarse sizing by trommels.
- Coarse separation on Harz jigs of 1¼-inch and ⅞-inch feed.
- Middlings crushing in rolls.
- Middlings sizing by trommels.
- Middlings separation on fine jigs of 7, 5, 2½, 1½, and 1 millimetre feed.
- Finest crushing in Huntingdon mills.
- Fines settling by spigot settlers.
- Fines separation on Wilfley tables (471 are in use on the plant).
The muddy water goes to enormous settling ponds, where the slime settles down, gradually drains, and dries, and it is afterwards used for various purposes during the smelting operations; being dug out in the form of a fine clay. A new form of centrifugal apparatus (the Peck) is now being installed for the separation of this material. The subsequent treatment of the products from the concentrating operation is indicated in the diagram (fig. 12), from which it will be seen that the—
- Coarse Concentrates, 1¼, ⅞ (and ⅜) inch size, are smelted in the blast furnaces.
- Fine Concentrates, 7, 5, 2½, 1½, and 1 millimetre size, pass to the roasters, and thence to the reverberatory furnaces.
- Slimes are used for briquetting, and several other operations. Tailings pass to the dump.
Fig. 12.—Outline of Smelting Scheme at the Anaconda Smelter, Montana, U.S.A.
B. Agglomeration of Fines.—It has just been seen that the wet concentration of ores (considered advisable in a large number of cases) results in the production of a considerable quantity of fine concentrate, a form of material not well suited for immediate blast-furnace treatment.