The technical results obtained in the smelting of an ore of the above mentioned composition are as follows:
| Ordinary Method | Bormettes Method | |
|---|---|---|
| Coke, per cent. of the charge | 14 | 12 |
| Blast pressure, water gage | 12 to 20 cm. | 12 to 14 cm. |
| Tons of charge smelted per 24 hr | 20 | 25 |
| Tons of ore smelted per 24 hr | 8 | 10 |
| Lead assay of slag | 0.80 to 0.90% | 0.20 to 0.40% |
| Matte-fall, per cent. of ore charged | 5 to 10 | 10 to 15 |
| Lead extraction | 90% | 92% |
| Silver extraction | 95% | 98% |
Fig. 24.—Latest Form of Converter. (Section on C D.)
The higher extractions of lead and silver are explained by the fact that the loss of metals in roasting is reduced, while, moreover, the slags from the blast furnace are poorer than in the ordinary process of smelting. The economy in coke results from the greater quantity of sulphur which is utilized as fuel, and from the increased fusibility of the charge for the blast furnace.
The new system of desulphurization enables the charge to be smelted with a less quantity of fresh flux, by the employment in its place of a greater proportion of foul slag. The reduction in the necessary amount of flux is due not only to the increased fusibility of the agglomerated charge, but principally to the fact that in this system the formation of silicates of lead (which are produced abundantly in ordinary slag-roasting) is almost nil. It is therefore unnecessary to employ basic fluxes in order to reduce scorified lead.
Fig. 25.—Latest Form of Converter. (Plan.)