Papers - Lead - Lead Blast-furnace Practice at Trail, B. C.

Lead blast-furnace work at Trail is unique in that this is the only plant in the world where blast-furnace smelting on a large scale for both lead and zinc recovery is carried on under one management. On this account the factors that determine economic practice differ from those of other lead smelters. In addition to this different metallurgical outlook, a great deal of structural investigation has been carried on, which has resulted in the development of a furnace which should prove of interest to all who are faced with similar problems. This description may be conveniently divided into various heads as follows: (1) General—make-up of charge, etc.; (2) structural—(a) hoods and charging methods, (b) shaft construction, (c) crucible construction; (3) handling slag; (4) handling bullion; (5) metallurgy. The Charge The Trail plant is an old one, on a congested site. As with most old plants, this limits the method of charge preparation. In general, lead metallurgists will agree that sinter when it reaches the blast furnace should contain as small an amount as possible of actual fines. There would be some difference of opinion as to the maximum size as well as of the minimum required, but to obtain the optimum condition some form of screening is indicated. This screening should take place immediately before the blast furnace if possible, and because sinter deteriorates in storage there should be as little as possible. There should also be the minimum amount of handling between the sinter machines and the furnaces. Unfortunately, at Trail the sinter must be handled considerably before it is charged to the furnace, and no feasible scheme of screening has yet been devised. Trail practice, then, demands that the sinter be a strong one physically. Dependent upon the amount of lead in it, it has been found advantageous to incorporate granulated slag into the final sinter, the amount varying inversely as the lead content. The addition of this slag makes a harder sinter, which arrives at the blast furnace in a better condition, but it entails some lack of efficiency, because desulphuriza-tion is not so rapid nor so complete.