Ores are smelted raw if the fall of matte (metallic sulphide) does not exceed 5%; otherwise they are subjected to a preliminary oxidizing roast to expel the sulphur, unless they run too high in silver, say 100 oz.
The slag and matte formed float upon the lead in the crucible and are tapped, usually together, at intervals into slag-pots, where the heavy matter settles on the bottom and the light slag on the top. When cold they are readily separated by a blow from a hammer.
The leading products of the blast-furnace are argentiferous lead (base bullion), matte, slag and flue-dust (fine particles of charge and volatilized metal carried out of the furnace by the ascending gas current).
Sulphuretted hydrogen, obtained by treating iron sulphide or a coarse matte with dilute sulphuric acid, is forced in similarly.
The lowest layer of the molten mass is principally metallic bismuth, the succeeding layers are a bismuth copper matte, which is subsequently worked up, and a slag.
In the wet process the ores, in which the bismuth is present as oxide or carbonate, are dissolved out with hydrochloric acid, or, if the bismuth is to be extracted from a matte or alloy, the solvent employed is aqua regia or strong sulphuric acid.
When the former is used it is roasted with calcium sulphate or alkali waste to form a matte which is then blown in a Bessemer converter or heated in a reverberatory furnace with a siliceous flux with the object of forming a rich nickel sulphide.
The process adopted for the Canadian ores, which are poor in copper and nickel, consists in a preliminary roasting in heaps and smelting in a blast furnace in order to obtain a matte, which is then further smelted with a siliceous flux for a rich matte.
This rich matte is then mixed with coke and salt-cake and melted down in an open hearth furnace.
For a wet method of extraction of the matte see Christofle and Bouilhet, French Patent 111591 (1876).
The roasted ore is then smelted to a mixture of copper and iron sulphides, known as copper " matte " or " coarse-metal," which contains little or no arsenic, antimony or silica.
The matte is treated either in reverberatory furnaces (English process), in blast furnaces (German process), or in converters (Bessemer process).
The " American process " or " Pyritic smelting " consists in the direct smelting of raw ores to matte in blast furnaces.
The " English process " is made up of the following operations: (i) calcination; (2) smelting in reverberatory furnaces to form the matte; (3) roasting the matte; and (4) subsequent smelting in reverberatory furnaces to fineor white-metal; (5) treating the fine-metal in reverberatory furnaces to coarseor blistercopper, either with or without previous calcination; (6) refining of the coarse-copper.
The " Welsh process " closely resembles the English method; the main difference consists in the enrichment of the matte by smelting with the rich copper-bearing slags obtained in subsequent operations.
It is made up of the following operations: (z) calcination, (2) smelting in blast-furnaces to form the matte, (3) roasting the matte, (4) smelting in blast-furnaces with coke and fluxes to " black- " or " coarse-metal," (5) refining the coarse-metal.
The " AngloGerman Process " is a combination of the two preceding, and consists in smelting the calcined ores in shaft furnaces, concentrating the matte in reverberatory furnaces, and smelting to coarse-metal in either.
In America the usual method is to roast ores or concentrates so that the matte yielded by either the reverberatory or cupola furnace will run from 45 to 50% in copper, and then to transfer to the Bessemer converter, which blows it up to 99%.
But even when the old type of reverberatory is preferred, as at the Argo works, at Denver, where rich goldand silver-bearing copper matte is made, the growth of the furnace in size has been steady.
The low percentage of sulphur in the roasted ore is little more than enough to produce a matte of 40 to 45%, and therefore the escaping gases are better fitted than those of most copper cupola furnaces for burning in a stove.
As the matte contains on an average o.
The largest furnaces are those of the Boston & Montana Company at Great Falls, Montana, which have put through soo tons of charge daily, pouring their melted slag and matte into large wells of io ft.
A combined brickand water-cooled furnace has been adopted by the Iron Mountain Company at Keswick, Cal., for matte concentration.
One of the earliest and most exhaustive series of experiments was made on Rio Tinto ores at the John Brown works by John Hollway, with the aim of both smelting the ore and concentrating the matte in the same furnace, by the heat evolved through the oxidation of their sulphur and iron.
The difficulty of effecting this double object in one operation was so great that in subsequent experiments the aim was merely to concentrate the matte to metallic copper in converters of the Bessemer type.
Practice, however, in treating copper matte differs essentially from the treatment of pig iron, inasmuch as from 20 to 30% of iron must be eliminated as slag and an equivalent quantity of silica must be supplied.
The quantity of air consumed in a converter which will blow up about 35 tons of matte per day is about 3000 cub.
The operation of raising a charge of so% matte to copper usually consists of two blows.
The matte also, in all economically planned works, is conveyed, still molten, by electric cranes from the furnace to the converters.
When lead or zinc is not present in notable quantity, the loss of the precious metals by volatilization is slight, but more than 5% of these metals in the matte is prohibitive.
Under favourable conditions in the larger works of the United States the cost of converting a 50% matte to metallic copper is generally understood to be only about 1 o to iw of a cent per lb.
Pyritic smelting is a development of the Russian engineer Semenikov's treatment (proposed in 1866) of copper matte in a Bessemer converter.
Since John Hollway's and other early experiments of Lawrence Austin and Robert Sticht, no serious attempts have been made to utilize the heat escaping from a converting vessel in smelting ore and matte either in the same apparatus or in a separate furnace.
Lump ore alone was fed, and the resulting matte showed a concentration of only 3 into i.
When, however, a hot blast is used on highly sulphuretted copper ores, a concentration of 8 of ore into i of matte is obtained, with a consumption of less than one-third the fuel which would be consumed in smelting the charge had the ore been previously calcined.
The resulting matte runs 25%.
A portion of the white metal is calcined to such a degree of oxidation that when fused with the unroasted portion, the reaction between the oxygen in the roasted matte and the sulphur in the raw VII.
If it contains more than 55% of copper it is directly refined, while if it contains a lower percentage it is smelted with matte or calcined copper pyrites.
Many attempts have been made to use crude sulphide of copper or matte as an anode, and recover the copper at the cathode, the sulphur and other insoluble constitutents being left at the anode.
Gaz., 1907-1909); Matte, Recherches sur l'appareil libero-ligneux des Cycadacees (Caen, 1904).