The principal ores of nickel are magnetic nickeliferous pyrites, nickel arsenides (especially kupfer nickel, and nickel arseno-sulphide or grey nickel), and the hydrosilicates of nickel and magnesia.

The first-named ore is simply magnetic pyrites containing a certain proportion of nickel sulphide, and is one of the most important. It is met with in Spain, Sweden, Scotland, Piedmont, and the United States. The nickel yield of this kind of ore is usually very small. That from Val Sesia (Piedmont) contains about 1 1/2 Per cent. nickel; that from Sagmyra (Sweden) about 1/2 per cent.; those from Scotland, 7 to 22 (rarely) per cent.; while the celebrated Gap mine, in Lancaster Co., Pennsylvania, which supplied all American wants, and even contributed to European supplies for many years, affords an ore containing only 3 Per cent. of nickel, and very difficult to work.

Kupfer nickel is less abundant but richer than the preceding, and occurs in veinlets, especially in Scotland and Saxony. The percentage of nickel varies from 20 to 30.

Arseno-sulphide or grey nickel is met with more particularly in the Harz, Sweden, and Styria. The percentage of grey nickel, corresponding to the formula Ni2AsS2, is 35-48.

The hydrosilicates of nickel and magnesia are obtained chiefly from New Caledonia, and carry about 10 Per cent. of nickel.

Processes Of Extraction

The processes employed in obtaining nickel differ widely, according as it is derived from the sulphuretted or arseniuretted ores commonly found in Europe, or from the oxidized ores of New Caledonia. For the former, the first step is the elimination of the two metals nickel and cobalt in an intermediate product called "matte" or "speiss," according as the original ore was a sulphide or an arsenide; these products are then gradually concentrated by a succession of roastings and fusions; finally, there remain oxides of nickel and cobalt, which are reduced in a closed retort.

For the New Caledonian ore, the most interesting of the methods employed is related to the metallurgy of iron: the initial operation is to make a pig of iron and nickel, followed by a refining process on the hearth of a reverberatory furnace, to remove the foreign matters and give pure nickel.

Treating Sulphides

By sulphides are understood magnetic pyrites containing small proportions of the sulphides of nickel and cobalt, with 50 Per cent. of gangue. In treating this ore by the dry method, the following observations have been made:-(1) In the presence of an acid silicate, the nickel sulphide is not nearly decomposed, while the cobalt sulphide is so completely, and a part of the cobalt is lost in the slag; (2) run down with a material containing sulphur, the nickel oxide is decomposed, and all the nickel combines with the sulphur, while with the cobalt oxide the reaction is only partial; (3) under the same conditions, that is to say in contact with sulphur free or combined, nickel silicate is only partially decomposed, cobalt silicate not at all. Consequently, the object must be to slowly oxidize the matters other than the nickel and cobalt, so that they can be easily removed in the cinder, while the nickel and cobalt are retained by the sulphur in the mattes formed; but care must be had to avoid the oxidation of these 2 metals, and especially their silication. The first roastings are generally effected in stalls; the oxidation is achieved by preference on the hearth of a reverberatory furnace.

The roasting is much more moderate according as there is more cobalt, and greater care is needed to avoid scorification. The first fusions are made in a blast furnace, and the last in a reverberatory.

The Sagmyra works, in Sweden, treat very poor ores, containing 0.6 Per cent. nickel and 0.7 copper. The roasting of the ores is done in pyramidal heaps of 300 to 400 tons, and lasts 3 to 4 weeks. The first fusion takes place in a blast furnace measuring 12 ft. high between the level of the twyers and that of the throat.; the section is trapezoidal; 3 twyers are placed in the rear wall and 1 in each of the lateral ones, making a total of 5; a sixth opening is reserved in front for withdrawing the slag and tapping the matte; this last has a mean richness of 4 Per cent. nickel and 4 1/2 copper. Next comes another roasting; the first matte, in masses of about 25 tons, is put through 4 or 5 tires, the object of which operation is to oxidize a fresh quantity of foreign metals. This result is not attained without the nickel and cobalt- also oxidizing a little, but, as scorification is avoided, the reduction of the oxides thus formed is readily achieved. The roasted matters are smelted in another blast furnace 10 ft. high, with a closed breast: the new matte contains about 25 Per cent. nickel and 25 copper.

The second enriched matte is granulated at the moment of running out, then roasted in a rever-beratory furnace; the roasting lasts 24 hours, and the heat is furnished by the gases of the blast furnace of the first fusion. A final fusion on the hearth of a reverberatory furnace gives a matte holding 35 Per cent. nickel, 40 of copper, and less than 1/2 of iron. Efforts have been made to suppress the second roasting and second fusion; in that case the first matte is granulated and treated with weak sulphuric acid, by which a great part of the iron is dissolved out, and but little of the nickel, thus separating the iron and nickel; but the process has the inconvenience of producing a great quantity of iron sulphate, which is not always marketable.

Treating Arsenides

Arsenides, like sulphides, are subjected to a series of roastings and fusions: the nickel and cobalt are at once united by the first fusion in a new product termed "speiss," a complex mixture of arsenides formed with all the metals contained in the ore; the nickel and cobalt are then concentrated in the speiss by freeing this latter of the more oxidizable metals which it contains. To regulate these operations, regard is had to the following peculiarities:- (1) Arsenides of nickel and cobalt, in presence of slag having 33 per cent. of. iron, oxide, scarcely yield any nickel or" cobalt; (2) nickel oxide fused in the. presence of arsenic or mispickel is entirely decomposed, the nickel uniting with the arsenic-this only partially takes place with cobalt oxide; (3) nickel silicate fused in presence of free or combined arsenic is partially decomposed, but cobalt silicate is much less attacked.