From the preceding considerations, the roastings are conducted in a manner to avoid oxidation, and especially silica-tization, of the nickel and cobalt. In general, reverberatory furnaces are used for the roastings; but for rich speiss, the first roastings are done in heaps. The fusion is performed in little cupola furnaces; that shown in Fig. 154 is of the form employed at Hopfriesen. The speiss once concentrated, the fusion is sometimes exchanged for a roasting in a "Hungarian" furnace, as illustrated in Fig. 155. Sufficient concentration is generally attained after 3 successive series of roasting and fusion; the table below, taken from the experience of the Georges works near Dobrina, in 1876, gives an example of the progressive character of the speiss; but sometimes the final richness is pushed as far as 65 to 70 per cent. of nickel and cobalts.

Fig. 154.

Nickel Ores Part 2 300161Nickel Ores Part 2 300162

Treating Very Poor Orel Worked For Other Metals

The preceding remarks refer only to ores which are sufficiently simple and rich to be worked chiefly or perhaps exclusively for their nickel and cobalt; but it is sometimes desirable to recover these metals from intermediate products which have been the chief consideration in treating the ore. For example, copper ores are met with containing so little nickel and cobalt as not to be worth dealing with for the direct extraction of these 2 metals. In this case, the treatment for copper extraction is proceeded with as if that were the only metal present; the nickel and cobalt concentrate with the copper in the matte, then by a fresh fusion in a cupola furnace, these metals are separated by favouring the formation of a speiss in which the nickel and cobalt are contained. To achieve this it may be necessary to add some sulphur or arsenic to facilitate the formation of the several compounds.

Fig. 156.

Treating Very Poor Orel Worked For Other Metals 300163

The poor ores thus treated are generally very complex, and contain at once antimony and arsenic. The antimony must be signalized as likely to cause certain difficulties: for example, after having separated the copper in the form of a matte, there often remain in it a little nickel and antimony. When the nickel is alone, its elimination is still sufficiently easy towards the end of the refining; but if antimony is also present, it is difficult to avoid the formation of a double antimoniate of copper and nickel, which successive roastings cannot get rid of; it is then necessary to add a little sodium chloride (common salt), when the antimony is removed as a chloride. There remains only to recover the nickel, which is done, as already described, at the moment of refining; the refinery slags are smelted for black copper, containing up to 30 Per cent. of nickel.

Treating Matte And Speiss

The matte or speiss, once prepared as above described, the nest object is to obtain the oxides of nickel or cobalt. To accomplish this, either the dry or the wet method may be pursued, according as the proportion of cobalt mixed with the nickel is great or small.

(1) Dry Process

When the foreign matters present in the matte or speiss are only sulphur, arsenic, and antimony, simple roasting conducted with care suffices to eliminate them by the formation of volatile oxides, yielding the nickel oxide nearly pure. The speiss may also be treated with soda nitrate, which produces alkaline arseniates and antimoniates easily removable by washing. The presence of copper does not increase the difficulty; after the roast-iug there remains a mixture of copper and nickel oxides, which furnish, finally, a marketable alloy of the 2 metals. As to the separation of the nickel and cobalt, if the proportion of cobalt be small, advantage can be taken of its superior oxidizability; if the cobalt is abundant, recourse must be had to the wet way. The roasting alluded to above is performed on the hearth of an ordinary reverberatory furnace, or in more complicated special furnaces, such as those at Sagmyra, Sweden, shown in Fig. 156.

Treating Matte And Speiss 300164

The materials, granulated mattes, are charged through the openings in the arch; they are roasted by the oxidizing flame of a sort of blow-pipe entering at the centre; and the oxide vapours escape by the lateral flues which descend into a pit. The roasted matters are removed in trucks, into which they full through apertures in the sole of the furnace.

(2) Wet Process

Mattes or speisses containing both nickel and cobalt in some considerable quantity, are first roasted, and then dissolved in hydrochloric acid, with or without the addition of nitric acid. If there is much iron, the solution is evaporated, and the residue calcined to remove a portion of the iron in the state of a chloride, taking up again in water; thus, on adding lime carbonate, the remainder of the iron, as well as some copper and arsenic, is precipitated; finally, the cobalt is removed in the state of sesquioxide by means of lime chloride and carbonate, and the copper and nickel are generally precipitated together as oxides by the lime.

Preparing Metallic Nickel

The oxides once obtained, either by the dry or by the wet way, it remains only to reduce them. With this object, they are mixed with a little meal and water, and made into a paste, which is cooked and cut into cubes measuring about 1/2 in. on the face; these cubes are then strongly heated in contact with pulverized wood charcoal. Generally the metal does not fuse, though the melting-point of copper may be reached and surpassed: it retains the form of little cubes, and is thus met with in commerce, when it has been obtained from arsenical and anfimonial ores; but it is then never quite pure. (Badoureau.)

Nickel ores mostly come to this country for reduction after having undergone a process of "concentration" abroad. They come here either as a matte-a combination of nickel, cobalt, copper, and iron with sulphur; or as a speiss-a combination of the uickel and copper with arsenic. In the preparation of nickel from the matte or speiss, nuisance is apt to arise. The earlier steps in the reduction of the matte or speiss consist of processes very similar to those employed in the smelting of copper. The objects sought are the further concentration of the material, i.e. the separation of iron from it by alternate calcination and melting, by which the iron is slagged oft.; and then the conversion of the valuable metals present into oxides or soluble salts. The calciners and melting furnaces used are similar in construction to those employed in copper smelting, and for the oxidation of the nickel, etc, free access of air is given in the last process. The product of the last operation at the furnaces is then subjected to a series of wet processes. It is first dissolved, by the aid of steam, in water to which hydrochloric acid is added in sufficient quantity, and then the iron present is precipitated from the solution by means of milk of lime, and the solution is again filtered.