Sulphuretted hydrogen is then passed through the solution to separate the copper and arsenic present, and the solution is again filtered. After this the whole process is a wet one, in which nothing of an offensive character is or can be given off, The foul slags from the melting processes are melted with coke in a cupola furnace, a form of cold-blast furnace. A matte separates, which is tapped off from the well at the bottom of the furnace. During melting and the tapping of the slag, arsenical fumes, recognisable by their alliaceous odour, may be freely given off. (Dr. Ballard.)

Fig. 156.

At the works of Wiggin & Co., nickel refiners, Birmingham, the speiss is roasted in reverberatory furnaces, where the arsenic is driven off as arsenious acid, and condensed in coke scrubbers. The calcined ore is treated with hydro-chloric acid in earthenware pans, and the mixed solution is ladled into wooden vats, where it is diluted, and treated with lime chloride sufficient to form sesquioxide of all the iron present, which is then thrown down by adding milk of lime, and carries some of the arsenic with it. The residue left in the earthenware pans is subjected to repeated calcinations and lixiviations till it contains no more nickel. The precipitate formed in the wooden vats is well washed on a flannel filter. The portion remaining behind is sufficiently arsenical to serve for subsequent smelting purposes; the solution is treated with sulphuretted hydrogen to precipitate the bismuth, copper, and lead as sulphides; then with lime chloride at a higher temperature to throw down the cobalt. as sesquioxide, and finally with milk of lime to give hydrated oxide of nickel.

The New Caledonian and other non-arsenical ores, are first fused with iron pyrites to get the nickel as sulphide. The mixed sulphides are subjected to a series of calcinations and smeltings to remove the iron and sulphur, after the manner of the copper smelting-process used at Swansea. The nickel oxide obtained is reduced as already described.

Galbraith makes some objections to the existing methods, and indicates improvements. The success in treating the mixed sulphides of nickel and iron with dilute hydrochloric acid depends on the circumstances under which the precipitation takes place; and in precipitating with sulphuretted hydrogen, it is impossible to dissolve all the iron without also dissolving some of the nickel. He overcomes the difficulty by using calcium sulphide as the precipitant; by this means, especially if the solution is hot, the nickel is thrown down as a dense flaky precipitate of sulphide, which dissolves only with difficulty in strong hydrochloric acid, and is almost completely insoluble in a mixture of 1 part concentrated acid to 4 of water. On this he has based a patent for extracting nickel from its ores. The New Caledonian ore is dissolved in acid (hydrochloric or sulphuric), the solution is neutralized with lime-water, and the yellow liquor from "tank waste," or a solution of waste gas lime, is used as the precipitant, being less expensive than the sulphide prepared by boiling sulphur in a thin lime paste.

Any iron, magnesia, etc, present in the ore is precipitated, and quite easily separated, without dissolving any of the nickel, by means of dilute hydrochloric acid. (Jl. Soc, Chem. Ind.)

Garnier's Dry Method For New Caledonian Ores

This is analogous to the process followed in the metallurgy of iron: carbon is selected as the reducing agent, and as a vehicle for the nickel and cobalt, instead of the sulphur or arsenic usually employed. The intermediate product is therefore a more or less complex carbide of iron and nickel. The treatment resolves itself into 2 operations:-

(1) Fusion Of The Ore To Make Nickel Pig

This is effected by mixing the ore and suitable fluxes with charcoal, which is, however, performed in 2 ways, according as the ore treated is poor in nickel and in iron, or rich in nickel and poor in iron.

In the former case, corresponding to a richness of about 3 Per cent. of nickel, there is reason to fear, from the relatively small proportion of the metal, a considerable loss; this is avoided by adding some rich iron ore to the bed of the furnace, so that the total metal may amount to 15 Per cent. of the weight of the mass. This process is well adapted to ores having approximately the following composition:-

Ordinarily, with selected dressed ore, the composition will more nearly resemble:-

In this second case, the preceding operation is not called for; sometimes even only a portion of the iron present is run into the pig with the nickel, which result is easily attained owing to the greater oxidizability of the iron. Part of it then passes into the slag, to which it gives great fluidity, and thus tends to avoid loss by mechanical removal of particles of metal.

The reduction and fusion are conducted in furnaces about 12 ft. high. To avoid complete reduction of the iron, the shaft is made low; and to prevent too great heat, cold air can be introduced at low pressure. The carbide of nickel and iron obtained may vary from 46 1/2 nickel and 51 iron to 27 nickel and 68 iron, while the carbon fluctuates between 2 1/4 and 5 per cent.

(2) Refining The Pig

The pigs whose richness does not permit them to be employed directly in alloys are treated either for nickel, for copper and nickel alloys, or for nickel salts (double sulphate of nickel and ammonia), used in electro-plating. For the last-named the wet method is available, but for the 2 first-named the dry way is required. The operation is conducted on the sole of a furnace resembling that used for making steel. For the commercial alloy of nickel and copper, the charge consists of the nickel and iron carbide with a certain amount of copper. Once these matters are in a state of fusion, the carbon and then the silicon are removed by the oxidizing atmosphere maintained, and finally the iron oxidizes. In order to hasten the operation, sometimes oxidizing agents are added, such as the oxides of copper and manganese. During the process, and especially towards the end, repeated samples are taken to ascertain the progress of the refining, and thus the charge can be run out at the moment when the alloy contains the desired proportions of nickel and copper.