The purification of nickel

Nickel can be refined electrolytically or by dry processes. The commercial electrolytic processes have been indicated above. In some cases, efforts are directed to obtaining a purified nickel oxide, and reducing that to the metal. According to C. Schnabel, the purification of nickel by an oxidizing fusion in a kind of puddling furnace, removes only those impurities which are more readily oxidized than is nickel itself - e.g., carbon, silicon, and iron. P. Manhes, and P. C. Gilchrist and S. G. Thomas exposed the metal to the action of oxidizing agents like air, nitre, etc., at a red-heat. J. Gamier proposed to remove sulphur by heating the metal in a reverberatory furnace with a bed of powdered limestone which, giving off carbon dioxide, agitates the metal, and the lime takes up the sulphur. R. Fleitmann used manganese to remove sulphur from the metal. P. Manhes removed sulphur by heating the metal with a mixture of lime and calcium chloride on a basic hearth in a reverberatory furnace. W. S. Smith and co-workers used lime and silica with some fluorspar for desulphurizing the molten metal; O. Lellep, and H. Watle used gases containing oxygen. The Berndorfer Metallwarenfabrik removed carbon by soaking cubes of nickel, reduced at a moderate heat, in a 4 per cent. soln. of alkali manganate or permanganate, and fused the product at a high temp. J. Gamier removed iron by smelting the metal with quartz as a flux. L. Jordan and co-workers recommended crucibles made from purified magnesia, for melting nickel.

When nickel is fused in crucibles or furnaces during the reduction of nickel oxide, the product may contain nickel oxide which remained dissolved in the metal as in the corresponding cases of copper and iron. This makes the nickel brittle. Carbon monoxide may be absorbed by the nickel, making the metal inclined to springiness; and nickel cyanide may be formed which, according to T. Fleitmann, makes the metal brittle. T. Fleitmann showed that if magnesium be added to molten nickel, these three impurities are decomposed. The refining of nickel was described by C. Schnabel, E. T. Richards, G. Masing and L. Koch, K. Styffe, and R. Fleitmann. From one-twentieth to one-eighth per cent, of magnesium may suffice, and the resulting metal - the so-called malleable nickel - is ductile, and it can be welded to itself or to iron and steel. Without some such purifying agent nickel, in general, cannot be rolled or forged. The amount of magnesium required can in some cases be reduced if hydrocarbons, carbon monoxide, or hydrogen be first blown through the metal. C. Schnabel reported the following results of the fusion of nickel with 1-5 ozs. of magnesium per 70 lbs. of metal in graphite crucibles lined with fireclay:

		Ni	Co	Fe	Cu	Si or SiO2	C	S	Mg
I	Before	97.87	1.45	0.45	0.10	0.19	trace	0.05	-
	After	98.24	1.09	0.36	0.10	0.06	-	-	0.11
II	Before	98.21	1.19	0.25	0.07	0.24	trace	trace	-
	After	98.38	1.04	0.32	0.07	0.07	-	-	0.12

Other substances can be used, but less advantageously, than magnesium - e.g. aluminium, calcium, or a calcium-zinc alloy; black flux and coal have been tried, and here it is thought that the deoxidation is due to the formation of the vapour of potassium. The Societe Anonyme Fonderie de Nickel et Metaux Blancs recommended aluminium or potassium cyanide. J. Gamier, and G. A. Boeddicker recommended, say, 1.5 to 3 per cent, of manganese as a purifier; F. Osmond, R. Fleitmann, G. Selve and F. Lotter proposed mixing manganese dioxide with the nickel oxide before the oxide is reduced; P. D. Merica used aluminium. H. C. C. de Ruolz, H. C. C. de Ruolz and A. L. M. de Fontenay tried phosphorus to deoxidize nickel, but J. Gamier said that if over one-three thousandth part of phosphorus is present the nickel becomes harder, but less malleable; he therefore recommended a phosphor-nickel with about 6 per cent, of phosphorus as a deoxidizer. L. Schmal used a magnesium-manganese phosphide; this was discussed by C. Roberts.

P. D. Merica and R. G. Waltenberg showed that the magnesium, etc., act not by removing oxygen, for they found that the presence of carbon, silicon, iron, copper, arsenic, cobalt, manganese, and oxygen had little effect on the malleability of nickel, and similarly also with the occluded gases carbon monoxide and dioxide, hydrogen, and nitrogen. They found that sulphur, and sulphur alone, is responsible for the brittleness of ordinary nickel. Commercial nickel with less than 0.005 per cent, of sulphur is malleable both hot and cold, before and after remelting, and without any addition of manganese, and magnesium. As little as 0.01 of sulphur makes the metal almost completely non-malleable. This profound effect is due to the formation of a film of nickel sulphide which surrounds each metallic grain of nickel and lowers the intercrystalline cohesion of the mass even at low temp. The addition of 0.5 to 1.0 per cent, of manganese improves the malleability of nickel with 0.01 per cent, of sulphur; and the addition of 0.5 to 0.10 per cent, of magnesium completely restores its malleability. The facts also apply to monel metal.

A number of wet processes have been employed for purifying nickel; Thus, H. St. C. Deville evaporated the nitric acid soln. of the metal in order to remove the iron; the residue was taken up with water and treated with hydrogen sulphide. The filtrate was boiled and filtered to remove sulphur, and then treated with oxalic acid and boiled a few minutes; nickel oxalate separates from the acid soln. The oxalate was then treated in a lime crucible while protected from air. The oxalate can also be reduced by heating it in dry air, and then in hydrogen. Modifications of the process were employed by R. Schneider, H. Baubigny, and C. Zimmermann. L. Thompson finally fused the metal under borax in a fireclay crucible. Methods of purification were also employed by F. Claudet, G. Delvaux, P. Dirvell, N. W. Fischer, P. J. Robiquet, F. Gauhe, A. Guyard, M. Ilinsky and G. von Knorre, A. Laugier, J. von Liebig, A. Patera, R. Phillips, F. Pisani, F. Rose, H. Rose, R. Schneider, S. P. L. Sorensen, A. Terreil, and L. Thompson. The separation of nickel and cobalt is discussed in connection with the latter element.

Elaborate methods of purification have been employed in atomic weight determinations (q.v.); thus, C. Winkler dissolved the carbonate in hydrochloric acid, heated the soln. repeatedly with bleaching powder to precipitate iron and cobalt oxides; precipitated arsenic and copper by hydrogen sulphide; heated the liquid freed from hydrogen sulphide with sodium carbonate; dissolved the washed carbonate in hydrochloric acid and evaporated the soln. to dryness; sublimed the nickel chloride in a current of dry chlorine; and finally reduced the chloride in a current of purified hydrogen. T. W. Richards and A. S. Cushman treated a soln. of the commercial salt (or nickel derived from the carbonyl) with hydrogen sulphide; boiled the filtrate to drive off the excess of hydrogen sulphide; oxidized the soln. with a few drops of nitric acid, and made the soln. alkaline with ammonia; the filtered liquid was treated with hydrogen sulphide; the precipitated nickel sulphide was washed with hot water and dissolved in hydrochloric acid; the filtrate was evaporated to dryness and taken up with hot water; the clear soln. was twice fractionally precipitated as hydroxide by the method of E. F. Anthon; the hydroxide was transformed into bromide by heating it in a porcelain tube in a current of hydrogen bromide; and the sublimed bromide was then purified as nickel hexamminobromide. C. Winkler obtained the metal by the following electrolytic process from the purified sulphate:

An aq. soln. of nickel sulphate with 32.84 grms. of nickel per litre was prepared, and 200 c.c. mixed with 30 grms. of ammonium sulphate, 50 grms. of aq. ammonia of sp. gr. 0.905, and 250 c.c. of water. The cathode was a polished nickel plate 9.7 cms. By 7.9 cms. and the anode was a piece of platinum foil of the same dimensions. A current of 0.8 ampere at 2.8 volts was employed. As soon as the nickel deposit had acquired a certain thickness, it curled off the cathode in flakes of white lustrous metal with a yellowish tint. The metal had a high degree of purity since repeated heating in hydrogen failed to produce any loss of weight.