By-products in nickel ores.-While the silicate ores of nickel have been treated essentially for the one metal, they also contain iron and attempts have been made to smelt them to ferronickel. In almost all other ores, the nickel is accompanied by other metals. The cobalt ores are valuable chiefly for their silver. The cobalt, nickel, and arsenic contents have been less important. Ores of the Sudbury district often are found containing as much or more copper than nickel, together with small amounts of gold, silver, and platinum metals. There is also a preponderating amount of iron. The saving of this enormous amount of iron now wasted as slag is the subject of considerable investigation which, if successful, will be of great economic importance.

In addition to by-product metals, sulphuric acid or other form of sulphur may eventually be saved. It is estimated that, from the Sudbury ores alone, fully 300,000 tons of sulphur, capable of producing nearly a million tons of sulphuric acid is annually lost (Ont. Nickel Com. Rept., p. 488).

DOMESTIC PRODUCTION.

Although the United States is the largest refiner of nickel, our refineries operate on foreign matte, and no production of the metal from domestic nickel ore is known to have been made since 1909. In that year the smelter at Fredericktown, Mo., which had operated intermittently, closed down. Compared with the ore bodies of Ontario or even the less extensive deposits of New Caledonia, the nickel deposits of this country are unimportant except as ultimate reserves. From time to time, deposits have been exploited in California, Oregon, Pennsylvania, Virginia, and Washington. Considerable information in regard to these deposits is summarized in Mineral Resources (1915), U. S. Geological Survey, Pt. I, pp. 743-766. An equivalent of about 441 short tons of nickel was saved in 1918 as a by-product in the electrolytic refining of copper. Of this tonnage, American ores furnished fully two-thirds. The balance was derived from the refining of copper from many countries and from every continent.

METHODS OF PRODUCTION.

Mining methods.-The sulphide deposits of the Sudbury district are mined by open-pit or quarry methods for the first 100 or 200 feet, or until the height of the pit wall is excessive for safety, or, in the case of inclined ore bodies, an excessive amount of waste rock from the hanging wall must be handled. In the deeper open pits the ore can not be swung to the surface by derricks, but is dumped from the pit floor into pockets, loaded into skips, and hoisted through a shaft sunk in the footwall. In the deeper mines underground methods are necessary. No special problems are involved. Like the ore bodies, the inclosing rocks are hard and little timbering is required. Overhead stoping is employed. Practically all the ore is mined by air drills. Electric power is largely used for haulage underground and hoisting. Hand sorting at the mine is almost universal.

Trus oli plant was remodeled and additions made in 1917-18 by a Canadian corporation. The projected rapaty w from 800 to 1,000 tons of nickel annually. Some copper and lead were produced during the perio 1 but the quantity of nickel produced is not known. Large reserves of ore are said to be available the average analysis given as 2 per cent copper, 0.9 per cent nickel, 0.5 per cent cobalt, and less than 2 per cent lead.

In New Caledonia the workable deposits always occur in the saddles or spurs from the main mountain range at considerable elevation above the surrounding country. The ore is invariably overlain by barren overburden and is generally richer on the upper part of the deposit. Larger ore bodies, after their extent has been outlined by the sinking of prospective holes, are worked in benches. A series of tracks is laid along the side o the hill about 25 feet apart vertically (like contour lines). On each bench the overburden for a few feet back is first removed and then the ore picked or barred down and carefully sorted. Shells of ore around the bowlders are picked off and the waste rock trammed to the dump. This procedure is repeated, working into the hillside, until the face of the ore becomes too low grade to pay. Extreme care is necessary in sorting and sampling the New Caledonian ore. Large pieces are broken by hand hammers to not over 2 inches in diameter. The ore is swept up into 10-ton lots, which are carefully sampled. Each lot is marked with its assay. Considerable sampling is necessary, because the ore is not uniform and because it is difficult to judge its grade by the first appearance.

Concentration.-Sudbury ores lend themselves generally to hand sorting; mechanical concentration has not been necessary. It is not applicable to the massive pyrrhotite ores nor to the silicate and oxide ores.

Smelting. The processes of smelting sulphide ores of nickel or of nickel and copper are remarkably similar to those of copper smelting and differ chiefly in the grades of the intermediate products. Nickel is more easily slagged than copper, so it is found advisable to make a low-grade, highly ferruginous matte in the blast or reverberatory furnace and to later eliminate most of the iron in the Bessemerizing process.

The ore is generally roasted roughly in order to remove a part of the sulphur before charging to the blast furnace. The Sudbury mixtures of ore derived from various mines are practically self-fluxing and only a small amount of quartz is required. Pyritic smelting (the oxidation of a large amount of sulphur and iron in the blast furnace with consequent saving of coke) has not been successful.

Furnace matte from either blast or reverberatory furnaces is rarely allowed to exceed a content of about 25 per cent nickel plus copper. Slag losses are in direct proportion to the grade of the matte, and the high-grade furnace product of the copper smelter would result in an excessive waste of nickel. This low-grade matte is poured into basic converters and Bessemerized. Crude siliceous ore is added as flux.

Instead of blowing to metal in the converter, as is done in copper practice, Bessemerizing is stopped as soon as the iron is practically removed and before the sulphur combined with the nickel and copper is consumed. The final product of the smelting operation is a highgrade matte containing about 80 per cent nickel plus copper and nearly 20 per cent sulphur. Further Bessemerization is not profitable, as the chemical reaction between copper oxide and copper sulphide, which is the fundamental reaction of the last stages of copper converting, is not paralleled in the case of nickel oxide and nickel sulphide. Metallic nickel can not, therefore, be produced in the converter; it would all pass into oxide (provided a temperature high enough to prevent freezing could be maintained).

New Caledonia and other oxide ores are also smelted in a blast furnace to matte which is later either Bessemerized or less often

roasted and smelted with sand in a reverberatory furnace. As these ores contain no sulphur, alkali waste (calcium sulphide) or gypsum must be added to the furnace charge. Since these ores are free from copper, the final matte requires no special separating treatment, and can be dead-roasted and reduced to metal by melting in a crucible with charcoal.

Refining nickel matte.--The term "refining" in nickel metallurgy is taken to cover the process of producing nickel of commercial grade from the high-grade Bessemer matte and does not designate, as in the case of other metals, only the final stages of purification of, say. 95 per cent pure metal.

There are three standard processes of nickel refining: (1) The Orford process, (2) the Mond process, and (3) the electrolytic process. The Orford process consists of a series of furnace treatments, cheap to operate, but subject to high slag losses of both nickel and copper and very low recoveries of precious metals. It is the original Welsh process modified and adopted by the International Nickel Co. The matte is melted with salt cake (sodium sulphate) and coke; the salt cake is reduced to sodium sulphide, which dissolves the sulphides of copper and iron and rises to the top, leaving pure nickel sulphide at the bottom of the melted mass.

The "tops" are leached with water to remove sodium salts, which, after evaporation, are returned to the "top and bottom" smelting. The copper and iron residue containing most of the gold and silver is Bessemerized to "blister" copper containing about 2.5 per cent nickel, which is sold to the copper refiners who recover the nickel as well as the copper and precious metals.

The "bottoms" (which sometimes require purification by a second smelting with sodium sulphide), consisting of a matte very rich in nickel but still containing a little copper, are ground and roasted with common salt in a reverberatory furnace to form soluble sulphate and chloride of copper and insoluble nickel oxide. Leaching of this product yields a solution containing most of the copper with some silver, platinum, palladium, and rhodium and a residue of nickel oxide. The solution after a treatment for the removal of the precious metals is treated with hot powdered matte or scrap iron which precipitates the copper. The nickel oxide is reduced to commercial metal in oil-fired reverberatory furnaces.

The International Nickel Co. also produces considerable electrolytic nickel and thereby recovers platinum, palladium, iridium, and rhodium, which in general follow the nickel, whereas the gold and silver follow the copper in the top and bottom smelting. Nickel sulphate and nickel ammonium sulphate are also obtained by crystallization from the leached solutions. Neither copper sulphate nor nickel oxide is sold as such by this company.

Monel metal is produced by carrying on the top and bottom smelting only far enough to remove a part of the copper and then roasting the matte and reducing the mixed oxides so obtained to metal.

The Mond process is used only by the Mond Nickel Co. at its plant in Wales. The process yields exceptionally pure metal with unusually small losses, even of the precious metals. It is automatic and continuous but requires an expensive plant and skilled operators. The Mond Co. derives its ore supply from the Sudbury district. although Clydach. Wales, was chosen as the refinery site for the fol

lowing reasons: Anthracite for producer gas is mined in the neighborhood, cheap supplies of chemicals are accessible, suitable skilled labor is readily available, and there is cheap ocean transport for raw material and products.

The essential feature of the Mond process is the formation of nickel carbonyl (Ni(CO),) by passing carbon monoxide gas over metallic nickel at 500° C. This nickel compound is a gas and is readily decomposed at 150° C. to metallic nickel and carbon monoxide. The matte, after being crushed and ground in ball mills, is roasted to contain not over 2 per cent of sulphur in mechanical roasting furnaces. The roasted matte is leached with warm dilute sulphuric acid, which dissolves about 70 per cent of the copper and a little nickel. The residue is sent through a reducing tower, fitted with hollow shelves and with mechanical rabbles for moving the ore from one shelf to the next. The furnace is heated to 250° C. by producer gas. Water gas is passed upward through the furnace in contact with the ore and reduces the nickel oxide to the metal. The reduced metal then passes to another tower similar to the preceding but not heated. Volatile nickel carbonyl is formed and swept along by the gas current to the decomposer. The roasted material, after passing through the volatilizer, returns to the reducing tower, then again to the volatilizer, circulating in this way for one or two weeks. About 70 per cent of the nickel is thus removed. The residue containing about 30 per cent copper, 30 per cent nickel, and 5 per cent iron is smelted with gypsum and reducing agents to a matte similar to the original 80 per cent material to which it is added. The nickel carbonyl gas is decomposed in a special tower heated to about 200° C. The nickel is deposited in the form of granules which are kept in constant movement so as not to cohere. To produce shot of about one-eighth inch in diameter two months are required, as the growth of concentric deposit is very slow; three-eighths inch shot require six months. The shot nickel is screened and sold in various sizes. The copper sulphate leached from the roasted matte in the Mond process is a valuable product and is sold largely to vineyard owners in southern Europe. Electrolytic refining may be carried out on the unroasted, partly roasted, or dead roasted matte. The matte is commonly cast into anodes, or the solution obtained by treating the raw or roasted matte with acid or other solvent may be used with insoluble anodes, or, as is common, a combination of the two processes may be employed. The Hybinette process, used in Norway on matte similar to that of the Sudbury district, is an example of the last type. The Bessemerized matte (with commonly 47 per cent nickel and 32 to 34 per cent copper) is received from the smelter in granulated form. It is partially roasted to remove most of the sulphur, and leached with 10 per cent sulphuric acid. This dissolves out a very large proportion of the copper. The residue is melted and cast into anodes about 3 feet by 6 feet 6 inches and nearly one-half inch thick. The anodes contain about 65 per cent nickel, 3 to 8 per cent sulphur, the remainder being copper with a trace of iron.

The plants for depositing the nickel and copper are quite independent. The anodes are contained in canvas bags and the nickel cathodes are made of iron plates coated with a thin wash of graphite. Nickel is deposited on both sides and is stripped off in sheets of the usual warty and corrugated appearance. After washing off basic

salts with acid the sheets are dried and cut up into oblongs about 2 inches by 3 inches and sold in that form, being preferred in the German market to the remelted product. The metal is guaranteed 99 per cent nickel but can be made purer. The scrap anodes amounting to about 30 per cent of the original castings are used instead of scrap iron for the precipitation of copper from the electrolyte liquor, which is thereby depleted of copper and enriched in nickel. It is said that no trouble is experienced from the building up of impurities in the electrolyte, as the latter is sufficiently purified by the above cementation process. The previous metals become concentrated in the anode slime as in copper refining.

HISTORY.

Nickel was not separated as a distinct metal until 1774, but in very early times a nickel-copper zinc alloy was made by the Chinese by the direct smelting of a mixture of the crude ores. This alloy was largely used in gongs and musical instruments and, under the name of "pack-tong" (white copper), pahfong, or "pock-fong," was introduced into Europe in the eighteenth century.

Nickel ore was discovered in New Caledonia in 1865 and was proved to exist in economic quantities about 10 years later. Previous to this there had been only a limited consumption of nickel and the small requirements were supplied by Germany.

In 1879 a smelter was built in New Caledonia and about 4,000 tons of matte were exported in the following six years. The demand for the metal did not increase in proportion to the production. At the close of 1881 the price had dropped to 70 cents per pound and in 1884 to 53 cents. Production, which just previous to the opening of these new mines had not exceeded 400 tons a year, more than doubled and quickly passed the needs of consumers. At the end of 1884, stocks of ore had accumulated in New Caledonia and there was an excess of metal in Europe, and before the end of the following year the furnaces in New Caledonia were shut down. The price per pound of nickel in the ore dropped to 1.3 to 1.4 cents and the grade of the ore which at first had averaged from 10 to 12 per cent lowered to 7 or 8 per cent. The growing use of nickel in steel and a steady extension of the older industries that had used nickel as their raw material resulted in increased markets and the New Caledonia smelter reopened in 1889.

In 1887 nickel derived from Canadian ore entered the market. On account of initial treatment difficulties encountered in the separation of the copper from the nickel and because of a strong trade prejudice that developed against the Canadian metal, it did not become a strong competitor in the world market until 1892.

Strong competition between the rival countries characterized the period from 1892 to 1897. Eventually an understanding was reached by the refiners whereby the relative output of each country was regulated. Since 1904, Canada has been the leading producer of nickel ore and matte, the greater part of which was refined in the United States. Agitation for the home refining of the matte has been in progress for several years and became especially active after the outbreak of the European war. This pressure resulted in the building of two refineries in Canada.