Jtdy 17, 1879] 



NATURE 



279 



Tliere is one metallurgical operation in which the first two 

 sources of loss are avoided, viz., "Bessemer's," where, by 

 fclowing air through molten crude iron, a very high temperature 

 is attained by the combustion of small quantities of carbon and 

 silicon contained in the crude iron ; this is, however, not the 

 case in the proce-s of puddling, where the oxidation is spread 

 over a considerable period of time, although the same consti- 

 tuents are frequently burnt in similar proportions. But even in 

 the Bessemer process the carbon is only half burned, and a 

 large amount of heat escapes with the carbonic oxide and 

 nitrogen. 



When, however, thin streams of air are forced through molten 

 sulphide of iron, lying on a tuyere hearth, a high temperature is 

 produced by the perfect combustion which ensues in the midst of 

 the sulphides, and no unburnt gases, excepting nitrogen and 

 sulphur vapour, escape from the surface of the molten mass. 

 The hot nitrogen and sulphurous acid may be caused to act upon 

 iron pyrites and other mineral matter, and when pyrites is thus 

 heated, an atom of sulphur held in feeble combination is in great 

 part expelled, and thus is obtained molten protosulphide of iron, 

 which is subsequently burnt by the oxygen of the air driven in at 

 the lower part of the furnace, thereby producing the heat neces- 

 sary for continuing the operation. The process may be defined 

 as a system of fractional oxidation, in which the numerous con- 

 stituents of a complex furnace charge can be separated from 

 each other and concentrated in different parts of the apparatus, 

 the heat necessary for the operation being obtained by the com- 

 bustion of a portion of the less valuable constituents. 



The principal ores of all our ordinary heavy metals, except 

 manganese and tin, are sulphides. Iron, although largely oc- 

 curring in an oxidised form, is abundantly found in combination 

 with sulphur ; and bisulphide of iron, or iron pyrites, is an 

 example of sulphurous and combustible minerals. Associated 

 with iron and sulphur in iron pyrites are invariably found small 

 quantities of other metals, notably cobalt, nickel, copper, silver, 

 gold, lead, zinc, and arsenic. Of these, zinc is almost as com- 

 bustible as iron itself, while lead and arsenic readily volatilise as 

 sulphides, and cobalt, nickel, and copper are distinctly less 

 readily oxidisable than iron, while silver and gold do not oxidise 

 under these conditions ; hence, in supplying air to such material, 

 the iron is the first of the elements to suffer oxidation, so that if 

 the oxidation be crrested before the whole of the iron has been 

 burnt, the cobalt, nickel, copper, silver, and gold present will 

 be found in the unburnt portion. This principle finds a parallel 

 in the Bessemer process of treating pig-iron for the manufacture 

 of steel, where a current of air is caused to bubble up through 

 a bath of molten crude iron, [the silicon is first oxidised, and 

 is closely followed and to a great extent accompanied by the 

 carbon, and no large amount of iron suffers oxidation, until the 

 whole of the silicon and carbon have been burnt out of the 

 molten material. 



The experiments made at Messrs. Canlmell's works, at 

 Penistone, in a Bessemer converter, have proved that by blowing 

 air through molten sulphide of iron, the iron and a portion of 

 the sulphur are oxidised, and if the oxidation is arrested before 

 the combus tion of the iron is complete, a heavy matt or regulus 

 is obtained, which contains but a small proportion of the iron of 

 the ore, but practically the whole or the greater part of the 

 copper and other lers oxidisable metals. In one of these experi- 

 ments the molten sulphides w ere run into the converter from a 

 cupola, in which they had been previously melted, and the tem- 

 perature was kept up until the operation was discontinued, viz., 

 for a period of ten hours, without the use of any carbonaceous 

 fuel, the heat being entirely derived from the oxidation of the 

 iron and a portion of the sulphur of the lumps of pyrites, which 

 were continuously thrown into the mouth of the converter. A 

 Bessemer converter being unsuited for the collection of the 

 gaseous products, the later experiments have been made in a 

 series of cupola furnaces belonging to Messri. John Brown and 

 Company, Limited. These experiments have proved the possi- 

 bility of obtaining a valuable regulus, a slag neariy free from 

 copper, and a considerable quantity of crude sulphur. M. 

 I'ourcel, the well-known chemist of the Terrenoire Company, 

 has also made some very interesting experiments, having treated 

 by this method a cupriferous sulphide of antimony containing 

 lead and zinc, using heavy spar and silica as fluxes ; he obtained 

 a regulus containing the whole of the copper in the form of 

 sulphide, a slag of light specific gravity, and the lead, zinc, and 

 antimony as two separate sublimates which were condensed in 

 different parts of the apparatus, owing to the superior volatility 



of sulphide of lead over the oxides of antimony and zinc. In 

 the experiments at Penistone and at Sheffield a cold blast of air 

 was employed, and the gases which passed from the converter or 

 furnace into the open air, carried away with them a large amount 

 of heat. In practice, however, it would be economical to 

 employ a hot blast, which could be heated by the waste heat 

 from the escaping gases. It is remarkable that the least valuable 

 metals, viz., iron and zinc, generate by their combustion the 

 largest quantities of heat. 



The process may be employed for the reduction of even the 

 more volatile metals ; for example, Mr. A. H. Allen, of Sheffield, 

 has thus obtained metallic antimony simply by the 'oxidation of 

 sulphide of antimony. It is well known that sulphide of lead 

 reacts upon oxide of lead with the production of metallic lead 

 and sulphurous acid. If, therefore, a limited amount of air is 

 blown into molten sulphide of lead, the oxide thus formed in 

 the lower part of the furnace will, in passing upward, come in 

 contact with the hot sulphide of lead, and metallic lead will 

 result, with the evolution of sulphurous acid. The furnace 

 having a quiescent hearth below the tuyeres, the metallic lead 

 will collect there, and can be from time to time withdrawn. A 

 limited amount of air must be employed, because if it is driven 

 in too quickly, the sulphide of lead will rapidly distil off. In 

 thus treating argentiferous lead ores, the silver (and gold if pre- 

 sent) would be found with the first metallic lead reduced. When 

 thus treating galena the furnace should have a basic lining. 



The process is peculiarly suitable : — 



1st. For the treatment of metalliferous substances which can- 

 not be advantageously treated by other processes. For the ex- 

 traction of sulphur by distillation, and simultaneously for the 

 concentration and separation of cobalt, nickel, copper, silver, 

 and gold from minerals in the form of metallic regulus ; while 

 lead, zinc, antimony, arsenic, &c. , accrue in the sublimates. 



2nd. For the treatment of complex ores, for example — Grey 

 antimonial copper ores, such as those experimented on by M. 

 Pourcel. Ores similar to those worked at the well-known Bottino 

 Mines, Seravezza, in the Italian Apennines, which contain thir- 

 teen or fourteen heavy metals, including silver and lead, for 

 which latter alone they have been worked for centuries. The 

 blende of lead mines, in Derbyshire termed "muck," usually 

 thrown away by the miners, because the large quantity of lead 

 with which it is associated renders the zinc obtained from it 

 worthless. 



3rd. For the treatment of auriferous and argentiferous pyrites. 

 It is well-known that in practice it is not possible to obtain the 

 whole of the gold from pyrites by amalgamation with quicksilver, 

 because the presence of sulphur and arsenic sickens and flours 

 the mercury, whereas by fusion the whole of the silver and gold 

 pre ent is obtained, 



4th, For the treatment of pyrites containing even only small 

 percentages of cobalt, nickel, and copper, which are thus con- 

 centrated into a rich regulus, whereas this result is now only 

 obtained by very tedious processes of alternate roasting and 

 reduction. Such ores containing 10 percent, and even 12 per 

 cent, of copper exist in South America and many other 

 parts of the world, but are not at present capable of economic 

 treatment, owing to the difficulty of obtaining a sufficient supply 

 of cheap fuel. The process can also be advantageously applied 

 to the treatment of richer ores of copper such as are at present 

 smelted at Swansea. 



5th. For the treatment of poor lead ores. If such ores are 

 added to a furnace charge of cupreous pyrites, the silica they 

 contain will be utilised and combine with the resulting oxide of 

 iron to form slag, the galena will be volatilised and be recovered 

 as a sublimate, while any silver present will enrich the regulus. 

 At present, by a costly process of crushing and washing these 

 ores, the galena is concentrated, although a large proportion is 

 left with the dibris, and passes with the water into the streams, 

 rendering the existence of fish in such waters impossible. The 

 water power now used for washing the ore could, in many cases, 

 be employed for producing the blast. 



When thus treating cupriferous iron pyrites, four products are 

 obtained : — 



1st. A matt or regulu? containing from 30 to 50 per cent, of 

 copper, any traces of cobalt, nickel, silver, or gold the ore rnay 

 contain, the rest of it being iron and sulphur ; it has a specific 

 gravity of 4J to 5. 



2nd. A slag consisting of silicate of iron from the resulting 

 oxide of iron combined with the siliceous matters contained in 

 the ore and the fluxes added. 



