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THE DISCOVERY, DEVELOPMENT, AND DIFFUSION OF NEW TECHNOLOGY: THE CYANIDE PROCESS FOR THE EXTRACTION OF GOLD, 1887–1914
Abstract
In the 1880s the gold mining industry encountered severe problems in the extraction of gold from unoxidised ores which were being met more frequently. The gold extraction technology of mercury amalgamation became more inefficient to the extent that little more than half the assayed gold content of the ore was being extracted. Clearly, a major breakthrough in metallurgy was required to overcome this problem. This occurred through the development of the cyanide process which not only raised the percentage of gold extracted from unoxidised ores but also, because of its cheapness, allowed much lower grade ores to be mined and treated than had been possible previously.
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NOTES AND REFERENCES
For an overview of these processes see, for example, J.E.S. Parker, The Economics of Innovation., Longman, London, 1978; Nathan Rosenberg, ‘Factors affecting the diffusion of technology’, Explorations in Economic History., 10, 1, 1972, pp. 3–33.
After it was cooled, the vaporised mercury liquified and could be used again.
‘The MacArthur-Forrest process of gold extraction’, Journal of the Society of Chemical Industry., 9, 3, 1890, p. 269.
In some gold-bearing regions with high rainfall, such as in Victoria, Australia, oxidised ores were to be found at relatively deep levels of 1,000 feet or more, whereas in relatively dry regions, such as the Transvaal and Western Australia, the water level was reached at a few hundred feet.
To convert to metric measure: one pennyweight per ton equals 1.86 grammes per tonne and one ounce per ton equals 37.3 grammes per tonne.
Geoffrey Blainey, The Rush That Never Ended., Melbourne University Press, Melbourne, 1963, p. 271.
J.S. MacArthur, ‘The discovery of cyanidation’, Mining and Scientific Press., 112, 24, 1916, p. 851. The interest in pyritic ores undoubtedly stemmed from the problems confronting certain Indian gold mining companies in which Sir Charles Tennant, the chairman of Tharsis, had large shareholdings. See S. G. Checkland, The Mines of Tharsis., George Allen and Unwin, London, 1967, pp. 126–7.
MacArthur, loc. cit., (1916).
The Cassel Gold Extracting Company, Board Minutes. (henceforth C.R.M.) (housed in the Cheshire County Records Office in Chester), 12 November 1886. The Company agreed to refund to the Syndicate all its cash outlays, pay a sum of £2,000 and one-third of the profits from the use of the invention with the option of capitalising such profits with shares on an agreed basis.
Ibid. It should be noted that it was widely known that potassium cyanide and other chemicals would dissolve gold in refined form. In addition, two American patents for the extraction of gold from its ores (those of Rae, 1867 and Simpson, 1885) included potassium cyanide in their specifications but the MacArthur-Forrest patent was the first to specify solely a dilute cyanide solution. Also, no one had used cyanide on any goldfield for this purpose before 1887.
The Research Syndicate was well rewarded for its efforts by the Cassel Company. In June 1892, an agreement between the two parties led to the former being allotted 60,000 paid-up shares in the Company. At the prevailing market prices of between 28s. and 33s., these shares could have been sold for over £84,000 at the time.
C.B.M., 1888–1892, passim;. C. J. Ellis, ‘Notes on the testing of gold ores, etc., in relation to their treatment by the cyanide process’, Journal of the Society of Chemical Industry., 17, 2, 1898, pp. 127–30; GT. Beilby, ‘Ten years’ progress of the cyanide process for the extraction of gold’, ibid., pp. 130–40.
J.S. MacArthur, loc. cit., (1916) p. 852.
J. McCombie, ‘The beginnings of cyanidation’, The Mining Magazine., VI, 6, 1911, p. 456; C.B.M., 1888 and 1889, passim.
C.B.M., 12 December 1888.
C.B.M., 20 June 1889.
See the Prospectus of the Company, The Times., 14 March 1891.
C.B.M., 17 June 1890.
It has been noted that: The rich surface zones were becoming exhausted, the grade of ore was falling and the dread of unoxidised pyritic reef, termed “blue-ground” … was tending to develop into widespread panic. While the rich outcrops had yielded a fair percentage of their gold to simple amalgamation, treatment of the unoxidised pyritic reefs was presenting considerable difficulty and recovery percentages were steadily falling. James Gray and J.A. McLachlan, ‘A history of the introduction of the MacArthur-Forrest cyanide process to the Witwatersrand goldfields’, Journal of the Chemical, Metallurgical and Mining Society of South Africa., 33, 2, 1933, p. 375. The authors also noted that only 55 per cent of the assayed gold in the ore was being recovered on average in 1890.
This stemmed from MacArthur's failure to reveal his costs of extraction during the public demonstration. In fact, he later admitted that he had used a strong cyanide solution to guarantee success (J.S. MacArthur, ‘Reminiscences of the early Rand’, Engineering and Mining Journal., 88, 8, 1909, p. 357). Hennen Jennings (in T.A. Rickard, ‘Hennen Jennings and mining on a big scale’, Mining and Scientific Press., 111, 26, 1915, p. 965) later noted that he and other mining magnates present at the demonstration considered the costs to be too high — as much as 30s. a ton. In 1890, the average yield of the ore on the Rand was 42s. a ton. Mining and amalgamation costs also had to be taken into account.
The Syndicate began cyanide operations before it completed the floating of the African Gold Recovery Company.
The Syndicate's costs at the Robinson site were given as 10s. a ton, which was acceptable to the mining companies. In fact, cyanide costs were halved shortly afterwards as larger production units were constructed, weaker cyanide solutions were used successfully, and the agitation of the cyanide-ore mixture gave way to percolation.
See J. MacDonald, ‘The cyanide process and some practical results’, Engineering and Mining Journal., 57, 12, 1894, p. 268.
For a discussion of the technical and other problems confronting the process in New Zealand, see Sybil Jack, ‘The introduction of cyaniding in New Zealand: a case study of the role of technology in history’, Prometheus, 2., 1, 1984, pp. 30–1.
These figures are derived from Beilby, loc. cit., pp. 132–4.
In the terminology of the times, the pulverised material could be classified into three types: sands, concentrates, and slimes. The sands were the easiest to treat by cyanide; the concentrates formed the larger particles of the refractory material, difficult to treat in that state by cyanide and were often sent to the smelters; slimes consisted of the smallest particles which, when subjected to water, tended to set like cement and it was difficult to penetrate them with the cyanide solution without much agitation.
For example, the use of zinc coated with precipitated lead for improving the precipitation of gold from copper-bearing ores, patented by MacArthur in 1894, was rejected by South African miners until 1898, when Betty re-discovered it. See J.S. MacArthur, ‘Gold extraction by cyanide a retropsect’, Journal of the Society of Chemical Industry., 24, 7, 1905, p. 314.
Direct cyanidation eliminated mercury amalgamation. The ore was crushed and then subjected to cyanide treatment. The method was used first in the United States in the early 1890s.
The combination of bromine and cyanide was suggested by the Sulman-Teed patent of 1895 and was used in the Diehl process by the London and Hamburg Gold Refining Company at Kalgoorlie at the turn of the century.
The use of tube or ball mills tended to turn all types of gold-bearing ore into slimes as the tubes containing the material revolved and the steel balls or other hard material pulverised the ore. The slimes were then placed in filter presses into which the cyanide solution was injected under pressure and eventually squeezed out as a gold-cyanide solution, leaving the dry material which was discarded.
It must therefore be stressed that the secondary innovations were incremental to the initial, primary, innovation: the application of a dilute solution of potassium cyanide to gold-bearing material and the precipitation of the gold by means of zinc shavings.
See Beilby, loc. cit., pp. 131–2. Note that the major cost-reducing advances had been achieved before the introduction of the major changes in technology, most of which added to the capital costs of the users.
For silver, as for gold, the costs of extraction of the ore from the mine and administrative costs were always factors to consider. There was a limit below which reduced cyanide costs could not make the exploitation of the (very low-grade) ore a viable economic proposition, given the price of the metal.
See papers by Philip Argall, cited in Engineering and Mining Journal., 84, 24, 1907, p. 1128, and William Neill, ‘The cyanide industry’, ibid., 91, 19, 1911, p. 902. By 1900, the use of cyanide was an integral part of the whole process of gold extraction at many plants and the division of output by milling and by cyanide was impossible.
See Anon., ‘Deutsche gold und silber scheideanstalt 1873–1923’, Die Chemische Industrie., 46, 1, 1923, p. 101.
By the turn of the century, Western Australia was also highly dependent upon the process for the extraction of gold from its highly refractory ores.
This expansion was also due to the new discoveries of gold in South Africa, Canada, Alaska and Australia.
It is not claimed that the connection between increased gold production and expanding economic activity is necessarily a causal one. See W. Arthur Lewis, Growth and Fluctuations 1870–1913., George Allen and Unwin, London, 1978, pp. 82–93.
See Alfred James, ‘The difficulties of developing invention: the story of the cyanide process’, Engineering and Mining Journal., 113, 1, 1922, p. 11. James attributes these costs to: the training of many metallurgists, the erection of cyanide manufacturing works to prevent the supply of cyanide to the mines being restricted, the dispatch of six expeditions, the fighting of two law suits, and the carrying out of much mechanical research … (into) … the effects of cyanide. The balance sheets of the Company confirm this estimate.
Most of the shares in the subsidiary companies were distributed as bonuses to the Cassel shareholders, mainly in 1896.
The MacArthur-Forrest B and C patents were set aside by the Transvaal Supreme Court (two judges against the patent and one in favour of it) because of the ‘want of novelty’. It was judged that they had been anticipated by the American patents of Rae and Simpson (see footnote 10 above). The British Court of Appeal judged the patent novel but set it aside because of weak specifications. Had the term ‘dilute’ been included, the judges would have upheld the patent.
See James, loc. cit., p. 11.