EXTRACTION OF GOLD

Evening Star, Issue 20586, 11 September 1930, Page 6

EXTRACTION OF GOLD

ITALIAN SCIENTIST'S HEW THEORY Striking claims are made by an Italian scientist, Professor Georgio Bartoli, who is at present on a visit to the Witwatersrand gold-mining area (states the Cape Town correspondent of the ‘Argus'). If his clams prove to be well founded, the result will be a revolution in gold mining practice even greater than that which followed the discovery of the cyanide method of treatment, and botli his theories of the content of gold-bearing rocks and his method of recovery of gold will be of the utmost importance to every goldproducing country in the world. Briefly, Professor Bartoli’s contention is that, contrary .to the belief hitherto generally held, where gold is found it exists not only in the free form, but also in salts, and that he has devised a process whereby the whole of the gold may be recovered. For tins process, certain features of which are at present kept secret though protected by provisional patents, the professor claims:—(l) That it will treat refractory ores, whether oxides or sulphides or silicates; (2) that it will extract much more gold than has been found possible by any known system up to the present; and (3) that the process is much cheaper than treatment by cyanide, chlorination, or any other process, and that it is much simpler in its operation. The preliminary processes ot mining, crushing, and milling the ore are carried out as in the systems at present in use; but after that, “ from the tube mill the pulp passes to the plant and remains in the plant, without further manual handling, till the final product, is obtained." GOLD IN SALTS. "I maintain ” says Professor Bartoll, " that gold exists as salts, just as in the case ol silver salts. Where your chemists will tell you that a sample of ore analysed contains only sdwt or Gdwt of gold to the ton, I will dements rate that there may be in reality GUdwt or 70dwt to the ton." in n sample of mine sand assayed according to current practice as showing a value ol only 2dwt to the ton Prolessor Bartoh claimed to have proved nearly 2(Jdwt of recoverable gold to the ton. One ore from the Far Fast Rand, assayed at a value of B.9dwt to the ton, produced, according to his assay, a value of' Iddwt to the ton. Another sample of ore taken from a Witwatersrand mine had been officially assayed at 9.sßdwt to the ton, but he was satisfied that it would actually yield 200dwt to the ton. Professor Bartoli says: ’* We shall want chemists more than mining engineers. Under present conditions the chemist is subordinated to the mining and the mechanical engineer; under my method the chemist will be supreme.” The process could bo imparted, ho said, to any qualified chemist, though it could not be safely left in the hands of a native or any unqualified labourer. The pulp would be passed through a series of tanks in which it would be subjected successively to six different chemical solutions; the gold would be precipitated, the effluent passing again through the circuit until the chemist in charge was satisfied that the utmost possible extraction had been effected. What these chemical solutions consist of Professor Bartoli is not prepared to dis close—except in the event of his process being acquired. He claims, however, that the chemicals are cheaper than existing practice, and that no other treatment is necessary for the great majority ot ores. THE PROBLEM. The first crucial point is the con urination of refutation of Professor BartoliV assertion that ‘‘ the greatest part of the gold in the rocks of South Africa—indeed, in every part ol tin world in which I have travelled- exists m the shape of salts, and not tree metallic gold, which is all that the cya nide would show an affinity for.” The second crux is his claim, “ My process not only extracts the metallic, the native, gold, hut also the salts ot gold.” The second claim cannot be tested until the process is tried; but if gold in the free state in rock is accompanied by greater quantities ol gold in chemical assoc ation with other elements, then no doubt some commercial process, the professor’s or another, will _be devised for recovering it. Criticism has therefore been directed mainly to the first point; and that criticism, so far, is mostly sceptical.

To such criticism Professor Bartoli replies that he supposes that tho onus of proof lies upon him. Ho proceeds:— “ Have not men since time immemorial known how to make various salts of gold and silver? Will Nature disregard it? Who dares say so? Not to mention the salts of silver which occur in Nature, and are described by mineralogists, what is the ' gold paint ’ of the mining man but salts of gold? He quotes authorities in reference to tin* action upon metals in the earth of sulphide of hydrogciii liberated by decaying vegetation. Other metals —■ examples are cited —decompose the sulphide of hydrogen and form their own metallic sulphides; why should not gold behave in tho same way Ho goes on to appeal to Professor Du Toit, one of tho chid authorities on South African geology, who wrote;—"lt might be remarked that tho reaction of sulphuretted hydrogen on magnetite, lervic sulphate being first formed, would dissolve any gold, while terrous sulphate or sulphide would precipitate it; hence no doubt the association of gold with pyrites." Professor Bartoli believes that gold in the form of sulphides has escaped the notice of chemists and mineralogists because, like free gold, it occurs in minute grains. He points out that free gold is found in mine dumps which have been exposed to the air for thirty or forty years. He believes this to be “ new gold," freed by the disintegration ot gold sulphides. There the matter rests for the ■imment. The professor has established an experimental plant on a fairly large male. It remains to be seen whether \c will succeed in persuading the magnates of the Band that Irs theories nro oiiind and his process effectual and economic.