EXTRACTION OF PRECIOUS METALS.

Evening Star, Volume VII, Issue 1937, 21 July 1869, Page 3

EXTRACTION OF PRECIOUS METALS.

Au improved method of working roasted gold and silver ores in pans and barrels by amalgamation has recently been patented by Mr Guido Kustel, whose high reputation as a metallurgist is well known. Simple as this process is, it elevates pan and barrel amalgamation to a higher degree of importance. The object of the process, which is applicable to ores from which only a low grade amalgam can be obtained (in consequence of the presence of iron, copper, lead, antimony, and arsenic), is to remove the base metal chlorides before the ore is subjected to amalgamation. For tin.spurpose Mr Kustel applies a very simple, old process—that of leaching. Most of the chlorides are soluble in hot water, and can be easily removed by lixiviation, Au addition of some sulphuric acid is in many instances very useful, but cannot be administered if some lead should be present in the ore, in which case muriatic acid should be employed ; generally, hot water is sufficient. The leaching is carried on as long as a reaction of dissolved metal is perceived in the leech. The ore so treated is then ready for amalgamation. To illustrate the effect of leaching, it may be stated that a charge of SOOlbs. of refractory ore from Idaho was equally divided after roasting, one of which was directly amalgamated, the other after leaching. The former amalgamation gave a retorted metal which melted into an intractable lump of iron, whilst the lixiviated portion yielded a silver bar ‘897 tine. In both cases the amalgamation was done in the usual manner, under application of heat. The advantage of leaching the roasted ore before amalgamation consists in obtaining a higher per centage of silver ; in saving a large proportion of quicksilver ; in making the pan last several years longer ; in saving a greater part of the copper ; and in a shorter roasting, as there is no necessity for decomposing the chlorides before amalgamation by an increased heat. The expense, compared with the advantages, is a mere trifle —the heating of water lor leaching. Even cold water will answer, although with a little less effect. Some ores, however, require to be treated first with cold water. It must be mentioned that, although the chloride of silver is not, like base metal chloride, soluble in water, some of it will, nevertheless, be carried out ; but this occurs only at the first attack of the water, when the solution of the uncomposed salt and of the chlo-. rides becomes so concentrated that a little silver chloride is dissolved on the Augistin principle. There is no difficulty practically, however, in preventing the escape of dissolved silver. Not all the copper contained in the ore is converted by the roasting into chloride of copper, there being also formed a subchloride which is not soluble in water ; but this is easily decomposed in the pans, so that in this case a considerable amount of copper would be found in this amalgam. There are several ways of reducing the subchloride of copper to a greater or less extent, according to circumstances. Mining Journal, March 27,