C.—3

178

This invention relates to processes used for obtaining gold from ores, minerals, and other goldbearing substances, and its object is to obtain the gold in a rapid, efficient, and inexpensive manner. The invention is carried into effect by treating the ore or other gold-bearing substance, after it has been reduced to a powder in any well-known manner, with a dilute solution containing about from 10 lb. to 20 lb. of strong sulphuric acid (oil of vitriol), about from 12 lb. to 201b. of chloride of sodium (common salt), and about from soz. to 9oz. of permanganate of potash, in about 100 gallons of water. A solution of from a quarter of the above strength to four times the above strength is serviceable in extracting the gold, but we prefer the strength as above. Bisulphate of soda may be used instead of sulphuric acid, but in the proportion of about two and and a half parts by weight of the bisulphate instead of one part by weight of the acid. Chloride of calcium, or chloride of potassium, or chloride of ammonium, or chloride of magnesium, or other suitable chlorides may be used instead of chloride of sodium, in their equivalent proportions. The manner in which the solvent is prepared is as follows : (1.) Mix together 50 gallons of fresh water and from 101b. to 201b. of sulphuric acid. (2.) Mix together 50 gallons of fresh water, 12 lb. to 201b. of chloride of sodium, and from soz. to 9oz. of permanganate of potash. These two mixtures are mixed together to form a dissolving liquor, which must be used within twenty-four hours-to keep its strength. It is advisable to keep the two mixtures apart until they are required for use. Manganate of potash, or permanganate of soda, or manganate of soda may be used instead of permanganate of potash, but if manganates are used about 40 per cent, more will be required and about a third more of the sulphuric acid. Ores or other gold-bearing substances containing pyrites or arsenical pyrites, or other sulphides or arsenides, or tellurides, or selenides, or antimonides, or organical substances, must be thoroughly roasted before treatment with the solution. In carrying out the invention any suitable apparatus may be used, but we prefer to provide tanks wherein to mix the solution, which tanks are of any convenient shape, and of any desired size, according to the quantity of the solution to be made. In one tank we mix fresh water and strong sulphuric acid, in the proportion previously given of 50 gallons of water to from 10 lb. to 20 lb. of acid, the water to be put into the tank before the acid, the mixture to be stirred while the acid is being put in, so as to insure a thorough mixture. In another tank we dissolve and mix permanganate of potash and chloride of sodium in fresh water, in the proportion previously given of from 5 oz. to 9 oz. of permanganate of potash and from 12 Ib. to 201b. of chloride of sodium in 50 gallons of water. The two mixtures are mixed together in another tank to form the dissolving liquor, which must be employed within twenty-four hours to keep its strength, as previously stated. The raw or roasted ore or other gold-bearing substance, in a finely powdered condition, is put into leaching-tanks having a false bottom, fixed at about lin. to 2 in. above the true bottom, and perforated with holes of about lin. in diameter and 6in. to 10in. apart. On this false bottom is placed a filter-bed of quartz pebbles and sand about 6 in. deep, larger pebbles resting immediately on the false bottom, with smaller pebbles above, the size gradually diminishing upwards, with coarse sand above and finally fine sand at the top. All the above tanks may be lined with enamelled iron, glazed earthenware, or a preparation of paraffin or other material upon which the solvent will not act. The leaching-tanks are filled to within about 10 in. of the top with raw or roasted ore or other gold-bearing substance, in a finely powdered condition, and the solvent solution is then added gradually until it stands at a depth of about 6 in. above the surface of the ore. A stop-cock communicating with the space between the two bottoms is afterwards opened, when the solution which will have filtered or percolated through the filter-bed and false bottom is drawn off into precipitat-ing-tanks, which are preferably made of wood. The tanks may be of any convenient size or shape, and lined as previously described. Instead of such filter-bed, the false bottom may be covered with any suitable textile material (such as asbestos) as will allow the liquid to pass through freely, and will not decolourise the purple-red colour of the permanganate solution. As it is necessary that the dissolving solution should be in contact with every particle of ore, it is necessary or desirable to agitate the mixture in the leaching-tanks to secure such contact. After agitation and standing some time—from about twelve to seventy-two hours, or longer if necessary, according to the coarseness of the particles of gold—the solution is drawn off into pre-cipitating-tanks by opening a stop-cock communicating with the space between the two bottoms. Should the reddish-violet colour of the solutions become faint or vanish during leaching, then more of the solution must be added; but so long as the solution retains its reddish-violet colour it may be used for dissolving gold. The methods of precipitating gold are well known, and the sulphurous-acid or the ferroussulphate solution is preferred. By this invention the gold is dissolved rapidly as soon as the solution conies into contact with it, tiie gold taking the chlorine of the salt, whilst the sulphuric acid in the presence of the nascent oxygen from the permanganate takes the soda and the potash from the common salt and the permanganate respectively, the reaction thus being a case of concurrent attraction or affinity, therefore specific. We do not claim as part of our invention the use of the permanganates or manganates of potash or of soda in the above solution, but only the use of sulphuric acid and chloride of sodium in combination with the permanganates or manganates. Having now particularly described and ascertained the nature of our said invention, and in what manner the same is to be performed, we declare that what we claim is,— 1. The improved process for extracting gold from ores, minerals, or other gold-bearing substances consisting in submitting such ores, minerals, or other gold-bearing substances in a powdered condition to the action of a dilute solution containing sulphuric acid, chloride of sodium, permanganates or manganates of potash, and water, substantially as described.