C.—3

212

Although we have herein indicated certain proportions in which the haloid-cyanogen compound may be added to the potassium-cyanide, or other suitable cyanide, we do not bind ourselves to these proportions, and may use any mixtures of the above substances or compounds in any state of dilution in water, and may act with such solvents upon ore in any convenient manner—either at the ordinary or at increased or reduced temperatures and pressures, and upon greater or less proportions of ore or precious metal containing compound. The second part of our invention relates to the precipitation of gold or other precious metal from solutions obtained either by the before-described process, or from those obtained in the ordinary way by the action of potassium-cyanide solutions upon ores containing precious metals. The process generally adopted at present on the latter class of solutions consists in passing these slowly in a continuous stream through large masses of closely-packed zinc-shavings or granules, upon which the gold is deposited as an adherent powder from the soluble potassic aurocyanide with the formation of the double cyanide of zinc and potassium. Owing to the fact, however, that the quantity of zinc employed is many hundred times in excess of the theoretical requirements, and is, beyond this, still more in chemical excess of the liquor passing through it at any given moment, this metal acts freely upon the unaltered excess of potassium-cyanide contained in the liquor, deteriorating the latter as regards their applicability for fresh solvent purposes ; in fact, it is here that the great desturction of cyanide takes place in the present cyanide gold-recovery processes. Owing to this method of depositing gold extensive deposition plant is also required, the consumption of zinc is much greater than the theoretical requirements, considerable trouble is experienced in recovering the gold-deposit from the zinc-shavings, and the product finally obtained, being largely contaminated with zinc and other impurities, is difficult to refine. We find, on the contrary, that if zinc or other suitable metal or alloy be reduced to a state of the finest powder or flour, and be added to the bulk of gold or silver cyanide containing liquor in any suitable manner —say, for example, by seiving it upon the surface of the solution, or by aiding it in a state of suspension in water or liquor—the precipitation of the precious metal is very rapid, and is obtained with a consumption of precipitant a great many times less in quantity than, by the before-described method. We prefer to employ moderate agitation, and this may be provided for in any desirable manner ; where, for example, the powdered metal is applied by a stream of water or solution, this stream may be used for the purpose of agitation. In considering the question of agitation it is important to note that excessive agitation must be avoided —that is, if it would tend to promote aeration or oxidation of the liquor—since the presence of oxygen would tend to dissolve the zinc or other metallic powder employed in the cyanide without necessarily effecting the precipitation of the gold. The agitation may be effected by mechanical stirrers or by suitable circulation—say, by means of a pump, or like appliance capable of circulating the liquor without aeration; and, if necessary, the tank or vessel in which the operation takes place may be entirely closed in, and the solution protected from the air by the application or introduction of an inert gas over the surface of the liquor. The agent we prefer to use is the extremely finely-divided zinc, obtained by the condensation of its metallic vapour, such a product as is known as " zinc-dust." Further, the cyanide is left unacted upon, the deterioration again in this substance being considerably less than by the ordinary methods, inasmuch as the amount of zinc actually used is so very much smaller; there is thus a great saving in precipitating material, a great gain in labour and time, and in the amount of plant required. We may not require, in the case of the haloid-cyanogen solvent, to use the liquor obtained from the zinc precipitation for fresh solvent purposes, but if we intend so to do we may proceed to treat these with chlorine or other halogen for regenerative purposes, as before described. Having now particularly described and ascertained the nature of the said invention, and in what manner the same is to be performed we declare that what we claim is,— 1. The use of the halogen compounds of cyanogen in a solvent to precious metals. 2. The combination with cyanide of potassium or other cyanide, or of the alkalies or alkaline earths, of the chlorides, bromides, or iodides of cyanogen in or as a solvent for precious metals. 3. In a solvent for precious metals the formation of halogen compounds of cyanogen by the addition to cyanide of potassium or other cyanide of the alkalies, or of the alkaline earths in solution, of chlorine, bromine, or iodine in suitable proportions. 4. In a solvent for precious metals the formation of halogen compounds of cyanogen by the addition of chlorine, bromine, or iodine, or of mixtures capable of yielding these, to a solution of any suitable double cyanide or other suitable cyanogen, yielding compound other than the cyanides of the alkalies or alkaline earths. 5. The employment for the precipitation of precious metals from their solutions of zinc or other suitable metal or alloy, in the exceedingly fine state of division set forth with or without exclusion of air, substantially as herein described. 6. In the precipitation of precious metals from their solutions, the employment of zinc or other metal or alloy in an extremely fine state of division, obtained by condensing the vapours of the said metal or alloy. 7. In the recovery of precious metals from their ores, the combination with the halogen compounds of cyanogen in a, solvent of zinc-dust as a precipitant. 8. In the recovery of precious metals from their ores, the combination with cyanide of potassium or other cyanide, or of the alkalies or alkaline earths, and of the chlorides, bromides, or iodides of cyanogen in or as a solvent of zinc-dust as a precipitant. Henet Livingstone Sulman. Dated this 26th day of October, 1894. Frank Litherland Teed.