The Chemistry Of Gold Extraction

The necessity for the presence of oxygen when gold dissolves in cyanide solution has been denied by Mr. The precipitate, however, is soluble in excess of either potassium cyanide or sodium hyposulphite. The solution would be made slightly acid by sulphuric or sulphurous acid, as might be most convenient. During smelting iron can be oxidized using nitre.

The Chemistry of Gold Extraction

Experiments were made with nitrate of silver, nitrate of lead, and mercurous nitrate. The present methods of precipitation, the electrical and the zinc-shavings method, both find in these dilute solutions their great difficulty. The filtrations were repeated through the same shavings four times. This reaction had also been given in almost the same words by Butters and Clennell.

The exact relation of these three reactions seems to depend on the strength of the cyanide-solution used. Sometimes gold is present as a minor constituent in a base metal e. It will be remembered that the formation of the insoluble cyanide of zinc is a feature of this reaction. It seems to be impossible to combine gold with sulphur alone in the dry way. There is no doubt that a certain tendency to form this reaction exists, for electrolysis proves it.

This explanation of the reaction was made. The turning-point would seem to be, is hydrogen formed as these reactions require, or is it absent, as called for by the substitution-reaction? Magnetic separation is also very effective for separating iron impurities. But it is just here that the cuprous method of precipitation comes into play most efficiently.

Since the date of its first discovery, this method of recovery of gold from cyanide-solutions has been repeatedly used in my laboratory, and has stood the most rigid tests. The gold will be contained in the residue. Recalling the fact that the sulphide of copper had been suggested by C.

Gravity concentration has been historically the most important way of extracting the native metal using pans or washing tables. There is one serious difficulty that it would meet. However, froth flotation processes may also be used to concentrate the gold. The result of my investigation was an entire confirmation of the accuracy of the Elsner reaction.

In fact, in some cases not the slightest trace of a precipitate will form for several hours, the liquor remaining clear as crystal. In the electrical process the resistance of such solutions is something enormous. Still a few words on the application of the process to ores may not be out of place. These experiments throw light on the statements often made that it has been possible to extract the gold from the ore but not from the solution.

The Chemistry of Gold Extraction

MacArthur, who claims the honor of the invention of the cyanide process. There still remains a great difference of opinion as to the condition in which gold occurs in its ores. Another method that was used was to add copper sulphate and then sulphydric acid to the acidified solution. Normally, the ore is crushed and agglomerated prior to heap leaching. The turnings have an infinite number of ragged edges, which favor the escape of the hydrogen gas, and the relief of the condition of polarization, and thus allow the reaction to proceed.

This led me to investigate the reaction which occurs. Or, as the two reactions are in reality simultaneous, this may be expressed, as has already been done by Mr.

The amount of gold that comes down at this point seems to depend on the amount of free acid contained in the zinc sulphate. Hence, this was one of the first points to which I turned my attention. Ellis, the nascent hydrogen may be at once seized by the excess of cyanide present and ammoniacal compounds formed.

In fact, it is well known that certain copper-minerals are active obstacles to the successful extraction of gold from its ores. The results of these studies, made on a large variety of ores, was to show in all cases a partial extraction of gold. Almarin Paul at his cyanide-works in Shasta county, Cal.

The Chemistry of Gold Extraction - John Marsden Iain House - Google Books


The Chemistry of Gold Extraction. Clennell and Edgar Smart, have contributed on the chemistry of the process, were among the first to give any adequate idea of its nature. It was also noticed that when copper sulphate was added to a strong solution of aurocyanide, microstation v8 software a white precipitate formed which contained gold and copper. The result of the experiments so far made has been to show that the tellurides of gold and silver experimented on both dissolve in the cyanide solution with the greatest difficulty. There is evidently no call here for oxygen or an oxidizing agent to increase the solubility of the gold.

The next experiments were made with lathe-turnings from the same sheet-zinc which, in the polished state, had failed to precipitate gold. In reality, these are the two opposite aspects of the same question. We have treated an ore with cyanide with free access of air, and then a parallel experiment was done with boiled water, the bottle filled to the stopper with solution and ore, and the stopper sealed. An antimonide of gold produced by fusion of the pure metals acted very much as did the telluride of gold. Pressure oxidation is an aqueous process for sulfur removal carried out in a continuous autoclave, operating at high pressures and somewhat elevated temperatures.

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From the filtrate from the zinc cyanide precipitate the gold may be recovered by sulphurous acid and copper sulphate, or cuprous chloride direct, as already described. Then there would be added a copper sulphate solution with common salt, which had been saturated with sulphurous acid.

Oxidizing agents, such as permanganate of potassium and peroxides of manganese and lead in acid solutions, also facilitate the precipitation. In the filtrate from the aurous cyanide the mercury could be saved and the cyanide recovered by adding, very exactly, the amount of sulphide of potassium to throw down the mercury as sulphide.

The Chemistry of Gold Extraction Second Edition (2nd ed.)

In such a case, and with richer ores and stronger solutions, there is sometimes a distinct advantage in the use of oxidizing agents. The latter may be entirely saturated without loss by using two vessels for condensation, the first receiving the saturated and the second a weaker solution. It is true that electrolytic methods of precipitation are used in the analytical laboratory as convenient methods of analysis.