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tion, where the two metals are brought into close contact with the easily reducible sulphurets. The successful and continued operations in Washoe, without the aid of any other chemical agents, sufficiently prove this statement. The experiments already cited in treating argentite and iron filings with mercury confirm the fact. Humboldt, in speaking of the amalgamation problem in Mexico, draws attention to this point and remarks upon the rapidity with which amalgamation was secured when the two metals were triturated together with argentite. This action of iron is obtained not only from the constant agitation maintained, which brings the pulp and metal in contact with the sides and bottom of the pan, but also from the amount of iron dissseminated, in a fine condition, through the ore, produced by the wear of the stamps, shoes, and dies.
This consumption of metal from the batteries and pans varies very much in the different mills, depending partly upon the details of construction and grinding effects of the pans and partly upon the hardness of the castings employed. The following figures from two mills serve to show the quantity of iron reaching the pulp from this source, per ton of ore worked. The quantity of ore treated is sufficiently large to afford a very fair estimate of the metal consumed:
The fine iron coming to the ore in this way is very considerable in proportion to the other minerals present. If ten pounds per ton are added from this source it is equal to one-half of one per cent. In the Kentuck ore, of which an analysis has been given, there is, including the iron from the batteries, less than 24 per cent. of ore-bearing minerals present.
Mercury and iron, under the proper conditions, undoubtedly are the principal agents in the extraction of the precious metals by the Washoe method. The results depend, however, in a great measure, upon the mechanical treatments employed to reduce the oro to an exceedingly fine state of division, and to maintain, with the proper degree of consistency, a constant agitation of the entire mass; the essential conditions of the amalgamation being that the mercury should be thoroughly incorporated in the pulp, and every particle of the reducible minerals brought in direct contact and triturated with the metal, in the manner so well accomplished by the friction and grinding action of the pan. The mercury should also at all times retain a bright, clean surface, free from any film of metallic salts, such as sub-chloride of mercury or sulphate of lead, and any coating of oil or grease. The slightest tarnish appears to retard very greatly the activity of the metal. The iron seems to act as an electro-chemical agent; the immediate contact of the two metals, aided by heat and friction, causing a local electric current, which renders the amalgamating energy of the mercury much more intense. Mercury, when perfectly pure, does not apparently possess to so great an extent the power of taking up other metals, or of decomposing mineral combinations, as when it holds a minute quantity of some foreign metal in solution. The experience among amalgamators in Mexico is that the yield of gold is increased by the presence of silver; also, that the latter metal is extracted with greater facility if a considerable proportion of the amalgam is already present. This opinion is held by most mill-men in Washoe.
It is stated by some writers upon the question that silver is absorbed with increased activity when copper is employed, and as the former is amalgamated the latter will be expelled. Both iron and copper cause the formation of copper-amalgam. On the other hand, sulphate of copper exhibits a tendency to drive out lead. Karsten mentions the property of this salt to purify the mercury from both zinc and antimony. Any one who has witnessed the intensity which sodium-amalgam exerts cannot fail to have been impressed with the rapidity with which it attacks gold, silver, and silver compounds; yet its application in Washoe, in practical operations, did not give such results as would warrant its general introduction in the process.
Although the presence of a small quantity of several metallic bodies enhances the amalgamating energy of the mercury, yet a slight excess "sickens" it; that is, it loses its fluidity and becomes dull and inactive. The peculiar phenomena attending the mercury, by which both electro-positive and electro-negative metals are absorbed, and the effects which they produce in increasing or neutralizing its action, are very little understood.
The loss in quicksilver during the operation arises from two sources; the one mechanical, the other chemical. The former depends largely upon the manner in which
the final washing from the pulp is conducted; the separation being more or less perfect according to the skill and care with which it is executed. A considerable quantity of the metal, however, is so cut up and ground to such a fine state of division that it is impossible to save it. The chemical loss is occasioned by the formation of the chlorides of mercury, which escape with the tailings.
In the patio the chemical loss is frequently very considerable; the amounts of common salt and magistral employed are large, while, at the same time, there is no reducing agent present to act upon the calomel formed, as is the case in the pan. In the patio the loss is said to increase in proportion to the richness of the ore in the sulphurets of silver, owing to the fact that for every atom of chloride of silver reduced by the mercury a corresponding atom of the latter metal is consumed as sub-chloride.
In the Washoe process the chemical loss would seem to be small in proportion to the entire consumption. This is probably due to the beneficial effects of the iron, which combines with the chlorine of the calomel, setting the quicksilver free.
The more the metal is ground the more it must be cut up, and the greater the difficulty in recovering it. Now, if the consumption of iron is assumed to measure the grinding effect exerted by the pan, the relation between the loss of mercury and that of iron should be, in a certain degree, proportional.
The following table, compiled from the results of several mills, furnishes some interesting details in regard to the loss of mercury:
Part 1 shows that the loss of mercury is independent of the consumption of chemical agents.
Part 2 shows that the loss of mercury is, in some measure, dependent upon the consumption of the iron of the pan.
Tons of ore.
5,400 8,603 4, 713 35,000
The following is the result of an analysis of some artificial crystals of Washoe amalgam:
They have the composition, very closely, of three atoms of mercury to one of silver. From the foregoing considerations of the principal features of the Washoe process it appears
That the ore consists chiefly of native gold, native silver, and argentiferous sulphurets, associated with varying proportions of blende and galena.
That the action of chloride of sodium and sulphate of copper in the pan produces chloride of copper.
That the presence of metallic iron necessarily causes the formation of the sub-chloride of copper.
That both the chlorides of copper assist in the reduction of the ore by chloridizing the sulphurets of silver, and in decomposing the sulphurets of lead and zinc.
That sulphate of copper enhances the amalgamating energy of mercury, by causing the formation of a small quantity of copper-amalgam. It also tends to expel the lead.
That notwithstanding the importance of chemical agents, as above indicated, the quantities added to the pulp, in the ordinary practice of Washoe mills, are too small to effect any very beneficial results.
That mercury and iron, aided by heat and friction, are the principal agents in the extraction of the precious metals by the Washoe process.
That the essential conditions in the amalgamation of the gold and silver are that the mercury be kept perfectly bright and pure, in order to produce a direct contact of that metal with the iron and sulphide of silver.
That the consumption of mercury in the Washoe process may be considered chiefly a mechanical, and, only to a limited extent, a chemical loss.
The Washoe process in Owyhee, Idaho.-I am indebted to Mr. John M. Adams, the superintendent of the Owyhee and other mills at Silon City, Idaho, for interesting notes upon certain details of the pan process as practiced by him.
The chemicals employed for different purposes connected with the amalgamation are salt, sulphate of copper, sulphate of iron, sal ammoniac, sulphuric acid, potash, gum catechu and cyanide of potassium, of which sal ammoniac and sulphate of iron are used by some mill-men of the district, but not by Mr. Adams. Chemical action is also due to the quicksilver, the iron pans, the friction of the grinding surfaces, and the heat given by the introduction of steam.
The exact effect of some of the chemicals is a moot question. Mr. Adams, whose scientific training and practical experience entitle his opinion to great respect, speaks substantially as follows concerning the subject, as connected with the Owyhee ores.
He does not think that salt alone chloridizes the ore in the pans, though it exercises a stimulating effect of some kind upon the amalgamation, as he has proved to his own satisfaction by working different charges of the same ore with nothing but quicksilver, and with nothing but salt and quicksilver. He finds, however, that the effect, though decidedly beneficial, is not very strong. I am inclined to infer from these observations that the salt does decompose, and therefore chloridize, certain minerals in the ore, possibly blende and galena, and that these minerals are minor elements of the ore.
Sulphate of copper, when added alone to the quicksilver in the pan, assists the amalgamation. This Mr. Adams explains as follows: the sulphate of copper is decomposed in contact with the iron of the pan, forming sulphate of iron and metallic copper; the latter continues the decomposition of already partially decomposed silver sulphurets in the ore. But this effect does not amount to a complete reduction of the silver sulphurets; which, indeed, cannot be accomplished with either salt or sulphate of copper alone.
These two chemicals together, however, give rise to a strong reducing agent, the sub-chloride of copper. Mr. Adams finds that this substance, employed in the proper proportion and for a sufficient time, will entirely reduce any of the minerals of silver, except those containing antimony, which salt and sulphate of copper, even employed together, fail to attack.
Any effect from sulphate of iron or sal-ammoniac he has failed to discover. Sulphuric acid will, to a certain extent, decompose sulphides of iron and copper, thus freeing some gold; and it attacks in a similar manner argentiferous compounds of iron, lead, and copper which do not contain antimony. Moreover, if kerosene, tar, or machine-grease, gets into the pan with the pulp, sulphuric acid will destroy it, and thus prevent the contamination of the quicksilver, which is detrimental to amalgamation. This acid also serves to keep clean the surface of the iron of the pan, which is thus enabled to exert continuously the reducing action.
Frequently tallow, grease, and candle-ends are brought in the ore from the mines, and pass into the pulp, where, if not counteracted, they will coat the mercury. The use of potash in the pan destroys the grease, and frequently, in drawing a charge into the settler, a thick scum, like soft-soap, will be seen floating on the surface of the liquid, while the quicksilver comes out perfectly clean and as bright as a mirror.
Cyanide of potassium has a beneficial effect in the pan; but its use in adequate quantity is too expensive at present prices. It may be em
ployed with advantage, however, to clean the quicksilver, or to collect it when floured or granulated. Gum catechu also is a cleansing agent.
The mill process at Owyhee is essentially the Washoe process. In the Owyhee mill the ore is broken in a Blake crusher, and delivered to the stamp-batteries, where it is pulverized with water, and discharged though screens, having 144 holes per square inch, into tanks. In these the pulp settles, and the water passes through other settling-tanks and out of the mill to the slime reservoirs, of which there are five. In these the light slimes are precipitated, to be reconveyed by means of a tramway, bull-wheel, rope, and car, to the mill for further treatment.
The pulp is taken by means of a car from the battery-tanks to the pans. Here it is mixed, ground, and amalgamated for six hours, steam and chemicals being employed to assist the process. From the pans the charge passes into settlers, thence into agitators, thence to Hungerford concentrators and Evans's riffles; and finally, the tailings pass over a string of blanket-sluices. The average yield of this mill, without reckoning the results of the reworking of the slimes, is 92 per cent. of the fire assay. This must certainly be regarded as the most successful application of the Washoe process in the country. The character of the ores no doubt facilitates their economical reduction; but the extraordinary efficiency of the mill is certainly due in large part to well-constructed machinery and to most skillful and faithful superintendence, coupled with constant study of the mechanical and metallurgical problems involved.
Those who find in the supposed imperfections of this or that process an excuse for heavy losses of the precious metals in reducing ores would do well to note such instances as this and profit by the example.
The Washoe process, as practiced by the Meadow Valley Mining Company in Ely District, Nevada, is described in the article upon Lincoln County in this report.
The extraction of gold by chlorination was introduced by the celebrated metallurgist, Plattner, a professor in the School of Mines, at Freiberg, Saxony. It is practiced in a few localities in Silesia, Hungary, Transylvania, etc., and is acknowledged to be the most complete method of gold extraction on a large scale. It was first introduced in this country, thirteen years ago, by G. W. Deetken, of Grass Valley, California, a skillful metallurgist, who has added some mechanical improvements to the process, and successfully overcome many difficulties arising in its local application. In the present chapter a general outline of the method will be given. For more detailed information recourse may be had to the work of Mr. Guido Küstel on Concentration and Chlorination, published in 1868 at San Francisco; and for later improvements and particulars not contained in that work, to Mr. Deetken himself, who still resides in Grass Valley, and may be considered the best authority on the subject.
The principle involved is the transformation of metallic gold, by means of chlorine gas, into soluble chloride of gold, (the aurum potabile of the alchemists,) which can be dissolved in cold water, and precipitated in the metallic state by sulphate of iron, or as sulphide of gold by sulphureted hydrogen gas. This precipitate may then be filtered, dried, and melted with suitable fluxes, to obtain a regulus of malleable gold.
From this brief statement, it follows that the following conditions are necessary to the success of the process:
1. The gold in the material subjected to the chlorine must be in a metallic state, and accessible to the gas.
2. There must be no other substances in the charge which will unite with free chlorine, since this would occasion a great waste of gas, and a failure in the desired separation of gold from other metals.
3. There must be nothing in the chlorine employed which will attack and render soluble other metals or bases; since this would render the subsequent solution and precipitate impure.
4. There must be no reaction in the mass treated with chlorine which will prematurely precipitate the gold before the final solution is obtained and drawn off.
5. In a word, it is required that all the gold, and, if possible, nothing else, shall be obtained in the final solution. Precipitation and melting then present no special difficulties.
The process naturally divides itself, therefore, into the preparation of the ore for the action of chlorine; the preparation of the chlorine; the chlorination proper; and the lixiviation, precipitation, and melting.
PRELIMINARY TREATMENT OF THE ORE.
Ores, consisting of quartz and free gold, without admixture of other earths or sulphurets, require no further preliminary treatment than reduction to powder. As the material subjected to chlorination has almost invariably been concentrated mechanically beforehand, no appa
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