DE1049106B - Process for preparing gold-bearing ores for cyanide leaching - Google Patents

Description

The invention relates to a method for preparing gold-bearing arsenic-containing ores with iron and sulfur content for the cyanide leach.

Some otherwise valuable ores are only not mined and processed because of their high arsenic content. This particularly applies to some complex gold, silver, platinum, radium, uranium, nickel and cobalt ores often contained in or from iron or arsenic minerals such as arsenic pyrite Minerals are accompanied. This problem is also with some copper ores and to a lesser extent with some iron and pyrite "sulfur" ores.

Industrially, this reluctance to attempt to process ores with a significant arsenic content is based on a number of technical and economic factors. For example, most of the common metallurgical processes for the recovery of valuable metals from such ores involve the oxidation and removal of arsenic by evaporation. This is usually done in mechanically stirred roasters. Since the volatile arsenic compound formed in this treatment is a medium-valued oxide, in order to remove most of the arsenic, the roasting must be very carefully regulated between oxidation and reduction conditions. Roasting to completely remove arsenic is therefore a slow, multiple, and costly process. Another difficulty arises from the toxicity of these substances. Arsenic oxides are extremely toxic to both animal and vegetable life. Accordingly, they must be completely removed from the exhaust gases almost everywhere. The removal and collection of the arsenic is costly and requires extensive facilities. Also, there is usually little or no market for this product. Since As ₂ O _{3 is} somewhat soluble, the removal of arsenic vapor is a very serious problem. Waste lying on or under the ground, e.g. B. always bring a risk of poisoning for the water supply of a large area. The only economic method at hand for safely removing arsenic is to convert it into insoluble compounds which can be safely removed, or to dump the oxide from ships far out at sea. Both procedures are costly.

It was already known to use ores containing arsenic at higher temperature under pressure by means of oxygen or to treat oxygen-containing air and thereby convert the metals contained in the ores into soluble compounds convict. In this process, however, the leaching occurs under such conditions performed that all of the arsenic, the whole process

for the preparation of gold-bearing ores for cyanide leaching

Applicant:

Chemical Construction Corporation,
ίο New York, NY (V. St. A.)

Representative: Dr. F. Zumstein, patent attorney,
Munich 2, Brauhausstr. 4th

Claimed priority:
V. St. v. America January 19, 1951

Patrick John McGauley, Glen Cove, N.Y.,

and Swain Joseph Swainson, Darien (V. St. A.),

have been named as inventors

Sulfur and much of the iron goes into solution. According to the method according to the invention on the other hand, worked under conditions in which only minimal amounts of iron and arsenic are dissolved.

The known method is much more expensive, because for almost complete dissolution of the arsenic gas compressed against a pressure of over 40 atü must be supplied, which also has the disadvantage that it is then with very strong acidic, high arsenic solutions.

It is therefore the main aim of the present invention to develop a method which does not have these disadvantages and in which these metals, usually found together with arsenic, are simpler, lighter and

4.0 can be won more economically. The content of gold and other precious metals from such ores is easier to extract than can be obtained by the conventional procedures currently being carried out. Other valuable metals, in particular the non-ferrous metals, can also be extracted at the same time. According to the invention, the crushed ore is slurried with water or an aqueous mineral acid and the slurry an oxidation treatment with air, with oxygen-enriched air or with oxygen at temperatures between about 115 and about 345 ° C and a pressure which is greater than the vapor pressure of the slurry at the Reduction temperature, subjected and the p _E value of the slurry for re-evaluation

809 730/354

precipitation of the dissolved arsenic as iron arsenate is regulated so that it does not rise above 4.5, However, the acidity remains below 10% and the gold-containing residue in a known manner from the Solution is separated.

The sequence of the individual stages can be clearly seen from the flow chart.

According to the present process, not only the troublesome arsenic is removed, and indeed most of it together with iron, which is just as worthless, the resulting chemical bonds are not only in Water, but also completely insoluble in the lye. Hence, at least part of the iron becomes and all of the arsenic easily collected by filtering off, settling, etc. The insoluble arsenic compounds can be thrown away easily and openly, even in open rubbish ponds. The gold and others Metals in the retained solids can be more complete and economical than any previously known method can be obtained.

Although the process of the present invention has been applied to a wide variety of arsenic-sulfur-gold ores the main problems and their solution should be presented by discussing an example ore will. There are many different copper, cobalt, nickel ores, including some gold, silver 11. Like. Included. One such ore will now be described for discussion and illustration.

It is not necessary to adjust the particle size in the to be tied Reduce concentrate more than is necessary to remove the valuable mineral from dead rock to separate and to allow the appropriate transfer ils water slurry.

The liquid for slurrying and leaching the particles can be water, since it is sulfuric acid arises during oxidative leaching when the concentrate contains sulfur. The initial presence however, any acid helps initiate the reactions. Hence it is a thinned one Sulfuric acid solution is appropriate and usually used. Of course this could be an introduction Another cheap mineral acid could be added to the reaction, but this would not be useful. A sufficient amount of a suitable liquid containing sulfuric acid is considered to be one at inwhose steps of the overall process, e.g. B. in ft'Ietallgewinnungsschätze, which are discussed further below recirculated solution available. The content of this returned liquid Sulfuric acid can be very low, even very low. In almost all cases it will be more than enough Sulfuric acid formed during the oxidative leaching in order to carry out the necessary reactions. . '

A low degree of acidity favors the removal of the arsenic. The acid content should therefore not be greater than about 10%. He other hand, should fall below a p _H of about 4.5. ■ - -

. The oxidation by itself is carried out by passing an oxidizing gas through the slurry blows in a pressure vessel. For this purpose there is oxygen to prefer. For various reasons, however, economic considerations can be opposed speak of its use. Air enriched with oxygen or air alone can provide satisfactory Result to be used. When using the latter, the noticeable difference is what needs to be handled Volumes a disadvantage. Economic considerations become the optima for different locations and determine conditions. - -

The reaction is exothermic under oxidizing conditions. This makes it an easy-to-regulate process. The regulation is carried out in such a way that ¹ steam, nitrogen and / or other exhaust gases are allowed to flow out of the pressure vessel, in amounts which are sufficient to regulate the pressure and thus the temperature corresponding to it. With many sulfidic ores, this allows enough steam to be obtained for various steps of the process in and out of the facility. In some cases this may e.g. B. obtain the generation of at least a part of the force that is required to compress air for the oxidation reaction.

The operational facilities and conditions for the particular leaching may vary depending on the requirements the treatment and nature of the concentrate or residue can be varied. The leaching can be carried out in batches; expediently it is directed so that enriched Fluid is drained continuously. For example, a battery of caustic jars can gradually be used. Each vessel can be drained and in sequence at successive intervals be refilled to a river of treated. Material on the remainder of the procedure too to back up. With some types of equipment it is also tnög-Hch, a continuous supply and discharge of each the boiler.

A successful process requires insolubilizing all of the dissolved arsenic from the concentrate. This is usually done at least in part Presence of iron achieved during oxidation. The concentrates must therefore contain iron.

Some iron, usually as ferric salt, may also be available in the recycle liquors. If all of the available iron placed in the autoclave, ie in the caustic solution and / or as feed solids, is not equivalent to arsenic, then what is missing must be made up. If so desired, additional iron can easily be supplied by adding inexpensive iron minerals such as pyrite and the like.
Adding iron and sulfur to the

⁴ ^ Dispatch is, however, generally undesirable,

if neither is a winning ingredient represents. The arsenates of alkaline earth metals, especially those of calcium and magnesium, are just as or even more insoluble than that

so of iron. Lime, limestone, dolomite and the like can, be used. ·

. As shown in the flow chart, the addition of materials such as limestone may be performed as Erdalkajimetallquelle for setting a p _H in various ways. As shown above, e.g. B. favors high extraction of acid soluble metals at low arsenic extraction by p _H values below about 4 to 5, but with a content of less than 8 ° to 10 ° / o sulfuric acid. Limestone can be used to help maintain these conditions

■ or the like can be added / added directly to the tub as shown in the flow diagram. It can "also be added when the liquid is removed from this tank or tanks. This, however, requires treatment under pressure, a process; - requires a special apparatus and it is not desirable to eliminate this need _can.. you do, after "the slurry cooled and the pressure has been reduced · Accordingly, as favorable in 'the

Claims (2)

Flow paths shown, this operation can be performed after the slurry has cooled. Arsenates, which are deposited during a pH adjustment that takes place after leaching, are, however, free from gold-containing substances, since they are precipitates of substances which have previously been dissolved. Therefore, if it is desirable to process the residue left after leaching, the dissolved arsenic can be precipitated by adding cations to form arsenate after the undissolved leach residue has been collected and removed. Thus, as shown, the operation can be performed after the liquor slurry has been filtered. The filtrate is very easy to treat, any precipitate is filtered off, the arsenic residue is washed and discarded, and the treated filtrate and washing liquids are sent to the acid-soluble metals recovery system. The caustic residue collected during the first filtration is usually washed as shown. At least the first few wash fluids contain some dissolved salts. They are sent to the acid-soluble metal recovery system. The pjj setting can also be applied to the filtrate and washing liquids. However, there is no particular need for it. Usually the separated solids are washed to ensure recovery of all soluble salts. As shown in the flow sheet, the filtrate and wash liquids are usually combined. They now contain almost all of the acid-soluble metals originally present in the form of dissolved sulfates. The present process primarily relates to the extraction of precious metals such as gold. The solids remaining after the filtration are therefore subjected to cyanide leaching in a known manner in order to obtain the gold. With regard to cyanide leaching, one striking observation must be made. Because of the effective iron-arsenic removal and the precipitation of the solids in an easily leachable form, a noticeable saving in cyanide consumption is obtained. Complete recovery of gold, platinum, and the like can be achieved using one-twentieth to one-fourth the amount of cyanide that would be required to recover an equal amount of gold from another sample of the same ore by conventional cyanide treatment procedures. An illustration of the effectiveness of the overall process is given in the following examples. Two concentrates were treated for these samples, the analyzes of which were as follows: Arsenic .., Iron .., Sulfur Gold Sample I 16.72% 48.0 g / t Sample II 30.79% 31.32% 19.90% 33.8 g / t Example I A part of sample I was mixed with about 3 parts of an alkaline solution of sodium cyanide and the resulting slurry was ground to an extremely fine powder in the course of 20 milling hours. The enriched liquor was removed with the solids washed, analyzed and discarded. The solution was examined for gold content and loss of cyanide. In various approaches, 77 to 82% of the gold content was recovered with a cyanide consumption of 8160 to 9500 g per ton of concentrate. Example II One part of Sample I was mixed with 3 parts of a leach liquor containing 10%> sulfuric acid to form an aqueous slurry and the slurry was placed in an autoclave and heated to approximately 232 ° C for about 2 hours while it was subjected to an oxidation treatment with oxygen at a partial pressure of about 10 atm. The treated slurry was depressurized, the slurry cooled, filtered, and the residue washed and neutralized with limestone. The neutralized and washed residue was further treated with an alkaline solution of sodium cyanide and calcined lime for 20 hours. The solid was separated from the liquid, washed, analyzed and discarded. The liquid was analyzed for its gold content and loss of cyanide. About 97% of the gold was found in the cyanide solution, but cyanide reagent had been consumed in the extremely low amount of less than 453 grams of reagent per ton of concentrate treated. Example III 1 part of Sample 2 was mixed with approximately 3 parts of water to form an aqueous slurry and the resulting slurry was placed in an autoclave and further treated according to the procedure described in Example II with the following exceptions: Limestone was added to the was added to the hot autoclave after the pressure was removed to bring the pH to about 4.0, and the washed slurry from the autoclave was briefly grinded by treatment with cyanide prior to extraction of the gold. Approximately 99.6% of the gold was found in the cyanide solution. Cyanide reagent had been consumed to an extent of less than 226 grams per tonne of ore treated. Patent claims: 1. A process for the preparation of gold-bearing, arsenic-rich ores with iron and sulfur content for cyanide leaching, characterized in that the crushed ore is slurried with water or an aqueous mineral acid and the slurry is an oxidation treatment with air, with oxygen-enriched air or with oxygen at temperatures between that is greater than about 115 and about 345 ° C and a pressure is subjected than the vapor pressure of the slurry at the reduction temperature and the _pH value is regulated to the slurry for the purpose of reprecipitation the previous in solution arsenic as ferric arsenate so that it does not 4.5 increases, but the acid content remains below 10% and the gold-containing residue is separated from the solution in a known manner. 2. The method according to claim 1, characterized in that the oxidized liquid so much