FI117709B - Procedure for the extraction of gold - Google Patents

Description

117709

METHOD FOR RECOVERY OF GOLD FIELD OF THE INVENTION

The present invention relates to a process for recovering gold from sulfur and iron-containing intermediate or waste from the leaching of a sulphidic raw material. Other precious metals and gold are recovered in the chloride environment. The gold contained in the intermediate or waste is dissolved in divalent copper and chlorine in a copper (II) chloride-sodium chloride solution under conditions of oxidation-reduction potential in the range of 650-10 750 mV and pH in the range of 1- 1.6. The acid formed by the chlorine feed is neutralized with a suitable base. Neutralization prevents costly dissolution of iron.

BACKGROUND OF THE INVENTION

In the prior art, some methods are known which have been used to dissolve gold from sulfur and iron-containing materials in the copper chloride-based recovery process.

U.S. Patent 4,551,213 describes a process by which gold can be dissolved in sulfur-containing materials, particularly hydrometallurgical materials. waste from processes. A preferred starting material for the process is CLEAR- * · · -.

process waste. The CLEAR process is a hydrometallurgical copper recovery • · · * · process that occurs in a chloride environment and under elevated pressure.

• · · ·

The gold-containing waste is slurried in water and the resulting suspension has a chloride content of * * · 25 adjusted to contain 12 to 38% by weight of chloride. The oxidation-reduction potential is adjusted within the range 650-750 mV and the pH is below 0.

«· ·

Copper (II) chloride or iron (III) chloride is added to the suspension to oxidize the gold in the · · · · raw material to dissolve it.

···· ··· • · ···. ·. ' ···. ···. EP 646185 relates to the recovery of copper from sulphide concentrates. chloride leaching under atmospheric conditions. Gold from the leaching residue is dissolved in an electrolyte containing at least two halides, such as 117709 2 sodium chloride and sodium bromide. The purpose is to store the oxidizing force at the anode of copper electrolysis into the bromine complex and thereby dissolve the gold in the waste.

5 The above methods have some drawbacks. In the process of U.S. Patent 4,551,213, the dissolution conditions are very stringent. It is stated in the patent that sulfur is not soluble under patent conditions but is not universal since the solubility properties of elemental sulfur and the iron compounds mentioned in the patent depend on the nature of the sulfur and the compounds in question. In our experiments, it has been found that when the leaching residues formed under atmospheric conditions are treated with the above-mentioned solution. under the conditions of the patent, the dissolution of sulfur and iron is considerable. Since the publication states that sulfur and iron do not dissolve, it does not mention how they are recovered from the solution. Again, the bromine complex leaching method used in EP 646185 is not advantageous from an environmental hygiene point of view, since the leaching steps of the concentrate can lead to harmful bromine emissions.

WO patent application 03/091463 describes a process for dissolving gold ..... from iron and sulfur-containing leaching residue or intermediate formed by atmospheric chloride leaching of copper sulphide concentrate.

• ··. . ·. It is stated in the publication that it is possible to dissolve gold in the material containing iron and sulfur • · 1J • ·· in an aqueous solution of copper (II) chloride-sodium chloride, · · · with bivalent copper and oxygen under oxidative conditions; the reduction potential is less than 650 mV and the pH of the solution is in the range 1-3.

· 1 · 25 Under these conditions, the iron is not yet soluble and sulfur is largely insoluble. ·: · This avoids the cost of removing iron and sulfur from the solution. The recovery of gold from the solution is done in a manner known per se, such as by electrolysis or activated carbon. That ··· 1- '.3 ·; The method itself is quite good, but in practice it is somewhat ··· 30 slow.

• ♦ • 1 φ · «· · ··· 2 • · 3 • · 1 117709 3

PURPOSE OF THE INVENTION

A process has now been developed for the recovery of gold from sulfur and iron containing intermediates or wastes from leaching of sulphidic raw materials. The leaching of the raw material is carried out with an aqueous solution of concentrated alkali chloride-5 (II) chloride under atmospheric conditions. When oxygen or oxygen-containing gas is fed to the leaching steps of the sulfide concentrate, the iron oxidizes and precipitates as an oxide or hydroxide, and the precious metals dissolve. The leaching of the gold from the remaining precipitate is carried out with aqueous alkali chloride-copper (II) chloride and chlorine under 10 atmospheric conditions. With the help of chlorine, the oxidation-reduction potential of the leaching step is raised to 650-750 mV. The high oxidation-reduction potential also causes the precipitate element to dissolve, and as a result, an acid is formed in the step, which is neutralized with a suitable base. By simultaneous neutralization of the acid, the pH is maintained at 1.0 to 1.6, thereby preventing the dissolution of iron.

The dissolved gold is recovered by any method known per se.

The essential features of the invention will be apparent from the appended claims.

* · · 20 • * ·

SUMMARY OF THE INVENTION

* · · * · *. ···. The gold-containing intermediate or waste is slurried in a suspension containing copper (II) chloride * ······························································ *** *** *** juuri juuri *** juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri juuri If the feed for gold leaching still contains *: * insoluble copper or other sulfide, an oxygen-containing gas may be introduced at the beginning of the leaching step to dissolve it. The oxidation-reduction potential is measured with Pt and Ag / AgCl electrodes and kept at * * · · 1 at 650-750 mV. The amount of divalent copper, Cu2 +, in the solution is * · · 30 preferably 20 to 80 g / l and sodium chloride in the order of 200 to 330 g / l. Gold • dissolves as a chloro complex according to the following reaction: · ·

Au + 3 Cu2 + + 6 Cl '-> AuCl4' + 3 Cu + + 2 Cl '(1) 4 117709

The dissolution takes place under atmospheric conditions at a temperature ranging from room temperature to the boiling point of the suspension, preferably at 80 ° C to the boiling point of the suspension.

5

Thus, it has now been found in experiments that the so-called reactive sludge with chlorine gas increasing the redox potential will accelerate the dissolution of gold. However, acceleration has its downsides. Increasing the redox potential increases the dissolution of the elemental sulfur (S °) in the material to be dissolved, which is likely to occur according to the following reaction (2).

S ° + 3 Cl 2 + 4 H 2 O 2 H 2 SO 4 + 6 HCl (2)

Reaction (2) shows that a large amount of acid is formed (8 mol H + / mol S °). However, the acid generated in the solution must be neutralized because below pH 1 the iron in the solids begins to dissolve. The dissolution of iron entails a cost to the process as the dissolved iron circulates and consumes the reagents. A preferred pH range for retaining iron in the precipitate is 1.0 - ..... 1-6 · • ·. . 20 • · · ...

• · ·

For acid neutralization, use is made of a suitable base which is one of the groups • · *

NaOH, KOH, CaO, CaCO 3 or MgO. If the process is combined with copper * · ***. chloride-based hydrometallurgical manufacturing process where: ···. the precipitation of divalent copper from leaching has produced • ♦ • · · 25 basic copper (II) chloride, the use of which is most advantageous. When:. *. the basic copper (II) chloride is soluble, the resulting copper (II) chloride can be I * · ·; ***. used to dissolve the raw material. The neutralization of hydrochloric acid and the leaching of copper oxide chloride is carried out according to the following reaction: • 3 · 4 · 3 · 4 · 4 · 4 * ♦ * · ·.

• · ··· • ·

The resulting sulfuric acid can be neutralized, for example, with lime: 5 117709 H2SO4 + CaCO3 · * CaSO4 2H2O + CO2 (4)

Gold is recovered from solution by any means known per se, such as activated carbon, electrolysis, or chemical precipitation.

LIST OF FIGURES

The process of the invention is further illustrated in the flow chart of Figure 1, where gold recovery is combined with copper hydrometallurgical recovery.

DETAILED DESCRIPTION OF THE INVENTION

As shown in Figure 1, a sulfide feedstock such as copper sulfide concentrate 2 is fed to the first leaching step 1, and the solution 3 from the subsequent process step, which is an aqueous solution of copper (II) chloride-sodium chloride, is also recycled. Thicker arrows represent the solids and thinner arrows the flow of the solution. The step always includes one or more reactors and thickening. The copper and other precious metals of the concentrate are mainly soluble in the process solution and the resulting solution 4 contains 20 copper chloride containing about 70 g / l of copper, mainly monovalent.

• ·. . ·. Further treatment of the copper chloride solution is not described in more detail herein * * *.

• * * • * * • * · ·

Dissolution of the solid 5 from the first leaching step is continued in the second leaching step 6 with the solution 7 obtained from the subsequent process step. Air is introduced into the reactors to enhance leaching of precious metals * · * and to precipitate iron in this step. At the end of the step is * ·· thickening.

Solution 3 from the second leaching step is led to the first leaching step 1 to dissolve the concentrate. The leaching of the solids 8 from the second leaching step is continued in the third step 9 to leach the remaining copper 6 117709 and gold. In the third leaching step, the gold leaching step, the precipitate is leached with copper (II) chloride-sodium chloride solution 10 having a Cu 2+ content of 20 to 80 g / l and a sodium chloride concentration of 200 to 330 g / l. If the precipitate entering this leaching step still contains insoluble sulfide, oxygen may also be introduced into the first reactor, most preferably in the form of air. Copper and other sulfides must be dissolved out of the precipitate before gold dissolves. Chlorine gas 11 is also introduced into the reactor to increase the redox potential to 650-750 mV. Due to its high potential, sulfur begins to dissolve and results in acid formation in step ίο. To ensure that the pH of the step does not fall below 1.0, a base 12 such as NaOH, KOH, CaO, CaCO 3 or MgO is added thereto. If the process is combined with a copper chloride-based hydrometallurgical manufacturing process where basic copper (II) chloride is precipitated upon precipitation of divalent copper from leaching, this is used.

15

The gold chloride complex solution 13 from the leaching step is passed either as such or filtered to the gold recovery, which in this exemplary case takes place on the carbon column 14 with activated carbon. The columns yield a gold product 15. The solution leaving column 14 is a gold-free solution 16, * *: 20, which is recycled to the second leaching step 6 and, if necessary, there. . *. passing a sodium chloride solution for dissolution to obtain a suitable concentration of copper (II) chloride. The gold recovery step precipitate is • * · * ·· after normal post-treatment such as filtration and washing (not shown in detail) »* ··, the final leaching residue 17 containing almost all of the concentrate sulfur 25 and iron. The precipitate filtrate and washings are returned, for example, to the leaching *: * process.

The flow chart of Figure 1 shows the gold leaching process * · · · in connection with the leaching of the copper-containing raw material, but is not bound by the method of the invention ··· ···, 30 • · copper leaching process. It is central to our process that the leaching of gold • · ♦ · material is carried out with bivalent copper and chlorine 7 117709 under conditions that increase the redox potential of the solution to 650-750 mV and neutralize the acid formed during sulfur dissolution to a pH of at least 1 , preferably at least between 1.0 and 1.6.

5 ••••••••••••••••••••••••• ·· • · · * ♦ • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·– EN EN products

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Claims (9)

A process for extracting gold from an intermediate or leach residue containing iron and sulfur formed by atmospheric chloride leaching of sulfidic raw material, gold being leached from the intermediate or ether in an aqueous solution of copper (II) chloride-sodium chloride under atmospheric conditions. the use of divalent copper in the solution and chlorine, whereby the oxidation reduction potential of the suspension formed is poured at a value of 650 - 750 mV, * *. ; Characterized in that the acid formed in the leaching of sulfur is neutralized with alkali and thus the pH is poured at a value of 1 to 1.6, whereby iron remains largely dissolved; the gold is extracted in some way in a manner known per se. * * * • * • · * * * 25 Process according to claim 1, characterized in that the amount of divalent: copper in the solution is 20 - 80g / l. • * · • · * • * * · • t *. ···. Process according to claim 1 or 2, characterized in that the amount of sodium chloride in the solution is 200 - 330g / l. 30 Method according to any of claims 1-3, characterized in that the temperature is poured into the range of 80 ° C - the boiling point of the suspension. 10 117709 Process according to any one of claims 1-4, characterized in that the acid formed during the leaching of sulfur is neutralized with basic copper (II) chloride. 5 6. A process according to any one of claims 1-4, characterized in that the acid formed in the leaching of sulfur is neutralized with alkali which is one of the group NaOH, KOH, CaO, CaCO3 or MgO. ίο Process according to any one of claims 1-6, characterized in that the leached gold is extracted by means of active koi. > Process according to any of claims 1-6, characterized in that the leached gold is recovered by electrolysis. 15 Method according to any of claims 1-6, characterized in that the leached gold is recovered by chemical precipitation. • ·. . 20 ··· * · · • · ... * • · * • · · * * * tt · • • • · * * tt • • · · · · · · · · · · · · · · · · • · * f f f f ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦