WO2011018550A1

WO2011018550A1 - Method for leaching of ore containing copper and cobalt

Info

Publication number: WO2011018550A1
Application number: PCT/FI2010/050619
Authority: WO
Inventors: Justin Salminen; Jari Tiihonen; Jussi Vaarno; Teemu Ritasalo; Jukka SÄÄMÄNEN
Original assignee: Outotec Oyj
Priority date: 2009-08-11
Filing date: 2010-08-06
Publication date: 2011-02-17
Also published as: ZA201201717B; FI20090294A; FI20090294A0; FI125439B

Abstract

The invention relates to a method for leaching an ore containing copper and cobalt in a reactor, where the copper and cobalt minerals of the ore are mainly oxidic and partially sulphidic. The copper and cobalt of the ground ore are leached at ambient pressure by means of a solution containing sulphuric acid, the pH of which has been regulated to the region of 0.8 - 3. The temperature has been adjusted at the start or at some stage of leaching to be above 5O0C and a maximum of the boiling point of the solution in order to leach the oxidic and sulphidic part of the ore. Oxygen-containing gas may be used as an aid to leaching.

Description

METHOD FOR LEACHING OF ORE CONTAINING COPPER AND COBALT

FIELD OF THE INVENTION

The invention relates to a method for leaching ore containing copper and cobalt in a reactor, whereby the copper and cobalt minerals of the ore are mainly oxidic and partly sulphidic. The copper and cobalt of the ground ore are leached with a solution containing sulphuric acid, where the pH is regulated to the region of 0.5 - 3 and the temperature at the start or at some stage of the leaching is regulated to be above 5O⁰C. Leaching is performed at ambient pressure.

BACKGROUND OF THE INVENTION

Copper recovery from copper sulphide ores takes place in the majority of cases pyrometallurgically, but hydrometallurgical methods have also been developed. Hydrometallurgical methods include pressure leaching, bio- leaching and leaching methods that occur by means of trivalent iron (Fe³⁺).

The copper content of oxidic copper ores is often lower than that of sulphide ores. Additionally, the flotation of oxidic ores does not produce such good results as the flotation of sulphide ores. Most often the copper mineral is present in oxidic ores for instance as carbonate, phosphate or sulphate and the copper concentration in the ores is around 0.1 -7%. If the copper content is low, heap leaching or bioleaching with weak sulphuric acid solution is often the copper recovery method used, after which the copper sulphate solution formed or the copper solution that forms is subjected to solution purification by means of extraction and the electrolytic recovery of metallic copper. The advantage of heap leaching and bioleaching is that grinding is not required, as crushing is sufficient, but the drawback is a low yield, which is generally around 60 - 80%, and long leaching times.

In addition to heap leaching, both ammoniacal leaching and chloride leaching have been used to recover copper from oxidic ores. The article by Mwema, M. et al: "Use of sulphur dioxide as reducing agent in cobalt leaching at Shituru hydrometallurgical plant", in the Journal of the South African Institute of Mining and Metallurgy, Jan/Feb. 2002, describes how, although copper oxide minerals dissolve easily into sulphuric acid solution, cobalt oxides are difficult to leach, particularly when they are in trivalent form. According to the study, trivalent cobalt dissolves best when sulphur dioxide is fed into the solution to reduce the cobalt to divalent. A test was carried out at a temperature of 4O⁰C, but the temperature was not found to have an effect on the leaching result. The pH of the solution at the start of leaching was about 4 and at the end about 2. However, even in the best results the cobalt yield was around 86%. Copper dissolves in these conditions quite little, so that the leaching thereof requires a separate process step.

PURPOSE OF THE INVENTION

The purpose of the invention now presented is to leach copper and cobalt from an ore in which the valuable metals in question are mainly in oxidic form, but some are also as sulphides. Harmful additives are avoided in leaching and the operation is run as simply as possible.

SUMMARY OF THE INVENTION

The essential features of the invention will be made apparent in the attached claims.

The invention relates to a method for leaching an ore containing copper and cobalt in a reactor at ambient pressure, where the copper and cobalt minerals of the ore are mainly oxidic and partially sulphidic. It is typical of the method that the copper and cobalt of the ground ore are leached by means of a solution of sulphuric acid, where the pH is regulated to the region of 0.5 - 3 and the temperature is adjusted at the start of leaching and at some leaching stage to be above 5O⁰C and a maximum of the boiling point of the solution. The sulphidic mineral of the ore is typically carrollite.

It is typical of the method that the ore is ground to a fineness of less than 100 μm, preferably to a fineness of 10 - 50 μm.

According to one embodiment of the method, the temperature is regulated at the start of leaching to be above 5O⁰C. According to another embodiment of the method, the temperature is adjusted in two or several stages so that at the start of leaching the temperature is the ambient temperature, whereby the oxide phases of the ore dissolve, and in the final part of the leaching stage the temperature is adjusted to be above 5O⁰C in order to leach the sulphidic and only partially dissolved oxidic minerals. It is typical of the method accordant with the invention that the sulphuric acid concentration of the solution used for leaching is 0-50 g/l.

According to one embodiment of the invention, oxygen-containing gas is fed into the leaching stage.

LIST OF DRAWINGS

Figure 1 presents a graph of the copper dissolution in the tests as a function of time, and

Figure 2 presents a graph of cobalt dissolution as a function of time.

DETAILED DESCRIPTION OF THE INVENTION

When the copper concentration in oxidic ore is higher than in an ore normally fed to heap leaching, for example above 2%, and the ore also includes another valuable metal, such as cobalt, ore leaching can also be performed in a reactor. In this case the ore must be ground to a suitable fineness before leaching treatment. The purpose of the method developed is to leach the copper and cobalt as effectively as possible from an ore mainly containing oxidic, but also sulphidic, minerals in a reactor using leaching under atmospheric pressure. The use of sulphur dioxide as an additive in the leaching of oxidic ore, especially ore containing cobalt, is mentioned in the prior art. However, the use of sulphur dioxide increases the ore processing costs. In addition, sulphur dioxide is poisonous, so its use is not desirable, especially in conditions where a high degree of safety has not been ensured.

When developing a suitable leaching method, ore was ground to a fineness of 18 - 50 μm. At the start of leaching the pH was adjusted to a value of 0.5- 3, so that the amount of sulphuric acid in solution was around 0-35 g/l. At the start of leaching the temperature was the ambient temperature and rose at the end of leaching to a value of about 40 - 5O⁰C. Sulphur dioxide was fed into the reactor to optimize leaching. The copper dissolved well, so that the yield was at most over 95%, but the cobalt yield remained at a maximum of around 85%. When the matter was studied it was found that the mineral in the ore that had remained undissolved was sulphidic carrollite (Cu(Co₅Ni)₂S₄), which contained about 30% of the cobalt in the ore.

Various alternatives were tested in order to improve the cobalt yield. When ore was used that had been ground to the same fineness as in the tests of the prior art, surprisingly the yield of both copper and particularly of cobalt improved when the sulphur dioxide feed was omitted. At the same time, the leaching temperature was raised so that at the start of leaching it was already above 5O⁰C, but nevertheless below the boiling point of the solution. The tests were conducted at ambient pressure. It was found in the research that the oxidic part, containing tenorite and heterogenite, dissolved easily even at a lower temperature, but the sulphidic carrollite, containing a significant amount of cobalt, dissolved only when the temperature was above

5O⁰C. Therefore the leaching conditions may be regulated so that the first stage of leaching is operated at ambient temperature and in the final stage of leaching the temperature is regulated to be above 5O⁰C, whereby the carrollite and any only partially dissolved oxidic minerals will dissolve. The yield was also improved by the fact that the pH of the leaching stage was adjusted at the start of the leaching stage to the region of 0.5 - 3. The feed of an oxygen-containing gas also speeded up the dissolution of the residue. The oxygen-containing gas is usually air, but it may also be oxygen-enriched air or oxygen. When feeding in oxygen-enriched air, the leaching yield of copper after six hours was 98% and that of cobalt 94%. When leaching was continued, the yield of copper was at best 99% and that of cobalt 95% with a leaching time of 12 hours. The yields were calculated from the solids content and are expressed as mass percentages.

After the leaching stage, copper and cobalt are in solution as sulphates and solution purification is carried out in the normal way by means of extraction, after which the copper is recovered electrolytically and the cobalt by extraction or precipitation.

EXAMPLES

Example 1

The ore used in the leaching tests was ground to a fineness of 25 - 28 μm.

Some was ground even finer, (20 μm), but grinding was not shown to have any significant effect on the final result. Copper was present in the ore mainly as tenorite (CuO), and cobalt as heterogenite (CoO(OH)) and carrollite (Cu(Co₅Ni)₂S₄). The gangue consisted mostly of silicate minerals (quartz and mica). In the first tests the ore was leached in an acidic solution of sulphuric acid at pH values of 0.8-1.5 (8-34 g/l H₂SO₄). At the start of leaching the temperature was the ambient temperature and rose at the end of the leaching stage to a value of around 40 - 5O⁰C as a consequence of the reaction heat. Sulphur dioxide was also fed into the reactor. The yield of copper into the solution was already over 94% after two hours of leaching and about 95% after six hours, as shown in the lowest curve in the graph of Figure 1. The lowest curve of the graph in Figure 2 shows that in these conditions the yield of cobalt into solution after two hours was only around 87% and after six hours a little over 88%.

In the following tests, the feed of sulphur dioxide was left out in accordance with the invention, but the temperature of the solution at the start of leaching was raised to a value of 6O⁰C. When the pH value of the solution was kept the same as when feeding sulphur dioxide (0.8-1.5 at the start of leaching), the leaching yield of copper after six hours was 98% and that of cobalt at 92%. When leaching was performed correspondingly with a feed of oxygen, the yield of copper was still the same, but the leaching yield of cobalt rose to a value of 95% after six hours. After 12 hours the cobalt concentrations of the tests with and without oxygen feed stabilised at a reading of about 94%. Both the leaching time and the yield are of great importance for the usability and economy of the method.

The method described can also be used to leach the sulphidic part of the ore (carrollite) and to improve considerably the recovery yield of cobalt in particular.

Claims

PATENT CLAIMS

1. A method for leaching ore containing copper and cobalt in a reactor at ambient pressure, where the copper and cobalt minerals of the ore are mostly oxidic and partially sulphidic, characterised in that the copper and cobalt of the ground ore are leached by means of a solution of sulphuric acid, the pH of which is regulated to the region of 0.5 - 3 and the temperature at the start of leaching or at some stage of leaching to be above 5O⁰C and a maximum of the boiling point of the solution.

2. A method according to claim 1 , characterised in that the ore is ground to a fineness of less than 100 μm.

3. A method according to claim 2, characterised in that the ore is ground to a fineness of 10 - 50 μm.

4. A method according to claim 1 , characterised in that the pH of leaching is regulated to the region of 0.8 - 1.5.

5. A method according to claim 1 , characterised in that the temperature is regulated at the start of leaching to be above 5O⁰C.

6. A method according to claim 1 , characterised in that the temperature is adjusted in two or multiple stages so that at the start of the leaching stage the temperature is the ambient temperature, whereupon the oxide phases of the ore dissolve and at the end of the leaching stage the temperature is adjusted to be above 5O⁰C in order to leach the sulphidic and only partially dissolved oxidic minerals.

7. A method according to claim 1 , characterised in that the sulphuric acid concentration of the solution used for leaching is less than 50 g/l.

8. A method according to claim 7, characterised in that the sulphuric acid concentration of the solution used for leaching is 8 - 34 g/l.

9. A method according to claim 1 , characterised in that the sulphidic mineral of the ore is carrollite.

10. A method according to claim 1 , characterised in that oxygen- containing gas is fed into the leaching stage.