WO2015075311A1

WO2015075311A1 - Method for direct leaching of coarse material

Info

Publication number: WO2015075311A1
Application number: PCT/FI2014/050884
Authority: WO
Inventors: Janne Karonen; Jari Tiihonen; Marko Latva-Kokko
Original assignee: Outotec (Finland) Oy
Priority date: 2013-11-20
Filing date: 2014-11-19
Publication date: 2015-05-28
Also published as: FI20136158L

Abstract

The invention relates to a method and an arrangement for recovering valuable metals by direct leaching of coarse material, such as material obtained from granulation of a molten metal, matte or slag.

Description

METHOD FOR DIRECT LEACHING OF COARSE MATERIAL

FIELD OF THE INVENTION

The present invention relates to a method for direct leaching of coarse material, especially material with poor grinding properties. BACKGROUND OF THE INVENTION

In many metallurgical processes, materials such as molten metal, matte or slag are granulated with water to produce relatively coarse material (a typical particle size in the range of 1 to 5 mm) for further processing. Today further processing as a rule comprises pyrometallurgical treatment, but also hydrometallurgical processes are known and considered. Before the hydro- metallurgical treatment, the material as a rule must be crushed and ground to achieve reasonable leaching rates. However, the crushing and grinding is challenging, because many metallic materials tend to deform in grinding, whereby inefficient grinding results are obtained. Consequently, improved crushing/- grinding methods or direct leaching technology have been applied.

US 6 319 389 B1 discloses a process of recovering copper values from a copper ore, such as secondary sulphides. The process comprises crushing and grinding the ore to a particle size between Tyler 4 mesh and 20 mesh (0.84 to 4.76 mm), classifying the ore to a fines fraction and one or more coarse fractions, followed by leaching the fractions separately. The leaching is performed by a batch or continuous mode in a counter-current reactor system. The leach solutions are then subjected to solvent extraction and electrowinning to recover copper.

US 4 152 142 discloses a process for recovering copper from a crushed or granulated copper-containing slag, comprising a leaching step. The document does not disclose or discuss the particle size of the granulated slag, nor the reactor type used in the leaching.

US 4 360 500 discloses a method of leaching metals, such as uranium and copper, from a uranium ore. The process comprises crushing the ore, forming slurry of the crushed ore and liquid, forming a bed of coarse particles below a bed of fine particles by feeding the slurry into a leaching tank, followed by leaching the ore beds by circulating liquid from the bottom of the tank upwards through the ore beds. US 4 880 607 discloses a method for recovering uranium values from ground uranium ore by separating the ore to a coarse fraction and a fine fraction, adding a diluent solid material to said fines fraction and leaching the diluted fines fraction. The coarse fraction is leached separately. The diluent solid material to be added to the fines fraction may be a barren part obtained from separate leaching of said coarse fraction. In one embodiment of the invention, the total ground ore is leached, followed by separating the leached ore into a coarse fraction and a fines fraction and further leaching of the fines fraction of the leached ore.

RU 2 133 290 C1 discloses a multistep counter-current leaching process for metal-containing granular materials. The treatment with the leaching solution is performed in troughs with a filtering bottom, whereby the granular metal-containing material is placed on the troughs with their vibration in vertical plane relative to the leaching solution.

One of the problems associated with the above methods is that they rely on very complicated crushing and grinding technologies as pretreatment before leaching. On the other hand, the direct treatment technologies described therein have not provided efficient leaching results. Consequently, there is a need for improved direct leaching technologies to avoid crushing and grinding, especially for materials with poor grinding properties.

BRIEF DESCRIPTION OF THE INVENTION

It is thus an object of the present invention to provide a method and an arrangement for implementing the method so as to solve the above problems. The objects of the invention are achieved by a method and an arrange- ment, which are characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on direct leaching of coarse materials having a relatively large particle size, which are inefficient to crush or grind. The leaching takes place using a specific process arrangement, which allows low intensi- ty mixing at the bottom of the leaching reactor to enable the leaching and reduction of the particle size of the coarse material, but prevents vortex formation at the surface of the reactor. Particles with a reduced particle size suspend and flow as a leach slurry out from the leaching reactor and can be collected therefrom. Thereafter further leaching can be performed in a conventional agitated reactor, if desired. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an exemplary embodiment of the method of invention in a leaching reactor.

Figure 2 shows an exemplary embodiment of the method of the in- vention in two leaching reactors.

Figure 3 shows the particle size distribution of granulated non-milled feed material of the Example.

Figure 4 shows the particle size distribution of the comparative milled and screened material of the Example.

Figure 5 shows the results of cobalt and copper analyses in the leach solution for the granulated non-milled feed material of the Example.

Figure 6 shows the results of cobalt and copper analyses in the leach solution for the comparative milled and screened material of the Example.

Figure 7 shows the redox potential during the leaching of the Example. DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method for direct leaching of coarse material. The method comprises

feeding the coarse material and a leaching liquor into a leaching reactor, which is provided with agitation means comprising an impeller adapted for causing circulation movement in the bottom part of the reactor,

forming a bed of the coarse material in the bottom part of the reactor, bringing the bed of the coarse material in contact with circulating leaching liquor by the agitation means in the bottom part of the reactor, to cause at least partial leaching of the coarse material leading to a decreased particle size of the coarse material and producing a leach slurry, and

withdrawing the leach slurry from the leaching reactor.

The coarse material used as the feed has a typical particle size in the range of 100 to 10 000 μητι, preferably 1 000 to 5 000 μηη. It is typically selected from coarse mineral and metal alloy materials.

In an embodiment of the invention, the coarse material used as the feed is obtained from granulation of a molten metal, matte or slag.

The feeding of the coarse material and/or the leaching liquor may be performed continuously or batchwise. In a preferred embodiment of the invention, the feeding takes place in a continuous manner. It is also possible to realize one of the feedings continuously and the other batchwise. The feeding of the coarse material is performed in downwards direction above the bed of coarse material, which is formed in the bottom part of the reactor. The feeding of the coarse material typically takes place from the top of the reactor. The feeding of the leaching liquor may also be performed in downwards direction, typically from the top of the reactor, but it is also possible to feed the leaching liquor for example from the bottom of reactor in upwards direction.

In a preferred embodiment of the invention, the feeding of the coarse material and the leaching liquor is performed concurrently in down- wards direction.

In an embodiment of the invention, said leaching reactor is further provided with baffles extending vertically on the inner walls of the reactor. In an embodiment of the invention, said leaching reactor is further provided with baffles extending vertically on the inner walls of the upper part of the reactor. In a further embodiment of the invention the leaching reactor is further provided with baffles extending vertically on the inner walls of the reactor from the upper part of the reactor to the bottom part of the reactor.

The agitation means adapted for causing circulation movement in the bottom part of the leaching reactor typically comprise a shaft and agitation impeller. When the reactor is provided with baffles, typically in the upper part of the reactor, the impeller is installed beneath said baffles. The agitation impeller may comprise one or more blades installed beneath said baffles, for example.

The agitation means in the bottom part of the reactor, preferably together with the baffles in the upper part of the reactor, allow slow rotating swirl- ing (circulation) movement with low mixing intensities at the bottom of the reactor, but still prevent vortex formation at the surface of the reactor. This arrangement provides the advantages of low energy requirement and low wear of the impeller blades. During the agitation, the particle size of the coarse material is decreased to a size where the material suspends and flows as a leach slurry out from the reactor.

The leach slurry withdrawn from the leaching reactor contains particles having a typical particle size of up to 500 μιτι.

In an embodiment of the present invention, the method comprises further leaching of the leach slurry to produce a pregnant leach solution and a solid leach residue. Said further leaching may be performed by any conventional means, for example in a further leaching reactor, which is provided with agitation means adapted for suspending solids in the reactor.

Said agitation means for suspending solids in said further leaching reactor typically comprise a shaft and an agitating impeller. The agitation impeller may comprise one or more blades, for example.

In an embodiment of the invention, said further leaching reactor is further provided with baffles extending vertically on the inner walls of the reactor from the upper part of the reactor to the bottom part of the reactor. Fur- thermore, in an embodiment of the invention, said baffles extend beneath the agitation impeller of the agitation means.

The leaching may be performed as acid, neutral or basic leaching. In acid leaching, the acid may be selected from sulphuric acid, for example.

The method may further comprise feeding a gas to the leaching. The method of the invention is typically applied to the recovery of valuable metals from the coarse material used as the feed. The valuable metals to be recovered may be any precious metals, for example copper or cobalt.

The invention also relates to an arrangement for recovering valuable metals by direct leaching of coarse material. The arrangement comprises

a leaching reactor (10), which is provided with agitation means (20) comprising an impeller adapted for causing circulation movement in the bottom part of the reactor.

In an embodiment of the invention, the leaching reactor is further provided with baffles (30) extending vertically on the inner walls of the upper part of the reactor.

The agitation means adapted for causing circulation movement in the bottom part of the leaching reactor (10) typically comprise a shaft (22) and an agitation impeller (25). When the leaching reactor is provided with baffles in the upper part of the reactor, the impeller is installed beneath said baffles (30). The impeller may comprise one or more blades, for example. An example of suitable agitation means is a vertical radial impeller with the blade(s) thereof installed beneath the baffles.

In an embodiment of the arrangement of the invention, said leaching reactor (10) is followed by a further leaching reactor (10'). Said further leaching reactor (10') is typically provided with agitation means (20') adapted for suspending solids in the reactor and with baffles (30') extending vertically on the inner walls of the reactor from the upper part of the reactor to the bottom part of the reactor.

Said agitation means (20') adapted for suspending solids in said further leaching reactor typically comprise a shaft (22') and an agitating impeller (25'). The agitation impeller may comprise one or more blades, for example. An example of suitable agitation means is a vertical radial impeller. Said baffles (30') typically extend beneath the agitation impeller (25') of the agitation means.

In the following, the invention will be described by referring to exemplary embodiments of Figures 1 and 2, which are not meant to limit the scope of the invention in any way.

Referring to Figure 1 , coarse feed material and leach liquor are con- tinuously and concurrently introduced to the top of a leaching reactor. The coarse feed material may be copper-containing metal smelt, matte or slag, for example. The leaching liquor is typically acid leaching liquor containing copper and iron sulphates. The leaching reactor is provided with baffles (30) in the upper part of the reactor as well as with a radial impeller (20) with the blades (25) beneath the baffles (30).

During the operation of the reactor, the coarse material with a relatively large particle size falls downwards in the reactor, forming a bed of the coarse material in the bottom part of the reactor. When the radial impeller is rotating, the bed of the coarse material is brought into contact with the circulat- ing leach liquor. At least partial leaching of the coarse material takes place, leading to a decreased particle size of the coarse material. Particles with a decreased particle size flow upwards in the reactor, forming a leach slurry together with the leach liquor. The leach slurry thus formed is withdrawn from above the bed of the coarse material of the reactor.

Referring to Figure 2, the leaching arrangement contains two reactors (10, 10'). The first leaching reactor (10) corresponds to that of Figure 1 . The second leaching reactor (10') is a conventional leaching reactor and differs from the first reactor in that the baffles (30') on the inner walls of the reactor extend from the upper part of the reactor to the lower part of the reactor, so that the baffles extend beneath the blades (25') of the agitation means (radial impeller). With this arrangement of the baffles and the radial impeller, further leaching takes place. The leach product is withdrawn from the top of the reactor and subjected to solid/liquid separation (S/L). A pregnant leach solution (PLS) containing desired metals and a solid leach residue are obtained.

In the following, the invention will be described with a further exem- plary embodiment of the invention, which is not meant to limit the scope of the invention in any way.

EXAMPLE

Following leaching tests were carried out with two different starting materials, i.e. (1 ) granulated non-milled cobalt and copper containing alloy and (2) milled cobalt and copper containing alloy (screened to a particle size below 1 mm). The granulation of starting material (1 ) was performed in a conventional way with water. The composition of the alloy used as the feed material is presented in Table 1 . The particle size distribution of the starting material (1 ) representing the coarse material of the invention is presented in Figure 3. The particle size distribution of the starting material (2) representing a reference material is presented in Figure 4.

Table 1. Chemical composition of the feed material

The alloy was pulped in a leaching solution containing copper and iron as sulphates in the amounts of 12 g/l and 6 g/l, respectively. The leaching test was carried out in an agitated reactor (volume 2 litres) corresponding to the arrangement of Figure 1 . The reactor was equipped with pH control (sulphuric acid), heating and oxygen feeding system. The process conditions and set-up are presented in Table 2. Table 2. Process conditions

Copper and cobalt leaching curves are presented in Figures 5 and 6. It can be seen that milling enhances the leaching kinetics but leaching is not considerably faster and thus the alloy can be efficiently leached also without any pre-treatment. In 15 hours high recoveries are reached for both cobalt and copper (98-99%). A better view on the difference between the non-milled and milled material behaviour can be seen in Figure 7 where the redox potential in the two tests has been shown. It can be concluded that milled material leaches initially faster (0-10 h), whereas the non-milled granules require approximately 3 hours longer leaching time. This is acceptable, since the milling process can be omitted.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The in- vention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. A method for direct leaching of coarse material, characterized in that the method comprises

feeding the coarse material and a leaching liquor into a leaching re- actor, which is provided with agitation means comprising an impeller adapted for causing circulation movement in the bottom part of the reactor,

forming a bed of the coarse material in the bottom part of the reactor,

bringing the bed of the coarse material in contact with circulating leaching liquor by the agitation means in the bottom part of the reactor, to cause at least partial leaching of the coarse material leading to a decreased particle size of the coarse material and producing a leach slurry, and

withdrawing the leach slurry from the leaching reactor.

2. The method as claimed in claim 1, characterized in that the coarse material used as the feed has a particle size in the range of 100 to

10000 pm, preferably 1000 to 5000 μηη.

3. The method as claimed in claim 1, characterized in that the coarse material used as the feed is selected from coarse mineral and metal alloy materials.

4. The method as claimed in any one of claims 1 to 3, c h a r a c - t e r i z e d in that the coarse material used as the feed is obtained from granulation of a molten metal, matte or slag.

5. The method as claimed in any one of the preceding claims, characterized in that the feeding of the coarse material and the leach- ing liquor is performed concurrently.

6. The method as claimed in any one of the preceding claims, characterized in that the leaching reactor is further provided with baffles extending vertically on the inner walls of the reactor.

7. The method as claimed in any one of the preceding claims, characterized in that the leaching reactor is further provided with baffles extending vertically on the inner walls of the upper part of the reactor.

8. The method as claimed in any one of the preceding claims, characterized in that leaching reactor is further provided with baffles extending vertically on the inner walls of the reactor from the upper part of the reactor to the bottom part of the reactor.

9. The method as claimed in any one of the preceding claims, characterized in that the leach slurry withdrawn from the leaching reactor contains particles having a particle size of up to 500 μιτι.

10. The method as claimed in any one of the preceding claims, characterized in that it comprises further leaching of the leach slurry to produce a pregnant leach solution and a solid leach residue.

11. The method as claimed in claim 10, characterized in that said further leaching is performed in a further leaching reactor.

12. The method as claimed in claim 11, characterized in that said further leaching reactor is provided with agitation means adapted for suspending solids in the reactor.

13. The method as claimed in claim 12, characterized in that said further leaching reactor is further provided with baffles extending vertically on the inner walls of the reactor from the upper part of the reactor to the bot- torn part of the reactor.

14. The method as claimed in any one of the preceding claims, characterized in that leaching is performed as acid, neutral or basic leaching.

15. The method as claimed in any one of the preceding claims, characterized in that the method further comprises feeding a gas to the leaching.

16. An arrangement for direct leaching of coarse material, characterized in that it comprises

17. The arrangement as claimed in claim 16, characterized in that it is further provided with baffles (30) extending vertically on the inner walls of the upper part of the reactor.

18. The arrangement a claimed in any one of claim 16 or 17, characterized in that said leaching reactor (10) is followed by a further leaching reactor (10').

19. The arrangement as claimed in claim 18, characterized in that said further leaching reactor (10') is provided with agitation means (20') adapted for suspending solids in the reactor and with baffles (30') extending vertically on the inner walls of the reactor from the upper part of the reactor to the bottom part of the reactor.