AU2008207581A1 - Vat Leaching of Nickel Laterite Ores - Google Patents

Description

00 VAT LEACHING OF NICKEL LATERITE ORES (Ni ;FIELD OF THE INVENTION 00 C1 5 The present invention relates to the dissolution of nickel and cobalt from nickel laterite ores by means of the so-called vat leaching technology.

00 BACKGROUND TO THE INVENTION 00 In this specification, where a document, act or item of knowledge is referred C to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was, at the priority date: a) part of the common knowledge; or b) known to be relevant to attempt to solve any problem with which this specification is concerned.

Laterite ores constitute the dominant source of nickel and are known to have complex and variable compositions as a direct consequence of their mode of formation and almost without exception occur as surface deposits. Laterite ores typically have a rocky, crumbly, earthy or clayey nature and typically have a low strength. Nickel, and to a lesser extent cobalt, is known to be directly associated with a wide range of minerals that make up the lateritic ore. In simple terms, the upper zone tends to have a relatively high iron/magnesium ratio, this zone often been known as the ferruginous zone. A significant proportion of the nickel is generally associated with iron oxide type minerals such as goethite. The bottom zone, the saprolite or silicate zone, has a relative low iron/magnesium ratio in which the nickel is generally present as a lattice component of a number of sheet and three-dimensional silicate minerals. The intermediate zone is a mixture of the two end members.

The most favorable technically and commercially viable processing option for nickel laterite ores is determined by, amongst other things, the nickel cobalt grade, tonnage, mineralogy, particularly the iron/magnesium ratio, process water quality and availability and other infrastructure considerations.

00 O Nickel laterite ores that have a relatively high iron/magnesium ratio are generally most economically treated by leaching with sulphuric acid of the appropriate ;concentration.

Where the nickel content is relatively high, say above and significant 00 C' 5 tonnages of ore are available, such ores are generally leached with sulphuric acid at temperatures typically about 215-230 0 C the so-called High Pressure Acid Leach (HPAL) 00 process. These aggressive conditions have considerable cost implications with respect to materials of construction, process control strategies, maintenance requirements, etc.

Alternative process technologies with lower capital costs are generally 00 required for lateritic ores of a lower nickel grade and/or higher to low grade nickel laterite ores of modest to small deposit size. One such process is heap leaching. This technology has and continues to be applied to the recovery of base and precious metals from a wide range of ores and concentrated and has recently undergone evaluation for nickel laterite processing at the demonstration scale.

The efficiency of a heap leaching process is determined by a combination of physical and chemical factors, including but not limited to the feed mineralogy, any changes in heap porosity and permeability because of dissolution and/or precipitation processes that occur during the leach process, external factors such as excessive rainfall, process water quality, downstream unit processes, etc.

A potential major problem with heap leaching of nickel laterite ores is the geotechnical stability of the heap during the leach and subsequent washing cycles that will typically last for a total of 200-400 days. A critical factor in determining the rate and extent of nickel dissolution is directly related to the heap permeability. Because heap leaching of nickel laterite ores is non-selective, a considerable proportion of the iron, magnesium and aluminium contents of the feedstock, as well as the nickel and cobalt contents, will go into solution as leaching proceeds, at least in the initial stages. Typically there is a mass/volume reduction of 30-40% and this potentially leads to physical instability of the heap. The situation is further complicated by generation of channels that lead to short circuiting of the leachant as it flows down through the heap and thus incomplete dissolution of the nickel and cobalt components, but also in situ precipitation of iron-containing products such as jarosites. These jarosite precipitates can also induce short circuiting and can eventually plug the system such that the leachant cannot pass through the heap.

00 O Because of the different reactivities of the different ore zones that make up the overall lateritic orebody, heap leaching of nickel laterites is, almost without exception, ;carried out with a blended feedstock that is based on a detailed analysis of the total ore resource. In this manner, the feed or irrigation rate and composition of the leachant can be 00 5 fixed and ultimately controlled within a relatively small but controllable range.

In a number of instances, nickel laterite heap leach efficiency can 00 potentially be improved and subjected to great control by agglomerating the feedstock as part of the heap construction operation. This adds to both capital and operating costs.

C From a production point-of-view, heap leaching of nickel laterites can be 00 O 10 characterised as having an extended ramp-up period, as there will be virtually no pregnant N, nickel-containing liquor recovered from the heap for a considerable period, say for 3-6 months after leaching is commenced that can be directly forwarded to the downstream nickel and/or cobalt recovery circuit(s). This has considerable implications with respect to project cashflow.

The present invention involves an alternative method of subjecting the nickel laterite ore to an acidic sulphate leaching process that overcomes many of the problems that characterise both the HPAL and the heap leaching technologies.

DESCRIPTION OF THE INVENTION According to one non-limiting aspect of the present invention there is provided a method for acidic sulphate leaching of nickel and/or cobalt contents of a nickel laterite ore or concentrate using a vat leaching method comprising the steps of: a) preparing a feedstock containing a nickel laterite ore or a nickel laterite concentrate and loading the feedstock into a vat leaching vessel or series of vessels; and b) passing the acidic sulphate leachant through the feedstock body and collecting a nickel- and cobalt-containing pregnant leach solution overflow.

In some embodiments, the acidic sulphate leachant is passed up through the feedstock body. Upflow of the leachant is a preferred mode of operation because fines present in the leaching vessel will tend to be carried upwardly by the solution flow and will exit with the overflow from the top of the vessel. In contrast, using downflow of the leachant could result in a tendency for the fines to be carried towards the bottom of the leaching vessel and cause plugging. Furthermore, it is believed that "channelling" (in 00 0 which the leachant establishes flow channels through the ore body and flows through those flow channels, which undesirably minimises contact between the ore body and the ;leachant) is likely to be minimised if upflow of the leachant is utilised.

The pregnant leach solution may be sent for appropriate downstream 00 5 treatment for the recovery of appropriate nickel- and cobalt-containing product(s). The dissolved nickel and cobalt may ultimately be recovered as a marketable product, such 00 product including but not limited to a mixed nickel-cobalt hydroxide, a mixed nickelcobalt carbonate, a mixed nickel-cobalt sulphide, nickel metal, cobalt metal, or another ,I suitable nickel- and/or cobalt-containing salt. The downstream processing of the pregnant 00 leach liquor may utilise any known techniques or processes to recover nickel, a nickel- N, containing material, cobalt or a cobalt-containing material from the leach solution.

The feedstock may be prepared using conventional techniques. In some embodiments, preparation of the feedstock may include one or more of the following steps: forming an approximate average blend of the major ore zones of the entire nickel laterite orebody; crushing the blended ore feedstock to an appropriate top size.

An appropriate top size may be, for example, 5-15 mm.

In some embodiments, the feedstock comprises nickel laterite ores that have undergone a physical beneficiation process whereby the nickel and/or cobalt grades of the as-mined ore have been increased by means of rejection of gangue material that is essentially low in nickel and/or cobalt or even nickel and/or cobalt free.

In some embodiments, feedstock comprises as-mined nickel and cobalt laterite ores. In other embodiments, the feedstock comprises from as-mined nickel and cobalt laterite ores that have been physically upgraded by appropriate beneficiation methods, in which the feedstock has been subjected to an agglomeration process prior to dissolution of the nickel and cobalt by means of the acidic leachant.

In some embodiments, the process uses an acidic leachant, said acidic leachant including sulphuric acid, nitric acid or hydrochloric acid of the appropriate concentration.

In some embodiments, the leachant is sulphuric acid.

In some embodiments, the feedstock is agglomerated using an agglomeration process which is carried out with a sulphuric acid-containing solution. The composition of the sulphuric acid-containing solution may be adjusted by mixing the 00 O appropriate volume of fresh concentrated sulphuric acid with an appropriate volume of fresh process water and/or recycled process water from another section of the overall ;process flowsheet.

In some embodiments, the agglomeration process incorporates the addition 00 C' 5 of a suitable binding agent.

In some embodiments, the vat leaching vessels may be constructed from 00 suitable materials of construction, having a circular, square or rectangular cross-section

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and a vertical height for the volume of contained nickel- and cobalt-containing feedstock I appropriate for the required reaction (retention) time to achieve the required nickel and/or 00 0 10 cobalt dissolution as determined by the volume and concentration of the acidic sulphate CI leachant passed through the body of the feedstock. The vertical:horizontal height dimension ratio of the vat leaching facility will typically fall in the range 1:4 to 1:10.

In some embodiments, the present invention relates more particularly but not exclusively to the process whereby the nickel- and cobalt-containing feedstock is placed in a suitable vat leaching facility that incorporates appropriate means of addition of the acidic leachant to the bottom of the vat with a suitable overflow system at the top of the vat to collect and draw off the nickel- and cobalt-containing solution generated by the upflow of the acidic leachant through the body of nickel- and cobalt-containing feedstock contained within the vat leaching facility. In some embodiments, the leachant is evenly dispersed across the horizontal aspect of the leaching vessel. This may be achieved, for example, by providing a plurality of leachant outlets that supply leachant to the leaching vessel. The plurality of leachant outlets may be evenly spaced around the vessel.

In some embodiments, the present invention relates more particularly but not exclusively to the process whereby the nickel- and cobalt-containing feedstock is placed in a suitable vat leaching facility that incorporates appropriate means of addition of the acidic leachant to the top of the vat with a suitable solution discharge system at the bottom of that vat to collect and draw off the nickel- and cobalt-containing solution generated by the downflow of the acidic leachant through the body of nickel- and cobaltcontaining feedstock contained within the vat leaching facility. In some embodiments, the leachant is evenly dispersed across the horizontal aspect of the leaching vessel. This may be achieved, for example, by providing a plurality of leachant outlets that supply leachant to the leaching vessel. The plurality of leachant outlets may be evenly spaced around the vessel.

00 O In some embodiments, means are provided whereby the acidic sulphate N, leachant is dispersed evenly across the cross-section of the nickel- and cobalt-containing tb3 ;feedstock contained within the vat leaching facility using either the downflow or the 0 upflow passage of the acidic sulphate leachant through the feedstock.

00 C' 5 Subject to resource property considerations including but not limited to ore mineralogy, tonnage, nickel and cobalt dissolution kinetics as a function of acidic sulphate 00 leachant concentration and flowrate, the run-of-mine feedstock may or may not be

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subjected to an initial physical beneficiation step as an additional component of the feed I preparation (crushing) step, and may or may not be subjected to an agglomeration step 00 following the crushing step ahead of loading the vat(s) prior to commencement of the leaching stage.

To enhance the overall rate and extent of nickel and cobalt dissolution the composition of the acidic sulphate leachant passed upwards through the feedstock contained within the or each vat may be adjusted from time to time in order to prevent any undesirable precipitation reactions occurring within the feedstock as acid is consumed. For convenience, this is controlled by ensuring that the pH of the pregnant liquor overflowing from each vat is less than about 2.8.

To enhance the overall rate and extent of nickel and cobalt dissolution the acidic sulphate leachant passed upwards through the feedstock contained within the or each vat may be recycled a number of times before the pregnant nickel- and cobalt-containing solution is forwarded to the downstream areas of the overall process flowsheet where suitable nickel- and cobalt-containing products are recovered. In this manner the nickel and cobalt contents of the overflowing liquor can be increased to a suitable level before the final product recovery stages.

Once the desired level of nickel and cobalt dissolution has been achieved, the nickel- and cobalt-containing solution held within each vat is removed and the solids washed free of any soluble nickel and cobalt. This can be achieved by passing several bed volumes of a fresh, slightly acidic solution up through the leached feedstock and recovering this solution in a separate circuit. This wash solution can be used to make up fresh leachant for the next vat leaching cycle. Alternatively, the vat can be drained ahead of a water flush stage.

In some embodiments, the leachant may be heated. This is believed to increase the rate and efficiency of leaching/extraction. The leachant may be heated prior to 00 0 feeding it to the leaching vessel(s) or it may be heated in the vessel(s). Any suitable form of heating may be used. As laterite deposits are often located in hot regions, solar heating ;may be useful.

Once leaching and washing has been completed, the leached solids can be 00 C 5 removed from each vat by suitable means and transferred to a suitable impoundment facility.

00 Fresh feedstock can now be loaded into the vat(s) and the leach cycle Vt) recommenced.

The skilled person will understand that the vat leaching operating 00 parameters, such as the crushing top size, any requirement for agglomeration ahead of N, leaching, the concentration and flowrate of the acidic sulphate leachant, the extent of recycle of pregnant leach liquor ahead of final product recovery, the degree of leached solids washing, etc., are determined by a number of technical and economic factors that are a reflection of the nickel laterite resource itself, as well as local infrastructure facilities.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a schematic diagram of a leaching vat suitable for use in an embodiment of the present invention; and Figure 2 shows a schematic flow sheet of a leaching process in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS It will be understood that the figures show preferred embodiments of the present invention. Therefore, the invention should not be considered to be limited solely to the features as shown in the attached drawings.

Figure 1 shows a leaching vat suitable for use in an embodiment of the present invention. The leaching vat comprises a vessel 12 having a bottom 14 and a top 16. Top 16 is an open top. The vessel 12 includes a side wall 18. The vessel 12 may be of any particular shape, although a cylindrical vessel is suitably used.

The vessel includes a plurality of pipes 20 (only some of which are numbered in figure Pipes 20 extend through the top and downwardly into the vessel 00 O and have openings at their lower ends. The pipes 20 are connected to respective manifolds N, 22A, 22B, etc. The manifolds 22A, 22B, etc in turn are connected to a supply pipe 24.

;Supply pipe 24 receives a leaching solution, such as from acid supply pump 26.

0 Alternatively, the supply pipe 24 may receive leaching solution in the form of an oO 5 intermediate leaching solution from pump 28. There also exists the capability of adding brine or raw water 30 in order to control the concentration or pH of the leaching solution.

00 The leaching solution(s) is provided via pipe 24 and into manifolds 22A, 22B, etc and thereafter into pipes 20. The leaching solution exit the lower end of pipes 20 and flow upwardly through the leaching vat 10 and overflows the top 16 of the vessel 12.

00 The overflow liquid from leaching vat 10 contains dissolved metal. The CI overflow liquid is collected in collection gutter 32. In this regard, the overflow liquid flows downwardly over the side wall 18 of loaded leaching solution from leaching vat This liquid may either be sent to a metals recovery circuit or a metal compound recovery circuit, or it may be fed as a leaching solution to a further leaching vat. In this regard, the overflow gutter 32 has outlet pipes 34 having a control valve 35 thererin. Pipes 34 provide the overflow liquid to pump 36 which then passes the overflow liquid to the desired next processing step.

It will be appreciated that the leaching vat 10 is filled with ore or concentrate prior to passing the leaching solution there through. Once the ore or concentrate has been leached, it is removed via line 38 to a tailings pump box.

The leaching vat 10 shown in figure 1 may also include other piping, generally denoted by reference numeral 40, arranged to be placed in fluid communication with the liquid feed streams 26, 28, 30, to enable the liquid feed streams to be passed to other parts of the overall flow sheet.

Figure 2 shows a flow sheet showing one embodiment of the present invention. The flow sheet showing in figure 2 represents a snapshot of the operation of a flow sheet at a particular stage in time. In figure 2, the flow sheet includes six leaching vats 100, 102, 104, 106, 108 and 110. The vat 100 is denoted as a filling vat and it is filled with ore, concentrate or agglomerates 112.

The flow sheet is also provided with piping to enable appropriate liquid solutions to be transferred to each of the vats. In particular, an acid supply 114 is connected via line 116 to a leaching solution pond 118. Leaching solution pond also has an overflows storm pond 119 that can receive overflow leaching solution in the event of a 00 O storm or heavy rainfall event. Similarly, return water and acid from other parts of the N, overall metals recovery flow sheet 120 is supplied via line 122 to the leaching solution ;pond 118. Similarly, redox anolyte bleed solution 124, which may be obtained from an 0 electrowinning plant, is conveyed via line 126 to the leaching solution pond 118.

oO C' 5 A leaching solution supply line 128 is fitted with a leaching solution pump 130 and is used to transfer leaching solution from the leaching solution pond 118 to the 00 filling vat 110.

Vats 102, 104 and 106 are leaching vats. Vat 106 receives leaching solution I via line 132 and pump 134. The leaching solution passes through vat 106 and extracts or 00 oO leaches some of the metal values from the ore, concentrate or agglomerates contained in N, the vat 106. After the appropriate liquid residence time has passed, the leaching solution overflows vat 106 and is recovered and sent to vat pond 136.

The leaching solution (which now contains some dissolved metal values) from the vat pond 136 is transferred via pump 138 and line 142 to the leaching vat 104.

The leaching solution extracts or leaches further metal values from the ore, concentrate or agglomerates contained in vat 104. After the appropriate residence time has passed, the leaching solution overflows vat 104 and is recovered and sent to vat pond 142. Additional makeup acid can be added to vat pond 142 via line 144.

The solution from vat pond 142 is sent via pump 146 and line 148 to leaching vat 102. After extracting further metal values from the ore, concentrate or agglomerates, the leaching solution overflows vat 102 and is supplied to vat pond 150.

The leaching solution recovered from vat 102 represents pregnant leaching solution and it is transferred via line 152 into pregnant leach solution pond 154. The pregnant leach solution may then be transferred via pump 156 and line 158 to a metals recovery circuit. For example, the pregnant lead solution may be bled to an ion exchange recovery circuit, as represented schematically by reference 160 in figure 2. Other metal recovery operations may also be used.

As a further option, precipitated solids 164 from a part of the metals recovery circuit may also be fed to vat 102 to leach further valuable metal values therefrom.

It will be appreciated that leaching vats 102, 104, 106 are arranged to be counter currently leached with the leaching solution.

00 Once the ore, concentrate or agglomerates have been leached to the desired extent, it is necessary to wash the solid residue and remove the solid residue from the vat.

;In the flow sheet shown in figure 2, the vat 108 is a rinsing vat. Vat 108 receives water 0 from a raw water pond 170. In this regard, raw water is pumped via pump 172 and line 00 S 5 174 into rinsing vat 108. The overflow liquid coming from rinsing vat 108, which contains acid values, is sent via line 176 to the leach solution pond 118.

00 After rinsing the solid residue in vat 108, the solid residue is removed at vat Vt) r 110. Water filter backwash 186 and NF concentrate 188 may also be provided to vat 110

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N in order to assist in removal of the solid residues from the vat 110. For example, pump 180 00 S 10 pumps the sludge or slurry of containing solid residue via 182 to a residue slurry tailings dam 184.

It will be appreciated that, as mentioned above, the flow sheet shown in figure 2 represents a snapshot taken at a particular time during operation of the flow sheet.

In the flow sheet shown in figure 2, each vat is filled with ore, concentrate or agglomerate at the vat filling stage. Each vat is also provided with appropriate piping and control valves so that, rather than having to transfer the solid material from one vat to next vat, the flow of liquid products to the vat is changed (by simply opening and closing appropriate control valves) so that the ore, concentrate or agglomerate is subjected to each of the steps described above in the overall leaching process.

In the preceding description of the invention and in the claims which follow, except where the context requires otherwise due to express language or necessary implication, the words "comprise" or variations such as "comprises" or "comprising" are used in an exclusive sens, specify the presence of the stated features, but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that this invention and the preferred embodiments are not limited to the particular materials described, as these may vary. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only, and it is not intended to limit the scope of the present invention in any way.

It is also to be noted that, as used herein, the singular forms of"a", "an" and "the" include the plural unless the context requires otherwise. Unless defined otherwise, all technical and scientific terms herein have the same meanings as commonly understood by one of ordinary skill in the art to which the invention belongs.

Claims (14)

1. A method for acidic sulphate leaching of nickel and cobalt contents 00 5 of a nickel laterite ore or concentrate using a vat leaching method comprising the steps of: a) preparing a feedstock containing a nickel laterite ore or a nickel laterite 00 concentrate and loading the feedstock into a vat leaching vessel or series of vessels; and b) passing an acidic sulphate leachant through the feedstock body and N collecting a nickel- and cobalt-containing pregnant leach solution overflow. 00

2. A method as claimed in claim 1 wherein the leachant passes through i the vessel or vessels in an upflow mode.

3. A method as claimed in claim 1 or claim 2 wherein the feedstock has been upgrade by physical beneficiation and subject to an agglomeration step.

4. A method as claimed in any one of claims 1 to 3 wherein the feedstock is agglomerated using an agglomeration process which is carried out with a sulphuric acid-containing solution. A method as claimed in claim 4 wherein the agglomeration process incorporates the addition of a binding agent.

6. A method as claimed in any one of the preceding claims wherein the vat leaching vessel has a vertical:horizontal height dimension ratio in the range 1:4 to 1:10.

7. A method as claimed in any one of the preceding claims wherein the nickel- and cobalt-containing feedstock is placed in a vat leaching vessel that incorporates addition means for adding the acidic leachant to the bottom of the vat, the vat leaching vessel having an overflow system at or near the top of the vat to collect and draw off the nickel- and cobalt-containing solution generated by the upflow of the acidic leachant through the body of nickel- and cobalt-containing feedstock contained within the vat leaching vessel.

8. A method as claimed in claim 7 wherein the vat leaching vessel includes a plurality of leachant outlets that supply leachant to the leaching vessel such that the leachant is evenly dispersed across a horizontal aspect of the leaching vessel.

9. A method as claimed in claim 8 wherein the vat leaching vessel comprises a plurality of leachant outlets evenly spaced around the vessel. 00 A method as claimed in claim 1 wherein the nickel- and cobalt- N containing feedstock is placed in a vat leaching vessel or vessels, the vat leaching vessel(s) ;incorporating addition means for supplying the acidic leachant to the top of the vat with a solution discharge system at the bottom of that vat to collect and draw off the nickel- and 00 C 5 cobalt-containing solution generated by downflow of the acidic leachant through the body of nickel- and cobalt-containing feedstock contained within the vat leaching vessel(s). 00 11. A method as claimed in any one of the preceding claims wherein the Vt') pH of a pregnant liquor leaving the vat leaching vessel is less than about 2.8. S12. A method as claimed in any one of the preceding claims wherein the 00 0 10 acidic sulphate leachant passed through the feedstock contained within the or each vat C leaching vessel is recycled one or more times before the pregnant nickel- and cobalt- containing solution is forwarded to a downstream processing area for recovery of nickel and cobalt containing products.

13. A method as claimed in any one of the preceding claims wherein once a desired level of nickel and cobalt dissolution has been achieved, the nickel- and cobalt-containing solution held within each vat is removed and the solids washed free of any soluble nickel and cobalt.

14. A method as claimed in claim 13 wherein washing is achieved by passing several bed volumes of a fresh, slightly acidic solution up through the leached feedstock and recovering the solution in a separate circuit. A method as claimed in claim 14 wherein this wash solution is used to make up fresh leachant for a next vat leaching cycle

16. A method as claimed in any one of the preceding claims wherein the leachant is heated to an elevated temperature prior to feeding it to the leaching vessel(s) in the vessel(s).

17. A method as claimed in any one of claims 1, 2 and 6 to 16 wherein preparation of the feedstock prior to placing the feedstock in the vat leaching vessel includes one or more of the following steps: 0 forming an approximate average blend of the major ore zones of the entire nickel laterite orebody; 0 crushing the blended ore feedstock to top size of from 5-15 mm. 00

18. A method for the dissolution of the nickel and/or cobalt contents of a i nickel laterite ore, the method comprising the steps of: preparing an approximate average blend of the major ore zones of the entire nickel laterite orebody; 00 CI 5 b) crushing the blended ore feedstock to an appropriate top size; c) agglomerating the crushed, blended ore feedstock with an 00 acidic sulphate liquor if required; d) allowing the agglomerated ore feedstock to cure ("harden") ,i prior to loading into one or more appropriately sized vat leaching vessels; 00 0 10 e) passing the acidic sulphate leachant, using either the upflow ,i or downflow mode, through the ore feedstock to dissolve the nickel and/or cobalt contents of the ore feedstock; f) collecting the pregnant leach liquor exiting the vat leach vessel(s) and, if appropriate, adjusting the pH of the liquor ahead of recycling through one ore more of the vat leach vessels; g) forwarding the final pregnant leach liquor to a final product recovery circuit; and h) draining any nickel- and cobalt-containing liquor from the vat leach vessel(s) and washing any entrained soluble nickel and cobalt from the leached solids prior to removal of the leached solids from the vat leach vessel(s) for disposal.

19. A method for leaching a lateritic ore, concentrate or agglomerate substantially as herein before described with reference to the accompanying drawings.