OF METAL FROM A METAL-BEARING

MATERIAL

FIELD OF APPLICATION OF THE INVENTION

The present invention relates to an improved apparatus for economically extracting metal from a metal-bearing material. In particular, the present invention relates to an improved apparatus for extracting metal, including inter alia base metal (i.e. copper) and gold, from a metal-bearing ore, concentrate or other metal-bearing material. The present invention further extends to a process for the extraction of such metal which is carried out in accordance with the aforementioned apparatus.

BACKGROUND TO THE INVENTION

The economics of metal extraction are not only dependent on the quality of the ore and the cost of extraction, but also depend on the market price and demand. In addition hereto, it is possible to improve the technology of metal extraction so as to enable companies to produce greater quantities of metal from metal-bearing ore than was previously possible and to even utilise low grade ores previously discarded or not considered worthwhile mining.

One such metal which has received a considerable amount of attention in the past few years is copper.

Copper is one of the world's most important industrial minerals with Africa being an important world producer thereof. The physical properties of copper, including malleability and workability, corrosion resistance and durability, high electrical and thermal conductivity and ability to alloy with other metals, have made it an important metal to a number of diverse industries. The main copper-producing countries which dominate copper mining in Africa are Zambia, South Africa and the Katanga Province in the Democratic Republic of Congo. In 2008, Zambia produced 502 998 tonnes of copper, South Africa produced 89 700, and the DRC produced 131 400 - this, against a global production of 15.8 mega tonnes of copper in 2009.

Copper deposits typically have copper-bearing zones at different depths that contain different copper-bearing minerals. Copper oxides, such as malachite and chrysocolla, are located in an upper weathered zone. A mixture of copper sulphides, such as chalcocite, covellite and chalcopyrite, and copper oxides are generally located below the upper weathered zone in an intermediate enriched zone. Chalcopyrite is generally located in a primary mineralized zone below the intermediate enriched zone.

The beneficiation process begins at the comminution stage. Typically, this is accomplished by sequential size reduction operations commonly referred to as crushing and grinding, where mined ore - from open cast mines or underground mines - is crushed or ground into small particles. Said particles are then separated to remove any gangue material. Thereafter, the process involves the physical liberation of metal from the rock by either hydrometallurgical liberation or by froth flotation, depending on whether the ore is oxide ore or sulphide ore, respectively. Accordingly, and with reference to copper, copper in the ores from the various zones is recovered by different techniques. The copper in the ore from the upper weathered and intermediate enriched zones is typically recovered by heap leaching techniques to solubilise the copper oxides. For copper sulphides, flotation processes are widely used to separate copper sulphides from the remaining ore materials, with the copper in the copper sulphides being recovered by smelting.

Copper is increasingly recovered by solution, or hydrometallurgical, methods. These include dump, heap, and vat leaching techniques, as well as underground (or in situ) leaching methods. Each of these methods results in a pregnant leach solution (PLS). Copper is recovered from the PLS through precipitation or by solvent extraction/electrowinning.

Most ores occur as mineral compounds that are insoluble in water; leaching involves chemical reactions that convert the metal into a water-soluble form followed by dissolution. The leaching agent used by each operation is dependent on the mineralogical composition of the ore material. Acid leaching of ores and concentrates is the most common method of hydrometallurgical extraction. Its use is confined to acid-soluble, oxide-type ores that are not associated with acid-consuming rock types containing high concentrations of calcite (such as limestone and dolomite).

Agitation (tank) leaching and vat leaching are usually performed on relatively higher oxidized ores. Agitated tank leaching refers to the relatively rapid leaching of fine particles of metal oxide with a strong sulphuric acid solution in agitated tanks. The tanks are stirred or agitated by mechanical devices or piped stream discharge. Vat leaching typically is used to extract metal from oxide ores by exposing the crushed ore to concentrated sulphuric acid (lixiviant) in a series of large tanks or vats. The vats are usually designed in a series configuration, which acts to concentrate the metal content of the solutions as a function of ore-lixiviant contact time.

The art teaches of the wide spread use of systems involving a combination of process steps such as, inter alia, leaching and precipitation in the recovery of metals from ores. US Patent No. 4,242,129 to Klockner-Humboldt-Wedag is a patent that discloses a leaching, precipitation and flotation method pertaining to the recovery of metals from ores, in particular, the recovery of copper from oxygen containing copper ores. In terms of this method, the leaching and precipitation steps are simultaneously and continuously carried out in an oscillating reaction vessel. Additionally, the process is carried out at elevated temperatures in order to improve the reaction kinetics of the process. Following leaching and precipitation, the slurry is piped into a separate vessel for foam flotation of metallic copper. It is discussed in this patent that the claimed method simplifies and speeds up the recovery of metals from ores and makes the recovery of metals from very low grade sources economically feasible. However, the process requires the reaction chamber to double as both an oscillating grinding mill and leaching vessel, with the leaching liquid being stored in an outlet chamber prior to recirculation. Additionally, the patent does not include any mention of combined or modular operation of the apparatus. This process should thus be understood as a high efficiency process, capable of extraction from low-grade copper oxide ores, rather than an economically efficient process suitable for multiple ore grades and types.

European Patent No. 0102725 to Broken Hill Associated Smelters describes a process for the recovery of copper from copper-containing material (in particular, copper-bearing sulphide materials) and teaches primarily of the leaching process that is involved therein. This patent further teaches that the leaching process is advantageously conducted in a single reaction vessel. In contrast to USPatent No. 4,242,129, this process does not make use of iron. Instead, relatively high concentrations of sodium chloride are used to provide CI ^" ions as cofactors in the acid leaching reaction. Extraction of copper is mainly by means of the leach solution, with techniques such as electrowinning being used to recover the metal. Unfortunately, this process is taught as requiring finely ground ores and increased temperatures in order to reach useful efficiencies. Additionally, oxygen injection is required in order to complete the reaction. Finally, relatively high concentrations (20% or more) must be used. Given the above, this process should be understood as a means of isolating and extracting copper and other metals from mixed ore concentrates, rather than as a means of extracting metal from low-grade ores.

It is wide known in the art that the economics of current mining and recovery methods often hinder or even prevent the mining of metal ore deposits that either contains insufficient metal values or requires extensive site preparation or operating expenses. In particular, low grade copper deposits of typically 1.5 to 2.0% Cu with a life of mine of approximately two years are generally not exploited due to the significant upfront capital requirement and lengthy installation and erection time which render the process uneconomical. This is especially the case in most of Africa where the traditional capital requirements are greater and construction abnormally delayed relative to similar projects on other continents.

It is also well known that ideally all hydrometallurgical operations want to operate at the limit of the refining capacities (for in example, the limit of their tank house plating capacity when considering electrowinning). It is quite common that the leaching and solid/liquid separation process becomes the bottleneck and results in an under-utilised tank house hence lower production. Therefore a market exists for the ability to "fill" the available tank-house capacity by producing PLS from concentrates decoupled from the existing operation.

The art teaches of small modular reactors (SMR's) - a field that is drawing a great deal of attention from governments, utilities (large and small) and communities in the nuclear industry. Fluor http://www.fluor.com is a well known majority investor in NuScale Power, a SMR technology company. In terms of these SMR's, the individual nuclear reactor components are modular in design and thereby provide flexibility for installing at sites in remote locations. Westinghouse http://westinghousenuclear.com/smr similarly teaches of modular nuclear plant reactors.

Accordingly, and in view of the foregoing, it is evident that despite the currently used technology there is a clear need in the art for an apparatus and a process which enables the general exploitation of low grade, small scale metal-bearing deposits as well as underutilised refineries (including inter alia, base metal and gold-bearing deposits) from both oxide and sulphide ores in a cost effective manner whilst affording a significantly reduction in both the cost and time associated with the erection and construction of a plant. OBJECT OF THE INVENTION

Accordingly, it is an object of the present invention to provide an apparatus and process for the improved economic extraction of metal, from metal-bearing material which will address the shortcomings associated with the prior art and currently employed technology.

It is a further object of the present invention to provide an apparatus and process which combines the process steps of leaching and liquid/solid separation in a single, readily transported and assembled apparatus in order to reduce the capital cost and time required to first production and, in doing so, rendering previously uneconomic deposits viable.

SUMMARY OF THE INVENTION

According to a first aspect thereof, the present invention provides an apparatus for extracting metal from a metal-bearing material, said apparatus

including a feed receptacle for receiving a metal-bearing feed stream; a reaction vessel; at least one pump means for delivering the metal-bearing feed stream to the reaction vessel; a means for introducing leaching agents, in the form of a leaching agent solution, to the reaction vessel; an agitator or stirring means for circulating the metal-bearing feed stream and leaching agent solution in the reaction vessel so as to allow for a combination of agitation (tank) leaching and vat leaching to take place; a means for achieving liquid/solid separation; and a means for extracting a metal containing product,

wherein said apparatus is re-locatable and transportable in order to allow the apparatus to be assembled easily on site without being geographically bound to one specific site. Once liquid/solid separation has taken place, the resulting solution is subjected to conventional process steps in order to recover inter alia the metal so extracted. It will be appreciated that these conventional process steps are not included in the apparatus and process of the invention as encompassed by the present application.

In terms of the invention, the metal to be extracted may be any suitable metal, including inter alia base metal or gold.

The metal-bearing material may be a metal-bearing ore material, a metal concentrate, or the like. The metal-bearing material may be in the form of an oxide or a sulphide. The metal- bearing material may include other metals such as (but not limited to) inter alia, gold, silver, platinum group metals, and mixtures thereof.

The metal-bearing ore may be a metal oxide ore which may either be unprocessed or previously processed, such as spiral concentrate or tailings.

In one embodiment, the metal to be extracted is copper (Cu).

In terms of this embodiment, the metal-bearing material may be a copper-bearing ore material, a copper concentrate recovered through a spiral plant, or the like. The copper- bearing material may be in the form of an oxide or a sulphide. The copper-bearing material may include other metals such as inter alia, gold, silver, platinum group metals, and mixtures thereof.

The present invention is especially useful for liberating copper from copper oxide ore, especially copper from the following non-limiting examples of copper oxides, namely malachite green [CuC0 ₃ Cu(OH) ₄ ], azurite blue [2CuC0 ₃ Cu(OH) ₄ ], melaconite (CuO), cuprite (Cu ₂ 0) and chrysocolla [Cu ₄ H ₄ Si ₄ O ₁₀ (OH) ₈ ]. In terms of this embodiment of the present invention, the copper-bearing ore is a copper oxide ore which may either be unprocessed or previously processed, such as spiral concentrate or tailings.

Feed receptacle

In terms of the present invention, the metal-bearing feed stream is introduced into the feed receptacle in dry form. The feed receptacle is equipped with at least one pump means for delivering the metal-bearing feed stream to the reaction vessel. In one embodiment of the invention, the at least one pump means is a jet pump. In particular, the jet pump produces a vacuum by means of a venturi effect. In terms of the invention, said jet pump allows for dry feeding of the metal-bearing feed stream and therefore eliminates the need for agitators in this section of the apparatus. The other benefit with dry feeding the reactor vessel is that the water balance becomes much easier as the amount of fresh water required in the system is eliminated.

In one embodiment, a centrifugal pump may be used as the drive pump for generating the flow through the at least one jet pump. Said jet pump is capable of delivering up to 55% dry metal-bearing feed material to the reaction vessel.

In an embodiment of the invention, the feed receptacle is rectangular in shape, the dimensions thereof being 2896 mm in length and 2438 mm in breadth. The height thereof (exclusive of the height of the closing means) is 3000 mm. Reaction vessel

In an embodiment of the invention, process water may be introduced into the reaction vessel for start-up conditions. Alternatively, a leaching agent solution may be utilized during the circulation process. It will be appreciated that the required volume of process water or leaching agent solution will vary depending on the quantity of dry metal-bearing feed material introduced into the reaction vessel.

In an embodiment of the invention, the reaction vessel is rectangular in shape, the dimensions thereof being 2896 mm in length, 2438 mm in breadth and 12192 mm in height.

In accordance with the invention, the reaction vessel is designed and configured to receive and process at least 40 tons of dry metal-bearing feed material (up to -5mm) at a density of 50% solid material.

In an embodiment of the invention, the apparatus includes a means for introducing leaching agents into the reaction vessel. Typical acidic leaching agents used include hydrochloric acid (HCI), sulphuric acid (H ₂ S0 ₄ ), raffinate and iron sulphate (Fe ₂ (S0 ₄ )). In terms of one embodiment of the present invention, raffinate or sulphuric acid are introduced into the reaction vessel in order to achieve leaching.

Copper minerals such as cuprite, azurite, malachite, tenorite, and chrysocolla, are soluble in sulphuric acid at room temperature. Other, less oxidized, and sulphide ores, such as chalcocite, bornite, covelite and chalcopyrite, requires the addition of ferric sulphate and oxygen to accomplish leaching. The apparatus does not include an agitator as the required mixing is achieved by circulating the metal-bearing feed stream and leaching agent solution in the reaction vessel through the jet pump so as to allow for a combination of agitation (tank) leaching and vat leaching to take place.

In terms hereof, the centrifugal drive pump is configured to draw leaching agent solution from an upper section of the reaction vessel and to circulate the solution through the jet pump and return the same to the reaction vessel. The venturi created by the jet pump draws solid material from a lower section of the reaction vessel and circulates the solid material with the leaching agent solution to form a slurry containing the metal-bearing feed material and the leaching agent solution. In this way, a liquid/solid interface is established. Accordingly, the upper section of the reaction vessel will contain primarily the liquid phase, including the pregnant leaching solution (PLS), and the lower section of the reaction vessel will contain mainly the slurry phase. This upper and lower solid differential is enhanced by a so-called "down comer" pipe.

In terms of the invention, a portion of the circulated leaching agent solution is used as sparging liquid in order to create a fluidized bed system and therefore reduces dead volume and enhances reaction kinetics.

The apparatus further includes a means for achieving liquid/solid separation. In terms hereof, the solid material is allowed to settle and the bulk of the PLS is drawn from the upper section of the reaction vessel and pumped to the next process or to PLS storage. In terms of an embodiment hereof, the invention provides for the aspect ratio (3.93 to 4.66 H:W) to be such that it will enhance liquid/solid separation.

The remaining PLS in the slurry phase at the lower section of the reactor phase may be washed with process water via the centrifugal drive pump and jet pump combination. The apparatus further includes a means for extracting the metal containing material. In this regard, the washed leaching agent solution may be transferred from the upper section of the reaction vessel to a next/subsequent process or to PLS storage whilst the remaining solid material in the lower section of the reaction vessel may be pumped out to tailings.

In accordance with the present invention, the apparatus is designed in a manner that enables it to be easily transportable thereby allowing the apparatus to be easily re-locatable. In this way, the apparatus may be assembled easily on site and thus may be re-located and re-used at many further additional sites.

The invention provides for the reaction vessel to be rectangular in cross section thereby preventing centrifuging of slurries as experienced in circular tanks.

In an embodiment of the invention, the apparatus is modular. Preferably, the upper and lower sections of the reaction vessel are modular thereby allowing the reaction vessel to be dismantled and assembled easily on site or at further sites.

In a further embodiment of the invention, the apparatus, in particular, the reaction vessel is skid mounted with little to no civil requirement.

In a further embodiment of the invention, the dimensions and configuration of the apparatus are such that they compliment a containerized truck dimensions in order to facilitate ease of transportation of the apparatus. Preferably, the reaction vessel is designed according to specific containerized truck dimensions in order to ease transportation and to allow for pre- construction and assembly in workshops/factories. In terms of the invention, the modular design of the apparatus together with the complimentary design to that of the containerized truck dimension, allows the apparatus to be easily transported and easily assembled on site. In addition hereto, the apparatus is able to be re-locatable to a further site for additional use in the beneficiation of further metal ore deposits thus negating the considerable costs and lengthy time incurred in setting up a permanent plant.

In terms of the invention, the aforementioned design creates significant capital cost savings when compared to the conventional processes. The combination of the processes and modular design of the apparatus reduces the overall mechanical equipment and construction time requirements.

According to a second aspect thereof, the invention provides for a plurality of apparatuses, as described in accordance with the first aspect of the present invention, for extracting metal (including, inter alia base metal and gold) from a metal-bearing material. In terms of this aspect of the invention, said plurality of apparatuses are arranged in series in order to produce a continuous flow of pregnant leaching solution thereby simulating a semi-batch operation.

According to a third aspect thereof, the present invention provides a one-stage process for extracting metal from metal-bearing material, said process including the steps of:

(i) providing a feed stream containing metal-bearing material;

(ii) subjecting the metal-bearing feed stream to a combination of agitated (tank) leaching and vat leaching to yield a product comprising a combination of slurry and pregnant leach solution (PLS);

(iii) subjecting the product of step (ii) to liquid/solid separation techniques in order to separate the solids in the slurry and the PLS. Step (i)

According to this aspect of the invention, the metal to be extracted by the process of the present invention may be any suitable metal, including inter alia base metal or gold.

The metal-bearing material may be a metal-bearing ore material, a metal concentrate, or the like. The metal-bearing material may be in the form of an oxide or a sulphide. The metal- bearing material may include other metals such as (but not limited to) inter alia, gold, silver, platinum group metals, and mixtures thereof.

The metal-bearing ore may be a metal oxide ore which may either be unprocessed or previously processed, such as spiral concentrate or tailings.

In one embodiment of the invention, the metal to be extracted by the process of the present invention is copper (Cu).

In terms of this embodiment, the metal-bearing material may be a copper-bearing ore material, a copper concentrate, or the like. The copper-bearing material must be in the form of an oxide. The copper-bearing material may include other metals such as inter alia, gold, silver, platinum group metals, and mixtures thereof.

The present invention is especially useful for liberating copper from copper oxide ore, especially copper from the following non-limiting examples of copper oxides, namely malachite green [CuC0 ₃ Cu(OH) ₄ ], azurite blue [2CuC0 ₃ Cu(OH) ₄ ], melaconite (CuO), cuprite (Cu ₂ 0) and chrysocolla [Cu ₄ H ₄ Si ₄ Oi ₀ (OH) ₈ ]. In terms of a preferred embodiment of the present invention, the copper-bearing ore is a copper oxide ore which may either be unprocessed or previously processed, such as spiral concentrate or tailings.

In terms of step (i), the metal-bearing feed stream is fed dry into a feed receptacle of the type described and defined herein before in accordance with the first aspect of the invention.

In an embodiment of the invention, a mineral processing step may, optionally, be included prior to step (i). In terms of this mineral processing step, the metal-bearing feed material is liberated from waste constituents, such as inter alia, alumina, limestone, pyrite and silica, and thereafter such waste constitutes are removed.

Step (ii)

In terms of this step, the metal-bearing feed stream of step (i) is delivered from the feed receptacle into a reaction vessel. In an embodiment of the invention, the metal-bearing feed stream is delivered to the reaction vessel by means of at least one pump. Once introduced into the reaction vessel, the metal-bearing feed stream is mixed with an aqueous solution in order to form a slurry containing the metal-bearing feed material.

Said slurry is thereafter subjected to a combination of agitated (tank) leaching and vat leaching. In terms of one embodiment, the slurry is contacted with a leaching solution at ambient operating conditions in order to allow for the metal material to leach from the slurry containing the metal-bearing feed material into solution.

The difference between vat leaching and agitated (tank) leaching resides in the physical handling of the slurry. In agitated (tank) leaching, as discussed herein above, the metal- bearing feed stream is mixed with an aqueous solution in order to form a slurry containing the metal-bearing feed material and thereafter leaching agents are added to achieve the leaching reaction. Agitation is achieved by means of mechanical devices or piped stream discharge. Agitation ensures that the solids remain in suspension and improves the solid-to- liquid-to-gas contact. Accordingly, in terms of agitated (tank) leaching, the slurry is actively mixed to enhance solid-liquid interaction.

In vat leaching, the slurry containing the metal-bearing feed material is contacted with the leaching agent and no agitation is required. The vat leaching kinetics is significantly slower than agitated (tank) leaching and therefore requires longer retention time.

Typical acidic leaching agents used in this step include hydrochloric acid (HCI), sulphuric acid (H ₂ S0 ), raffinate and iron sulphate (Fe ₂ (S0 ₄ )). In terms of one embodiment of the present invention, raffinate or sulphuric acid are introduced into the reaction vessel in order to achieve leaching.

Step (Hi)

Once the leaching process is complete and equilibrium is reached, the product of step (ii), which comprises a combination of slurry and PLS, is subjected to liquid/solid separation techniques in order to separate the solids in the slurry and the PLS.

Accordingly, the typical aims of liquid/solid separation are to rapidly and efficiently separate liquids from solids, in order to recover the liquor (namely, the PLS) for re-use or further treatment, while capturing and concentrating the solids for the values they may contain.

In terms of this invention, solid/liquid separation is achieved by stopping the circulation and allowing the solids to settle within the reactor vessel. In terms of an embodiment of the invention, liquid/solid separation is accelerated through the use of flocculants, i.e. polymers that are added to the product of step (ii) to encourage fine particulates within the product to clump together to form large aggregates.

The PLS is transferred for further processing and subsequent recovery which, as mentioned herein above, is achieved outside of the extremities of the invention.

According to a fourth aspect thereof, the present invention provides the use of the apparatus, as described and defined in accordance with the first aspect of the invention, in the abovementioned process.

According to a fifth aspect thereof, the present invention provides the use of a plurality of apparatuses, as described and defined in accordance with the second aspect of the invention, in the abovementioned process.

According to a sixth aspect thereof, the present invention provides a product formed from the process described and defined in accordance with the third aspect of the invention.

Advantages

An advantage of the process of the present invention is economical in that multiple process steps usually carried out in dedicated equipment are performed in a single apparatus operated in a batch or semi-batch nature. Additionally, multiple leaching and separation approaches can be performed using the same equipment, allowing cost-effective implementation of processes tailored to specific ore types and grades. The presently disclosed invention thus affords a significant reduction in capital by combining the multiple process steps into a single-stage process concomitant with simplifying the design of the reaction vessel with a view to reducing construction time on site significantly.

In addition hereto, a single plant will thus be used for treating several metal ore deposits by virtue of the fact that the present apparatus is easily re-locatable and transportable (and thus not geographically bound) to more than one site.

The present invention advantageously provides the following benefits, namely that it has a compact, modular construction thus achieving a smaller site footprint; the respective modules are largely pre-assembled in workshops/factories for ease of site establishment; reduced construction time of the plant concomitant with reduced erection costs; and the apparatus is easily dismantled and re-assembled to ensure quick site relocation.

A further advantage exists in utilising this invention for "debottlenecking" current hydrometallurgical operations. Ideally all hydrometallurgical operations want to operate at the limit of the refining capacities (for in example, the limit of their tank house plating capacity when considering electrowinning). It is quite common that the leaching and solid/liquid separation process becomes the bottleneck and results in an under-utilised tank house hence lower than expected production. This invention provides the ability to "fill" the available tank-house capacity by producing PLS from concentrates decoupled from the existing operation.

The presently disclosed subject matter will now be described more fully hereinafter with reference to the accompanying Figures and Example, in which a representative embodiment is shown. The presently disclosed subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of the apparatus according to the present

invention, showing inter alia, the feed receptacle and the reaction

vessel;

Figure 2 is a side view of the apparatus as depicted in Figure 1 ;

Figure 3 is a further side view of the apparatus as depicted in Figure 1 ;

Figure 4 is a top view of the apparatus as depicted in Figure 1;

Figure 5 is an isoview of the piping configuration of the apparatus as depicted in

Figure 1 ;

Figure 6 is a top view of the apparatus as depicted in Figure 1 ;

Figure 7 is a bottom view of the apparatus as depicted in Figure 1 ;

Figure 8 depicts a diagram showing the leaching efficiency results from a prototype plant (commercial scale) in the DRC; and Figure 9 depicts a diagram showing the leaching kinetic results for a 20t leach test in the prototype plant located in the DRC.

DESCRIPTION OF THE INVENTION

Figures 1 to 7 represent the apparatus of the present invention, designed to scale for commercial purposes, showing inter alia, the feed receptacle and reaction vessel.

Example 1 : Improved economic extraction of copper from a copper-bearing feed material

Solids or copper-rich feed material (not shown) is fed dry into a feed receptacle, in the form of a feed bin 2 of the apparatus 1. The bottom of the feed bin is equipped with a jet pump 4 which transfers the solids from the feed bin 2 to the reaction vessel, in the form of a reactor 3. The jet pump 4 produces a vacuum by means of the venturi effect. A centrifugal drive pump 5 is used as the drive pump for generating the flow through the jet pump 4. The reactor 3 is equipped with an additional jet pump 6 similar to the jet pump 4 located in feed bin 2. The jet pump 6 is capable of pumping up to 55% solids and uses either process water for start-up conditions or leach solution during the circulation process.

The reactor 3 is designed to treat a batch of 40 tons of dry feed (up to -5mm) at a density of 50% solids. The 40 tons of feed material is loaded into the reactor 3 through the feed bin 2 and jet pump 4 once the reactor 3 is filled with either process water (not shown) or leach solution (not shown) to the required volume. The filling process is achieved via the centrifugal drive pump 5. Leach reagents (not shown) are introduced through the feed system 7 until the required free acid levels are obtained. The combination of agitation (tank) leaching and vat leaching commences by circulating the solids and leach solution through the reactor 3. The centrifugal drive pump 5 draws leach solution from the top of the reactor 3 and then circulates the solution through the jet pump 6 and back into the reactor 3.

The venturi created by the jet pump 6 draws solids from the bottom of the reactor 3 and circulates with the leach solution back to the reactor 3. The circulated slurry is introduced to the reactor 3 through a down pipe 8 developing a liquid-solid interface. The top part of the reactor 3 mainly comprises liquid phase and the bottom section mainly slurry phase. A portion of the circulated leach solution is used as sparging liquid in the cone section of the reactor 3 in order to create a fluidized bed system. The cone fluidization aids as agitation and prevents the solids from settling and improves leaching kinetics.

Once the leaching process is complete and equilibrium is reached, the circulation and fluidization process is stopped. The solids are allowed to settle and liquid/solid separation takes place. The bulk of the pregnant leach solution (PLS) is now drawn from the top of the reactor 3 and pumped to the next process or PLS storage.

The PLS left behind in the slurry phase at the bottom of the reactor 3 is washed with process water via the centrifugal drive pump 5 and jet pump 6 combination. Once the slurry is sufficiently washed from all the remaining copper in solution, it is allowed to settle and the final liquid/solid separation step will commence. The final washed leach solution is then transferred from the top of the reactor 3 to the next process or PLS storage whilst the remaining solids in the bottom compartment of the reactor 3 are pumped out to tailings.

The reactor 3 is now ready for the next batch. A series of batch reactors 3 can be used in order to produce a continuous flow of PLS, simulating a semi-batch operation. Having described the invention in detail and by reference to the aspects and embodiments thereof, the scope of the present invention is not limited only to those described characteristics, aspects or embodiments. As will be apparent to persons skilled in the art, modifications, analogies, variations, derivatives and adaptations to the above-described invention can be made on the base of art-known knowledge and/or on the base of the disclosure (e.g. the explicit, implicit or inherent disclosure) of the present invention without departing from the spirit and scope of this invention.

A prototype unit was constructed on commercial scale and tested in the DRC on copper concentrate from an existing mining operation. The copper material tested was a spiral concentrate. The material composition and test results are indicated in table 1 & 2 below. The Cu extraction achieved was above 90% similar to other conventional methods.

Table 1 : Results from 20t leach

Table 2: Results from 40t leach