Abstract:
A process for the recovery of nickel and/or cobalt from a nickel and/or cobalt containing solution comprising: (i) contacting the nickel and/or cobalt containing solution with metallic particles of at least one metal that is more electronegative than nickel and/or cobalt thereby enabling a cementation process to occur between the nickel and/or cobalt in the solution and the metallic particles to produce a nickel and/or cobalt cementate; and (ii) separating the nickel and/or cobalt cementate from the metallic particles thereby producing a slurry including nickel and/or cobalt cementate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to a process for the recovery of nickel and/or cobalt from a leach solution. In particular, the present invention provides an improved hydrometallurgical method of recovering nickel and/or cobalt from a pregnant leach solution (PLS) from a leaching process of a nickel and/or cobalt containing ore using a cementation process and it will be convenient to hereinafter disclose the invention in relation to that exemplary application. However, it is to be appreciated that the invention is not limited to that application and could be used to recover nickel and/or cobalt from any nickel and/or cobalt ion containing solution. 
       BACKGROUND OF THE INVENTION 
       [0002]    The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application. 
         [0003]    Laterite nickel containing ore deposits generally contain oxidic type ores, limonites, and silicate type ores, saprolites, in the same deposits. The higher nickel content saprolites tend to be treated by a pyrometallurgical process involving roasting and electrical smelting techniques to produce ferro nickel. The lower nickel content limonite and limonite/saprolite blends are normally commercially treated by a combination of pyrometallurgical and hydrometallurgical processes, such as the High Pressure Acid Leach (HPAL) process, Caron reduction roast-ammonium carbonate leach process, atmospheric pressure agitation acid leach processes and heap leaching process. 
         [0004]    Nickel containing sulfide ore deposits are commercially treated in a number of ways. One such way is to produce a flotation concentrate, from which the nickel content is then oxidatively leached. Other processes such as smelting to matte followed by leaching, or direct heap leaching of the ore itself, also produce a nickel containing solution. 
         [0005]    In each of these processes, a leach solution, containing nickel salts and cobalt salts, is produced which is then passed to a processing plant where the metal nickel is recovered. Currently nickel and cobalt is recovered from the PLS using methods such as precipitation as a sulphide or mixed hydroxide, treatment by solvent extraction, ion exchange processes, hydrogen reduction or other known metallurgical processing routes to extract and separate the nickel and cobalt. 
         [0006]    United Kingdom Patent No. GB1311294 provides an alternative process for obtaining nickel metal in the form of a composite metal powder. In this patent, a cementation process is proposed in which a salt solution containing nickel ions is added in a mixing vessel with an aluminium metallic powder or a paste of aluminium metal consisting of particles with a dimension lower than 40 microns. The solution is agitated until the grains of the metallic aluminium powder are completely replaced by nickel metal. No industrial application for this process is described. 
         [0007]    The present invention aims to provide an alternate method of recovering nickel and/or cobalt from a leachate solution or a solution containing nickel and/or cobalt ions generally. 
       SUMMARY OF THE INVENTION 
       [0008]    According to the present invention, there is provided a process for the recovery of nickel and/or cobalt from a nickel and/or cobalt containing solution comprising: 
         [0009]    (i) contacting the nickel and/or cobalt containing solution with metallic particles of at least one metal that is more electronegative than nickel and/or cobalt thereby enabling a cementation process to occur between the nickel and/or cobalt in the solution and the metallic particles to produce a nickel and/or cobalt cementate; and 
         [0010]    (ii) separating the nickel and/or cobalt cementate from the metallic particles thereby producing a slurry including nickel and/or cobalt cementate. 
         [0011]    Cementation is a heterogeneous process in which ions are reduced to zero valence at a solid metallic interface. The process allows powders to be obtained directly from metallic salt solutions containing said metals. In a cementation process, a salt solution of a metal A (for example a nickel and/or cobalt salt), is contacted with grains of a metal B which is more electronegative than metal A, there is produced in the grains, from their periphery to their centre, a displacement of metal B by metal A. If the process is run to completion, the solution will contain either only grains of metal A in the case where the grains of metal B initially introduced in the solution of metal A are very small. If the process is only partially completed, composite grains including a central core of metal B and an exterior layer of metal A may be produced. 
         [0012]    The cementation process according to the present invention can be used to extract nickel and/or cobalt metal from any type of nickel and/or cobalt ion containing solution. However, the nickel and/or cobalt ion or salt containing solution will generally be a pregnant leach solution (PLS) from a process of leaching nickel and/or cobalt bearing ores. In most cases, a nickel and/or cobalt containing PLS will result from a leaching process applied to a nickel and/or cobalt containing ore such as nickel and/or cobalt bearing laterite and/or sulfide ores. In one embodiment, the nickel and/or cobalt containing PLS is obtained from a leaching process applied to a nickel and/or cobalt containing laterite ore. In another embodiment, the nickel and/or cobalt containing PLS is obtained from a leaching process applied to a nickel and/or cobalt containing sulphide ore. As indicated in the background, several types of leaching process are known for extracting nickel and/or cobalt from nickel and/or cobalt containing ores. It is intended that the present invention could be used with any of these leaching processes. In this regard, the leaching process, which is applied to a nickel and/or cobalt containing laterite ore and which provides a nickel and/or cobalt containing PLS for the process of the present invention, could be obtained from at least one of a High Pressure Acid Leach (HPAL) process, Caron reduction roast-ammonium carbonate leach process, atmospheric pressure agitation acid leach processes and heap leaching. Furthermore, the leaching process, which is applied to a nickel and/or cobalt sulfide containing material and which provides a nickel and/or cobalt containing PLS for the process of the present invention, could be obtain by leaching of the nickel and/or cobalt sulfide containing material by oxidative pressure leaching, atmospheric leaching or heap leaching. 
         [0013]    It is important to obtain good solid-liquid contact between the nickel and/or cobalt containing solution and the metallic particles to assist in the cementation process. In most instances this will entail ensuring the solid metallic particles and the nickel and/or cobalt containing solution are sufficiently mixed. In some embodiments, this can entail the step of contacting the nickel and/or cobalt containing solution with metallic particles being conducted is a suitable process vessel including a mixing device or agitator. In other embodiments, the step of contacting the nickel and/or cobalt containing solution with metallic particles is conducted in a fluidised bed of the metallic particles. Preferably, the process further includes the step of fluidising the fluidised bed of metallic particles using a generally upwardly directed flow of the nickel and/or cobalt containing solution. Generally, this would entail the nickel and/or cobalt containing solution being fed into a fluidisation chamber of a process vessel into a bed of metallic particles from a location substantially underneath the bed of metallic particles. 
         [0014]    The metallic particles can comprise any suitable metal that is more electronegative than nickel and/or cobalt. The applicant has found that the process of the present invention advantageously works when the metallic particles include aluminium metal. More preferably, the metallic particles comprise aluminium metal. Aluminium metal has the advantage of having a low density, making this metal suitable for fluidising in a fluidising column as is desirable in one form of the present invention. Furthermore, with the aluminium-nickel cementation system and the aluminium-cobalt cementation system, only a small amount, by weight, of aluminium is required compared to nickel and/or cobalt to obtain a good yield of nickel and/or cobalt. The chemistry for the nickel reaction is: 
         [0000]      3Ni 2+ +2Al 0 →3Ni 0 +2Al 3+   (1)
 
         [0015]    As the molecular weight of aluminium is 26.98 compared to nickel at 58.69, the theoretical amount of aluminium for the reaction is 306.47 kg per tonne of nickel. 
         [0016]    The corresponding reaction for cobalt(II) is: 
         [0000]      3Co 2+ +2Al 0 →3Co 0 +2Al 3+   (2)
 
         [0017]    The above cementation reactions (1) and (2) can be allowed to run to completion to completely replace the aluminium with nickel and/or cobalt or could be controlled to permit only partial cementation of the metallic particles. By “partial cementation” it is meant the incomplete replacement of the grains of the metallic powder by nickel and/or cobalt from the nickel and/or cobalt containing solution. In some embodiments, the cementation process is partially completed to the point that composite grains are produced including a central core of the metal of the metallic particles and only a thin layer of nickel and/or cobalt cementate. Preferably, this thin surface layer of nickel and/or cobalt cementate can then be broken, sheared or otherwise separated from the central core of the metallic particles. 
         [0018]    It should be appreciated that when both nickel and cobalt cementation reactions ((1) and (2) respectively) occur simultaneously in solution that both nickel metal and cobalt metal can replace the metallic grains on the metallic particle. This can result in a mixed nickel-cobalt cementate product. 
         [0019]    As can be appreciated, this extent of the cementation reaction can be controlled by selectively controlling at least one parameters of the process including (but not limited to) at least one of the flow rate of nickel and/or cobalt containing solution being fed through the metallic particles, the residence time of the metallic particles in the nickel and/or cobalt containing solution, the pH of the nickel and/or cobalt containing solution and the particle size distribution of the metallic particles. Preferably, the particle size distribution of the metallic particles is selected to permit only partial cementation of the metallic particles. 
         [0020]    The applicant has found that aluminium powder may be usefully used to cement nickel and/or cobalt from a nickel and/or cobalt containing process solution produced by the means described. In this respect, the conditions may be chosen so that a large proportion of the aluminium is consumed during the cementation process, and a large yield of a highly concentrated nickel and/or cobalt containing cementate is obtained. 
         [0021]    Furthermore the applicant has found that while the use of aluminium powder is convenient, it has the disadvantage of excessive surface oxidation compared to volume of metal. In one embodiment therefore, the process of the present invention uses a larger sized particle for the cementation reaction. In some embodiments, at least some of the metallic particles are in the form of pellets. Preferably, the metallic particles have an average particle size of between 0.1 mm and 25 mm. More preferably, the metallic particles have an average particle size of between 5 mm and 15 mm. 
         [0022]    It is preferable for the unprocessed and unreacted metallic particles (cementation reagent particles) to be separated from the desired nickel and/or cobalt cementate product once the cementation reaction has been completed. Accordingly in some embodiments, the step of separating the nickel and/or cobalt cementate from the metallic particles includes separation on the basis of size. In these embodiments, the form of the cementation reagent may be chosen by size to allow a substantial portion of small nickel and/or cobalt cementate particles to be separated from the cementation reagent particles. In one embodiment, this separation step includes the step of passing the mixed particles through a screen which has a mesh size chosen to substantially pass the nickel and/or cobalt cementate particles, and to substantially retain the cementation reagent particles. In another embodiment, this separation step includes the step of fluidising the mixture of particles in a fluidisation chamber and adjusting the fluidisation velocity to cause larger cementation reagent particles to be retained and the smaller nickel and/or cobalt cementate particles to be swept out of the fluidisation chamber. 
         [0023]    In some embodiments, there is provided a fluidisation vessel for contacting the nickel and/or cobalt containing solution with the metallic particles. The nickel and/or cobalt containing solution is fed into the fluidisable bed of metallic particles so as to enable a cementation process to occur between the nickel and/or cobalt in a solution and the metallic particles to produce a nickel and/or cobalt cementate. 
         [0024]    The fluidisation vessel can be any suitable process vessel in which a fluidisation stage can be located. Preferably, the fluidisation vessel is a vertical fluidisation column having at least one fluidisation stage. 
         [0025]    In one embodiment of the process of the present invention, the metallic particles are comprised of aluminium pellets with an average particle size of between 5 mm and 15 mm. 
         [0026]    In order to enable the nickel and/or cobalt containing solution to cause a bed of aluminium pellets to fluidise, it is preferred for the nickel and/or cobalt containing solution to be fed into the fluidisation vessel from a location underneath the bed of aluminium pellets so as to fluidise the pellets. 
         [0027]    Again, it has been found that if the aluminium pellets are agitated, this agitation can break, shear or otherwise separate the resulting nickel and/or cobalt cementate from an unreacted central core of the aluminium pellets. Accordingly, it is preferable for the fluidised bed to be configured to allow the aluminium pellets in the fluidised bed to have a degree of agitation to promote separation of the nickel and/or cobalt cementate from the surface of the pellets. 
         [0028]    This partial cementation process can aid in the recovery of the resulting nickel and/or cobalt cementate because the resulting nickel and/or cobalt cementate has a much smaller particle size to the unreacted central core of the aluminium pellets thereby allowing filtering processes to substantially separate the aluminium pellets and nickel and/or cobalt cementate from an outflow from a process vessel in which the cementation reaction occurred. Accordingly, it is preferred for the fluidisation vessel to further include a screen, sized to allow a substantial portion of the nickel and/or cobalt cementate to pass, and to substantially retain the metallic particles. Preferably, the screen is located before the outlet of the fluidisation vessel. 
         [0029]    Alternatively, or in addition to the inclusion of a screen, it is preferred for the fluidisation vessel to include a section of larger cross sectional area, which allows the velocity of the solution to fall below the fluidisation velocity of the aluminium pellets, but not below the fluidisation velocity of the smaller nickel and/or cobalt cementate particles, such that the nickel and/or cobalt cementate particles are swept out from the fluidisation vessel and the aluminium pellets fall back into the vessel. 
         [0030]    The pH of the nickel and/or cobalt containing solution is preferably adjusted to allow maximum yield of nickel and/or cobalt cementate from solution, whilst minimising the consumption of aluminium by the unwanted side reaction of aluminium reacting with hydrogen ions to produce hydrogen gas. Furthermore, the pH of the nickel and/or cobalt containing solution may be chosen such that aluminium which is dissolved from the pellets is not hydrolysed and precipitated from solution. In addition, the pH may be chosen to maximise the reactivity of the aluminium metal surface, for example by removing the naturally occurring layer of oxide from the surface. Preferably, the pH may be adjusted or maintained in the range from 0 to 4.5. More preferably, the pH may be adjusted or maintained in the range of 2 to 3.5. 
         [0031]    Further enrichment steps can also be used in the process of the present invention to enrich the solid content of the slurry produced from the cementation process. In some embodiments, the process of the present invention further includes the step of: 
         [0032]    (a) thickening the resulting slurry including a nickel and/or cobalt cementate. 
         [0033]    Additionally or alternatively, the process of the present invention can further include the step of: 
         [0034]    (b) filtering the resulting slurry including a nickel and/or cobalt cementate. 
         [0035]    Furthermore, or alternatively, the process of the present invention can include the step of: 
         [0036]    (c) magnetic separation of the nickel and/or cobalt. 
         [0037]    While operation at the preferred pH of 2 to 3.5 advantageously retains aluminium in solution, an alternative is to operate at a pH of 3.5-6, whereby the aluminium is hydrolysed and precipitates as aluminium hydroxide. In this embodiment of the invention it is useful to use magnetic separation to recover the metallic and magnetic nickel and/or cobalt particles of the nickel and/or cobalt cementate from the non magnetic aluminium hydroxide particles. Alternatively or additionally after separation of the solids the aluminium hydroxide particles may be removed by leaching using a suitable leaching lixiviant. A convenient leaching lixiviant is an alkaline reagent such as a sodium hydroxide solution. 
         [0038]    In the normal course of the leaching of a nickel containing ore or material an amount of cobalt will also be present in the resulting nickel containing PLS. In the present invention, cobalt may be recovered from the solution by cementation at the same time as nickel is recovered by cementation. In these embodiments, the metallic particles is preferably selected to be more electronegative than nickel and cobalt thereby enabling a cementation process to occur between the nickel and cobalt in the leachate and the metallic particles to produce a nickel cementate and a cobalt cementate or a combined nickel/cobalt cementate where separation cannot be maintained. Once the cementation process has run to a desired conversion of metallic particles to nickel and/or cobalt cementate, the nickel and/or cobalt cementate can then be separated from the metallic particles thereby producing a slurry that includes a cementate having a nickel content and a cobalt content. 
         [0039]    Alternatively, the cobalt content of the PLS could be removed prior to conducting the cementation reaction. This would allow for a nickel cementate product to be produced substantially free of cobalt. Similarly, where it is desirable to recover cobalt, the nickel content of the PLS could be removed prior to conducting the cementation reaction. This would allow for a cobalt cementate product to be produced substantially free of nickel. 
         [0040]    Unlike existing intermediate nickel and/or cobalt containing products produced from alternative nickel and/or cobalt recovery process, the nickel and/or cobalt containing cementate produced from certain embodiments of the present invention is highly suitable for direct conversion to an alloy, for example by melting in a furnace. In these embodiments, the present invention can further include the steps of: 
         [0041]    (i) feeding the nickel and/or cobalt cementate into a direct melting furnace to produce a molten nickel and/or cobalt metal; and 
         [0042]    (ii) casting the molten nickel and/or cobalt metal to produce a cast nickel and/or cobalt metal product. 
         [0043]    It is preferable for the nickel content of the cementate to be formed into briquettes (preferably after enrichment steps on the slurry) and added to the feed of a furnace, where the nickel and/or cobalt is rendered molten. Preferably, heating in the furnace separates impurities from the nickel cementate briquette such as any residual aluminium in the material. Further, as aluminium can be added to furnace feed to remove oxygen from the melt, the residual aluminium in the cementate serves a valuable purpose by displacing the need for a separate aluminium addition. Preferably, the cementate briquette is subject to melting in an electric furnace. 
         [0044]    In another preferred embodiment of this process, the nickel cementate is formed into briquettes and these briquettes are introduce into a container, crucible or furnace which contains molten alloy substantially comprising iron and nickel (also known as “ferronickel”). 
         [0045]    According to another aspect of the present invention, there is provided a process for the recovery of nickel from a nickel containing ore comprising:
       (a) subjecting a nickel containing ore to a leach process to produce a nickel containing pregnant leach solution;   (b) contacting the nickel containing pregnant leach solution with aluminium metal particles thereby enabling a cementation process to occur between the nickel in the pregnant leach solution and the aluminium metal particles to produce a nickel cementate;   (c) separating the nickel cementate from the aluminium metal particles thereby producing a slurry including nickel cementate;   (d) forming the nickel cementate into a briquette; and   (e) introducing the nickel cementate briquettes into a container, crucible or furnace which contains a molten alloy substantially comprising iron and nickel.       
 
         [0051]    In this aspect of the process of the invention, nickel is leached from ore, cemented by means of aluminium metal, the cementate briquetted, and the briquettes added to molten ferronickel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]    The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein: 
           [0053]      FIG. 1  is a flowsheet illustrating a process for the recovery of nickel and cobalt from a nickel and cobalt containing ore according to one embodiment of the present invention. 
           [0054]      FIG. 2  is a schematic representation of a fluidised bed column according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0055]      FIG. 1  shows a flowsheet of a process for the recovery of nickel and cobalt from a nickel and cobalt containing ore according to one embodiment of the present invention. The process utilises a cementation process to recover a nickel and cobalt metal content from a nickel and cobalt containing pregnant leach solution (PLS) which is then melted in an electric furnace to produce a nickel melt suitable for casting. 
         [0056]    As shown in the process set out in  FIG. 1 , a laterite nickel and cobalt containing ore is subject to a leaching process step using a sulfuric acid solution. The leaching process could be for example at least one of a High Pressure Acid Leach (HPAL) process, Caron reduction roast-ammonium carbonate leach process, atmospheric pressure agitation acid leach processes and heap leaching. While the illustrated process relates to a laterite nickel containing ore, it should be appreciated that a similar process as set out in  FIG. 1  could be used for a nickel containing sulphide ore, concentrate, matte or intermediate. When using a nickel containing sulphide material, the leaching process step shown in  FIG. 1  could be for example at least one of oxidative pressure leaching, atmospheric leaching or heap leaching. 
         [0057]    A nickel ion and cobalt ion containing PLS is produced from the process in process stream, which is then subject to a solid, liquid separation step such as filtration or similar to separate the spent ore from the PLS solution. The PLS solution is then passed through a purification stage in which impurities such as iron and aluminium are removed. One such suitable purification stage is an ion exchange process such as the process disclosed in International Patent Publication No. WO/2006/029443 in the name of BHP Billiton SSM Technology Pty Ltd. In other forms, various impurities can be removed through the addition of extractors such as limestone, ammonium carbonate or similar. Impurities such as iron and aluminium are discarded in a waste stream and a purified nickel ion and cobalt ion containing PLS is produced. 
         [0058]    If desired the cobalt may be separated from the purified PLS to produce a cobalt product and a substantially cobalt free nickel containing solution. This can be achieved using separation processes such as ion exchange, selective precipitation or other suitable selective extractive processes such as solvent extraction by the phosphinic acid Cyanex 272. 
         [0059]    The nickel and/or cobalt containing solution is thence subjected to cementation. The cementation stage can be conducted in any suitable process vessel including a mixing device, agitator or other solid-liquid mixing means. One preferred embodiment of the cementation process vessel is a fluidised column shown in  FIG. 2 . This form of the cementation process vessel will be explained in more detail in relation to this Figure later in the specification. The cementation process vessel is used to contact the purified nickel ion and cobalt ion containing solution with aluminium metal particles. In this respect, aluminium metal pellets or aluminium metal powder is fed or otherwise placed into the cementation process vessel. In the cementation process vessel a cementation process is allowed to occur between the nickel and cobalt in the PLS and the aluminium metal particles to produce mixture of nickel and/or cobalt cementate and unprocessed and unreacted reagent aluminium particles. The cementation reaction can therefore result in cementate particles including nickel, cobalt or a combined nickel/cobalt content where separation cannot be maintained. 
         [0060]    Once the cementation reaction has progressed to the desired cementation conversion, typically partial conversion of the aluminium powder or pellets to nickel metal and cobalt metal, a separation stage is used to separate the unprocessed and unreacted aluminium particles from the desired nickel and/or cobalt cementate product. The separation stage can be separate from the cementation process vessel in which the cementation reaction takes place, or could be an integral part of this process vessel. In one embodiment, the separation stage can include a screen, which has a mesh size chosen to substantially pass the nickel cementate particles, and to substantially retain the cementation reagent particles or another process. The unprocessed and unreacted (spent) aluminium particles or pellets can be recycled back into the cementation process vessel for use in a further cementation reaction. 
         [0061]    The nickel and/or cobalt cementate product exits the separation stage as a slurry of solid nickel and/or cobalt cementate mixed with a solution of aluminium sulfate and other PLS impurities such as magnesium sulfate and manganese sulfate. This slurry is processed through one or more solid/liquid stages such as magnetic separation, washing, thickening and/or filtering processes to substantially remove excess solution from the nickel and/or cobalt cementate product. 
         [0062]    The resulting nickel and/or cobalt containing cementate product may then be sent to market. Alternatively, it may then be formed into briquettes which are fed into a furnace to produce a nickel and/or cobalt rich melt. The melt can then be processed in a suitable casting process to produce a cast nickel and/or cobalt product. 
         [0063]    Advantageously, the separation of cobalt from the nickel in the previously described optional cobalt separation process allows the production of nickel briquettes substantially free of cobalt. In this case, as shown by the dashed line in  FIG. 1 , the nickel cementate briquettes can be introduced into a container, crucible or furnace which contains a molten ferronickel alloy. The resulting ferronickel melt can then be processed in a suitable casting process to produce a cast ferronickel alloy product. 
         [0064]    It should also be appreciated that in other embodiments, the cobalt content of the PLS can be extracted from solution prior to the cementation stage using extractive processes such as selective precipitation, solvent extraction such as Cyanex 272 SX, or similar to provide a nickel-rich solution for the cementation reaction. Cementation of this nickel-rich solution would produce a nickel rich slurry which could be subsequently fed to a furnace to produce a nickel melt for casting. 
         [0065]      FIG. 2  shows a vertical fluidised bed column  10  which can be used to conduct a cementation reaction for the recovery of nickel from a nickel containing solution in a nickel recovery process according to the present invention. The vertical fluidised bed column  10  can be used for the Ni/Co cementation step shown in  FIG. 1 . 
         [0066]    The illustrated fluidised bed column  10  includes a single fluidised bed stage  12  containing aluminium metal pellets. The particle size distribution of the aluminium metal pellets is selected so as to permit only partial cementation of the aluminium metal pellets. Accordingly, the aluminium metal pellets have an average particle size of between 5 mm and 15 mm. 
         [0067]    In use, a nickel containing solution is fed into the fluidisable bed  12  of aluminium metal pellets so as to enable a cementation process to occur between the nickel ions and cobalt ions in the PLS and the aluminium metal pellets to produce a cementate having a nickel metal and cobalt metal content. The PLS is fed into the fluidised bed column  10  from an inlet  14  underneath the fluidisable bed  12  of aluminium metal pellets so as to fluidise the aluminium metal pellets. The fluidisation agitates the aluminium metal pellets in the bed  12  causing the formed nickel and/or cobalt cementate to break, shear or otherwise separate the resulting nickel and/or cobalt cementate from an unreacted central core of the aluminium metallic pellets. 
         [0068]    The pH of the nickel containing solution is adjusted or maintained in the range of 2 to 3.5 prior to the solution being fed into the fluidised bed column  10  to allow maximum yield of nickel cementate from solution, whilst minimising the consumption of aluminium from the pellets by the unwanted side reaction of aluminium reacting with hydrogen ions to produce hydrogen gas. This pH also substantially prevents aluminium dissolved from the pellets from being hydrolysed and precipitated from solution. If desired the column may be operated at other pH ranges as are compatible with the application, for example pH 3.5-6 in an acid leaching process or pH 7.5-10 in the Caron ammoniacal process. In these alternatives some contamination of the product by aluminium hydroxide might result, desirably requiring a removal process, such as alkaline leaching or magnetic separation. 
         [0069]    The illustrated fluidisation column  10  also has a mesh screen  16  located before the outlet  18  of the fluidisation column  10 . The mesh screen  16  is sized to allow a substantial portion of the nickel and/or cobalt cementate to pass to the product outlet  18  and to substantially retain the aluminium metal pellets within the fluidisation column  10 . The outflow from the outlet  18  is in the form of a slurry containing a nickel and cobalt containing cementate which can then be treated by other concentration and/or thickening processes. The fluidisation column  10  can also include a section of larger cross sectional area, which allows the velocity of the solution to fall below the fluidisation velocity of the aluminium pellets, but not below the fluidisation velocity of the smaller nickel cementate particles. The nickel and cobalt cementate particles are therefore swept out from the fluidisation column  10  and the aluminium pellets fall back into the fluidisation column  10 . 
         [0070]    The present invention provides an alternative process for the recovery of nickel and/or cobalt from solutions, for example a pregnant leach solution produced by leaching nickel and/or cobalt containing materials. The advantages of the present invention are several. One advantage is the production of a higher grade nickel and/or cobalt containing material than may be produced by other recovery processes that use precipitation reagents such as sulfide ions or hydroxide ions. The resulting cementate from the process of the present invention can contain more nickel by weight and by volume than other similar intermediate nickel and/or cobalt containing products formed using conventional recovery processes, and therefore can be less costly to transport. A further advantage of the present invention is that the cementate from the process of the present invention is readily able to be settled and filtered, and therefore is more easily handled than similar materials formed using conventional recovery processes such as sulfide precipitates. Another advantage of those forms of the present invention that use aluminium pellets, is that aluminium pellets may be safely and conveniently transported, handled and stored, and thus the process of the present invention is particularly suitable for remotely located operations and mine sites. 
         [0071]    Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention. 
         [0072]    Throughout the description and claims of the specification the word “comprise” and variations of the word, such as “comprising” and “comprises”, is not intended to exclude other additives, components, integers or steps.