Background of the Invention

Field of the Invention

[0001] The present invention concerns an apparatus and a method for the enhanced recovery of nickel and cobalt from nickel laterites, proceeding via the use of superheated steam in a heat treatment step.

Description of Related Art

[0002] About 70% of the Earth's land-based nickel resources are contained in laterites. Typically, nickel and cobalt are obtained from such laterites by leaching, including an atmospheric sulphatization.

[0003] Nickel is relatively weakly bound to iron or silicate minerals in laterites. It is easily leached, but typically at the expense of solubilising vast amounts of iron.

[0004] Most prior art methods utilize acid leaching, such as described in FR2459295, since nickel has been found to be dissolved in e.g. sulphuric acid solutions. Acid leaching has, however, been found not to be an efficient alternative when desiring to separate the nickel from the iron. Further, the amount of acid required for acid leaching is high.

[0005] High-pressure leaching has also been used, as in AU 2002223341. High- pressure leaching is, however, a harsh step that requires the use of an autoclave. This leads to high operating costs. Further, safety can be improved if the high-pressure step can be omitted from the process. .

[0006] Thus, there is an existing need for an economical, efficient and environmentally friendly procedure for recovery of nickel and cobalt from nickel laterites, while avoiding large amounts of iron in the pregnant leach solution (PFS) obtained in the leaching step, and while also utilizing the waste heat and steam from sulphuric acid production. Summary of the Invention [0007] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0008] According to a first aspect of the present invention, there is provided an arrangement and a method for extracting metals from nickel-containing laterites.

[0009] According to a second aspect of the present invention, there is provided an arrangement and a method for extracting metals, proceeding via the sulphatization of the raw material at atmospheric pressure, prior to leaching. [0010] According to a further aspect of the invention, steam is used to facilitate the sulphatization, whereby said steam preferably can be selected from recycled steams or waste steams, e.g. from a sulphuric acid plant that is already required on site. Such a sulphuric acid plant can thus advantageously be placed next to the arrangement for extracting metals from nickel-containing laterites.

[0011] The sulphatization prior to leaching has the specific advantage that it enables the leaching of nickel and cobalt in water with minimal dissolution of iron. The iron can instead be recovered from the leach residue in the form of hematite, thus providing a more efficient separation of iron as compared to existing procedures. Hematite is only formed at higher temperatures against moderate acidities, whereby low-temperature methods or acid leaching steps are ineffective in forming hematite.

[0012] Many prior methods for processing nickel laterites utilize pressurized leaching. The expenses of pressure leaching are, however, high, particularly since they require the use of autoclaves.

[0013] Since the iron is reacted into hematite prior to the solubilisation of nickel and cobalt, the present invention also minimizes the acid consumption in the required acidification step. Brief Description of the Drawings

[0014] FIGURE 1 is a diagram illustrating the units of the arrangement according to the invention;

[0015] FIGURE 2 illustrates the units of the arrangement according to some preferred embodiments of the invention.

Embodiments of the Invention

[0016] Definitions In the present context, the term “nickel- containing laterite” is intended to encompass laterites with particularly high nickel and cobalt contents, such as limonite-type laterites or silicate-type laterites.

The term “super-heated steam” means steam that has been heated to a temperature above the boiling point of water, typically at least to a temperature of 150°C.

The term “pregnant leach solution” (or PLS) is commonly used to define the liquid phase separated from the solids after a leaching step, which is intended to contain the components of interest that have been extracted from the raw material.

[0017] The present invention relates to an arrangement and a method for extracting metals from nickel- containing laterites. Said arrangement comprises the following units (see Fig. 1): an acid treatment unit 1 for mixing and distributing acid into a ground laterite material, a heat treatment unit 2 for reacting metals present in an acid-containing laterite material, a leaching unit 3 for transferring reacted metals into the leach solution i.e. the PLS, a solid/liquid separation unit 31 , connected to and downstream from the leaching unit 3, for separating remaining solids from the leach solution (the PLS), and one or more precipitation units 4,5 for separating one or more product fractions from a leach solution.

[0018] In an embodiment of the invention, the acid treatment unit 1 and the heat treatment unit 2 are separate units, but connected to each other.

[0019] The heat treatment unit 2 can be in the form of any vessel that can withstand high temperatures. Typically, a kiln is used. Preferably, the heat treatment unit 2 includes an inlet for supplying super-heated steam into the heat treatment unit 2. In order to maintain the temperature at a sufficient level, also the vessel, e.g. the kiln, can include separate heating means.

[0020] In preferred embodiments of the invention, additional units are included in the arrangement. For example, a grinding unit for forming ground laterite material can be connected to, and upstream from, the acid treatment unit 1. Another optional further unit is a crushing unit 21, preferably being connected to and upstream from the leaching unit 3, typically positioned between the heat treatment 2 and leaching units 3 (see Fig. 2).

[0021] In another embodiment of the invention, the acid treatment unit 1 is any kind of mixing vessel configured to cause mixing of acid into the material passed through said unit 1, preferably to cause agglomeration of said material.

[0022] The heat treatment unit 2 is typically connected to the acid treatment unit 1 via line 102, and thus positioned downstream from said acid treatment unit 1.

[0023] In an embodiment, the heat treatment unit 2 is a contacting vessel, which is configured to cause mixing. According to one alternative, the contacting vessel is selected from the vessels that cause mixing of the material by turning or rotating, the vessel preferably being a rotary kiln. According to another alternative, separate means for mixing are included in the contacting vessel. According to a further alternative, a turning or rotating vessel can be equipped with separate means for mixing. [0024] In an embodiment, the leaching unit 3 is connected to the heat treatment unit 2, via line 203, and is thus positioned downstream from said heat treatment unit 2. Optionally, a crushing unit 21 is positioned between the heat treatment 2 and leaching 3 units (see Fig. 2). In this case, a line 203 connects the heat treatment unit 2 to the crushing unit 21, whereas a line 213 connects the crushing unit 21 to the leaching unit 3. Said crushing unit 21 is, however, not essential if all agglomerates obtained in the heat treatment unit 2 remain smaller than 300mhi, particularly if the leaching unit 3 is supplied with means for mixing. The means for mixing should in such a case be sufficient to break up any agglomerates which are still present in the laterite mixture after heating.

[0025] The leaching unit 3 is preferably a water leaching unit 3, more preferably in the form of a stirred tank reactor. [0026] As stated above, the arrangement comprises a solid/liquid separation unit 31 connected to the leaching unit 3 via line 303, and thus being positioned downstream from the leaching unit 3. Typically, this solid/liquid separation unit 31 is provided with a waste outlet for solids, whereby the remaining solution can be carried to downstream units of the arrangement.

[0027] In an embodiment, one or more precipitation units 4,5 are connected to the leaching unit 3, with the solid/liquid separation unit 31 being positioned between the leaching 3 and precipitation 4,5 units. Thus, the liquid side of the solid/liquid separation unit 31 is connected to a precipitation unit 4,5 via line 314.

[0028] Preferably, there are two or more precipitation units 4,5, arranged in series (see Fig. 2), preferably with solid/liquid separation units 41,51 provided after each precipitation unit 4,5. According to this alternative, it is preferred that at least one of the precipitation units 4,5 is an impurity precipitation unit 4, provided with an inlet for an alkaline agent intended to cause precipitation by an increase of the pH of the leach solution, thus leaving a purified leach solution containing nickel and cobalt. The impurity precipitation unit 4 is typically connected to a solid/liquid separation unit 41 via line 405.

[0029] Likewise, it is preferred that at least one of the precipitation units 4,5 is a product precipitation unit 5, provided with an inlet for an alkaline agent, intended to cause precipitation of a product fraction containing nickel and cobalt by an increase of the pH of the leach solution. The product precipitation unit 5 is also typically connected to a solid/liquid separation unit 51, this connection arranged via line 506.

[0030] In case the arrangement includes both the impurity precipitation unit 4, with its solid/liquid separation unit 41, and the product precipitation unit 5, with its solid/liquid separation unit 51, these are preferably connected to each other via line 415. Typically, the product precipitation unit 5 is positioned downstream from the impurity precipitation unit 4, whereby line 415 connects the separation unit 41 positioned downstream from the impurity precipitation unit 4 to the product precipitation unit 5.

[0031] It is particularly preferred that the arrangement of the above described embodiments is configured to be suitable for use in the method of the invention.

[0032] The method of the present invention is used for extracting metals from nickel-containing laterites. The method comprises the following steps:

- an acid treatment step, wherein a ground laterite material and an acidic solution are added, and thereafter mixed to cause distribution of the acid into the formed laterite mixture,

- a heat treatment step, wherein an increased temperature is used to react metals present in the acid-containing laterite mixture, in order to form a heat-treated laterite mixture,

- a leaching step for transferring the reacted metals from the heat-treated laterite mixture into the leach solution, in order to form a metal- containing leach slurry, - a separation step, wherein remaining solids are separated from the leach solution (i.e. the PLS),

- one or more precipitation steps, wherein one or more fractions are precipitated from the metal-containing leach solution, in order to form one or more product fractions, and - recovering one or more product fractions.

[0033] In an embodiment of the invention, the acid treatment step and the heat treatment step are carried out separately, with the heat treatment step immediately following the acid treatment step. [0034] Depending on the source of the raw material, and particularly on the size of the particles in the material, the acid treatment step may be preceded by a grinding step.

[0035] The raw material is a nickel-containing laterite. Laterites are typically rich in iron and aluminium, but in the present invention, they are used as a source of nickel and cobalt, whereby laterites with particularly high nickel and cobalt contents are preferred, such as limonite-type or silicate laterites.

[0036] Said optional grinding step is carried out on the nickel-containing laterite raw material, preferably forming laterite particles having a size of 60 pm or smaller, more preferably about 20 pm or smaller, and resulting in said ground laterite material. If the starting material fed to the method is already present in sufficiently small particles, no separate grinding step is, however, required.

[0037] In an embodiment of the invention, the acid treatment step is carried out using an acidifying agent comprising sulphuric acid, typically in the form of concentrated sulphuric acid, optionally comprising also one or more further sulphate, such as sodium sulphate.

[0038] Typically, the acid treatment step results in agglomeration of the ground laterite material, thus forming pellet-like agglomerates. Therefore, said step of the method can also be called an “acid agglomeration” step. Thus, it is preferred to adjust the amount of acidifying agent in each case to the amount needed to cause formation of agglomerates. Typically, this amount of sulphuric acid is in the range of 100-500 g/kg of ground laterite material, preferably 400-500 g/kg. If the amount is increased further from 500 g/kg, the process becomes uneconomical. Further, hematite is only formed at moderate acidities, whereby a larger amount of acid is undesirable.

[0039] The heat treatment step is carried out by adding super-heated steam.

[0040] In an embodiment of the invention, the heat treatment step is carried out by feeding superheated steam, preferably at a temperature adjusted to 250-600°C, more to a temperature of 300-550°C, most suitably to a temperature of 300-500°C. In addition, the vessel in which the heat treatment step is carried out, e.g. the kiln, can be heated separately, as needed. This option will ensure that a sufficient temperature is maintained in the vessel. A sufficiently high temperature is required to ensure that all the desired reactions take place. For example, the formation of hematite only takes place at high temperatures.

[0041] Preferably, the heat treatment step is carried out in the presence of sulphuric acid, which causes sulphatization of metals in the laterite mixture, which are in the solid state. This is typically accomplished by performing the heat-treatment step on the acid- containing laterite mixture obtained from the acid-treatment step, whereby the required sulphuric acid has been added to the laterite material already in the acid-treatment step. [0042] The residence time of the laterite mixture in the heat treatment step is preferably 1-7 h, more preferably 3-6 h, most suitably 5-6h. Typically, longer residence times than 7h cause no harm, but have no further effect on the process.

[0043] The sulphatization of metals during the heat treatment occurs by reactions (l)-(3) shown below. In addition, the added superheated steam promotes the hydrolysis of iron sulphate to occur in the solids phase by reaction (4) also presented below.

2CoOOH + 3H ₂ S0 ₄ Co ₂ (S0 ₄ ) ₃ + 4H ₂ 0 (3)

Fe ₂ (S0 ₄ ) ₃ + H ₂ 0 (superheated steam) -> Fe ₂ 0 ₃ + H ₂ S0 ₄ (4)

[0044] Conversion of goethite to hematite during the process liberates nickel, as nickel is present in many limonite-type laterites in the lattice substitutions of goethite. The overall reaction for nickel liberation from goethite due to hematite conversion is presented in reaction (5) below. (liberated) + Fe ₂ 0 ₃ + H ₂ 0 (5)

[0045] Since the agglomerates typically formed in the acid-treatment step are not broken down in the heat-treatment step, it is preferred to break them down at least partially, by other means before the leaching step. This can be accomplished for example using a separate crushing step. Preferably, the crushing step is used to reduce the size of the agglomerates to less than 300mhi. [0046] According to another option, the crushing step can be omitted provided that the mixing in the subsequent leaching step is sufficient to break up any agglomerates still present in the mixture to less than 300iun.

[0047] After an optional crushing step, the heat-treated mixture is in a form that is suitable for feeding to the subsequent leaching step. Particularly, it is expected that the nickel and cobalt after the heat treatment are in the form of water-leachable sulphates, whereas iron is expected to be in the form of an insoluble hematite.

[0048] In an embodiment of the invention, the leaching step is carried out as a water leaching, whereby no chemical additions are made to the mixture being fed to the leaching step, and only water is added to provide a suitable solids content in the slurry. [0049] The solids content of the slurry formed in the leaching step is preferably first adjusted to 100-500 g/1, more preferably to 250-500 g/1, most preferably to 250-400 g/1. The leaching is typically carried out at a temperature of above 50°C, preferably at a temperature of 50-95°C, more preferably at a temperature of 70-95°C, and most suitably at a temperature of 90-95°C, while the pressure preferably is atmospheric. The residence time in the leaching step is preferably ½ h or more, more preferably ½ - 5 h, and most suitably 1-4 h.

[0050] In an embodiment of the invention, the solids of the metal-containing leach slurry are separated from the liquid (i.e. the PLS) after the leaching step, e.g. by filtration, whereby the solids can be discarded, and the remaining fraction(s) of the metal-containing leach solution (i.e. the PLS), is/are carried to the following step of the method.

[0051] The discarded solids contain iron in the form of hematite, as well as quartz. The metal-containing leach solution, or PLS, in turn, contains the desired metals, such as the nickel and the cobalt, and typically also the aluminium present in laterites. Thus, one option is to recover a fraction of this solution as a product fraction.

[0052] However, typically this leach solution, or a remaining fraction thereof, is purified further, preferably by using one or more precipitation steps.

[0053] In an embodiment of the invention, two or more precipitation steps are carried out on the metal-containing leach solution (i.e. the PLS) separated from the solids in the preceding solid/liquid separation step, in order to provide a further purified product. Preferably, solid/liquid separation steps are also carried out after each precipitation step.

[0054] Since the leach solution (the PLS) may still contain impurities, such as iron and aluminium, it is preferred to carry out at least one precipitation step in a manner that precipitates these impurities. This can be done by increasing the pH of the metal- containing leach solution carried to said precipitation step, preferably using limestone, to a level that precipitates these impurities from the leach solution, thus leaving a purified solution containing nickel and cobalt. The purified solution remaining after this precipitation step can then be recovered as a product fraction.

[0055] Another option is to carry out at least one precipitation step by increasing the pH of the optionally purified metal-containing leach solution (the PLS) carried to said precipitation step, preferably using magnesium oxide or lime milk, to a level that precipitates a product fraction from the optionally purified leach solution. This precipitation typically provides a precipitated product fraction containing nickel and cobalt, whereas the filtrate contains manganese and magnesium. The obtained precipitate can be recovered as a product fraction.

[0056] Depending on the manner in which the precipitation(s) is/are carried out, the obtained product fraction(s) may contain the product metals in different forms. One common option is to precipitate the nickel and the cobalt as a mixture of their hydroxides.

[0057] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0058] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0059] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. In addition, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0060] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0061] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention.

[0062] The following non-limiting example is intended merely to illustrate the advantages obtained with the embodiments of the present invention. EXAMPLE

[0063] Experiments were carried out on a nickel laterite raw material in order to demonstrate the effect of the present invention on the results of common nickel laterite treatments. Table 1 presents the chemical composition of the used nickel laterite material. Table 1. Chemical composition.

[0064] The tests were carried out using lab-scale equipment. Acid agglomeration of the laterite was performed in a rotating reactor with introduction of sulphuric acid solution. Formed agglomerates were transferred to a rotary kiln with steam inlet to perform a heat treatment, carried out using steam. After the heat treatment, agglomerates were crushed and fed to water leaching. Leaching was conducted in a 3 L reactor, with 20 wt% (about 250g/l) solids concentration and temperature of 90 °C. During leaching, pH was changing freely.

[0065] Test parameters and nickel, cobalt and iron yields to solution after water leaching are listed in Table 2. Sulphuric acid ratio indicates the ratio between used sulphuric acid gram per used laterite kilogram. In the experiments, a constant feed of steam was maintained in the heat treatment.

Table 2. Test parameters and metal yields for example tests.

[0066] From the results it can be seen that high nickel and cobalt yields with moderate dissolution of iron are achieved with the laterite process of the present invention. Industrial Applicability [0067] The present arrangement and method can be used to replace conventional alternatives for recovery of nickel and cobalt from nickel laterites.

[0068] In particular, the present arrangement and method provides an economical, efficient and environmentally friendly procedure for separating nickel and cobalt from the other components of such laterites, while avoiding large amounts of iron in the solution.

Reference Signs List

As shown in the Figures (see Fig. 1 and Fig. 2), the following units and lines can be included in the arrangement of the present invention, according to one or more embodiments of the invention:

1 Acid treatment unit

102 Line leading from the acid treatment unit 1 to the following downstream unit

2 Heat treatment unit

203 Line leading from the heat treatment unit 2 to the following downstream unit

21 Crusher

213 Line leading from the crusher 21 to the following downstream unit

3 Leaching unit

303 Line leading from the leaching unit 3 to the following downstream unit

31 Separation unit downstream from the leaching unit 3

314 Line leading from the separation unit 31 to the following downstream unit

4 Impurity precipitation

405 Line leading from the impurity precipitation 4 to the following downstream unit

41 Separation unit downstream from the impurity precipitation 4

415 Line leading from the separation unit 41 to the following downstream unit

5 Product precipitation unit

506 Line leading from the product precipitation 5 to the following downstream unit

51 Separation unit downstream from the product precipitation unit 5