OA21507A - Recovery of metals from metallic or metalbearing materials. - Google Patents

Abstract

A method of treating a metallic or metal-bearing material includes, in an oxidative or reductive digestion step, contacting the metallic or metalbearing material with a reagent selected from ferric chloride (FeCI3), hydrochloric acid (HCI), and a combination thereof, thus producing a ferrous chloride (FeCI2) solution.

Description

RECOVERY OF METALS FROM METALLIC OR METAL-BEARING MATERIALS

FIELD OF THE INVENTION

THE INVENTION relates to the recovery of metals from solid metallic or metal-bearing materials. The invention provides a method of treating a solid metallic or metal-bearing material, to recover one or more metals from the metallic or metal-bearing material via a chloride medium. In this sense, “métal” has a broad meaning, including both metals in elemental metallic form and métal compounds. The invention extends to a process for performing the method.

BACKGROUND TO THE INVENTION

IN MANY MINERAL CONCENTRATES, and other metallic and metal-bearing materials, iron is a major contaminant. Dealing with iron generally results in high acid consumption and waste génération when such materials are beneficiated using hydrometallurgical processes. The présent invention seeks to provide a more efficient and cost-effective approach, while not limiting itself to the beneficiation iron-contaminated metallic and metal-bearing materials.

OBJECT OF THE INVENTION

IT IS AN OBJECT OF THE INVENTION to provide for the treatment of metallic or metalbearing materials that contain metals other than iron and, optionally, also contain iron, the iron then typically being comprised by a matrix containing the other metals, to liberate such metals other than iron from such matrices. In this sense, again, “métal” has a broad meaning, including both metals in elemental metallic form and métal compounds. In respect of métal compounds, it is envisaged that such compounds would be in a form that may be more readily beneficiated than the original form in which such metals manifested in the metallic or metal-bearing material.

SUMMARY OF THE INVENTION

IN THIS SPECIFICATION the provision of features in parenthesis contribute to the substantive content of the spécification and therefore to the characterisation of the invention. In particular, in cases in which generic Chemical formulae and numerical values for symbols of such generic formulae are provided in parenthesis, this should be interpreted as contributing substantively to the characterisation of the invention.

IN ACCORDANCE WITH A FIRST ASPECT OF THE INVENTION IS PROVIDED a method of treating a solid metallic or metal-bearing material, comprising one or more metals in metallic or compound form, to recover one or more of the metals from the metallic or metalbearing material in metallic or compound form, the method including, in an oxidative or 5 reductive digestion step, producing a ferrous chloride (FeCk) solution by contacting the metallic or metal-bearing material with a digestion reagent selected from ferrie chloride (FeCI₃), typically in aqueous solution, gaseous hydrochloric acid (HCl), HCl, in aqueous solution, and optionally, a combination or any two or more thereof, and reducing any FeCk in solution, produced from the contacting of the metallic or metal-bearing material with the digestion reagent, to FeCI₂ in solution.

The contacting of the metallic or metal-bearing material with the digestion reagent may be 15 performed in aqueous medium. Thus, the FeCk solution may be an aqueous FeCk solution.

When the digestion reagent is HCl, contacting the metallic or metal-bearing material with the HCl may include contacting the metallic or metal-bearing material directly with gaseous HCl (i.e. not in 20 the form of an aqueous HCl solution); or contacting the metallic or metal-bearing material with HCl in aqueous solution, preferably of a concentration above 30% v/v, e.g. between 30% and 36% v/v, e.g. 33% v/v.

When contacting the metallic or metal-bearing material with gaseous HCl, the metallic or 25 metal-bearing material may, in particular, be a hydrous ore material, which may be an ore material comprising chemically bound water (as opposed to “free water”, i.e. not chemically bound water), typically in.a range of from about 5% to about 70% by weight, e.g. in the form of métal hydrates and/or métal hydroxides. Optionally, such a hydrous ore material may be slightly wetted with free water, e.g. up to about 5% by mass of the mass of the hydrous ore, 30 before being subjected to digestion in the digestion step.

The gaseous HCl may, preferably, be anhydrous gaseous HCl, e.g. produced according to the third aspect of the invention.

When contacting the metallic or metal-bearing material with an aqueous HCl solution, the method may include preparing an aqueous HCl solution by scrubbing gaseous HCl with water, and contacting the metallic or metal-bearing material with the aqueous HCl solution thus prepared; or preparing an aqueous suspension or slurry of the metallic or metal-bearing material and scrubbing gaseous HCl with the suspension or slurry of the metallic or metal-bearing material.

The gaseous HCl may, in particular, be gaseous HCl, and more specifically anhydrous gaseous HCl, produced according to the third aspect of the invention.

Reducing FeCI₃ produced from the contacting of the metallic or metal-bearing material with the digestion reagent to FeCI₂ may be effected using a reducing agent, e.g. metallic iron (Fe).

Depending on the composition of the metallic or metal-bearing material, contacting the metallic or metal-bearing material with the digestion reagent may produce a solution of FeCI₃ to the exclusion of FeCI₂ or a solution comprising both FeCh and FeCI₂, which would thus require réduction of the FeCI₃ to be effected using the reducing agent.

It is also possible that a solution comprising no FeCI₃ would be produced, in which case no réduction would be required.

It will be appreciated that réduction is therefore only required if the digestion of the metallic or metal-bearing material produces FeCI₃

The digestion reagent may therefore, for example, be gaseous HCl, e.g. produced in accordance with the third aspect of the invention;

an aqueous solution of HCl, e.g. produced by scrubbing gaseous HCl produced in accordance with the third aspect of the invention with water;

an aqueous solution of HCl, e.g. produced by scrubbing gaseous HCl e.g. produced in accordance with the third aspect of the invention with an aqueous suspension or slurry of the solid metallic or metal-bearing material;

an aqueous solution of FeCI₃, e.g. produced by contacting solid hématite (Fe₂O₃), e.g. produced in accordance with the third aspect of the invention, with an aqueous solution of HCl produced by scrubbing gaseous HCI e.g. produced in accordance with the third aspect of the invention with water; or is an aqueous solution of FeCI₃, e.g. produced by scrubbing gaseous HCl e.g. produced in accordance with the third aspect of the invention with an aqueous suspension of solid Fe₂O₃, e.g. produced in accordance with the third aspect of the invention.

When the metallic or metal-bearing material comprises iron, in metallic or compound form, such iron would be converted to ferrous chloride as described above and thus be présent as ferrous chloride in the FeCI₂ solution. When the metallic or metal-bearing material comprises metals (M) other than iron, in metallic or compound form, then at least some such metals other than iron would advantageously also be converted to soluble, e.g. divalent, chlorides (M²⁺CI₂) thereof.

IN ACCORDANCE WITH A SECOND ASPECT OF THE INVENTION IS PROVIDED a method of treating a solid metallic or metal-bearing material, comprising one or more metals in metallic or compound form, to recover one or more of the metals from the metallic or metal-bearing material in metallic or compound form, the method including, in a displacement crystallisation step, contacting a FeCI₂ solution, typically an aqueous FeCI₂ solution, produced by oxidative/reductive digestion of the metallic or metal-bearing material, with a displacement crystallisation reagent, preferably HCl, most preferably gaseous HCl, that displaces FeCI₂ from the FeCI₂ solution and thus produces a solid ferrous chloride hydrate (FeCI₂-xH₂O, wherein x>1, more preferably x>1), typically solid ferrous chloride tetrahydrate (FeCI₂-4H₂O, i.e. x=4).

The HCl in gaseous form may be anhydrous gaseous HCl.

The HCl in gaseous form that may be used in effecting the displacement crystallisation may, in particular, be HCl in gaseous form, and more specifically anhydrous HCl in gaseous form, produced in accordance with the third aspect of the invention.

Producing the FeCI₂ solution by oxidative/reductive digestion of the metallic or metal-bearing material may hâve included contacting the metallic or metal-bearing material with a digestion reagent selected from

FeCI₃, typically in aqueous solution, gaseous HCl,

HCl, in aqueous solution, and optionally, a combination of any two or more thereof, and reducing any FeCh in solution, produced from the contacting of the metallic or metal-bearing material with the digestion reagent, to FeCI₂.

The FeCk solution may, for example, be a FeCI₂ solution that has been produced according to the digestion step of the first aspect of the invention.

As noted above, the FeCI₂-xH₂O may, in particular, be FeCI₂-4H₂O, i.e. x=4.

The displacement crystallisation step may include, or may more typically be followed by, a déhydration (i.e. drying) step, which may include subjecting the FeCI₂-xH₂O to température treatment to produce a dehydrated solid ferrous chloride hydrate (FeCI₂-yH2O, wherein x>y>0). The FeCI₂-yH₂O may, in particular, be FeCI₂-H₂O (ferrous chloride monohydrate), i.e. y=1.

In the sense used in this spécification, in the context of the déhydration step, the terms “déhydration” and “dehydrated” therefore do not require complété déhydration, to provide an anhydrous form, although that possibility is included within the meaning of the word. The déhydration step may therefore more accurately be characterised as a “partial” déhydration step, at least in terms of the change in the hydration of the ferrous chloride.

The température treatment to which the FeCI₂.xH₂O is subjected in the déhydration step, may include subjecting the FeCI₂.xH₂O to a température in a range of from 70°C to 200°C, more preferably in a range of from 70°C to less than 200°C, i.e. at a température less than 200°C but not lower than 70°C. For example, the température may be in a range of from 70°C to 150°C.

The déhydration step may be performed under non-oxidising conditions, i.e. under conditions that avoid oxidation of the FeCI₂.xH₂O. This may include avoiding, or at least limiting, the presence of exogenous oxygen in the déhydration step. This may, in turn, include performing the déhydration step under positive pressure in a steam environment, which steam may be that which is produced as a resuit of the déhydration of the FeCI₂-xH₂O.

When crystallisation is effected by means of displacement crystallisation, the digestion reagent would typically not be, or be produced using, gaseous HCl produced in the décomposition step, then rather being or being produced using the aqueous HCl solution produced in the displacement crystallisation step.

When the metallic or metal-bearing material comprises iron, in metallic or compound form, such iron would be converted to ferrous chloride in the digestion step and then displaced as ferrous chloride hydrate from the FeCI₂ solution in the displacement crystallisation step.

When the metallic or metal-bearing material comprises metals (M) other than iron, in metallic or compound form, then at least some such metals other than iron would advantageously also be converted to soluble, e.g. divalent, chlorides (M²⁺CI2) thereof in the digestion step and would then also, advantageously, be displaced from solution as divalent métal chloride hydrates (M²⁺CI2.zH₂O, wherein z>0) thereof in the displacement crystallisation step.

IN ACCORDANCE WITH A THIRD ASPECT OF THE INVENTION IS PROVIDED a method of treating a solid metallic or metal-bearing material, comprising one or more metals in metallic or compound form, to recover one or more of the metals from the metallic or metalbearing material in metallic or compound form, the method including, in a thermal décomposition step, subjecting FeCI₂-xH₂O, wherein x>1, more preferably x>1, x most preferably being 4, produced by crystallisation thereof from a FeCI₂ solution produced by oxidative/reductive digestion of the metallic or metal-bearing material, and/or FeCI₂-yH₂O, wherein x>y>0, y preferably being 1, produced by subjecting the FeCI₂-xH₂O to déhydration, to température treatment, thus decomposing the FeCI₂-xH₂O or FeCI₂-yH₂O to produce solid ferrie oxide (Fe₂O3) and gaseous HCl.

The gaseous HCl may, in particular, be anhydrous gaseous HCl.

It is noted that, in the context of the thermal décomposition step and the invention generally, it is preferred that it is FeCI₂.xH₂O or FeCI₂.yH₂O that is subjected to thermal décomposition, to the exclusion of FeCI₃. This is since FeCI₃ would, when subjected to thermal décomposition, not décomposé to produce gaseous HCl and Fe₂O₃, but would instead sublimate.

Producing the FeCI₂ solution by oxidative/reductive digestion of the metallic or metal-bearing material may hâve included contacting the metallic or metal-bearing material with a digestion reagent selected from

FeCI₃, typically in aqueous solution, gaseous HCl,

HCl in aqueous solution, and optionally, a combination thereof, and reducing any FeCL in solution, produced from the contacting of the metallic or metal-bearing material with the digestion reagent, to FeCL.

The FeCL solution may, for example, be a FeCl2 solution that has been produced according to the method of the first aspect of the invention.

Crystallisation of FeCI₂.xH₂O from the FeCL solution may hâve been achieved by conventional methods, e.g. by means of evaporative crystallisation.

More preferably, however, crystallising the FeCI₂-xH₂O from the FeCL solution may hâve been effected, in accordance with the second aspect of the invention, by displacement crystallisation from a FeCL solution, which may hâve included contacting a FeCL solution, produced by oxidative/reductive digestion of the metallic or metal-bearing material, with a 15 displacement crystallisation reagent, preferably hydrochloric acid (HCl), most preferably gaseous HCl, that displaced FeCL from solution and thus produced FeCI₂-xH₂O.

The gaseous HCl may, in particular, hâve been anhydrous gaseous HCl, preferably produced by the thermal décomposition step of the invention.

l

The use of displacement crystallisation, as characterised above in accordance with the invention, over evaporative crystallisation, is preferred since, in the case of evaporative crystallisation, the pH shift that results from the évaporation of water from an FeCI₂ solution makes the FeCL in the solution significantly more susceptible to oxidation to FeCL, which 25 should be avoided in the context of the invention, in light thereof that, as mentioned above,

FeCL sublimâtes when subjected to high températures such as those exploited by the invention in the thermal décomposition step that is described herein.

When crystallisation is effected by means of displacement crystallisation, the digestion 30 reagent would typically not be, or would typically not be produced using, gaseous HCl produced in the décomposition step, then rather being or being produced using the aqueous HCl solution that is produced in the displacement crystallisation step.

Furthermore, producing FeCL.yH₂O through déhydration of the FeCI₂-xH₂O and subjecting 35 the FeCI₂.yH₂O to thermal décomposition, is preferred. Such déhydration may be effected, as described with reference to the second aspect of the invention, by subjecting the

FeCI₂.xH₂O to température treatment, at a température in a range of from 70°C to 200°C, more preferably in a range of from 70°C to less than 200°C, i.e. at a température less than 200°C but not lower than 70°C. For example, the température may be in a range of from 70°C to 150°C.

It is regarded as a particular inventive advantage of the invention that by subjecting FeCI₂.yH₂O to thermal décomposition, an effect of producing anhydrous gaseous hydrochloric acid is inventively achieved and exploited.

The solid FeCI₂-xH₂O, or the FeCI₂-yH₂O, may, for example, be FeCI₂-xH₂O, or FeCI₂-yH₂O, that has been produced according to the method of the second aspect of the invention.

When the metallic or metal-bearing material comprises iron, in metallic or compound form, then such iron would be converted to ferrous chloride, would be displaced from solution as ferrous chloride hydrate, would be dehydrated, and would be decomposed as described.

When the metallic or metal-bearing material comprises metals (M) other than iron, in metallic or compound form, then at least some of such metals other than iron would advantageously also be converted to soluble, e.g. divalent, chlorides (M²⁺CI2) thereof, would be displaced from solution as divalent chloride hydrates (M²⁺CI2.zH₂O, wherein z>0) thereof, would be partially or fully dehydrated (to produce M²⁺CI2.aH2O, wherein z>a>0), and would subjected to décomposition as described (to produce anhydrous M²⁺CI2).

In contrast to the ferrous chloride hydrate when subjected to décomposition, such other divalent métal chlorides or chloride hydrates would therefore not décomposé. They would remain intact, at most being completely dehydrated to their anhydrous divalent chloride forms. In such forms, such metals are soluble and may thus be easily separated from the solid ferrie oxide by solid-liquid séparation.

IN ACCORDANCE WITH A FOURTH ASPECT OF THE INVENTION IS PROVIDED a method of treating a solid metallic or metal-bearing material, comprising one or more of the metals in metallic or compound form, to recover one or more of the metals from the metallic or metal-bearing material in metallic or compound form, the method including in an oxidative or reductive digestion step, producing a ferrous chloride (FeCI₂) solution by contacting the metallic or metal-bearing material with a digestion reagent selected from ferrie chloride (FeCL), in aqueous solution gaseous hydrochloric acid (HCl), HCl in aqueous solution, and optionally, a combination of any two or more thereof, and reducing any FeCh in solution, produced from the contacting of the metallic or metalbearing material with the digestion reagent, to FeCI₂ in solution;

in a crystallisation step, crystallising a solid ferrous chloride hydrate (FeCI₂-xH₂O, wherein x > 1, preferably x > 1, most preferably being 4) from the FeCI₂ solution;

optionally, in a déhydration step, subjecting the FeCI₂-xH₂O to température treatment to produce dehydrated ferrous chloride hydrate (FeCI₂-yH₂O, wherein x>y>0, preferably being 1); and in a thermal décomposition step, subjecting the FeCI₂-xH₂O and/or the FeCI₂-yH₂O to température treatment and thus decomposing the FeCI₂xH₂O and/or the FeCI₂-yH₂O to produce solid ferrie oxide (Fe₂O₃) and gaseous HCl.

The oxidative or reductive digestion step may be that of the method of the first aspect of the invention.

Crystallisation of FeCl2.xH₂O from the FeCI₂ solution may be achieved by conventional methods, e.g. by means of a evaporative crystallisation.

More preferably, however, crystallising the FeCI₂-xH₂O from the FeCI₂ solution may be effected by displacement crystallisation from the FeCI₂ solution (i.e. the crystallisation step may be a displacement crystallisation step), which may include contacting, and saturating, the FeCI₂ solution with a displacement crystallisation reagent, preferably HCl, more preferably HCl in gaseous form, most preferably HCl in anhydrous gaseous form, e.g. gaseous HCl recovered from the thermal décomposition step, thus dispiacing FeCI₂ from solution and producing the FeCI₂-xH₂O.

In the displacement crystallisation step, the température of the FeCI₂ solution may be from 10°C to 60°C.

When the displacement crystallisation reagent is HCl in gaseous form, the displacement crystallisation may comprise, for example, scrubbing the gaseous HCl with the FeCI₂ solution.

In the displacement crystallisation step, an aqueous solution of HCl (i.e. diluted HCl) may therefore be formed.

When displacement crystallisation is used, the method may include separating solid FeCl2.xH₂O, and any other solid métal chloride hydrates that crystallised along with the FeCI₂.H₂O in the crystallisation step (M²⁺Cl2.zH₂O wherein z>1, as described below), from the aqueous solution of HCl thus produced; and using the aqueous solution of HCl as, or in producing, the digestion reagent in the digestion step.

The method may therefore include, in a second séparation step, performed after the displacement crystallisation step and before the déhydration step, recovering solid FeCI₂xH₂O, and any other solid métal chloride hydrates (M²⁺CI2-zH2O, as described herein) that may be présent, from the resulting HCl solution by means of solid-liquid séparation, thus recovering FeCI2-xH2O and any solid M²⁺CI2-zH₂O that may hâve been présent.

As mentioned above, the method may also include recycling the HCl solution produced in the displacement crystallisation step to the digestion step of the method and/or using the HCl solution to produce a FeCIs solution for use in the digestion step, by reaction of the HCl in the HCl solution with Fe₂Os, which may be Fe₂O₂ which is produced in the thermal décomposition step of the invention.

It is noted that recycle of the HCl solution produced in the displacement crystallisation step may include recycle of some métal chlorides not converted to métal chloride hydrates, e.g. as a resuit of low concentration. It is expected that build-up of such métal chloride hydrates would ultimately resuit in such conversion, once a sufficiently high concentration has been achieved.

The displacement crystallisation step may be that of the method of the second aspect of the invention.

The thermal décomposition step may be that of the third aspect of the invention.

The following statements apply to ail of the abovementioned first to fourth aspects of the invention:

The one or more metals comprised by the metallic or metal-bearing material may include one or more of chrome (Cr), copper (Cu), vanadium (V), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), manganèse (Mn) and iron (Fe), in metallic and/or compound forms.

Typically, the metallic or metal-bearing material would include at least iron, in a metallic or compound form, and preferably at least one métal (M) other than iron, in a metallic or compound form. Such other metals (M) may for example be one or more of those listed above, other than iron.

In cases in which the metallic or metal-bearing material includes iron, in metallic or compound form, the digestion reagent may comprise at least HCl.

In some embodiments of the invention, the metallic or metal-bearing material may, for example, be one or more of a polyoxide material (containing multiple métal oxides), a polysulphide material (containing multiple métal sulphides), an alloy material, a métal slag material, a métal fines material, and a metallic material.

Thus, metals in the metallic or metal-bearing material may, for example, be in one or more of métal oxide form, métal sulphide form, and metallic from.

In one spécifie embodiment of the invention, the metal-bearing material may be an ore material. For example, the metal-bearing material may be a titaniferous magnetite ore material, e.g. a vanadium-containing titaniferous magnetite ore material. Generally, it is envisaged that the invention may find application to any métal sulphide and/or métal oxide bearing ore material, particularly those comprising iron in a metallic or compound form.

Depending on the composition of the metal-bearing material, the FeCI₂ solution may therefore contain, in addition to FeCI₂, other métal chlorides, typically at least other divalent métal chlorides (M²⁺CI₂), but not excluding monovalent métal chlorides, in solution, e.g. CuCI₂or Cu₂CI₂.

Thus, the digestion step may hâve to effect that at least some metals contained in the metallic or metal-bearing material in metallic or métal compound form, are converted to métal chlorides (FeCI₂ and, if other metals (M) are présent, M²⁺CI₂) in solution, contained in the FeCI₂ solution. This is desired.

The digestion step may be performed at a température of from 10°C to 120°C.

If an FeCI₃ digestion reagent is used in the digestion step, it may be in solution. Typically, it may be in aqueous solution at a concentration of from 5wt% to 70wt%.

It is noted that in order to produce FeCI₃ in solution for use as the digestion reagent in the digestion step, solid Fe₂O₃ may be used in conjunction with HCl, thus producing a FeCI₃ solution in the digestion step, instead of producing it separately as a feed to the digestion step.

HCl, when used as digestion reagent in the digestion step, may be in solution, and may be produced as described in accordance with the first aspect of the invention. Typically, it may be in aqueous solution at a concentration of from 5wt% to 40wt%, more preferably 30% to 36%, e.g. 33%.

Alternative^, the HCl, when used as digestion reagent in the digestion step, may be gaseous HCl, as described in accordance with the first aspect of the invention.

The digestion reagent may therefore be, for example, gaseous HCl, e.g. produced in the thermal décomposition step;

an aqueous solution of HCl, e.g. produced by scrubbing gaseous HCl e.g. produced in the thermal décomposition step with water;

an aqueous solution of HCl, e.g. produced by scrubbing gaseous HCl e.g. produced in the thermal décomposition step with an aqueous suspension or slurry of the solid metallic or metal-bearing material;

an aqueous solution of FeCI₃, produced by contacting solid Fe₂O₃ e.g. produced in the thermal décomposition step with an aqueous solution of HCl produced by scrubbing gaseous HCl e.g. produced in the thermal décomposition step with water; or an aqueous solution of FeCI₃, produced by scrubbing gaseous HCl e.g. produced in the thermal décomposition step with an aqueous suspension of solid Fe₂O₃ e.g. produced in the thermal décomposition step.

When crystallisation is effected by means of displacement crystallisation, the digestion reagent would typically not be, or would not be produced using, gaseous HCl produced in the décomposition step, then rather being or being produced using the aqueous HCl solution produced in the displacement crystallisation step.

Metallic iron may be used as the reducing agent.

In using metallic iron as the reducing agent, in addition to réduction of Fe³⁺ to Fe²⁺ (i.e. FeCL to FeCI₂), other metals may be reduced, possibly to solid metallic form, thus rendering such metals readily recoverable by solid-liquid séparation.

Réduction may only be required if there is FeCh in solution that forms from treatment of the metallic or metal-bearing material with the digestion reagent.

The method may include, in a first séparation step performed after the digestion step, separating solids from the FeCI₂ solution by means of solid-liquid séparation, thus recovering the FeCL solution (inclusive of other divalent métal chlorides in solution) substantially free of solids.

When the FeCI₂ solution contains other métal chlorides (M²⁺CI2) in solution, the crystailisation step may form, in addition to solid FeCI2-xH2O, other solid métal (M) chloride hydrates (M²⁺CI2-zH₂O, wherein z>0 and M may, for example, be selected from one or more of chrome (Cr), copper (Cu), vanadium (V), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), and manganèse (Mn)).

As mentioned above with reference to the crystailisation step when the crystailisation step comprises displacement crystailisation, the method may include, in a second séparation step, performed after the crystailisation step and before the déhydration step, recovering solid FeCI₂-xH₂O, and any solid M²⁺CI₂-zH₂O that may be présent.

The déhydration step is preferably performed.

The déhydration step may be effected, as described with reference to the second aspect of the invention, by subjecting the FeCI₂.xH₂O, and any M²⁺CI₂.zH₂O that may be présent, to température treatment, at a température in a range of from 70°C to 200°C, more preferably in a range of from 70°C to less than 200°C, i.e. at a température less than 200°C but not lower than 70°C. For example, the température may be in a range of from 70°C to 150°C.

Thus, FeCl2.yH₂O and, if M²⁺CI2.zH2O was présent, dehydrated solid divalent chloride hydrate or anhydrous solid divalent chloride of the other métal (M²⁺CI2.aH₂O wherein z>a>0) may be produced.

The method may then comprise subjecting the FeCI₂.yH₂O and any M²⁺CI₂.aH₂O produced by the déhydration step, to thermal décomposition.

The déhydration step may be performed under non-oxidising conditions. This may include avoiding, or at least limiting, the presence of exogenous oxygen in the drying step. This may, in turn, include performing the déhydration step under positive pressure in a steam environment, which steam may be that which is produced as a resuit of the déhydration of the FeCI₂-xH₂O.

As indicated above, when solid M²⁺CI2.zH2O, in addition to FeCI2-xH2O, is recovered from the crystallisation step, such solid M²⁺CI2.zH₂O would also be subject to déhydration in the déhydration step, along with the FeCI₂-xH₂O, such that, in addition to FeCI₂-yH₂O, dehydrated solid divalent chloride hydrate and/or anhydrous solid divalent chloride of the other métal (M²⁺CI₂-aH₂O, wherein z>a>0, thus including anhydrous forms when a=0) are also produced in the déhydration step.

The thermal décomposition step may be performed at a température of from 200°C to 600°C, more preferably at a température above 200°C, up to 600°C.

The thermal décomposition step may be performed under oxidising conditions, i.e. in the presence of oxygen which may be supplied, for example, by air.

The gaseous HCl that is produced in the thermal décomposition step may be substantially dry, i.e. devoid of moisture (anhydrous).

Reactions that occur in the drying (déhydration) and thermal décomposition steps therefore comprise (i) Drying (déhydration) at températures described above, under non-oxidising conditions

FeCI₂.4H₂O (s) FeCI₂.H₂O (s) + 3H₂O (g) (ii) Thermal décomposition under oxidising conditions, in the presence of oxygen (¹/₂O₂) supplied by air, at températures described above

2FeCI₂.H₂O (s) Fe₂O₃ (s) + 4HCI (g)

As mentioned above, when solid M²⁺CI2.zH2O, in addition to FeCl2-xH2O, is recovered from the crystallisation step, and the déhydration step is performed and, in addition to FeCI2.yH2O, solid M²⁺CI2.aH₂O is produced in the déhydration step, such solid M²⁺CI2.zH2O and/or M²⁺CI2.aH₂O would be subjected to température treatment in the thermal décomposition step along with the FeCI₂-xH₂O / FeCI₂-yH₂O.

Thermal décomposition of FeCI₂-xH₂O / FeCl₂-yH₂O would occur to the exclusion of solid M²⁺CI2.zH2O and/or M²⁺CI2.aH₂O, however which M²⁺CI2.zH2O and/or M²⁺CI2.aH₂O would, to the extent that they were not already fully dehydrated, become fully dehydrated in the thermal décomposition step and thus remain as fully dehydrated solid M²⁺CI2 (i.e. a=0) post thermal décomposition of the FeCI2.xH2O / FeCI2-yH2O (preferably FeCI2.yH2O) to Fe2O3 and gaseous HCl. As will be appreciated from the foregoing discussions, however, it is preferred that only FeCI2-yH2O and M²⁺CI2.aH₂O are subjected to the thermal décomposition step, to produce ferrie oxide, anhydrous HCl gas and solid M²⁺CI₂.

Therefore, the thermal décomposition step would typically produce a mixture of solid Fe₂O₃ and solid M²⁺CI₂, in addition to gaseous HCl which is then used as described herein.

The method may then include, in a third séparation step, dissolving the M²⁺CI2 in water, and performing a solid-liquid séparation to recover the insoluble Fe2O3 from the resulting solution of M²⁺CI2.

In the resulting solution of M²⁺CI₂, metals (M), other than iron, that were originally contained in the metallic or metal-bearing material, hâve thus been liberated from the matrix in which they were held in the metallic or metal-bearing material, which matrix may hâve included iron. Such other metals may now be recovered by conventional methods, e.g. hydrometallurgical methods, from the resulting solution.

The method thus also produces saleable Fe₂O₃ and products suitable for recycle to earlier method steps. For example, and significantly it is noted that the thermal décomposition of FeCI₂-xH₂O / FeCI₂-yH₂O (preferably FeCI₂.yH₂O) by means of température treatment releases gaseous HCl, desirably in an anhydrous form particularly when FeCI₂.yH₂O is subjected to thermal décomposition.

The method may include recycling this HCl gas to be used in the crystallisation step, when performed as displacement crystallisation. Alternative^, it may be recycled to the digestion step, to be used as digestion reagent or in producing digestion reagent.

Furthermore, as noted earlier, the Fe₂O₃ may be reacted with HCl solution from the displacement crystallisation step, and more specifically from the second séparation step, to produce a FeCI₃ solution for use in the digestion step.

It is regarded as a particular advantage, and inventive feature, of the invention as described, that the production of FeCI₂.xH₂O and subséquent déhydration to FeCI₂.yH₂O enables, through subséquent décomposition of the partially dehydrated FeCI₂.yH₂O, the production of HCl in gaseous form which is, as will be appreciated, concentrated and undiluted HCl which, in addition, is in the context of the invention substantially dry, i.e. devoid of moisture (anhydrous). This is in stark contrast to conventional methods exploiting HCl in the digestion of solid metal-bearing feedstocks, which unavoidably form dilute solutions of HCl due to water balances that are unfavourable to the production of concentrated HCl, and even to the production of desired concentrations of diluted HCl. For example, while the maximum concentration of HCl at room température is around 33% v/v, existing methods exploiting HCl rarely achieve a régénération of diluted HCl above 18% v/v. The présent invention addresses this elegantly, by taking a route of iron précipitation as FeCI₂.xH₂O, partial déhydration thereof to produce FeCI₂.yH₂O, and décomposition thereof in turn to produce undiluted gaseous HCl for use in earlier method steps.

THE INVENTION EXTENDS, AS A FIFTH ASPECT THEREOF, TO a process for performing the method of the first to fourth aspects of the invention, which process includes process stages and process operations corresponding to and for performing the respective method steps.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

THE INVENTION WILL NOW BE DESCRIBED IN MORE DETAIL with reference to the accompanying diagrammatic drawing which shows a process according to the fifth aspect of the Invention.

Referring to the drawing, reference numéral 10 generally indicates a process according to the fifth aspect of the Invention, for performing a method of the first to fourth aspects of the Invention.

The process 10 includes the following process stages:

- an oxidative/reductive digestion stage 12;

- a réduction stage 14;

- a first séparation stage 16;

- a displacement crystallisation stage 18;

- a second séparation stage 20;

- a drying stage 22;

- a thermal décomposition stage 24;

- a third séparation stage 26;

- a ferrie chloride génération stage 28; and

- a metals recovery stage 30.

In the process 10, the following feed, transfer, withdrawal, and recycle lines are identified:

- feed line 32;

- feed line 34

- feed line 36

- transfer line 38;

- feed line 40;

- transfer line 42;

- withdrawal line 44;

- transfer line 46;

- feed line 48;

- recycle line 50;

- transfer line 52;

- recycle line 54;

- recycle line 56;

- transfer line 58;

- transfer line 60; .

- transfer line 62;

- transfer line 64;

- transfer line 66;

- recycle line 70;

- withdrawal line 72;

- feed line 74; and

- recycle line 76.

In using the process 10 to perforai the method of the first to fourth aspects of the Invention, a metallic or metal-bearing material is fed to the digestion stage 12 along feed line 32, along with one or a combination of a solution of FeCI₃ and a solution of HCl, respectively along feed line 34 and/or recycle line 70 and along feed line 36 and/or recycle line 54. Alternative/additional approaches to providing a solution of HCl and a solution of FeCI₃ to the digestion stage 12, with reference.to recycle lines 54, 70 and 76, are discussed below.

Oxidative/reductive digestion of the metallic or metal-bearing material proceeds in the digestion stage 12, and produces a FeCI₂ solution, possibly containing residual FeCI₃, and possibly containing one or more other métal (M) chlorides, e.g. chlorides of copper (Cu), vanadium (V), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), and manganèse (Mn).

The FeCI₂ solution is transferred from the digestion stage 12 to the réduction stage 14 along transfer line 38, where it is contacted with a reducing agent that is fed to the réduction stage 14 along feed line 40.

The FeCI₂ solution is then transferred from the réduction stage 14 to the first séparation stage 16 along transfer line 42, where solids contained in the FeCI₂ solution are separated from the FeCI₂ solution and are withdrawn along withdrawal line 44.

The recovered FeCI₂ solution is then passed from the first séparation stage 16 to the displacement crystallisation stage 18 along transfer line 46. Here the FeCI₂ solution is contacted with gaseous HCl which is fed to the displacement crystallisation stage 18 along feed line 48 and/or along recycle line 50.

Contacting the FeCI₂ solution with gaseous HCl in the displacement crystallisation stage 18 produces solid FeCI₂-xH₂O, and solid M²⁺CI₂-zH₂O if there are other métal (M) chlorides présent in the FeCI₂ solution, (x,z>1), in an aqueous solution of HCl (i.e. diluted HCl).

Typically, the value of x would be 4, and therefore the solid FeCI₂-xH₂O would be FeCI₂-4H₂O (i.e. ferrous chloride tetrahydrate).

The solid FeCI₂-xH2O, solid M²⁺CI2-zH2O, if présent, and aqueous solution of HCl are transferred to the second séparation stage, along transfer line 52, where the solid FeCI2xH2O and solid M²⁺CI2-zH₂O, if présent, are separated from the aqueous solution of HCl and are withdrawn along transfer line 58. The aqueous solution of HCl is recycled along recycle line 54 to the digestion stage 12 and/or along line 56 to the FeCI₃ génération stage 28. The solid FeCI₂-xH₂O and solid M²⁺CI₂-zH₂O, if présent, are transferred to the déhydration stage 22 along transfer line 58.

It is noted that recycle of the aqueous solution of HCl may include recycle of some métal chlorides not converted to métal chloride hydrates, e.g. as a resuit of low concentration. Build-up of such métal chloride hydrates would ultimately resuit in such conversion, once a sufficiently high concentration has been achieved.

In the déhydration stage 22, the solid FeCI₂-xH₂O and solid M²⁺CI2-zH2O, if présent, are subjected to déhydration in a non-oxidising environment, using température treatment at a température below 200°C but not less than 70°C, more preferably at a température in a range of from 70°C and 150°C, thus producing solid FeCI2-yH2O and solid M²⁺CI2-aH₂O, if présent, (x>y>0; z>a^0).

More specifically, the solid FeCI₂-xH₂O and solid M²⁺CI2-zH2O, if présent, are fed into, and through, a non-vented vessel in which the température treatment is carried out, thus producing a slight positive pressure relative to atmospheric pressure inside the vessel resulting from steam that is formed inside the vessel due to the température treatment and the resulting déhydration of the FeCI2-xH2O and M²⁺CI2-zH₂O, which steam serves to displace oxygen that may be présent in the vessel, e.g. in the form of air, thus avoiding oxidisation of the ferrous chloride.

The solid FeCI₂yH₂O and solid M²⁺CI2-aH2O are transferred, along transfer line 60, to the thermal décomposition stage 24, in which the solid FeCI2-yH2O and solid M²⁺CI2-aH₂O are subjected to température treatment to décomposé the solid FeCI₂-yH₂O to produce solid Fe₂O₃ and HCl gas, to the exclusion of the solid M²⁺CI2-aH2O which remains intact and is therefore not decomposed, but would typically be dehydrated so that in any case of M²⁺CI2-aH₂O where a>1 being présent in the décomposition stage such M²⁺CI₂-aH₂O would be converted to anhydrous M²⁺CI2 (i.e. a=0). The température treatment is effected under conditions that favour the thermal décomposition of FeCI2-yH2O over that of M²⁺CI2-aH₂O, and it is in fact so that no thermal décomposition of the M²⁺CI₂-aH₂O (z>a>0) would take place at any température at which décomposition of the FeCI₂.yH₂O is performed. The température treatment in the thermal décomposition stage 24 is performed at a température above 200°C, but not higher than 600°C, under oxidising conditions, i.e. in the presence of oxygen, e.g. being supplied by air.

The HCl gas produced in the thermal décomposition stage 24 is recovered and is recycled along recycle line 50 to the displacement crystallisation stage 18.

To favour or effect oxidising conditions in the thermal décomposition stage, a blower may be employed to blow air into the thermal décomposition stage and thus also expel gaseous hydrochloric acid from the thermal décomposition stage, for recovery and use as described herein.

It will be appreciated that gaseous HCl is concentrated, i.e. undiluted and thus substantially pure, HCl which, in addition, is substantially dry (i.e. devoid of moisture, and thus anhydrous). Thus, the process as described enables the achievement of a favourable water balance that, in turn, enables the production of concentrated substantially dry HCl in gaseous form, for use upstream in the process. This is in contrast to existing processes that exploit HCl in métal recovery operations, which produce diluted HCl solutions, rarely at concentrations higher than 18%v/v.

In the absence of déhydration of the FeCl₂.xH₂O, the gaseous HCl produced from the thermal décomposition stage 24 would be moist/dilute (i.e. contain water vapour), which would not be effective in displacing dissolved FeCI₂ in the manner described in the displacement crystallisation stage 18. The inventive approach that the invention follows therefore further avoids any need for an évaporation operation to recover gaseous HCl for use in the displacement crystallisation stage 18.

The solid Fe₂O₃ and solid M²⁺CI2 are transferred to the third séparation stage 26, along transfer line 62, in which the solid M²⁺CI2 is dissolved in water to produce a M²⁺CI2 solution, and solid-liquid séparation is carried out to recover the M²⁺CI2 solution and solid Fe₂O₃.

The M²⁺CI₂ solution is transferred to the metals recovery stage 30 along transfer line 64, for recovery of the metals contained therein.

The Fe₂O₃ is withdrawn, as a saleable product, along withdrawal line 72, and/or is transferred, along transfer line 66, to the FeCI₃ génération stage 28 where it is contacted with HCl that is fed to the génération stage 28 along feed line 74 or that is recycled to the génération stage 28 along recycle line 56, and/or is recycled to the digestion stage 12 along recycle line 76 where it is contacted with HCl to produce a FeCI₃ solution in situ.

The generated (re-generated) FeCI₃ is then recycled from the génération stage 28 to the digestion stage 18.

EXAMPLES

Example 1 - Beneficiation ofmixed oxide and sulphide copper concentrate

The ore concentrate beneficiated in this example, has a composition as set out in Table 1 below.

1. 100g concentrate (refer to table 1) as received from the mine (milled to -75um) was digested with 250g FeCI₃ (43 wt%) solution, 55 g HCl (33 wt%) solution and 100 ml water for 4 hours at 105°C in a reflux glass beaker.

Table 1: Chemical composition of feed

Place	Total Cu	Acid sol Cu	S	AI2O3	K2O	SiO2	Fe
UIS	26.6%	5.01%	8.99%	7.43%	5.52%	29.9%	7.33%

2. After oxidative digestion of the above concentrate major soluble chlorides FeCI₂, CuCI₂ and Cu₂CI₂ were produced in solution. Via filtration, the water-soluble fraction was separated from the insoluble fraction. The insoluble fraction comprised 51g (30%, or 16g, moisture) and, after washing and drying at 110°C, was found to comprise sulphur, silicates and other insolubles (refer to table 2). Referring to the Chemical composition of the insoluble fraction, it follows that 99.6% of the available Cu was extracted.

Table 2: Chemical composition of insolubles

Place	Cu	S	AI2O3	K2O	SiO2	Fe
UIS	0.087%	18%	11.75%	7.5%	55.5%	0.7%

3. Approximately 400 ml filtrate (470g) was obtained after filtration. To this filtrate, 19.8 g iron powder was added while stirring. After 30 minutes, the resulting réduction reaction was completed.

4. The copper cernent, resulting from the réduction, was washed, filtered and dried, and 27.4g Cu was recovered. It is noted that this copper can be pressed and melted or used to produce CuSO4.5H₂O crystals.

5. The remaining filtrate, approximately 350 ml (470g), was used as a scrubbing solution to scrub 84 g of HCl gas (originating from the décomposition step 8, below). During the scrubbing of the HCl gas, the température of the solution was kept at 30 - 35 °C.

6. 228g of FeCl2.4H₂O crystals were formed in step 5. These were filtered from the remaining HCl solution (326g).

7. These crystals were dried at 150°C to give approximately 166 g FeCI₂.H₂O (s). This dried product was milled in situ to -2mm.

8. The milled product was then heated in air at 400°C. At this température, ail the FeCI₂.H2O was oxidized into Fe₂O3(s) and HCI(g).

9. 91.5g of Fe₂O₃ was recovered. 38.5g can be sold while 53 g is recycled with 326g HCl solution (step 6), 18 g new HCl (33 wt%) solution as a top reagent and 108 g water. To this 100g of feed may be added to restart the next digestion run.

For more information, refer to Figure 2 as well.

Example 2 - Beneficiation of nickel sulphide concentrate

The ore concentrate beneficiated in this example, has a composition as set out in Table 3 below.

Table 3: Chemical composition of feed

Major oxides	Feed	Insolubles (62% of feed)	Digestion efficiency
SiO2	10.8%	17.6%
Fe (total)	30.4 %	23%	52.7%
MgO	5.6 %	5.6 %
Co	0.5 %	0.23 %	71.25%
Cu	5.1 %	0.11 %	98.65%
Ni	7.73 %	0.26 %	97.9%
S	29.8 %	52.5 %*	110%
Ag	15 ppm	5.2 ppm
Au	0.96 ppm	1.5 ppm
Ir	0.2 ppm	0.41 ppm
Os	2.3 ppm	4.2 ppm
Pd	16.6 ppm	30 ppm
Pt	7.4 ppm	11.4 ppm
Rh	1.13 ppm	1.48 ppm
Ru	1.17 ppm	1.8 ppm
Total PGM’s		56 ppm

*Note: If the S of the insoluble fraction is floated off, the PGM’s > 100 ppm

Table 4: Morphology of the feed

Phases	Pyrite	Chalcopyrite	Pentlandite	Talc	Actinolite	Pyrrhotite
Feed	23.04 %	14.21 %	14.69%	39.07 %	1.1 %	3.1%

FeCI3

Insoluble

Soluble

Soluble

Insoluble

Insoluble

Soluble

Note: These values are semi quantitative

1. To 100g concentrate (-45pm), 85g Fe₂O3 (recycled) was added. This feed was digested with 400 ml HCI(c), approximately 33%, via reflux at 105°C for 4 hours.

2. Directly after digestion, while the solution was still warm, the slurry (including insoluble) was pumped through a tank containing an excess of scrap Fe. This served to neutralize excess HCl, reduce excess FeCI₃ into FeCb and cernent Cu. Approx 6g of Fe scrap was used in this step.

3. The slurry was then filtered and washed to produce 62g of insolubles plus 5g of Cucement and 370 ml filtrate.

4. The insolubles together with the copper cernent was treated with a dilute solution of H₂SO₄ and HNO3 to produce a CUSO4 solution. After filtration and wash, the CUSO4 can be crystallized into CUSO4.5H2O while the insolubles contain the upgraded PGM’s.

5. The 370 ml filtrate was used to scrub approximately 100g HCI(g). The température was kept between 15 -20°C. The scrubbing of the HCI(g) displaced the ferrous, nickel and cobalt chlorides from the solution, forming solid hydrated crystals thereof. The resulting solution contained approximately 30-36% HCl.

6. After filtration of the crystals, the crystals were washed with a new filtrate solution to rid it from the HCI(c) background. Approximately 95% of the ferrous and 70% of the Ni/Co crystals were obtained this way. The balance was recycled with the HCl solution back to digestion and would build-up in further runs where more will crystallize as the concentrations increase.

7. The washed crystals were dried at 150°C while clean steam was produced.

8. The dried crystals were then decomposed at 400°C to produce Fe₂O₃, anhydrous Ni(Co)Cl2 and HCI(g) to be recycled to step 5.

9. Cold water was added to the Fe₂O₃ to dissolve the Ni(Co)CI₂. After filtration and wash, the excess Fe₂O₃ can be sold while the Ni(Co)CI₂ can beneficiated from solution.

For more information, refer to Figure 3 as well. 5

Claims (10)

1. A method of treating a solid metallic or metal-bearing material, comprising one or more metals in metallic or compound form, to recover one or more of the metals from the metallic or metal-bearing material in metallic or compound form, the method including in an oxidative or reductive digestion step, producing an aqueous ferrous chloride (FeCI₂) solution by contacting the metallic or metal-bearing material with a digestion reagent selected from gaseous hydrochloric acid (HCl),

HCl in aqueous solution, and an aqueous solution of ferrie chloride (FeCI₃) produced by reacting iron (III) oxide (Fe₂O₃) with HCl, in aqueous medium, and reducing any FeCI₃ in solution, produced from the contacting of the metallic or metalbearing material with the digestion reagent, to FeCI₂ in solution;

in a crystallisation step, crystallising a solid ferrous chloride hydrate (FeCI₂-xH₂O, wherein x > 1) from the FeCI₂ solution;

in a déhydration step, subjecting the FeCI₂-xH₂O to température treatment in a nonoxidising environment at a température from 70°C to 150°C, to produce dehydrated solid ferrous chloride hydrate (FeCI₂-yH₂O, wherein x>y>0); and in a thermal décomposition step, subjecting the FeCI₂-yH₂O to température treatment in an oxidising environment at a température above 200°C but not higher than 600°C and thus decomposing the FeCI₂-yH₂O to produce solid ferrie oxide (Fe₂O₃) and anhydrous gaseous HCl.

2. The method according to claim 1, wherein the digestion reagent is gaseous HCl, produced in the thermal décomposition step;

an aqueous solution of HCl, produced by scrubbing gaseous HCl produced in the thermal décomposition step with water;

an aqueous solution of HCl, produced by scrubbing gaseous HCl produced in the thermal décomposition step with an aqueous suspension or slurry of the solid metallic or metal-bearing material;

an aqueous solution of FeCI₃, produced by contacting solid Fe₂O₃ produced in the thermal décomposition step with an aqueous solution of HCl produced by scrubbing gaseous HCl produced. in the thermal décomposition step with water; or an aqueous solution of FeCh, produced by scrubbing gaseous HCl produced in the thermal décomposition step with an aqueous suspension of solid Fe₂O₃ produced in the thermal décomposition step.

3. The method according to claim 1, wherein crystallising the FeCI₂-xH₂O from the FeCI₂ solution is effected by means of displacement crystallisation, by contacting, and saturating, the FeCI₂ solution with gaseous HCl produced in the thermal décomposition step, thus producing solid FeCI₂.xH₂O in an aqueous solution of HCl.

4. The method according to claim 3, which includes separating solid FeCI₂.xH₂O, and any other solid métal chloride hydrates that crystallised along with the FeCI₂.H₂O in the crystallisation step, from the aqueous solution of HCl thus produced; and using the aqueous solution of HCl as, or in producing, the digestion reagent in the digestion step.

5. The method according to any of daims 1 to 4, wherein the metals of the metallic or métal bearing material include iron (Fe) and one or more other metals (M) selected from chrome (Cr), copper (Cu), vanadium (V), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), manganèse (Mn), in metallic or compound forms selected from métal oxide form and métal sulphide form;

the FeCI₂ solution thus contains, in addition to FeCI₂, one or more additional métal chlorides (M²⁺CI₂, wherein M is selected form chrome (Cr), copper (Cu), vanadium (V), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), and manganèse (Mn)), in solution; and the crystallisation step thus forms, in addition to FeCI₂-xH₂O, one or more other solid métal chloride hydrates (M²⁺CI₂-zH₂O, wherein M is selected from one or môre of chrome (Cr), copper (Cu), vanadium (V), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), and manganèse (Mn), and z>0).

6. The method according to any of daims 1 to 5, which includes, in a first séparation step, performed after the digestion step, separating solids from the FeCI₂ solution by means of solid-liquid séparation, thus recovering the FeCl₂ solution substantially free of solids; and in a second séparation step, performed after the crystallisation step and before the déhydration and décomposition steps, recovering solid FeCI₂-xH₂O and any solid M²⁺CI₂-zH₂O that crystallised with the FeCI₂.xH₂O in the crystallisation step.

7. The method according to claim 6, wherein, in the déhydration step recovered solid M²⁺CI2-zH2O also subjected to déhydration, along with recovered FeCI2-xH2O, thereby producing, in addition to FeCI2-yH2O, dehydrated other solid métal chloride hydrates or 5 anhydrous métal chlorides (M²⁺CI2-aH₂O, wherein and z>a^0).

8. The method according to claim 7, wherein solid M²⁺CI₂-aH₂O recovered from the déhydration step is subjected to température treatment in the thermal décomposition step along with the FeCI₂-yH₂O; and

10 thermal décomposition of FeCI₂-yH₂O occurs to the exclusion of solid M²⁺CI₂-aH₂O, of which hydrates thereof are fully dehydrated in the thermal décomposition step, thus producing a mixture of solid Fe₂O₃ and solid other anhydrous métal chlorides (M²⁺CI₂).

9. The method according to any of daims 1 to 8, wherein the thermal

15 décomposition step is performed at a température above 200°C but not higher than 600°C.

10. The method according to any of daims 1 to 9, wherein x = 4 and y = 1.