Patent Application
20240218480
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, “metal” has a broad meaning, including both metals in elemental metallic form and metal compounds. The invention extends to a process for performing the method.
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 generation when such materials are beneficiated using hydrometallurgical processes.
The present 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.
IT IS AN OBJECT OF THE INVENTION to provide for the treatment of metallic or metal-bearing 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, “metal” has a broad meaning, including both metals in elemental metallic form and metal compounds. In respect of metal 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.
IN THIS SPECIFICATION the provision of features in parenthesis contribute to the substantive content of the specification 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 metal-bearing material in metallic or compound form, the method including, in an oxidative or reductive digestion step, producing a ferrous chloride (FeCl2) solution by contacting the metallic or metal-bearing material with a digestion reagent selected from
The contacting of the metallic or metal-bearing material with the digestion reagent may be performed in aqueous medium. Thus, the FeCl2 solution may be an aqueous FeCl2 solution.
When the digestion reagent is HCl, contacting the metallic or metal-bearing material with the HCl may include
When contacting the metallic or metal-bearing material with gaseous HCl, the metallic or 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 metal hydrates and/or metal 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, 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
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 FeCl3 produced from the contacting of the metallic or metal-bearing material with the digestion reagent to FeCl2 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 FeCl3 to the exclusion of FeCl2 or a solution comprising both FeCl3 and FeCl2, which would thus require reduction of the FeCl3 to be effected using the reducing agent.
It is also possible that a solution comprising no FeCl3 would be produced, in which case no reduction would be required.
It will be appreciated that reduction is therefore only required if the digestion of the metallic or metal-bearing material produces FeCl3
The digestion reagent may therefore, for example, be
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 present as ferrous chloride in the FeCl2 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+Cl2) 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 FeCl2 solution, typically an aqueous FeCl2 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 FeCl2 from the FeCl2 solution and thus produces a solid ferrous chloride hydrate (FeCl2·xH2O, wherein x≥1, more preferably x>1), typically solid ferrous chloride tetrahydrate (FeCl2·4H2O, 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 FeCl2 solution by oxidative/reductive digestion of the metallic or metal-bearing material may have included contacting the metallic or metal-bearing material with a digestion reagent selected from
The FeCl2 solution may, for example, be a FeCl2 solution that has been produced according to the digestion step of the first aspect of the invention.
As noted above, the FeCl2·xH2O may, in particular, be FeCl2·4H2O, i.e. x=4.
The displacement crystallisation step may include, or may more typically be followed by, a dehydration (i.e. drying) step, which may include subjecting the FeCl2·xH2O to temperature treatment to produce a dehydrated solid ferrous chloride hydrate (FeCl2·yH2O, wherein x>y>0). The FeCl2·yH2O may, in particular, be FeCl2·H2O (ferrous chloride monohydrate), i.e. y=1.
In the sense used in this specification, in the context of the dehydration step, the terms “dehydration” and “dehydrated” therefore do not require complete dehydration, to provide an anhydrous form, although that possibility is included within the meaning of the word. The dehydration step may therefore more accurately be characterised as a “partial” dehydration step, at least in terms of the change in the hydration of the ferrous chloride.
The temperature treatment to which the FeCl2·xH2O is subjected in the dehydration step, may include subjecting the FeCl2·xH2O to a temperature 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 temperature less than 200° C. but not lower than 70° C. For example, the temperature may be in a range of from 70° C. to 150° C.
The dehydration step may be performed under non-oxidising conditions, i.e. under conditions that avoid oxidation of the FeCl2·xH2O. This may include avoiding, or at least limiting, the presence of exogenous oxygen in the dehydration step. This may, in turn, include performing the dehydration step under positive pressure in a steam environment, which steam may be that which is produced as a result of the dehydration of the FeCl2·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 decomposition 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 FeCl2 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+Cl2) thereof in the digestion step and would then also, advantageously, be displaced from solution as divalent metal chloride hydrates (M2+Cl2·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 metal-bearing material in metallic or compound form, the method including, in a thermal decomposition step, subjecting FeCl2·xH2O, wherein x≥1, more preferably x>1, x most preferably being 4, produced by crystallisation thereof from a FeCl2 solution produced by oxidative/reductive digestion of the metallic or metal-bearing material, and/or FeCl2·yH2O, wherein x>y>0, y preferably being 1, produced by subjecting the FeCl2·xH2O to dehydration, to temperature treatment, thus decomposing the FeCl2·xH2O or FeCl2·yH2O to produce solid ferric 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 decomposition step and the invention generally, it is preferred that it is FeCl2·xH2O or FeCl2·yH2O that is subjected to thermal decomposition, to the exclusion of FeCl3. This is since FeCl3 would, when subjected to thermal decomposition, not decompose to produce gaseous HCl and Fe2O3, but would instead sublimate.
Producing the FeCl2 solution by oxidative/reductive digestion of the metallic or metal-bearing material may have included contacting the metallic or metal-bearing material with a digestion reagent selected from
The FeCl2 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 FeCl2·xH2O from the FeCl2 solution may have been achieved by conventional methods, e.g. by means of evaporative crystallisation.
More preferably, however, crystallising the FeCl2·xH2O from the FeCl2 solution may have been effected, in accordance with the second aspect of the invention, by displacement crystallisation from a FeCl2 solution, which may have included contacting a FeCl2 solution, produced by oxidative/reductive digestion of the metallic or metal-bearing material, with a displacement crystallisation reagent, preferably hydrochloric acid (HCl), most preferably gaseous HCl, that displaced FeCl2 from solution and thus produced FeCl2·xH2O.
The gaseous HCl may, in particular, have been anhydrous gaseous HCl, preferably produced by the thermal decomposition step of the invention.
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 evaporation of water from an FeCl2 solution makes the FeCl2 in the solution significantly more susceptible to oxidation to FeCl3, which should be avoided in the context of the invention, in light thereof that, as mentioned above, FeCl3 sublimates when subjected to high temperatures such as those exploited by the invention in the thermal decomposition step that is described herein.
When crystallisation is effected by means of displacement crystallisation, the digestion reagent would typically not be, or would typically not be produced using, gaseous HCl produced in the decomposition step, then rather being or being produced using the aqueous HCl solution that is produced in the displacement crystallisation step.
Furthermore, producing FeCl2·yH2O through dehydration of the FeCl2·xH2O and subjecting the FeCl2·yH2O to thermal decomposition, is preferred. Such dehydration may be effected, as described with reference to the second aspect of the invention, by subjecting the FeCl2·xH2O to temperature treatment, at a temperature 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 temperature less than 200° C. but not lower than 70° C. For example, the temperature 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 FeCl2·yH2O to thermal decomposition, an effect of producing anhydrous gaseous hydrochloric acid is inventively achieved and exploited.
The solid FeCl2·xH2O, or the FeCl2·yH2O, may, for example, be FeCl2·xH2O, or FeCl2·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+Cl2) thereof, would be displaced from solution as divalent chloride hydrates (M2+Cl2·zH2O, wherein z>0) thereof, would be partially or fully dehydrated (to produce M2+Cl2·aH2O, wherein z>a≥0), and would subjected to decomposition as described (to produce anhydrous M2+Cl2).
In contrast to the ferrous chloride hydrate when subjected to decomposition, such other divalent metal chlorides or chloride hydrates would therefore not decompose. 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 ferric oxide by solid-liquid separation.
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
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 FeCl2 solution may be achieved by conventional methods, e.g. by means of a evaporative crystallisation.
More preferably, however, crystallising the FeCl2·xH2O from the FeCl2 solution may be effected by displacement crystallisation from the FeCl2 solution (i.e. the crystallisation step may be a displacement crystallisation step), which may include contacting, and saturating, the FeCl2 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 decomposition step, thus displacing FeCl2 from solution and producing the FeCl2·xH2O.
In the displacement crystallisation step, the temperature of the FeCl2 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 FeCl2 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
The method may therefore include, in a second separation step, performed after the displacement crystallisation step and before the dehydration step, recovering solid FeCl2·xH2O, and any other solid metal chloride hydrates (M2+Cl2·zH2O, as described herein) that may be present, from the resulting HCl solution by means of solid-liquid separation, thus recovering FeCl2·xH2O and any solid M2+Cl2·zH2O that may have been present.
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 FeCl3 solution for use in the digestion step, by reaction of the HCl in the HCl solution with Fe2O3, which may be Fe2O3 which is produced in the thermal decomposition step of the invention.
It is noted that recycle of the HCl solution produced in the displacement crystallisation step may include recycle of some metal chlorides not converted to metal chloride hydrates, e.g. as a result of low concentration. It is expected that build-up of such metal chloride hydrates would ultimately result 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 decomposition step may be that of the third aspect of the invention.
The following statements apply to all 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), manganese (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 metal (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 metal oxides), a polysulphide material (containing multiple metal sulphides), an alloy material, a metal slag material, a metal fines material, and a metallic material.
Thus, metals in the metallic or metal-bearing material may, for example, be in one or more of metal oxide form, metal sulphide form, and metallic from.
In one specific 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 metal sulphide and/or metal oxide bearing ore material, particularly those comprising iron in a metallic or compound form.
Depending on the composition of the metal-bearing material, the FeCl2 solution may therefore contain, in addition to FeCl2, other metal chlorides, typically at least other divalent metal chlorides (M2+Cl2), but not excluding monovalent metal chlorides, in solution, e.g. CuCl2 or Cu2Cl2.
Thus, the digestion step may have to effect that at least some metals contained in the metallic or metal-bearing material in metallic or metal compound form, are converted to metal chlorides (FeCl2 and, if other metals (M) are present, M2+Cl2) in solution, contained in the FeCl2 solution. This is desired.
The digestion step may be performed at a temperature of from 10° C. to 120° C.
If an FeCl3 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 5 wt % to 70 wt %.
It is noted that in order to produce FeCl3 in solution for use as the digestion reagent in the digestion step, solid Fe2O3 may be used in conjunction with HCl, thus producing a FeCl3 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 5 wt % to 40 wt %, more preferably 30% to 36%, e.g. 33%.
Alternatively, 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,
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 decomposition 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 reduction of Fe3+ to Fe2+ (i.e. FeCl3 to FeCl2), other metals may be reduced, possibly to solid metallic form, thus rendering such metals readily recoverable by solid-liquid separation.
Reduction may only be required if there is FeCl3 in solution that forms from treatment of the metallic or metal-bearing material with the digestion reagent.
The method may include, in a first separation step performed after the digestion step, separating solids from the FeCl2 solution by means of solid-liquid separation, thus recovering the FeCl2 solution (inclusive of other divalent metal chlorides in solution) substantially free of solids.
When the FeCl2 solution contains other metal chlorides (M2+Cl2) in solution, the crystallisation step may form, in addition to solid FeCl2·xH2O, other solid metal (M) chloride hydrates (M2+Cl2·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 manganese (Mn)).
As mentioned above with reference to the crystallisation step when the crystallisation step comprises displacement crystallisation, the method may include, in a second separation step, performed after the crystallisation step and before the dehydration step, recovering solid FeCl2·xH2O, and any solid M2+Cl2·zH2O that may be present.
The dehydration step is preferably performed.
The dehydration step may be effected, as described with reference to the second aspect of the invention, by subjecting the FeCl2·xH2O, and any M2+Cl2·zH2O that may be present, to temperature treatment, at a temperature 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 temperature less than 200° C. but not lower than 70° C. For example, the temperature may be in a range of from 70° C. to 150° C.
Thus, FeCl2·yH2O and, if M2+Cl2·zH2O was present, dehydrated solid divalent chloride hydrate or anhydrous solid divalent chloride of the other metal (M2+Cl2·aH2O wherein z>a≥0) may be produced.
The method may then comprise subjecting the FeCl2·yH2O and any M2+Cl2·aH2O produced by the dehydration step, to thermal decomposition.
The dehydration 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 dehydration step under positive pressure in a steam environment, which steam may be that which is produced as a result of the dehydration of the FeCl2·xH2O.
As indicated above, when solid M2+Cl2·zH2O, in addition to FeCl2·xH2O, is recovered from the crystallisation step, such solid M2+Cl2·zH2O would also be subject to dehydration in the dehydration step, along with the FeCl2·xH2O, such that, in addition to FeCl2·yH2O, dehydrated solid divalent chloride hydrate and/or anhydrous solid divalent chloride of the other metal (M2+Cl2·aH2O, wherein z>a≥0, thus including anhydrous forms when a=0) are also produced in the dehydration step.
The thermal decomposition step may be performed at a temperature of from 200° C. to 600° C., more preferably at a temperature above 200° C., up to 600° C.
The thermal decomposition 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 decomposition step may be substantially dry, i.e. devoid of moisture (anhydrous).
Reactions that occur in the drying (dehydration) and thermal decomposition steps therefore comprise
FeCl2·4H2O (s)→FeCl2·H2O (s)+3H2O (g)
As mentioned above, when solid M2+Cl2·zH2O, in addition to FeCl2·xH2O, is recovered from the crystallisation step, and the dehydration step is performed and, in addition to FeCl2·yH2O, solid M2+Cl2·aH2O is produced in the dehydration step, such solid M2+Cl2·zH2O and/or M2+Cl2·aH2O would be subjected to temperature treatment in the thermal decomposition step along with the FeCl2·xH2O/FeCl2·yH2O.
Thermal decomposition of FeCl2·xH2O/FeCl2·yH2O would occur to the exclusion of solid M2+Cl2·zH2O and/or M2+Cl2·aH2O, however which M2+Cl2·zH2O and/or M2+Cl2·aH2O would, to the extent that they were not already fully dehydrated, become fully dehydrated in the thermal decomposition step and thus remain as fully dehydrated solid M2+Cl2 (i.e. a=0) post thermal decomposition of the FeCl2·xH2O/FeCl2·yH2O (preferably FeCl2·yH2O) to Fe2O3 and gaseous HCl. As will be appreciated from the foregoing discussions, however, it is preferred that only FeCl2·yH2O and M2+Cl2·aH2O are subjected to the thermal decomposition step, to produce ferric oxide, anhydrous HCl gas and solid M2+Cl2.
Therefore, the thermal decomposition step would typically produce a mixture of solid Fe2O3 and solid M2+Cl2, in addition to gaseous HCl which is then used as described herein.
The method may then include, in a third separation step, dissolving the M2+Cl2 in water, and performing a solid-liquid separation to recover the insoluble Fe2O3 from the resulting solution of M2+Cl2.
In the resulting solution of M2+Cl2, metals (M), other than iron, that were originally contained in the metallic or metal-bearing material, have thus been liberated from the matrix in which they were held in the metallic or metal-bearing material, which matrix may have 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 decomposition of FeCl2·xH2O/FeCl2·yH2O (preferably FeCl2·yH2O) by means of temperature treatment releases gaseous HCl, desirably in an anhydrous form particularly when FeCl2·yH2O is subjected to thermal decomposition.
The method may include recycling this HCl gas to be used in the crystallisation step, when performed as displacement crystallisation. Alternatively, 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 separation step, to produce a FeCl3 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 FeCl2·xH2O and subsequent dehydration to FeCl2·yH2O enables, through subsequent decomposition of the partially dehydrated FeCl2·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 temperature is around 33% v/v, existing methods exploiting HCl rarely achieve a regeneration of diluted HCl above 18% v/v. The present invention addresses this elegantly, by taking a route of iron precipitation as FeCl2·xH2O, partial dehydration thereof to produce FeCl2·yH2O, and decomposition 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.
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 numeral 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:
In the process 10, the following feed, transfer, withdrawal, and recycle lines are identified:
In using the process 10 to perform 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 FeCl3 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 FeCl3 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 FeCl2 solution, possibly containing residual FeCl3, and possibly containing one or more other metal (M) chlorides, e.g. chlorides of copper (Cu), vanadium (V), nickel (Ni), cobalt (Co), zinc (Zn), titanium (Ti), and manganese (Mn).
The FeCl2 solution is transferred from the digestion stage 12 to the reduction stage 14 along transfer line 38, where it is contacted with a reducing agent that is fed to the reduction stage 14 along feed line 40.
The FeCl2 solution is then transferred from the reduction stage 14 to the first separation stage 16 along transfer line 42, where solids contained in the FeCl2 solution are separated from the FeCl2 solution and are withdrawn along withdrawal line 44.
The recovered FeCl2 solution is then passed from the first separation stage 16 to the displacement crystallisation stage 18 along transfer line 46. Here the FeCl2 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 FeCl2 solution with gaseous HCl in the displacement crystallisation stage 18 produces solid FeCl2·xH2O, and solid M2+Cl2·zH2O if there are other metal (M) chlorides present in the FeCl2 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 FeCl2·xH2O would be FeCl2·4H2O (i.e. ferrous chloride tetrahydrate).
The solid FeCl2·xH2O, solid M2+Cl2·zH2O, if present, and aqueous solution of HCl are transferred to the second separation stage, along transfer line 52, where the solid FeCl2·xH2O and solid M2+Cl2·zH2O, if present, 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 FeCl3 generation stage 28. The solid FeCl2·xH2O and solid M2+Cl2·zH2O, if present, are transferred to the dehydration stage 22 along transfer line 58.
It is noted that recycle of the aqueous solution of HCl may include recycle of some metal chlorides not converted to metal chloride hydrates, e.g. as a result of low concentration. Build-up of such metal chloride hydrates would ultimately result in such conversion, once a sufficiently high concentration has been achieved.
In the dehydration stage 22, the solid FeCl2·xH2O and solid M2+Cl2·zH2O, if present, are subjected to dehydration in a non-oxidising environment, using temperature treatment at a temperature below 200° C. but not less than 70° C., more preferably at a temperature in a range of from 70° C. and 150° C., thus producing solid FeCl2·yH2O and solid M2+Cl2·aH2O, if present, (x>y≥0; z>a≥0).
More specifically, the solid FeCl2·xH2O and solid M2+Cl2·zH2O, if present, are fed into, and through, a non-vented vessel in which the temperature 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 temperature treatment and the resulting dehydration of the FeCl2·xH2O and M2+Cl2·zH2O, which steam serves to displace oxygen that may be present in the vessel, e.g. in the form of air, thus avoiding oxidisation of the ferrous chloride.
The solid FeCl2·yH2O and solid M2+Cl2·aH2O are transferred, along transfer line 60, to the thermal decomposition stage 24, in which the solid FeCl2·yH2O and solid M2+Cl2·aH2O are subjected to temperature treatment to decompose the solid FeCl2·yH2O to produce solid Fe2O3 and HCl gas, to the exclusion of the solid M2+Cl2·aH2O which remains intact and is therefore not decomposed, but would typically be dehydrated so that in any case of M2+Cl2·aH2O where a≥1 being present in the decomposition stage such M2+Cl2·aH2O would be converted to anhydrous M2+Cl2 (i.e. a=0). The temperature treatment is effected under conditions that favour the thermal decomposition of FeCl2·yH2O over that of M2+Cl2·aH2O, and it is in fact so that no thermal decomposition of the M2+Cl2·aH2O (z>a≥0) would take place at any temperature at which decomposition of the FeCl2·yH2O is performed. The temperature treatment in the thermal decomposition stage 24 is performed at a temperature 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 decomposition 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 decomposition stage, a blower may be employed to blow air into the thermal decomposition stage and thus also expel gaseous hydrochloric acid from the thermal decomposition 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 metal recovery operations, which produce diluted HCl solutions, rarely at concentrations higher than 18% v/v.
In the absence of dehydration of the FeCl2·xH2O, the gaseous HCl produced from the thermal decomposition stage 24 would be moist/dilute (i.e. contain water vapour), which would not be effective in displacing dissolved FeCl2 in the manner described in the displacement crystallisation stage 18. The inventive approach that the invention follows therefore further avoids any need for an evaporation operation to recover gaseous HCl for use in the displacement crystallisation stage 18.
The solid Fe2O3 and solid M2+Cl2 are transferred to the third separation stage 26, along transfer line 62, in which the solid M2+Cl2 is dissolved in water to produce a M2+Cl2 solution, and solid-liquid separation is carried out to recover the M2+Cl2 solution and solid Fe2O3.
The M2+Cl2 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 FeCl3 generation stage 28 where it is contacted with HCl that is fed to the generation stage 28 along feed line 74 or that is recycled to the generation 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 FeCl3 solution in situ.
The generated (re-generated) FeCl3 is then recycled from the generation stage 28 to the digestion stage 18.
The ore concentrate beneficiated in this example, has a composition as set out in Table 1 below.
For more information, refer to
The ore concentrate beneficiated in this example, has a composition as set out in Table 3 below.
For more information, refer to
| Number | Date | Country | Kind |
|---|---|---|---|
| 2027874 | Mar 2021 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB22/53009 | 3/31/2022 | WO |
