METHOD FOR THE PRODUCTION OF COBALT AND ASSOCIATED OXIDES FROM VARIOUS FEED MATERIALS

Abstract

A method is disclosed for the recovery of cobalt, nickel and manganese from ores, concentrates, tailings, scrap alloys and spent batteries in an oxidic form, which is suitable for direct use in the manufacture of lithium-ion batteries, in particular. The process is unique in being able to recover cobalt, in particular, from concentrated solutions wherein the nickel to cobalt ratio is close to unity, rather than the more common 10:1 or 1:100. The process comprises selective oxidative precipitation of each metal under differing conditions of pH and ORP (oxidation-reduction potential). Sodium hypochlorite is the preferred precipitant, since it does not generate any acid, and is therefore self-buffering at the selected pH. A unique aspect of the process is to use Mn(VII) to effect the precipitation of Mn(ll).

Claims

1. A method for the recovery of cobalt from a Co- and Ni-containing aqueous solution, the method including: providing a Co- and Ni-containing aqueous solution having a pH of from about 4.5 to about 6.5 and an oxidation-reduction potential of from about 750 to about 900 mV as measured against a PtAg/AgCl electrode; treating the Co- and Ni-containing aqueous solution with an amount of a hypochlorite to oxidise and precipitate a portion of the cobalt as CoOOH and form a Co-lean Ni-aqueous solution; and separating the CoOOH from the Co-lean Ni-containing aqueous solution.

2. The method of claim 1, wherein the amount of hypochlorite is a sub-stoichiometric amount.

3. The method of claim 2, wherein the sub-stoichiometric amount of hypochlorite is sufficient to precipitate up to 90% of the cobalt as CoOOH.

4. The method of claim 2, wherein the method further includes: treating the Co-lean Ni-containing aqueous solution with an amount of hypochlorite to substantially oxidise and precipitate the remaining cobalt in the Co-lean Ni-containing aqueous solution as CoOOH and form a Co-barren Ni-containing aqueous solution; and separating the CoOOH from the Co-barren Ni-containing aqueous solution.

5. The method of claim 1, wherein the pH of the Co- and Ni-containing aqueous solution is from about 5.0 to about 5.5.

6. The method of claim 1, wherein the oxidation-reduction potential of the Co- and Ni-containing aqueous solution is from about 800-850 mV.

7. The method of claim 1, wherein the step of treating the Co- and Ni-containing aqueous solution is conducted for a time of less than 2 hours.

8. The method of claim 1, wherein the step of treating the Co- and Ni-containing aqueous solution is conducted for a time of at least 30 minutes.

9. The method of claim 1, wherein the Co- and Ni-containing solution has a Co:Ni ratio of from about 100:1 to about 1:10.

10. The method of claim 9, wherein Co:Ni ratio is less than or equal to about 5.

11. The method of claim 1, wherein the method further includes a Ni-precipitating step including adding a precipitant to the Co-barren Ni-containing aqueous solution to precipitate nickel; and separating the nickel from the solution.

12. The method of claim 11, wherein the precipitant is a carbonate.

13. The method of claim 11, wherein prior to adding the precipitant, the pH of the Co-barren Ni-containing aqueous solution is adjusted to a value of from about 7.5 to 8.5.

14. The method of claim 11, wherein the Ni-precipitating step is conducted at a temperature of from 45-80 C.

15. The method of claim 1, wherein the Co- and Ni-containing solution is substantially free of Cu, Fe, and Mn.

16. The method of claim 1, wherein the method includes: treating a precursor solution containing at least Mn, Co, and Ni with a precipitant to selectively form a Mn-precipitate; and separating the Mn-precipitate to form the Co- and Ni-containing aqueous solution.

17. The method of claim 16, wherein prior to treating the precursor solution with the precipitant, the pH of the precursor solution is adjusted to a value of from about 3.5 to about 5.0.

18. The method of claim 16, wherein the precipitant is a permanganate, and the permanganate oxidises the Mn to form a precipitate of MnO.sub.2.

19. The method of claim 18, wherein sufficient permanganate is added to adjust the oxidation-reduction potential of the precursor solution to a value of from about 700 to about 800 mV as measured against a PtAg/AgCl electrode.

20. The method of claim 16, wherein prior to treating the precursor solution with the precipitant, the precursor solution is treated to remove iron and copper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1: Process flow diagram of an embodiment of the invention.

[0046] FIG. 2: XRD spectrum of solids produced according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The description, and the embodiments described therein, is provided by way of illustration of examples of particular embodiments of principles and aspects of the present invention. These examples are provided for the purposes of explanation and not of limitation, of those principles of the invention. In the description that follows, like parts and/or steps are marked throughout the specification and the drawing with the same respective reference numerals.

[0048] The embodiments of the present invention shall be more clearly understood with reference to the following description and FIG. 1.

[0049] FIG. 1 provides a schematic representation of an embodiment of the invention for a method for the recovery of cobalt, manganese and nickel from a Co-, Ni- and Mn-containing aqueous feed solution. The Co, Ni and Mn are present in the solution in ionic form. The Co-, Ni-, and Mn-containing feed solution may be a sulphate and/or chloride based aqueous solution, in which case the Co, Ni, and Mn are present as sulphate and/or chloride salts and are in the form of Co(II) Ni(II), or Mn(II) respectively.

[0050] In this particular embodiment, the feed solution has been pre-treated to remove metal ions which may interfere with the recovery of cobalt from the Co-,Ni-, and Mn-containing aqueous feed solution to form a pre-purified feed solution 10. Such metal ions include at least Fe and Cu. Fe and Cu may be removed by methods known to those skilled in the art. Such methods may include precipitation with a base such as lime, electrowinning, solvent extraction or ion exchange. The Co-, Ni-, and Mn-containing aqueous feed solution may be subjected to additional treatment steps to remove other metal ion contaminants if necessary.

[0051] In this embodiment, the pre-purified feed solution 10 (being substantially free of Fe and Cu) additionally includes Mn ions (generally in the form of Mn(II)). The inventors have found that Mn(II) can be effectively removed in an oxidation/precipitation process that involves treating the pre-purified feed solution 10 with permanganate.

[0052] The pre-purified feed solution 10 is first adjusted 11 with caustic soda 12 to raise the pH to a value in the range of from about 3.5 to about 5.0, preferably from about 4.0 to about 4.5, and most preferably to a pH value of about 4.2. Sodium permanganate 14 is then added in order to preferentially and selectively oxidise the divalent manganese in solution 10 and form a precipitate slurry 15 that includes a manganese dioxide precipitate 17. In order to achieve this, sufficient permanganate is added to adjust the oxidation-reduction potential (ORP) of the pre-purified feed solution 10 to a value of from about 700 to about 800 mV (versus the PtAg/AgCl electrode), and preferably to about 750 mV. Under these pH and ORP conditions, manganese can be selectively and quantitatively recovered while avoiding precipitation of cobalt or nickel according to Equation (1) below in a sulphate medium:

3MnSO.sub.4+2NaMnO.sub.4.fwdarw.5MnO.sub.2+H.sub.2SO.sub.4+Na.sub.2SO.sub.4 (1)

[0053] It is important to adjust the concentration of the permanganate solution, such concentration being dependent upon the concentration of manganese in the feed solution (see equation (1)) and ensure that it is efficiently dispersed, since it may form localised areas of very high ORP promoting the formation of cobaltic oxide.

[0054] Sodium permanganate 14 is the preferred oxidant, because it is sufficiently powerful to affect the oxidation of divalent manganese in solution. Hydrogen peroxide, for instance, a commonly-employed oxidant, does not work in this system. Potassium permanganate, a more common chemical than sodium permanganate, can also be used. However, this is more expensive to prepare than sodium permanganate.

[0055] The precipitation slurry 15 then undergoes solid-liquid separation 16. This may be effected by any convenient means, such as, but not limited to, flocculation and thickening, filter press or vacuum belt filter. The solids 17 are a pure form of manganese dioxide, part of which 19 are recycled to make sodium permanganate 14. To regenerate sodium permanganate, the solids portion 19 is first fused 20 with solid caustic soda 21, and the liquid melt 22 is quenched in water 23, where it dissolves 13 to form sodium permanganate solution 14. Sodium permanganate solution can be unstable if stored, but in this case it is used immediately, so no such issues arise. The remaining manganese dioxide solids 18 form a product for sale.

[0056] The treated feed solution 24 from solid-liquid separation 16 then proceeds to a first stage of cobalt precipitation 25 which is effected by the addition of sodium hypochlorite 27. The pH of the treated feed solution 24 is first adjusted by the addition of an alkali, such as caustic soda 26, to a value of from about 4.5 to about 6.5, preferably from about 5.0 to about 5.5. The ORP is then adjusted by the addition of sodium hypochlorite 27 to a value of from about 750 to about 900 mV, preferably from about 800 to about 850 mV (relative to the PtAg/AgCl electrode). The inventors have found that these pH and ORP values allow for the preferential and selective oxidation of the cobalt (e.g. from Co(II) to Co(III)) and the precipitation of the cobalt in the form of a heterogenite, a hydrated cobaltic oxide, CoOOH. Equation (2) shows the reaction from a chloride medium:

2CoCl.sub.2+3NaOCl+H.sub.2O.sub.2.fwdarw.2CoOOH+3NaCl (2)

[0057] Sodium hypochlorite is a common chemical, often referred to as household bleach, and is a powerful oxidising agent. It is rarely used in extractive metallurgy, however, because it introduces both sodium and chloride into predominantly sulphate-based processing schemes. However, it has been determined that its use is particularly suited to the recovery of cobalt when the concentration of both cobalt and nickel is high as described in this invention, since it does not generate any acid, unlike the processes described in the prior art, and therefore requires no additional base, which is a major issue in conventional processing schemes.

[0058] Nickel can also react under these conditions which is undesirable. The reaction with nickel is very slow, given this, one option for preventing the reaction of nickel is by limiting the residence time. The inventors have found that by limiting the residence time, such as to a time of limited to less than two hours (and preferably of from about 30 to about 60 minutes) the co-precipitation of nickel can be avoided allowing an essentially pure cobalt product to be obtained (i.e. a cobalt precipitate that does not include additional metal co-precipitate). Further, using a sub-stoichimetric amount of sodium hypochlorite relative to cobalt can also avoid co-precipitation of nickel. In this regard, a multi-stage cobalt oxidation and precipitation process can be used. By way of example, and as shown in FIG. 1 in the first cobalt precipitation stage 25, sufficient sodium hypochlorite is used to precipitate 80 to 90% of the cobalt to ensure that no other metals, notably nickel, co-precipitate. The precipitation slurry 28 undergoes solid-liquid separation 29, which may be effected by any convenient means, such as, but not limited to, flocculation and thickening, filter press or vacuum belt filter. The solids 30 may, if desired, be dried to form cobaltic oxide, Co.sub.2O.sub.3.

[0059] The solution 31 then undergoes a second stage of cobalt precipitation 32 by the addition of excess sodium hypochlorite 33. This ensures that all of the cobalt is recovered. This may also result in the co-precipitation of a small amount of nickel. The second cobalt precipitation slurry 34 undergoes solid-liquid separation 35, which may be effected by any convenient means, such as, but not limited to, flocculation and thickening, filter press or vacuum belt filter. The solids 36 are returned to the leaching stage (not shown) of the flowsheet.

[0060] The solution 37 now substantially free of cobalt, then undergoes nickel precipitation 38. This is achieved by the addition of sodium carbonate 39 at a temperature from about 45 to about 80 C., preferably from about 60 to about 65 C. The pH of the solution is adjusted to and/or controlled at about 7.5 to about 8.5, and preferably about 8.0 to about 8.2. The precipitation slurry 40 undergoes solid-liquid separation 41, which may be effected by any convenient means, such as, but not limited to, flocculation and thickening, filter press or vacuum belt filter. The solids 42 are pure nickel carbonate.

[0061] The solution 43, containing a mixture of sodium sulphate and sodium chloride if the original solution was sulphate, or just sodium chloride if the original solution was chloride, may be treated for their recovery if warranted, or simply disposed of.

[0062] The principles of the present invention are illustrated by the following example, which is provided by way of illustration, and should not be taken as limiting the scope of the invention.

EXAMPLE 1

[0063] A solution containing 80 g/L Co and 20 g/L Ni was adjusted to pH 5.5 with caustic soda, and then sodium hypochlorite was added to raise the ORP to 850 mV (versus PtAg/AgCl). Black solids were formed immediately, which after filtering, washing and air drying were found to contain 59% Co and just 0.2% nickel, with the balance being primarily oxygen. FIG. 2 shows an XRD scan of the solids which indicates that the solids are primarily heterogenite (CoOOH), together with a small amount of a mixed cobaltic-nickelic oxide.

[0064] This example demonstrates the ability of the process to recover a high-purity form of trivalent cobalt oxide from a solution containing high levels of nickel.

[0065] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.