WO2014000023A1

WO2014000023A1 - Method for recovering cobalt from cobalt-containing ores

Info

Publication number: WO2014000023A1
Application number: PCT/AU2013/000665
Authority: WO
Inventors: Garry Mervyn Johnston; Matthew Leslie Sutcliffe; Nicholas James Welham
Original assignee: Metaleach Limited
Priority date: 2012-06-29
Filing date: 2013-06-20
Publication date: 2014-01-03
Also published as: AU2013202009A1; AU2013202009B2

Abstract

A method for recovering cobalt from an oxidised cobalt-containing ore, the method comprising the steps of: Applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent; Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gl:1 cobalt, and a spent ore; Separating the cobalt containing solution from the spent ore; and Recovering cobalt from the cobalt-containing solution.

Description

"Method For Recovering Cobalt from Cobalt-Containing Ores" Field of the Invention

[0001 ] The present invention relates to a method for recovering cobalt from cobalt- containing ores. More particularly, the present invention relates to a method for recovering cobalt from oxidised cobalt-containing ores.

Background Art

[0002] Current practice for oxidised cobalt-containing ores is to reduce the particle size of the as-mined cobalt ore by a combination of crushing and grinding. The ground ore is then added to large leaching tanks containing sulfuric acid. A reductant, most commonly sulfur dioxide, is then added to the tank to reduce insoluble trivalent cobalt to soluble divalent cobalt.

[0003] At the Shituru plant, 0.8 tonnes of sodium metabisulfite (SBMS, Na₂S₂0₅) and 1.2 tonnes of copper powder were required per tonne of cobalt produced. These consumption figures make cobalt extraction expensive as these reagents comprised 47% of the operating costs for cobalt production. (M.D.Mwema, M.Mpoyo, and

K.Kafumbila, Use of sulfur dioxide as reducing agent in cobalt leaching at Shituru hydrometallurgical plant, Journal of The South African Institute of Mining and Metallurgy volume 102, issue 1 , 2002, p. 1-4)

[0004] To reduce these costs, gaseous sulfur dioxide has been trialled as a

replacement for sodium metabisulfite ('SMBS') and copper powder. Tests were performed at 40°C using ore ground to 80% <74μηι, It was found that by sparging S0₂ into the slurry cobalt recovery reached 86% after three hours. However, the sulfur dioxide also reduced iron and manganese within the ore, rendering them soluble in the acidic solution. This increased solubility necessitates further processing to remove these elements from solution giving an increasingly complex, and therefore expensive, flowsheet.

[0005] Miller (G.Miller, Design of copper-cobalt hydrometallurgical circuits, Metallurgical Plant Design and Operating Strategies (MetPlant 2008), AusIMM, p.447-460) notes that "[i]n an acid solution the SMBS disassociates to form S0_{2 (aq)} which lowers the Eh in solution and reduces the cobalt oxidation state. SMBS is costly and is only partially utilised with side reactions producing sulfuric acid - particularly in the presence of manganese ions in solution." Additionally, "newer projects are considering the use of liquefied S0₂" to remove some of the problems surrounding the direct use of S0₂ in smelter off gas.

[0006] The paper by Miller also examines the removal of impurities from the acidic leach solution, notably iron, manganese, calcium and zinc all of which require removal prior to cobalt concentration and recovery. In this paper, it is stated that

[0007] "Iron removal has been undertaken for many years in many hydrometallurgical process plants. The classic method is air oxidation to iron (III) and precipitation with lime and or limestone. All the current and previous Zambian and DRC project use this basic method. However the older style plants all suffer from the usual problems of: downstream gypsum precipitation and fouling of process equipment and pipes."

Miller also noted that for manganese removal

"The process used to date in Zambia and DRC has been a combined iron and manganese precipitation. This has removed the copper and some zinc; but also co-precipitated significant cobalt which has been lost."

[0008] The above summary shows that the acid system for leaching of cobalt has considerable problems, most notably the requirement to remove a suite of impurities by a variety of different methods without significant cobalt losses before cobalt can be recovered.

[0009] The method of the present invention has as one object thereof to overcome the abovementioned problems associated with the prior art, or to at least provide a useful alternative thereto.

[0010] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers

[0011 ] The discussion of the background art is included exclusively for the purpose of providing a context for the present invention. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was common general knowledge in the field relevant to the present invention in Australia or elsewhere before the priority date.

Disclosure of the Invention

[0012] In accordance with the present invention there is provided a method for recovering cobalt from an oxidised cobalt-containing ore, the method comprising the steps of:

Applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent;

Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gL^"1 cobalt, and a spent ore;

Separating the cobalt containing solution from the spent ore; and

Recovering cobalt from the cobalt-containing solution.

[0013] In accordance with the present invention there is further provided a method for recovering cobalt from an oxidised cobalt-containing ore, the method comprising the steps of:

Applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash; Washing the cured ore with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gL^"1 cobalt, and a spent ore; Separating the cobalt containing solution from the spent ore; and

Recovering cobalt from the cobalt-containing solution.

[0014] In accordance with the present invention there is further provided a method for recovering cobalt from an oxidised cobalt-containing ore, the method comprising the steps of:

Applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution and an at least partially spent aqueous solution of cobalt reducing-agent ;

Washing the cured ore and the at least partially spent aqueous solution of cobalt reducing-agent with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gL^"1 cobalt, and a spent ore;

Separating the cobalt containing solution from the spent ore; and

Recovering cobalt from the cobalt-containing solution.

[0015] As would be understood by a person skilled in the art, rendering the oxidised cobalt-containing ore more amenable to washing with an aqueous wash solution means effecting one or more of: an improved cobalt recovery, in a shorter time, under milder wash conditions. Milder wash conditions may include, but are not limited to, lower temperatures, lower pressures, or combinations thereof. For example, a given cobalt recovery may be effected in a shorter time, or by using milder leach conditions, or both, as a result of the curing step of the method of the present invention.

[0016] The inventors have discovered that the application of a reducing agent to an oxidised cobalt-containing ore under mild conditions is surprisingly effective at solubilising the cobalt contained in the ore, to the extent that economically viable quantities of the cobalt can be recovered by merely washing the ore under similarly mild conditions and for a relatively brief period of time, without the need to use any leaching agents. Avoiding the use of leaching agents and the like has obvious economic benefits in terms of reagent consumption and flow sheet simplicity. Furthermore, the inventors have discovered that the volume of wash solution required to dissolve the solubilised cobalt is surprisingly low, enabling the straightforward generation of cobalt containing solutions of sufficient concentration to be economically recovered by existing means for metal recovery. Furthermore, the inventors have discovered that the reducing agent is effective under mild conditions within a relatively short timeframe. Further still, the inventors have discovered that economically relevant quantities of cobalt are dissolved by the relatively low volume of the wash solution, under the mild temperature and pressure conditions, relatively quickly, providing advantages in terms of process design.

[0017] As would be understood by a person skilled in the art, in many applications, it is virtually impossible to completely retain a solution in contact with the ore to be leached. For example, in a heap leaching context, it is virtually impossible to stop some degree of drainage from the ore. The methods of the present invention encompass methods where some incidental separation of the oxidised cobalt-containing ore and the aqueous solution of the cobalt reducing agent occurs.

[0018] The present invention encompasses simultaneously extracting one or more target metals other than cobalt. The target metals may be separated by the means for metal recovery, such as by solvent extraction.

Oxidised cobalt-containing ores

[0019] Throughout this specification, unless the context requires otherwise, the term "ore" or variations thereof, will be understood to include, for example, the product of one or more pre-treatment steps, such as a roast or calcination steps, or one or more concentration steps, but is not limited thereto.

[0020] In one form of the invention, the oxidised cobalt-containing ore contains trivalent cobalt. In one form of the invention, the oxidised cobalt-containing ore contains mixed manganese-cobalt phases. In one form of the invention, the oxidised cobalt-containing ore contains heterogenite (CoOOH) and/or the cobalt/manganese phase known as wad and/or a manganese oxide mineral containing cobalt at <50wt% Co. In one specific form of the invention, the oxidised cobalt-containing ore contains absolane. [0021 ] In one form of the invention, the oxidised cobalt ore has a cobalt content in excess of any nickel content.

Cobalt reducing agents and aqueous solutions thereof

[0022] In one form of the invention, the cobalt reducing agent is selected from the group: iron (II) salts, sulfite salts, sulfur dioxide, and combinations thereof.

[0023] In one form of the invention, the cobalt reducing agent is ferrous sulfate, FeS0₄. In one form of the invention, the cobalt reducing agent is ferrous chloride, FeCI₂. In one form of the invention, the cobalt reducing agent is ferrous nitrate, Fe(N0₃)₂. In one form of the invention, the cobalt reducing agent is an acidic solution of sodium sulfite, Na₂S0₃. In one form of the invention, the cobalt reducing agent is an acidic solution of potassium sulfite, K₂S0₃. In one form of the invention, the cobalt reducing agent is an acidic solution of ammonium sulfite, (NH₄)₂S0₃. In one form of the invention, the cobalt reducing agent is an acidic solution of sodium hydrogen sulfite, NaHS0₃. In one form of the invention, the cobalt reducing agent is an acidic solution of potassium hydrogen sulfite, KHS0₃. In one form of the invention, the cobalt reducing agent is an acidic solution of ammonium hydrogen sulfite, NH₄HS0₃. In one form of the invention, the cobalt reducing agent is an aqueous solution of sulfur dioxide, S0₂. In one form of the invention, the cobalt reducing agent is sodium metabisulfite, Na₂S₂0₅. In one form of the invention, the cobalt reducing agent is potassium metabisulfite, K2S2O5. In one form of the invention, the cobalt reducing agent is ammonium metabisulfite, (NH₄)₂S₂0₅.

[0024] Throughout this specification, unless the context requires otherwise, reference to aqueous solutions of sulfite encompasses sulfite derivatives such as bisulfite and metabisulfite.

[0025] The present invention encompasses methods where the aqueous solution of a cobalt reducing agent is generated in situ.

[0026] In one form of the invention, the step of: applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent;

[0027] more specifically comprises: applying to the oxidised cobalt-containing ore, water or aqueous solution thereby generating an oxidised cobalt-containing ore-water or aqueous solution mixture; contacting the oxidised cobalt-containing ore-water or aqueous solution mixture with a cobalt reducing agent thereby generating an aqueous solution of a cobalt reducing agent; at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent.

[0028] In this form of the invention, the cobalt reducing agent is preferably a solid or a gas. In a highly preferred form of the invention, the cobalt reducing agent is sulphur dioxide.

[0029] The aqueous solution applied to the oxidised cobalt-containing ore may be an aqueous solution of a cobalt reducing agent. That is, in a convenient form of the invention, a solid or gaseous cobalt reducing agent may be used to supplement the reducing power of the aqueous solution of the reducing agent. For example, if the aqueous solution of the reducing agent is recovered and recycled, this step may be particularly advantageous.

Extent of cobalt recovery

[0030] In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gL^"1 cobalt, and a spent ore more specifically comprises the step of:

Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gL¹ cobalt, and a spent ore, and in which at least 20% of the cobalt initially present in the oxidised cobalt-containing ore is dissolved, and a spent ore.

[0031 ] In one form of the invention, the cobalt-containing solution contains at least 25% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 30% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 35% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 40% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 50% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 55% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt- containing solution contains at least 60% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 65% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 70% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 75% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 80% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt- containing solution contains at least 85% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 90% of the cobalt initially present in the oxidised cobalt ore. In one form of the invention, the cobalt-containing solution contains at least 95% of the cobalt initially present in the oxidised cobalt ore. [0032] In one form of the invention, the cobalt-containing solution contains a percentage of the cobalt initially present in the oxidised cobalt ore within a range having a lower value of 20%. In one form of the invention, the lower value is 25%. In one form of the invention, the lower value is 30%. In one form of the invention, the lower value is 35%. In one form of the invention, the lower value is 40%. In one form of the invention, the lower value is 45%. In one form of the invention, the lower value is 50%. In one form of the invention, the lower value is 55%. In one form of the invention, the lower value is 60%. In one form of the invention, the lower value is 65%. In one form of the invention, the lower value is 70%. In one form of the invention, the lower value is 75%. In one form of the invention, the lower value is 80%. In one form of the invention, the lower value is 85%. In one form of the invention, the lower value is 90%. In one form of the invention, the lower value is 95%.

[0033] In one form of the invention, the cobalt-containing solution contains a percentage of the cobalt initially present in the oxidised cobalt ore within a range having an upper value of 100%. In a preferred form of the invention, the cobalt-containing solution contains a percentage of the cobalt initially present in the oxidised cobalt ore within a range having an upper value of 99%. In a preferred form of the invention, the cobalt- containing solution contains a percentage of the cobalt initially present in the oxidised cobalt ore within a range having an upper value of 95%.

[0034] Throughout this specification, reference to the cobalt initially present in the oxidised ore means a reference to the recoverable cobalt initially present in the oxidised cobalt ore. Throughout this specification, unless the context requires otherwise, the phrase "recoverable cobalt" is that fraction of the total cobalt that may be recovered from the ore, of any specific particle size distribution, by using aqua regia (nitro-hydrochloric acid). digestion. As would be understood by a person skilled in the art, aqua regia digestion is used to ascertain the head grade of a given ore.

Particle size

[0035] In one form of the invention, the cobalt-containing ore to which the aqueous solution of a cobalt reducing agent is applied is an as-mined ore.

[0036] In one form of the invention, the cobalt-containing ore to which the aqueous solution of a cobalt reducing agent is applied is a crushed ore. [0037] In another form of the invention, the cobalt-containing ore to which the aqueous solution of a cobalt reducing agent is applied is a ground ore.

[0038] As would be recognised by those skilled in the art, the extent of particle size reduction is a function of the dissemination of the cobalt within the ore. Finely disseminated ores may require grinding to expose the cobalt particles to the reducing solution. However, the actual size to which particles of ore are ground is an economic function of cobalt headgrade and recovery.

[0039] In one form of the invention, the 80% passing size (P80) is 1 mm. In one form of the invention, the 80% passing size (P80) is 2 mm. In one form of the invention, the 80% passing size (P80) is 3 mm. In one form of the invention, the 80% passing size (P80) is 4 mm. In one form of the invention, the 80% passing size (P80) is 6 mm. In one form of the invention, the 80% passing size (P80) is 9 mm. In one form of the invention, the 80% passing size (P80) is 12 mm. In one form of the invention, the 80% passing size (P80) is 15 mm. In one form of the invention, the 80% passing size (P80) is 18 mm. In one form of the invention, the 80% passing size (P80) is 21 mm. In one form of the invention, the 80% passing size (P80) is 25 mm.

Aqueous wash solutions

[0040] Throughout this specification, unless the context requires otherwise, the term "aqueous wash solution" should be understood to refer to aqueous solutions capable of dissolving cobalt (II) phases.

[0041] In one form of the invention, the aqueous wash solution is not adapted to reduce cobalt (III) phases. In one form of the invention, the aqueous wash solution does not contain a reducing agent. As would be understood by a person skilled in the art, it is virtually impossible to completely exclude reducing agents from an aqueous solution and a preferred form of the invention encompasses concentrations of reducing agent having no practical effect on the oxidation state of the cobalt. In a highly preferred form of the invention the wash solution is water.

[0042] In one form of the invention, the aqueous wash solution does not contain a complexing agent. Although cobalt ions do form complexes with water, for the purposes of this specification, and as would be generally understood by a person skilled in the art, water is not considered a complexing agent, As would be understood by a person skilled in the art, it is virtually impossible to completely exclude complexing agents from an aqueous solution and a preferred form of the invention encompasses concentrations of complexing agent having no practical effect on the complexation of the cobalt.

[0043] In a preferred form of the invention the wash solution is a solution adjusted to a pH of less than 6 using acid. In a preferred form of the invention the wash solution is a solution adjusted to a pH of less than 5 using acid. In a preferred form of the invention the wash solution is a solution adjusted to a pH of less than 4 using acid. In a preferred form of the invention the wash solution is a solution adjusted to a pH of less than 3 using acid. In a preferred form of the invention the wash solution is a solution adjusted to a pH of less than 2 using acid. In a preferred form of the invention the wash solution is a solution adjusted to a pH of less than 1 using acid.

[0044] In a preferred form of the invention the wash solution is a solution adjusted to a pH with an upper limit selected from: 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 and a lower limit selected from: 0, 0.5, 1 , 1.5, 2, 2.5, 3 ,4, 4.5, 5 using acid, where the lower limit is less than the upper limit.

[0045] In a highly preferred form of the invention the wash solution is a solution adjusted to a pH with an upper limit selected from: 3, 3.5, 4, 4.5 and a lower limit selected from: 2, 2.5, 3, 3.5 using acid, where the lower limit is less than the upper limit.

[0046] In a preferred form of the invention the wash solution is a solution adjusted to pH5-6 using acid. In a preferred form of the invention the wash solution is a solution adjusted to pH4-5 using acid. In a preferred form of the invention the wash solution is a solution adjusted to pH3-4 using acid. In a preferred form of the invention the wash solution is a solution adjusted to pH2-3 using acid. In a preferred form of the invention the wash solution is a solution adjusted to pH1 -2 using acid. In a preferred form of the invention the wash solution is a solution adjusted to pH0-1 using acid.

Treatment time

[0047] In one form of the invention, after the step of; Applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent

[0048] and before the step of:

Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gL^"1 cobalt, and a spent ore;;

[0049] the method comprises the step of: resting the cured ore-aqueous solution of the reducing agent mixture for less than one week.

[0050] In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than ninety six hours. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than forty eight hours. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than twenty four hours. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than sixteen hours. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than eight hours. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than four hours. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than two hours. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than one hour. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than forty five minutes. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than thirty minutes. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than fifteen minutes. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than ten minutes. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is rested for less than five minutes.

Wash time

[0051] In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 5 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 10 minutes. In one form of the invention, the period for which the cured ore- aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 20 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 40 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 60 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 90 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 120 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 180 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 240 minutes. In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 360 minutes.

[0052] In one form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution has a range with an lower limit selected from one of the following: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 1 10, 1 15 mins and an upper limit selected from one of the following: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 1 10, 1 15, 120 mins, where the upper limit is greater than the lower limit. [0053] In a preferred form of the invention, the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution has a range with an lower limit selected from one of the following: 5, 10, 15 mins and an upper limit selected from one of the following: 15, 20, 25 mins, where the upper limit is greater than the lower limit.

Solids content of the ore-solution mixture

[0054] The cured ore-aqueous solution of the reducing agent mixtures of the of the invention encompass mixtures with extremely high solids contents, such as pastes, and mixtures where solid ore is merely moistened by the addition of aqueous solution of the cobalt reducing agent. In one form of the invention, the cured ore-aqueous solution of the reducing agent mixture is a paste. In one form of the invention, the cured ore- aqueous solution of the reducing agent mixture comprises solid ore moistened by the aqueous solution of the cobalt reducing agent.

[0055] In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 100 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 200 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 400 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 700 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 1000 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 2000 g/L. In a preferred form of the invention, the cured ore- aqueous solution of the reducing agent mixture has a solids content not less than about 4000 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 7000 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 10000 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 20000 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 40000 g/L. In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 50000 g/L.

[0056] In a preferred form of the invention, the cured ore-aqueous solution of the reducing agent mixture has a solids content range with an lower limit selected from one of the following: 100, 200, 400, 1000, 2000, 4000, 7000, 10000, 20000 and 40000 g/L and a upper limit selected from one of the following: 200, 400, 1000, 2000, 4000, 7000, 10000, 20000, 40000 and 50000 g/L where the upper limit is greater than the lower limit.

[0057] In one form of the invention, the solids content of the cured ore-aqueous solution of the reducing agent mixture falls within a range of contents having a lower limit of 100 g/L. In a preferred form of the invention, the range of contents has a lower limit of 200 g/L. In a preferred form of the invention, the range of contents has a lower limit of 400 g/L. In a preferred form of the invention, the range of contents has a lower limit of 700 g/L. In a preferred form of the invention, the range of contents has a lower limit of 1000 g/L. In a preferred form of the invention, the range of contents has a lower limit of 2000 g/L. In a preferred form of the invention, the range of contents has a lower limit of 4000 g/L. In a preferred form of the invention, the range of contents has a lower limit of 7000 g/L. In a preferred form of the invention, the range of contents has a lower limit of 10000 g/L. In a preferred form of the invention, the range of contents has a lower limit of 20000 g/L. In a preferred form of the invention, the range of contents has a lower limit of 40000 g/L. In a preferred form of the invention, the range of contents has a lower limit of 50000 g/L.

[0058] In one form of the invention, the solids content of the cured ore-aqueous solution of the reducing agent mixture falls within a range of contents having an upper limit of 100000 g/L. In one form of the invention, the solids content of the mixture falls within a range of contents having an upper limit of 50000 g/L. In one form of the invention, the solids content of the mixture falls within a range of contents having an upper limit of 40000 g/L. In one form of the invention, the solids content of the mixture falls within a range of contents having an upper limit of 20000 g/L.

[0059] As would be obvious to those skilled in the art, the volume and concentration of the reducing solution will vary according to several factors. The product of concentration and volume is the dose of reductant applied. The specific dose required by an ore can be applied using a low volume of a high concentration or a high volume of low concentration. The volume to be used is a function of the surface area of the ore. A large particle size will require a lower volume than a fine particle size as the surface area is smaller. An ore with a high cobalt headgrade will require more solution and / or higher concentration than an ore with a low cobalt headgrade.

Volume of the aqueous wash solution

[0060] The volume of the aqueous wash solution should be as small as possible to maximise the concentration of the cobalt in the solution.

[0061 ] In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 50m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 20m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 10m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 5m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 2m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 1 m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 0.5m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 0.2m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 0.1 m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 0.05m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 0.02m³/t ore. In one form of the invention, the volume of aqueous wash solution used falls within a range of volume having an upper limit of 0.01 m³/t ore.

[0062] In one form of the invention, the volume of aqueous wash solution used falls within a range having a lower limit of 0.001 m³/t ore. [0063] The wash solution may be recycled several times through the bed of particles in order to build-up the concentration of cobalt before passing it to recovery. This may be performed in a counter-current manner to maximise washing efficiency.

Concentration of the cobalt-containing solution

[0064] In one form of the invention, cobalt-containing solution contains at least 0.1 gL^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 0.2 gl_^"1cobalt. In one form of the invention, the cobalt-containing solution contains at least 0.5 gl_^"1cobalt. In one form of the invention, the cobalt-containing solution contains at least 1 gl_^"1cobalt. In one form of the invention, the cobalt-containing solution contains at least 0.2gl_^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 0.5gl_^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 0.7 gL^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 1.OgL^"1 cobalt. In one form of the invention, the cobalt- containing solution contains at least 2.0gL^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 5. OgL^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 10gL^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 20gL^"1 cobalt. In one form of the invention, the cobalt-containing solution contains at least 50gL^"1 cobalt.

Treating temperature

[0065] In one form of the invention, the step of applying to the oxidised cobalt- containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between about 10°C and 50°C. In one form of the invention, the step of applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between about 10°C and 45°C. In one form of the invention, the step of applying to the oxidised cobalt- containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between about 10°C and 40°C, In one form of the invention, the step of applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between about 10°C and 35°C. In one form of the invention, the step of applying to the oxidised cobalt- containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent ore takes place at a temperature between about 10°C and 30°C.

[0066] In one form of the invention, the step of applying to the oxidised cobalt- containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between ambient temperature and 50°C. In one form of the invention, the step of applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between ambient temperature and 45°C. In one form of the invention, the step of applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between ambient temperature and 40°C. In one form of the invention, the step of applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between ambient temperature and 35°C. In one form of the invention, the step of applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at a temperature between ambient temperature and 30°C.

[0067] In a highly advantageous form of the invention, the step of applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at ambient temperature.

Washing temperature

[0068] In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between about 10°C and 50°C. In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between about 10°C and 45°C. In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between about 10°C and 40°C. In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between about 10°C and 35°C. In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between about 10°C and 30°C.

[0069] In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between ambient temperature and 50°C. In one form of the invention, the step of washing the cured ore- aqueous solution of the reducing agent mixture takes place at a temperature between ambient temperature and 45°C. In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between ambient temperature and 40°C. In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between ambient temperature and 35°C, In one form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at a temperature between ambient temperature and 30°C.

[0070] In a highly advantageous form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at ambient temperature.

Treating pressure

[0071 ] In a highly advantageous form of the invention, the step applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent takes place at atmospheric pressure.

Washing pressure

[0072] In a highly advantageous form of the invention, the step of washing the cured ore-aqueous solution of the reducing agent mixture takes place at atmospheric pressure.

Cobalt reducing agent dosage

[0073] In one form of the invention, the aqueous solution of the cobalt reducing agent contains an amount of cobalt reducing agent corresponding to between 0.2 and 50.0 times the amount of recoverable cobalt present in the oxidised cobalt-containing ore, on a stoichiometric basis.

[0074] In one form of the invention, the amount of cobalt reducing agent is between about 0.5 and 20.0 times the amount of recoverable cobalt present in the oxidised cobalt-containing ore, on a stoichiometric basis. [0075] In one form of the invention, the amount of cobalt reducing agent is between about 0.5 and 10.0 times the amount of recoverable cobalt present in the oxidised cobalt-containing ore, on a stoichiometric basis.

[0076] In one form of the invention, the amount of cobalt reducing agent is between about 0.5 and 3.0 times the amount of recoverable cobalt present in the oxidised cobalt- containing ore, on a stoichiometric basis.

[0077] As would be understood by a person skilled in the art, the equation representing the reduction of cobalt (III) by iron (II) is as follows

Fe²⁺ + Co³⁺→ Fe³⁺ + Co²⁺

[0078] As would be understood by a person skilled in the art, the equation representing the reduction of cobalt (III) by sulfite (using sodium sulfite as an example) /sulfur dioxide are as follows:

S0₂ + 2Co³⁺ + 2H₂0→ S0₄ ^2" + 2Co²⁺ + 4H⁺; or

Na₂S0₃ + 2Co³⁺ + H₂0→ Na₂S0₄ + 2Co ⁺ + 2H⁺.

[0079] Accordingly, where the cobalt reducing agent is iron (II), the amount of cobalt reducing agent corresponding to between 0.2 and 50.0 times the amount of recoverable cobalt present in the oxidised cobalt-containing ore, on a stoichiometric basis corresponds to between 0.2 and 50.0 times the amount of recoverable cobalt present in the oxidised cobalt ore on a molar basis. Where the cobalt reducing agent is sulfite/sulfur dioxide, the amount cobalt reducing agent corresponding to between 0.2 and 50.0 times the amount of recoverable cobalt present in the oxidised cobalt- containing ore, on a stoichiometric basis corresponds to between 0.4 and 30.0 times the amount of recoverable cobalt present in the oxidised cobalt ore on a molar basis.

[0080] Anyone skilled in the art will recognise that the reductant necessary to perform the desired dissolution is not solely determined by the cobalt concentration in the ore and chemical stoichiometry as there may well be other reducible species, such as manganese, present in the ore. Consequently, the actual stoichiometry will be different for each ore and can only be determined by test work. pH and concentration of the aqueous solution of the cobalt-reducing agent

[0081] In one form of the invention, where the cobalt-reducing agent is an iron (II) salt, the concentration of the iron (II) salt is between about 0.5 g/L and about 100 g/L

(expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 5 g/L and about 100 g/L (expressed in terms of iron (I I) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 10 g/L and about 100 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 25 g/L and about 100 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 50 g/L and about 100 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is about 100 g/L (expressed in terms of iron (II) sulfate).

[0082] In one form of the invention, where the cobalt-reducing agent is an iron (II) salt, the concentration of the iron (II) salt is between about 0.5 g/L and about 200 g/L

(expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 5 g/L and about 200 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 10 g/L and about 200 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 25 g/L and about 200 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 50 g/L and about 200 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is between about 100 g/L and about 200 g/L (expressed in terms of iron (II) sulfate). In one form of the invention, the concentration of the iron (II) salt is about 200 g/L (expressed in terms of iron (II) sulfate).

[0083] In one form of the invention, where the cobalt-reducing agent is an iron (II) salt, the concentration of the iron (II) salt is between about 0.5 g/L and saturation. In one form of the invention, the concentration of the iron (II) salt is between about 5 g/L and saturation. In one form of the invention, the concentration of the iron (II) salt is between about 10 g/L and saturation. In one form of the invention, the concentration of the iron (II) salt is between about 25 g/L and saturation. In one form of the invention, the concentration of the iron (II) salt is between about 50 g/L and saturation. In one form of the invention, the concentration of the iron (II) salt is between about 100 g/L and saturation, In one form of the invention, the solution is saturated by the iron (II) salt.

[0084] In one form of the invention, where the cobalt-reducing agent is an iron (II) salt, the pH of the aqueous solution of the iron (I I) salt is between about 1.0 and about 4.5. In one form of the invention, the pH of the solution is between about 1.5 and 4.5. In one form of the invention, the pH of the solution is between about 2.0 and 4.5. In one form of the invention, the pH of the solution is between about 2.5 and 4.5. In one form of the invention, the pH of the solution is between about 3.0 and about 4.5. The latter pH range corresponds to the inherent acidity of iron (II) solutions, across the range of concentrations of utility in the present invention, without the addition of further acid. As will be recognised by a person skilled in the art, the inherent pH of an iron (II) solution will vary with the concentration and identity of the counter ion.

[0085] The concentration of the solution of the cobalt-reducing agent that may be used will be affected by the pH. The solubility of iron (II) ions decreases with increasing pH until it reaches a minimum at around pH 1 1. However, to maintain a concentration of iron (II) ions suitable for use as a reductant requires a pH below around 7. Iron (II) converts to iron (III) after completing the reduction reaction and iron (III) solubility is also affected by pH reaching a minimum solubility at pH 4-9. At a pH below around 3, the iron (III) ions formed may be sufficiently soluble to migrate away from the reduction site thereby preventing blocking of the surface through formation of a solid iron (III) phase. The examples presented below do not indicate any blocking of the surface by iron (III) precipitates at pH 3.

[0086] In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the concentration of the sulfite salt is between about 0.5 g/L and about 100 g/L (expressed in terms of sodium sulfite). In one form of the invention, the

concentration of the sulfite salt is between about 10 g/L and about 100 g/L (expressed in terms of sodium sulfite). In one form of the invention, the concentration of the sulfite salt is between about 50 g/L and about 100 g/L (expressed in terms of sodium sulfite). In one form of the invention, the concentration of the sulfite salt is between about 100 g/L and about 100 g/L (expressed in terms of sodium sulfite). In one form of the invention, the concentration of the sulfite salt is about 100 g/L (expressed in terms of sodium sulfite). [0087] In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the concentration of the sulfite salt is between about 0.5 g/L and about 200 g/L (expressed in terms of sodium sulfite). In one form of the invention, the

concentration of the sulfite salt is between about 10 g/L and about 200 g/L (expressed in terms of sodium sulfite). In one form of the invention, the concentration of the sulfite salt is between about 25 g/L and about 200 g/L (expressed in terms of sodium sulfite). In one form of the invention, the concentration of the sulfite salt is between about 50 g/L and about 200 g/L (expressed in terms of sodium sulfite). In one form of the invention, the concentration of the sulfite salt is between about 100 g/L and about 200 g/L

(expressed in terms of sodium sulfite). In one form of the invention, the concentration of the sulfite salt is about 200 g/L (expressed in terms of sodium sulfite).

[0088] In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the concentration of the sulfite salt is between about 0.5 g/L and about saturation. In one form of the invention, the concentration of the sulfite salt is between about 10 g/L and about saturation. In one form of the invention, the concentration of the sulfite salt is between about 100 g/L and about saturation. In one form of the invention, the concentration of the sulfite salt is between about 50 g/L and about saturation. In one form of the invention, the concentration of the sulfite salt is between about 100 g/L and about saturation. In one form of the invention, the solution is saturated by the sulfite salt.

[0089] For sodium sulfite the main effect of pH is to change the speciation of the sulfite ion, below about pH 4.0 it is present as dissolved S0₂ sometimes written S0₂ (aq), above pH 4.0 the predominant species is HS0₃ ^". Sulfur dioxide has a limited solubility in water and this also decreases with pH, so losses of S0₂ to atmosphere will be greater at lower pH. In the preparation of the pH adjusted sulfite solutions utilised in the examples discussed below the odour of S0₂ was increasingly strong as the desired starting solution pH was decreased.

[0090] In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the pH is less than 10. In one form of the invention, where the reductant is a sulfite salt and/or S0₂, the pH is less than 8. In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the pH is less than 6. In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the pH is less than 5. In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the pH is less than 4. In one form of the invention, where the cobalt- reducing agent is a sulfite salt and/or S0₂, the pH is less than 3. In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the pH is less than 2. In one form of the invention, where the cobalt-reducing agent is a sulfite salt and/or S0₂, the pH is less than 1. In one form of the invention, where the reductant is a sulfite salt and/or S0₂, the pH is between about 5 and 6. In one form of the invention, where the reductant is a sulfite salt and/or S0₂, the pH is between about 4 and 5. In one form of the invention, where the reductant is a sulfite salt and/or S0₂, the pH is between about 3 and 4. In one form of the invention, where the reductant is a sulfite salt and/or S0₂, the pH is between about 2 and 3. In one form of the invention, where the reductant is a sulfite salt and/or S0₂, the pH is between about 1 and 2.

[0091 ] As would be realised by those skilled in the art, utilising a lower pH will increase the consumption of acid and an optimum pH can be determined using economic principles.

Means for cobalt recovery

[0092] In one form of the invention, the step of recovering cobalt from the cobalt- containing solution comprises a solvent extraction step. In a more specific form of the invention, the step of recovering cobalt from the cobalt-containing solution comprises a solvent extraction step, followed by an electrowinning step comprising the formation of a cobalt cathode. In an alternate form of the invention, the step of recovering cobalt from the cobalt-containing solution comprises a solvent extraction step, followed by a precipitation step comprising the formation of an insoluble cobalt salt. In an alternate form of the invention, the step of recovering cobalt from the cobalt-containing solution comprises a precipitation step. In an alternate form of the invention, the step of recovering cobalt from the cobalt-containing solution comprises a crystallisation step.

Brief Description of the Drawings

[0093] The present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:-

Figure 1 is a schematic flow sheet of a method for extracting cobalt from a cobalt- containing ore in accordance with the present invention; Figure 2 shows the extent of cobalt leaching of the samples of Example 3 as a function of rest time;

Figure 3 shows the extent of cobalt leaching of the samples of Example 4 as a function of leaching time;

Figure 4 shows the extend of cobalt recovery for the samples of Example 5 as a function of curing time;

Figure 5 shows the extend of cobalt dissolution for the samples of Example 6 as a function of leach time; and

Figure 6 shows the extend of cobalt dissolution for the samples of Example 7 after the treatment of example 8 as a function of cure time.

Best Mode(s) for Carrying Out the Invention

[0094] A heterogenite bearing ore is used as the basis for this disclosure; metal recovery is by solvent extraction and electrowinning. After crushing to a P80 of 3mm, the ore is placed onto a conveyor belt 16 where it is sprayed with 0.1 m³/t of a solution containing 100g/L FeS0₄ 10. The sprayed ore remains on the belt for 1 h to enable the majority of the cobalt(ll l) present in heterogenite to be reduced to cobalt(ll) thereby giving a cured ore. The cured ore is then tipped onto a 0.25mm vibrating screen 18 where it is washed by spraying firstly with wash solution 12 recycled from the PLS pond 20. This can be repeated several times in order to build up the concentration of cobalt in solution before it is sent to the solvent extraction plant. The partly metal-depleted ore is then washed with raffinate recycled from the solvent extraction plant 14. The washed ore is disposed of as tailings. A fraction of the solution in the PLS pond 20 is passed to a solvent extraction plant where the cobalt is selective extracted from the solution which is then recycled to wash the ore 14. The extracted metal is recovered by electrowinning to produce cobalt cathode.

[0095] The vibrating screen 18 is intended to retain the majority of the ore whilst allowing the wash solution to pass through without significant loss to the tailings. [0096] The present invention will now be described with reference to a series of examples. The description of the examples should not be understood to be limiting the generality of the preceding description of the invention.

Examples

EXAMPLE 1

[0097] 100g of a <4mm particle size cobalt-bearing ore containing 3.45%Co as the minerals heterogenite (CoOOH) and spherocobaltite (CoC0₃) was mixed with 40mL of a solution of 100g/L sodium sulphite adjusted to pH 4 using sulphuric acid. The acidified sodium sulphite reduces the insoluble trivalent cobalt present in heterogenite to soluble divalent cobalt. The wet ore was packed into a 25.4mm ID acrylic column and gently compacted. The ore was physically supported by a 0.053mm stainless steel mesh. The packed column was allowed to drain for 24h and a total of 26.5mL was collected.

[0098] The column was then irrigated by dripping water onto the top of the column and allowing the solution to percolate through the bed of particles. As the solution dripped out of the column it was collected into separate tubes. The volume of solution and concentration of Co were measured for all samples.

[0099] The table below shows the volume and cobalt concentration of the first five solutions collected. A total solution volume of 0.98L was irrigated through the column. All subsequent samples contained <0.1 g/L Co. no volume / ml_ g/L Co notes

1 26.5 1 .08 drainage

2 6.5 25.30

3 13 0.39

4 13 0.12

5 13 0.13 [00100] The total cobalt recovery was low at 6.4% because of the high proportion of insoluble spherocobaltite present and the inaccessibility of a proportion of the heterogenite due to the particle size. On the basis of the total recovery the proportion of cobalt leached in the first two solutions was 88%, the solution tenor of cobalt on combining the first two samples was 5.85g/L.

EXAMPLE 2

[00101 ] 10Og of the same ore as in Example 1 was mixed with 20ml_ of a saturated solution of ferrous sulphate and gently tumbled to ensure all particles were wetted. The ferrous sulphate reduces the insoluble trivalent cobalt present in

heterogenite to soluble divalent cobalt. The wet ore was packed into a 25.4mm ID acrylic column and gently compacted. The ore was physically supported by a 0.053mm stainless steel mesh. The packed column was allowed to drain for 24h but no drainage was collected. The column was then irrigated by dripping water onto the top of the column and allowing the solution to percolate through the bed of particles. As the solution dripped out of the column it was collected into separate tubes according to time. The volume of solution and concentration of Co were measured for all samples.

[00102] The table below shows the volume and cobalt concentration of the first four solutions collected. A total solution volume of 425ml_ was irrigated through the column. All subsequent samples contained <0.01g/L Co.

[00103] The total cobalt recovery was 15.6%, notably higher than in Example 1. This is believed to be mainly due to the greater efficacy of the ferrous sulphate in solubilising the cobalt minerals present. no volume / ml_ g/L Co

1 13.50 27.35

2 19.75 8.75

3 19.75 0.55

4 19.75 0.01 [00104] The initial two solutions contained 97.6% of the total cobalt recovered at a mean solution tenor of 16.3g/L Co.

EXAMPLE 3

[00105] A series of tubes each containing 10.Og of a pulverised ore containing 0.64% Co had added to each of them 5ml_ of a saturated solution of sodium sulphite acidified to pH 2.0 using sulphuric acid. After specific rest times, tubes had 250ml_ of water added. A tube containing 10. Og of ore was also leached without any pretreatment in water. All tubes were shaken for 24h at which time the solution was separated and analysed for cobalt. Figure 2 shows the extent of cobalt leaching as a function of rest time. The sample where there was no pretreatment is shown at 1 minute on the logarithmic x-axis.

[00106] As is clear, direct leaching resulted in <20% of the cobalt in the ore being dissolved. Resting for as little as five minutes in the acidified sodium sulphite solution resulted in a very significant increase in the extent of cobalt leaching to >80%.

Extending the resting time did not provide any further increase in cobalt recovery.

EXAMPLE 4

[00107] 50.0g of the same ore as in Example 4 was pretreated by adding 14mL of a saturated solution of sodium sulphite acidified to pH 2.0 using sulphuric acid. After resting for 4h 500mL of water was added. Solution samples were removed periodically and analysed for cobalt. Figure 3 shows the extent of cobalt leaching as a function of leaching time.

[00108] The vast majority of leaching (84%) is completed within the initial 0.5h (168% / h). Beyond the initial hour, the rate of leaching was very substantially slower at 0.55%Co / h. Clearly, the extra cost of leaching for more than 0.5h needs to be covered by the increase in value of cobalt obtained by extending the leaching beyond 0.5h. An increase in the leach time to 24h would necessitate a series of leaching vessels 48 times greater in volume than those needed for 0.5h. This represents a significant increase in the capital costs of the plant. The operating expenses would also increase due to the necessity to continue agitating the ore during the increased leaching time. [00109] Without wishing to be bound by theory, the cobalt is believed to be present in two phases, one containing around 80% of the total cobalt which is readily reduced and dissolves in the initial 5 min of leaching, and a second phase with the remaining 20% of the total cobalt which is more resistant to reduction and requires a longer leaching time.

EXAMPLE 5

[001 10] An ore containing 0.235%Co was treated using acidified sodium sulphite, the resultant paste was rested for increasing time up to 24h at which time it was slurried with water. After 24h of leaching the solution was analysed for Co and the recovery, shown in Figure 4, determined. Also shown is the extent of cobalt leaching (7.5%) without any pretreatment. For this ore a longer resting time provides increased cobalt recovery. The extent of cobalt dissolution increased to 52.7% after 0.25h resting and to 61 .8% after 0.5h resting.

[0011 1] Clearly, from an economic view the extra cobalt recovered after using a longer resting time needs to cover the capital and operating costs associated with lengthening the resting period.

[001 12] In this example, extending the rest time to 4h may well be warranted on an economic basis.

EXAMPLE 6

[00113] The same ore as in Example 5 was pretreated using acidified sodium sulphite, the resultant paste was rested for 24h at which time it was slurried with water. After increasing leaching time the solution was analysed for Co and the recovery, shown in Figure 5, determined.

[00114] The leaching was initially extremely rapid with 72.5% Co dissolution occurring in the initial 15mins. Beyond this time the increase in cobalt dissolution was small.

EXAMPLE 7 [001 15] Two different ores containing 0.797 (Ore 1 ) and 0.408% Co (Ore 2) were pretreated using a solution of ferrous sulphate. The resultant pastes were rested for up to 24h at which time sufficient water was added to form a slurry. After 24h leaching the solutions were analysed for Co and the recovery determined.

[001 16] As with the earlier examples, the recovery of the cobalt is most affected by the occurrence of the pretreatment rather than its duration. The maximum recovery is determined by the mineralogy of the cobalt present.

EXAMPLE 8

[001 17] The same ores as in Example 7 were pretreated for 24h using a solution of ferrous sulphate. The resultant pastes were dispersed with water and leached for up to 24h. After the required leaching time the solutions were analysed for Co and the recovery determined. The results are shown in Figure 6.

[001 18] For Ore 1 the leaching time of 24h gave the highest recovery of 77.5%, 1 h was sufficient to give 57.3%. In this case, the extra recovery is probably sufficient to cover the cost of the extra leaching time. Ore 2 was somewhat different with 1 h giving 46.9%Co, extending the leaching time to 96h resulted in an increase to 55.9%. Thus, the increase from Ore 2 is somewhat less than for Ore 1 and it may not be economically worthwhile leaching Ore 2 for more than the initial hour.

Claims

- 30 - The Claim Defining the Invention is as Follows:

1. A method for recovering cobalt from an oxidised cobalt-containing ore, the method comprising the steps of:

Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gl_^"1 cobalt, and a spent ore;

Separating the cobalt containing solution from the spent ore; and

Recovering cobalt from the cobalt-containing solution.

2. A method according to any one of the preceding claims characterised in that the oxidised cobalt-containing ore contains heterogenite (CoOOH).

3. A method according to any one of the preceding claims characterised in that the oxidised cobalt-containing ore contains mixed manganese-cobalt phases including but not limited to wad and/or asbolane and/or a manganese oxide mineral containing cobalt at <50wt% Co.

4. A method according to any one of the preceding claims wherein the cobalt reducing agent is selected from the group: iron (II) salts, sulfite salts, sulfur dioxide, and combinations thereof. - 31 -

5. A method according to any one of the preceding claims wherein the cobalt reducing agent is any one of the following, or any combination thereof: ferrous sulfate, FeS0₄; ferrous chloride, FeCI₂; ferrous nitrate, Fe(N0₃)₂; an acidic solution of sodium sulfite, Na₂S0₃; an acidic solution of potassium sulfite, K₂S0₃; an acidic solution of ammonium sulfite, (NH₄)₂S0₃; an acidic solution of sodium hydrogen sulfite, NaHS0₃; an acidic solution of potassium hydrogen sulfite, KHS0₃; an acidic solution of ammonium hydrogen sulfite, NH₄HS0₃; an aqueous solution of sulfur dioxide, S0₂; sodium metabisulfite, Na₂S₂0₅; potassium metabisulfite, K₂S₂0₅; ammonium metabisulfite, (NH₄)₂S₂0₅.

6. A method according to any one of the preceding claims wherein the step of: applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent; more specifically comprises: applying to the oxidised cobalt-containing ore, water or aqueous solution thereby generating an oxidised cobalt-containing ore-water or aqueous solution mixture; contacting the oxidised cobalt-containing ore-water or aqueous solution mixture with a solid or gaseous cobalt reducing agent thereby generating an aqueous solution of a cobalt reducing agent; - 32 - at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent.

7. A method according to claim 6 characterised in that the cobalt reducing agent is sulphur dioxide.

8. A method according to any one of the preceding claims wherein the aqueous solution applied to the oxidised cobalt-containing ore is an aqueous solution of a cobalt reducing agent, and wherein a solid or gaseous cobalt reducing agent is used to supplement the reducing power of the aqueous solution of the reducing agent.

9. A method according to any one of the preceding claims characterised in that the step of:

Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gl_^"1 cobalt, and a spent ore more specifically comprises the step of:

Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at - 33 - least 0.01 gL^"1 cobalt, and a spent ore, and in which at least 20% of the cobalt initially present in the oxidised cobalt-containing ore is dissolved, and a spent ore.

10. A method according to any one of the preceding claims wherein the aqueous wash solution is not adapted to reduce cobalt (III) phases and does not contain a complexing agent.

1 1. A method according to any one of the preceding claims wherein the aqueous wash solution is water.

12. A method according to any one of the preceding claims characterised in that after the step of;

Applying to the oxidised cobalt-containing ore an aqueous solution of a cobalt reducing agent at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, to provide a cured ore more amenable to washing with an aqueous wash solution in mixture with the aqueous solution of a cobalt reducing agent and before the step of:

Washing the cured ore-aqueous solution of the reducing agent mixture with an aqueous wash solution for a period of less than 24 hours at a pressure of between about atmospheric pressure and about 5 atmospheres, at a temperature between about 5°C and about 65°C, producing a cobalt-containing solution containing at least 0.01 gL^"1 cobalt, and a spent ore;; the method comprises the step of: - 34 - resting the cured ore-aqueous solution of the reducing agent mixture for less than one week.

13. A method according to any one of the preceding claims characterised in that the period for which the cured ore-aqueous solution of the reducing agent mixture is washed with the aqueous wash solution is less than 360 minutes.

14. A method according to any one of the preceding claims characterised in that the cured ore-aqueous solution of the reducing agent mixture has a solids content not less than about 100 g/L.

15. A method according to any one of the preceding claims characterised in that the volume of aqueous wash solution used falls within a range of between of 0.001 m³/t ore and 50m³/t ore.

16. A method according to any one of the preceding claims characterised in that the cobalt-containing solution contains at least 0.1 gl_^"1 cobalt.

17. A method according to any one of the preceding claims wherein the aqueous wash solution is acidic.

18. A method according to any one of claims 1 to 16 wherein the aqueous wash solution is alkaline.