WO2019138316A1

WO2019138316A1 - Process for the recovery of copper and cobalt from a material sample

Info

Publication number: WO2019138316A1
Application number: PCT/IB2019/050117
Authority: WO
Inventors: Yotamu Stephen Rainford HARA; Mazwi Douglas MUSOWOYA; Golden KALUBA; Jimmy MACHONA; Peter CHAMA
Original assignee: Anglo African Solutions Limited; The Copperbelt University; Mabel Claudine Lewis-Meintjes
Priority date: 2018-01-10
Filing date: 2019-01-08
Publication date: 2019-07-18
Also published as: ZA202104526B; GB202010538D0; ZA202004244B; GB202108560D0; GB2596651A; GB2583628B; GB2583628B8; GB2596651B; GB2583628A

Abstract

The invention provides a process for recovering copper (Cu) and cobalt (Co) from a copper–cobalt containing material sample, and which is adapted for treating both low and high grades of copper–cobalt source material, such as Cu-Co slag, Cu-Co low grade ores, Cu-Co high grade ores / concentrates, Cu-Co tailings and Cu ores. The process is characterised therein that recovery is achieved through electro-cementation. It comprises the steps of (i) leaching the material sample in an acidic pH; (ii) separating waste material solids through solid/liquid separation to recover a solution containing copper, cobalt and iron (Fe); (iii) recovering copper from solution through electro-cementation such that copper is electro-cemented onto a mild steel plate anode and cathode, leaving a solution containing cobalt and iron; (iv) recovering iron from the solution through precipitation as iron oxide; and (v) recovering cobalt from the solution through precipitation.

Description

PROCESS FOR THE RECOVERY OF COPPER AND COBALT FROM A

MATERIAL SAMPLE

BACKGROUND TO THE INVENTION

Cobalt (Co) has important applications in high temperature alloys, energy storage in lithium cobalt oxide batteries and magnetic materials. On the other hand, copper (Cu) is widely used in electric cables and electrical equipment, such as wiring and motors, as it is a good conductor of both heat and electricity. The worldwide demand for both copper and cobalt has been increasing. Therefore, there is a need for extracting these metals from all available sources. Copper smelting and converting slag are important sources of copper and cobalt. In Zambia, for example, most copper smelting and converting slag contains more than 0.8 weight % copper and 0.5 weight % cobalt. The copper in the slag is present as: i. Entrapped metallic copper

ii. Entrapped matte (CU2S and Cu5FeS4)

iii. Dissolved copper oxide (CU2O and CuO) in the complex iron silicate matrix.

By comparison, nearly all cobalt in the slag is dissolved in the complex iron silicate matrix. Prior art processes for recovery of copper and cobalt from slag

One prior art process for recovering copper and cobalt from slag is the COSAC process, which is disclosed by Jones, R.T., et al in the article entitled“Recovery of cobalt from slag in a DC arc furnace at Chambishi, Zambia". According to this process, slag is smelted with carbon at a temperature above 1500 degrees Celsius (°C) to form an iron rich, copper-cobalt-iron (Cu-Co-Fe) alloy. The Cu-Co-Fe alloy is atomised and leached in an autoclave to dissolve all the copper and cobalt and part of the iron. Copper is recovered from the leach solution by electro-winning. The spent solution after electro-winning of copper is purified to remove iron, manganese and nickel. The cobalt in the solution is upgraded via solvent extraction, after which the cobalt is recovered from solution via electro-winning.

The COSAC process was implemented at Chambishi Metals in Zambia, but it was found to be uneconomical when the cobalt metal price dropped from $120,000 to $60,000 per tonne. The main challenges of the COSAC process are:

i. The process is not economical for treating low grades of copper-cobalt materials, such as slag and tailings.

ii. The process is not flexible, as it can only be applied to source materials that include both copper and cobalt.

iii. The process has very high energy and operational costs, since the material is smelted at very high temperature (above 1500 degrees Celcius). Special refractory bricks are required for withstanding high operational temperatures. iv. Copper and cobalt are recovered from the solution through electro winning, but this stage has a very long cycle time of typically 2 - 7 days.

v. The process requires that copper and cobalt are upgraded in solution through solvent extraction, prior to electro-winning. However, solvent extraction is a hazardous process.

In short, the COSAC process is only economical at a high cobalt metal price, owing to high processing costs. Another prior art method for processing copper smelting slag is through froth flotation, as disclosed by Hara Y.R.S and Jha A (2016) in the article entitled "Carbothermic Processing of Copper-Cobalt Mineral Sulphide Concentrates and Slag Waste for the Extraction of Metallic Values". According to this method, slag is crushed and ground down to particle sizes of 75% passing through a 75 microns sieve size. The ground slag is fed into the flotation unit and the matte phase (CU2S, CusFeS^ is floated with the help of the collector and frother reagents. The copper sulphide (matte phase) is recovered as a concentrate with grade of copper at 20 - 35 weight %. Several plants treat copper smelting slag via this technique. However, a flotation process has the following major disadvantages:

i. Low recoveries of copper (i.e. 40 - 70% recovery), as the process only recovers copper that is in the sulphide form (CU2S, CusFeS^ CuFeS2 etc.). However, some of the copper in the slag is present as a complex iron silicate matrix, meaning that flotation is unable to recover this copper. ii. The process is unable to recover cobalt, which is dissolved in the complex iron silicate matrix. By comparison, the cobalt metal price is nearly 10 times higher than that of copper and hence any process for treating slag should be adapted to recovery of cobalt as well.

Most tailings (waste) from slag flotation plants in Zambia contain an average of 0.9 weight % cobalt and 0.6 weight % copper. As such, flotation is not a good process for treating copper smelting slag, due to its failure to recover cobalt and only a part of the copper.

A third method of recovering copper and cobalt from slag via leaching is disclosed in an article by Deng L. and Ling Y, entitled " Processing of copper converter slag for metal reclamation. Part I: extraction and recovery of copper and cobalt". Copper smelting slag is leached in strong acid. However, iron silicate, which is the main host phase for cobalt, is also leached out, thereby causing formation of silica gel, which then makes filtration practically impossible. As such, this method has not been adopted in the industry today.

Another method of treating copper smelting copper-cobalt slag involves roasting of the slag with sulphuric acid and / or ammonium sulphate, as disclosed by Sukla L.B, Panda S.C and Jena P.K, in an article entitled " Recovery of cobalt, nickel and copper from converter slag through roasting with ammonium sulphate and sulphuric acid'. Copper, cobalt and iron form respective sulphates during roasting, which are then leached in water. As a result, a solution containing low concentrations of copper, cobalt and iron is produced. Even though copper and cobalt are leached out into the solution or extracted, these metals are not recovered from the solution. The article does not disclose a novel method for recovering copper and cobalt from solution. It is proposed in the article that solvent extraction may be employed in upgrading copper and cobalt and that the metals can then be recovered by electro-winning. The downsides of this route are discussed below. Moreover, the amount of sulphuric acid used during roasting is very high, i.e. nearly 0.8 tonne sulphuric acid per tonne of slag.

Recovery of copper and cobalt from leach solution

Leaching is one of the key steps in the extraction of copper and cobalt from copper- cobalt materials. Leaching is the dissolution of the metal in an aqueous solution. In the copper-cobalt processing industry, the materials are leached with sulphuric acid and hence copper, cobalt and iron sulphates are formed. The copper and cobalt are commonly extracted from the leach solution via electro-winning and to a lesser extent, cementation.

Electro-winning process Electro-winning is a common method of recovering copper and cobalt from a solution. According to this method, copper or cobalt is electro-deposited onto a cathode. However, the method has two main disadvantages:

i. The process cannot be applied directly to dilute copper-cobalt leach solutions (i.e. less than 5 grams per litre). Leaching of low-grade copper-cobalt materials yields dilute copper-cobalt leach solutions, which then need to be upgraded via an additional step of solvent extraction. Solvent extraction requires special reagents and it is a hazardous process.

ii. The process is extremely slow as it has a cycle time of 2 - 7 days.

Copper cementation process

According to this method, an exchange reaction between copper ions, which are copper sulphate, and iron occurs as shown in equation (1 ) (below). It is clear from equation (1 ) that 0.88 tonne of iron is consumed per tonne of metallic copper produced. However, in practice the consumption of iron is actually higher, because excess sulphuric acid in the leach solution also dissolves part of the iron, as explained by equation (2). The overall consumption of iron during conventional cementation has been found to be more than two tonnes, per tonne of copper metal produced. Therefore, the high consumption of iron in the form of scrap is the main disadvantage of conventional cementation. As such, conventional cementation has found little use in the industry today.

CuS0₄ ( aq ) + Fe(s) = Cu(s) + FeS0₄ (1 ) H₂SO_A (aq) + Fe(s) = FeSO + H₂ ( g ) (2)

Moreover, conventional cementation of copper from a solution containing cobalt may create a serious problem. Iron concentration in the solution might increase, which would then require its removal prior to cobalt recovery. It is worth noting that iron must be removed before recovering cobalt from the solution. SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a process for recovering copper (Cu) from a copper containing source material sample, the process being characterised therein that recovery is achieved through electro-cementation, the process comprising the steps of - leaching the material sample in an acidic pH;

separating waste material solids through solid/liquid separation to recover a solution containing copper and iron (Fe); and

recovering copper from solution through electro-cementation such that copper is electro-cemented onto a mild steel plate anode and cathode, leaving a solution containing iron.

The material sample may be leached in water in order to solubilise metal sulphates / chlorides / nitrates while the pH of the solution may be adjusted according to iron content of the material sample by using ammonia hydroxide in order to reduce the presence of iron in solution.

Electro-cementation may be undertaken in the presence of a catalyst. In particular, about one millilitre (1 ml) of a catalyst may be added per 200 grams of the material sample. The catalyst may be the solution of sodium nitrate (NaN03), potassium hydroxide (KOH), hydrochloric acid (HCI), nitric acid (HNO3), hydrogen peroxide (H2O2) and/or oxalic acid (C2H2O4). The electro-cemented copper may be recovered as copper flakes, which may be filtered out of solution. The copper flakes may subsequently be dried and melted.

According to a second aspect of the invention there is provided a process for recovering copper (Cu) and cobalt (Co) from a copper-cobalt containing material sample, the process being characterised therein that recovery is achieved through electro-cementation, the process comprising the steps of - leaching the material sample in an acidic pH;

separating waste material solids through solid/liquid separation to recover a solution containing copper, cobalt and iron (Fe);

recovering copper from solution through electro-cementation such that copper is electro-cemented onto a mild steel plate anode and cathode, leaving a solution containing cobalt and iron;

recovering iron from the solution through precipitation as iron oxide; and recovering cobalt from the solution through precipitation.

The iron may be precipitated out of solution at a pH of less than 7. The iron precipitation may be undertaken either in a single stage or in two stages, the decision of which depending on the initial iron concentration in the solution. The iron may be precipitated by using ammonia ((NH3)2S04). Alternatively, or additionally, the iron may be precipitated by using calcium oxide (CaO) and/or sodium carbonate (Na₂C0₃). The cobalt in the solution may be precipitated as a sulphide by using sodium sulphide (Na2S), calcium oxide (CaO), sodium carbonate (Na2C03), and/or sodium isobutyl xanthate, or SIBX (C4HgNaOS2). The processes of the invention may include the additional steps of - first crushing and/or grinding the source material sample;

mixing the ground sample with sulphuric acid (H2SO4), hydrochloric acid (HCI), nitric acid (HNO3) or a mixture of any two or three thereof; and

then baking or roasting the ground sample in air to form metal sulphates, chlorides and/or nitrates.

The process may include the step of alternatively or additionally roasting the material sample with sodium hydrogen sulphate (NaHS04). The material sample may be roasted with sodium hydrogen sulphate at a temperature of between approximately 300 degrees Celcius and 700 degrees Celcius. By roasting the material sample with sodium hydrogen sulphate, the iron precipitation step may be bypassed. In particular, the material sample may be roasted with a mixture of sodium hydrogen sulphate and sulphuric acid so as to prevent iron from dissolving into solution during the leaching stage, and minimise sintering of the sample during roasting.

The process is adapted for treating low and high grades of copper-cobalt source material. The source material sample may be Cu-Co slag, Cu-Co low grade ores, Cu-Co high grade ores / concentrates, Cu-Co tailings and Cu ores. According to a third aspect of the invention there is provided a process for recovering copper from a copper containing material sample, the process comprising the steps of - crushing and/or grinding the material sample;

mixing the ground sample with sodium hydrogen sulphate (NaHS04);

roasting the ground sample in air to form metal sulphates;

leaching the material sample in an acidic pH;

separating waste material solids through solid/liquid separation to recover a solution containing copper and iron;

doing solvent extraction to increase the presence of copper in solution; and recovering the copper through electro-winning.

According to a fourth aspect of the invention there is provided a process for recovering copper and cobalt from a copper-cobalt containing material sample, the process comprising the steps of - crushing and/or grinding the material sample;

mixing the ground sample with sodium hydrogen sulphate;

roasting the ground sample in air to form metal sulphates;

leaching the material sample in an acidic pH;

doing solvent extraction to increase the presence of copper in solution;

recovering the copper through electro-winning; and

recovering the cobalt through electro-winning. SPECIFIC EMBODIMENT OF THE INVENTION

Without limiting the scope thereof, the invention will now further be discussed, illustrated and exemplified with reference to the accompanying drawings and photographs, in which:

FIGURE 1 is a simplified process flow sheet of the process according to a first aspect of the invention;

FIGURE 2 is a digital image, showing an arrangement of equipment used for electro-cementation;

FIGURE 3 is a digital image showing the presence of cemented copper flakes during electro-cementation;

FIGURE 4 is a digital image of melted copper;

FIGURE 5 is a digital image of a cobalt rich solution, after removal of iron; and

FIGURE 6 is a simplified process flow sheet for the treatment of copper ore.

A process for recovering copper and cobalt from slag, waste and ore is disclosed in Figure 1. Initially, ground slag, ore or tailings is mixed with sulphuric acid, hydrochloric acid or a mixture of the two. The mixture is baked or roasted in air to form metal sulphates and/or chlorides. The temperature is well-controlled such that maximum copper and cobalt sulphates and/or chlorides are formed. The main reactions that occur during baking with sulphuric acid are shown in equations 3 - 14:

CU0 + H₂S0₄ = CUS0₄ + H₂O (3) CoSi0₃ + H₂S0₄ = COS0₄ +Si0₂ + H₂0 (4) FeSiO ₃ + H₂SO ₄ = FeS0₄ + SiO ₂ + H₂0 (5)

CU₂S + H₂S0₄ + 2.50₂ = 2CUS0₄ + H₂0 (6)

CuO + 2HC1 = CuCl₂ + H₂0 (7)

CoSiO ₃ + 2HC1 = CoCl₂ + SiO ₂ + H₂0 (8) FeSiO ₃ + 2HC1 = FeCl₂ + SiO ₂ + H₂0 (9)

Cu ₂S + 2HC1 + 2.50₂ (g) = CuCl₂ + CuS0₄ + H₂0 (10)

CuO + 2HN0₃ = CU(N0₃ ) ₂ + H20 (1 1 )

CoSiO ₃ + 2HN0₃ = CO(N0₃ ) ₂ + SiO ₂ + H20 (12)

FeSiO ₃ + 2HN0₃ = Fe(N0₃ )₂ + SiO ₂ + H20 (13) Cu₂S + 2HN0₃ + 2.50₂ (g) = CU(N0₃ )₂ + CuS0₄ + H₂0 (14)

The material may alternatively or additionally be roasted with sodium hydrogen sulphate (NaHS04) and, or potassium hydrogen sulphate (KHSO4). Roasting with sodium hydrogen sulphate and/or potassium hydrogen sulphate occurs at a slightly higher temperature, i.e. 200 - 400 degrees Celcius higher than the temperature required to roast with sulphuric acid or hydrochloric acid. The main reactions occurring during roasting are shown in equations (15) - (20). The advantage of roasting with sodium hydrogen sulphate and, or potassium hydrogen sulphate is that it is less corrosive than sulphuric acid, hydrochloric acid and nitric acid. Furthermore, iron sulphate reacts with potassium and/or sodium sulphate to form a water insoluble double salt and hence the iron-removal step may be by-passed in the overall process. Sodium hydrogen and/or potassium hydrogen sulphates have never been used in sulphating any copper and/or cobalt material and is now reported for the first time herein.

CoSiO ₃ + 2NaHS0₄ = CoS0₄ + Na₂S0₄ +Si0₂ + H₂0 (15) FeSiO ₃ + 2NaHS0₄ = FeS0₄ + Na₂S0₄ + SiO ₂ + H₂0 (16)

Cu₂S + 2NaHS0₄ + 2.50₂(g) = 2CuS0₄ + Na₂S0₄ + H₂0 (17)

CoSiO ₃ + 2KHSO, = CoS0₄ + K₂S0₄ +Si0₂ + H₂0 (18)

FeSiO ₃ + 2KHS0₄ = FeS0₄ + K₂S0₄ + SiO ₂ + H₂0 (19)

Cu₂S + 2KHS0₄ + 2.50₂ (g) = 2CuS0₄ + K₂S0₄ + H₂0 (20)

The baked or roasted material is leached in water in order to solubilise the metal sulphates and/or chlorides. pH of the solution is adjusted by using ammonia hydroxide in order to keep less iron in solution. The leached sample is filtered off to remove calcium (Ca), aluminium (Al), iron (Fe) and silicon (Si) oxides as waste solid products, leaving a solution containing copper (Cu), cobalt (Co) and some iron (Fe). The concentration of copper is typically 0.5 - 4.0 grams per litre, whereas that of cobalt is typically 0.1 - 2.0 grams per litre.

It is important to note that copper from such solutions cannot be recovered directly by conventional electro-winning methods. In the present invention, copper is recovered first by means of electro-cementation. Electro-cementation has never been used in recovering copper and cobalt. A typical arrangement of an electro-cementation cell is shown in Figure 2, in which anode and cathode mild steel plates can be observed. The anode and cathode are created by insulating the contacts points. Copper is electro-cemented onto mild steel plates (anode and cathode). The process combines both principles of conventional cementation and electro-winning and hence the downsides of each of the process are overcome. About one (1 ) millilitre of a catalyst is added per 200 grams of the slag material. The catalyst may be sodium nitrate (NaN03), potassium hydroxide (KOH), hydrochloric acid (HCI), nitric acid (HNO3), hydrogen peroxide (H2O2) and/or oxalic acid (C2H2O4). The catalyst promotes the formation of larger flakes of cemented copper, which is necessary in the subsequent process of filtration.

The key benefits of electro-cementation over conventional electro-winning and cementation are outlined as follows:

i. The process completes within a short period of time (i.e. within 2 hours). ii. The process does not consume the mild steel plate, which is not the case in conventional cementation. As a result, the mild steel plate can be used and re-used for a very long period of time.

iii. The process does not increase the concentration of iron in solution, because iron does not dissolve during the process. Therefore, electro cementation is ideal for recovering copper from a copper-cobalt containing solution.

iv. The process is flexible for treating low and high grades copper-cobalt source material, such as Cu-Co slag, Cu-Co ores, Cu-Co tailings and Cu ores.

v. Sodium hydrogen sulphate and, or potassium hydrogen sulphate may be also used in sulphating slag. The use of sodium hydrogen sulphate and, or potassium hydrogen sulphate, eliminates the release of fumes, which is the case when sulphuric acid is used

vi. The sample may be roasted with a mixture of sulphuric acid and, sodium hydrogen sulphate and, or potassium hydrogen sulphate. Doing so, (i) prevents iron from dissolving into solution during the leaching stage, and (ii) minimises sintering of the sample during roasting.

The cemented copper comes out in the form of flakes as shown in Figure 3 and is filtered off. The cemented copper flakes may then be dried and melted at 1 150 degrees Celsius to form a copper anode as shown in Figure 4. The melting process is highly economic, since the material is pure copper (with less than 3 weight % impurities). The final concentration of copper in the solution is less than 0.05 grams per litre, thereby giving a recovery of more than 95%.

The solution after electro-cementation contains cobalt and iron. Iron is recovered from the solution via precipitation with lime at a pH of less than 7. Iron precipitation is done in either a single stage or in two stages, the decision of which depending on the initial iron concentration in solution. The cobalt in the solution is then precipitated as a sulphide by using sodium bisulphide.

Examples

Slag material was obtained from Nkana slag dump in Kitwe in the Copperbelt province of Zambia. The material sample was collected from fifty (50) different locations of the slag dump in order to have a better representation of the sample. The sample was then mixed thoroughly, and a representative portion was obtained and analysed via atomic absorption spectrometry (AAS) and scanning electron microscopy (SEM) techniques. Full elemental analysis of the sample is shown in Table 1 , from which it is clear that the sample contained 1.4 wt.% Cu and 0.9 wt.% Co. The main constituents in the sample were S1O2, Fe, CaO, MgO and AI2O3.

Scanning electron microscopy analysis revealed that cobalt was dissolved in the silicate matrix phase. It is worth noting that the dissolved copper and cobalt in the complex matrix cannot be recovered via flotation or leaching processes, which are otherwise the simplest metallurgical processes.

Table 1 - Analysis of the as-received Nkana slag sample (wt %) Example 1

The slag sample was crushed and ground to a particle size of less than 106 pm. A 200g batch of the ground sample was mixed with sulphuric acid, hydrochloric acid and water to form a paste. The paste was baked for between 0.5 - 2 hours at 70°C - 300°C in an open atmosphere.

The baked sample was leached in water for 10 - 120 minutes at room temperature. The metal sulphates and all chlorides (copper, cobalt and iron sulphates/chloride) dissolved during the leaching process. The leach residue was separated from the leach solution via filtration. A full analysis of the leach residue is shown in Table 2, from which it is evident that the residue had only 0.3 wt.% Cu and 0.02 wt.% Co. Considering the weight decrease of the sample during leaching and the results in Table 2, the recovery of copper and cobalt into the solution was 93% and 98%, respectively.

Table 2 - Analysis of leach residue (wt.%), the sample was baked and water leached

Copper was recovered from the solution by electro-cementation for a period of 1 .5 hours. The electro-cemented copper was dried at 50°C and then melted in a crucible for 30 minutes at 1 150°C. The melted copper was then cooled down to room temperature by atomic absorption spectrometer technique. The digital image is shown in Figure 4. The analysis of the melted copper is presented in Table 3, from which it is evident that high grade copper anode was produced.

Table 3 - Analysis of the copper anode which was produced by mel ing the electro cemented copper

The solution from the electro-cementation process had about 60 grams per litre (gpl) Fe and 2 gpl Co. The removal of iron from such a solution via conventional methods may take more than 10 hours. In the present invention, iron was removed within 5 hours at a pH of 4 - 5, by adding a mixture of ammonia and lime. The removal of iron is very essential as it may affect the grade of cobalt in the next process step. The final concentration of iron in the solution after precipitation was 0.2 gpl. The digital image for the solution after the removal of iron is shown in Figure 5 from which the pink colour can be observed, thereby concluding that cobalt sulphate is the main constituent. The precipitated iron was high grade, i.e. over 65 wt.% Fe and hence it can used as feed material for iron production.

The cobalt in the purified solution was precipitated to cobalt sulphide (CoS) by adding barium sulphate (BaS), sodium isobutyl xanthate (C4HgNaOS2), and sodium sulphide (Na2S) solution. Cobalt sulphate reacts to form cobalt sulphide. The precipitation of cobalt sulphide was extremely rapid, completed within 30 minutes.

Table 4 - Analysis in weight % of the precipitated cobal (cobalt concentrate)

Example 2

In another experiment, the experiment in Example 1 was repeated, but sulphuric acid was replaced with hydrochloric acid. The analysis of the leach residue is shown in Table 5, from which it can be observed that the iron content increased in the leach residue. In other words, less iron was dissolved into the leach solution. The concentration of iron in solution was only 9.5 grams per litre (gpl) and hence its removal from the solution only took about 3.5 hours. The experiment with hydrochloric acid was found to have three key advantages; (i) cementation of copper was 25% faster than for the experiment with sulphuric acid, (ii) there was less generation of fumes, and (iii) there was less sintering of the baked sample.

Table 5 - Analysis of leach residue (wt.%), the sample was baked and water leached

Example 3

In another experiment, ground slag sample at particle size of less than 106 microns was mixed with 30 weight % sodium hydrogen bisulphate and/or potassium hydrogen sulphate. The mixture was roasted in an open atmosphere for one hour at a temperature of less than 700 degrees Celcius. The roasted sample was leached in water for one hour at room temperature. The leach efficiency of copper was nearly 100% and the concentration of iron in solution was only 1.4 grams per litre (gpl). On the other hand, cobalt concentration was 0.8 gpl. Iron dissolution during the leaching step was minimal as a result of double salt formation with sodium sulphate and/or potassium sulphate. The cementation of copper was completed within 2 hours. The iron in the solution was removed within 1.5 hours since it was in the lower concentration. The precipitated cobalt concentrated had 26.9 weight % cobalt.

Example 4: Extraction of copper and cobalt from ores

In order to determine the flexibility of the present invention on this type of material, a copper-cobalt ore was used instead of the slag. The elemental analysis of the ore is shown in Table 6. Mineralogical analysis revealed that most of the copper was in the malachite form, whereas cobalt was in the form of magnesium silicate and heterogenite (CoO(OH)). Even though copper in the malachite form can easily be leached out, cobalt in the magnesium silicate and heterogenite cannot be leached out. 200 g of the ore sample was prepared as described in Example 1. The material was mixed with sulphuric acid and the experiment was carried out similar to Example 1. The leach residue was found to have 0.02% copper and 0.01 % cobalt, thereby giving recoveries of over 96%. Copper was electro-cemented in about 1.5 hours. The melted electro-cemented copper had a purity of about 99.7%.

As shown in Table 6, the sample had a lower iron content and hence the removal of iron from the solution occurred in only 2 hours. The precipitated cobalt had about 39.5% cobalt owing to the absence of nickel and manganese in the feed materials.

Table 6 - SEM-EDX analysis (wt.%) showing overall composition o the sample

Example 5: Extraction of copper and cobalt from slag flotation tailings

In order to further determine the flexibility of the present invention on the type of material, slag flotation tailings containing copper and cobalt were used. Slag flotation tailings are waste material obtained after processing slag via froth flotation. The slag flotation tailings had 0.7 weight % copper and 0.85 weight % cobalt. Nearly all the copper and cobalt in this material were in the complex iron silicate materials since free copper sulphide phases had been recovered by froth flotation. The material was already fine, with a particle size of 75% passing through a 75 microns sieve size.

The material was mixed with sulphuric acid, but at 30% less than in Example 1. This is because some of the copper in this material had already been recovered by froth flotation. The experiment was carried out according to Example 1 and nearly all copper and cobalt in the material were dissolved into the leach solution. Copper was electro-cemented from the solution. Iron was removed from the solution via precipitation over a period of 4 hours. The precipitated cobalt concentrate had 27.2 weight % cobalt.

Example 6 (Extraction of Copper from Low Grade Copper Oxide Ores)

The process was applied in treating Zambian copper ores (0.5 wt.% Cu) according to Figure 6. The copper in this material was contained in the malachite mineral. The material was ground to a particle size of 150 microns. The ground material was leached in sulphuric acid solution at a pH of less than 3 for one hour. Copper was recovered from the leach solution through an electro-cementation process over a period of 1.5 hours. The advantages of treating the low-grade copper oxide material via the present invention are that (i) the running costs are low, since the mild steel plate is not consumed as in the case of conventional cementation, and (ii) there is no need for an extra hazardous process of solvent extraction, which is the case when copper is recovered by electro-winning. Example 7: Extraction of copper and cobalt from copper-cobalt oxide material In another experiment, material from Zambia with 1.8% copper, 1.2% cobalt and 2.4% iron, was ground to a particle size of less than 106 microns. The material was leached out in sulphuric acid. A few drops of a catalyst were added into the leach solution and copper was recovered by electro-cementation. The leach solution, after recovering copper by cementation, had equal concentrations of cobalt and iron. As such, cobalt was precipitated without prior removal of iron. The cobalt concentrate had 21 weight % cobalt.

It will be appreciated that other embodiments of the invention are possible without departing from the spirit or scope of the invention as defined in the claims.

References · Jones, R.T., et al., Recovery of cobalt from slag in a DC arc furnace at

Chambishi, Zambia. Journal of The South African Institute of Mining and Metallurgy, 2002. 102 (Compendex): p. 5-9.

• Hara Y.R.S and Jha A, arbothermic Processing of Copper-Cobalt Mineral Sulphide Concentrates and Slag Waste for the Extraction of Metallic Values, Sustainability in the Mineral and Energy Sectors, Taylor and Francis,

(2016)

• Deng L. and Ling Y, Processing of copper converter slag for metal reclamation.

Part I: extraction and recovery of copper and cobalt, Waste Management and Research, 2007: 25: 440-448.

· Sukla L.B, Recovery of cobalt, nickel and copper from converter slag through roasting with ammonium sulphate and sulphuric acid, Hydrometallurgy, 16 (1986) 153-165

Claims

1. A process for recovering copper (Cu) from a copper containing source material sample, the process being characterised therein that recovery is achieved through electro-cementation, the process comprising the steps of - leaching the material sample in an acidic pH;

2. The process according to claim 1 wherein the material sample is leached in water in order to solubilise metal sulphates / chlorides / nitrates while the pH of the solution may be adjusted according to iron content of the material sample by using ammonia hydroxide in order to reduce the presence of iron in solution.

3. The process according to claim 1 wherein the electro-cementation is undertaken in the presence of a catalyst.

4. The process according to claim 3 wherein about one millilitre (1 ml) of a catalyst is added per 200 grams of the material sample.

5. The process according to claim 3 wherein the catalyst is a solution selected from the group consisting of sodium nitrate (NaN03), potassium hydroxide (KOH), hydrochloric acid (HCI), nitric acid (HNO3), hydrogen peroxide (H2O2) and/or oxalic acid (C2H2O4).

6. The process according to claim 1 wherein the electro-cemented copper is recovered as copper flakes, which is filtered out of solution and which may subsequently be dried and melted.

7. A process for recovering copper (Cu) and cobalt (Co) from a copper-cobalt containing material sample, the process being characterised therein that recovery is achieved through electro-cementation, the process comprising the steps of - leaching the material sample in an acidic pH;

recovering iron from the solution through precipitation as iron oxide; and

recovering cobalt from the solution through precipitation.

8. The process according to claim 7 wherein the iron is precipitated out of solution at a pH of less than 7.

9. The process according to claim 7 wherein the iron precipitation is undertaken either in a single stage or in two stages, the decision of which depending on the initial iron concentration in the solution.

10. The process according to claim 7 wherein the iron is precipitated by using ammonia ((NH3)2S04), calcium oxide (CaO) and/or sodium carbonate (Na₂C0₃).

1 1. The process according to claim 7 wherein the cobalt in the solution is precipitated as a sulphide by using sodium sulphide (Na2S), calcium oxide

(CaO), sodium carbonate (Na2C03) and/or sodium isobutyl xanthate, or SIBX (C4H₉NaOS₂).

12. The process according to either one of claims 1 or 7 wherein the process includes the additional steps of - first crushing and/or grinding the source material sample; mixing the ground sample with sulphuric acid (H2SO4), hydrochloric acid (HCI), nitric acid (HNO3) or a mixture of any two or three thereof; and

13. The process according to claim 12 wherein the process includes the step of alternatively or additionally roasting the material sample with sodium hydrogen sulphate (NaHS04).

14. The process according to claim 13 wherein the material sample is roasted with sodium hydrogen sulphate at a temperature of between approximately 300 degrees Celcius and 700 degrees Celcius.

15. The process according to claim 14 wherein the material sample is roasted with a mixture of sodium hydrogen sulphate and sulphuric acid so as to prevent iron from dissolving into solution during the leaching stage, minimising sintering of the sample during roasting, and optionally bypassing the iron precipitation step.

16. The process according to either one of claims 1 or 7 wherein the process is adapted for treating low and high grades of copper-cobalt source material and wherein the source material sample is Cu-Co slag, Cu-Co low grade ores, Cu- Co high grade ores / concentrates, Cu-Co tailings and Cu ores.

17. A process for recovering copper from a copper containing material sample, the process comprising the steps of - crushing and/or grinding the material sample;

mixing the ground sample with sodium hydrogen sulphate (NaHS04); roasting the ground sample in air to form metal sulphates; leaching the material sample in an acidic pH;

18. A process for recovering copper and cobalt from a copper-cobalt containing material sample, the process comprising the steps of - crushing and/or grinding the material sample;

mixing the ground sample with sodium hydrogen sulphate; roasting the ground sample in air to form metal sulphates; leaching the material sample in an acidic pH;

doing solvent extraction to increase the presence of copper in solution; recovering the copper through electro-winning; and

recovering the cobalt through electro-winning.