GB1560873A

GB1560873A - Nickel recovery

Info

Publication number: GB1560873A
Application number: GB6002/78A
Authority: GB
Original assignee: Tohoku University NUC
Current assignee: Tohoku University NUC
Priority date: 1977-03-01
Filing date: 1978-02-15
Publication date: 1980-02-13
Also published as: FR2382505A1; AU3334978A; DE2808263C2; JPS5536692B2; FR2382505B1; AU513480B2; JPS53106623A; CA1097927A; DE2808263A1; IN150307B; NL7802008A

Description

(54) NICKEL RECOVERY (71) I, The President of Tohoku University is a Japanese citizen of No. 1-1, Katahira 2-chome, Sendai-shi, Miyagi-ken, Japan 980, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of recovering nickel from a nickel-containing residue such as coal ash, and more particularly, to a method of recovering nickel selectively from a residue obtained after a carbonaceous material such as coal is gasified in the presence of a nickelcontaining catalyst.

It is well known that carbonaceous materials like coal are gasified, for example, to produce coal gas. According to conventional methods, carbonaceous materials or those pretreated with heat and/or various solvents are gasified at elevated temperatures in the absence of a catalyst using a gasifying agent such as hydrogen, steam, carbon dioxide and the like.

The present inventors have previously proposed an improvement in such gasification, which is disclosed in Patent Specification No. 1,496,410. Carbonaceous materials are gasified by pretreating them with liquid ammonia at room temperature to 1500C to extract the matters soluble in ammonia and treating the extraction residue with a gasifying agent at a temperature of 400 to 1,0000C at atmospheric pressure or under pressure in the presence or absence of a catalyst.

Nickel-containing catalysts are useful in the above gasification. Nickel catalysts should be present in an amount which is effective for catalytically promoting the gasification of carbonaceous materials.

Upon gasification, the nickel used is discharged partly with the gas produced and partly with residues such as coke and ash.

Loss of nickel is detrimental because nickel is so expensive. In order to carry out such catalytic gasification methods commercially advantageously and successfully, it is important to recover expensive nickel efficiently in a more simple manner and to regenerate it for reuse. However, no method has yet succeeded in the efficient separation or recovery of nickel because nickel is contained in minor amounts and relatively large amounts of impurities coexist.

The present inventors have made intensive and extensive investigations on the recovery of nickel; and have found that nickel can be selectively extracted or separated in the form of an aqueous nickel amine solution from a nickel-containing residue obtained after gasification and that, although the solubility of nickel ammine in water is considerably high at about room temperature, it rapidly decreases to a substantially insoluble level as the concentration of free ammonia increases.

The concentration of free ammonia can be increased simply by adding ammonia to the solution. The term "free ammonia" used herein designates an excess amount of ammonia which exceeds 6 molar equivalents per mole of nickel in the residue.

According to the present invention there is provided a method of recovering nickel from a nickel-containing residue such as coal ash remaining after a carbonaceous material is gasified in the presence of a nickel-containing catalyst, which comprises the steps of: (a) adding an aqueous ammonia solution or aqueous solution containing ammonia and an ammonium salt to the nickelcontaining residue in the presence of oxygen and/or air to dissolve the nickel in the solution in the form of a nickel ammine complex salt: (b) separating the aqueous nickel ammine solution from insoluble contents; (c) further adding ammonia to the separated aqueous nickel ammine solution to increase the concentration of free ammonia to a value high enough to precipitate the nickel ammine; and (d) separating the nickel ammine precipitate from the solution.

The separated nickel ammine may be converted into nickel oxide or nickel salts or into any desired form ready for reuse in a circulating manner, for example, metallic nickel. Such conversion is generally performed by heating.

The term "nickel ammine" designates a nickel ammine complex salt in this specification.

A preferred embodiment of the invention includes the following additional steps: (e) heating the separated nickel ammine to decompose it into nickel oxide or a nickel salt and ammonia; and (f) circulating the saturated nickel ammine solution resulting from the separation step (d) to step (a) and the ammonia resulting from the decomposition step (e) to step (c) for the reuse thereof.

The carbonaceous materials used herein include brown coal, lignite, bituminous coal, tar pitch, coke and their analogues.

After they are gasified with a gasifying agent in the presence of a nickel-containing catalyst, there remains a residue which contains the catalyst as well as ash. The nickel in the residue, which may vary depending upon the type of the gasifying agent, temperature and other reaction conditions, is generally present in the form of metallic nickel or nickel sulfide because it is subject to a reducing atmosphere.

The nickel which is metallic in the residue may be dissolved in the form of a nickel ammine by adding an aqueous ammonia solution or an aqueous solution containing ammonia and an ammonium salt to the nickel-containing residue in the presence of oxygen and/or air. Illustrative of the dissolution process are the following reaction equations. When ammonium chloride is used as the ammonium salt, nickel is dissolved in the form of nickel ammine chloride. Similarly, when ammonium carbonate, sulfate, and nitrate are used, nickel is dissolved in the form of nickel ammine carbonate, sulfate, and nitrate, respectively.

Ni+2NH4C1+4NH3+, 2= Ni(NH3)6C12+ H2O Ni+(NH4)2CO3+4NH3±02= Ni(NH3)6CO3+H2O & (NH4)2S 4+4NH3+ v 2= Ni(NH,),SO,+H,O Ni+2NH4NO3+4NH3++02= Ni(NH3)6(NO3)2+H2O The ammonium salts added dissociate into anions which can form nickel ammine salts as complex salts. Therefore, other ammonium salts which dissociate into anions capable of forming complex salts may also be employed to gain a similar effect.

It is only required to recover nickel in the form of a nickel ammine complex salt according to the invention. The ammonium salt need not be added when nickel ispresent as nickel sulfide in the residue.

Nickel sulfide reacts with ammonia as follows.

NiS+6NH3+202=Ni(NHa)6SO4 In this case, an aqueous ammonia solution is added to a nickel-containing residue.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which: Fig. I is a graph showing solubility curves of nickel ammine chloride at different temperatures, the concentration ( t by weight) of free ammonia in the saturated nickel ammine chloride solution being plotted as abscissa and the solubility (g/100 g-saturated solution) as ordinate; Fig. 2 is a graph similar to Fig. 1, showing solubility curves of nickel ammine carbonate; Fig. 3 is a graph similar to Fig. 1, showing solubility curves of nickel ammine sulfate; Fig. 4 is a graph similar to Fig. 1, showing solubility curves of nickel ammine nitrate; Fig. 5 is a block diagram showing an embodiment of the invention in which nickel is recovered as nickel chloride; and Fig. 6 is a block diagram showing another embodiment of the invention in which nickel is recovered as nickel carbonate.

As clearly shown in Figs. 1 to 4, the nickel ammine complex salts are highly soluble at room temperature. When free ammonia has a concentration of 0 to 3 ' by weight, both nickel ammine chloride and nitrate have solubilities of about 20 to 25 g per 100 g of the saturated solution and both nickel ammine carbonate and sulfate have higher solubilities of about 40 to 50 g per 100 g of the saturated solution at a temperature of 55"C.

Although the nickel ammine complex salts are highly soluble at comparatively lower concentrations of free ammonia, the solubility rapidly decreases and eventually reaches near zero as the concentration of free ammonia increases.

The present process utilizes this difference in solubility. The nickel ammine can effectively be precipitated by increasing the concentration of free ammonia from a low level at which the solubility is high to a high level at which the solubility is low. In addition, the temperature may be lowered to precipitate nickel ammine more effectively.

The type of the ammonium salt to be added, the concentration of free ammonia.

the temperature of the solution, the partial pressure of oxygen and other conditions may be adjusted to any desired values.

depending upon the content and chemical state of nickel in the residue.

In step (a), nickel is dissolved and extracted in the form of a nickel ammine complex salt from the residue. To this end, the concentration of free ammonia may generally be 0 to 18.0 /" by weight, preferably 3.5 to 150 by weight to maintain the solubility of a nickel ammine high enough. Although lower concentrations of free ammonia are advantageous in view of solubility as described above in connection with Figs. 1--4, it takes a comparatively long time for nickel to react with an ammonium salt at a concentration of free ammonia below 3.5 /n by weight. Therefore, the above range is preferred from the point of view of commerical dissolution and extraction efficiency.Further, a larger partial pressure of oxygen is advantageous as understood from the reaction equations set forth above. The partial pressure of oxygen may generally be 1 to 50 atm, preferably 2 to 10 atm, in consideration of design and maintenance of equipment including a reactor. The temperature of the solution may generally be 10 to 1500C, preferably 30 to 1200C.

According to the invention, after a nickel containing residue is mixed with an aqueous ammonia solution to dissolve and extract the nickel in the solution, the resulting aqueous nickel ammine solution and the insoluble contents consisting of ash and other impurities are separated from each other, for example, by filtration. Thereafter the nickel ammine is precipitated from its solution by adding ammonia to the separated aqueous solution to increase the concentration of free ammonia. At the same time, the temperature of the separated aqueous solution may preferably be lowered to facilitate precipitation.

When crystals are precipitated from the aqueous nickel ammine solution in step (c), it is preferred to maintain the temperature of the solution to below 25"C, especially below 15"C and the concentration of free ammonia to 15 to 300/, by weight, as understood from Figs. 1 to 4. In order that those skilled in the art may better understand how to practice the present invention, the following examples are given by way of illustration.

EXAMPLE PLE Into an autoclave were admitted 88.8 g of a residue containing 16.9",, by weight of nickel which was obtained after coal was gasified in the presence of a nickel chloride catalyst to produce coal gas mainlv consisting of hydrogen. and 200 ml of an ammoniacal. aqueous ammonium carbonate solution containing 1.5 moles/liter of ammonium carbonate solution containing 1.5 moles/liter of ammonium carbonate and 8.0 moledliter of free ammonia and having a specific gravity of 1.01. The mixture was allowed to react for 60 minutes at a temperature of 50"C. an oxygen partial pressure of 4 atm. and an agitation rate of 2,000 r.p.m. It was found that 98 , of nickel was dissolved in the form of nickel ammine carbonate.

The insoluble contents were then removed by filtration. With cooling in an ice bath, ammonia gas was bubbled into the filtrate until the concentration of free ammonia reached 35 ,, by weight. There was precipitated 75.8 g of crystals. Analysis was carried out to determine the composition. It was found that 97.0", of nickel was recovered. The results are shown below.

Ni (when) NH3 (wt0',) Found 18.8 32.4 Calculated for Ni(NH3)6.5H2O 18.9 32.8 EXAMPLE 2 Into an autoclave were admitted 87.2 g of a residue containing 17.2% by weight of nickel which was obtained after coal was gasified in the presence of a nickel chloride catalyst to produce coal gas mainly consisting of steam, and 200 ml of an ammoniacal, aqueous ammonium sulfate solution which contained 1.5 moles/liter of ammonium sulfate and 8.0 moles/liter of free ammonia and had a specific gravity of 1.04. The mixture was allowed to react for 75 minutes at a temperature of 50"C. an oxygen partial pressure of 4 atm. and an agitation rate of 2,000 r.p.m.It was found that 96.5", of nickel was dissolved in the form of nickel ammine sulfate.

The insoluble contents were then removed by filtration. With cooling in an ice bath, ammonia gas was bubbled into the filtrate until the concentration of free ammonia reached 35/n by weight. There was precipitated 66.4 g of crystals. Analysis was carried out to determine the composition. It was found that 98*5 ó of nickel was recovered. The results are shown below.

Ni (wit%) NH3 (wit0,0) Found 21.5 38.2 Calculated for Ni(NH3)6 22.1 38.4 SO4.+H2O Reference is again made to the drawings.

Fig. 5 shows a preferred embodiment, in which the starting material is a nickelcontaining residue which is obtained after coal is gasified in the presence of a nickel chloride catalyst. In a reactor 10 for gasifying coal are supplied a carbonaceous material (in this example, coal), a nickel chloride catalyst, and a gasifying agent through lines 1, 2, and 3, respectively. The gasification is carried out in the reactor maintained under predetermined conditions. A useful gas mixture containing hydrogen, methane and the like is generated, while a nickel-containing residue including ash remains. The useful gas mixture is taken out from the reactor 10 to a washing unit 11 by way of a line 5. Into the washing unit 11 is also introduced a washing liquid, for example, water or an aqueous, diluted hydrochloric acid solution through a line 7.The washing liquid serves to remove hydrochloric acid from the gas, which is then taken out through a line 6. The removed hydrochloric acid is fed to a unit 12 for forming ammonium chloride through a line 8. Ammonia fed through a line 9a is added to hydrochloric acid in the unit 12 to form ammonium chloride, which, in turn, is fed through a line 9b to an extractor 20 for dissolving and extracting nickel in the form of nickel ammine. The washing unit 11 and the ammonium chloride-forming unit 12 may be combined to perform both the removal of hydrochloric acid and the formation of ammonium chloride.

The catalyst may sometimes be activated before it is used in gasification. In this case, ammonia or hydrogen chloride gas is discharged together with an activating gas.

By feeding the gas mixture to the washing unit 11, ammonium chloride may be recovered. Alternatively, an activation apparatus may separately be installed in addition to the gasifying reactor 10 in order to carry out the activation of the catalyst.

On the other hand, the residue in the gasifying reactor 10 is introduced into the extractor 20 through a line 4. Into the extractor 20 are also introduced ammonia, oxygen and/or air, and water through lines 21, 22, and 23, respectively. In addition, the aqueous ammonium chloride solution is fed to the extractor 20 through the line 9b, as described above. With temperature, oxygen partial pressure and other conditions set to predetermined levels, nickel in the residue is dissolved and extracted in the form of nickel ammine chloride. The mixture may preferably be stirred to facilitate dissolution. This dissolution and extraction process may be carried out in any desired manner, for example, by a batchwise or continuous, parallel current or counter current operation. The operation may be chosen according to the amount of the residue to be treated and the nickel content.

After the dissolution and extraction process is completed, the treated mixture is transferred to a separator 30 through a line 24. The insoluble contents including ash are separated therein and discharged through a line 32, while the aqueous nickel ammine chloride solution is fed to a precipitator 40 through a line 31. Ammonia fed through a branch line 66 is added to the solution to increase the concentration of free ammonia in the solution, precipitating nickel ammine chloride. The temperature of the solution may optionally be reduced in the precipitator 40.

The precipitate is transferred together with the solution to a separator 50 through a line 41. In the separator 50, the precipitate is separated from the solution, which is then fed to a first recovery apparatus 51 through a line 54. Ammonia gas is liberated from the solution due to temperature rise or pressure reduction and then combined with another ammonia gas flow from a second recovery apparatus 61 to be described hereinafter.

The combined ammonia gas is circulated through lines 55 and 65 for reuse. The remaining solution in the first recovery apparatus 51, which contains a small amount of nickel ammine chloride, is returned to the precipitator 40 or extractor 20 through the line 56 or 57 for reuse. If the amount of impurities accumulated in the solution becomes larger due to repeated use, such a contaminated solution is discharged through a line 53 and a fresh solution is supplied.

The separated precipitate of nickel ammine chloride is introduced into a heater 60 for decomposing the complex salt through a line 52, in which nickel ammine chloride is decomposed into nickel chloride and ammonia by heating. The separated nickel chloride is, if necessary, circulated to the gasifying reactor 10 through a line 63 for reuse as the catalyst, while the ammonia is fed to the second recovery apparatus 61 through a line 62 and dried therein. If desired, the dried ammonia gas is circulated to the ammonium chloride-forming unit 12 and the precipitator 40 through the lines 65, 66 and 9a for reuse. The waste water resulting from the above drying procedure may optionally be discharged through a line 64.

The above-described system may be designed so that when any of reagents, for example, ammonium chloride or ammonia deviates from the range ensuring a suitable relative proportion, such a deviation may immediately be compensated.

The embodiment employing nickel chloride as the catalyst is illustratively described above, whereas the invention can be applied in a similar manner to the cases employing nickel salts such as nickel sulfate, nitrate and carbonate, metallic nickel and nickel oxide as the catalyst. It is to be noted that when metallic nickel or nickel oxide is used as the catalyst, the nickel salt resulting from decomposition by heating in the heater 60 may further be treated by conventional methods before it is circulated.

Another preferred embodiment is shown in Fig. 6, in which nickel in the residue is recovered as nickel carbonate. Referring to Fig. 6, the residue is introduced in an extractor 20 for dissolving nickel through an inlet line 75. To this extractor 20 is also fed water through a line 74. Oxygen or air, carbon dioxide, and ammonia fed through lines 71, 72, and 73, respectively, are blown into the water. With stirring, nickel in the residue is dissolved and extracted in the form of nickel ammine carbonate. The treated mixture is fed to a separator 30 through a line 76. The insoluble contents including ash are separated therein and discharged through a line 77, while the separated solution of nickel ammine carbonate is fed to a precipitator 40 through a line 78.Ammonia fed through a branch line 87 is added to the solution to increase the concentration of free ammonia in the solution, precipitating nickel ammine carbonate I he precipitate is transferred together with the solution to a separator 50 through a line 79. In the separator 50, the precipitate is separated from the solution, which is then fed to a recovery apparatus 82 through a line 80. The solution is subject to elevated temperature or reduced pressure to recover ammonia and the remaining waste liquid is discharged from a line 83. The above recovered ammonia is combined with another ammonia flow from a heater 60 to be described hereinafter. The combined ammonia gas is circulated to the extractor 20 and the precipitator 40 for reuse.

The separated precipitate of nickel ammine carbonate is introduced into the heater 60 through a line 81, in which nickel ammine carbonate is decomposed into nickel carbonate or nickel oxide and ammonia by heating. The generated ammonia is fed to the extractor 20 and the precipitator 30 through lines 85, 87, and 73 for reuse. The resulting nickel carbonate or nickel oxide is taken out through a line 86 and then may either be circulated to the gasifying reactor or be stored in a suitable reservoir (not shown).

As described above, nickel can be effectively recovered from a residue resulting from the gasification of carbonaceous materials using nickelcontaining catalysts.

In the present invention, modification and variation may be made depending upon the type of a nickel compound used as the catalyst. For example, when nickel ammine is used as the catalyst, the nickel ammine crystals separated after precipitation may be readily circulated for reuse without further processing.

Moreover. if nickel in the residue takes a form other than metallic nickel or nickel sulfide, it should be converted into metallic nickel or nickel sulfide before the invention is applied thereto.

Since nickel is fixed and recovered in the form of a nickel ammine salt according to the invention, useful reagents, for example, ammonia can easily be circulated for reuse.

As a result, nickel is economically recovered and environmental pollution is minimized.

WHAT WE CLAIM IS: 1. A method of recovering nickel from nickel-containing residue obtained after a carbonaceous material is gasified in the presence of a nickel-containing catalyst.

which comprises the steps of: (a) adding an aqueous ammonia solution or an aqueous solution containing ammonia and an ammonium salt to said nickelcontaining residue in the presence of oxygen and/or air to dissolve and extract the nickel in the solution in the form of a nickel ammine complex salt; (b) separating the mixture into an aqueous nickel ammine solution and insoluble contents; (c) further adding ammonia to the separated aqueous nickel ammine solution to increase the concentration of free ammonia to a value high enough to precipitate the nickel ammine, and (d) separating the nickel ammine precipitate.

2. A method as claimed in claim 1 which further comprises a step (e) of converting the separated nickel ammine into nickel oxide, a nickel salt or metallic nickel.

3. A method as claimed in claim I or 2 wherein said carbonaceous material from which said nickel-containing residue is obtained is selected from brown coal, lignite, bituminous coal, tar pitch, coke and their analogues.

4. A method as claimed in claim 1, 2 or 3 wherein an aqueous solution containing ammonia and an ammonium salt is added to said nickel-containing residue in step (a) when the nickel is present in a metallic form.

5. A method as claimed in claim 4 wherein said ammonium salt is selected from ammonium chloride, ammonium carbonate, ammonium sulfate and ammonium nitrate.

6. A method as claimed in claim 1, 2 or 3

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. be applied in a similar manner to the cases employing nickel salts such as nickel sulfate, nitrate and carbonate, metallic nickel and nickel oxide as the catalyst. It is to be noted that when metallic nickel or nickel oxide is used as the catalyst, the nickel salt resulting from decomposition by heating in the heater 60 may further be treated by conventional methods before it is circulated. Another preferred embodiment is shown in Fig. 6, in which nickel in the residue is recovered as nickel carbonate. Referring to Fig. 6, the residue is introduced in an extractor 20 for dissolving nickel through an inlet line 75. To this extractor 20 is also fed water through a line 74. Oxygen or air, carbon dioxide, and ammonia fed through lines 71, 72, and 73, respectively, are blown into the water. With stirring, nickel in the residue is dissolved and extracted in the form of nickel ammine carbonate. The treated mixture is fed to a separator 30 through a line 76. The insoluble contents including ash are separated therein and discharged through a line 77, while the separated solution of nickel ammine carbonate is fed to a precipitator 40 through a line 78.Ammonia fed through a branch line 87 is added to the solution to increase the concentration of free ammonia in the solution, precipitating nickel ammine carbonate I he precipitate is transferred together with the solution to a separator 50 through a line 79. In the separator 50, the precipitate is separated from the solution, which is then fed to a recovery apparatus 82 through a line 80. The solution is subject to elevated temperature or reduced pressure to recover ammonia and the remaining waste liquid is discharged from a line 83. The above recovered ammonia is combined with another ammonia flow from a heater 60 to be described hereinafter. The combined ammonia gas is circulated to the extractor 20 and the precipitator 40 for reuse. The separated precipitate of nickel ammine carbonate is introduced into the heater 60 through a line 81, in which nickel ammine carbonate is decomposed into nickel carbonate or nickel oxide and ammonia by heating. The generated ammonia is fed to the extractor 20 and the precipitator 30 through lines 85, 87, and 73 for reuse. The resulting nickel carbonate or nickel oxide is taken out through a line 86 and then may either be circulated to the gasifying reactor or be stored in a suitable reservoir (not shown). As described above, nickel can be effectively recovered from a residue resulting from the gasification of carbonaceous materials using nickelcontaining catalysts. In the present invention, modification and variation may be made depending upon the type of a nickel compound used as the catalyst. For example, when nickel ammine is used as the catalyst, the nickel ammine crystals separated after precipitation may be readily circulated for reuse without further processing. Moreover. if nickel in the residue takes a form other than metallic nickel or nickel sulfide, it should be converted into metallic nickel or nickel sulfide before the invention is applied thereto. Since nickel is fixed and recovered in the form of a nickel ammine salt according to the invention, useful reagents, for example, ammonia can easily be circulated for reuse. As a result, nickel is economically recovered and environmental pollution is minimized. WHAT WE CLAIM IS:

1. A method of recovering nickel from nickel-containing residue obtained after a carbonaceous material is gasified in the presence of a nickel-containing catalyst.

6. A method as claimed in claim 1, 2 or 3

wherein an aqueous ammonia solution is added to said nickel-containing residue in step (a) when the nickel is present in the form of nickel sulfide.

7. A method as claimed in any one of claims I to 6 wherein the concentration of free ammonia in the solution is in the range of 0 to 18.0 ' by weight in step (a).

8. A method as claimed in claim 7 wherein the concentration of free ammonia is in the range of 3.5 to 15.0% by weight.

9. A method as claimed in any one of claims 1 to 8 wherein the partial pressure of oxygen is in the range of 1 to 50 atm. in step (a).

10. A method as claimed in claim 9 wherein the partial pressure of oxygen is in the range of 2 to 10 atm.

11. A method as claimed in any one of claims I to 10 wherein the temperature of the solution is in the range of 10 to 1500C in step (a).

12. A method as claimed in claim 11 wherein the temperature of the solution is in the range of 30 to 1200C.

13. A method as claimed in any one of claims 1 to 12 wherein the concentration of free ammonia in the solution is in the range of 15 to 30% by weight in step (c).

14. A method as claimed in any one of claims 1 to 13 wherein the temperature of the solution is lowered to promote precipitation in step (c).

15. A method as claimed in claim 14 wherein the temperature of the solution is lowered to below 25"C.

16. A method as claimed in claim 14 wherein the temperature of the solution is lowered to below 15 C.

17. A method as claimed any one of claims 2 to 16 which further comprises a step (e) of heating the separated nickel ammine to decompose it into nickel oxide or a nickel salt and ammonia, and a step (f) of circulating the saturated nickel ammine solution remaining after the separating step (d) to step (a) and the ammonia resulting from the decomposition step (e) to step (c).

18. A method of recovering nickel from a nickel containing residue obtained after a carbonaceous material is gasified in the presence of a nickel containing catalyst substantially as described in Example 1 or Example 2, or with reference to Figure 5 or Figure 6 of the accompanying drawings.

19. Nickel or a nickel compound recovered by a method according to any one of claims 1 to 18.