GB2498955A

GB2498955A - Nickel recovery

Info

Publication number: GB2498955A
Application number: GB1201637.4A
Authority: GB
Inventors: Paul Fitzpatrick
Original assignee: C Tech Innovation Ltd
Current assignee: C Tech Innovation Ltd
Priority date: 2012-01-31
Filing date: 2012-01-31
Publication date: 2013-08-07
Anticipated expiration: 2032-01-31
Also published as: GB201201637D0; GB2498955B; WO2013114089A1

Abstract

with R1 and R2 being the same or different and selected from an akyl group and an aromatic group and may together form a cyclic compound. The complexing agent can be dimethylglyoximine. The ionic liquid can be betanium bis(trifluoromethylsulphonyl) imide or trifluoromethylsulphonylmethyl imide. The nickel waste can be a filter cake or a nickel-cadmium battery.

Description

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Nickel Recovery

The invention relates to a method of recovering nickel from a nickel-containing waste.

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Nickel-containing waste is generated in industries such as metal finishing, coin production, battery production, coatings production and aerospace manufacturing. Heavy metal pollutants created by these industries are primarily removed via precipitation as an insoluble hydroxide sludge, which is then 10 normally subject to de-watering to generate a filter cake of typically 30% solids content. This filter cake is then destined for off-site disposal and ultimately to landfill. Nickel-containing batteries are currently not recycled in the UK. Selective extraction of the valuable nickel contents of these wastes in high purity form would have economic advantages, as well as enhancing the value of other 15 recovered metals and, in the case of cadmium-containing waste such as end of life nickel-cadmium batteries, enabling the safe handling of toxic cadmium.

The only existing commercially viable approach to nickel recovery is thermal recovery of low value mixed metal products. This is effectively the only current

2 0 alternative to landfill and is approximately cost neutral versus landfill in the instance of nickel as a waste. This process has limitations in that the treatment is not in-situ, is restricted to low additional metal (e.g. zinc) content and is not carried out locally but in large centralised smelting operations requiring substantial international transport of the input material.

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Other existing metal treatment processes are mostly limited to corrosive chemical treatments and, in the extreme, incineration systems. These are only partially effective, require maintenance, create secondary disposal problems, and can be capital intensive. For example, electro dialysis is selective for nickel but is very

3 0 energy intensive. Acid leaching followed by electrowinning is a well developed technique for scale up but has a poor environmental impact due to high energy demands and high levels of toxic chemicals. A combination of an ion exchange

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resin with an acid sorption resin has been used to recover nickel, which requires reduced quantities of chemical reagents. However, such a technique requires the use of strong acids. The use of pH selective precipitation provides a simple means for recovery nickel but is not very chemically specific.

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There is a need to provide an alternative and sustainable approach in the face of increasingly stringent legislative and toxic handling demands. In particular, there is a need to provide an alternative method of recovery nickel which does not rely on the use of large volumes of strong acids.

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The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.

15 The invention provides a method for recovering nickel from a nickel-containing waste, the method comprising:

(1) contacting the nickel-containing waste with a solvent to dissolve nickel from the nickel-containing waste;

(2) contacting the dissolved nickel with a glyoxime-based complexing

2 0 agent to form a nickel complex;

(3) contacting the nickel complex with an ionic liquid to extract nickel from the nickel complex to form a nickel-containing ionic liquid; and

(4) recovering nickel from the nickel-containing ionic liquid.

2 5 The present inventors have discovered that such a method is capable of recovering nickel selectively and in high purity without the need to use harmful, toxic chemicals, such as strong acids, which are hard to dispose of. Without wishing to be bound by theory, it is understood that the ionic liquid cracks the hydrogen bonds of the nickel complex, resulting in a solution of Ni2+ ions in the

30 ionic liquid.

Further advantages of the method are as follows:

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• it does not require the use of a nickel recovery agent, meaning that the method is less time-consuming, less complex and less expensive;

• the solvent and ionic liquid can be re-used, eliminating the problem of 5 disposal;

• since ionic liquids have very low vapour pressures, they produce virtually no hazardous vapours;

• it can be applied to many mixed metal wastes of transition metals; and

• unlike most current method of nickel recovery, it does not rely on very 10 precise temperatures and pH to achieve high performance.

Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular any feature indicated as being preferred or advantageous may be combined with 15 any other feature or features indicated as being preferred or advantageous.

Definitions:

The term "ionic liquid" as used herein refers may encompass a salt which melts 2 0 below 100 9C and which, in its molten form, is composed solely of ions. Ionic liquids are sometimes referred to as "molten salts".

The term "task specific ionic liquid" (TSIL) as used herein may encompass an ionic liquid in which the ions not only serve as components of a solvent but also 2 5 manifest specific types of interactions with dissolved substrates.

The term "deep eutectic solvent" as used herein may encompass an ionic solvent composed of a mixture which forms a eutectic with a melting point lower than either of the individual components.

The term "choline chloride" as used herein may encompass 2-hydroxyethyl-trimethylammonium chloride.

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The term "dimethylglyoxime" as used herein may encompass to 2,3-butanedione dioxime.

5 The term "electrowinning" as used herein may encompass the electrodeposition of metals that have been put in solution. Electrowinning is also known as "electroextraction".

Preferably the solvent comprises a choline-chloride-based deep eutectic solvent. 10 Such solvents are particularly effective at dissolving nickel from the nickel-

containing waste. Alternatively the solvent may comprise an aqueous solvent or a non-choline-chloride-based deep eutectic solvent.

Preferably the choline-chloride-based deep eutectic solvent comprises one or 15 more of ethanoic acid, urea and lactic acid. Lactic acid is particularly preferred. Such solvents are particularly effective at dissolving nickel from the nickel-containing waste. In addition, such solvents are cheap, widely available and easy to handle/dispose of. Examples of such solvents include a mixture of choline chloride and urea in 1:2 ratio and a mixture of choline chloride and lactic acid in a 2 0 1:1 ratio. Such solvents are typically prepared by mixing the components in the desired ratio and, if required, heating the resultant mixture to cause melting thereof.

Preferably the choline-chloride-based solvent comprises tartaric acid. The 2 5 presence of tartaric acid suppresses chromium dissolution, so is particularly effective for use on nickel-containing wastes with high levels of chromium. Preferably the solvent comprises up to 20 %w/w tartaric acid, more preferably up to 10 % w/w, even more preferably from 2 to 8 %w/w, still even more preferably about 5 % w/w.

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Preferably the choline-chloride-based solvent comprises citric acid. The presence of citric acid suppresses iron dissolution, so is particularly effective for use on

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nickel-containing wastes with high levels of iron. Preferably the solvent comprises up to 20 %w/w citric acid, more preferably up to 10 % w/w, even more preferably from 2 to 8 %w/w, still even more preferably about 5 % w/w.

5 Preferably the glyoxime-based complexing agent is according to the following formula:

R1

R2

10 wherein R1 and R2, which may be the same or different, are selected from an alkyl group and an aromatic group, and wherein R1 and R2 may together form a cyclic compound. More preferably the the glyoxime-based complexing agent is dimethylglyoxime. Such complexing agents are particularly selective for nickel. The complexing agent may be in the form of an alcohol solution, such as an 15 ethanol solution. Alternatively, the complexing agent may be in the form of a sodium salt in aqueous solution.

Preferably during step (1) at least one of the following is true: (a) the temperature is from 60 to 90 QC; and (b) the pH is less than 7. These conditions aid the 2 0 dissolution of nickel.

After step (1) the nickel-depleted waste may be removed from the solvent, for example by filtration.

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Preferably during step (2) the pH is from 4 to 6, more preferably about 5. This aids complex formation of dissolved nickel with the glyoxime-based complexing agent.

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Preferably between steps (2) and (3) the pH is greater than 7, and/or the temperature is from 10 to 40 QC. This aids precipitation of the nickel complex so that it can be more easily recovered, for example by filtration, and contacted with the ionic liquid.

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The nickel-containing waste may be a filter cake or battery, such as a nickel-metal hydride battery or nickel-cadmium battery. Such wastes contain high levels of nickel and are generated in large volumes. In addition, there are currently no commercially viable methods of recovering nickel from such wastes. Where the 10 waste material comprises cadmium, for example a nickel-cadmium battery, the method may further comprise a post-treatment unit, such as a filter, to remove the cadmium.

Preferably step (3) comprises extracting the nickel complex from the solvent, 15 more preferably by filtration. This makes it easier to contact the nickel complex with the ionic liquid. In addition, the solvent may then be re-used.

Preferably the ionic liquid is a task specific ionic liquid. Task specific ionic liquids are particularly effective at extracting nickel from the nickel complex. More 2 0 preferably, the ionic liquid is selected from betanium bis(trifluoromethylsulphonyl) imide and trifluorosulphonylmethyl imide. Such ionic liquids are particularly effective at extracting nickel from the nickel complex. Without being bound by theory, it is considered that these liquids crack the hydrogen bonds of the nickel complex releasing the nickel into the ionic liquid as Ni2+ into the ionic liquid. In

2 5 addition, these ionic liquids are able to phase separate from choline-chloride-

based deep eutectic solvents at reasonably high temperatures, typically at about 5 QC. Other task-specific ionic liquids only have one or other of these advantages.

Preferably the step of contacting the nickel complex with an ionic liquid is carried

3 0 out at a temperature of from 40 to 50 QC. Such a temperature range aids cracking of the nickel complex.

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Preferably the method further comprises contacting the nickel-containing ionic liquid with an aqueous acidic solution to dissolve at least some of the nickel thereby forming a nickel-containing aqueous acidic solution. Accordingly the ionic liquid can be re-used. In addition, since the nickel is in aqueous solution, it is 5 capable of being extracted using techniques such as electrowinning and precipitation.

When the ionic liquid is selected from betanium bis(trifluoromethylsulphonyl)

imide and trifluorosulphonylmethyl imide the method preferably further comprises 10 cooling the nickel-containing aqueous acidic solution to from greater than 3 QC to less than 10 QC, preferably to from 4 QC to 8 QC, more preferably to about 5 QC. Cooling the nickel-containing aqueous acidic solution aids phase separation, so that the ionic liquid may be re-used and the nickel can be more easily extracted from the aqueous solution. If the solution is cooled to 3 QC or lower, then the ionic 15 liquid may freeze.

The method may further comprise either carrying out electrowinning on the nickel-containing aqueous acidic solution to extract metallic nickel therefrom. Electrowinning is a particularly effective technique for extracting metallic nickel. 2 0 Alternatively the method may further comprise extracting a nickel salt from the nickel-containing aqueous acidic solution by precipitation. Precipitation is a particularly effective technique for extracting a nickel salt.

The method may be a continuous process. During the process the solvent and/or

2 5 complexing agent and/or ionic liquid may be re-cycled. The method preferably does not use large quantities of strong acid, more preferably the method does not use any strong acid.

The present invention is described by way of example in relation to the following

3 0 figure:

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Figure 1 shows a flow chart of one embodiment of the method of the present invention.

Examples

5 A deep eutectic solvent was prepared by combining lactic acid and choline chloride in a 1:1 molar ratio. 25 kg of this solvent was added to 47 kg of nickel-containing filter cake containing 360 g of nickel. The temperature was then raised to 75 9C in order to promote the dissolution of nickel from the filter cake. The majority of the undissolved, nickel-depleted filter cake was fine material, which 10 was then removed by filtration (1.6 |im glass fibre (GF/A)).

0.880 NH4OH was added to the leachate in order to raise the pH from 3 to 5, followed by an excess quantity of an aqueous solution of dimethylglyoxime (dimethylglyoxime disodium salt octahydrate, 97 %, obtained from Sigma Aldrich™). A fine, red precipitate was then formed which was recovered by 15 filtration. NMR analysis indicated that Ni(dmg)2 had formed. The Ni(dmg)2 contained 70% water.

The recovered precipitate was then added to betanium bis(trifluoromethylsulphonyl) imide ionic liquid (obtained from Sigma Aldrich™) and stirred at approximately 45 QC until the red colour had disappeared,

2 0 indicating that all of the nickel complex had been cracked and converted into Ni2+

in the task specific ionic liquid. 2% sulphuric acid solution was then added to the solution and the mixture was stirred for one hour in order to extract the Ni2+ from the task specific ionic liquid into the sulphuric acid solution. On cooling to 5 QC the sulphuric acid solution phase separated from the ionic liquid phase. The ionic 25 liquid phase was retained for subsequent re-use.

50% NaOH solution was then added to the sulphuric acid solution phase in order to lower the pH to 4. The solution was then charged into a "Chemelec" cell for subsequent electrowinning. The electrowinning 'Chemelec' cell had electrodes immersed in a fluidised bed of small glass beads in order to improve the mass

3 0 transfer to the electrode by minimising the depth of the boundary layer adjacent

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to the electrode surface. The cell was provided with four double-sided mild-steel cathodes, but at the required current density of 100-200A/m2 Control of pH was provided by dosing in 10% NaOH using a pump and controller. Flakes of electrowinned nickel were collected from the steel cathodes and were found to be 5 consistent with that expected for pure nickel. Approximately 180 g of nickel was recovered, indicating a recovery level of approximately 50%. As the filter-cake is 70% water, this is conveniently within process capacity.

The foregoing detailed description has been provided by way of explanation and 10 illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

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Claims

Claims:

1. A method for recovering nickel from a nickel-containing waste, the method 5 comprising:

(2) contacting the dissolved nickel with a glyoxime-based complexing agent to form a nickel complex;

10 (3) contacting the nickel complex with an ionic liquid to extract nickel from the nickel complex to form a nickel-containing ionic liquid; and

(4) recovering nickel from the nickel-containing ionic liquid.

2. The method of claim 1 wherein the solvent comprises a choline-chloride-based 15 deep eutectic solvent.

3. The method of claim 2 wherein the choline-chloride-based deep eutectic solvent comprises one or more of ethanoic acid, urea and lactic acid.

2 0

4. The method of claim 2 or claim 3 wherein the choline-chloride-based solvent comprises tartaric acid and/or citric acid.

5. The method of any preceding claim wherein the glyoxime-based complexing agent is according to the following formula:

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R1

R2

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wherein R1 and R2, which may be the same or different, are selected from an alkyl group and an aromatic group, and wherein R1 and R2 may together form a cyclic compound.

5

6. The method of claim 5 wherein the glyoxime-based complexing agent is dimethylglyoxime.

7. The method of any preceding claim wherein during step (2) the pH is from 4 to 6, preferably about 5.

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8. The method of any preceding claim wherein the ionic liquid is a task specific ionic liquid.

9. The method of any preceding claim wherein the ionic liquid is selected from 15 betanium bis(trifluoromethylsulphonyl) imide and trifluorosulphonylmethyl imide.

10. The method of any preceding claim wherein between steps (2) and (3) the pH is greater than 7, and/or the temperature is from 10 to 40 QC.

2 0

11. The method of any preceding claim wherein the nickel-containing waste is a filter cake or battery, preferably a nickel-cadmium battery.

12. The method of any preceding claim wherein step (3) comprises:

extracting the nickel complex from the solvent, preferably by filtration.

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13. The method of any preceding claim wherein the step of contacting the nickel complex with an ionic liquid is carried out at a temperature of from 40 to 50 QC.

14. The method of any preceding claim further comprising:

3 0 contacting the nickel-containing ionic liquid with an aqueous acidic solution to dissolve at least some of the nickel thereby forming a nickel-containing aqueous acidic solution.

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15. The method of claim 14 wherein the ionic liquid is selected from betanium bis(trifluoromethylsulphonyl) imide and trifluorosulphonylmethyl imide, the method further comprising:

5 cooling the nickel-containing aqueous acidic solution to from greater than

3 QC to less than 10 QC, preferably to from 4 QC to 8 QC, more preferably to about 5 9C.

16. The method of claim 14 or claim 15 further comprising:

10 carrying out electrowinning on the nickel-containing aqueous acidic solution to extract metallic nickel therefrom.

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17. The method of claim 14 or claim 15 further comprising:

extracting a nickel salt from the nickel-containing aqueous acidic solution by precipitation.