WO2013114089A1

WO2013114089A1 - Nickel recovery

Info

Publication number: WO2013114089A1
Application number: PCT/GB2013/050178
Authority: WO
Inventors: Paul Fitzpatrick
Original assignee: C-Tech Innovation Limited
Priority date: 2012-01-31
Filing date: 2013-01-28
Publication date: 2013-08-08
Also published as: GB2498955A; GB201201637D0; GB2498955B

Abstract

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 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.

Description

Nickel Recovery

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

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 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 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 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.

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 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 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.

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.

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. 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 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. 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 ionic liquid. Further advantages of the method are as follows:

• 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 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 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 any other feature or features indicated as being preferred or advantageous.

Definitions:

The term "ionic liquid" as used herein may encompass a salt which melts below 100 ^QC 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 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.

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

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

"electroextraction". The term "betainium" as used herein refers to 1 -carboxy-A/,A/,A/- trimethylmethanaminium inner salt.

Preferably the solvent comprises a choline-chloride-based deep eutectic solvent. 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 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 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 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.

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

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

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

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.

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 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. The method is particularly effective for recovering nickel from nickel-cadmium batteries. For example, the method is particularly effective for recovering nickel from the mass of nickel oxide black (e.g. comprising N12O3) contained in nickel-cadmium batteries. The stainless steel shell of the nickel- cadmium battery is typically removed to expose the nickel oxide black prior to carrying out the nickel recovery.

Preferably step (3) comprises extracting the nickel complex from the solvent, 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, such as a betainium- based ionic liquid. Task specific ionic liquids are particularly effective at extracting nickel from the nickel complex. More preferably, the ionic liquid is selected from betainium bis(trifluoromethylsulphonyl) imide and trifluorosulphonylmethyl imide. Betainium bis(trifluoromethylsulfonyl)imide has the following structure:

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

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 capable of being extracted using techniques such as electrowinning and precipitation.

When the ionic liquid is selected from betainium bis(trifluoromethylsulphonyl) imide and trifluorosulphonylmethyl imide the method preferably further comprises 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 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. 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 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 non-limiting figures:

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

Figure 2 shows a flow chart of one embodiment of the method of the present invention.

Referring to Figure 1 , step (1 ) of the method involves contacting nickel containing waste with a solvent to dissolve nickel from the nickel-containing waste. Step (2) involves contacting the dissolved nickel with a glyoxime-based complexing agent to form a nickel complex. Step (3) involves contacting the nickel complex with an ionic liquid to extract nickel from the nickel complex to form a nickel-containing ionic liquid. Step (4) involves recovering nickel from the nickel-containing ionic liquid. In the embodiment shown in Figure 2, nickel from a filter cake of battery waste is subjected to non-selective dissolution in a choline chloride/lactic acid mixture. The dissolved nickel is then precipitated with sodium dimethyldioxime. The nickel dimethyldioxime complex is then cracked with a task specific ionic liquid. Phase separation of acidic nickel ions from the task specific ionic liquid is then carried out, followed by electrowinning of nickel from the acidic solution onto steel cathodes. The present invention will now be further described with reference to the following non-limiting example.

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 ^QC in order to promote the dissolution of nickel from the filter cake. The majority of the un-dissolved, nickel-depleted filter cake was fine material, which was then removed by filtration (1 .6 μιη 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 filtration. NMR analysis indicated that Ni(dmg)₂ had formed. The Ni(dmg)₂ contained 70% water.

The recovered precipitate was then added to betainium

bis(trifluoromethylsulphonyl) imide ionic liquid (obtained from Sigma Aldrich™) and stirred at approximately 45 ^QC until the red colour had disappeared, 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 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 transfer to the electrode by minimising the depth of the boundary layer adjacent 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 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 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.

Claims

Claims:

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

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

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

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:

R2 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.

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.

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 betainium 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.

1 1 . The method of any preceding claim wherein the nickel-containing waste is or comprises 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.

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:

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.

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

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.

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

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

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

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