Increasing environmental standards mean that it is important to recover heavy metals such as nickel from waste materials as efficiently and effectively as possible. Conventionally, there are a number of methods available to recover nickel from waste materials such as electro less plating waste. Typically, a recovery agent is used to recover nickel which must then undergo further processing, which is relatively complex, time-consuming and expensive.

According to a first aspect of the present invention there is provided a nickel recovery process, the process including a first reaction in which a waste material comprising nickel is reacted with a recovery agent to form an intermediate complex and a nickel depleted waste material.

Possibly, the process includes a second reaction, in which the intermediate complex is reacted with a decomposing agent to form a nickel rich material and a regenerated recovery agent.

Possibly, the regenerated recovery agent is recycled to take part in the first reaction.

Possibly, the process is a continuous process.

Possibly, the recovery agent comprises an oxime, and the recovery agent may be in the form of a solution.

In one embodiment the recovery agent comprises dimethylglyoxime (DMG), which may be in an alcohol solution, and may be in a methanol solution. In a further embodiment the recovery agent is in the form of an aqueous solution of dimethylglyoxime sodium salt.

Possibly, the regenerated recovery agent comprises an oxime, and may comprise dimethylglyoxime (DMG).

Possibly, the intermediate complex comprises nickel dimethylglyoxime.

Possibly, the decomposing agent comprises a mineral acid, and may comprise any mineral acid selected from the group containing sulphuric acid, hydrochloric acid, nitric acid.

Possibly, the first reaction is carried out at a temperature of between 10 and 40° C, and may be carried out at around 20° C.

Possibly, the second reaction is carried out at a temperature of between 10 and 40° C, and may be carried out at around 20° C.

The first reaction may be carried out at a slightly basic pH, which may be in the range 7.1 - 7.5, and the basic pH may be achieved by the addition of aqueous ammonia.

The waste material may be electro less plating waste material.

An embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawing, in which:-

Figure 1 is a schematic flowchart of a nickel recovery process according to the invention.

General Process Referring to figure 1 , a nickel recovery process 10 includes a first reaction 12 which is a complexation reaction and a second reaction 14 which is a decomposition reaction.

In the first reaction 12, a waste material 16 comprising nickel, which could, for example, comprise electro less plating waste material, is reacted with a recovery agent comprising dimethylglyoxime (hereinafter referred to as DMG), to form an intermediate complex 22 comprising nickel DMG, and a nickel depleted waste material 20. This reaction is carried out at slightly basic pH, approx 7.1-7.5. This is achieved by the addition of a small volume of aqueous ammonia.

The waste material 16 could be in the form of an aqueous solution. The recovery agent 18 could comprise DMG in an alcohol solution, and could comprise DMG in a methanol solution. Alternatively the recovery agent 18 could comprise an aqueous solution of dimethylglyoxime sodium salt.

The resulting nickel DMG is in the form of a highly coloured red precipitate which can be relatively easily filtered off.

Advantageously, DMG is highly selective for nickel. Thus, the nickel DMG formed is relatively free from other compounds which could form impurities, while the nickel depleted waste material 20 has a very low remaining nickel content, for example between 1 and 10 ppm. In one example, the extraction rate of nickel was found to be 99.8%, the nickel content being reduced from 6000 ppm in the waste material to 16 to 8 ppm in the nickel depleted waste material 20.

The nickel depleted waste material 20 is taken for further processing to recover materials such as phosphites. The first reaction 12 could be undertaken readily and conveniently at a temperature of between 10 and 40° C. In one example the first reaction 12 could be carried out at room temperature, that is around 20° C.

The waste material 16 could be "washed" with recovery agent 18 a number of times, with removal of the precipitated intermediate complex 22 between each washing. In one example, the waste material 16 is washed three times with recovery agent 18.

In the second reaction 14, the nickel DMG precipitate is reacted with a decomposing agent 24 comprising a mineral acid such as sulphuric acid to produce regenerated DMG 28 and a nickel rich material 26. The nickel rich material 26 can be taken for further processing. The regenerated DMG 28, which is in the form of a white solid, is separated from the nickel rich material 26 by filtration and washing with water, and is then dissolved in alcohol, and can then be recycled in a recycling step 30 to take part in the complexation reaction 12.

In the example in which the mineral acid is sulphuric acid, the nickel rich material 26 comprises nickel sulphate in the form of a green coloured solution which can then be re used, for example, in a plating process. In this example, therefore, and advantageously, the reaction products of the second reaction are reusable.

The pathway of the second reaction 14 has been confirmed by isotopic labelling. Deuterated sulphuric acid was reacted with the intermediate complex to form deuterated DMG.

The second reaction 14 could be undertaken readily and conveniently at a temperature of between 10 and 40° C. In one example the second reaction 14 could be carried out at room temperature, that is around 20° C. The process 10 provides the advantage that the recovery agent 18 can be continuously reacted in the complexation reaction 12, the decomposition reaction 14 and then recycled, reducing the consumption of recovery agent 18. Advantageously, as the recovery agent 18 is recycled, it can be added to the first reaction 12 in excess, that is in an amount that is greater than the stoichiometric amount required to fully react with all of the nickel in the waste material 16.

The chemical formulae for the reactions 12, 14 are as follows:

Experimental Illustration of Process Materials table:

Stage 1 - complexation and separation of nickel

To a 20 litre flange head flask equipped with a paddle stirrer containing 1 litre of deionised water, 312g (1.01 moles, 2.05 eq) of dimethyl glyoxime disodium salt (sodium dimethylglyoximate, DMGNa) was added to dissolve in the water (full dissolution was observed to ensure a homogeneous reaction medium). Proportionate addition of the nickel waste (pH 7.0, 5000ml, 0.490 moles,) was added to the DMGNa solution. Without external cooling, an exotherm with an overall increase of 2°C was noted. During addition of nickel waste the generation of a foam was observed, effectively doubling the overall reaction volume, to approximately 15 litres volume. Following completion of the addition of the nickel waste, the mixture was allowed to stir out for approximately 3.5 hours.

The reaction mixture was then filtered at a pump using a No 3 sinter funnel of 15cm diameter. Approx 2 litres of the filtrates were used as washings to remove residual complex from the flask.

The collected solid was left to dry under vacuum for several hours. The nickel depleted filtrate was analysed by inductively couple plasma (ICP) spectroscopy then put aside (yielding the following results):

Volume: 6200mls sample Nitec 1

The residual red solid, the nickel (II) dimethylglyoxime complex was then similarly analysed by ICP and the water content determined.

Mass of red complex as obtained from filter:

Mass = 198.8g sample Nitec 2

The loss of water on drying and confirmed by Karl Fisher analysis was

19.4%.

ICP Results

Sample identity Ni (ppm or mg/l) P (total)(ppm or mg/l)

Nitec 1 14 19700

Filtrate (nickel depleted

waste)

Nitec 2 176,000 (ppm or mg/Kg) 29,200

Ni(DMG) ₂ RED SOLID Mass balance calculations regarding nickel dimethylglyoxime

complexation:

(i) Nited:

Residual aqueous nickel in depleted solution:

6700 ^* 14 = 93.8mg

(ii) Nitec 2:

Maximum theoretical dry yield of nickel DMG complex : 0.49 ^* 288g = 141.20g This equates to 28.81g nickel as the element.

198.8 - (198.8 * 19.4/100) = 160.23g

This equates to an obtained yield of 113.50% of the complex. The excess is made up of carry over phosphorus containing mineral. The actual nickel content is as follows:

(58.69/288.2) ^* 141.2 = 28.75g

Total recovered nickel so far is 93.8mg + 28.75g = 28.84g

This equates to a recovered yield of nickel so far as

(28.84/28.84) ^* 100/1 %

= 100.00%!

Stage 2: Mineral acid decomposition of Ni(DMG complex to generate an aqueous solution of nickel ions:

To a 20 litre flange head flask equipped with an elliptical paddle and overhead stirrer, filled with sulphuric acid (5mol, 650ml) and deionised water (650ml, therefore 2.5 mol concentration), the nickel complex (198.8g) was added over 20 minutes. An exotherm of 4 °C was observed. A colour change was noted, initially the red turned to a pink hue, as more complex was added this became a much more vivid pink. The solution became thick and smooth in texture. This was left to stir in an atmosphere of air for a further 60 minutes, agitation was poor.

The solution was filtered using a buchner filter under vacuum. The pH of the first batch was 1.1. An additional 100ml of 2.5 mol concentrated solution of sulphuric acid was added to the solid on the filter. This was then placed under vacuum (diaphragm, approx 150-200mBar) for 20 minutes. The solid was then placed under further vacuum continued to dry the solid for an additional 30minutes. The pink (damp) solid (Nitec 3) was then collected and placed on a watch glass to dry further, and the green filtrate (Nitec 4) (pH 1 ) isolated ready for the next process.

Mass of recovered pink solid sample Nitec 3: 198g, 104g after water content correction (49% water content).

Content of nickel within the recovered dimethylglyoxime reagent: 104g ^* 7250mg/kg = 0.754g

Volume of regenerated nickel sulphate solution, sample Nitec 4: 1600ml

Nickel content. 17.12g/l concentration (by analysis and extraplolation). This also corresponds to an approximately 0.3 molar solution.

This equates to a total nickel content of 27.39g

Total nickel recovery following the breakdown of the DMG nickel complex:

39g + 0.754g This equates to a mass balance of (28.14/28.84) ^* 100/1 = 97.59 %

ICP Results and supporting data:

Stage 3: Recycling of regenerated recovery agent

Materials table:

Reagents Concentration Quantity Hazard

assessment

Regenerated Nickel 1712mg/ml 1600mls Assume as toxic solution Nitec 4

Deionised water n/a 1 ,150mls LOW

Ammonium 33% Approx 650mls corrosive hydroxide Experimental

To a 5000ml beaker fitted with a paddle type overhead stirrer containing aqueous nickel sulphate solution Nitec 4 (1600mls, 1712mg/l nickel, 27.39g, 0.46mol), 88 aqueous ammonium hydroxide (650ml) was added via a pressure equalised dropping funnel while maintaining a gentle agitation. There was observed a temperature rise of 2°C. The pH was observed using a pH probe from pH 1 to pH 5.9. Large amounts of blue/green crystals were observed via precipitation at 22°C. Also significant amounts of a red flocculant precipitate of nickel dimethyl glyoxime complex was formed. It is believed that this due to solvation of the oxime complexing agent in the nickel solution under acidic pH.

The solution was heated to 70°C in order for the nickel crystals to go back into solution. A hot filtration was conducted to collect the insoluble red crystals. This was only partially successful as not all of the blue/green solids re-dissolved. At this point the solution with a volume of approx 2250ml was split into two batches. To each batch an additional 575ml of deionised water was added to effect dissolution. This was successful. Each volume (approx 1700ml) was subjected to heating to 70°C for 60 minutes followed by a hot filtration at 50°C to separate the red nickel oxime complex. Following filtration the vivid green solution was isolated (pH 5.9) and cooled. This resulted in the crystalisation of 2 batches of blue/green aqueous nickel sulphate and nickel ammonium sulphate crystals within each solution.

The green crystals were then cooled to 20°C where they were immediately filtered at the pump.

Combined yield of both batches: 28.6g, Nitec 5 Further observations:

After being left overnight at ambient temperature (12°C), each of the filtrates remained green in colour with further quantities of blue/green crystals forming at the base of the vessels in each case. A small amount of additional red precipitate was also noticed in both, but was minimal in comparison to the precipitated nickel species. Nevertheless, this progressively smaller amount of complex was removed by further heat treatment as follows

Reflux:

Both batches were heat treated using a reflux reaction, being taken up to around 70°C for 60 minutes in order to solubilise the blue/green nickel precipitate. The insoluble red Ni(DMG)2 precipitate that remained was filtered as before.

This reflux procedure was repeated three times in total until there was no visible red precipitate forming.

Following the third heat treatment the blue/green precipitate from the cooled solution appeared free of visible impurities. The additional combined purified nickel solids were then isolated by filtration at the pump.

Additional combined yield: 14.2g, Nitec 6

Total recovered nickel species (assumed as nickel ammonium sulphate hexahydrate ^* ) :

142.8g, Nitec 7. This equates to 22.33g by ICP.

The ^* denotes X-ray crystallography mixed morphology of crystal form. The filtrate left over was labelled as Nitec 8 Volume = 2736ml containing 2,400mg/l nickel by ICP.

This equates to 6.56g nickel. Subsequently, this solid was analysed by ¹ H nmr spectroscopy and High Pressure Liquid Chromatography/Mass spectroscopy. In each case of the nmr analysis no detectable signs of dimethylglyoxime was found. In the case of the LC/MS which had sub microgram limits of detection, a peak was observed but was of an intensity of no more than background interference. It was deemed to therefore be insignificant. See appendices for spectra and method details.

This solution has reduced in volume by approximately 650ml due to evaporation from the open vessel. No nickel or other mineral components from the solution have been lost. This solution was now ready for further volume reduction by distillation and repeat precipitation/filtration as described above.

The collected combined nickel DMG complex recovered from the heat treatment as described above:

4.86g Nitec 9 This is a dry mass sample containing (58.69/288.2) ^* 4.86g nickel

= 0.99g nickel.

A portion of sample Nitec 7 (105.2g) was dissolved into deionised water ( ,400mls) to produce a deep green solution:

Sample Nitec 10: 1 ,400 mis volume containing 11 ,750mg/l nickel.

This equates to: 16.45g nickel.

Overall mass balance for nickel during purification stage of purification: Initial amount of nickel at start: sample Nitec 4:

Amount of nickel accounted for

Sample Nitec 7 (combined Nitec 5&6 solids) = 22.33g

Sample Nitec 8 (lower grade solution) = 6.56g

Sample Nitec 9 (combined Ni(DMG) ₂ ) = 0.99g

Sub total = 29.88g

29.88/27.37 = 109% recovery.

ICP Results and supporting data:

Substance Nickel Content mg/L Total Phosphorus mg/L

Crude Nickel sulphate

(green solution) Nitec 4 17012 4300

Residual nickel sulphate 2400 1630

solution Nitec 8

Purified nickel 1 750 180

sulphate/nickel

ammonium sulphate

solution

Nitec 10 Conversion of impure recovered dimethylglyoxime (nitec 3) to sodium dimethylglyoximate salt:

To a solution of sodium hydroxide (0.75g) in water (30mls) with stirring is added, 1 g of recovered dimethylglyoxime (Nitec 3). The solution is placed under reflux and the mixture is filtered from any slight residue (essentially nickel hydroxide). The solution is poured while hot into refluxing ethanol (50mls). After cooling to 5°, with stirring, the crystals which form are filtered, then washed with ethanol, cold (50ml) and again filtered, and finally dried at 25° over 48 hours. The yield is 2.10g Nitec 11 ,(82 %) of the sodium salt.

A sample of this material was dissolved in a little water and added to a solution of depleted nickel waste. The result was the formation of a red precipitate of nickel (II) dimethylglyoxime complex. This observation demonstrated the overall recoverability and desired repeatability of the chemistry loop.

APPENDIX:

The following data shows liquid chromatographic conditions for the method used for the detection of any residual dimethylglyoxime.

Method:

Nuclear Magnetic Resonance Spectroscopy:

Instrument: Bruker DRX 500 - 500MHz instrument

¹ H NMR (500 MHz, D ₂ 0, ppm): δ 2.85 (br s, 2 x 3H, methyl protons) exchanges upon D2O shake, 4.70. (s, 2 x 1 H, oxime proton, observed in CD ₃ OD ). Liquid chromatography-Mass spectroscopy:

Instrument: Waters Alliance 2695 Liquid Chromatograph

A = Water (0.1 % formic acid) B = Acetonitrile (0.1 % formic acid)

Time A% B% C% D% Flow (ml/min)

0.00 95.0 5.0 0.0 0.0 0.400 1

25.00 5.0 95.0 0.0 0.0 0.400 6

26.00 5.0 95.0 0.0 0.0 0.400 6

30.00 95.0 5.0 0.0 0.0 0.400 1

Column: Phenomenex Cie x 30 cm

Mass selective detector : Micromass Waters LCT quadrupole.

Retention time data: 5.4 minutes.

MS (m/e): 1 17 (M=H ^+' ) dimethylglyoxime

The chromatograms below was obtained from an LC/MS analysis of the regenerated DMG free sample. It is evident that the peak at approximately 5.4mins has a mass spectrum of that of dimethylglyoxime. The intensity of this peak however is no bigger than other baseline signals and is, at present unquantifiable. Reference spectra are shown for comparison. It is worthwhile noting that this very low level is noT detected by nmr spectroscopy which is also shown.

¹ H nmr (D ₂ 0 as solvent) showing absence of detectable dimethylglyoxime as sodium salt within the sample of purified nickel species. The solution was prepared by treatment of crystals with sodium deuteroxide in deuterium oxide followed by direct analysis. Any presence of dimethylglyoxime would be indicated by a clear singlet at 1.8-1.9ppm as shown in the reference spectrum below:

Summary

The applicants have found that relative to conventional similar processes the process is extremely efficient and economic, providing a high level of nickel recovery from the waste material.

Various modifications may be made without departing from the scope of the invention. The recovery agent could comprise any suitable oxime. The decomposing agent could comprise any suitable mineral acid, such as sulphuric acid, hydrochloric acid and/or nitric acid.

There is thus provided a novel, efficient and economic process for the recovery of nickel from waste material.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.