Claims:We claim:

1. A process for preparing cobalt aluminate pigment using spent lithium ion batteries, the process comprising:
a) extracting cobalt sulphate heptahydrate from spent lithium ion batteries;
b) neutralizing the extracted cobalt sulphate heptahydrate with an alkali, followed by heating to a temperature ranging between 165-170oC to obtain cobalt (II) oxide;
c) processing the cobalt (II) oxide such that cobalt (II) oxide has 65-70 % cobalt; and
d) sintering the obtained cobalt (II) oxide with aluminium (III) hydroxide
to obtain cobalt aluminate pigment.

2. The process as claimed in claim 1, wherein cobalt sulphate heptahydrate is extracted from spent lithium ion batteries by:
- discharging the batteries, followed by shredding, crushing and sieving thereof to obtain a black powder;
- subjecting the black powder to acid leaching with an acid selected from a group consisting of sulfuric acid, hydrogen peroxide or mixtures thereof;
- filtering the acid leach to obtain a filtrate;
- subjecting the filtrate to inorganic precipitation and solvent-solvent extraction to obtain cobalt sulphate heptahydrate.

3. The process as claimed in claim 1, wherein in step (b), neutralization of the extracted cobalt sulphate heptahydrate is carried out with stoichiometric quantities of the alkali.

4. The process as claimed in claim 1, wherein in step (d), cobalt (II) oxide and aluminium (III) hydroxide are subjected to mixing and grinding until a uniform color is observed.

5. The process as claimed in claim 4, wherein in step (d), cobalt (II) oxide and aluminium (III) hydroxide are mixed and ground for a time period in a range of 10-15 minutes to obtain homogeneous mixture.

6. The process as claimed in claim 5, wherein after grinding, the mixture is sintered at a temperature in a range of 880oC to 1200oC and is then allowed to cool.

7. The process as claimed in claim 6, wherein the sintering is carried out for a time period ranging between 1-3 hours.

8. The cobalt aluminate pigment obtained from process as claimed in claim 1, wherein the pigment comprising of 29.8% cobalt has UV-Vis reflectance of 25.54%, NIR reflectance of 51.62% and total solar reflectance of 37.24%.

9. The cobalt aluminate pigment obtained from process as claimed in claim 1, wherein the pigment comprising of 34.8% cobalt has UV-Vis reflectance of 23.28 %, NIR reflectance of 48.47 % and total solar reflectance of 34.37 %.

Dated this 14th day of August 2020

Essenese Obhan
Of Obhan & Associates
Agent for the applicant
Patent Agent No. 864
, Description:Field of Invention

The present disclosure relates to a process for preparing cobalt aluminate pigment. Particularly, a process for preparing cobalt aluminate pigment using cobalt extracted from spent lithium ion batteries is disclosed.

Background

Cobalt is a chromatic element that provides distinct blue color and finds a special place in pigment industry. Cobalt is also a key element used in lithium ion batteries for making materials for energy storage. Cobalt accounts for around 20% of spent lithium ion batteries. However, end of life spent lithium ion batteries are usually discarded and only less than 5% of end of life lithium ion batteries are recycled. The use of recycled cobalt back into the energy storage devices is relatively less. It is costly as well as laborious to recycle the cobalt for use in battery. Therefore, researchers have attempted to produce downstream specialty chemicals from cobalt extracted from spent lithium ion battery waste.

CN102942227B provides a method for producing a cobalt blue pigment by using waste lithium batteries. The disclosed method includes the following steps: a) preparing a cobalt sulphate solution; b) preparing cobalt carbonate; c) preparing cobalt oxide; and d) preparing the cobalt blue pigment. It has been found that the final product in the disclosed method is mixed oxide pigment that contains cobalt along with oxides of zinc, aluminium, barium and magnesium.

Summary

A process for preparing cobalt aluminate pigment using spent lithium ion batteries is disclosed. Said process comprises:
a) extracting cobalt sulphate heptahydrate from spent lithium ion batteries;
b) neutralizing the extracted cobalt sulphate heptahydrate with an alkali, followed by heating to a temperature ranging between 165-170oC to obtain cobalt (II) oxide;
c) processing the cobalt (II) oxide such that cobalt (II) oxide has 65-70 % cobalt; and
d) sintering the obtained cobalt (II) oxide with aluminium (III) hydroxide
to obtain cobalt aluminate pigment.

Brief Description of Drawings
Figure 1 shows various cobalt aluminate pigment containing 29.8% and 34.8% of cobalt as illustrated in Example 3 and 4 respectively, in accordance with an embodiment of the present invention.

Detailed Description

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.

Reference throughout this specification to “one embodiment”, “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

In its broadest scope, the present disclosure relates to a process for preparing cobalt aluminate pigment using cobalt extracted from spent lithium ion batteries. Specifically, said process comprises:
a) extracting cobalt sulphate heptahydrate from spent lithium ion batteries;
b) neutralizing the extracted cobalt sulphate heptahydrate with an alkali, followed by heating to a temperature ranging between 165-170°C to obtain cobalt (II) oxide;
c) processing the cobalt (II) oxide such that cobalt (II) oxide has 65-70% cobalt; and
d) sintering the obtained cobalt (II) oxide with aluminium (III) hydroxide to obtain cobalt aluminate pigment.

In accordance with an embodiment, in step (b), neutralization of the extracted cobalt sulphate heptahydrate is carried out with stoichiometric quantities of the alkali. In accordance with yet another embodiment, the alkali is selected from a group consisting of NaOH and KOH. Preferably, the alkali is NaOH.

In accordance with an embodiment, in step (d), cobalt (II) oxide and aluminium (III) hydroxide are mixed and ground until a uniform color is observed. In accordance with yet another embodiment, cobalt (II) oxide and aluminium (III) hydroxide are mixed and ground for a time period in a range of 10-15 minutes to obtain homogeneous mixture. After grinding, the mixture is sintered at a temperature in a range of 880oC to 1200oC and is then allowed to cool. The sintering is carried out for a time period ranging between 1-3 hours. In accordance with an embodiment, sintering is carried out in one or more steps by varying the temperature and time period at each step. For example, the mixture is sintered at a temperature of 880oC for one hour followed by sintering at 1200oC for one hour.

In accordance with an embodiment, cobalt sulphate heptahydrate is extracted from spent lithium ion batteries by:
- discharging the batteries, followed by shredding, crushing and sieving thereof to obtain a black powder;
- subjecting the black powder to acid leaching with an acid selected from a group consisting of sulfuric acid, hydrogen peroxide or mixtures thereof;
- filtering the acid leach to obtain a filtrate;
- subjecting the filtrate to inorganic precipitation and solvent-solvent extraction to obtain cobalt sulphate heptahydrate.
Any known method of discharging the batteries known to a person skilled in the art can be used. For example, the batteries can be discharged using 25% brine solution. After the batteries are discharged, the batteries are subjected to shredding and crushing. Any known methods of shredding and crushing can be used. After crushing, the material obtained is sieved using meshes corresponding to 0.125 mm openings.
In accordance with an embodiment, the black powder comprises of metals such as Ni, Mn, Co, Cu, Al, Fe and Li, amongst others. By way of an exemplary embodiment, the black powder comprises metals in ratio - Ni: Mn: Co: Cu: Al: Fe: Li 0.1:0.7:1:0.5:0.5:0.01:0.3.
In accordance with an embodiment, the black powder obtained after sieving was subjected to leaching with one or more acid with pulp density ranging between 50-60 gm/L. The leaching was carried out at a temperature ranging between 60-70 oC for a time period ranging between 3-5 hours. The residue settled on top comprising of graphitic carbon was separated by filtration. The resultant filtrate was subjected to solvent-solvent extraction technique to obtain cobalt sulphate heptahydrate. To extract cobalt sulphate heptahydrate, the pH of resultant acidic filtrate was increased to pH 3 using 1-5 M NaOH. Subsequently, solvent- solvent extraction technique was employed with ligand to metal ratio ranging between 3:1 to 2:1.
The present disclosure also relates to a cobalt aluminate pigment obtained from spent lithium ion batteries. Said pigment comprises cobalt in an amount ranging between 29.8-34.8% by weight of the pigment.
The cobalt aluminate pigment of present disclosure exhibits a total solar reflectance (TSR) similar to commercially available cobalt aluminate pigment obtained from standard cobalt and aluminum substrates. Herein, the disclosed cobalt aluminate pigment was compared with the commercial cobalt aluminate pigments. Pigment Blue 28 available from Ferro Pigments comprises 33.3% of cobalt and has a TSR of 38.5%, and Pigment Blue 214 from The Shepherd Color Company comprises 33.3% of cobalt and has a TSR of 28%. In accordance with an embodiment of present disclosure, cobalt aluminate pigment comprising 29.8% of cobalt was found to have total solar reflectance of 37.24%. In accordance with another embodiment, pigment comprising 34.8% of cobalt was found to have total solar reflectance of 34.37%.
In order that this invention may be better understood, the following examples are set forth. These examples are for the purpose of illustration only and the exact compositions, methods of preparation and embodiments shown are not limiting of the invention, and any obvious modifications will be apparent to one skilled in the art.

Examples:
¬¬¬¬¬¬
Example 1: Extraction of cobalt sulphate heptahydrate
Spent, end of life lithium ion batteries were discharged in 25% brine solution until all batteries were thoroughly discharged. Discharged batteries were rinsed, dried and collected to process further. Dried batteries were shredded, crushed and sieved to obtain black powder. The pulverized black powder was acid leached using a mixture of 200 ml of 30% H2SO4 and 80 ml of 30% H2O2, followed by heating for 3 hours. The float on acid leach, graphite, was that filtered away to separate the filtrate. It was found 95-96% of metal was recovered in the filtrate. The filtrate holds all the essential transition metals (Cu, Mn, Co, Ni , Al, Li) in sulphate form. Using a scheme of inorganic precipitation and solvent-solvent extraction the cobalt is obtained as cobalt sulphate heptahydrate with purity >98% from recycling of spent lithium ion batteries. To achieve this, the pH of acidic filtrate was increased to pH 3 using 1-5 M NaOH. Subsequently, solvent-solvent extraction was employed with ligand to metal ratio between 3:1 to 2:1 to obtain cobalt sulphate heptahydrate.
Following steps were followed to carry out solvent-solvent extraction:

1. Removal of Copper: The pH of acidic filtrate comprising of Cu, Mn, Co, Ni, Al, Li was adjusted to 3, by addition of 2M NaOH followed by addition of ligand- LiX 86 I (5dodecylsalicylaldoxime) in n-Hexane (Ligand and Cu ratio 2:1; Hexane Solvent to Aq. Ratio 2:1). The resultant mixture was mixed for 10 minutes at room temperature, followed by separation of aqueous layer comprising Mn, Co, Ni, Al and Li, and organic layer comprising of Cu-ligand complex.

2. Removal of Manganese: The pH of aqueous layer comprising Mn, Co, Ni, Al and Li was adjusted to 4.5 by addition of 2M NaOH followed by addition of ligand-D2EHPA (Di-(2-ethylhexyl)phosphoric acid) in n-Hexane (Ligand and Mn ratio 2:1; Hexane Solvent to Aq. Ratio 2:1). The resultant mixture was mixed for 10 minutes at room temperature, followed by separation of aqueous layer comprising Co, Ni, Al and Li, and organic layer comprising a complex of Co, Mn and ligand. The organic layer was mixed with 10M H2SO4 solution to obtain Co and Mn sulphate, followed by neutralization of the sulphate solution by addition of NaOH/CaO. This was followed by recrystallization/evaporation of water to obtain solid MnSO4 comprising of impurities- 3-4% of CoSO4 and 2-3%Na2SO4.

3. Removal of Nickel: The pH of aqueous layer comprising Co, Ni, Al and Li was adjusted to 6-7.5 by addition of 2M NaOH followed by addition of ligand- DEHPA (Di-(2-ethylhexyl)phosphoric acid)/Cynex 272 (Bis(2,4,4-Trimethylpentyl)-Phosphinic Acid) (Ligand and “Co + Ni” ratio 2:1; Hexane Solvent to Aq. ratio 2:1). The resultant mixture was mixed for 10 minutes at room temperature, followed by separation of aqueous layer and organic layer comprising a complex of Co, Ni and ligand.

4. Extraction of cobalt sulphate heptahydrate (CoSO4.7H2O): The organic layer comprising a complex of Co, Ni and ligand was mixed with 10M H2SO4 solution to obtain a Co and Ni sulphate solution. This sulphate solution was neutralized by addition of NaOH/CaO followed by recrystallization/evaporation of water to obtain solid CoSO4.7H2O with 96-97 % purity and a small amount of impurities comprising 1-2% of NiSO4 and about 2% of Na2SO4.

Example 2: Preparation of cobalt (II) Oxide
300 grams of cobalt sulphate heptahydrate obtained from spent lithium ion battery was dissolved in water to prepare 3M solution of cobalt sulphate. Cobalt sulphate solution was neutralized with 3M NaOH, followed by filtration, drying, crushing and heating at 168°C in vacuum for overnight. After this step, the cobalt concentration was analyzed by MP-AES. Cobalt (II) oxide that has around 66% cobalt by weight (MP-AES verified) is taken in particular molar ratio.

Example 3: Preparation of cobalt aluminate with 29.8% cobalt
2.6586 grams cobalt (II) oxide and 5.46 grams aluminium (III) hydroxide hydrate were mixed and ground uniformly for 10 minutes. Ground material was kept for sintering at 880°C for 1 hour and 1200°C for 1 hour. The material was allowed to cool at room temperature. The pigment thus formed was transferred into a sample container and taken out according to characterization requirement.

Example 4: Preparation of cobalt aluminate with 34.8% cobalt
3.1017 grams cobalt (II) oxide and 5.07 grams aluminium (III) hydroxide hydrate were mixed and ground uniformly for 10 minutes. Ground material was kept for sintering at 880°C for 1 hour and 1200°C for 1 hour. The material was allowed to cool at room temperature. The pigment thus formed was transferred into sample container and taken out according to characterization requirement.

Pigment Characterization

The corresponding cobalt aluminate pigment was characterized with X-ray diffractometer for crystallographic phase formations. The UV-Vis-NIR spectrum of all the samples was collected using Varian’s Cary UV-Vis-NIR Spectrophotometer with Barium sulphate standard. The spectra for all the samples were recorded between 200-3000 nm to obtain UV–Vis-NIR Diffuse reflectance spectra. The corresponding data from UV–Vis-NIR Diffuse reflectance spectra was used to re-plot as NIR absorbance (Kubelka-Munk) spectra using the following Kubelka Munk function (K-M) as given by Eq. 1
(F)R= (K-M) =a= (1-R)2/ 2R ---------------------------------------------------Eq. 1
F(R) is Kubelka Munk function, a is absorption coefficients.

The band gap of the synthesized powder can be determined using the following Eq. 2
(F (R) h?) = (ah?) = A (h?-E) Z ------------------------------------------------Eq. 2
h and ? are constants,
F (R) is Kubelka Munk function,
F (h?) is energy function,
R is the reflectance of the powdered samples,
a is absorption coefficients
Z is the value between 1/2, 3/2, 2 and 3 depending on the direct allowed, direct forbidden, indirect allowed and indirect forbidden electronic transitions, respectively.

The total solar reflectance (TSR) is represented as the integral of the present reflectance times the solar irradiance divided by the integral of the solar irradiance when integrated over NIR (?1–?2) nm range as given in Eq. 3
TSR = (?1??2 r(?) i(?) d?) / (?1??2 i(?) d? ----------------------------------------Eq. 3
Where r(?) is the spectral reflectance obtained from the experiment and i(?) is the standard solar spectrum (Wm-2 nm-1). The NIR Solar reflectance was arrived at by using ASTM Standard G173-03.

Table 1 shows the thermal reflectance behavior of cobalt aluminate pigments prepared using various percentage of cobalt obtained from recycled spent lithium ion batteries.

% of cobalt UV-Vis reflectance (%) NIR reflectance (%) Total solar reflectance (%)
29.8 (Example 3) 25.54 51.62 37.24
34.80 (Example 4) 23.28 48.47 34.37
Table 1: Thermal reflectance behavior of cobalt aluminate pigment

Observations: The crystallographic pattern and phases of the cobalt aluminate pigment obtained using the disclosed method was found to be same as that of standard cobalt based benchmark cobalt aluminate pigment- Pigment Blue 28 available from Ferro Pigment, and Pigment Blue 214 from The Shepherd Color Company. Also, the NIR reflective behavior of cobalt (recycled) aluminate was observed to be similar to that of benchmark cobalt aluminate pigment as observed from the total solar reflectance profiles.

Industrial Applicability

The disclosed process is cost effective and environmentally sustainable. Said process enables preparation of the cobalt aluminate pigment through sustainable recycling of spent lithium ion batteries.
The cobalt aluminate pigment obtained through recycling of spent lithium ion batteries is cheaper than the benchmark cobalt aluminate obtained from standard cobalt and aluminum substrates without any compromise in thermal reflectivity performance of solar irradiation. By way of an example, the recycled cobalt containing cobalt aluminate pigment with 29.8 % and 34.8 % cobalt has shown total solar reflectivity of nearly 37 % and 34% respectively. The commercial sample with 33.3% Cobalt has shown 38% TSR. This highlights that there was no significant variation in solar reflectivity.
The disclosed pigment finds application as thermally reflective blue coloring in coating compositions- such as exterior paints for buildings, paints for vehicles, and polymer compositions to impart blue colour.