Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[See section 10, Rule 13]

TITLE OF INVENTION
A method for recovery of nickel from copper refinery waste effluent

APPLICANT
Hindalco Industries Limited, having address at One Unity Center (Formerly called as One International Center), Tower 4, 21st Floor, Senapati Bapat Marg, Prabhadevi, Mumbai – 400013, Maharashtra, India.

The following specification describes the nature of the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
[001] The present invention relates to a method for preparing metal concentrate from de-copperized waste effluent of copper refinery. The present invention also relates to a metal concentrate of nickel obtained from de-copperized waste effluent of copper refinery.

BACKGROUND OF THE INVENTION
[002] Copper refineries generate around 130-150 m3/day of effluent which contains heavy metals like Cu (~2-3 g/L), Ni (~3-5 g/L), As (~6-7 g/L) along with other metal impurities like Sb, Pb and Bi. From this effluent Cu is recovered in the copper recovery plant in the form of Cu2S cake, whereas Nickel is lost in the effluent treatment plant (ETP). The loss of nickel value in the waste has a significant impact on subsequent treatment in effluent treatment plants.
[003] Conventionally known method for recovering nickel from copper electrorefining effluent involve complex and energy-intensive processes, such as acid purification, solvent extraction, and carbonation. These methods require higher chemical consumption and also generate solid or liquid waste, which needs to be handled and disposed of properly. The simplest known method is to use acid purification and carbonation to produce nickel as nickel carbonate, but the selective recovery and product purity is very low. Hence, recovering selective nickel metal with high purity of about 50-60% is challenging using the conventional methods.
[004] Owing to the foregoing problems, method for nickel recovery is provided which addresses the issues known in the art. Particularly, invention provides the selective precipitation of nickel from a de-copperized waste effluent of copper refinery in simplified and cost-efficient manner.

SUMMARY OF THE INVENTION
[005] One aspect of the present invention provides a method for preparing nickel metal concentrate from de-copperized waste effluent of copper refinery, comprising the following steps: (a) pre-treatment of de-copperized waste effluent to a pre-determined pH range with a neutralizing agent and treating with ferric sulphate for a pre-determined time, followed by filtration to achieve metal concentrate liquor, (b) treating the metal concentrate liquor with an alkali hydroxide to adjust to a predetermined pH, (c) treating the metal concentrate liquor obtained from step (b) with a predetermined dose of precipitating agent followed by filtration at predetermined pH range, (d) washing the precipitate from step (c) with water to achieve solid metal concentrate, (e) drying the solid metal concentrate.
[006] Another aspect of the present invention relates to a metal concentrate comprising nickel sulphide in the range of 90 – 95%.
[007] Another aspect of the present invention relates to the use of the nickel metal concentrate in recovering at least 92-97% nickel metal from the de-copperized waste effluent of copper refinery.

BRIEF DESCRIPTION OF THE DRAWINGS
[010] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows a diagrammatic representation of process flow diagram of the method for preparing metal concentrate from de-copperized waste effluent of copper refinery.
Figure 2 shows a process flow diagram of the method for recovery of nickel from copper refinery waste effluent.

DETAILED DESCRIPTION OF THE INVENTION
[008] The present invention discloses a method for preparing nickel metal concentrate from de-copperized waste effluent of copper refinery. Specifically, the method provides for selective nickel value extraction from de-copperized refinery waste effluent with more 92% nickel recovery and 92-95% nickel sulphide (NiS) purity with more than 40% nickel metal concentration.
[009] In an aspect, the method for preparing nickel metal concentrate from de-copperized waste effluent of copper refinery, comprising the following steps:
a. pre-treatment of de-copperized waste effluent to a pre-determined pH range with a neutralizing agent and treating with ferric sulphate for a pre-determined time, followed by filtration to achieve metal concentrate liquor,
b. treating the metal concentrate liquor with an alkali hydroxide to adjust to a predetermined pH,
c. treating the metal concentrate liquor obtained from step (b) with a predetermined dose of precipitating agent for selective nickel precipitation followed by filtration at predetermined pH range,
d. washing the precipitate from step (c) with water to achieve solid nickel metal concentrate,
e. drying the solid nickel metal concentrate obtained from step (d).
Cu As Ni Fe Bi Sb Pb Zn
<1 3–7 3–5 0.1–0.3 <0.2 0.05-0.08 ND 0.15–0.3
[010] In an embodiment, the de-copperized waste effluent of copper refinery comprises the following elements (g/L):

[011] In an embodiment, the de-copperized waste effluent of copper refinery has a pH range of 0.5 – 1.
[012] In an embodiment, pre-treatment of de-copperized waste effluent in step (a) is carried out at a pre-determined pH range of 3 – 4.5 and pre-determined time of 1-3 hours, preferably 2.5 hours. The neutralizing agent is selected from a sodium base compound preferably selected from, but not limited to, calcium hydroxide, sodium hydroxide, sodium carbonate etc.
[013] In an embodiment, pre-treatment of de-copperized waste effluent in step (a) is carried by addition of ferric sulphate provided in the ratio (Fe/As) between the 1.2 to 1.5, preferably the ratio is 1.5.
[014] In an embodiment, treatment of the metal concentrate liquor is done with an alkali hydroxide to adjust to a predetermined pH within the range of 4.5 – 6. The alkali hydroxide may preferably be selected from, but not limited to, sodium hydroxide, lithium hydroxide, potassium hydroxide, rubidium hydroxide, caesium hydroxide and francium hydroxide.
[015] The precipitating agent may preferably be selected from a sulphur base compound. The sulphur base compound may be preferably selected from, but not limited to, sodium sulphide, barium sulphide and hydrogen sulphide.
[016] In an embodiment, the sulphur base compound is fed in the ratio (Ni/S) between the range of 1.0 to 1.5 i.e. Ni/S is between 1:1 to 1:1.5, preferably ratio is 1.5.
[017] In yet another embodiment, the concentration of precipitating agent is in the range of 10 – 20% and fed through perforated dosing system.
[018] In an embodiment, the drying the solid metal concentrate is preferably done in the temperature range of 90 to 150 oC, followed by keeping the solid metal concentrate to remove the moisture.
[019] In a preferred embodiment, the method involves three stages: neutralization, pH control, and sulphidation to achieve the nickel metal recovery and product purity as nickel concentrate from de-copperized waste effluent of copper refinery.
[020] The method process flow has been provided in Figure 1 preferably includes treating the de-copperized effluent with neutralizing agent to adjust the pH of effluent in the pH range of 3 – 4.5, followed by arsenic precipitation which removes the arsenic from the effluent solution. The pH of the mother liquor solution is adjusted to PH 4.5 or more; followed by adding an alkali metal sulphide such as sodium sulphide to the nickel solution whose pH has been adjusted to 4.5 or more to obtain a nickel sulphide precipitate. When the pH range of 5.5 – 6.5 is maintained during nickel sulphide precipitation, there is no liberation of gas. The obtained nickel precipitate is dried for 3 hours and then kept in desiccator to remove moisture. The filtrate received post separating the precipitate through filtration, having neutral pH in the range of 7.5 – 8, thereby can be further sent to ETP.
[021] In an embodiment, the pretreatment reaction can be represented as follows:
H2SO4 + Ca(OH)2 ? CaSO4(s) +2H2O
As2O3 + Fe2(SO4)3 + 3H2O ? 2FeAsO3 (s) + 3H2SO4
[022] In an embodiment, the nickel precipitation reaction can be represented as follows: NiSO4 + Na2S ? NiS + Na2SO4
[023] Thus, the method follows 3 stages followed by Neutralization, pH control and sulphidation as demonstrated in Figure 2. De-copperized effluent (1) was collected from outlet of Copper Recovery Plant. Filtration was done using vacuum pump for elimination of solid particles if any in the process. As the effluent is highly acidic, it was neutralized (2) using Ca(OH)2 upto 1 pH and CaSO4 (3) is removed. As there is also Arsenic present in the effluent, which is very dangerous and hazardous compound and harmful for environment, it is also targeted to eliminate from the effluent so that it will not affect the desirable product quality and purity.The pH was Control using Sodium hydroxide (4) and also Ferrous Sulphate (5) was added for Arsenic precipitation (6). Later in 3rd Stage, Sodium Sulphide (7) was used for Ni precipitation (8) as Nickel sulphide adjusting pH through Sodium hydroxide for minimizing solid waste generation.
[024] In another aspect, present invention discloses a metal concentrate comprising nickel sulphide in the range of 90 – 95% with more than 40% nickel and remaining comprising copper/arsenic compounds and trace impurities.
[025] In a preferred embodiment, present invention discloses a metal concentrate comprising nickel sulphide in the range of 90 – 95% with more than 40% nickel, copper compounds in the range of 0.2 – 0.5%, arsenic compounds in the range of 1.0-2.5% and trace impurities in the range of 0.5-1.0%.
[026] Advantageously, the solid metal concentrate achieved from the process of the invention comprises nickel sulphide with purity in the range of 90 – 95% and nickel concentration in product is in the range of 37-45%, preferably in the range of 40 - 45%. Accordingly, the metal concentrate is particularly useful for enhancing sustainability is the utilization / value recovery from waste.

EXAMPLE
[027] The following examples are illustrative of the invention but not limitative of the scope thereof.
[028] Method: The method involves the following stages:
Stage-1: Pre-treatment: De-copperized effluent of specified composition having pH 0.5 – 1 will be first neutralized and pH will be adjusted in the range of 3.5 to 4.5 along with the addition of 10% ferric sulphate slurry to react with arsenic. Around 2 hours’ reaction time will be provided after which the slurry will be filtered, and sludge and liquor will be separated. Sludge generated will be disposed off in the SLF as per current practice.
Stage-2: pH adjustment: The mother liquor which is generated from stage-1 will be nickel concentrated feed. To increase pH from range of 3.5 – 4.5 till 4.5 – 6, few drops of Caustic soda is to be added for pH adjustment between 4.5 – 6.
Stage-3: Selective Precipitation: After adjusting pH in the range of 4.5 – 6, sulphur-based compound is used to precipitate nickel as nickel sulphide. Dosing of sulphur-based compound after making 5-15% solution keeping dosing pipe deep inside the solution. Around 1-hour reaction time is given to precipitate nickel. The slurry is then filtered out using vacuum pump. The black colour precipitates are obtained, and the colourless treated water can further send to ETP. The precipitates obtained are then washed to remove remaining odium in the filtrate.
Step 4: Product Drying: The obtained precipitates are dried at 100 oC for 3 hours and kept in desiccator to remove moisture.
[029] De-copperized effluent of various concentration were treated according to the above method to prepare nickel concentrate as follows:
[030] Example-1
Stage-1: Pretreatment: 2 Liters of de-copperized effluent was taken in 5 liters of beaker having pH in between 0.5 – 1. 2 liters of 5-10% calcium hydroxide slurry was prepared using magnetic stirrer. The slurry was added slowly and gradually through cylindrical beaker in the de-copperized effluent through continuous stirring till pH is increased to 3.5 – 4.5. Add 10-20% ferric sulphate solution in the ratio of Fe/As = 1.5. After adding ferric sulphate, 2.5 hours of reaction time is given. The slurry is then filtered through vacuum filter pump and whatman filter paper of mesh size 41. The entire reaction is carried out at normal atmospheric temperature and pressure. The filtrate will be a nickel concentrated liquor.
Stage-2: pH adjustment: Nickel precipitates at the pH range above 5. To bring pH of the filtrate from stage-1 in the range of 5-6, few drops of 10% Caustic solution is added in the filtrate for selective precipitation of Nickel.
Stage-3: Selective Precipitation: After achieving pH in the range of 4.5 – 6, 10-20% solution of sulphur-based compounds is dosed in the ratio of Ni/S = 1.5 (little on higher side compare to stoichiometry ratio) using burette at flow rate of 5 ml/min. After dosing, 1-hour reaction time is given to precipitate Nickel present in the solution in the form of NiS at normal atmospheric temperature and pressure. As precipitates of NiS formed are very fine in size, poly is added to let settle the precipitates and filtered using whatman filter paper of mesh size 40. The precipitates are then washed with water properly to wash out remaining sodium. The treated water after filtration can be further send to ETP.
Stage-4: Product Drying: The washed-out precipitates are then dried at 100 oC for 3 hours to remove the moisture.
The parameters such as % nickel recovery and % nickel sulphide purity in nickel sulphide cake were evaluated using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP OES), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) to quantify process efficiency as shown in Table 1 below:
De-copperized effluent 1st stage
Solid
waste Mother Liquor Product Recovery Treated effluent
Ni: 3.2g/L
Ni: 0.45 %
Ni: 1.25 g/L
Ni: 41.43%
Ni: 90.63%
Ni: 8 ppm

Cu: 0.5 g/L
Cu: 0.09 %
Cu: 0.0241g/L
Cu: 0.17%
Cu: ND

As: 3.1 g/L As: 1.07 % As: 0.6g/L As: 3.07% As: ND

[031] Example-2
Stage-1: Pretreatment: 2 Liters of de-copperized effluent was taken in 5 liters of beaker having pH in between 0.5 – 1. 2 liters of 5-10% calcium hydroxide slurry was prepared using magnetic stirrer. The slurry was added slowly and gradually through cylindrical beaker in the de-copperized effluent through continuous stirring till pH is increased to 3.5 – 4.5. Add 10-20% ferric sulphate solution in the ratio of Fe/As = 1.5. After adding ferric sulphate, 2.5 hours of reaction time is given. The slurry is then filtered through vacuum filter pump and whatman filter paper of mesh size 41. The entire reaction is carried out at normal atmospheric temperature and pressure. The filtrate will be a nickel concentrated liquor.
Stage 2: pH adjustment: Nickel precipitates at the pH range above 5. To bring pH of the filtrate from step 1 in the range of 5-6, few drops of 10% Caustic solution is added in the filtrate for selective precipitation of Nickel.
Stage-3: Selective Precipitation: After achieving pH in the range of 4.5 – 6, 10-20% solution of sulphur-based compounds is dosed in the ratio of Ni/S = 1.5 (little on higher side compared to stoichiometry ratio) using burette at flow rate of 5 ml/min. After dosing, 1-hour reaction time is given to precipitate Nickel present in the solution in the form of NiS at normal atmospheric temperature and pressure. As precipitates of NiS formed are very fine in size, poly is added to let settle the precipitates and filtered using whatman filter paper of mesh size 40. The precipitates are then washed with water properly to wash out remaining sodium. The treated water after filtration can be further send to ETP.
Step 4: Product Drying: The washed-out precipitates are then dried at 100 oC for 3 hours to remove the moisture.
The parameters such as % nickel recovery and % nickel sulphide purity in nickel sulphide cake were evaluated using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP OES), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) to quantify process efficiency as shown in Table 2 below:
De-copperized effluent 1st stage Solid waste Mother Liquor Product Recovery Treated effluent
Ni: 2.81g/L
Ni: 0.08 %
Ni: 0.9 g/L
Ni: 38%
Ni: 92%
Ni: 15 ppm

Cu: 1.02 g/L
Cu: 0.3 %
Cu: 0.4 g/L
Cu: 1.5%
Cu: ND

As: 4.0 g/L As: 0.9 % As: 1.5g/L As: 2.5% As: 37 ppm

[032] Example-3
Stage-1: Pretreatment: 2 Liters of de-copperized effluent was taken in 5 liters of beaker having pH in between 0.5 – 1. 2 liters of 5-10% calcium hydroxide slurry was prepared using magnetic stirrer. The slurry was added slowly and gradually through cylindrical beaker in the de-copperized effluent through continuous stirring till pH is increased to 3.5 – 4.5. Add 10-20% ferric sulphate solution in the ratio of Fe/As = 1.5. After adding ferric sulphate, 2.5 hours of reaction time is given. The slurry is then filtered through vacuum filter pump and whatman filter paper of mesh size 41. The entire reaction is carried out at normal atmospheric temperature and pressure. The filtrate will be a nickel concentrated liquor.
Stage-2: pH adjustment: Nickel precipitates at the pH range above 5. To bring pH of the filtrate from step 1 in the range of 5-6, few drops of 10% Caustic solution is added in the filtrate for selective precipitation of Nickel.
Step 3: Selective Precipitation: After achieving pH in the range of 4.5 – 6, 10-20% solution of sulphur-based compounds is dosed in the ratio of Ni/S = 1.5 (little on higher side compared to stoichiometry ratio) using burette at flow rate of 5 ml/min. After dosing, 1-hour reaction time is given to precipitate Nickel present in the solution in the form of NiS at normal atmospheric temperature and pressure. As precipitates of NiS formed are very fine in size, poly is added to let settle the precipitates and filtered using whatman filter paper of mesh size 40. The precipitates are then washed with water properly to wash out remaining sodium. The treated water after filtration can be further send to ETP.
Step 4: Product Drying: The washed-out precipitates are then dried at 100 oC for 3 hours to remove the moisture.
The parameters such as % nickel recovery and % nickel sulphide purity in nickel sulphide cake were evaluated using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP OES), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) to quantify process efficiency as shown in Table 3 below:
De-copperized effluent 1st stage Solid waste Mother Liquor Product Recovery Treated effluent
Ni: 2.13 g/L
Ni: 0.02 %
Ni: 0.9 g/L
Ni: 41%
Ni: 91%
Ni: 11 ppm

Cu: 0.05 g/L
Cu: 0.9 %
Cu: 0.1 g/L
Cu: 0.67%
Cu: ND

As: 2.31 g/L As: 1.01 % As: 0.9 g/L As: 1.16% As: 15.3 ppm

[033] Example-4
[034] A comparative study of the % nickel metal recovery from nickel concentrate of the present invention compared to the products known in the art is provided below: in Table 4:
Elements De-Cu effluent (feed), ppm Trial -1
Trial -2 Lagoon Nickle concentrate currently available
Product (Nickel Contrate according to present method), % Final Effluent, ppm Product (Nickel Contrate according to present method), % Final Effluent, ppm Quality
Ni 2715.5 40.58 40.4 41.43 40 <2 ppm 10%
As 1500 5.15 143 3.6 ND <2 ppm 0.50%
Bi 3.3 ND ND ND ND - -
Pb 0.7 - ND - ND <0.2 ppm -
Zn 185.6 2.39 ND 1.83 ND <0.2 ppm 0.02%
Cu 125.6 0.86 ND 0.6 ND - 0.22%
Co 61.3 0.83 ND 0.89 ND <0.5 ppm 0.03%
Fe 299.9 1.56 ND 600 ppm ND - 17.15%
Cd 0.8 - ND - ND <0.2 ppm -
Mg 44.9 - 35 - 34 - 22.47%

[035] As observed from Table 1-4, that various metallic impurities such as arsenic have been efficiently removed using the present method, whereby de-copperized effluent is treated with neutralizing agent to adjust the PH of effluent in the range pH 3 – 4.5, followed by arsenic precipitation which removes the arsenic from the effluent solution.
[036] Specifically, % Nickel recovery from mother liquor followed by nickel precipitation is around 95% and % Nickel product purity is more than 40% which is confirmed by multiple samples (see Tables 1-4) which is extracted in accordance with the present invention. Thus, the method for preparing metal concentrate from de-copperized waste effluent of copper refinery successfully provides for selective nickel value extraction from de-copperized refinery waste effluent with more than 95% nickel sulphide (NiS) recovery and more than 40% nickel metal recovery.
[037] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.
, C , Claims:We Claim
1. A method for preparing nickel metal concentrate from de-copperized waste effluent of copper refinery, comprising the following steps:
a. pre-treatment of de-copperized waste effluent to a pre-determined pH range with a neutralizing agent and treating with ferric sulphate for a pre-determined time, followed by filtration to achieve metal concentrate liquor,
b. treating the metal concentrate liquor with an alkali hydroxide to adjust to a predetermined pH,
c. treating the metal concentrate liquor obtained from step (b) with a predetermined dose of precipitating agent for selective nickel precipitation followed by filtration at predetermined pH range,
d. washing the precipitate from step (c) with water to achieve solid nickel metal concentrate,
e. drying the solid nickel metal concentrate obtained from step (d).
Cu As Ni Fe Bi Sb Pb Zn
<1 3–7 3–5 0.1–0.3 <0.2 0.05-0.08 ND 0.15–0.3
2. The method as claimed in claim 1, wherein the de-copperized waste effluent of copper comprises the following elements (g/L):

3. The method as claimed in claim 1, wherein the de-copperized waste effluent of copper has a pH range of 0.5 – 1.
4. The method as claimed in claim 1, wherein the pre-determined pH range of step (a) is 3 – 4.5 and pre-determined time is 1-3 hours, preferably 2.5 hours.
5. The method as claimed in claim 1, wherein the neutralizing agent is selected from calcium hydroxide, sodium hydroxide and calcium carbonate.
6. The method as claimed in claim 1, wherein the ferric sulphate is provided in the ratio (Fe/As) from the range of 1.2 -1.5, preferably 1.5.
7. The method as claimed in claim 1, wherein the pre-determined pH range of step (b) is from the range of 4.5 – 6.
8. The method as claimed in claim 1, wherein the pre-determined pH range of step (c) is from the range of 5.5 – 6.5.
9. The method as claimed in claim 1, wherein the alkali hydroxide is sodium hydroxide.
10. The method as claimed in claim 1, wherein the precipitating agent is a sulphur base selected from sodium sulphide, hydrogen sulphide.
11. The method as claimed in claim 1, wherein the sulphur base is in the ratio (Ni/S) from the range of 1-1.5, preferably 1.5.
12. The method as claimed in claim 1, wherein the concentration of precipitating agent is from the range of 5 – 20 %.
13. The method as claimed in claim 1, wherein the precipitating agent is fed through a perforated dosing system.
14. The method as claimed in claim 1, wherein the predetermined dose of precipitating agent is selected from sodium sulphide and hydrogen sulphide.
15. The method as claimed in claim 1, wherein the solid metal concentrate comprises nickel sulphide in the range of 90 – 95% with Ni concentration in range of 37-47% preferably from the range of 40 - 45%.
16. The method as claimed in claim 1, wherein the nickel recovery from refinery effluent is in the range of 92 – 97%.
17. A nickel a metal concentrate comprising nickel sulphide in the range of 90 – 95% with more than 40% nickel and remaining comprising copper/arsenic compounds and trace impurities.

Dated this 30th day of March 2024
Hindalco Industries Limited
By their Agent & Attorney

(Nisha Austine)
of Khaitan & Co
Reg No IN/PA-1390