Claims: We claim:

1) A method for extraction and recovery of vanadium from vanadium sludge comprising the steps of:
(a) acid leaching the vanadium sludge at a predetermined temperature and duration under atmospheric pressure;
(b) filtering the leachate of step (a) at vacuum;
(c) treating the filtrate from step (b) with ferrous sulfate.
(d) Allowing precipitation of the vanadium as ammonium metavandate by treating the purified filtrate from step (c) with a precipitating agent;

2) The method as claimed in claim 1, wherein the acid leaching of step (a) is conducted using industrial spent acid.

3) The method as claimed in claim 1, wherein the vanadium sludge to spent acid proportion in the leaching step is in the range of 1: 3 to 1: 4.

4) The method as claimed in claim 1, wherein the residence time of the acid leaching is in the range of 45 to 60 minutes.

5) The method as claimed in claim 1, wherein the acid leaching is carried out at a temperature in the range of 30 oC to 60 oC.

6) The method as claimed in claim 2, wherein the concentration of spent acid is in the range of about 20 % to 25 % w/w.

7) The method as claimed in claim 1, comprises of adding spent acid to the vanadium sludge slurry of step (a) to maintain a pH in the range of 6 to 8.

8) The method as claimed in claim 1, wherein the quantity of ferrous salt to leachate in step (c) is in the range of 1.5 to 2.0 times the quantity of arsenic in the leachate.

9) The method as claimed in claim 1, wherein the residence time of step (c) of treating of leachate with ferrous salt is in the range of 60 to 90 minutes.

10) The method as claimed in claim 1, comprises a further step of filtering the ammonium metavanadate precipitate of step (d).

11) The method as claimed in claim 1, wherein the residence time for precipitation of step (d) is in the range of 2 to 3 hr.

12) The method as claimed in claim 1, wherein the proportion of V2O5 in the leachate to ammonium sulphate in step (d) is in the range of 1: 1.2 to 1: 1.5.

13) The method as claimed in claim 1, wherein the ammonium metvanadate precipitate is subjected to drying at a temperature in the range of 50oC to 70oC.

Dated this 11th Day of November 2020
-Digitally Signed-
M. Kisoth
IN/PA-2259
Agent for the Applicant
, Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE OF THE INVENTION
A NOVEL PROCESS FOR VANADIUM RECOVERY FROM VANADIUM BEARING SLUDGE USING INDUSTRIAL SPENT ACID

APPLICANTS
HINDALCO INDUSTRIES LIMITED
Of address
6TH FLOOR, BIRLA CENTURION, PANDURANG BUDHKAR MARG, WORLI, MUMBAI 400030, MAHARASHTRA, INDIA

PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
[001] The present invention relates to the field of extraction and recovery of vanadium from vanadium sludge of Bayer process, as ammonium metavanadate using industrial spent acid from copper refinery, sulphuric acid plant etc.

BACKGROUND ART
[002] Vanadium is a medium-hard, steel-blue metal used in the manufacturing industry due to its malleable, ductile and corrosion-resistant properties. The ubiquitous vanadium is employed in a wide range of alloys in combination with iron, titanium, nickel, aluminum, chromium, and other metals for a diverse range of commercial applications extending from train rails, tool steels, catalysts, to aerospace. Vanadium consumption in the iron and steel industry represents about 85% of the vanadium-bearing products produced worldwide.
[003] Traditionally, vanadium is extracted and recovered from its ores through a pyrometallurgical process that involves a salt roasting step followed by water leaching. The global supply of vanadium originates from primary sources such as ore feedstock, concentrates, metallurgical slags, and petroleum residues.
[004] The alkaline leaching of vanadium-bearing materials is a known process for the recovery of vanadium values from carbonaceous residues. It is also known that alkaline leaching can be used to extract vanadium from base-containing residues provided that vanadium is in an oxidized state (pentavalent) or that an oxidant is present during the leaching procedure. Although alkaline leaching generally represses the dissolution of priority pollutant metals, vanadium recoveries are frequently lower.
[005] Various methods have been proposed in the literature for the recovery of vanadium values by leaching with alkaline materials. For example, in U.S. Pat. No. 3,873,669, there is disclosed a process for the recovery of vanadium from fly ash by treating the fly ash with a concentrated caustic soda solution to selectively solubilize vanadium, and then adding calcium oxide to precipitate silica before recovering the vanadium.
[006] A further method has been disclosed in the patent literature for the recovery of vanadium values by leaching the vanadium-containing material with caustic and thereafter precipitating insoluble salts of vanadium with an ammonium containing compound such as gaseous ammonia or ammonium hydroxide. This method is disclosed in U.S. Pat. No. 4,061,712 and is indicated to provide greater yields of the desired product.
[007] Other methods of recovering vanadium values from a vanadium containing material are described in GB1394024, IN153384 and IN266519.
[008] ZHAO Zhuo et al developed process to recover Vanadium pentaoxide (V2O5) from Bayer spent liquor by ion exchange. The experimental results of Zhuo et al shows that in the conditions of 105°C and 0.20-0.25 mass ratios between CaO in lime and Al2O3 in spent liquor, the precipitation rate of vanadium in Bayer liquor is more than 85%.
[009] WO 2010/057410 A1 recites a clean production method of vanadium oxide by reusing vanadium extraction wastewater.
[010] However, the efficient and economic extraction of vanadium from these carbonaceous residues without the simultaneous extraction of deleterious amounts of priority pollutant metals, such as lead, cadmium, and chromium, has remained a problem.
[011] Accordingly, prior to the present invention there had been no simple and efficient method for the recovery of vanadium from residues in yields higher than many of the methods currently employed in commercial operations.

OBJECT OF THE INVENTION
[012] It is therefore an object of this invention to provide a process for recovering vanadium values from vanadium-containing sources.
[013] A further object of this invention is found in an improvement in the process for obtaining vanadium values from vanadium-containing sources whereby the process may be effected in a more advantageous economic manner.
[014] Further object of invention is to extract vanadium from industrial by-products such as vanadium sludge using industrial spent acid.

SUMMARY OF THE INVENTION
[015] The aim of the present invention is to provide a process for recovering vanadium from vanadium sludge using industrial spent acid, thereby achieving recovery of vanadium from industrial by-products.
[016] In an aspect, the invention provides a method for extraction and recovery of vanadium from vanadium sludge comprising the steps of:
a) acid leaching the vanadium sludge at a predetermined temperature and duration under atmospheric pressure;
b) filtering the leachate of step (a) at vacuum;
c) treating the filtrate from step (b) with ferrous sulfate.
d) precipitation of the vanadium as ammonium metavandate by treating the purified filtrate from step (c) with ammonium sulphate;

BRIEF DESCRIPTION OF THE DRAWINGS
[017] The foregoing summary, as well as the following detailed description of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of assisting in the explanation of the invention, there are shown in the drawings embodiments which are presently preferred and considered illustrative. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown therein. In the drawings:
[018] FIG 1 is an illustration of vanadium recovery process known in the art
[019] FIG 2a is an illustration of vanadium recovery process of present invention using ammonium chloride
[020] FIG 2b is an illustration of vanadium recovery process of present invention using ammonium sulphate
[021] FIG 2c is an illustration of vanadium recovery process of present invention using Ferrous sulphate and ammonium sulphate

DESCRIPTION OF THE INVENTION
[022] In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual process parameters, substituents, and ranges are for illustration only; they do not exclude other defined values or other values falling within the preferred defined ranges.
[023] As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.
[024] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention
[025] As used herein, the terms “comprising” “including,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, i.e. to mean including but not limited to.
[026] As used herein, the term leaching refers to extraction of vanadium from the vanadium sludge using spent acid.
[027] As used herein, the term precipitation refers to separation of the dissolved vanadium from the leachate using ammonium salt as ammonium metavanadate.
[028] Figure 1 describes a vanadium recovery process known in the art where the vanadium sludge was thoroughly mixed with the spent acid (~23%) at ~70°C and the pH of the slurry is maintained around neutral. The leaching process continued for around 1 hr. After leaching the slurry was vacuum filtered and the leachate, also referred as mother liquor was treated with ammonium sulfate to precipitate out the leached vanadium as ammonium metavanadate. The residence time for precipitation reaction found to vary from 2 to 3 hours. However, a major challenge in the already known process of recovering vanadium is the higher arsenic penetration in ammonium metavanadate (~2600 – 4000 ppm).
[029] Figure 2c is a representation of vanadium recovery process claimed in present application. In the process, after leaching step the slurry was mixed with ferrous salt to check for further reduction in the level of arsenic in the product.
[030] Accordingly, in an embodiment, the invention provides a method for extraction and recovery of vanadium from vanadium sludge comprising the steps of:
a) acid leaching the vanadium sludge at a predetermined temperature and duration under atmospheric pressure;
b) filtering the leachate of step (a) at vacuum;
c) treating the filtrate from step (b) with ferrous sulfate.
d) precipitation of the vanadium as ammonium metavandate by treating the purified filtrate from step (c) with ammonium sulphate;
[031] The leaching of step (a) is carried out in any suitable leach vessel, such as an agitated tank; a pachuca tank can be used where oxygen or air is to be added. Pressure vessels also can be used; however, it is advantageous to carry out leaching at atmospheric pressure.
[032] In an embodiment, acid leaching of step (a) is conducted using spent acid. In another embodiment, the concentration of spent acid is in the range of 20 % to 25 % w/w.
[033] In an embodiment, the proportion of vanadium sludge to spent acid in the leaching step (a) is in the range of 1: 3 to 1: 4.
[034] The temperature of leaching should be such to give good vanadium extractions in a reasonable time period. Operating temperature between 50 to 70oC at atmospheric is preferred because the reaction rate is the highest possible without resorting to pressurized equipment. As such in an embodiment, residence time of acid leaching of step (a) is in the range of 45 to 60 minutes. In a further embodiment, said acid leaching of step (a) is carried out at a temperature in the range of 30oC to 75oC.
[035] In another embodiment, the pH of leachate obtained from leaching of step (a) is maintained at a pH in the range of 6 to 8, as maximum dissociation of vanadium from other compounds occurs at neutral pH.
[036] In another embodiment, the proportion of V2O5 in the leachate of step (a) to ammonium sulphate in step (d) is in the range of 1: 1.2 to 1: 1.5.
[037] In an embodiment, the step (c) of treating the filtrate with ferrous sulfate is carried out for removal of impurities such as an impurity (arsenic) removal
[038] In another embodiment, residence time of step (c) of treating of leachate with ferrous salt is in the range of 60 to 90 minutes.
[039] In another embodiment, the quantity of ferrous salt to leachate in step (c) is in the range of 1.5 to 2.0 times the quantity of arsenic in the leachate.
[040] In another embodiment, ammonium metavanadate precipitated in (d) is treated with ammonium chloride.
[041] In another embodiment, the residence time for precipitation of step (d) is in the range of 2 to 3 hours.
[042] In another embodiment, the ammonium metavanadate precipitate obtained in step (d) is subjected to drying at a temperature in the range of 50oC to 70oC.
[043] In the present invention, the arsenic impurities are removed by the treatment with ferrous sulphate. Accordingly, the ammonium metavanadate obtained from the claimed method has a purity in the range of 99.2 to 99.5% as NH4VO3. The overall recovery of vanadium is in the range of 97 to 99 % as V2O5, thus providing a process which does not require additional stages, devices or reagents for the extraction of vanadium.
[044] In another embodiment, the ammonium metavanadate can be converted into a variety of useful oxide products by calcining.
[045] In another embodiment, the claimed process may be carried out continuous or as a batch process.
[046] In accordance with the process of present application, industrial by-products such as vanadium sludge and spent acid are not wasted, but is actually used again to leach more vanadium from residues.
[047] The process of the present invention is advantageous where vanadium sludge contains significant amounts of alkaline earth bases and ferrous or ferric iron bases, etc. It is preferable to have the residues in a finely grounded state for optimum extraction. As known in the art, leaching is generally at as high a percent solids slurry as practicable, e.g., about 10%-40% solids depending on the rheological properties of the residue. The higher percent solids allow a stronger reagent concentration to be used without increasing the reagent/residue weight ratio. Stronger base concentrations normally will increase the rate of extraction.
[048] The following examples are intended to illustrate some possible embodiments of the process according to the present invention, without thereby limiting in any way the scope defined herein.

WORKING EXAMPLES
[049] In order to demonstrate the benefits of leaching in accordance with the process of the present invention, four tests were conducted.
EXAMPLE 1
[050] 500gm of vanadium sludge was leached with 500 ml of 25% sulphuric acid and 300ml water. The pH of the solution was maintained at 6.8. The concertation of arsenic impurity in the sludge was typically 10300 ppm. The percentage of vanadium pentoxide in the vanadium sludge was 16%. The leaching was carried out at a temperature of 70oC. After leaching, the leachate as cooled at a temperature between 25-30oC. The leachate was filtered at vacuum and 90.1 gm a dry residue was obtained. After filtration, 900ml of mother liquor was treated with 132.5gm of ammonium chloride for 90 minutes. After treatment with ammonium chloride, the mixture was allowed to precipitate for a duration of 3 hours. After the precipitation, the precipitate was dried at a temperature between 60-70oC. 126gm of dry ammonium metavanadate was obtained at the end of process. The amount of arsenic impurity in ammonium metavanadate at the end of the process was 2800 ppm. The percentage of recovery of vanadium from the vanadium sludge was of 99.06% and purity of ammonium metavanadate was 99.72%. Rest of the process parameters are disclosed in Table 1.

EXAMPLE 2:
[051] 500gm of vanadium sludge was leached with 500 ml of spent acid having 22.5% sulphuric acid and 300ml water. The pH of the solution was maintained at 7.1. The concertation of arsenic impurity in the sludge was 10300 ppm. The percentage of vanadium pentoxide in the vanadium sludge was 16%. The leaching was carried out at a temperature of 70oC. After leaching, the leachate as cooled at a temperature between 25-30oC. The leachate was filtered at vacuum and 90 gm a dry residue was obtained. After filtration, 870 ml of mother liquor was treated with 132.5gm of ammonium chloride for 90 minutes. After treatment with ammonium chloride, the mixture was allowed to precipitate for a duration of 3 hours. After the precipitation, the precipitate was dried at a temperature between 60-70oC. 124.2 gm of dry ammonium metavanadate was obtained at the end of process. The amount of arsenic impurity in ammonium metavanadate at the end of the process was 4680 ppm. The percentage of recovery of vanadium from the vanadium sludge was of 98.85% and purity of ammonium metavanadate was 99.53%. Rest of the process parameters are disclosed in Table 1.

EXAMPLE 3:
[052] 500gm of vanadium sludge was leached with 500 ml of spent acid having 22.5% sulphuric acid and 300ml water. The pH of the solution was maintained at 7.1. The concertation of arsenic impurity in the sludge was 10300ppm. The percentage of vanadium pentoxide in the vanadium sludge was 16%. The leaching was carried out at a temperature of 70oC. After leaching, the leachate as cooled at a temperature between 25-30oC. The leachate was filtered at vacuum and 89.5 gm a dry residue was obtained. After filtration, 875 ml of mother liquor was treated with 132.5gm of ammonium sulphate for 90 minutes. After treatment with ammonium sulphate, the mixture was allowed to precipitate for a duration of 3 hours. After the precipitation, the precipitate was dried at a temperature between 60-70oC. 123.87 gm of dry ammonium metavanadate was obtained at the end of process. The amount of arsenic impurity in ammonium metavanadate at the end of the process was 1233.3 ppm. The percentage of recovery of vanadium from the vanadium sludge was of 99.16% and purity of ammonium metavanadate was 99.85%. Rest of the process parameters are disclosed in Table 1.

EXAMPLE 4:
[053] 500gm of vanadium sludge was leached with 500 ml of spent acid having 22.5% sulphuric acid and 300ml water. The pH of the solution was maintained at 6.5. The concertation of arsenic impurity in the sludge was 10300ppm. The percentage of vanadium pentoxide in the vanadium sludge was 16%. The leaching was carried out at a temperature of 70oC. After leaching, the leachate as cooled at a temperature between 25-30oC. The leachate was filtered at vacuum and 90.5 gm a dry residue was obtained. After filtration, 880 ml of mother liquor was treated with ferrous sulfate salt (~1.5 to 2 times of arsenic in the leachate) for 60 to 90 minutes. Later the purified filtrate was treated with 132.5gm of ammonium sulfate and the mixture was allowed to precipitate for a duration of 3 hours. After the precipitation, the precipitate was dried at a temperature between 60-70oC. 125.3 gm of dry ammonium metavanadate was obtained at the end of process. The amount of arsenic impurity in ammonium metavanadate at the end of the process was 579.0 ppm. The percentage of recovery of vanadium from the vanadium sludge was of 99.52% ad purity of ammonium metavanadate was 99.94%. Rest of the process parameters are disclosed in Table 1.

S No. Streams Unit Experiments
Exp 1.1 Exp 1.2 Exp 1.3 Exp 1.4
Leachant Used Sulphuric Acid 25% Birla Copper Effluent
(Sulphuric Acid 22.5%) Birla Copper Effluent
(Sulphuric Acid 22.5%) Birla Copper Effluent
(Sulphuric Acid 22.5%)
Reagent used NH4Cl NH4Cl (NH4)2SO4 (NH4)2SO4
Arsenic Control N.A. N.A. N.A. Ferrous sulfate
Ph 6.8 7.1 7.1 6.5

1 V-Sludge G 500 500 500 500
2 As in V-sludge Ppm 10300 10300 10300 10300
3 V2O5 in V-sludge % 16 16 16 16
4 Leachant Ml 500 500 500 500
5 Leachant density g/ml 1.154 1.16 1.16 1.16
6 As in leachant Ppm 0 2670 2670 2670
7 V2O5 in leachant % 0 0 0 0
8 Water Ml 300 300 300 300
9 Mother Liquor Ml 900 870 875 880
10 Mother Liquor density g/ml 1.282 1.282 1.282 1.282
11 As in Mother liquor Ppm 2850 4910 4950 2000
12 V2O5 in Mother liquor % 6.78 6.98 6.96 6.92
13 Reagent G 132.5 132.5 132.5 132.5
14 Residue G 90.1 90 89.5 90.5
15 Moisture in residue % 30.71 29 30 30.5
16 As in Residue Ppm 8950 10950 14000 9100
17 V2O5 in Residue % 4.46 4.69 4.51 5.1
18 AMV (Dry) G 126 124.2 123.87 125.3
19 Moisture IN AMV % 35.5 37.21 37.21 37.21
20 As in AMV Ppm 2800 4680 1500 650
21 V2O5 in AMV % 61.5 61.96 62.5 62.01
22 Effluent Ml 800 810 795 808
23 Effluent density g/ml 1.204 1.24 1.24 1.17
24 As in Effluent Ppm 1940 4000 3800 4100
25 V2O5 in Effluent % 0.04 0.03 0.049 0.03

% Extraction of V2O5 97.78 97.31 97.59 97.58
% Recovery of V2O5 99.06 98.85 99.16 99.52
% Purity AMV 99.72 99.53 99.85 99.94
Table 1
[054] Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described. All publications and other references mentioned herein are incorporated by reference in their entirety. Numeric ranges are inclusive of the numbers defining the range.