DESC:TECHNICAL FIELD
The present disclosure relates to a process for extracting vanadium, and more specifically to a process for extracting vanadium from vanadium bearing slag.
BACKGROUND OF THE DISCLOSURE
Vanadium is an important strategic resource, which plays a critical role in production of steel for aviation, national defense facilities, vehicles, and home electrical appliances. Vanadium finds wide application in catalysts and ceramic industries as well. Also, Vanadium redox flow batteries make vanadium an important metal for rechargeable batteries.
Vanadium bearing slags play a dominant role in the list of secondary sources of vanadium. These slags are generated in large quantities in steelmaking plants and also in petroleum refineries as pet coke gasification slag. The vanadium bearing slags contains about 4-10% vanadium which makes them a very attractive raw material for vanadium.
The presence of high level of carbon along with sulphur and other metals makes vanadium extraction technologically challenging. Hence, there is an urgent need to develop techno-commercially viable process for vanadium extraction from vanadium bearing slags.

SUMMARY OF THE DISCLOSURE

The process for extraction of vanadium from vanadium bearing slags is disclosed. In one embodiment the process includes oxidative roasting of slag at high temperatures which ranges from 600-1000oC for 2-6 hr. in the presence of air. Roasting resulted in loss of slag weight to the tune of 40-60% due to the removal of carbon and sulphur present in the slag. The roasted mass is pulverized to obtain minus 200 mesh (BSS) particles. The process further includes leaching of roasted slag using 1-2 M H2SO4 in combination with sodium meta bisulphite as lixiviant at 70-90oC for 2-4 hr while keeping the pulp density at 5-10% (wt/wt). After leaching, leach residue is separated from slurry via filtration. Leach solution as obtained is first subjected to pH adjustment of 2.0-3.0 and then to purification through solvent extraction using 15-25% D2EHPA for the selective extraction of vanadium. Di-(2-ethylhexyl) phosphoric acid (D2EHPA) is an organophosphorus compound with the formula (C8H17O)2PO2H. The colorless liquid is a diester of phosphoric acid and 2-ethylhexanol. Vanadium is selectively loaded during extraction and is then stripped using 1.5-2.5 M H2SO4. The vanadium is precipitated from stripped solution as ammonium salt of vanadium by increasing the pH to 6.0-7.0 using NH4OH. The precipitated cake is first washed using 2-5% (NH4)2SO4 solution and then dried in an oven at 108oC for 8 hr. till constant weight is achieved. The dried ammonium salt of vanadium is roasted in a furnace at temperature of 450-550oC for 2-3 hr. to get high purity V2O5. The purity of V2O5 obtained was found to be 99.0%.

BRIEF DESCRIPTION OF DRAWINGS

The disclosed process will be described and explained with additional specificity and detail with the accompanying figures in which:
Fig. 1 is a schematic representation of a flowsheet of a process for recovering vanadium from vanadium bearing slag, according to an embodiment of the disclosure.
Further, persons skilled in the art to which this disclosure belongs will appreciate that elements in the figures are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the figures by conventional symbols, and the figure may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the figure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
DETAILED DESCRIPTION OF THE DISCLOSURE
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiment illustrated in the figures and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Such alterations and further modifications to the disclosure, and such further applications of the principles of the disclosure as described herein being contemplated as would normally occur to one skilled in the art to which the disclosure relates are deemed to be a part of this disclosure.
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.
The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such a process or a method. Similarly, one or more devices or sub-systems or elements or structures or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other devices, other sub-systems, other elements, other structures, other components, additional devices, additional sub-systems, additional elements, additional structures, or additional components. Appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
Unless otherwise defined, 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 disclosure belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.
Embodiments of the present disclosure will be described below in detail with reference to the accompanying figure.
V2O5 is a versatile material in terms of properties and importance in high tech applications. It can be used as counter electrode (CE) in dye-sensitized solar cell. It is also used as a catalyst in the manufacture of H2SO4. It also finds wide applications in electronics industry. One of the potential applications is in the production of vanadium redox flow batteries.

The present technology for extracting vanadium from vanadium bearing slag has high overall vanadium recovery = 85%. Because of solvent extraction technique used for removal of impurities high purity V2O5 is obtained.

A process (100) for extracting vanadium from vanadium bearing slag is disclosed. In one embodiment, the process includes, roasting (102), pulverization (104), leaching (106), filtration (108), solvent extraction (110), precipitation (112), filtration (114), washing (116), drying (118) and roasting (120). The slag generally contains 4-10% vanadium
At step 102, the slag is subjected to oxidative roasting at high temperatures which ranges from 600-1000oC for 2-6 hr in presence of air. The roasted slag is pulverized at step 104 to obtain 100% minus 200 mesh (BSS) particles. The powder obtained after pulverization 104 is leached at step 106 using 1-2 M H2SO4 along with a reductant sodium meta bisulphite as lixiviant at 70-90oC for 2-4 hr. After leaching, leach residue is separated from slurry via filtration at step 108. Leach solution after pH adjustment is purified through solvent extraction at step 110 using 15-25% D2EHPA. The vanadium is precipitated at step 112 from stripped solution as ammonium salt of vanadium by increasing the solution pH to 6.0-7.0 using NH4OH. Ammonium salt of vanadium is filtered at step 114. Step 114 is followed by 116 where the precipitated cake is first washed using 2-5% (NH4)2SO4 solution and then dried at step 118 in oven at 108oC for 8 hr. till constant weight is achieved. The dried ammonium salt of vanadium is roasted in furnace at temperature of 450-550oC for 2-3 hr. to get V2O5 at step 120. The purity of V2O5 was found to be = 99.0%.
Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by the specific example. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible.
Using sodium meta bisulphite in combination with sulphuric acid enhances the recovery during leaching step. In the present process an overall vanadium recovery of >85% is achieved. The final product V2O5 with 99% purity is obtained. Further, this process is applicable to all types of vanadium bearing slags.
A specific example of the entire process is given below:
Example
200g of vanadium bearing slag having the following composition as given in Table 1 was roasted at a temperature of 800 oC for a period of 4 hr. The weight of roasted material was 112 g. During roasting a weight loss of 44% was observed. The elemental analysis of the as received and roasted material is given in Table 1.
TABLE-1
METAL ANALYSIS OF VANADIUM BEARING AND ROASTED SLAG
Fe Al V
As Received Material % 1.76 4.73 5.09
Roasted material % 3.14 8.45 9.10

The roasted material was pulverized to obtain 100% passing through 200 MESH (BSS) particle size and leached under the following conditions:
Leaching temperature 70oC
Leaching time 2 hour
H2SO4 1.1kg/kg of roasted slag
Sodium meta bisulphite 0.2kg/kg of roasted slag
Pulp density 5% (wt/wt)
The resulting slurry was taken for filtration wherein the leach residue is discarded and the leach liquor (filtrate) of following composition was obtained as given in Table 2.
TABLE-2
LEACH SOLUTION COMPOSITION

Leach solution composition Fe, ppm Al , g/l V, g/l
550.00 4.15 4.82

Vanadium recovery during leaching was found to be 93.6 %
The leach liquor so obtained was subjected to solvent extraction after adjusting the pH in the range of 2.0-3.0 using dilute NaOH. 20% D2EHPA neutralized with dilute NaOH was used as the extractant in solvent extraction. Three stages of extraction were used to load 92.1% vanadium from the leach liquor followed by single stage scrubbing using 20g/l H2SO4 solution. The stripping was carried out in 2 stages. 2 M H2SO4 was used to selectively strip vanadium. The stripping efficiency was 99%. The organic was then subjected to second stage of stripping using 6M HCl to remove iron and aluminum loaded during extraction. The organic was finally washed with DM water in a single stage washing. The stripped solution containing vanadium is taken for precipitation. The composition of vanadium rich stripped solution is given in Table 3.
TABLE-3
PURIFIED STRIPPED SOLUTION COMPOSITION

stripped solution composition Fe , ppm Al , ppm V, g/l
50.00 270.00 24.30

The precipitation of vanadium from stripped solution as ammonium salt of vanadium was carried out by pH adjustment to 6.5-7.0 using ammonium hydroxide solution followed by filtration and washing of cake with 4% (NH4)2SO4 solution. The cake so obtained was first dried at a temperature of 108oC followed by roasting (120) at 500oC for a period of 2 hours to obtain V2O5. The V2O5 so obtained was 99.05 % pure.
TABLE-4
FINAL PRODUCT (V2O5) ANALYSIS

Elemental Analysis % V2O5 % Al % Fe
99.05 0.20 0.05

Overall recovery of vanadium was 85.34% resulting 99.05% of V2O5.
,CLAIMS:We claim
1. A process (100) for treating vanadium bearing slag to recover vanadium, the process comprising:
oxidatively roasting (102) the vanadium bearing slag to obtain a roasted slag;
pulverizing (104) the roasted slag to obtain a pulverized slag having a particle size of 100% passing through 200 mesh BSS;
leaching (106) the pulverized slag with sulphuric acid and sodium meta bisulphite to form a leached slurry;
filtering (108) the leached slurry to separate a leach residue and a leach liquor;
adjusting pH of the leach liquor;
subjecting the leach liquor to a solvent extraction (110) to obtain a stripped solution;
treating the stripped solution with ammonium hydroxide solution to adjust pH and to precipitate (112) vanadium as ammonium salt of vanadium;
filtering (114) to separate the ammonium salt of vanadium;
washing (116) and drying (118) the ammonium salt of vanadium; and
roasting (120) the ammonium salt of vanadium to obtain V2O5.

2. The process (100) as claimed in claim 1, wherein the vanadium bearing slag is oxidatively roasted (102) at a temperature ranging from 600 to 1000oC for a period of 2-6 hours.

3. The process (100) as claimed in claim 1, wherein leaching (106) the pulverized slag comprises leaching with sulphuric acid having a molarity of 1-2 M and sodium meta bisulphite at a temperature of 70 to 90oC for 2 to 4 hours.

4. The process (100) as claimed in claim 1, wherein the leach residue is a solid.

5. The process (100) as claimed in claim 1, wherein leach liquor is subjected to solvent extraction (110) using 20% Di-(2-ethylhexyl) phosphoric acid (D2EHPA) for loading vanadium.

6. The process (100) as claimed in claim 1, wherein 91 to 93 % of the vanadium is loaded to D2EHPA solvent.

7. The process (100) as claimed in claim 6, wherein the vanadium loaded D2EHPA solvent is stripped with 2 M H2SO4.

8. The process (100) as claimed in claim 1, wherein pH of the vanadium loaded D2EHPA solvent is adjusted to 6.0 to 7.0 to precipitate (112) vanadium as an ammonium salt of vanadium.

9. The process (100) as claimed in claim 1, wherein the precipitated ammonium salt of vanadium is dried (118) at 108oC.

10. The process (100) as claimed in claim 1, wherein the dried ammonium salt of vanadium is roasted (120) in furnace to obtain V2O5 having a purity of 99.05%.