Process for the separation of vanadium

Abstract

The present invention relates to a process for the separation of vanadium in the form of vanadium oxide, iron-vanadium-oxide, or iron-vanadium from solutions containing both dissolved iron and dissolved vanadium, wherein an aqueous solution containing dissolved iron and vanadium in a molar iron-to-vanadium ratio of above 1:1, preferably above 1:1 and up to 10000:1, more preferably between 5:1 and 1000:1, even more preferably between 5:1 and 100:1, and most preferably between 10:1 and 50:1 and optionally also other elements is oxidized in an oxidation step with a gaseous oxidation media, and wherein the amount of acid in the aqueous solution is kept below the stoichiometric amount of acid required during bivalent iron oxidation and the precipitate thus formed is removed from the solution.

Claims

1. A process for separating vanadium in the form of vanadium oxide, iron-vanadium-oxide, or iron-vanadium from solutions containing both dissolved iron and dissolved vanadium, the method comprising oxidizing an aqueous solution containing dissolved iron and vanadium in a molar iron-to-vanadium ratio of above 1:1, and optionally also other elements at a reaction temperature of between 100 and 300 C. with a gaseous oxidation media, wherein acid is present in the aqueous solution during the oxidation and the acid is kept in an amount below the stoichiometric amount of acid required during bivalent iron oxidation, and removing precipitate thus formed from the aqueous solution.

2. The process according to claim 1, wherein the removing the precipitate from the solution comprises a solid/liquid separation process.

3. The process according to claim 1, wherein the reaction temperature is from 120 C. to 200 C.

4. The process according to claim 1, wherein the gaseous oxidation media is a gas mixture comprising inert gas and oxygen.

5. The process according to claim 1, wherein the gaseous oxidation media comprises air, mixtures of air and oxygen, and pure oxygen.

6. The process according to claim 1, wherein the oxidizing is carried out at an operating pressure above the aqueous solution's vapor pressure at the reaction temperature.

7. The process according to claim 1, wherein the aqueous solution is preconcentrated prior to the oxidizing.

8. The process according to claim 1, wherein the acid in the aqueous solution is controlled by adding a base to the aqueous solution.

Description

EXAMPLE 1 (COMPARATIVE EXAMPLE)

(1) An aqueous solution containing 34 wt % FeCl.sub.2, 9 wt % FeCl.sub.3, 10 wt % HCl, 2 wt % MgCl.sub.2, 0.2 wt % VCl.sub.3, and 0.9 wt % other chlorides has been prepared (molar iron-to-vanadium ratio=255:1). The solution was heated in an autoclave to 150 C. and oxygen gas was introduced as oxidation media for the oxidation step. The total pressure within the autoclave was approx. 5 bar(g), with an initial vapour pressure of the aqueous solution at the chosen temperature of approx. 3.5 bar(g), where bar(g) here and in the following refers to bar above atmospheric pressure. At the end of the oxidation step, no solids were found in the oxidised solution, the entire amount of ferrous chloride FeCl.sub.2 has been converted to ferric chloride FeCl.sub.3 and no vanadium precipitated. Regarding molar amounts, the initial concentration of FeCl.sub.2 was 0.27 mol per 100 g solution and the initial concentration of HCl was 0.28 mol per 100 g solution (i.e. 102% acid of the stoichiometric amount required). No oxide precipitated from the solution during the oxidation step.

EXAMPLE 2

(2) An aqueous solution containing 31 wt % FeCl.sub.2, 8 wt % HCl, 1 wt % MgCl.sub.2, 0.8 wt % VCl.sub.3, and 0.5 wt % AlCl.sub.3 was prepared (molar iron-to-vanadium ratio=48:1). This solution was heated in an autoclave to 150 C. and oxygen gas was introduced as oxidation media for the oxidation step. The total pressure within the autoclave was approx. 5 bar(g), with an initial vapour pressure of the aqueous solution at the chosen temperature of approx. 2.6 bar(g). The molar amount of HCl as present in the starting solution was below the molar amount of FeCl.sub.2 (90% acid of the stoichiometric amount required), and therefore at the end of the oxidation step and after filtration, a filter cake formed by the precipitates could be separated from the oxidized solution. This filter cake was washed with water and then dried. The dried filter cake contained 29 wt % Fe, 26 wt % V, 0.9 wt % Al, and 0.01 wt % Mg. Phase analysis of the filter cake revealed a major amount of the solid contents being present in the form of iron vanadate (triclinic FeVO.sub.4).

(3) The aqueous solution that has been used in this example initially contained 5.7 g of dissolved vanadium. The major amount of this vanadium ended up in the filter cake; in the filtrate and in the wash water, 0.09 g (that is 2% of 5.7 g) and 0.006 g (that is 0.1% of 5.7 g) vanadium, respectively, was found.

EXAMPLE 3

(4) An aqueous solution containing 33 wt % FeCl.sub.3, 5 wt % FeCl.sub.2, 0.6 wt % HCl, 1 wt % MgCl.sub.2, 0.8 wt % VCl.sub.3, and 0.5 wt % AlCl.sub.3 was prepared (molar iron-to-vanadium ratio=48:1). The solution was heated in an autoclave to 150 C. and oxygen gas was introduced as oxidation media for the oxidation step. The total pressure within the autoclave was approx. 5 bar(g) with an initial vapour pressure of the aqueous solution at the chosen temperature of approx. 1.5 bar(g). The molar amount of HCl as present in the starting solution was below the molar amount of FeCl.sub.2 (42% acid of the stoichiometric amount required), and therefore at the end of the oxidation step and after filtration, a filter cake formed by the precipitates could be separated from the oxidized solution. This filter cake was washed with water and then dried. The dried filter cake contained 29 wt % Fe, 27 wt % V, 1.5 wt % Al, and Mg below limit of detection. Scanning electron microscope images revealed a similar appearance as the filter cake from Example 2 above.

(5) The aqueous solution that has been used in this example initially contained 4 g dissolved vanadium. The major amount of this vanadium ended up in the filter cake; in the filtrate and in the wash water, 0.2 g (that is 5% of 4 g) and 0.01 g (that is 0.3% of 4 g) vanadium, respectively, was found.

EXAMPLE 4

(6) 1.7 g of the washed and dried filter cake from Example 3 was leached with 12.8 g caustic soda (25 wt % NaOH) at 100 C. The remaining solids (iron oxide) were separated with a centrifuge and washed with water, which washing water was then added to the filtrate. The combined filtrates were then neutralized slowly with hydrochloric acid (37 wt % HCl), and at a pH of 11 approx. 2 mL of ammonia (32 wt % NH.sub.3) were added. Then, further hydrochloric acid was added and at a pH of 7.8, the addition of acid was stopped. The precipitate thus formed was filtered off and dried (vanadium product).

(7) Regarding the contents of iron and vanadium, the solids separated by the centrifuge in example 4 (iron oxide) contained 43 wt % Fe and 0.2 wt % V, while the product obtained from the filtrate after neutralisation (vanadium product) contained 56 wt % V and 0.2 wt % Fe. Phase analysis of the iron oxide revealed that mainly hematite was formed.

EXAMPLE 5

(8) Example 2 was repeated at different operating conditions: The oxidation step was carried out at 130 C. and a total pressure of approx. 3.5 bar(g). The initial vapour pressure of the aqueous solution at the chosen temperature was approx. 1.3 bar(g). The filter cake formed by the precipitates contained 34 wt % Fe, 26 wt % V, 0.02 wt % Al, and 0.00 wt % Mg.

(9) In this example, the aqueous solution contained initially 3.9 g of dissolved vanadium. 2.9 g vanadium ended up in the filter cake (73% of 3.9 g).

EXAMPLE 6

(10) An aqueous solution containing 39 wt % FeCl.sub.2, 3.5 wt % HCl, 0.07 wt % VCl.sub.3, and traces of other metal chlorides was prepared (molar iron-to-vanadium ratio=8500:1). The solution was heated in an autoclave to 150 C. and oxygen gas was introduced as oxidation media for the oxidation step. The total pressure within the autoclave was approx. 7 bar(g). The molar amount of HCl as present in the starting solution was below the molar amount of FeCl.sub.2 (31% acid of the stoichiometric amount required), and therefore at the end of the oxidation step and after filtration, a filter cake formed by the precipitates could be separated from the oxidized solution. Almost the entire amount of vanadium ended up in the filter cake; in the aqueous solution, it was found to be below its limit of quantification.

REFERENCES

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