GB2456537A

GB2456537A - Process for vanadium recovery from residues

Info

Publication number: GB2456537A
Application number: GB0800799A
Authority: GB
Inventors: Matthew Stephen Grimley
Original assignee: GRIMLEY SMITH ASSOCIATES
Current assignee: GRIMLEY SMITH ASSOCIATES
Priority date: 2008-01-17
Filing date: 2008-01-17
Publication date: 2009-07-22
Also published as: GB0800799D0

Abstract

A process is disclosed for extracting vanadium from power station oil and refinery residues which comprises forming an aqueous slurry of powdered residue, oxidising the slurry, filtering out the solids, treating the filtrate with ammonium ions to precipitate vanadium salts, and filtering the precipitated vanadium salts from the solution. The oxidising agent may be hydrogen peroxide or oxygen. The source of ammonium ions may be ammonium sulphate. The pH of the oxidising step may be controlled to 8.5-9.0, with the colour of the filtrate being monitored as part of the control process. The salt precipitated may be ammonium metavanadate or ammonium polyvanadate. Also disclosed is a process for removing vanadium ions from aqueous solution which comprises treating the solution with excess iron (II) ions to precipitate iron (II) vanadate. The solution may be maintained at pH 7.0-7.5. The solution may be heated to 80 {C.

Description

2456537

-1 -

PROCESS FOR VANADIUM RECOVERY FROM POWER STATION AND

REFINERY RESIDUES

Field of the Invention

This invention relates to a process for the recovery of vanadium from cer-5 tain power station and oil refinery residues, and to a process for removing vanadium ions from an aqueous solution, for example the waste resulting from the recovery process of the invention.

Background to the Invention

In petroleum refining, crude petroleum is distilled to separate it into useful 10 products such as jet fuel, gasoline, diesel oil, motor oils and waxes. A heavy tar-like residue remains, which can be processed at high temperatures and pressures to crack the large molecules into smaller molecules, yielding further useful products. The residue of this process is a hard petroleum coke consisting mainly of carbon, with some hydrocarbons, sulphur and trace amounts of 15 metals. Further processing may extract the residual hydrocarbons.

Crude petroleum from some oilfields, notably those in Venezuela and Canada, are high in vanadium, and so the petroleum cokes from refineries handling such petroleum can have significant concentrations of this metal, which has a range of industrial uses, including as a component of specialist steels 20 and, in oxide form, as a catalyst in chemical processes.

In addition, power stations burning fuels high in vanadium produce residues in which the metal is concentrated, and these residues require treatment both to permit their safe disposal and to extract the valuable metal for industrial use.

25 Summary of the Invention

According to the invention, there is provided a process for extracting vanadium from power station and oil refinery residues, for example petroleum cokes, comprising:

a. forming an aqueous slurry of powdered residue; 30 b. oxidising the slurry;

c. filtering out the solids;

-2-

d. treating the filtrate with ammonium ions to precipitate vanadium salts; and e. filtering the precipitated vanadium salts from the solution.

The solids to liquid ration of the slurry is preferably controlled so as to 5 maintain the highest possible vanadium concentration in the resulting filtrate.

Oxidation of the slurry is preferably carried out by the addition of gaseous oxygen or hydrogen peroxide. Gaseous oxygen may be bubbled through the slurry using a sparge system. Alternatively, 40% by volume aqueous hydrogen peroxide may be added.

10 The addition of ammonium ions to the filtrate can be achieved by the in troduction of ammonia gas, liquefied ammonia, or solid ammonium sulphate, added in powder form to the filtrate.

Different processes to precipitate out different vanadium salts may be employed, as defined in the claims.

15 The resulting filtrate after removal of the precipitated vanadates will still contain some dissolved metal, as the vanadates are slightly soluble. These will need to be removed prior to disposal or discharge of the filtrate. Accordingly, another aspect of the invention provides a process for removing vanadium ions from an aqueous solution, comprising treating the solution with excess iron (II) 20 ions to precipitate insoluble iron (II) vanadate Fe2V03 and filtering off the solids.

Preferably, the process is carried out at a pH of 7.0 - 7.5, which may be achieved by the addition of sodium hydroxide. The filtrate is preferably heated to at least 80°C before addition of the iron (II) sulphate, which is preferably added in a quantity seven times excess of the stoichiometric amount. 25 It has been found that the vanadium content of the filtrate can be re duced to less than 2 ppm.

Brief Description of the Drawings

In the drawings, which illustrate in flow diagram form exemplary processes according to different aspects of the invention:

30 Figure 1 illustrates a process according of extracting vanadium from power station and refinery residues; and

-3-

Figure 2 illustrates a process of removing soluble vanadium compounds from process waste.

Detailed Description of the Illustrated Embodiment

Referring first to Figure 1, the powdered petroleum coke is mixed with 5 hot water at approximately 60°C in a mixing tank 1 in a weight ratio of one part of coke to two parts of water, the mixing continuing until uniform consistency is achieved - approximately one hour. The slurry is then transferred to the process tank 2, where the pH is adjusted by the addition of sodium hydroxide to 8.5 - 9.5. Oxygen is introduced into the slurry and mixing is carried out while moni-10 taring the pH, adding further sodium hydroxide to maintain its value. The temperature of the slurry in the tank is maintained at 60°C by means of steam through a heating coil, or introduced direct into the slurry. When the pH stabilises, it is adjusted to a value of 7.9 to 8.3 using sodium hydroxide or sulphuric acid as required. The colour of the filtrate is then checked. If the filtrate is col-15 ourless at this stage, the reaction mixture is passed to a filter 3, but if not the mixture is heated in the tank 2 to at least 80°C and held at this temperature until a filtrate sample is colourless. The heat treatment changes the state of the vanadium from decavanadate to metavanadate. It is essential that the filtrate is colourless before the precipitation stage is carried out.

20 The filter 3 removes the residual carbon, which can then be used in, for example, the manufacture of carbon electrodes, or simply burned as a fuel for its calorific value. The filtrate is passed to a precipitation tank 4, where ammonium sulphate is added. When precipitation of the ammonium metavanadate begins, the solution is cooled (the colder the mixture at this stage, the better). 25 The mixture is stirred until precipitation is complete. On completion, the vanadium concentration in the filtrate will be 0.20 to 0.3%, dependent on the temperature. The mixture is then passed through a second filter 5 to separate off the ammonium metavanadate, the filtrate being passed for further treatment as hereinafter described with reference to Figure 2. The solids typically have a 30 moisture content of less than 25% and are pure white.

The filtrate resulting from the extraction process contains a low concentration of ammonium metavanadate, since it is slightly soluble in water

-4-

(4.8g/dm3 at 20°C), but sufficient to require removal before discharge of the waste water. Figure 2 illustrates a process for removal of substantially all the residual vanadium salt. The filtrate is passed to a final treatment tank 6 where it is heated to 80°C by means of steam heating coils and its pH is adjusted to 7.0 5 to 7.5 by the addition of sodium hydroxide. While the contents of the tank are agitated by air injection, iron (II) sulphate is added to the tank in an amount equivalent to seven times the stoichiometric amount. The pH is maintained at 7.0 to 7.5 while the iron (II) sulphate reacts with the vanadium compound to form iron (II) vanadate Fe(V03)2, which is substantially insoluble in water and 10 therefore forms a precipitate, which can be filtered off in a further filter 7, together with the excess iron (II) sulphate, which forms an insoluble hydroxide. The filtrate will contain less than 2 ppm V (as vanadium ions).

-5-

Claims

1. A process for extracting vanadium from power station and oil refinery residues, comprising:

a. forming an aqueous slurry of powdered residue;

5 b. oxidising the slurry;

c. filtering out the solids;

d. treating the filtrate with ammonium ions to precipitate vanadium salts, and e. filtering the precipitated vanadium salts from the solution.

10 2. A process according to Claim 1, wherein step b. comprises treat ing the slurry with gaseous oxygen or hydrogen peroxide.

3. A process according to Claim 1 or 2, wherein step d. comprises adding ammonium sulphate solution to the filtrate.

4. A process according to any preceding claim, wherein step b. is

15 carried out while maintaining the pH of the slurry at at least 8.5.

5. A process according to Claim 4, wherein sodium hydroxide is added to the slurry to adjust the pH.

6. A process according to Claim 4 or 5, comprising periodically obtaining samples of a filtrate from the slurry during the oxidation step b. and de-

20 termining the colour of the filtrate, and carrying out step c. only when the filtrate sample is colourless.

7. A process according to Claim 4 or 5, comprising monitoring pH during the oxidation process and when the pH stabilises adjusting the pH to 7.9-8.3, then determining the colour of a sample filtrate from the slurry and, if the

25 filtrate is colourless, proceeding to step c., or if the filtrate is not colourless, heating the slurry to 80°C and maintaining the temperature while periodically obtaining samples of a filtrate from the slurry and carrying out step c. only when the filtrate sample is colourless.

8. A process according to any of Claims 1 to 3, wherein step b. is

30 carried out at a pH of 8.5 to 9.0 while periodically obtaining samples of a filtrate from the slurry and determining the colour of the filtrate, and when the filtrate

-6-

sample is a clear pale yellow adjusting the pH to 9.0 and maintaining this pH while stirring for 2 hours before proceeding to step c.

9. A process according to any preceding claim, wherein the step d. is carried out at a pH of 7.9 to 8.3 and the vanadium salt precipitated out is am-

5 monium metavanadate NH4VO3.

10. A process according to any of Claims 1 to 8, wherein in step d. the pH is reduced to 2.4 to 2.6 and the temperature of the filtrate is maintained at 80°C while ammonium ions are introduced, the vanadium salt precipitated out being ammonium polyvanadate (NH^VeOie.

10 11. A process according to Claim 10, wherein the pH is reduced by the addition of sulphuric acid.

12. A process according to any of Claims 1 to 8, wherein in step d. the pH is reduced to 5.3 to 5.8 using sulphuric acid before addition of ammonium ions to precipitate out sodium ammonium vanadate (NhUJNasVsC^.

15 13. A process for removing vanadium ions from an aqueous solution,

comprising treating the solution with excess iron (II) ions to precipitate insoluble iron (II) vanadate Fe(VC>3)2 and filtering off the solids.

14. A process according to Claim 13, comprising maintaining the pH of the solution at 7.0 - 7.5.

20 15. A process according to Claim 13 or 14, which comprises heating the solution to 80°C.

16. A process according to Claim 13, 14 or 15, comprising adding a quantity of iron (II) sulphate equal to seven times stoichiometric.