AU641593B2

AU641593B2 - Oxalate salt roasting of vanadium bearing concentrates

Info

Publication number: AU641593B2
Application number: AU18453/92A
Authority: AU
Inventors: Wayne Ronald Seabrook
Original assignee: PRECIOUS METALS AUSTRALIA LIMI
Current assignee: Windimurra Vanadium Pty Ltd
Priority date: 1991-07-15
Filing date: 1992-06-19
Publication date: 1993-09-23
Anticipated expiration: 2012-06-19
Also published as: AU1845392A

Description

COMPLETE SPECIFICATION For a Standard Patent

ORIGINAL

.00.

*to* t.* .0 Name of Applicant: Actual Inventor(s): PRECIOUS METALS AUSTRALIA LIMITED WAYNE RONALD SEABROOK Address for Service: WRAY ASSOCIATES, Primary Industry House, terrace, Perth, Western Australia, 6000.

239 Adelaide Attorney code: WR Invention Title: OYL-ATE S/kt-r 90~f 4 \Jc1 OF VAONAUbWM 8E-AKWr.7A COMCEktrKATE 9 Details of Associated Provisional Application: No: PK7 222 Thce following statement is a full description of this invention, including the best method of performing it known to us:- 1- 2 The present invention relates to vanadium processing.

The invention has particular relevance to the salt roast processing of vanadium concentrates such as vanadiferous titanomagnetite concentrates. However, it must be appreciated that the invention may also find use in the salt roast processing of other vanadium bearing concentrates such as fly ashes, oil residues and slag material.

Titaniferous magnetite deposits containing vanadium are widely distributed throughout the world and constitute the world's largest vanadium reserves. Vanadium exists as a replacement of the ferric ion within titaniferous magnetite.

Vanadium bearing ore is usually crushed and milled, and is 15 then processed by magnetic separation and/or gravity separation techniques to produce a vanadiferous titanomagnetite concentrate. This beneficiation is generally carried out by magnetic separation. Such upgrading also has the benefit of decreasing the silica, 20 calcium and magnesium content of the concentrate thereby *:*"giving greater recovery in the vanadium extraction process.

The most effective method of recovering vanadium from a vanadiferous titanomagnetite concentrate is salt roasting followed by water leaching and precipitation of ammonium vanadates. The purpose of salt roasting refractory metal ores such as these is to render metal values water soluble.

Roasting converts the metal to an oxidic anion of its maximum valence state, and in this case vanadium may be then converted from the tri-valent state V 2 0 3 to the pentavalent state V 2 0 5 The salts of sodium are most frequently used as the flux for salt roast processes due to their effectiveness and 3 cost, such salts being sodium chloride (NaCI), sodium carbonate (Na 2

CO

3 and sodium sulphate (Na 2 S04). It will be understood that "salt" is referred to in its general sense, meaning a combination of a metal cation and an acid anion.

Salt roast procesEes specifically for vanadium date to the turn of the century. One such process involved roasting a vanadium ore with sodium chloride and/or an alkali sodium salt such as sodium carbonate, followed by water leaching and acid leaching to extract any residual vanadium. Many variations on this theme have since appeared. However, the salt of sodium most frequently used today is sodium carbonate. Sodium chloride, being a cheaper alternative, has previously been used but was discontinued as the resultant chlorides caused emission problems and produced HC which caused corrosion problems. The cost of sodium carbonate is one of the four major operating costs of the salt roast process project, the others being the cost of energy used, labour costs and the mining or concentrate 20 supply.

It is an object of this invention to provide an alternative to the often used sodium carbonate for the salt roast processing of vanadium bearing concentrates. With this in mind, the present invention is characterised by the salt roasting of vanadium bearing concentrates, such as vanadiferous titanomagnetit.e, with sodium oxalate (Na 2

C

2 O4).

The results obtained by using sodium oxalate as an alternative flux in the salt roasting of vanadiferous titanomagnetite concentrate show sodium oxalate to be superior to both sodium carbonate and sodium sulphate in terms of recovery. Further, as the oxalate is more reactive than either of those fluxes it allows roasting at a lower temperature and for a shorter residence time. This 4 of course results in considerable energy savings, which makes the use of the oxalate cost effective.

Sodium oxalate is a by-product of the Bayer process for alumina production. Particularly in Western Australia, the alumina refineries produce large volumes of sodium oxalate as an unwanted contaminant of their liquor stream which may present environmental problems on disposal. Thus, as sodium oxalate can be successfully used in the salt roasting of vanadium bearing concentrates it provides a 10 salt for the roasting process which is relatively cheap (being sold as an unwanted contaminant) and thus provides further significant economic advantages when compared to other salts such as sodium carbonate and sodium sulphate.

The composition of sodium oxalate is variable and may 15 contain a range of impurities, and the term "sodium .":'oxalate" as used throughout this specification includes compositions that fall within the following typical ranges:- Na2C204 Sodium Oxalate 30-100% S 20 H20 Water 0-50%.

Na2CO3 Sodium Carbonate NaAlO 2 Sodium Aluminate 0-10% NaOH Sodium Hydroxide Other Sodium Salts Further, the sodium oxalate filter cake obtained as a byproduct of the Bayer process also contains some alumina.

The presence of the aluminium in this for, has been found to be beneficial in that it is able to form insoluble compounds with silica, reducing the amount of silica solubilised in the leach liquor.

The use of sodium oxalate is additionally advantageous when compared to sodium carbonate as the sodium oxide produced 5 thereby reacts more efficiently with the vanadiferous ore to produce sodium vanadate. The reasons why this is so are not completely understood but the following are believed to contribute: The exothermic reaction involving the decomposition of sodium oxalate may increase the oxidation rate of the titano magnetite.

A solid-solid reaction may occur between the slightly caustic oxidising agent sodium oxalate and the ore S 10 concentrate, which increases the oxidation rate of the titano magnetite.

The sodium oxide formed from sodium oxalate may be more reactive than that formed from sodium carbonate due to a finer grain size, or higher porosity.

The sodium carbonate formed from sodium oxalate may have a slightly lower melting point due to impurities.

In a preferred form, the process of the invention may be used to recover vanadium (in the form of vanadium pentoxide

V

2 0 5 from an ore deposit of vanadiferous titanomagnetite such as that found at Windimurra in Western Australia. A vanadiferous titanomagnetite concentrate may be produced from the ore by normal beneficiation techniques such as crushing and grinding followed by gravity and/or magnetic separation. The concentrate may have a grind size ranging from 45 to 425 microns, and may have the following average range of compositions: V205 (equivalent) 1-30% Total Fe 10-60% (as Fe 3 0 4 FeTiO 3 TiO 2 10-20% (as FeTi0 3 SiO 2 1-50% Al203 1-50% MnO 0.1-0.5% 6 In this preferred form, t roasting of the concentrate a Sodium Oxalate (Na 2

C

2 0 4 Roast temperature Roast Duration he parameters for the salt re preferably: 1-10% 900-1350 deg C 45-120 minutes *5 The sodium oxalate preferably decomposes via an exothermic reaction to sodium carbonate at a temperature of between 250 deg C to 520 deg C. The sodium carbonate then decomposes to sodium oxide at approximately 1000 deg C.

The reactions of the sodium oxalate are as follows:

S

.55*5 Na2C204 Na2CO 3 Na 2

CO

3 CO(gas) (exothermic) Na 2 0 CO2(gas) at 1000 deg C In general, the sodium oxide Na20 would react with most of the metal ions present in the concentrate in the order of:

V

2 0 5 Cr 2 0 3 SiO 2 TiO 2 Al 2 0 3 Fe20 3 CaO During the heating the concentrate is oxidised to hematite Fe 2 0 3 pseudo brookite FeTiO 5 and vanadium pentoxide V205' For example:

V

2 0 3 02

V

2 0 The sodium oxide reacts to form water soluble sodium vanadate:

V

2 0 5 Na20 2NaVO 3 Other soluble compounds which may form are sodium silicate, sodium aLuminate, and sodium dichromate. While some sodium 7 ferrate and sodium titanite may also form, these quickly decompose in water to form their respective insoluble metal oxides and sodium hydroxide.

Subsequent water leaching of the roast calcine dissolves the pentavalent vanadium as sodium vanadate NaVO 3 Leach water temperature is normally 70 to 100 deg C and leach time may vary from 10 minutes to several days depending on the particular process route and the materials handling parameters. Most leaching is done on a batch system with a 10 solid-liquid ratio of about 1:5. The leach solution and solids are normally agitated during the entire leach time.

Silicas may be removed from the pregnant leach liquor by the addition of sulphuric acid and aluminium sulphate, and the vanadate ion may then be removed by the addition of an 15 ammonium ion in the form of ammonium sulphate or ammonium chloride which causes the precipitation of ammonium metavanadate (AMV) or ammonium polyvanadate (APV). The AMV contains vanadium in the pentavalent state whereas the APV contains vanadium in the trivalent state, while the form of the precipitate, APV or AMV, is governed by the pH of the chemical reaction (APV is formed in a more acid reaction than AMV). The addition of sulphuric acid or sodium hydroxide controls the pH.

The ammonium metavanadate may be roasted in a rotary "deammoniation" furnace at approximately 200 deg C to about 500 deg C to drive off the ammonia and cause oxidation to vanadium pentoxide. The ammonium polyvanadate may also be de-ammoniated by roasting at about 450 to 500 deg C in an oxidising atmosphere. Following these steps the vanadium pentoxide powder may be melted in a fusion furnace at about 900 deg C and poured onto a cooled wheel to form irregular flakes.

8 Alternatively, the ammonium vanadates may be roasted in a rotary "deammoniation" furnace at temperatures up to 900 deg C and under reducing conditions to form vanadium trioxide

(V

2 0 3 The process steps described above that take place after roasting with sodium oxalate, that is from watei leaching through to the production of pure vanadium oxides, are presented to provide a complete description of a preferred *process flowsheet. However, the use of Na2C204 or Na2CO3 10 does not significantly affect those subsequent process operations, hence modifications to the process including and subsequent to water leaching are not to affect the generality of the invention described above.

In order to better illustrate the effectiveness of the 15 preferred embodiment of the invention described above, results of various roasting trials have been included in Figure 1. These trials involved roasting using the following parameters: *aa* Vanadium Concentrate 1.25% V205 20 Sodium Oxalate Cake 4.25% equiv Na 2

CO

3 (49% Na2C204)

H

2

O)

Na 2

CO

3 NaAl02) NaOH) Other Sodium Salts) Roast Temperature 1,200 deg C Roast Time 60 minutes Extraction efficiency achieved was 91% of available vanadium (Figure as compared to 80% extraction efficiency if 4.25% of Na 2

CO

3 was used to treat identical concentrate at 1,200 deg C and 60 minutes roast time.

9 It can be seen from the graph of Figure 1, which compares the extraction of vanadium to the presence of an amount of sodium oxalate, that for equivalent levels of flux significantly better extraction results are obtained with sodium oxalate than with sodium carbonate.

Of eaurse these skilled in th art will appreciate tthere may be many variations a d---fit ations of the general proces e aabove which are within the scope .the proocnt invention.

Claims

1. A method for the salt roast processing of vanadium bearing concentrates, wherein a vanadium bearing concentrate is salt roasted with sodium oxalate.

2. A method according to claim 1 wherein the vanadium bearing concentrate is vanadiferous titanomagnetite.

3. A method according to claim 1 or claim 2 wherein the sodium oxalate is a by-product of the Bayer process for alumina production. 0,

4. A method according to any one of claims 1 to 3 wherein S the sodium oxalate contains alumina which is capable of forming insoluble compounds with silica thus reducing the amount of silica solubilised in leach liquor. %6 A method according to any one of claims 1 to 4 wherein an ore deposit of vanadiferous titanomagnetite is subjected 00. to beneficiation techniques to produce a vanadiferous titanomagnetite concentrate for salt roasting.

6. A method according to claim 5 wherein the vanadiferous titanomagnetite concentrate has a grind size ranging from to 425 microns, and comprises: V 2 0 5 (equivalent) 1-30% Total Fe 10-60% (as Fe 3 0 4 FeTiO 3 TiO 2 10-20% (as FeTiO 3 SiO 2 1-50% Al203 1-50% MnO 0.1-0.5%

7. A method according to any one of claims 1 to 6 wherein the salt roast is conducted at 900 to 1350 deg C and for a duration of 45 to 120 minutes. 11

8. A method according to any one of claims 1 to 7 wherein 1 to 10% sodium oxalate is used.

9. A method according tc any one of claims 1 to 8 wherein the sodium oxalate comprises: Na2C204 30-100% 0-50% Na CO 3 2 3 NaAlO 2 0-10% NaOH Other Sodium Salts o o A method according to any one of claims 1 to 9 wherein the calcine produced by the salt roast is subsequently S. subjected to water leaching to dissolve pentavalent vanadium as sodium vanadate.

11. A method according to claim 10 wherein the water leach is conducted at a temperature from 70 to 100 deg C, for times of from 10 minutes to several days, in a batch system with a solid-liquid ratio of about 1 to 9

12. A method according to claim 10 or claim 11 wherein the pregnant leach liquor produced by the water leach is subjected to the addition of sulphuric acid and aluminium sulphate to remove silicas.

13. A method according to claim 12 wherein ammonium sulphate or ammonium chloride is then added to remove vanadate ion to precipitate ammonium metavanadate or ammonium polyvanadate. 12

14. A method according to claim 13 wherein the ammonium metavanadate is roasted in a rotary deammoniation furnace of from 200 to 500 deg C to remove ammonia and cause oxidation to vanadium pentoxidi. A method according to claim 13 or claim 14 wherein the ammonium polyvanadate is deammoniated by roasting at from 450 to 500 deg C in an oxidising atmosphere to produce vanadium pentoxide.

16. A method according to claim 14 or claim 15 wherein the vanadium pentoxide in powder form is melted in a fusion furnace at about 900 deg C and is poured onto a cooled wheel to form irregular flakes.

17. A method according to claim 13 wherein the ammonium Svanadates are roasted in a rotary deammoniation furnace at temperatures up to about 900 deg C under reducing conditions to form vanadium trioxide.

18. A method according to claim 1 substantially as herein described in relation to the example. DATED this NINETEENTH day of JUNE 1992 PRECIOUS METALS AUSTRALIA LIMITED Applicant. WRAY ASSOCIATES, Perth, Western Australia, Patent Attorneys for the Applicant. ABSTRACT A method of salt roast processing of vanadium bearing concentrates, such as vanadiferous titanomagne-tite concentrates, by salt roasting with sodium oxalate. 4* r 9 9 99 9 9 9 9 9. 9 99 9 *99*s9 9 99 9 9* 9. 9. 9. 9 9 .9.9 9 .99. 09 999999