WO1997012071A1

WO1997012071A1 - Recovery of vanadium

Info

Publication number: WO1997012071A1
Application number: PCT/AU1996/000614
Authority: WO
Inventors: John Sydney Hall; Roy Randall Lovel; Ronald Miles Anthony
Original assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date: 1995-09-27
Filing date: 1996-09-26
Publication date: 1997-04-03
Anticipated expiration: 1998-03-27
Also published as: ZA968141B; AUPN564495A0

Abstract

This invention relates to processes for the recovery of vanadium and optionally other metal values from vanadium-bearing materials, especially mineral ores such as titaniferous magnetites, and industrial wastes such as iron ores slag and spent sulphuric acid catalyst. The method of the invention utilises leaching with polycarboxylic organic acid. In a preferred embodiment, the organic acid is citric acid or tartaric acid. The process may be applied to heap leaching.

Description

RECOVERY OF VANADIUM

This invention relates to the recovery of vanadium from a variety of sources. In its general aspect the invention provides a process for the recovery of vanadium from vanadium-bearing materials by leaching with one or more polycarboxylic organic acids. In particular, the invention relates to processes for recovery of vanadium values from vanadium-bearing minerals, mineral slags, and from industrial wastes such as spent vanadium pentoxide catalyst used in preparation of sulphuric acid. Citric acid is the preferred leaching agent.

Citric acid may be produced by many different bacteria and fungi, including organisms naturally occurring in soils, and the preβent invention iβ ideally suited to a biological heap leach process.

BACKGROUND OF THE INVENTION

Vanadium iβ a valuable metal uβed inter alia in production of catalysts, for use for example in sulphuric acid manufacture, and in the production of special metals. In particular, vanadium pentoxide is uβed as catalyst in sulphuric acid production, and in dyes, inks and glasses; vanadium trichloride and vanadium oxytrichloride are used as mordants for dyeβ, and in the manufacture of alloy steels and vanadium-aluminium alloys.

Vanadium is an abundant element in the earth's crust, and is more abundant than many of the familiar metals, such as lead, zinc, nickel, copper and tin. It is found in patronite (V₂S₅+S), carnotite (KV0₂V0₄1.5H₂0) , vanadinite (Pb₅(V0₄)₃Cl), roscoelite, and certain phosphate rocks and crude oils. Nearly 50% of the total known vanad.um

"deposits" occurs in titaniferous magnetite in which V³⁺ has replaced Fe³* within the magnetite (Fe₃0₄) - ulvospinel (Fe₂Ti0₄) mineral series, but the vanadium grade (wt% V₂0₅) iβ generally less than 1.6%, and vanadium is usually extracted either as a co-product or a by-product of other processes. For example mineral processing slags may contain over 8% vanadium, aβ well aβ iron and exotic and precious metals. In many cases, these slags are discarded rather than reprocessed, resulting in the lose of metal values.

Conventional vanadium extraction processes vary, due to the range of chemistry and mineralogy of the resources used. Examples of Vanadium recovery from industrial wastes include a) calcium reduction of vanadium pentoxide, which is able to yield 19.8% pure ductile vanadium; reduction with aluminium, cerium, or other metals can be uβed, but the product is of low purity. b) the solvent extraction of petroleum ash or ferrophoβphoruβ slag resulting from phosphorus production; and c) electrolytic refining, using a molten salt containing vanadium chloride as the electrolyte.

The major unit operations of hydrometallurgical processes are similar, ie. physical beneficiation, one or two salt roasts, a combination of water, alkali or acid leaching, solvent extraction or ion exchange and precipitation. See for example Gupta C.A and Krishnaπrurthy (1992), Extractive Metallurgy of Vanadium, Process Metallurgy 8, Elsevier Science Publishers B.V.

The key to conventional vanadium extraction is the formation of soluble or volatile vanadium salts._ This is generally achieved by roasting the vanadium (eg v₂0₃) with a sodium source to produce a pentavalent vanadium salt, a βtep referred to as "fluxing". Water leaching of the vanadium salt is most commonly used, although acid leaching with H₂S0₄ is used in some operations to attack insoluble vanadates, βuch aβ calcium, iron and magnesium vanadates. Alkali leaches are uβed in other processes to extract vanadium together with uranium, for example from camotite.

It would be highly desirable to provide a low capital cost, natural leaching process for selectively solubilizing vanadium. In developing the preβent invention we have noted that bio-geochemical systems have been uβed extensively in the field for mineral sampling, and Russian researchers have explored applications for bio-geochemical reactions in the mineral industry. (Kovalevβkii A.L., Biochemical Exploration For Mineral Deposits 1987: Utrecht: VMU Science Press) Of particular interest are the mechanisms by which apparently insoluble minerals are extracted from βoilβ and absorbed by plants. For example, vanadium, the target mineral in our study, has been shown to replace phosphorus in phosphorus- deficient biological systems, and it therefore appears that there are natural mechanisms which solubilize vanadium.

Direct acid leaching has been used in commercial leaching procedures, but the non-selective nature of the acid and the high consumption of H₂S0₄ (100 kg per tonne of ore) results in a large volume of low grade solution, high cost, and problems associated with disposal of acid waste.

Organic substances are part of the natural system involved in mineral solubilization. They are preβent in βoilβ, sediments and water and although the nature of the organic compounds making up this material is not completely understood it has been divided into two categories.

i. Nonhumic substances; those with recognisable physical and chemical characteristics (eg. sharp melting, definite Infra-Red Spectrum) ; and ii. Humic substances; those that no longer exhibit specific physical and chemical characteristics. On the basis of solubility in acid and alkali, Schnitzer M and Su (in "Soil Organic Matter", Developments in Soil Science, 1978, New York,

Elsevier Publishing) Cresβer M, Killam K and Killam E T (in "Soil Chemistry and its Applications", Cambridge Environmental Chemistry Series 1993, Cambridge University Press) and others have divided humic substances into three components:

a. Humic acid, which iβ soluble in dilute alkali but is precipitated on acidification of the alkaline extract; b. Fulvic acid, which is soluble in dilute alkali and remains in solution after acidification of the alkaline extract (i.e. it iβ soluble in both dilute alkali or acid) ; and c. Humin, which is the humic fraction that cannot be extracted from the Humic substance.

We have addresβed the posβibility of using humic substances as a solubilizing agent because Jackson W (in "Humic, Fulvic and Microbial Balance: And Organic Soil

Conditioning" 1993 Colarado: Jackson Research Centre) and others, believe that humic substances facilitate "disβolution of moβt otherwiβe insoluble metallic salts and that fulvic acids and humic acids in conjunction with many micro-organism are involved in the weathering of mineral matter.

We have selected citric acid and tartaric acid to demonstrate the invention because they are both low molecular weight, naturally occurring polycarboxylic acid. They are commercially available and both can be produced via fermentation processes. For example, citric acid is produced commercially by fermentation of Aspergillus niger in aerated submerged culture, or by growing Candida lipolytica on long-chain n-alkanes.

It will be clearly understood that the invention contemplates the use of materialβ such as humic acids and fulvic acids in which acids, particularly polycarboxylic acids, similar too and including citric acid and tartaric acid, are active components.

SUMMARY OF THE INVENTION

According to a first aspect, the invention provides a process for recovery of vanadium values and optionally other metal values from a vanadium-bearing material, comprising the step of leaching the vanadium-bearing material with one or more polycarboxylic organic acids. Preferably the polycarboxylic organic acid is present in a humic subβtance. In a particularly preferred embodiment, the polycarboxylic organic iβ citric acid. Alternatively, another polycarboxylic organic acid produced during metabolism of soil microorganisms, for example in the tricarboxylic cycle in metabolism of an aerobic soil microorganism may be used. Citric acid and tartaric acid have both been demonstrated as effective leachantβ.

The vanadium-bearing material may be a naturally-occurring vanadium ore, preferably a titaniferous magnetite; a mineral slag, such as an iron ore βlag reβulting from the refining of iron ore; or may be a by product of industrial processes, such as spent catalyst resulting from sulphuric acid production. The person skilled in the art will be aware of other vanadium-containing industrial by- products which may be used in the process of the invention.

The vanadium-bearing material may also comprise many different βpecieβ including βpecieβ which do not comprise vanadium and βpecieβ which compriβe other metal values such as main group metals, transition metals, Lanthanides or Actinides.

Depending upon the nature of the vanadium-bearing material, it may be necessary to subject the material to pretreatment before the leaching step. For example, iron ore slag is oxidised prior to leaching, usually by roasting in air at temperatures between 550°C and 1100°C, conveniently for 24 hours. Magnetite may be roasted (fluxed) in the presence of a sodium source to convert hexavalent V₂0₃ to a pentavalent vanadium salt. Suitably the material is fluxed at 750°C with sodium borate. Spent vanadium pentoxide catalyst from sulphuric acid processes does not require pretreatment.

While significant solubilization of vanadium iβ achieved by leaching at room temperature, the rate of leaching iβ enhanced by carrying out the leaching βtep at elevated temperature, preferably aβ demonstrated by the test conducted at 90°C.

The leaching step may most conveniently be performed by heap leaching, which provides a very low cost process.

Following the leaching step, vanadium values may be recovered as vanadium pentoxide from solution using standard chemical procedures. In one preferred embodiment, the leachate is subjected to solvent extraction, ion exchange, or carbon adsorption and desorption followed by recovery of a vanadium salt. Preferably vanadium is precipitated as an ammonium salt by the addition of ammonium hydroxide, and then the_ precipitate is heated to decompose the precipitate to vanadium pentoxide^*. In one preferred embodiment of the invention vanadium may be recovered from vanadium-bearing slags which contain oxides of iron. We have found that oxidising the spinel mineral structures enables over 80% of the vanadium to be extracted with either dilute citric acid or dilute tartaric acid leaving the iron oxideβ essentially untouched.

In a second preferred embodiment vanadium may be recovered from spent catalyβt by the process of the present invention. More preferably the catalyst is vanadium pentoxide. As vanadium waste iβ highly toxic, recycling of βpent catalyβt in thiβ manner will provide reduction of the total amount of toxic vanadium metal in circulation in the environment.

DETAILED DESCRIPTION OF THE INVENTION The invention will now be deβcribed in detail by way of reference only to the following examples, and to Figure 1, which is a graphical depiction of the major mineral specieβ solubilized by leaching of slag samples after oxidation at various temperatures.

We have assessed the potential for leaching vanadium with citric acid on three different sources, an iron ore slag, a titaniferous magnetite and a spent catalyst and we have assessed the potential of leaching vanadium with tartaric acid on an iron ore slag. The chemical analysis of these materialβ iβ shown in the following table.

Feedstock Fe (wt%) V (wt%) Mn (wt%) Ti (wt%)

Titaniferous 55.3 0.3 n/a 7.4 magnetite

Iron ore slag 25.3 8.0 9.4 -8.4

Spent catalyst 3.6 4.2 0 0 The following examples illustrate preferred embodiments of the invention in leaching vanadium from these materials.

It will be noted that metals other than vanadium (for example manganeβe) may be complexed by citric acid and feedstock may be manipulated to prevent leaching of other metals such aβ iron.

Example 1. Treatment of vanadium-bearing slags

After crushing to improve diffusion kinetics, the vanadium bearing slag, a metallurgical iron making βlag, was heated in air over a range of temperatures, then treated with various leachantβ. We found that vanadium begins to solubilize from βampleβ fired to 550°C. Over 85% of the vanadium was solubilized from samples fired at temperatures in excess of 900°C. Figure 1 is a graph depicting the major mineral specieβ βolubilized by hot (90°C) 0.4 M citric acid in a 5 hr leach.

In thiβ study, vanadium solubilization was observed to be related to oxidation of the iron, vanadium, manganese and titanium spinel, to haematite, vanadium oxide (in which the valency of vanadium iβ 3+ or greater) , and the other metal oxideβ. Increasing roasting temperature increases the extent of oxidation, allowing more vanadium (and manganese) to be βolubilized. Iron solubilization is initially high, but decreases with the formation of haematite.

We also found that although vanadium could be solubilized by leaching at room temperature, although leaching rates were higher at 90°C. Solubility in distilled water was very low, and leaching in dilute nitric acid (pH 2) was 50% slower than in citric acid at the equivalent pH. Table 1 summarises vanadium solubilization rates for a range of leachants. Table 1. A comparison of the solubilization of vanadium achieved with various leachants on an oxidized βlag sample after firing in air for 24 hrs at 750°C.

Temperature Initial Time % (°C) PH (hr) vanadium solubilized

0.1 M Citric acid 90 2 4 43

0.4 M Citric acid 90 2 V4 44

0.4 M Citric acid 90 2 5 59

0.4 M Citric acid 20 2 4 39

0.4 M Tartaric 90 1.5 2 46 acid

0.4 M Tartaric 90 1.5 4 50 acid

0.4 M Tartaric 90 1.5 8 89 acid

Nitric acid 90 2 4 29

Distilled water 90 5 4 0.4

A practical embodiment of the process of the preβent invention for solubilizing vanadium from iron slag wastes using citric acid leaching is aβ follows. After crushing, iron metal (up to 10% by weight) is separated from the powder using magnetic or density separation techniques. Oxidation is achieved by fluid bed roasting at temperatures between 750°C and 1100°C. To minimise processing steps it may be possible to remove iron metal during fluid bed roasting. The oxidised βlag iβ then heap leached by biologically produced citric acid.

Example 2. Treatment of complex iron oreβ

Titaniferous magnetites are a major source of vanadium, and citric acid leaching procedures offer considerable promise. This example uβed βampleβ of titaniferous magnetite from Chong Qing. Test work on βampleβ fluxed at 750°C with sodium borate indicate that citric acid is an ideal leachant. The results, summarised in Table 2, show that hot O.I M citric acid iβ a more aggressive leachant than either distilled water (hot or cold) or hot nitric acid (pH 2)

Table 2. A comparison of the solubilization of vanadium achieved with various leachants on a sample fluxed at 750°C with 15% sodium borate.

Temperature Initial Time % (°C) PH (hr) vanadium solubilized

Distilled water 20 5 4 14

Distilled water 90 5 4 32

Nitric acid 90 2 4 37

0.1 M Citric acid 90 2 4 43

Example 3. Spent catalyβt

Although the catalyst used at sulphuric acid plants, vanadium pentoxide, contains approximately 4.2 percent vanadium, the current literature (Gupta C.A. and

Krishnamurthy; Extractive Metallurgy of Vanadium, Process Metallurgy 8, Elsevier Science Publishers B.V.) suggests that vanadium is not recovered from spent material. This example, using spent catalyβt from a Tasmanian sulphuric acid plant, demonstrates that a significant proportion of vanadium can be recovered.

Leaching of vanadium with citric acid (pH 2) was compared with leaching with two inorganic acids (ie sulphuric acid or nitric acid at pH 2) . The test results, summarised in Table 3, show that vanadium extraction with hot citric acid was approximately 3 times more efficient than with either inorganic acid.

Table 3. A comparison of leaching of vanadium from spent sulphuric acid catalyst by citric acid and inorganic acids Temperature Initial Time % vanadium (°C) pH (hr) solubilized

0.1 M Citric acid 90 2 5 65

Nitric acid 90 2 5 23

Sulphuric acid 90 2 5 18

Theβe reβultβ confirm that citric acid βolutionβ βolubilize vanadium from oxidised slags without the need for sodium fluxing, and that citric acid is a more aggressive leachant than those currently used for vanadium extraction. The reβultβ demonβtrate that citric acid can be uβed to recover vanadium from βpent catalyβt.

It will be apparent to the person skilled in the art that while the invention has been described in some detail for the purposes of clarity and understanding, various modifications and alterations to the embodiments and methods described herein may be made without departing from the βcope of the inventive concept disclosed in this specification.

Claims

1. A process for recovery of vanadium values and optionally other metal values from a vanadium bearing material, comprising the βtep of leaching the vanadium- bearing material with one or more polycarboxylic organic acidβ.

2. A process according to claim 1 wherein the other metal values compriβe transition metal valueβ.

3. A process according to Claims 1 or 2 wherein the polycarboxylic acid is preβent in a humic substance.

. A process according to Claim 3 wherein the humic substance is fulvic acid.

5. A process according to Claims 1 or 2 wherein the polycarboxylic acid is one produced in the tricarboxylic acid cycle.

6. A process according to any of claims 1, 2 or 5 wherein the polycarboxylic acid is citric acid.

7. A procesβ according to any of claimβ 1, 2 or 5 wherein the polycarboxylic acid is citric acid.

8. A procesβ according to any one of Claims 1 to 7 wherein the vanadium-bearing material is βelected from the group consisting of vanadium ores, mineral slags, and by¬ products of industrial processes.

9. A process according to Claim 8 wherein the vanadium-bearing material is iron ore slag or spent sulphuric acid catalyst.

10. A process according to Claim 8 wherein the vanadium-bearing material is titaniferous magnetite.

11. A procesβ according to any one of claimβ 8, 9 or 10 wherein the vanadium-bearing material iβ subjected to pretreatment at elevated temperature before leaching.

12. A process according to any one of Claims 1 to 10 wherein the vanadium-bearing material is subjected to heap leaching.

13. A process according to any one of Claims 1 to 12 in which the leaching iβ performed at above ambient temperature.

1 . Vanadium produced by a process according to any one of Claims 1 to 12.

15. A process for recovery of vanadium valueβ and optionally other metal valueβ βubβtantially aβ herein deβcribed with reference to the examples.