AU667432B2 - Processes for the production of intermediates useful in the processing of mineral sands and related materials - Google Patents

Description

667432

AUSTRALIA

Patents Act 1952

COMPLE

T

E SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Regulation 3.2 ra t I Ir r t rarp S00 *0 Name of Applicant: Actual Inventor(s): Address for Service: The University of Melbourne O'DONNELL, Thomas Aloysius BESIDA, John PONG, Teresa Kit Hing WOOD, David George DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

Processes for the Production of Intermediates Useful in the Processing of Mineral Sands and Related Materials Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me/us: -1i l I 2- 1 la- PROCESSES FOR THE PRODUCTION OF INTERMEDIATES USEFUL IN THE PROCESSING OF MINERAL SANDS AND RELATED MATERIALS The invention relates to a processes for the production of intermediates useful in the processing of mineral sands and related materials. In particular, the invention relates to the purification of tetravalent halides of metals, such as titanium and zirconium fluorides or chlorides, and their safe and easy conversion to cumplex fluoride salts.

Various processes exist for treating mineral sands and related materials to produce the tetravalent halides of metals through a fluoridation or chlorination step. The metal halides produced from the ore usually contain small quantities of impurities, such Si as metal oxides or other metal halides, which must be separated. Furthermore, metal halides such as TiF 4 and TiC14 are difficult to handle because they readily react with 15 moisture in the air to form oxides. The present invention provides a route for isolating the metal halides of interest in a pure form in solution, and then converting them to complex fluoride salts. The complex fluoride salts may subsequently be processed to produce high purity metal oxides or metals.

i i In the process for the production of pigment grade TiO 2 the purified tetravalent Smetal halides are usually converted to metal oxides in an oxidation or hydrolysis step.

For the chloride process, the oxidation of TiC1 4 to TiO 2 is carried out at about 1000°C, and the metal oxide produced is refractory in nature which leads to difficulties in the Idownstream treatment stages. The aqueous hydrolysis of metal fluorides may be performed under relatively mild conditions, however, corrosive aqueous HF is generated in the reaction leading to high equipment costs and contamination problems.

On a laboratory scale, the complex fluoride salts of metals such as titanium and zirconium are usually prepared by dissolving the metal oxides in aqueous hydrofluoric acid followed by the addition of an alkali metal salt such as a carbonate or hydroxide.

The products prepared in this way can be contaminated with residual oxides and oxide fluorides.

951018,pAoper'dab,6183& 5pe, I i.

-2- A requirement accordingly exists to provide an improvement on existing processes by employing a non-aqueous route to the preparation of pure ammonium fluorometallate salts and to then convert these salts to substantially pure alkali fluorometallate salts.

This has been achieved by purifying the metal halides by dissolution in an organic solvent in which contaminants such as oxides and oxide halides are insoluble.

The soluble halides are then precipitated from this solvent as complex fluoride salts having a high purity.

According to one aspect of the present invention there is provided a process for the production of intermediates useful in the processing of mineral sands and related materials characterised in that the process comprises: dissolving a metal fluoride compound in an organic solvent; adding an ammonium fluoride to the metal fluoride compound dissolved in the organic solvent in step to precipitate an ammonium fluorometallate from the organic solvent; and dissolving the ammonium fluorometallate from step in water and S: adding an alkali fluoride to produce an alkali fluorometallate and an ammonium 20 fluoride.

According to another aspect of the present invention there is provided a process B o for the production of intermediates useful in the processing of mineral sands and related materials characterised in that the process comprises: dissolving a metal fluoride compound in an organic solvent; and adding the metal fluoride compound dissolved in the organic solvent in step to an alkali fluoride dissolved in water or in aqueous hydrogen fluoride to produce an alkali fluorometallate directly.

According to a further aspect of the present invention there is provided a process for the production of intermediates useful in the processing of mineral sands and related A materials characterised in that the process comprises: V -o 951018,p:\oper\dab,61838.spe,2 t 1 dissolving a metal chloride or metal fluoride compound in an organic solvent; adding ammonium fluoride to the metal chloride or metal fluoride compound dissolved in the organic solvent in step to precipitate an ammonium fluorometallate from the organic solvent; and dissolving the ammonium fluorometallate from step in water and adding an alkali chloride or an alkali nitrate to produce an alkali fluorometallate and or an ammonium chloride or an ammonium nitrate.

The mineral sands and related materials may include, for example, ilmenite and other titaniferous ores such as rutile, titaniferous slags or zircon.

.',The organic solvent from step may be optionally recycled to step and the ammonium fluoride from step may be optionally recycled to step Preferably the metal fluoride or chloride compound in step is selected from titanium tetrafluoride, titanium tetrachloride, zirconium tetrafluoride, zirconium tetrachloride, tin tetrafluoride or tin tetrachloride.

The metal fluoride compound in step is often contaminated with impurities such as metal oxides, metal oxidehalides or other non-volatile metal halides. For example, during the fluoridation of titaniferous ores, the titanium tetrafluoride may be contaminated with titanium oxide, titanium oxide fluoride, and iron fluoride. Since the metal fluoride in step is essentially molecular in nature and as such is soluble in an appropriate organic solvent, whereas the impurities are not, these impurities can be j separated from the titanium fluoride compound by dissolving the mixture in an organic solvent. The impurities, remaining as a solid residue after treatment with the organic solvent, can be separated for further processing or disposal.

The organic solvent in step may be an alcohol, such as, for example, methanol, ethanol or isopropanol or any other non-aqueous medium in which A contaminants are insoluble.

951018,p:\oper\dab,61838.spe,3 i i a -4- 4 Preferably the ammonium fluoride in step is selected from ammonium fluoride (NH 4 F) or ammonium bifluoride (NH 4

HF

2 The ammonium fluorometallate produced in step may be ammonium fluorotitanate, such as, for example, ammonium hexafluorotitanate ((NH 4 2 TiF 6 or ammonium fluorozirconate, such as, for example, ammonium heptafluorozirconate

((NH

4 3 ZrF 7 and ammonium hexafluorozirconate ((NH 4 2 ZrF 6 or ammonium hexafluorostannate ((NH4) 2 SnF 6 Preferably the alkali fluoride in step is potassium fluoride sodium fluoride (NaF) or lithium fluoride (LiF).

Preferably the alkali fluoride in step is sodium fluoride (NaF) or potassium fluoride (KF) or lithium fluoride (LiF).

The alkali fluorometallate produced in step or may be K 2 TiF 6 Na 2 TiF6, Li 2 TiF 6

K

2 ZrF 6 Na 2 ZrF 6 Li 2 ZrF6, K 2 SnF 6 Na 2 SnF 6 Li 2 SnF 6

K

3 ZrF 7 Na 3 ZrF 7 or Li 3 ZrF 7 t The alkali fluorometallate from step or may be isolated by any suitable known technique, such as, for example, by adding an organic solvent such as an alcohol, for example, methanol, ethanol or isopropanol or any other non-aqueous medium miscible with water to precipitate the alkali fluorometallat,.

In an alternative process, water and optionally base is added to the metal fluoride compound dissolved in the organic solvent in step to produce a hydrated metal oxide.

The hydrated metal oxide product from the alternative process may be treated to produce, for example, a metal oxide pigment or a refractory ceramic.

In a further alternative process, the ammonium fluorometallate from step is pyrohydrolyzed to produce a hydrated metal oxide, an ammonium fluoride and hydrogen sf^ .oride, each of which may be recycled into the process.

951018,p:\oper\dab,61838.spe,4 I 5 The further alternative process may be performed using any suitable pyrohydrolysis technique. In a particularly preferred embodiment, a flow system having air with entrained water vapour may be streamed over a bed of the ammonium fluorometallate at temperatures sufficiently low to prevent sublimation of, for example, TiF 4 from a fluorotitanate (200-300 0 C) or ZrF 4 from a fluorozirconate (450-500 0

C).

After an appropriate reaction time, typically 4 to 5 hours, the residues are hydrated TiO 2 or ZrO 2 Volatile HF and NH 4 F are carried out of the reaction zone in the air stream and may be condensed separately to form solid NH 4 F, NH 4

HF

2 and an aqueous solution of HF. The solid NH 4 F or NH 4

HF

2 may be optionally recycled in step or alternatively, according to the present invention may be dissolved in an organic solvent, preferably methanol, and treated with SiO 2 to form a precipitate of ammonium hexafluorosilicate. The (NH 4 2 SiF 6 may be dissolved in water and treated with KF or NaF to form K 2 SiF 6 or Na 2 SiF 6 and an ammonium fluoride which may be recycled.

*o e e t 15 The aqueous HF solution may be treated with SiO 2 and KF or NaF to form

K

2 SiF 6 or Na 2 SiF 6 which may be recovered and heated to about 600 to 700 C to yield SiF 4 which is recycled to a mineral sand reactor bed to produce further TiF 4 and ZrF 4 as disclosed in Australian Patent Application No. 48186/90. The KF or NaF residues may be recycled to step 100% recovery of TiO 2 or ZrO 2 and all of the fluoride in S 20 the compounds volatilized during pyrohydrolysis has been demonstrated experimentally for pyrohydrolysis of (NH 4 2 TiF 6 and (NH 4 3 ZrF 7 under such conditions.

The TiO 2 and ZrO 2 produced by the pyrohydrolysis in the further alternative process are hydrated and therefore more chemically reactive than the TiO 2 and ZrO 2 obtained from conventional processes. In the conventional processing of ilmenite and related minerals such as zircon, high-temperature oxidation or hydrolysis reactions are used to convert intermediates into titanium dioxide (TiO 2 or zirconium dioxide (ZrO2).

In the chloride process for pigment-grade TiO 2 production, titanium tetrachloride (TiC1 4 is burned in oxygen above 1000 0 C to produce TiO 2 In the conventional production of ZrO 2 zircon is fused with alkaline materials at about 1000 0 C and then leached with aqueous solution. Sometimes the zircon is preheated by plasma techniques to about 2000°C before leaching. As a result the TiO 2 and ZrO 2 products obtained in R ATiO 2 an ZrO 2 productsobandi 951018,p:\oper\dab,61838.s!pe,5 -1 1 -6these conventional processes are chemically refractory and not particularly amenable to subsequent purification or other processing.

A particularly preferred embodiment of the process of the invention is shown in Figure 1.

i The invention is further described in and illustrated by the following Examples.

J These Examples are not to be construed as limiting the invention in any way.

Example 1 3 .60g of a commercial sample of crude TiF 4 containing large amounts of S'titanium oxidefluoride as an impurity, was stirred for several hours in methanol. The I" resulting solution was separated from the white insoluble residue and added to a 15 saturated solution of NH 4

HF

2 in 250 ml of methanol. An insoluble white precipitate of (NH 4 2 TiF 6 was formed immediately. After filtration, washing with methanol and drying in air, the mass of (NH 4 2 TiF 6 was 5.10g, corresponding with an initial weight of 3.19g of TiF 4 in the crude starting sample.

This example demonstrates the ease of recovery of (NH 4 2 TiF 6 from TiF 4 and Sthe efficiency of the separation by dissolution in methanol of TiF4 from accompanying oxidefluorides.

Example 2 J 0.638g of a commercial sample of crude TiC14 was added to 0.939g of NH 4

HF

2 dissolved in 80 ml of methanol. An insoluble white precipitate of (NH 4 2 TiF 6 was formed immediately. The solid was collected by filtration, washed with methanol and dried in air. The mass of (NH 4 2 TiF 6 was 0.534g, corresponding to an 80% conversion.

951018,p:\oper\dab,61838.spe,6 I-i i -7- Example 3 A solution consisting of 0.129g of TiF 4 dissolved in 20 ml of methanol, obtained from crude TiF 4 as in Example 1, was added to a solution consisting of 0.089g of NaF dissolved in 10 ml of water and 1 ml of 40% w/w aqueous HF. A white precipitate of Na 2 TiF 6 was formed immediately and this was collected by filtration, washed with methanol and dried in air at 120 0 C. 0.197g of Na 2 TiF 6 was recovered.

Example 4 A solution consisting of 0.129g of TiF 4 dissolved in 20 ml of methanol, obtained from crude TiF 4 as in Example 1, was added to 0.169g of KHF 2 dissolved in 20 ml of water. A white gelatinous precipitate of K 2 TiF 6 was formed immediately. The solid S, was collected by filtration, washed with methanol and dried in air at 120 0 C. 0.

22 9g of 15 K 2 TiF 6 was recovered.

i e Example S0.183g of (NH 4 2 TiF 6 produced as in Example 1, and 0.082g of NaF were 20 dissolved in 15 ml of water. 40 ml of methanol was added and this produced a white precipitate ofNa 2 TiF 6 The solid was collected by filtration, washed with methanol and dried in air at 120 0 C. The mass of Na 2 TiF 6 recovered was 0.147g.

Example 6 0.274g of (NH 4 2 TiF 6 produced as in Example 1, and 0.258g ofNaNO 3 were dissolved together in 10 ml of water. Addition of 50 ml of methanol resulted in the precipitation ofNa 2 TiF 6 as a white powder. After filtration, washing with methanol and drying in air at 120 0 C, the mass of Na 2 TiF 6 recovered was 0.247g.

951018,p:opedab,61838.spe, -V o g 951018,p:\opedab61838.spe,7 ~e r i. C I C li=- -8- Example 7 0.318g of (NH 4 2 TiF 6 produced as in Example 1, in 5 ml of water was added dropwise to a solution of 0.218g of KF in 1 ml of water, cooled in an ice bath. The gelatinous white precipitate formed was collected by filtration and washed with 5 ml of ice-cold water to remove KF. Drying at 105 0 C yielded 0.287g of anhydrous pure

K

2 TiF 6 The filtrate was reduced by boiling to one-third of its volume and cooled to 0 0 C. A second yield of 0.088g of K 2 TiF 6 was collected. Overall, the conversion rate of (NH 4 2 TiF 6 to K 2 TiF 6 was 97%. Under process conditions, product recovery could be optimised by using a solution saturated with K 2 TiF 6 throughout.

Example 8 0.1232g of (NH 4 2 TiF 6 produced as in Example 1, was pyrohydrolysed at 200- 250 0 C for 5 hours. The weight of hydrated,TiO 2 after pyrohydrolysis was 0.0524g, representing a nominal recovery of 105%. When this material was dehydrated by calcining, the weight of TiO 2 was 0.0499g, representing 100.4% recovery. Analysis for total fluoride in the NH 4

HF

2 sublimate and in the aqueous condensate containing HF indicated 99.3% recovery.

Example 9 Three pyrohydrolyses of the compound (NH 4 3 ZrF 7 which was produced in a similar manner as outlined in Example 1, for periods of 4 to 5 hours at 450-500 0 C, gave recoveries of 99%, 101% and 103% for ZrO 2 and 99%, 102% and 104% for total fluoride.

Example 0.115g of SiO 2 was added to a stirred solution of ammonium hydrogen difluoride (0.507g) in methanol (30 ml). The mixture was stirred at room temperature for 3 hours after which time the liquid was separated from the solid by decanting. The residue was 9 50o8,popezAa,,61 83 8.sp,8 ML 940503,q:\operdab,12747.div,1 i 1 i i- i I 1: -9washed three times with methanol (3 X 30 ml) and then dried in air at room temperature. The mass of white powder (NH 4 2 SiF 6 was 0.318g (93% conversion).

Exampl' 11 0.050g of sodium fluoride was added to a stirred solution of ammonium hexafluorosilicate (0.107g) in water (5 ml). A gelatinous white precipitate was formed immediately. The solid was allowed to settle and the solution was removed by decanting. After washing with 20 ml of methanol and drying in air, the mass of solid recovered was 0.069g. The methanol washing (20 ml) was added to the original solution ml) to precipitate a further quantity of solid. The residue was again separated from the liquid by decanting, washed with methanol (15 ml) and air dried to give a fiurther 0.35g of Na 2 SiF 6 The total Na 2 SiF 6 mass was 0.104g and the overall conversion was 92%.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

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Claims (23)

1. A process for the production of intermediates useful in the processing of mineral sands and related materials characterised in that the process comprises: dissolving a metal fluoride compound in an organic solvent; adding an ammonium fluoride to the metal fluoride compound dissolved in the organic solvent in step to precipitate an ammonium fluorometallate from the organic solvent; and dissolving the ammonium fluorometallate from step in water and adding an alkali fluoride to produce an alkali fluorometallate and an ammonium fluoride.

2. A process for the production of intermediates useful in the processing of mineral sands and related materials characterised in that the process comprises: dissolving a metal fluoride compound in an organic solvent; and *4#44(b) adding the metal fluoride compound dissolved in the organic solvent in step to an alkali fluoride dissolved in water or in aqueous hydrogen fluoride to produce an alkali fluorometallate directly. 6 4 t

3. A process for the production of intermediates useful in the processing of mineral 4: sands and related materials characterised in that the process comprises: dissolving a metal chloride or metal fluoride compound in an organic solvent; 4(b) adding ammonium fluoride to the metal chloride or metal fluoride compound dissolved in the organic solvent in step to precipitate an 3 amonim floroetalatefrom the organic solvent; and dissolving the ammonium fluorometallate from step in water and adding an alkali chloride or an alkali nitrate to produce an alkali fluorometallate and or an ammonium chloride or an anmmonium nitrate.

4. A process as claimed in Claim 1 or Claim 3, characteried in that the organic F.A~J solvent from step is recycled to step 95101 8,p:Aopv.Adab,61838.spe, L -11- A process as claimed in Claim 1, characterised in that the ammonium fluoride from step is recycled to step

6. A process as claimed in any one of Claims 1, 2, 3, 4 and 5, characterised in that the metal fluoride compound in step is selected from titanium tetrafluoride, zirconium tetrafluoride and tin tetrafluoride.

7. A process as claimed in any one of Claims 3 to 5, characterised in that the metal chloride compound in step is selected from titanium tetrachloride, zirconium tetrachloride and tin tetrachloride.

8. A process as claimed in any one of the preceding claims, characterised in that the organic solvent in step is an alcohol or any other suitable non-aqueous medium.

9. A process as claimed in Claim 8, characterised in that the alcohol is methanol, ethanol or isopropanol. A process as claimed in any one of Claims 1 and 3 to 9, characterised in that the ammonium fluoride in step is selected from ammonium fluoride (NH 4 F) or ammonium bifluoride (NH 4 HF 2 4 t

11. A process as claimed in any one of Claims 1 and 3 to 10, characterised in that the ammonium fluorometallate produced in step is ammonium fluorotitanate, ammonium fluorozirconate or ammonium fluorostannate.

12. A process as claimed in Claim 11, characterised in that the ammonium fluorotitanate is ammonium hexafluorotitanate ((NH 4 2 TiF 6

13. A process as claimed in Claim 11, characterised in that the ammonium fluorozirconate is selected from ammonium heptafluorozirconate ((NH 4 3 ZrF 7 and ammonium hexafluorozirconate ((NH 4 2 ZrF 6 951018,p:\oper\dab,61838.spe, 11 L I i i WAvll AA^u AuluuvA^u- .1 l.V %CUll/ ,UIVCIIL III step to an alkali fluoride dissolved in water or in aqueous hydrogen fluoride to. produce an alkali fluorometallate directly. /2 12-

14. A process as claimed in Claim 11, characterised in that the ammonium fluorostannate is ammonium hexafluorostannate ((NH 4 2 SnF 6 A process as claimed in any one of Claims 1, 2 and 4 to 14, characterised in that the alkali fluoride in step or is potassium fluoride sodium fluoride (NaF) or lithium fluoride (LiF).

16. A process as claimed in any one of Claims 3 to 5 and 7 to 15, characterised in that the alkali nitrate in step is sodium nitrate (NaNO 3

17. A process as claimed in any one of Claims 1 to 10, 15 and 16, characterised in that the alkali fluorometallate produced in step or is K 2 TiF 6 Na 2 TiF 6 Li 2 TiF 6 K 2 ZrF 6 Na 2 ZrF 6 Li 2 ZrF6, K 2 SnF 6 Na 2 SnF 6 Li 2 SnF 6 K 3 ZrF7, Na 3 ZrF 7 or SLi 3 ZrF 7

18. A process according to any one of the preceding claims, characterised in that the alkali fluorometallate from step or is isolated by adding an organic solvent or any other non-aqueous medium miscible with water to precipitate the alkali fluorometallate.

19. A process according to Claim 18, characterised in that the organic solvent is an alcohol. i 20. A process according to Claim 19, characterised in that the alcohol is methanol, S ethanol or isopropanol.

21. A process as claimed in any one of Claims 1, 2 and 6, 8 and 9, characterised in that water and optionally base is added to the metal fluoride compound dissolved in the organic solvent in step to produce a hydrated metal oxide.

22. A process as claimed in any one of Claims 1, 3 and 6, 8 and 9 to 14, characterised in that the ammonium fluorometallate produced in step is Spyrohydrolyzed to produce a hydrated metal oxide, an ammonium fluoride and hydrogen 95101 8,p:\oper\dab,61838.spe,12 13 fluoride.

23. A process as claimed in Claim 22, characterised in that the ammonium fluoride is recycled to step

24. A process as claimed in Claim 22 or Claim 23, characterised in that the hydrogen fluoride or an ammonium fluoride is treated with silicon dioxide and an alkali fluoride to produce an alkali fluorosilicate.

25. A process as claimed in Claim 24, characterised in that the alkali fluorosilicate S' is heated to produce silicon tetrafluoride and an alkali fluoride and the alkali fluoride is recycled to step o CQ

26. A process as claimed in Claim 24 or Claim 25, characterised in that the alkali fluoride is sodium fluoride (NaF) or potassium fluoride (KF).

27. A process for the production of intermediates useful in the processing of mineral S. sands and related materials, substantially as hereinbefore described with reference to the Examples and/or drawing. DATED this 18th day of October, 1995 The University of Melbou-ne By Its Patent Attorneys A DAVIES COLLISON CAVE 951018,p:\oper\dab,61838.spe, 13 r i ~y~i~L; ucsIL metnoa or perrormmg it Known to me/us: -1- 00 14- ABSTRACT The present invention relates to a process for the production of intermediates useful in the processing of mineral sands and related materials characterized in that the process comprises: dissolving a metal fluoride or metal chloride compound in an organic solvent; and either adding an ammonium fluoride to the metal fluoride or metal chloride compound dissolved in the organic solvent in step to precipitate an ammonium fluorometallate from the organic solvent; and 00 (ii) dissolving the ammonium fluorometallate from step in water and adding an alkali fluoride or an alkali chloride or an alkali nitrate to produce an alkali fluorometallate and an ammonium fluoride or an ammonium chloride or an ammonium nitrate; or optionally adding the metal fluoride compound dissolved in the organic solvent in step to an alkali fluoride dissolved in water or in aqueous hydrogen oo0 fluoride to produce an alkali fluorometallate directly. o0 0 9405OZp:\oper\dab,uniofnelb.pro,4 L 1~