AU639178B2 - Conversion of ilmenite to synthetic rutile e.g. by the becher process - Google Patents

Description

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F

Regulation 3.2

AUSTRALIA

Patents Act 1952 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

AMC -MNRAL SANDS LTd AA4C-4, A7_O '1TTC Name of Applicant: Actual Inventor(s): 0 90 9r 0 0999 o 0 900 f a 9 a Br la 4 oa 0 0a 0 cs w 0 esoo 0 4 DOll o o

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O O 0O~l Martin Richard HOUCHIN Halil ARAL Warren John BRUCKARD David Edward FREEMAN Harold Robert HARRIS Ian Edward GREY Christina LI ii s I-if Address for Service: Invention Title: DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

CONVERSION OF ILMENITE TO SYNTHETIC RUTILE E.G. BY THE BECHER PROCESS Details of Associated Provisional Application(s): No(s); PK5709/91 The following statement is a full description of this invention, including the best method of performing it known to me/us, 1 la- CONVERSION OF ILMENITE TO SYNTHETIC RUTILE e.g. BY THE BECHER PROCESS This invention relates generally to the conversion of ilmenite to synthetic rutile and is concerned particularly but not exclusively with a process for substantially enhancing the reactivity of ilmenite with respect to the Becher process for effecting this conversion.

Ilmenite (FeTiO 3 and rutile (TiO 2 are the major, commercially-important, mineral feedstocks for titanium metal and titanium dioxide production. Although ilmenite and rutile almost invariably occur together in nature as components of "mineral sands" or "heavy minerals" (along with zircon (ZrSiO 4 and monazite La, Th)P0 4 ilmenite is usually the most abundant. Natural weathering of ilmenite results in partial oxidation of the iron, originally present in ilmenite in the ferrous state (Fe 2 to ferric iron To maintain electrical neutrality, some of the oxidised iron must be removed from the ilmenite lattice. This results in a more porous structure with a higher titanium (lower iron) content. Such .a "weathered materials are known as "altered" ilmenites and may have TiO 2 contents in excess of 60% TiOz, compared with 52.7% TiO 2 in stoichiometric (unaltered) a. 20 ilmenite. As weathering, or alteration, of the ilmenite proceeds, impurities such as alumina-silicates (clays) are often incorporated into the porous structure as discrete, small grains that reside in the pores of the altered ilmenite. Most of the world's mined ilmenite is used for the production of titanium dioxide for use in the paint pigment industry. Pigment'-grade titania (titanium dioxide, TiO 2 has been traditionally produced by reacting ilmenite with concentrated sulphuric acid, with subsequent hydrolysis of the titanium sulphate to titania the so-called sulphate route. However this process is becoming increasingly unpopular due to environmental considerations. The chloride route, which involves reaction with chlorine to produce volatile TiC1 4 which in turn is converted to TiO 2 presents fewer environmental problems and is currently the preferred method for pigmentgrade titania production. However rutile or "synthetic rutile" (rather than 920414,ginspe.003,AMC.C3,1

I__

-2ilmenite) are the preferred feedstocks for the chloride route because the large amount of iron in ilmenite causes excessive consumption of chlorine during processing. Hence an increasing amount of the world's production of ilmenite is being converted to synthetic rutile (TiO 2 content 90%) for use in the chlorideroute, pigment-production process. A number of different processes have been developed to upgrade ilmenite to synthetic rutile, the most widely used, commercially, being the Becher process.

The Becher process, as referred to herein, involves reducing the iron in ilmenite (preferably altered ilmenite) to metallic iron, using a carbonaceous reducing agent such as coal and char, in a reduction kiln at high temperature, eg in the range 750 0 C to 1200 °C then oxidising the metallic iron in an aerator to produce a fine iron oxide that can be physically separated from the coarse titanium-rich grains. The product of the Becher process typically undergoes a final dilute acid leach. The titanium-rich synthetic rutile so produced contains typically >92% TiO 2 US patent 3777013 is one of a number of patents concerned with earlier approaches to the upgrading of ilmenite to synthetic rutile. These generally entailed acid leaching of ilmenite, typically with either hydrochloric or sulphuric acid, and then treating the solid residue in a dilute alkaline solution. According to US 3777013, pre-leaching with hydrochloric acid increases the ilmenite reactivity, allowing the subsequent reduction stage to be carried out in shorter Pt« times and at lower temperatures.

Australian patent 580017 discloses treatment of ilmenite with alkali hydroxide to remove aluminium, silicon and arsenic contaminants.

We have now found that the reactivity of ilmenite, including altered ilmenite, can be substantially enhanced with respect to the reduction step of the Becher process by first reacting the ilmenite with a basic reagent. By achieving enhanced reactivity, it is possible to carry out the iron reduction stage in shorter times and at lower temperatures, with substantial economic benefits. Enhanced reactivity can, however, be measured objectively by comparing, eg reduction or metallisation after a standardized reduction treatment. The enhanced reactivity observed for the reduction step is thought to be carried through to the 920414,gjnspc.003,AMC.C3,2 -3oxidation/aeration step and acid-leaching step of the Becher process.

The invention therefore affords a process for treating titaniferous material eg ilmenite comprising pre-treating the titaniferous material with a basic reagent under conditions effective to enhance the reactivity of the titaniferous material with respect to reduction of its iron content, and thereafter reducing the iron in the pre-treated material. Such reduction is preferably to metallic iron.

Preferably, the process further includes oxidising the metallic iron to iron oxide, and separating the iron oxide to leave a titanium richer product. The titaniferous material is preferably ilmenite, more preferably altered ilmenite, whereby the titanium richer product is synthetic rutile. The reduction, oxidation and separation steps are preferably carried out in accordance with the aforementioned Becher process.

The process may further include, after the pre-treatment with a basic o reagent and before said reduction, treating the pre-treated titaniferous material i 15 with acid to remove acid-soluble impurities. It is found that this additional step, i which may be desirable for other purifying purposes, does usually diminish the reactivity enhancement otherwise obtainable with the basic pre-treatment, but that there is nevertheless still a net substantial improvement in the reactivity of the material for the reduction step. The conditions of this acid leach should be such that there is substantially no dissolution of titanium values in the titaniferous material.

40 4"Substantially no dissolution" herein indicates less than 10% dissolution, preferably less than most preferably less than 2%.

Said pre-treatment is preferably effected by contacting the titaniferous material with an aqueous solution of said basic reagent. Any suitable basic reagent can be used for the pre-treatment eg an alkali metal dr alkaline earth compound such as an oxide, hydroxide or carbonate, or ammonia. An alkali metal oxide or hydroxide is preferred. The most preferred reagent is sodium hydroxide or potassium hydroxide. Similarly any suitable acid can be used for the acid treatment, for example sulphuric, hydrochloric or nitric acid, but sulphuric acid is most preferred.

It will be appreciated that the conditions used for the process of the 920414,gjnspe.003,AMC. C3,3 -4present invtntion, in particular the conditions used for the basic treatment, including the temperature, reagent concentrations and times required, will depend upon the degree of enhanced reactivity desired, and on the nature of the titaniferous starting material (in particular its degree of alteration and its purity).

In general, a greater degree of enhanced reactivity with respect to the Becher process can be achieved by using higher temperatures, higher reagent concentrations (especially for the basic reagent), and longer reaction times. The acid concentration and temperature that can be used in this treatment are limited by the propensity of ilmenite to react with acid, thereby resulting in loss of titanium value. In general, process conditions are preferably chosen so as to minimise or eliminate loss of titanium value through reaction of titanium with said acid.

i To be effective, the pre-treatment with a basic reagent is performed with a basic reagent solution of greater than about 0.1 molar concentration, most preferably greater than about 1 molar, at a temperature greater than 15 most preferably greater than 60 C. The process may be carried out over an extended period at ambient temperatures, eg by heap leaching. The upper limits for reagent concentrations and temperatures is determined by economic conditions, but it appears that no substantial additional benefit is gained for concentrations greater than 10 molar and temperatures greater than 125 The time elapsed for said pre-treatment is preferably at least 10 mins. A practical upper limit is about 4 or 5 hours, preferably 0.5 to 2 hours.

Preferably, said pre-treatment is carried out at or near atmospheric ij I V '':pressure.

It has been further found that pre-treatment with a basic reagent may have the further benefits of significant removal of some impurities, for example A1 2 0 3 and SiO 2 contents, and an increase in the titanium content of the final product as a result of the removal of impurities. It will be appreciated that the degree of removal of impurities, and the consequent increase in titanium content of the product, will also depend on the severity of the conditions used.

The process of the present invention can be performed at various solid concentrations on a batch or continuous basis. For example, at concentrations up 920414,gjnspe.003,AMC.C3,4 approximately 75% w/w solids, the process can be performed on a stirred suspension in a heated reactor. At higher solid contents the process can be performed on an appropriately wetted solid in saggers in an oven, or in a rotary kiln.

The enhanced reactivity of the product of the present invention can be exploited in a known reduction treatment by lowering the temperature at which the reduction step is performed, by decreasing the time-at-temperature used in the reduction step, by increasing the feed rate in the reduction kiln or by any other appropriate modification of the operating conditions. A benefit of lowering the temperature at which the reduction step is performed is that the different phases occur in the reduced ilmenite and it is possible to obtain a more pure product.

SThe invention is further described and illustrated in the following nonlimiting examples.

4 920414,gjnspe.003,AMC.C3,5 EXAMPLE 1 100 g of ilmenite (from Eneabba North, Western Australia) was reacted with 150 cm 3 of 4 molar sodium hydroxide solution in a reactor fitted with a stirrer rotating continuously at 750 rev/min., a thermopocket containing a thermometer (or thermocouple) and a reflux condenser. The reactor was heated by a heating mantle that was connected via a temperature controller to the thermocouple. In this way, the reaction mixture could be maintained at the desired temperature. The mixture was heated at 105°C for 30 mins. The solid residue was then filtered, thoroughly washed with water and analysed. (This product is sample 2 in Tables 1 and 2 below).

The caustic-treated product was then returned to the reactor and leached with 300 cm 3 of 5 molar sulphuric acid solution at 85 0 C for 2 hr. The solid residue was again filtered, washed thoroughly with water, dried and analysed. (This product is sample 3 in Tables 1 and 2 below).

Samples of the ilmenite feed (sample the caustic-treated product (sample 2) and t I the caustic and acid leached product (sample 3) were then reduced in a laboratory kiln it t under conditions designed to simulate Becher-reduction-kiln conditions. (Previous' trials have confirmed the correspondence of results obtained in commercial practice and the laboratory simulations).

In the laboratory trials, the ilmenite samples were reduced at 11000C for 30 mins, using a 2:1 ratio of ilmenite to char. The extent of reduction achieved was measured by the Reduction, defined as the ratio of oxygen lost during reduction to theoretical oxygen loss, expressed as a percentage. The oxygen loss was determined by quantitative re-oxidation of iron and titanium to Fe 2 0 3 and TiO 2 in air at 9000C.

The theoretical oxygen loss was calculatedfrom the chemical analysis of the feedstock, together with published information on Fe-Ti-O compositions in equilibrium with solid carbon CO at 11000C, -7 (ii) Metallisation, as measured by ihe ratio of metallic iron to total iron, from the chemical analysis of the reduced product. The results are summarised in Tables 1 and 2.

TABLE 1 Caustic treatment Acid treatment Sample No [NaOH] time (hr) temp.

0

C)

Source [H S04] time (hr) temp

(OC)

1 Eneabba N I 2 Eneabba N 4 0.5 105 3 Eneabba N 4 0.5 105 I 5 2 TABLE 2 Sample XRF Analysis M Surf 2area (m 2/g) Redn results Redo Metal" TiO 2 Fe 0~ Mn 3

O

4 Si0 2 A1 2 0 3 M90

I

59.99 61.94 63.25 34.12 35.09 34.88 1.34 1.36 1.38 1.00 0.44 0.42 0.64 0.44 0.31 0.23 0.21 0.19 3.9 6.3 13.3 64.6 83.5 77.9 57.8 90.7 81.5 44 4 4

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44 I 4444 4444 4 4 4444 44 4 444444 4 4

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ii 1~ i r tt

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j i i 1 i ii :i "i jH i 1 i., ;_i 8 EXAMPLE 2 To demonstrate the effects of various caustic and acid treatments on reducibility.

The experimental methods for the following experiments were as described for Example 1. The conditions used are summarised in Table 3. The results are summarised in Table 4.

N.B. Samples 2 to 8 all refer to Sample 1 (Eneabba Nth ilmenite) treated under various conditions.

Samples 9 to 16 refer to different ilmenite samples treated under various conditions TABLE 3 Caustic treatment Acid treatment Causticeatment Sample No Source [NaOH] time (hr) temp.

(oC)

[HSO

4 J time M) (hr) temp.

I

Eneabba N Eneabba N Eneabba N Eneabba N Eneabba N Eneabba N Eneabba N Eneabba N Narngulu Narngulu Florida Florida Florida Capel Capel Capel 1 1 1 1 1 1 TABLE 4 XRF Analysis Sample Surf area (m2/g) Red n results Red" Metal" Tio 2 Fe 2

O

3 Mn 3

O

4 Si2A1 2 0 3 MgO 4 4 59.99 61.94 63.25 61.39 60.64 60.67 62.13 61.42 62.20 62.95 34.12 35.09 34.88 34.11 34.51 34,10 34.70 34.05 32.03 32.02 1.34 1.36 1.38 1.33 1.32 1.32 1.35 1.32 1.00 0.44 0.42 0.14 0.80 0.50 0.33 0.27 0.64 0.44 0.31 0.24 0.54 0.44 0.34 0.30 0.23 0.34 0.38 0.27 '0.25 0.28 0.27 0.27 1.14 1.07 1.15 0.54 1.01 0.21 0.64 0.21 3.9 6.3 13.3 9.7 4.5 9.4 8.5 11.5 12.0 7.1 8.3 20.2 7.4 8.7 64.6 83.5 77.9 85.3 75.6 72.7 79.3 79.8 71.4 82.6 78.9 87.8 81,0 58.7 84.9 79.0 57.8 90.7 81.5 93.2 77.4 73.7 82.1 88.1 69.1 92.8 78.1 94.0 91.9 52.7 94.1 88.1 64.5 30.3 1.26 0.4 0.72 0.20 66.89 30.40 1.44 0.30 0.38 0.30 54 5 42.0 1.47 0.86 0.64 0.16 56.74 42.94 1.68 0.35 0.19 0.26 It will be seen from Table 4 that, in most cases, the acid leach, if used for other purposes, diminishes the reactivity enhancement of the basic pre-treatment but that the net benefit remains substantial.

Claims (19)

1. A process for treating titaniferous material eg ilmenite comprising pre- treating the titaniferous material with a basic reagent under conditions effective to enhance the reactivity of the titaniferous material with respect to reduction of its iron content, and thereafter reducing the iron in the pre-treated material.

2. A process according to claim 1 wherein the iron is reduced to metallic iron.

3. A process according to claim 2, further comprising oxidising the metallic Ao iron to iron oxide, and separating the iron oxide to leave a titanium richer product. S 15

4. A process according to claim 4 wherein the titaniferous material is ilmenite, whereby said titanium richer product is synthetic rutile. A"oA

5. A process according to claim 4 wherein said reduction, oxidation and o separation steps are carried out in accordance with the Becher process, as defined herein.

6. A process according to claim 4 or 5 wherein said ilmenite is altered A AA ilmenite. o A

7. A process according to any preceding claim wherein said basic reagent is an alkali metal oxide or hydroxide.

8. A process according to claim 7 wherein said alkali metal hydroxide is sodium hydroxide or potassium hydroxide.

9. A process according to any preceding claim wherein said pre-treatment is effected by contacting the titaniferous material with an aqueous solution of said 920415,9jnspe.003,AMC.C3,10 CT -^iHran~igmtP-i~nj i« I l*|ijM-uKJ liti>fK 11 basic reagent.

A process according to claim 9 wherein said aqueous solution has a concentration of basic reagent greater than 0.1 molar.

11. A process according to claim 9 wherein said aqueous solution has a concentration of basic reagent greater than 1 molar.

12. A process according to any preceding claim wherein said pre-treating is effected at a temperature of at least 60 C.

;13. A process according to any preceding claim, further including, after said o oo pre-treatment with a basic reagent and before said reduction, treating the titaniferous material with acid to remove acid-soluble impurities.

14. A process according to any preceding claim wherein the solids concentration is not more than about 75% w/w solids, and the process is performed on a stirred suspension in a heated reactor.

15. A process according to -any one of claims 1 to 13 wherein the solids 4o90 concentration is greater than 75% w/w solids and the process is performed on an -00 appropriately wetted solid in saggers in an oven, or in a rotary kiln. 9 a 4

16. A process according to any preceding claim wherein said pre-treatment is carried out at or near atmospheric pressure.

17. Synthetic rutile produced by th. process of claim

18. A Becher process for producing synthetic rutile from ilmenite, wherein the ilmenite is first pre-treated with a basic reagent under conditions effective to enhance the reactivity of the titaniferous material with respect to reduction of its iron content. 920416,gjnspe.003,ANMCC3,11 I t 12

19. A process according to claim 1 substantially as set forth in one or more of the Examples. steps or featnres Hiwosed he-rein ry n% obntonteef Dated this 16th day of April, 1992 'Rkc By its Patent Attorneys Davies Collison Cave tit.' it~ 920416,gjnspe.003,AMCC3,12