AU677245B2 - Agglomerates - Google Patents

Description

AUSTRALIA

Patent Act COMPLETE SPECIFICATI ON

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: Related Art: Names(s) of Applicant(s): COMMONWEALTH SCIENTIFIC INDUSTRIAL RESEARCH ORGANISATION Actual Inventor(s): Timothy R. BARTON John S. HALL Barry J. ROBSON Our Address for service is: PHILLIPS ORMONDE FITZPATRICK !Patent and Trade Mark Attorneys 367 Collins Street MELBOURNE, Australia 3000 Complete Specification for the invention entitled:

AGGLOMERATES

The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 1 6076L

AGGLOMERATES

This invention relates to microagglomeration of alumina containing material substantially comprising A120 3 nH 2 0, where is in the range of from zero to 3. The invention relates specifically to an improved microagglomerate product of such alumina material, and to a method of producing that product.

In the Bayer process for the production of alumina, crystalline alumina hydrate i§ produced, and then subjected to calcination to provide dehydrated alumina.

The calcined alumina, in a narrow size range, is supplied to smelters for recovery of aluminium by fused salt electrolysis. Fine alumina powder is a by-product of both the calcination and smelting operations. The powder, comprising fine or superfine dust or powder, sometimes referred to as ESP dust in the case of material from such calcination, often has a particle size of less than 30pm. The powder is difficult to handle, has poor flow 2 characteristics and can not be readily digested if 20 returned to the Bayer process. However, aluminium producers typically add the by-product powder into coarser alumina product for smelting, adversely increasing the size range and dustiness of the product.

Micron sized alumina powder also gives rise to 25 difficulties in its use in the ceramics industry. This again is due to factors such as poor flow characteristics and dustiness. Frequently, the powder is agglomerated by spray drying a slurry of the powder to form weak granules, using PVA as a binder. The purpose is to provide granules S 30 suitable as a flowable precursor, to facilitate low S. porosity pressing of ceramics prior to firing. However, the granules are essentially friable and weakly bonded, and can degrade when handled or transported. Thus, while the granules are an improvement over use of the alumina powder per se, the granules exhibit their own deficiencies. Also, those deficiencies are such that use of a PVA binder, to agglomerate fine alumina dust produced in the alumina/aluminium production industries, does not result in an agglomerate able to withstand the handling requirements of those industries.

5982L 2 L I There is a need for an improved form of microagglomerate product of alumina material, and for a method for producing this. The present invention is directed to meeting these needs.

In one aspect, the present invention provides a microagglomerate product of an alumina material, comprising granules of fine alumina containing dust or powder (hereinafter referred to as "alumina powder") of the material, and an organic polymeric binder system which binds the alumina powder of the granules, with the binder system providing the granules with sufficient strength to withstand handling, such as in bulk handling equipment; the alumina material substantially comprising A2 0 3 .nH 2 0, where is in the range of from zero to 3.

The alumina material may be fully dehydrated alumina, fully hydrated alumina, partially hydrated alumina or a mixture of these forms. Where resulting from calcination of alumina trihydrate, the material may be of high purity. However, the material may be other than of high purity, comprising for example relatively high grade bauxite fines or powder. Where the alumina material is other than of high purity, it preferably has an alumina content (calculated as Al 2 0 3 i.e. with being zero) of at least about 80 wt%.

The binder system includes first and second polymeric binder components. The first component may be an acrylic polymer o- co-polymer, such as one comprising or based on a polyacrylic acid, a polymethacrylic acid, a polyacrylate or a polymethacrylate. The first component preferably is a methacrylate polymer or copolymer, with the methacrylate polymer formulation DP6 3791 available from Allied Colloids (Australia) Pty. Ltd. being particularly suitable.

The second component of the binder system may be a synthetic rubber, such as one based on a butadiene polymer or co-polymer. A styrene-butadiene rubber is preferred, such as a carboxylated styrene-butadiene. The carboxylated styrene-butadiene latex formulation Hycar 26120, available from Geon Australia Ltd., is particularly 5982L 3 suitable for use as the second component.

Suitable first components for the binder system may react or bond with the surface of particles of the alumina powder. The first component can act to provide a degree of bonding between the particles, although attachment or anchoring to the particles appears to be the principal action. With the first component reacted or bonded in this manner, the second component appears to act principally to bond the particles together in granules by a bridging or consolidation effect. Thus, a degree of compatibility is required between the first and second components. Also, the second component most preferably is in the nature of a rubber, preferably provided as a latex, and appears to enhance the integrity of granules in providing an impact buffering action between particles, which imparts improved attrition resistance to the granules. Within these constraints, polymers other than those exemplified above but of similar respective functioning can be used as the first and second components 20 of the binder system.

The binder system preferably is substantially resistant to degradation by water. Some acrylic polymers normally do not meet this requirement. However, where this is the case, it is believed that a degree of resistance to such degradation can be imparted to the acrylic polymer component of agglomerated granules due to .the presence of the second component.

The binder system preferably is substantially resistant to degradation in a caustic solution, such as 30 that used in the Bayer process. This is the case where the first component is a methyl methacrylate polymer, such as DP6 3791, and the second component is provided by a carboxylated styrene-butadiene latex, such as Hycar 26120. If the binder system is substantially resistant to caustic solution such as used in the Bayer process, it has the benefit of enabling microagglomerate granules in which it is used to function as high surface area "seeds" suitable as feedstock for addition into process solutions.

The present invention also provides a method for 5982L rl

S.

producing microagglomerate granules from alumina powder.

In the method, there first is formed an aqueous slurry of the alumina powder with the slurry containing an organic polymeric binder system having first and second components as described above. The slurry then is subjected to spray drying to provide dried granules, essentially in the form of microspheres, which are handleable for transportation.

The alumina powder solids content of the slurry can vary substantially, subject to its suitability for spray drying. The binder system can be used at levels such that, in the microagglomerate granules, it is present at up to 30 wt%. However, it is preferred that the binder be present at a substantially lesser amount in the granules, such as less than about 5 wt%. The binder most preferably is present at less than 2 wt% in the granules, such as at about 1.5 wt%.

If required, a dispersing agent can be provided in the slurry to minimise the water content of the slurry for efficient spray drying. However, at least with the preferred components of a methyl methacrylate polymer and carboxylated styrene-butadiene rubber latex for the binder system, it is found that the binder system provides a similar beneficial effect, obviating the need for use of a dispersing agent.

The alumina powder may have an average particles size of less than about 30pm. It may be alumina powder collected by a dust collection device, such as ESP dust.

Preferably the microagglomerate granules are of a size less than about 1mm. More preferably, the granules are of a size in the range of about 50pm to about 150pm.

Thus, at least where the alumina powder is ESP powder, the size range of the resultant microagglomerated granules is such that the microagglomerate is suitable for recycling for addition into alumina product sent to a smelter for recovery of aluminium.

The microagglomerate granules of the invention are somewhat spherical. It is found that the alumina powder particles of the granules are close packed into a substantially ordered structure, as distinct from a disordered structure, and the effect can be seen in SEM 5982L 5 photomicrographs of samples. Also, the binder system generally provides, with alumina powder particles, a close packed shell on the exterior of the graniiules.

The ratio of the two components of the binder system used in the invention can vary substantially. However, for microagglomerate granules having maximum resistance to attrition, the ratio of the first and second components preferably is from about 1:1 to 1:3, and more preferably from about 1:2 to 1:3, i.e. with a higher proportion of the second component than of the first component.

Due to the microagglomerate granules being somewhat spherical, and the size range in which they are produced by spray drying, they provide a flowable alumina product.

Hence the alumina product is suitable for use in ceramics production. In the latter regard, it is to be noted that while the binder system provides granules of enhanced strength and integrity and enhanced resistance to :'":attrition during handling, bonding provided by the binder system can be broken down by application of pressure 20 and/or heat necessary in green body fabrication and binder burn-out stages used in ceramics production.

Additionally, at least where based on use of high purity alumina powder, the granules have the benefits of being white and substantially free of metal species other S: 25 than aluminium. Each of these factors are desirable where the granules are for addition to alumina product for smelting or for use in ceramics production.

I The following non-limiting Examples are provided to assist in an understanding of the invention.

Example 1 Samples A to D of microagglomerate granules were prepared using -30m alumina powder. In each case, the powder was slurried in water with up to 1.5 wt% (on a dry basis) of an organic polymer binder. The binder for sample A was of a single polymer corresponding to the first component in the above description of the binder system for the invention. For samples B to D, the binder was a binder system in accordance with that description.

Details on the binder used were as shown in Table I.

5982L 6 ~II TABLE I Sample Polymer I Polymer II A 1.5% 0.0% B 1.0% C 0.66% 0.33% D 0.5% Polymer I methylmethacrylate copolymer Polymer II carboxylated SBR latex The respective slurries were spray dried through a twin fluid atomizer, using preheated air, and received in a collection chamber. The inlet air temperature was 180 0

C,

and the exit temperature was 130 0

C.

A sample of 2.5 grams was collected from the microagglomerated granules resulting from each spray drying operation. Each sample was added to a quantity of approximately 100 ml of fresh, spent liquor (NaOH, Na 2 CO3, NaAlO 2 in a respective bottle, and each bottle then was rotated for 20 minutes on rollers located 20 within a water bath maintained at 74 0 C. The samples then were analysed in a Malvern sizer, producing the results shown in Table II.

TABLE II 25 Sample Granules Granules after spent as Produced Liquor at 74 0

C

-46pm -21pm -46pm -21pm fraction fraction fraction fraction A 7.6% 4.4% 43.2% 37.2% 30 3 9.8% 4.1% 24.6% 12.0% C 5.6% 3.5% 38.8% 22.4% D 3.4% 2.3% 7.7% 5.8% The results shown in Table II indicate that the granules of sample D, having a 1:2 ratio of the first and second polymer components for the binder system, show a significantly enhanced resistance to caustic degradation.

The other samples were less satisfactory in this regard.

However, granules from which samples B to D were collected also exhibited significant enhancement in strength, and 5982L 7 I I also in resistance to attrition, than the granules from which sample A was collected.

Example 2 Further eight samples E to L of microagglomerate granules were obtained by the slurrying/spray drying procedure of Example 1. In each case, the alumina powder was ESP dust obtained from one of three different calcination units of a commercial refinery operation. As a consequence, the ratio of c-alumina, boehmite and gibbsite varied, depending on which unit the ESP powder was from, although this ratio does not appear to be a significant parameter in the context of the present invention.

In each of samples E to L, binder was present at wt%, based on use of polymer I and/or polymer II as identified in Example 1. The quantity of the polymers used was as shown in Table III.

9 9 TABLE III 20 Sample Polymer I Polymer II Ratio E 1.5% 0.0% F 1.0% 0.5% 2:1 G 0.75% 0.75% 1:1 H 0.5% 1.0% 1:2 25 I 0.38% 1.12% 1:3 J 0.25% 1.25% 0.14% 1.37% 1:10 L 0.0% 1.5% 0:1 S 30 The samples were subjected to Rotap testing in which .they were subjected to uniform standard tapping on a series of root 2 screen sizes from 212pm to 53pm, for intervals of 5 and 30 minutes. The percentage retained by each screen and passing the finest screen was determined for each test interval, and attrition values (AV) determined by the relationship: AV 100 (x-y) 100-y where x is the -53pm sample wt% after 30 minutes and y is the -53pm sample wt% after 5 minutes.

5982L 8 Ir I The results for samples L, G and F are shown in Table IV.

TABLE IV Sample Polymer Ratio Attrition Value L Polymer II only 2.62% G 1:1 1.24% F 2:1 1.8% The results of Table IV demonstrate the minimum level of polymer I required to bond to the surface of the alumina powder. Using the lowest AV as an indication of greatest attrition resistance, the optimum ratio for polymers I and II is 1:1 (sample An increase in the polymer blend ratio to 2:1 (sample F) resulted in an increase in the corresponding AV and, hence, a lowered attrition resistance.

The effect of polymer II, in providing bridging between alumina powder particles in microagglomerate 20 granules, is shown in the results of Table V.

TABLE V Sample Polymer Ratio Attrition Value E Polymer I only 1.94% 25 G 1:1 1.24% H 1:2 0.97% I 1:3 0.95% J 1:5 1.41% K 1:10 1.34% As shown in Table V, sample E has the lowest (zero) content of polymer II, while sample K has the highest content of that polymer. These two extremes have the highest AV percentages. The lowest AV percentages are shown by samples H and I. At least for the specific polymers I and II, a blend ratio of from 1:2 to 1:3 is indicated as providing the maximum attrition resistance for the alumina powder microagglomerate granules.

While the Examples show use of a binder system as required by the invention at a level of 1.5 wt%, higher 5982L 9 IL~ I levels of course can be used if required. However, it clearly is beneficial in terms of cost to be able to use the binder system at such low level. Also, such low level reduces problems of contamination where it is required to use the microagglomerated alumina as part of the alumina feed to a smelter or in the manufacture of ceramics.

Moreover, it is likely to be acceptable to reduce the level of the binder system still further, depending on the specific application of the alumina product and the level of strength and attrition resistance required in that application. Additionally, as indicate herein, there is a wide range of alternatives to the polymer I and/or II used in the Examples which are able to be adopted. In the latter regard, important requirements are the compatibility of the alternatives, the ability of the polymer I alternatives to bond to the alumina dust particles, and the ability of the polymer II alternatives to provide "bridging" or bonding between those particles.

Finally, it is to be understood that various 20 alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

0* 5982L 10 1 IC$ __II

Claims (14)

1. A microagglomerate product of an alumina material, the product comprising microagglomerate granules of fine alumina containing dust or powder (hereinafter collectively referred to as "alumina powder") of the material, and an organic polymeric binder system which binds the alumina powder of the granules, wherein the binder system provides the granules with sufficient strength to withstand required handling, such as in bulk handling equipment, and wherein the binder system includes first and second polymeric binder components; the alumina material substantially comprising Al203. nH 2 0, where is in the range of from zero to 3.

2. A product according to claim 1, wherein the first component is an acrylic polymer or copolymer.

3. A product according to claim 2, wherein the first component is a polymer or copolymer based on a polyacrylic acid, a polymethacrylic acid, a polyacrylate or a 2" polymethacrylate. 20 4. A product according to any one of claims 1 to 3, wherein the second component is a synthetic rubber. A product according to claim 4, wherein the second component is based on a butadiene polymer or copolymer.

6. A product according to claim 5, wherein the second 25 component is a carboxylated styrene-butadiene rubber or other styrene-butadiene rubber.

7. A product according to any one of claims 1 to 6, wherein the first component reacts or bonds with the surface of particles of the alumina powder while bonding S: 30 between particles of granules substantially is provided by the second component.

8. A product according to any one of claims 1 to 7, wherein the second component is a rubber and is provided as a latex.

9. A product according to any one of claims 1 to 8, wherein the binder system is substantially resistant to degradation by water. A product according to any one of claims 1 to 9, wherein the binder system is substantially resistant to degradation in a caustic solution such as used in a Bayer 5982L 11 ~sl~ ~p rr 1 ~sr r I process operation.

11. A product according to any one of claims 1 to wherein the binder system is present at up to 30 wt% in the granules.

12. A product according to any one of claims 1 to wherein the binder system is present in the granules in an amount substantially less than 30 wt%.

13. A product according to claim 12, wherein said amount is less than 5 wt%.

14. A product according tc claim 13, wherein said amount is less thia 2 wt%. A product according to any one of claims 1 to 14. wherein said alumina powder has an average particle size less than

16. A product according to any one of claims 1 to wherein said alumina powder is ESP dust.

17. A produce according to any one of claims 1 to 16, wherein said granules are of a size less than Imm. !0 18. A product according to any one of claims 1 to 17, 20 wherein said granules are of a size in the range of to 150pm.

19. A product according to any one of claims 1 to 18, wherein said first and second components are present in a ratio of from 1:1 to 1:3. 25 20. A product according to claim 19, wherein said ratio is from 1:2 to 1:3. .i 21. A method of producing a microagglomerate product according to any one of claims 1 to 20, including the steps of forming an aqueous slurry of said alumina powder 30 with the slurry containing said binder system, and subjecting the slurry to spray drying to form said microagglomerate granules. DATED: 23 December 1993 COMMONWEALTH SCIENTIFIC INDUSTRIAL RESEARCH ORGANISATION By PHILLIPS ORMONDE FITZPATRICK Patent Attorneys per: 5982L 12 -I- ABSTRACT A nicroagglomerate product of an alumina material, comprises microagglomerate granules of fine alumina containing dust or powder of the material, and an organic polymeric binder system which binds the dust or powder of the granules. The binder system provides the granules with sufficient strength io withstand required handling, such as in bulk handling equipment, and includes first and second polymeric binder components. The alumina material substantially comprising Al 2 0 3 nH 2 0, where is in the range of from zero to 3. *o 30 4 o. So 5982L 13 I