NZ238178A - Converting aluminium dross into particulate material - Google Patents

Description

238178 No.: 238178 Date: 17 May 1991 COMPLETE SPECIFICATION "Improvements in or Relating to Recovery and Use of Products from Aluminium Smelter Dross and the Production Processes Thereof" WE, H E MELHOP LIMITED, a company duly incorporated under the laws of New Zealand of 159 North Road, Invercargill, New Zealand DO HEREBY DECLARE this invention to be described in the following statement: NEW ZEALAND PATENTS ACT, 1953 14 APf .

Rirrf ■ 2o817 8 I The present invention relates to improvements in and/or relating to blasting media, the production process thereof and downstream uses, products and processes.

Currently little use is made of the dross sourced from aluminium smelters such as the New Zealand Aluminium Smelter at Tiwai Point, near Bluff, New Zealand, which is currently high in aluminium metal but does include a proportion of hard aluminium oxides, which aluminium oxides may provide a feedstock for the production of an improved blasting media.

Currently "sand" blasting often employs as a blasting media glass beads. Such a blasting media may be used, for example, for the abrasive blasting of cylinder heads etc in the engine reconditioning trade.

Other potential downstream uses arise as soon as it is realised that there might be some merit in processing the dross from an aluminium smelter. Such other possible downstream uses for some of the inclusions in the dross, if appropriately treated include, as additives in bricks, particularly fire bricks that might be useful by an aluminium smelter itself, granulated superphosphate fertiliser compositions, coating materials for the purpose of adding texture, as a filler or additive in paving or roading materials and/or as a filler or additive in agricultural or domestic drainage tiles.

It is an object of the present invention to provide recovery procedures for use with smelter dross, blasting media and/or processes, means and uses related to use of smelter dross which at least provide the public with a useful choice.

Accordingly in a first aspect the invention consists in a method of providing a particulate material high in aluminium oxide, said method comprising: (i) washing dross with both an aluminium metal and aluminium oxide content from an aluminium smelter in acid, and (ii) therafter harvesting the particles from the liquor produced.

Preferably said washing is with dilute acid without preliminary use concentrated acid.

Preferably said dilute acid is 5% W/V or less sulphuric acid optionally at an elevated temperature.

In other forms said washing can be with hot water alone where there has been strong acid pre-washing.

Preferably the feedstock is pretreated, eg. by screening or other process to remove most of that part of the feedstock of a particle size above 0.80mm.

Preferably the harvested particles have greater than 70% aluminium values expressed by weight as A1203 with metallic aluminium removed by strong acid if the end use may so require.

Preferably the washing with dilute acid is in a (rotary) screen washing apparatus and/or cyclone washing to classify particle sizes.

Preferably the particles harvested comprise in excess of 75% aluminium values expressed by weight as A1203 in the form of sharp angular grit substantially of a 0.06mm to 0.80mm particle size range.

Preferably the invention also extends to a method of producing a blasting media when performed using a process previously defined, the harvested particles being the blasting media.

In a further aspect the invention consists in a method of providing particles as previously defined (whether for blasting media purposes or not) wherein the feedstock is substantially of a content: 23817 ?3B178 A1?0, A1 K20 CaO MgO Na20 Si Op Fe203 Ammonia 39 - 57 % W/W -20 % W/W 0.1 % W/W 3.8 % W/W 2.1 % W/W 4.4 % W/W 0.8 % W/W 0.4 % W/W 6.4 % W/W 2.6 % W/W, 70 - 89 % W/W 0 - 10 % W/W 0.1 % W/W 0.5 % W/W 2.8 % W/W 0.8 % W/W 0.6 % W/W 0.3 % W/W 3.8 % W/W 0.2 % W/W. is acid washed and the particles are substantially of a content: Al-O, A1 K20 CaO MgO Na20 SiO-Fe203 Ammonia In yet a further aspect the present invention consists in a method of producing a brick which involves, first, the use of a method as previously defined to produce said particles, and, then, the use of the harvested particles thereof in the manufacture of a brick having a composition substantially as follows: COMPOUND % COMPOSITION BY WEIGHT Aluminium values expressed as A1203 25 to 30 Si02 50 to 65 CaO 0.0 to 2 Fe203 1 to 6 MgO 0 to 2 Na20 0 to 3 Ti02 0 to 2.

In still a further aspect the present invention consists in a fire brick of the following composition: COMPOUND % COMPOSITION BY WEIGHT Aluminium values expressed as A1203 25 to 30 Si02 50 to 65 CaO 0.0 to 2 Fe203 1 to 6 Mgu 0 to 2 0 to 3 0 to 2, 2381 the fire brick having been made using particles harvested from a method in accordance with the present invention as the primary aluminium values source.

In a further aspect the present invention consists in a blasting medium comprising harvested particles from a method in accordance with the present invention, said particles comprising in excess of 75% weight for weight aluminium values expressed as A1203 in the form of sharp angular grit substantially of a 0.06mm to 0.80mm particle size range.

In yet a further aspect the present invention consists in a granulated superphosphate fertiliser composition which includes less than a 10% weight for weight addition of particles as harvested from a method previously defined (preferably about 2%).

In yet a further aspect the present invention consists in a superphosphate granulated fertiliser which includes about a 2% weight for weight inclusion of particulate material produced by a method of any one of claims 1 to 10 having in excess of 75% weight for weight aluminum values expressed as AI2O3 in the form of sharp angular grit substantially of a 0.06mm to 0.80mm particle size range.

In yet a further aspect the present invention consists in a method of producing " an improved granulated superphosphate fertiliser as previously defined which involves the addition into the superphosphate material prior to granulation of about 2% of the harvested particles produced as previously defined.

In a further aspect the present consists in the use of the harvested particles of a method of the invention as a texture providing inclusion in a coating material such as paint paving or roading materials.

The present invention also consists in the use of particles harvested from a method in accordance with the present invention as a filler or additive in agricultural or domestic drainage tiles.

Accordingly in a further aspect the present invention consists in a method of providing a blasting media high in aluminium oxide (eg. A1203) (preferably greater than 70% weight for weight) which comprises using as feedstock the dross from an aluminium smelter which is high in aluminium values including A1203 (optionally reacting that material in strong acid in a separate reactor to remove most of the metal), washing that material (optionally before or after the removal of oversize and/or undersize particles) in dilute acid, and thereafter removing the particles of a desired size from the liquor and any undersized particles, or at least some undersized particles, so as to provide a blasting media as aforesaid.

Preferably said blasting media contains in excess of 75% (and preferably in excess of 80%) weight for weight A1203.

Preferably there is screening of the feed dross material prior to the optional reaction in strong acid (eg. 30 - 60% w/v sulphuric acid) prior to washing in dilute acid.

Preferably the prior reaction with strong acid in an acid reactor may be needed for some end uses. This is followed by washing in dilute acid in a rotary screen washing apparatus.

In a further aspect the present invention consists in a blasting media produced by a process as aforesaid or substantially as hereinafter described in more detail or substantially as defined hereinafter with reference to the accompanying drawings.

In still a further aspect the present invention consists in a blasting ?38 1 78 media derived from the dross of. an aluminium smelter, said media comprising in excess of 75% weight for weight A1203 in the form of a sharp angular grit substantially of a 0.80mm to 0.06mm particle size range.

In still a further aspect the present invention consists in the use of a blasting media in accordance with the present invention, or a fertiliser made as a by-product to the use of the process of the invention.

The invention consists in the foregoing and also envisages embodiments of which the following gives examples only.

Preferred forms of the present invention will now be described with reference to the accompanying drawings in which; Figure 1 is a photograph (x 30 magnification) of the grit particles primarily of aluminium oxide of a blasting media in accordance with the present invention and/or produced by a process in accordance with the present invention, said particles being in the 0.80mm to 0.06 particle size range.

Figure 2 is a similarly magnified photograph of a glass bead media as is currently employed, Figure 3 is a flow diagram of one form of the process of the preferred process, and Figure 4 is a flow diagram showing alternative process in accordance with the present invention in the form of a flow sheet.

The blasting media of the present invention or produced by a process of the present invention is preferably substantially as depicted in Figure 1 being in the form of a sharp angular grit having a particle range substantially in the range of 0.80mm to 0.06mm which contrasts with the glass bead media depicted in Figure 2 with its smooth spherical particles substantially in the particle size range of from 0.20mm to 0.02mm.

One additional blasting media currently available is the GLASSDEK media 238178 which unlike the glass bead media has a sharp angular grit but is of a smaller range of particle sizes (eg. substantially 0.10mm to 0.02mm).

The micrographs show graphically (x 30 magnification) the more standard sizing of the aluminium oxide grit of the present invention in relation to the conventional glass bead media. The angular sharpness of the aluminium oxide grit will provide a superior cutting ability over the conventional glass bead media and it will have a superior hardness over convention glass bead media. Such a blast media product therefor should be superior in speed and effectiveness on hard carbon or corrosion than other media products and is likely, for example, in the cylinder head blasting usage to provide approximately 30% more cylinder heads per kg of blasting media than the conventional glass beads additionally with a labour reduction of six minutes per head.

Moreover the extreme hardness of the primarily aluminium oxide grit as opposed to glass bead media means that there can be a longer usage thereof before break down into dust. Tests to date indicate that such an aluminium oxide blasting media improves into almost dust-free reusable grit which is a real advantage to the operator.

Currently there is available from the New Zealand Aluminium Smelter at Tiwai Point near Bluff a waste dross material high in aluminium values including aluminium metal and A1203. This dross arises from the reduction of aluminium oxide to its metallic state which takes place in electrolytic cells in the presence of a mixture of fluorides of calcium, sodium, and aluminium. When a cell is broken up or crusts are removed, the waste produced is a mixture of these fluorides plus aluminium oxides and aluminium metal. After removal of larger metal particles the remaining waste is available for dumping or some form of recycling. It is this material that is referred to as "dross" and this after optional prescreening 238178 (e.g. to exclude particles requiring grinding or crushing) is the starting material for the preferred process or after any processing, is the feedstock material for the primarily aluminium oxide blast media in accordance with the present invention.

A preferred method for the production of blast media in accordance with the present invention is as follows. 1. Optional prescreening to remove oversized material (e.g. over 0.8mm). Obviously if desired processes can also be employed to remove some of the aluminium values present as aluminium metal itself as opposed to the aluminium oxides. 2. Charging the dross into a stainless steel rotary tumble/screening processor with a centre washing facility and recircling system i.e. the washing solution is sprayed from the centre line of the drum and passes through the material carrying fines through the aperture of the sieve cloth to the recirculating tank. 3. Washing the dross as in step 2 for about 1 hour at about 90°C with recirculation using preferably sulphuric acid at a concentration not greater than substantially 5% weight per volume water. Obviously other acids such as nitric acid or hydrochloric acid of similar strength can be used but sulphuric acid is readily available relatively cheaply near Tiwai Point. 4. Drain the system to a storage tank and remove the product from the inside of the rotary screen. Drying the material on a flat bed drier and checking for absence of dust (e.g. ensuring screen does exclude particle below 0.06mm). Bag or otherwise ready the product for distribution and/or use.

. Optionally recovering the fines (preferably below 0.06mm) for alternative uses and recharging the system for the next cycle. 6. Optionally, in relation to any liquor left, when sufficiently liquor is 2381 stored, neutralising the same with soda ash or other appropriate neutralising agent and spray irrigating the same onto pastures as nitrogenous fertiliser.

Figure 3 sets out one preferred sequence not inconsistent with the foregoing.

The use of a process as aforesaid provides (with appropriate screen sizes for any preferred but optional pre-screening and the screening during the washing procedures of steps 2, 3 and 4) a blast media substantially as depicted in Figure 1.

Table 1 here below provides (1) an analysis on a weight to weight percentage basis of the acid washed blasting media in accordance with the present invention and (2) a similar analysis of the feedstock dross material available from the New Zealand Aluminium Smelter.

While the aluminium oxide (A1203) appears somewhat similar it must be remembered that at least currently much of the aluminium oxide stated presence in the feedstock dross is in fact aluminium expressed as the oxide. In reality the dross is much lower in aluminium oxide than the figure of 75.8 per cent W/W denotes, eg. 10% metal is equivalent to 18.9% A1203.

Table 1 Compound %W/W %W/W (Acid Washed) Blasting Media (NZAS Dross) K20 CaO MgO Na?0 s-in 0.1 0.5 2.8 0.8 0.6 0.3 89.0 0.1 3.8 2.1 4.4 0.8 0.4 75.8 (total A1 expressed as oxide) F 3.8 0.2 6.4 2.6 Ammonia ?38178 The results given in Table 1 are typical results only but conclusively show that the preferred acid washing is removing a significant measure of the soluble material to leave a harder and so more chemically inert material. Obviously while the acid washing is preferred it is optional.

Also to be noted from Table 1 is the fact that silica is low and accordingly the blasting media produced in accordance with the present invention or the blasting media itself in accordance with the present invention is excellent from a health requirement view since the dust ultimately produced from attrited media during its use in blast operations is correspondingly low in silica.

Of course by using a now useless waste product of aluminium smelting, a blasting media of economic significance is being provided to replace currently used quartz based media with its associated health risks in major industries everywhere and of course with significant cost advantages over glass bead media.

The present invention includes the processes in whole or in part as previously defined (e.g. including the fertilizer) and of course the blasting media produced by any such processes or as defined hereinbefore by chemical analysis or as depicted in Figure 1 of the accompanying drawings. Indeed as previously stated the present invention also consists in any blasting media of a particular form derived from smelter dross which is high in aluminium oxide i.e. such a media may have, for example on a weight for weight basis, 74% aluminium oxide, 10% silicon oxide, 6% other oxides and 10% carbides, nitrides, etc.

A combination of oversize, blasting media and fines can be added to the raw materials used in the manufacture of fire bricks in varying amounts to adjust the chemical composition of the bricks to suit specific end uses 2381 within the Aluminium Industry and other areas requiring high temperature bricks. Such chemical composition required for the above purposes are outlined in the following table 2.

Table 2 Typical uses for bricks of similar composition to table 2 in the Aluminium smelting industry would be as: Pot Barrier Bricks, Carbon Baking Furnace Bricks, Hot Facing Bricks and Open Furnace Flue Wall Bricks.

As well as the brick making use described above similar techniques can be used to produce both construction bricks and paving bricks based around local clays and brick works. In an identical fashion to fire bricks the chemical composition can be similarly adjusted to improve the quality of the poorer quality materials used in the normal production of these constructions materials.

The same process will also improve the quality of agricultural drainage tiles produced in the same pipe works facilities.

The washed material is also a potential additive for paving and roading materials such as concrete paving stones or asphalt. The advantage of the harvested particles is that it is of predictable or even specific size range and is a hard wearing filling agent adding long life of the products it is added to.

Experiments have shown that a 2% addition to superphosphate fertiliser at the manufacturing stage will improve granule strength. The dross is added to the rock phosphate prior to mixing it with sulphuric acid COMPOUND % COMPOSITION BY WEIGHT CaO 0.0 to 2 1 to 6 0 to 2 0 to 3 0 to 2 to 30 50 to 65 238178 and water in a Broadfield, or other, Mixer. Mixing then takes place in the usual way. After granulation and curing the breaking strengths of the granules will be 2 - 3 times higher than low aluminium materials so improving the handling, storage and cartage characteristics of the fertiliser.

The fine fraction of the media can be of use in adding the texture to non slip surface coating paints for walkways, boat decks, footpaths, etc.

The above is an indication of the usefulness of this invention in producing a multipurpose material out of what is currently a world wide waste problem for Aluminium Smelters.

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Claims (20)

WHAT WE CLAIM IS: 238178

1. A method of providing a particulate material high in aluminium oxide, said method comprising: (i) washing dross with both an aluminium metal and aluminium oxide content from an aluminium smelter (hereafter "the feedstock") in acid, and (ii) therafter harvesting the particles from the liquor produced.

2. A method as claimed in Claim 1 wherein said washing is with dilute acid.

3. A method as claimed in Claim 2 when said dilute acid is 5% W/V or less sulphuric acid.

4. A method of claim 3 wherein said acid is at an elevated temperature.

5. A method of any one of the preceding claims wherein the feedstock is pretreated to remove most of that part of the feedstock of a particle size above 0.80mm and/or most of the aluminium metal.

6. A method as claimed in any one of the preceding claims wherein the harvested particles have greater than 70% aluminium values expressed by weight as A1203.

7. A method as claimed in any one of the preceding claims wherein the washing with acid is in a rotary screen washing apparatus and/or a cyclone washing apparatus.

8. A method as claimed in any one of the preceding claims wherein the particles harvested comprise in excess of 75% aluminium values expressed by weight as Al203in the form of sharp angular grit substantially of a 0.06mm to 0.80mm particle size range.

9. A method of producing a blasting media when performed using a process of any one of the preceding claims, the harvested particles being the blasting media.

10. A method of any one of the preceding claims wherein the feedstock is substantially of a content: k2o 0.1 % W/W CaO 3.8 % W/W MgO 2.1 % W/W Na20 4.4 % W/W Si02 0.8 % W/W Fe203 0.4 % W/W A1203 39-59 % W/W F 6.4 % W/W Ammonia 2.6 % W/W A1 (metal) 10 - 20 % W/W, is acid washed and the particles are substantially of a content: K20 0.1 % W/W CaO 0.5 % W/W MgO 2.8 % W/W Na20 0.8 % W/W Si02 0.6 % W/W Fe203 0.3 % W/W A1203 70-89 % W/W F 3.8 % W/W Ammonia 0.2 % W/W A1 0 - 10 % W/W.

11. A method of any one of claims 1 to 10 substantially as hereinbefore described with reference to any example thereof and/or any of the accompanying drawings.

12. A method of producing a brick which involves, first, the use of a method as claimed in any one of the preceding claims to produce said particles, and, then, the use of the harvested particles thereof in the manufacture of a brick having a composition substantially as follows: COMPOUND % COMPOSITION BY WEIGHT Aluminium values expressed as A1203 Si02 CaO Fe203 MgO Na20 TiO, 25 to 30 50 to 65 0.0 to 2 1 to 6 0 to 2 0 to 3 0 to 2. 15 1 6 AUG 1994 23 8 1 78 %

13. A fire brick of the following composition: COMPOUND % COMPOSITION BY WEIGHT Aluminium values expressed as A1203 25 to 30 Si02 50 to 65 CaO 0.0 to 2 Fe203 1 to 6 MgO 0 to 2 Na20 0 to 3 Ti02 0 to 2, the fire brick having been made using particles harvested from a method as claimed in any one of Claims 1 to 11 as the primary Aluminium values source.

14. A blasting medium comprising harvested particles from a method as claimed in any one of Claims 1 to 11, said particles comprising in excess of 75% weight for weight Aluminium values expressed as A1203 in the form of sharp angular grit substantially of a 0.06mm to 0.80mm particle size range.

15. A granulated super phosphate fertiliser composition which includes less than a 10% weight for weight addition of particles as harvested from a method as claimed in any one Claims 1 to 11.

16. A super phosphate granulated fertiliser which includes about a 2% weight for weight inclusion of particulate material produced by a method of any one of claims 1 to 11 having in excess of 75% weight for weight aluminum values expressed as A1203 in the form of sharp angular grit substantially of a 0.06mm to 0.80mm particle size range.

17. A method of producing an improved granulated super phosphate fertiliser as claimed in Claim 15 or Claim 16 which involves the addition into the super phosphate material prior to granulation of about 2% of the harvested particles produced by a method as claimed in any of Claims 1 to 11.

18. The use of the harvested particles of a method as claimed in any one Claims 1 to 11 as a texture providing inclusion in a coating_material such as paint. - 16- 23 8 178

19. The use of particles harvested from a method as claimed in any one of Qaims 1 to 11 as a filler or additive in paving or roading materials.

20. The use of particles harvested from a method as claimed in any one of Claims 1 to 11 as a filler or additive in agricultural or domestic drainage tiles. DATED THIS /^A DAY OF A.J. E>A&K.& SON a PER AGENTS'POR THE APPLICANT - 17- N.Z. PATC-njt r-.rr-^p 1 6 AUG 1994