WO2000006313A1

WO2000006313A1 - New products and methods using foundry dust

Info

Publication number: WO2000006313A1
Application number: PCT/AU1999/000617
Authority: WO
Inventors: Brett David Reich
Original assignee: Brett David Reich
Priority date: 1998-07-30
Filing date: 1999-07-30
Publication date: 2000-02-10

Abstract

Foundry dust is heat treated at particular temperatures to form useful products. At lower temperatures, the pellets are robust enough to be handled, and when placed in water will gel which makes the pellets useful as a water or leaching impermeable layer, for instance for dams and toxic waste dumps. At higher temperatures, hard non-gelling pallets are formed which have a structure which allows the pellets to be used for drainage or water purification, but also for other uses such as a decorative landscaping product.

Description

NEW PRODUCTS AND METHODS USING FOUNDRY DUST

FIELD OF THE INVENTION This invention relates to new products and compositions which contain, as a component thereof, foundry dust, and also relates to methods of use of such products and compositions.

BACKGROUND ART Foundries manufacture cast iron products by pouring molten iron into sand moulds. The sand moulds have a box-like arrangement and are filled with clean sand (usually purified beach sand). An impression is pressed into the sand, and various additives can be added to the sand such that the impression does not collapse before or during pouring of the molten iron into the impression. When the molten iron has been poured into the impression in the sandbox, the box is air cooled and then passes to a knockout area which is usually a rotating drum which breaks up the sand. The drum has perforations through its wall such that the sand passes through the drum with the moulded items passing from the drum and onto a conveyor belt. Not all the sand breaks into small particles, and some of the sand remains as rather large clumps which also pass along the drum and onto the conveyor belt. These clumps are recycled. The sand which passes through the drum perforations is collected and re-used as mould sand. However, the intense heat of the molten iron degrades a considerable amount of sand which cannot be reused. It appears that the degraded sand (also called "spent sand") is unable to maintain a mould shape and, if not removed, tends to flake into the mould before or during pouring of the molten iron. The spent sand is removed and discarded.

As well as spent sand being formed, the intense heat of the molten iron converts a fairly large amount of the mould sand into particles having a very small size and referred to as "foundry dust". This dust must also be removed before the remaining sand can be re-used as the dust is also unable to properly retain a mould shape in the sand. The dust is removed using well-known techniques including cyclones and other types of dust extractors. The dust is transported to disposal sacks each sack holding approximately 1 ,000kg and, to date, the dust has been dumped.

The dust problem is significant as approximately 25% of the fresh mould sand turns to dust after contact with molten iron. Even in a fairly small plant, approximately 6,000 to 10,000kg of dust is removed and dumped each working day. In larger plants, the amount of dust produced each day can be up to 30,000kg.

The foundry dust is characterised by a fine dust-like particle size and is black in colour due to the coal dust involved in the moulding process. The chemical composition of the foundry dust shows that the main composition is quartz and the quartz composition is about that of beach sand. Interestingly, the foundry dust is free from public pollutants such as heavy metal material, and contains a fairly high quantity of clay compositions including active bentonite. Chemical analysis shows that foundry dust can be made up of the following:

(i) Si0₂ 70 to 80%

(ϋ) Al₂0₃ 10 to 13%

(iii) Fe₂0₃ 2 to 3% ( (iivv)) T TiiOO,₂ 0.1 to 0.2%

(v) Mn₃O 1 to 3%

(vi) K₂0 0.5 to 1%

(vϋ) CaO 1 to 1.5%

(viii) MgO 1 to 3% T Toottaall CCllaayy 30 to 50%

The granule distribution of foundry dust can be considered as that which passes through a mesh 140 - mesh 200. Coarser grains are called "sand grains" while the finer grains which pass through the mesh are called "foundry dust". It should be appreciated that the chemical composition in the granule distribution may vary from foundry to foundry but in each case the foundries produce foundry dust which is a waste product characterised by a fine dust-like particle structure.

OBJECT OF THE INVENTION After much research and experimentation, the present invention is directed to the realisation that foundry dust has unique properties if the dust is re-heated to specified temperatures.

While not wishing to be bound by theory, in a first broad form of the invention, it appears that when the foundry dust is re-heated to specified temperatures, the clay portion of the foundry dust will (by thermal expansion) become perforated and turn into a ceramic type of material. Products containing such treated foundry dust can have advantageous uses.

In one form, the invention resides in a product containing as a component thereof foundry dust which has been heat treated between 300 to 1 ,200°C. In another form, the invention resides in a product containing as a component thereof foundry dust which has been heat treated between 300 to 1 ,200°C for a time sufficient to at least partially perforate clay which is in the dust.

In a second broad form of the invention, it has been realised that unique properties can be obtained if compositions containing foundry dust are formed without strong heating.

It has also been realised in this form of the invention, that these compositions have a variety of uses, one use being as a water barrier for instance in a dam, lake and the like. While not wishing to be bound by theory, it appears that when the foundry dust-containing composition is heated at relatively low temperatures, and pelletised, the pellets are able to be properly handled and transported to site without appreciable degradation, and will at least partially swell or gel when contacted with water to form a water barrier. In this second broad form, the invention resides in a pellet which is formed from foundry dust mixed with sufficient liquid to form the pellet, and which has been subsequently dried to provide sufficient strength to the pellet to allow it to be handled.

In the first broad form of the invention, to take advantage of the properties of the heat treated foundry dust, it is preferred that the dust forms the major component of the products. In this form, the foundry dust, before heat treatment, can be clumped or bound together to form larger particle sizes such as granules, pellets, beads and the like, and this granular material can be subsequently heat treated as described above to form a desirable product.

Various additives can be added to the product. For instance, sand and colouring agents can be added, preferably prior to the heat treatment.

If the foundry dust is converted to larger particle sizes prior to heat treatment, it is preferred that the particle size is between 1 to 50mm. The granular material can be formed by mixing the foundry dust with sufficient water to cause clumping or granules and the like to be formed. Commercially available pelletisers can be used to form the granular material.

It is preferred that the product or the granular material is heat treated between 500 to 900°C and for between about 10 minutes to 120 minutes as this appears to provide a useful product using the least amount of energy and with reduced waste material or unsuitable material being formed.

Of course, the temperature and the time can be varied depending on the granular size, the composition of the material before heat treatment, and the degree of perforation desired.

It is preferred that a granular material is manufactured prior to heat treatment such that the heat treated product is also granular in configuration which can allow for improved transportation, storage, handling, and various uses.

The heat treatment can also harden the granular material and it is preferred that the granular material is subjected to heat treatment at a temperature and time sufficient to provide a strength (anti-breakage) of between 15 to 40N, and preferably between 19 to 30N.

The heat treated granular material has a surprising and unexpected advantage in water treatment systems. It is found that the granules can clarify turbid or otherwise impure water by mixing the water with the granules. While not wishing to be bound by theory, it appears that the heat treated granules have apertures, cracks, pin holes, and sometimes a sponge-like condition which facilitates trapping or turbidity inducing materials in water.

It is also found that the heat treated granular material provides a good support for beneficial bacteria and/or algae which can be used to condition water. The heat treatment process ensures that the granulated material is sterile and free from organic and biological contaminants prior to use. The granular material can be in the form of cultured pebbles (cultured in the sense that the pebbles are formed artificially by heat treatment of dust).

The hardness of the granules makes them suitable for decorative use such as for garden landscaping purposes.

It is also found that controlled heat treatment of the foundry dust can change the colour of the dust (or granular material) from black to brown, red, or even other colours especially if colourants are added.

In the second broad form of the invention, the pellet can be dried at fairly low temperatures by which is meant temperatures less than that which will thermally expand and perforate the pellet. It is found that temperatures of around about 500°C and higher will cause such perforation. It is therefore preferred that the pellet is dried at less than this temperature, and for the sake of convenience and reduced energy expenditure and reduced capital equipment, a temperature of between 50 to 300°C and typically about 150°C is preferred. It is found that at 150°C, the pellets can be dried fairly rapidly, however if the pellets are maintained at this temperature for a prolonged period, appreciable perforation does not seem to occur.

The pellet can be of various sizes and shapes. It is preferred that the pellet is of a size which allows it to be used conveniently and transported easily. It is found that a size of between 5 to 50mm and preferably between 10 to 20mm is suitable. We prefer the pellet to be substantially ball-like in configuration, but other shapes can also be envisaged. For instance, the pellet may adopt an irregular shape which will allow a layer of the pellets to adhere together and therefore be suitable on steeper inclines than if the pellet was round. The pellets can be formed using known pelletising devices. It should be appreciated that the pellet which is formed from foundry dust mixed with sufficient liquid, can have the liquid comprising water or other type of liquid or liquid mixture which is suitable to assist in the pelletisation of the dust.

The second broad form of the invention is further directed to various uses of foundry dust and pellets formed from foundry dust.

In a third broad form of the invention, the foundry dust, can be mixed with sufficient liquid to form a gel. The liquid is typically water however other liquids which will allow the foundry dust to form a gel can also be used.

The gel is found to be substantially water impervious and therefore may be suitable as a layer or lining in a dam, or other applications where this property can be utilised.

The gel formed from foundry dust mixed with sufficient liquid can be spread using appropriate tools over an area or substrate which is required to be water impervious or substantially water impervious. Alternatively, the pellets or foundry dust can be layered or applied to the substrate followed by addition of the liquid (typically water) to form the gel. For instance, a dry dam can be lined with foundry dust or the pellets followed by filling of the dam.

If the foundry dust or pellet layer is sufficiently thick, it is found that only an upper portion (that is the area which contacts the liquid) will gel with the remainder of the layer remaining in its powder or pellet form. This has the advantage that should the layer become perforated or broken, the water will contact the ungelled dust or pellet which will swell and seal the perforation. Therefore, another advantage of the invention is the ability of a layer of the dust or pellets to be self-sealing.

In another form, the invention resides in a gel formed from pellets, or of foundry dust mixed with sufficient liquid to form the pellet and which has been subsequently dried to provide sufficient strength to the pellet to allow it to be handled, and to which additional liquid has been added to form the gel. The liquid is typically again water.

It is found that if water, or a water mixture consists of the liquid, the water does not have to be extremely clean or pure and muddy water, cloudy water or contaminated water will still cause the powder or pellets to swell and form the sealing layer.

This makes the invention particularly suitable for sealing waste dumps which may contain liquids, sludge pits, contaminated water dams or lakes, as well as fresh water, dams or lakes, salt water bodies and the like.

A major advantage of the invention is that the pellets or dust can replace traditional ways of lining dams which is by using plastic sheets. Plastic sheets are large and cumbersome and are difficult to unroll and correctly place within the dam confines. The sheets need to be correctly overlapped and sealed together. The upper parts of the sheets extend above the water and are unsightly and prone to damage. The plastic sheets are easily ripped or torn during installation and in use. The ripped or torn sheets cannot self-seal, and if the tear is substantial, the dam needs to be pumped dry for repair. The present invention vastly improves on the use of plastic sheets, as the plastic sheets need no longer be required.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an illustration of the use of the pellets as a dam sealer and the use of the high temperature treated pellets as a filter. Figure 2 is a plan view of how a contaminated dam can be cleaned with a boom containing the higher temperature treated pebbles.

Figure 3 illustrates how the invention can be used to line a land fill site.

Figure 4 illustrates how the invention can be used in retaining walls. Figure 5 illustrates how the invention can be used on sporting ovals. Figure 6 illustrates how the invention can be used for irrigation crops.

BEST MODE In an embodiment of the first form of the invention, foundry dust is collected and with the addition of water and mixing in a conventional pelletiser apparatus, granules of between 1 to 15mm are formed.

The granules are baked at high temperature of 900°C for 60 minutes and upon cooling, the granules changed in colour from black to a clear brick colour, and had a strength of about 19.6 to 29.4N. At this level of strength, there is little or no possibility of grain damage during handling of the product.

During the heating process, the colour of the granules is black at 500°C and becomes browner at 600°C. Further heating to between 800 to 1 ,000°C produces a relatively bright brick red colour which is advantageous should the product be required for decorative use.

In further examples, the granular material was heated for 1 hour at different heating temperatures. Generally, the granular material changes depending on the heating temperature with the grain surface beginning to distort or melt at approximately 1 ,000°C. Prolonged burning above this temperature causes melting of the granular material and can result in a dead burnt product.

Granular material heated for 1 hour at 600, 1 ,000 and 1 ,100°C produced acceptable results while prolonged heating at 1 ,200°C provided significant melting of the granular material. Granular material which had been baked at 900°C for 1 hour displayed relatively large cracks together with fine cracks on the surface of the grains and also penetrating into the grain body. Parts of the grain body had adopted a complicated cellular-type structure and approximately 30 to 40% of the grains consisted of voids. In a further example, granular material prepared by heating at

900°C for 60 minutes followed by cooling and as described above, could be used to clarify cloudy water. In this example, cloudy water was re-circulated once an hour through 2.5kg of the granular material. After about 48 circulations, the cloudy water which initially had a limpidity of approximately 10cm had improved to a limpidity of approximately 100cm (limpidity being an indication of the clarity of the water). A parallel test where water was merely circulated but not through the granular material showed almost no improvement in the clarity of the water.

In a further example, the granular material as described above was added to a fish tank and formed the bottom of the fish tank. Fish were fed in the tank for approximately 3 to 4 years and, during this time, there was no significant change noticed in pollution or smell. The granular material provides a favourable ecological environment for the fish and caused by the decomposition of ammonia and hyponitric acid brought about by the digestive effect of bacteria living on or in the granular material. It appears that the granular material creates an environment which can filter biologically and physically the floating substances in the water and promotes its decomposition by beneficial bacteria.

To determine this, the granular material was inspected and more than 10 different kinds of bacteria and several algae were found to be on the granular material. After 4 years in the fish tank, the acidity of the tank water showed no dramatic changed with the neutral features of the water being maintained.

The granular material finds use in a variety of applications. For instance, the granular material can be used to purify water in a contaminated dam or lake by making the water pass through a body of the granular material. It is found that the granular material is beneficial in reducing algae such as blue-green algae in waterways. In this arrangement, a quantity of the granulated material (which can also be called cultured filtered pebbles) can be placed within a floatation basket and dragged or otherwise moved over the dam to trap and collect the blue-green algae (see Figure 2). The granulated material can also find use in drainage areas, hydroponics, building applications, for draining re-claimed land and the like. In an embodiment of the second form of the invention, pellets containing foundry dust are formed by mixing with sufficient water and pelletising in a known pelletising apparatus. The pellets are subjected to a temperature of 150 degrees centigrade. The heating time will depend on the volume of pellets being treated.

An earth dam is formed in the usual manner by excavation. The walls of the dam can be smoothed in the usual manner. Thereafter, the pellets are layered onto the wall and, if necessary, can be pressed into the earth to provide some stability. The thickness of the layer can vary depending on the degree of water impermeability required (it being appreciated that some soils are more permeable than others). A typical thickness would be between 10 to 100mm, although other values are envisaged. Once the layer of pellets or dust has been applied over the inside wall of the dam, the dam can be filled either by natural rain water or by pumping. As the water contacts the pellets or dust, swelling and gelling occurs which forms a water impermeable layer. If the layer is thick enough, the inner part of the layer does not swell but instead remains as pellets or dust. Should the dam wall become cut open, the pellets or dust will become exposed to the water and will swell to seal the cut. Another advantage of the invention is that should the dam water level lower and the gelled foundry material become exposed, the gel dries to a crust which is sufficiently strong to prevent the material from dislodging or blowing out of the dam. As the water level raises, the crust again converts to a gel. It appears that this process is repeatable many times. Should a portion of the dam require maintenance or repair, the pellets or dust can be simply scraped away from the dam and replaced (or fresh pellets or dust replaced) upon completion of the repair.

The dam could be lined with foundry dust instead of pellets.

Referring to the drawings and initially to Figure 1 , there is illustrated a side view of an earth dam 10 which is made in the usual manner by excavation. The walls of the dam are smoothed in the usual manner. A layer 11 of pellets is layered onto the walls of the dam and even above the level of water 12. The layer is up to 100mm thick although this can vary depending on the size of the dam, the possible porosity and softness of the earth and the like. If desired, the pellets can be pressed into the earth to keep them in place. The pellets are formed using the lower temperature heating and therefore will gel when exposed to water. When the dam is filled, the topmost layer of the pellets gel to form a water impermeable layer while the bottommost layer of the pellets remain ungelled. Should the dam wall become cut open, the ungelled pellets become exposed and will gel to cause a self-sealing or self-repair system. In Figure 1 , the dam has a spillway 13 which contains a bulk of pebbles or granular material which has been subject to the high temperature treatment and therefore act as a purifying or filtering system.

Figure 2 is a plan view of a dam which is being decontaminated. Dam 14 is being cleaned using a boom 15 which is formed from water permeable woven or sack material (other materials are also suitable) which is filled with the culture filter pebbles formed by high temperature treatment of foundry dust. As the boom is drawn over the surface of the dam, it will trap and encapsulate the contamination which may be an oil slick or blue-green algae 16. The boom can then be slowly drawn to one corner of the dam and the trapped material can be pumped or otherwise removed. The culture filter pebbles in boom 15 function to only allow purified water to pass through the boom.

Figure 3 illustrates a land fill or waste dump site containing land fill 17 which may be contaminated. The land fill 17 is isolated by a layer of pelletised sealer 18 which is the same as the pellets 11 described with reference to Figure 1. The land fill is further sealed by a top layer 19 of pelletised sealer over which a thick layer of top soil 20 is placed. It can be seen that the land fill site is properly isolated from the surrounds and there is no need for plastic sheets or membranes to be used. Should settling occur of the land fill, causing opening or rupture of the pelletised sealer 18, ground water will cause swelling or gelling to again result in a self-sealing system. The pellets 18 can be easily transported or dumped at the land fill site and can then be spread using heavy machinery. This is more advantageous than the far more cumbersome lining of the site with plastic sheets.

Figure 4 shows a retaining wall consisting of a brick or block wall 20. In order to prevent water from seeping through the brick or block wall, a layer of pelletised sealer 21 is provided the pellets being the same as used in the dam wall. The wall is back filled with additional pebbles 22 and a layer of top soil 23 can be applied to the top. The pelletised sealer 21 does away with the need for plastic sheets.

Referring to Figure 5, there is shown a sporting oval which has a top playing surface 25 under which is a layer of pebbles 26 acting as a filter or a drain. Underneath this is a layer of the pelletised sealer 27 which prevents water from being wasted but instead forces the water to drain to drainage pipes 28 which allows the water to be reused or removed without the formation of soggy patches and the like. Figure 6 illustrates an agricultural field 30 which can be any suitable size and which has one end 31 slightly higher than the other end 32 which means that water will flow across the field in the direction of arrows 33.

Water will flow across the field and into a drainage gully 34 which is angled such that water flows according to arrow 35 into a catchment area 36 which is filled with filter pebbles or pellets to purify and treat the water.

It should be appreciated that various other changes and modifications can be made to the embodiments described without departing from the spirit and scope of the invention.

Claims

CLAIMS:

1. A product containing, as a component thereof, foundry dust which has been heat treated between 300 to 1 ,200┬░C.

2. The product of claim 1 , wherein the foundry dust has been heat treated between 300 to 1 ,200┬░C for a time sufficient to at least partially perforate clay which is in the dust.

3. The product of claim 2, wherein the foundry dust is the major component of the product.

4. The product of claim 3, wherein the foundry dust, before heat treatment, is clumped or bound together to form larger particle sizes such as granules, pellets, and beads.

5. The product of claim 4, wherein the particle size is between 1 to 50mm, and is formed by mixing the foundry dust with sufficient water to cause clumping or granules and the like to be formed.

6. The product of claim 1 wherein the product is heat treated between 500 to 900┬░C and for between about 10 minutes to 120 minutes.

7. The product of claim 6, wherein the product is heat treated at a temperature and time sufficient to provide strength (anti-breakage) of between 15 to 40N, and preferably between 19 to 30N.

8. A pellet which is formed from foundry dust mixed with sufficient liquid to form the pellet, and which has been subsequently dried to provide sufficient strength to the pellet to allow it to be handled.

9. The pellet of claim 8, wherein the pellet is dried by heating at a temperature of between 50 to 300┬░C.

10. The pellet of claim 9, wherein the pellet has a cross section size of between 5 to 50mm and preferably between 10 to 20mm.

11. The pellet of claim 8, wherein the liquid is water.

12. A method for forming a water impervious layer on a surface, the method comprising forming a layer of pellets as claimed in claim 8 onto the surface, and treating the layer with water to cause the pallets which are in contact with the water to at least partially gel to form the water impervious layer.

13. The method of claim 12, wherein the surface is the walls of an earth dam.

14. The method of claim 12, wherein the surface is the walls of a land fill site or waste dump.

15. A method of treating water comprising passing the water through a plurality of pellets formed from the product of claim 4.

16. A loose fiowable landscaping product formed from pellets formed from the product of claim 4.