GB2596789A

GB2596789A - Waste asbestos processing

Info

Publication number: GB2596789A
Application number: GB2009956.0A
Authority: GB
Inventors: John Somerville Colin
Original assignee: Twisted Glass Recycling Ltd
Current assignee: Twisted Glass Recycling Ltd
Priority date: 2020-06-30
Filing date: 2020-06-30
Publication date: 2022-01-12
Also published as: GB202009956D0

Abstract

A method and apparatus for processing an asbestos containing bulk material such as building construction or demolition waste materials which are suspected to contain one or more asbestos minerals as well as non-asbestos materials and a glass product derived from a mixture of asbestos containing bulk materials and glass cullet. The method comprises combining the asbestos containing bulk material with a glass cullet to form a mixture, heating the mixture to a temperature and for a time period sufficient for the glass cullet to melt and the at least one asbestos mineral to thermally decompose into a non fibrous solid material and combine with the molten glass cullet to form a molten mixture, and cooling the molten mixture to form a glass product. Ideally, the mixture is heated by electromagnetic induction to a temperature of at least 1350°C for less than 2 hours. The apparatus comprises a furnace 32 capable of thermally decomposing the asbestos minerals and melting the glass cullet, an asbestos containing bulk material loading mechanism 40 and a glass cullet loading mechanism 52. Ideally, the furnace is an induction furnace and the glass cullet loading mechanism and the asbestos containing material loading mechanism comprise airlocks 55, 44.

Description

Waste Asbestos Processing

Field of invention

The present invention relates to the processing of waste asbestos and in particular to the processing of waste asbestos containing materials such as waste building and demolition 20 materials.

Background art

Asbestos is a collective term for a group of minerals which have a long, thin fibrous crystal structure in their naturally occurring form. Asbestos minerals are categorised into two classes based on the shape of the fibres: serpentine class minerals have curly fibres and amphibole class minerals have needle-like fibres. Chrysotile ("white" asbestos) is the only asbestos mineral belonging to the serpentine group. The amphibole class includes amosite ("brown" asbestos), crocidolite ("blue" asbestos), tremolite, anthophyllite and actinolite.

The fibrous structure of asbestos together with other desirable properties such as excellent heat resistance, fire retardancy, sound absorbance and electrical resistance led to the widespread use of asbestos worldwide through the 20th Century and into the 21st Century.

Asbestos was incorporated into building materials including boards, panels, plaster, paints, floor and roofing tiles as well as pipe insulation and fireproof coatings. Chrysotile is flexible enough to be spun or woven and was often used in protective clothing and heat blankets.

The toxic effects of asbestos dust became apparent during the 1930s. Asbestos is a friable material which easily breaks down into smaller fibres and fibrils when rubbed, contacted or otherwise manipulated. Airborne fibres may be inhaled and remain in the lungs for many years. This causes irritation and inflammation which can lead to cell and tissue damage, which in turn may lead to asbestosis, mesothelioma and lung cancer.

The mining and use of asbestos had been banned in many western countries by the end of the 20th Century. However, asbestos persists in many buildings in the UK and around the world. If asbestos containing materials (ACIVIs) are disturbed, then there is a risk of fibre inhalation. As buildings are demolished, refurbished or restored, any asbestos containing material must be removed and disposed of safely. In the UK, any waste material containing more than 0.1 % asbestos is considered hazardous.

Currently most asbestos containing waste material in the UK is double bagged and buried in landfill. However, asbestos is resistant to chemical and thermal degradation and will therefore persist in landfill sites. Future disruption of buried asbestos risks releasing airborne fibres. The only way to eliminate the risk of asbestos fibre inhalation is to destroy the fibrous structure of the mineral completely.

Asbestos minerals are hydrous silicates which can thermally decompose at high temperatures through the loss of physically and chemically bound water molecules. The resulting decomposition products include a range of non-fibrous minerals. This process is very energy intense, and if heating time is too short or temperature too low then there is a risk that fibrous asbestos will remain. US4678493 discloses a method for vitrifying asbestos where asbestos is mixed with glass cullet and heated. The glass cullet and asbestos melt to form a glass product and the fibrous structure of the asbestos is lost. However the process of US4678493 requires extended heating times, melt accelerators and works only with a purified asbestos. The formation of a glass product is also dependent upon a precise ratio of melt accelerator, asbestos and glass cullet. This is therefore of limited applicability when considering the disposal of ACMs, which may contain very low and undetermined amounts of asbestos mineral. The separation of pure asbestos from an impure waste material is undesirable as it risks exposing workers to airborne fibres.

Summary of the Invention

The present invention aims to provide a method of vitrifying waste ACMs without requiring any hazardous pre-processing or purification of the waste material. In the present invention, ACMs can be heated with glass cullet without any pre-processing. Bags containing waste material can be transported from a building or demolition site and added directly to the furnace without opening. This reduces the risk of airborne contaminants.

The present invention also aims to provide a method of vitrifying waste ACMs to form a glass product which is substantially homogenous, i.e. without substantial inclusions of non-glass matter. By limiting the maximum weight ratio of ACMs to glass cullet, all the asbestos minerals and a majority of non-asbestos material will melt and form part of the molten glass mixture. Combustible materials such as wood, plastic (Including the bags containing the ACMs) and paint will burn when heated, in effect contributing to the heat of the melt and reducing the weight ratio of ACMs to glass cullet. Any remaining material which does not readily melt can be removed from the molten mixture before cooling to form the solid glass product. As the solid glass product is substantially homogenous, it has a wide range of applications such as glass containers, building materials and aggregates. The presence of non-asbestos materials does not significantly affect the quality of the glass product.

The present invention also seeks to improve the speed and energy efficiency of the vitrification of asbestos waste. In certain embodiments the heating effect is provided by an induction furnace. The use of an induction furnace reduces or eliminates the need for melt accelerants or other techniques to increase the rate of melting, as the heating can be localised to ferromagnetic materials within the mixture. Chtysotile, crocidolite and amosite all contain iron as part of their crystal structure and/or as trace impurities and can therefore be targeted by induction heating. In addition to this, iron-based additives used to produce green and brown glasses allow glass cullet to be targeted by induction heating. Waste building materials may also contain ferromagnetic materials such as metal nails or staples Viewed from a first aspect the present invention provides a method for processing an asbestos containing bulk material, comprising: combining an asbestos containing bulk material with a glass cullet to form a mixture, the asbestos containing bulk material comprising at least one asbestos mineral and at least one non-asbestos material; heating the mixture to a temperature and for a time period sufficient for the glass cullet to melt and the at least one asbestos mineral to thermally decompose into one or more molten or non-fibrous solid materials and combine with the molten glass cullet to form a molten mixture; and cooling the molten mixture to form a glass product.

The thermal decomposition of the at least one asbestos mineral may arise from the loss of 15 physically bound water molecules within the asbestos structure and/or the loss of chemically bound water molecules or dehydroxylation. This destroys the fibrous structure of the asbestos The asbestos containing material may contain a variety of non-asbestos materials commonly used in building construction such as paint, wood, cement, polymers, insulation material and metal foils and nails. The temperature may be sufficient for a weight percent majority of the non-asbestos material to combust, thermally decompose and/or melt and combine with the molten glass cullet and the molten or non-fibrous solid materials into the molten mixture. By incorporating a majority of the material present in the asbestos containing material the amount of waste from the process is reduced.

Some non-asbestos solid material from the asbestos containing material may not readily melt The method may fiirther comprise removing any solid material from the molten mixture before cooling. By removing any residual solid material, the glass product is 30 substantially homogenous.

The asbestos containing bulk material may be any material which contains or is suspected to contain any asbestos mineral. The asbestos containing bulk material may be a building construction or demolition waste material. The building construction or demolition waste material may be any material such as thermal or electrical insulation, thermal rope, fabrics or tiles removed from a building during demolition or renovation and suspected to contain one or more asbestos minerals. The asbestos containing bulk material may be contained within plastic bags and may be damp to prevent escape of asbestos fibres.

The asbestos containing bulk material may contain any amount of asbestos. The amount of asbestos in the asbestos containing bulk material may be unknown. The asbestos containing bulk material may only be suspected to contain asbestos whilst actually containing no asbestos. In this manner, all waste suspected of containing asbestos can be treated by this method and it is not necessary to determine the actual amount of asbestos in the asbestos containing bulk material. The asbestos containing bulk material most likely contains up to 30% asbestos mineral by weight.

The asbestos containing bulk material is mixed with the glass cullet to form a mixture This mixing step may happen before or at the same time as the heating step. Preferably the asbestos containing bulk material comprises between 1% and 30% of the mixture by weight. A weight percent of up to 30% asbestos containing bulk material allows substantially all of the asbestos containing bulk material to incorporate with the molten mixture to yield a substantially homogenous glass product without significant solid inclusions. This ensures a high-quality glass product which may have a wide range of applications. The asbestos containing bulk material may comprise between 10% and 25% of the mixture by weight.

Preferably the mixture is heated by electromagnetic induction in an induction furnace. An induction furnace directly heats ferromagnetic centres within the mixture by inducing eddy currents. This improves the energy efficiency and speed of the heating and melting process by providing localised heating. Heating by electromagnetic induction also improves decomposition of asbestos minerals due to its ability to directly target the metals present in many asbestos minerals. Compared to conventional convective heating means, electromagnetic induction is more energy efficient and faster.

Where an electromagnetic induction furnace is used, the time period of heating may be less than 2 hours, for example 20-30 minutes or less or 1 hour or less. This enables a greater processing rate of asbestos containing materials, therefore increasing the amount of material which can be processed without requiring large scale processing facilities. The residency time required to ensure complete destruction of fibrous asbestos materials may depend on the size of the furnace, the ratio of ACM to glass eullet used, the heating power input and the nature of the ACIVIs. A suitable residency time can be readily determined in practice. Preferably the residency time is at least 20 minutes.

Preferably the temperature is sufficient for the molten mixture to have a dynamic viscosity of less than 50 pascal-seconds. This ensures that the molten mixture can be transferred or poured from where it is heated to other locations for cooling or further processing. Preferably the temperature is at least 1350 °C.

1.5 Cooling of the molten material after removal from where it is heated may be aided by exposing the molten mixture to cold water. This causes rapid cooling of the molten mixture to produce a glassy aggregate product. Alternatively the molten material may be cooled slowly in a mould or another suitable vessel to produce larger glass products such as bottles or building blocks.

The method may further comprise measuring a mass of the asbestos containing bulk material before combining with the glass cullet, and using the measured mass of the asbestos containing bulk material to calculate a quantity of glass cullet to be combined with the asbestos containing bulk material, wherein the mixture is a combination of the mass of asbestos containing bulk material and the calculated quantity of glass cullet. This ensures an accurate weight ratio of asbestos containing bulk material to glass cullet in the mixture to improve the homogeneity of the molten mixture and the resulting glass product.

Viewed from a further aspect the present invention provides a glass product, comprising non-fibrous material derived from an asbestos containing bulk material and material derived from glass cutlet, wherein the glass product contains substantially no fibrous asbestos material.

Reference within this specification to "substantially no fibrous asbestos material" encompasses a glass product having no residual fibrous asbestos material. In certain aspects the product may contain only a trace amount of fibrous asbestos material. By trace amount it is meant less than 1 ppm by mass of fibrous asbestos material as identified and quantified by polarised light microscopy.

Preferably the glass product is substantially homogenous. In the context of this invention, substantially homogenous means that there are fewer than 10 solid inclusions with a diameter greater than 1 mm in 100 cm' of solid glass product.

The glass product may contain up to 30 weight percent non-fibrous material derived from 15 an asbestos containing bulk material This may include non-fibrous thermal degradation products of asbestos minerals as well as thermal degradation products of other non-asbestos components of an asbestos containing bulk material Viewed from yet another aspect the present invention provides apparatus for the processing of asbestos containing materials, comprising: a furnace capable of attaining and sustaining a core temperature within a furnace cavity sufficient to melt glass cutlet and thermally decompose asbestos minerals into one or more molten or non-fibrous solid materials; wherein the furnace has a first inlet and an outlet in fluid connection with the furnace cavity; an asbestos containing material loading mechanism fluidly connected to the first inlet and suitable for transferring asbestos containing materials into the furnace cavity; and a glass cullet loading mechanism suitable for loading glass cutlet into the furnace cavity.

The glass cutlet loading mechanism may be configured to deliver glass cullet to the furnace through the first inlet together with the asbestos containing bulk materials from the asbestos containing material loading mechanism. For example the glass cutlet loading mechanism and the asbestos containing material loading mechanism may be fluidly connected to a mixing chamber which is fluidly connected to the first inlet.

Alternatively, the glass cullet loading mechanism may be connected to a second inlet on the furnace, wherein the second inlet is fluidly connected to the furnace cavity. In this embodiment, the glass cullet enters the furnace through a different inlet to the asbestos 5 containing bulk material.

The asbestos containing material loading mechanism may comprise an air-lock system in a flow path between an exterior of the apparatus and the first inlet, wherein the air-lock system has a sealable void between the exterior of the apparatus and the first inlet. This prevents any asbestos containing material or harmful gases escaping through the asbestos containing material loading mechanism.

The glass cullet loading mechanism may be operable at variable speed to adjust a rate of glass cullet entering the furnace cavity. For example the glass cullet loading mechanism may comprise a conveyor operable at variable speed. This enables the amount of glass cullet entering the furnace to be controlled to ensure that an optimal ratio of glass cullet to asbestos containing bulk material is maintained.

The glass cullet loading mechanism may have an air-lock system to prevent asbestos containing material or harmful gases escaping through the glass cullet loading mechanism and to control the rate at which the glass cullet is added to the furnace cavity.

The asbestos containing material loading mechanism may further comprise a device for measuring the mass of asbestos containing bulk materials. This device may be in communication with a control interface which is capable of adjusting the speed of the glass cullet loading mechanism in response to a measured mass of asbestos containing bulk materials This ensures that an optimal ratio of glass cullet to asbestos containing bulk material is maintained The furnace may further comprise a gas vent at an upper end of the furnace cavity, the gas vent having a filter suitable for trapping asbestos fibres and hazardous gases. The filter may comprise a ITEPA filter and/or a scrubber. This minimises the risk of asbestos fibres and harmful gases escaping from the furnace. The gas vent may be equipped with an air pump to draw air from the furnace cavity through the filter. This creates an airflow through the system from the inlet(s) through the furnace and through the filter to an outlet This reduces the risk of asbestos fibres or harmful gases escaping through the inlet(s).

The apparatus may further comprise at least one drain outlet connected to the furnace cavity to enable removal of residual solid material from the molten mixture. The drain outlet may also be used to empty the furnace after use or for maintenance or cleaning.

The furnace cavity may be equipped with a skimmer to enable removal of solid material from the molten mixture.

Brief description of drawings

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which Figure 1 shows the chemical structure and assembly of chrysotile fibres Figure 2 shows an example of a batch scale apparatus suitable for the processing of waste asbestos containing material.

Figure 3 shows an example of an apparatus suitable for the continuous processing of waste asbestos containing material Figure 4 is a detailed view of part of the apparatus of Figure 3.

Detailed description of preferred embodiment of the invention Referring initially to Figure 1, the chemical structure 1 of chrysotile is shown. Chrysotile is a sheet silicate with a tetrahedral silicate layer 2 and an octahedral bnicite layer 3. The lattice dimension of the brucite layer 3 is slightly larger than the silicate layer 2. Some of the magnesium ions are often replaced by iron or other cations. This causes the layers 2, 3 to roll up to form scroll type fibrils 4. These scroll type fibrils 4 combine through intermolecular forces to form fibre bundles 5. The fibre bundles 5 may be strengthened by the presence of physically bound water molecules between the fibrils 4. Each fibre bundle can contain several hundred fibrils 4, and typically has a diameter of between 0.1 gm and 10 gm The fibres 5 have particularly desirable physical properties which led to their widespread use in a variety of applications. For example, the fibres Shave high tensile strength and are flexible enough to be spun and woven into fabrics. This is combined with good thermal, electrical and acoustic insulation. These properties made chrysotile the most widely used asbestos mineral, accounting for around 95% of global asbestos use. Typical building materials which may contain chrysotile include drywall panels, plaster, floor tiles, roofing 10 panels, acoustic enhancers, thermal pipe insulation and fire doors.

The structure shown in Figure 1 is specific to serpentine asbestos (chrysotile). Amphibole fibres tend to form needle-like fibres and are typically less flexible than chrysotile. The primary uses of amphibole asbestos was in insulation boards, ceiling tiles and lagging.

Commonly reported chemical formulae of amphibole asbestos minerals are shown in Table 1.

Table Chemical formulae of amphibole asbestos minerals Asbestiform mineral Chemical Formula Amosite (Mg, Fe2-)7Sis022(OH)2 Crocidolite Na2(Mg, Fe2+)3Fe3+2Sis.022(OH)2 Tremolite Ca2(NIg, Fe)5Sis022(OH)2 Anthophyllite (Mg, Fe2-)7Sig022(0I-1)2 Actinolite Ca2(Mg, Fe)5S4022(011)2 These various asbestos containing materials (ACNIs) used in construction are still prevalent in many buildings. In many cases the material is left undisturbed in situ and monitored periodically for damage. Where the material has become damaged there is a risk that airborne asbestos fibres are released. Damaged asbestos containing material must therefore be removed. In addition to this, when buildings are demolished or renovated any ACNIs must be removed and disposed of In most cases the amount of asbestos present in the ACMs is very low. For example, typical insulation boards will contain no more than 5 wt.% asbestos. Certain specialist materials such as thermal insulation rope may contain higher amounts of asbestos, typically up to 30 wt.%. Other (non-asbestos) materials present in ACMs may include cement, aggregates, plasters, wood, paint, plastics, metal fasteners, and foils. ACMs may also include waste material which is liberated from landfill sites and may therefore include surrounding landfill material such as earth, clay or soil.

Batch scale apparatus Referring now to Figure 2, a batch scale apparatus 10 for the processing of asbestos containing materials is shown. The batch scale apparatus 10 is suitable for the small-scale processing of waste asbestos containing materials and is suitable for use (for example) in the processing of asbestos containing laboratory waste or small amounts of asbestos containing material. The batch scale apparatus 10 could reasonably be scaled up through the use of higher power induction heaters and/or larger crucibles to allow the batch processing of asbestos containing materials on a larger scale than described in this example.

The batch scale apparatus 10 has a crucible 12 with an opening 11 at an upper end into a cavity 14. The crucible 12 is supported by a clamp 20 and an insulated mat 22 and is removably positionable within the centre of an electromagnetic coil 18. The crucible 12 is sized suitably to sit within the centre of the coil 18 without contacting the coil 18.

The crucible 12 is surrounded by an insulation material 16. The insulation material 16 is a high temperature refractory ceramic fibre insulation material. This is intended to minimise temperature loss from within the crucible 12 when the apparatus 10 is in operation and thus improve energy efficiency. An upper rim 13 of the crucible 12 has a pouring spout 24 to facilitate removal of molten materials.

The electromagnetic coil 18 is a copper induction coil. An internal space 17 within the coil 30 18 suitable for receiving the crucible 12 has a diameter of approximately 8 cm and a height of around 30 cm. The electromagnetic coil is water cooled and is connected to an induction heating power module (not shown) capable of producing a power output of 15 KW at a frequency of between 30 and 80 KHz The crucible 12 is formed from graphite and is capable of withstanding temperatures in 5 excess of 1600 °C. The electromagnetic coil 18 has an insulation sleeve 19 to prevent damage or short circuit to the coil 18 from molten material or sparks Asbestos containing material, such as waste building or construction materials is loaded into the cavity 14 of the crucible 12 together with glass cullet in a weight ratio of one part asbestos containing material to three parts glass cullet. In this particular example, the total mass of material added to the crucible is approximately 100 g. The crucible 12 is then placed within the internal space 17 of the coil 18 and secured in position using the clamp 20 and the insulated mat 22. The induction heating power module is then activated to deliver an oscillating current to the coil 18. This generates an oscillating magnetic field within the internal space 17 of the coil 18.

Glass cutlet, particularly glass cutlet derived from coloured glass such as green or brown glass typically contains iron and other transition metals. For example, iron (II) oxide is commonly used in green glass bottles. The ferromagnetic metal content of glass cullet makes it suitable for heating by electromagnetic induction. As shown in Table 1, asbestos minerals also contain iron and other transition metals and can therefore also be targeted with electromagnetic induction heating. In addition to this, asbestos containing materials removed from buildings are likely to be composite materials containing metal components such as nails, staples and foils, as well as paints or other components in which metal compounds or complexes may be present. The presence of ferromagnetic materials (even in trace quantities) enables these materials to be heated by electromagnetic induction.

The oscillating magnetic field generated within the internal space 17 induces eddy currents within the conducting materials in the cavity 14 of the crucible 12. These electrical currents are typically flowing through a material with high electrical resistance, causing much of the energy to dissipate as heat through Joule heating. This method of heating is therefore highly localised and efficient, enabling the glass cullet and asbestos containing material to melt rapidly to form a molten melt 26. Any organic material present in the asbestos containing material (for example paper, wood or paint) will burn in the crucible due to the heat generated 100 g of the glass cullet and asbestos containing material mixture was completely melted within the crucible after approximately 2 minutes of heating.

After the molten melt 26 is formed, the induction heating power module is then deactivated and the crucible 12 is removed from the internal space 17 by lifting via the clamp 20. The molten mixture 26 can then be poured from the crucible 12. Any remaining solid material on the surface of the molten mixture 26 can be skimmed off during pouring from the pouring spout 24. The molten mixture 26 can then be cooled to form a glass product.

The amount of asbestos containing material is sufficiently low compared to the glass cullet that it is incorporated into the molten mixture 26 and forms a homogenous glass product.

The intense and localised heat generated by the induction furnace is sufficient to thermally decompose and melt the asbestos minerals present in the asbestos containing material. Due to the loss of water and mixing with other components of the molten mixture this decomposition process is irreversible. The glass product therefore contains no fibrous asbestos. As the hazard with asbestos containing materials derives from the fibrous structure of the asbestos mineral there are no asbestos-related health risks associated with the glass product.

Continuous processing of asbestos containing waste Referring now to Figures 3 and 4, apparatus 30 for the continuous processing of asbestos containing materials is shown. Unlike the apparatus 10 for batch scale asbestos processing shown in Figure 2, the apparatus 30 enables asbestos containing material to be processed in a continuous process. The apparatus 30 is therefore more applicable to industrial scale processing of large quantities of asbestos containing material removed (for example) from buildings during demolition or renovation.

The apparatus 30 comprises a furnace 32. The furnace 32 is cylindrical in shape (shown as a cross-section in Figure 3) with a shallow cone-like lower end 31 tapering inwards to a central lowest point 33. The furnace 32 is insulated with a high temperature refractory ceramic fibre insulation material 36. The furnace 32 has an internal cavity 34 and has a primary inlet 50 located at an upper end of the internal cavity 34. The furnace 32 has a first outlet 56 in fluid communication with the cavity 34 towards the lower end 31. The first outlet 56 can be isolated from the cavity 34 with a first outlet valve 58. The first outlet 56 connects the cavity 34 with a cooling chamber 60.

The cavity 34 has two drain outlets in fluid communication with the cavity 34. A surface waste drain outlet 64 is located towards the upper end of the internal cavity 34 and is intended (in use) to be adjacent to an upper surface of a molten mixture 70 within the furnace 34. The surface waste drain outlet 64 can be isolated from the cavity 34 with a surface waste drain outlet valve 66. A lower waste drain 78 is positioned at the central lowest point 33 of the furnace 32. The lower waste drain 78 can be isolated from the cavity 34 with a lower waste drain valve 80.

An electromagnetic coil 38 is positioned around external walls of the furnace 32. The electromagnetic coil 38 is surrounded by an insulation material to protect against damage or short circuiting. The electromagnetic coil 38 is connected to a suitable high frequency power supply (not shown) and is water cooled to enable sustained operation without overheating.

An air vent 81 is situated at an upper end of the furnace 32. The air vent 81 is intended to enable the escape of gases and steam from within the cavity 34 during operation. To prevent any asbestos fibres escaping from the furnace 32, the air vent 81 is equipped with a filter 82. The filter 82 is a high-efficiency particulate air (HEPA) filter capable of filtering at least 99.95% of particles of 0.3 pm diameter. The filter 82 catches any asbestos fibres and prevents their release through the air vent 81. The filter 82 is replaceable at regular intervals or when it becomes saturated. Saturated filters can be safely disposed of by placing into the furnace 32.

The air vent 81 is also equipped with a scrubber 84 which is designed to capture harmful gases and other pollutants which may be given off as asbestos containing materials are heated. The asbestos containing materials may also contain organic materials such as paints and plastics which will combust in the furnace and give off harmful gases such as hydrochloric acid gas or ammonia. The scrubber 84 is capable of removing these gases from the air stream in the air vent 81. The air vent 81 is equipped with a pump 86 which draws air from the cavity 34 out through the filter 82 and the scrubber 84.

The primary inlet 50 is connected to a mixing chamber 48 which is fed by a glass cullet inlet 52 and an ACM inlet system 40. The glass cullet inlet 52 comprises a conveyor 54 configured to transport glass cullet 72 from a loading device such as a hopper (not shown) to the mixing chamber 48. Part of the conveyor 54 is enclosed within a glass cullet inlet chamber 53. This is intended to prevent any escape of asbestos containing material from the mixing chamber 48 or cavity 34 through the glass cullet inlet 52. The escape of asbestos containing material through the glass cullet inlet is further assisted by the operation of the pump 86 to maintain airflow through the system. The conveyor 54 is operable at variable speed to adjust the rate of addition of glass cullet 72 to the furnace 32.

The ACM inlet system 40 has an ACM inlet pipe 46 extending from the mixing chamber 48 to an air-lock system 44. In this particular embodiment, the air-lock system 44 is a rotary airlock. This is intended to prevent the escape of asbestos containing material through the ACM inlet system 40 and can also be used to regulate the rate of addition of asbestos containing material to the furnace 32. The air-lock system 44 has a hopper 42 where asbestos containing material (preferably contained in bags 74) can be loaded.

As best shown by Figure 4, glass cullet 72 is loaded onto conveyor 54 and transported through the glass cullet inlet chamber 53 and a rotary airlock 55 to the mixing chamber 48. The rotary airlock 55 has a series arms with bristle edges which rotate at a fixed height above the conveyor 54 to regulate the depth of the glass cullet 72 on the conveyor 54. The rotary airlock 55 also helps to prevent any asbestos dust escaping from the mixing chamber 48 through the glass cullet inlet chamber 53. Once in the mixing chamber 48 the glass cullet 72 falls through the first inlet 50 and into the cavity 34 of the furnace 32. For an initial loading of the furnace 32, only glass cullet 72 is added. Once the cavity 34 is filled approximately level to the surface waste drain outlet 64, the electromagnetic coil 38 is activated and the glass cullet 72 is rapidly heated. This causes the glass cullet 72 to melt to form a molten mixture 70 The pump 86 ensures that air flows in through the glass cullet inlet 52 and out through an air outlet 88 Bags of asbestos containing material 74 are added to hopper 42 and fall into air-lock system 44. These pass through the air-lock system 44 and the ACM inlet pipe 46 into the mixing chamber 48. Here the asbestos containing material 74 passes together with the incoming glass cullet 72 through the primary inlet 50 into the furnace 32. The speeds of the conveyor 54 and the rotary airlock 44 are controlled to ensure that a weight ratio of incoming asbestos containing material to incoming glass cullet is maintained between one part ACM to three parts glass cullet and one part ACM to nine parts glass cullet.

The asbestos containing material 74 and glass cullet 72 fall into the molten mixture 70. The temperature of the molten mixture 70 is in excess of 1350 °C. This high temperature compared with continued heating by the electromagnetic coil 38 causes the incoming glass cullet 72 to rapidly melt into the molten mixture 70. The incoming asbestos containing material 74 will also undergo rapid decomposition in the high temperature environment. Combustible components of the asbestos containing material 74 (such as the plastic containment bags, paint, wood and polymeric materials) will combust. Asbestos containing material is usually sprayed with water during removal from a building to limit dust escape. The asbestos containing material 74 within the bags will therefore likely be damp. Explosive boiling of water as the asbestos containing material 74 contacts the molten mixture 70 helps together with combustion of organic materials helps to physically break down the asbestos containing material 74.

The temperature within the furnace 32 is sufficient to thermally decompose the asbestos minerals, initially through the loss of physically and chemically bound water. In the case of crocidolite and amosite, the loss of chemically bound water results in the oxidation of iron centres within the crystal structure which ultimately results in complete break down of the mineral to non-fibrous minerals such as acmite, magnetite, cristobalite and hematite. The serpentine structure of chrysotile shown in Figure 1 depends on both physically and chemically bound water. The loss of physically bound water causes the fibre bundles to break apart, then a dehydroxylation process leads to the formation of non-fibrous minerals such as forsterite, silica and enstatite. A residence time in the furnace of 30 minutes is sufficient to ensure complete destruction of fibrous asbestos and incorporation of the resulting decomposition products into the molten mixture 70.

In spite of the high temperatures within the furnace, there may be some non-asbestos construction material within the asbestos containing materials 74 which does not decompose or melt. Any such solid residue will either float on the surface of the molten mixture 70 as solid surface waste 68 or sink to the bottom of the cavity 34 as sunken solid waste 76. This depends on the density of the solid residue.

In order to maintain efficient operation of the apparatus 30, it is necessary to periodically remove solid surface waste 68 and sunken solid waste 76. The surface waste 68 can be removed by opening the surface waste drain outlet valve 66 to divert an uppermost portion of the molten mixture 70 (including solid surface waste 68) out of the furnace 32 through the surface waste drain outlet 64. Similarly the sunken solid waste 76 can be removed by opening the lower waste drain valve 80 to divert a lowermost portion of the molten mixture 70 (including sunken solid waste 76) out of the furnace 32 through the lower waste drain 78.

After the asbestos containing material 74 has decomposed and incorporated into the molten mixture 70 so that no solid fibrous asbestos remains, the molten mixture 70 can be removed from the furnace 32. The first outlet valve 58 is opened to allow the molten mixture 70 to drain through the first outlet 56 into a cooling chamber 60. Here the molten mixture 70 is cooled to form a solid glass product 62.

Any asbestos present in the asbestos containing material 74 will have decomposed, melted and become part of the molten mixture 70. As the asbestos containing material 74 makes up a maximum of around 25% of the molten mixture 70 by weight, most of the non-asbestos material will also have melted and been incorporated into the molten mixture 70. Any remaining solid material is removed from the furnace 32 through the surface waste drain outlet 64 or the lower waste drain 78. The molten mixture 70 exiting the furnace 32 through the first outlet 56 is therefore substantially homogenous and contains no asbestos fibres. The solid glass product 62 is therefore homogenous.

Claims

Claims 1 A method for processing an asbestos containing bulk material, comprising: combining an asbestos containing bulk material with a glass cullet to form a mixture, the asbestos containing bulk material comprising at least one asbestos mineral and at least one non-asbestos material; heating the mixture to a temperature and for a time period sufficient for the glass cullet to melt and the at least one asbestos mineral to thermally decompose into one or more molten or non-fibrous solid materials and combine with the molten glass cullet to form a molten mixture; and cooling the molten mixture to form a glass product.
2. The method of claim 1, wherein the temperature is sufficient for a weight percent majority of the non-asbestos material to combust, thermally decompose and/or melt and 15 combine with the molten glass cullet and the molten or non-fibrous solid materials into the molten mixture.
3. The method of claim 1 or 2, further comprising removing any solid material from the molten mixture before cooling.
4. The method of any preceding claim, wherein the asbestos containing bulk material is a building construction or demolition waste material.
5. The method of any preceding claim, wherein the asbestos containing bulk material 25 contains up to 30% asbestos mineral by weight.
6 The method of any preceding claim, wherein the asbestos containing bulk material comprises between 1% and 30% of the mixture by weight
7. The method of any preceding claim, wherein the asbestos containing bulk material comprises between 10% and 25% of the mixture by weight.
8. The method of any preceding claim, wherein the mixture is heated by electromagnetic induction in an induction furnace
9. The method of claim 8, wherein the time period is less than 2 hours.
10. The method of any preceding claim, wherein the temperature is sufficient for the molten mixture to have a dynamic viscosity of less than 50 pascal-seconds.
11. The method of any preceding claim, wherein the temperature is at least 1350 °C. 10
12. The method of any preceding claim, further comprising: measuring a mass of the asbestos containing bulk material before combining with the glass cullet; and using the measured mass of the asbestos containing bulk material to calculate a 15 quantity of glass cullet to be combined with the asbestos containing bulk material; wherein the mixture is a combination of the mass of asbestos containing bulk material and the calculated quantity of glass cullet.
13. A glass product, comprising: non-fibrous material derived from an asbestos containing bulk material; and material derived from glass cullet, wherein the glass product contains substantially no fibrous asbestos material.
14. The glass product of claim 13, wherein the product contains up to 30 wt% non-fibrous 25 material derived from an asbestos containing bulk material.
15. Apparatus for the processing of asbestos containing materials, comprising: a furnace capable of attaining and sustaining a core temperature within a furnace cavity sufficient to melt glass cullet and thermally decompose asbestos minerals into one 30 or more molten or non-fibrous solid materials; wherein the furnace has a first inlet and an outlet in fluid connection with the furnace cavity; an asbestos containing material loading mechanism fluidly connected to the first inlet and suitable for transferring asbestos containing bulk materials into the furnace cavity; and a glass cullet loading mechanism suitable for loading glass cullet into the furnace cavity.
16. The apparatus of claim 15, wherein the glass cullet loading mechanism is connected to a second inlet on the furnace, wherein the second inlet is fluidly connected to the furnace cavity.
17. The apparatus of claim 15, wherein the glass cullet loading mechanism and the asbestos containing material loading mechanism are fluidly connected to a mixing chamber which is fluidly connected to the first inlet.
18 The apparatus of claims 15-17, wherein the asbestos containing material loading mechanism comprises an air-lock system in a flow path between an exterior of the apparatus and the first inlet, wherein the air-lock system has a sealable void between the exterior of the apparatus and the first inlet.
19. The apparatus of claims 15-18, wherein the glass cullet loading mechanism is operable at variable speed to adjust a rate of glass cullet entering the furnace cavity.
20. The apparatus of claims 15-19, wherein the glass cullet loading mechanism further comprises an air-lock system.
21 The apparatus of claim 19, wherein the asbestos containing material loading mechanism further comprises a device for measuring the mass of asbestos containing bulk materials
22. The apparatus of claim 21, further comprising a control interface capable of adjusting the speed of the glass cullet loading mechanism in response to a measured mass of asbestos containing bulk materials.
23. The apparatus of claims 15-22, wherein the furnace further comprises a gas vent at an upper end of the furnace cavity, the gas vent having a filter suitable for trapping asbestos fibres and hazardous gases.
24. The apparatus of claims 15-23, further comprising at least one drain outlet connected to the furnace cavity to enable removal of residual solid material from the molten mixture.
25. The apparatus of claims 15-24, wherein the furnace cavity is equipped with a skimmer 10 to enable removal of solid material from the molten mixture.