WO2017219091A1

WO2017219091A1 - Encapsulation of hazardous waste

Info

Publication number: WO2017219091A1
Application number: PCT/AU2017/050639
Authority: WO
Inventors: Mohammad Ali Sanagooy MOHARRER
Original assignee: Hazprotect Pty Ltd
Priority date: 2016-06-23
Filing date: 2017-06-23
Publication date: 2017-12-28

Abstract

A solid integral mass is disclosed comprising a matrix of non-biodegradable thermoplastic polymer and wax blend, wherein hazardous waste is distributed throughout and encapsulated by the matrix. A method is also disclosed for encapsulation of hazardous waste, the method comprising melt mixing an encapsulating composition comprising non-biodegradable thermoplastic polymer and wax with the hazardous waste, thereby encapsulating the waste in the composition.

Description

ENCAPSULATION OF HAZARDOUS WASTE

FIELD OF THE INVENTION The present invention relates in general to containment and storage of hazardous waste such as radioactive waste. In particular, the invention relates to encapsulated hazardous waste and to a method for encapsulation of such waste, thereby providing means for the containment and safe storage of the waste. BACKGROUND OF THE INVENTION

Hazardous wastes come from a number of sources. With respect to radioactive waste, the majority originates from the nuclear fuel cycle and nuclear weapons reprocessing. Other sources include medical and industrial wastes, as well as naturally occurring radioactive materials (NORM) that can be concentrated as a result of the processing or consumption of coal, oil and gas, and some minerals. For example, coal contains a small amount of radioactive uranium, barium, thorium and potassium, and residues from the oil and gas industry often contain radium and its decay products. Materials that are known or tested to exhibit characteristics such as ignitability, reactivity, corrosivity and flammability also constitute hazardous waste. Such waste is typically generated in the course of industrial and commercial applications, including dry cleaning, automotive industry, hospitals, exterminators, and photo-processing centers. Some hazardous waste generators are larger companies such as chemical manufacturers, electroplating companies, and oil refineries, whilst households also contribute to generation of such waste.

Hazardous waste can be distinguished from other types of general waste because it typically cannot be disposed of by common or routine means . For example, radioactive waste cannot be disposed of in regular landfills, but must be contained and stored until the radioactive component of the waste has "cooled". Similarly, hazardous waste that cannot be recycled or processed must be disposed of in a way that prevents leaching of the waste into the environment, for example into groundwater located in proximity to landfills.

The radioactivity of all nuclear waste diminishes (cools) with time. However, certain radioactive materials require special considerations with respect to their storage, primarily due to their long decay half-life compared to other radioactive elements. For example, radioactive elements (such as plutonium-239) in "spent" fuel will remain hazardous for hundreds or thousands of years, whilst some radioisotopes remain hazardous for millions of years (such as iodine- 129). Therefore, waste containing such isotopes must be stored and shielded appropriately for extended periods of time. In any event, even isotopes with a relatively short half -life must be contained in a similar manner in order to prevent leaching into the environment during the cooling period.

It is well established that uncontrolled exposure to radioactive material is harmful to biological tissue. Accordingly, in considering appropriate storage systems for radioactive and other hazardous waste, the potential for disruption of the integrity of the system is of critical concern. For example, in situations which rely on underground storage of the waste, immobilization of the waste against dispersion by ecological forces must be taken into account. Various attempts have been made to effectively store such wastes. These include the sealing of the waste in metal or plastic containers followed by storage underground or in the ocean, or the incorporation of wastes into the matrix of materials (such as cement). However, such strategies have shown to be inefficient given that cementitious-type materials are highly susceptible to cracking due to drying and/or earth movement. Metal containers are prone to rusting and plastic containers will often lack mechanical strength to withstand the demanding condition under which such waster is typically stored.

Such issues have led to the need for a robust, efficient and reliable means for safely storing hazardous waste.

Before turning to a description of the present invention, it is to be appreciated that the above discussion of the background to the present invention is included to explain the context of the present invention. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. SUMMARY OF THE INVENTION

In an attempt to address one or more of the aforementioned difficulties associated with storing hazardous waste, the inventor has developed a method for encapsulation of hazardous waste. Accordingly, the present invention provides a method for encapsulation of hazardous waste, the method comprising melt mixing an encapsulating composition comprising nonbiodegradable thermoplastic polymer and wax with the hazardous waste, thereby encapsulating the waste in the encapsulating composition. The melt mixing feature according to the method of the invention advantageously enables rapid and efficient formation of an intimate distribution of the waste within a nonbiodegradable thermoplastic polymer and wax blend. The melt mixed composition produced in accordance with the method, upon cooling, forms a solid integral mass comprising the polymer and wax blend with the hazardous waste distributed and safely encapsulated therein. The polymer and wax blend provides for an encapsulating matrix that is advantageously mechanically robust and resistant to leaching of the waste out from the encapsulating matrix.

In one embodiment, the method further comprises depositing the so formed melt mixed encapsulated waste while molten into a container, thereby containing the encapsulated waste in the container.

The present invention further provides a solid integral mass comprising a matrix of nonbiodegradable thermoplastic polymer and wax blend, wherein hazardous waste is distributed throughout and encapsulated by the matrix.

In one embodiment the hazardous waste is radioactive waste. Described herein is an encapsulating composition for the encapsulation of hazardous waste, the encapsulating composition comprising:

(i) a non-biodegradable thermoplastic polymer; and

(ii) a wax.

The present invention also provides a composition for preventing leaching of hazardous waste into the environment, the composition comprising:

(i) hazardous waste; and

(ii) an encapsulating composition comprising:

(a) a non-biodegradable thermoplastic polymer; and

(b) a wax;

wherein hazardous waste is distributed throughout and encapsulated by the encapsulating composition.

As a result of the present invention, efficient encapsulation and containment of hazardous wastes can be readily achieved. The waste is in effect stabilised by binding with, and being held by, the constituents of the encapsulating composition, which provides for a stable monolithic waste form that is resistant to leaching of waste components.

Further aspects and embodiments of the invention are discussed in more detail below.

BRIEF DESCRIPTION OF THE FIGURES The invention will herein be described with reference to the following non-limiting drawings in which:

FIGURE 1 - illustrates a flow diagram of a method of encapsulation and containment of hazardous waste according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

The present invention is predicated in part on use of an encapsulating composition, the components of which, when melt mixed with hazardous waste, enables robust and efficient encapsulation of that waste.

The encapsulating composition comprises non-biodegradable thermoplastic polymer and wax.

The inventor has found that the encapsulating composition can be readily melt mixed with the hazardous waste, then cooled to form a solid mass, to provide robust and efficient encapsulation of the waste.

Reference herein to "hazardous waste" refers to waste that poses, or has the potential to pose, a danger to human health and the environment if it is not properly treated, stored, transported, disposed of, or otherwise managed in an appropriate manner.

Hazardous waste includes material that is known or tested to exhibit one or more of the following hazardous traits: radioactivity, ignitability (i.e., flammable), reactivity, corrosivity, and toxicity. Listed hazardous wastes are materials specifically listed by regulatory authorities as a hazardous waste which are from non- specific sources, specific sources, or discarded chemical products.

For example, hazardous waste may include radioactive materials, explosive materials, flammable liquids/ and solids, poisonous substances, toxic substances, ecotoxic substances and infectious substances, clinical wastes, waste oils/water, hydrocarbons/water mixtures, emulsions, wastes from the production, formulation and use of resins, latex, plasticizers, glues/adhesives, wastes resulting from surface treatment of metals and plastics, residues arising from industrial waste disposal operations; and wastes which contain certain compounds such as copper, zinc, cadmium, mercury, lead and asbestos, household waste; and residues arising from the incineration of household waste. For the purpose of describing features of the invention an emphasis is placed herein on the hazardous waste being radioactive waste. However, it is to be understood the invention can be applied using all forms of hazardous waste. Reference herein to "radioactive waste" refers to waste that contains radioactive material. Radioactive waste is typically a by-product of nuclear power generation, or is produced from the use of radioactive materials in scientific research, industrial, agricultural and medical applications, and the production of radiopharmaceuticals. Furthermore, in the mining industry, radioactive waste arises from naturally occurring radioactive materials (NORM) that are concentrated as a result of the processing or consumption of coal, oil and gas, and some minerals.

Radioactive waste may be divided into 6 categories- exempt waste (EW), very short lived waste (VSLW), very low level waste (VLLW), low level waste (LLW), intermediate level waste (ILW) and high level waste (HLW).

Exempt waste (EW) contains such a low concentration of radionuclides that it can be excluded from nuclear regulatory control because radiological hazards are considered negligible. Very short lived waste (VSLW) can be stored for decay over a limited period of up to a few years and subsequently cleared of regulatory control to be disposed of as regular waste.

Very low level waste (VLLW) does not need a high level of containment and isolation and therefore is suitable for disposal in near-surface landfill-type facilities with limited regulatory control.

Low level waste (LLW) contains limited amounts of long- lived radionuclides. This classification covers a very wide range of radioactive waste, from waste that does not require any shielding for handling or transportation up to activity levels that require more robust containment and isolation periods of up to a few hundred years. There are a range of disposal options from simple near- surface facilities to more complex engineered facilities. LLW may include short lived radionuclides at higher levels of activity concentration, and also long-lived radionuclides, but only at relatively low levels of activity concentration. LLW is generated from hospitals, medical research and industry (such as mining), as well as the nuclear fuel cycle. LLW therefore typically includes radioactive material found in evaporator concentrate, ion exchange resins, incinerator bottom ash, filtration sludge, and contaminated filters and membranes.

Intermediate level waste (ILW) typically includes resins, chemical sludge and metal reactor nuclear fuel cladding, as well as contaminated materials from reactor decommissioning. ILW contains increased quantities of long-lived radionuclides and needs an increase in the containment and isolation barriers compared to LLW. ILW needs no provision for heat dissipation during storage and disposal. Long-lived radionuclides such as alpha emitters will not decay to a level of activity during the time for which institutional controls can be relied upon. Therefore ILW requires disposal at greater depths of tens to hundreds of metres.

High level waste (HLW) is produced by nuclear reactors. It contains fission products and transuranic elements generated in the reactor core. HLW has high levels of activity that generate significant quantities of heat by radioactive decay that need to be considered in the design of a disposal facility. Disposal in deep, stable geological formations usually several hundreds of metres below the surface is generally recognised as the most appropriate option for HLW. The two primary classes of civilian HLW are used fuel from nuclear power reactors and separated waste arising from the reprocessing of that used fuel.

In one embodiment, low level radioactive waste is used in accordance with the invention. As indicated above, sources of such waste include hospitals, medical research and the mining industry. The main radioactive isotopes used in hospitals and the mining industry for example include those set out in Tables 1 and 2, respectively. TABLE 1

Radioisotopes used in Hospitals

*EC: Orbital electron capture by the nucleus resulting in the emission of X-rays characteristic of the daughter element. IT: This mode of decay may give rise to either radiation or internal conversion electrons both.

TABLE 2

Mining Radioactive Waste

Radioisotopes Application or Type of Intensity Half life

Source radiation

Uranium235(U^{2 S}) / 4.18-4.56/0.095- 7xl0⁴ years

0.185

;iniiiiu .

Th-231 From 0.3 25.6 hours

Uranium235

Pa-231 4.66-5.046 34300 years

According to one embodiment of the invention, the waste used is substantially dry (i.e. in a dry or near-dry form). In that regard, the waste may have moisture content in a range from about 0% to about 10% by weight. However, it should be made clear that the waste need not be in such a dry or near-dry form. The advantages of the waste being in a dry or near dry form include reducing waste volume prior to encapsulation and also facilitating melt mixing of the waste with the encapsulation composition (i.e. for minimisation or avoidance of undesirable vaporisation of water during melt mixing). When waste is to be provided in a dry or near-dry form, pre-treatment steps may be required to render the waste substantially anhydrous. This can include heating the waste in an incinerator or oven, or by using a vacuum dryer system.

The amount of waste melt mixed with the encapsulation composition may be from about 5% to about 85%, or from 10% to about 85%, by weight relative to the total mass of the waste and the encapsulating composition.

If required, prior to being melt mixed with the encapsulating composition the waste may be comminuted. Comminution may be achieved using techniques known in the art such as grinding, shredding, crushing or milling.

In one embodiment, the hazardous waste undergoes comminution before being melt mixed with the encapsulating composition. The encapsulating composition used in accordance with the invention comprises nonbiodegradable thermoplastic polymer and wax. The non-biodegradable thermoplastic polymer, together with the wax, forms a blend that functions as a binder to bind together and encapsulates the waste. The non-biodegradable thermoplastic polymer and wax blend provides for an matrix throughout which the hazardous waste is distributed and encapsulated.

As a binding composition the non-biodegradable thermoplastic polymer and wax blend has a number of advantages over the use of conventional binders such as cement. For example, it enables higher waste loading than the use of cement, solidification of the composition upon cooling is assured (by virtue of being thermoplastic - both the wax and polymer are thermoplastic) given that no chemical curing is required, and the composition can accommodate a wide range of waste types because constituents in the waste will not interfere with its solidification upon cooling.

Any non-biodegradable thermoplastic polymer can advantageously used in the encapsulating composition. Those which are softened or in a molten form from about 100°C to about 260°C are most convenient in terms of reducing energy costs when formulating the composition or when mixing the composition with the hazardous waste. Such polymers are known in the art, and include, but are not limited to, polyethylene (including high density polyethylene (HDPE) and low density polyethylene (LDPE)), polypropylene, acrylic, polyvinyl acetate, polyvinyl chloride (PVC), polystyrene, nylon, polybutadiene, and mixtures thereof.

Polyethylene is a particularly useful non-biodegradable thermoplastic polymer for use in accordance with the invention being relatively inert and having melting temperatures that can range from about 105°C (for lower density polyethylene) to about 130°C (for higher density polyethylene).

Polyethylene may be classified into several different categories based on characteristics such as its density and degree of branching. Its mechanical properties depend significantly on variables such as the extent and type of branching, the crystal structure and the molecular weight. When categorised according to density, polyethylene exists in a number of forms, the most common being high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and low density polyethylene (LDPE). HDPE is typically defined by a density of greater or equal to 0.941 g/cm .

HDPE has a low degree of branching and thus has stronger intermolecular forces and tensile strength than LLDPE and LDPE. HDPE may be produced using chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler- Natta catalysts) and reaction conditions. HDPE is used in products and packaging such as milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes. The properties of HDPE, as shown in Table 3 below, make it suitable for use in the encapsulating composition. TABLE 3

Properties of HDPE

LLDPE is typically defined by a density range of 0.915-0.925 g/cm³. LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1- hexene and 1-octene). LLDPE has higher tensile strength than LDPE, and exhibits a higher impact and puncture resistance than LDPE. LLDPE is commonly used in packaging, particularly film for bags and sheets, saran wrap, and bubble wrap.

LDPE is typically defined by a density range of 0.910-0.940 g/cm . LDPE has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties. LDPE is most commonly used for manufacturing containers, dispensing bottles, wash bottles, tubing, and plastic bags. However, its most common use is in plastic bags.

In some embodiments of the present invention, the encapsulating composition comprises HDPE.

In other embodiments of the present invention, the only non-biodegradable thermoplastic polymer used in the encapsulating composition is polyethylene. In some embodiments, the encapsulating composition comprises the non-biodegradable thermoplastic polymer in an amount from about 10% to about 95%, from about 20% to about 95%, from about 30% to about 95%, from about 30% to about 90%, from about 30% to about 85%, from about 30% to about 80%, from about 30% to about 75%, from about 30% to about 70%, from about 30% to about 65%, from about 30% to about 60%, from about 30% to about 55%, from about 30% to about 50%, from about 30% to about 45%, from about 30% to about 40%, or from about 30% to about 35%, by total volume of the encapsulating composition.

The encapsulating composition also comprises wax. As would be understood by a person skilled in the art, waxes belong to a class of chemical compounds that are malleable near ambient temperatures. Characteristically, waxes melt above 45°C to give a low viscosity liquid. Waxes are hydrophobic but are soluble in organic, nonpolar solvents. All waxes are organic compounds which are both synthetic and naturally derived. Natural waxes are typically esters of fatty acids and long chain alcohols. Synthetic waxes are long-chain hydrocarbons lacking functional groups. Suitable waxes for use in accordance with the invention include any of various hydrocarbons (straight or branched chain alkanes or alkenes, ketone, diketone, primary or secondary alcohols, aldehydes, sterol esters, alkanoic acids, turpenes, monoesters), such as those having a carbon chain length ranging from C12-C38. Also suitable are diesters or other branched esters. The compound may be an ester of an alcohol (glycerol or other than glycerol) and a C is or greater fatty acid.

In some embodiments of the present invention, the wax is selected from one or more of mineral waxes such as paraffin, beeswax (e.g. White Beeswax SP-422P available from Strahl and Pitsch of West Babylon, New York), Chinese wax, lanolin, shellac wax, spermaceti, bayberry wax, candelilla wax, vegetable waxes such as carnauba wax, insect wax, castor wax, esparto wax, Japan wax, jojoba oil, ouricury wax, rice bran wax, soy wax, lotus wax (e.g., Nelumbo Nucifera Floral Wax available from Deveraux Specialties, Silmar, California), ceresin wax, montan wax, ozocerite, peat waxes, microcrystalline wax, petroleum jelly, Fischer-Tropsch waxes, substituted amide waxes, cetyl palmitate, lauryl palmitate, cetostearyl stearate, polyethylene wax (e.g. PERFORMALENE 400, having a molecular weight of 450 and a melting point of 84°C, available from New Phase Technologies of Sugar Land, Texas), and silicone waxes such as C₃o-₄5 alkyl methicone and C₃o-₄5 olefin (e.g. Dow Corning AMS- C30, having a melting point of 70°C, available from Dow Corning of Midland, Michigan).

In some embodiments of the present invention, the encapsulating composition comprises paraffin.

In other embodiments of the present invention, the only wax used in the encapsulating composition is paraffin.

Paraffin wax is a type of petroleum product consisting of hydrogen and carbon molecules with 20-40 carbon atoms. Paraffin is widely used in industry and daily life for various applications. The properties of paraffin are shown below in Table 4.

TABLE 4

Properties of Paraffin

In some embodiments, the wax may be present in the encapsulation composition in an amount from about 5% to about 90% by total volume of the encapsulating composition. In some embodiments, the wax may be present in an amount, from about 5% to about 80%, from about 5% to about 70%, from about 10% to about 70%, from about 15% to about 70%, from about 20% to about 70%, from about 25% to about 70%, from about 30% to about 70%, from about 35% to about 70%, 40% to about 70%, from about 45% to about 70%, from about 50% to about 70%, from about 55% to about 70%, 60% to about 70%, or from about 65% to about 70%, by total volume of the encapsulating composition.

In some embodiments, the encapsulating composition may also include an additive such as an anhydrous, anti-leaching agent. Such agents can form precipitates with the hazardous waste and thereby reduce the potential for leaching. Examples of suitable anhydrous, anti-leaching agents include, but are not limited to, sodium sulphide, calcium hydroxide, sodium hydroxide, calcium oxide, magnesium oxide, and mixtures thereof.

In some embodiments, sodium sulphide is the preferred anhydrous, anti-leaching agent to use in the encapsulating composition.

The volume % of each component in the encapsulating composition will be selected to provide for a total volume % of 100%. When present in the encapsulating composition, an additive will be used typically in the range of from about 5% to about 10% by total volume of the encapsulating composition.

In some embodiments, the anhydrous, anti-leaching agent is used in an amount from about 5% to about 10% by total volume of the encapsulating composition.

In one embodiment, the encapsulating composition comprises from about 15-80 volume % non-biodegradable thermoplastic polymer, from about 15-80 volume % wax and from about 5- 10 volume % additive. The encapsulating composition may be used in accordance with the invention in the form of (a) individual components that make up the composition (i.e. where the polymer and wax are separate isolated components), or (b) solid pellets comprising a blend of the polymer and wax.

Such solid pellets (b) can be prepared using standard techniques known in the art. Typically, these involve heating the polymer and the wax (together or separate) to a molten or liquid phase, mixing the two molten components together (if heated separately), and then forcing the molten composition to flow through a die plate before being cut into pellets and allowed to solidify. . This can be achieved using melt mixing equipment as herein described. If the encapsulating composition is to include an anhydrous, anti-leaching agent, the agent can be added either to the molten polymer or the molten wax prior to mixing, or to the molten polymer and wax when combined. Having selected a specific combination of a non-biodegradable thermoplastic polymer and wax that provides a robust and reliable encapsulating composition for use with the hazardous waste, the present invention provides for encapsulation of the waste by melt mixing the waste with the encapsulating composition.

As used herein the expression "melt mixing" is intended to mean a mechanical process whereby the encapsulating composition and the waste are mechanically mixed with the encapsulating composition while it is in a molten or liquid state. Melt mixing is therefore intended to be distinct from the mere addition of molten encapsulating composition to the waste (where mixing and dispersion of the waste through the encapsulating composition will be limited (or non-extistant) and rather ineffective.

The expression "melt mixing" may therefore also be referred to as "mechanical melt mixing".

Melt mixing can advantageously be performed using techniques and equipment known in the art. For example, melt mixing may be achieved using continuous extrusion equipment such as twin screw extruders, single screw extruders, other multiple screw extruders and Farell mixers. When preforming the method of the invention, the encapsulating composition and the waste may be introduced into the melt mixing equipment together or separately. The components that make up the encapsulating composition may also be introduced into the melt mixing equipment together or separately. The encapsulating composition may itself have been formed prior to performing the method of the invention by melt mixing non-biodegradable thermoplastic polymer, the wax and optionally one or more additives such as the anhydrous anti-leaching agent.

The encapsulating composition used in accordance with the invention can advantageously provide for a relatively low viscous molten compositing which effectively and efficiently coats and encapsulates the waste thereby enabling excellent distribution of the waste throughout the matrix of the non-biodegradable thermoplastic polymer and wax blend. This in turn enables the waste to be effectively and efficiently encapsulated at high loadings while still maintaining safe and secure encapsulation.

The method according to the invention may be illustrated with reference to the flow diagram of Figure 1. Here it can be seen that the hazardous waste is fed into a melt mixing device via a hopper (hopper 1). The feeding process can be automated and preferably microprocessor controlled. The waste can be fed into the hopper in its native state, or it can be first subject to drying and/or comminution using methods as described herein. The waste may also be subject to drying within the melt mixing device, as effected by a heating element in, or associated with, the device (heater 1) prior to being melt mixed with the encapsulating composition.

In one embodiment, the waste is comminuted, for example by being ground, crushed or milled, prior to being melt mixed with the encapsulating composition. The encapsulating composition, for example in the form of pellets comprising a blend of the non-biodegradable thermoplastic polymer, the wax and optionally one or more additives, can be added to the melt mixing device separate from the waste via an independent hopper (hopper 2). The melt mixing device may comprise a screw conveyor which facilitates mixing of the waste and encapsulation composition and conveys the resulting mixture through a heated zone(s) to convert the encapsulating composition into a molten state. The melt mixing device may have 1 or more heating elements (e.g. heaters 1-4). This allows a homogeneous, molten mixture of all components to be obtained which ensures appropriate encapsulation of the waste. As indicated above, the feeding process for addition of the encapsulating composition and waste to the melt mixing device may be automated and preferably microprocessor controlled. In that regard, multiple feeders may be used with each individual feeder being regulated by a master controller which monitors and adjusts the delivery of the waste and encapsulating composition to maintain the required or desired weight or volume ratio amongst the components of the mixture. An advantage of using the encapsulating composition described herein is that it may be reused for future encapsulation requirements. With respect to radioactive waste as an example, once the encapsulated radioactive waste has decayed sufficiently (according to applicable regulations) after storage, the encapsulating composition can be reheated to a molten form allowing its separation from the decayed waste. The molten encapsulating composition can then be reused for subsequent encapsulation needs. Furthermore, for waste containing heavy metals the radioactivity of which has decayed sufficiently, the heavy metals may be harvested for reuse in subsequent applications . This recycling of components is simply not possible with conventional binding agents such as cements and the like.

During the method of the invention the molten encapsulating composition comprises the waste encapsulated in the encapsulating composition. Upon cooling, this molten mixture will solidify into a monolithic solid which can be readily transported for subsequent storage. The solidified encapsulating composition comprising the waste encapsulated therein is very robust and not prone to leaching of the waste.

This molten encapsulating composition (comprising the waste encapsulated in the encapsulating composition) may be deposited into a container and allowed to cool to an ambient temperature such that a monolithic solid is formed within the container, thereby containing the waste for subsequent storage.

Accordingly, in one embodiment the method further comprises depositing the so formed encapsulated waste while still in a molten form into a container, thereby containing the encapsulated waste.

By depositing the so formed encapsulated waste while still in a molten form into a container the encapsulated waste forms the shape of the container. The container can be designed for easy of sealing, transport and storage. Any suitable container may be used. For example, the container may be a container that is regulatory approved for containing hazardous waste. In one embodiment, the container is a United Nations approved container for hazardous waste.

Once the encapsulated waste has been contained in the container, the container will generally be sealed. This can be effected by a number of means as would be understood by a person skilled in the art. For example, the container may have a dedicated lid that is sealed to the container by any one or more of various means, including reliance on a seal being created by the solidification of molten encapsulation composition present on top of the encapsulated waste, use of an independent adhesive, or use of clips or the like which are located where the walls of the container engage with the lid.

It is to be noted that where a range of values is expressed herein, it will be clearly understood that this range encompasses the upper and lower limits of the range, and all values in between these limits. The term "about" as used in the specification means approximately or nearly and in the context of a numerical value or range set forth herein is meant to encompass variations of +/- 10% or less, +/- 5% or less, +/- 1% or less, or +/- 0.1% or less of and from the numerical value or range recited or claimed. It will be apparent to the person skilled in the art that while the invention has been described in some detail for the purposes of clarity and understanding, various modifications and alterations to the embodiments and methods described herein may be made without departing from the scope of the inventive concept disclosed in this specification. The invention is further illustrated in the following examples. The examples are for the purpose of describing particular embodiments only and are not intended to be limiting with respect to the above description. PREPARATIVE EXAMPLE 1

Preparation of Encapsulating Compositions

The encapsulating composition includes a non-biodegradable thermoplastic polymer and a wax. As indicated herein, the polymer is present in the composition in an amount from about 30% to about 95% by total volume of the encapsulation composition, and the wax is present in an amount from about 5% to about 70% by total volume of the encapsulating composition. To determine the optimal amount of these constituents to include in the composition, in terms of minimising leaching of the waste from the composition, various formulations can be prepared and tested according to standard methodologies as described in detail below. Representative formulations are provided in Table 5. TABLE 5

In some embodiments of the present invention, the encapsulating composition also includes an anhydrous, anti-leaching agent. As indicated above, the agent may be present in the composition in an amount from about 5% to about 10% by total volume of the encapsulating composition. In that regard, the formulations provided in Table 6 can be prepared in determining the optimal amount of constituents to include in the composition, in terms of minimising leaching of the waste from the composition.

TABLE 6

In some embodiments, the waste is in a dry or near-dry form in which case the waste may be present in the composition in an amount from about 10% to about 85% by weight of the composition. In this regard, the formulations provided in Table 7 can be prepared in determining the optimal amount of constituents to include in the composition, in terms of minimising leaching of the waste from the composition whilst maximising the amount of waste encapsulated.

TABLE 7

Formulation Encapsulation Composition (% wt) Waste (% wt)

1 90 10

2 85 15

3 80 20

4 75 25

5 70 30

6 65 35

7 60 40

8 55 45

9 50 50

10 45 55

11 40 60

12 35 65

13 30 70

14 25 75

15 20 80 16 15 85

EXAMPLE 1

Preparation of Encapsulated Waste

Encapsulated waste is prepared by melt mixing in a extruder (a) an encapsulating composition comprising (i) non-biodegradable thermoplastic polymer, for example 60 volume % HDPE, and (ii) wax, for example 40 volume % paraffin wax, and (b) 20 weight % hazardous waste. Each component is separately fed into the extruder and all components are melt mixed to afford the encapsulated waste. The encapsulated waste exits the extruder in a molten state and is deposited into a container. Once deposited into the container a lid is placed over the opening of the container and on top of the molten encapsulated waste. The molten encapsulated waste can bond securely to the lid resulting in the encapsulated waste being fully contained within the container.

Performance Testing of Exemplary Encapsulation Compositions

Encapsulation of waste is the first of a number of barriers that may be employed to isolate and contain the waste from leaching into the environment. The durability of such encapsulated waste over extended periods of time and in various environmental conditions therefore plays an important role in ensuring that the contaminants in the encapsulated waste remain isolated and contained. Accordingly, it is important to test the encapsulation compositions of the present invention to ensure that they are structurally stable, and therefore sufficiently retain the waste encapsulated therein, over time. In this regard, appropriate tests will involve the application of short-term conditioning and property evaluations that reflect as accurately as possible the anticipated conditions of disposal, storage and containment of the waste.

The following tests may be applied to waste encapsulated by the exemplary compositions of the present invention. The tests are standardised techniques recognised by relevant regulatory authorities such as the American Society for Testing and Materials (ASTM) International, the International Organisation for Standardisation (ISO), and the Environmental Protection Authority/Agency (EPA) on a jurisdictional basis.

Flammability Testing

The encapsulating compositions used in present invention (with waste encapsulated therein) can be subject to a flammability assessment according to a number of testing modalities. These include, but are not limited to the following.

Cone calorimeter (ISO 5660/ASTM E-1354) - this test is comprehensive in that it provides data on most of the fundamental combustion characteristics of a sample material under evaluation (e.g. ease of ignition, rate of heat release, weight of sample as it burns, temperature of sample as it burns, rate of weight loss, rate of smoke release, and yield of smoke) under a wide range of heater and ignition conditions. As a result of the vast amount of data available from this test, a model of the combustion of the sample material might be developed, thus enabling an estimation of the potential effects of a fire on surrounding areas and occupants.

Ignition test (ISO 871-1996/ASTM D-1929) - this test is used to measure and describe the response of a sample material under evaluation to heat and flame under controlled conditions. However, the test does not by itself incorporate all factors required for fire-hazard or fire-risk assessment of the material under actual fire conditions.

Radiant Panel Test (ASTM E-162) - this test measures and compares the surface flammability of sample material under evaluation when exposed to a prescribed level of radiant heat energy. It is intended for use in measurements of the surface flammability of the sample materials when exposed to fire.

Limiting Oxygen Index, LOI (ISO 4589-2/ASTM D-2863) - in this test, a sample material under evaluation is suspended vertically inside a closed chamber (usually a glass or clear plastic enclosure). The chamber is equipped with oxygen and nitrogen gas inlets so that the atmosphere in the chamber can be controlled. The sample material is ignited from the bottom and the atmosphere is adjusted to determine the minimum amount of oxygen to just sustain burning. This minimum oxygen content, expressed as a percentage of the oxygen/nitrogen atmosphere, is called the oxygen index. Higher numbers are associated with decreased flammability. Compressive Strength Testing

Compression tests provide information about the compressive properties of the sample material under evaluation when employed under conditions approximating those under which the tests are made. Compressive properties include modulus of elasticity, yield stress, deformation beyond yield point, and compressive strength (unless the sample material merely flattens but does not fracture). Sample materials possessing a low order of ductility may not exhibit a yield point. In the case of a sample material that fails in compression by a shattering fracture, the compressive strength has a very definite value. In the case of a sample material that does not fail in compression by a shattering fracture, the compressive strength is an arbitrary one depending upon the degree of distortion that is regarded as indicating complete failure of the sample material. Representative tests include the ASTM Standard Test Method for Compressive Properties of Rigid Plastics - ASTM D695 (technically equivalent to ISO 604).

Leachability Tests

These tests are designed to analyse the effectiveness with which the encapsulation composition can retain or reduce the leaking or leaching from the composition of marker contaminants present within the encapsulated waste. The marker contaminants can be artificially loaded into the waste for measurement purposes. Such marker contaminants typically include various metals such as lead, silver, nickel, mercury, chromium, arsenic, cadmium, beryllium, and barium.

The most common leachability test employed is the Toxicity Characteristics Leaching Procedure (TCLP) as provided by the US EPA (Method 1311). In the TCLP procedure the sample material is leached in one of two buffer solutions. A first buffer solution (pH 4.93) is used for neutral to acidic materials whilst a second buffer solution (pH 2.88) is used for alkaline wastes. The leachate mixture is sealed in extraction vessel and tumbled for 18 hours to simulate an extended leaching time in the ground. It is then filtered so that only the solution (not the sample) remains and this is then analyzed, for example by inductively coupled plasma spectroscopy. Alternatives to the TCLP are available. These include the ASTM D3987-85 Shake Extraction of Solid Waste with Water, and the Standards Australia Bottle Leaching Procedure (AS 4439- 1997). The ASTM D3987-85 procedure provides a half-way point between acidic TCLP conditions and in situ conditions by allowing a leach in deionised water. The AS 4439-1997 procedure differs from the TCLP in two main ways - (1) maximum sample particle size for AS 4439 is 2.4 mm in contrast to the TCLP that allows 9.5 mm; and (2) in addition to the standard TCLP buffers, AS 4439 allows the use of three alternate buffers depending on the application, namely (i) reagant water (applicable when a waste is undisturbed and left on site); (ii) tetraborate pH 9.2 (for acid volatile target analytes); and (iii) local water (when exposure to local ground, surface or sea water is expected).

As would be understood by a person skilled in the art, other rigorous testing regimes may be employed to test the effectiveness of the encapsulation composition to retain the waste encapsulated therein. These include crash or drop tests, or more extreme "gorilla" or "torture" tests.

Whilst the tests referred to above evaluate the effectiveness of the encapsulating composition to retain waste encapsulated therein, testing of the ability of a container to maintain containment of the encapsulated waste under stress or duress can also be employed. With respect to radioactive waste, tests may also be employed to identify the level of radioactivity being emitted through the container. Such tests are conducted according to relevant national and international standards as required by various regulatory bodies such as the International Atomic Energy Agency, and the Environmental Protection Authority/Agency (EPA) on a jurisdictional basis. Such tests would include crash or drop tests, or more extreme "gorilla" or "torture" tests.

Claims

1. A method for encapsulation of hazardous waste, the method comprising melt mixing an encapsulating composition comprising non-biodegradable thermoplastic polymer and wax with the hazardous waste, thereby encapsulating the waste in the composition.

2. The method according to claim 1, wherein the hazardous waste is heated prior to mixing with the encapsulating composition so that the waste is substantially dry.

3. The method according to claim 1 or 2, wherein the encapsulating composition further comprises an anhydrous, anti-leaching agent selected from sodium sulphide, calcium hydroxide, sodium hydroxide, calcium oxide, magnesium oxide, and mixtures thereof..

4. The method according to any one of claims 1 to 3, wherein the non-biodegradable thermoplastic polymer is selected from high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene, acrylic, polyvinyl ethylene, polyvinyl acetate, polyvinyl chloride (PVC), polystyrene, nylon, polybutadiene, and mixtures thereof.

5. The method according to any one of claims 1 to 4, wherein the non-biodegradable thermoplastic polymer is HDPE.

6. The method according to any one of claims 1 to 5, wherein the non-biodegradable thermoplastic polymer is present in the encapsulating composition in an amount of from about 20% to about 95% by total volume of the encapsulation composition.

7. The method according to any one of claims 1 to 6, wherein the wax is selected from one or more of paraffin, beeswax, Chinese wax, lanolin, shellac wax, spermaceti, bayberry wax, candeliUa wax, camauba wax, insect wax, castor wax, esparto wax, Japan wax, jojoba oil, ouricury wax, rice bran wax, soy wax, lotus wax, ceresin wax, montan wax, ozocerite, peat waxes, microcrystalline wax, petroleum jelly, Fischer-Tropsch waxes, substituted amide waxes, cetyl palmitate, lauryl palmitate, cetostearyl stearate, polyethylene wax, C30-45 Alkyl Methicone and C30-45 Olefin.

8. The method according to any one of claims 1 to 7, wherein the wax is paraffin.

9. The method according to any one of claims 1 to 8, wherein the wax is present in the encapsulating composition in an amount of from about 5% to about 70% by total volume of the encapsulating composition.

10. The method according to claim 3 or 9, wherein the anhydrous, anti-leaching agent is present in the encapsulating composition in an amount of from about 5% to about 10% by total volume of the encapsulating composition.

11. The method according to any one of claims 1 to 10 further comprising depositing the so formed melt mixed encapsulated waste while molten into a container, thereby containing the encapsulated waste in the container.

12. The method according to any one of claims 1 to 11, wherein the hazardous waste is radioactive waste.

13. A solid integral mass comprising a matrix of non-biodegradable thermoplastic polymer and wax blend, wherein hazardous waste is distributed throughout and encapsulated by the matrix.

14. The solid according to claim 13 , wherein the non-biodegradable thermoplastic polymer is selected from high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene, acrylic, polyvinyl ethylene, polyvinyl acetate, polyvinyl chloride (PVC), polystyrene, nylon, polybutadiene, and mixtures thereof.

15. The solid according to claim 13 or 14, wherein the wax is selected from one or more of paraffin, beeswax, Chinese wax, lanolin, shellac wax, spermaceti, bayberry wax, candelilla wax, carnauba wax, insect wax, castor wax, esparto wax, Japan wax, jojoba oil, ouricury wax, rice bran wax, soy wax, lotus wax, ceresin wax, montan wax, ozocerite, peat waxes, microcrystalline wax, petroleum jelly, Fischer-Tropsch waxes, substituted amide waxes, cetyl palmitate, lauryl palmitate, cetostearyl stearate, polyethylene wax, C30-45 Alkyl Methicone and C30-45 Olefin.

16. The solid according to any one of claims 13 to 15, wherein the hazardous waste is radioactive waste.