EP0006329A1

EP0006329A1 - Encapsulating wastes

Info

Publication number: EP0006329A1
Application number: EP79301080A
Authority: EP
Inventors: Parry BP Chemicals Limited Williams
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1978-06-08
Filing date: 1979-06-07
Publication date: 1980-01-09
Also published as: WO1980000047A1; JPS55500406A; ES481367A1

Abstract

Wastes e.g. radio active wastes are encapsulated by setting under aqueous alkaline conditions a mixture of unsaturated polyester, hydraulic filler and an initiator which is activated by aqueous alkaline conditions e.g. a persulphate.

Description

The present invention relates to a process for encapsulating hazardous wastes. It is known to encapsulate various hazardous wastes by incorporating the waste into a fluid material which is then allowed to set to a solid so as to bind the waste. This enables the waste to be handled more easily and prevents hazardous components of the waste escaping to the environment. Thus it is known from British patent specification 1 116 319 to incorporate radio active wastes in bitumen, cement or a polymerisable resin. If bitumen is used the waste must be subjected to the elevated temperatures used to melt the bitumen. This is not always desirable and the requirement for a heating step leads to additional complications. The use of bitumen is not very suitable for wet wastes because the elevated temperature will lead to the evolution of steam which may carry with it hazardous components of the waste and because bitumen is hydrophobic.
The use of cement as an encapsulating agent is not very satisfactory as the time required for the cement to set is usually undesirably long.
The resulting product is friable and does not retain its structural integrity.
British patent specification 938 211 discloses a process for solidifying or encapsulating an aqueous radio active waste by mixing the waste with a finely divided hydraulically setting absorption material e.g. Portland Cement.
After the hydraulically setting absorbtion material has set the resulting dry block is then impregnated with a self-hardening synthetic or casting resin e.g. "Palatal P6" sold by BASF. This is a mixture of unsaturated polyester and styrene and as is well known in the polyester art such resins are cured by the action of conventional organic peroxide curing agents. The process is an impregnation process and is clearly only applicable to a block which has set and is free from water as otherwise the resin will not penetrate the block. Pressure is required for the impregnation process and it will be difficult to obtain satisfactory penetration of the resin into the core of the block. The speed of the encapsulation process is dependent on the setting time of the hydraulic filler. The specification mentions setting times of 2 days. The process is thus not a very satisfactory method of encapsulating wastes.
Among the polymerisable resins which have been suggested for the encapsulation of wastes are unsaturated polyester resins. Thus British patent specification 1 353 121 discloses the encapsulation of a radio active waste in the form of a dry powder using a mixture of (1) an unsaturated polyester prepared from maleic and phthalic anhydride reacted with propylene glycol and (2) a copolymerisable monomer e.g. styrene. Polymerisation is initiated by an initiator such as methyl ethyl ketone peroxide. While most unsaturated polyester resin systems are not intended to be used in the presence of water there is a well known method of using unsaturated polyester resins in the presence of water, namely in the production of a so-called WEP or water extended polyester. This is described in an article by R.E. Carpenter in "Encyclopedia of Polymer Science and Technology" 15, 375 (1971). WEPs are produced by dispersing water into the unsaturated polyester resin under conditions of high shear to form an emulsion of water in resin. The polymerisation initiators used are organic peroxides.
The use of WEPs to encapsulate hazardous wastes is disclosed in a paper entitled "Polyester Encapsulation of Hazardous Industrial Wastes" by R.V. Subramanian et al., presented at the National Conference on Treatment and Disposal of Industrial Waste Waters and Residues" Houston Texas, April 26-28 1977.
British patent specification 1 479 150 also discloses the encapsulation of wet wastes (specifically radio active ion exchange resins) using an unsaturated polyester resin. The specification does not specifically state that a WEP was used but this would be apparent to a person skilled in the art in view of the reference to a methyl ethyl ketone/cobalt naphthenate initiator/activator system.
The use of WEPs to encapsulate wastes has a number of disadvantages. The requirement for high shear to create an emulsion or dispersion means that special expensive mixing equipment is required. There can be difficulties in obtaining a solid product in a reasonable length of time. This is because it is important to avoid an excessive temperature rise within the material being polymerised due to exothermic nature of the polymerisation reaction. Thus if waste material is being cast into a block it is important to prevent the temperature at the centre of the block rising excessively while the material sets as stresses may be produced which will cause cracking of the block. There may also be undesirable evolution of vapours from the block. Certain wastes subjected to high temperature will swell or disintegrate. An excessive temperature rise can be avoided by using low concentrations of initiator and activator but the setting time is then undesirably long. Associated with the problem of heat evolution is the problem of scale-up. A WEP type polyester resin formulation which is suitable for use in small scale tests may be completely unsatisfactory when attempts are made to cast large blocks. A formulation which is suitable for use with a waste with a given water content may be unsatisfactory when used with a waste with a different water content.
There has been a long felt want for a method of encapsulating hazardous wastes, particularly radio active wastes but the methods previously proposed have had considerable disadvantages.
According to the present invention the process for encapsulating a hazardous waste by allowing to set an encapsulation mixture containing an unsaturated polyester an ethylenically unsaturated monomer copolymerisable with said polyester, and an initiator,which mixture incorporates the hazardous waste, is characterised in that the mixture contains a hydraulic filler, the initiator is an initiator which is activated by aqueous alkaline conditions and setting takes place under aqueous alkaline conditions.
The process of the present invention may be applied to a variety of wastes providing that they do not interfere with setting reaction to any substantial extent. Thus the process may be applied to wastes containing toxic heavy metals or mercury, or organochlorine compounds. It is particularly useful for the encapsulation of radioactive wastes. The wastes may be pieces of contaminated equipment or clothing, but the process is particularly suitable for the encapsulation of particulate wastes. The wastes may be dry in which case water must be added to the mixture to cause it to set. The process is particularly suitable for the treatment of wet particulate radio active wastes which are usually difficult to handle by alternative methods. The quantity of water present in the waste may, for example, be in the range 20% to 60% by weight of waste, preferably below 50% by weight. The process of the present invention is particularly suitable for the encapsulation of wet ion-exchange resins both anionic and cationic. Other wet solid wastes to which the process of the invention may be applied are molecular sieves, graphite, sand and aluminosilicates, Magnox sludges (sludges containing magnesium hydroxide mixed with magnesium carbonate) filtration sludges.
The process of the present invention may also be used to encapsulate wastes in the form of aqueous solutions. It will be necessary to use sufficient hydraulic filler to bind all the water on setting.
Unsaturated polyesters and ethylenically unsaturated monomers copolymerisable with the polyesters are well known to those skilled in the art. A description of suitable polyesters is found in British patent 1 065 053 (Cement Marketing Company), the disclosure of which is incorporated by reference.
It is preferred to use a mixture which gels in 30 to 90 minutes, for example one which gels in less than 1 hour. M.xtures gelling in the range 10 to 30 minutes can be used however and a standard polyester made from a mixture of an ether glycol and a non-ether glycol e.g. from diethylene glycol and ethylene glycol, may be used together with a metal accelerator e.g. copper naphthenate, a reducing agent e.g sodium metabisulphite and a soap emulsifier. Alternatively an unsaturated polyester may be used which is inherently more reactive e.g. an unsaturated polyester produced from one or more glycols which are substantially all ether glycol in which case metal accelerators and reducing agents are not required.
The hydraulic filler may be any substance which on mixing with water at ambient temperature reacts to form a crystalline lattice structure exhibiting a degree of mechanical stability and/or physical strength. Examples of hydraulic fillers are gypsum, calcium sulphate hemihydrate (plaster of Paris),.and pulverised fuel ash. The alkaline conditions required to activate the initiator may be provided by the addition of a substance which is not a hydraulic filler. However in a preferred embodiment of the invention, the substance which produces the alkaline conditions also acts as a hydraulic filler, and it is preferred to use an alkaline reacting hydraulic cement. Examples of hydraulic cements are high alumina cements, blast furnace cements, lime-pozzolana cement. It is preferred however to use mixtures containing Portland cement. The Portland cement may be substantially the only hydraulic filler present in the mixture. Alternatively it may be desirable to use mixtures of Portland cement with other fillers e.g. pulverised fuel ash. The Portland cement content in such mixtures may be from 6 to 95% by weight of total hydraulic filler, but is more preferably greater than 10% by weight, in particularly greater than 20% by weight.
The initiator used in the process of the present invention is one which is activated by aqueous alkaline conditions, which distinguishes it from the organic peroxides usually used in polyester moulding compositions. It is preferred to use a water soluble salt of a per acid, in particular salts of persulphuric acid, e.g. ammonium, sodium and potassium persulphate. It is particularly preferred to use ammonium persulphate. The quantity of initiator used will depend on the speed of gelling required. Examples of suitable amounts are those in the range 1% to 5% by weight of the encapsulation mixture.
The quantity of waste incorporated in the encapsulation mixture may vary over a wide range. For economic reasons it is desirable to incorporate a large quantity of waste into the mixture. However an excessive amount of waste may lead to a reduction in the physical strength of the final product obtained. The man skilled in the art will be able to determine by simple tests the maximum amount of waste which can be incorporated consistent with his requirements for the physical strength and integrity of the final product. Thus the quantity of waste may be 30% to 60% of the total weight of encapsulation mixture and waste and is preferably more than 40% by weight of the total. It is preferred to use sufficient quantity of encapsulation mixture to prevent the appearance of excess water on the surface of the set product, when treating a wet waste.
The relative proportions of unsaturated polyester, ethylenically unsaturated monomer and hydraulic filler may vary over a wide range. For example suitable compositions may contain 50 to 70 parts of polyester resin, 25 to 65 parts of unsaturated monomer and 80 to 150 parts of hydraulic filler and 3 to 5 parts of initiator.
Where the waste does not contain water it will be necessary to add it so as to cause the encapsulation mixture to set. Even if some water is present in the waste it may be desirable to add additional water. The quantity of water initially present may for example be at least 50% by weight of the hydraulic filler. If the dry encapsulation mixture is prepared in advance of the encapsulation step it may be desirable to add fumaric acid to stabilise it. It may be desirable to add non-ionic surfactants. The addition of fatty acids to control pot life (i.e. the time for which the mixture remains fluid after water is added) and give ease of dispersion of the encapsulation mixture after prolonged storage may be useful. ^* The quantities of waste, hydraulic filler unsaturated polyester and copolymerisable monomer are preferably such as give a product which has a specific gravity of at least 1.2. This is important if the encapsulated material is to be disposed of by dumping in the ocean.
The encapsulation mixtures of the present invention may be prepared by simple low speed mixing apparatus without the necessity • (see GB 1 098 132, GB 1 091 325, GB 1 092, 747). of using expensive high shear mixers such as are used in the production of WEPs (water extended polyesters). If the waste is particulate it may be introduced into the mixing apparatus with the other ingredients. The mixture is then discharged into a mould in which it is allowed to set. For non-particulate waste e.g. pieces of machinery, encapsulation mixture may be fed to the mould, the waste added and the mould may then be filled with additional encapsulation mixture.
After the mixture has set to a sufficient extent it may be removed from the mould. The resulting moulded block may then be if required be inserted into a protective container and disposed of by dumping. Alternatively the mould in which the block is formed may act also as a container.
The invention will now be illustrated by reference to the following Examples.
In these Examples three different polyester resins were used.

Polyester Resin A

Condensation product of phthalic anhydride, maleic anhydride, 1,2 propylene glycol and diethylene glycol in mole ratios 2:1 : 2.18 : 1.18 dissolved in styrene to give a 70% solution by weight.

Polyester Resin B

Condensation product of phthalic anhydride, maleic anhydride and diethylene glycol in mole ratios 1:1 : 2.2 dissolved in styrene to give a 60% solution by weight.

Polyester Resin C

Similar to polyester resin A except this was processed to a higher viscosity and contained less inhibitors.

Example 1

Polyester resin A (60 parts by weight) was mixed at ambient temperature with a hydraulic cement (40 parts by weight) (sold under the name Hydracrete) ammonium persulphate (2 parts by weight), sodium metabisulphate (0.5 parts by weight), copper naphthenate (equivalent to 5 ppm copper) and liquid soap (1.0 parts by weight). Ion exchange resin (50 parts by weight) containing about 47% by weight of water was then mixed in and the mixture was allowed to set in a mould. The mixture gelled in 11 minutes and had set sufficiently to allow the block of encapsulated ion exchange resin to be removed from the mould in 2 to 3 hours.

Example 2

A composition was made by mixing together at ambient temperature polyester resin C, Portland cement and ammonium persulphate in the proportions shown in Table 1.
Waste in the form of wet ion exchange resin (75 grams) containing 47% by weight of water was added to the mixture and cast in a mould. The mixture in the mould gelled in 30 minutes and readily demoulded in 2 to 3 hours showing no signs of separated water.

Example 3

This was carried out in the same way as Example 2 except that potassium persulphate was used in place of ammonium persulphate. The mixture in the mould gelled in 1-1 hours and was readily demoulded in 6 to 7 hours showing no significant signs of separated water.

Comparative Tests A, B and C

These were comparative tests not according to the invention and were carried out as Example 2 except that cumene hydroperoxide paramenthane hydroperoxide and methyl ethyl ketone peroxide respectively were used in place of ammonium persulphate. The mixture in the mould thickened over a period of 4 to 6 hours without properly gelling. Overnight a sticky uncured soft mass was produced showing large quantities of free water and liquid polyester resin.

Example 4

This was carried out in a similar way to Example 2 but using polyester resin B in place of polyester resin C. The quantities used are shown in Table 2 and the same quantity (75 grams) of the wet ion exchange resin was added as in Example 2.
The mixture was poured into a mould. It gelled after 11 minutes and could be readily demoulded in 1-12 hours showing no signs of separated water.

Example 5

This was carried out as in Example 4 but using potassium persulphate. The quantities used are given in Table 2.
The mixture in the mould gelled in 25 minutes and could be readily demoulded in 3 to 4 hours showing no signs of separated water.

Comparative Tests D and E

These were comparative tests not according to the invention using cumene hydroperoxide, and paramenthane hydroperoxide respectively as initiator. The mixture in the mould thickened over 6-8 hours without gelling. Overnight a sticky uncured soft mass was produced showing large quantities of free water and liquid polyester resin.

Examples 6, 7, 8 and 9

The ingredients set out in Table 3 were mixed together at an ambient temperature of 20°C and allowed to set in a mould. The pot life of the mixtures i.e. the time required for gelling to take place was measured and is given in Table 3. All the mixtures were readily demoulded in 1-2 hours and exhibited no separated water. The white cement, high early strength cement, and oil well cement are all different types of cement well known to those skilled in the cement art.

Comparative Test F

This was carried out as in Example 6 but using PFA (pulverised fuel ash). The mixture did not gel for 1-2 days and could only be demoulded after 3 days.

Examples 10 to 17

The compositions set out in Table 4 were prepared in the same way as in the previous examples at an ambient temperature of 20°C.
All mixes were readily demoulded in 3-4 hours showing no signs of separated water.

Examples 17 to 21

The following compositions were made up in the manner of previous Examples.
The mixes of Examples 17, 18, 19 and 21 were readily demoulded in 1-2 hours and showed no separated water.
The mixture of Example 20 was demoulded in 6-8 hours and showed a slight surface wetness.

Example 22

The following composition was made up:
To 102 g aliquots of this composition were added various wet waste materials as follows.
All mixes were readily demoulded in 2-3 hours showing no evidence of water separation.
The mixed waste was a mixture of ion-exchange resins.

Example 23

Blocks of 10 litre, 50 litre and 200 litre size were cast into polythene moulds cylindrical in shape using the composition below.
Composition of Mixed Waste Resin
Pot lives of these mixes were approximately 1t hours and these had cured sufficiently to be demoulded within 4 hours.
Exothermic cure temperatures were recorded over this period by means of thermocouples embedded at various points near the edges and centre of the blocks.
The results are summarised in Table 7.
At 1 day all blocks were well cured, homogeneous and free from surface or internal cracks.
Volume shrinkage was approximately 2.5% in all cases.

Example 24

The following composition was prepared at an ambient temperature of 20°C and submitted for resistance to gamma radiation. Table 8 shows the results.

Example 25

Binder for encapsulation mixture as for Example 24 replacing the crushed Lewatit by 9 parts by weight of water.
Cast specimens were submitted to varying dosages of gamma radiation and tested before and after exposure. Table 9 shows the results.
These results compare very favourably with gas evolution from similar ion exchange resin wastes encapsulated in the conventional concrete or bitumen binders.

Radiation Leach Testing

Specimens were prepared using the formulation of Example 24 using radio active waste ion exchange resin contaminated with Caesium 137 isotope. These specimens were prepared and tested in accordance with "Leach Testing of Immobilised Radio active Waste Solids", A Proposal for a Standard Method, E. D. Hespe Atomic Energy Review Vol. 9 page 195 (1971).
Over a period of 6 months' immersion in water, the levels of leached radio activity were categorised as low and were noticeably lower than that obtained when similar radio active wastes were encapsulated in concrete or bituminous binders.

Example 26

The following mixes were made up on 10 litre scale at an ambient temperature of 20°C in polythene cylindrical moulds.
Peak exotherm measurements were made using thermocouples positioned at the centre points of the castings.
Blocks based on Portland cement alone were readily demouldable within 2-3 hours.
Blocks based on Portland cement/PFA were demouldable in 4-6 hours.
All blocks on demoulding were uniform, free from internal cracks or voids other than occasional minor air inclusion and were handleable without risk of being readily damaged.
The various types of wet waste resins in the Examples described by trade names had the following compositions:

Lewatit cationic phenol-formaldehyde based ion exchange resin
Decalso Y cationic alumino silicate gel based ion exchange resin
Zeolit 225 cationic polystyrene based ion exchange resin
Zeolit FF or anionic polystyrene based ion exchange Deacidite FF resin
IRN-78 anionic polystyrene based ion exchange resin
AW - 500 cationic modified alumino silicate zeolite molecular sieve.

The mixed waste resin used in Examples 1 to 22 inclusive was that described in Example 6. The water content in Examples 1 to 21 was 47% but in Example 22 was 42%.

Examples 27 to 31 and Comparative Test G

The following compositions were made up in the manner of the previous Examples:

^* Composition as given in Example 22.
Compositions were hand mixed and were readily pourable prior to gelation. Compositions of Examples 27 to 30 could be demoulded between 1 and 4 hours after mixing showing no signs of separated water and on demoulding they were homogeneous and free from cracks and voids other than minor air inclusions. The composition of Comparative Test G did not set within 24 hours. The composition of Example 31 was demouldable within 24 hours.
^* Composition as given in Example 22.Compositions mixed by hand were readily pourable prior to gelation. The compositions of Examples 32 to 34 were demouldable within 1 to 4 hours after mixing showing no signs of separated water, and on demoulding were homogeneous and free from cracks and voids other than minor air inclusions. The composition of Comparative Test H did not set within 24 hours.
The mixtures according to the present invention were pourable and easily handled before setting and were prepared using low shear paddle mixers in contrast to the high shear mixers used to make water extended polyester mixtures. It should be noted that the water-in- polyester emulsions used in making water extended polyesters are often very thick and difficult to pour.
The mixtures of the present invention when set were uniform, free from major cracks and voids other than small air inclusions. They were mechanically strong and could be transported without crumbling or breaking.

Claims

1. A process for encapsulating a hazardous waste by allowing to set an encapsulation mixture containing an unsaturated polyester, an ethylenically unsaturated monomer copolymerizable with said polyester and an initiator, which mixture incorporates the hazardous waste, characterised in that the mixture contains a hydraulic filler, the initiator is an initiator which is activated by aqueous alkaline conditions and setting takes place under aqueous alkaline conditions.

2. A process according to claim 1 wherein the waste is a radioactive waste.

3. A process according to either of claims 1 or 2 wherein the waste is a wet particulate waste.

4. A process according to claim 3 wherein the waste contains 20% to 60% by weight of water.

5. A process according to claim 4 wherein the waste is an ion exchange resin.

6. A process according to any one of claims 1 to 5 wherein the encapsulation mixture is of such a composition as to have a setting time less than 1 hour.

7. A process according to any one of claims 1 to 6 wherein the unsaturated polyester is produced from one or more glycols which are substantially all ether glycol.

8. A process according to any one of claims 1 to 7 wherein the hydraulic filler includes an alkaline reacting hydraulic cement.

9. A process according to claim 8 where the cement is Portland cement.

10. A process according to claims 8 or 9 wherein the hydraulic filler includes a material which is not an alkaline reacting hydraulic cement.

11. A process according to any one of claims 1 to 10 wherein the initiator is a water soluble salt of a per acid.

12: A process according to claim 11 wherein the initiator is an ammonium or alkali metal persulphate.

13. A process according to any one of claims 1 to 12 wherein the quantity of water initally present in the encapsulating mixture plus waste is 5% by weight of hydraulic filler.

14. A process accroding to any one of the preceding claims wherein the mixture is allowed to set in a mould to form a block which is then transported to a dumping site.