GB2226814A

GB2226814A - Treating solid refuse

Info

Publication number: GB2226814A
Application number: GB8929238A
Authority: GB
Inventors: Walter Lukas; Hans Spannbauer; Berntd Meixner; Adolf Hubl
Original assignee: SALZBURGER STADTWERKE AG
Current assignee: SALZBURGER STADTWERKE AG
Priority date: 1989-01-07
Filing date: 1989-12-28
Publication date: 1990-07-11
Anticipated expiration: 2009-12-28
Also published as: GB2226814B; FR2641485B1; AT394661B; CH680418A5; FR2641485A1; ATA276189A; DE3900328C1; GB8929238D0

Description

1 1' j 1 Process for reducing the release of Ras from dumped solid refuse

This invention is concerned with a process for reducing the release of gas from dumped solid refuse, that is household and other refuse dumped in landfill sites.

It is known that such dumped solid refuse produces gases over a long period of time which are inflammable and/or explosive and which must be regarded as toxic. This gives rise to a not insignificant degree of environmental pollution. It is also known that such dumped solid refuse tends to compress further over an extended period of time and thus sinks; areas covered by such refuse cannot, therefore, be subjected to loads, or used, or built on for a long time.

It is an object of this invention to reduce the evolution of gas from dumped solid refuse and to neutralise toxic components thereof as far as possible. It is also desirable to accelerate the consolidation of such refuse so that areas covered by it can be subjected to loads and, in particular, so that such areas can be built on.

1 We have found that these objects can be met by injecting dumped solid refuse with a liquid slurry containing a particular kind of cementitious material.

According to the present invention, there is provided a process for reducing the release of gas from dumped solid refuse, which comprises injecting into the solid refuse a liquid slurry formed by mixing a solid mixture.comprising a) at least one siliceous component which is actually or latently hydraulic, b) at least one alkaline earth component based on CaO, Ca(U)2, MgO or Mg(OH)2 as initiator for the hydraulic component, and c) calcium sulphite and/or calcium sulphate in anhydrous or hydrated form, the weight ratio of component a) to the sum of components b) and c) being from 60:92 to 8:40 and the amount of component b) being at least 5% by weight of the solid mixture, with water to form said liquid slurry.

The liquid slurry should, of course, have such a consistency that it can be injected into the solid waste so as to fill the voids therein; such injection is preferably effected by means of lances. In general, the water/solids weight ratio of the slurry should be at least 0.8 to 1.0.

The solid mixture preferably also comprises a liquefying agent and/or a sealant. These additives are preferably present in an amount of from 0.1 to 2% by weight with respect to the components which participate in the hydraulic reaction. Suitable liquefying agents include, for example, melamine resin, naphthalene sulphonate, lignosulphate, and the like; the presence of such an agent enables the water content of the slurry to be reduced while maintaining the consistency of the 1 i - 3 slurry at the same level and facilitating the injection of the slurry into the solid refuse.

Suitable sealants include, for example, waterglass and stear ates; these additives improve the compactness of the slurry upon setting.

The injecting of the slurry into the voids of the solid refuse is preferably carried out continuously from the bottom of the dump to the surface thereof. In this way, the solid refuse is, as it were, encapsulated. The slurry then sets relatively quickly; the setting time depends on the composition and may range from a few hours to a few days. After a week at the latest, the consolidation has, in general, advanced to such a degree that mechanical loading of the area is possible. The strength of the injected material depends on the amount and composition of the injected slurry and is at least 3N/mm2; it can properly support buildings with flat foundations. At the same time, encapsulation and inner sealing of the solid refuse takes place so as to significantly reduce or prevent the formation and release of gas. This phenomenon is not only observed with fresh household refuse, but also with special refuse dumps and old dumps. The process is therefore also suitable for the rehabilitation of old dumps.

In certain cases, it may be advantageous to add a setting accelerator, such as waterglass or sodium aluminate, to the slurry.

Other additives which may be present include alcohol-soluble silicon compounds and silicon powder. These and the other additives previously mentioned serve to stabilise the slurry so that undesirable sedimentation or separation of the slurry is reduced or avoided during setting. The consistency of the slurry is preferably such that it has a spreadability as measured by DIN 1045 of at least 60 cm.

t '.

Component c) of the solid mixture is preferably the dry residue of a sulphur dioxide spray absorption plant. Such plants are generally operated with calcium oxide or aqueous calcium hydroxide or calcium carbonate solutions. The dry.residues contain, in addition to calcium sulphite and calcium sulphate, which may be present in the form of hydrates, unreacted calcium hydroxide so that a part of component b) is simultaneously introduced by the use of these materials. The amount of component c) in the solid mixture is preferably from 3 to 25% by weight. If the proportion is less than 3% by weight, there is a risk that toxic substances which are incorporated in the set material may be leached out; if more than 25% of component c) is present, the mechanical resistance of the treated dump tends to deteriorate, probably due to decomposition of the set material arising from the increased formation of ettringite.

Suitable siliceous components a) are, for example, fly ash, boiler ash and finely divided slags or clinkers. If fly ash is used which contains free calcium oxide, then it will provide some of component b). The Si02 content of component a) should be at least 40% by weight.

Component a) preferably has a particle size of less than 100 pm and, more preferably, less than 40 pm. If the material is not obtainable in this fineness, it should be separately ground, preferably directly down to a particle size of less than 40 pm since it has been found that the reactivity increases with increasing fineness. Also, the finer component a), the greater the capacity to bind toxic components in the solid refuse, such as heavy metals or organic compounds. The use of the alkaline earth initiator, component b), improves the hydraulic setting and also allows increased binding of toxic substances.

We have found that the use of 3% to 6% by weight of alumina cement, with respect to the solid mixture, is particularly favourable in this respect; the alumina cement replaces part of component b). It appears that as a result of a synergistic interaction with the other components, extremely low leaching and water permeability values are obtained by the use of alumina cement.

Ground or finely divided fillers can also be included in the solid mixture. Suitable materials for this purpose are, for example, ashes which are contaminated with toxic substances, for example ashes from refuse incineration including special refuse incineration. The Si02 content of such ashes is usually below 40% by weight and may be below 10% by weight. Other suitable fillers are clay minerals, mineral slurries and mineral powders, of which up to 30% by weight, based on the solid mixture, can be added.

In order that the invention may be more fully understood the following example, in which all proportions are by weight, is given by way of illustration. Example A solid mixture of the following composition was prepared:

a) 80% of boiler ash (particle size less than 40,pm, 80% less than 10 pm), -b) 8/1. of calcium hydroxide, and C) 12% of dry residues from an NIRO spray absorption plant which was operated with an aqueous calcium hydroxide solution; dry residues comprised 45% of calcium sulphate/calcium sulphite and 55% of ash and free CaO and had a particle size of less than 40 pm.

f 1 1 1 - 1k - 6 This mixture was mixed with water to form a liquid slurry having a water/solids ratio of 1.0.

Immediately following the formation of the slurry, it was injected by means of lances into a solid refuse dump under pressure. The lances were first introduced into the bottom zone of the dump and then gradually pulled upwards towards the top. The slurry was atomised in a finely divided form from a spray head at the end of the lance. Finally the top surface of the dump was covered with an approximately 20 cm thick layer of the slurry.

After as little as one week, substantial consolidation had taken place. After 4 weeks, the treated material had a strength of 12N/mm2. Measurements showed that no gases were being released from the treated dump and the usual sinking and deformation of the dump did not occur.

Chemical analysis of the set slurry showed that it contained substantial amounts of toxic components, in particular heavy metals and organic compounds, derived from the solid refuse.

C.

1

Claims

CLAIMS:

1. A process for reducing the release of gas from dumped solid refuse, which comprises injecting into the solid-refuse a liquid slurry formed by mixing a solid mixture comprising a) at least one siliceous component which is actually or latently hydraulic, b) c) at least one alkaline earth component based on CaO, Ca(H)2, MgO or Mg(OH)2 as initiator for the hydraulic component, and calcium sulphite and/or calcium sulphate in anhydrous or hydrated form, the weight ratio of component a) to the sum of components b) and c) being from 60:92 to 8:40 and the amount of component b) being at least 5% by weight of the solid mixture, with water to form said liquid slurry.

2. A process according to claim 1, in which component a) is fly ash, boiler ash, or slack having a particle size of less than 100pm.

3. A process according to claim 1 or 2, in which component a) has a particle size of less than 40 p M.

4. A process according to any of claims 1 to 3, in which component c) is the dry residue of a sulphur dioxide spray absorption plant.

5. A process according to any of claims 1 to 4, in which component c) constitutes from 3 to 25% by weight of the solid mixture.

6. A process according to any of claims I to 5, in which component b) is replaced in part by alumina cement.

7. A process according to claim 6, in which the alumina cement constitutes from 3 to 6% by weight of the solid mixture.

8. A proces-s-according to any of claims I to 7, in which the solid mixture also comprises a liquefying agent and/or a sealant.

9. A process according to claim 8, in which the liquefying agent and/or the sealant is/are present in an amount of from 0.1 to 2% by weight with respect to the components which participate in the hydraulic reaction.

10. A process according to any of claims 1 to 9, in which the consistency of the slurry is such that it can be injected into the solid refuse by means of injection lances.

11. A process according to claim 10, in which the slurry has a spreadability as measured by DIN 1045 of at least 60 cm.

12. A process according to any of claims 1 to 11, in which the water used to form the slurry is water containing toxic substances.

13. A process according to any of claims 1 to 12, in which the slurry is continuously injected into the voids in the solid refuse from the bottom of the dump to the surface thereof.

14. A process according to claim 13, in which a continuous layer of the slurry is first applied over the area on which the solid refuse is dumped.

14. A process according to claim 13, in which a continuous layer of the slurry is first applied over the area on which the solid refuse is then dumped.

15. A process according to any of claims 1 to 14, in which the slurry is introduced into the voids in the solid residue through a spray head.

16. A process according to any of claims 1 to 15 in which, after injection of the slurry into the solid refuse, a layer of a slurry is applied over the surface thereof.

I0 Amendments to the claims have been filed as follows 1. A process for reducing the release of gas from dumped solid refuse, which comprises injecting_into the solid refuse a liquid slurry formed by mixing a solid mixture comprising a) at least one siliceous component which is actually or latently hydraulic, b) at least one alkaline earth component based on CaO, Ca(W2, MgO or Mg(OH)2 as initiator for the hydraulic component, and c) calcium sulphite and/or calcium sulphate in anhydrous or hydrated form, the weight ratio of component a) to the sum of components b) and c) being from 60:92 to 8:40 and the amount of component b) being at least 5% by weight of the solid mixture, with water to form said liquid slurry.

2. A process according to claim 1, in which component a) is fly ash, boiler ash, or slag having a particle size of less than 100 Y M.

5. A process according to any of claims 1 to 4, in which component c) constitutes from 3 to 25%,o by weight of the solid mixture.

1 6. A process according to any of claims I to 5, in which component b) is replaced in part by alumina cement.

1 1k 7. A process according to claim 6, in which the alumina cement constitutes from 3 to 6% by weight of the solid mixture.

8. A process according to any of claims 1 to 7, in which the solid mixture also comprises a liquefying agent and/or a sealant.