GB2199179A - Encapsulation of waste material - Google Patents

Abstract

The grout-permeable inner basket of a waste-encapsulation drum is formed with two bottom walls spaced from one another (and from the drum bottom wall) and a layer of grouting material covering the lower bottom wall of the basket is allowed to set before the drum is used. This layer (reinforced by the lower bottom wall) catches any fine and possibly contaminated particles which fall from waste material during filling and/or grouting, and ensures they are adequately spaced from the drum bottom wall when encapsulation is complete. <IMAGE>

Description

Encapsulation of Waste Material This invention relates to the encapsulation of waste material, in particular potentially dangerous -waste material such as chemical or radioactive waste material which it is required to maintain isolated from its environment.

It is known to encapsulate such waste material in a drum provided with an inner basket in which the waste material is contained, the drum being filled with an encapsulating material, such as a cement grout, which interpenetrates the waste material to form a solid mass therewith within the basket and also fills a surrounding space between the basket and the drum walls to form a surrounding skin of hardened grout which, at least in intention, is free of the potentially dangerous waste material and isolates it physically from the environment.

In order to provide good interpenetration of the waste material and the encapsulating material within the inner basket, it is desirable to provide vibration of the drum and its contents during filling; but there is then a risk that any fine component of the waste material will be shaken free of the remainder of the waste material and, if it is denser than the encapsulating material, will escape from the basket and sink through that part of the still-liquid encapsulating material between the bottom of the basket and the bottom of the drum, and settle in a layer on the bottom of the drum.If the drum bottom should subsequently become rusted or otherwise damaged, such a layer of settled fine waste material would be inadequately retained and isolated by the encapsulating material; and even in the absence of such damage to the drum, it is not provided with the intended degree of physical spacing from the exterior surface of the drum.

It is an object of the present invention to provide a method and means of encapsulating waste material in a drum provided with an inner basket such that even fine components of the waste material are satisfactorily encapsulated with adequate spacing from the drum exterior.

According to a first aspect of the invention, therefore, there is provided a method of encapsulating solid material within an inner basket positioned inside an outer container, comprising the steps of positioning and securing the basket within the container in spaced relation to side walls thereof, feeding the solid material into the basket, then feeding solidifiable liquid encapsulating material into ttie container to fill space therein surrounding the basket and interstitial space in the solid material by interpenetration thereof, and allowing the encapsulating material to solidify, wherein the basket is secured in position within the container by introducing into the bottom of the container a layer of solidifiable liquid encapsulating material to a depth at which a bottom wall of the basket is submerged in and penetrated by the material of the layer, and allowing the layer to solidify with the said bottom wall of the basket embedded there before feeding the said solid material into the basket.

Preferably the method includes the step, prior to introducing the said layer, of introducing solidifiable liquid encapsulating material and forming therefrom a solid spacer collar, peripherally within the bottom of the container, which acts to locate the basket in spaced relationship to the side walls of the container.

Preferably also the basket is positioned in the container before the material for the collar is introduced, and an impermeable zone at the bottom of the basket and surrounding the basket bottom wall serves as a former for the collar, the solidifiable material for the collar being introduced between the said zone and the surrounding side walls of the drum.

According to another aspect of the invention there is provided a container for encapsulation of solid material, comprising an outer container, having side walls and a bottom wall, an inner basket having side walls and at least one bottom wall spaced upwardly from a lower edge of the basket side walls and from the bottom wall of the outer container when engaged by said lower edge, and a layer of solidified liquid encapsulating material on and adhered to the outer container bottom wall and having the said one bottom wall of the basket submerged and embedded in and penetrated by it and thereby secured in position relative to the outer container.

Preferably the container comprises a collar of solidified liquid encapsulating material cast peripherally within the bottom of the outer container between the side walls thereof and the lower part of the side walls of the basket, the collar extending upwardly, outside the side walls of the basket, to a height above that of the said one bottom wall of the basket.

Also, in a preferred form of container according to the invention, the inner basket is formed with a second bottom wall spaced above the said one bottom wall and also above the said layer of solidified encapsulating material in which the said one bottom wall is submerged and embedded, but at a height less than that to which the collar extends.

The invention will be understood from the following description with reference to the accompanying drawing, which is a cut-away perspective view of a drum embodying the features of the invention and filled in accordance with the invention with encapsulated waste material.

As shown in the drawing, a drum 11 has a base wall 12 and a generally cylindrical side wall 13 which is formed with rolling rings 14 and has a rolled-over or beaded upper edge 15. A lid16 of the drum has a profiled outer rim 17 which is a close-seating fit on the drum upper edge 15 and in practice would be clamped to it by a lid-clamping ring 18 (shown for the sake of clarity only in part and in an exploded view) whose ends are tightened together by means of a bolt 19.

Within the drum is an inner basket 20 fabricated from perforated sheet metal, comprising a cylindrical wall 21 standing on the drum base wall 12 and spaced inwardly from the cylindrical drum wall 13. The basket 20 has lower and upper base walls 22 and 23, spaced from one another and from the drum base wall 12, and an annular top wall 24 defining a central filling aperture for which a circular closure member 25 is provided. Conveniently the basket 20 is secured in place within the drum 11 as follows. With the lid 16 removed and the basket 20 not yet inserted, an annulus 26 of suitable setting encapsulating material is first cast in the lower peripheral part of the drum 11 (conveniently by use of a suitable former (not illustrated) inserted temporarily into the drum and then removed when the annulus 26 is self-supporting).The the basket 20 is inserted into the drum to its illustrated position in which it is located by the annul us 26 in the desired spaced relationship from the drum wall 13. It will be appreciated that, although the basket wall 21 is represented as being perforated right down to its lower edge, its lower part (up to the intended height of the annulus 26) may be unperforated or wrapped with unperforated blanking-off material and may then itself serve instead of a separate former for the annulus 26, the basket being then positively located in position in the drum while the material for the annulus 26 is introduced and then allowed or caused to set.

With the basket 20 located in position by the annulus 26, a further quantity of encapsulating material is introduced and allowed to run through the basket bottom walls 23 and 22 to form a bottom encapsulating layer 27 which also sets and in which the basket lower bottom wall 22 is embedded and constitutes reinforcement.

The drum is then ready for filling of its basket with waste material 28, through the aperture which is then closed by means of the closure member 25 (which is preferably bolted down or otherwise secured to the inner edge of the basket top wall 24). Preferably then the drum lid 16 is fitted and clamped to the drum by means of the ring 18 and its bolt 19 before further encapsulating material is filled into the drum. To enable encapsulating medium to be introduced after the lid has been fitted the lid 16 is provided with a central filling aperture (not visible in the drawing) which is adapted to receive a filling nozzle and is eventually closed and covered by a closure cap 29.

As encapsulating material is fed into the drum to surround and penetrate into the waste material 28 already contained within the basket 16, the drum is preferably vibrated in known manner to minimise the possibility of pockets of trapped air and to encourage the penetration of encapsulating material into the waste material 28.If the waste material 28 (which may be shredded plastic material) is less dense than the encapsulating material (which may be a cement-and-water grout) it will tend to float, though kept captive by the closure member 25, and the encapsulating material in addition to filling an annular space 30 will also form a largely waste-free layer 31 below the mass of waste material 28; but any heavy loose contaminating particles in the waste material will tend to be shaken free and fall through the layer 31, before it has set, to form a layer 32 of coarser particles which are retained by the basket upper base wall 23 and also, perhaps, a layer 33 of finer particles able to penetrate the upper base wall 23.

In accordance with the invention, however, even this layer 33 of finer particles is prevented by the preliminary encapsulating layer 27 and the annul us 26 from coming undesirably close to the walls of- the drum basket.

The filling of the drum may be continued until complete.

Preferably, however, it is first stopped at an earlier point, when a layer 34 already covers the basket top wall 24 and closure member 25, and only after that has set is the filling continued to provide a final capping layer 35.

Claims (12)

Claims

1. A method of encapsulating solid material within an inner basket positioned inside an outer container, comprising the steps of positioning and securing the basket within the container in spaced relation to side walls thereof, feeding the solid material into the basket, then feeding solidifiable liquid encapsulating material into the container to fill space therein surrounding the basket and interstitial space in the solid material by interpenetration thereof, and allowing the enapsulating material to solidify, wherein the basket is secured in position within the container by introducing into the bottom of the container a layer of solidifiable liquid encapsulating material to a depth at which a bottom wall of the basket is submerged in and penetrated by the material of the layer, and allowing the layer to solidify with the said bottom wall of the basket embedded therein before feeding the said solid material into the basket.

2. A method as claimed in Claim 1 and including the step, prior to introducing the said layer, of introducing solidifiable liquid encapsulating material and forming therefrom a solid spacer collar, peripherally within the bottom of the container, which acts to locate the basket in spaced relationship to the side walls of the container.

3. A method as claimed in Claim 2, wherein the basket is positioned in the container before the material for the collar is introduced, and an impermeable zone at the bottom of the basket and surrounding the basket bottom wall serves as a former for the collar, the solidifiable material for the collar being introduced between the said zone and the surrounding side walls of the drum.

4. A method as claimed in any of Claims l to 3 and including the steps of vibrating the drum and basket while feeding the solid material into the basket through an aperture thereof, then closing the aperture before feeding encapsulating material into the drum to almost fill the same, then closing the drum with a lid having a relatively small filling aperture, and thereafter filling, through the filling aperture, the remaining space within the drum.

5. A method of encapsulating solid material within an inner basket positioned inside an outer container, substantiaily as described herein with reference to the accompanying drawing.

6. A container for encapsulation of solid material, comprising an outer container, having side walls and a bottom wall, an inner basket having side walls and at least one bottom wall spaced upwardly from a lower edge of the basket side walls and from the bottom wall of the outer container when engaged by said lower edge, and a layer of solidified liquid encapsulating material on and adhered to the outer container bottom wall and having the said one bottom wall of the basket submerged and embedded in and penetrated by it and thereby secured in position relative to the outer container.

7. A container as claimed in Claim 6, wherein the inner basket is formed with an upwardly open aperture and is provided with a closure member securable to close the same.

8. A container as claimed in Claim 6 or Claim 7, wherein the outer container is an upwardly open drum and is provided with a lid securable to close its upper end.

9. A container as claimed in Claim 8 wherein the lid is formed with a filling aperture. which permits a final filling of the outer container after the lid has been secured thereto.

10. A container as claimed in any of Claims 6 to 9 and comprising a collar of solidified liquid encapsulating material cast peripherally within the bottom of the outer container between the side walls thereof and the lower part of the side walls of the basket, the collar extending upwardly, outside the side walls of the basket, to a height above that of the said one bottom wall of the basket.

11. A container as claimed in Claim 10, wherein the inner basket is formed with a second bottom wall spaced above the said one bottom wall and also above the said layer of solidified encapsulating material in which the said one bottom wall is submerged and embedded, but at a height less than that to which the collar extends.

12. A container for encapsulation of solid material, substantially as described herein with reference to the accompanying drawing.