Patent Number: 048470066
Section: description

In the drawing the reference numberal 1 identifies a mixing tank for mixing together pulverulent ion-exchange resin, evaporator concentrate, and granular ion-exchange resin, delivered to the tank through a delivery conduit 2. The mixing tank 1 is provided with a heating jacket 3, through which the dry ion-exchanger is pre-heated with steam. A stirrer or agitator 4 provided with a motor is arranged in the tank 1. The pre-heated ion-exchange resin is passed through a conduit 5, which incorporates a valve, to a further mixing tank 11 which is provided with a heating jacket 13 and a stirrer or agitator 14. The tank 11 is heated with steam. Liquid bitumen is passed from a bitumen tank 21 to the further mixing tank 11, through a heated conduit 22. The embedded ion-exchange resin obtained in the mixing tank 11 is transferred to a storage barrel 41, through a conduit 25. When full, the barrels are placed on one side for the bitumen and ion-exchange resin to cool. The barrels are then sealed with a respective lid and the activity of the barrel contents is measured, whereafter the barrels are moved to their place of storage. The bitumen arriving from the bitumen tank 21 has a temperature of a least 130.degree. C., normally 150.degree. C. and higher. Partial degradation of the ion-exchange resin has been observed therewith. According to the present invention there is used an emulsion of water and bitumen instead of liquid bitumen, the emulsion also containing emulsion stabilizing substances. Such emulsions are known to the art and are retailed under various tradenames. One example in this regard is the emulsion sold by Shell under the name "CARILAS". This emulsion is a cationic emulsion containing at most 30% by weight water and having a pH of at most 4. The water content of the emulsion varies in magnitude. Other, similar emulsions, both anionic and cationic, may contain up to 50% by weight water. The ion-exchange resin used may be either cationic or anionic, depending on whether it is anions or cations that are dealt with. Normally there is used a mixed ion-exchanger, i.e. a blend of cation exchanger and anion exchanger in differing quantitative proportions. According to a preferred embodiment a dry or moist ion-exchange resin is added to a given quantity of emulsion until reaching the break point of the emulsion, at which there is obtained a solidifying mass of bitumen which encapsulates the granular and/or pulverulent material and optionally separated water. This water is removed and treated in an ion-exchanger for removal of any radioactive ions present, or is evaporated-off. Other granular and/or pulverulent waste material, preferably radioactive waste, may also be added together with the ion-exchange resin. When a dry ion-exchanger is used, the emulsion preferably has a higher water content than when using a moist ion-exchanger, since when coming into contact with water the dry ion-exchanger absorbs water and swells. When changing dry ion-exchangers to the system heat is generated, which in the case of vacuum-dried Dowex 50H.sup.+ constitutes about 30 cal/g of ion-exchanger. In accordance with one particularly preferred embodiment the water content of the emulsion and the moisture content of the ion-exchange resin are so adapted that substantially no water is separated during solidification of the bitumen. In other words, the ion-exchange resin, until saturated and swollen, absorbs from the broken bitumen emulsion precisely so much water as to leave no residual water in the final product. PREFERRED EMBODIMENT This embodiment will now be described in more detail with reference to the enclosed FIG. 2. Wet ion-exchange resin is charged in a dryer 51 through a conduit 52 and the resin is dried to a predetermined moisture content. Vapours developed during drying are discharged through a conduit 53. The dryer is preferably placed in a radioactively controlled area, separated from uncontrolled areas by means of walls 54. A bitumen emulsion is charged in one or more containers 55, provided with stirrers, from a storage tank 56 through a conduit 57. This operation may suitably be carried out in an uncontrolled area. The containers 55 are brought into the controlled area and the stirrers are connected to driving means 58. The ion-exchange resin is charged into the containers 55 during stirring until it is essentially homogenously distributed. The water in the emulsion is absorbed by the ion-exchange resin, which swells to its maximum volume, whereby the emulsion is broken and the product forms a solid mass. The stirring is discontinued and the driving means 58 are disconnected. The stirrers may be left in the containers to avoid the decontamination of them. After capping and sealing, the containers are ready for final storage. The method can be carried out advantageously in existing equipment and apparatus, such as the apparatus illustrated in the drawing. In this case, however, the jacketed tanks 1 and 11 are operated with water instead of steam,or preferably no heating step is applied. In the absence of preheating, the ion-exchange resin is passed directly to the tank 11, optionally together with other waste material to be embedded with said resin. Instead of containing bitumen the tank 21 contains an emulsion of water and bitumen, for example "CARILAS" when the ion-exchanger used is a cation exchanger, this exchanger being the one preferred. Ion-exchanger and emulsion can be supplied to the process continuously or batchwise, and the matrix of bitumen with encapsulated ion-exchanger can be removed from the tank 11 and delivered to the barrel 41 either continuously or batchwise. Water, which is optionally separated from the system in the tank 11, can be removed continuously. According to one highly preferred embodiment ion-exchange resin is supplied to the emulsion in an amount which results in solidification, said ion-exchange resin being optionally supplied together with other material to be encapsulated, such as radioactive or toxic material, or material which is harmful in some other way. Any water that may form is removed prior to sealing the barrel for terminal storage purposes. The method is carried out within a temperature range of 1.degree.-90.degree. C., preferably 5.degree.-60.degree. C. A particularly preferred temperature in this regard is room temperature or ambient temperature, which ambient temperature must be higher than 1.degree. C., preferably higher than 5.degree. C. This obviates the need of pre-heating the system components. The solid product resulting from the embedment process can be heated or maintained at a temperature of 50.degree.-60.degree. C. in order to shorten the time taken for the product to solidify. This subsequent treatment of the product is not necessary however. When practicing the method according to the present invention the ion-exchanger may have a pulverulent form or a granular form, and particular preference is given to the use of a moist ion-exchanger. Pulverulent and granular evaporation residues can also be incorporated together with the ion-exchange resin. It has been found that the resultant product can contain more then 50% by volume particulate material. It has been found that no appreciable losses of water in the ion-exchange resin are experienced when heating the resultant, full solidified product for two hours at 150.degree. C. On the other hand, a volatile fraction of the bitumen is vaporized off.