Patent Number: 044617224
Section: summary

It is the endeavor of the technical experts in the art to create the possibility of safely handling waste materials, which have no further industrial use, during their transport or storage so as not to endanger the environment. One of the requirements to accomplish this, for instance during the transport or storage of aqueous solutions which contain radioactive materials, consists in treating these solutions prior to their transport or storage so as to convert them into solid end products. However, in this connection it is not sufficient to confine or seal the aqueous solution in permanent containers. A heretofore known method of solidifying aqueous solutions which contain radioactive materials consists in adding the solutions which result from chemical separations, activation anaylses, extractions, decontamination operations, or also from recovery of fuels, to a mixture of cement and vermiculite, whereby a solidification of the aqueous solution from the reaction with the cement is obtained. However, a drawback of this known method consists in that a troublesome development of gas and heat during the solidification of aqueous, acidic solutions occurs, leading to long delays and, therefore, making the method uneconomical. In addition thereto, during solidification of strongly acidic aqueous solutions, a safe accomplishment of the method can no longer be assured for the operating personnel since, because of the great heat development, bubbling-up and spattering of the solution cannot be avoided. Furthermore, there also exists the possibility of contaminating the environment. A further drawback consists in that the vermiculite contained in the mixture, because of its light weight, is partially carried on the surface of the aqueous solution, resulting in a non-homogeneous end product which does not meet the requirements for the solidification of the aqueous solution. It is an object of the present invention to provide a method of solidifying aqueous solutions containing radioactive or toxic materials, which makes it possible to produce an end product which contains the waste materials in a homogeneous distribution and can be produced in such a manner as to be safe to the operating personnel. It is a further object of the present invention to provide a method as set forth in the preceding paragraph which can be carried out even if the aqueous solution to be solidified is strongly acidic or alkaline, without having to make allowance for, or put up with, long delays. Yet another object of the present invention consists in that the substances necessary for carrying out the method should be as inexpensive as possible. With these and other objects and advantages in mind, the method according to the present invention is characterized primarily in the aqueous solution, which contains one of the mineral acids, such as HF, H.sub.2 SO.sub.4, HClO.sub.4, HCl or HNO.sub.3, or one of the alkalies, such as KOH, NaOH, NH.sub.3 or Ca(OH).sub.2, up to 40% by weight, or water soluble organic compounds up to 50% by weight, is mixed with a porous, solid substance having a carbonate content of less than 1%, the substance comprising a ceramic material, pumice, or the like having a granulation from about 2 mm up to an average diameter of about 20 mm. The aqueous solution is also mixed with gypsum having 4.7 to 6.6% water of crystallization and a carbonate content of less than 1%. The mixture ratio of gypsum to porous, solid substance is from 1 to about 0.5 to 3, and the mixture ratio of the aggregate of gypsum and porous, solid substance to aqueous solution is about 0.7 to 1.3 kg to 500 ml. No disturbing gas or heat development occurs while carrying out the method according to the present invention. Since by using the porous, solid substance, which may be comprised, for example, of ceramic tile chippings having a specific weight between 1.0 and 1.4 kg/dm.sup.3, a good inter-mixture of the gypsum with the waste materials contained in the aqueous solution is realized, the waste materials are correspondingly homogeneously distributed in the solid end product. During mixing, the components of the mixture of gypsum, solid substance, and aqueous solution are expediently mechanically agitated by means of a stirring apparatus, agitator, or the like, and the requisite amounts are added in a sequence adapted or proportional to the requisites of the mixture. In this connection it may be expedient by batches or continuously to add the quantities of gypsum, solid substance, and aqueous solution. In the event that also non-aqueous organic compounds are used, alcohol and water are added to these compounds in such an amount that the mixture contains about 20% non-aqueous organic compound, the thus formed mixture of non-aqueous organic compound, alcohol, and water is then intermixed with an appropriate amount of gypsum and solid substance. A particularly advantageous specific embodiment of the method according to the present invention consists in first intermixing the gypsum and porous, solid substance and subsequently adding the aqueous solution to the thus formed mixture. This makes it possible to produce a homogeneous end product without necessitating a mechanical agitation of the components which are to be intermixed. Since, in addition, the gypsum and solid substance mixture may be stored for several months in a closed container without becoming unusable, the solidification of aqueous solution is a very simple manner is possible. To do so, it is merely necessary to pour the mixture of gypsum and solid substance into the container intended for the final storage and then to add the aqueous solution. An alternative solution to the previously stated objects as taught by the method according to the present invention is characterized primarily or first in the substance which promotes the intermixing of binding agent and aqueous solution be so formed that gypsum having a crystal content of about 4.7 to 6.6% and a carbonate content of less than 1% be mixed together with water glass having a specific gravity in the range of from 1.2 to 1.8 kg/dm.sup.3 ; the mixing proportion is about 1 kg gypsum to 100 to 500 ml water glass. To the thus formed, partially granular, partially pulverous mixture there is added the aqueous solution which contains one of the mineral acids, such as HF, H.sub.2 SO.sub.4, HCIO.sub.4, HCl, or HNO.sub.3, or one of the alkalies, such as KOH, NaOH, NH.sub.3, Ca(OH).sub.2, up to 40% by weight, or water soluble organic compounds up to a content of 50% by weight; the mixing proportion is about 1 kg of the gypsum and water glass mixture to 500 ml aqueous solution. Sodium as well as potassium water glass (Me.sub.2 SiO.sub.3, Me.sub.2 SiO.sub.4, Me.sub.2 SiO.sub.5) may be used. With this alternative solution also no disturbing gas or heat develops if strongly acidic or alkaline aqueous solutions are being solidified. When intermixing gypsum and water glass, it is expedient to add water glass by batches while stirring the added water glass into the gypsum. The thus formed, partially granular, partially pulverous mixture, which may be stored for about a week, for the solidification of an aqueous solution is placed in a container intended for the final storage, and the aqueous solution is added. In this connection the advantage is obtained that no mechanical agitation of the mixture is required, so that also by this alternative method according to the present invention a simple and safe solidification of the aqueous solution may be carried out.