US 4,297,304 AGranted

Method for solidifying aqueous radioactive wastes for non-contaminating storage

AssigneeKernforschungszentrum Karlsruhe GmbH

InventorsKnut Scheffler, Ulrich Riege

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Abstract

Method for solidifying high and medium radioactivity and/or actinide containing aqueous waste concentrates or fine-grained solid wastes suspended in water for final noncontaminating storage. The waste concentrates or suspensions are set, by evaporation, to a water content in the range between 40 and 80 percent by weight, and a solid content whose metal ion and/or metal oxide component lies between 10 and 30 percent by weight of the evaporate being formed. The pH of the evaporate is set to between 5 and 10. The evaporate is kneaded with a clay-like substance containing a small quantity of cement or such a clay-like substance or mixture of a clay-like substance with a small quantity of cement containing an additive for suppressing the volatility of the alkalis or alkali earths and/or an additive for suppressing the volatility of any decomposing anions which may be present in the evaporate from the group including sulfate, phosphate, molybdate and uranate ions. The kneading occurs at a weight ratio range of evaporate to clay-like substance of 1:1 to 2:1. Molded bodies are produced from the resulting kneaded mass. The molded bodies are then heat treated including drying at temperatures between room temperature and about 150.degree. C., calcining at temperatures up to about 800.degree. C. and subsequently firing at temperatures between 800.degree. C. and 1400.degree. C. to form practically undissolvable mineral phases. The molded bodies of fired mineral phases are enclosed on all sides in a dense, continuous ceramic or metallic matrix.

Claims24

Dependent claims

Method for solidifying high radioactivity aqueous waste concentrates, medium radioactivity aqueous waste concentrates, actinide containing aqueous waste concentrates, or suspensions of fine-grained solid wastes suspended in water, which concentrates or suspensions contain a metal ion and/or metal oxide, for final noncontaminating storage in which the waste concentrates or the suspensions are subjected together with an absorbing and/or hydraulically binding inorganic material, to a ceramic firing process so as to produce a solid sintered body, comprising the steps of:

(a) treating the waste concentrates or suspensions by evaporation, to form an evaporate, to a water content in the range between 40 and 80 percent by weight and a solid content whose metal ion and/or metal oxide concentration lies between 10 and 30 percent by weight of the evaporate being formed, and adjusting the pH of the evaporate to between 5 and 10;
(b) kneading the evaporate obtained from step (a) with a clay-like substance containing a small quantity of cement or mixture of a clay-like substance with a small quantity of cement containing an additive for suppressing the volatility of alkali metals or alkaline earth metals which may be present in the evaporate and/or an additive for suppressing the volatility of any decomposable anions which may be present in the evaporate selected from the group consisting of sulfate, phosphate, molybdate and uranate ions, at a weight ratio range of evaporate to clay-like substance of 1:1 to 2:1, said clay-like substance being at least one substance selected from the group consisting of pottery clays, stoneware clays, porcelain clay mixtures and kaolins;
(c) producing molded bodies from the kneaded mass obtained from step (b);
(d) heat treating the molded bodies, including drying at temperatures between room temperature and 150.degree. C., calcining at temperatures of about 150.degree. to 800.degree. C., and subsequently firing at temperatures between 800.degree. and 1400.degree. C. to form practically undissolvable mineral phases having a chemical composition corresponding approximately to that of natural, stable minerals or rocks;
and
(e) enclosing the molded bodies containing the fired mineral phases on all sides in a dense, continuous ceramic or metallic matrix.

3 more elements

(a) treating the waste concentrates or suspensions by evaporation, to form an evaporate, to a water content in a range between 40 and 80 percent by weight and a solid content whose metal ion and/or metal oxide concentration lies between 10 and 30 percent by weight of the evaporate being formed, and adjusting the pH of the evaporate to between 5 and 10;
(b) kneading the evaporate obtained from step (a) with a clay-like substance containing an additive for suppressing the volatility of alkali metals or alkaline earth metals which may be present in the evaporate and/or an additive for suppressing the volatility of any decomposable anions which may be present in the evaporate selected from the group consisting of sulfate, phosphate, molybdate and uranate ions, at a weight ratio range of evaporate to clay-like substance of 1:1 to 2:1, said clay-like substance being at least one substance selected from the group consisting of pottery clays, stoneware clays, porcelain clay mixtures and kaolins;
(c) producing molded bodies from the kneaded mass obtained from step (b);
(d) heat treating the molded bodies, including drying at temperatures between room temperatures and 150.degree. C., calcining at temperatures of about 150.degree. to 180.degree. C., and subsequently firing at temperatures between 800.degree. and 1400.degree. C. to form practically undissolvable mineral phases having a chemical composition corresponding approximately to that of natural, stable minerals or rocks;
and
(e) enclosing the molded bodies containing the fired mineral phases on all sides in a dense, continuous ceramic or metallic matrix.

3 more elements

Dependencies are inferred from the claim text.