#13: Solidifaction of various radioactive waste in geopolymer and long-term stability

Solidification of various radioactive residues by géopolymère with special emphasis on long-term-stability
by E. HERMANN (1), C. KUNZE (1), R. GATZWEILER (2),

(1) B.P.S. Engineering GmbH
(3) Cordi-Géopolymère SA

published in the Géopolymère ‘99 Proceedings, 2nd International Conference on Geopolymers

Sludges containing radionuclides, toxic heavy metals and hydro-carbons can be solidified by geopolymer with excellent long-term structural, chemical and microbial stability, satisfying high standards of contaminant retention. The novel technology gives a monolithic product which can be easily handled, stored and monitored. It requires only simple mixing and moulding technology known from conventional solidification methods.

Extensive laboratory investigation has been carried out to demonstrate the performance of the novel solidification method under adverse stress conditions. In particular, the sludges of a treatment facility for uranium mining effluents and sludges from a settling pond, contaminated organically, radioactively and by heavy metals, have been treated. An optimized two-step technology, known as geopolymer, was successfully adapted to the specific characteristics of these sludges. Moreover, the geopolymer process has been shown to deliver excellent results for radioactive and arsenic-loaded sludges from municipal drinking water purification plants that are sensitive with respect to public risk perception and regulatory policy.

Pilot-scale experiments that show the method’s maturity for industrial use and to provide realistic material and operation cost estimates were done for the uranium mine sludges. Several tons were solidified in WISMUT’s Schlema-Alberoda water treatment plant in 1998. Our results clearly show that geopolymer solidification is a prime candidate to fill cost-efficiently the gap between conventional concrete technology and vitrification methods. Due to the reduced effort to prepare, operate and close the landfill, solidification by geopolymer leads to approximately the same unit cost as by conventional portland cement, but provides in most aspects the performance of vitrification.

The paper is divided into two parts. Part I describes in detail the basic principles of geopolymer and the laboratory investigations carried out to develop a viable solidification technology. After briefly introducing the basic principles of the Geopolytec® process and comparing it to conventional solidification methods, our paper shows promising results that were obtained for the long-term stability and contaminant retention of under several testing procedures. Subsequently, the experience from the pilot-scale experiment in the water treatment facility of WISMUT is presented. It shows that the Geopolytec® process is now mature for industrial application.

Part II is devoted to a pilot-scale experiment in which about 10 tons of radioactive and toxic sludges were solidified by the Geopolytec® process.

Finally, the prospects and market potential for the solidification of sludges by geopolymer are discussed, and an outlook to future activities is given.

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