COMPRESSING STRENGTH LIMIT OF COMPOUNDS PRODUCED BY CEMENTATION ON HIGH SALINE BORON-CONTAINING LRW WITH GEOPOLYMER BINDERS

Abstract

The prospects of boron-containing liquid radioactive waste (LRW) solidification using cement with geopolymer binders have been considered. It is known that geopolymer compounds can be produced on the basis of industrial wastes – ground slag from metallurgical plants, TPPs’ ash-slag, etc. Geopolymers may comprise alkalis that are part of LRW. The strength of geopolymers may increase by 1.5 – 2 times over time. The synthesis of geopolymers does not pollute the air with CO2. The properties of a LRW simulator, which was a concentrated salt solution at the temperature above 60 °C, were taken into account. During the cooling of the simulator, the phenomena of hypothermia and spontaneous crystallization of sodium metaborate have been observed. If <140 μm fraction of dispersed zeolite was added in the amount of 10 mass% to the simulator together with liquid glass and 1 : 1 mixture of slag and ash, the hypothermia was not observed, while sodium metaborate crystallized in the form of small-er crystals. It has been experimentally validated that the amount of alkalis present in the LRW simulator was not sufficient for formation of strong geopolymer compounds. It is attributed to the fact that in the process of sodium tetraborate convertion to metaborate, water and sodium hydroxide were partially removed from the solution. To increase the alkalinity of the simulator, experimentally determined amounts of alkali were added. To study the compressive strength limit, the ratio of the components has been experimentally determined and a basic sample con-taining the LRW simulator, liquid glass, ash and slag mixture, alkalis (KOH) and zeolite was produced. As to the basic composition, the mass of the components (factor experiment) in the samples varied. The mass increased by 17%, while the mass of simulator and zeolite was constant. Compound samples were made under the same conditions with different ratios of the components. The compressive strength was measured after exposure and drying. The average value for all samples was 9.6 ± 1.5 MPa. Some samples had different compressive strength limits depending on the composition of the compounds. The calculations allowed generating an equation according to which liquid glass and alkali (KOH) reduce the compressive strength limit in the variation interval, while the ash and slag mixture increases it. This should be taken into account in further experiments on application of geopolymers for LRW cementation.