engleski

Stabilization of Hazardous Zeolite Wastes in Cement Composites and its Effect on Hydration Progresses

Hazardous waste containing Zn^2+-ions was stabilized by means of solidification of cement pastes by hydration of industrial portland cement PC-45B. Cement pastes were prepared with different additions of zeolite tuff, WZ=(0, 0 - 50, 0%), saturated by Zn^2+-ions. The addition relates to the mass of the solid (cement + zeolite) and to predefined W/S (water/solid) ratios with constant addition of the plasticizer admixture. Solidification was carried out by hydration at 20 °C. Computer-guided conductometry, differential microcalorimetry and UV/Vis spectrophotometrical analysis were used in examinations. The analysis of conductograms shows the relation between the measured specific conductivity and the content of the zeolite tuff in the cement paste. The higher the zeolite tuff content in the composite, the lower the measured specific conductivity. With the increase of the zeolite content, the conductogram maximums shift proportionally to later hydration times. Microcalorimetrical measurements also indicate that the hydration heat and the reaction degree depend on the quantity of the zeolite addition. The hydration heat of the composite decreases with the increase in the zeolite content. The relative reaction degree for cement changes relative to the content of the zeolite addition. The amplitudes of major thermal effects, i.e. their maximums, assume increasingly lower values with the increase of the zeolite addition content in the composite. The locations of these maximums can be mathematically predicted and described by the functional dependence between the time and the zeolite addition content. The content of Zn^2+ - ions when rinsing with water and/or 0, 5M HAc in eluates indicates that the Zn^2+ ion concentration decreases with the time of solidification and increases with the increase of the zeolite addition content. The results obtained indicate that hazardous waste can be successfully stabilized in hydration processes by solidification in cement composites, thereby reducing its harmful effects on the environment to acceptable values. Moreover, such harmful wastes can, to some degree, become components used to form new composites.

cement composite; cement hydration; stabilization/solidification; hazardous waste

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