Milan Vondruska

Characterization of products from fluidized-bed combustion of coal.

ABSTRACT The technology of fluidized-bed combustion (FBC) of coal generates byproducts that have a series of unique characteristics and potential uses in technological practice. In this study, the products of fluidized-bed combustion (FBC-P) of coal derived from Moravian heat stations, a.s. Zlin, Cinergy Global Resources, Czech Republic, were characterized. Particular attention was paid to determining the chemical composition of FBC-P, the content of polycyclic aromatic hydrocarbons (PAHs) and toxic metals in the water leachates of these FBC-P, the content of unburned carbon, the capability of FBC-P to solidify with water and form a solid matrix, and the method for discovering optimum mixing water content for FBC-P solidification. The results suggest that one of the qualitatively more important means of utilizing FBC-P could be their application during solidification/stabilization (S/S) of wastes, particularly wastewa-ter treatment sludges.

Stabilization-solidification of salt from a waste incinerator

ABSTRACT A laboratory procedure was developed and verified for stabilizing salt produced by an industrial waste incinerator. This procedure is based on salt stabilization by means of an asphalt binder. Conductivity values and relevant anion contents in leachates of stabilized waste with an asphalt coating were near zero. The pH value of these leachates equaled the pH value of the water used, so that the stabilized waste salt represented inert material, posing no environmental hazard. An unusually significant reduction in the volume of processed salt occurred during stabilization. After compacting under 10.4 MPa pressure, the volume of test specimens was almost 55% smaller than the initial salt volume. In practice, this would mean more than a doubling of landfill waste capacity. Volume reduction was successfully explained by means of a mathematical model.

Polycondensation of Silicate with Hydroxocomplexes of Some Amphoteric Elements in Aqueous Solution

Reactions of aqueous solution of silicate with hydroxocomplexes of Al(III), Sn(IV), Zn(II) and Ga(III) have been experimentally studied. All studied reactions have produced gel in the whole volume of reaction mixture, and according to our hypothesis the essence of these reactions is polycondensation between silicate anions and anions of hydroxocomplex of the given amphoteric element, with formation of crosslinked inorganic polymer. Criterion for studying the course of the tested reactions has been the gel-point time of the reaction mixture. Dependences of the gel-point time on temperature, on KOH concentration and on molar ratios of silicate/amphoteric element in reaction mixture have been recorded. Products of the studied reactions have been analyzed by means of X-ray fluorescent spectrometry. All obtained results are in accord with the hypothesis of polycondensation reaction between silicate and hydroxocomplexes, and indicate that the reaction between silicate and hydroxoaluminate is merely one case of a more general chemical reaction.

Diminishable/removable sources of greenhouse gases

To the purpose of a balanced, comprehensive approach to reducing and eliminating emissions of greenhouse gases, a list of their diminishable/removable sources has been worked out. This list cannot be complete and the authors expect it to provoke discussion in professional magazines and that this list will be expanded and modified.

Reaction between Silicate and Hydroxoaluminate Ions in Aqueous Solution

The chemical status and kinetics of the reaction between silicate ions and hydroxoaluminate ions (at Si/Al molar ratio 2:1) in KOH aqueous solution has been experimentally studied. It is assumed that condensation of OH groups bonded to silicon and aluminum occurs in this reaction forming a cross-linked polymer; and that the reaction represents the essence of synthesis of so-called geopolymer from alumino-silicate minerals. Time required for the change of the solution to a gel was measured as the reaction rate criterion. Measured dependences of the gel-point time on KOH concentration in the reaction solution exhibit a linear trend. The gel-point time decreases with increasing temperature. A measurable increase in pH value of the solution appears during the reaction. Measurement of the gel-point time for different Si/Al molar ratios has confirmed that the selected ratio 2:1 has been optimal. For a quantitative description of the reaction course and for explanation of the observed phenomena, the theories of polycondensation reactions and protolytic equilibria have been applied. Theoretically calculated dependences of the gel-point time on KOH concentration are in accord with experimentally determined values, which confirms anticipated polycondensation mechanism of the reaction under study.