Long-term interaction of coal combustion by-product with water

A terrestrial disposal of the fly ash has been regarded as a potential source of contamination due to the enrichment and surface association of trace elements in ash particles. In laboratory conditions the leaching of soluble components existing in ashes proceeds in a different way than in land deposits.

On the landfill site coal combustion by-products are under the pressure of atmosphere agents, especially water, sun and rain activity (drying and wetting alternately), freeze/thaw (in cold climate) and gases included in the air. Also the time of exposition is an important parameter.

In the presented experiment the observed dynamics of ash solubility over a long period of time provides the evidence that in the ash-water system, a variety of precipitation processes dominate the solubility of solid mass. Simulating the weathering by the freeze/thaw test approximates the effectuated changes in ash particles structure.

The leaching of a particular ash component depends on reactions in the ash-water systems.

Solidification by compaction of the material is often favoured because of the cementitious properties of ashes being in contact with water. Secondary hydrated minerals such as ettringite, portlandite and calcite are formed during a contact with water. Calcium -silicate hydrates, aluminate-hydrates and gypsum can occur as secondary minerals. The solubility of such new phases and the solidification process determine the leaching characteristics of the ash mass.