MOBILITY OF CADMIUM IN COAL FLY ASH - Management of Hazardous Residues Containing Cd - page 172

characterization of mobility fraction of Cd soluble in water and in acids
(carbonate and adsorb fractions) was performed. It were found that Rudd
and Sposito methods yielded maximum Cd amounts under these
conditions. Mobility fractions of Cd contain of 22% of its total
concentration in the fly ash in environmental conditions. Their method
for cadmium determination is proposed for highest delectability for
fractions of interest.
1. I NTRODUCTION
The coal fly ash as source of heavy metals emission to environment was
researched. Environmental pollution caused by harmful compounds and
chemical elements accumulation is an important particular problem relating to
coal fly ash degradation. Nowadays, the research concerning speciation of
metals in the environment, especially of Cd is acquiring importance [12-21].
In the view of toxic properties and biological activity of cadmium in living
organisms [9-13], and cadmium contribution in food chain: coal fly ash - soil
- plant - animal - man [14], it is necessary to determine the amount of
cadmium in coal fly ash, where cadmium exists in different oxidation states,
and evaluate the methods of separation and determination of various cadmium
species. Studies on Cd contents and its forms in coal fly ash [15-20],
conditions of Cd extraction from coal fly ash to solutions [19,20,43] as well as
extraction methods and investigations of various chemical fraction of Cd have
been reported [14, 15, 34-46].
Influence of Cd on the course of biochemical reactions in the environment
depends among others on possibility of its migration from coal fly ash to coal
fly ash solutions. In practice this process is investigated by performance of the
sequential extraction of coal fly ash. The Cd sequential extraction for a given
coal fly ash depend among others on the type of coal fly ash, leaching reagent,
conditions of the process, and the initial condition of coal fly ash (air-dried
coal fly ash, wet coal fly ash). Recovery factor of chemical fraction of
cadmium from coal fly ash eluates depends on its distribution among various
chemical fractions in coal fly ash and influences its mobility and availability
for living organisms. Most often the studies evaluate the chemical fraction of
metals in coal fly ash as: exchangeable, carbonate, oxide, organic, sulfide and
residue forms. Many procedures of sequential extraction of coal fly ash and
bottom sediments were described [1-6, 20, 21, 47-52], which include group
extraction of metals.