Caracterisation physico-chimique de cendres volantes de charbon avec desulfuration primaire - essais de lixiviation. (Physico-chemical characterization and leaching of desulfurization coal fly ash)
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Fly-ash issued from two kinds of desulfurization processes during coal combustion are studies: a conventional Pulverized-Coal boiler equipped with lime injection (PCL ash), and a Circulating Fluidized Bed Combustion boiler with limestone injection (CFBC ash). The ashes are completely characterized: granulometry morphology, mineralogy, chemical composition and behaviour to water contact. PCL ash and CFBC ash present similar features: fine granulometry, presence of anhydride phase and sulphate content. PCL ash shows also lots of spherical particles, unlike CFBC ash, and much higher lime content, due to the lower desulfurization rate in PC boilers. Unlike CFBC ash, most of the trace elements in PCL, ash show an inverse concentration-particle size dependence. Leachates obtained from both samples are rich in soluble salts (CaSO(sup 4) and Ca(OH)(sub 2)) and arsenic and selenium are prevented from solubilizing by high lime content. In wetted PCL ash, the formation of ettringite crystals stabilizes Ca(sup 2+) and SO(sub 4)(sup 2-) ions. Simultaneously, arsenate, selenate and chromate anions are trapped in the crystal. CFBC ash do not really harden, because the lime content is too low. However, the leached selenium concentration is cut down in wetted CFBC ash samples. (author) 20 refs.
Caracterisation physico-chimique de cendres volantes de charbon avec desulfuration primaire - essais de lixiviation. (Physico-chemical characterization and leaching of desulfurization coal fly ash)