DETERMINATION OF AS, SB AND SE SPECIATION IN FLY-ASH LEACHATES

Several studies have been carried out to determine the speciation of A s and Se in fly ashes in order to understand the leaching behaviour of these elements and have reported widely varying results. Many of thes e studies make use of pH-selective hydride generation with sodium tetr ahydroborate to determine the speciation of As. We found that these me thods gave unreliable results for the speciation in fly-ash leachates. In this study the valency states of As, Sb and Se are determined by s peciation methods which were specifically tested for fly-ash leachates . Coprecipitation with dibenzyldithiocarbamate appeared to be a good m ethod to determine As(III) and Sb(III) in fly-ash leachates. It was po ssible to obtain the total leached amount of As and Sb by a one-step h ydride generation method. Precipitation of Se(IV) on activated carbon appeared to be the most adequate of the methods tested in this study f or Se. Only minor amounts of the more toxic and mobile oxyanions of As (III), Sb(III) and Se(VI) were leached from the five fly ashes investi gated in this study.