Seshadri, and 4 co-authors, reported in 2011 that leaching of arsenic (As) and selenium (Se) from coal combustion fly ash for the submicron particle size range was assessed using a modified Toxicity Characteristic Leaching Procedure (TCLP) protocol. Size segregated fly ash samples were collected from the combustion of Powder River Basin (PRB) subbituminous coal at 1723 K and 1838 K. These ash samples were leached under acidic, neutral and basic pH conditions. Qualitative data on the solubility of As and Se for each pH environment were determined as a function of combustion temperature for submicron particle sizes. For both temperature samples, arsenic showed slight to moderate mobility under acidic conditions and was not mobile in basic and neutral mediums. Selenium, on the other hand, was found in the 1723 K samples to be highly soluble in an acidic medium but mobility decreased as the pH increased towards basic conditions. And in samples from the 1838 K run Se was found to be highly soluble under all three pH conditions.
The authors concluded that Fly ash samples were collected from the combustion of PRB coal at two different combustion temperatures. The leachability of As and Se in the submicron size under three different pH conditions was determined using a modified TCLP protocol. Selenium was found to be mobile under all pH conditions for the high temperature samples but had high solubility only under acidic conditions for the low temperature run. Arsenic showed some solubility under acidic conditions for 1723 K samples, was only slightly soluble in a neutral medium for both temperatures, and did not leach out at all in a basic environment for either sample.
The results presented here are the preliminary findings of a more comprehensive study. Analysis is ongoing for the remaining particles in the fine fragment and bulk size regimes that were collected during the sample runs described here. Additionally, experiments will be carried out using another PRB coal that has different ash chemistry. Ash samples from the co-combustion of coal and wood chips will also be characterized to determine leachability of trace elements under mixed fuel conditions.
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