Determination of Arsenic(III) and Arsenic(V) in Coal and Oil Fly Ashes

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Abstract
Total arsenic has been determined for fly ashes generated by conventional combustion of pulverized western coal, oil, a coal-oil mixture, a coal-water mixture, and from the fluidized-bed combustion of North Dakota lignite. For most of the ashes the total arsenic levels were between 100 and 200ppm, but the coal-water mixture ash contained 348 ppm. Leaching with 0.5 N H2SO4 or a pH 5 1 M citrate solution resulted in the removal of 78 to 97% of the total arsenic from the particles. This clearly indicates a high surface enrichment of arsenic on the particles, in agreement with numerous previous studies on coal fly ash. The pH5 citrate solution was more effective for the removal of arsenic from the particles without significant oxidative loss of arsenic(III). Speciation of arsenic in the citrate leachate by hydride atomic absorption spectrometry indicated that in most cases less than 2% of the soluble arsenic was arsenic(III). The only exception was the leachate of the coal-oil mixture ash, which contained about 7% arsenic(III). The actual arsenic(III) levels in the ashes never exceeded 6 μg per g of ash.

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