Adsorption of arsenic(V) onto fly ash: a speciation-based approach

Arsenic (As) poses a significant water quality problem and challenge for the environmental engineers and scientists in the world. The large volume of coal fly ash produced around the world is a potentially significant anthropogenic source of arsenic. Currently the leaching behavior of arsenic from fly ash is not well understood. Batch methods were used in this study to investigate arsenic leaching using a raw ash, and arsenic adsorption using a clean, washed ash. Experimental results indicated that pH had a significant effect on arsenic leaching or adsorption. Between pH 3 and 7, less arsenic was in the dissolved phase. When pH was less than 3 or greater than 7, increasing amounts of arsenic were leached or desorbed from fly ash. The leaching and adsorption behavior of arsenic was interpreted with the speciation of surface sites and arsenic. In a new approach, a speciation-based model was developed to quantify the arsenic adsorption as a function of pH and surface acidity parameters. This work is important in offering insight into the leaching mechanism of arsenic from coal fly ash, and providing a robust model based upon specific, measurable parameters to quantify arsenic adsorption by other solid media in addition to fly ash.