Effect of coal blending on the leaching characteristics of arsenic in fly ash from fluidized bed coal combustion

Abstract

The leaching characteristics of arsenic (As) in fly ash collected from lab-scale fluidized bed reactor have been systematically investigated through the combustion of two bituminous coals (A and B) and their mixture with different blending ratio. Leaching tests were conducted according to Japanese Industrial Standard (JIS).The results indicate that, the fly ash derived from the combustion of coal B, which contains abundant calcium, shows a larger capture ability for arsenic vapor than that from coal A, due to the chemical reaction of arsenic with CaO. This reaction is however competed by the sulfation of CaO at coal combustion temperature, therefore, a nonlinear increase was observed with increasing the blending ratios of high-calcium coal B with coal A. Leaching performance of arsenic from fly ash is largely dependent on the finally pH of the leachate. CaO in fly ash preferentially generates a high-pH leachate during leaching test and subsequently promotes the combination of calcium with arsenic to form precipitate. Improving Ca/S ratio through the combustion of blending coal is a promising method to prevent the emission of arsenic into ambient and reduce its leachability from fly ash.