An Experimental and Thermodynamic Equilibrium Analysis on the Leaching Process of Arsenic (As) from Coal Fly Ash

Abstract

The leaching process of arsenic (As) from coal fly ash collected from the coal-fired power plant in Japan was investigated with six different kind of paper sludge ashes (PS ash XA, XB, XC, YA, YB, and YC) as an inhibitor and their mass addition ratio 0 to 30%. To study the arsenic leaching mechanism, thermodynamic calculation (FactSage 7.2) was used to predict the possible As-bearing compounds in the fly ash and its distribution during the combustion and leaching process. The results indicated AlAsO 4 (s) was the most probable species resulting compound from arsenic interaction with fly ash components under the combustion process. PS ash YB containing the highest calcium content shows a considerable immobilization ability for arsenic due to arsenic reaction with calcium compound in the leaching process. CaO in PS ash generates high pH leachate during the leaching process and promotes calcium with arsenic to form a precipitate. The arsenic leaching ratio by thermodynamic calculation and experimental, again PS ah YB, shows the best effect in the arsenic leaching concentration with addition ratio in the range 15-30%. It was found that the arsenic fixation capacity of PS ash increases as the calcium content in PS ash increases because the chemical reaction between calcium compounds and arsenic is accelerated during the leaching process. Predicting arsenic species based on the combustion and leaching process will be useful to choose the best available control technology to minimize the effect of arsenic into the environment.