Effect of Additives on Arsenic, Boron and Selenium Leaching from Coal Fly Ash

Abstract

The establishment of an inexpensive leaching control method to prevent the leaching of trace elements from fly ash is required for the utilization of large-scale fly ash as an embankment material. This study examined the effects of the additives on suppressing As, B, and Se leaching from coal fly ash using Ca(OH)2, paper sludge ashes (PS Ash 3, PS Ash 4 and PS Ash 5), and filter cake (FC). PS Ash and FC are waste generated in the papermaking and lime industry processes and contain high levels of calcium. The treated fly ash H (FAH) and the resulting mixtures were subjected to a leaching test as per the Environmental Agency of Japan Notifications No. 13. The results indicate that the leaching concentrations of As, B, and Se could be greatly reduced in FAH with the highest effect given by Ca(OH)2, followed by PS Ash 3 and PS Ash 5. Ca(OH)2 greatly reduced both the leaching concentrations of As, B, and Se by about 91–100%, while PS Ash 3 reduced the As and B leaching concentrations by approximately 89–96% and 83–92%, respectively; and PS Ash 5 reduced the Se leaching concentration by about 87–96%. FC did not have any impact on As and B leaching, but reduced Se leaching by about 58–78%. A reason for the decrease in leaching concentrations of As, B, and Se may be the precipitation with calcium or the formation of ettringite. The presence of leached Ca and Na ions are key factors affecting the decrease of As, B, and Se leaching concentrations from fly ash. The utilization of PS Ash 3 and PS Ash 5 as inexpensive additives is a promising method to control the leaching of As, B, and Se into the environment.