The Leachability and Speciation of Arsenic and Selenium in Coal Fly Ash

Batch leaching tests were employed to investigate the leaching potential of arsenic (As) and selenium (Se) from two fly ash samples. The effect of pH and solid-to-liquid (S/L) ratio on As and Se leaching was examined in this preliminary study. Maximum As leaching occurred at pH 7-8, and soluble As concentration slightly increased with decrease of S/L ratio. Se displayed consistently increasing leaching with increase of pH, and soluble Se concentration increased with the increase of S/L ratio. Speciation of As and Se in fly ash leachates obtained under both atmosphere and nitrogen conditions was determined using HPLC-ICP-MS. Only one arsenic species, As(V), and one selenium species, Se(IV), were detected in all leachate samples. Total As analysis using ICP-MS agreed well with the speciation analysis with HPLC-ICP-MS, while Se concentration showed a deviation between the two methods, which may be due to formation of undetected species or the higher detection limit with HPLC system. Further study will be conducted for a wide range of fly ash samples and under varying conditions.