Leaching Characteristic of Arsenic in Coal Fly Ash

The leaching characteristics of arsenic from six CFA (coal fly ash) samples collected from a large scale power plant in Japan were investigated to evaluate more fully the rate of leaching of arsenic and related factors on determining arsenic leaching from different type of CFAs.The procedure of standard leaching tests according to Environmental Agency of Japan Notifications No. 13 was employed in this work.The results indicate that the leaching fractions of arsenic were low levels below 15%, and it was affected by CaO content in CFA.Leaching test results were compared with solution equilibrium calculation to consider the leaching mechanisms: however, experimental results were significantly lower than the equilibrium calculation results.To elucidate the leaching mechanisms, the leaching rate was investigated by extending the leaching tests for a long-term.The concentration of arsenic in the leachate was increased with time, and equilibrium between the solid phase (ash) and the leaching solution was reached in approximately 120 days.It is found that the constant a has a good relationship with CaO content in CFAs, in which the constant a (indicated leaching rate of arsenic) was decreased with an increase of CaO content in fly ash.Therefore, the value of the rate constant a can be said to be the main factor determining arsenic leaching.