EFFECT OF AMMONIA ON METAL LEACHING FROM FLY ASH

Effect of ammonia on heavy metal leaching from a class F fly ash was investigated under different pH conditions. Cu(II), Cd(II), Ni(II), and Pb(II) were used as representative metals in the experiment. The surface physical-chemical characteristics of fly ash that affect metal adsorption, such as the density and acidity constant of metal-binding site on ash surface, were also studied. Results showed that the fly ash contain one type of acid site that is responsible for metal adsorption. The site density and acidity constant (pKH) are 1.8×10−5 mol/g and 7.8, respectively. Without ammonia, the adsorption of interested metal cations, increased with the increase of pH. The adsorption constants (log KS) of Cu(II), Cd(II), Ni(II), Pb(II) onto fly ash surface are 6.36, 4.88, 4.84, 8.59, respectively. Results also showed that ammonia can enhance the leaching of heavy metals that form metal-ammonia complexes, especially when ammonia concentration is greater than 5000 mg/L.