Leaching of heavy metals from artificial soils composed of sewage sludge and fly ash.

The purpose of this study was to determine the leaching characteristics of heavy metals from artificial soils composed of sewage sludge and fly ash. A leaching experiment was carried out over a period of 90 days. The leachates from artificial soils were collected every 15 days, and the concentrations of cadmium, lead, copper, zinc, chromium, and nickel in leachates were determined. Results showed that pH values of the artificial soils leachate were stable, ranging from 6.71 to 7.62 at the end of the experiment. Except of the cadmium, the concentrations of chromium, nickel, and copper in leachates of the artificial soils reached a stable level at the end of the experiment. The final concentrations of copper in leachates varied from 27.1 to 127.5 μg L(-1), which was lower than European threshold value for drinking water, (1,000 μg L(-1)), while final nickel and chromium concentrations in leachates exceeded the European threshold ones. Amorpha fruticosa and Robina pseudoacacia grown in the artificial soils had different effects on cadmium, nickel, chromium, and copper leaching behavior. Amorpha fruticosa resulted in higher Ni and Cu concentrations in leachates, while Robina pseudoacacia enhanced leaching concentration of Cr.