Nobuo Hasegawa

Tohoku-gakuin University, Faculty of technology
(1-13-1 Chuo, Tagajo, Miyagi 985 Japan)

Abstract

At general wastes incineration plants, there are problems regarding HCl in PVC, mainly Pb which is added to intensify the heat stability of PVC. Pb changes to fumes (ie. PbO) in incineration and is contained in fly ash. The maximum concentration of Pb amounted to 240mg/l in the fly ash by the leaching test, but Pb was not detected in a leachate of the landfill buried in the fly ash. This paper describes adsorption and desorption of Pb in cover soil. It was found that Pb2+ was adsorbed according to the Freundlich formula, and the strength of adsorption was affected considerably by pH. Ca (OH) 2 which was added for removal of HCl increases pH at the leaching test to almost 12.4, so PbO liquefies as complex ion of Pb (OH) 42-. In the landfill, Pb is adsorbed in cover soil at strong alkaline and physically according to a decrease of pH. Generally, pH of the leachate is almost neutral, so concentration of Pb was less than 0.005mg/l. Author pointed out that it is possible for Pb to leach from the landfill if pH of the leachate changes extremely high or low.

Key words: fly ash, Pb, leaching test, landfill, adsorption