Immobilizatoin of lead compounds in fly ash by mixing with asphalt, sulfur and sodium hydroxide

The present paper is concerned with a novel heavy metal immobilization by mixing with additives of asphalt, sulfur and sodium hydroxide. To immobilize heavy metals, fly ash were mixed with each additive by using a bi-axial kneader heated at 403 K. Then the dissolution test was carried out based on the Japan Environment Agency notification No. 13. Seven samples of fly ash discharged from the melting process of MSW incineration fly ash were employed. The present immobilization of heavy metal were considered to consist of the conbination of the following two advantages; (1) common advantage of asphalt solidification, (2) additional advantage of low solubility by metal sulfuration. Results of the experiment show that the lead concentration in the eluted solution of the treated sample satisfied Japan's lead emission standard of 0.3 mg/l. It was considered that sodium sulfides, which were produced from the reaction of sulfur and sodium hydroxide, react with heavy metals to form insoluble metal sulfides. The minimum amounts of sulfur and sodium hydroxide needed to achieve the allowable limit had a linear relationship with the heavy metal content in fly ash.