Abstract: The pH of environmental medium was the key factor to control the release of heavy metals in fly ash. Therefore， it was necessary to study the leaching behavior of heavy metals in fly ash in different acidic environments. The dissolution behavior of heavy metals in four acidic environment provided by HJ/T 300—2007 Solid Waste-Extraction Procedure for Leaching Toxicity-Acetic Acid Buffer Solution Method， HJ/T 299—2007 Solid Waste-Extraction Procedure for Leaching Toxicity-Sulphuric Acid & Nitric Acid Method， Toxicity Characteristic Leaching Procedure（TCLP） and NEN 7341 Leaching Test of Leaching Characteristics of Building Materials and Solid Wastes Standards was discussed. And the leaching characteristics of heavy metals in four kinds of solidified fly ash， such as chelating agent TS-300， chelating agent SDD， cement and chelating agent SDD+cement， were analyzed when the acid neutralization capacity was completely consumed in the simulated acidic environment of landfill. The results showed that HJ/T 300—2007 had strict requirements for heavy metal leaching. The order of fixing ability of different additives to heavy metals from strong to weak was TS-300， SDD， SDD+cement and cement. The amount of cement added was positively related to the acid neutralization capacity of solidified fly ash and the dilution effect of heavy metal leaching. In order to reduce the environmental safety risk of fly ash landfill， the use of cement solidification as pretreatment should be avoided as far as possible.

Key words: fly ash, chelating agent, cement, heavy metal, acid neutralization capacity