A novel process utilizing subcritical water and nitrilotriacetic acid to extract hazardous elements from MSW incinerator fly ash

An effective process for hazardous element extraction from municipal solid waste incinerator fly ash was developed. The key trait of the process was to extract most of the hazardous elements out of the ash but leave Ca and Si inside the residue. In the extraction process, the ash was firstly pre-washed with water, then subjected to subcritical water (SC water) treatment and nitrilotriacetic acid (NTA) extraction. SEM images indicated that SC water is strong enough to destroy the ash particles, thus greatly improving hazardous elements extraction efficiency in the subsequent NTA extraction process. The extraction percentages for Cr, As, Se, Cd and Pb under SC water+NTA treatment were around 2–6 times higher than those treated by NTA at room conditions. The preferable SC treatment temperature was 573 K and the treatment time was 3 h. The optimum NTA concentration, vibration time and liquid/solid ratio were 0.8 M, 5 h and 10:1 (ml/g), respectively. Furthermore, it was found that introduction of a suitable amount of sulfuric acid into the extraction solution could extract more than 90% of most of the hazardous elements out of the ash.