Mechanochemical stabilization of heavy metals in fly ash from coal-fired power plants via dry milling and wet milling.

Abstract

Fly ash from coal-fired power plants has become the world's largest solid waste pollutant. The mechanochemical (MC) method used as a non-thermal method shows good stability to heavy metals in soil and municipal solid waste incineration (MSWI) fly ash. It is first uesd to stabilize the heavy metals in fly ash from coal-fired power plants. In this paper, dry milling and wet milling MC methods were carried out on fly ash from a 300MW supercritical circulating fluidized bed (CFB) boiler. The relative leaching rate (RLR) is defined to indicate the degree of leaching. Experimental results show that after mechanochemical treatment for 10h, the RLRs of Cu, Cr, Pb, Zn, Cd, and Ni by dry milling decrease by 52.10%, 70.16%, 89.80%, 22.97%, 3.15%, and 23.49% respectively, and the RLRs of Cu, Cr, Pb, Zn, Cd and Ni by wet milling decrease by 58.11%, 70.92%, 89.64%, 23.26%, 10.59%, and 30.77% respectively. Compared with dry milling, the fly ash particle size is smaller after wet milling, indicating that the presence of water will weaken the agglomeration of fine particles. A continuous extraction experiment shows that the water-and acid-soluble fraction of the six heavy metals in fly ash can be reduced by dry or wet milling, and the residual fraction can be increased.