Recycling municipal solid waste incineration fly ash in fired bricks: An evaluation of physical-mechanical and environmental properties

Municipal solid waste incineration fly ash is usually listed as hazardous waste because of inorganic contaminants (heavy metals) and organic contaminants (dioxin). This study examined influences of fly ash introduction in physical, mechanical, porosity and environmental risk in the production of fired clay brick. The introduction of fly ash declined physical and compressive strength of products, and involvement of soluble salts (NaCl and KCl) in fly ash also negatively impacted physical and mechanical properties. The morphology of fired bricks shows coarse and irregular due to the addition of fly ash containing soluble salts, while became smooth and homogeneous when soluble salts were removed by washing. Meanwhile, the introduction of fly ash containing soluble salts increased surface area and pore size of products remarkably. The desalination by washing process is thus necessary for obtaining a high performance fired brick. Mineral phase analysis indicated that soluble salts hindered the formation of complex silicoaluminates (e.g. mullite), which impacted the combination of raw materials. The environmental risk of fired bricks containing fly ash are evaluated by simulated environmental leaching test, including acid rain leaching, underground water leaching and seawater leaching. Leaching results suggested fired brick incorporating 10 wt% of washed fly ash can satisfy regulation limitation, and can be used in the harsh scenarios. It is showed fly ash could be introduced in the production of fired brick after removing soluble salts by washing, and release risk of heavy metals meet regulation requirements completely.