Synthesis of low-costing 4A-zeolite and stabilization of heavy metals from municipal solid waste incineration fly ash and activated red mud

Abstract

To handle the increasing environmental issues caused by red mud and municipal solid waste incineration (MSWI) fly ash, an integrated technology for its comprehensive utilization was developed through the activation of red mud followed by synthesis of 4A-zeolite. Three influencing factors on the thermal-alkali activation effect of red mud were investigated. Afterwards, activated red mud was combined with fly ash to synthesize 4A-zeolite and solidify heavy metal simultaneously. The results indicated that the maximum extraction ratios of Si (57.77%) and Al (76.34%) from red mud were achieved at the NaOH/red mud mass ratio of 1.8, alkali fusion temperature of 800°C, and alkali fusion time of 120 min. Furthermore, the mixture of activated red mud and MSWI fly ash could be served as low-costing raw materials to synthesize zeolite products with a compact structure. The solidification effect of typical heavy metals could meet GB 16889–2008 and HJ/300–2007 completely. Especially, the solidification efficiency for Cu, Zn, Pb, and Cd could reach 98.23%, 99.09%, 99.72%, and 98.21%, respectively. This paper not only solved the red mud accumulation and heavy metal pollution caused by fly ash under a relatively low-temperature environment but also synthesized zeolite products containing huge economic benefits.