Mineral Transformation Behavior During Ash Melting Process And The Potential Risk Analysis Of Heavy Metals

In recent years, the treatment fly ash generated from waste incineration method is increasing; effective treatment of fly ash has become a serious problem. Melting volume reduction can effectively achieve the reduction, heavy metal is stable, slag can also be made high-quality glass-ceramic, and scholars at home and abroad have their research. But few studies can be found which the evolution of behavior in melting process and the potential risk analysis of heavy metals. This paper is based on municipal solid waste incineration fly ash as the base material, study co-melt mechanism of Multi oxide. The effect of glass-ceramic alkalinity on the mineral composition, properties and its microstructure was investigated. Combined with molecular modeling software analysis combined glass-ceramics during formation of mineral crystals and crystal chemical reactivity capability. Heavy metal toxicity assessment model STIM was established for fly ash, slag and glass-ceramics in ecological risk. The main conclusions are as follows:SiO₂ and shale ash both of them can reduce the ash fusion temperature characteristics, but shale ash effect is remarkable. As the increases of alkalinity, the mixed ash‘s melting point also increased, and the glass-ceramics have high crystallinity, polycrystalline coexistence. Grain changes from an irregular polyhedron full spheroid, and then becomes attached to a cylinder-shaped body. Water absorption of glass-ceramics after first decreases with the increase of alkalinity, resistance to acid and resistance to alkali increased with the increase of alkalinity. In all the main crystal phase, binding energy of anorthite can be minimized, fluxing best. Anorthite and wollastonite are easy to lose electrons; chemical reactivity of anorthite is higher than wollastonite.In molten slags, the content of Zn was the highest, followed by Cu, As, Ni, and Pb. During melting process, the average enrichment order of heavy metals is Pb> Cd> Cr> Zn> Cu> As> Ni, heavy metals migrate from reducible form to residual form. Calculated by STIM, the most toxic ash as FSA5, toxicity is 54.18; the highest for the toxic slag FSA3, toxicity is 8.17; toxic glass ceramics up to FSA1, toxicity is 0.019. Three orders decreasing of the toxicity in heavy metals after crystallization process.