Bayuseno, A. P.; Schmahl, Wolfgang W.
Understanding the chemical and mineralogical properties of the inorganic portion of MSWI bottom ash.
In: Waste Management, Vol. 30, No. 8-9: pp. 1509-1520
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This paper investigates the changes of mineralogical composition ofbottom ash in the environment. The chemical and mineralogical bulkcomposition was determined by X-ray fluorescence (XRF) and X-ray powderdiffraction (XRPD) Rietveld method. Single bottom ash particles wereinvestigated by optical microscopy, scanning electron microscopy withquantitative energy-dispersive X-ray microanalysis (SEM/EDX) andelectron probe micro analysis (EPMA). SEM/EDX and EPMA are valuablecomplement to bulk analysis and provide means for rapid and sensitivemulti-elemental analysis of ash particles. The fresh bottom ash consistsof amorphous (>30 wt.\%) and major crystalline phases (>1 wt.\%) such assilicates, oxides and carbonates. The mineral assemblage of the freshbottom ash is clearly unstable and an aging process occurs by reactiontowards an equilibrium mineral phase composition in the environmentalconditions. The significant decrease of anhydrite and amorphous contentswas observed in the aged bottom ash, leading to the formation ofettringite, hydrocalumite and rosenhahnite under atmospheric conditions.In the water-treated sample, the calcite contents increasedsignificantly, but ettringite was altered by the dissolution andprecipitation processes in part, to produce gypsum, while the remainingpart reacted with chloride to form hydrocalumite. Gypsum and other Cabased minerals may take up substantial amounts of heavy metals andsubsequently control leaching behaviour of bottom ash.