pH dependent leaching characterization of major and trace elements from fly ash and metakaolin geopolymers

The leaching characteristics of Cl-, SO42, Na, K, Al, Si, Ca, Mg, Ba, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, Se, Sr, Tl, V, Zn from fly ash and metakaolin geopolymer mortars were characterized in a broad pH range (1-14) in this work. Apart from revealing the partitioning of chemical species between the solid and aqueous phase, the acid neutralization property of both geopolymers were studied. In contrast with the virtually pH independent characteristic of chloride and sulfate, the leaching of the other elements showed pH dependent features, which can be further divided into amphoteric, cationic and oxyanionic patterns. Formation of montmorillonite and amorphous silica were detected by X-ray diffraction after the leaching. The leaching results and mineralogical measurement were coupled with geochemical modelling to identify the solubility controlling phases of Al, Si, Ca and Mg.