Application of advanced analytical techniques to elucidate structural and chemical evolution of combustion-generated ash

This work reveals the characteristics of the ash obtained from the combusti on of paper mill sludge. A model of the ash pellet was synthesized from a m ixture of oxides of Al, Si, Na, K, Ca, Mg, and Ti using TG furnace at 1500 degreesC. The ash pellet was doped with heavy metals such as Cr, Cd and Pb prior to the combustion in order to establish their behavior during ash for mation. The atomic force microanalysis (AFM) of the ash (10 x 10 mum size) revealed a smooth and continuous outer surface topography. The maximum vert ical height variation of the surface was 3.8 nm. The ash material contained a compact, dense rigid internal morphology as evidenced from the scanning electron microscopy analysis. The ash material contained crystalline mullit e, corundum and alumino silicate glass phases. The Al-27 and Si-29 solid-st ate nuclear magnetic resonance spectra with magic angle spinning of the ash also supported the formation of the above three phases. It was shown by th e presence of both AlO6 octahedral peak (10.0 ppm) and AlO4 tetrahedral pea k (50.0 ppm) for aluminum present in these compounds. Silica showed a chara cteristic SiO4 tetrahedral peak at - 99 ppm, which is due to the presence o f SiO4 group in alumino silicate matrix. The final ash material was compose d of alumino silicate glass with embedded corundum and mullite crystals. Th e electron probe microanalysis showed the inclusion of Cr into the corundum phase, which lead to the Cr immobilization against leaching. The outer sur face of the ash was found to be rich in alkali oxides compared to the inner core in which the other two heavy metals Pb and Cd are enriched. The final pellet was considered non-hazardous. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.