Solidification/stabilization of a heavy metal sludge by a Portland cement/fly ash binding mixture

A Portland cement/Class F fly ash binder was used to solidify a heavy-metal sludge containing Cr, Ni, Cd, and Hg. The cement/fly ash ratio was 0.4, and the sludge/solids ratio was 1.43. Samples were cured at room temperature for a minimum of 28 days, then examined by scanning electron microscopy, energy dispersive x-ray spectrometry, optical microscopy, and x-ray diffractometry. The sludge was composed of the hydration products of cement/fly ash mixtures, and impure, complex compounds of the waste metals. The sludge formed a simple mixture with the binder, retarded hydration, and affected microscopic phase composition; calcium hydroxide did not form. Reaction products near the surfaces of fly ash particles contained minor amounts of Cr and Ni, suggesting some chemical stabilization of these toxic metal ions

A study of the effects of nickel chloride and calcium chloride on hydration of portland cement

Portland cement samples containing amounts of CaCl and NiCl ranging from approximately 1% to 20% by weight have been examined by Si and Al solid-state MAS NMR as a function of time, and some of the mature pastes have been characterized by X-ray diffraction. Changes in physical properties that had been previously observed as a function of amounts of salt added are clearly traceable to differences in the silicate matrices. Low concentrations of both salts promote Q formation, but high concentrations result in formation of much more Q at the expense of Q . Both salts accelerate both aluminate and silicate hydration, and the effects appear to be almost entirely due to chloride. Minor variations in hydration rates at high Ni concentrations may be the result of nickel salt precipitation. © 1993. 2 2 29 27 1 2