Physical Properties and Leachability of MLW Stream Containing Cr, Ni and Cd Immobilized in a Cement Matrix

Abstract

Cement samples containing variable amounts of Cr(III) or Ni(II) or Cd(II) as chloride admixtures present in a MLW stream from reprocessing of spent fuel were prepared under established procedure. Due to the high pH generated in the cement clinker hydration, respective metal hydroxides are formed and improve the physical characteristics of the cement matrix. An increase in the value of the compressive strength was observed when about 7% of the above elements were blended in cement. The increase depends on the nature of the element in the sequence Cr >Ni >Cd.The leach tests confirm the formation of insoluble hydroxide presenting a low concentration in the leachate corresponding to 0.05, 0.004 and 0.052 mg.L−1 for Cr, Ni and Cd, respectively. On the other hand, the hydro-lyzed chloride ions seem to react with calcium with consequent increased degradation of the cement matrix.

Environmental Pollution Remediation through Solidification/Fixation of Heavy Metal Ions in Portland Cement

“…The two principal constituents of most commercial fixing agents are cementitious materials (Portland cement, fly ash, lime and sodium carbonate) but a combination of cement and soluble silicates was found to be best binder in the solidification of a largely inorganic residue with trace concentrations of organic contaminants [93]. Many researchers studied the effect of heavy metals on solidification of cement [94][95][96][97][98][99].…”

Stabilization of chromium salt in ordinary portland cement

“…Wang & Vipulanandan (2000) concluded that addition of Cr(VI) in the form K 2 CrO 4 extended the initial and final setting time and decreased the compressive strength. Zamorani et al (1989) discovered that low Cr(III) levels in cement system accelerated the setting time. Pera et al (1997) notified that the immobilization of Cr(VI) by hydraulic binders takes place by one or a combination of the following mechanisms: addition, substitution or precipitation of new components.…”