Immobilization mechanisms in solidifiction/stabilization of cadmium and lead salts using portland cement fixing agents

Abstract

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Comparison of immobilisation of air pollution control residues with cement and with silica

“…This decrease in Pb leaching could be due to co-precipitation with Ca(OH) 2 , formed upon reaction of CaCl 2 with NaOH. The decrease could also be attributed to the formation and precipitation of CaPb 2 (OH) 6 or CaPb(OH) 4 related products in alkaline environment. Although no data about the formation of these minerals is available, it would be similar to the formation of CaZn 2 (OH) 6 [8,10].…”

“…As host for heavy metals in real cement-based waste systems, C-S-H finds more support than ettringite although the binding mechanism was still not determined univocally. Different mechanisms were observed for different metals and for different concentrations [6][7][8][9][10].…”

Effects of Curing Temperature on the Leachability of Lead Undergoing Solidification/Stabilization with Cement

“…The addition of an impurity such as a hazardous waste to the matrix may inhibit the setting and curing of the cement by interfering with the wetting process by coating the reacting surfaces. In fact, the rateretarding effect of lead salts on cement hydration may be due to the rapid formation of a gelatinous coating of mixed lead salts around cement clinker grains (14,15). This agrees well with our results here.…”

Incorporation and substitution mechanism of cadmium in cement clinker

“…Threedimensional structures up to 100e300 nm thick containing heavy metal can form coatings around cement grains (Cartledge et al, 1990;Chen et al, 2009;Crannell et al, 2000). According to Poon et al (1986), metals that form the least soluble hydroxides retard hydration reactions; those that form more soluble hydroxides exhibit only a slight degree of retardation; and metals forming soluble hydroxides behave as accelerators of cement hydration.…”