Abstract
In this study, statistical EDS point analysis was conducted to understand the binding mechanisms of Cu2+ and Zn2+ in Portland cement immobilization systems based on their correlation with compositions of Al incorporated into calcium silicate hydrate (C-A-S-H). Cu2+ and Zn2+ significantly retarded early hydration and strength development within the first day but exerted an accelerating effect at later ages. The uptake of Cu2+ by C-A-S-H occurs through two types of binding forms, which are dominated by the adsorption of Cu2+ on the Al sites of substituted bridging silicate tetrahedra and on deprotonated silanol group sites. These binding forms result in competitive adsorption between Cu2+ and Ca2+. Zn2+ is primarily bound to the outer-product C-A-S-H. Zn anion species were adsorbed on the positively charged sites of the C-A-S-H surface, which were generated from the adsorption of Ca2+. Consequently, the uptake of Zn exhibits a noncompetitive relationship with Ca2+ and increased with Ca content in C-A-S-H.
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