Heavy Metals Immobilization Property and Mechanisms of LDHs-modified Cementitious Materials

Abstract

Layered double hydroxide (LDH) has a positive effect on the adsorption and immobilization of heavy metals. The compressive strength and the heavy metal ions Pb2+ immobilization of CaAl-LDH modified cement paste were studied in this paper. Through research, it was found that compared with the cement paste sample with a Pb2+ content of 1% after curing for 7d and 28d, the addition of CaAlLDH to the cement paste sample increased the compressive strength by 6.1% and 1.6%, respectively, demonstrating the enhancing effect of CaAl-LDH on the strength of cement paste. Compared with the sample containing only Pb2+, the addition of CaAl-LDH to the cement increased the immobilization rate by 0.3% after 12 hours of leaching time and showed varying degrees of improvement at different leaching times. The immobilization mechanism of heavy metals in LDH blended cement paste was revealed by microstructure characterization. It was founded that Pb2+ can replace Ca2+ in AFt, AFm, and LDH, and can co-precipitate with OH-.

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