Immobilization of Cu(II) and Zn(II) into hydrocalumite - An X-ray absorption fine structure (XAFS) investigation

The fate of heavy metals is crucial to the reuse of municipal waste incineration ash (MWIA) as construction materials. It is, however, not completely clear how they interact with cementitious phases at the molecular scale. This study investigated the uptake and speciation of Cu(II) and Zn(II) during the generation of Al-hydrocalumite-type high-pH phases through co-precipitation and adsorption experiments. Hydrocalumite (Hc) and minor phases, such as calcite and hydrogarnet, were identified as primary phases using X-ray diffraction (XRD). The characterization of Hc+Cu(II), Hc+Zn(II), and Hc+Cu(II)+Zn(II) via XRD, SEM, and bulk Cu(II)/Zn(II) EXAFS showed that both Cu(II) and Zn(II) exists as the surface/interlayer adsorption on the Hc+Cu(II)/Hc+Zn(II) and Hc+Cu(II)+Zn(II). Thermodynamic calculations support the experimental observations for the bulk phase. This study help understand the interacting mechanism between Cu(II)/Zn(II) and Hc phase, and pave the way of safe utilization of heavy-metal-containing waste as supplementary cementitious materials.