Strength, leaching characteristics and microstructure of CGF plus P all-solid-waste binder solidification/stabilization Cu(II) contaminated soil

Utilizing solid waste -based binder to solidify/stabilize (S/S) heavy metal contaminated soils is a sustainable approach. This paper implemented microscopic tests on Cu(II)-doped paste and macro -microscopic tests on S/S Cu(II) contaminated pure clay -particles soil (P -CS), pure silt -particles soil (P -ST), pure sand -particles soil (P -SD), and their mixed soil (CSSM), respectively, with CGF+P all -solid -waste binders (abbreviated as CGF+P binders) composed of calcium carbide residue (CCR), ground granulated blast furnace slag (GGBS), fly ash (FA), and phosphogypsum (PG). The results showed that the clay -minerals in soil determine the S/S efficiency, and Cu(II) threshold content exist in the presence of clay -minerals and absent without clay -minerals. The strength of P -CS and CSSM containing clay -minerals first increased and then decreased with the increase of Cu(II) content, while the leached Cu(II) were lower than 2 mg/kg. The strength of P -ST and P -SD without clay -minerals decreased gradually, and the leached Cu(II) concentration far higher than 2 mg/kg. Cu(II) ions are immobilized by CGF+P paste and clay -minerals in soil. The S/S mechanism of Cu(II) by CGF+P binders rely on precipitation, adsorption, encapsulation, chemical compound, and ion exchange, and the immobilized mechanism of Cu(II) by clayminerals through electrostatic attraction, ion exchange, and physical adsorption. However, the binder paste and clay -minerals have the immobilization capacity on Cu(II) ions, is related to the component of the binder and the type of clay -minerals, respectively. The findings provided useful reference for the design and development of solid waste -based binders suitable for S/S heavy metal contaminated soils.