Strength, leaching characteristics and microstructure of CGF+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 clay-minerals 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.