Study on the strength and toxic leaching characteristics of CGF-solidified/stabilized ion-type rare earth tailings

The resource reutilization of ion-adsorbed rare earth tailings contributes to the sustainable development of ion-adsorbed rare earth mines. This study uses a full solid waste slag stabilizer (CGF) composed of calcium carbide slag, granulated blast furnace slag, and fly ash in a mass ratio of 4.5:4.5:1 to treat ion-adsorbed rare earth tailings through solidification/stabilization. The results indicate that CGF can significantly improve the compressive strength of rare earth tailings, with compressive strengths exceeding 350 kPa after a curing period of 7 days. As the amount of CGF increases and the curing age extends, the strength of the cured rare earth tailings continually improves. The leaching concentrations of Pb and Zn toxicity in the cured rare earth tailings decrease with increased curing time, meeting the requirements of Pb < 5 mg/L and Zn < 100 mg/L after 28 days of curing, whereby a higher amount of CGF is beneficial for the stabilization of Pb and Zn in the rare earth tailings. In the cured rare earth tailings, Pb and Zn primarily exist in a stable residue form, with the Risk Assessment Code values not exceeding 10 %, indicating a low-risk status. The curing of rare earth tailings with CGF results in the formation of a significant amount of amorphous hydration gel (C-(A)-S-H), which aids in enhancing the strength of the rare earth tailings. Additionally, these amorphous hydration gels can transform Pb²⁺ and Zn²⁺ in rare earth tailings into low-mobility stable forms through multiple pathways such as precipitation reactions, physicochemical adsorption, and encapsulation.