Solidification/stabilization of gold ore tailings powder using sustainable waste-based composite geopolymer

Solidification/stabilization (S/S) is a low-cost and efficient method for enhancing the mechanical properties of gold ore tailings powder (GTP) and decontaminating tailings. However, the traditional cement-based stabilization method is associated with environmental pollution and questionable sustainability. In this study, industrial waste residue was mixed with alkaline activators to prepare a sustainable waste-based composite geopolymer (WCG) to stabilize the GTP. Considering the cost of the novel geopolymer and the economic constraints of mining enterprises, a ratio of 5% geopolymer and 95% GTP was selected. The hydration mechanism, microstructure, mechanical properties, and leaching characteristics were analyzed after curing periods of 3, 7, 14, 28, and 90 days (d). The tests included phase structure analysis via x-ray diffraction analysis, thermogravimetric analysis and unconfined compression strength tests to evaluate the hydration products and strength of the stabilized GTP. The results showed that the increase in amorphous/unidentified content was not obvious after 28 d of curing and that the stabilized tailings with the same content of WCG had higher mechanical strength than those stabilized with ordinary Portland cement (32.5 MPa). Scanning electron microscope-energy dispersive spectroscopy and nitrogen adsorption tests were used to characterize the microstructure of the stabilized materials. These results indicate that the formation of C-(A)-S-H gels contributed to improvement in the degree of compaction of the stabilized samples. The immobilization mechanism of arsenic included precipitation, physical encapsulation, adsorption, and ion substitution. The stabilized materials had a dual-pore fabric characterized by interaggregate and intra-aggregate pores. The properties of the leaching solution, including the pH, electrical conductivity, oxidation-reduction potential, and heavy metal ion leaching concentrations, were determined to evaluate the leaching performance of the stabilized GTP. The relationship between the chemical properties of the leaching solution and the concentration of the leaching ions was analyzed to explain the immobilization mechanism of harmful elements. All harmful elements were well immobilized after 7 d of curing, and the leaching concentration remained constant over a longer curing time. This study provides a reference for the sustainable management of GTP and for improving the stabilization of tailings dams.