Synthesis and optimization of green one-part geopolymer from mine tailings and slag: Calcium carbide residue and soda residue as supplementary alkali sources

Abstract

• Activated tailings acted as an alkaline activator for the one-part geopolymer production. • Waste treatment by waste: Calcium carbide residue was used as a supplementary alkali source. • Waste calcium carbide residue prompted the hydration reaction and increased the sample strength. • This study provides promising guidance for the rational and cost-effective utilization of tailings. The use of mine tailings (MTs) as the precursor for producing geopolymers is an effective way to reduce their storage and mitigate their negative effects on the environment. MTs were firstly activated through hydrothermal pretreatment in the presence of NaOH at 200 °C. Then one-part geopolymer (OPG) samples were synthesized from activated MTs and slag, and calcium carbide residue (CCR) and soda residue (SR), the solid industry wastes, were added as supplementary alkali sources to improve the strength of OPG samples. The effects of alkali sources on the setting time, fluidity, compressive strength, pH, hydration kinetics, hydration products, and microstructure of OPG samples were investigated. Both alkali sources shortened the setting time, decreased the fluidity, and increased the strength of OPG samples, and the CCR showed a more significant effect on these properties than SR. These clear differences in sample performances were associated with the pronounced mineralogical differences between SR and CCR. Compared to SR, CCR rich in Ca(OH) 2 produced a higher pH of the pore solution, which significantly promoted the slag dissolution, shortened the induction period, and accelerated the hydration process. Calcium–sodium aluminosilicate hydrate (C(N)-A S H) gel was the dominant reactant in all samples that enhanced the strength of OPG samples. More geopolymer gel was generated in CCR-doped samples and thus a much higher strength than SR-doped samples. However, the incorporation of excessive alkali sources induced the high carbonization degree of samples, and it was likely responsible for the reduction in strength.