Effect of alkali cation type on compressive strength and thermal performance of the alkali-activated omphacite tailing

Storage of mine tailings in mining industry has led to a series of economic, ecological, and environmental problems. Alkali activation is an effective way to make use of tailings, but pan-alkali and environmental pollution caused by the use of strong alkali is also another knotty problem. In this work, omphacite tailing was employed as a precursor of alkali-activated material, and the relatively mild alkali (NH4OH) was adopted to investigate the effects of alkali cation type (Na+ and NH4+) on the mechanical and thermal performance of alkali-activated omphacite tailing. Results show that the alkali-activated omphacite tailing with high mechanical performance can be synthesized by both types of alkali cations via compression molding, and the highest compressive strength of NH4-sample and Na-sample can reach 119.39 MPa and 71.51 MPa, respectively. Comparing the two, Na-samples have higher compressive strength but lower heat-resistance temperatures. With the increase of Na/Na + NH4 ratio, the compressive strength exhibits a rising trend while the heat-resistance temperature is the opposite. By TG-DTA, FTIR, XRD, CT, and SEM characterization analysis, the effects of different cations on the mechanical and thermal properties were revealed. It indicates that omphacite tailing and NH4OH are feasible as a precursor and alkali activator of alkali-activated materials, and the alkali-activated omphacite tailing can be tailored, in mechanical strength and thermal performance, for structural application.