Abstract: In order to promote the sustainable utilization of mineral resources and protect the ecological environment of mines,a certain amount of alkali-activated fly ash was used to replace cement to prepare copper tailings filling paste. The strength,impermeability and environmental effects of copper tailings filling paste test blocks were evaluated by systematic mechanical, permeability and heavy metal precipitation tests. The mineral composition of cementitious materials and the microstructure characteristics of filling paste test blocks were analyzed by X-ray diffraction and scanning electron microscopy. The influence of alkali-activated fly ash on the comprehensive performance of filling paste test blocks and its microscopic mechanism were revealed. The results showed that alkali activation could significantly improve the activity of fly ash. Under the action of 1 mol/ L NaOH alkali activator,the compressive strength of 20% fly ash based copper tailings filling paste test blocks after 28 d curing was 17. 8% higher than that of cement cementitious test blocks,and the permeability coefficient was reduced by 68. 0%. The comprehensive cementation effect was remarkable. The addition of alkali-activated fly ash reduced the precipitation of heavy metals during the hardening process of copper tailings filling paste test blocks,which was helpful to control the pollution of groundwater resources. Using the filling effect of fine particles and the composite cementitious effect of fly ash,the porosity of copper tailings could be effectively reduced,and new hydration products could be formed to enhance the bonding force between tailings particles,thereby improving the strength and stability of the material.

Key words: alkali-activated fly ash,copper tailings,strength properties,heavy metal leaching,microstructure