Characterization of lead–zinc mill tailings, fly ash and their mixtures for paste backfilling in underground metalliferous mines

Surface disposal of mill tailings and fly ash is a major concern for many countries, as it pollutes the environment including air, water, and soil. Paste backfilling is an emerging mine backfilling technique, wherein the industrial wastes such as mill tailings, fly ash and blast furnace slag are backfilled inside the stopes. This study examines the physico-chemical characteristics of lead–zinc mill tailings, fly ash and their mixtures for their possible utilization in paste backfilling in underground metalliferous mines. Three different mill tailing–fly ash mixtures, viz., 95:5, 92:8 and 90:10 (wt%), have been considered. The chemical, morphological and mineralogical compositions are analyzed by XRF, SEM and XRD. The morphological analysis revealed that the mill tailings are irregular in shape and fly ash particles are almost spherical in nature. The filling of inter-particle spaces of irregular mill tailings with spherical fly ash and finer mill tailings (− 20 µm) particles will enhance the rheology of mill tailing–fly ash mix paste backfill. Chemically, the lead–zinc mill tailings is enriched in SiO₂, CaO, Fe₂O₃, and Al₂O₃, whereas fly ash is mainly composed of SiO₂ and Al₂O₃ with small amounts of Fe₂O₃, CaO, K₂O, TiO₂, MgO, SO₃, Na₂O, and P₂O₅. The XRD analysis revealed that the lead–zinc mill tailings mainly contain quartz, pyrite, dolomite, hematite and calcite, while fly ash contains quartz, mullite, kaolinite and hematite. This study proved that lead–zinc mill tailings and fly ash together can be suitably used for paste backfilling in underground metalliferous mines.