Utilisation of lead-zinc mill tailings and slag as paste backfill materials

Paste backfilling is an incipient underground mine backfill technology in India. It facilitates maximum use of mill tailings with enhanced stability of the underground workings and minimises rehandling of water, as well as provides bulk disposal of mining solid waste. Binder type and dosage plays an important role in paste backfill performance. This paper highlights environmentally friendly utilisation of solid wastes like lead-zinc mill tailings and lead-zinc smelter fuming furnace slag (FFS) as paste backfilling for an underground metalliferous mine. Various experiments were conducted to study the effect of use of FFS as a fractional replacement for ordinary portland cement (OPC) in paste backfilling. The physico-chemical properties of both the lead-zinc mill tailings and fuming furnace slag (FFS) have been examined. In the first set of experiments, raw slag (FFS) was used for paste backfill preparation and experimentation for uniaxial compressive strength (UCS) development, whereas in the second set of experiments, FFS was crushed to -75 mu m (80 wt%) and used for the study. Multiple regression analysis of strength development was also conducted up to fifth order. The regression analysis is in accordance with the strength development and justifies the significance of OPC, crushed fuming furnace slag (CFFS) and waste chemistry on the strength gain with curing time. Use of crushed fuming furnace slag as OPC replacement in paste backfill showed encouraging results of strength development in contrast to raw FFS. Also, the economic analysis revealed that the paste backfilling cost per tonne reduced significantly with slag replacement in the binder phase.