Paste backfill reticulation optimisation using high shear mixing at DeGrussa Mine

This paper investigates the work carried out by DeGrussa Mine and the Weir Technical Centre (WTC) of Weir Minerals Australia, in developing a process to produce a consistent cemented paste backfill that is fully sheared and presents the lowest possible yield stress and pressure gradients during the underground transport phase. The existing twin shaft paste mixer on DeGrussa Mine was not providing sufficient shear or time of shear to deliver a fully homogenised product. The project to improve the paste backfill rheology involved quantifying the performance of the twin shaft mixer as well as the required rheological parameters of yield stress and pressure gradient of the paste backfill product. In order to achieve the required outcome, a centrifugal pump was installed after the mixer to provide the shear energy required to produce a fully sheared paste backfill rapidly and continuously. A fully sheared consistent paste backfill is required to ensure predictable transport of the paste backfill throughout the DeGrussa Mine reticulation system. This predictability of paste backfill performance results in a safe and robust reticulation system, together with ensuring pipeline integrity. The lower pressure gradients, manifest by the fully sheared paste backfill, also allow DeGrussa Mine to fill stopes that are at a distance that would otherwise require a positive displacement pumped system.