Operational considerations regarding the impact of variations in muscovite content in mine tailings on the flowability of cemented paste backfill

The detrimental effect of muscovite on the mechanical and rheological properties of cementitious materials is likely to be observed in cemented paste backfills (CPBs) made from muscovite-rich tailings. Once a CPB mix design is formulated with tailings containing a specific muscovite content, variations in muscovite content may present operational and performance challenges. This study assesses the impact of increasing muscovite content on the consistency (slump) and rheological properties (yield stress, flow index and viscosity at high shear rates) of CPBs prepared with varying solids contents by weight. Pure muscovite was added to tailings initially containing 15% muscovite by dry mass of tailings up to the maximum expected muscovite content (25%) at the mine site where the tailings were sampled. CPB mixtures were prepared in the laboratory with solids contents ranging from 68 to 72%, using tap water and 5% high early (HE) strength cement. The CPB mixtures underwent standard Abrams cone slump tests and triplicate rheological analyses. For a given solids content of the CPBs, the results indicate that an increase in muscovite content reduces the slump while increasing the rheological properties mentioned earlier. This necessitates the addition of water to maintain a specific slump, which lowers the solids content and increases the water-to-binder (W/B) ratio, potentially compromising the mechanical strength. Results are discussed in evaluating the impact of the muscovite content on the pressure loss during CPB transportation in pipelines and in proposing a method for estimating both the amount of water required to maintain the target slump and the amount of binder required to maintain the initial W/B in the CPB.