Effect of polyphosphate and naphthalene sulfonate formaldehyde condensate on the rheological properties of dewatered tailings and cemented paste backfill

The rheological properties of dewatered tailings and cemented paste backfill have been measured and subsequently altered using polymeric dispersants. Polyphosphate and naphthalene sulfonate formaldehyde condensate (NSF) were selected as potential candidates to reduce the yield stress (τB) of the two slurries. Adsorption isotherms, acoustophoresis, and rheology measurements indicate that the polymers adsorb onto the dewatered tailings, causing an increase in the particle zeta potential, accompanied by comparably low values of τB for both polymers. The reduction in τB was due to electrostatic repulsion (polyphosphates and NSF) and steric repulsion (NSF). However, the efficacy of the polymers in reducing the yield stress of the cemented paste is complicated by hydration reactions in the cement phase. Polyphosphate was found to be less effective in lowering the τB of the cemented paste than NSF. Rheology measurements performed on the cement phase alone in the presence of the dispersants indicate that cement plays a major role in the adsorption of both NSF and polyphosphate in the cemented paste backfill. This is in spite of the fact that cement makes up only a small fraction of the total solids content of the paste. Adsorption isotherms determined for the cement phase alone indicate that NSF adsorbs strongly, whereas polyphosphate was seen to form a precipitate with calcium ions, released due to cement hydration. Acoustophoresis measurements mirrored this result, with NSF alone causing charge reversal and subsequently increasing the negative charge present on the surface of the cement phase.