Rheology of aging aqueous muscovite clay dispersions

In hydrometallurgical mineral processing, time and pH dependent rheology of dispersions comprising reactive particles can exert a striking influence on material processability and handleability. Rheological studies of 0.32 solid volume fraction (57 wt% solid) aqueous dispersions of muscovite clay mineral aging at pH 7 and 1 for 4 h were undertaken to investigate the temporal, pulp chemistry-mediated particle interactions. In particular, the dispersions’ flow and deformation behaviour in tandem with viscoelastic structure changes over time were probed. Dispersions at both pH 7 and 1 displayed non-Newtonian, Bingham plastic behaviour and strong time-dependent viscosities and yield stresses. Fresh dispersions showed a weak rheology at pH 7 initially, accompanied by thixotropy which transformed to anti-thixotropic and rheopectic behaviour upon aging. Furthermore, the viscosities, yield stresses and both the viscous (G″) and elastic (G′) moduli accentuated dramatically with time, reflecting an elastic to a more sol-like viscoelastic gel transformation. In contrast to pH 7, the particle interactions at pH 1 initially led to the formation of a highly networked gel structure which displayed thixotropic and predominantly elastic behaviour. Upon aging however, systematic attenuation of thixotropy, suspension viscosity, shear yield stress and viscoelasticity occurred. Above certain shear stresses, viscoelastic gel to sol structure transformation occurred, the creep behaviour being distinctly pH and time dependent. Differing pH-mediated pulp chemistries which prevailed at pH 7 and 1 upon aging were responsible for the contrasting, temporal particle interactions and microstructure evolution.