During the aqueous processing of concentrated mixed layered clay (e.g. chlorite and muscovite) and metal oxide (e.g. quartz) mineral dispersions at low pH (e.g. 1) and high temperature (e.g. 70 ºC) where the clay mineral component dissolve, a difficulty sometimes arises due to the formation of a viscous gel. The cause of the intractable gel formation is not well understood but may be attributed to synergistic pulp mineralogy, interfacial chemistry, solution speciation and particle interactions which emerge in the course of dissolution. In hydrometallurgical mineral extraction processes pulp gelation may invariably reduce the yield or recovery of value minerals.

In order to understand the gelation phenomenon which prevail during mixed clay-oxide pulps processing, the roles of interfacial and pulp chemistry, crystallographic characteristics and particle interactions (rheology) of single clay mineral (muscovite) dispersion are investigated as a function of pH (1 vs. 6), temperature (25 vs. 70 ºC), solid content (50 - 65 wt%) and time. The results show that both temperature and pH exert dramatic influence on the dissolution behaviour and pulp chemistry of muscovite which impact on dispersion rheology significantly. The time-dependent, non-Newtonian rheological characteristics (viscosity and shear yield stress) observed are rationalized in terms of changes in solution speciation, interfacial chemistry, particle mineralogy and associated interactions. The implications of the outcomes are discussed in terms of a possible gelation mechanism which may prevail in mixed clay-oxide dispersions at low pH values.