Rheology measurements for flotation slurries with high clay contents – a critical review

As a result of the complexity of some ores with high clay contents, rheology is becoming a useful tool to investigate the effect of high viscosities in mineral processing operations including flotation. It has been observed that the presence of clay minerals in flotation slurries has a detrimental effect on concentrate grade and recovery. Concentrate grade is affected by the mechanical entrainment of clay particles that form compact loose aggregates. The detrimental effect on concentrate recovery is mainly caused by cross-linked clay network structures such as the house-of-cards or honeycomb with high pulp viscosity. For flotation slurries, the most common rheology measurements are yield stress and apparent viscosity at different shear rates including the one reported as an average in a flotation cell. The Binghman and Herschel-Bulkley models are frequently used to calculate yield stress by fitting the data from rheograms. Although these measurements are useful, they do not give information about the type of particle associations. In some cases, similar high apparent viscosity or yield stress values do not imply the same effect on the flotation performance since this depends on the type of clay particle associations. In other words, yield stress and apparent viscosity are not enough to predict flotation behaviour of slurries with high clay contents. This review paper recommends some methods for rheology measurements of flotation slurries with high clay contents and proposes that oscillatory rheology be more useful to classify particle associations. This type of rheology measurements is more suitable for slurries with high viscosities. Key information about rheology, clay minerals, and the way they can modify rheology in flotation slurries is also presented