Rheological properties of palygorskite–bentonite and sepiolite–bentonite mixed clay suspensions

• Mixed palygorskite–bentonite and sepiolite–bentonite suspensions were studied.
• The bentonites consisted of smectites with different layer charge.
• Interaction between end members is maximum at 10–20% bentonite in the mixtures.
• The layer charge of smectite affects the rheological properties of the mixtures.

This study examines the influence of layer charge and smectite content on the rheological properties of mixed bentonite–palygorskite suspensions. Eight bentonite samples containing smectite with layer charge ranging between 0.38 and 0.54 e/huc were used to prepare 5% w/v mixed palygorskite–bentonite aqueous suspension at pH 7. The influence of smectite on the apparent viscosity and yield point of palygorskite suspensions depends on the proportion of the smectite in the mixture and the layer charge and charge localization of the smectite. The interaction between the two end member clay minerals is maximum at low percentage (10 to 20%) of bentonite in the mixture. Low charge and high charge smectite tended to improve and deteriorate, respectively, the yield point and apparent viscosity of the suspension. This behaviour seemed to be related to the influence of layer charge of smectite on the degree of delamination and the thickness of smectite quasicrystals, which consequently determine the number of particles involved in the interaction and the strength of particle–particle linkages.

In mixed palygorskite–bentonite suspensions maximum interaction is observed after addition of 10% bentonite in the mixture. The layer charge of smectite affects this interaction. For low charge smectites both the apparent viscosity and the yield point tend to improve for 10% smectite in the mixture. In contrast for high charge smectites and for smectites with tetrahedral charge, the apparent viscosity and the yield point decrease for 10% smectite in the mixture.Figure optionsDownload as PowerPoint slide