Studies on the thixotropic behaviour of ‘Akli’ bentonite suspensions

Summary Thixotropic behaviour of dilute (1.5%) and concentrated (5.3% to 8.3%) suspensions of Akli bentonite has been studied by different methods. Dilute suspensions gave soft gels on the addition of small amounts of KCl and KCNS and the equation log=A-BC (where was time of gelation,C was concentration of the electrolyte,A andB were constants) was found to hold good. The rotational viscometer method gave hysteresis loops (equatione ^y =a x ^b ; wherey was torque,x was r.p.m. anda andb were constants) with concentrated suspensions containing varying amounts of caustic soda. Regression equation has been given for various gel forming mixtures.Thanks are due to Messrs.A. R. Konkan andAbdul Aleem for helping in mathematical derivations.     

Ageing and collapse of bentonite gels—effects of Li,Na, K and Cs ions

The state of bentonite gels at the start of the ageing experiment must be well-defined, and this required the gels to be at a constant surface chemistry condition. This is achieved by allowing the freshly prepared gels to rest for a day. At this state, the yield stress is constant, provided that the gel is at an equilibrium breakdown state after stirring prior to each measurement. This point is also the yield stress at zero aged time. Ageing study then commenced, and the behaviour is generally characterised by an increasing yield stress with wait time. Alkali metal ion type and concentration affect the gel ageing and stability behaviour significantly. The ageing behaviour is most pronounced at low salt concentrations for the smallest and most strongly hydrated cations, Li ⁺and Na ⁺. The yield stress at any given aged time and its rate of increase are generally larger. Coarsening of these suspensions was observed. The opposite is true for the weakly hydrated K ⁺and Cs ⁺ions. At high concentrations of 0.5 and 1.0 M Cs, K and Na ions, the gels became unstable over time and phase-separated. The stability time of these weak gels was found to increase with decreasing cation size, Na > K > Cs. This stability time displayed a very strong quantitative correlation with the hydration bond length. Coarsening was also expected, but not observed due to the lack of integrity of these weak aggregates during particle size measurement. The recovery or ageing behaviour was fitted with both the Nguyen–Boger and Leong models.