Rheology of clay-water and clay-water-salt systems: Sol-gel transition and flocculation
The effect of clay percentage and NaCl addition on the rheological behavior of aqueous suspensions of a purified bentonite was investigated. The solgel transition (SGT) was detected using three methods: (i) the grump of viscositywith clay percentage, (ii) the steady flowcurves and (iii) the detection of hysteresis buckle by increasing-decreasing shear stress cycles. Results showed a SGT (at 6.5%(w/w)) of clay. The effect ofNaCl addition was studied on sol suspensions (1.5%, 3.25% and 4.5% (w/w) of clay) and on gels (6.5% and 7.5% (w/w) of clay). For diluted sols the electrovisquous effect was detected at about 0.01% (w/w) of NaCl by a slight minimum of viscosity. The critical flocculation concentration (CFC) corresponded to 0.04% (w/w) of NaCl and suspensions stayed stable until 0.1% (w/w) of NaCl (maximumof viscosity) after which, sedimentationwas observed. The CFC value of the semi diluted sol was 0.05% (w/w) of NaCl and since the flocculation; the suspension became a stable gel until (0.1%(w/w)) of NaCl (max of viscosity) where a thin film of water surmounted it. For gels, the flocculation seemed to occur by stages; it started at 0.02% and continued until (0.2%(w/w)) of NaCl where a thin layer ofwater appeared.