The effect of the electrolyte concentration and pH on the rheological properties of the original and the Na2CO3-activated Kütahya bentonite

The effect of the Na2CO3 activation on the rheological properties of a bentonite from Kütahya (Turkey) was investigated. The bentonite was activated with Na2CO3 at different dosages (1–15 g Na2CO3/100 g bentonite). The activated samples were examined by chemical and X-ray diffraction analysis. The calcium bentonite was completely converted to sodium bentonite when the Na2CO3/bentonite ratio was 2.5%. The rheological values showed a maximum after addition of 2.5% Na2CO3 (bentonite concentrations 2–6% w/w). At 2.5 g Na2CO3/100 g bentonite, the shear stress was also measured at several NaCl and Na-hexametaphosphate concentrations. NaCl addition decreased the rheological properties up to NaCl concentrations of 0.005 mol l−1. Further addition of NaCl increased the rheological properties again. The addition of Na-hexametaphosphate caused a decrease in the rheological properties to a constant value higher phosphate concentrations. The lowest yield stress was obtained around pH 7.