Since soda ash activates bentonite increasing its swelling capacity, it
is interesting to knowhowit affects the rheology of bentonite slurries in
the presence of calciumbearingminerals. Fig. 10 shows the comparison
of rheograms for 15wt.% bentonite and itsmixtureswith 5 wt.% calcite,
dolomite and quartz at pH 10 andwith 5 wt.% gypsumat pH 8.4 adjusted
by soda ash. The maximum pH soda ash could adjust the bentonite–
gypsum mixture was 8.4. It was found that the gypsum–bentonite
mixture still had the lowest shear stress with the addition of soda ash,
and this pH modifier could not activate bentonite at all. In contrast,
soda ash activated bentonite in the absence and presence of quartz,
dolomite and calcite and increased the shear stress compared to their
counterparts at natural pH. Clearly, calcite enhanced soda ash to activate
bentonite more than dolomite.