Abstract:
A calcium bentonite clay from Boane region (Mozambique) was subjected to an Na2CO3
activation process. The methylene blue test together with energy-dispersive X-ray spectroscopy
(EDX) analysis indicated the successful ion exchange of Ca2+ by Na+ ions since the cation exchange
capacity (CEC) increased from 67.5 to 74 meq/100 g and the Na/Ca ratio from 2.91 up to 15.8, as the
concentration of Na2CO3, activation temperature, and activation time were varied from 2 to 6 wt.%,
from 25 to 65 C, and from 2 to 4 h, respectively. However, the increase in the CEC did not follow
the same trend as the increase in the Na/Ca ratio, and for the case of Na2CO3 concentration, the
increase in the CEC was limited. The X-ray diffraction (XRD) patterns also confirmed that Ca-rich
bentonite was effectively modified into Na-bentonite since after the activation, the d(001) decreased
from 1.52 nm to 1.30 nm. The statistical design of the experiments showed that as well as the time and
the temperature time linear interactive effect, all the other independent factors and their interactive
effects had a significant influence on the CEC. The response surface methodology (RSM) indicated
that higher values of the CEC can be obtained under the optimal activation conditions of 4 wt.%
Na2CO3, at a temperature of 45 C, and with an activation time of 3 h. A statistical model was used
to predict the CEC, and the R2 value was 0.99529, which denotes a satisfactory result in predicting
the CEC.
