Response surface optimisation for activation of bentonite with microwave irradiation

Abstract

In this study, the statistical design of the experimental method was applied on the process of acid activation of bentonite with microwave irradiation. The influence of activation parameters (time, acid normality and microwave heating power) on the selected process response of the activated bentonite samples was studied. The specific surface area was chosen for the process response, because the chemical, surface and structural properties of the activated clay determine and limit its potential applications. The relationship of various process parameters with the specific surface area of bentonite was examined. A mathematical model was developed using a second-order response surface model (RSM) with a central composite design incorporating the above mentioned process parameters. The developed mathematical model helped to predict the variation in specific surface area of activated bentonite with time (5-21 min), acid normality (2-7 N) and microwave heating power (63-172 W). The calculated regression models were found to be statistically significant at the required range and presented little variability. Furthermore, high values of R2 (0.957) and R2 (adjusted) (0.914) indicate a high dependence and correlation between the observed and the predicted values of the response. These high values also indicate that about 96% of the result of the total variation can be explained by this model. In addition, the model shows that increasing the time and acid normality improves the textural properties of bentonites, resulting in increased specific surface area. This model also can be useful for setting an optimum value of the activation parameters for achieving the maximum specific surface area. An optimum specific surface area of 142 m2g-1 was achieved with an acid normality of 5.2 N, activation time of 7.38 min and microwave power of 117 W. Acid activation of bentonite was found to occur faster with microwave irradiation than with conventional heating. Microwave-assisted processes have the potential to develop into a cost efficient route for acid activation of bentonite.