Low Energy Mesoporous Silica Recovery from a Nigerian Kaolinite …
91
Fig. 2 SEM (left) and TEM (right) images of HCl-4M-100 °C. (Color figure online)
with type IV adsorption isotherm which occurs via multilayer adsorption followed
by capillary condensation [7].
Isotherms with type H3 hysteresis are characterized with non-rigid aggregates
of plate-like particles or assemblages of slit-shaped pores noticed in the electron
microscopy studies (Fig. 2) [8].
Kinetics of Dissolution Studies
The variation of the leaching rate with leaching time for the different leaching parameters such as concentration, temperature and solid-to-liquid ratio. It is evident that
acid concentration and reaction temperature plays significant role in the dissolution
activities [9–11]. The phase ratio of the leachants to the calcined kaolinite showed
that at a lower solid-to-liquid ratio, the rate of dissolution is higher [12]. Hence, the
dissolution rates were studied by subjecting the leaching results to the various reaction kinetic models. All tested models fit the data and most data point lies outside
the 95% prediction interval. The ability of so many different reaction models to
give good fits is due to the possible appearance of X in various forms in the model
functions [12] (Fig. 3).
The correlation coefficient (R
2 ) of Avrami model was always >0.98 as compared
with the other models, the Avrami model is more suitable for describing the dissolution subsequent pore formation with average Avrami model parameter (n) of 0.80.
Consequently, the plots of lnk versus 1000/T in Fig. 4 were used to calculate apparent
activation energy of the leaching reaction. The calculated apparent activation energy
of 7.22 kJ/mol suggests the leaching process is controlled by the diffusion process
[13].
91
Fig. 2 SEM (left) and TEM (right) images of HCl-4M-100 °C. (Color figure online)
with type IV adsorption isotherm which occurs via multilayer adsorption followed
by capillary condensation [7].
Isotherms with type H3 hysteresis are characterized with non-rigid aggregates
of plate-like particles or assemblages of slit-shaped pores noticed in the electron
microscopy studies (Fig. 2) [8].
Kinetics of Dissolution Studies
The variation of the leaching rate with leaching time for the different leaching parameters such as concentration, temperature and solid-to-liquid ratio. It is evident that
acid concentration and reaction temperature plays significant role in the dissolution
activities [9–11]. The phase ratio of the leachants to the calcined kaolinite showed
that at a lower solid-to-liquid ratio, the rate of dissolution is higher [12]. Hence, the
dissolution rates were studied by subjecting the leaching results to the various reaction kinetic models. All tested models fit the data and most data point lies outside
the 95% prediction interval. The ability of so many different reaction models to
give good fits is due to the possible appearance of X in various forms in the model
functions [12] (Fig. 3).
The correlation coefficient (R
2 ) of Avrami model was always >0.98 as compared
with the other models, the Avrami model is more suitable for describing the dissolution subsequent pore formation with average Avrami model parameter (n) of 0.80.
Consequently, the plots of lnk versus 1000/T in Fig. 4 were used to calculate apparent
activation energy of the leaching reaction. The calculated apparent activation energy
of 7.22 kJ/mol suggests the leaching process is controlled by the diffusion process
[13].