## 4 Results and Discussions
### Effect of Acid-Activation
The results are illustrated in Table 1.  
The chemical analysis of raw clay (S\({}_{0}\)) proved the presence of silica, alumina, iron and calcium as major constituents, along with traces of sodium, potassium, phosphate and titanium oxides. The higher mass percentage of silica and alumina reveals that clay mineral is an alumino-silicate matter. After acid-activation, the SiO\({}_{2}\) content of clay (S\({}_{0}\)) increased from 49.87% to 50.82%, 52.69% and 67.63% for S\({}_{1}\), S\({}_{2}\) and S\({}_{3}\), respectively. However the content of Al\({}_{2}\)O\({}_{3}\), Fe\({}_{2}\)O\({}_{3}\) and MgO are decreased from 14.27%, 6.07% and 1.46% to 13.58%, 5.56%, 1.23% and to 12.38%, 4.89%, 0.98% and to 9.4%. 1.89%, 0.43%, for S\({}_{1}\), S\({}_{2}\) and S\({}_{3}\), respectively. This may be due to the partial destruction (dissolution) of the octahedral layer (Al,Fe,Mg-O layers) and the exposure of the tetrahedral layers (Si-O layers) in acid solution. The N\({}_{2}\) adsorption/desorption isotherms of raw material and activated clays presented in Figure 9 showed that isotherms are reversible for lower equilibrium pressure but at higher relative pressure, they exhibited a hysteresis loop of H\({}_{3}\) type [39]. Such hysteresis loops exist in the slit-shaped pores or in the ink-bottle pores (pores with narrow necks and wide bodies). \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Samples** & **MgO** & **Fe\({}_{2}\)O\({}_{3}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **SO\({}_{3}\)** & **CaO** & **K\({}_{2}\)O** & **Na\({}_{2}\)O** & **P\({}_{2}\)O\({}_{5}\)** & **TiO\({}_{2}\)** & **ZnO** & **Li.I. at 975 \({}^{o}\)C** \\ \hline
**S\({}_{0}\)** & 1.46 & 6.07 & 14.27 & 49.87 & 0.77 & 7.00 & 1.09 & 0.53 & 0.19 & 1.41 & 0.18 & 17.62 \\
**S\({}_{1}\)** & 1.23 & 5.56 & 13.58 & 50.82 & 0.76 & 0.86 & 1.03 & 0.23 & 0.06 & 1.62 & 0.37 & 16.54 \\
**S\({}_{2}\)** & 0.98 & 4.89 & 12.38 & 52.69 & 0.75 & 0.58 & 0.97 & 0.11 & 0.01 & 1.80 & 0.51 & 15.27 \\
**S\({}_{3}\)** & 0.43 & 1.89 & 9.40 & 67.63 & 0.68 & 0.14 & 0.61 & 0.13 & 0.01 & 2.26 & 0.24 & 11.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical analyses of raw material (S\({}_{0}\)) and acid activated clay samples (S\({}_{1}\), S\({}_{2}\), S\({}_{3}\)). Figure 8: Infra-red spectra of raw material (**S\({}_{0}\)**) and acid-activated clays (**S\({}_{1}\)**, **S\({}_{2}\)**, **S\({}_{3}\)**). The textural properties of raw clay (S\({}_{0}\)) and acid-activated clays (S\({}_{1}\), S\({}_{2}\), S\({}_{3}\)) are presented in Table 2.  
It can be noted that surface area, total pore volume and average pore diameter were changed as the severity of acid treatment was increased. Data presented in Table 2 shows that surface area depends on acid attack but the relation between surface area and acid treatment is non-linear. [PERSON] et al. have reported that surface area increases with acid concentration [25]. As it can be seen from Table 2, acid activation improves the volume of pores. The pore volume was only 0.1374 cm\({}^{3}\)/g for natural clay (S\({}_{0}\)) but after acid treatment it becomes much higher and reaches 0.4558 cm\({}^{3}\)/g for more severe treatment (sample S\({}_{3}\)). Assuming that the pores are cylindrical, the mean pore diameter was calculated from the formula d = 4V\({}_{\rm p}\)/S\({}_{\rm p}\). where, V\({}_{\rm\bf P}\) is the pore volume and S\({}_{\rm p}\) is the specific surface area of the pores. The average pore diameter for starting material (S\({}_{0}\)) is 79.56 A. It decreases for low acid treatment and average condition and then increases at higher conditions for sample S\({}_{3}\), to reach the value of 98.9 A. This can be explained by the fact that acid-activated samples had a greater increase in percentage of pore volume of micro pores than meso pores. As a consequence the lower values of the average pore diameter for samples S\({}_{1}\) and S\({}_{2}\) were obtained compared to that of natural clay.