The experimental data obtained were analyzed statistically using a multi regression analysis to obtain quadratic response surface model for the leaching of alumina from the clay. The resulting quadratic polynomial model equation obtained for the analysis of alumina dissolution from Ozoro clay using hydrochloric acid is presented in Equation (1) as follows:
\begin{equation} Y_{\ Al2O3}\ =\ 79.56\ +\ 3.39X_{1}\ +2.23X_{2}\ +\ 3.54X_{3}\ +\ 1.64X_{4}\ -1.94X_{5}\ \ 0.55X_{1}X_{2}-0.76X_{1}X_{3}\ \ 0.24X_{1}X_{4}\ \ 0.31X_{1}X_{5}-\ 0.91X_{2}X_{3}\ \ 0.87X_{2}\ \ 0.70X_{2}X_{5}+\ 0.91X_{3}X_{4}-\ 0.41X_{3}X_{5}\ \ 2.05X_{4}X_{5}\ \ 3.01X_{1}^{2}\ \ 3.72X_{2}^{2}\ -3.67X_{3}^{2}-\ \ 4.22X_{4}^{2}-3.41X_{5}^{2}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (1)\nonumber \\ \end{equation}
The summary of the model adequacy tested using the sequential model sum of squares is presented in Table 4 as follows:
Table 4: Adequacy of the model