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