2.2 Design of Experiment
The combined influence of five factors (calcinations temperature, leaching temperature, acid concentration, liquid-solid ratio and stirring speed) on the yield of alumina from the dissolution process using HCl was studied to derive a model. The design was done using the Central Composite Rotatable Design of 25 = 32 plus six centre points and (2x6=12) star points giving a total of 50 experiments. Table 1 is a summary of the factors levels with the corresponding real values while Table 2 is the experimental design based on the range of the variables in Table 1.
Table 1: Levels of the process variables