Independent variables Symbols Range and levels Range and levels Range and levels Range and levels Range and levels
-1 0 +1
Calcinations temp. (oC) X1 89.9 400 625 900 1160
Leaching temp. (oC) X2 13.9 45 67.5 85 121
Acid conc. (mol/cm3) X3 -1.22 0.5 1.75 3.0 4.72
Liquid-solid ratio (cm3/g) X4 -4.27 4 10 16 24.27
Stirring speed (rpm) X5 -344 90 405 720 1154