Table 5: Experimental design and result.

No. of experimentsX1: HCl (%)X2: temperature (°C)X3: stirring (rpm)X4: S/L ratio (%)X5: time (min)Y: response (ppm)

1132510020603.870
2232510020308.932
3126510020304.801
42365100206013.970
5132530020303.104
62325300206011.452
7136530020607.523
82365300203010.134
9132510050302.055
10232510050604.833
11136510050602.144
12236510050304.343
13132530050602.020
14232530050305.343
15136530050302.430
16236530050606.343
17184520035452.903
18184520035453.010
19184520035453.001
20184520035453.020
21184520035453.890