Table 1: The 23 full factorial design and the data used for modelling. Experiments 5, 6, and 7 represent the replicates of the center point of the full factorial, and experiment 12 is an additional center point for one of the corners of the experimental plan. The total number of experiments was 24.

Number , °COxalic acidSyntheticIndustrial
, mol/L Fe, mg/L Fe, mg/L

1150.0819422576
2350.0819962536
3500.0831814021
4150.3375234014
5350.33110568114
6350.33117047252
7350.33116737825
8500.33135228307
9150.60180413193
10350.602100110215
11500.602122411289
12250.47160517332