Application of Central Composite Design in the Adsorption of Ca(II) on Metakaolin Zeolite

Table 3

Least squares regression data for Ca(II) removal.

Factor	Coefficient estimate	DF	Standard error	for		VIF
				Coeff. = 0
Intercept	2.16972	1	0.2366
A: pH	0.062119	1	0.0110	5.64648	<0.0001	1.01478
B: contact time	0.008357	1	0.0015	5.48405	<0.0001	8.79209
C: concentration	−0.0863	1	0.0065	−13.279	<0.0001	47.681
D: dosage	0.149761	1	0.0463	3.23304	0.0042	1.01478
	0.0005	1	0.0000	10.147	<0.0001	44.4523
BC		1	0.0000	−3.6024	0.0018	14.1953
	0.984