Removal of Hexavalent Chromium from Aqueous Solutions Using Natural Zeolite Coated with Magnetic Nanoparticles: Optimization, Kinetics, and Equilibrium Studies

Table 5

CCD based experimental design (actual and coded levels) and responses (removal efficiencies).

Run order	Design type	Actual levels				Coded levels				Removal efficiency (%)
		Dose; (g/L)	Time; (min)	Cr(VI) conce; (mg/L)	pH	A	B	C	D	Actual	Predicted	Residue
1	Center	1.2	45	50	4.5	0	0	0	0	55.74	56.28	-0.54
3		1.2	45	50	4.5	0	0	0	0	54.24	56.28	-2.04
7		1.2	45	50	4.5	0	0	0	0	57.65	56.28	1.37
10		1.2	45	50	4.5	0	0	0	0	57.27	56.28	0.99
11		1.2	45	50	4.5	0	0	0	0	55.36	56.28	-0.92
12		1.2	45	50	4.5	0	0	0	0	60.98	56.28	4.70
4	Factorial	0.8	60	70	3	-1	1	1	-1	73.25	73.15	0.10
5		0.8	60	30	3	-1	1	-1	-1	76.66	77.43	-0.77
8		1.6	30	30	3	1	-1	-1	-1	73.23	71.64	1.59
13		0.8	30	30	3	-1	-1	-1	-1	65.87	64.91	0.96
14		1.6	30	70	6	1	-1	1	1	39.81	38.64	1.17
15		1.6	30	30	6	1	-1	-1	1	57.92	56.72	1.20
16		0.8	60	70	6	-1	1	1	1	63.45	64.63	-1.18
17		0.8	30	70	6	-1	-1	1	1	49.91	49.91	0
18		0.8	30	70	3	-1	-1	1	-1	55.95	55.55	0.40
20		1.6	60	30	3	1	1	-1	-1	94.88	93.57	1.31
22		0.8	60	30	6	-1	1	-1	1	66.38	66.38	0
23		1.6	60	30	6	1	1	-1	1	75.76	75.76	0
24		1.6	60	70	3	1	1	1	-1	78.29	78.06	0.23
25		1.6	60	70	6	1	1	1	1	63.12	62.77	0.35
29		0.8	30	30	6	-1	-1	-1	1	56.92	56.75	0.17
30		1.6	30	70	3	1	-1	1	-1	52.35	51.04	1.31
2	Axial	0.4	45	50	4.5	-2	0	0	0	53.99	52.98	1.01
6		1.2	45	90	4.5	0	0	2	0	55.28	56.61	-1.33
9		2	45	50	4.5	2	0	0	0	55.13	57.85	-2.72
19		1.2	45	10	4.5	0	0	-2	0	76.59	77.97	-1.38
21		1.2	45	50	1.5	0	0	0	-2	87.28	88.99	-1.71
26		1.2	15	50	4.5	0	-2	0	0	38.88	41.43	-2.55
27		1.2	75	50	4.5	0	2	0	0	78.91	78.07	0.84
28		1.2	45	50	7.5	0	0	0	2	65.55	65.55	0