Adsorption studies on coir pith for heavy metal removal

Figures & data

Table 1. Characteristics of coir pith.

Parameters	Value
Lignin (%)	29.6
Hollocellulose (%)	42.3
Bulk density (g/cc)	0.097
Particle density (g/cc)	0.985
Pore space volume (%)	88.5
Particle size (micron)	344

Figure 1. Scanning electron microscopic (SEM) photograph of raw coir pith at 50 μm magnification before adsorption of heavy metals.

Figure 2. Scanning electron microscopic photograph of raw coir pith at 10 μm magnification.

Figure 3. Scanning electron microscopic (SEM) photograph of raw coir pith at 50 μm magnification after the adsorption of heavy metals.

Figure 4. Effect of pH variation on removal efficiency (%) of metals.

Figure 5. Effect of varying metal concentration on metal removal efficiency.

Table 2. Effect of adsorbent dosage on the adsorption of heavy metals.

Heavy metals	Efficiency of removal of metals (%)for varying adsorbent dosage
	0.5 g	1 g	2 g	3 g	4 g	5 g
Ni	76	82	80	79	78	77
Cu	70	74	82	80	79	77
Zn	80	88	85	83	80	80

Table 3. Competitive adsorption of zinc, copper and nickel onto coir pith.

Time (min)	Zinc concentration		Copper concentration		Nickel concentration
	Final concentration (ppm)	% Removal	Final concentration (ppm)	% Removal	Final concentration (ppm)	% Removal
0	50	0	50	0	50	0
10	7.31	85.38	7.7	84.6	10.12	79.76
20	7.04	85.92	7.15	85.7	13.09	73.82
30	7.08	85.84	7.15	85.7	12.98	74.04
40	6.27	87.46	6.38	87.24	10.34	79.32
50	6.71	86.58	7.37	85.26	11.33	77.34
60	6.71	86.58	7.44	85.12	11.88	76.24

Table 4. Pseudo-first-order kinetic study for the adsorption of nickel at different concentrations (mg/L).

Time (min)	10 mg/L		20 mg/L		30 mg/L		40 mg/L		50 mg/L
	(qe = 1.275)		(qe = 2.04)		(qe = 2.925)		(qe = 3.255)		(qe = 3.57)
	q (mg/g)	log(qe − q)	q (mg/g)	log(qe − q)	q (mg/g)	log(qe − q)	q (mg/g)	log(qe − q)	q (mg/g)	log(qe − q)
4	0.81	−0.33	1.55	−0.31	2.28	−0.19	2.91	−0.46	3.05	−0.28
8	0.87	−0.39	1.8	−0.62	2.45	−0.32	2.99	−0.57	3.11	−0.33
12	0.98	−0.52	1.88	−0.78	2.66	−0.57	3.12	−0.87	3.23	−0.47
16	1.16	−0.92	1.95	−1.05	2.72	−0.68	3.21	−1.35	3.39	−0.74

Figure 6. Plots of the pseudo-second-order model for different concentrations of nickel.

Table 5. Comparison between model parameters of Lagergren pseudo-first-order and pseudo-second-order kinetic models for nickel.

Co (ppm)	qe exp. (mg/g)	First-order model			Second-order model
		K1 (min^−1)	qe.cal (mg/g)	R^2	K2 × 10^−3 (g/mg min)	qe.cal (mg/g)	R^2
10	1.275	0.108	0.855	0.854	0.2688	1.34	0.996
20	2.04	0.136	0.809	0.986	0.5311	2.066	0.999
30	2.925	0.096	0.977	0.976	0.294	2.976	0.999
40	3.255	0.168	0.845	0.927	0.7211	3.278	0.999
50	3.57	0.0875	0.845	0.895	0.284	3.649	0.999

Table 6. Isotherm constants for the adsorption of nickel, copper and zinc onto coir pith.

Metal	Langmuir constants			Freundlich constants			D–R constants
	Qo (mg/g)	b (1/mg)	R^2	n	Kf (L/g)	R^2	β	qm (mg/g)	R^2	E (kJ/mol)
Ni	4.17	0.21	0.99	2.67	1.09	0.98	0.67	3.13	0.80	0.86
Cu	2.06	0.33	0.99	3.07	0.69	0.98	0.39	1.65	0.89	1.14
Zn	5.49	0.30	0.99	2.63	1.71	0.91	0.28	4.18	0.96	1.33