Adsorption of chromium (III) from aqueous solution using vesicular basalt rock

Figures & data

Figure 1. Infrared spectrum of powdered VB sample between wavenumber ranges 4000–400 cm^−1.

Table 1a. Elemental analysis of the VB before adsorption and after adsorption.

Element	Weight %	Atomic %
O K	48.46	63.42
Si K	17.37	14.62
Al K	9.55	6.95
Mg K	0.87	0.7
Ca K	8.8	4.31
Fe K	8.83	3.93
Na K	4.87	5.27
K K	1.25	0.8
Total	100	100

Table 1b. Elemental analysis of the VB before adsorption using EDS spectroscopy.

Element	Weight %	Atomic %
O K	48.46	63.42
Si K	17.37	14.62
Al K	9.55	6.95
Mg K	0.87	0.7
Ca K	8.8	4.31
Fe K	8.83	3.93
Na K	2.64	3.17
K K	0.51	0.6
Cr K	2.97	2.3
Total	100	100

Figure 2. SEM images of VB before (a) and after adsorption (c) of Cr (III); EDS spectra before (b) and after adsorption (d) of Cr (III).

Figure 3. Effect of pH and ionic strength for Cr (III) adsorption onto the VB (dose 50 g L⁻¹; Cr (III) conc. 100 mg L⁻¹; temperature 25 ± 0.5°C) (a); Determination of pHpzc of Crushed VB in 0.01 mol L⁻¹ KNO₃ solution (b).

Figure 4. Effect of contact time on adsorption of different concentrations of Cr (III) ions (20, 60 and 100 mg L⁻¹) on VB. (Adsorbent dose 50 g L⁻¹, solution pH 6 and reaction temperature 25 ± 0.5°C).

Table 2. Kinetic parameters for Cr (III) adsorption onto VB

$C_o$$\left(mg{L}^{-1}\right)$	Pseudo-first-order			Pseudo-second-order				Elovich
	$k_1$(min^−1)	$q_e$(m$g{g}^{-1})$	R^2	$k_2$($mi{n}^{-1}$)	$q_e$($mg{g}^{-1})$	R^2	$q_e$ (Mg g^−1)	α(mg g^−1 min^−1)	$\beta$(g mg^−1)	$R^2$
20	0.009	0.269	0.967	0.067	0.384	0.993	0.361	0.039	16.129	0.934
60	0.020	0.746	0.982	0.039	0.921	0.997	0.897	0.140	6.993	0.946
100	0.017	0.553	0.998	0.068	0.997	0.999	1.009	0.705	7.937	0.980

Figure 5. Adsorption kinetics: pseudo-first order kinetic linear plot (a); pseudo-second order kinetic linear plot (b) and Elovich kinetic linear plots for adsorption of Cr (III) onto VB {initial concentration (20, 60 and 100 mg L⁻¹), solution pH 6,adsorbent dosage 50 g L⁻¹, temperature 25 ± 0.5°C)}.

Table 3. Adsorption mechanism models for the adsorption of Cr (III) onto the VB

$C_o$$\left(mg{L}^{-1}\right)$	Adsorption mechanism
	Intraparticle diffusion Model			Bangham model			Boyd model
	$k_{id}$ (mg g^−1  min^−0.5)	$C$	R^2	$k_o$	$\alpha$	R^2	R^2
20	0.013	0.269	0.912	1.328	0.488	0.946	0.971
60	0.024	0.746	0.881	−1.21	0.372	0.946	0.947
100	0.029	0.553	0.830	−1.137	0.233	0.966 1.009	0.928

Figure 6. Linear plots of Intraparticle Diffusion (a), Bangham (b), and Boyd models (c) for adsorption mechanism of Cr (III) onto the VB rock.

Table 4. Adsorption isotherm models

Isotherms	Non-linear form	Linear form	Reference	Equations no
Langmuir	$q_e=q_{max}\frac{k_L{C}_e}{1+k_L{C}_e}$	$\frac{C_e}{q_e}=\frac{1}{b{q}_{max}}+\frac{C_e}{q_{max}}$	(Langmuir, 1918)	(12)
Freundlich	$q_e=k_f{C_e}^{1/n}$	$log{q}_e=log{K}_f+\frac{1}{n}log{C}_e$	(Freundlich, 1906)	(13)
Temkin	$q_e=BlogA{C}_e$	$q_e=BlogA+Blog{C}_e$	(Temkin & Pyzhev, 1940)	(14)

Figure 7. The fitting of Langmuir (a), Freundlich (b) and Temkin (C) isotherms of Cr (III) adsorption onto VB volcanic rock, pH 6, dose 50 g L^−1.

Table 5. Langmuir, Freundlich and Temkin isotherm parameters for adsorption of Cr (III) onto VB

	Langmuir	Value	Freundlich	Value	Temkin	Value
Linear plots	qmax(mg g^−1)	0.872	KF	2.153	A (L g^−1)	0.58
	b (Lmg^−1)	1.04	1/n	0.207	B (L g^−1))	1.384
	R^2	0.998	R^2	0.878	R^2	0.961
Non-linear plots	qmax(mg g^−1)	0.91	KF	2.01	A (L g^−1)	0.63
	b (Lmg^−1)	1.12	1/n	0.387	B (L g^−1)	0.987
	R^2	0.978	R^2	0.986	R^2	0.975

Table 6. Comparison of adsorption capacity Cr (III) onto VB with other adsorbents

Adsorbents	pH	Particle size(μm)	Adsorbent dose(g L^−1)	Metal conc. (mg L^−1)	Adsorption capacity (mg g^−1)	Reference
Bentonite	2	-	50	50	0.570	(Khan, Rehman, & Khan, 1995)
Bentonite	7	Up to 160	20	100	4.640	(Chen et al., 2012)
kaolinite	2	-	25	100	1.924	(Koppelman, Emerson, & Dillard, 1980)
Natural Scolecite	6	<200	10	50	3.000	(Bosco, Jimenez, & Carvalho, 2005)
Kaolin	4.5	-	25	300	0.898	(Liu et al., 2016)
VB	6	90–500	50	100	0.976	This study

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