Study of equilibrium and kinetic adsorption of rhodamine B onto purified bentonite clays

Duarte Neto, J. F.; Pereira, I. D. S.; Silva, V. C. da; Ferreira, H. C.; Neves, G. de A.; Menezes, R. R.

doi:10.1590/0366-69132018643722429

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Articles • Cerâmica 64 (372) • Oct-Dec 2018 • https://doi.org/10.1590/0366-69132018643722429 linkcopy

Study of equilibrium and kinetic adsorption of rhodamine B onto purified bentonite clays

Estudo do equilíbrio e da cinética de adsorção da rodamina B em bentonitas purificadas

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Currently, the removal of contaminants such as wastewater dye has become an essential task. In view of this, improving the performance of the adsorbents in order to improve the adsorption technique and reduce the total cost of the adsorption process is of great interest to the industrial sector. This study investigated the adsorption process of natural and purified bentonite clay adsorbents, using rhodamine B in an aqueous media. Rhodamine B is very toxic to aquatic organisms and may cause long-term adverse effects in the aquatic environment. These clays were used both in the natural form and after purification by centrifuge. All adsorbents were characterized. The kinetics and equilibrium isotherms were studied. In equilibrium, the Freundlich isotherm model was the best fit to the experimental data. In kinetics study, the data were best fit by the pseudo-second order model. The purified clays efficiently removed the rhodamine B.

Keywords: adsorption; bentonite; purification; rhodamine B

Table I Granulometric compositions of the natural and centrifuged clay samples.

Sample	D<2µm	2<D<20µm	D>20µm	Average diameter
BR	24.71%	72.65%	2.64%	6.10 µm
BRPuri	98.14%	1.86%	0.0	0.98 µm
RF	19.91%	78.18%	1.92%	5.91 µm
RFPuri	100.0%	0.0	0.0	0.62 µm
VI	21.27%	73.75%	4.98%	6.59 µm
VIPuri	100.0%	0.0	0.0	0.62 µm

Table II Chemical analysis of the natural and purified clays (wt%).

Constituent	BR	BRPuri	RF	RFPuri	VI	VIPuri
Si_O2	45.8	43.0	45.2	43.9	45.9	44.5
Al₂O₃	19.6	23.6	20.8	22.7	21.0	25.6
Fe₂O₃	2.5	1.5	6.4	6.0	6.3	5.9
CaO	2.9	1.9	2.3	0.9	1.4	0.6
MgO	3.1	2.9	2.9	2.8	3.1	2.3
Other oxides	1.3	1.0	1.5	1.2	1.4	2.5
LOI*	24.8	26.1	20.9	22.5	20.9	18.6

Table III Parameters of adsorption isotherms.

Model	Parameter	BR	BRPuri	RF	RFPuri	VI	VIPuri
Langmuir	Q_max (mg.g^-1)	76.33	58.82	58.82	344.82	123.46	344.82
	K_L (10^-2 L.mg^-1)	1.22	2.08	1.17	0.64	0.11	0.11
	R²	0.66	0.19	0.40	0.29	0.54	0.50
Freundlich	1/n	0.81	0.82	0.73	0.95	0.84	0.99
	K_F (mg^1-1/n.L^1/n.g^-1)	1.32	1.61	2.35	2.23	1.13	2.90
	R²	0.99	0.99	0.99	0.99	0.99	0.99
Temkin	b_T (J.mol^-1)	117.12	64.79	85.00	80.22	83.23	87.30
	K_T (L.mg^-1)	0.14	4.07	0.47	0.30	2.34	1.58
	R²	0.68	0.89	0.71	0.77	0.73	0.77
D-R	Q_max (mg.g^-1)	22.46	60.70	30.41	43.15	35.62	37.11
	K_D (mol².J^-2)	1.00	4.00	5.00	2.00	3.00	1.00
	R²	0.66	0.91	0.76	0.76	0.72	0.63

Table IV Kinetic parameters.

Model	Parameter	BR	BRPuri	RF	RFPuri	VI	VIPuri
Pseudo-first order	Q_max (mg.g^-1)	13.84	9.74	13.92	8.62	11.73	8.72
	K₁ (min^-1)	<0.01	<0.01	<0.01	<0.01	<0.01	<0.01
	R²	0.69	0.23	0.50	0.66	0.59	0.82
Pseudo-second order	Q_max (mg.g^-1)	7.56	11.41	7.48	11.45	9.55	11.05
	K₂ (g.mg^-1.min^-1)	0.064	0.267	0.058	0.046	0.113	0.027
	R²	0.99	0.99	0.99	0.99	0.99	0.99
Intraparticle diffusion	C_L (mg.g^-1)	6.86	10.97	6.81	12.61	8.97	12.55
	K_I (g.mg^-1.min^-1/2)	0.042	0.032	0.038	0.071	0.038	0.084
	R²	0.72	0.35	0.47	0.71	0.75	0.80

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[TFN1] * - loss on ignition at 1000 °C.