Adsorption and desorption kinetics of toxic organic and inorganic ions using an indigenous biomass; Terminalia ivorensis seed waste

†Jonathan O. Babalola*, †Funmilayo T. Olayiwola, †Joshua O. Olowoyo, †Helen A. Alabi, ‡Emmanuel I. Unuabonah, ǂAugustine E. Ofomaja, ǂ,‡Martins O. Omorogie╬

ǂAdsorption&Catalysis Research Laboratory, Department of Chemistry, Vaal University of Technology, Private Bag X021, Andries Potgieter Boulevard, Vanderbijlpark, 1900, South Africa.

‡Environmental and Chemical Processes Research Group, Department of Chemical Sciences, Redeemer’s University, P.M.B. 230, Ede, Osun State, Nigeria.
†Department of Chemistry, University of Ibadan, 200284, Ibadan, Nigeria.

Electronic Supporting Information (ESI)

Corresponding Authors: ╬ , ╬ , *

Figure S1

Figure S1: Fourier Transform Infra Red spectra of (a) unloaded, (b) Methylene Blue loaded, (c) Congo Red loaded, (d) Cadmium loaded, (e) Lead loaded by Terminalia ivorensis seed waste.

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S1.0 Biosorption studies

One thousand milligrammes/Litre stock solutions were prepared by dissolving accurately weighed amounts of Pb(NO3)2, CdSO4.8H2O, Methylene Blue (MB) and Congo Red (CR) in 1 L of de-ionised water. Experimental solutions were prepared by serial dilution of the stock solutions into various working concentrations. The initial pH values of experimental solutions were adjusted using 0.1 M HCl or 0.1 M NaOH solution and the pH values were read by the Jenway 3520 pH meter.

The pH study for the biosorption of Cd2+, Pb2+, MB and CR by TISW was carried out. As the pH of MB solutions increased from 2.0-12.0 and the pH of CR solutions increased from 2.0-7.0, the colour intensities of these solutions changed. For this study, the colour stability of MB and CR solutions was pH dependent. Also, 25 mg of TISW was contacted with 25 mL of 100 mg L-1 of aqueous solutions of Cd2+, Pb2+, MB and CR in 100 mL plastic containers and agitated in a thermostatic shaker (Haake Wia Model) at 200 rpm for 180 min and at a temperature of 300 K. The Cd2+ and Pb2+ solutions were adjusted from pH 2.0-7.0 and the MB and CR solutions were also adjusted from pH 2.0-12.0. Thereafter, the suspensions were centrifuged and the supernatants were collected for residual Cd2+, Pb2+ and MB, CR concentrations using Flame Atomic Absorption Spectrophotometer (Buck Scientific 205 Model) for Cd2+ and Pb2+, and UV/Visible Spectrophotometer (Cecil Model) at λmax=666 nm for MB and λmax=496 nm for CR.

The influence of biosorbent dose on the adsorption of Cd2+, Pb2+, MB and CR was carried out by contacting 10-1000 mg of TISW with 25 mL of 100 mg L-1 of Cd2+, Pb2+, MB and CR solutions in 100 mL plastic containers at the pH of maximum uptake, agitated in a thermostatic shaker (Haake Wia Model) at 200 rpm for 180 min and at a temperature of 300 K. The suspensions were centrifuged and the supernatants were collected for residual Cd2+, Pb2+ and MB, CR concentrations using Flame Atomic Absorption Spectrophotometer (Buck Scientific 205 Model) for Cd2+ and Pb2+, and UV/Visible Spectrophotometer (Cecil Model) at λmax=666 nm for MB and λmax=496 nm for CR.

The influences of agitation time and temperature on the adsorption of Cd2+, Pb2+, MB and CR was carried out by the agitation of 25 mg of TISW with 25 mL of 100 mg L-1 of Cd2+, Pb2+, MB and CR solutions in 100 mL plastic containers at the pH of maximum uptake, from 0.5-180 min (agitation time) and 300-340 K (temperature), agitated in a thermostatic shaker (Haake Wia Model) at 200 rpm. The suspensions were centrifuged and the supernatants were collected for residual Cd2+, Pb2+ and MB, CR concentrations using Flame Atomic Absorption Spectrophotometer (Buck Scientific 205 Model) for Cd2+ and Pb2+, and UV/Visible Spectrophotometer (Cecil Model) at λmax=666 nm for MB and λmax=496 nm for CR.

The influence of initial solute ion concentration on the adsorption of Cd2+, Pb2+, MB and CR was carried out by agitating 25 mg of TISW with 25 mL of 25-500 mg L-1 of Cd2+, Pb2+, MB and CR solutions in 100 mL plastic containers at the pH of maximum uptake, agitated in a thermostatic shaker (Haake Wia Model) at 200 rpm for 180 min and at a temperature of 300 K. The suspensions were centrifuged and the supernatants were collected for residual Cd2+, Pb2+ and MB, CR concentrations using Flame Atomic Absorption Spectrophotometer (Buck Scientific 205 Model) for Cd2+ and Pb2+, and UV/Visible Spectrophotometer (Cecil Model) at λmax=666 nm for MB and λmax=496 nm for CR.

The various amounts of CR, MB, Cd2+ and Pb2+ adsorbed onto TISW, (mg/g) were calculated by difference using;

(1)

where , , , , , and are the number of experimental data points, maximum experimental data point, amounts of solute ions adsorbed at equilibrium by TISW (mg/g), initial concentration of solute ions (mg/L), final concentration of solute ions at equilibrium (mg/L), mass of TISW (g) and volume of the solute ions (L) respectively.

Experimental data were fitted with some equilibrium, kinetic and thermodynamic models, which are Freundlich model [1], Langmuir model [2], Temkin model [3], pseudo-first order model [4], pseudo-second order model [5], Weber-Morris intraparticle diffusion model [6] and Erying thermodynamic model [7] respectively. The mathematical forms (linear equations) of these models are given as;

Freundlich model (2)

Langmuir model (3)

Temkin model (4)

pseudo-first order model (5)

pseudo-second model (6)

intraparticle diffusion model (7)

Erying thermodynamic equation (8)

Where , , , , , ,, , , , , , , , , and , are Freundlich constant (L/mg)1/n(mg/g), an empirical constant that represents the adsorption affinity, Langmuir adsorption constant (L mg-1), for a complete monolayer (mg/g), is related to , Temkin binding constant in (L mg-1), amounts of solute ions adsorbed at time (min) by TISW (mg/g), pseudo-first order rate constant (min-1), pseudo-second order rate constant (g mg-1 min-1), entropy change (J mol-1 K-1), enthalpy change (J mol-1), universal gas constant (8.314 J mol-1 K-1), absolute temperature (K), Weber-Morris intraparticle diffusion constant (mg/g min1/2), is a constant that represents boundary layer thickness, Boltzmann constant (1.381×10-23 J K-1) and Planck constant (6.626× 10-34 J s) respectively.

To maximise the use of TISW, desorption study was carried out at two different concentrations of HNO3. Twenty five milliliters of 0.01 and 0.1 M HNO3 were added to 25 mg of TISW loaded with 50 mg/L of Cd2+, Pb2+ and MB, CR. These suspensions were agitated in a thermostatic shaker (Haake Wia Model) at 200 rpm for 1-30 min at 300 K. The suspensions were centrifuged and the supernatants were collected for residual Cd2+, Pb2+ and MB, CR concentrations using Flame Atomic Absorption Spectrophotometer (Buck Scientific 205 Model) for Cd2+ and Pb2+, and UV/Visible Spectrophotometer (Cecil Model) at λmax=666 nm for MB and λmax=496 nm for CR. The percentage of solute ions desorbed was calculated using;

(9)

References

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2. Langmuir I (1916) The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 40: 1361-1403

3. Temkin M, Pyzchev V (1939) Kinetics of the synthesis of ammonia on promoted iron catalyst. J. Phys. Chem. (USSR) 13: 851-855

4. Lagergren S (1898) About the theory of so-called adsorption of soluble substances. Kungliga SVenska Vetenskapsakademiens Handlingar. Band. 124: 1-39

5. Ho YS, McKay G (1999) Batch lead(II) removal from aqueous solution by peat: equilibrium and kinetics. Trans Chem. E. B 77: 165-173

6. Weber Jr WJ, Morris JC (1963) Kinetics of adsorption on carbon from solution. J. Sanit. Eng. ASCE 89: 31-59

7. Ho YS, Ng JCY, Mckay G (2000) Kinetics of pollutant sorption by biosorbents: review. Sep. Purif. Meth. 29: 186-232

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