Abstract

The effect of 48-kHz ultrasound on the adsorption and desorption of phenol from aqueous solutions onto coconut shell-based granular activated carbons was studied at 25 °C. Experiments were performed at different carbon particle sizes (1.15, 2.5, 4.0 mm), initial phenol concentrations (1.06–10.6 mol/m³), and ultrasonic powers (46–133 W). Regardless of the absence and presence of ultrasound, the adsorption isotherms were well obeyed by the Langmuir equation. When ultrasound was applied in the whole adsorption process, the adsorption capacity decreased but the Langmuir constant increased with increasing ultrasonic power. According to the analysis of kinetic data by the Elovich equation, it was shown that the initial rate of adsorption was enhanced after sonication and the number of sites available for adsorption was reduced. The effect of ultrasonic intensity on the initial rate and final amount of desorption of phenol from the loaded carbons using 0.1 mol/dm³ of NaOH were also evaluated and compared.

Keywords: Ultrasound; Adsorption; Desorption; Activated carbons; Phenol

Nomenclature

a

initial adsorption rate defined in Eq. (4) (mol/(kg min))

b

constant defined in Eq. (4) (kg/mol)

C_e

liquid-phase concentration at equilibrium (mol/m³)

C_t

liquid-phase concentration at time t (mol/m³)

C₀

initial liquid-phase concentration (mol/m³)

D_s

diffusivity within the particle (m²/s)

k_ads

adsorption rate constant

k_des

desorption rate constant

K_L

Langmuir constant defined in Eq. (12) (m³/mol)

q

amount of adsorption defined in Eq. (7) (mol/kg)

q_e

amount of adsorption at equilibrium (mol/kg)

q_mon

amount of adsorption corresponding to monolayer coverage (mol/kg)

q_t

amount of adsorption at time t (mol/kg)

r

radial direction of adsorbent particle (m)

r_p

radius of adsorbent particle (m)

R²

correlation coefficient (–)

t

time (s)

V

volume of the solution (m³)

W

weight of the adsorbent used (kg)

Article Outline

Nomenclature

1. Introduction

2. Materials and methods

2.1. Apparatus and solutions

2.2. Activated carbons

2.3. Experimental procedures

3. Results and discussion

3.1. Physical properties of the carbons before and after sonication

3.2. Effect of ultrasound on adsorption rates

3.3. Effect of ultrasound on adsorption equilibrium

3.4. Effect of ultrasound on phenol desorption

4. Conclusions

Acknowledgements

References