Optimization of adsorption of Cr(VI) from aqueous solution by adsorbent prepared from Leucaena leucocephala seed shell using design of experiment

ABSTRACT

The activated carbon was prepared from Leucaena leucocephala seed shell and used as adsorbent for the removal of hexavalent chromium [Cr(VI)] from aqueous solution. The variables affecting the adsorption process were optimized using response surface methodology (RSM). ANOVA revealed that all the variables studied had significant effects on the process. The obtained data showed that 71.49 mg/L initial Cr(VI) concentration, 4.22 solution pH, 0.57 g adsorbent dosage and 26.2 °C temperature resulted in 95.62% adsorption. Equilibrium adsorption isotherm and kinetic studies showed that Freundlich isotherm and the pseudo-second-order kinetic model fitted well to the experimental data.

KEYWORDS:

• Activated carbon
• hexavalent chromium
• characterization
• kinetic
• isotherm

List of Symbols

$\lambda$	=	X-ray wavelength [m]
$\theta$	=	angle of diffraction [°]
$\beta$	=	full width at half maximum of the peak
R	=	Cr(VI) removal efficiency
bis	=	regression coefficients for linear terms
bik	=	regression coefficients for quadratic terms
$C_o$	=	initial concentration of Cr(VI) in aqueous solution [mg/L]
$C_e$	=	equilibrium concentration of Cr(VI) in aqueous solution[mg/L]
V	=	volume of the Cr(VI) solution [L]
w	=	weight of adsorbent used [g]
$q_e$	=	amount of Cr(VI) adsorbed at equilibrium [mg/g]
$q_{max}$	=	maximum adsorption capacity [mg/g]
b	=	Langmuir equilibrium constant [L/mg]
$R_L$	=	separation factor
$k_F$	=	adsorption capacity of the adsorbent [mg/g(L/mg)1/n]
n	=	adsorption intensity
$q_t$	=	amount of Cr(VI) adsorbed at time t [mg/g]
$k_1$	=	pseudo-first-order rate constant [(min−1]
$k_2$	=	pseudo-second-order rate constant [g mg−1min−1]
C	=	initial Cr(VI) concentration, [mg/L]
p	=	solution pH
d	=	adsorbent dosage [g]
T	=	temperature [°C]
$k_D$	=	intra-particle diffusion rate constant [mg g−1min−0.5]
C	=	intercept
R	=	universal gas constant (8.314 J/mol K)
A	=	equilibrium binding constant (L/mg)