Comparison of Activated Carbon and Physic Seed Hull for the Removal of Malachite Green Dye from Aqueous Solution

Abstract

In the present work, the effectiveness of physic seed hull, PSH (Jatropha curcas L.), as an alternative low-cost adsorbent for the removal of malachite green (MG) dye from simulated wastewater has been studied. It has been observed that PSH has remarkable adsorption capacity compared to granular activated carbon. The PSH adsorbent was characterized by SEM-EDX, BET, CHNS, zeta potential, and FTIR techniques. The adsorption behaviors such as adsorption kinetics, adsorption dynamics, and adsorption isotherms of PSH for the removal of MG dye from aqueous solution were studied in detail. The kinetic data fitted well with the pseudo second-order kinetic model for MG adsorption. Langmuir isotherm was found to be the model best fitted to describe the adsorption process.

Appendix

The dye concentration retained in the adsorbent phase:

$$ {q}_t=\frac{\left(\;{C}_0-{C}_t\right)\;V}{m} $$

(1)

The Lagergren pseudo first-order model (Lagergren and Svenska 1898):

$$ \log\;\left({q}_{\mathrm{e}}-{q}_t\right)\kern0.36em =\kern0.36em \log \kern0.24em {q}_{\mathrm{e}}-\frac{K_1}{2.303}t $$

(2)

Pseudo second-order model (Jain 2001; Ho and Mckay 1998):

$$ \frac{\mathrm{dq}}{\mathrm{dt}}={K}_2\;{\left(\;{q}_{\mathrm{e}}-{q}_t\;\right)}^2 $$

(3)

Integrating and applying boundary conditions t = 0 to t = t and q = 0 to q = q _t gives:

$$ \frac{t}{q_t}=\frac{1}{K_2\;{q}_{\mathrm{e}}^2}+\frac{1}{q_{\mathrm{e}}}\;t $$

(4)

A plot between t/q _t versus t allows the value of the constants K ₂ (g/mg h) and q_e (mg/g) to be calculated. The constant K₂ is used to calculate the initial sorption rate h, at t → 0, as follows:

$$ h\kern0.36em ={K}_2\;{q}_{\mathrm{e}}^2 $$

(5)

The linearized form of Langmuir isotherm (Langmuir 1918):

$$ \frac{1}{q_{\mathrm{e}}}=\left(\frac{1}{K_{\mathrm{a}}\;{q}_{\mathrm{m}}}\right)\;\frac{1}{C_{\mathrm{e}}}\kern0.36em +\frac{1}{q_{\mathrm{m}}} $$

(6)

Dimensionless constant separation factor R_L (Hall et al. 1966):

$$ {R}_{\mathrm{L}}=\frac{1}{1+{\mathrm{bC}}_0} $$

(7)

The value of R_L indicates R_L = 1, favorable (0 < R_L < 1) or irreversible (R_L = 0).

The linearized form of Freundlich adsorption isotherm (Adamson 1967; Freundlich 1926):

$$ \ln\;{q}_{\mathrm{e}}=\ln {K}_{\mathrm{f}}+\frac{1}{n}\left(\ln {C}_{\mathrm{e}}\right) $$

(8)

1.1 Notation

A:

Area, m²

V:

Volume, m³

R_L:

Separation factor

C ₀ :

Initial concentration, mg/L

C_e:

Equilibrium concentration, mg/L

h :

Initial adsorption rate

k ₁ :

Rate constant for first-order model, per minute

k ₂ :

Rate constant for second-order model, g/mg h

k _a :

Rate constant for Langmuir, mg/g

k _f :

Rate constant for Freundlich

n :

adsorption intensity for Freundlich

b :

Langmuir constant, L/mg

q _e :

Adsorbed amount at equilibrium, mg/g

q _t :

Adsorbed amount at t time, mg/g

q _m :

Adsorbed amount at maximum monolayer, mg/g

t :

Time, min

t _1/2 :

Half-time for adsorption, min

m :

Mass, g

R ² :

Regression correlation coefficient

T :

Temperature, °C

1.2 Greek letters

Ǻ:

Angstrom

λ _max :

Maximum wavelength, nm