02-02-2013, 11:08 AM
Removal of an azo-metal complex textile dye from colored aqueous solutions using an agro-residue
1Removal of an azo-metal.pdf (Size: 497.89 KB / Downloads: 53)
INTRODUCTION
The pine leaves which are an agricultural residue were used in its natural form as biosorbent for the removal
of Acid Yellow 220 (AY 220) dye from aqueous solutions. The sorption experiments were carried out as a
function of solution pH, biosorbent dosage, biosorbent size, dye concentration, temperature, contact time and
ionic strength. The sorption isotherms closely followed the Langmuir model. The monolayer sorption capacity
of the pine leaves for AY 220 was found as 40.00 mg g−1. It was shown that pseudo-second order equation
could best describe the sorption kinetics. The thermodynamic data indicated that the sorption system was
spontaneous, endothermic and physical process. Based on the results of present investigation.
Introduction
Synthetic dyes are among the most notorious organic contaminants
that are discharged into the environment from textile, tanning,
leather, paints, paper, food processing and pharmaceutical industries
[1]. There are more than 100 000 types of dyes commercially available,
with over 0.7 million tons of dyestuff produced annually. About 15% of
these dyes are reported to get lost in the effluent [2,3]. Most of the
dyes are toxic and carcinogenic compounds; they are also recalcitrant
and thus stable in the receiving environment, posing a serious threat
to human and environmental health [4,5]. Accordingly, to protect
humans and the receiving ecosystem from contamination, the dyes
must be eliminated from industrial effluents before discharging into
the environment.
Among treatment technologies, the most efficient method for the
removal of synthetic dyes from aqueous effluents is the adsorption
procedure. This process transfers the dyes from the water effluent to a
solid phase thereby keeping the effluent volume to a minimum.
Subsequently, the adsorbent can be regenerated or stored in a dry
place without direct contact with the environment [5,6]. Activated
carbon is the most commonly used sorbent for the treatment of dye
bearing wastewaters. However, this process is proved to be
uneconomical due to the high cost of activated carbon and also the
additional cost involved in regeneration [7].
Materials and methods
Preparation of biosorbent material and dye solution
P. brutia leaves used in this work were collected from the forest of
Burc, Gaziantep, Turkey. They were firstly washed with distilled
water, dried at 70 °C for 24 h, crushed in a domestic grinder and
sieved to obtain particle size in the range of 63–500 μm. The
powdered biosorbent was stored in an airtight container until use.
No other chemical or physical treatments were used prior to sorption
experiments.
Acid Yellow 220 (AY 220) was supplied by a local textile factory
and used without further purification. The AY 220 dye was of
commercial purity. The some properties of dye are shown in Table 1. A
stock solution of 500 mg L−1 was prepared by dissolving accurately
quantity of the dye in distilled water. The test solutions were prepared
by diluting the stock solution to the required concentrations. Fresh
dilutions were used for each experiment. The pH of the working
solutions was adjusted to desired values with dilute HCl or NaOH
using a pH-meter (Hanna, pH 211).
Results and discussion
Effect of solution pH
The pH of the aqueous solution plays an important role in the
sorption capacity of sorbent molecule largely due to its influence on
the surface characteristics of the sorbent and ionization/dissociation
of the dye molecule [12]. The results of the pH studies at different pH
values are shown in Fig. 1. It is evident that the AY 220 sorption is
higher at lower pH and as the pH of the solution increases, it decreases
sharply. Lower sorption of the anionic dye at alkaline pH could be
attributed to the abundance of OH− ions which will compete with the
dye anions for the same sorption sites [13]. Similar pH trends were
reported by other researchers for coffee husk, orange peel and wheat
residue [4,12,14].
Effect of contact time
The equilibrium time is one of the most important parameters in
the design of economical wastewater treatment systems [27]. Fig. 5
shows the effect of contact time on the sorption of AY 220 by the pine
leaves. The dye sorption rate was very high for the first 30 min and
finally equilibrium was established after about 90 min. The rapid dye
sorption at the initial stages of contact time could be attributed to the
abundant availability of active sites on the surface of pine leaves.
Afterwards with the gradual occupancy of these sites, the sorption
became less efficient. This is in accordance with the results obtained
for rice husk and hazelnut shell [28,29].
Sorption kinetics
The kinetic studies provide useful data regarding the efficiency of
sorption process and feasibility of scale-up operations [45]. Several
kinetic models are available to describe the sorption kinetics. Mostly
used models including the pseudo-first order, pseudo-second order,
Ritchie, Elovich and intraparticle diffusion were applied to the
experimental data to evaluate the kinetics of AY 220 sorption by the
pine leaves [46–50]. In this investigation, the kinetic studies were
performed at pH 2, biosorbent dose of 1 g L−1, particle size of 63–
125 μm, dye concentration of 100 mg L−1, temperature of 45 °C and
contact time of 90 min.
Conclusions
The present study investigated the removal of AY 220 dye by the
pine leaves from aqueous solutions. The equilibrium data fitted well
with the Langmuir isotherm. The monolayer sorption capacity of the
sorbent was found as 40 mg g−1 by using Langmuir equation. The
kinetic data were best described by the pseudo-second order model.