Laboratory investigation of insecticide O,O diethyl O-2 isopropyl 6- methyl pyrimidin-4-yl phosphorothioate insecticide adsorption using olive stones activated by phosphoric acid was carried out. The influence of several factors governing insecticide adsorption such as dosage, temperature, pH and time in addition to specific surface area of the prepared carbon was investigated. The obtained results showed that the adsorption was found to increase with increasing temperature and pH and the activated carbon prepared from olive stones has higher surface area (>700 m2g-1). Also, the removal of insecticide increased with the lapse of time; an olive stone activated by phosphoric acid has 75.6 % insecticide removal efficiency in comparison with that of activated carbon. The experimental results have been fitted with Langmuir and Freundlich isotherms. The Langmuir isotherm better fitted the experimental data since the average percent deviations were lower than with Freundlich isotherm. Moreover, activated carbon from olive stones is a suitable adsorbent and adsorption of 90% is possible in the high temperature, pH and adsorbent dosages.

1. Removal of insecticide O,O diethyl O-2 isopropyl 6- methyl
pyrimidin 4-yl phosphorothioate insecticide from aqueous solutions
using olive stones activated by phosphoric acid
Salah M. Hussein1
, Hussein A. Khalaf2
1-
Plant Protection Dept. (Insecticides) Faculty of Agric.Minia University, Egypt
2-
Chemistry Dept., Faculty of Science, Omer Almoukhtar Univ., El-Beida, Libya
smhhussein@yahoo.com
Abstract
Laboratory investigation of insecticide O,O diethyl O-2 isopropyl 6-
methyl pyrimidin-4-yl phosphorothioate insecticide adsorption using
olive stones activated by phosphoric acid was carried out. The influence
of several factors governing insecticide adsorption such as dosage,
temperature, pH and time in addition to specific surface area of the
prepared carbon was investigated. The obtained results showed that the
adsorption was found to increase with increasing temperature and pH and
the activated carbon prepared from olive stones has higher surface area
(>700 m2
g-1
). Also, the removal of insecticide increased with the lapse of
time; an olive stone activated by phosphoric acid has 75.6 % insecticide
removal efficiency in comparison with that of activated carbon. The
experimental results have been fitted with Langmuir and Freundlich
isotherms. The Langmuir isotherm better fitted the experimental data
since the average percent deviations were lower than with Freundlich
isotherm. Moreover, activated carbon from olive stones is a suitable
adsorbent and adsorption of 90% is possible in the high temperature, pH
and adsorbent dosages.
Keywords: Diazinone, adsorption, Removing
1. INTRODUCTION
1

2. Many human-made organic chemical compounds are currently possible to
be detected in drinking water sources; hence, they are of increasing
interest, because of their potential toxicity, carcinogenicity and
mutagenicity effects. Among them, pesticides constitute a pollutant class
of particular importance and priority; they can enter drinking water
supplies, either from (industrial waste discharges, accidental spills,
pesticide application, drift in the field and agricultural run-off). The fate
of pesticides during drinking water treatment has been already examined
using bench, pilot, as well as full-scale, experiments (Robeck et al., 1965;
Miltner et al., 1989; Pirbazari et al., 1991) The adsorption onto activated
carbon, have proved to be the most efficient and reliable method for the
removal of aqueous-dissolved organic pesticides (Pirbazari et al., 1991);
Kouras et al. 1998).
For the removal of pesticides from water solutions a number of
adsorbents like agricultural products such as date pith, sawdust, corn
curb, barley husk, and rice hull have a potential to be used as an
alternative sorbent (Bosseto, et al. 1992) Chemical modifications of these
materials enhance their sorption capacities and thus improve the
treatment processes.
The purpose of the present study is to study of activated carbon prepared
from olives stones to adsorb diazinone insecticide from aqueous solution.
The work is directed primarily towards studying the adsorption isotherm.
The main goal of adsorption isotherm is, firstly, to measure the
adsorption capacity of the adsorbent concerned and secondly, to ascertain
the liquid-solid equilibrium distribution of the adsorbent concerned. In
the present study, the classical isotherms models (Langmuir and
Freundlish) have been used to simulate the experimental data. Moreover,
results of batch kinetics studies of diazinone adsorption on the prepared
2

3. activated carbon using variables such as dosage, temperatures and pH are
investigated.
2. EXPERIMENTAL
2.1 Synthesis of activated carbon
Local olive’s stones, a by-product of food processing, were purified to
remove the undesired contaminant prior to use them as adsorbents. The
stones were washed, crushed and finally ground in a laboratory mill to a
size of 0.5 - 3.0 mm followed by soxhlet extraction using ethanol solvent
for 24 hours for an exhaustive extraction of oily substances from stones.
After extraction, the solid matter was dried in an air oven. Impregnation
with H3PO4 (0.34 g/g carbon) was done and left the impregnating solution
overnight followed by drying at 383 K and carbonization at 673 K for
two hours.
2.2 Insecticide used
From the above structure we can observe that diazinone is a
phosphrothioate compound with a pyrimidine ring attached to it and there
are polar bonds in the molecule such as P=S, the non polar pyrimidine
ring with its alkyl substituent's makes this compound relatively
hydrophobic.
Chromatography coupled with Electron Capture Detection (GC-ECD)
and was used as standard for the experiments. For the evaluation of the
3

4. removal efficiency of the examined treatment methods a stock solution of
1000 mg/ml was prepared in acetone. All aqueous diazinone solutions
contained also 30 mg /L of Mg++
(as MgSO4) in order to induce the
following coagulation process (Gregory, 1978). Diazinone solutions, with
initial concentration 10 mg/L, were prepared in distilled water, by
dilution of the stock solution. For the calculation of the adsorption
isotherms and for the diazinone (technical grade,) has 99.5% purity, as
found by Gas adsorption rate experiments, stock solutions containing up
to 90% of the limiting solubility concentration of diazinone were
prepared, in distilled water. The solubility of diazinone in aqueous
solutions is around 30 mg/L, depending upon the preparation conditions.
(El-Dib, et al.1978)
2.3 Kinetic Sorption Study
Batch sorption experiments were performed by using the following
parameters e.g. stay time, dosage of carbon, pH, and temperature and
insecticide concentration. Batch adsorption experiments were carried out
using bottle-point method (McKay et al.1985) in which different
concentration taken in various flasks (100 ml) placed in a shaking
thermostat (120 rpm). At the end of predetermined intervals, the
adsorbent was collected by centrifugation and the progress of adsorption
was determined. The different parameters studied are:
Stay time; the stay time of diazinone activated carbon system was
determined by adding 0.1 g of carbon in 100 ml of diazinone solution (40
mg L-1
) for different time intervals. The absorbance was extracted and
determined at different time intervals. The amount of adsorption at time t,
qt (mg g-1
), was calculated by:
4

5. Insecticide concentration; 0.1 g of carbon added to different
concentration of insecticide solution with continuous stirring for 4 hours.
After time finishing, the absorbance of insecticide was determined. The
adsorption capacity of the carbon was determined from the concentration
difference of the solution, at the beginning and at equilibrium:
where Ci and Ce are the initial and the equilibrium insecticide
concentrations (mg L-1
), V is the volume of solution (mL), and m is the
mass of carbon used (g).
pH; solutions of different pH’s solutions were prepared by using of 0.1
M HCl and 0.1 M NaOH. 100 ml of insecticide solution was added using
0.1 g of carbon and then shacked for 4 hours, followed by measuring the
absorbance.
Temperature; Three different temperatures (293, 303 and 313 K) were
selected to study the effect of temperature on the adsorption process.
Isotherm models; Obtained adsorption isotherm data were plotted in the
linear Langmuir and Freundlich isotherm models.
3. RESULTS AND DISCUSSIONS
3.1 Diazinone adsorption
As shown in Fig. 1, the amount of insecticide adsorbed at various
intervals of time indicates the removal of the insecticide initially increase
with time, the adsorption process was found to be rapid initially but attain
equilibrium within 45 min. However, all equilibrium experiments were
5

6. allowed to run for 4 hours. Moreover, by increasing the initial
concentration of diazinone (100, 400 and 800 mg L-1
) the amount of
adsorbed insecticide also increased as shown in Fig. 1. The adsorption
capacity of the solid phase is important for characterizing the usefulness
of the adsorption process and for determining the usefulness and
applicability of a mathematical model.
Fig. 1: Adsorption of insecticide as a function of time.
Fig. 2 shows the removal percentage (R%) of diazinone at different
dosages from activated carbon. From the figure, it is clear that the
removal is increases by increasing the amount of activated carbon.
6

7. Fig. 2: Adsorption of diazinone at different dosages of carbon.
3.2 Adsorption isotherms
When the experimental data points of the adsorption of diazinone onto
adsorbents were plotted as qe (mg g-1
) against Ce (mg L-1
), the
characteristic L-shape curves have been obtained as shown in Fig. 3.
According to the shape of the curve, the isotherms corresponding to the
diazinone may be classified as type-L (Gupta, et al.2008) who suggested
moderate affinity of insecticide molecules for the active sites of the
adsorbents.
The analysis of this isotherm is important to know which models are
acceptable for design purposes. The first isotherm tested was that of
Langmuir which may be represented by the equation:
Ce/qe = 1/KL + (aL /KL)Ce
The plot of Ce/qe against Ce, Fig. 4, is seen to be linear over a certain
concentration range. Values of KL and aL have been calculated using the
7

8. least-squares method and are cited in Table 1. The value of the constant,
KL/aL, corresponds to the maximum adsorption capacity (qmax) of the dye.
Linear plots of KL/aL against Ce for the diazinone suggest the applicability
of the Langmuir isotherm of the present systems, and demonstrate
monolayer coverage of the adsorbate at the outer surface of the adsorbent
(Hsieh,and Teng.,2000).
Fig. 3: Adsorption isotherm of diazinone onto activated carbon at 293 K.
8

9. Fig. 4: Langmuir adsorption isotherm for diazinone onto activated carbon
Fig. 5: Freundlich adsorption isotherm for diazinone onto activated carbon
9

10. Table 1: Parameters in the Langmuir and Freundlich Adsorption Models
Langmuir 1st
part of Freundlich
isotherm
2nd
part of Freundlich
isotherm
KL aL qmax R Corr.
Coef
KF n Conc
range
Corr.
Coef.
KF n Conc
range
Corr.
Coef.
28.4 0.09 312.5 0.027 0.999 14.9 1.8 0-25 0.99 198.3 13.7 25-
501
0.98
The essential characteristics of the Langmuir isotherm can be expressed
in terms of a dimension less equilibrium parameter, R, (ref.) which is
defined by:
R = 1/(1+ aL . Cref)
Value of R for has been calculated and cited in Table 1. The R value
(0.027) indicates that adsorption of diazinone onto activated carbon is
very favorable (0< R <1) (Gupta et al 2011a).
The experimental equilibrium data for the adsorption of diazinone onto
activated carbon has also been analyzed using the Freundlich isotherm as
given by the following equation:
Log qe = Log KF + (1/n) Log Ce
Inspection of the results derived from the Freundlich analysis shows that
a plot of log qe against log Ce exhibits some curvature (Fig. 5). Certainly,
two straight lines may represent the results. The Freundlich parameters,
KF and n, for the diazinone have been calculated using the least-squares
method applies to the straight lines shown in Fig. 5 and are cited in Table
1. This shows that the values of n are higher than one, indicating that the
tested diazinone is favourably adsorbed by activated carbon. By using the
10

11. appropriate constants of Langmuir and Freundlich equations, the
theoretical isotherm curves were predicted using known values of Ce.
Fig. 6 shows a comparison of the experimental points with Langmuir and
Freundlich equations to establish which equation yields the “best fit”. It is
clear that Langmuir isotherm fits the data significantly better than
Freundlich model.
Fig. 6: Comparison between the experimental and theoretical isotherms.
3.3 Kinetic Sorption Study
Kinetic equations have been developed to explain the transport of dyes
onto various adsorbents. These equations include the generalized rate
constant (Annadurai, 2002), the pseudo-first order equation (Lagergren,
1898), the pseudo–second order (Ho and Mckay, 1998) and the
intraparticle diffusion model (Weber and Morris, 1984). These Kinetic
models are only concerned with the effect of the observable parameters
on the over all rate of sorption (Ho, 2006). However, for this study both
generalized rate constant and Lagergrens’ models were chosen to analyze
11

12. the rate of sorption of diazinone onto activated carbon prepared from
olive stones at different temperatures. Fig.6 presents the generalized rate
constant according to the equation:
1/qt = k/qref *1/t + 1/qref
A plot of 1/qt vs. 1/t at different temperatures is shown in Fig. 7. The
amount of diazinone adsorbed at different time intervals for increasing
temperature was found to be increasing. From the intercept and slope, the
generalized rate constant (k) were 8.96, 6.17 and 6.82 min-1
at 293, 303
and 313 K, respectively (Table 2).
The first-order Lagergren equation were evaluated from the experimental
data to evaluate the rate of adsorption of diazinone onto the activated
carbon:
Log (qref-qt) = log qref – kadt/2.303
A plot of log (qref-qt) vs. t is represented in Fig. 8. A linear relation was
observed indicating the applicability of the above equations, and the first
order nature of the process (Namito and Manzoor, 1993). The adsorption
rate constants (kad) were determined from the slopes of the plots and were
found as: 0.015, 0.022 and 0.021 at 293, 303 and 313 K, respectively
(Table 2).
12

13. Table 2: Rate constants of diazinone sorption onto activated
carbon.
Temp.
K
Generalized Rate Constant Lagergren Rate Constant
K(min-1
) kad (min-1
)
293 8.96 0.015
303 6.17 0.022
313 6.82 0.021
3.4 Effect of Temperature
Although there are many factors to be considered when studying
the kinetics of sorption, such as pH, the concentration of the sorbent, the
nature of the solute and its concentrations, amongst others, temperature
is, in fact, one of the parameters with the greatest influence on the
process, as revealed by the modification in the rate constant, k (Najm et
al. 1991). Three temperatures were used in this study for the kinetic study
(293, 303 and 313 K) keeping the other parameters constant. The values
13
Fig. 7: Generalized rate constants at
different temperatures
Fig. 8: Lagergren rate constants at
different temperatures

14. for qt have been plotted against the contact time, t, for the three
temperatures tested in Fig. 9. The sorption process can be seen to occur
very rapidly at all temperatures as the maximum sorption capacity is
reached practically within the first 45 min, as had been shown in the
study on the influence of contact time. Also a slight influence of
temperature is also seen. Increased adsorption at higher temperature is
difficult to explain. The higher removal due to increasing temperature
may be attributed to chemical reaction taking place between the
functional groups of the adsorbate/adsorbent and the dye.
3.5 Effect of pH
The effect of pH on adsorption process was studied at different pH values
keeping other parameters constant. The result of variation on diazinone
adsorption at these pH values is shown in Fig. 10. This may be due to the
number of positive charges on the adsorbent surface, which leads to the
attraction of the negatively charged diazinone molecule and thereby,
increasing the diazinone adsorption.
14
Fig. 9: Adsorption isotherm of diazinon onto
activated carbon at different Temp.
Fig. 10: Adsorption isotherm of diazinone
onto activated carbon at different pH.

15. 4. CONCLUSION
Laboratory investigation of diazinone adsorption onto activated carbon
prepared from olive stones and activated by phosphoric acid has been
conducted in this study and the following major points can be extracted
from the results:
• The adsorbent has higher maximum adsorption capacity.
• The Langmuir isotherm better fitted the experimental data since
the average percent deviations were lower than with Freundlich
isotherm.
• Results show that 90.6% adsorption is possible by increasing
temperature, dosage and pH.
• The Kinetics of the adsorption of diazinone was rapid in the
initial stage followed by a slow rate. The adsorption data
indicated the applicability of the 1st
order reaction.
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18. O diethyl O-2 isopropyl 6- methyl pyrimidin 4-yl
phosphorothioate
123
1-
2
3––
)293303313.75.6
6%0.0150.0220.021-1
.
18