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, Libyasmhhussein@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 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.

Keywords: Diazinone, adsorption, Removing

1. INTRODUCTION1

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

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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

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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:

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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

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.

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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

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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.

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

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

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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

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

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generalized rate constant and Lagergrens’ models were chosen to analyze

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).

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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

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Fig. 7: Generalized rate constants at

different temperatures

Fig. 8: Lagergren rate constants at

different temperatures

(293, 303 and 313 K) keeping the other parameters constant. The values

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.

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Fig. 9: Adsorption isotherm of diazinon onto

activated carbon at different Temp.

Fig. 10: Adsorption isotherm of diazinone

onto activated carbon at different

pH.

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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O diethyl O-2 isopropyl 6- methyl pyrimidin 4-yl مبيد ازالة

phosphorothioate تقنية باستخدام المائية المحاليل من

الزيتون انوية من الناتج الكربون باستخدام وذلك االمتزاز

بحمضالفوسفوريك تنشيطة بعد علي شوقي محمد – 2خلف الفتاح عبد حسين – 1حسين محمد صالح

3الجندي

) النبات وقاية قسم الزراعة كلية-1 كلية( المنيا جامعة الزراعة مبيداتالكيمياء قسم العلوم كلية- 2 ليبيا – المختار عمر جامعة – الكيميائية الهندسة قسم الهندسة كلية- 3

العربي الملخص

على المائية المحاليل من الديازينون مبيد إمتزاز دراسة تم البحث هذا فى

الفوسفوريك بحمض كيميائيا والمنشط الزيتون بذور من المنتج الفحم سطح

المادة تركيز ، الهيدروجيني الرقم ، الحرارة درجات من مختلفة ظروف عند

لعالقات طبقا اإلمتزاز عملية حركية دراسة تم كما ، الممتزة والمادة المازة

313 و 303 ، 293) مختلفة حرارة درجات وعند الرتبة أحادية التفاعالت

مع تزداد الفحم سطح على الممتز المبيد كمية أن النتائج أظهرت. كلفن(

من ظهر وقد ، %75.6 الي وصلت حيث الفحم وتركيز الحرارة درجة زيادة

الفحم سطح على الديازينون مبيد إمتزاز أن اإلرتباط معامل قيم إرتفاع

بين حيود أقل أظهرت والتى الظاهرية األولي الرتبة معادلة يتبع المنشط

التفاعل معدل ثوابت وكانت .%6 عن تزيد ال والتى والعملية النظرية القيم

ذلك على عالوة .1-دقيقة 0.021، 0.022 ، 0.015 الظاهرية األولي للرتبة

الداخلية والمسام الخارجية السطح مساحة فيها تشارك اإلمتزاز عملية فإن

اإلنتشار. نموذج نتائج من ظهر كما

18