Removal of Tetrachloroethylene by copper-coated pumice

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ABSTRACT: Tetrachloroethylene is being used increasingly, which is led to be a crucial micropollutant in the environment.The aim of this empirical study was to ...
International Research Journal of Applied and Basic Sciences © 2015 Available online at www.irjabs.com ISSN 2251-838X / Vol, 9 (10): 1780-1788 Science Explorer Publications

Removal of Tetrachloroethylene by copper-coated pumice Ali Almasi1, Mohamad Soltanian1, Fateme Asadi1*, Ahmad Mohamadi1, Kiomars Sharafi1,2 1. Department of Environmental Heath Engineering, Kermanshah University of Medical Sciences, Kermanshah, Iran 2. Department of Environmental Health Engineering, Tehran University of Medical Sciences, Tehran, Iran Correspondence author email: [email protected] ABSTRACT: Tetrachloroethylene is being used increasingly, which is led to be a crucial micropollutant in the environment.The aim of this empirical study was to evaluate the effectiveness of copper-impregnated pumice in the removal of tetrachloroethylenefrom aqueous solution. The study was carried out empericaly, used impregnated granular pumice with a mesh of 4 (4.8mm),that were processed by copper ion, using copper sulfate. The free pumice and copper-impregnated pumice were prepared in doses of 1,2 and 3 g/L, and then,it has beenexpoused on the samples includingtetrachloroethylenein three concentrations (25, 75 and 125 mg/L) considering four retention times (20,40,60 and 80 min) and three pH levels (3,7 and 11).The results of SEM imaging of free pumice and copper-impregnated pumice sample with accuracies of 10 and 100 µm showed that the structure of the SEM image of free pumice with an accuracy of 100 µm involved pores with relatively homogeneous dimensions which indicates the extended structure of the pumice. The removal rate of tetrachloroethylenedepends on adsorbent dose and tetrachloroethyleneconcentration. The maximum capacity of tetrachloroethyleneremoval by free pumice and copper-impregnated pumice were achieved as 105.61 and 120.86 mg/g respectively. The minimum and maximum removal rates of tetrachloroethyleneby free and copper-impregnated pumice were 10.7 and 98.4%; 80 and 99.7%, respectively. Comparing both forms of pumice bed, could be concluded that although the removal rate of copperimpregnated pumice was more than free pumice but the difference is not significant (P value>0.05). Keywords: Pumice,Copper,tetrachloroethyleneRemoval, Aqueous solution INTRODUCTION Halogenated aliphatic compounds are considered as the most hazardous pollutantsof the environment (soil and water resources), which leachate to groundwater and surface water through sanitary landfill and disposal of hazardous waste. Amongst those arenamedchlorinated compounds such as tetrachloroethyleneor Perchloroethylene(PCE) which have wide applicationin pesticides and industrial solvents being used inlaundry. The properties of these compoundsinclude highly volatility and stability or against aerobic decomposition (Vogel et al., 1987; Kaseros& Sleep, 2000; Chaudhry&Chapalamadugu, 1991). These compounds are widely applied in dry cleaning and textile industry as a solvent,removing grease and oil stainsand, therefore, are disposed intothe aquatic environment through industrial and domesticwastewaterresulted from various processes which use tetrachloroethylene(Ye &Fei, 2008). Tetrachloroethylene has the potential of causing hazards to human health and the environment.Oncology tests on mice liver tissue confirmedthe increased risk of liver cancer due to inhaling or swallowing tetrachloroethylene(NTP, 1986). Tetrachloroethylene resistance to aerobic decomposition and production of Vinyl chloride isomer during its anaerobic decomposition increase its health risks.Owing to the above mentioned reasons researchers have always been looking for economical ways to remove tetrachloroethylene from hazardous wastewater. Among these methods, using adsorbents were always of attention (Karagozoglu et al., 2007).Since these kinds of pollutants are present in trace amounts in water resources, the adsorption process could be applied as a rational physicochemical method to remove those.In this regard various adsorbents have been of use, such as granular and powdered activated carbon, silicon dioxide, and activated alumina. Pumice is a light material with a highly porous structure which was formed during volcanic activities.Being inexpensive, available,having low specific weight and large surface area have caused its use as adsorbent (Kitis et al., 2005).Various studies have been conducted on the removal of organic compounds by pumice impregatedwith different metals such as iron, aluminum, manganese and copper.In these works, pumice impregnated with different

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metals have shown relatively high removal efficiency for some organic compounds.Asgard et al., (2012) studied on pumice modified with copper under three different pH; 6 retention times, 8 adsorbed concentrations and 4 adsorbent concentrations, which their results indicated that the removal efficiency of phenol was increased up to 93% by increasing modified pumice dose, retention time and initial concentration of phenol while having an inverse relationship with increasing pH.Asgari et al., (2012) and Gucziet al., (1999)showed that the behavior of catalyst in removingphenylacetylenethrough the pumice modified by copper-palladium and converting it into different isomers is affected by different temperatures(Guczi et al., 1999).Kitis et al., (2007)showedthat in adsrobing organic compounds of waterby iron-impregnated pumice, all the samples experienced considerable increase in adsorbing organic compounds(Kitis et al., 2007). Bardakc (2009)demonstrated that when usingcopper-and-zincimpregnatedpumicefor the removal ofmonochlorophenol, the process of adsorption on the pumice surface boosts by attachingmetalcationsand thatmetal oxidescould weaken the chlorophenol molecules bondsby increasing the contact surfaceof pumice (Bardakçı, 2009). As there exists no experimental work regarding tetrachloroethyleneremoval by free form and impregnated pumice, here, it has been attempted to assess the comparative performance of free pumice and copper-impregnated pumice in the removal of tetrachloroethylene from aqueous solution and to compare the advantages of these two forms of pumice in yielding of the beds. MATERIALS AND METHODS Adsorbent preparation The pumice mine was purchased from construction materials stores in Kermanshah city. The required amount of pumice was sieved with mesh 4 (4.8mm) and washed with distilled water to remove its accompanying powder. Then the washed granules were placed in an oven at 103 º C for 6 hours to be dried and dehumiditized. To prepare the copper-impreganted pumice, the pumice granules wereexpousedin hydrochloric acid 1% (Merck Company) for 24 hours and then the samples were thoroughly washed with distilled water, and finally dried at 103 º C. Subsequently the samples were placed in an oven for 72 hours(Asgari et al., 2012).Eventually to determine the amount of copper and its combinations being stabilized onto the pumice, it has been charactrisedusing X-ray scattering techniques, (XRD) X-Ray diffraction and (XRF) X-Ray Fluorescence Model APD 2000 Made in Italy. To ascertain the structural and morphological properties of the copper-supported pumice, which has been utilized Scanning electron microscopy (SEM) Model JEOL 840 A Made in Japan. Solutions preparation The stock solutions of Tetracholoroetylen were prepared in concentrations of 25, 75, 125 mg/l. Then the solutions were transferred into a conical flask containing 1, 2, 3g of free pumice and copper-impregnated pumice, which then were filtered after retention times of 20, 40, 60 and three pH ranges of 3, 7 and 11. The samples were extracted by normal pentane. After that it has been measured foreTetracholoroetylen amount of the samples by GC / MASS instrument. The measurement devices have been used are the Chromatography instrument (GC 6890N, AGILENT & MS 5975C, MODE EI), the Chrompack capillary column Model DB-5 MS (30 m Length, 0.25 mm diamete and film thickness of 0.5µ), and helium carrier gas with a flow rate of 1 ml / min and Split of 1/50.The analysis program were deteremined by a gas chromatograph equipped with MASS detectors via standard samples with the following specifications: the inlet temperature of 150°C, oven temperature of 40°C, retention time equaled 1min, then the temperature raised with a slope of 5 °C/min and and 1-minute retention time up to100°C, which the axillary temperature was at 280°C.The sample flow rate was equal to 1 microlitre via a special syringe. The volume of samples was calculatedat3 concentrations of adsorbent, 3 doses foreachabsorbent type, 4 retention times and three pH ranges through Design Expert software, which by considering three iteractions and a control sample for each sample there was 432 samples extracted.The data analysis was carried out using SPSS-Ver.16, conducting ANOVA and Kruskal-Wallis statistical testsat the significance level of α=0. 05. RESULTS AND DISCUSSION The results of Electron microscope image of free Pumice and copper-impregnated pumice sample with an accuracy of 10 and 100 µm showed that the structure of the SEM image with an accuracy of 100 µm of free pumice involved homogeneouspores which indicated the development of the pumice structure. The SEM image (Figure 1) shows the intra-pore structural capacities for the establishment and increase ofchemical, physical and mechanical adhesion capabilitiesof the most surfaces of the pores with condensed units of copper sulfate. It is notable that such structural pattern inside pores causes stability and increased repeatability of tetracholoroetylen adsorption onto thecopper-supported pumice and thusthe recovery of the modified pumice. (Figure 1-4).

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Figure 1. SEM image of free pumice in scale of 100 µm

Figure 2.SEM image of free pumice in scale of 10 µm

Figure 3.SEM image of copper-impregnated pumice in scale of 100 µm

Figure 4. SEM image of copper-impregnated pumice in scale of 10µm

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XRD results showed that the most part of the pumice structure composesofquartz (SiO2). Table 1.Spectrum ofpumiceingredients based on XRF analysis Ingredient SiO2 Al 2 O3 K2O Na 2 O Fe2O3 CaO MgO Total

Percentage (%) 64.05 23.72 66.5 65.2 0.98 3.16 0.32 0.32

Furthermore the results of the XRF analysis on the copper-impregnated pumice showed that 4 different types of copper compoundstructurewere placed on the pumice, the maximum and minimum amount of copper were seen in Bonattite (Trihydrate mineral) (58.3%) with blue color and Chromite (1.45%), respectively. Figure 1 illustrates thenomogram of the XRD analysis. Variouscoppr minerals being placed onto the pumice are presented in Table 2.

Figure 5.Nomogram of copper compounds being placed onto the pumice based on XRD analysis Table 2.Spectrum of copper compounds being placed onto the pumice based on XRD analysis Compound Bonattite Paderaite Mgriite Chromite

Chemical formula CuSO43(H2O) Cu7((Cu,Ag)0/33Pb1/33Bi11/33)13S22) (Cu, Fe) 3AsSe3 Cu3SnS4

Percentage (%) 58.3 32.05 8.2 1.45

With increasing Tetracholoroetylene concentration, the removal efficiency by free pumice and copperimpregnated pumice, and also mg of tetrachloroethyleneper g of pumice (q) increased so that with increasing tetracholoroetylene concentration from 25 mg/l to 125 mg/l, the removal efficiency of free pumice at pH=3 increased from 84% to 98%; at pH=7 this increase was from 54.2% to 85% and at pH=11, it has been seen an increasingfrom 10.7% to 86%. Also the removal efficiency using copper-impregnated pumice at pH of 3, 7 and 11 was increased from 75% to 99%, 80% to 98% and 92% to 99%, respectively. Furthermore by increasing the tetrachloroethylene concentration, q value increased for free pumice and copper-impregnated pumice from 7.5 to 105 mg/g and from 8 to 120.8 mg/g, respectively. The results indicated that with increasing

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tetrachloroethyleneconcentrationfrom 25 to 125 mg/l, the removal efficiency offree pumice and copper-impregnated pumice has decreased underfixed dose and retention time. But with increasing adsorbent dose from 1 to 3g, the removal rate increased and with increasing retention time from 20 to 80 minutes, the removal rate of tetrachloroethyleneby free pumice and copper-impregnated pumice has increased.Based on the Kruskal-Wallis test, there was a significant difference between adsorb and adsorbent dose (P value =0. 024). In other words, the difference between the removal rates of tetrachloroethyleneby free pumice and pumice-supported copper was significant at concentrations of 25-125mg/L. Figure 6 represents the effect of tetrachloroethylene concentration in removal efficiency of free and copper-impregnated pumice according to the frequency of tetrachloroethyleneunderthe GC mass curve.

Figure 6. Effect of tetrachloroethylene concentration on removal rate by free and copper-impregnated pumice

The effect of retention time on tetrachloroethylene removal is shown in figure 7. However, the removal rate of copper-impregnated pumice was more than free pumice at retention times of 20-80 minutes. Although the figure depicts that with increasing retention time, the removal rate will increase, based on the ANOVA analysis there was no significant difference between the removal rate at various retention times of 20 to 80 minutes (p value>0.05).

Figure 7. Effect of retention time on removal of tetrachloroethylene

The results of analyzing pH influence on the removal results indicated that with increasing pH from acidic range tetrachloroethylenewas decreased from 98% to 10.7% and impregnated pumice, respectively. However, the removal

process are presented in figures 8, 9 and 10. The to neutral and alkaline range, the removal rate of from 99.7% to 93.8% in free pumice and copperof tetrachloroethyleneby the copper-impregnated

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pumiceat pH of 11 was more than that of free pumice. According to the results of ANOVA and Kruskal-Wallis test, there was no significant difference between the removal rates at three pH ranges (p value>0.05). 100

Removal Percentage

80 60 pH3 40

pH7 pH11

20 0 0min

20min

40min

60min

80min

Retention time(min) Figure 8. The effect of pH on tetrachloroethylene removal by free pumice 100

Removal Percentage

80 60 pH3 40

pH7 pH11

20 0 0min

20min

40min

60min

80min

Retention time(min) Figure 9. The effect of pH on tetrachloroethylene removal by copper-impregnated pumice

Figure 10. The effect of pH on tetrachloroethylene removal by free and copper-impregnated pumice

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Figures 11 and 12 show the anaylsis results of the influence of adsorbent dose on the removal rate oftetrachloroethylene.These results showed that with increasing the pumice dose in both forms, the removal efficiency increased while q decreased.Withincreasing adsorbent dosefrom 1 to 3g/ l, the removal efficiencyinreasedfrom 50% to 90% for free pumice and from 86% to 97% for copper-impregnated pumice. Also with increasing the adsorbent dose,q decreasedfrom 20 to 7.56 mg/ g for free pumice and from 24 to 7.03 mg/g forcopper-impregnated pumice. The ANOVA test has also confirmed the influence of increasing adsorbent on tetrachloroethyleneremoval(001/0>Pvalue). y = 1/84x + 93/2 R² = 0/7386

Removal Percentage

100

99/1

98/7

Copper-impregnated pumice

96

93/7

92

y = 2/24x + 82/6 R² = 0/8915

88

88/2

86/5

85/6

84

Free pumice Linear (Copper-impregnated pumice) Linear (Free pumice)

80 0

0/5

1

1/5

2

2/5

3

Dose(g) Figure 11. Effect of adsorbent dose on tetrachloroethylene removal by free and copper-impregnated pumice

Figure 12. Effect of adsorbent dose on tetrachloroethylene removal

Determiningcompounds being present inthe structure of an adsorbent is one of the most important issues in absorption process which needs to be put under attention. The results of the pumice structure analysis showed that about 74% of pumice constitutes of Quartz (SiO2). The presence of these metal oxides in aqueous solutions causes the formation of surface functional groups which have an effective role in removing pollutants from water resources (Kitis et al., 2005; Ghanizadeh et al., 2009). Eghbal et al. and Kitis et al. reported that the main ingredient of pumice was SiO2, whichconforms to our result (Kitis et al., 2007; Ozturket al., 2000).StudyingtheSEM imagesof copper-impregnated pumice with an accuracy of 10 and 100µm revealed that this structure appears to be highly capable of mechanical adsorption and in other words we could say that such structure has a significant surface to volume ratio. These properties improve the selective adsorption feature of pumice relative to the surfaces with less porosity. The other interesting point is that the structural conditions of pumice and the experimental conditions applied during copper sulfate coating onto the pumice surface have provided the possibility of creating some micro-meter copper sulfate crystalline structures. Observation of the related figures (Figures 2-4)

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with an accuracy of 10µm shows the existence of crystals with dimensions below 20-30 µm. It has been proven that the mechanical, chemical, physical, crystallic and especially the catalytic properties of materials in nano and micro dimensions are different from those of bulky dimensions.The mechanical properties show interesting changes in the process of the reduction of particle sizes from microscopic scale to nano-and micro-meter scale. Preliminary studies demonstratedbehaviors such as less elastic modulus, higher hardness and strength, less steep in hardness curve for microstructure materials in comparison with materials having larger particle size.The structural property of pumice surface and copper sulfate,which often take crystalline form,justifies the mechanical strength and in trunits reproducibility and recovery of pumice coated with copper sulfate against tetrachloroethylene. The reactivity and selectivity of microstructure catalysts could change by the shape of microcrystal (nano- and micro- scales). Also shape and the number of the atoms placed on the edges and corners are influential on catalytic efficiency.Under the created conditions, the significant results regardingtetrachloroethylene absorption by copper-impregnated pumice are justifiable by evaluating the the structural patterns mentioned. Copper as a heterogeneous catalyst could break the double bond of carbon by reducing the activation energy, creates the oligomerizationphenomenon,and weaken the bond between tetrachloroethylene molecules by increasing the contact areaof pumice. Due to the lack of monomer, dimmer, trimmer, and tetramer peaks in the gas chromatograph, the possibility of tetrachloroethyleneoligomerizationbythe copper present in pumice is null. Even if such reactions have taken place, its complex with copper being presented in pumice was so strong that it didn’t lead to the removal of copper from the system. In other words,tetrachloroethylene removal by pumice modified with copper could be due to the physical adsorption of tetrachloroethylene by copper or due to a chemical process (oligomerization) in which coppercauses chemical alterations on tetrachloroethylenewhich in turn makes the product and its link with the copper present in pumice longer and heavier,thus preventing this chemical compound to be given out.The results indicated that by increasing pH from acidic to neutral and alkaline range, removal efficiency of free pumice would be decreased. The reduction in tetrachloroethyleneabsorption in alkaline conditions (high pH)isdue to the electrostatic repulsion of adsorbent and tetrachloroethylene. This is in conformance with the results obtained byAsgariet al., (2012), Banat et al., (2000), and Varghese&Vinod,(2004 ). The increase of removal efficiency of Tetrachloroethyleneby copperimpregnated pumicein alkaline pH range could be explained by the competition between copper cations and protons present in pumice.This study showed that with increasing retention time,tetrachloroethylene removal rate increases. With increasing time up to 80 minutes, the removal rate reaches to its maximum. The results also showed that the removal efficiency increases with extended retention time in all doses and retention times. There was a significant relationship between the retention timeand removal efficiency (pvalue