Use of treated asbestos waste in the adsorption of BTEX, MTBE and TAME

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1 Use of treated asbestos waste in the adsorption of BTEX, MTBE and TAME A.Kousaiti*, K.Anastasiadou*, M.Aivalioti*and E. Gidarakos* *Department of Environmental Engineering, Technical University of Crete, University Campus, 73100, Chania, Greece *Corresponding author: Tel , Fax: Abstract Asbestos wastes, pure chrysotile asbestos and asbestos cement were treated under hydrothermal conditions using different acids in various temperatures in order to produce a material which is non toxic and can be used as an adsorbent for petroleum pollutants. The scope was to cover the surface of the asbestos fibers with organic chemicals to hinder those elements that are believed to react to human cells and cause fibroses and cancer. Decomposition of asbestos waste was determined by analysis of magnesium, by calculating the Magnesium Leaching Degree MLD. The morphological degradation also leads to a loss in crystallinity and an increase in BET surface area. According to the results, the efficiency of the treated chrysotile asbestos material in the adsorption of selected petroleum pollutants from aqueous solutions was greater than the untreated one. Keywords: chrysotile; asbestos cement; hydrothermal treatment; adsorption; petroleum contaminants; 1. INTRODUCTION Chrysotile asbestos has a chemical formula Mg 6 Si 4 O 10 (OH) 8 with some Mg substituted by Fe 2+. It has an outer layer of brucite (Mg(OH) 2 ). This mineral has a layered type structure consisting of parallel sheets of silicon tetrahedral and magnesium octahedral. In general, although finely fibrous in habit, chrysotile is a sheet silicate. As shown in Figure 1, the sheets composed of alternative layers of SiO 2 tetrahedra bound together by a second layer MgO 2 (OH) 4 octahedra through the sharing of oxygen atoms [1]. The composite double layer of laminar structure results in a tubular scroll-like morphology with hollow tubes called fibrils [2]. Figure 1 presents chrysotile's tubular structure, curled sheets developed from lateral misfits and cross section showing Mg-octahedral sheet overlying Si-tetrahedral sheet. In the early years of the past century asbestos found application in over 1000 production technologies and in about 3000 products [3]. The asbestos minerals have been used for a number of applications due to their excellent physical properties that include non-flammability, high tensile strength, heat and electrical insulation, resistance to chemical and biological attack. Nevertheless, asbestos was also used in the building industry in the form of asbestos-cement roofing, called eternit planks [3, 4]. The evidence concerning the asbestos carcinogenicity began to be demonstrated increasingly since the sixties. The first ban on use of the material started in eighties. Asbestos is considered to be extremely hazardous for people, causes lung diseases such as asbestosis or lung cancer [5]. Considering the nature of asbestos products as time passes, it is certain that, at some point, asbestos fibers will be released. The most dangerous are fibers which have an aspect ratio equal to or greater than 3:1 and a length equal to or greater than 5 μm [4]. Once an asbestos product loses its characteristics, or has been abandoned, or is due to be abandoned, it is deemed Asbestos Containing Waste ACW. In Greece the main ACW s are pure chrysotile asbestos and asbestos cement containing 10-15% chrysotile asbestos [6]. The most common way is the transportation and Proceedings of the 3 rd International CEMEPE & SECOTOX Conference Skiathos, June 19-24, 2011, ISBN

2 rejection of ACW s in suitable landfills and disposal of this kind is forbidden without pre-treatment. Few treatment technologies of ACW s have been developed, such as chemical, thermal, thermochemical, mechanical and others. Figure 1. Chrysotile's curled sheets developed from lateral misfits and cross section showing Mgoctahedral sheet overlying Si-tetrahedral sheet and Chrysotile Fibrils [1, 7]. In the present work, asbestos waste (pure chrysotile asbestos and asbestos cement) was treated under hydrothermal conditions using different acids in various temperatures in order to produce a material which is non toxic and can be used as an adsorbent for petroleum pollutants, BTEX, MtBE and TAME. These pollutants are some of the most common contaminants for both soil and groundwater that usually come from leaking tanks or rupture pipelines and can make surface water and/or groundwater unsuitable for many uses, due to their toxic and/or carcinogenic properties. 2. MATERIALS AND METHODS 2.1 Materials The chrysotile asbestos used in the experiments was supplied by the Asbestos Mines of Northern Greece [8]. The asbestos cement used in the experiments came from a public building in Crete which was restored because the roof was build of asbestos cement plates. The particle size of both material was approximately <0.5mm after grinding. The mineralogical phase analysis of the asbestos samples was conducted before and after treatment. The samples were pulverized using acetone to prevent the diffusion of the fibers and to ensure the health protection of the researchers during the placing of these samples in the sample holder for XRD measurement. Acetone was used as dispersing liquid because it reduces grinding times and consequently the risks of amorphization [9, 10]. The entire procedure of sampling preparation took place in a closed environment in a glove box under negative pressure. The test sample was placed in a holder which was then placed in a Rigaku XRD. An S2 Ranger EDS (Bruker Ltd) was used to qualitatively analyze the chemical composition of the asbestos samples. EDS analysis of chrysotile asbestos samples before treatment revealed that the major elements were SiO 2 (57.1%), MgO (29%) and CaO (2.8%). The major elements of the asbestos cement samples were CaO (63.9%), SiO 2 (20.9%) and MgO (3.9%). 2.2 Method It is well known that acids destroy the fiber structure of chrysotile asbestos. According to literature various acids such as HCl, oxalic acid, phosphoric acid are used for the destruction of the crystal body of chrysotile asbestos [2, 11]. The hydrothermal treatment was conducted under continuous stirring for a period of time varied from 0.5hr to 8 weeks. Small amounts of chrysotile asbestos and asbestos cement ( g) were treated in each experiment. The ratio of water solution and asbestos waste was equal to 20 for chrysotile and equal to 10 for asbestos cement. The operational temperature was between 25 to 100ºC. Organic and inorganic acids were used for the acidic attack of asbestos waste. The acid concentration varied from zero to 6 Normality. To make the process more effective but also less hazardous, additives such as lactic and formic acid in different 416

3 concentrations were used. The concentration between N for all the acids was chosen mainly to maintain acidity levels as low as possible. Indeed, while HCl is considered to be the best solution for chemical treatment, nevertheless it is a very strong acid. The concentration was decreased in order to maintain the environmentally friendly character of the hydrothermal treatment. So, normality 2.5 was chosen for acids, HCl and H 2 SO 4 that appeal to be the best to the decomposing of asbestos waste. Decomposition of asbestos waste determined by analysis for magnesium which had gone into the solution by calculating the Magnesium Leaching Degree MLD, which was calculated as follows: MgOi MgO f MLD(%) 100 (1) MgO where (MgO)i and (MgO)f are the magnesium oxide content of the samples before and after leaching, respectively [12]. The MLD was used to follow the gradual physico-chemical modifications during the leaching process. The total amount of magnesium (Mg) removed during the hydrothermal treatment was determined by Atomic Absorption Spectrometry. The crystal phases of the samples were determined by X-ray diffraction (XRD). The morphology of the fibrous bodies was characterised using the SEM technique (Figure 3). The analysis of the solid residue was carried out by means of X-ray Diffractometry. Specific surface area measurements were performed on a classical multipoint BET volumetric apparatus at liquid nitrogen temperature Adsorption experiments In order to investigate the adsorbent capacity of untreated and treated asbestos materials, kinetics batch experiments were carried out in glass beakers of 40ml contained adsorbate solution 5mg/l of each contaminant and 0.5gr of each adsorbent material, BTEX, MTBE and TAME. Specific surface of each absorbent was determined, mean pore size and pore volume distribution using the Nitrogen Gas Adsorption Method and a Nova 2200 Quanta Chrome analyzer. The chemicals tested in this study were benzene, toluene (Riedel-de Haen, purity: 99.7%), ethylbenzene, p-xylene, o-xylene (Fluka, 99%), methyl tertiary butyl ether (Riedel-de Haen, purity: 99%) and tert-amyl-methyl-ether (Supelco, purity: 99%). These chemicals were used for the creation of a water solution for both the kinetics batch and isotherm determination experiments Kinetics batch and isotherm determination experiments Kinetics experiments and isotherm determination experiments were carried out in 40ml glass beakers with gas tight. For the kinetics experiments, each beaker contained adsorbate solution 5mg/L of each groundwater contaminants and 0.5gr of treated and untreated asbestos waste. The contact time of the adsorbate and the adsorbent varied, from the minimum contact time of 1 hour to the maximum of 48 hours. To the other hand, for the isotherm determination experiments each beaker contained adsorbate solution 5mg/L of each groundwater contaminants and material in different quantities: 0.1gr, 0.25gr, 0.5gr, 1gr, 1.5gr, 2gr. The contact time, in that case, was hours. Headspace within each beaker was minimized (to exclude any contaminant volatilization phenomena), while agitation and temperature (20 o C) were stable. Then all the solution samples were filtered with 0.45μm pore filter and analyzed Chemical analysis method The solution samples were analyzed in a Gas Chromatographer couple to a mass spectrometer (GCMS-QP2010 Plus), using the Solid Phase Micro Extraction (SPME) method. i 417

4 3. RESULTS AND DISCUSSION Under mild leaching conditions (MLD<60%), the leached asbestos materials basically retained the fiber morphology. Above 60%, acid leaching of chrysotile resulted in a rather rapid morphological degradation which was accompanied by a more rapid loss in crystallinity and a high increase in BET surface area. As the MLD approached 100%, a very porous and highly divided residue consisting of some fragments of amorphous silica was obtained. Figure 2 shows the MLD of chrysotile asbestos treatment using HCl and H 2 SO 4 with a concentration of 2.5N for a period of 6 hours and a steady temperature of 80ºC. According to the XRD analysis chrysotile fibers decomposed completely. Table 1 shows an increase in the surface area of the treated asbestos wastes because of the fiber sheets destruction. P ercent of Mg leached from as bes tos chrys otile s amples in to th e s o lu tio n ML D (% ) T ime (hr) HC l s olution H2S O4 s olution Figure 2. Percent of Mg leached from the asbestos chrysotile samples into the solution (MLD). Table 1. Specific surface area measurements to the pure chrysotile and asbestos cement waste before and after treatment with acid solutions (2.5N) after thermal in 80 o C for 6 hours. Samples Specific surface (SBET ) m 2 /gr Asbestos Cement (AC) 10,0865 Chrysotile asbestos (Asb) 16,4000 Chrysotile asbestos treated with HCl 271,4000 Asbestos Cement treated with HCl 367,9209 Chrysotile asbestos treated with H 2 SO 4 380,6007 Asbestos Cement treated with H 2 SO 4 86,2855 The proportion and rate of chrysotile asbestos dissolution depends on the operational temperature, the concentration of the acid used, and on the type and origin of the mineral.the dissolution of chrysotile asbestos in water can be expressed as the reaction [13] : Mg 3 Si 2 O 5 (OH) 4 + 5H 2 O 3Mg +3 +6OH - + 2H 4 SiO 4 (2) Clearly, the highest concentrations of dissolved Mg are observed after hydrothermal treatment of chrysotile asbestos using HCl and H 2 SO 4 2.5N for 6hr at 80º C (MLD = 94.3 and 92.9%). Generally when MLD is over 80%, structural collapse takes place. In fact, none of the fibrous-needle-like morphology, with length equal to or greater than 5μm and diameter less than 3μm, which was responsible for the toxicity of the original material, is visible in the solid (Figure 3). 418

5 Figure 3. Chrysotile asbestos untreated(a), Chrysotile asbestos treated with 2.5N HCl for 6hr at 80ºC (b) and Chrysotile asbestos treated with 2.5N H 2 SO 4 for 6hr at 80ºC (c). After adsorption experiments it was concluded that the kinetic model of pseudo-second order fits best to the experimental data, under the selected experimental conditions with correlation coefficient R 2 varied from about to 0.999%. Moreover it was concluded that the achievement of equilibrium was reacted at 12 hours. In addition the results of adsorption equilibrium experiments were also fitted to the Freundlich, Langmuir and linear adsorption models. It was realized that the Freundlich model fits best to the adsorption of BTEX, MTBE and TAME, in all samples, under equilibrium conditions and steady temperature with correlation coefficient R 2 varied from about to %. Figure 4 presents the adsorbed mass of each contaminant (48hours) per mass of the adsorbate used (mg/gr) (q e ) for chrysotile asbestos, treated with HCl (6hr, 80 o C) and treated with H 2 SO 4 (6hr, 80 o C). According to the results, the efficiency of the treated chrysotile asbestos material in the adsorption of selected petroleum pollutants from aqueous solutions was greater than the untreated one. This can be attributed to the acid treatment of the materials that increase its specific area which favorable the adsorption of these contaminants and increase the adsorption capacity of the treated material. As it can be concluded the adsorbent preference in the different available adsorbates, seems to be different. This different order can be related to the adsorbates descending order of hydrophobicity (based on their octanol water coefficient log values: , 1.55, 1.06 respectively), molecular weight (106-78, 102, 88 gr mol -1, respectively) and approximately ascending order of water solubility ( , and 45gr/L, respectively) [14]. Although contaminants seem to have more tendency to adsorb onto the asbestos material treated with HCl. Figure 4. The adsorbed mass of each contaminant (48h) per mass of the adsorbate used (mg/gr) for treated asbestos waste with HCl (6hr, 80 o C) and H 2 SO 4 (6hr, 80 o C). 419

6 4. CONCLUSIONS In this study, the parameters governing the leaching behaviour of chrysotile fibers in acidic media were investigated. In the presence of strong mineral acid, the main factors which governed the leaching of chrysotile fibers were the normality of the acid solution, the temperature and the time. Weak organic acid acted more slowly in the removal of magnesium than mineral acids and their leaching effects were dependent on the acid strength and the ph of the solutions. Treated materials with HCl and H 2 SO 4 were used as an adsorbent material for selected petroleum pollutants (MTBE, BTEX and TAME) from aqueous solutions. The results showed that treated materials present higher adsorption capacity, which is directly connected to structural changes, such as specific area, caused by the acidic treatment. The highest adsorption percentages were achieved for BTEX components. The adsorption kinetics of the examined contaminants onto the diatomite samples can be well predicted by the pseudo-second order model. Furthermore, the Freundlich model appeared to fit the experimental data best. References 1. Kipkemboi P., 1988, Preparation and characterization of Leached Asbestos Materials, Concordia University, National Library of Canada, A thesis in Department of Chemistry. 2. Heasmant L., Baldwint G., 1985, The destruction of chrysotile asbestos using waste acids. Waste Management & Research 4, Trefler B., Pawelczyk A., Nowak M., 2004, The waste free method of utilizing asbestos and the products containing Asbestos, Polish Journal Chemical Technology, 6, 4, Zaremba T., Krza kała A., J. Piotrowski et al, 2010, Study on the thermal decomposition of chrysotile asbestos, Journal of Thermal Analysis and Calorietry, 101, Addison J., McConnell E., 2008, A review of carcinogenicity studies of asbestos and nonasbestos tremolite and other amphiboles, Regulatory Toxicology and Pharmacology, 52, S187 S Gidarakos E, Anastasiadou K., Koumantakis E., Stappas N., 2008, Investigative studies for the use of an inactive asbestos mine as a disposal site for asbestos wastes, Journal of Hazardous Materials, 153, Sugama T., Sabatini R., Petrakis L., 1998, Decomposition of Chrysotile Asbestos by Fluorosulfonic Acid, Ind. Eng. Chem. Res., 37, pp Anastasiadou K., Gidarakos E., 2006, Toxicity evaluation for the broad area of the asbestos mine of Northern Greece, Journal of Hazardous Materials, 139, pp Cattaneo A., Gualtieri Ζ.A.F., Artioli Ζ.G., 2003, Kinetic study of the dehydroxylation of chrysotile asbestos with temperature by in situ XRD, Phys. Chem. Minerals, 30, pp Plescia P., Gizzi D., Benedetti S., Camilucci L., Fanizza C., Simone P., Paglietti F., 2003, Mechanochemical Treatment to Recycling Asbestos Containing Waste, Waste Management, 23, Turci F., Tomatis M., Mantegna S., Cravotto G., Fubini B., 2007, A New Approach to the Decontamination of Asbestos-Polluted Waters by Treatment with Oxalic Acid under Power Ultrasound, Ultrason. Sonochem. 15, 4, Vaillancourt A., Denes G., Le Van Mao R., 1997, Reactivity of Chrysotile Asbestos in Acids: Mechanism of Transformation to Silicon Dioxide Hemihydrate Upon Leaching of Magnesium, Mat. Res. Soc. Symp. Proc., Vol Choi I., Smith R. (1972) Kinetic Study of Dissolution of Asbestos Fibers in Water, J. Colloid Interface Sci., 40 (2), Aivalioti M., Papoulias P., Kousaiti A., Gidarakos E., 2011, Adsorption of BTEX, MTBE and TAME on natural and modified diatomite, Journal of Hazardous Materials, Article in press. 420

7 Proceedings of the Third International Conference on Environmental Management, Engineering, Planning and Economics (CEMEPE 2011) & SECOTOX Conference Organized by: Department of Planning and Regional Development, University of Thessaly, Greece Department of Mechanical Engineering, Aristotle University of Thessaloniki, Greece & International Society of Ecotoxicology and Environmental Safety (SECOTOX) In collaboration with: Sector of Industrial Management and Operations Research, School of Mechanical Engineering, National Technical University of Athens, Greece Food Technology Department, TEI of Thessaloniki, Greece Technical Chamber of Greece Under the aegis of: Ministry of Environment, Energy and Climate Change Municipality of Skiathos EDITORS: A. Kungolos A. Karagiannidis K. Aravossis P. Samaras K.W. Schramm Skiathos, June 19-24, 2011