Optimization of pyrolysis conditions and adsorption properties of bone char for fluoride removal from water

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1 Instituto Tecnologico de Aguascalientes From the SelectedWorks of Adrian Bonilla-Petriciolet Optimization of pyrolysis conditions and adsorption properties of bone char for fluoride removal from water Karina Rojas-Mayorga Adrian Bonilla-Petriciolet Ismael A. Aguayo-Villarreal Virginia Hernandez-Montoya Ma. del Rosario Moreno-Virgen, et al. Available at:

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3 Journal of Analytical and Applied Pyrolysis () Contents lists available at ScienceDirect Journal of Analytical and Applied Pyrolysis journa l h om epage: ww w.elsevier.com/locate/jaap Optimization of pyrolysis conditions and adsorption properties of bone char for fluoride removal from water C.K. Rojas-Mayorga a, A. Bonilla-Petriciolet a,, I.A. Aguayo-Villarreal a, V. Hernández-Montoya a, M.R. Moreno-Virgen a, R. Tovar-Gómez a, M.A. Montes-Morán b a Instituto Tecnológico de Aguascalientes, Aguascalientes, Av. López Mateos No., C.P., México b Instituto Nacional del Carbón, INCAR-CSIC, Apartado E-, Oviedo, Spain a r t i c l e i n f o Article history: Received June Accepted 9 September Available online 9 October Keywords: Fluoride adsorption Pyrolysis Bone char Water treatment a b s t r a c t This study reports the optimization of a pyrolysis process for the synthesis of bone char for fluoride removal from water. Specifically, we have performed a detailed analysis of the adsorption properties of bone char samples obtained at different operating conditions of pyrolysis. Results show that the pyrolysis temperature plays a major role to synthetize an effective bone char for water defluoridation. In particular, the best adsorption properties of bone char for fluoride removal are obtained with those samples synthetized at C. Pyrolysis temperatures higher than C cause the dehydroxylation of the hydroxyapatite of bone char reducing its fluoride adsorption capacity. The maximum fluoride adsorption capacity of the bone char obtained in this study (i.e.,. mg/g) is higher than those reported for commercial bone chars. Finally, adsorption experiments were performed using the optimized bone char for determining kinetic, equilibrium and thermodynamic parameters of the fluoride removal from water using this adsorbent. In summary, this study shows that the optimization of pyrolysis conditions for the synthesis of bone char is useful to obtain an effective adsorbent for fluoride removal from water. Elsevier B.V. All rights reserved.. Introduction Pyrolysis has been traditionally employed for the synthesis and production of adsorbents for air pollution control and wastewater treatment [,]. In particular, pyrolysis is useful for the synthesis of bone char, which has been recognized as an effective adsorbent for fluoride removal from water [ ]. Defluoridation of drinking water for human consumption is a relevant concern in the context of health protection and water pollution control []. It has been estimated that million human beings worldwide are exposed to the consumption of drinking water with fluoride concentrations higher than mg/l, which has been established as the fluoride concentration limit to prevent the development of dental and skeletal fluorosis in exposed population []. Therefore, the production of low-cost bone char for the treatment of drinking water polluted by fluoride ions has increased its importance and relevance especially in developing countries. Bone char is considered as a mixed adsorbent constituted by carbon and calcium phosphate, which is in the hydroxyapatite form [9]. This adsorbent has shown fluoride adsorption capacities higher than those obtained for other carbonaceous materials [,] and Corresponding author. Tel.: address: petriciolet@hotmail.com (A. Bonilla-Petriciolet). commercial adsorbents such as activated alumina [,]. Several studies have concluded that the fluoride adsorption properties of bone char are attributed to their content of mineral components, especially, the hydroxyapatite content [,,]. Bone char can be synthetized by the calcination of bones under a low-oxygen environment (i.e., partial calcination) or by pyrolysis, where no oxygen is present during the thermal treatment. In particular, thermal processes with restricted presence of air at C are commonly used for the synthesis of bone char for water defluoridation [9]. In fact, some authors have suggested that bone char produced by partial calcination are suitable for fluoride removal if the synthesis temperatures do not exceed C []. However, several studies available in the literature have reported discrepancies and different results with respect to the effect of the synthesis conditions on the adsorption properties of bone char for fluoride removal from water. For example, Mwaniki [] determined the fluoride removal performance of white, gray and black bovine bone chars, which were obtained from thermal treatments at C (black), C (gray) and C (white). This study concluded that black bone char showed the best adsorption properties. On the other hand, Phantumvanit and LeGeros [] reported a comparison of fluoride removal performances of bone chars obtained by calcination of bone meal (i.e., cow and pig bones) for min at different temperatures:, and C. This study concluded that bone char obtained at C showed the highest fluoride uptakes. -/$ see front matter Elsevier B.V. All rights reserved.

4 C.K. Rojas-Mayorga et al. / Journal of Analytical and Applied Pyrolysis () In other study, Kaseva [] reported that thermal treatment of cattle bones at temperatures higher than C may damage the apatite structure affecting the fluoride adsorption properties of bone char, while thermal treatments of bones at temperatures below C may produce a bone char that is not hygienically acceptable for water defluoridation since the water treated with this adsorbent may have bad taste and odor. Recently, Kawasaki et al. [] studied the synthesis of bone char using cow, pig, chicken and fish bones and a pyrolysis process at and C. This study concluded that the fluoride adsorption properties of bone char obtained at low pyrolysis temperature are higher than those obtained at C. The fluoride uptakes of synthetized bone chars ranged from. to. mg/g. Finally, Leyva-Ramos et al. [] reported that the bone char produced by partial calcination at C and a charring time of h is suitable for the fluoride removal from water. Even though these studies have reported inconsistent results, it is clear that the operating conditions for the synthesis of bone char play an important role to determine the final adsorption properties of the adsorbent and, consequently, its performance in water defluoridation. In general, the fluoride adsorption capacities of commercial bone chars may range from. to. mg/g [,,], where bone chars obtained from pyrolysis process may show the best adsorption properties. Herein, it is convenient to remark that, in a controlled synthesis process, the precursor is pyrolyzed under a suitable temperature and inert environment; and the adsorption properties of the obtained adsorbent depend on the operating conditions used. The experimental parameters of pyrolysis that have the largest influence on the physicochemical properties of the final adsorbent are the precursor particle size, temperature of thermal treatment, nitrogen flow rate, residence time and heating rate [,]. These process conditions can be optimized to improve the adsorption properties of the final product for a desired application. Based on these facts, this study reports a detailed analysis of the effect of pyrolysis conditions on the physicochemical properties of the bone chars and their ability for fluoride removal from water. Specifically, the optimal conditions of the pyrolysis process that improve the fluoride uptakes of bone char have been determined. Results show that the bone char prepared using the optimum pyrolysis conditions has fluoride uptakes higher than those reported for commercial bone chars available in the market.. Methodology.. Pyrolysis conditions for the synthesis of bone char Cow femur residues were used as precursor for the synthesis of bone char. These bone residues were washed with boiling and deionized water to eliminate fat and meat residues. Bone samples were then dried for h, crushed and sieved to obtain a particle size of mm. These bone samples were used for the preparation of bone char using a pyrolysis process. A tubular furnace Carbolite Eurotherm CTF / with a quartz sample holder was used for the synthesis of bone char samples. Samples of bone char were synthetized at specific conditions of heating rate, pyrolysis temperature and thermal treatment time, which were defined using a full factorial design A k, see Table. For pyrolysis process, nitrogen gas ( ml/min) was used to provide an inert atmosphere during the synthesis of bone char. All synthetized bone char samples were washed with deionized water until obtaining a constant ph and dried for their use in fluoride adsorption experiments. For all experiments established in the experimental design (Table ), the product yield was quantified and the fluoride adsorption properties of bone char samples were determined. Specifically, the adsorbed amount of fluoride on bone chars was used as the response variable of this experimental design. This fluoride uptake was measured in batch adsorption experiments, which were performed by triplicate using a fluoride solution with an initial concentration of mg/l and an adsorbent dosage of g/l at C and ph. Fluoride uptakes of bone chars (mg/g) were calculated using a mass balance ( ) [F ] [F ] f q F = V () m where [F ] and [F ] f are the initial and final fluoride concentration in adsorption experiment given in mg/l, m is the mass of bone char samples in g and V is the volume of fluoride solution given in L, respectively. Fluoride concentration in solution was quantified using a selective electrode and TISAB chemical reagent according to the procedure described in the Standard Methods of Examination of Water and Wastewater [9]. A statistical analysis of the results obtained from this experimental design was performed to determine the effect of pyrolysis conditions on the fluoride adsorption properties of bone char. In addition, this analysis was used to identify those operating parameters of pyrolysis process that improve the performance of this adsorbent for fluoride removal from water. Statistica software was used for data analysis. The best pyrolysis conditions were identified and the synthetized adsorbent was used in additional removal experiments for determining kinetics, isotherms and thermodynamic parameters of the fluoride adsorption on bone char at different conditions of temperature and ph. Specifically, the optimized bone char sample was used for determining the fluoride adsorption rates at initial fluoride concentrations of, and mg/l, respectively. On the other hand, the fluoride adsorption isotherms using this bone char were obtained at ph, and and, and C. Residence time used for batch adsorption experiments ranged from. to h. These results were used for the calculation of adsorption thermodynamic parameters... Physicochemical characterization of raw precursor and bone chars Several characterization techniques were used for determining the most relevant physicochemical properties of both raw precursor (i.e., bovine femur) and bone char samples obtained in this study. Specifically, the thermogravimetric analysis of the raw bone was performed from room temperature to C under an Ar atmosphere employing an SDT Q automatic analyzer from TA Instruments. The content of C, H, N and S in the raw bone and bone char samples was determined using appropriate elemental micro analyzers from LECO. The functional groups were determined using a Nicolet- FT-IR spectrometer (Thermo Electron Co.) equipped with a deuterated triglycine sulfate (DTGS) detector. FT-IR spectra were collected in the spectral range of cm. On the other hand, SEM/EDX analyses were performed in a FE-SEM system (Quanta FEG, FEI) to determine possible changes in the morphology and composition of both raw bone wastes and bone char samples. The crystalline structure of bone char samples was analyzed using a Bruker D Advance X-ray diffractometer. Finally, the textural parameters of adsorbent samples were determined using nitrogen adsorption desorption isotherms at K with a Micromeritics ASAP. Results of physicochemical characterization of the bone char samples were related to the fluoride adsorption and used for analyzing the fluoride removal mechanism.

5 C.K. Rojas-Mayorga et al. / Journal of Analytical and Applied Pyrolysis () Table Experimental design used for the synthesis of bone char via pyrolysis. N flow: ml/min. Sample Pyrolysis conditions Bone char performance Temperature, C Heating rate, C/min Residence time, h Yield, % Fluoride uptake, mg/g Results and discussion.. Optimization of pyrolysis conditions for the synthesis of bone char for fluoride removal Product yields and fluoride adsorption capacities of the bone char samples obtained at different pyrolysis conditions of the experimental design are reported in Table. Specifically, the yields of bone char ranged from. to.% at tested experimental conditions and these results indicate that the tested pyrolysis conditions do not have a significant impact on the product yield of bone chars, see Table. However, an increment of the residence time seems to systematically cause a slight decrement ( %) of the bone char yield. This trend agrees to results reported in other studies, e.g. []. Overall, the product yields of bone char obtained in this study are higher (i.e., >%) than those obtained by Kawasaki et al. [] using bones from cow, pig, chicken and fish as precursors. On the other hand, the results of fluoride adsorption experiments for the full factorial experimental design are also reported in Table. Statistical analysis (i.e., variance analysis) of the experimental design indicated that the pyrolysis temperature has the most significant effect on the fluoride adsorption properties of bone char (p-level <.), whereas both the heating rate and thermal treatment time do not affect significantly the performance of the bone chars (p-level >.). It is interesting to remark that, when the pyrolysis temperature is higher than C, the fluoride adsorption capacity of bone char decreased significantly from. mg/g to. mg/g. In fact, the removal performance of bone char synthetized at C decreased significantly showing fluoride adsorption capacities of. mg/g. This trend of adsorbent performance is in agreement with the study of Kawasaki et al. [], which indicates that bone chars obtained at higher temperatures may show low fluoride uptakes due to the thermal degradation of functional groups that may be involved in fluoride removal. With illustrative purposes, Fig. a shows the fluoride adsorption isotherms of bone chars obtained at different pyrolysis temperatures from to C, using a residence time and heating rate of h and C/min, respectively. Maximum fluoride adsorption capacities ranged from. to. mg/g, respectively. On the other hand, adsorption isotherms reported in Fig. b confirmed that dwell time and heating rate of the thermal treatment do not have a significant impact on the fluoride adsorption properties of bone char. A detailed analysis of the effect of pyrolysis temperature was performed and additional bone char samples were prepared at 9,, and C, keeping all other variables of the pyrolysis process constant ( C/min and h). Maximum fluoride adsorption capacities of the synthetized bone chars are reported in Fig.. These results show that the best fluoride removal performance of bone char corresponds to a pyrolysis temperature of C. In fact, this pyrolysis temperature is the optimum condition for the synthesis of bone char where ( ) qf = () T p t p,r p q e, mg/g q e, mg/g a) Pyrolysis temperature C C C 9 C C [F - ] e, mg/l b) Pyrolysis conditions C/min, h C/min, h C/min, h C/min, h [F - ] e, mg/l Fig.. Fluoride adsorption isotherms at ph and C on bone chars obtained at different pyrolysis conditions.

6 C.K. Rojas-Mayorga et al. / Journal of Analytical and Applied Pyrolysis () Maximum fluoride uptake, mg/g R² = Pyrolysis temperature, C Fig.. Effect of pyrolysis temperature on the maximum fluoride uptake of bone chars at ph and C. [F - ] t /[F - ] [F - ], mg/l t, h where q F is the fluoride adsorption capacity of bone char, r p is the residence time and T p is the pyrolysis temperature, respectively. For this pyrolysis temperature, the bone char showed the maximum fluoride adsorption capacity, i.e.,. mg/g at ph and C. Based on the statistical analysis of the experimental design, the best conditions for the synthesis of bone char via pyrolysis are: a pyrolysis temperature of C, a heating rate of C/min and a residence time of h. These pyrolysis conditions fulfill the lowest energy requirements for the synthesis of bone char without compromising the product yield and its fluoride adsorption properties. It is convenient to highlight that the maximum fluoride adsorption capacity of bone char prepared in this study is higher than those reported for commercial bone chars, e.g.: Fija fluor. mg/g [], Brimac. mg/g and Carbones Mexicanos. mg/g []. Also, the removal performance of this bone char outperforms the results reported by Abe et al. [] and Kawasaki et al. [], where the fluoride adsorption capacities ranged from. to. mg/g. In summary, the optimization of pyrolysis conditions for the synthesis of bone char is useful to obtain an effective adsorbent for fluoride removal from water, which shows better fluoride adsorption properties than those reported for other commercial bone chars... Kinetic, equilibrium and thermodynamic parameters of fluoride adsorption on bone char prepared using the optimal pyrolysis conditions Fluoride adsorption kinetics at ph and C for the bone char obtained at the best pyrolysis conditions are given in Fig. and the adsorption rates were calculated using the pseudo-second order kinetic model, see Table. This kinetic model was used because preliminary calculations indicated that it may offer a better correlation performance than those obtained for other traditional adsorption kinetic models. Adsorption rates of fluoride on bone char ranged from.e to.9e g/mg min at tested experimental conditions. In particular, the initial adsorption rate (h) increased with Fig.. Fluoride adsorption kinetics at ph and C on the bone char synthetized at the optimal pyrolysis conditions. the initial concentration of fluoride in the solution and the adsorption equilibrium was obtained at h. Kinetic data of fluoride adsorption were also analyzed using the Weber Morris intraparticle diffusion model. Fig. shows the plots of q t versus t. for fluoride adsorption kinetic data at ph and C. It is clear that several steps are involved in the adsorption process of fluoride on bone char because the plot q t t. is multi-linear. First stage of fluoride adsorption is related to surface diffusion, second stage comprises the intraparticle or pore diffusion, and the final stage is given by the adsorption equilibrium. So, the fluoride adsorption rate is controlled by these stages. Note that the value of intercept C of diffusion model increased with the fluoride concentration (see Table ), thus indicating that the surface diffusion has a larger role as the rate-limiting step in fluoride removal using this adsorbent. Fluoride adsorption isotherms on the optimized bone char at different conditions of ph and temperature are reported in Fig.. Overall, the fluoride uptakes of bone char decreased with increments of solution ph, while the fluoride adsorption capacities increased with the temperature. These results are consistent with studies performed by Abe et al. [], Kawasaki et al. [] and Medellin- Castillo et al. [], which have reported the performance of different bone chars for water defluoridation. In particular, solution ph has a higher impact on the fluoride uptakes of bone char than the adsorption temperature. Results of removal experiments indicated that the fluoride adsorption process using bone char is endothermic. Thermodynamic parameters of fluoride adsorption on bone char were calculated using the results of adsorption isotherms at, and C. Specifically, the Gibbs free energy ( G, kj/mol) was determined using G = RT ln K a () Table Kinetic data of fluoride adsorption from water on the bone char synthetized at optimal pyrolysis conditions. Model Parameter [F ], mg/l Pseudo-second order kinetic: q t = q te kt +q te kt Intraparticle diffusion: q t = k d t. + C R k, g/mg min.9e.e.9e q te, mg/g... h = q te k.e.e.e R k d, mg/g min.... C...

7 C.K. Rojas-Mayorga et al. / Journal of Analytical and Applied Pyrolysis () q t, mg/g q t, mg/g q t, mg/g.... a) t., min. b) c) mg/l t., min. mg/l mg/l t., min. Fig.. Linear analysis of fluoride adsorption kinetic data at ph and C using bone char synthetized at the optimal pyrolysis conditions. ln K a = S R H () RT where S is the standard entropy change in kj/mol K, H is the standard enthalpy change in kj/mol, R is the gas universal constant (.E kj/mol K), T is temperature in K and K a is q e, mg/g q e, mg/g 9 9 a) [F - ] e, mg/l b) [F - ] e, mg/l ph T, C Fig.. Fluoride adsorption isotherms at different conditions of ph and temperature using bone char synthetized at the optimal pyrolysis conditions. the adsorption equilibrium constant, respectively. The adsorption equilibrium constant K a was obtained from data fitting of fluoride adsorption isotherms using Langmuir model []. Results of these thermodynamic calculations are reported in Table. Thermodynamic calculations confirmed that the fluoride adsorption on bone char is endothermic and spontaneous. The positive values of standard entropy and enthalpy changes indicate a strong affinity of the bone char to fluoride ions. These results are consistent to those findings of Abe et al. [] and Kawasaki et al. []. Finally, Langmuir and Freundlich models were used for fitting the fluoride adsorption isotherms obtained at tested experimental conditions, see Table. Langmuir model provides the best correlation results for fluoride adsorption isotherms using bone char and the monolayer adsorption capacities ranged from.9 to.9 mg/g at tested experimental conditions... Physicochemical characterization of bone char obtained at optimal pyrolysis conditions and its relationship with fluoride removal mechanism Fig. shows the TG and DTG curves of bovine bone used as precursor for the synthesis of bone chars. There is a weight loss ( %) Table Thermodynamic parameters of the fluoride adsorption from water on the bone char synthetized at optimal pyrolysis conditions. T, C H, kj/mol S, kj/mol K G, kj/mol.....9

8 C.K. Rojas-Mayorga et al. / Journal of Analytical and Applied Pyrolysis () Table Results of data modeling of fluoride adsorption isotherms on the bone char samples obtained from pyrolysis process. Conditions Adsorbent Results of data fitting for isotherm model ph T, C Langmuir Freundlich R K a, L/mg q ml, mg/g R K F, mg/g N Bone char at C Bone char at C Bone char at C Bone char at 9 C Bone char at C Bone char at C Bone char at C Bone char at C Bone char at C Weight, % 9 TGA. dtga DTG T, C Fig.. Results of TGA in Ar of raw bone sample. from room temperature to C, which is related to the loss of moisture. From to C, there is a continuous weight loss (i.e., %) caused by the thermal degradation of organic substances such as proteins, collagen and fat tissues [,]. Finally, a weight loss of % was observed between and C, which is mainly caused by the partial dehydroxylation process of hydroxyapatite and the decomposition of carbonates [ ]. In the dehydroxylation process, the hydroxyapatite loses OH during thermal treatment and this process is given by [] Ca (PO ) (OH) Ca (PO ) (OH) ( x) O x x + xh O () where is a vacancy. This dehydroxylation process may begin at C depending on the operating conditions of the thermal treatment [9,]. Fig. shows the morphology of bone char samples obtained at, and C. Overall, these samples have a similar morphology, which is rough without a defined geometry. Table shows the results of elemental composition and EDX analysis for both raw bone and bone char samples obtained at different pyrolysis temperatures. Overall, the EDX analysis indicates that the raw bone is mainly composed of calcium (Ca) and phosphorus (P) and there are also some minor components such as oxygen (O) and carbon DTG (C). On the other hand, the calculated molar ratio Ca/P of bone char samples, which can be associated to the crystallinity index, decreased with the pyrolysis temperature used for the synthesis of these adsorbents. In general, the Ca/P ratios ranged from. to. for bone char samples obtained at and C, respectively. These Ca/P ratios are higher than the stoichiometric value of. and are in agreement with the results reported in other studies [,]. Particularly, the presence of carbonate in the hydroxyapatite tends to decrease the crystallinity index []. FT-IR spectra of raw bone and bone char samples obtained at different pyrolysis conditions are reported in Fig.. Specifically, Fig. a shows the FT-IR spectrum of the raw precursor where the band at cm corresponds to the stretching vibration of O H [] and the band at 9 cm is assigned to the CH stretching vibration []. Additionally, the bands of groups C O, C C and C N corresponding to the organic phase of the bone matrix are identified at cm []. The band of the phosphate group PO was observed at cm, the peaks of the carbonate group CO are evident at, and cm [,]. On the other hand, Fig. b f shows the FT-IR spectra of the bone char samples obtained at different temperature of pyrolysis. Overall, FT-IR spectra of bone char has 9 bands at,,,,,,, and cm, respectively. These bands correspond to the structure of natural hydroxyapatite (i.e., non-stoichiometric), which contains carbonate groups [,]. The main differences between FT-IR spectra of bone char samples obtained at different pyrolysis temperatures are related to the bands of OH and CO groups; see Fig. b f. Therefore, the dehydroxylation process of hydroxyapatite and the loss of carbonate groups of bone chars caused that the absorption bands of these groups disappear with the increment of the pyrolysis temperature used for the synthesis of adsorbents especially at > C. Similar findings have been also reported by other studies using bone calcination process [,,]. Note that the bands corresponding to the phosphate group remain constant regardless of the pyrolysis temperature used for the bone char synthesis. Fig. 9 reports the XRD patterns of raw bone and bone char samples. XRD patterns confirmed that the diffraction peaks correspond Table Results of elemental analysis and EDX of the raw precursor and bone char samples. Sample Elemental analysis, wt% EDX, wt% C H N S O P Ca Raw bone Bone char at C Bone char at C Bone char at C Bone char at 9 C Bone char at C

9 C.K. Rojas-Mayorga et al. / Journal of Analytical and Applied Pyrolysis () Fig.. SEM images of bone chars obtained at different pyrolysis temperatures: (a, b) C, (c, d) C and (e, f) C. Heating rate: C/min and residence time of h. to the crystal structure of hydroxyapatite in all samples. Note that XRD patterns showed a gradual increase in the intensity of peaks for those bone char samples obtained at high pyrolysis temperature. The differences of XRD patterns (i.e., their narrowness and shape) suggest that the analyzed samples show different degrees of crystallinity. These findings are in agreement to results reported by Younesi et al. []. In addition, the dehydroxylation of the hydroxyapatite may also cause a shifting in the peaks of XRD patterns []. Finally, the textural parameters of selected bone char samples obtained at, and C are reported in Table. The specific surface areas of selected bone chars is relatively low and they do not show significant differences. The bone char obtained from the optimized pyrolysis process showed the following main textural parameters: specific surface area = m /g, total pore volume =. cm /g, and pore size =. nm. The volume of mesopores represents approximately.% of the total pore volume of this adsorbent. The textural properties of commercial bone char have been reported in previous studies and the values obtained in this study are consistent to the results reported in the literature [,]. In summary, the characterization results suggest that the dehydroxylation process of the hydroxyapatite with temperature should play an important role for determining the fluoride adsorption properties of bone char. The hydroxyl groups present on bone chars are thought to be in the fluoride removal using bone char according to the reaction [,] Ca (PO ) (OH) + F Ca (PO ) F + OH () Table Textural parameters of selected bone chars prepared at different temperatures of pyrolysis. Pyrolysis temperature, C Textural parameters of bone char S BET, m /g V Total, cm /g V DR, cm /g V Mesopore, cm /g Pore size, nm

10 C.K. Rojas-Mayorga et al. / Journal of Analytical and Applied Pyrolysis () f) e) Then, by reducing the OH groups decreases the exchange between ions OH and F, directly affecting the adsorption capacity of the bone char obtained from a pyrolysis process. Therefore, the synthesis of bone char at C helps to reduce the effect of the hydroxyapatite dehydroxylation on its fluoride adsorption properties. Transmittance, (%) d) c) b) a) Wavenumber, cm - Fig.. FT-IR spectra of raw precursor and bone chars obtained at different pyrolysis temperatures. Sample: (a) raw bone, (b) C, (c) C, (d) C, (e) 9 C and (f) C. Intensity, a.u. f) e) d) c) b) a) Ca (PO ) (OH), Fig. 9. XRD patterns of raw precursor and bone chars obtained at different pyrolysis temperatures. Sample: (a) raw bone, (b) C, (c) C, (d) C, (e) 9 C and (f) C.. Conclusions This study has performed a systematic analysis and the optimization of the pyrolysis conditions for the synthesis of bone char for fluoride removal from water. Pyrolysis temperature is a critical operating parameter for the synthesis of bone char for fluoride removal from water. Specifically, this temperature has a major effect on the fluoride adsorption properties of bone char due to the dehydroxylation process of the hydroxyapatite contained in this adsorbent. An optimum fluoride uptake of. mg/g can be obtained if a pyrolysis temperature of C is used for bone char synthesis. The fluoride removal performance of the optimized bone char is better than those reported for several commercial bone chars up to %. Fluoride adsorption isotherms on bone char were well fitted using the Langmuir model and the thermodynamic parameters of adsorption process indicated that the fluoride removal from water using this adsorbent is a spontaneous and endothermic process. Finally, this study highlights the relevance of optimizing the pyrolysis conditions for the synthesis of effective adsorbents for water and wastewater treatment. References [] K. Mahapatra, D.S. Ramteke, L.J. Paliwal, Production of activated carbon from sludge of food processing industry under controlled pyrolysis and its application for methylene blue removal, J. Anal. Appl. Pyrol. 9 () 9. [] C. Wu, M. Song, B. Jin, Y. Wu, Z. Zhong, Y. Huang, Adsorption of sulfur dioxide using nickel oxide/carbon adsorbents produced by one-step pyrolysis method, J. Anal. Appl. Pyrol. 99 (). [] J. Albertus, H. Bregnhoj, M. Kongpun, Bone char quality and defluoridation capacity in contact precipitation, in: Proceedings of rd International Workshop on Fluorosis Prevention and Defluoridation of Water,, pp.. [] I. Abe, S. Iwasaki, T. Tokimoto, N. Kawasaki, T. Nakamura, S. Tanada, Adsorption of fluoride ions onto carbonaceous materials, J. Colloid Interface Sci. () 9. [] N. Kawasaki, F. Ogata, H. Tominaga, I. Yamaguchi, Removal of fluoride ion by bone char produced from animal biomass, J. Oleo Sci. (9) 9. [] R. Leyva-Ramos, J. Rivera-Utrilla, N.A. Medellin-Castillo, M. Sanchez-Polo, Kinetic modeling of fluoride adsorption from aqueous solution onto bone char, Chem. Eng. J. (). [] M. Mohapatra, S. Anand, B.K. Mishra, D.E. Giles, P. Singh, Review of fluoride removal from drinking water, J. Environ. Manage. 9 (9). [] A. Bhatnagar, E. Kumar, M. Sillanpaa, Fluoride removal from water adsorption a review, Chem. Eng. J. (). [9] J.C. Moreno-Piraján, R. Gómez-Cruz, V.S. García-Cuello, L. Giraldo, Binary system Cu(II)/Pb(II) adsorption on activated carbon obtained by pyrolysis of cow bone study, J. Anal. Appl. Pyrol. 9 (). [] V. Hérnandez-Montoya, L.A. Ramírez-Montoya, A. Bonilla-Petriciolet, M.A. Montes-Morán, Optimizing the removal of fluoride from water using new carbons obtained by modification of nut shell with a calcium solution from egg shell, Biochem. Eng. J. (). [] V. Hérnandez-Montoya, M.P. Elizalde-González, R. Trejo-Vázquez, Screening of commercial sorbents for removal of fluoride in synthetic and groundwater, Environ. Technol. () 9. [] N.A. Medellin-Castillo, R. Leyva-Ramos, R. Ocampo-Perez, R.F. Garcia de la Cruz, A. Aragon-Piña, J.M. Martinez-Rosales, R.M. Guerrero-Coronado, L. Fuentes- Rubio, Adsorption of fluoride from water solution on bone char, Ind. Eng. Chem. Res. () 9 9. [] D.L. Mwaniki, Fluoride sorption characteristics of different grades of bone charcoal based on batch tests, J. Dent. Res. (99). [] P. Phantumvanit, R.Z. LeGeros, Characteristics of bone char related to efficacy of fluoride removal from highly-fluoridated water, Fluoride (99). [] M.E. Kaseva, Optimization of regenerated bone char for fluoride removal in drinking water: a case study in Tanzania, J. Water Health () 9. [] R. Tovar-Gómez, M.R. Moreno-Virgen, J.A. Dena-Aguilar, V. Hernández- Montoya, A. Bonilla-Petriciolet, M.A. Montes-Morán, Modeling of fixed-bed adsorption of fluoride on bone char using a hybrid neural network approach, Chem. Eng. J. () 9 9.

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