Environ. Sci. Technol. 2008, 42, 1479–1484
Arsenic Transformation and Volatilization during Incineration of the Hyperaccumulator Pteris vittata L. X I U - L A N Y A N , † T O N G - B I N C H E N , * ,† XIAO-YONG LIAO,† ZE-CHUN HUANG,† JIA-RONG PAN,‡ TIAN-DOU HU,§ CAN-JUN NIE,† AND HUA XIE† Center for Environmental Remediation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China, Institute of Agro-Food Science and Technology, Chinese Academy of Agricultural Sciences, Beijing 100094, China, and Laboratory of Synchrotron Radiation, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, China
Received July 16, 2007. Revised manuscript received November 7, 2007. Accepted November 19, 2007.
Safe incineration of harvested hyperaccumulators containing high content of heavy metals to avoid secondary environmental pollution is a problem for popularizing phytoremediation technology. The As volatilization behavior and its mechanism during incineration of Pteris vittata, an As-hyperaccumulator, was investigated. Incineration results reveal that 24% of total As accumulated by P. vittata (H-As) containing high As content (1170 mg/kg) is emitted at 800 °C, of which 62.5% of the total emitted As is volatilized below 400 °C. A study of the extended X-ray absorption fine structure (EXAFS) shows that part of As(III) was identified in the thermal decomposition residue of dried P. vittata (H-As), As2O5 + P. vittata (L-As) containing low As content (14.7 mg/kg), and As2O5 + charcoal (C) at 200 °C, suggesting that carbon originating from biomass incineration might catalyze As(V) reduction. This speculation was tested through thermogravimetric experiments, in which either C or P. vittata (L-As) markedly catalyzed the volatilization of pure As2O5 at low temperature. Therefore, the reduction of As(V) to As(III) is responsible for As volatilization during incineration of P. vittata below 400 °C. This study provides important insights into As behavior during incineration of As-hyperaccumulators, which is helpful to safely dispose harvested biomass with high As content.
Introduction The use of phytoremediation to accumulate metals from contaminated lands by applying hyperaccumulators is considered to be an efficient and cost-effective technology (1). Pteris vittata, an arsenic (As)-hyperaccumulator, has a * Corresponding author e-mail:
[email protected]. † Center for Environmental Remediation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences. ‡ Institute of Agro-Food Science and Technology, Chinese Academy of Agricultural Sciences. § Laboratory of Synchrotron Radiation, Institute of High Energy Physics, Chinese Academy of Sciences. 10.1021/es0717459 CCC: $40.75
Published on Web 02/05/2008
2008 American Chemical Society
great capacity to phytoextract As from soils (2, 3), and has been proven to successfully remediate As-contaminated land (4). It was reported (5) that P. vittata could produce large frond biomass in the phytoremediated site in Hunan Province, China. Therefore, it is of great concern that large quantities of biomass containing several thousands of mg As/kg would be produced by the plants widely grown in Ascontaminated soils for phytoremediation. The safe and economical disposal of the harvest to avoid environmental pollution is a puzzling problem for researchers. Through comparing the general contaminated biomass disposal methods, such as composting, compaction, incineration, ashing, pyrolysis, direct disposal, and liquid extraction, incineration is recommended by Sas-Nowosielska et al. (6) as a feasible and economically acceptable method. But then, heavy metals in the plant might be emitted into the environment during the thermal processing of biomass. Koppolu et al. (7) found that the losses of Ni acetate, Zn acetate, and Cu acetate in synthetic hyperaccumulator biomass varied between 25% and 30% under the condition of pyrolysis in an oxygen free (N2) environment at 600 °C and 1 atm. In a separate study, it was found (8) that a large amount of Cd, Pb, and Zn was volatilized during the gasification of willow wood harvested from contaminated sites. Arsenic is a well-known volatile metalloid and is likely to enter the atmosphere by vaporization during thermal treatment of materials containing As (9, 10). Understanding the behavior of As during incineration of harvested As-hyperaccumulators is crucial to reduce the possible emission of volatile As into air. The main objectives of this research were to examine the fate of As, and identify the mechanism responsible for the As behavior during incineration of P. vittata containing high content of As.
Materials and Methods Sample Preparation. Plant Samples. The aerial parts of P. vittata (H-As) containing high As content (1170 mg/kg) were collected from an As-phytoremediation field in the Hunan Province of Southern China during January 2005. P. vittata (L-As) containing low As content (14.7 mg/kg) were obtained from sandy cultures using Hoagland nutrient solution (without As) which was renewed every 3 days. Details concerning the planting process are given elsewhere (11). After an 8-week culture, the aerial parts of the P. vittata (LAs) were harvested. All samples were washed with tap water, rinsed with deionized water, dried at 70 °C for 2 days, and then pulverized by agate mortar and sieved through a 2-mm mesh. Mixture Samples. The samples were the mixtures of As2O5.aq and P. vittata (L-As) and of As2O5.aq and activated charcoal (C). As2O5.aq and C are powders. Since As2O5.aq is hygroscopic the preparation of the mixtures had to be performed in a chamber purged with dry air. The mixtures were prepared by adding P. vittata and C to the As2O5 and stirring the mixture with a small metal spoon. The mixtures had an As2O5/P. vittata (L-As) ratio or an As2O5/C ratio of 1. Incineration Experiment. The influence of incineration temperature on the As concentration of the resulting incineration residues of P. vittata (H-As) was determined using a muffle furnace. Each dry powder of 0.2000 g was accurately weighed directly into a crucible fitted with a loose lid to prevent loss of the light ash. The reactor temperature was varied between 100 and 800 °C with the heating rate of 25 °C/min, and the duration of the incineration process was VOL. 42, NO. 5, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Effect of temperature on As volatilization and sample weight during incineration of Pteris vittata (H-As). Heating rate is 25 °C/min. Error bars represent ( SE (n ) 3). 4 h. The weight of the plant sample and As concentration in the incineration residues were recalculated to obtain the percentages of weight loss resulting from As volatilization during incineration at different temperatures. These percentages are calculated as follows:
(
weight loss (wt %) ) 1 -
(
As loss (wt %) ) 1 -
) )
mres × 100 mdw
[As]resmres × 100 [As]dwmdw
(1) (2)
where [As]res and [As]dw correspond to the As concentrations (in mg/kg) in the residue and dried plant sample, respectively, and mres and mdw correspond to the masses (in g) of the residue and dried plant sample, respectively. Thermogravimetric Analysis. Thermogravimetric (TG) experiments were carried out using Pyris 1 TGA (Perkin-Elmer Co.) supported by a PC and software for control and data handling. Approximately 0.0200 g of the sample was introduced into a platinum sample pan and then heated to a preset temperature with the heating rate of 25 °C/min. Dry air was used as a purge gas with the flow rate of 65 mL/min. 1480
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Arsenic Speciation Determination. X-ray absorption spectroscopy (XAS) was used in the study to determine the As speciation of different samples. Samples were packed into a 3 cm × 0.7 cm sample holder. The solutions of model As compounds (Na2HAsO4 and NaAsO2) were pipetted into a Lucite liquid holder of the same size. Arsenic K-edge (11867 eV) X-ray absorption spectra were collected using a double crystal monochromator (Si 111) in the fluorescence mode at room temperature, operated at the EXAFS station on Beamline 1W1B of the Beijing Synchrotron Radiation Facility (BSRF). The electron storage ring was operated at 2.2 GeV, with the angle between the monochromator crystal faces being adjusted to purposely mistune the incident beam by 30%. The XAS data were scanned from 11.72 to 12.66 keV. The entire XAS spectra were background corrected and normalized. Then, near-edge spectra (XANES) were extracted from the total spectra with a range of 11.84-11.94 KeV. EXAFS spectra were extracted after E-K conversion, and then k3 weighted and Fourier transformed to obtain the radial distribution functions (RDFs). Final fittings of the interatomic distance (R) and coordination number (N) were performed
FIGURE 2. Fourier transforms (A) and XANES data (B) of As K-edge EXAFS of samples from P. vittata (H-As) and As model compounds. Solid lines show the data and the dashed lines show the best fit (Table 1). The spectra were offset vertically but were plotted with the same relative scale.
TABLE 1. Results of Fitting As K-edge EXAFS of P. vittata (H-As) and Model Compoundsa sample or model temperature compound (°C) Na2HAsO4 NaAsO2 P. vittata (H-As) P. vittata (H-As) P. vittata (H-As) P. vittata (H-As)
25 25 70 200 400 800
type As-O As-O As-O As-O As-O As-O
CN R (Å) residual 4.0 3.0 3.3 2.8 4.1 4.1
1.69 1.80 1.71 1.83 1.69 1.69
18.6 28.3 29.9 16.0 16.2
σ2 0.003 0.007 0.008 0.004 0.002 0.002
a The coordination type (type), coordination number (CN), interatomic distance (R), measure of the static disorder of the shell (σ2), and goodness-of-fit (R-value) are presented.
using WinXAS 2.3 software (12). Theoretical EXAFS simulations were performed using FEFF V 7.0 (13). Arsenic Analysis. The sample weight change and As concentration were measured. After cooling, the residues were carefully rinsed with 10 mL of 50% HCl, then dried at 100 °C. The dried samples were digested by 5 mL of concentrated HNO3 and 1 mL of concentrated HClO4 solutions (2, 14), and 5 mL of 15% Mg(NO3)2 solution and 0.2 g of MgO were also added to avoid As loss. Arsenic in solution was then detected using an atomic fluorescence spectrometer (AFS-2202, Haiguang Instrumental Co., China). Standard reference materials for plants (GBW-07603 and GBW-08501), obtained from the China National Center for Standard Reference Materials, were also treated and determined along with the samples and used for the QA/QC program.
Results and Discussion Arsenic Release during Incineration. It is obvious that incineration can largely reduce the sample weight of P. vittata (Figure 1). It was found that 80% of the biomass had been decomposed at 400 °C, and when the incineration temper-
ature increased to 800 °C, the biomass of P. vittata decomposed thoroughly with a weight loss of 94%. During incineration at the temperature range of 100–800 °C, As volatilization presented an increasing trend, and the release of As in sample reached a value of 24% at 800 °C (Figure 1). The work of Vassileva et al. (15) indicated that no As losses occurred when plants of terrestrial origin (vegetable, grass, rice flour, tomato leaves, citrus leaves, cabbage) with As concentrations of several mg/kg were mineralized during the dry ashing procedure using a muffle furnace. Therefore, the As behavior observed during incineration may be related to the As concentration in the samples. Additionally, 15% of the As volatilized below 400 °C, i.e., nearly 62.5% of the total volatilized As emitted during this period (Figure 1), suggesting that As volatilization at low incineration temperatures plays an important role in its emission. Previous studies have found that either combustion or pyrolysis of coal and CCA-treated wood would unavoidably produce As volatilization, which is one of the main sources of atmospheric As pollution (16–20). A large proportion of As was observed to be released below 400 °C during the incineration of P. vittata in the study, and the phenomenon was also found in thermal decomposition of CCA-treated wood (18, 19, 21). Whereas, other reports show that As is mostly volatilized within the high-temperature combustion zone (above 1000 °C) for coal and CCA-treated wood (20, 22, 23). Kryukova et al. (24) concluded that the extent of As volatilization from coal is controlled by the mineralogical residence of As, such as the contents of organic-bound As, pyrite-bound As, and micromineral As. Although CCA-treated wood and P. vittata are both biomass materials, the As present in CCA-treated wood is an artificially additive element and mainly coordinated with Cr to form the CrAsO4 precipitate (21), while As in fresh pinna leaves of P. vittata is a biological accumulation element and exists predominantly as arsenite (11, 25). One possible reason resulting in the difference between P. vittata and other combustible materials could be related to the way As is bound in the materials. VOL. 42, NO. 5, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 3. Profiles of TG and DTG of each combustible. The ratio of mixtures of As2O5 + C and As2O5 + P. vittata (L-As) are both 1:1. The heating rate was 25 °C/min and the residence time at the final temperature was 15 min.
FIGURE 4. Fourier transforms (A) and XANES data (B) of As K-edge EXAFS of samples. Solid lines show the data and the dashed lines show the best fit (Table 2). The spectra were offset vertically but plotted with the same relative scale. The As concentrations in P. vittata (L-As) and C are 14.7 mg/kg and 0.38 mg/kg, respectively. The As concentration in the ash incinerated at 800 °C averages 13,000 mg/kg, which increased by nearly 11 times compared to the concentration of dry P. vittata (H-As) (Figure 1). This ash with such high As concentration can be considered as a rich “ore” or As concentrate which can be further processed for recovery of As. As Transformation during Incineration. To further understand the release of As during incineration of P. vittata, the As speciation of samples treated at different temperatures was analyzed by EXAFS (Figure 2 and Table 1). For the sample of P. vittata (H-As) dried at 70 °C, As was coordinated with oxygen in the first coordination shell at a distance of 1.71 ( 1482
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0.008 Å, which was similar to that of As(V)-O. With the temperature rising to 200 °C, the sum of the As coordination number (CN) approximated 2.8 and the interatomic distance (R) of As-O approximated 1.83 Å, indicating that As is partly presented as As(III) in the residue. The As-O coordination in the incineration residues at both 400 and 800 °C was found to be similar to that of As(V)-O (Figure 2 and Table 1), meaning that As was mainly presented as As(V) in the two residues. The presence of As(III) in the incineration residue of 200 °C indicated that the As(V) component in dried P. vittata (H-As) comprising a high As content was partly reduced to As(III) during the incineration process.
TABLE 2. Results of Fitting As K-edge EXAFS of Samplesa sample or model compound
temperature (°C)
As2O5 As2O5 + P. vittata (L-As) As2O5 + C
200
As-O 3.8 1.70
25.9
0.005
200 200
As-O 2.9 1.78 As-O 3.2 1.74
22.2 25.2
0.004 0.004
type
CN R (Å) residual
σ2
a
The coordination type (type), coordination number (CN), interatomic distance (R), measure of the static disorder of the shell (σ2), and goodness-of-fit (R-value) are presented.
It was found that As(III) was present in the pyrolysis residue of CCA-treated wood at 350 °C, and speculated that As release might be described by two consecutive reactions (reduction followed by volatilization) (21, 26). It can be concluded from the experiment with P. vittata that As reduction may be the main reason responsible for As release below 400 °C. As Reduction during Incineration of P. vittata. It was found that pure As2O5 would not decompose (or reduce) nor volatilize at temperatures lower than 600 °C (Figure 3). The TG and DTG curves of a mixture of As2O5 + P. vittata (L-As) containing little As were not a simple addition of pure As2O5 and P. vittata (L-As) (Figure 3A and B), meaning that the two materials reacted with each other during the incineration process, and special phenomenon could be found. First, the weight loss of the As2O5 + P. vittata (L-As) mixture is nearly 20% around 200 °C, which is much higher than that of either pure As2O5 or P. vittata (L-As) at the same temperature, indicating that some materials produced during the incineration of P. vittata can catalyze As2O5 decomposition below 200 °C. Second, the temperature at which the As2O5 + P. vittata (L-As) mixture was thoroughly decomposed was found to occur at 528 °C, which is higher than the temperature (450 °C) at which P. vittata (L-As) is thoroughly decomposed, but much lower than that (812 °C) of pure As2O5. Therefore, the presence of P. vittata (L-As) ensures that As2O5 decomposition happens at much lower temperature. For the As2O5 + C mixture, the lower DTG peak temperature (namely the temperature at a maximum rate of weight loss) of 217 °C was the same as that for pure As2O5. However, the higher peak temperature which appeared at 473 °C was lower than the values for pure As2O5 and pure C. When the temperature was above 600 °C, the As2O5 + C mixture totally volatilized. It is observed that C catalyzed the volatilization of As2O5 below 300 °C, which is similar to the phenomenon observed by Helsen et al. (27) in an inert N2 atmosphere. According to the results of the TG experiments, both C and P. vittata (L-As) markedly influenced the thermal behavior of As2O5: The temperature at the onset of thermal decomposition and the DTG peak temperature were both lowered. To gain further insights, the As speciation of As2O5 following different treatments was studied using EXAFS (Figure 4 and Table 2). The As coordination number (CN) and interatomic distance (R) of As-O in As2O5 at 200 °C were approximate with those of As(V), indicating that the As species did not change. However, when the mixture of As2O5 + P. vittata (L-As) was thermally decomposed at 200 °C, R of As-O in the sample was 1.78 Å, similar to that of As(III)-O. The result means some material produced from the biomass incineration could catalyze As2O5 partial reduction to As(III). The primary pyrolysis of biomass materials usually presents in the range of 200–400 °C, which results in bulk product volatilization and the formation of a solid char residue (28). In previous study of pyrolysis of CCA-treated wood, Hata et al. (18) have found that carbon could catalyze
the As2O5 transformation from As(V) to As(III) (As(V)2O5 + 2CfAs(III)2O3 + 2CO) at temperatures of 150–200 °C. Once As trioxide is formed, it will be released as As4O6 at temperatures as low as 200 °C (27, 29). In this experiment, when As2O5 is blended with C and thermally decomposed at 200 °C, the As CN was 3.2 and R of As-O was 1.74 Å, which was an R value between As(V)-O and As(III)-O, meaning that part of the As(III) is presented in the thermally decomposed residue. The reduction of As(V) might be the main reason for C or P. vittata (L-As) markedly lowering the temperature at the onset of thermal decomposition of As(V)2O5, as discovered in the TG experiments. According to the results of TG and EXAFS, the reason for As release from P. vittata below 400 °C may be controlled by the reduction of As(V) to As(III) when catalyzed by carbon originating from biomass incineration. When the temperatures exceeded 400 °C, the carbon may become completely oxidized and As release might be related with volatilization of some As compounds in P. vittata. The indication obtained from this study provides important information for the safe disposal of harvested As-hyperaccumulators and other biomass having a high As content.
Acknowledgments This work was supported by the National Science Foundation for Distinguished Young Scholar (Grant 40325003).
Literature Cited (1) Lasat, M. M. Phytoextraction of toxic metals: a review of biological mechanisms. J. Environ. Qual. 2002, 31, 109–120. (2) Chen, T. B.; Wei, C. Y.; Huang, Z. C.; Huang, Q. F.; Lu, Q. G.; Fan, Z. L. Arsenic hyperaccumulator Pteris vittata L. and its arsenic accumulation. Chin. Sci. Bull. 2002, 47 (11), 902–903. (3) Ma, L. Q.; Komar, K. M.; Tu, C.; Zhang, W. H.; Cai, Y.; Kennelley, E. D. A fern that hyperaccumulates arsenic. Nature 2001, 409, 579. (4) Chen, T. B.; Liao, X. Y.; Huang, Z. C.; Lei, M.; Li, W. X.; Mo, L. Y.; An, Z. Z.; Wei, C. Y.; Xiao, X. Y.; Xie, H. Phytoremediation of As-contaminated soil in China. In Phytoremediation: Methods and Reviews; Willey, N., Ed.; Humana Press: NJ, 2007; pp 393– 404. (5) Liao, X. Y.; Chen, T. B.; Xie, H.; Xiao, X. Y. Effect of application of P fertilizer on efficiency of As removal from As-contaminated soil using phytoremediation: Field study. Acta Sci. Circumstantiae 2004, 24 (3), 455–462. (6) Sas-Nowosielska, A.; Kucharski, R.; Małkowski, E.; Pogrzeba, M.; Kuperberg, J. M.; Kryn ´ ski, K. Phytoextraction crop disposal - an unsolved problem. Environ. Pollut. 2004, 128, 373–379. (7) Koppolu, L.; Prasad, R.; Clements, L. D. Pyrolysis as a technique for separating heavy metals from hyperaccumulators. Part III: Pilot-scale pyrolysis of synthetic hyperaccumulator biomass. Biomass Bioenerg. 2004, 26, 463–472. (8) Vervaeke, P.; Tack, F. M. G.; Navez, F.; Martin, J.; Verloo, M. G.; Lust, N. Fate of heavy metals during fixed bed downdraft gasification of willow wood harvested from contaminated sites. Biomass Bioenerg. 2006, 30, 58–65. (9) Yudovich, Ya.E.; Ketris, M. P. Arsenic in coal: a review. Int. J. Coal Geol. 2005, 61, 141–196. (10) Mahuli, S.; Agnihotri, R.; Chauk, S.; Gosh-Dastidar, A.; Fan, L. S. Mechanism of arsenic sorption by hydrated lime. Environ. Sci. Technol. 1997, 31 (11), 3226–3231. (11) Huang, Z. C.; Chen, T. B.; Lei, M.; Hu, T. D. Direct determination of arsenic species in arsenic hyperaccumulator Pteris vittata by EXAFS. Acta Bot. Sin. 2004, 46 (1), 46–50. (12) Ressler, T. J. WinXAS: a program for X-ray absorption spectroscopy data analysis under MS-Windows. Synchrotron Radiat. 1998, 5, 118–122. (13) Ankudinov, A. L.; Ravel, B.; Rehr, J. J.; Conradson, S. D. Realspace multiple-scattering calculation and interpretation of x-rayabsorption near-edge structure. Phys. Rev. B 1998, 58 (12), 7565– 7576. (14) Yin, M.; Li, B. Determination of rare earth elements in human hair and wheat flour reference materials by inductively coupled plasma mass spectrometry with dry ashing and microwave digestion. Spectrochim. Acta B 1998, 53, 1447–1454. (15) Vassileva, E.; Docˇekalová, H.; Baeten, H.; Vanhentenrijk, S.; Hoenig, M. Revisitation of mineralization modes for arsenic VOL. 42, NO. 5, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1483
(16)
(17) (18)
(19) (20) (21) (22)
1484
and selenium determinations in environmental samples. Talanta 2001, 54, 187–196. Germani, M. S.; Zoller, W. H. Vapor-phase concentrations of arsenic, selenium, bromine, iodine, and mercury in the stack of a coal-fired power plant. Environ. Sci. Technol. 1988, 22 (9), 1079–1085. Zajusz-Zubek, E.; Konieczyn ´ ski, J. Dynamics of trace elements release in a coal pyrolysis process. Fuel 2003, 82, 1281–1290. Hata, T.; Bronsveld, P. M.; Vystavel, T.; Kooi, B. J.; De Hosson, J. Th. M.; Kakitani, T.; Otono, A.; Imamura, Y. Electron microscopic study on pyrolysis of CCA (chromium, copper and arsenic oxide)-treated wood. J Anal. Appl. Pyrol. 2003, 68/69, 635–643. Helsen, L.; Bulck, E. V. D. Metal retention in the residue after low-temperature pyrolysis of chromated copper arsenate (CCA) treated wood. Environ. Eng. Sci. 2003, 20 (6), 569–580. McMahon, C. K.; Bush, B. B.; Woolson, E. A. How much arsenic is released when CCA treated wood is burned? Forest Prod. J. 1986, 32 (11/12), 45–50. Helsen, L.; Bulck, E. V. D. Metal behavior during the lowtemperature pyrolysis of chromated copper arsenate-treated wood waste. Environ. Sci. Technol. 2000, 34, 2931–2938. Miller, B. B.; Dugwell, D. R.; Kandiyoti, R. Partitioning of trace elements during the combustion of coal and biomass in a suspension-firing reactor. Fuel 2002, 81 (2), 159–171.
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 5, 2008
(23) Furimsky, E. Characterization of trace element emissions from coal combustion by equilibrium calculations. Fuel Process. Technol. 2000, 63, 29–44. (24) Kryukova, V. N.; Kindeeva, V.; Bas’kova, L. V.; Latyshev, V. Arsenic in Eastern Siberian coals. Khim. Tverd. Topliva [Chem. Solid Fuels] 1985, 1, 129–132. (25) Zhang, W. Y.; Cai, Y.; Tu, C.; Ma, L. Q. Arsenic speciation and distribution in an arsenic hyperaccumulating plant. Sci. Total Environ. 2002, 300, 167–177. (26) Helsen, L.; Bulck, E. V. D.; Van Bael, M. K.; Mullens, J. Arsenic release during pyrolysis of CCA treated wood waste: current state of knowledge. J. Anal. Appl. Pyrol. 2003, 68, 613–633. (27) Helsen, L.; Bulck, E. V. D.; Van Bael, M. K.; Vanhoyland, G.; Mullens, J. Thermal behaviour of arsenic oxides (As2O5 and As2O3) and the influence of reducing agents (glucose and activated carbon). Thermochim. Acta 2004, 414, 145–153. (28) Fisher, T.; Hajaligol, M.; Waymack, B.; Kellogg, D. Pyrolysis behavior and kinetics of biomass derived materials. J Anal. Appl. Pyrol. 2002, 62, 331–349. (29) Kercher, A. K.; Nagle, D. C. TGA modelling of the thermal decomposition of CCA treated lumber waste. Wood Sci. Technol. 2001, 35 (4), 325–341.
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