TREATMENT OF 1,1,1-TRICHLOROETHANE WITH REACTIVE NANOSCALE IRON PRODUCT IN SIMULATED GROUNDWATER

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1 Paper 2E-01, in: A.R. Gavaskar and A.S.C. Chen (Eds.), Remediation of Chlorinated and Recalcitrant Compounds Proceedings of the Fourth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2004). ISBN , published by Battelle Press, Columbus, OH, TREATMENT OF 1,1,1-TRICHLOROETHANE WITH REACTIVE NANOSCALE IRON PRODUCT IN SIMULATED GROUNDWATER Kenji Okinaka (Toda Kogyo Corporation, Yamaguchi, Japan) Andreas D. Jazdanian (Burns & McDonnell, Oak Brook, Illinois, U.S.A.) Hisashi Shimizu (Toda America Incorporated, Schaumburg, Illinois, U.S.A.) Tomoko Okita (Toda Kogyo Corporation, Hiroshima, Japan) Koji Kakuya (Toda Kogyo Corporation, Yamaguchi, Japan) ABSTRACT: In this study the degradation of 1,1,1-trichloroethane (TCA) with a reactive nanoscale iron product (RNIP) that is produced in bulk quantities was investigated. TCA degradation was determined with various RNIP and TCA concentrations, and for different solution alkalinities and ionic strengths. The experiments were spiked with 1.31 mg to 13.1 mg TCA, resulting in initial aqueous concentrations of 26.3 to mg/l. The three different solutions used in this study consisted of deionized water, a solution with 95 mg/l alkalinity and total ionic strength of 0.05 M, and a solution with 383 mg/l alkalinity and total ionic strength of 0.1 M. For static tests (no shaking), overall mass reductions of more than 80% for 1 g/l RNIP and more than 99% for 8.3 g/l RNIP were observed. The large reactive surface area of RNIP reduced the high TCA concentrations with low treatment dosages (1 to 4.2 g/l). The production of 1,1-dichloroethene (DCA), ethene and ethane was not proportional to the degradation of TCA. The acidity resulting from the dechlorination (HCl) consumed the alkalinity and diminished degradation rates. Hydrogen concentrations had a positive correlation with increasing RNIP concentrations and hydrogen acidity. INTRODUCTION Recently, an increasing interest in the use of nanoscale metallic materials for aquifer remediation has developed. The reduction of chloroalkanes and chloroalkenes with laboratory grade metallic and bimetallic nanoscale materials has received considerable attention. In this work, a reactive nanoscale iron product (RNIP) that is produced in bulk quantities was used for the degradation of dissolved phase 1,1,1-trichloroethane (TCA). The degradation of TCA was investigated with various RNIP and TCA concentrations, and for different solution alkalinities and ionic strengths. The investigated initial TCA concentrations were representative of ground water source area contamination and ranged from 26.3 mg/l to mg/l. MATERIALS AND METHODS Aqueous RNIP suspension was produced using the method described in the European and United States patents by Uegami et al. (2003). For this study an aqueous suspension of RNIP-10DS was prepared. 1,1,1-trichloroethane (TCA) was obtained in high purity (98.0%) and was used as received. Further, sodium sulfate (Na 2 SO 4 ) and sodium bicarbonate (NaHCO 3 ) were obtained in 95% purity and were used as received.

2 The sulfur content of RNIP was determined with an element analyzer by complete combustion and thermal conductivity detection. X-ray powder diffraction (XRD) patterns were recorded with a diffractometer using a monochromatic CuKa radiation in the angular range from 10 to 90 (2θ). The scanning electron microscope (SEM) analysis was performed with an operating voltage of 10 kv. The specific surface area was determined with the BET gas adsorption method using nitrogen gas. Stock solutions with ionic strength of 0.05 M and 0.1 M were prepared with NaHCO 3 and Na 2 SO 4. Stock solution I with 0.05 M ionic strength was prepared with 2.0 mm NaHCO 3 and 16.0 mm Na 2 SO 4. Stock solution II with 0.1 M ionic strength was prepared with 8.0 mm NaHCO 3 and 30.7 mm Na 2 SO 4. The total dissolved solids (TDS) concentration of stock solution I and II was calculated to be 2,440 mg/l and 5,027 mg/l, respectively, based on the concentration of the dissolved ionic species (HCO 3 -, SO 4 2- and Na + ). The ph of the stock solutions was measured with a calibrated ph meter and was ph 8.1 ± 0.05 and 8.4 ± 0.05 for stock solutions I and II, respectively. The CaCO 3 alkalinity of stock solution I and II was calculated to be about 100 mg/l and 400 mg/l, respectively, based on the solution ph and concentration of bicarbonate (HCO 3 - ). Initially a series of calibration experiments were performed without RNIP in crimp-sealed 68 ml amber bottles. Each bottle received 30 ml of deionized water (ph 6.1). Standard gases were prepared for the volatile organic compounds (VOCs) TCA, 1,1- dichloroethene (DCA), ethene and ethane. Experiments were prepared with various concentrations of VOCs. After 24 h an equilibrium gas sample (30 µl) was withdrawn and the gas sample was analyzed for the VOCs. The aqueous VOC concentrations were calculated based on the concentrations determined for the gas phase. TCA degradation experiments were conducted with DIW, solutions I and II (Sol I and II), and RNIP. The volume of TCA added was 1, 5 or 10 µl, which was equivalent to 1.31 mg, 6.56 mg and 13.1 mg TCA, respectively. The mass of added TCA resulted in initial aqueous concentrations (C o ) of 26.3 mg/l, mg/l and mg/l, respectively. Four different RNIP concentrations were tested: 1, 2, 4.2 and 8.3 g/l. The experiments were prepared by first adding dry RNIP, followed by 30 ml DIW or Sol I or Sol II to the reaction bottles. The 68 ml reaction bottles were crimp-sealed with PTFE/rubber septa. TCA was injected with a microliter syringe. All experiments were static (no shaking) and were conducted in the isothermal room kept at 24 C. The experiments were sampled after three different reaction times by withdrawing µl of headspace gas for analysis. The total reaction times ranged from 168 h to 336 h, based on the initial determination of approximate reaction endpoints. The gas was analyzed for TCA and DCA with a gas chromatograph-mass spectrometer (GC-MS), and ethene, ethane, hydrogen (H 2 ) and carbon dioxide (CO 2 ) were analyzed with a GC. Control experiments with DIW and TCA were also conducted. All experiments were prepared in duplicate. At the end of the experiment the solution was filtered with a glass fiber filter (0.6 µm pore size) using an aspirator pump. The solution was qualitatively analyzed for degradation products. The final solution ph was determined using a calibrated ph-meter. The final solution alkalinity was determined with titration to an endpoint ph 4.8 using a titrator and 20 mm hydrochloric acid (HCl).

3 RESULTS AND DISCUSSION Toda Kogyo s reactive nanoscale iron particles (RNIP-10DS) consisted of an elemental iron core (a-fe) and a magnetite shell (Fe 3 O 4 ) determined with x-ray diffraction methods. The approximate composition of RNIP-10DS is 50 wt.% a-fe core and 50 wt.% Fe 3 O 4. The density of the aqueous RNIP suspension was 1.27 g/ml, and its solids concentration was 25.6 wt.%. The average particle size was determined with a scanning electron microscope (SEM) and was 70 nm (0.07 µm). The average BET surface area of RNIP- 10DS was 28.8 m 2 /g. RNIP-10DS sulfur content was 4,580 mg/kg. The sulfur originates from the ferrous sulfate starting material that is used for the production of RNIP. The results presented are averages of duplicate experiments. The degradation of TCA depended on the mass of RNIP and the reaction time. Table 1 presents the overall reduction of the initial mass of TCA (M0) for each combination of solution composition and RNIP concentration tested. The RNIP masses investigated were 0.03 g, 0.06 g, and 0.25 g (for 1, 2, 4.2 and 8.3 g/l), which resulted in a total reactive surface area of 0.86 m 2, 1.73 m 2, 3.63 m 2 and 7.17 m 2 (about 9.3 ft 2, 18.6 ft 2, 39.1 ft 2 and 77.2 ft 2 ), respectively. The overall mass reductions presented in Table 1 encompass TCA reduction in both the gas and the aqueous phase at the end of the experiments. The overall TCA mass of 1.31 mg was reduced by up to 92.9% with 2 g/l RNIP. TCA mass reductions of more than 95% were observed for the initial masses of 6.56 mg and 13.1 mg with 4.2 g/l RNIP. TABLE 1. TCA mass reduction in percent (%) for the solution compositions and RNIP concentrations tested M 0 = 1.31 mg M 0 = 6.56 mg M 0 = 13.1 mg RNIP DIW Sol I Sol II DIW Sol I Sol II DIW Sol I Sol II 1 g/l g/l g/l g/l The final aqueous TCA concentrations for each experimental condition are presented in Table 2. The final TCA concentration decreased with increasing RNIP concentration. Figure 1 presents the degradation of the initial aqueous TCA concentration of mg/l by the four different RNIP concentrations in Sol I and II. The production of DCA, ethene and ethane was not proportional to the degradation of TCA. In general, final TCA concentrations were slightly lower for the experiments with Sol II than the experiments with Sol I. Conversely, final DCA, ethene and ethane concentrations were slightly higher for the experiments with Sol II than the experiments with Sol I. The DCA present at the end of the experiment ranged from 7.9 mole% to 14.5 mole% of the initial molar mass of TCA (6.56 mg = mm TCA). The final ethene concentration ranged from 3.4 mole% to 4.8 mole%, and the final ethane concentration ranged from 15.2 mole% to 32.0 mole% of the initial molar mass of TCA. Other degradation products such as ethanetiol, diethyl sulfide, diethyl disulfide, and C 4 -C 6 alkanes and alkenes were also detected in the aqueous phase, but were not quantified.

4 TABLE 2. Final aqueous TCA concentration for the solution compositions and RNIP concentrations tested C 0 = 26.3 mg/l C 0 = mg/l C 0 = mg/l RNIP DIW Sol I Sol II DIW Sol I Sol II DIW Sol I Sol II 1 g/l g/l g/l g/l Notes: Unit for concentration is milligram per liter (mg/l). TCA (mg/l) TCA-Sol I TCA-Sol II 1,1-DCA-Sol I 1,1-DCA-Sol II Ethene-Sol I Ethene-Sol II Ethane-Sol I Ethane-Sol II RNIP (g/l) CVOC Products (mg/l) FIGURE 1. TCA degradation and daughter products in Sol I and Sol II for C 0 = mg/l The overall observed degradation rate (k obs ) of TCA increased with RNIP concentration. The degradation rates were calculated with the concentrations measured in the headspace gas samples that were collected at three different times. The negative natural logarithm for the ratio of the initial concentration (C 0 ) to the concentration at the time of sampling (- ln C 0 /C) was plotted versus time to evaluate the degradation kinetics (data not shown). The four temporal concentration data points (T 1 through T 4 ) were used to generate linear plots. The linearity of the plots (regression coefficients (r 2 ) were greater than 0.95) indicated a first-order or pseudo-first order reaction kinetic for the degradation of TCA. The degradation rates (k obs ) were derived by calculating the slope of these linear curves. The degradation rates for the experiments with initial gas and aqueous phase concentration of 68.8 mg/l and mg/l, respectively, are presented in Table 3. The half-lives (k 1/2 ) were also derived from - ln C o /C versus time plots and are also presented in Table 3. The following are some factors that may affect the degradation rate: the available surface area, diffusion of TCA into the RNIP layer at the bottom of the reaction bottle, adsorption of ions and VOCs to RNIP, formation of ferrous sulfide or carbonate on RNIP surfaces, and the surface deactivation due to oxidation. For the experiments

5 TABLE 3. Degradation rates (k obs ) and half-lives (k 1/2 ) for TCA Deionized Water Solution I Solution II RNIP Phase Phase Phase (g/l) k obs k 1/2 k obs k 1/2 k obs k 1/ Notes: Unit for k obs is the inverse of hour (1/h), and for k 1/2 is (h) Initial aqueous concentration: mg/l; Initial gas phase concentration: 68.8 mg/l with 1 g/l RNIP (0.86 m 2 ), the experiments with DIW had a lower degradation rate than the experiments with Sol I or Sol II (see Table 3). For the experiments with higher RNIP concentrations, the degradation rates were more or less comparable for experiments with DIW, Sol I or Sol II. These results suggest that the effect of ionic strength (TDS) is insignificant, whereas alkalinity influences the degradation rate at low RNIP concentrations. The dechlorination of TCA produces acid (HCl), which is neutralized by bicarbonate. In catalytic dehalogenation bases are utilized to maintain alkaline ph conditions which enhance the dehalogenation activity of metal catalysts by neutralizing the acids produced (Rylander, 1967). The change in solution ph and alkalinity for the three solution compositions investigated is presented in Table 4. Although the molar amounts of bicarbonate in Sol I and Sol II (2 mm and 8 mm, respectively) are greater than the molar amounts of chloride (Cl - ) that may be released by dechlorination (about 0.15 mm chloride for M 0 = 6.56 mg), the reaction of RNIP with TCA resulted in a decline of solution ph. The decline in ph is less for Sol II than for Sol I. The reaction of zerovalent iron (Fe 0 ) with water releases Fe 2+ TABLE 4. Change in ph and alkalinity for C 0 = mg/l for the solution compositions and RNIP concentrations tested RNIP ph Alkalinity CO 2 Initial Final Initial Final Pressure (g/l) (mg/l) (mg/l) (log atm) Deionized Water Solution I Solution II

6 and OH - ions into the solution (see Eq. 1). Bicarbonate (HCO 3 - ) reacts with OH - to yield carbonate ions (see Eq. 2). The hydrogen acidity can be buffered by carbonate (CO 3 2- ) or bicarbonate (see Eq. 3). Fe 0 + 2H 2 O Fe 2+ + H 2 +2OH - (1) HCO OH - CO H 2 O (2) H + + CO 3 2- HCO 3 - (3) However, the carbonate alkalinity was consumed by the reactions of TCA with RNIP. The partial carbon dioxide (CO 2 ) pressures, calculated with the final solution ph and the initial alkalinity for the experiments with Sol I and Sol II are listed in Table 4. With the exception of the experiment with the final ph of 9.66, the calculated partial pressures are by orders of magnitude greater than the atmospheric partial pressure for CO 2 ( atm). The calculated partial pressures are 1.8 to 1,016 times the atmospheric partial pressure for CO 2. These results indicate that CO 2 degassed from the solution into the headspace of reaction bottles and escaped the reaction bottles upon opening of the seal. Besides the dechlorination of TCA, the reactions of Fe 2+ with water can yield hydrogen acidity (Eq. 4). Another source of acidity may be the dissociation of carbonic acid that results from the combination of dissolved CO 2 with water. In addition, the dissociation of hydrogen sulfide from the reaction of elemental sulfur (S 0 ) with hydrogen gas can produce hydrogen acidity (Eqs. 5-7). Fe 2+ + H 2 O Fe(OH) + + H + (4) S 0 + H 2 H 2 S (5) H 2 S HS - + H + (6) HS - S 2- + H + (7) Fe 2+ + S 2- FeS (8) The evolution of both hydrogen and carbon dioxide gas was detected in the experiments (see Figure 3). RNIP-10DS contained sulfur that participated in the dechlorination reactions. Several organic sulfide compounds were detected in the aqueous phase. The sulfur containing compounds detected were ethanethiol, diethyl sulfide and diethyl disulfide. The sulfur seems to have participated in the dechlorination reactions in the form of the HS - or S 2- bases (Vogel et al. 1987; Lipczynska-Kochany et al., 1994). The sulfur bases may have stemmed from the dissociation of hydrogen sulfide, which was not detected in either the gas or the aqueous phase (see Eqs. 5-7). The activity of sulfur species may have contributed to the high degradation rates of experiments with DIW and RNIP concentrations greater 1 g/l (see Table 3). The absence of hydrogen sulfide could also be a result of ferrous sulfide (FeS) formation, which occurs in reducing environments (see Eq. 8). Lipczynska-Kochany et al. (1994) have reported that mixtures consisting of Fe 0 and ferrous sulfide (FeS) have a greater degradation rate for carbon tetrachloride than Fe 0 only.

7 The effect of TCA concentration on the degradation rate is shown in Figure 2. The degradation rates for two initial aqueous concentrations and two RNIP concentrations are juxtaposed in Figure 2. In experiments with C 0 = mg/l, the carbonate alkalinity was almost completely consumed and the solution ph declined from ph 8.1 for Sol I and ph 8.5 for Sol II to ph 5.6 (data not shown). For experiments with 8.3 g/l RNIP, the degradation rates for C 0 = mg/l were more than 2.5 times the degradation rates for C 0 = mg/l. For experiments with 4.2 g/l RNIP, the degradation rates for the two initial concentrations were about the same. Degradation Rate (1/h) RNIP 4.2 g/l RNIP 8.3 g/l DIW Sol I Sol II DIW Sol I Sol II Co=131.4 mg/l Co=262.9 mg/l FIGURE 2. TCA degradation rates for the solution compositions and RNIP concentrations tested Hydrogen (mm) RNIP 1 g/l RNIP 2 g/l RNIP 4.2 g/l RNIP 8.3 g/l DIW Sol I Sol II DIW Sol I Sol II Co=131.4 mg/l Co=262.9 mg/l FIGURE 3. Hydrogen gas concentrations for the solution compositions and RNIP concentrations tested

8 This comparison of degradation rates suggests that acidity resulting from the dechlorination of high TCA concentrations diminishes the degradation rate. The influence of acidity on the degradation rate was observed for closed aqueous systems. However, in an aquifer the groundwater flowing through an RNIP treated area will replenish the alkalinity. In addition, the acidity will liberate equilibrium bicarbonate from carbonate minerals in the aquifer soil or bedrock. The hydrogen concentrations for two initial aqueous concentrations and two RNIP concentrations are shown in Figure 3. The generation of hydrogen gas increased with increasing RNIP and initial TCA concentration. The reduction of water by Fe 0 is described with Eq. 1. The increase in hydrogen generation also correlates with the hydrogen acidity (ph). In general, experiments with greater hydrogen acidity had higher hydrogen gas concentrations. Eq. 9 describes the reaction underlying the generation of hydrogen gas from hydrogen acidity. Fe H + Fe 2+ + H 2 (9) CONCLUSIONS The large reactive surface area of RNIP reduces high TCA concentrations (26 mg/l to 263 mg/l) with low treatment dosages (1 g/l to 4.2 g/l). The sulfur compounds associated with RNIP participate in dechlorination reactions and may also contribute to the relatively high degradation rates. In absence of acid buffering soil or rock minerals, the acidity generated during the dechlorination of high TCA concentrations diminishes the degradation rate in closed aqueous systems. REFERENCES Lipczynska-Kochany, E., S. Harms, R. Milburn, G. Sprah and N. Nadarajah Degradation of Carbon Tetrachloride in the Presence of Iron and Sulphur Containing Compounds. Chemosphere, 29: Rylander, P.N Organic Synthesis with Nobel Metal Catalysts. Academic Press. New York. 355 p. Uegami et al Iron Particles for Purifying Contaminated Soil or Ground Water. U.S. Patent: US2003/ A1 Vogel, T.M., C.S. Criddle, and P.L. McCarty Transformation of Halogenated Aliphatic Compounds. Environmental Science Technology, 21:

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