Environ. Sci. Technol. lQS4, 28, 1243-1247
Destructive Adsorption of Carbon Tetrachloride on Iron( I I I ) Oxide Paul D. Hooker and Kenneth J. Klabunde'
Department of Chemistry, Kansas State University, Manhattan, Kansas 66506 The reaction between a-FezO3 and cc14 has been studied in order to investigate the potential of iron oxide as a destructive reagent for chlorinated organic compounds. The reaction has been studied between 400 and 620 "C in a fixed-bed pulse reactor. The effect of temperature, the contact time of the pulse of C C 4 with the cr-FeaO3, and the ratio of iron oxide to C C 4have been investigated. The products have been analyzed ( ( 2 0 2 , FeClz + FeCl3, Clz, and small amounts of C2C14 and graphite; COC12 is a shortlived intermediate), and a mechanism has been proposed for the decomposition of the CC14 over the oxide. Introduction
There is a widespread and growing concern over the environmental and health impact of chlorinated organics as a class of compound ( I ) . Several are known to cause ozone depletion, while others produce adverse effects on the human central nervous system and have been linked to diseases such as cancer. As well as minimizing the use of these compounds, it is important to find methods for their safe and complete destruction. The most efficient way to destroy chlorocarbons is by incineration (2, 3). However, even the best incinerators require afterburners and scrubbers for efficient operation. There is also the problem of products of incomplete combustion or PIC. The PIC of even simple compounds such as C C 4can produce other compounds that are more thermally stable and have a higher toxicity than the parent compound, e.g., hexachlorobenzene ( 4 , 5 ) . Other destruction technologies for chlorocarbons that are at various stages of development are catalytic decomposition (6-8), reverse burn gasification (9),plasma arc thermal decomposition ( Z ) , and using genetically engineered microbes (10).
There appears to be a need for the development of simpler and cleaner methods for safely destroying bulk quantities of chlorocarbons. Therefore, we have undertaken the study of a new approach; the destructive adsorption on metal oxide fine particles. Thus, it is our aim to use relatively cheap and abundant metal oxides to act as both the destructive and the adsorption agent for the chlorocarbon. In this paper, the thermal decomposition of ccl4 over a-Fe203 has been studied using a fixedbed pulse reactor. The purpose is to decompose a model chlorocarbon compound, CCb, at lower temperatures than are necessary for incineration and to adsorb the chlorine as chloride ions, accordingto the followingsimple equation:
-
2Fe,03(s) + 3CC14(g) 4FeC13(s)+ 3C02(g)
(1)
a-FezO3 was chosen because in initial experiments it was found to have a significantly higher activity than other metal oxides. The effect of temperature, the contact time of the ccl4 pulse with the FezO3, and the molar ratio of the CCl4 pulse to the amount of Fez03 present have been 0013-936X/94/0928-1243$04.50/0
0 1994 American Chemical Society
investigated. Complementary work on the decomposition of CC14 over CaO has been reported earlier (11). The chlorination reactions of Fez03 with Cc4, COClz, and C1p with Fez03 have been previously studied by thermogravimetric techniques (12-14). Anisothermal thermogravimetric measurements indicated the temperature at which the chlorination of Fez03 begins. These temperatures are 327 "C for Cc4,277 "C for COC12, and >527 "C for Clz. Kinetic data have been obtained from isothermal thermogravimetric measurements, and the activation energies have been calculated. These are 130 kJ mol-' (452-552 "C) for CC14,60 kJ mol-l(297-447 "C), for COC12, and 188 kJ mol-l(597-777 "C) for Cl2. Kinetic studies on the reactions of Ti02 and V Z O with ~ CC14 indicate that dissociative adsorption of CC14 is considered to precede the chlorination of these oxides and that the transformation of C C 4to COz is assumed to occur via the formation of an adsorbed COClz intermediate (15). The thermal decomposition or pyrolysis of CC14has also been investigated using an empty silica tubular flow reactor ( 5 ) . Although a substoichiometric amount of gaseous oxygen was present (CC14:02 molar ratio 3:1), rather surprisingly, no C02 or CO was formed. Only the pyrolytic products C2C14, C2C16,and Cl2 were detected in significant amounts. Cyclic C6C16 formed at temperatures above 727 "C, and significant carbonaceous deposits formed above 750 "C. The decomposition process was proposed to occur via a radical mechanism, with the cleavage of C-C1 bonds of the CCl4 being the initial step. Experimental Section
Reagents. Guaranteed grade a-FezO3 (99% purity) was analyzed by low-temperature gas adsorption measurements (BET method) showing the surface area = 9.2 m2 gJ. Carbon tetrachloride and C&14 were obtained commercially and used without further purification. Phosgene (COC12) was synthesized by the reaction of CC14with fuming sulfuric acid, free so3 content 27-33 % , and purified by a trap-to-trap distillation method (16). (Caution: COC12 is a toxic substance and must be handled with care.) A mass spectrometric analysis revealed CC14 as an impurity, but below 1%concentration. Fixed-BedPulse Reactor. The fixed-bed pulse reactor allowed a carrier gas to pass over the a-FezO3and directly into a GC or GC/MS monitoring system. The C C 4 was injected at regular intervals into the carrier gas stream. The device has been described in detail previously (17). The reactor, constructed from stainless steel, contained the a-Fe203 sandwiched between two wads of alumina wool. (Saffil brand name purchased from I. C. I. Co.) An external heater allowed the reactor temperature to be set at the required value between 400 and 620 "C. In order to investigate the temperature dependence of the CC14/ iron oxide reaction, 20 X 2 p L of CC14 was pulsed over 0.2 g of the oxide. This gives a final molar ratio of cr-FezO3: CC14 of 3.04:l. The ccl4 was injected (injector heated to 120 "C) into the flowing carrier gas (helium or air, 20 cm3 Environ. Sci. Technol., Vol. 28. No. 7, 1994
1243
min-I) and passed over the heated oxide. The volatile products then passed into a GC column for separation. In the case of the GUMS system, this was either a column supplied by GOW-MAC Instrument Co. (122 cm x 0.28 em stainless steel column, packed with 5 % OV-101 on Chromasorb P, AW DMCS, 80/100 mesh) or an empty steel tube which allowed the detection of gaseous (212. The volatile products then entered a jet separator, which allowed part of the sample to enter the MS ionization chamber. The MS system was a Finnegan 40214 instrument. The energy of the ionizing electrons was set at 20 eV, and the emission current from the filament was held at 0.25 mA. Electron multiplier voltage was set at 1726 V, ionizer chamber temperature was set at 150 "C, and the manifold temperature was set at 110 "C. MS spectra for all compounds of interest in this study were obtained as standards and compared satisfactorily with the literature
In t en s i !v
0
I
i
= Peaks Assigned
0 =
IO
a-PaO,
Peaks Assigned io F;CII.4H,0
Bragg Angle, 28 (deprecs)
Flgure 1. Powder XRD pattern of a-Fe203after reaction wlth CCI, at 460
'C.
(18).
The GC system used for the quantitative determination of the gaseous products was a GOW-MAC series 580 instrument equipped with a thermal conductivity detector. The detector current was set at 100mA, and the detector temperature was set at 140 "C. The GC oven was set at 53 "C. The column used was a 5% OV-101 column on chromasorb P, the same as used on the GC/MS system. This relatively low temperature allowed adequate separation of CO, COz, and COClz (CO was not a product as shown by GC/MS using ultrapure He as the carrier gas, so that N2 did not interfere with detection of CO). Known amounts of COS, COC12, cc4, and C2Cl4 were injected under the conditions described above, and calibration curves were constructed which relate peak height or peak area to the amount of compound injected. The amount of products formed in each injection, and hence for the 20 X 2 p L total C C 4 injected, could then be calculated. An investigation into the effect of contact time of the C C 4 with the a-FezO3 was made by adjusting the flow rate of the helium carrier gas. The contact time can be calculated by considering the length of the fixed bed of iron oxide (1.5 cm for 0.2 g of sample), the dimensions of the reactor, and the flow rate of the carrier gas (19). By altering the flow rate of the helium, the contact time could be varied between 0.25 and 0.90 s. An investigation into the effect of the molar ratio of the CC4 pulse to the amount of iron oxide present was also undertaken by varying the amount of oxide contained in the reactor. Quantitative chloride analyses for the sublimed iron chlorides and chloride remaining with the Fez03 was done using a gravimetric procedure (20). Powder X-ray diffraction (XRD) patterns were obtained using a Scintag XDS 2000 scanning diffractometer over the range 20100" at a rate of 2"/min. Phase identification of FeC12, FeC13, FeCly4Hz0, and a-FezO3 was done by comparison to the JCPDS powder diffraction file (21). BET surface area values were obtained with a Micrometrics Flowsorb I1 2300 apparatus.
Results Solid Product Formation. The four solid products detected after decomposition of the CC14over the a-Fe2O3 were FeC12, FeC13, carbon, and unreacted a-Fe203. Powder XRD of the solid remaining in the reaction zone for decomposition temperatures less than 500 "C showed a-Fe203and FeClr4Hz0 to be present (Figure 1). The 1244
Environ. Sci. Technol., Vol. 28,
No. 7, 1994
hydrated form of FeClz was produced on exposure to the atmosphere and not in the actual decomposition reaction. FeCl3 sublimed to the cooler parts of the reactor and was found as brown deposits downstream from the reaction zone (identified by XRD). A small amount of black, insoluble material identified as carbon deposited on the walls of the reactor prior to the reaction zone (identified by XRD). To confirm this, 10 X 2 p L of ccl4 was decomposed over Fez03 at 500 "C using He as the carrier gas. The sample was then allowed to cool, and the carrier gas changed to air. On reheating the sample to 600 "C, a small amount of COZwas evolved,indicating the reaction of the carbonaceous deposit with the 02 present to form
coz.
Temperature Dependence Studies. GUMS studies gave a sensitive qualitative analysis of the gaseous products of the thermal decomposition. To complement the quantitative GC results described later, the reactor temperature was varied between 400 and 620 "C in 20 "C increments for 1 2 separate experiments, and 20 X 2 p L of CCld was injected. C02 and C&l4 were detected as major products at all temperatures, but it was apparent that more CCl4 was decomposed as the temperature was increased. Phosgene (COClz) was detected as a product at temperatures between 400and 540 "C, but not at higher temperatures. The amount of Clz produced increased as the temperature was raised, and traces of CzC16 were observed at temperatures between 400 and 460 "C. The GC studies give a quantitative analysis of the gaseous products COz, Cc4, COClz, and C2C14 formed in the decomposition. Clz was absorbed completely by the GC column, and C2C16could not be detected as it was not produced in a large enough concentration. The amounts of product (or reactant that did not decompose) are listed in Table 1 for the 20 X 2 p L injections of CC14 at each of the temperatures. Also listed in the table are the amounts of C C 4decomposed before it was detected in the gaseous products, or the "breakthroughn number; CC14 could be detected when a peak of 0.5 mm was observed on the GC trace, i.e., at a concentration 0.13% of the injected Cc4. The carbon balance indicates the mole percentage of carbon accounted for in the gaseous products. Some of the missing carbon is due to the formation of carbonaceous deposits. Similarly, the chlorine balance indicates the amount of chlorine that cannot be accounted for quantitatively in the gaseous products or the solid chloride products. Presumably, this is mainly due to the evolved
Table-1. Material Balances for Reaction of a-FezO3 with 40 1-rL Pulses of CCId at Various Temperature& reactor temperature (OC) carbon accounted for as
400
coz ( % ) COClz CCld (remaining unreacted) CzCh % total carbon (carbon accounted for as volatile products) % total chloride (sum of volatiles plus chloride in solid residue) first observed breakthrough of CCL (injection no.)
420
440
460
480
16 30 36 43 50 2 4 2 6 2 7 2 0 1 0 3 0 1 8 1 5 8 1 3 9 6 5 8 7 79 90 1
80 97 3
83 93 4
79 98 6
80 99 6
500
520
540
560
580
600
620
77
80 0 1
78 0 1
76 0 1
60 0 0 3
74 0 0 7
75 0 0 4
0 3 5
8 85 88 8
6 89 90 8
2 85 92 7
1
79 73 81 79 93 97 92 91 9 > 2 0 1 7 > 2 0
*
a The amount of C and C1 in 40 p L of CC4 was the theoretical amount that we attempted to account for. According to statistical analysis of variability, the values are precise to within 3%; for example, 24 f 1% or 80 f 2%.
Table 2. Amount of Volatile Products Detected (Normalized) a t 560 OC with Different Amounts of a-FezO3 Contained in R e a ~ t o r ~ * ~ mass of a-FezOdg)
COz
CC4
C2C4
(%)
(%)
(%)
breakthrough injection no.
0.00 0.05 0.10 0.15 0.20
4 44 54 64 65
27 1 0 0 0
69 54 46 36 35
1 9 9 9 9
*
a Calculated by considering 24 p L of CC4 as 100%. According to statistical analysis of variability, the values are precise to within 5%; for example, 4 f 0.2% or 65 f 3%.
Clz. (Detection of Clz was done by using an unpacked GC column; other products were not separated under these conditions.) Molar Ratio Studies. To study the effect of decreasing the amount of available a-Fe~03,20 X 2 ,uL of cc14 was injected over different amounts of oxide in separate experiments with the temperature set at 560 "C. The total amounts of gaseous products for these injections and the total amount of C c 4 decomposed before breakthrough are listed in Table 2. When there is no iron oxide present, the reactor is empty except for the alumina wool present. Reducing the amount of available a-FezO3 does not influence the breakthrough injection number. However, the amount of COz formed decreases and the amount of CpCl4 increases as the amount of available oxide decreases. Contact Time Studies. For the contact time experiments, temperatures of 500 and 560 "C were chosen, and the flow rate of the He was adjusted accordingly. At 500 "C, four separate experiments with contact times of 0.28, and 0.75 s were performed. However, there was 0.47,0.59, no change in the amount of ccl4 decomposed before the breakthrough of CC&occurred,that is, the amount of CCl4 decomposed was the same in each case and found not to be dependent on the contact times over the interval studied. At 560 "C, a similar result was obtained. With contact times of 0.29 and 0.47 s, exactly 16 p L of CC14 could be decomposed before breakthrough. However, a contact time of 0.87s decomposed slightly more CC4,i.e., 22 pL. The product distributions also were not affected much by contact time. These results suggest that, under these conditions, even the shorter contact times are sufficient and therefore not product limiting. Decomposition of COClz. The decomposition of gaseous COClz over a-FezO3 was studied at 400 and 500 "C by GC and GC/MS. COClz was found to decompose more readily than CCl4, confirming earlier literature reports. At 400 "C, COClz was detected in the first
injection of COClz, i.e., it was not all decomposed. However, at 500 "C, COClz was not detected until after 14 injections, the only gaseous decomposition product being C02. CzCl4 was not detected in any of these experiments. Use of Air as a Carrier Gas. A qualitative analysis of the gaseous decomposition products at 400, 500,and 600 "C was carried out using the MS instrument and air as the carrier gas. For 20 X 2 pL of CC4 injections, the major products observed at 400 "C were CC4, COC12, and COZ,with small amounts of Clz. No CzC14 was detected. At 500 "C, C02 and COClz were the dominant products, and the amount of Cl2 increased. Less CC14 was observed, and again no CzC14 was detected. At 600 "C, Clz was a dominant product. Less C02 was formed, and no CCl4 was detected. However, traces of CzC14 were observed at this temperature. Quantitative analysis of the amount of soluble chloride formed in these three experiments showed that much less had been produced compared to the decomposition reactions at the same temperatures using He as the carrier gas, especially at 500 and 600 "C. At 400 "C, 30.9%, at 500°C,28.6%,andat600"C,21.2%oftheinjectedchlorine ended up as chloride ions. (Compare with the results in Table 1.) Other Iron Oxides as Decomposition Agents. Using different iron oxides or iron hydroxy oxides did not improve the efficiency of C C 4destruction, e.g., using ferrihydrite, FesHOv4Hz0, with a BET surface area of 280 m2g-l. This is because the ferrihydrite sinters and undergoes a phase change to a-FezO3 at the reaction temperatures. Discussion The thermal decomposition of ccl4 over a-Fe2O3 at temperatures of 400-620 "C in a fixed-bed pulse reactor results in the formation of FeCl3, FeClz, COz, Clz, CzC14, CzC16, COC12, and carbonaceous deposits. The formation of FeCl3 and COz represents the preferred reaction, eq 1. The thermal decomposition of FeCl3 produces FeClz and Cl2, and the thermal decomposition of CCl4 results in the formation of carbon and presumably more Clz. COClp is an intermediate product. The formation of C2C4 and small amounts of C2Cb are competing side reactions. The tendency to form COz and chloride ions is favored when the a-FezO3 is fresh, i.e., in the initial injections of the CC4, and also at higher temperatures. (This is to be expected since Fez03 solid is being consumed by surface reaction, and so fresh surface would have more oxide available. This will be discussed further when the proposed mechanism is presented.) Between 480 and 500 "C, the Environ. Sci. Technol., Vol. 28, No. 7, 1994
1245
8C
Idealized Fe,O, Surface
7c
Mole % of Products
Release of C1,O
6C
j/
Net Gain By Fq0, = 2CI Net Loss B y FRO, = 0"
CI
CI
'-1 L
-0-Fe-CI
50
I
2.
I
0
I1
40
11 Cl-Fe-0I 1
0
0 II
C
3c
Idealized FRO, Surface
I
20
I
Release of CO,
400 4 2 0 4 4 0 460 480 5 0 0 520 5 4 0 560 5 8 0 600 6 2 0
Reactor Temperature ("C) Figure 2. Plot showing the increase of Conand Ci- products formed as the reactor temperature increases.
amounts of these products formed increase significantly because the COClz decomposes almost completely, with eq 1 becoming the dominant reaction. From 500 to 620 "C there is no apparent increase in the amounts of COz and chloride ions formed, even though above 580 "C the C c 4 is decomposed muchmore efficiently (Figure 2). This is because raising the temperature is likely to increase the formation of Cl2 by increasing the thermal decomposition of FeC13 and the pyrolysis of CC4. Theoretically, the mole percentage amounts of COz and chloride ions should be the same if they are produced only according to eq 1. As the amount of chloride ions is invariably greater, it indicates that the C12 produced can further chlorinate the FezO3. The reaction between gaseous CC4 and the solid a-Fe2O3 must occur at the surface of the iron oxide particles, and it is interesting to consider whether just the surface of the iron oxide reacts, or if the bulk of the iron oxide is involved in the decomposition process. Knowing the surface area and assuming the Fez03 particles are small cubes with the corundum structure, the percentage of iron oxide exposed on the surface can be estimated compared to that in the bulk of the sample. For a surface area of 9.2 m2 g-l, approximately 1.3% of the oxide is on the surface (as determined by calculating the surface occupied by Fez03 moiety, calculating the number necessary to yield 9.2 m2, and determining its fraction of the mass compared to lg). For the experiments with 0.200 g of oxide contained in the reactor, there would be 1.63 X 10-5m0l of surface a-FezO3. The amount of CCl4 for each 2 pL injection of C C 4is 2.06 X mol, but as (according to eq 1) it takes 2 mol of Fez03 to decompose3 mol ccl4, there is an excess of surface oxide present. However, it is obvious that if we were observing only a surface reaction, it would not be possible to decompose much more than 2 p L of cc14. Clearly, this is not the case, especially at higher temperatures as much more C C 4 is decomposed and much more chloride 1246
V
Net Gain By F40,= ZCI Net Loss By FhO, = Oi
io
Environ. Sci. Technol., Vol. 28, No. 7, 1994
o-,cccO -0-Fe-CI
I
I
CI-Fc-0-
I
1
Figure 3. Proposed mechanism for the decomposition of CCi, over cu-Fe203.
produced than can be accounted for in just a surface reaction. The surface of the a-FezO3is being regenerated during the 20 X 2 pL injections. More surprisingly, only 0.05 g of a-FezO3will completely decompose a 2-rL pulse of CCl, at 560 "C. With these amounts of the reactants present, there is a 3.4 molar excess of CCl4 compared to the surface iron oxide available. This implies that the surface of the oxide must also be at least partially regenerated during the time the pulse is in actual contact with the oxide. This is not the contact time given earlier, but is the bandwidth of the pulse and is related to the volume of the gaseous CCl4 and the pressure of the carrier gas. It is estimated to be approximately 9 s. (However, the surface regeneration must be a relatively slow process since a change in contact time did not have a large effect on product distribution or breakthrough number, but allowing extended times between pulses does have a significant effect.) These results are rationalized in the following section. Reaction Mechanism. The above results allow speculation regarding the mechanism taking place. When the CC14 contacts the Fen03 surface, it may undergo dissociative chemisorption to form a carbene, CCl2, species (Figure 3). Extraction of an 0%ion leads to the formation of COClz, a presumed intermediate. COC12 is known to be an intermediate in the analogous CaO/CC14 reaction (11). It is very likely an intermediate in this Fe03/CC14 reaction too, and we have shown that COClz reacts under our conditions and forms COz and iron chlorides; see Results section. The chlorine abstracted from the cc14 to form the carbene becomes incorporated as chloride ions in the solid product. The formation of C2C4 is a competing side reaction that occurs when two carbene species bond to each other. The formation of CzC14 is favored as the amount of available oxide ions decreases, because there is less chance of abstraction of an oxide ion and, therefore, a greater
probability of two CC12 species reacting with each other. It should be noted, however, that the pyrolytic decomposition of CCl4 to give CzCl4 via a radical mechanism not involving Fez03 would become increasingly important as the temperature is raised. We have no indication of whether the carbene is formed in a concerted fashion or whether it is formed via a CC13 intermediate. The observation of trace amounts of C2C16implies that some CC13 fragments are formed in the reactor, but whether they are formed on the iron oxide surface or by radical decomposition is not clear. When the a-Fe~O3 is fresh or at temperatures above 500 "C, the COClz intermediate can further react with the oxide surface to give COZ and chloride ions (Figure 3). This is confirmed by the fact that these are the only two major products formed when pure COClz is decomposed over Fe203. Also, if COClz decomposed over Fez03 to give CC12species, CzCl4 would be an expected side product. It is not observed in this reaction. This decomposition pathway becomes less efficient as the surface of the Fez03 becomes covered with chloride ions, but as discussed in the previous section, the oxide surface regenerates itself. There are two possible ways this could occur'. Either the chloride could migrate into the bulk of the oxide thus exposing more oxide ions, or the chloride could be removed by sublimation as FezCl6, a dominant vapor species in the vaporization of solid FeC13. The formation and migration of FeCl3 out of the hot zone must occur rather rapidly since solid FeC13 is known to decompose at about 315 "C. The latter option is the most likely, as solid FeCl3 is observed as a sublimate after the reaction zone, Le., it has been carried along by the flow of carrier gas. There is a distinct advantage in forming relatively volatile iron chlorides because they can be easily separated from the involatile a-FezO3. By simple dissolution and control of pH, the iron oxide can be precipitated quantitatively, with the chlorine ultimately ending up as a saline solution. But there is an inherent problem with FeCl3 in that it decomposes fairly readily under these conditions (22)to give gaseous Clz. Another undesirable side product is CzCl4. It was hoped that using air as a carrier gas would increase the amount of COZformed and decrease CzC14 formation. However, the amount of C1- produced decreased dramatically, although at the lower temperatures (400 and 500 "C) CzC14 was not formed. So the presence of 02 caused a different reaction path to be followed,which further work may elucidate. Investigations are underway using metal oxides such as MgO and metal oxides coated with transition metal oxides, e.g., Fez03 deposited onto CaO, where more thermally stable chlorides are formed and large surface areas are accessible under the reaction conditions.
Acknowledgments
The support of the Army Research Office is acknowledged with gratitude. Partial support was provided by the U.S.Environmental Protection Agency under Assistance Agreement R-815709, Regions 7 and 8. Literature Cited (1) Hileman, B. Chem. Eng. News 1993, April 19th) 11. (2) Lee, C. C.; Huffman, G. L. Environ. Prog. 1989,8, 190. (3) Lee, C. C.;Huffman, G. L. In Innovative Hazardous Waste Treatment Technology Series, Vol. 1, Thermal Processes; Freeman, H. M., Ed.; Technomic: Lancaster, Basel, 1990; P 1. (4) Josephson, J. Environ. Sci. Technol. 1984, 18 (7)) 222A. (5) Taylor, P. H.; Dellinger, B.; Tirey,D. A. Int. J.Chem.Kinet. 1991,23, 1051. (6) Imamura,S.; Tarumoto, H.; Ishida, S. Ind. Eng. Chem.Res. 1989,28,1449.
(7) Getty, E. E.; Petrosius, S. C.; Drago, R. S. J.Mol. Catal. 1991, 67, 127. (8) Hung, L. S.; Pfefferle, L. D. Environ. Sci. Technol. 1989, 23, 1085. (9) Kinner, L. L.; McGowin, A,; Manahan, S. E. Environ. Sci. Technol. 1993, 27, 482. (10) Illman, D. L. Chem. Eng. News 1993, July 12th, 26. (11) Koper, 0.;Li, Y. X.; Klabunde, K. J. Chem. Mater. 1993, 5,500. (12) Bertbti,I.;Pap, I. S.; Szbkely,T.;Babievskaya,I. Z. J.Therm. Anal. 1987,32, 281. (13) Pap, I. S.;Bertbti,I.;SzBkely, T.;Babievskaya, I. Z.; Bottyhn, L. Thermochim. Acta 1985, 92, 587. (14) Bertbti, I.;Pap, I. S.; Szbkely,T.; Babievskaya,I. Z.; Bottyhn, L. Thermochim. Acta 1985,85, 87. (15) Mink, G.; Bertbti, I.; Pap, I. S.; Szbkely, T.; Battistoni, C.; Karmazsin, E. Thermochim. Acta 1985,85, 83. (16) Erdmann, H. Berichte 1893, 26, 1990. (17) Li, Y. X.; Koper, 0.;Atteya, M.; Klabunde, K. J. Chem. Mater. 1992, 4, 323. (18) Atlas of Mass Spectral Data; Stehnagen, E., Abrahamsson, S., McLafferty, F. W., Eds.; Interscience Publishers: New York, 1969; Vols. 1 and 2. (19) Giordano, N.; Bossi, A.; Paratella, A. Chem.Eng. Sci. 1966, 21, 621. (20) Vogel's Textbook of Quantitative Chemical Analysis, 5th ed.;Jeffrey, G. H., Barret, J., Mendham, J., Denney, R. C., Eds.; Wiley: New York, 1989. (21) Powder Diffraction File: Inorganic Phases; JCPDS, International Center for Diffraction Data: Swarthmore,PA, 1985. (22) The thermal stability of FeC4 is about 315 OC; Klabunde, K. J. Chemistry of Free Atoms and Particles; Academic Press: New York, 1980; p 122.
Received for review August 13, 1993. Revised manuscript received December 29, 1993. Accepted April 4, 1994.' *Abstract published in Advance ACS Abstracts, May 15, 1994.
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