Treatment of gaseous hydrogen chloride using Mg−Al layered double hydroxide intercalated with carbonate ion

Chemosphere 81 (2010) 658–662

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Technical Note

Treatment of gaseous hydrogen chloride using MgAl layered double hydroxide intercalated with carbonate ion Tomohito Kameda ⇑, Naoya Uchiyama, Toshiaki Yoshioka Graduate School of Environmental Studies, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan

a r t i c l e

i n f o

Article history: Received 20 May 2010 Received in revised form 29 July 2010 Accepted 30 July 2010 Available online 25 August 2010 Keywords: MgAl layered double hydroxide Gaseous HCl Treatment HCl removal

a b s t r a c t It is important to treat gaseous HCl from incineration streams efficiently to avoid adverse environmental consequences. In this paper, a new treatment method for gaseous HCl is presented—the application of MgAl layered double hydroxide (LDH) intercalated with CO2 3 (CO3MgAl LDH) to treat gaseous HCl continuously. The degree of HCl removal without water vapor is higher than that with water vapor; further, this reaction does not require H2O. In addition, the degree of HCl removal increases with increasing temperature, CO3MgAl LDH quantity, HCl concentration, and improved contact between CO3MgAl LDH and HCl gas. The treatment of HCl gas by CO3MgAl LDH leads to the production of MgAl LDH intercalated with Cl. Further, HCl is also absorbed on the surface of CO3MgAl LDH. Our proposed treatment method works effectively for the treatment of gaseous HCl from incinerator streams. Ó 2010 Elsevier Ltd. All rights reserved.

Mg1x Alx O1þx=2 þ x=nAn þ ð1 þ x=2ÞH2 O

1. Introduction In Japan, HCl generated from garbage incineration is treated by blowing Ca(OH)2 powder into the exhaust gas, thereby converting HCl into CaCl2. CaCl2 is then collected as fly ash and discharged into landfill sites. In order to prevent salt damages in the surrounding water environment by highly soluble CaCl2 leachates, Ca2+ is converted to insoluble CaCO3 by treatment with Na2CO3 while Cl concentrations are decreased by dilution of the leachates with water. However, this method requires considerable amounts of water, and landfill lifetimes decrease due to the mass disposal of fly ash. Hence, it is necessary to develop new methods for the treatment of gaseous HCl from incineration streams. Magnesium–aluminum layered double hydroxide (MgAl LDH) is known to intercalate various types of anions in the interlayer (Miyata, 1983; Cavani et al., 1991). MgAl LDH is given by the for3þ n mula [Mg2þ )x/nmH2O, where x denotes the Al/ 1x Alx ðOHÞ2 ](A  (Mg + Al) molar ratio (0.20 5 x 5 0.33) and An is CO2 3 , Cl , etc. (Ingram and Taylor, 1967; Allmann, 1968). The MgAl LDH that intercalates with CO2 (CO3MgAl LDH) can be transformed into 3 MgAl oxide by calcination at 450–800 °C; the reaction is given as follows:

Mg1x Alx ðOHÞ2 ðCO3 Þx=2 ! Mg1x Alx O1þx=2 þ x=2CO2 þ H2 O

ð1Þ

The MgAl oxide can rehydrate and combine with anions to reconstruct the LDH structure in the following manner. ⇑ Corresponding author. Tel./fax: +81 22 795 7212. E-mail address: [email protected] (T. Kameda). 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.07.066

! Mg1x Alx ðOHÞ2 Ax=n þ xOH

ð2Þ

For the preservation and purification of water environments, MgAl LDH and MgAl oxide have been examined for the removal of inorganic and organic anions such as terephthalate, benzoate, 4-methyl-benzoate, 2,4-dichlorophenoxyacetate, fluoride, chromate, bromide, and dye from an aqueous solution (Cardoso and Valim, 2004, 2006; Chitrakar et al., 2008; Lv et al., 2008; Mandal and Mayadevi, 2008; Prasanna and Kamath, 2008; Chao et al., 2009; Gaini et al., 2009). MgAl oxide also has the capacity to neutralize acid and solve for Cl for the treatment of HCl (Kameda et al., 2000, 2002, 2003, 2006). Furthermore, the produced ClMgAl LDH can be calcined, yielding HCl and reforming MgAl oxide (Kameda et al., 2007a,b). In our previous study, MgAl oxide was examined to treat gaseous HCl for potential recyclability (Kameda et al., 2008). MgAl oxide could remove gaseous HCl by the reconstruction of MgAl LDH and the production of MgCl2. However, the produced MgCl2 does not contribute to the reformation of MgAl oxide by its calcination. Therefore, we propose a new treatment method of gaseous HCl using CO3MgAl LDH (Fig. 1). The gaseous HCl is treated with CO3MgAl LDH to produce ClMgAl LDH. The produced ClMgAl LDH is then treated with CO2 3 by anion exchange to produce CO3MgAl LDH, thereby making it available for the retreatment of gaseous HCl. No CaCl2 was generated by our method, thus avoiding the problems caused by CaCl2 leachates. Furthermore, our method decreased the amount of fly ash disposal, which ensures longer landfill lifetimes. The Cl intercalated in the interlayer of MgAl LDH is well known

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alumina balls (5 mm diameter) up to a height of 225 mm. At the top of the balls, 0.4–3.0 g of CO3MgAl LDH was placed. The alumina balls were used to adjust the LDH layer in the middle of the hot reactor zone, additionally ensuring the mixing of both gas streams. The electric furnace was set at 130, 160, and 190 °C. The quartz tube reactor was preheated for 1 h under air flow. Subsequently, HCl gas was added to the air flow in a gas mixer for 60–360 min at a flow rate of 150 mL min1, adjusting the HCl gas concentrations to 1500–10 000 ppm. To examine the effects of the added water vapor on the reactions in the quartz tube reactor, water was simultaneously pumped into the water vapor generator set at the same temperature as the electric furnace at a rate of 0.6 mL min1. After the HCl gas flow was stopped, air was purged into the quartz tube reactor for 15 min. In an additional set of experiments, CO3MgAl LDH was mixed with SiO2 in order to investigate the effect of the height of the CO3MgAl LDH layer. The evolved gas was collected in three NaOH traps (0 °C). The chloride collected in the traps was quantified using a Dionex DX-120 ion chromatograph and a Dionex model AS-12A column (eluent: 2.7 mM Na2CO3 and 0.3 mM NaHCO3; flow rate: 1.3 mL min1). The amount of HCl removal was calculated by subtracting the amount of Cl in all the traps from the total amount of chlorine in the HCl gas. The products remaining after the removal of HCl by CO3MgAl LDH were identified by X-ray diffraction (XRD) analysis using Cu Ka radiation.

HCl (gaseous)

Cl•Mg−Al LDH

CO3•Mg−Al LDH

Cl− (aqueous)

CO32− (aqueous)

Fig. 1. Proposal for treatment of gaseous HCl using CO3MgAl LDH.

to exchange easily with CO2 3 in aqueous solutions (Miyata, 1983). On the other hand, we have already reported that CO3MgAl LDH has the potential to treat HCl (Kameda et al., 2000, 2002). In this study, therefore, the treatment of gaseous HCl using CO3MgAl LDH has been examined in detail. Furthermore, the effects of temperature, water vapor, CO3MgAl LDH quantity, HCl concentration, and time have been investigated. 2. Experimental CO3MgAl LDH was prepared by co-precipitation, i.e., a mixed Mg(NO3)2 and Al(NO3)3 solution (2.0 M) with Mg/Al molar ratio of 4.0 was added to a 0.6 M Na2CO3 solution at 30 °C while stirring. When the pH of the reaction mixture approached 10.5, a solution of 5.0 M NaOH was added to maintain the pH at this value, and the mixture was stirred continuously at 40 °C for 4 h and then at 70 °C for 40 h. The CO3MgAl LDH that formed was isolated by filtering the resulting suspension, washing it thoroughly with deionized water, and drying it at 40 °C under reduced pressure. CO3MgAl LDH contained 25.0 wt.% of Mg and 7.0 wt.% of Al, and the Mg/Al molar ratio was 4.0. The chemical composition of the CO3MgAl LDH was calculated to be Mg0.80Al0.20(OH)2(CO3)0.100.72H2O. The particle size was within 0.8–5.5 lm, and the BET specific surface area was 84 m2 g1. The CO3MgAl LDH quantities used for the treatment of gaseous HCl were 1.0– 2.0 times the stoichiometric quantities, as given by Eq. (3):

3. Results and discussion Fig. 3 shows the effects of temperature on the degree of HCl removal by CO3MgAl LDH (stoichiometric quantities) with and without water vapor. At all temperatures, the degree of HCl removal without water vapor was higher than that with water vapor. Eq. (3) indicates that the HCl removal by CO3MgAl LDH does not require H2O, in contrast to the case of MgAl oxide (Kameda et al., 2008). The low degree of HCl removal with water vapor is attributed to the increase in the HCl gas flow speed due to the water vapor flow. The degree of HCl removal without water vapor increased slightly with increasing temperature. This is because the increase in temperature probably results in an increase in the HCl activity, which leads to increased contact with CO3MgAl LDH. Fig. 4 shows the XRD patterns for (a) CO3MgAl LDH and the products after HCl removal without water vapor at (b) 130, (c) 160, and (d) 190 °C. The XRD peaks of CO3MgAl LDH are ascribed to hydrotalcite (Joint Committee on Powder Diffraction Standards card 22–700), which is a hydroxycarbonate of magnesium and aluminum (Mg6Al2(OH)16CO34H2O) that occurs in nature. Since the XRD peaks of LDH are generally indexed based on the hexagonal unit cell, the basal spacing of LDH is equivalent to 1/nth of the c

Mg0:80 Al0:20 ðOHÞ2 ðCO3 Þ0:10 0:72H2 O þ 0:20HCl ! Mg0:80 Al0:20 ðOHÞ2 Cl0:20 þ 0:10CO2 þ 0:82H2 O

ð3Þ

Fig. 2 shows the experimental apparatus for the treatment of gaseous HCl by CO3MgAl LDH. An electric heated quartz tube reactor (inner diameter: 21 mm; length: 450 mm) was filled with

5 4 3 3

1

11

2 6

CO3•Mg−Al LDH 9

10

7

8 Fig. 2. Experimental apparatus for the treatment of gaseous HCl by CO3MgAl LDH. (1) Hydrogen chloride cylinder; (2) air cylinder; (3) mass flow controller; (4) gas mixer; (5) electric furnace; (6) quartz tube reactor; (7) alumina ball; (8) water; (9) pump; (10) water vapor generator; (11) NaOH trap (0 °C).

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100

Water vapor

Non water vapor

HCl removal / %

80

60

40

20

0

130

160

190

Temperature / Fig. 3. Effect of temperature on the degree of HCl removal by CO3MgAl LDH (stoichiometric quantities) with and without water vapor. HCl concentration: 10 000 ppm; time: 60 min.

parameter, where n is the number of layer repeats in the unit cell (Newman and Jones, 1998). The calculated basal spacing for CO3MgAl LDH was 8.0 Å. In the case of the XRD patterns for the products shown in Fig. 4bd, a new XRD peak, indicated by N, was observed at around 12°, corresponding to a change in the

basal spacing. This is probably caused by the intercalation of Cl in the interlayer of MgAl LDH, in accordance with Eq. (3). In general, the basal spacing for ClMgAl LDH is almost similar to that for CO3MgAl LDH (Sato et al., 1986); therefore, it is difficult to distinguish between the intercalation of Cl and CO2 3 . However, Constantino (Constantino and Pinnavaia, 1995) has reported that the basal spacing for ClMgAl LDH shifted from 7.80 to 7.53 Å when ClMgAl LDH was heated from room temperature to 150 °C. This supports the assertion that the intercalation of Cl was responsible for the new peak, indicating a reduced basal spacing for the products in Fig. 4bd. In sum, the intercalation of Cl occurred due to the treatment of HCl gas by CO3MgAl LDH at 130–190 °C. This is in good agreement with Costantino’s data that the reaction of CO3MgAl LDH with gaseous HCl at 150 °C has given ClMgAl LDH (Costantino et al., 1998). CO3MgAl LDH was found to have a higher uptake of HCl in the absence of water vapor. Therefore, the treatment of gaseous HCl by CO3MgAl LDH without water vapor was examined in this study. Fig. 5a shows the effect of the quantity of CO3MgAl LDH on the degree of HCl removal without water vapor. The degree of HCl removal increased with increasing CO3MgAl LDH quantity and reached more than 99% at 1.75 times the stoichiometric quantity. This can be attributed to the improvements in the contact of

(a) 100

HCl concentration: 10000 ppm

3000 cps

80

006

d = 8.0 Å 003

HCl removal / %

Hydrotalcite

40

20

110 1013 0114

018

009 015

(a)

60

0

d = 7.5 Å

Intensity

d = 8.0 Å

1.0

(b)

(b) 100

10

(d)

HCl removal / %

d = 7.5 Å

(c)

d = 7.1 Å

d = 8.0 Å

d = 8.1 Å

80

0

1.5

1.75

2.0

CO3•Mg−Al LDH quantity / stoichiometric quantity CO3 •Mg−Al LDH: 1.75 times the stoichiometric quantities

60

40

20

20

30

40

50

60

70

2 θ /deg.(CuKα) Fig. 4. XRD patterns for (a) CO3MgAl LDH and products after HCl removal by CO3MgAl LDH (stoichiometric quantities) without water vapor at (b) 130 °C, (c) 160 °C, and (d) 190 °C. HCl concentration: 10 000 ppm; time: 60 min.

0 1500

3000

5000

8000

10000

Concentration / ppm Fig. 5. Effects of (a) CO3MgAl LDH quantity and (b) HCl concentration on the degree of HCl removal without water vapor. Temperature: 190 °C; time: 60 min.

T. Kameda et al. / Chemosphere 81 (2010) 658–662

CO3MgAl LDH with HCl gas. Fig. 5b shows the effect of HCl concentration on the degree of HCl removal by CO3MgAl LDH at 1.75 times the stoichiometric quantities without water vapor. The degree of HCl removal increased with increasing HCl concentration. In the case of 1500 ppm, the degree of HCl removal was the lowest at 71%. When low HCl concentrations were used, the height of the CO3MgAl LDH layer (Fig. 2) was also low due to the fixed CO3MgAl LDH/HCl ratio, leading probably to a limited contact between the HCl gas and the LDH particles. In order to improve the contact, CO3MgAl LDH was mixed with SiO2, and the height of the LDH layer was adjusted as high as required for the treatment of 10 000 ppm HCl gas. In the case of 1500 ppm, the degree of HCl removal by 1.75 times the stoichiometric quantities of

100

HCl removal / %

80

60

40

661

CO3MgAl LDH mixed with SiO2 was 89% at 190 °C. The expanded height of the CO3MgAl LDH layer caused by SiO2 was found to result in increasing degrees of HCl removal from 71% to 89% due to the improvement in the contact. Fig. 6 shows the effect of time on the degree of HCl removal by CO3MgAl LDH at 1.75 times the stoichiometric quantities without water vapor. The degree of HCl removal gradually decreased with time. Theoretically, the degree of HCl removal is 100% in 105 min, but in practice, it was actually 76% after 90 min. However, CO3MgAl LDH continued to remove some amount HCl after 90 min—the degree of HCl removal was still around 50% after 360 min. This suggests that in addition to the treatment in accordance with Eq. (3), HCl was also absorbed on the surface of CO3MgAl LDH. Fig. 7 shows the XRD patterns for the products after HCl removal without water vapor after (a) 60, (b) 120, (c) 180, (d) 240, and (e) 360 min. A new XRD peak (N) corresponding to ClMgAl LDH was observed with the d value of 7.1 Å after 60 min, and the peak intensity became larger than that with the d value of 7.9–8.0 Å corresponding to CO3MgAl LDH with time. The intensity of the XRD peak corresponding to the basal spacing of CO3MgAl LDH decreased with time, and the peak disappeared after 360 min. This indicates that CO3MgAl LDH was completely changed to ClMgAl LDH. CO3MgAl LDH was confirmed to be required for the high degree of HCl removal. It is noteworthy that CO3MgAl LDH has the potential to treat HCl gas continuously.

20

4. Conclusions 0

0

60

90

120

150

180

240

360

Time / min

d = 7.1 Å d = 7.1 Å d = 7.1 Å

Hydrotalcite (a)

(b)

(c)

References

d = 7.1 Å

d = 7.9 Å d = 8.0 Å d = 8.0 Å

(d)

d = 7.0 Å

d = 8.0 Å

Intensity

3000 cps

Fig. 6. Effect of time on the degree of HCl removal by CO3MgAl LDH at 1.75 times the stoichiometric quantities without water vapor. Temperature: 190 °C, HCl concentration: 10 000 ppm.

0

10

In this study, we examined whether the treatment of gaseous HCl by CO3MgAl LDH, which produces ClMgAl LDH in accordance with Eq. (3), is possible and effective. We conducted experiments and found that the degree of HCl removal without water vapor was higher than that with water vapor, thereby confirming that this reaction did not require H2O. Further, the degree of HCl removal increased slightly with temperature. The degree of HCl removal increased with the quantity of CO3MgAl LDH, and it reached more than 99% at 1.75 times the stoichiometric quantity after 60 min for 10 000 ppm HCl gas. The degree of HCl removal also increased with increasing HCl concentration. The expanded height of CO3MgAl LDH layer caused by SiO2 was found to increase the degree of HCl removal due to the improved contact between CO3MgAl LDH and HCl. Although the degree of HCl removal decreased gradually with time, CO3MgAl LDH continued to remove HCl more than the theoretical amount. This suggests that HCl was absorbed on the surface of CO3MgAl LDH as well. These results confirm our proposal for the treatment of gaseous HCl from incinerator streams using CO3MgAl LDH. Our proposed technique can be useful in alleviating environmental issues.

(e)

20

30

40

50

60

70

2 θ /deg.(CuKα) Fig. 7. XRD patterns for products after HCl removal by CO3MgAl LDH at 1.75 times the stoichiometric quantities without water vapor in (a) 60 min, (b) 120 min, (c) 180 min, (d) 240 min, and (e) 360 min. Temperature: 190 °C; HCl concentration: 10 000 ppm.

Allmann, R., 1968. The crystal structure of pyroaurite. Acta Crystallogr. B24, 972– 977. Cardoso, L.P., Valim, J.B., 2004. Competition between three organic anions during regeneration process of calcined LDH. J. Phys. Chem. Solids 65, 481–485. Cardoso, L.P., Valim, J.B., 2006. Study of acids herbicides removal by calcined Mg– Al–CO3–LDH. J. Phys. Chem. Solids 67, 987–993. Cavani, F., Trifiro, F., Vaccari, A., 1991. Hydrotalcite-type anionic clays: preparation, properties, and applications. Catal. Today 11, 173–301. Chao, Y.F., Lee, J.J., Wang, S.L., 2009. Preferential adsorption of 2,4dichlorophenoxyacetate from associated binary-solute aqueous systems by Mg/Al–NO3 layered double hydroxides with different nitrate orientations. J. Hazard. Mater. 165, 846–852. Chitrakar, R., Tezuka, S., Sonoda, A., Sakane, K., Hirotsu, T., 2008. A new method for synthesis of Mg–Al, Mg–Fe, and Zn–Al layered double hydroxides and their uptake properties of bromide ion. Ind. Eng. Chem. Res. 47, 4905–4908. 3þ Constantino, V.R.L., Pinnavaia, T.J., 1995. Basic properties of Mg2þ layered 1x Alx double hydroxides intercalated by carbonate, hydroxide, chloride, and sulfate anions. Inorg. Chem. 34, 883–892.

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T. Kameda et al. / Chemosphere 81 (2010) 658–662

Costantino, U., Marmottini, F., Nocchetti, M., Vivani, R., 1998. New synthetic routes to hydrotalcite-like compounds – characterisation and properties of the obtained materials. Eur. J. Inorg. Chem. 1998, 1439–1446. Gaini, L.E., Lakraimi, M., Sebbar, E., Meghea, A., Bakasse, M., 2009. Removal of indigo carmine dye from water to Mg–Al–CO3-calcined layered double hydroxides. J. Hazard. Mater. 161, 627–632. Ingram, L., Taylor, H.F.W., 1967. The crystal structures of sjogrenite and pyroaurite. Mineral. Mag. 36, 465–479. Kameda, T., Miyano, Y., Yoshioka, T., Uchida, M., Okuwaki, A., 2000. New treatment methods for waste water containing chloride ion using magnesium-aluminum oxide. Chem. Lett. 29, 1136–1137. Kameda, T., Yabuuchi, F., Yoshioka, T., Uchida, M., Okuwaki, A., 2003. New method of treating dilute mineral acids using magnesium-aluminum oxide. Water Res. 37, 1545–1550. Kameda, T., Yoshioka, T., Uchida, M., Miyano, Y., Okuwaki, A., 2002. New treatment method for dilute hydrochloric acid using magnesium-aluminum oxide. Bull. Chem. Soc. Jpn. 75, 595–599. Kameda, T., Yoshioka, T., Hoshi, T., Uchida, M., Okuwaki, A., 2006. Treatment of hydrochloric acid with magnesium-aluminum oxide at ambient temperatures. Sep. Purif. Technol. 51, 272–276. Kameda, T., Yoshioka, T., Watanabe, K., Uchida, M., Okuwaki, A., 2007a. Dehydrochlorination behavior of a chloride ion-intercalated hydrotalcite-like compound during thermal decomposition. Appl. Clay Sci. 35, 173–179.

Kameda, T., Yoshioka, T., Watanabe, K., Uchida, M., Okuwaki, A., 2007b. Dehydrochlorination and recovery of hydrochloric acid by thermal treatment of a chloride ion-intercalated hydrotalcite-like compound. Appl. Clay Sci. 37, 215–219. Kameda, T., Uchiyama, N., Park, K.S., Grause, G., Yoshioka, T., 2008. Removal of hydrogen chloride from gaseous streams using magnesium-aluminum oxide. Chemosphere 73, 844–847. Lv, L., Wang, Y., Wei, M., Cheng, J., 2008. Bromide ion removal from contaminated water by calcined and uncalcined MgAl–CO3 layered double hydroxides. J. Hazard. Mater. 152, 1130–1137. Mandal, S., Mayadevi, S., 2008. Cellulose supported layered double hydroxides for the adsorption of fluoride from aqueous solution. Chemosphere 72, 995–998. Miyata, S., 1983. Anion-exchange properties of hydrotalcite-like compounds. Clay Clay Miner. 31, 305–311. Newman, S.P., Jones, W., 1998. Synthesis, characterization and applications of layered double hydroxides containing organic guests. New J. Chem. 22, 105– 115. Prasanna, S.V., Kamath, P.V., 2008. Chromate uptake characteristics of the pristine layered double hydroxides of Mg with Al. Solid State Sci. 10, 260–266. Sato, T., Wakabayashi, T., Shimada, M., 1986. Adsorption of various anions by magnesium aluminum oxide (Mg0.7Al0.3O1.15). Ind. Eng. Chem. Prod. Res. Dev. 25, 89–92.