**5.2 Characteristics of calcination and hydration reaction with oyster shells**

Fig. 6 shows the change of specific surface area of calcined hydration limestone. As shown in Fig. 6A, specific surface area of calcined hydration limestone particle increases rapidly with increasing hydration time up to 6 hours and then slowly increases to 12 m2/g. Effects of hydration temperature on the specific surface area of the calcined limestone has been shown in Fig. 6B. When the initial water temperature was in the range of 30∼90°C with every 10°C, up to the 70°C BET surface area was not changed largely. However, rapid increase of BET surface area of absorbent appears above the temperature of 80°C, indicating the rapid hydration reaction occurs. We can conclude the optimum range of temperature and time for hydration reaction of absorbent is about 80∼90°C and 24 hours, respectively [Jung et al, 2000].

Fig. 7A∼B shows the adsorbed volume with relative pressure on the waste oyster shells and limestone. This figure shows the difference of amount of nitrogen gas according to the change of relative pressure absorbed to waste shell and limestone. We can conclude each of the sorbent shows a similar BET value in the condition of raw material.

Fig. 8 shows pore size distribution of waste oyster shells, clam, and seashell according to pore diameter. The results lead to the finding that shells have larger average pore size with the value of pore volume of 0.013∼0.024 cm3/g, which is higher than that of limestone. And, other result is pore size distribution according to the change of pore diameter of oyster manufactured as an absorbent with calcination and hydration. It was appeared that the average pore diameter of oyster was much bigger than that of raw materials. This result also indicates that calcination and hydration processes can enhance the removal capacity of acid gases [Jung et al, 2005].

To clarify the effect of temperature, TGA analysis of the waste oyster shells and limestone were examined under N2 atmosphere by Automatic Derivative Differential Thermo-balance (Fig. 9). Heating rate in the calcination, which was conversion from calcium carbonate to calcium oxide, was 10.0 °C/min in the temperature range of 600.0∼ 900.0°C. As can be seen in Fig. 9, calcinations of the oyster-shells started at 645.0°C and completed at 780.0°C, whereas Jungsun limestone started over the temperature 680.0°C and completed at 845.0°C. The mass of waste oyster shells and limestone in the calcinations under N2 atmosphere

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 313

**Volume absorbed (cm3/g)**

0

**Volume absorbed (cm3/g)**

shells, (B) limestone.

0.0

0.2

0.4

0.6

0.8

1.0

2

4

6

8

10

**Relative pressure (P/Po)** 0.0 0.2 0.4 0.6 0.8 1.0

**Relative pressure (P/Po)** 0.0 0.2 0.4 0.6 0.8 1.0

(B)

Fig. 7. N2 BET results of various waste oyster shells, seashell and limestone. (A) waste oyster

**Danyang limestone desorption**

(A)

**Oyster desorption**

**Oyster adsorption**

0.0

**Adsorption**

0.2

0.4

0.6

0.8

1.0

decreased 44.8% and 44.0%, respectively. From this analysis, it could be confirmed that mass decreasing resulted from the reaction CaCO3→CaO+CO2. Also, in the case of Jungsun limestone, the temperature of the calcinations should be over about 850.0°C [Jung et al, 2007].

Fig. 6. (A) Variation of surface area of calcined limestone as a function of hydration time. (B) Effect of hydration temperature on the surface areas of calcined limestone.

(B)

decreased 44.8% and 44.0%, respectively. From this analysis, it could be confirmed that mass decreasing resulted from the reaction CaCO3→CaO+CO2. Also, in the case of Jungsun limestone, the temperature of the calcinations should be over about 850.0°C [Jung et al,

Unhydrated Hydrated

8.512

Hydration time (hr)

Hydrated

Hydration temperature (<sup>o</sup>

(B) Fig. 6. (A) Variation of surface area of calcined limestone as a function of hydration time.

(B) Effect of hydration temperature on the surface areas of calcined limestone.

30 40 50 60 70 80 90

C)

(A)

6 hr 12 hr 24 hr

9.552

11.979

2007].

Surface ares (m2/g)

0

Surface ares (m2/g)

0

2

4

Unhydrated

6

8

10

12

14

2

2.314

4

6

8

10

12

14

Fig. 7. N2 BET results of various waste oyster shells, seashell and limestone. (A) waste oyster shells, (B) limestone.

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 315

dx/dt=k(1-X)n (2)

Table 7 shows kinetic data of the waste oyster shells and limestone. It was calculated from the results of calcinations experiment (Fig. 9). Activation energies, reaction constants, and reaction orders were 176±8.90 kJ/mole, 15.07±1.14 sec-1, and 0.42±0.10 for oyster shells and 201.72±5.17 kJ/mole, 16.47±0.63 sec-1, and 0.37±0.08 for Jungsun limestone, respectively. These values were similar to those of other calcium-based sorbents (Jung et al., 2000). The activation energy of the oyster shells was smaller than that of Jungsun limestone. As can be seen in Fig. 10, this is because structural elements of natural limestone is inorganic materials, whereas oyster shells was comprised of thin CaCO3 layer and created by living things thus

(WOS) 176.1±8.90 0.42±0.10 15 – 16 N2 Isothermal

Jungsun limestone 201.72±5.17 0.37±0.08 15 – 16 N2 Isothermal

Fig. 10 shows scanning electron micrographs (SEM) of the various solid Jungsun limestone and waste oyster shells. Parts (a), (a'), (b), and (b') of Fig. 10 show the scanning electron micrographs of the fresh and calcined samples, respectively. SEM pictures for the hydrated and calcined/hydrated samples are shown in Parts (c), (c'), (d), and (d') of Fig. 10, respectively. Observation of the waste oyster shells morphology indicates some agglomeration of the particle/grains in the hydrated waste oyster shells (H-WOS) as compared to the fresh oyster. However, as shown in Fig. 10(b'), in the SEM photograph of the calcined sample, enormous amount of agglomerations by sintering were observed.

(a) (a')

its surface was irregular and porous.

Table 7. Kinetic data of tested absorbents.

Waste oyster shells

Absorbents Ea [kJ/mole] Order[n] Sample

() () ( ) <sup>k</sup> CaCO s CaO s + CO g 3 2 ⎯⎯→ (1)

k=A· exp(-Ea/RT) (3)

wt.[mg] Flow gas Conditions

dx/dt= A· exp(-Ea/RT) (1-X)n (4)

Fig. 8. Pore volume of waste oyster shells, seashell and limestone.

Fig. 9. TGA profiles of the waste oyster shells and limestone in the temperature range of 600 - 900°C.

The calcination reaction of waste oyster shells and limestone, main components is CaCO3(s), is gas-solid reaction, in which we assumed that the calcinations reaction is n-order reaction. The activated energy and reaction order of waste oyster shells and limestone are calculated using the following equations and TGA experimental results. Where x=mass of waste oyster shells and limestone, k=reaction rate, X=conversion, n=reaction order, A=preexponential factor, Ea=activation energy, R=gas constant, T=absolute temperature.

**Clam**

**Oyster**

Fig. 8. Pore volume of waste oyster shells, seashell and limestone.

**Pore volume(cm3/g)/104**

Weight loss (wt. %)


TGA Curves

0

50

100

150

200

250

300

**Pore diameter(A)** 0 2000 4000 6000 8000

Temperature (<sup>o</sup>

Fig. 9. TGA profiles of the waste oyster shells and limestone in the temperature range of 600

The calcination reaction of waste oyster shells and limestone, main components is CaCO3(s), is gas-solid reaction, in which we assumed that the calcinations reaction is n-order reaction. The activated energy and reaction order of waste oyster shells and limestone are calculated using the following equations and TGA experimental results. Where x=mass of waste oyster shells and limestone, k=reaction rate, X=conversion, n=reaction order, A=preexponential

factor, Ea=activation energy, R=gas constant, T=absolute temperature.

100 200 300 400 500 600 700 800 900

C)

0

Limestone

50

100

150

**Seashell**

Oyster

200

250

300

$$\text{CaCO}\_3(\text{s}) \xrightarrow{\text{k}} \text{CaO}(\text{s}) + \text{CO}\_2(\text{g}) \tag{1}$$

$$\text{d} \mathbf{x} / \text{d} \mathbf{t} \mathbf{=} \mathbf{k} (\mathbf{1} \cdot \mathbf{X})^{\mathbf{n}} \tag{2}$$

$$\mathbf{k} \equiv \mathbf{A} \cdot \exp(-\mathbf{E}\_\mathbf{a}/\mathbf{RT})\tag{3}$$

$$\mathbf{A}\mathbf{x}/\mathbf{dt} = \mathbf{A} \cdot \exp(-\mathbf{E}\_\mathbf{a}/\mathbf{RT}) \,\mathrm{(1-\lambda)^n} \tag{4}$$

Table 7 shows kinetic data of the waste oyster shells and limestone. It was calculated from the results of calcinations experiment (Fig. 9). Activation energies, reaction constants, and reaction orders were 176±8.90 kJ/mole, 15.07±1.14 sec-1, and 0.42±0.10 for oyster shells and 201.72±5.17 kJ/mole, 16.47±0.63 sec-1, and 0.37±0.08 for Jungsun limestone, respectively. These values were similar to those of other calcium-based sorbents (Jung et al., 2000). The activation energy of the oyster shells was smaller than that of Jungsun limestone. As can be seen in Fig. 10, this is because structural elements of natural limestone is inorganic materials, whereas oyster shells was comprised of thin CaCO3 layer and created by living things thus its surface was irregular and porous.


Table 7. Kinetic data of tested absorbents.

Fig. 10 shows scanning electron micrographs (SEM) of the various solid Jungsun limestone and waste oyster shells. Parts (a), (a'), (b), and (b') of Fig. 10 show the scanning electron micrographs of the fresh and calcined samples, respectively. SEM pictures for the hydrated and calcined/hydrated samples are shown in Parts (c), (c'), (d), and (d') of Fig. 10, respectively. Observation of the waste oyster shells morphology indicates some agglomeration of the particle/grains in the hydrated waste oyster shells (H-WOS) as compared to the fresh oyster. However, as shown in Fig. 10(b'), in the SEM photograph of the calcined sample, enormous amount of agglomerations by sintering were observed.

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 317

Pore volume(cm3/g)

pore diameter.

0.000

0.005

0.010

0.015

0.020

Pore diameter(A) 0 1000 2000 3000 4000 5000 6000

Fig. 11. Cumulative pore volume curves for two types of waste oyster shells as a function of

Fig. 11 shows pore volume with respect to pore diameter. The calcined oyster had a decreased pore volume relative to that of the fresh oyster. The specific surface area of oyster shells and limestone as a function of different calcination temperatures is shown in Fig. 12. The specific surface area of the oyster shell changed from 2.4465 m2/g before calcination to 2.3950 m2/g at 700.0°C, 2.2810 m2/g at 750.0°C, 2.2120 m2/g at 800.0°C, 2.1209 m2/g at 850.0°C, 1.9510 m2/g at 900.0°C, 1.8000 m2/g at 950.0°C, and 1.7000 m2/g at 1,000.0°C. The specific surface area of waste oyster shells was larger than that of calcined oyster shells and it was decreased with increasing calcination temperature. It is indicated that some agglomerations by sintering were blocking the specific surface area of calcined oyster shells. On the contrary, specific surface areas of limestone increased from 1.2368 m2/g before calcinations to 1.3100 m2/g at 700.0°C, 1.3200 m2/g at 750.0°C, 1.5100 m2/g at 800.0°C, 2.1544 m2/g at 850.0°C, 2.3205 m2/g at 900.0°C, 2.0210 m2/g at 950.0°C, and 1.2124 m2/g at 1,000.0°C. The specific surface area of limestone increased with increasing calcination

The specific surface area at 850.0°C was similar to that at 900.0°C. Therefore, we conclude that the calcination temperature had a positive effect on the development of the specific surface area for limestone, unlike waste oyster-shells. The change of surface area in oyster shells and limestone by processing (calcination/hydration) is shown in Fig. 13. As Fig. 13 shows, specific surface areas of oyster shells and limestone were changed from 2.4465 m2/g and 1.2368 m2/g before calcination/hydration to 12.9780 m2/g and 11.3380 m2/g by pretreating process, respectively. From this result, we could expect that the sulfating reactivity of oyster-shells sample increases to about 5 times by calcination/hydration reaction due to the increase of specific surface area and pore volume. Because of acid gas

temperature up to maximal 900.0°C and then a little decreased.

Fresh WOS

Calcined oyster

Fig. 10. SEM micrographs of limestone and oyster shells ; (a) fresh limestone, (a') fresh oyster shells, (b) calcined limestone at 850°C, (b') calcined oyster shells at 850°C, (c) hydrated limestone, (c') hydrated oyster shells, (d) hydrated limestone after calcinations, and (d') hydrated oyster shells after calcinations.

(b) (b')

(c) (c')

(d) (d')

(c) hydrated limestone, (c') hydrated oyster shells, (d) hydrated limestone after calcinations,

Fig. 10. SEM micrographs of limestone and oyster shells ; (a) fresh limestone, (a') fresh oyster shells, (b) calcined limestone at 850°C, (b') calcined oyster shells at 850°C,

and (d') hydrated oyster shells after calcinations.

Fig. 11. Cumulative pore volume curves for two types of waste oyster shells as a function of pore diameter.

Fig. 11 shows pore volume with respect to pore diameter. The calcined oyster had a decreased pore volume relative to that of the fresh oyster. The specific surface area of oyster shells and limestone as a function of different calcination temperatures is shown in Fig. 12. The specific surface area of the oyster shell changed from 2.4465 m2/g before calcination to 2.3950 m2/g at 700.0°C, 2.2810 m2/g at 750.0°C, 2.2120 m2/g at 800.0°C, 2.1209 m2/g at 850.0°C, 1.9510 m2/g at 900.0°C, 1.8000 m2/g at 950.0°C, and 1.7000 m2/g at 1,000.0°C. The specific surface area of waste oyster shells was larger than that of calcined oyster shells and it was decreased with increasing calcination temperature. It is indicated that some agglomerations by sintering were blocking the specific surface area of calcined oyster shells. On the contrary, specific surface areas of limestone increased from 1.2368 m2/g before calcinations to 1.3100 m2/g at 700.0°C, 1.3200 m2/g at 750.0°C, 1.5100 m2/g at 800.0°C, 2.1544 m2/g at 850.0°C, 2.3205 m2/g at 900.0°C, 2.0210 m2/g at 950.0°C, and 1.2124 m2/g at 1,000.0°C. The specific surface area of limestone increased with increasing calcination temperature up to maximal 900.0°C and then a little decreased.

The specific surface area at 850.0°C was similar to that at 900.0°C. Therefore, we conclude that the calcination temperature had a positive effect on the development of the specific surface area for limestone, unlike waste oyster-shells. The change of surface area in oyster shells and limestone by processing (calcination/hydration) is shown in Fig. 13. As Fig. 13 shows, specific surface areas of oyster shells and limestone were changed from 2.4465 m2/g and 1.2368 m2/g before calcination/hydration to 12.9780 m2/g and 11.3380 m2/g by pretreating process, respectively. From this result, we could expect that the sulfating reactivity of oyster-shells sample increases to about 5 times by calcination/hydration reaction due to the increase of specific surface area and pore volume. Because of acid gas

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 319

The desulfurization efficiency of the raw material was shown in Fig. 14. From a comparison of SO2 removal quantities between waste oyster shells and limestone, the desulfurization capability of waste oyster shells was higher about 50% than that of Jungsun limestone. This means that the SO2 removal capacity of oyster shells was superior to the limestone due to

> Time (min) 0 2 4 6 810

Fig. 14. Comparison of SO2 removal quantities between waste oyster shells and limestone.

Tested absorbents

In general, a power plant discharges SO2 of 1800 ∼ 1900 ppm, O2 of 6%, CO2 of 13%, N2 of 74%, water content of 10%, and NO of 600 ppm to the air during the combustion. The

CH-WOS CH-L Ca(OH)2

**0.78 mmole/g 0.75 mmole/g**

0.78 mmole/g 0.76 mmole/g

Limestone

SO2 removal amount (mmole/g)

0.0

0.2

0.4

0.6

0.8

1.0

NOx SO2

WOS

**5.3 Characteristics of waste oyster shells as a SO2/NOx removal reaction** 

the specific surface area as can be seen in Fig. 13.

SO2 total removal quantity (mmole)

NOx removal amount (mmole/g)

0.00

Fig. 15. SO2/NOx removal amounts of tested absorbents.

0.02

0.04

0.06

0.08

0.10

0.00

0.01

0.02

0.03

0.04

removal capacity of absorbents was proportional to the specific surface area (Jung et al., 2005).

Fig. 12. Effect of calcinations temperature on the surface area.

Fig. 13. Variation of surface area of oyster shells and limestone with and without pretreatment.

removal capacity of absorbents was proportional to the specific surface area (Jung et al.,

Fresh oyster surface area : 2.4465 m<sup>2</sup>

Fresh limestone surface area : 1.2368 m<sup>2</sup>

Oyster calcination temp. = 780 <sup>o</sup>

/g

/g

C

Surface area (m2/g)

0

3

6

9

12

15

C Limestone calcination temp. = 850 <sup>o</sup>

After pretreating

11.3380 m<sup>2</sup>

/g

Temperature (<sup>o</sup>

Before pretreating After pretreating

Raw material Pretreating material

Absorbents

WOS Limestone CH-WOS CH-L

Fig. 13. Variation of surface area of oyster shells and limestone with and without

1.2368 m<sup>2</sup> /g

700 750 800 850 900 950 1000

C)

12.9780 m<sup>2</sup>

/g

2005).

Surface area (m2/g)

0.0

Surface area (m2/g)

0

pretreatment.

1

2

2.4465 m<sup>2</sup> /g

3

4

5

0.5

WOS Limestone

Fig. 12. Effect of calcinations temperature on the surface area.

1.0

1.5

2.0

2.5

3.0

#### **5.3 Characteristics of waste oyster shells as a SO2/NOx removal reaction**

The desulfurization efficiency of the raw material was shown in Fig. 14. From a comparison of SO2 removal quantities between waste oyster shells and limestone, the desulfurization capability of waste oyster shells was higher about 50% than that of Jungsun limestone. This means that the SO2 removal capacity of oyster shells was superior to the limestone due to the specific surface area as can be seen in Fig. 13.

Fig. 14. Comparison of SO2 removal quantities between waste oyster shells and limestone.

Fig. 15. SO2/NOx removal amounts of tested absorbents.

In general, a power plant discharges SO2 of 1800 ∼ 1900 ppm, O2 of 6%, CO2 of 13%, N2 of 74%, water content of 10%, and NO of 600 ppm to the air during the combustion. The

Reuse of Waste Shells as a SO2/NOx Removal Sorbent 321

Enormous amount of waste oyster-shells were dumped into public waters and landfills, which cause a bad smell as a consequence of the decomposition of organics attached to the shells. Also, marine pollution by waste oyster shells has become one of the serious problems in mariculture industry in Korea. The present study has conducted to develop a means of converting waste oyster shells into useful absorbent for removal SO2/NOx from industry. In this study, feasibility of waste seashell as absorbents for the control of air pollution has been investigated in a fixed bed reactor. To seek for a feasibility to recycle the waste oyster shells as desulfurization/denitrification sorbent, pretreating experiments and SO2/NOx removal activity were investigated. Physicochemical properties of waste oyster shells have been

By pretreating process, such as calcinations and hydration, the specific surface area and pore volume of waste oyster-shell were increased than that of the fresh particles, which makes it possible to enhance the removal capacity in acid gases. XRD analysis of calcined waste oyster shells were exhibited peaks characteristic of calcium oxide, whereas raw waste

And it was concluded that the optimal temperatures for calcination and hydration were 800.0 ~ 850.0°C and 90.0°C respectively. Pores of absorbent are formed by the emission of CO2 during the high temperature calcination but it was agglomerated by sintering. Therefore, the specific surface area decreased and it was completely different from limestone. SO2/NOx removal experiments have been carried out to test the reactivity of absorbents in a fixed bed reactor. SO2 removal activity and reaction rate of calcined/hydrated waste oyster-shells were higher than that of calcined/hydrated limestone. It is clearly indicated that absorbent prepared by waste oyster-shells are substituted for commercial limestone and can be directly applied to industries which try to

Asaoka, S. et al. (2009). Removal of hydrogen sulfide using crushed oyster shell from pore

Chu, K-J. et al. (1997). Characteristics of gypsum crystal growth over calcium-based slurry in

Garea, A. et al. (2001). Kinetics of dry flue gas desulfurization at low temperatures using

Jung, J-H. (1999.2). A study on reaction characteristic of SO2/NOx simultaneous removal for

Jung J.-H. et al. (2000). Physicochemical Characteristics of Waste Sea Shell for Acid Gas

desulfurization reaction. *Materials Research Bulletin*, 32(2), 197. EPRI, (1988). FGD chemistry and analytical methods handbook, CS-3612.

Cleaning absorbent. *Korean J. Chem. Eng.,* 17(5), 585-592.

water to remediate organically enriched coastal marine sediments. *Bioresource* 

Ca(OH)2: competitive reactions of sulfation and carbonation. *Chem. Eng. Sci*., 56(4),

alkali absorbent/additive in FGD and waste incinerator Process, Ph.D thesis, *Pusan* 

oyster-shells showed that the main peaks were characteristic of calcium carbonate.

**6. Conclusions** 

characterized using the XRD, SEM, and BET.

reduce their emissions of SO2 and NOx.

*Technology*. 100, 4127–4132.

*National University*, Korea.

**7. References** 

1387.

SO2/NOx removal capacity of the calcined/hydrated limestone (CH-L) and calcined/hydrated waste oyster shells (CH-WOS) was carried out in a fixed bed reactor. As can be seen in Fig. 15, desulphurization capacity of the adsorbent was one order of magnitude higher than the denitrification capacity regardless of absorbent species. This is because the Henry's Law constant and diffusion coefficient in the gas phase for SO2 is much higher than those for NO (Yuan, 1990). And, SO2 and NOx removal quantities of CH-WOS were higher just a little than that of CH-L. It can be inferred that waste oyster shells is a good sorbent for the removal of SO2 and NOx in the flue gas cleaning processes. The SO2 and NOx absorption mechanism on absorbent can be explained by combining equations listed below (Nakamura, 1995).

$$\text{CaCO}\_3(\text{s}) + \text{SO}\_2(\text{g}) + 2\text{H}\_2\text{O}(\text{l}) \leftrightarrow \text{CaSO}\_3\cdot2\text{H}\_2\text{O}(\text{s}) + \text{CO}\_2(\text{g})\tag{5}$$

$$\text{CaO(s)} + \text{H}\_2\text{O(l)} \leftrightarrow \text{Ca(OH)}\_2\text{(s)}\tag{6}$$

$$\text{Ca(OH)}\_{2}\text{(s)} + \text{SO}\_{2}\text{(g)} + \text{H}\_{2}\text{O(l)} \leftrightarrow \text{CaSO}\_{2}\text{2H}\_{2}\text{O(s)}\tag{7}$$

$$\text{CaCO}\_3(\text{s}) + 2\text{NO}(\text{g}) + 1/2\text{O}\_2(\text{g}) \leftrightarrow \text{Ca(NO}\_2)\_2(\text{s}) + \text{CO}\_2(\text{g})\tag{8}$$

$$\text{Ca(OH)}\_{2}\text{(s)} + 2\text{NO(g)} + 1/2\text{O}\_{2}\text{(g)} \leftrightarrow \text{Ca(NO}\_{2}\text{)}\_{2}\text{(s)} + \text{H}\_{2}\text{O(l)}\tag{9}$$

Removal of SO2 (Ca(OH)2 conversion ratio) in simulated flue gas by the CH-L and CH-WOS absorbents was examined under different reaction conditions to study effects of the coexistence of NOx in a flue gas (Fig. 16). As depicted in Fig. 16, the reaction rate of desulphurization by CH-WOS increased about 30% higher than that of CH-L. In addition, SO2 removal activity was enhanced in the presence of NOx, which might be due to its oxidizer role of SO2 (Tsuchiai et al., 1996).

Fig. 16. Ca(OH)2 conversions by SO2 and SO2/NOx reaction for limestone and waste oyster shells.

#### **6. Conclusions**

320 Material Recycling – Trends and Perspectives

SO2/NOx removal capacity of the calcined/hydrated limestone (CH-L) and calcined/hydrated waste oyster shells (CH-WOS) was carried out in a fixed bed reactor. As can be seen in Fig. 15, desulphurization capacity of the adsorbent was one order of magnitude higher than the denitrification capacity regardless of absorbent species. This is because the Henry's Law constant and diffusion coefficient in the gas phase for SO2 is much higher than those for NO (Yuan, 1990). And, SO2 and NOx removal quantities of CH-WOS were higher just a little than that of CH-L. It can be inferred that waste oyster shells is a good sorbent for the removal of SO2 and NOx in the flue gas cleaning processes. The SO2 and NOx absorption mechanism on absorbent can be explained by combining equations

CaCO3(s) + SO2(g) + 2H2O(l) ↔ CaSO3·2H2O(s) + CO2(g) (5)

Ca(OH)2(s) + SO2(g) + H2O(l) ↔ CaSO3·2H2O(s) (7)

CaCO3(s) + 2NO(g) + 1/2O2(g) ↔ Ca(NO2)2(s) + CO2(g) (8)

 Ca(OH)2(s) + 2NO(g) + + 1/2O2(g) ↔ Ca(NO2)2(s) + H2O(l) (9) Removal of SO2 (Ca(OH)2 conversion ratio) in simulated flue gas by the CH-L and CH-WOS absorbents was examined under different reaction conditions to study effects of the coexistence of NOx in a flue gas (Fig. 16). As depicted in Fig. 16, the reaction rate of desulphurization by CH-WOS increased about 30% higher than that of CH-L. In addition, SO2 removal activity was enhanced in the presence of NOx, which might be due to its

CH-WOS : SO2/NOx simultaneous removal reaction

CH-WOS : SO2 removal reaction CH-L : SO2 removal reaction

Time (min) 0 2 4 6 8 10 12 14 16 18 20

Fig. 16. Ca(OH)2 conversions by SO2 and SO2/NOx reaction for limestone and waste oyster

CaO(s) + H2O(l) ↔ Ca(OH)2(s) (6)

listed below (Nakamura, 1995).

oxidizer role of SO2 (Tsuchiai et al., 1996).

Ca(OH)2 conversion (%)

0

shells.

2

4

6

8

10

Enormous amount of waste oyster-shells were dumped into public waters and landfills, which cause a bad smell as a consequence of the decomposition of organics attached to the shells. Also, marine pollution by waste oyster shells has become one of the serious problems in mariculture industry in Korea. The present study has conducted to develop a means of converting waste oyster shells into useful absorbent for removal SO2/NOx from industry. In this study, feasibility of waste seashell as absorbents for the control of air pollution has been investigated in a fixed bed reactor. To seek for a feasibility to recycle the waste oyster shells as desulfurization/denitrification sorbent, pretreating experiments and SO2/NOx removal activity were investigated. Physicochemical properties of waste oyster shells have been characterized using the XRD, SEM, and BET.

By pretreating process, such as calcinations and hydration, the specific surface area and pore volume of waste oyster-shell were increased than that of the fresh particles, which makes it possible to enhance the removal capacity in acid gases. XRD analysis of calcined waste oyster shells were exhibited peaks characteristic of calcium oxide, whereas raw waste oyster-shells showed that the main peaks were characteristic of calcium carbonate.

And it was concluded that the optimal temperatures for calcination and hydration were 800.0 ~ 850.0°C and 90.0°C respectively. Pores of absorbent are formed by the emission of CO2 during the high temperature calcination but it was agglomerated by sintering. Therefore, the specific surface area decreased and it was completely different from limestone. SO2/NOx removal experiments have been carried out to test the reactivity of absorbents in a fixed bed reactor. SO2 removal activity and reaction rate of calcined/hydrated waste oyster-shells were higher than that of calcined/hydrated limestone. It is clearly indicated that absorbent prepared by waste oyster-shells are substituted for commercial limestone and can be directly applied to industries which try to reduce their emissions of SO2 and NOx.

#### **7. References**


**13** 

Yu-Chu Peng

*China,Taiwan* 

*University of Science and Technology,* 

**Carbon Steel Slag as Cementitious** 

*Graduate Institute of Construction Engineering, National Taiwan* 

*Depart of Leisure Management, Taiwan Hospitality & Tourism College,* 

In Taiwan, self-consolidating concrete (SCC) exhibiting high-flow behaviour is a widely used concrete material to prevent conventional concrete problems such as honeycomb structures that occur as a result of poor practice. SCC is also used as the material of choice for heavily reinforced concrete structures located in seismic zones [Paczkowski Piotr,Kaszynska Maria,2007.]. Pozzolanic materials are important ingredients for making SCC [Mihashi H, Yan X,1995.]. For many years, pozzolanic admixtures, such as blast furnace slag (BFS), pulverized coal ash (fly ash), silica fumes, and copper slag have been recycled to partially replace Portland cement in concrete mixtures. The main advantages of using pozzolanic materials are improvements in performance and significant reduction in the life-cycle costs of concrete structures; the latter, in particular, continues as a significant problem for engineers [Khalifa AJ, Ramzi T,2002. Li G, Zhao X.,2003. Zhang MH, Bilodeau A, Malhotra VM, Kim KS, Kim JC,1999.]. Materials such as steel slag, normally considered as waste, have promising applications as partial Portland cement replacements in concrete mixtures. Considerable research and development has been conducted to develop new concrete technologies such as SCC. Further, the construction of durable concrete has also been pursued. Initially, pozzolanic admixtures were solid waste and it was extremely costly to treat and dump them into a final storage area. Today, however, in the concrete industries in Taiwan and elsewhere, these admixtures are important materials for the production of low-cost durable concrete, and an

In Taiwan, carbon steel slag (CSS) is a by-product of the reduction during the production of refining carbon steel in an arc furnace, and is seldom recycled. On average, the production of one ton of carbon steel yields 10 kg of CSS waste, and hence, in Taiwan, more than 56,000 tons of CSS is produced each year. Due to the relatively small amounts of CSS relative to blast furnace slag (BFS), environmental protection agency (EPA) regulations had previously permitted the dumping of CSS. Today, the dumping of such waste is not permitted, and the proper disposal of CSS has become a huge problem. Since lime, coke and silicon iron are added to promote the reducing process during high-temperature-refinery scrap steel procedures, the CSS contains large amounts of CaO, SiO2 and Al2O3. This waste composition, however, is similar to BFS or Portland cement [Chiang CC, Chenn YY, Lin TY,

example of environmental protection and resource conservation.

**1. Introduction** 

**Material for Self-Consolidating Concrete** 

