Processes

The most widespread desulfurization process in the developed countries is the wet lime slurry method, whose byproduct is mostly pure gypsum. In the developing countries, on the other hand, a semi-dry process tends to be adopted, owing to its low construction and running costs. However, the byproducts from a semi-dry process contain Ca(OH)2 (calcium hydroxide), CaCO3 (calcium carbonate) and fly ash, as well as gypsum. Among several

Table 10.2. Salt composition of soil profile of Haplic Solonchak (non-alkali soil)

Depth

pH

TSS

co32

hco3-

ci

SO42-

Ca2+

Mg2+

NA+ + K+

ESP

(cm)

g/kg)

cmol/kg

soil

(%)

0-32

8.1

171.1

0.04

0.22

224.0

53.0

29.1

34.9

190.0

12.8

32-55

8.3

89.0

0.09

0.20

28.2

17.4

13.9

30.0

30.5

10.5

55-90

7.9

69.0

0.09

0.27

30.0

19.9

14.6

28.0

29.7

10.06

90-100

7.7

66.0

0.05

0.30

40.0

17.7

20.9

29.8

30.6

9.5

100-150

7.9

70.7

0.01

0.45

56.4

15.6

24.6

30.2

30.2

10.9

TSS; Total soluble salts;

ionic determination was done by water extraction in soil: water=1:5.

Table 10.3. Salt composition of soil profile of Alkali Solonchak

Depth

pH

TSS

co32

hco3-

ci

SO42"

Ca2+

Mg2+

NA+ + K+

ESP

(cm)

(g/kg)

cm

iol/kg soil

(%)

0-2

10.6

20.9

21.9

3.5

8.4

3.6

0.02

0.07

38.7

78.9

2-17

10.3

9.9

2.1

3.8

5.3

0.9

0.03

0.04

18.9

60.3

17-31

10.4

6.9

1.9

3.8

4.9

0.6

0.02

0.07

19.4

70.4

31-57

10.6

4.5

2.6

4.0

3.3

0.4

0.10

0.15

10.5

50.1

57-80

10.4

3.9

2.0

3.3

2.1

0.4

0.20

0.19

17.5

42.9

TSS; Total soluble salts;

ionic determination was done by water extraction in soil: water=1:5.

Fig. 10.2. Concept of reclamation of Alkali soils by calcium sulfate.

semi-dry processes, the byproducts from the ash recovery activation method (ARAM) were examined, because the Japanese government has already installed a working plant at Qingtao City, Shandong province in China. ARAM is the process by which a slurry of the polycrystal substance called Ettringite, which is formed through hot water treatment of a mixture of CaO (calcium oxide), fly ash and gypsum, is sprayed into the flue gas to absorb SO2 (sulfur dioxide) as gypsum.10 The chemical properties of byproducts from desulfur-ization processes are shown in Table 10.4. The byproduct from the wet process is almost pure gypsum, while the byproduct from the semi-dry process includes only 20 wt % gypsum and 20 wt % calcium hydroxide, which would increase the pH of the soil.

Until now, there have been very few applications of the byproduct from the semi-dry process to the alkali soils in China, because it is considered to be only waste.

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