Geochemistry

The study of the geochemical composition of Fe-Mn concretions and nodules originally started with samples mainly from marine sediments (Li 1982). The researchers found that the Fe-Mn nodules from the oceans contained significant quantities of Ni, Cu and Co of economic value (Chauhan et al. 1994; Dutta et al. 2001). The geochemical study of soil Fe-Mn concretions and nodules began in the mid 1970s (Childs 1975) and was expanded during the last decade (Ram et al. 2001; Cornu et al. 2005).

Table 11.3 presents data of enrichment factor (EF) for each element which calculated as "element concentration in concretion-nodule/element concentration in surrounding soil" (Dawson et al. 1985; Gasparatos et al. 2004b). The EF data show that the degree of enrichment varies from element to element, with lower values of Si, Al concentrations in the Fe-Mn concretions and nodules than the soil matrix (EF < 1). On the contrary, concretions and nodules are enriched 30-60 times in Mn with respect to the host soil. They are moderately enriched in Fe, whereas they are in most cases depleted in major alkaline earth metals (Ca and Mg). According to the data in Tables 11.4 and 11.5, Fe-Mn concretions and nodules are composed mainly of Si, Al, Fe and Mn. Liu et al. (2002) showed that Si, Al, Fe, Mn, Ca, K and Ti were the main elements presents in Fe-Mn concretions and nodules isolated from a Chinese Alfisol.

Table 11.3 A literature review of the enrichment factor (EF) for various elements in Fe-Mn concretions and nodules

EFsi

Mg

efk

Na

Tan et al. (2006)

0.70

0.78

2.11

57.8

2.29

0.77

0.66

1.49

Palumbo et al. (2001)

0.95

2.34

30.7

0.14

0.56

0.78

0.47

Zaidelman and Nikiforova (1998)

0.80

0.80

5.9

30.0

1.1

0.70

-

-

Childs (1975)

0.72

0.83

3.5

25.7

0.71

-

0.89

-

Table 11.4 Major (%) and trace element (ppm) composition of Fe- Mn concretions and nodules of different sizes from Greek Alfisols (Gasparatos 2007)

Fe-Mn concretions Fe-Mn nodules

Table 11.4 Major (%) and trace element (ppm) composition of Fe- Mn concretions and nodules of different sizes from Greek Alfisols (Gasparatos 2007)

Fe-Mn concretions Fe-Mn nodules

4.76-2.00 mm

2.00-1.00 mm

4.76-2.00 mm

2.00-1.00 mm

Total concentrations (%)

SiO2

61.90

57.85

56.63

54.80

Al2O3

10.50

10.45

9.88

11.22

Fe2O3

12.30

16.55

10.15

10.30

MnO

1.82

0.70

5.17

5.05

CaO

0.57

0.58

0.60

0.70

MgO

0.95

1.00

1.06

1.30

K2O

1.70

1.57

1.80

1.70

Na2O

2.30

2.55

2.30

2.30

Total concentrations (ppm)

Ba

695-6,790

120-1,586

1,835-11,670

995-8,092

Co

191-622

115-226

786-1,198

595-1,280

Pb

302-395

350-640

375-735

450-943

Ni

201-592

186-332

506-1,874

515-3,360

Cr

155-351

337-529

144-230

188-302

Cu

35-48

35-67

41-96

54-97

Zn

80-244

87-109

80-161

84-526

Many studies have shown the general enrichment of Fe - Mn concretions and nodules in trace elements with respect to the surrounding soil matrix (Childs 1975; Sidhu et al. 1977; Dawson et al. 1985; Gasparatos et al. 2004b).

For example, high enrichment factors were observed, in nodules from Sicilian soils for Mn (296), Co (93), Ce (45), Pb (31), Ba (18), Ni (17), Cd (15) and Fe (2.6) (Palumbo et al. 2001). Figure 11.9 shows average enrichment factors of Ba, Co, Ni, Pb, Cr, Cu and Zn in the Fe-Mn concretions and nodules of different sizes from Greek soils (Gasparatos 2007) . The EF values vary from element to element and have a great range for elements such as Ba and Co.

Childs and Leslie (1977) found that in each case, the Fe-Mn concretions from soils in New Zealand had high concentrations of Fe, Mn, Ti, Co, S, P, Mo, Cu, V in relation to the surrounding soil mass.

Gasparatos et al. (2004b) show that the Fe-Mn concretions absorbed significant amounts of metals and especially Pb and Cd from the soil system. According to the enrichment factors, the affinity of metals for the concretions due to the charged

Table 11.5 Major (%) and trace element (ppm) composition of Fe- Mn nodules from a lateritic subsoil (Neaman et al. 2004)

Enrichment

Element

Soil

Nodules

factor

(%)

SiO2

31.94

14.67

0.46

Al2O3

27.98

12.55

0.45

Fe2O3

18.36

41.88

2.28

MnO

0.91

13.00

14.29

MgO

0.20

0.22

1.10

CaO

<0.01

<0.01

-

Na2O

<0.01

<0.01

-

K2O

0.17

0.32

1.88

TiO2

2.59

1.11

0.43

P2O5

0.14

0.32

2.29

(ppm)

As

288

1,252

4.3

Ba

176

2,435

13.8

Cd

0.3

2.8

9.3

Co

24.3

216

8.9

Cr

296

2,771

9.4

Cu

57.5

333

5.8

Mo

22.6

130

5.8

Ni

60.6

419

6.9

Pb

32.9

357

10.9

Zn

103

273

2.7

Ba Co Ni Pb Cr Cu Zn

Fe-Mn concretions 4.76-2,00 mm -«- Fe-Mn concretions 2.00-1.00 mm Fe-Mn nodules 4,76-2.00 mm — Fe-Mn nodules 2.00-1,00 mm

Fig. 11.9 Average enrichment factors of elements in the Fe-Mn concretions and nodules of different sizes from Greek Alfisols (Gasparatos 2007)

surfaces of Fe and Mn oxides, follow the order Pb > Cd > Mn > Co > Ni > Fe. McKenzie (1980) also found adsorption of Co, Mn, Ni and Pb at the same order on nine synthetic Mn oxides. In Fe-Mn nodules form nine main soils in China, Pb, Cd, Ba and Co had high accumulation, Ni moderate accumulation and Cu, Zn accumulated to a minor degree (Tan et al. 2006).

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