1

Oxidation Potential of Chromium

in Basic Oxygen Furnace Slag

in Contact with Soil

2016.11.15

Yenhan Lin

Office of Energy and Environmental Affairs,

China Steel Corporation

2016 ASEAN Iron and Steel Sustainability Forum

SESSION 9 - Waste Management and Emissions Control

2

1. Introduction

2. Experimental Methods

3. Results and Discussion

4. Conclusion

Outline

Oxidation Potential of Cr in BOF Slag in Contact with Soil

3

1. Introduction

References: 1) U.S. Department of Health and Human, Agency for Toxic Substances and Disease. (2011). Services Registry Case Studies in Environmental Medicine, Chromium Toxicity.

2) National Slag Association Common Uses for Slag. (2013).

• Chromium

Trivalent Cr(III): essential nutrient

Hexavalent Cr(VI): toxic, carcinogenic

• BOF Slag

Cr is present mostly as Cr(III)

Toxicity Characteristic Leaching Procedure test

results conform to the Taiwan EPA standard

Applications: agricultural purposes, filling, land

reclamation, road construction, etc.

Does Cr(VI) in soil therefore increase?

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• Materials

BOF slag samples: CSC

Soil samples: Representative soil series for Taiwan

2. Experimental Methods

Soil Series

1 2 3 4 5 6

Con-tent (%)

Soil 32 71 41 15 21 37

Silt 40 17 31 50 34 42

Clay 28 12 28 35 45 21

pH 9.7 8.4 8.1 7.2 4.8 7.7

Free Mn (mg/kg)

98 47 173 347 98 285

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2. Experimental Methods

• Experimental Settings

Case 1 Case 2

Slag-Soil Contact

Slag layer on soil Slag-soil 1:1 mixture

Variables Fertilization,

Water content None (All saturated

with sea water)

Sample Soil Series 1, 2, 3, 4, 5 2, 4, 6

Corresponding Slag Utilization

Road construction Land reclamation

Slag

Soil

Mix

6

2. Experimental Methods

• Analysis and Monitoring

Cr(VI) concentration

pH

Oxidation-reduction potential (ORP)

• Timeframe

147 days

7

• Cr(VI) Concentration: Background Level

0

5

10

15

20

25

30

Total-Cr

Cr(VI)

mg/kg

Soil Series 1 2 3 4 5 6 Slag Fertilizer

310

– BOF slag is lower in Cr(VI) concentration than 5 of the 6 soil series

despite being higher in total-Cr.

3. Results and Discussion

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Compost

Time (day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147C

r(V

I) (

mg/k

g)

1

2

3

4

5

6

7

8

0 Bar

1 /3 Bar

8

7

6

5

4

3

2

1

0

Cr(

VI)

(m

g/k

g)

Time (day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

Cr(

VI)

(m

g/k

g)

0

1

2

3

4

5

6

7

8

0 Bar

1 /3 Bar

8

7

6

5

4

3 2

1

0

Cr(

VI)

(m

g/k

g)

Fertilization 0 bar

1/3 bar

0 bar

1/3 bar

– Cr(VI) remained on the same level in the 140 days testing time

– Mostly below 4 mg/kg regardless of water content and fertilization

• Cr(VI) Concentration: Case 1

3. Results and Discussion

Soil Series 3 (highest background Cr(VI))

9

Compost

Time (day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147C

r(V

I) (

mg

/kg

)

1

2

3

4

5

6

7

8

0 Bar

1 /3 Bar

Time (day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

Cr(

VI)

(m

g/k

g)

1

2

3

4

5

6

7

8

0 Bar

1 /3 Bar

8

7

6

5

4

3

2

1

0

Cr(

VI)

(m

g/k

g)

8

7

6

5

4

3 2

1

0

Cr(

VI)

(m

g/k

g)

Fertilization 0 bar

1/3 bar

0 bar

1/3 bar

3. Results and Discussion

– Mostly below 4 mg/kg regardless of water content and fertilization

– Cr(VI) remained on the same level in the 140 days testing time

• Cr(VI) Concentration: Case 1

Soil Series 4 (highest free Mn)

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– Cr(VI) remained on the same level

in the 140 days testing time

• Cr(VI) Concentration: Case 2

Seawater

Time (day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

Cr(

VI)

(m

g/k

g)

0

1

2

3

4

5

6

7

8

1

2

3

8

7

6

5

4

3

2

1

0

Cr(

VI)

(m

g/k

g)

2

4

6

– Soil Series 2, 4:

Cr(VI) lower than in Case 1

3. Results and Discussion

Soil Series 2, 4, 6

11

Time(day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

pH

10.5

11.0

11.5

12.0

12.5

13.0

0 Bar

1/3 Bar

Compost

Time(d)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

pH

10.5

11.0

11.5

12.0

12.5

13.0

0 Bar

1/3 Bar

Fertilization 0 bar

1/3 bar

0 bar

1/3 bar

Soil Series 3 (highest background Cr(VI))

• pH: Case 1

– Varies between 11 and 12.5

3. Results and Discussion

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Soil Series 3 (highest background Cr(VI))

Time(day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

OR

P(m

V)

-300

-250

-200

-150

-100

-50

0 Bar

1/3 Bar

Compost

Time(day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

OR

P(m

V)

-300

-250

-200

-150

-100

-50

0 Bar

1/3 Bar

Fertilization 0 bar

1/3 bar

0 bar

1/3 bar

• ORP: Case 1

– Negative

– Generally lower for 0 bar (moisture saturation)

3. Results and Discussion

Soil Series 3 (highest background Cr(VI))

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• pH, ORP: Case 2

– pH varies between 11 and 12

– ORP is negative and lower than in Case 1

3. Results and Discussion

Seawater

Time(day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

OR

P(m

V)

-300

-250

-200

-150

-100

-50

1

2

3

2 4 6

Seawater

Time(day)

0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105112119126133140147

pH

10.5

11.0

11.5

12.0

12.5

13.0

1

2

3

2

4

6

2

4

6

Soil Series 2, 4, 6

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• Cr(VI) remains on the same level for all soil series and

experimental settings. The abundant Cr(III) in BOF slag

does not oxidize to increase the level of Cr(VI) in soil.

• Soil contribution to Cr(VI) is significant; background

level of Cr(VI) should be discerned regarding the

attribution of slag.

• ORP of soil in contact with slag are sufficiently low to

limit the Cr(III) oxidation.

• Relieves the safety concerns regarding Cr(VI) for BOF

slag utilization involving slag-soil contact.

4. Conclusion

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Thank you