Recovery of Manganese and Phosphorus from Dephosphorization Slagwith Wet Magnetic Separation
Yong-Soo Jeong, Kazuyo Matsubae-Yokoyama, Tetsuya Nagasaka
Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan
Key words: dephosphorization slag, magnetic separation, phosphorus, manganese

Abstract
The dephosphorization slag has a great potential as the secondary resources of manganese andphosphorus, while quite a large amount of slag is landfilled and simply reused such as cement. The
objective of this study is to investigate the recovery of manganese and phosphorus by wet magnetic
separation technique. The hot metal pretreatment slag (dephosphorization slag) generally contains a
Ca3P2O8-Ca2SiO4 (phosphorus enriched phase) and FeO-MnO (manganese enriched phase) solid solutions
together with FeO-CaO-SiO2 matrix phase. Since the difference in their magnetic properties is significant,it is possible to separate each phase with the aid of wet magnetic separation. By applying strong magnetic
field to the crushed slag (<32μm), 31% of phosphorus enriched slag and 14% manganese enriched slag
could be successfully recovered.

1. Introduction
Security of resources becomes more important than ever due to the recent trend in commodity prices forminerals and natural resources. Manganese and phosphorus are important resources for many advanced
countries like Japan and South Korea. More importantly, they are not produced in the countries, although
domestic use of each is increasing. 1~3) Manganese is an indispensable element in industrial and consumer
products, and phosphorus is in global demand, particularly for mainly fertilizer production. However, in thesteel industry, phosphorus is typically recognized as a harmful element for high-quality steel, whereas
manganese is considered to be an important alloying and deoxidizing element in the steelmaking process.
Because of its ability of desulfurization and deoxidation for steel, manganese plays a key role in thesteelmaking. Manganese and phosphorus exist in coal, iron ore, and limestone, 4) which are essential raw
materials for iron- and steel-making processes. Since manganese and phosphorus are less noble in chemical
nature, they are easily oxidized and mostly distributed into the steelmaking slag, particularly hot metal
pretreatment slag (dephosphorization slag). Because total amount of crude steel production in Japan andSouth Korea is huge, the amount of manganese and phosphorus transferred to steelmaking slag is alsohuge.
The recovery of valuable mineral resources such as manganese and phosphorus from steelmaking slag is－ 11 －

important for several reasons. First, reserves of high manganese and phosphorus content resources are very
limited. Second, industrial processes for mining, producing, and distributing can cause environmental anduneconomical problems. Therefore, as a secondary resource, steelmaking slag could be an importantalternative because of high manganese and phosphorus content.
Despite the economic and ecological importance, however, only a few researchers have paid attention torecovering valuable elements from slag. 5~8) In general, dephosphorization slag can be divided into threemajor phases in its solidified micro-structure: a FeO-free phosphorus-rich phase (Ca3P2O5-Ca2SiO4), a
phosphorus-free manganese-enriched phase (mangano-wustite phase), and a phosphorus-free matrix phase(FeO-CaO-SiO2) containing minor part of manganese. Therefore, in principle, it is possible to recover
mangano-wustite using a weak first magnetic separation followed by a relatively strong second magnetic
separation to recover phosphorus as calcium phosphate from residues. With such a background, the authors
have developed a new process to recover manganese and phosphorus from steelmaking slag by wet
magnetic separation.
2. Manganese and phosphorus material flows through steel industry
Different forms of phosphorus are widely used in industry and other human activities; common uses
include fertilizers, soaps, detergents, and surface preparation agents. In these situations, phosphorus isviewed as an important but limited natural resource that should be used efficiently, economically, and inenvironmentally friendly ways. However, in the steel industry, phosphorus is known as a typical harmful
element for high-quality steel products. Phosphorus is thus removed from hot metal (molten pig iron) toslag. Since the total crude steel production in Japan and South Korea is extremely huge (118 and 53 million
tons in 2008 respectively) 9~10), the amount of phosphorus removed to steelmaking slag must also be large.
The authors have found by material flow analysis 11~15) that phosphorus removed to the steelmaking slag
shares a significant part of total phosphorus flow in Japan and South Korea. The amount of phosphorustransferred to steelmaking slag is estimated to be 96.4 and 35.7kt-P/year in Japan and South Korea,
respectively.
Manganese material flow for the steel industry in both countries is shown in Fig. 1. In the ironmaking
process, pig iron (hot metal) is produced as the main product and BF slag is generated from the blast
furnace (BF) as a by-product. The input of manganese to the ironmaking process is iron ore, ferruginous
manganese ore, and steel scrap. The manganese output to pig iron and ironmaking slag is evaluated to be
95.1 kt-Mn/year and 15.9 kt-Mn/year, respectively. 15) In the case of Japan, the manganese output to pig
iron and slag are estimated to be 208.9 kt-Mn/year and 55.4 kt-Mn/year. 14) In the steelmaking process,crude steel is produced as the main product and steelmaking slag is generated as a by-product from thebasic oxygen furnace (BOF) and electric arc furnace (EAF) processes. Steelmaking slag is generallyclassified into some categories depending on the refining processes such as desiliconization,dephosphorization, desulfurization, BOF and EAF slags while manganese flow in each slag has beensummarized as a whole “steelmaking slag” in Fig. 1. It should be noted that, among these slags, our major
target to recover manganese and phosphorus is the hot metal dephosphorization slag8) because manganeseand phosphorus tend to be highly concentrated into the slag. The sources of manganese in the steelmaking－ 12 －

process are hot metal, steel scrap, ferro-manganese, silico-manganese, and manganese metal. The
manganese outputs from the steelmaking process were evaluated to be 260.0 kt-Mn/year in crude steel and
146.0 kt-Mn/year in slag in South Korea while in the case of Japan the manganese outputs are 590.3
kt-Mn/year in crude steel and 530.7 kt-Mn/year in slag, respectively. It should be noted that the amount ofmanganese loss into steelmaking slag is almost equivalent to that of manganese input into steelmaking
process as ferro-manganese etc. in both countries. The results of material flow analysis suggest that asignificant ripple effect can be expected if the recovery of manganese and phosphorus from iron- andsteel-making slag becomes possible.

Unit: kt-Mn/year (South Korea & Japan)

Iron making

Ferrous resource(111.1 & 266.2)

BF slag(15.9 & 55.4)(0.1 & 1.9)

Blast furnace

Dust

Pig iron(95.1 & 208.9)

Steel making(62.9 & 241.7)

Scrap(158.0 & 450.6)(5.0 & 92.8)

BOF/EAF
Steel making
Slag

Iron-Mn ore/Mn ore(146.0 & 530.7)

Ladle(243.0 & 577.6)

Ferro-Mn
Si-Mn(260.0 & 590.3)

Crude steel

Figure 1 Material flow of manganese in Japanese and South Korean steel industries (2005)

3. Experimental procedures
3.1 Morphology of dephosphorization slag
The FeO-CaO-SiO2-P2O5(-MgO-MnO) system is the typical dephosphorization slag. The morphology ofsolidified dephosphorization slag has been discussed in a number of previous studies. According to thereport of Futatsuka et al., 16) dephosphorization slag after solidification generally consists of (1) iron freecrystalline phase that contains phosphorus (herein-after “phosphorus enriched phase”) and (2) phosphorus
free another phase that contains iron. The authors have made more detail analysis on the manganese andphosphorus morphology in the practical dephosphorization slag to develop a manganese and phosphorus
recovery process from the slag.

It was found that the above-mentioned phosphorus free another phase canbe further divided into two kinds of phases; FeO-CaO-MnO based mangano-wustite phase (herein-after“manganese enriched phase”) and FeO-CaO-SiO2 phase which contains manganese as minor component(herein-after “matrix phase”).

Figure 2 shows the examples of element mapping image in thedephosphorization slag by EPMA.
－ 13 －

㎛㎛㎛

Figure 2 Examples of microstructures of dephosphorization slag C

Though the composition and morphology widely vary in general depending on the produced steel
categories and operating conditions, most of dephosphorization slag approximately consists of three major
phases as it was explained earlier. Table 1 gives the compositions of dephosphorization slag supplied forthe present experimental runs. The authors measured the magnetic properties of FeO-CaO-MnO based slagwith a vibrating sample magnetometer (VSM) as part of a quantitative investigation of the possibility ofmagnetic separation of manganese enriched phase from slag.

Table 1 Chemical composition of the steelmaking slag

Table 2 Experimental condition

Composition (%)

Slag

FeO

Run
No.

<32

A

1

O

SiO2

P2O5

MnO

22.51 42.36

11.05

2.24

3.49

A phosphorus enriched phase

2.79

61.96

27.41

6.82

0.28

manganese enriched phase

63.75

2.33

0.04

0.01

9.00

22.85 32.30

21.80

6.85

9.90

3

phosphorus enriched phase

0.99

56.32

12.31 32.65

1.69

4

manganese enriched phase

76.68

averageaverage
B

0.26

0.07

0.01

16.98

40.40 24.20

12.70

7.85

6.05

phosphorus enriched phase

1.53

55.95

10.78 35.08

1.11

manganese enriched phase

64.54

4.74

4.04

15.48

average

0.69

2

B

C

0.02

-0.02

-0.03
-5000 -4000 -3000 -2000 -1000

0

％

FeO

CaO

MnO

1

55

25

20

2

55

30

15

3

55

40

5

O

X

6

O

O

1000 2000 3000 4000 5000

H[Oe]Figure 3 The magnetization curves for FeO-CaO-MnO based slag

－ 14 －

X

5

-0.01

Remark

X
X

O

2
1

0.00

Air
pump
X

O

3

0.01

<52
O

0.03

M[emu/g]C

Size (μm)

Slag

CaO

slag: 10g
water:
200ml

The VSM sample was made by mixing and premelting reagent grade chemicals at desired ratios asshown in Fig. 3. A MoSi2 heater electric furnace was used for preparing VSM sample. The result is shownin Fig. 3 in terms of magnetization as a function of the magnetic filed. The magnetization curves of
FeO-CaO-MnO based phase, that is manganese enriched slag, seem to be ferromagnetism orparamagnetism depending on MnO composition. On the other hand, the magnetic property of phosphorus
enriched phase has been found as anantimagnetism. 8) Since the magnetic property of each phase has

found to be significantly different, the authors have tried wet magnetic separation process to recover
manganese enriched phase and phosphorus enriched phase from the dephosphorization slag as a new
manganese and phosphorus resource.
3.2 Magnetic separation
A magnetic separation experiment was carried out using a Wet High Intensity Magnetic Separators (Eriez
Series L Model 4 Laboratory). Three kinds of dephosphorization slag as shown in Table 1 were prepared
for the experiments. The hot metal dephosphorization slag specimen was provided from JFE steel. This slag
was crushed in zirconia ball mills (ball size: 10mm diameter) under 32μm and 52μm. Table 2 gives theexperimental condition.
P-enrich phase

Feed

Mn-enrich phase

10g slag + 200g water
1st stage
0.03T
Trapped 1

Untrapped 1
2nd stage
0.10T

Trapped 2

Untrapped 2
3rd stage
0.30T

Trapped 3
STS mesh

STS mesh

Figure 4 Schematic of the experimental magnetic field

Untrapped 3

Figure 5 Magnetic separation steps

10g of the sample was dispersed in approximately 200ml of ion exchanged water to avoid coagulationand poured the sample into constant surface magnetic field strength in a controlled separation cell. 11
pieces of stainless steel mesh filters which were magnetized were inserted in the cell, and these mesh filters
themselves also contributed to separation. The magnetized particles in the charged samples weremagnetically trapped by the filters, and then, the particles which were not magnetized were untrapped fromthe cell by opening the valve equipped at the lower part of the cell as shown in Fig. 4. Magnetically trapped
and untrapped particles were respectively collected and analyzed their compositions by ICP. Figure 5 shows
the magnetic separation process and applied magnetic intensity. At first, a sample was separated atmagnetic field strength of 0.03T and, the magnetically trapped sample in the cell was collected. The－ 15 －

untrapped sample from the cell without magnetization was supplied into a new cell with stronger magnetic
field. This procedure was repeated for several times up to maximum 0.3T. In some experimental runs, air
was injected into the cell by air pump to promote homogeneous dispersion of particles in the water.
4. Experimental results
Figure 6 shows the experimental result of the magnetic separation in Run No. 1. The manganeseconcentration in the recovered sample becomes smaller at higher intensity of the magnetic field. On thecontrary, the phosphorus concentration in the recovered sample increased with higher magnetic fieldstrength. In other words, because the concentration of manganese and phosphorus recovered has indicatedopposite tendency, separating manganese and phosphorus individually by magnetic field fromdephosphorization slag could be possible. According to the morphology study of dephosphorization slag
and element mapping image by EPMA, manganese coexisted with FeO in most cases. That is, relatively
small crystalline phase of manganese enriched phase dispersed on the matrix phase. Therefore, manganese
tends to be collected at higher intensity of the magnetic field. Due to such reason, individual separation ofmanganese enriched phase and matrix phase was not well done in the present experimental condition. The
phosphorus content at untrapped 3 of 0.30T becomes almost double of the average composition in spite of
low phosphorus concentration of tested slag. However, it is not satisfactory for the usage of phosphate
fertilizer. P2O5 content in natural phosphate ore for phosphate fertilizer is over 25~30wt%.17) Phosphorus
segregation in slag A was not remarkable and suitable. Therefore, other slag which had higher manganeseand phosphorus segregations were used for magnetic separation.
FeO

MnO

CaO

60

P2O5

10

55
8

45

MnO, P2O5 wt%

FeO, CaO wt%

50
40
35
30
25
20
15

6

4

2

10
5
0

0

Trapped 1

Trapped 2

Trapped 3

Untrapped 3

Trapped 1

Trapped 2

Trapped 3

Untrapped 3

Magnetic separation steps

Magnetic separation steps

Figure 6 Magnetic concentration of slag A in Run No. 1

Run No. 2 and 3 were carried out for magnetic separation with slag B. The average composition of thisslag was MnO 9.9% and P2O5 6.9%, and MnO and P2O5 contents in manganese and phosphorus enriched
phases were respectively MnO 17.0 and %P2O5 32.7% as shown in Table 1. The particle size prepared was
32μm (Run No.3) and 53μm (Run No.2). Figure 7 shows the influence of the particle size to recovery
efficiency of manganese and phosphorus. Manganese and phosphorus recovery efficiencies somewhat
increased with smaller particle size, indicating that the population density of the isolated manganese andphosphors enriched phases would be increase in the charged slag powder if the particle size is smaller and－ 16 －

thus the recovery efficiency becomes higher. It should be noted that, however, the suitable particle size
depends on the initial morphology of slag. That is, if the crystal sizes of manganese and phosphors enriched
phases were initially large in the supplied slag, the relatively large particle size even after crushing would
result in sufficient recovery. The morphology of slag strongly depends on the operating conditions, inparticular, slag cooling conditions.
FeO (Run No.2)

MnO (Run No.2)

CaO (Run No.2)

P2O5 (Run No.2)

FeO (Run No.3)

MnO (Run No.3)

CaO (Run No.3)

55

P2O5 (Run No.3)

30

50
25

MnO, P2O5 wt%

FeO, CaO wt%

45
40
35
30
25
20
15
10

20
15
10
5

5
0

Trapped 1

Trapped 2

Trapped 30Untrapped 3

Trapped 1

Magnetic separation steps

Trapped 2

Trapped 3

Untrapped 3

Magnetic separation steps

Figure 7 Magnetic concentration of slag B in Run No. 2&3

Run No. 4, 5 and 6 were carried out for the magnetic separation with slag C. The average composition ofthis slag was MnO 6.1% and P2O5 7.9%, and MnO and P2O5 contents in manganese and phosphorus
enriched phases were respectively MnO 15.5% and P2O5 35.1% as shown in Table 1. Figure 8 shows theinfluence of the particle size after crushing on the recovery efficiency of manganese and phosphorus. On
the basis of this result, the following experiment was made under 32μm.

FeO (Run No.4)

MnO (Run No.4)

CaO (Run No.4)

P2O5 (Run No.4)

FeO (Run No.5)

MnO (Run No.5)

CaO (Run No.5)

55

P2O5 (Run No.5)

35

50
30

MnO, P2O5 wt%

FeO, CaO wt%

45
40
35
30
25
20
15
10

20
15
10
5

5
0

25

Trapped 1

Trapped 2

Trapped 3

Untrapped 30Trapped 1

Magnetic separation steps

Trapped 2

Trapped 3

Magnetic separation steps

Figure 8 Magnetic concentration of slag C in Run No. 4&5－ 17 －

Untrapped 3

Run No. 6 was conducted for magnetic separation with physical agitation with slag C. The sample wassufficiently agitated by injecting air into the cell. The flow rate of air was controlled by the flow meter at
0.03L/min. Figure 9 shows the influence of air agitation. The results of Run No. 4, 5, and 6 indicated thatthe effect of the particle size and physical agitation could improve the recovery efficiency significantly. In
the present experimental conditions, about 31% P2O5 could be recovered as “untrapped 3” of 0.30T, andabout 14% MnO can be recovered as “trapped 1” of 0.03T where particle size was less than 32μm with air
agitation, which was the best result. Figure 10 shows the rate of consisted phases in each recovery step. The
higher magnetic field intensity resulted in the higher P2O5 recovery ratio. The P2O5 concentration of 31% at
untrapped 3 is good enough to use for phosphate fertilizer. In addition, it is possible to reduce other phase
contamination under 5%. The results obtained in Run No.6 are also summarized in Fig. 11. Separation
efficiency should be improved in the future work, but sufficiently high P2O5 content was achieved in
Untrapped 3 in the present work.
MnO

FeO
CaO

55
50

30

MnO, P2O5 wt%

45
40
35
30
25
20
15
10

25
20
15
10
5

5
0

0

Trapped 1

Trapped 2

Trapped 3

Untrapped 3

Trapped 1

Trapped 2

Figure 9 Magnetic concentration of slag C in Run No. 6

Matrix and manganese enriched phase
Phosphorus enriched phase
100
90
80
70
60
50
40
30
20
10
0

Trapped 1

Trapped 3

Magnetic separation steps

Magnetic separation steps

Rate of consisted phase wt%

FeO, CaO wt%

P2O5

35

Trapped 2

Trapped 3

Untrapped 3

Magnetic separation steps
Figure 10 Rate of phosphorus enriched phase and other phase－ 18 －

Untrapped 3

Manganese enriched phase

Trapped 1

Sample weight

1.4g (14 wt%)

MnO

14.0 %

P2O5

3.0 %

Sample weight

7.5g (75 wt%)

MnO

5.2 %

P2O5

5.4 %

Sample weight

1.1g (11wt%)

Phosphorus enriched phase
Matrix phase

Trapped 2 & 3

Slag C
Sample weight

10g (100 wt%)

MnO

6.1 %

P2O5

7.9 %

Unrapped 3

MnO

2.0 %

P2O5

31.0 %

Figure 11 Concentration and weight in recovered slag

5. Conclusion
The quantity of recyclable manganese and phosphorus form slag waste in Japanese and South Korean
steel industries has been evaluated with the methodology of the material flow analysis. In the case of Japan,
manganese and phosphorus contained in steelmaking slag was 530.7 kt-Mn/year and 96.4 kt-P/year
respectively in 2005. The recovery of manganese and phosphorus from steelmaking slag could have asignificant impact on a national mineral strategy and on the environment. In the case of South Korea, theamount of manganese and phosphorus contained in steelmaking slag was estimated to be 146.0 kt-Mn/year
and 35.7 kt-P/year respectively in 2005.
Magnetic separation was applied to the recovery of manganese and phosphorus from dephosphorization
slag. Dephosphorization slag consists of phosphorus enriched phase and manganese enriched phase
together with matrix phase. The magnetic property of each phase has found to be significantly different. In
the present experiment, about 31% of phosphorus enriched slag could be recovered with less than 10% of
matrix and manganese enriched phase contamination at untrapped 3 of 0.30T and about 14% of manganeseenriched slag could be recovered with less than 20% of phosphorus enriched phase contamination at
trapped of 0.03T, particle size of less than 32μm with physical agitation. For better recovery of manganeseand phosphorus, it is emphasized that compositions and morphology of slag should be controlled for easiermagnetic separation for manganese and phosphorus recovery. The steelmaker should be encouraged to
produce not only high quality steel but also good slag as the secondary resources of manganese andphosphorus, while they basically don’t care the slag quality in the view point of its recovery. However, thepresent authors believe that it is possible to convert “steelmaking slag” to “secondary resources ofmanganese and phosphorus” with additional small technologies like slow cooling and composition control.
The present authors call such concept as “Slag-making technology”.
－ 19 －

This research was supported by JFE 21st Century Foundation for FY 2008 and FY 2009, the authors
wish to express their gratitude to the support.

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