Thermodynamic Analysis of Separating Synchronously Copper and Iron Components from Copper Smelting Slags

Procedia Environmental Sciences 31 ( 2016 ) 675 – 682

1878-0296 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Tsinghua University/ Basel Convention Regional Centre for Asia and the Pacific doi: 10.1016/j.proenv.2016.02.124

Available online at www.sciencedirect.com

ScienceDirect

The Tenth International Conference on Waste Management and Technology (ICWMT)

Thermodynamic analysis of separating synchronously copper and

iron components from copper smelting slags

Hongyang Cao

a,b,_*

_{, Guojuan Li}

a

_{, Jimin Wang}

a

_{, Zhiqiang Liu}

a,b

a_{Guangzhou Research Institute of Non-Ferrous Metals Guangzhou 510651, China}

b_{Guangdong Province Key Laboratory of Rare Earth Development and Application Guangzhou 510651, China}

Abstract

The occurrence state changes and the possibility of synchronous separation of the components with copper and iron were researched by detailed calculation and derived, from the thermodynamics point of view in the oxidation modification process of copper smelting slag. The relationship between oxygen and sulfur potential of coexistence stage for metallic copper and the magnetite was concluded by analyzed the advantage area chart of CuFeSO system. The Thermodynamic studies show that, there was a stability range of the oxygen and sulfur potential in CXFeSO system, which made the metallic copper and the magnetite coexistence. The research will provide theoretical support for the synchronous separation between copper and iron components from copper smelting slag.

© 2015 The Authors. Published by Elsevier B.V.

Peer-review under responsibility of Tsinghua University/ Basel Convention Regional Centre for Asia and the Pacific.

Keywords: Thermodynamic analysis; separating synchronously; oxygen potential; sulfur potential

1.

Introduction

In recent years, the production of refined copper is increasing significantly in China, the production was 4.25 million tons in 2009, and it reached to 7.67 million tons in 2014, and more than 15 million tons of copper smelting

Foundation item: Project(2015B010105010) Supported by Science and Technology Planning Project of Guangdong Province, China * Corresponding author. Hongyang CAO; Tel.: +86-20-6108-6372; fax: +86-20-3723-8536.

E-mail address: caohongyang2004@163.com

© 2016 The Authors. Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

slags were produced every year. The content of iron is about 40wt% in the slags, which is much higher than the 27wt% recoverable ore grade, and that of copper is from 0.2wt% to 5wt%, and there are other valuable metals, such as nickel, cobalt and molybdenum, et al [1, 2]_{. At present, the utilization ratio of copper is below 12wt%, and that of}

iron is below 1wt% in copper smelting slags. The slags have become the negative factor of hindrance sustainable development of copper smelting enterprise, because that most of the slags were discarded at slag yard, which not only occupancy soil but pollute environment, it is also enormous waste. It has a positive role to alleviate the pressure of iron and copper concentrate ore resources to realize the valuable components of efficient recycling copper slag.

Though recovery valuable constituents from copper smelting slags were extensive researched, the separation effect is not sufficient because of using raw slag as studied object [3, 4]_{, it is difficult to recovery the iron constituents}

in raw slag by means of traditional separation technology because of the iron constituents mainly existed as fatality

(Fe2SiO4) and fine mineral dissemination, and small grain size. The smelting reduction technology for extracting

iron was studied by Li Lei, and the reduction reaction thermodynamics theory of each element was researched [5]_.

The selective chloridizing roasting treatment was applied in disposing copper slag by Ren-jie zhang, the copper chloride was obtained through the method of chloride volatile, but the iron components such as magnetite and

fayalite were not chloride, and the thermodynamics analysis was studied in detail [6]_{. High temperature melt}

oxidatioQroom temperature crushing magnetic separation method was adopted by Lin-nan zhan, but the research did not account for recycling copper components in the process [7̚_9]

.

The high temperature melt oxidation was researched to realize the selective and synchronize enrichment copper and iron components in this paper, by controlling the oxygen and sulfur potential in reaction process, and the thermodynamics of oxidation reaction was researched to clear the effects of oxygen potential on the synchronous enrichment.

2. Experimental

The chemical components of some converter slag were showed in Table 1, it is difficult to synchronously recover the valuable components from the raw slag, because they were distributed in many minerals, such copper matte, metallic copper, chalcopyrite, cuprites, pyrite, magnetite, fayality, hematite, et al.

Table 1. Mineral composition of copper smelting slag

Component Copper matte Magnetite Copper Hematite Iron Fayalite Silicate Feldspar Others

Content (%,ω) 5.2 26.8 0.9 2.5 0.5 47.3 11.7 2.5 2.6

3. Thermodynamic analysis of separating synchronously copper and iron components

3.1 Thermodynamic analysis of major reactions

The major occurrence statue of copper and iron component in raw slag was copper matte, which was the eutectic

of cuprous sulfide and ferrous fulfide in slag, the following reactions will happen under the oxidizing atmosphere as equation 1 to 7. The reaction of generating metal between sulfide and oxidant will be determined by the relationship

between

'

G

qDQGT of sulfide and oxidant. From fig.1, we can know that, the oxidation reaction of ferrous fulfide

will happen firstly, then the reaction of generating metallic copper will proceed when the ferrous fulfide was oxidized completely, when the ferrous fulfide was concurrent synchronously with cuprous sulfide;

)

(

)

(

3

)

(

2

)

(

l

FeO

l

Fe

l

SO

₂

g

FeS





₍₁₎

)

/

(

32

.

69

255864

T

J

mol

rG



'

4

)

(

)

(

6

)

(

2

)

(

_{2 2} 2

S

l

Cu

O

l

Cu

l

SO

g

Cu





(2)

)

/

(

87

.

58

35982

T

J

mol

rG



'

4

)

(

3

2

)

(

3

2

)

(

)

(

3

2

Cu

₂

S

l



O

₂

g

Cu

₂

O

l



SO

₂

g

₍₃₎

)

/

(

17

.

81

268194

T

J

mol

rG





'

4

)

(

3

2

)

(

3

2

)

(

)

(

3

2

FeS

l



O

₂

g

FeO

l



SO

₂

g

(4)

)

/

(

71

.

52

303557

T

J

mol

rG





'

4

)

(

)

(

)

(

)

(

l

Cu

₂

O

l

Cu

₂

S

l

FeO

l

FeS





₍₅₎

)

/

(

48

.

85

105437

T

J

mol

rG





'

4

)

(

2

1

)

(

3

FeO



O

₂

Fe

₃

O

₄ ˄6˅

)

/

(

17

.

169

376337

T

J

mol

rG





'

4

)

(

2

1

)

(

2

FeO



O

₂

Fe

₂

O

₃ ˄7˅

)

/

(

158

330500

T

J

mol

rG





'

4 1400 1500 1600 1700 1800 1900 2000 -300 -250 -200 -150 -100 -50 0 50 100 150 ' * q ,kJ Temperature. y  FeS(l)+2FeO(l)=3Fe(l)+SO₂ c Cu₂S(l)+2Cu 2O(l)=6Cu(l)+SO2(l) d 2/3Cu

2S(l)+O2=2/3Cu2O(l)+2/3SO2

e FeS(l)+Cu₂O(l)=Cu₂S(l)+FeO(l) f 3(FeO)+1/2O₂=(Fe₃O4)

¥ 2(FeO)+1/2O₂=(Fe₂O₃) ¡ 2/3FeS(l)+O₂=2/3FeO(l)+2/3SO₂

Fig.1. The relationship of reaction

'

G

qˉT between sulfide and oxidate 3.2 Predominance area diagram Analysis of Cu-Fe-S-O system

δ1εPlotting the predominance area diagram of Me-S-O system

The influence of gas chemical potential on the reaction rate and reaction process is significant in gas-solid reaction process. The chemical potentials of O2 and S2, SO2 and even SO3 were directly related to the equilibrium

constant and the reaction rate, and will affect the degree of oxidation in MeSO system. Under the condition of

proper sulfur and oxygen potential, the iron and copper component will exist as Fe3O4 and metallic copper in MeS

diagram of two components of chemical potential in MeSO system under the constant temperature. The steps of drawing the Me-S-O balance figure as following:

First, determine the possibility of all kinds of effective reactions in the system, and list the balance equations for each reaction;

Second, the thermodynamic data used in the construction is obtained by the following equation ΔG0= A + BT + CT lgT;

Third, calculate the relationship of the

lg p

S2ǃ

lg p

O2_and

lg p

SO2_{under a certain temperature for each} reaction;

Finally, the calculation result of each reaction showed in the Me-S-O balance figure, which used the

lg p

SO2_as the ordinate and

lg p

O2_{as abscissa.}

The drawing and applying of predominance area diagram in copper smelting was introduced in detail by Guo-rui Ye, the predominance area diagram of Fe-Cu-S-O system at 1573K was showed in Fig.2. There was a concurrent

area of metallic copper and magnetite as the value of

lg p



O2

p



q

from -8.98 to -4.03 and

lg p



S2

p



q

low

-5.62, in the condition that

a

Cu

a

Cu O2

1

_and

a

FeO

a

Fe O3 4

1

_{. But it’s not considering the situation of Fe3O4}

further oxidation. So, the coexistence region of metallic copper and Fe3O4 will be narrow.

-8 -7 -6 -5 -4 -3 -2 -1 0 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 D Fe=1 D FeO=1 lgP O2 lgP S2 Fe FeS Fe3O4 P_SO2=1atm D Fe3O4=1 D_FeO=1 FeO Cu 2O D Cu2S=1 DCu2S=0.1 D Cu2S=0.01 D Cu2S=0.001 DCu2O=1 DCu2O=1 DCu 2O =1 DCu 2O =1 Cu₂S D_Cu=0.3 D_Cu=0.5 D Cu2O=1 D Cu2O=1 D Cu2O=1 DCu=1 Cu Fig.2.

 

2 O

lg p

ˉ

 

2 S

lg p

of Cu-Fe-S-O at 1573K

The theoretical basis of synchronous separation copper and iron component from copper smelting slag was to choose the appropriate oxygen and sulfur potential, which make the copper component existing as metallic copper, and that of iron as magnetite under a certain fusion temperature.

(2) Predominance area diagram of Cu-S-O and Fe-S-O system

The following elements and compounds such as Cu (l), Cu2O (S) and Cu2S (S) should be considered when

describing the phase equilibrium, the equilibrium during the S2, O2 and SO2 were calculated at the fusion

temperature range from 1300K to 1700K.

The reactions of Cu-S-O and Fe-S-O system are as following:

2Cu+1/2O2=Cu2O 8 K1= ( 2 O

p

)-1/2₍ Cu

a

)-2 2Cu+1/2S2=Cu2S 9 K2= ( 2 S

p

)-1/2₍ Cu

a

)-2

Cu2O +1/2S2= Cu2S+1/2O2 10 K3=( 2 O

p

)1/2₍ 2 S

p

) -1/2 Fe+1/2O2= FeO 11 K5= ( 2 O

p

)-1/2₍ Fe

D

)-2 Fe+1/2S2= FeS 12 K6= ( 2 S

p

)-1/2₍ Fe

D

)-2 FeO +1/2S2= FeS+1/2O2 13 K7= ( 2 O

p

) 1/2₍ 2 S

p

) -1/2

1/

2 S2+ O2= SO2 (14)

   

2 2 2 1 1 2 4 SO O S

lg K

p

p



p



lg (

2 O

p )

4

=ˉlg K

4

ˉ1/2 lg (

2 S

p

)ˇ2 lg (

2 SO

p

)

From the thermodynamic data, the Equilibrium data of Cu-S-O and Fe-S-O system were respectively showed in Table.2 and Table 3, when the temperature range was from 1300K to 1700K every 100K.

Table 2. The data of equilibrium state of Cu-S-O system from 1300K to 1700K

T/K lgK1 lgK2 lgK3 lgK4 _lg( 2 O

p

)1 Cu

a

=1 lg( 2 S

p

)2 Cu

a

=1 lg( 2 O

p

)3 2 S

p

=100kPa lg( 2 O

p

)4+1/2 lg( 2 S

p

) 2 SO

p

=100kPa 1300 1400 1500 1600 1700 2.979 2.474 2.000 1.704 1.468 3.579 3.18 2.828 2.521 2.251 0.600 0.706 0.828 0.817 0.783 10.717 9.680 8.781 7.995 7.302 -5.958 -4.948 -4.000 -3.408 -2.936 -7.158 -6.360 -5.656 -5.042 -4.502 1.200 1.412 1.656 1.634 1.566 -10.717 -9.680 -8.781 -7.995 -7.302 Table 3. Data of equilibrium state of Fe-S-O system from 1300K to 1700K

T/K lgK5 lgK6 lgK7 lgK4 lg( 2 O

p

)5 Fe

a

=1 lg( 2 S

p

)6 Fe

a

=1 lg( 2 O

p

)7 2 S

p

=100kPa lg( 2 O

p

)4+1/2 lg( 2 S

p

) 2 SO

p

=100kPa 1300 1400 1500 1600 1700 7.554 6.780 6.111 5.527 5.036 3.208 2.760 2.404 2.318 1.904 -4.346 -4.020 -3.707 -3.209 -3.132 10.717 9.680 8.781 7.995 7.302 -15.108 -13.560 -12.222 -11.054 -10.07 -6.416 -5.520 -4.808 -4.636 -3.808 -8.692 -8.040 -7.414 -6.418 -6.264 -10.717 -9.680 -8.781 -7.995 -7.302

According to table.2 and table.3, the phase equilibrium diagram of Cu-S-O and Fe-S-O system can be obtained at 1300 k and 1700 k temperature (showed in fig.3). The solid line conditions for 1300 k, dotted line is 1700 k in the

fig.3, and we can know that, the metallic copper was existed at the

lg p



O2

p



q low to -5.96 and

lg p



S2

p



q -7.16 at 1300K, and the

lg p



O2

p



q

was low to -2.94 and

lg p



S2

p



q

-4.5 at 1700K, in the similar way, the magnetite was existed at the

lg p



O2

p



q

from -11.11 to -1.46 at 1300K and that is from -5.61 to -0.03 at 1700K. To ensure the copper and iron component exists as metallic copper and magnetite respectively in the smelting slag, the oxygen and sulfur potential need to be rose following the temperature rising.

-16 -14 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 2 $ n Fe₂O₃ FeO Fe₃O₄ +lg( p_SO 2 / pq 1700K FeS Fe lg ( pS 2 / p q lg( p_O 2 / pq Fe₂O₃ Fe₃O₄ FeO Fe FeS 1300K +lg( p_SO 2 / pq A n

Fig.3. The isothermal equilibrium diagram of Cu-S-O and Fe-S-O system at 1300K and 1700K (3) Predominance area diagram of Cu-Fe-S-O system

Through overlaying the advantage area map of two systems, the predominance area diagram of Cu-Fe-S-O system (as shown in fig.4) was obtained through superimposing. The five points of equilibrium coexistence line of

Cu/Cu2S, Cu2O/Cu and Fe/FeS were given respectively from the fig.4 at different temperature such as 1300,1400,

1500, 1600 and 1700 K (dotted and solid line), it can be seen that there has a three-phase line intersection point A and B respectively. The regional stable of metallic copper was constituent by the point B, horizontal and longitudinal axis at each temperature. With the increasing of temperature, point B will move to the direction of higher oxygen and sulfur potential, so, the metallic copper and magnetite phase area was expanded. The oxygen and sulfur potential of coexistence region from 1300K to 1700K was respectively 11.11, -5.958), (-Ğ to -7.158)], [(-9.49, -4.948), (-Ğ to -6.36)], [(-8.08, -4.00), (-Ğ to -5.656)], [(-6.84, -3.408), (-Ğ to -5.042)], [(-5.61, -2.936), (-Ğ to- 4.502)]. -16 -14 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 2 Fe₂O₃ Fe₃O₄ FeO lg( pS 2 / p q lg( p_O 2 / pq Fe FeS 1300K +lg( p_SO 2 / pq A n Cu Cu₂O Cu2S n B -16 -14 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 2 A +lg( p_SO 2 / pq 1400K FeS Fe₂O₃ Fe 3O4 FeO Fe lg( p_O 2 / pq lg( pS 2 / p q n Cu Cu₂O Cu₂S n B

-16 -14 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 2 lg ( pS 2 / p q lg( p O2 / pq $ n FeS Fe FeO _Fe 3O4 Fe₂O₃ +lg( p_S O2 / pq 1500K Cu Cu 2O Cu₂S n B -16 -14 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 lg ( pS 2 / p q lg( p_O 2 / pq n A FeS 1600K +lg( p_SO 2 / pq Fe₂O₃ Fe₃O₄ FeO Fe Cu Cu 2O Cu2S B n -16 -14 -12 -10 -8 -6 -4 -2 0 2 -12 -10 -8 -6 -4 -2 0 2 $ n Fe₂O₃ FeO Fe₃O₄ +lg( p_SO 2 / pq 1700K FeS Fe lg ( pS2 / p q lg( p_O 2 / pq Cu Cu2O Cu2S n B

Fig.4. Phase of Cu-Fe-S-O system at different temperatures (1300-1700K) ˄

a

_Cu

a

_Fe

1

˅, the condition of

drawing equalizing conductor of the chemical reaction 1/2 S2+ O2= SO2 is

2

SO

p

=100kPa

4. Conclusion

Through the thermodynamic research of separating synchronously copper and iron components from copper smelting slags, some conclusions were obtained:

(1) According to thermodynamics analysis, it is feasible to selectively separate copper and iron components in the form of metallic copper and magnetite respectively.

(2) The coexistence regions of metallic copper and magnetite were analysised at the modified temperature from 1300K to 1700K, according to the research on predominance area diagram of Cu-Fe-S-O system. The control points of oxygen potential from 1300K to 1700K was 11.11, -5.958), 9.49, -4.948), 8.08, -4.00), 6.84, -3.408) and (-5.61, -2.936) respectively.

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