ry

*, E

iversit

Nov

roced intnerat

thisgs isary r

eparau, ansour

# 2003 Elsevier Science Ltd. All rights reserved.

tions, slags have comparable or even better properties not important. However, steel slag is usually subjected

Waste Management 23water pollution. Therefore, it is desirable to recovermetals from slags and to utilise the slags.than their competitive materials. The third feature isthat some slags contain a notable amount of harmful orheavy metals. The release of these metals may causeenvironmental problems.The conventional method for disposal of slags is

dumping. The increasing dump of slags not only occu-pies plenty of land, but also wastes resources and canpotentially have an impact on the environment due to

to metal recovery prior to its application outside theiron and steel making process. The iron and steelindustry has applied mineral processing technology torecover steel scrap (Fe: 90%) and iron oxide concentrate(Fe555%) from steel slag and use them as feed materi-als for sintering, blast furnace and steel making (Huangand Wang, 2001). It was reported that the use of therecycled iron concentrate not only saves metal resource,1. Introduction

Various slags are produced as by-products in metal-lurgical processes or as residues in incineration pro-cesses. According to the origins and the characteristics,the main slags can be classied into three categories,namely ferrous slag, non-ferrous slag and incinerationslag. Slags usually contain a quantity of valuable metals.They are actually a secondary resource of metals, ratherthan an end-waste and have been applied as a resourcematerial in many areas. In addition, for some applica-

Ferrous slag mainly includes iron slag (blast furnaceslag), steel slag, alloy steel slag and ferroalloy slag. Blastfurnace slag (BF slag) and steel slag make up the majorpart of ferrous slag. The study and utilisation of BF slagand steel slag has a long history. For example, as earlyas in 1880 they were used as a phosphatic fertiliser(Geiseler, 1996). Today, BF slag and steel slag havefound a wide application, such as cement production,road construction, civil engineering work, fertiliser pro-duction, landll daily cover, soil reclamation, and so on.Since BF slag contains little Fe, recovery of Fe from it isAn overview of recove

Huiting Shen

Division of Mineral Processing, Lulea Un

Accepted 27

Abstract

Various slags are produced as by-products in metallurgical porigins and the characteristics, the main slags can be classieincineration slag. This paper analysed and summarised the ge

cussed the potential eects of the slags on the environment. Onfrom the slags was made. It can be seen that a large amount of slametals except for blast furnace slag and they are actually a second

such as crushing, grinding, magnetic separation, eddy current srecover metals such as Fe, Cr, Cu, Al, Pb, Zn, Co, Ni, Nb, Ta, Autilisation of the slags are important not only for saving metal reof metals from slags

. Forssberg

y of Technology, S-97187 Lulea, Sweden

ember 2002

sses or as residues in incineration processes. According to theo three categories, namely ferrous slag, non-ferrous slag andion, characteristics and application of various slags, and dis-

basis, a review of a number of methods for recovery of metalsproduced each year. They usually contain a quantity of valuableesource of metals. By applying mineral processing technologies,

tion, otation and so on, leaching or roasting, it is possible tod Ag etc. from the slags. Recovery of metals from the slags andces, but also for protecting the environment.

(2003) 933949

www.elsevier.com/locate/wasmanferroalloy slag usually contain high amounts of alloyelements, such as Cr, Ni, Mn, Ti, V, Mo. Recently,some research work has been done on the treatment of

0956-053X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0956-053X(02)00164-2

* Corresponding author. Tel.: +46-920-491313; fax: +46-920-

97364.

E-mail address: huiting.shen@km.luth.se (H. Shen).but also improves the iron and steel making process dueto Mn, CaO and MgO contents in the recycled material(Radosavljevic et al., 1996; Svyazhin et al., 1998; Dol-gorukov, 1991; Huang et al., 2001). Alloy steel slag and

a long history of over 100 years (Vircikova and Molnar,1992). There were numerous reports on recovery of Cu,

centrations of elements (including As, Ba, Cd, Cr, Pb,

an weeris durrati ica

are very tig released from the matrixr et ys

slag is utilised in many areas, such as cement produc-

on (Huang and Wang, 2001). Since BF slag contains

Management 23 (2003) 933949Ni, and Co from copper slag (Ziyadanogullari, 2000;Barnes et al., 1993; Herreros et al., 1998; Basir et al.,1999). Recently, attention was also paid to the treat-ment of salt slag since the increasing aluminium recy-cling has caused a rapid increase of toxic salt slag(Reynolds and Olper, 1990; Unger and Becker, 1992;Lopez et al., 1994). Industry now has found methods torecycle salts and aluminium scrap from salt slag andturn this toxic slag into useful materials (Reynolds andOlper, 1990; The Ends Report, 1999; Kirchner, 1991).In addition, recovery of Nb and Ta from tin slag andAu and Ag from tin slag and other slags were alsoreported (Gaballah et al., 1997; Li et al., 1995).Incineration slag is a relatively new ever-increasing

slag. Over recent years, several studies have been repor-ted on the treatment, utilisation and metal recoveryfrom incineration slag, mostly in Germany and Japan(Kaulbarsch et al., 1997; Pretz and Meier-Kortwig,2000; Schmelzer et al., 1996; Sakai and Hiraoka, 2000).Incineration slag processing by mechanical separationcan obtain Fe scrap and non-ferrous metals such as Al,Cu, Pb, Zn and Ag. This has been applied in industryalthough only a few papers were reported recently inGermany (Kaulbarsch et al., 1997; Pretz and Meier-Kortwig, 2000).The generation, characteristics and application of

various slags will now be analysed and summarised,along with a review of a number of methods for recov-ery of metals from such slags.

2. Ferrous slag

2.1. Iron slag

Iron slag is generated from Blast Furnace (BF slag) inthe iron production, with 220370 kg slag per ton ofiron being produced (Proctor et al., 2000). The amountof BF slag is the largest among the ferrous slags. Forexample, In USA and Japan, 13 and 24.3 million tons ofBF slag were produced each year (Proctor et al., 2000;Okumura, 1993). Leaching study shows that the con-the slags, especially on the treatment of stainless steelslag and charge chrome slag since the former containsexpensive metals Cr and Ni and the latter contains highamount of Cr (Kortbaoui et al., 1993; Das et al., 1997;Choudhury et al., 1996). Some commercial plants fortreatment of charge chrome slag and stainless steel slaghave been reported in operation (Lopez et al., 1997;Salamon, 1995; Khan et al., 2001).There are many dierent non-ferrous slags generated

from non-ferrous smelters. Perhaps copper slag wassubjected to the most extensive research work with also

934 H. Shen, E. Forssberg /Wastelittle iron (Fe

2 2 5

tricalciumsilicate and lime (CaO) become dominant in of natural aggregates by Geiseler, as shown in Table 4

ion of

F CaO M SiO2 2O5 3

slag l 1 4555 1218 2

slag h 1 4250 5 1215 2

slag l 1 3040 4 1217 1.5

slag h 2 2535 8 1015 1.5

slag ( 1 44.3 6 13.8 R

slag ( 1 38.0 6 19.0 R

slag 1 3448 2 915 .9 2.8

slag 1 1015

men leac ncen Exce erion

BOF BF BO E

0.00 No No N

0.88 No No N

0.01 No No N

(V ND No No N

(to 0.04 No No N

0.01 No No N

Mercury 0.2 ND 0.0005 0.00089 No No No

ND No No N

a From Method 1311 Toxicity Characteristic Leaching Procedure.steel slag (Huang and Wang, 2001). Other mineralsreported in steel slag include periclase, manganosite, Feand Mn monticellite, Mn-cordierite, glass, and (Fe, Mn,Mg) oxide solid solution (Radosavljevic et al., 1996).

2.2.1.2. Leaching behaviour of steel slag. The release ofmetals or harmful elements from slags will cause envir-onmental problems such as water pollution and soilpollution, and a toxicological risk to humans throughthe inhalation of small slag particles ( 2.5), of steel slags were investigated and compared with those

NR=no report.USA BOF 530 4050 510 510 13 2 NRChina BOF 727 1.56 .510 0 0.9 0.2Japan BOF

EAFconverter)

electric furnace oxidation)7.5

5.25.3

6.0.4

.0N

N1.5

7.00.07

0.38EAF igh MgO content 029

can also save manganese ore and improve the processr,ddf.eln

applied outside the iron and steel making process.s

(Okumura, 1993).

1993).

.1. S tion o ag. I to lillic ir ron-b iner steroce lag f ation educsary. achie o w e ising w hers. ushe eralle pr shin con er, ha

crusher or impact crusher is used for the secondarying. porte roll is n

stage dry autogenous grinding. One advantage is that

es

U

g/

w

w

w

w

N

ManTable 4

Technical properties of steel slags, in comparison with natural aggregat

Property

Bulk density

Resistance to impact determined on crushed aggregates (812 mm)

Absorption of water

Freeze/thaw resistance (particle size

85% slag product can be obtained (Liu, 1991). the liberation of minerals and the separation process.

Fig. 2. Recovery of metal from steel slag and slag processing.2.2.3.2. Classification and magnetic separation. Themagnetic separation method is used for separatingmetallic iron and iron minerals from steel slag. Com-monly-used magnetic machines are cross-belt magneticseparator, drum magnetic separator and magnetic-pulley separator. To improve magnetic separation e-ciency, the classication of steel slag fed to magneticseparation is carried out. A single or double-deckvibrating screen is used for this process. Screens (includ-ing bar screen) are also used in the crushing circuit or inclassication of nal slag product for dierent applica-tions, as shown in Fig. 2 (Huang and Wang, 2001).

2.2.3.3. Removal of P from steel slag. Since some steelslags contain a notable amount of P (13%), it isnecessary to remove the P to recycle more slag to theiron and steel making process. The study results repor-ted by Fregeau-Wu et al. (1993) show that P in steel slagoccurs predominantly in dicalcium silicate and to a lesserextent in dicalcium ferrite in solid solution. High gradientmagnetic separation was used to separate the P-bearingdicalcium silicate from the iron- and manganese-bearingAbout 70% of the P was removed from slow-cooled slagby high gradient magnetic separation.

2.3. Alloy steel slag

Various alloy steel slags are generated in the alloysteel making processes. Compared with BF slag andsteel slag, the amount of alloy steel slags is small butthey usually contain high amounts of alloy elements,such as Cr, Ni, Mn, V, Ti, Mo. Since the amount ofstainless steel slag is the largest among the alloy steelslags and since it contains high content of Cr and acertain amount of Ni, it is necessary to treat stainlesssteel slag prior to its application or landlling. Recoveryof Cr and Ni from stainlees steel slag is not only sig-nicant in economy, but also very important for theenvironment.

2.3.1. Chemical and mineralogical composition ofstainless steel slagIn the stainless steel production, EAF stainless steel

slag and Argon Oxygen Decarburization (AOD) stain-less steel slag are generated. Table 6 shows the chemicalone autogenous grinding machine can replace severalcrushers in multi-crushing so that its operation is sim-ple. Moreover, the metallic iron product dischargedfrom the grinding machine contains Fe as high as 80%.By autogenous grinding, magnetic separation andscreening, 8% metallic iron, 47% iron concentrate and

minerals. In a separation test of an as-received slag,50% of the P reported to the tailings. It was also foundthat slow cooling of steel slag promotes mineral graingrowth and the formation of calcium phosphate whichoccurs as ne-grained crystals associated with the dical-cium silicate matrix. Hence slow cooling will improve

Table 5

Production and utilization of converter slag in Japan (1991)

Utilization Production

(103 t/year)Ratio of utilization

(%)

Unit Metal recovery Road Cement Earth works Fertilizer Others Using in own works Total

103 t/year 195 814 692 3316 124 1080 3960 10,181 9965 102.2% 1.92 7.99 6.80 32.57 1.22 10.61 38.89 100

H. Shen, E. Forssberg /Waste Management 23 (2003) 933949 937

shown in Table 7. Similar to steel slags, AOD slags alsof dica and t m sili

alumin tes an e andhat t ain ch kel-malution of ch which

The leaching results in Table 8 show that AOD slagcan release a noticeable amount of Cr as high as 1 ppm,

Table 6

Chemical composit ess steel slags

Component OD slag

5 6

47.60 45.50 5.50

SiO2 31.24 26.32 27.61

Al2O3 1.66 9.69 1.65

3.65 7.30 7.30

1.60 2.06 1.41

FeTotal 1.75 3.50 7.40

Na2O 0.08 0.07 0.03

K2O 0.05 0.05 0.05

3.47 4.28 2.48

0.05 0.05 0.12

0.13 0.68 0.20

Loss on ignition 7.14

sition of ags

lement

a Si Al M

elilite

erwinite

2S

2S.SiO2luorite

Silicat Melili Si

pe

elilite

erwinite

i-Ca-

xide

Silicat Melili Si

periclase

elilite

erwinite

2S

2S.SiO2

Silicat Melili Si

pe

M .

C S, dicalcium silicate; C S, tricalcium silicate.

Table 8

Chemical analysis of leachates, ppm and EC50 values (mg/l)

CrTotal Pb Cd Fe Mn Ni Cu EC50 pH

1.0

minor phases include olivine, chromite and metallic pha-ses. The chromite comes from the unreacted chromite ore

action data a anningtron microscope (SEM) studies indicate that metallicphases are mainly (CrFe) C . Cr appears mainly in chro-

phase all am of Cr ir2O3: nd oliv O3