XX-th ARS SEPARATORIA – Szklarska Poręba, Poland 2005
LEACHING OF EAF DUST WITH ACIDIC SOLUTIONS
Jerzy GĘGA, Patrycja OSTROWSKA
Czestochowa University of Technology, Department of Chemistry
42-200 Czestochowa, Al. Armii Krajowej 19, Poland
E-mail: [email protected]
Electric arc furnace (EAF) dust is produced when iron and steel scrap is
remelted in an electric arc furnace. There are still several problems connected to the
treatment of the EAF dust. It is reported that 10 to 20 kg of the dust is produced per
tonne of steel [1-3]. Due to presence of significant amounts of some toxic metals,
namely lead, cadmium, chromium and others, the dust is classified as a dangerous
waste and needs further treatment. Most of commercially available processes for the
treatment of the EAF dust are pyrometallurgical. The processes have high
throughput rates but are energy intensive [3]. Recently several alternative
hydrometallurgical processes have been proposed for recovery of zinc from the dust
[3-10].
The presented work is devoted to investigations of the leaching process of
EAF dust in acidic media in a view of recovering of valuable and toxic metals.
EXPERIMENTAL
The EAF dust was obtained from Huta Zawiercie Ltd. and had the chemical
composition given in Table 1.
Table 1. Chemical composition of the investigated EAF dust.
Component
Mass %
Zn
Fe
Mn Pb
Cd
Cr Al2O3 CaO MgO Others
21.57 30.01 2.33 3.98 0.074 0.31 0.64 3.09 2.76 35.24
The leaching experiments were done at room temperature (i.e. 20±2 oC) in a
glass reactor of 500 ml capacity provided with a Teflon cap and a stirrer. Tests were
performed with a solution of 250 ml of sulfuric, hydrochloric as well as nitric acid at
appropriate concentration with range from 0.25 M to 6.0 M. The samples of dust
weighted about 10 g. During experiments several samples were taken for the
analysis of metal ions concentration. The samples were filtered into test tubes and in
the obtained clear solution the analysis of the concentration of metal ions were done
by AAS method with SOLAAR 939 spectrometer (ATI UNICAM, Great Britain).
The solid residue was filtered, dried and weighed. From the analytical results the
leaching efficiency was calculated as a percentage of initial amounts of each of
metal transferred into solution.
23
XX-th ARS SEPARATORIA – Szklarska Poręba, Poland 2005
RESULTS AND DISCUSSION
The results are presented in Fig. 1a to c where the leaching efficiency
obtained for investigated acids is shown and in Table 2 where the amounts of solid
residue from the leaching processes are shown.
As it was expected increasing of acid concentration caused increase of
leaching efficiency for all of analyzed metals (Fig.1) and decrease of solid residue
amount (Table 2). It was observed for all investigated acids. In the case of
hydrochloric acid as well as nitric acid the leaching efficiency was significantly
higher than for sulfuric acid. On the other hand in solutions of HCl and HNO3 all
metals were leached, however in the solutions of sulfuric acid calcium, zinc and
cadmium were leached better than other metals.
0,5 M
Leaching Efficiency, %
a)
3,0 M
6,0 M HCl
100
80
60
40
20
0
Fe
Zn
0,25 M
b)
Mn
Pb
1,5 M
Cd
Cr
Al
Ca
Al
Ca
3,0 M H2SO4
Leaching Efficiency, %
100
80
60
40
20
0
Fe
Zn
Mn
Pb
Cd
Cr
24
XX-th ARS SEPARATORIA – Szklarska Poręba, Poland 2005
c)
0,5 M
3,0 M
6,0 M HNO3
Leaching Efficiency, %
100
80
60
40
20
0
Fe
Zn
Mn
Pb
Cd
Cr
Al
Ca
Fig. 1. Leaching efficiency obtained in chosen solutions of a) HCl, b) H2SO4 and c)
HNO3. Conditions of experiments – see Experimental.
In all investigated solutions calcium was extracted completely. High values
of leaching efficiency were also observed for zinc and cadmium. In sulfuric acid
solutions lead did not extracted. It was expected due to poor solubility of lead(II)
sulfate. In these solutions small extracted amount of manganese, chromium, and
unexpectedly iron were observed.
As it can be seen from Fig. 1 in solutions of all acids at low their
concentration small part of iron from EAF dust (i.e. less than 10 %) was transferred
into leaching solution. Low extraction of iron is favorable for further treatment of
leaching solution, i.e. for metals ions separation and removal. The presence of large
amounts of Fe ions in technological solutions is a known hydrometallurgical
problem which makes ion separation processes difficult.
Table 2. Solid residue from the leaching processes.
Leaching solution
Residue, %
0.5 M HCl
52.6
3.0 M HCl
26.2
6.0 M HCl
15.0
0.25 M H2SO4
56.0
1.5 M H2SO4
50.5
3.0 M H2SO4
48.5
0.5 M HNO3
55.6
3.0 M HNO3
28.4
6.0 M HNO3
18.0
25
XX-th ARS SEPARATORIA – Szklarska Poręba, Poland 2005
Although leaching efficiency of metals in nitric acid solution is high,
emission of nitrous oxides during leaching process makes it difficult to apply thus
diluted solution of hydrochloric acid appears the best for leaching of EAF dust.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
T.M. Barnes, Canad. Metall. Quarterly, 15(1976) 53.
E.V. Akerlov, Iron and Steel Eng., 52(1975) 39.
D.K. Xia, C.A. Pickles, Canad. Metall. Quarterly, 38(1999) 175.
J. Frenay, J. Hissel, S. Ferlay, Met. Soc. AIME (1985) 195.
D.B. Dreissinger, E. Peters, G. Morgan, Hydrometallurgy, 25(1990) 137.
E.C. Barret, E.H. Nenniger, J. Dziwinski, Hydrometallurgy, 30(1992) 59.
Z.Youcai, R. Stanforth, J. Hazard. Materials, B80 (2000) 223.
C. Jarupisitthorn, T. Pimtong, G. Lothongkum, Materials Chem. Phys.,
77(2002) 531.
9. T. Havlik, B. Friedrich, S. Stopic, Erzmetall, 57 (2004) 113.
10. T. Havlik, M.Turzakova, S. Stopic, B. Friedrich, Hydrometallurgy 77(2005)
41.
26