Kinetics of the Volatilization Removal of Lead in Electric Arc Furnace Dust

Transcription

1 Materials Transactions, Vol. 46, No. 2 (25) pp. 323 to 328 #25 The Japan Institute of Metals EXPRESS REGULR RTILE Kinetics of the Volatilization Removal of Lead in Electric rc Furnace Dust Jae-Min Yoo, yung-su Kim*, Jae-chun Lee, Min-Seuk Kim and hul-woo Nam Minerals and Materials Processing Division, Korea Institute of Geoscience and Mineral Resources, 3 Gajeong-dong, Yuseong-gu, Daejeon, 35-35, Korea The selective removal of lead and chlorine with minimizing zinc loss from electric arc furnace (EF) dust is very important in the process for recovering high purity zinc from the EF dust by high temperature metal recovery (HTMR) processes. In this study, the volatilization reaction of lead contained in the EF dust was investigated at reaction temperatures between 973 and 1223 K in air. The main volatilization reaction equation of lead was found as follows: 2Nal þ PbO þ 2SiO 2 þ l 2 O 3 ¼ Pbl 2 (g) þ 2NalSiO 4 In the reaction time of 9 min at 1223 K, the volatilization ratio was about 98% for both lead and chlorine, while that was about 1% for zinc. Jander rate expression was found to fit reasonably well the volatilization reaction rate over the entire temperature range. The volatilization reaction rate of lead in the EF dust is controlled by solid-solid diffusion and has an activation energy of 175 kj/mol (41.8 kcal/mol). Keywords: electric arc furnace (EF) dust, high temperature metal recovery (HTMR) processes, lead, zinc (Received November 18, 24; ccepted December 21, 24) 1. Introduction Since the production of steel in electric arc furnace (EF) by recycling iron scraps is more attractive than the traditional integrated processes in terms of resource conservation and lower capital investment, the amount of EF dust emitted from the EF will continue to increase. 1 4) In a typical EF operation, approximately 1 2% of the steel production is converted into dust. In the current, over 3, tons of EF dust have been produced each year in Korea. 5,6) It is already well known that EF dust is a hazardous waste because of its unacceptable levels of leachable toxic metals such as lead and cadmium and so on. These metals are part of EF dust generated by the recycling of bearings, printing plates, battery plates, and electric scraps and so on. Thus, the disposal of the dust is environmentally dangerous if improperly managed. However, EF dust contains significant amounts of zinc and iron. Since the use of galvanized steel continues to increase in the automotive industry, the amount of zinc in the dust will rise concurrently. There are currently many different processes to recover zinc from EF dust. These can be categorized into the following classes: 1. High temperature metal recovery (HTMR) processes or pyrometallurgical processes, 2. Hydrometallurgical processes, 3. Hybrid processes such as thermal reduction followed by leaching. lthough hydrometallurgical and hybrid processes are developed recently, the major processes applied for recovering zinc from EF dust are still the HTMR processes. Various commercialized HTMR processes include Waelz rotary kiln process, 7) modified Waelz kiln process, 8) flame reactor process and several plasma processes. 9 12) In spite of the extensive process development related to the HTMR processes, very little fundamental kinetic data on the volatilization reaction of lead contained in EF dust are available. Only a few researchers reported that lead contained *orresponding author, bskim@kigam.re.kr in EF dust was volatilized as a form of lead chloride (Pbl 2 ) that was formed by the reaction of lead oxide and chlorides like Nal and Kl contained in the dust. 13,14) The volatilization reaction of lead in EF dust is of some interest in the process for recovering high purity zinc from the dust by the HTMR processes. Therefore, in the present study, the rate of the volatilization reaction of lead in EF dust was measured by using a weight-loss technique at the reaction temperatures between 973 and 1223 K in air. The rate data reported in this paper was determined by eliminating the effects of external mass transfer and diffusion between the particles. 2. Thermodynamic onsiderations The possible volatilization reactions of lead contained in EF dust with chlorides such as Nal and Kl in the dust were examined based on thermodynamic analysis. Equilibrium compositions at various temperatures were calculated to find the most suitable volatilization reactions of lead in EF dust. The thermodynamic analysis was performed by the use of HS chemical software developed by Outokumpu Research Oy, which is based on the principle of the Gibbs free energy minimization. The input data as well as the gaseous and solid phases considered in the equilibrium calculation are presented in Table 1. Here, the input data were obtained from the chemical composition of EF dust used in this study. Figures 1 and 2 show the calculated data as the number of moles of different gaseous and solid phases formed at the equilibrium state as function of reaction temperature. Figure 1 indicates that lead in the EF dust is volatilized as a form of Pbl 2. The figure also shows that the volatilization possibility of lead as a form of Pbl 2 is the highest, while that of zinc and iron as chlorides is almost negligible. Thus, it would be expected that the selective removal of lead and chlorine with minimizing zinc loss from the EF dust is possible. Figure 2 shows that many new phases such as NalSiO 4, KlSiO 4, Kal 3, al 2,

2 324 J.-M. Yoo,.-S. Kim, J. Lee, M.-S. Kim and.-w. Nam Table 1 Input data and chemical species considered in the calculation of equilibrium composition. Species Input data onsidered species amount Solid phase Gas phase (kmol) hlorides Oxides Gas phase O 2 (g) KO(g) Znl(g) NalO 3 NalO 2 ZnO ao KlSiO 4 O 2 (g) 4.7 N 2 (g) ll 2 (g) Pb(g) Znl 2 Nall 4 PbSiO 3 PbO 2 NaFe(SiO 3 ) 2 N 2 (g) 17.7 K 2 O(g) Znl 2 (g) llo(g) KlO 3 NalO 4 KO 2 KO 3 FeO Kl(g) NaO(g) Sil(g) lol Pbl 2 ZnFe 2 O 4 MgO KlSi 3 O 8 Solid phase ZnO(g) lo 3 (g) l 2 (g) ll 3 Kal 3 K 2 O 4 KlO 2 a 2 Pb 3 Si 3 O 11 Kl 2.88 Na 2 (g) PbO(g) Fel(g) Mgl 2 FeOl NaO 2 K 2 O 2 Pba 2 Si 3 O 9 Nal 2.27 Nal(g) FeOl(g) Zn(g) Nal Fel 3 PbO NalSiO 4 K 2 O l 2 O K(g) ll(g) l 2 O(g) llo NaFeO 2 KFeO 2 K 2 SiO 3 ao 1.62 K 2 (g) Pb 2 O 3 (g) al 2 (g) Kl Na 2 O K 2 O 3 KlSi 2 O 6 MgO 1.24 Pbl 2 (g) PbO 2 (g) llo(g) Fel 2 Fe 2 O 3 SiO 2 NalSi 3 O 8 PbO 1. Mgl 2 (g) Sil 2 (g) al(g) Kll 4 l 2 O 3 Pb 2 O 3 SiO llo 2 (g) l(g) Mgl(g) aol 2 K 2 FeO 2 Fe 3 O 4 Fe 2 O Pbl(g) OlO(g) Na 2 O(g) Mgl Zn 2 SiO 4 a 2 PbO 4 ZnO lo(g) Fel 2 (g) Na(g) al 2 ZnSiO 3 Na 2 SiO 3 Log ( kmol ) O2 (g) Temperature, T/K Kl (g) Pbl 2 (g) Nal (g) Znl2 (g) Fig. 1 Equilibrium composition of gaseous phase calculated from the data in Table 1. Log ( kmol ) 1-1 ZnFe2O4 Nal l2 O3 Kl a O Pb O Mg O Zn2SiO4 NalSiO4 KlSiO4 al 2 Kal3 SiO Temperature, T/K Fe 2 O3 ZnSiO3 Fig. 2 Equilibrium composition of solid phase calculated from the data in Table 1. Zn 2 SiO 4, and ZnSiO 3 are formed in the solid phase at the equilibrium state. ased on the results of these thermodynamic analyses, the possible volatilization reactions of lead in the EF dust are presented in Table 2 together the standard free energy (G ). s shown in Table 2, reactions (1) and (2) will be favored thermodynamically because the G values are negative in the temperature range 973 to 1223 K. The volatilization reactions of lead in the EF dust were thus investigated further by carrying out experimental work for chemical reagents and EF dust. 3. Experimental 3.1 Materials Materials used in this study were PbO, ZnO, l 2 O 3, SiO 2, Nal, Kl, and EF dust. nalytical grade PbO, ZnO, l 2 O 3, SiO 2, Nal, and Kl manufactured by Junsei hemical ompany in Japan were used to verify the reaction ratios and products for reactions of (1) (3). The particle sizes of the powder ranged 74 mm. The EF dust obtained from a steel making company in Korea was used to measure the volatilization reaction rate of lead in the dust. Here, humidity and some organic compounds contained in the dust was removed by drying at 773 K for 9 min to easy elucidate the kinetic data of the reaction. The elemental composition of the dust is shown in Table 3. The major elements in the dust are zinc and iron. lso, there are relatively high concentrations of the hazardous elements such as lead and cadmium as well as significant quantities of alkalis and halides. n X-ray diffraction pattern of the dust is shown in Fig. 3. The major identified peaks in the pattern indicate that the dust contains zincite (ZnO), franklinite (ZnFe 2 O 4 ), lead oxide (PbO), sodium chloride (Nal), and potassium chloride (Kl). However, lead and zinc chlorides were not detected. Thus, they were not considered in this study. lso, many low intense unidentified peaks were found. ased on the results of chemical analysis and X-ray diffraction analysis of the EF dust, the concentrations of some of the major compounds in the dust were calculated and shown in Table Procedure Experiments were carried out in a horizontal tube furnace with cooling system. Figure 4 shows the schematic diagram

3 Kinetics of the Volatilization Removal of Lead in Electric rc Furnace Dust 325 Table 2 Possible volatilization reactions of lead in the EF dust with standard Gibbs free energy. Reaction G (kj/mol) Reaction no. 973 K 1223 K (1) 2Nal + PbO + 2SiO 2 +l 2 O 3 = Pbl 2 (g) + 2NalSiO 4 ( 26:45) ( 6:46) (2) 2Kl + PbO +2SiO 2 +l 2 O 3 = Pbl 2 (g) + 2KlSiO 4 ( 12:31) ( 35:17) (3) 2Nal + ZnO + 2SiO 2 +l 2 O 3 = Znl 2 (g) + 2NalSiO 4 (23.5) ( 1:95) Table 3 Elemental composition of the EF dust treated at 773 K for 9 min in air. Intensity ( arb. unit ) Element oncentration (%) Pb 6:47 :7% Zn 34:75 1:4% K 3.51% Na 1.63% l 5:69 :8% Fe 15:36 1:35% Mn 1.14% Si 2.6% a 2.3% Mg.94% l 1.71% D,E,,E,E D E of experimental apparatus used in this study. In the experiment using chemical reagents,.5 g of each solid reactant was mixed thoroughly and placed in an 2 θ, ZnO ZnFe2O4 Nal D Kl E PbO,D Fig. 3 X-ray diffraction pattern of the EF dust treated at 773 K for 9 min in air. Table 4 Estimated concentrations of some common components in the EF dust. omponent oncentration (%) PbO 6.97 ZnO Fe 2 O Kl 6.69 Nal 4.14 MnO 1.47 SiO ao 2.83 MgO 1.56 l 2 O alumina boat (1.2 cm diameter and 8. cm length), while in the experiment using EF dust, the dust was thinly placed in the same boat. In the both experiments, the sample boat was first introduced in the less hot zone of the reactor. fter 5 min, the sample boat was pushed into the central hot zone of the reactor that was maintained at the desired temperature. This procedure helped in reducing the time required for the sample boat to attain the reaction temperature. The temperature of this hot zone was maintained constant by a highly accurate temperature controller connected to a R-type (Pt-Rh 13%/Pt) thermocouple located in the constant temperature zone on the inside of the reactor tube. The temperature in the hot zone was maintained within 2 K. ir purchased by ir Products ompany in Korea was used as a carrier gas. Zero time was counted when the boat containing the sample was pushed into the reactor that was maintained at the desired temperature. fter a stipulated time period, the reaction was stopped by sliding the boat from the central hot zone to the outer cool zone. The cooled residual solid was weighed, and this solid as well as the solid condensed from the gaseous product were analyzed. scanning electron microscope (JSM-64, JEOL Ltd, Tokyo, Japan) equipped with an energy dispersive X-ray spectrometer (Link Isis 3., Oxford Instrument plc, Oxon, U.K.) was utilized to obtain micrographs and to analyze the samples. The phases present in the samples were determined by the analysis of the X-ray diffraction patterns generated on a X-ray diffractometer (Rigaku D-max-25P, Rigaku/ MS, Inc., TX, U.S..). Zn, Pb, u, d, Mn, o, Ni, s, Sb, and r were analyzed by the induction coupled plasma (IP) method (JY-38 plus, Horiba Ltd, Kyoto, Japan), and K and Na analyzed by atomic absorption () method (Varian Spectr -4, Varian Inc.,, U.S..). In addition, Fe, Si, a, Mg, and l analyses were performed by wet chemistry, and the l and S contents were determined by the ion chromatography method (DX-3, Dionex orp.,, U.S.). arbon was also analyzed by a means of infrared detection system (arbon Determinator WR-112, LEO orp., MI, U.S..). 6 Fig. 4 Schematic diagram of the experimental apparatus. 1. Furnace. 2. Mullite tube. 3. lumina boat. 4. ondenser. 5. Exhaust gases. 6. ontrol box. 7. Flowmeter. 8. ir cylinder. 9. Thermocouple

4 326 J.-M. Yoo,.-S. Kim, J. Lee, M.-S. Kim and.-w. Nam 4. Results and Discussion 4.1 Reaction ratios and products ased on the thermodynamic consideration through the standard free energy (G ), it was expected that the reaction ratio of the reaction (1) might be larger than that of the reactions (2) and (3). However, it is not appropriate to judge the reaction ratios of reactions of (1) (3) only by the sign of G. Thus, to verify the reaction ratios and products from the reactions of (1) (3), experiments were conducted with chemical reagents and EF dust. For the reactions of (1) (3) using chemical reagents, air of 1 l/min was passed over the samples held in an alumina boat. Figure 5 shows the results of volatilization ratio for the reactions after reacting at the reaction temperatures of 973 and 1223 K for 3 min. The figure indicates that the reaction ratio of reaction (1) is very higher than that of reaction (2), and reaction (3) happens only slightly at the high temperature of 1223 K. Figure 6 shows the X-ray patterns of the cooled residual solid and the solid condensed by cooling the product gas for the reactions of (1) and (2). The X-ray patterns mean that reaction (1) and (2) are related to the volatilization reaction of lead because as explained above, NalSiO 4 and KlSiO 4 in the cooled residual solid phases and Pbl 2 in the condensed solid phases are detected. lso, the X-ray patterns show that Nal was not detected in the condensed solid phase for the reaction (1), while Kl was detected in the condensed solid phase for the reaction (2). It was thus found that the volatilization ratio shown in Fig. 5 for reaction (2) was somewhat related to the volatilization of Kl that did not participate in the reaction (2). This can be explained by the fact that Kl has relatively high vapor pressure compared with other compounds. On the other hand, for the volatilization reaction of lead contained in EF dust, experiments were performed for 5. g of the dust at the reaction temperature of 1223 K for 18 min in air of 1 l/min. Figure 7 shows the X-ray patterns of the cooled residual solid and the solid condensed by cooling the product gas obtained from the reaction. s explained above, NalSiO 4 in the cooled residual solid phase and Pbl 2 as well as Kl in the condensed solid phase are detected, while KlSiO 4 is not detected in the cooled residual solid phases. Thus, the results Volatilization ratio ( % ) PbO+ Nal+ l2o3+ SiO2 PbO+ Kl+ l2 O3 + SiO2 ZnO+ Nal+ l2 O3+ SiO Temperature, T/K Fig. 5 Volatilization ratio versus reaction temperature for the reactions (1) to (3). Intensity ( arb. unit ) ,, 2, 12 D,D D - Pbl 2 shown here as well as in Fig. 7 indicate that the volatilization reaction of lead contained in the EF dust in air is mainly related to the reaction (1). 4.2 Rates of the volatilization reaction of lead in the EF dust The rates of the volatilization reaction of lead in the EF dust were measured as small-scale batch experiments. Experiments were continued until the sample showed no D D D 2 θ, (a) (b) - lna(sio4) - l 2 O Kl - KPb 2 l 5 - Pbl 2 - l 2 O 3 - PbO - SiO 2 D - KlSiO 4 Fig. 6 X-ray diffraction patterns of samples produced from the reactions (1) and (2) at 1223 K for 3 min in air. (a) the condensed solid for the reaction (1), (b) the cooled residual solid for the reaction (1), (c) the condensed solid for the reaction (2), (d) the cooled residual solid for the reaction (2). Intensity ( arb. unit ) , D D D,D,D θ Kl * 2Pbl 2 Kl ZnO ZnFe2O4 Zn 2 SiO 4 D NalSiO 4, Fig. 7 X-ray diffraction patterns of the condensed gaseous phase (a) and the cooled residual solid phase (b) after the EF dust is treated at 1223 K for 18 min in air. (a) (b) (c) (d)

5 Kinetics of the Volatilization Removal of Lead in Electric rc Furnace Dust 327 noticeable further mass change. The conversion at a particular time was determined by dividing the mass change of lead in the solid sample at the time by the initial lead mass in the solid sample Elimination of mass-transfer effects To evaluate the effect of interstitial diffusion on the reaction rate of the volatilization of lead in the EF dust in air, sample beds of different height ( mm) were tested at 1223 K in air of 1. l/min. Figure 8 shows the mass loss of the EF dust. s shown in Fig. 8, the reaction rate is independent of a bed height below 3.7 mm. Thus, in all of the subsequent runs, a bed height of 3.7 mm was chosen to avoid the diffusion effects. The bed was formed by spreading 5. g of the EF dust on an alumina boat as a thin layer. The effect of gas flow rate in the range of l/min was also measured for a fixed amount (5: :1 g) of the EF dust at 1223 K in air. Figure 9 shows the mass loss of the EF dust. The results indicated that the reaction rate is independent of the gas flow rate above.8 l/min. Thus in all of the subsequent runs, a working gas flow rate of 1. l/min was chosen to avoid external mass-transfer effects Effect of the reaction temperature The effect of temperature on the lead volatilization ratio was examined by varying the temperature between 973 and 1223 K in air, while all other experimental variables such as sample mass and gas flow rate were kept constant. Figure 1 presents the results. Typical conversion-time curves, which were reproducible within 3:%, consist of two regions: an initial region of rapid reaction followed by a period of a slower rate. t 1223 K, about 98% for lead was volatilized in 9 min. It was also analyzed that about 98% for chlorine and about 1% for zinc were volatilized in 9 min at the same temperature. Thus, it was verified that the selective removal of lead and chlorine with minimizing zinc loss from the EF dust is possible, as stated in the above section Interpretation of the rate data Only a few researchers reported that lead contained in EF dust was volatilized as a form of lead chloride (Pbl 2 ) that was formed by the reaction of lead oxide and chlorides such as Nal and Kl contained in the dust. However, fundamental kinetic data on the reaction are not reported yet. Thus, the interpretation of the rate data was carried out using a Mass loss ( % ) ed height.7 mm ( 1. g ) 1.8 mm ( 2.5 g ) 3.7 mm ( 5. g ) 7.5 mm ( 1. g ) Fig. 8 Effect of bed height on the mass loss of the EF dust. (Temp. ¼ 1223 K) Mass loss ( % ) Gas flow rate 1.2 l /min.8 l /min.4 l /min.2 l /min Fig. 9 Effect of gas flow rate on the mass loss of the EF dust. (Temp. ¼ 1223 K) X K 1173 K 173 K K Fig. 1 Effect of reaction temperature on the volatilization ratio of lead in the EF dust. number of different rate equations such as the spherical shrinking-core expression, from which the Jander solid-solid kinetics 15 18) proved to yield the best results. The kinetic equation was derived for the reactions controlled by solidsolid diffusion. The applicability of this rate expression can be expected from the fact that the volume change of the EF dust before and after reacting is very small because the amount of lead and chlorine contained in the dust is relatively small. In this rate expression, the volatilization ratio of lead is related to the reaction time by ½1 ð1 XÞ 1=3 Š 2 ¼ k J t ð4þ Here, X is the volatilization ratio of lead, t is the reaction time (min), and k J is a constant (min 1 ) that is a function of temperature. It is apparent from eq. (4) that a plot of ½1 ð1 XÞ 1=3 Š 2 versus t should be linear with k J as the slope. The validity of the Jander rate expression for the lead volatilization reaction in the EF dust in air was verified by plotting the volatilization ratio-time curves of Fig. 1 according to eq. (4), as shown in Fig. 11. Examination of this figure reveals that the rate data follow well eq. (4). The values of k J were thus determined from the slopes of the figure. Figure 12 is an rrhenius plot of the rate constants.

6 328 J.-M. Yoo,.-S. Kim, J. Lee, M.-S. Kim and.-w. Nam [1 - (1 - X) 1/3 ] 2 Ln k J ( min -1 ) The slope of the straight line placed through the experimental points yield an activation energy of 175 kj/mol (41.8 kcal/ mol). The activation energy obtained is relatively high. The agreement of the rate data with the Jander equation as shown in Fig. 11 and the high activation energy indicate that the volatilization reaction of lead in the EF dust in air is controlled by solid-solid diffusion. It is thus obvious that when the EF dust is reacted by heating, the reactants must diffuse through a thin layer of the reaction products to react further. On the other hand, one of possible processes affecting the activation energy is probably the diffusion of sodium chloride (Nal) through the pores in the solid since the melting temperature of Nal is lower than other materials. However, no attempt was made in this work to elucidate the phenomenon. 5. onclusion 1323 K Experimental data est fit line 1273 K 1223 K 1173 K Fig. 11 Plot of the results in Fig. 1 according to eq. (4) Fig. 12 E = 41.8 kcal /mol ( 175 kj /mol ) T -1 / 1-4 K -1 rrhenius plot of the rate constants. The lead contained in the EF dust at temperature range 973 to 1223 K in air is volatilized as a form of Pbl 2 by reacting with Nal, l 2 O 3, and SiO 2 contained in the dust. The main reaction equation is 2Nal + PbO + 2SiO 2 + l 2 O 3 =Pbl 2 (g) + 2NalSiO 4. t the reaction temperature of 1223 K, about 98% for lead and for chlorine and about 1% for zinc were volatilized in the reaction time of 9 min. Thus, the selective removal of lead and chlorine with minimizing zinc loss from the EF dust would be possible. Jander rate expression was applicable over the entire temperature range. The volatilization reaction of lead in the EF dust is controlled by solid-solid diffusion and has an activation energy of 175 kj/mol (41.8 kcal/mol). REFERENES 1) D. Mishra, N. Lamaro, I. Gaballah and. Dupré: Fundamentals of dvanced Materials for Energy onversion, ed. by D. haridra and R. G. autista, (TMS, Warrendale, P, 22) pp ) D. K. Xia and.. Pickles: Minerals Engineering 12 (1999) ). Jarupisitthorn, T. Pimtong and G. Lothongkum: Mater. hem. Phys. 77 (22) ) T. agsarian: New Steel 15 (1999) ) J.-. Lee and Y. H. Kim: Development of technology for recovering valuable metals from EF dust, Ministry of ommerce, Industry and Energy Republic of Korea, (23) pp. 3. 6) J.-M. Yoo: Ph.D. Dissertation, honbuk National University, Jeonju, Republic of Korea, (24) pp. 2. 7) S. S. Thomas and E. D. lifton: Economic evaluation of the HTR process for treating EF Dust, ed., by R. Kaltenhauser, Disposal, recycling and recovery of electric arc furnace dust, (ISS-IME, US, 1987) pp ) J. F. Pusateri, R. hew and. E. Stanze: On-site treatment of EF dust via the St. Joe flame reactor, ed., by R. Kaltenhauser, Disposal, recycling and recovery of electric arc furnace dust, (ISS-IME, US, 1987) pp ) J.. une, K. erwitz-larsen, I. J. Eikeland and T. D. Pederson: Elkem multi-purpose furnace technology for reclamation of metal values in the treatment of hazardous materials, Recycling of metalliferrous materials, (IMM, London, 199) pp ) P. M. owx and. Roddis: The recovery of alloy elements from EF/ OD fume in the tetronics plasma system, ed., by R. Kaltenhauser, Disposal, recycling and recovery of electric arc furnace dust, (ISS- IME, US, 1987) pp ) S. Eriksson, H. G. Herlitz and S. O. Santen: pplication of plasma technology to the treatment of steelplant waste, ed., by R. Kaltenhauser, Disposal, recycling and recovery of electric arc furnace dust, (ISS- IME, US, 1987) pp ) S. Eriksson,. Johansson and S. O. Santen: Operating experience with the plasma dust process, ed., by R. Kaltenhauser, Disposal, recycling and recovery of electric arc furnace dust, (ISS-IME, US, 1987) pp ) K. Mager, U. Meurer,. Garcia-Egocheaga, N. Goicoechea, J. Rutten, W. Saage and F. Simonetti: Recovery of zinc oxide from secondary raw materials: New developments of the waelz process, 4th Int. Symposium on Recycling of Metals and Engineered Materials, ed. by D. L. Stewart, Jr. J.. Daley, R. L. Stephens, (TMS, Warrendale, P, 2) pp ) Guzhu Ye: haracterization and removal of halogens in the EF dust and zinc oxide fume obtained from thermal treatment of EF dust, 4th Int. Symposium on Recycling of Metals and Engineered Materials, ed. by D. L. Stewart, Jr. J.. Daley, R. L. Stephens, (TMS, Warrendale, P, 2) pp ) F. Habashi: Extractive Metallurgy, Gordon and breach, science publishers Inc., 1-2 (1969) pp ). H. amford and. H. F. Tipper: omprehensive chemical kinetics, 22, (Elsevier Scientific Publishing company, msterdam, 198) pp ) J.-M. Yoo,.-S. Kim, J.-c. Lee, J.-T. Park and J.-M. Yoon: Journal of the korean society for geosystem engineering 41 (24) ).-S. Kim, J.-M. Yoo, J.-. Lee,.-W. Nam and J.-M. Yoon: J. Kor. Inst. Met. Mater. 42 (24)