Open Chem., 2019; 17: 1146–1156
Research Article
Siqi He, Tongjiang Peng*, Hongjuan Sun, Dongshan Luo, Qing Xiao, Qian Geng Kinetics of Iron Removal From Ti-Extraction Blast Furnace Slag by Chlorination Calcination
https://doi.org/10.1515/chem-2019-0124 received June 1, 2019; accepted August 29, 2019. 1 Introduction
Abstract: In this research, ammonium chloride was used In Panzhihua, China, over 60 million tons of Ti-bearing to calcine Ti-extraction blast furnace slag (EBFS) with the blast furnace slag (TBFS) is produced. It causes aim of removing iron from it. The influences of calcination severe environmental problems such as groundwater temperature, ammonium chloride to EBFS mass ratio and contamination via the leaching of hazardous heavy particle size on the rates of iron removal were investigated. metals, while particulates are emitted into the surrounding The results show that the rate of iron removal increased to air [1]. At present, high-temperature carbonization-low- almost 100% with increases in calcination temperature temperature chlorination is the main process used to utilise and the NH4Cl to EBFS mass ratio, but decreased with TBFS [2]. This process has a high titanium extraction rate; increases in particle size. Iron is removed in the form however, it produces a chlorine-containing waste residue of ferric chloride gas, and ammonium chloride can called Ti-extraction blast furnace slag (EBFS), which is be recycled by recrystallization after decomposition. difficult to treat and can cause serious environmental The bagdasarrym model was used to describe the pollution. calcination process at temperatures below 261°C, which After chlorine removal, EBFS is mainly used to was controlled by nonisothermal crystallization. The produce low-value-added products such as cement mortar reaction kinetic equation was obtained and the apparent admixtures [3] and bricks [4-5]. Based on its complex activation energy of 67.21 kJ/mol. Ferric chloride reaction composition and amorphous phase structure, our research product existed in the calcined slag in an amorphous group used EBFS to produce glass-ceramics with good solid state. The shrinking core model was used to describe properties [6-7]. The chloride component escapes from the calcination process at temperatures above 261°C, EBFS during a calcination process; however, deleterious which was controlled by surface chemical reactions. The impurities can remain, usually in the form of iron reaction kinetic equation was obtained and the apparent compounds, which can discolour glass-ceramic products. activation energy was found to be 42.05 kJ/mol. This limits the commercial applications of glass-ceramics. Therefore, it is necessary to remove iron from EBFS before Keywords: Ti-extraction blast furnace slag; iron using it in glass-ceramics. Iron can be removed by two removal; chlorination calcination; kinetics methods including: 1) a physical separation process that aims to remove iron-containing minerals, and 2) chemical treatment that dissolves iron compounds bonded at the surface or existing as mineral grains [8]. The appropriate method for the removal of iron from an industrial solid *Corresponding author: Tongjiang Peng, Key Laboratory of Ministry waste depends on its mineralogical form and iron of Education for Solid Waste Treatment and Resource Recycle, distribution. Southwest University of Science and Technology, Mianyang 621010 Based on a mineralogical study of EBFS, this work Sichuan, China; Institute of Mineral Materials & Application, aims to investigate the iron removal from EBFS by Southwest University of Science and Technology, Mianyang 621010, ammonium chloride calcination. The iron component Sichuan, China, E-mail: [email protected] Siqi He, Hongjuan Sun, Dongshan Luo, Qing Xiao, Qian Geng, Key in EBFS reacts with ammonium chloride to form ferric Laboratory of Ministry of Education for Solid Waste Treatment and chloride, which escapes from the slag in a gaseous Resource Recycle, Southwest University of Science and Technology, state at a certain temperature. The process conditions, Mianyang 621010 Sichuan, China; Institute of Mineral Materials such as calcination temperature, mass ratio of NH4Cl to & Application, Southwest University of Science and Technology, EBFS and particle size, were assessed. Furthermore, the Mianyang 621010, Sichuan, China
Open Access. © 2019 Siqi He et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution alone 4.0 License. Kinetics of Iron Removal From Ti-Extraction Blast Furnace Slag by Chlorination Calcination 1147 chlorination calcination kinetics of iron was studied, Table 1: Design of the experiment. which can provide a theoretical guide for future process optimization and industrial applications. Parameters Levels Time (min) 0, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60
Temperature (°C) 180, 220, 260, 290, 310, 335, 350
2 Materials And Methods Mass ratio of NH4Cl to EBFS 1.0, 1.5, 2.0, 2.5 Average particle size (μm) 300, 200, 100, 74 2.1 Mineralogical analysis of EBFS Table 2: Chemical composition of EBFS samples (%). Samples of EBFS were collected from Panzhihua Iron and Steel Co. Ltd., Sichuan, China. X-ray Fluorescence CaO SiO2 Al2O3 TiO2 MgO Fe2O3 Cl SO3 (XRF) was used to analyse the chemical components of 32.45 27.72 13.37 8.68 7.62 4.39 2.96 0.84 EBFS, X-ray Diffraction (XRD) was used for mineral phase MnO K2O Na2O BaO SrO P2O5 ZrO2 Y2O3 analysis, X-ray Photoelectron Spectroscopy (XPS) was 0.81 0.67 0.26 0.1 0.06 0.04 0.03 0.01 used for valence analysis of the iron in EBFS, Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) was used to analyse the morphology and iron 3 Results And Discussion distribution of EBFS, and Thermogravimetric Analysis- Differential Scanning Calorimetry (TG-DSC) was used for 3.1 Characterization of EBFS samples thermal stability analysis. The loss on ignition (LOI) of EBFS was 12.92%. On the
basis of the XRF results, it contained 4.39% Fe2O3 (Table 2). 2.2 Process of calcination with ammonium XRD of the EBFS (Figure 1) shows that the main diffraction chloride peaks are d111=2.49 Å, d200=2.16 Å, d220=1.52 Å and d311=1.30 Å, which are characteristic peaks of its titanium carbide Calcination was carried out in a furnace with programmed (TiC) (reference code: 00-032-1383) [9]. Besides, there temperature control. Firstly, a certain amount of are some amorphous substances in EBFS, the chemical ammonium chloride was put into a 10 g EBFS sample and bond in amorphous compounds is easier to break and stirred in a 100 mL ceramic crucible, which was then placed synthesize than that in the crystal of the same substance. in the furnace. The experiments were repeated under So the EBFS sample had high reactivity [10]. XPS was various experimental conditions. The process design is used to characterize the Fe oxidation state (Figure 2). The represented in Table 1. After being calcined, The calcined supported Fe2O3 was characterized by a spin-coupled product obtained below 260°C was leached in water to doublet for curve fitting of Fe2p3/2 and Fe2p1/2 at 712.2 eV obtain the leached product. The leached product and the and 725.6 eV, respectively [11-12]. The supported FeO was calcined product obtained above 261°C was characterized characterized by a spin-coupled doublet for curve fitting by XRF. The % iron removal (R) was calculated according of Fe2p3/2 and Fe2p1/2 at 711 eV and 723.7 eV, respectively, to Equation (1): which indicates that both Fe2+ and Fe3+ species were present in the EBFS [13]. Figure 3 shows the SEM-EDS (1) determined distribution of iron in the EBFS samples. The EBFS particles had no specific morphology and where m1 and m2 are the masses of Fe2O3 in the EBFS and could be divided into two types: those with smooth and calcined product or leached product, respectively. dense surfaces, and those with rough and loose surfaces. Ethical approval: The conducted research is not Surface scanning analysis indicates that the distribution related to either human or animal use. of iron was very dispersed. Hence, it would be difficult to remove iron by beneficiation and a chemical method would be better. 800
700 1 600 1
1148500 Siqi He et al. a.u 400 800 1 300800 700 3.2 Effect of experimental conditions on iron 1 Intensity/ 1 removal 700 600 1 1 200 1 600 500 1 3.2.1 Effect of calcination temperature
100 a.u 500 400 1 The mixture of NH Cl and EBFS was calcined at 180, 220,
a.u 0 4 400 30020 30 40 50 60 70 80 260, 290, 310, 335 and 350°C for 1 h, with the mass ratio of Intensity/ 1 1 200 2 ° 1 NH Cl to EBFS and the particle size of EBFS held at 1.8:1 300 4
Intensity/ and 250 μm, respectively. The results shown in Figure 4 100 1 Figure 1. 200XRD pattern of EBFS samples. 1 = titanium1 carbiderevealed that temperature had a strong influence on the 0 iron removal rate, which was > 60% at temperatures > 100 20 30 40 50 60 70 80 335°C. Figure 5 shows the TG-DSC diagram for the mixture 2 ° 0 of NH4Cl and EBFS, which has four endothermic peaks 20 30 40 50 60 70 80 Figure 1. XRD pattern of EBFS samples. 1 = titanium carbideand two mass-loss regions from 170–350°C. The DSC curve Fe2p 2 ° Fe2p 1/2 3/2 of the mixture shows two small endothermic peaks at Fe(Ⅱ)Fe2p1/2 ( Fe O ) Figure 1: XRD pattern of EBFS2 samples.3 1=titanium carbide(. Fe2O3) 172.1°C and 210.9°C due to the reaction of solid ammonium Figure9600 1. XRD pattern of EBFSFe(Ⅲ samples.)Fe2p 1 = titanium carbide Satellite 3/2 chloride with iron components in the EBFS. The DSC curve Satellite Fe2p also shows a sharp endothermic peak at 261.1°C due to 9200 1/2 Fe2p3/2 Fe(Ⅱ)Fe2p ammonium chloride being decomposed into ammonia and 1/2 ( Fe2O3) ( Fe O ) 9600 Ⅲ 2 3 Satellite Fe( )Fe2p3/2 hydrogen chloride, resulting in a mass loss of 17.2% [14]. Fe2p Satellite Fe2p 8800 1/2 3/2 The DSC curve shows a small endothermic peak at 310.2°C Fe(Ⅱ)Fe2p 9200 1/2 ( Fe2O3) ( Fe O ) 9600 Ⅲ 2 3 due to the reaction of gaseous hydrogen chloride with iron Satellite Fe( )Fe2p3/2 Counts / s Fe2p components in the EBFS that formed ferric chloride gas, 8400 1/2 Satellite 8800 Fe(Ⅱ)Fe2p resulting in a mass loss of 5.2%. The reaction temperature 9200 (FeO) 3/2 Satellite is slightly lower than the thermodynamic calculation Counts / s Fe2p 8000 8400 1/2 Fe2p temperature of the reaction between Fe O and HCl. It may Fe(Ⅱ)Fe2p 3/2 2 3 8800 (FeO) 3/2 Satellite(FeO) be that other components in EBFS play a catalytic role in
Counts / s 8000 Fe2p the reaction [15]. Therefore, an increase in the removal Fe2p 3/2 8400740 735 730 725 1/2720 715 710 705 700 Fe(Ⅱ)Fe2p (FeO) rate with increases in temperature could be attributed to (FeO) 3/2 a change of the state of the calcination additives leading 740 735 Binding730 725 Energy 720Satellite (eV)715 710 705 700 8000 Fe2p to an increase in the reaction area between EBFS and the Binding Energy (eV)3/2 Figure 2. XPS spectra in the Fe2p(FeO) region of EBFS calcination additives. Figure740 2:Figure XPS735 spectra 2. 730XPS in the spectra725 Fe2p720 region in the715 of Fe2p EBFS.710 region705 of EBFS700
Binding Energy (eV) 3.2.2 Effect of the NH Cl to EBFS ratio 4 Figure 2. XPS spectra in the Fe2p region of EBFS The effect of increasing the mass ratio of NH4Cl to EBFS on iron removal is shown in Figure 6, with the calcination temperature and average particle size held at 335°C and
250 μm, respectively. An increase in the NH4Cl to EBFS mass ratio was observed to have some influence on the
iron removal rate. At low ratios, the NH4Cl decomposed less hydrogen chloride gas, resulting in a low overall concentration of hydrogen chloride in the reaction system. Meanwhile, an increase in the ratio contributed to an increased concentration of hydrogen chloride gas in the reaction system, thus increasing the reaction rate of calcination additives and iron-containing particles in the Figure 3. SEM-EDS images of EBFS EBFS. Figure 3:Figure SEM-EDS 3. images SEM of- EBFSEDS. images of EBFS
Figure 3. SEM-EDS images of EBFS
100 90 2.5 70 350℃ 2.0 335℃ 80 310℃ 1.5 60 70 50 ℃ 290 60 1.0 40 Kinetics of Iron Removal From Ti-Extraction50 Blast Furnace Slag by Chlorination Calcination 1149 260℃ 40 30 30 Removal rate / % 100 Removal rate / % 20 70 220℃350℃ 20 2.5 ℃ 90 10 335 10 2.0 60 180℃310℃ 80 0 0 1.5 70 500 10 20 30 40 50 60 70290℃ 0 10 20 30 40 50 60 70 Time / min 60 Time / min 1.0 40 50 Figure 4. Effect of temperature on iron removal rates260Figure with℃ time6. Effect of various NH Cl to EBFS mass ratios on iron removal rate over time 30 40 4
30 Removal rate / % Removal rate / % 20 220℃ 20
10 10 180℃ 0 0 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70
Time / min Time / min
Figure 4: Effect of temperature on iron removal rates with time. Figure 6: Effect of various NH Cl to EBFS mass ratios on iron removal Figure 4. Effect of temperature on iron removal Figure rates 6. with Effect time of various NH4Cl to 4EBFS mass ratios on iron removal rate over time rate over time.
110 262.1℃ 172.1℃ 210.9℃ 105 1
100 310.2℃ 0
95 -1 90
mW/mg 85 17.2% -2
Mass / % 80 -3 DSC / 75 5.2% -4 70 110 EXO
262.1℃ -5 172.1℃ 210.9℃ 1050 200 400 600 800 1000 1200 1 Temp. / ℃
100 310.2℃ 0 FigureFigure 5:5. TG-DSC TG-DSC analysis analysis of the of NH the4Cl NH and ClEBFS and mixture. EBFS mixture 95 4 -1 90 FigureFigure 7. Effect 7: Effect of of various particle particle sizes sizes on iron on removal iron removal rate over rate time. over time
3.2.3 Effect of particle size mW/mg 85 17.2% -2 Mass / % The 80influence of average particle size fractions on the 3.3 Phase analysis of calcined products and -3 DSC / removal rate of iron is shown in Figure 7, with the reaction condensated products temperature75 and mass5.2% ratio of NH Cl to EBFS held at 4 -4 335°C70 and 2.0:1. The results indicate that iron removal As seen in the XRD patterns of the calcined product at 220, EXO rates increased with decreases in the EBFS particle size. A-5 260, 335 and 350°C with the mass ratio of NH4Cl to EBFS decrease0 in particle200 size400 would600 contribute800 to 1000an increase1200 in and the particle size held at 1.8:1 and 250 μm in Figure 8, the specific surface area, leadingTemp. /to ℃ much-improved heat comparing with XRD of EBFS (Figure 1), the number and and mass transfer rates and facilitating faster liberationFigure of the 7. intensityEffect of ofvarious the diffraction particle sizes peaks on of iron titanium removal carbide rate over time Figurethe iron 5. component TG-DSC analysis [16]. of the NH Cl and EBFS mixture(TiC) decreased until they disappeared after calcination. 4 The diffraction peaks of ammonium chloride appeared in the calcined products at 220 and 260°C. However, there is no diffraction peaks of ammonium chloride in the calcined products at 335 and 350°C. This is consistent with the 1150 Siqi He et al.
TG-DSC result (Figure 5) that ammonium chloride being decomposed into ammonia and hydrogen chloride when 350C 2 2350C 2 the temperature is higher than 261°C. This phenomenon 2 2 shows that2 ammonium chloride will not remain in the 335C calcined product when the calcination temperature is 335C higher than 261°C, which is beneficial to the application 1 of EBFS after iron removal. There are no diffraction 260C 1 1 peaks of ferric chloride in calcined product. The reason 2601C 1 1 is that ferric chloride is gaseous when the calcination Intensity / a.u. 1 1
Intensity / a.u. temperature is higher than 310.2°C, and ferric chloride 220C may exist in amorphous state when the temperature is 220C 1 less than 310.2°C. 1 Gas produced by calcination of EBFS at 335°C, and 10 20 30 40 50 60 70 the products of gas condensation show three distinct 10 20 30 40 50 60 70 2 / color ranges on the wall of quartz tube (Figure 9). The 2 / XRD pattern of the condensated products in three color Figure 8. XRD patternsFigure of the8: XRD calcined patterns product of the calcined obtained product at differentobtained at temperatures: different ranges 1- Ammonium shown in Figure 9A, B, C revealed that white temperatures:Figure 8. X1-AmmoniumRD patterns Chloride, of the 2- cTitaniumalcined Carbide. product obtained at different temperatures: 1- Ammonium Chloride, 2- Titanium Carbide. condensated product was calcination additive ammonium Chloride, 2- Titanium Carbide. 12000 1 12000 1 10000 10000 8000 8000 6000
1 6000 4000
Intensity/a.u. 1 1 40001 2000 Intensity/a.u. 1 1 1 1 2000 1 1 0 0 10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80 2/° 2/° （A） （A）
4500 7000 4500 7000 4000 1 6000 3 4000 3500 2 1 6000 3 3500 2 5000 3000 5000 3000 4000 2500 2 4000 2500 2000 2 2 3000 2000 2 3000 Intensity/a.u. 1500 2 Intensity/a.u. 2000 3 3
Intensity/a.u. 1500 Intensity/a.u. 3 1000 1 2 2000 3 1000 33 3 3 2 1000 1 2 1 2 1 1 3 3 3 3 500 2 22 3 3 3 10003 3 33 3 3 1 2 2 1 3 500 2 2 1 2 1 0 3 3 3 3 3 0 2 22 3 3 3 3 3 2 2 1 0 10 20 30 40 50 060 70 80 10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80 10 20 30 40 50 60 70 80 2/° 2/° 2/° 2/° （B） （C） （B） （C） Figure 9. XRD patterns of condensation products of volatile gases calcined at 335 C: 1- Figure 9. XRD patterns of condensation products of volatile gases calcined at 335 C: 1- Ammonium ChlorideFigure (NH 9:4 ClXRD), patterns2- Ammonium of condensation Aqua products Iron Chloride of volatile ( (NHgases4 )calcined2FeCl5 Hat2 335O), ºC: 3- 1- Iron Ammonium Chloride (NH4Cl), 2- Ammonium Aqua Iron Chloride((NHAmmonium) FeCl ChlorideH O), 3- ( IronNH Chloride4Cl), 2- Hydrate Ammonium (FeCl ·6H AquaO). Iron Chloride ((NH4)2FeCl5H2O), 3- Iron Chloride4 2 5 Hydrate2 (FeCl3·6H2O). 3 2 Chloride Hydrate (FeCl3·6H2O). Kinetics of Iron Removal From Ti-Extraction Blast Furnace Slag by Chlorination Calcination 1151
Table 3: Integrated rate equations for the solid-solid reaction. chloride which is formed by hydrogen chloride gas and ammonia gas decomposed from ammonium chloride, Rate-controlling step Rate equation yellow condensated product was the mixture of -2/3 ammonium chloride and ammonium aqua iron chloride, Interfacial chemical reaction (1-rFe) -1=kr1t brown condensated product was iron chloride hydrate. Diffusion control 1-2rFe/3-(1-rFe)2/3=kr2t This phenomenon shows that iron can be successfully Nonisothermal crystallization ln[-ln(1-rFe)]=lnkr3+nlnt removed by calcination with ammonium chloride. Iron rFe- iron removal degree; t- time (min); kr- apparent rate constant exists in the form of ferric chloride and can be recovered (min-1); n- n=δ+α, δ is the number of steps in series reaction and α by condensation, the calcination additives ammonium is the number of growth directions of product nuclei. chloride can also be recycled by recrystallization after decomposition. Table 4: Parameters of ln[-ln(1-rFe)] vs lnt obtained at temperatures of 160°C, 200°C and 230°C.
3.4 Calcination kinetics analysis Temperature Apparent rate Fitting equation (°C) constant lnk
3.4.1 Temperatures less than 261°C 180 -8.40582 ln[-ln(1-rFe)]= -8.40582+1.31927lnt 220 -7.02595 ln[-ln(1-rFe)]= -7.02595+1.37603lnt Ammonium chloride is solid at calcination temperatures 260 -5.72542 ln[-ln(1-rFe)]= -5.72542+1.27014lnt lower than 261°C, so the chlorination reaction is a solid- solid reaction that forms a solid phase. The typical rate- where kr is the rate constant, A is the frequency factor, Ea controlling step of solid-solid reaction are the interfacial is the apparent activation energy (J/mol), R is the mole chemical reaction, diffusion control and nonisothermal gas constant (R = 8.314 J/mol) and T is the thermodynamic crystallization process. The step with the highest kinetic temperature. resistance is the rate controlling step [17-18]. Table 3 The corresponding relationship between lnkr and shows the integrated rate equations. Experimental data 1/T is shown in Figure 11. The apparent activation energy obtained at 180, 220 and 260°C were compared with the of iron removal is estimated to be 67.21 kJ/mol according three models, with the results shown in Figure 10 [19-21]. to the slopes of the straight lines in Figure 11, with A 3 It can be seen that the plots of ln[-ln(1-rFe)] had a very estimated as is 12.23 × 10 according to the intercept. good linear relationship with lnt, with a fitting degree Therefore, the semi-empirical kinetic equation is higher than 0.9. This indicates that the calcination rate was controlled by regional nucleation reactions, the most appropriate reaction model is the bagdasarrym model [19].
The reaction rate constant lnk and its model equation at where rFe is the fraction of Fe removed, R is the molar gas different temperatures are presented in Table 4. According constant (R = 8.314 J/mol), T is the calcination temperature to the kinetic equation, we can know that when n ≈ 1, the (K), t is the reaction time (min). number of growth directions of the product nucleus is α Because the ferric chloride calcined product is in = 0. So, it can be judged that the chlorination calcination an amorphous solid state at calcination temperatures reaction is completed in one step and the chlorination below 261°C, solid ferric chloride cannot escape from the product is amorphous at temperatures < 261°C [22]. This reaction system to achieve the purpose of iron removal. is consistent with the conclusions of the experiment—that Hence, the dynamics of different NH4Cl:EBFS mass ratios ferric chloride in the calcined product obtained at < 261°C and EBFS particle sizes at calcination temperatures below is in an amorphous phase. The relationship between 261°C are not discussed. reaction rate and temperature is well established and can be modelled with the Arrhenius equation, as expressed below. 3.4.2 Temperatures above 261°C
(2) Ammonium chloride decomposes into ammonia gas and hydrogen chloride gas at calcination temperatures higher (3) than 261°C. The reaction product, ferric chloride, is a gas at this temperature, so the reaction between hydrogen chloride and the iron component of EBFS is a solid-gas 1152 Siqi He et al.
0.4 0.020 2 0.4 2 2 0.020 180℃, R =0.91871 180℃, R =0.91871 180℃, R =0.68765 180℃, R2=0.68765 2 2 2 220℃, R =0.94953 220℃, R =0.94953 220℃, R =0.93240 220℃, R2=0.93240 2 2 2 0.3 260℃, R =0.88394 0.3 260℃, R =0.88394 0.015 260℃, R =0.88544 0.015 260℃, R2=0.88544 2/3 2/3 ) ) Fe Fe -1 0.2 -1 0.2 0.010 0.010 -2/3 -2/3 ) ) Fe Fe /3-(1-r /3-(1-r Fe Fe (1-r 0.1 (1-r 0.1 0.005 0.005 1-2r 1-2r
0.0 0.0 0.000 0.000
0 10 20 30 40 500 6010 20 30 40 500 6010 20 30 40 500 6010 20 30 40 50 60 Time/ min Time/ min Time/ min Time/ min
(a) (a) (b) (b)
0 0 -1 -1 -2 -2
)] -3
)] -3 Fe Fe -4 -4 -5 -5 ln[-ln(1-r ln[-ln(1-r 2 -6 ℃ 2 180 -6, R =0.97320 180℃, R =0.97320 2 ℃ 2 -7 220 -7, R =0.94993 220℃, R =0.94993 2 260℃, R =0.94497 2 -8 -8 260℃, R =0.94497 1.5 2.0 2.5 3.0 3.5 1.54.0 2.04.5 2.5 3.0 3.5 4.0 4.5 ln t ln t
(c) (c) Figure 10. Comparison between plots of (a) (1 − r )-2/3 − 1 and (b) 1 − 2r /3 -−2/3 (1 − r )2/3 vs time, 2/3 Figure 10. Comparison betweenFe plots of (a) (1 − FerFe) − 1 andFe (b) 1 − 2rFe/3 − (1 − rFe) vs time, Figure 10: Comparison between plots of (a) (1 − r )-2/3 − 1 and (b) 1 − 2r /3 − (1 −r )2/3 vs time, (c) ln[−ln(1 − r )] vs lnt . (c) ln[−ln(1 − r )] vs lnt Fe Fe Fe Fe Fe (c) ln[−ln(1 − rFe)] vs lnt
-5 -5 calcination, so the most appropriate reaction model is the
3 shrinking core model [23-25]. In the chlorination calcination lnk=9.41145-8.08346×10 /T lnk=9.41145-8.08346×103/T 2 system, the ferric chloride gas is formed by chlorination -6 R =0.99824 R2=0.99824 -6 of iron-containing minerals. Because the iron-containing minerals are widely distributed and the total iron content
r -7 r -7 in EBFS is relatively low, the release of ferric chloride gas ln k ln k does not have a significant impact on the morphology of -8 the EBFS particles. This results in the calcination process -8 being controlled by diffusion through the EBFS particle layer or chemical reactions at the surfaces of the EBFS -9 1.9 2.0 -92.1 2.2 particles [17]. Integrated rate equations for the shrinking 1.9 2.0 2.1 2.2 -1 -3 -1 T /10 K -1 -3 -1 core model are shown in Table 5 [20]. T /10 K The linear regression analysis of experimental data Figure 11: Arrhenius plot between lnkr and 1/T for the calculation obtained at temperatures of 290, 310, 335 and 350°C using Figure 11. Arrhenius plotof between activation ln energy.kr and The 1/ Tvalues for the of K calculation were calculated of byactivation using the energy. The values Figure 11. Arrhenius plot betweenr lnkr and 1/T for the calculationthe equations of activation in Table energy. 5. Figure The 12values compares the plots of bagdasarrym model. of Kr were calculated by using the bagdasarrym model 2/3 1/3 of Kr were calculated by using the bagdasarrym1 − 2(1 − rFe model) − 3(1 − rFe) and 1 − (1 − rFe) versus time at calcination temperatures of 290, 310, 335 and 350°C with reaction. Because EBFS particles have dense surfaces, a NH4Cl to EBFS mass ratio of 1.8:1 and average particle which can be considered as non-porous particles, and size of 250 μm. The results show that there are very good
1/3 the iron-containing particles gradually shrink during linear relationships in the plots of 1 − (1 − rFe) vs time.
0.35 0.45 290℃, R2=0.74901 290℃, R2=0.90197 2 0.40 2 0.30 310℃, R =0.95573 310℃, R =0.92765 335℃, R2=0.95867 0.35 0.25 2 2/3 ℃ 0.30 ) 350 , R =0.96847 Fe 0.20 0.25 1/3 )
0.15 Fe 0.20 )-3(1-r
Fe 0.15
0.10 1-(1-r 0.10
1+2(1-r 0.05 0.05 335℃, R2=0.96416 0.00 0.00 Kinetics of Iron Removal From Ti-Extraction Blast Furnace350℃ Slag, R2=0.94432 by Chlorination Calcination 1153 -0.05 0 10 20 30 0 5 10 15 20 25 30 35 Time/ min Time/ min 0.35 0.45 290℃, R2=0.74901 290℃, R2=0.90197 2 0.40 2 0.30 310℃, R =0.95573 310℃, R =0.92765 335℃, R2=0.95867(a) 0.35 (b) 0.25 2 2/3 ℃ 0.30 ) 350 , R =0.96847 2/3 1/3 FigureFe 0.20 12. Comparison of plots of (a) 1 + 2(1 − rFe) − 0.253(1 − rFe) and (b) 1 − (1 − rFe) vs time 1/3 )
0.15 Fe 0.20 )-3(1-r
Fe 0.15
0.10 1-(1-r 0.10
1+2(1-r 0.05 0.05 335℃, R2=0.96416 0.00 0.00 350℃, R2=0.94432 -0.05 0 10 20 30 0 5 10 15 20 25 30 35 Time/ min Time/ min
(a) (b)
2/3 1/32/3 1/3 FigureFigure 12; Comparison12. Comparison of plots of (a)plots 1 + 2(1of −(a) rFe ) 1− +3(1 2(1 − rFe −) r andFe) −(b) 3(1 1 − (1− −rrFeFe) vs and time. (b) 1 − (1 − rFe) vs time
0.7 2 1.0 g/g, R2=0.94409 300 μm, R =0.93109 1.0 2 0.6 1.5 g/g, R2=0.97944 200 μm, R =0.94525 2 2.0 g/g, R2=0.91473 100 μm, R =0.85489 0.5 0.8 2 2.5 g/g, R2=0.92144 74 μm, R =0.93812 0.4 1/3 1/3 0.6 ) ) Fe Fe 0.3 0.4 1-(1-r 1-(1-r 0.2 0.2 0.1 0.0 0.0 0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 Time/ min Time/ min 0.7 2 1.0 g/g, R2=0.94409 300 μm, R =0.93109 1.0 2 0.6 1.5 g/g, R2=0.97944 200 μm, R =0.94525 2 2(a) (b) 2.0 g/g, R =0.91473 100 μm, R =0.85489 0.5 0.8 2 2.5 g/g, R2=0.92144 74 μm, R =0.93812 Figure 13: Plots of 1 − (1 − r )1/3 vs time for1/3 different parameters: (a) ratio of NH Cl to EBFS mass and (b) particle size. Figure0.4 13. Plots of 1 Fe− (1 − rFe) vs time for different parameters:4 (a) ratio of NH4Cl to EBFS 1/3
1/3 0.6 ) ) Fe Fe 0.3 mass and (b) particle size. Table 5: Integrated rate equations for the shrinking core model. 0.4 1-(1-r 1-(1-r 0.2 additives and EBFS particle radius. The empirical 0.2 formulas can be established as per Eq. (4) [26]. Therefore, Rate-controlling0.1 step Rate equation the apparent rate constant can be calculated by the Diffusion control through the 1 + 2(1 - rFe) - 3(1 - rFe)2/3 = kr1t 0.0 0.0 relationships between kr and each factor. particle layer0 10 20 30 40 50 60 0 10 20 30 40 50 60 70 Time/ min 1/3 Time/ min Surface chemical reaction 1 - (1 - rFe ) = kr2t (4) rFe- iron removal degree; t- time (min); kr- apparent rate constant (min-1). (a) Where kr is the (b)apparent rate constant, k is the reaction
1/3 rate constant, C0 is the concentration of hydrogen chloride Figure 13. Plots of 1 − (1 − rFe) vs time for different parameters: (a) ratio of NH4Cl to EBFS This indicates that the calcination rate was controlled gas, M is the molecular weight of solid reactant, r0 is the by chemical reaction. Fitting the massexperimental and (b) particle data sizeinitial. radius of solid reactant, and ρ is the density of solid presented in Figures. 6–7 with chemically-controlled reactant (ρ = 1.8944 g/cm3). model. The fitting results of the model to the experimental The relationship between kr and calcination data is shown in Figure 13. The reaction rate constant k temperature obeys the Arrhenius equation as expressed r and its fitting equation are presented in Table 6. in Reactions (2) and (3), with the results shown in Figure
The apparent rate constant kr is affected by the 14a. The apparent activation energy of iron removal is calcination temperature, concentration of calcination calculated to be 42.05 kJ/mol, the relationship between kr
1154 Siqi He et al.
-4.0 -4.6 -4.2 -4.8 -4.4 r r -5.0 -4.6 lnk ln k
-4.8 -5.2 3 lnk=4.01914-5.05789×10 /T y=0.86725x - 6.37009 2 2 -5.0 R =0.87505 -5.4 R =0.97496
1.60 1.65 1.70 1.75 1.80 1.0 1.2 1.4 1.6 1.8 2.0 2.2 T-1/10-3K-1 ln (C ) 0
(a) (b)
-4.0
y=-0.61079x-10.3243 -4.2 R2=0.92409
-4.4 r
ln k -4.6
-4.8
-5.0 -10 -9 ln r 0
(c)
Figure 14: Relationships between lnkr and 1/T, ln(C0), and ln r0: (a) Arrhenius plot of the calcination process at 290, 310, 335 and 350 °C; (b) relationship between lnk and ln(C0); and (c) relationship between lnk and lnr0. Figure 14. Relationships between lnk and 1/T, ln(C0), and lnr0: (a) Arrhenius plot of the calcination process at 290, 310, 335 and 350 °C; (b) relationship between lnkr and ln(C0); and (c) and T can be expressed as per Equation (5). It is generally The plot of lnkr versus lnC is shown in Figure 14b. The relationship between lnk and lnr . 0 believed that high values of activation energy (>40 kJ/r slope0 of the fitting line is 0.86725, so the relationship mol) indicate chemical control, whereas values <20 kJ/ between kr and C is: 0 0.86725 mol imply diffusion-controlled processes [18-27-28], so the kr = A1C0 (7) calcination rate was controlled by chemical reaction. The radius of EBFS can be calculated by its particle size. -42051/ kr = 55.65e RT (5) When is regarded as the constant A2, Eq. (4) can be transformed into: Equation (4) shows that the apparent rate constant kr is positively proportional to the concentration of calcination lnkr = lnA2 − lnr0 (8) additives. The concentration of hydrogen chloride gas can be calculated by the mass ratio of NH4Cl to EBFS. When The plots of lnkr versus lnr0 are presented in Figure 14c.
is regarded as a constant, A1, Equation. (4) can be The slope of the fitting line is 0.61079, so the relationship transformed into: between kr and r0 can be written as:
lnkr = lnC0 + lnA1 (6) (9) Kinetics of Iron Removal From Ti-Extraction Blast Furnace Slag by Chlorination Calcination 1155
1/3 Table 6: Parameters of 1 − (1 − rFe) vs time for all experimental data. 4 Conclusions
Apparent rate Fitting equation The main minerals of EBFS are titanium carbide (TiC) constant k and some amorphous substances. EBFS contains about Temperature ( ) 4.39% Fe2O3 and the distribution of the iron component 2+ 3+ 290 ℃ 0.00738 1 - (1 - rFe)1/3 = 0.00738 t is very dispersed. Besides, both Fe and Fe species were present in the EBFS. Removal of the iron component 310 0.00836 1 - (1 - rFe)1/3 = 0.00836 t from EBFS uses ammonium chloride calcination. It was 335 0.01551 1 - (1 - rFe)1/3 = 0.01551 t found that the increase of calcination temperature, mass
1/3 350 0.01573 1 - (1 - rFe) = 0.01573 t ratio of NH4Cl to EBFS and the decrease of slag particle size are beneficial to iron removal from EBFS. Iron is Ratio of NH4Cl to EBFS mass (g/g) removed in the form of ferric chloride gas, the separation and recovery of ferric chloride and ammonium chloride 1.0 0.00445 1 - (1 - rFe)1/3 = 0.00445 t which decomposition from reaction system can be carried 1/3 1.5 0.00679 1 - (1 - rFe) = 0.00679 t out by recrystallization. The bagdasarrym model was 2.0 0.00869 1 - (1 - rFe)1/3 = 0.00869 t used to describe the calcination process at temperatures
2.5 0.00971 1 - (1 - rFe)1/3 = 0.00971 t below 261°C. The calculated apparent activation energy was 67.21 kJ/mol and the reaction product was ferric Particle size (μm) chloride in an amorphous solid state. The kinetic 300 0.00853 1 - (1 - rFe)1/3 = 0.00853 t equation is . 200 0.00941 1 - (1 - rFe)1/3 = 0.00941 t The experimental results at calcination temperature above 261 °C are matched the shrinking core model with surface 100 0.00966 1 - (1 - rFe)1/3 = 0.00966 t chemical control, and the apparent activation energy of 1/3 74 0.01233 1 - (1 - rFe) = 0.01233 t iron removal in the calcination reaction was estimated to be 42.05 kJ/mol. The relationships between the rate constants The relationships between the three factors and kr are and the process parameters were established. The kinetic established in Eqs. (5), (7) and (9). The semi-empirical equation is . kinetic equation can be obtained by synthesizing the three relationships. References
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