An Environmental Procedure to Extract Titanium Components and Metallic Iron from Ti-Bearing Blast Furnace Slag

Green Process Synth 2015; 4: 307–316

Wu Zhang, Li Zhang*, Yuhai Li and Xin Li An environmental procedure to extract titanium components and metallic iron from Ti-bearing blast furnace slag

DOI 10.1515/gps-2015-0031 technology for the disposal of industrial wastes has Received April 26, 2015; accepted June 29, 2015 attracted much attention. Typically, the efficient utilization of blast furnace slag is of great significance to the clean production smelting process and the global environ- Abstract: An environmental procedure to extract tita- ment; it can not only provide an outlet for the wastes but nium components and metallic iron from Ti-bearing blast can also reduce environmental pollution. furnace slag is accomplished via three steps, which are Ti-bearing blast furnace slag is a typical refractory high-temperature modification, gravity separation and industrial solid waste; it is generated during the blast hydrometallurgy method. The behaviors of metallic iron furnace smelting process of vanadium and titanium during the high-temperature modification process are magnetite. There are about 25% TiO2 and more than 5% studied. The feasibility of separating rutile from the matrix metallic iron in the slag due to the particularity of ferrous phase are investigated; based on the feasibility analysis minerals used during the melting process. A lot of slag results, the gravity separation experiment is carried out accumulates every year, polluting not only the environ- in order to improve the TiO2 content in the slag. The leach- ment but also waste resources. An environmental technol- ing behaviors and kinetics of non-titanium components in ogy to extract the titanium components and metallic iron the concentrate of gravity separation are investigated. The from the slag is necessary. Many methods are applied to activation energy of the leaching process is 62.868 kJ/mol, extract the titanium from Ti-bearing blast furnace slag, and circulatory leaching and preparation of synthetic such as acid leaching, fused salt chlorination, high-tem- rutile experiments are implemented. Finally, an environ- perature modification (HTM), preparing alloy process, etc. mental technological route is proposed for comprehensive [4–8]. However, the slag has not been utilized effectively utilization of Ti-bearing blast furnace slag. until now due to the various problems, such as water pollution and air pollution. Keywords: environmental procedure; iron; rutile; Based on the previous studies, the extracting Ti-bearing blast furnace slag. process in this work involves three steps: the first step is adjusting the chemical composition of the slag in order to transform the titanium component into the rutile phase; the second step is creating appropriate physi- 1 Introduction cal and chemical conditions to make the rutile crystals grown up. The above two steps could be called HTM Global concern about environmental problems is increas- process. The last step is separating the rutile and iron ing, such as solid waste pollution and air pollution. from the cooled slag by gravity separation and hydro- High-volume waste materials resulting from large-scale metallurgy method. Compared with other methods to industrial productions have long been considered to be a extract titanium from the slag, the HTM process can burden, due to the high costs of their associated post-treat- proceed without being heated during the actual indus- ment, storage and disposal [1–3]. The environment-friendly trial production process; thus, it does not require addi- tional energy. The energy that is required during the HTM process could be provided by high-temperature *Corresponding author: Li Zhang, School of Materials and slag that is discharged from the furnace. Moreover, the Metallurgy, Northeastern University, Shenyang, Liaoning 110819, experimental results of the HTM process showed that P. R. China, e-mail: [email protected] Wu Zhang, Yuhai Li and Xin Li: School of Materials Science and metallic iron would settle down to the bottom of the cru- Engineering, Shenyang Ligong University, Shenyang, Liaoning cible, and thus the metallic iron can be separated easily 110168, P. R. China after the HTM process. The rutile crystals are separated 308 W. Zhang et al.: Titanium and iron extracting from slag from the slag by gravity separation and hydrometal- therefore fully characterized by scanning severa1 areas during SEM- lurgy methods; the water used in the extracting process EDX analysis. Titanium enrichment ratio is a primary indicator for HTM pro- is recycled by circulatory process. No emission of waste cess. We use the volume fraction of rutile in the modified slag to water and pollution are expected during the production measure the titanium enrichment degree; the overall uncertainties process in this work. are ±0.3%. We convert the crystal size of rutile into equivalent cir- cle to describe the size of rutile crystals, and the overall uncertainty is ±0.7%. Line intercept method is applied to determine the average grain size and volume fraction of rutile crystals; the sample homo- geneity, magnification and numbers of measured fields are readily 2 Materials and methods sources of error during the measurement.

2.1 Materials 2.2.2 Titanium component separation process: The titanium The slag used in this work is obtained from the Panzhihua Iron and component separation process proceeds via two stages in this Steel Company, and the chemical composition is listed in Table 1. work; the first is gravity separation process, and the second

As shown in Table 1, the raw slag mainly consists of TiO2, CaO, SiO2, is leaching of non-titanium components. The equipment of

Al2O3 and MgO, and other oxides such as Fe2O3, which are inevitably gravity separation process is shaking table (model: 6-s, Hubei included in the slag, account for the remaining small proportion. Mining Machinery Factory, Hubei province, China), the vibration Prior to the heating experiment, the raw slag is ground and frequency and the shaking stroke are 360 per minute and 12 mm, screened by a 74-μm mesh to facilitate melting. Analytical grade respectively. oxides are mixed with the slag in order to make the titanium com- The materials used in leaching process are gravity separation ponents transform into rutile phase. All commercially available concentrates. Leaching experiments are carried out in a 1000-ml- chemical agents for experiments are without further purification. All capacity glass reactor fitted with multisockets, with the sockets being the reagents used in this work were produced by Shenyang reagents fitted with quick-fit glass adaptors and a condenser to prevent evapo- factory in Liaoning province, China. ration losses. The reactor is heated in a water bath with provision to control the bath temperature to maintain the reactor temperature within ±1 K. The leaching processes consist of two steps: (1) alkali 2.2 Experimental procedure leaching, process in which silicon and aluminum components could be removed; and (2) diluted hydrochloric acid (0.88% wt) leaching, process in which magnesium and iron components could be 2.2.1 High-temperature modification and samples analysis removed. process: The experiments of HTM process are carried out in a vertical furnace and the temperature controller is Shimaden FP93 (the temperature measurement accuracy is ±3 K). The working thermocouple is B type and calibrated against a standard thermocouple. 3 Results and discussion The modified slag samples are analyzed by X-ray diffraction [XRD, using a Philip X pert machine (PANalytical company, Almelo, Holland) with Cu Kα radiation]. Phases in the XRD patterns are 3.1 Phase transaction of titanium before analyzed by X pert high score plus software (PANalytical company, and after high-temperature modification Almelo, Holland) equipped with JCPDS PDF 4 database. A patch of modified slag is chipped and polished on a buffing process machine, and then metallographic microscope (201A-D, Shanghai optical instrument factory, Shanghai, China) and scanning electron Figure 1 shows the SEM images for the raw slag and microscope with the model of 201A-D and SSX-550 (Shanghai optical modified slag. As shown in Figure 1, combining with the instrument factory, Shanghai, China) are used to observe the micro- previous work [5, 7–9], there are five phases in the raw morphology of the modified slag. slag, which are perovskite, Ti-rich diopside, titanaugite, Scanning electron microscopy combined with energy-dispersive spinel and metallic iron, while there are only two phases X-ray (SEM-EDX, Shimadzu Corporation, Kyoto, Japan) analysis ena- bled the characterization of phases that are present in small con- in the modified slag; one is rutile phase, and the other centration and may not be analyzed by XRD analysis. The slags are is called matrix phase in this work. Table 2 shows the energy dispersive spectrometer (EDS) analysis results of the modified slag. Table 1: Chemical composition of raw Ti-bearing blast furnace slag As shown in Figure 1 and Table 2, most of the titanium (mass fraction, %). components in the slag are enriched in the rutile phase. Moreover, the grain size of the titanium-containing phase CaO MgO TiO2 Al2O3 SiO2 Fe2O3 Others had grown obviously, which is quite conducive to the sep- 27.07 8.04 21.36 14.13 25.20 3.4 0.8 aration process. W. Zhang et al.: Titanium and iron extracting from slag 309

50 µm 50 µm

Figure 1: Back scattering microscopic morphology of the modified slag: (A) before modification; and (B) after modification.

Table 2: EDS results of Figure 1B.

Area Element Weight %

White O 34.862 Ti 65.138 Gray O 44.469 Mg 2.759 Al 8.061 Si 24.795 Ca 15.277 Ti 1.168 Fe 3.471

3.2 The behavior of metallic iron in high- temperature modification process Figure 2: Photo of modified slag and iron.

During the vanadium-titanium magnetite blast furnace 2 2 r11(-ρρ2 ) smelting process, metal droplets are brought into the slag Vg=× × (1) 9 η due to high viscosity of the liquid slag; this part of metal 2 droplets is wrapped in the slag, and it is one of the most where V is the average settling velocity of iron (m/s); r1 is serious causes of metal loss [4]. In addition, the loss of the average radius of liquid iron droplets (m); g is gravity 2 metallic iron during the vanadium-titanium magnetite acceleration (m/s ); ρ1 and ρ2 are the density of iron and 3 blast furnace smelting process is much more than that molten slag (kg/m ); and η2 is the average viscosity of during ordinary blast furnace smelting process due to the molten slag (pa s). According to the references [5, 7, 8], special properties of the slag; thus, it is necessary to recover when the temperature is 1733 K, the viscosity of the liquid the metallic iron in the slag. During the experiments, we slag is about 0.0008 pa s, and the density of iron droplets found that most of the metallic iron in the slag moved to and molten slag are 7000 and 3600 kg/m3; according to the bottom of the container under the effect of gravity; this our experimental results, r1 is about 0.0002 m, and thus makes it easy for the metallic iron to be recovered. Figure 2 the settling velocity of iron droplets is is a photo of the modified slag and metallic iron. 2 20.002 ×−(7000 3600) The density of liquid iron is greater than slag; thus, V =× ×=10 0.38 (2) 90.0008 the iron would settle down to the bottom of the melt. The movement of iron in the liquid slag is similar to gas If the height of liquid level is 0.8 m, the obtained set- bubbles moving in the liquid; the settling velocity of iron tling time is about 2.05 s; thus, the liquid iron can settle can be calculated by Stokes theorem [10]: down to the bottom of the crucible at high temperatures. 310 W. Zhang et al.: Titanium and iron extracting from slag

3.3 Feasibility analysis and results of gravity Table 4: Degree of mineral liberation with different particle sizes. separation Particle ≥ 3/4 free 3/4~1/2 free 1/2~1/4 free < 1/4 free size (μm) particles (%) particles (%) particles (%) particles (%) 3.3.1 Feasibility analysis on gravity separation 150~250 47.53 19.75 19.76 12.96 The density difference between light and heavy minerals 74~150 58.15 19.87 11.02 10.96 48~74 37.93 10.76 5.12 5.43 is the most pivotal factor of gravity separation process. As 38~48 78.69 5.69 5.87 3.41 such, the density difference between rutile crystals and -38 85.33 5.32 5.36 3.99 matrix phase is crucial for the separation process. According to the reference [11], the difficulty degree of the gravity separation can be represented by According to the results in Equation (4), combining δρ- the criteria given in Table 3, the difficulty degree of gravity E= 2 (3) δρ- separation is easy. 1 The liberation degrees of minerals are another impor- where E is the difficulty coefficient of gravity separation; tant factor for the gravity separation process; liberation

δ1, δ2 and ρ are the densities of light mineral, heavy mineral degrees of different size particles of modified slag are and dressing medium, respectively. E can be divided into investigated in this work and are shown in Figure 3 and five levels which are shown in Table 3. Table 4. The density of rutile is about 4.2~4.5 g/cm, the inter- After the grinding process, there are two types of mediate is water during the separation process, and the particles: free particles and interlocking particles. As densities of water and pyroxene are 1.0 and 2.8 g/cm3. such, the free particles are rutile, and the interlock- According to Equation (3), the E value of the gravity sepa- ing particles are composed of the rutile and the matrix ration is phase. According to the reference [11], there are two liberation ways for minerals: one is detachment liberation, δρ- 4.35-1 E==2 =1.86 (4) and the other is size reduction liberation. In detachment δρ-2.80-1 1 liberation, the phases in locked particles separate from each other along the common boundary; it is an ideal and energy-saving liberation way. Size reduction libera-

Table 3: Difficulty level of gravity separation. tion is a way of liberation due to the regulatory volume decrease of particles. However, during actual produc- E value > 2.5 2.5~1.75 1.75~1.5 1.5~1.25 < 1.25 tion process, most mineral phases cannot be separated completely from the matrix phase; a particle which has Degree of Very Easy Medium Difficult Very difficulty easy difficult difficult more than 75% of mineral phase is suitable for separation. The experiment results in Figure 8 and Table 5 show that the liberation degree increases as the particle size decreases. When the particle size is 150~250 μm, the degree of libration for rutile is 47.53%, while when the particle size is 38~48 μm, the degree of libration of rutile Matrix phase Interlocking is 85.03%. Furthermore, the liberation degree increases particle slowly when the particle size is less than 74 μm, which indicates that the liberation way of rutile is detachment Free particle liberation.

Table 5: A group of experimental results of open-circuit mineral processing.

Products Yield (%) TiO2 (%)

100 µm Concentrate 20.02 66.15 Middling 8.31 15.35 Tailings 8.37 12.56 Figure 3: Microscopy image of modified slag. W. Zhang et al.: Titanium and iron extracting from slag 311

Table 6: Chemical composition of middling and tailings (mass fraction, %).

CaO MgO TiO2 Al2O3 SiO2 Fe2O3 Others Middling 29.33 9.85 11.07 15.15 29.76 4.14 0.7 Tailings 21.02 9.18 7.15 18.03 43.37 0.40 0.85

3.3.2 Results of gravity separation

Based on the analysis and experimental results in this work, gravity separation is carried out via open-circuit mineral process; Table 5 is a group of experimental results of open- circuit mineral processing. Table 6 shows the chemical composition of middling and tailings (mass fraction, %). As shown in Tables 5 and 6, there are three products during the gravity separation process which are concen- Figure 4: Effect of NaOH concentration on leaching rate of non- titanium components. trate, middling and tailings. The middling and tailings can be used as raw materials to produce cement [12]. There is

66.15% TiO2 in the concentrate, which is not propitious leaching process is sodium hydroxide solution leaching to be applied in the titanium industry; other methods are process. The experiment results under different NaOH still necessary to remove the impurities in the concentrate. solution concentrations are shown in Figure 4. Thus, alkali and acid leaching method is implemented in As we all know, the viscosity of the leaching system order to remove the non-titanium components in this work. increases as NaOH concentration increases, which impedes the diffusion process of the leaching reagents and the reaction product thereby affecting the leaching 3.4 Leaching process of non-titanium rate of non-titanium component. However, as shown in components Figure 4, the leaching rate of non-titanium component increases as the NaOH concentration increases. This indi- As shown in Table 1, the composition of the slag is cates that the leaching process is not controlled by out- complex. In general, the stoichiometry of metallic oxides diffusion process. dissolution in alkaline and acid solutions can be represented by Equations (5)–(8): 3.4.2 Effect of temperature on the leaching rates Al ON+=aOHNaAlO +HO (5) 23 22 of non-titanium components

MgO2+=HClMgClH22+ O (6) In this paper, at 10 wt% NaOH concentration, the effect of CaO2+=HClCaClH+ O (7) 22 temperature has been studied at 313, 333, 353 and 373 K.

Fe23O2+=HClCaClH22+ O (8) Figure 5 shows the effect of temperature on leaching rate of non-titanium components. The leaching behavior of silicon components is Figure 5 illustrates that non-titanium components complex; according to our experiment results and other dissolution increases dramatically as the temperature research results [13], the silicon components are floating in increases. However, at high temperature (373 K) it is aqueous solution in the form of orthosilicic acid (H SiO ), 4 4 found that the initial non-titanium components dissolve which can be separated by still stratification method from faster when the leaching time is less than 300 min. This the aqueous solution. is because higher temperature is more conducive to the chemical reaction process, which is consistent with other 3.4.1 Effect of NaOH solution concentration on the extracting processes [18–22]. As such, higher tempera- leaching of non-titanium component ture can promote the chemical reaction between NaOH and solid particles. Based on the experimental results Previous studies [14–17] show that hydrochloric acid in Figure 5, we choose 373 K as the optimal leaching leaching proceeds readily; thus, the control step of the temperature. 312 W. Zhang et al.: Titanium and iron extracting from slag

leaching system. Moreover, it can be seen that the leaching rate did not greatly change with varying solid-to-liquid ratio, which also can be found in other leaching processes [18–22]; thus, we can choose 1:5 as the optimal solid-to- liquid ratio, and less water would be consumed during the leaching process.

3.4.4 Leaching kinetics of non-titanium component

Figure 7 shows the back-scattering microscopic morphology of particles before and after leaching process. It can be seen that the particles without being leached are featured as compact solids with a smooth surface; the surfaces of the particles become rough and Figure 5: Effect of temperature on the leaching of non-titanium porous after leaching process due to the chemical reac- component. tions. The particle size decreases as the leaching reac- tions proceed. The morphology and chemical analysis of the slag illustrate that the leaching process of silicon and 3.4.3 Effect of solid-to-liquid ratio on the leaching aluminum component can be described by the unreacted of non-titanium component shrinking core model, the equation of which is shown as [16, 17, 22] Figure 6 summarizes the effect of solid-to-liquid ratio on the leaching rate of non-titanium component. 11RM21C xx++00[1-3(1-)332( 1-xx)]+×[1-( 1- )]= t As shown in Figure 6, the leaching rate of non-tita- 36KD kRσρ Me rea0 nium components in the modified slag decreases as the (9) solid-to-liquid ratio increases. The solid-to-liquid ratio is a critical factor for most of the leaching process. Liquid- where x is the reaction rate of the impurities in the slag, solid ratio affects the viscosity of the leaching system; the KM is the mass-transfer coefficient of the reactant from rea- viscosity of the leaching system decreases as the solid-to- gents in liquid boundary layer, R0 is the particle size of the liquid ratio increases. Low solid-liquid ratio means fewer slag, De is the mass-transfer coefficient of the reactant in particles in the system with the same volume of solution, the product layer, krea is the reaction rate constant, t is the which is conducive to improve the diffusion process of the reaction time, M is the molar weight of the slag, C0 is the concentration of the reactant when the leaching process is begun, ρ is the density of the slag, and σ is the coefficient of NaOH. When the leaching process is controlled by the liquid boundary layer diffusion process, the kinetics equation can be represented by [16, 17, 22] 3KMC xt= M 0 (10) σρR 0 Likewise, when the leaching process is controlled by solid product layer diffusion process, the kinetics equation can be represented by [16, 17, 22]

2 6DMC 12+=(1-)xx-3(1-)3 e 0 t (11) σρR2 0

1 kMC Figure 6: Effect of solid-to-liquid ratio on the leaching of non- 1-(1-)xt3 = rea0 (12) σρR titanium component. 0 W. Zhang et al.: Titanium and iron extracting from slag 313

A B

100 µm 10 µm

Figure 7: SEM micrograph of particles before and after leaching process: (A) before leaching; and (B) after leaching.

Figure 8 shows the relationship fitted by kinetics functions between non-titanium leaching rate and leaching time at 373 K. As can be seen in Figure 8, the linearly dependent coefficients of the above fitting lines are 0.76628, 0.9753 and 0.9375; thus, the optimal kinetics equation of the leaching process is

1 1-(1-)xk3 = t (13) Figure 9 is a plot of leaching kinetics at different leaching temperatures. To reveal the control step of the leaching process, kinetics experimental results in Figure 5 are calculated at different temperatures, and the calculating results are shown in Figure 10. Figure 9: Plot of leaching kinetics under different reaction Leaching rates of non-titanium with different tem- temperatures. peratures are fitted, and the value of k is obtained. The

Figure 8: Non-titanium leaching rate vs. time at 373 K fitted by Figure 10: Nature logarithm of reaction rate constant vs. reciprocal kinetics functions. temperature. 314 W. Zhang et al.: Titanium and iron extracting from slag apparent activation energy can be calculated based on carried out by the route of HTM-gravity separation-alkali Arrhenius equation [16, 17, 22]: and acid leaching. Table 8 is the chemical analysis results of the product. E 1 Ink=×InA- (14) It can be observed from Table 8 that there is not much RT difference in the composition between the final products where E is the apparent activation energy, A is pre-expo- of the present study and typical synthetic rutile; the prod- nential factor, and R is the molar gas constant. After cal- ucts are ideal material which can be used in titanium culating, the value of E in equation (14) is obtained to be industry. E = 62.868 kJ/mol.

1 62868 5 - 1-(1-)xe3 =×7.66 10 RT ⋅t (15) 3.6 Proposed environmental route for comprehensive utilization of the slag 3.5 Circulatory leaching and preparation Based on the experimental results in this work, combined of synthetic rutile with the other mature and applicable technologies in metallurgy industry, an environmental route for comprehen- 3.5.1 Circulatory leaching and solution purification sive utilization of the slag is proposed, which is shown in process Figure 11. As shown in Figure 11, the iron in the slag can easily No emission of waste water is expected during the produc- be separated by spontaneous sedimentation method due tion process in this work; thus, circulatory leaching and solution purification process are necessary to be carried out to make the process more environmental. Table 8: Chemical analysis results of rutile (mass fraction, %). The leaching solution of sodium hydroxide mainly consists of OH-, AlO - and Na+; the CO gas could be applied 2 2 TiO2 SiO2 Al2O3 MgO CaO Fe2O3 Others and piped into the leachate to adjust the acidity of the lea- - 93.75 2.78 0.98 0.58 0.87 0.12 0.82 chate in order to make AlO2 precipitate in the form of Al

(OH) 3; after several leaching cycles, when sodium and carbonate ions reach a certain concentration, cooling Raw slag crystallization method can be applied to remove most of O the sodium and carbonate ions. Likewise, the hydrochlo- 2 Modification Iron ric acid leaching leachate usually includes Fe3+and Mg2+. Sodium hydroxide can be added into the leachate to adjust Gravity separation acidity in order to make Fe3+and Mg2+ precipitate in the 3+ 2+ form of Fe (OH)3 and Mg (OH)2 to remove the Fe and Mg Water NaOH solution leaching from the leachate. Table 7 shows analysis results of main metal ions in the leachate before and after precipitation.

H SiO Solid containing TiO2 4 4 Still stratification 3.5.2 Results of synthetic rutile preparation experiment Water HCl leaching NaOH solution leaching 2 Based on the theoretical analysis experimental results CO2 in this paper, synthetic rutile preparation experiment is

Fe (OH) Al(OH) Rutile 3 Adjust acidity 1 3

Table 7: Analysis results of main metal ions in the solution. Cooling crystallization

Mg (OH)2 Adjust acidity 2 Solution Fe3+/(g/l) Al3+/(g/l) Ca2+/(g/l) Mg2+/(g/l) Na2CO3

Circulatory leaching 1 0.13 2.75 3.86 0.66 NaCl Cooling crystallization Circulatory leaching 2 0.18 3.42 4.59 0.82 Circulatory leaching 3 0.24 3.96 5.16 1.01 Figure 11: Flow sheet for the comprehensive utilization of Ti-bearing After precipitate < 0.001 < 0.001 < 0.001 < 0.001 blast furnace slag. W. Zhang et al.: Titanium and iron extracting from slag 315 to its larger density than the liquid slag; then gravity sepa- References ration process is implemented in order to separate the rutile phase from matrix phase, and then leaching process [1] Al-Khatib IA. Waste Manage. 2015, 36, 323–330. is carried out in order to get high-quality synthetic rutile. [2] Alibardi L, Cossu R. Waste Manage. 2015, 36, 147–155. After the alkali leaching process, the silicon components [3] Ambily PS, Umarani C, Ravisankar K, Prem PR, Bharatkumar BH, transformed into H SiO in forms of colloid, which floats Iyer NR. Constr. Build Mater. 2015, 77, 233–240. 4 4 [4] Zhang L, Zhang LN, Wang MY, Li GQ, Sui ZT. Miner. Eng. 2007, in solution and is easy to separate, while the aluminum 20, 684–693. - components exist in the solution in the form of AlO2 . CO2 [5] Sui ZT. Acta Mater. 1999, 47, 1337–1344. gas could be piped into the solution to adjust the solution [6] Li J, Zhang ZT, Zhang M, Guo M, Wang XD. Steel Res. Int. 2011, acidity to make the aluminum components precipitate in 82, 613–614. [7] Li J, Wang XD, Zhang ZT. ISIJ Int. 2011, 51, 1396–1402. the form of Al(OH) 3, and the by-product is Na2CO3, which can be separated by cooling crystallization method. The [8] Wang MY, He YH, Wang XW, Lou TP, Sui ZT. Nonferrous Met. Soc. China 2007, 17, 584–588. purified water can be applied in the leaching process [9] Zhang W, Zhang L, Feng NX. Adv. Mater. Res. 2013, 611, 363–366. 3+ 2+ again [23]. Likewise, there are Fe and Mg in the acid [10] Winkler MKH, Bassin JP, Kleerebezem R, van der Lans RGJM, leaching solution; NaOH can be used to adjust the pH in van Loosdrecht MCM. Water Res. 2012, 12, 3897–3902. order to make the Fe3+and Mg2+ precipitate in the form of [11] Tuazon D, Corder G, Powell M, Ziemski M. Miner. Eng. 2012, 29, Fe(OH) and Mg(OH) , and the by-product is NaCl, which 65–71. 3 2 [12] Zhang W, Zhang L, Zhang JH, Feng NX. Ind. Eng. Chem. Res. can be separated by cooling crystallization method. 2012, 51, 12294–12298. [13] Mazzocchitti G, Giannopoulou I, Panias D. Hydrometallurgy 2009, 4, 327–332. 4 Conclusions [14] Geveci A, Topkaya Y, Ayhan E. Miner. Eng. 2002, 15, 885–888. [15] Deakin D, West LJ, Stewart DI, Yardley BWD. Waste Manage. An environmental production procedure which can achieve 2001, 21, 265–270. [16] Johnson JA, McDonald RG, Muir D, Tranne JP. Hydrometallurgy the recovery of titanium and iron from Ti-bearing blast 2005, 78, 264–270. furnace slag is implemented. Based on the environmental [17] Parhi PK, Park KH, Senanayake G. J. Ind. Eng. Chem. 2013, 19, production procedure to extract titanium component and 589–594. iron from Ti-bearing blast furnace slag, an environmental [18] Rodriguez MH, Rosales GD, Pinna EG, Suarez DS. Hydrometallurgy route for comprehensive utilization of the slag is proposed 2015, 156, 17–20. [19] Yin SH, Li SW, Peng JH, Zhang LB. RSC Adv. 2015, 5, 48659–48664. in this work. The following conclusions can be obtained: [20] Xiao J, Li FC, Zhong QF, Bao HG, Wang BJ, Huang JD, Zhang YB. 1. Most of the titanium components in Ti-bearing slag Hydrometallurgy 2015, 155, 118–124. transform into rutile phase after modification pro- [21] Malenga EN, Mulaba-Bafubiandi AF, Nheta W. Hydrometallurgy cess, which is quite conducive to the separation of 2015, 155, 69–78. titanium components. [22] Ju ZJ, Wang CY, Yin F. Int. J. Miner. Pro. 2015, 138, 1–5. 2. The metallic iron in the slag would settle down to the [23] Aryal N, Reinhold DM. Ecol. Eng. 2015, 78, 53–61. bottom of the crucible during the HTM process, which does not require heating in industrial production, and it can be separated from the slag by sedimentation. Bionotes 3. Leaching behavior of non-component in the slag is Wu Zhang investigated; the optimal leaching temperature is 373 K, the optimal NaOH concentration is 10%, and the leaching activation energy is 62.868 kJ/mol. 4. Circulatory leaching and preparation of synthetic rutile experiments are accomplished, and the final product in this work can be used in titanium industry.

Acknowledgments: The authors gratefully acknowledge the financial support from the National Natural Science Wu Zhang obtained his PhD from the School of Materials and Metal- lurgy, Northeastern University, China in 2013. Currently, he serves Foundation of China no. 51304139. as an Associate Professor at the School of Materials Science and Engineering, Shenyang Ligong University, China. He is engaged in Conflict of interest statement: The authors declare no dealing with industrial solid waste and extracting valuable compo- competing financial interest. nents in Ti-bearing blast furnace slag. 316 W. Zhang et al.: Titanium and iron extracting from slag

Li Zhang Xin Li

Li Zhang is an Associate Professor at the School of Materials and Xin Li obtained her PhD from the School of Chemical Engineer- Metallurgy, Northeastern University, China. Between 2004 and ing, Dalian University of Technology, China. Currently, she is an 2005, he served as a postdoctor fellow in the Korean Academy of Associate Professor at School of Materials Science and Engineering, Sciences. He is known for his work on comprehensive utilization of Shenyang Ligong University, China. She is engaged in extracting Ti-bearing blast furnace slag. valuable components in industrial solid waste.

Yuhai Li

Yuhai Li is a Professor at the School of Materials Science and Engi- neering, Shenyang Ligong University, China. He worked as a postdoctor fellow at the Institute of Metal Research, Academia Sinica. He is a member of Shenyang Human Materials and Heat Treatment Association. He has done a lot of work in making comprehensive utilization of Ti-bearing blast furnace slag from 2011 to date.