ESTIMATING PHOSPHATE CAPACITIES OF MULTI-COMPONENT SLAGS BY MASS TRIANGLE MODEL

Transcription

1 J. Min. Meta. Sect. BMeta. 53 (1) B (2017) Journa of Mining and Metaurgy, Section B: Metaurgy ESTIMATING HOSHATE CAACITIES OF MULTICOMONENT SLAGS BY MASS TRIANGLE MODEL Y. Sun a, L. Wang a,b*, J. Xu c, K. Chou a,b a Coabrative Innovation Center of Stee Technoogy, University of Science and Technoogy Beijing, Beijing, China b State Key Laboratory of Advanced Metaurgy, University of Science and Technoogy Beijing, Beijing, China c Department of hysica Chemistry, Schoo of Metaurgica and Ecoogica Engineering, University of Science and Technoogy Beijing, Beijing, China Abstract (Received 29 March 2016; accepted 20 October 2016) Considering the importance of dephosphorization process in ironmaking and steemaking, this paper attempted to estimate the phosphate capacities of different systems. Mass triange mode coud approach the properties of muticomponent systems without the parameter for every component. This present work aso extended the mass triange mode to muticomponent systems appication to three systems containing as much as seven components proved the feasibiity and accuracy of this mode. The cacuated contour ines reveaed the reasonabe trend as experimenta resuts, and cacuation resuts for fixed compositions showed a ow error rate. Scattered points cacuation obtained more accurate resuts. Since this mode can aso evauate other properties of sag, such as density, viscosity, suphide capacity etc., this mode might shoot ight on the understanding of various properties of muticomponent sags accuratey, and thus offer insight on optimization of ironmaking and steemaking process. Keywords: hosphate capacities; Mass triange mode; Muticomponent system 1. Introduction There is an increasingy arge demand for cean stee. However, scarcity of high quaity resources urges the utiization of highphosphorus ores. hosphorus in stee coud ead to cod shortness. So the hot meta pretreatment and secondary refining processes are both deveoped for remova of suphur and phosphorus. Generay, phosphorus is removed by oxidization and stabiized as phosphate in sag. hosphate capacity of sags has been widey investigated by numerous studies. CaO based sag is widey used due to its ower price and high bound abiity with phosphate. However, it coud eevate the meting point of the fux. hosphate capacity of some imebased systems [16] has been reported. In the pretreatment process, the temperature is generay ow and CaF 2 is usuay added to ower the meting point of sag and improve the kinetic conditions [7]. Considering the toxicity of fuorides to the heath to human being, it is necessary to carify the infuences of other additives on dephosphorization. For CaF 2 free systems, A 2, * Corresponding author: ijunwang@ustb.edu.cn Na 2 O, MnO, BaO etc. are added to CaObase sags with high basicity and high FeO to decrease the meting temperature, increase fuidity and improve the dephosphorization abiity of sags [8]. Na 2 O has a stronger abiity for dephosphorization and a better fuidity, whie it woud erode the refractory due to its strong basicity [910]. Meanwhie, in the process with basic refractory, the sag woud be saturated by MgO. CaOMgO sat FeO x system has been studied commony concerning dephosphorization capacity [1112]. Despite various systems that have been studied, experimenta data was never enough. Some empirica equations have been derived reating the phosphorus distribution ratio to sag components, og L og (% ) [% ] which are shown in Tabe 1. Besides, as pointed out by Mori [16], phosphate capacity was reported to reate to the optica basicity at 1600 o C, as shown in C Eq. (3). og A C O 4 3 (3) DOI: /JMMB S

2 32 Y. Sun et a. / JMM 53 (1) B (2017) Tabe 1. Some previous equations on og L p Reseachers Heay[13] Suito et a.[14] Turkodgan[15] og og (% L ) [% ] (% CaO) 2. 5 *og(% Fe ). t 1600 T t T 411. *og(% CaO 03. % MgO % CaF2 T 00. 5% FetO) 25. *og(% FetO) 0. 05%*og( O 2 5) F T *(% CaO 03. % MgO) 25. *og(% Fet O) 987. T C 1 Obtaining an overa knowedge for the performance of a certain sag is very important for hot meta pretreatment since a sag shoud shouder various task and be optimized to the best property. In this work, the mass triange mode is empoyed to make an estimation of phosphate capacity for severa muticomponent sags, which was proposed by Chou et a [17]. In previous work, satisfactory resuts were obtained in estimation of density [18], surface tension [19] as we as suphide capacity [20] in ternary systems with imited soubiity. In the present study, another important chemica property of sag, i. e. the phosphate capacity was cacuated by the mass triange mode. Meanwhie, the mass triange mode was extended to cacuate some muticomponent systems. 2. Mode description To orient the author, the brief introduction of mass triange mode has been given in this section. The detaied information can be found esewhere [21]. For metaurgica sag, they are usuay imited soubiity system at certain temperature, which means no intersect point with binary systems. As shown in Fig.1. The area within the boundary represents a homogenous system. O is a composition point within this area. Three ines that parae to the three sides of the triange were drawn from O. They intersect with the sides at A, B and C and intersect with the soube boundary at A, B and C. A, B and C represent the property data of point A, B and C respectivey. WA, WB, and WC refer to the weight factors of these three points. The weight factor of A is determined by area ratios represented in Eq.[4]. W A' S S OB' C ' ABC ' ' ' (4) When the property data on the boundary are known, then the property of point O within the area O coud be expressed as the weight summation of properties of A, B and C, which is shown in Eq.[5]. O =W A A + W B B + W C C (5) Figure 1. Schematic graph of a ternary system with imited soubiity However, metaurgica sags aways have a compex component. For a muticomponent system, it is aways asked whether, if the avaiabe data points are restricted in some imited discrete points, we can sti extract some information from them and if so, how we can do that. Chou et a. has deveoped a genera method for cacuating properties based on imited data. It is sti based on the weight factor of a component point to the system. Detaied description can be drawn from iterature [22]. 3. Appication to various systems and discussion In this work, we wi dea with three muticomponent systems concerning dephosphorization. In one way, the system wi be approached as a pseudoternary system based on a certain principe. First, the contents of basic oxides, ike CaO, MgO and Na 2 O, wi be added together to make a basic ange. Simiary, and A 2 wi make a acid ange. Second, the content of iron oxides, which means FeO and Fe 2, wi be added together. In another way, discrete component point wi be cacuated based on other known data according to the method described in iterature [22]. 3.1 Estimation of various systems by pseudoternary method hosphate capacity of CaOMgO FeOx system Suito [11] studied the phosphorous distribution ratio of CaOMgO FeO x system in a magnesia crucibe, which ed to saturation of MgO in the sag. The temperature range was 1550 ~1650. Logatirhm vaue of phosphate capacity of this system was cacuated and the contour ines were shown through Fig. 2(a) to Fig. 2(c). The interva for two

3 Y. Sun et a. / JMM 53 (1) B (2017) adjacent ines is 0.4 for each figure. It can be seen ceary from the figures that dephosphorization is favored by reative ow temperature. Besides, with increase of basic oxides, the phosphate capacity aso eevates notaby. Suito mentioned that the effects of siica and iron oxides on the capacity were cose and substituting CaO with (a) 1550 o C (b) 1600 o C (c) 1650 o C Figure 2. hosphate capacity in ogarithm of CaOMgO FeO x system Tabe 2. Comparison of experimenta and cacuated vaue ( ogc ) of CaOMgO FeOx system at O4 different temperature 3 Composition (mass fraction) Temperature ReferenceCacuated Error CaO+MgO FeOx ( o C) Data Vaue Rate % % % % % % % % % % % % MgO woud cause the phosphate capacity to drop obviousy.the effect of FeO on the dephosphorization is compex. On one hand, the FeO coud reease more O 2 3, which can hep form O. On the other hand, FeO 4 3 coud bond O4 with and form an instabe compound 3FeO 2 O 5. Furthermore, high FeO contents diuted the concentration of CaO, which performs a main roe in dephosphorization. Therefore too much FeO wi hinder the dephosphorization process. The tota effect of FeO depends on the basicity of sag and there shoud exist an optimum vaue. The phenomenon was aso observed by Li [11] and ak [9]. To evauate the mode, some points were cacuated and the resuts are given in Tabe 1. Eq. (6) is introduced to cacuate the mean deviation. In this equation, K i,ca and K i,exp are the cacuated and experimenta vaue for the ith data point, respectivey. N represents the tota number of data. The mean deviation between the cacuated vaue and the experimenta vaue is 2.19 pct. The deviation is reativey ower than other empirica equations. N 1 ica, i,exp (6) N i 1 i,exp hosphate capacity of CaONa 2 OMgO FeO system In steemaking processes to produce high grade stees, the secondary refining is considered to be the very effective for the purpose of dephosphorization. Na 2 Obased sags aways have good performance in dephosphorization. But Na 2 O bring serious corrosion to refractory. Kunisada [10] reported phosphorous distribution between iquid iron and Na 2 OMgOFeO containing cacium. Based on simiar principe, pseudo ternary system was got and the contour ines for og C at 1600 o C were shown in Fig. 3. It can be O4 3 concuded that both CaO and Na 2 O have a positive effect of dephosphorization. But due to its negative effect, the content Na 2 O must be kept ow. Tabe 3 showed the comparison of experimenta and cacuated vaues of some seected points in Fig. 3. The mean deviation for this system is 2.08 pct, which aso suggests the vaidity of this mode. It is interesting to note that the authors aso investigated the reationship between phosphoate capacity and theoretica optica basicity and compared the resuts for the CaObased sags. They found that the phosphate capacities of the two sags coud not be represented uniquey by the theoretica optica basicity hosphate capacity of CaOMgO FeO x Na 2 OA 2 system Lade dephosphorization is an aternative to obtain ower phosphorus stee by using specia fuxes.

4 34 Y. Sun et a. / JMM 53 (1) B (2017) Figure 3. hosphate capacity in ogarithm of CaONa 2 O MgO FeO system at 1600 Tabe 3. Comparison of experimenta and cacuated vaue ( ogco ) of CaONa 2 OMgO FeO system at Composition (mass fraction) ReferenceCacuated Data Vaue Error Rate CaO+MgO+Na 2 O FeO % % % % Cacium fuoride is commony added to decrease the meting point and viscosity of sags. But considering the toxicity of fuorides, deveoping CaF 2 free sag is becoming urgent. A 2, Na 2 O, MnO are usuay added into the CaObased sag. Li [12] has studied phosphate capacity of highy basic CaO based sags saturated with MgO and the effect of Na 2 O and A 2 addition. Fig. 4 presented the cacuated phosphate capacity of this compex system.it is important to mention that this study aso shown the industria significance of MgO saturated highy basic CaO FeO x sags, which can be used as a substitution for CaF 2 containing sags. The idea condition, the fina phosphorus content wi be about 16 ppm. Therefore, the mass triange mode provides a method to predict whether a muticomponent system coud have industria advantage. Since this mode can aso estimate suphide capacity of moten sag and good resuts have been reported by Wang [20], this mode is supposed to offer a comprehensive understanding for a certain system. This wi certainy bring great convenienceto future optimization of sag component in various ironmaking and steemaking processes. The contour ines predicted that the phosphate capacity woud increase with the basicity. Besides, the Figure 4. hosphate capacity in ogarithm of CaOMgO FeO x Na 2 OA 2 system at 1600 addition of Na 2 O woud improve the dephosphorization process, whie the addition of A 2 woud probaby hinder it. The scattered points were aso cacuated by mass triange mode. Tabe 4 gives the resuts. The mean deviation for this compex system is 0.74 pct. It can be concuded that for systems which contained as much as seven components in this case, this mode was pretty competitive in predicting properties of moten sags. 3.2 Estimation of various systems by discrete component point In the first method, we get a pseudoternary based on the property of component. However, the difference of two kinds of basic oxides or acid oxides has not been discosed. To sove this probem, the mass triange was extended to muticomponent systems and the comparison of cacuated and experimenta resuts is shown in Fig. 5. The mean deviation is 1.03 pct. Tabe 4. Comparison of experimenta and cacuated vaue of ogc CaOMgO FeO x Na 2 OA 2 system at 1600 O 4 3 Composition (mass fraction) +A 2 CaO+MgO+Na 2 O FeOx ReferenceCacuated Data Vaue Error Rate % % % For sag at 1600 o C, the vaues are aso estimated by the optica basicity. The resuts are given in Tabe 5. It can be seen obviousy that the cacuation resuts obtained by optica basicity have a much arger

5 Y. Sun et a. / JMM 53 (1) B (2017) Figure 5. Comparison of experimenta and cacuated vaue ogc for various muticomponent systems deviation than present work. As pointed by Kunisada [10], the phosphate capacity or the apparent equiibrium constant for some sag woud not aways conform to Eq. (3). One of the reason may be that the interactions among sag components are not taken into consideration in the theoretica optica basicity determined arithmeticay. In the present work, the mass triange mode avoid the probem and provide a more convenient and accurate way for estimation. 4. Concusions O4 3 Dephosphorization is a very important process in steemaking. To gain a better understanding of phosphate capacities of moten sags, it is necessary to make modeing according to the imited experimenta data. Due to insufficiency of the phosphate capacity mode, mass triange mode was empoyed in this work. Tabe 5. Comparison of cacuated resuts for various systems at 1600 by optica basicity and present work System CaOMgO FeOx CaOMgO FeOx CaONa 2 OMgO FeO CaONa 2 OMgO FeO Exp. vaue Optica basicity Mass triange cacuated deviation cacuated deviation % % % % % % % % CaOMgO FeO x Na 2 OA % % Mass triange mode coud sove the probem of muticomponent systems by two ways. One is to make a pseudo ternary system and the other is cacuated the target point directy. Appication to three systems containing as much as seven components was made by both methods. The cacuated contour ines reveaed the reasonabe trend as experimenta resuts, and cacuation resuts for fixed compositions are very cose to the experimenta data within a ow error rate. Scattered points cacuation obtained a pretty ow deviation. Thus, the resuts have proved a good reiabiity and fexibiity of the mass triange mode. Since this mode can aso evauate other properties of sag, this mode might open a door to understand various properties of muticomponent sags accuratey. Acknowedgement The authors are gratefu for the financia support for this work from Nationa Nature Science Foundation of China (No , ), China ostdoctora Science Foundation (2014M560046), and Beijing Higher Education Young Eite Teacher roject (YET0349), as we as the Fundamenta Research Funds for the Centra Universities (FRFT15052A3). References [1] R. Inoue and H. Suito:Trans.ISIJ., 25 (2) (1985) [2] K. Ito, M. Yanagisawa and N. Sano:TetsutoHagane, 68 (2) (1982) [3] M. Muraki, H. Fukushima and Sano N:Tetsuto Hagane, 71 (6) (1985) [4] J. Im, K. Morita and N. Sano:ISIJ Inter., 36 (5) (1996) [5] K. Ito and N. Sano:TetsutoHagane, 69 (15) (1983) [6] W. H. Van Niekerk and R. J.Dippenaar:Meta. Mater. Trans. B, 29 (1) (1998) [7] H. Suito and R. Inoue:Trans. ISIJ., 22 (11) (1982) [8] R. Simeonov and N. Sano:Trans. ISIJ., 25 (10) (1985) [9] J. J. ak and R. J.Fruehan:Meta. Trans. B, 22 (1) (1991) [10] K. Kunisada and H. Iwai:Trans. ISIJ., 27 (4) (1987) [11] H.Suito and R.Inoue:Trans ISIJ., 21 (4) (1981) [12] G. Li, T. Hamano and F.Tsukihashi:ISIJ Inter., 45 (1) (2005) [13] G. W. Heay: J Iron Stee Inst., 208 (7) (1970) [14] H. Suito and R.Inoue:Trans ISIJ., 24 (1) (1984) [15] E. T. Turkdogan and J. earson:jiron Stee Inst., 175 (1953) 398. [16] T. Mori: Bu. JapanInst. Metas., 23 (1984) [17] K. C. Chou:CALHAD, 19 (1995) [18] L. J. Wang, S. L. Chen, K. C. Chou and Y. A. Chang. Computer Couping of hase Diagrams and Thermochemistry, 29 (2) (2005) 149.

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