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CHEMICAL PROBLEMS 2019 no. 4 (17) ISSN 2221-8688 551
UDC 66.099.2: 552.52
NONEQUILIBRIUM THERMODYNAMICS OF OXIDATIVE RECOVERY REACTIONS VANADIUM CONTAINING TITANOMAGNETITE CONCENTRATES
U.N. Sharifova1, A.M. Qasimova1, A.N. Mammadov1'2
1Nagiyev Institute of Catalysis and Inorganic Chemistry ANAS
H.Javidave.,113, AZ 1143, Baku
2
Azerbaijan Technical University H. JavidAve. 25, AZ-1073 Baku e-mail:asif.mammadov.4 7@mail.ru Received 12.10.2019
Abstract: Non-equilibrium and equilibrium thermodynamic conditions of direct reduction of magnetite to free iron and oxidation of vanadium (3) to vanadium (5) in granules fluxed by soda vanadist titanomagnetite concentrates using a mixture of natural gas and hydrogen were determined. To determine temperature dependences of Gibbs free energy of redox reactions, the Temkin-Schwartsman equation was modified with due regard for the Gibbs free energy of formation of magnetite-based substitution solid solutions and the vapor pressure of the components in the flow system where the mixture of methane and hydrogen is continuously fed while gaseous reaction products are removed . 3D modeling of the Gibbs free energy difference of reactions proceeding under equilibrium and non-equilibrium conditions was carried out. On the basis of the free energy of the system deviation from the equilibrium state, it revealed that the greatest effect of reducing the temperature of redox reactions is observed in terms of low values of the reaction products pressure As a result of the thermodynamic analysis, the temperature range of950-970K was chosen to produce metallic iron and sodium vanadate. Keywords: thermodynamics, equilibrium and non-equilibrium reactions, titanomagnetite, iron, vanadium.
DOI: 10.32737/2221-8688-2019-4-551-557
Introduction
Owing to the depletion of rich magnetite ore reserves, the research has been developed on technology of titanium ore processing to produce iron, titanium, chromium and vanadium [1-4]. To determine optimal conditions of oxidation-reduction reactions, thermodynamic calculations are widely used [5-8]. In [5], thermodynamic calculations and experiments showed principal possibility of one-stage processing of ilmenite concentrate for obtaining artificial rutile of commercial quality. In the works [6-8], natural gas was used as a reducing agent in the course of processing of titanium-magnetite concentrates fluxed with soda. In particular, in [6-8], on the basis of the physicochemical theory of granulation in a drum apparatus in line with thermodynamic-kinetic analysis, it was found that the reduction reactions of titanium-
magnetite concentrates with natural gas to produce iron powder proceed in the kinetically-diffusion region and are conjugate: in the reactions of reduction of CO and H2 -inductors, and CH4 - acceptor.
In [8], the equilibrium thermodynamic conditions for the direct reduction of magnetite to free iron and the oxidation of vanadium oxide (3) to vanadium oxide (4) and vanadium oxide (5) in granules with fluxed soda vanadium titanomagnetite concentrates were determined. The purpose of this work is to determine and model non-equilibrium thermodynamic conditions for the reduction of
3+
magnetite to iron and the oxidation of V to and V5+ in titanium-magnetite concentrates using a mixture of natural gas and hydrogen. Note that a subject of the study are titanomagnetite concentrates, in which the
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CHEMICAL PROBLEMS 2019 no. 4 (17)
content of the target components is as follows: Fe(total)- 51-54 mass. %, TiO2 - mass. 5-7% and 1-1.5 mass% V2O5 and V2O3. Thermodynamic equations of oxidative
reduction reactions. The total oxidation reaction of vanadium oxide (3) to vanadium (5) and the reduction of magnetite to iron has the following form:
3Fe3O4(s)+V2O3(s)+2CH4(g)+2H2(g)+Na2CO3(/)=
9Fe(s)+2NaVO3(/)+3CO2(g)+6H2O(g) (1 )
Titanium dioxide TiO2, not involved in the redox process, is not included in the reaction equation. To determine the temperature dependences of the Gibbs free energy of the reaction (1) in the temperature range 900-
AGr = Af/°M - A52V - T(Aa [in ( ^ ) -
1200K, Temkin-Schwartsman equation [9] was used with due regard for thermodynamic functions of the formation of solid solutions and the vapor pressure values of gaseous components: 298 \ —■-i) +
(I 2932
1 ' 2 T
+
T 2 298 v 6 3T
29S2 T~2 298-1 293~2
-) +Ac(--h-+-)
2 V 2 -T 2 J
RT[xhif(_x) + (1 - je) lrt(l - x)] + RT I] vt biPl
(2)
Equation (2) allows for the temperature dependence of the specific heat in the form as follows:
Cr, = a + bT + c*T2 + cT~
i^:: Aj-'ir-free energies, standard enthalpies and entropies of the reaction (1); vi - stoichiometric coefficients; Pi-partial pressures of components in a non-equilibrium state (reaction proceeds in the reactor under the flow regime of the gas mixture).
FT[xlnf{x) + {l- jc)ln(l-i)]-is the
free energy of formation of solid solutions due
3+
to the replacement of ions V in the crystal
cell Fe3O4 of ions Fe
3+
solid
solutions
,
formation of xFe20A -+- (1 - x~)V203
n- the total number of unlike cations in the solid solution;
The last term vilnPiof equation (2) allows for the deviation from the standard state. Therefore, the following equation presents the temperature dependence of the standard Gibbs free energy in the equilibrium as follows:
AGr — A ^293 —
accompanied by the
T \ 298
298/
\ (T 298
LJ + ¿¿[--f
V2
2T
-298 +
T2 29S3
AC* (—+-
v 6 3T
29S2 T~2 298"1 298~2
-) +Ac(--h-+-)
2 V 2 -T 2 J
(3)
Thermodynamic parameters of simple reactions arise from [10]. The following values substances and compounds involved in the were used in the calculations: A/ZjmO^ 0a) = -1218.7+2.5 kJ/mol; AH^tiaVO^-l 148.6+2.5; Aii^3(Fe304)=-
1117.2+2.5; Ai/2°53(JVa2C03}=-l 129.4+2.5; UI^CH^-IA 8+0 5; Aii2t>,3(CO:!)=-393.5+0.5;
AH°93(H20,gas)=-24\.8+0.5, S%B(y20J) = 9Q.32±l.5 J/(mol.K); S%3(NaV0^=99.98+1.5; 52093(^e3O4)=146.21+2.5; S°b(№i2CO^)=134.97+2; S°H (£7/*)= 18 6.19+2.5;
5i93(C02)=213.6+0.5; 5^B(H2Q>ra3)=l88.74+2.5, 5°93(H2)=130.61+1.5, 5^3(Fe)=27.15+0.5, = 103.2+0.5J/(mol.K); C %s(NaV03)= 97.6+0.5; C^3(Fe304>150.8+1.0; c£M(JtfazCOa)=l 12.3+1.5; c£,3(ctf4)=35.8+0.5; C^3(COZ)=37.1+0.5;
C^3(H20,ra3)=33.6+0.5, C^3(H2)=28.8+0.5,C^3(Fe)=25.2+0.5.
In this temperature range the sodium carbonate and sodium metavanadate melt as follows: Tm(Na2CO3)=1137K,
Tm(NaVO3)=963 K. Therefore, when determining the temperature dependence of the Gibbs free energy of the reaction (1) by
equation (2, 3), the enthalpy and entropy of melting of these compounds were used: AHm(Na2CO3)=28080 J/mol, AHm(NaVO3)=28310 J/mol, ASm(Na2CO3)=24.77 J/(mol.K), ASm(NaVO3)=31.38 J/(mol.K).
Results and discussion
Figure 1 presents the results of calculations using equations (2 and 3).
Fig. 1. Temperature dependences of the Gibbs energy of the reaction (1): 1- in the flow mode of the gas mixture (non-equilibrium state, Eq. 2); 2-equilibrium state (Eq. 3).
Fig. 1 shows the temperature dependences equation 2). In the reactor, where methane and
of the Gibbs free energies of the reaction (1) hydrogen are continuously supplied, the
for both the equilibrium state (line 2, gaseous reaction products are removed, so for
calculation by equation 3) and the non- the Gibbs free energy we can write: equilibrium state (line 1, calculation by
AG*/RT = (AGT - AG°)/RT = 2™ InP* (4)
where AG*in (4) is a measure of the system equilibrium state where gase°m products are
deviation from the equilibrium state. In terms of the equilibrium standard state, the total vapor pressure P.1'1 is equal to 1 atm. In a non-
removed, this value decreases. In particular, in the reaction (1) in the non-equilibrium state, the quantity P^P^o/Pcii,, Pj^ varies from 0.1
(dependence 1 in Fig. 1) to 1 atm. (dependence
2 in Fig. 1). From Fig. 1 it follows that the reaction 1 in the equilibrium state is directed towards the products starting from 1000 K, and under total pressure of 0.1 atm — starting from 900 K.
To identify the nature of dependence on the deviation from the equilibrium state, 3D
modeling of the dependence AG* (Eq. 4) on the total ratio of partial pressures in the flow-through mode of reducing iron and vanadium with a mixture of methane and hydrogen (Fig. 2) was carried out. For 3D modeling of the AG*, an analytical method was used and tested in [11-13].
Fig. 2. 3D model of dependence AG* (Eq. 4) on the total ratio of partial pressures in the flow mode of methane and hydrogen mixture in the reaction of iron reduction and vanadium oxidation.
350 1000 1 050 1100 1150 1 200 1250 1 300 1 350 14D0
t,k
Fig. 3. Temperature dependences of the Gibbs free energies of reactions (5 and 6) at temperature in the equilibrium state (lines 5, 6, calculation by Eq.3) and non-equilibrium state (lines 5/r, 6/r, calculation by Eq. 2).
In the work [8], for the oxidation of vanadium magnetite, only methane was used: oxide (3) to vanadium (5) and the reduction of
4Fe3O4(s)+V2O3(s)+CH4(g)+Na2CO3(s,/)=
12FeO(s)+2NaVO3(s,/)+2CO(g)+2H2O(g) (5)
Fe3O4(s)+V2O3(s)+CH4(g)+Na2CO3(/)= 3Fe(s)+2NaVO3(/)+2CO(g)+2H2O(g)
Temperature dependences of the Gibbs free energy for these reactions are shown in Fig. 3.
From Fig. 1 and 3 it follows that reactions 1, 5, 6 proceed at lower temperatures where gas products of the reaction are removed, and the reactions proceed under non-
(6)
equilibrium thermodynamic conditions. At the lowest temperature at 900 K, the reaction (1) begins. This is due to the fact that the redox gas phase in addition to methane still contains hydrogen.
Conclusion
In order to determine the equilibrium and non-equilibrium thermodynamic conditions of direct reduction of magnetite to free iron and
3 + 5 +
oxidation of V3 + to V5 + in granules of
vanadist titanomagnetite concentrates with the participation of natural gas, it is necessary to allow for free energies of the formation of solid solutions based on magnetite and the vapor pressure of the components in the flow system when methane is continuously supplied and gaseous reaction products are removed. The 3D model (Fig. 2) of the free energy of the system deviation from the equilibrium state depending on the total ratio of partial pressures in the flow mode of iron reduction and
Acknowledgements
This study was supported by SOCAR (project 12 LR AMEA)
References
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TdRKiBiNDd VANADiUM OLAN TiTANMAQNETiTKONSENTRATLARININ OKSiDLO^MO-REDUKSiYA REAKSiYALARININ QEYRi-TARAZLIQ TERMODiNAMiKASI
U.N. §arifova\ A.M. Qasimova1, A.N. Mammadov1'2
1 Akademik M.Nagiyev adina AMEA Kataliz vs Qeyri-uzvi Kimya institutu H.Cavidpr., 113, AZ 1143, Baki 2Azsrbaycan Texniki Universiteti H. Cavidpr. 25, AZ-1073 Baki e-mai/: asif.mammadov.47@mai/.ru
Tsbii qaz vs hydrogen qari§igindan istifads edsrsk soda s/avssi o/an vanadium tsrkib/i titanomaqnetit konsentratlarinin qranullarindaki magnetitin ssrbsst dsmirs reduksiyasinin vs vanadiumun (III)-dsn vanadium (V) qsdsr oksid/s§mssinin qeyri-tarazliq vs tarazliq termodinamik §srt/sri musyysn edilmi§dir. Redoks reaksiyalarinin Gibbs ssrbsst enerjisinin temperaturdan asililigini musyysn etmsk ugun Temkin-§vartsman tsn/iyi magnetit ssasli svszedici bsrk mshlullarin sms/sgs/mssinin Gibbs ssrbsst enerjisini vs axin sistemindski komponent/srin buxar tszyiqini nszsrs alaraq modifikasiya edilmi§dir. Proses zamani metan vs hydrogen qari§igi fasilssiz o/araq sistems daxi/ edi/ir vs qaz reaksiya mshsullari sistemdsn gixarilir. Tarazliq vs qeyri-tarazliq §sraitinds gedsn reaksiyalarin Gibbs ssrbsst enerji/srinin fsrqinin 3D mode//s§dirilmssi aparilmi§dir. Sistemin tarazliq vsziyystindsn ksnara gixmasinin ssrbsst enerjisi ssasinda, redoks reaksiyalarinin temperaturunun azaldilmasi reaksiya mshsullarinin tszyiq parametrinin gox kigik qiymst/sri bo/gssinds mu§ahids o/unur. Termodinamik ana/iz nsticssinds meta/ dsmir vs natrium vanadati almaq ugun 950-970K temperature interval segilmi§dir.
Agar sozlar: termodinamika, tarazliq vs qeyri-tarazliq reaksiyalari, titanomaqnetit, dsmir, vanadium.
НЕРАВНОВЕСНАЯ ТЕРМОДИНАМИКА ОКИСЛИТЕЛЬНО-ВОСТАНОВИТЕЛЬНЫХ РЕАКЦИЙ ВАНАДИЙСОДЕРЖАЩИХ ТИТАНОМАГНЕТИТОВЫХ КОНЦЕНТРАТОВ
У.Н. Шарифова1, А.М. Касимова1, А.Н. Мамедов1'2
1Институт Катализа и Неорганической химии им. М.Нагиева Национальной АН Азербайджана АЗ 1143, Баку пр. Г. Джавида, 113 2Азербайджанский Технический Университет А21073 Баку, пр.Г. Джавида, 25 e-mail:asif.mammadov.47@mail. ги
Определены неравновесные и равновесные термодинамические условия прямого восстановления магнетита до свободного железа и окисления ванадия (3) до ванадия (5) в гранулах ванадийсодержащих титаномагнетитовых концентратов, офлюсованных содой, с использованием смеси природного газа и водорода. Для определения температурных зависимостей свободной энергии Гиббса окислительно-восстановительных реакций было модифицировано уравнение Темкина-Шварцмана с учетом свободной энергии Гиббса образования твердых растворов замещения на основе магнетита и давления паров компонентов в проточной системе, когда смесь метана и водорода непрерывно подается, а газообразные продукты реакции удаляются. Проведено 3В моделирование разности свободных энергий Гиббса реакций, протекающих в равновесных и неравновесных условиях. На основании свободной энергии отклонения системы от равновесного состояния было выявлено, что наибольший эффект снижения температуры окислительно-восстановительных реакций наблюдается в области низких значений давления продуктов реакции. В результате термодинамического анализа был выбран температурный интервал 950-970 К для получения металлического железа и ванадата натрия.
Ключевые слова: термодинамика, равновесные и неравновесные реакции, титаномагнетит, железо, ванадий.
