Thermodynamics of Sulfur in Carbon Saturated Liquid Ferro-alloys Containing Ni, Mo and V at K

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1 IIJ Intenational, Vol. 58 (08, IIJ Intenational, No. 3 Vol. 58 (08, No. 3, pp Themodynamics of ulfu in Cabon atuated Liquid Feo-alloys Containing Ni, Mo and V at 873 K Do-Hyeong KIM, eung-yeon WON, Joon-uk HAN and Hong-ik NAM and Jong-Jin PAK * Depatment of Mateials Engineeing, Hanyang Univesity ERICA, Ansan, Koea. Hyundai teel Co., Dangjin, Koea. (Received on August 5, 07; accepted on Novembe 6, 07; J-TAGE Advance published date: Januay 3, 08 The spent catalysts discaded fom the petoleum efiney opeations contain a substantial amount of valued metals such as Ni, Mo and V togethe with high sulfu content. Recently, the smelting eduction pocess of this esouce using the cabothemic eaction is being developed and commecialized to ecove these metals in the fom of cabon satuated feo-alloys containing Ni, Mo and V. ulfu can be picked up into alloy melts fom the sulfu beaing spent catalysts duing the smelting pocess. Theefoe, themodynamics of sulfu in these alloy melts is vey impotant fo poducing low sulfu feo-alloys. In the pesent study, themodynamic inteactions between those alloying elements and sulfu in liquid ion was studied using the slag/metal equilibation technique at 873 K. The equilibium sulfu distibution was measued between a slag with a known sulfide capacity and cabon satuated liquid Fe V Ni Mo alloys of vaious compositions. The cabon solubility in liquid alloy was significantly changed with alloy composition. The specific effects of V, Ni and Mo on sulfu was detemined by consideing the effect of cabon on sulfu using Wagne s fomalism as the fist- and second-ode inteaction paametes as well as the second-ode coss-poduct tems. KEY WORD: sulfu; vanadium; nickel; molybdenum; feo-alloy; spent catalysts.. Intoduction olid spent catalysts fom the hydopocessing units of petoleum efining industies ae alumina based mateial and contain metallic constituents of Ni, Mo and V up to 30 mass% in the fom of oxides and sulfides with high sulfu content up to 5 mass%. These spent catalysts could be used as a cheap souce fo valuable metals. eveal industial scale wet pocesses such as oasting with soda salts, acid leaching and ammonia neutalization have been developed fo the ecovey of these metals., Howeve, the oasting pocess fo sulfu emoval by oxidation fom the catalysts and the leaching pocesses poduce unattactive by-poducts such as toxic gases, waste wate containing stong acids, bases and chloine etc. which equie a high level of envionmental pecautions and costs. Theefoe, ecently the pyo-metallugical pocess such as an electic ac funace smelting eduction of spent catalysts have been developed because of its supeioity in envionmental issues and cost-effectiveness. Alumina in the catalysts can be fluxed with lime to fom liquid slags and metallic oxides and sulfides can be ecoveed in the fom of feo-alloys by the cabothemic eaction. The slag can be used as cement o landfills, and the feo-alloys can be used extensively in the steel industy. * Coesponding autho: jjpak@hanyang.ac.k DOI: In this pocess, one of the main issues is how to keep the sulfu in the slag as much as possible and obtain low sulfu feo-alloys duing the smelting eduction. Theefoe, themodynamic infomation of sulfu in cabon satuated feoalloys of high Ni, Mo and V contents is vey impotant. In the pesent study, the sulfu distibution atio between a CaO Al O 3 slag of known sulfide capacity and cabon satuated Fe V, Fe Ni, Fe Mo, Fe V Ni, Fe Mo Ni and Fe V Ni Mo alloy melts was measued at 873 K. The cabon solubility in liquid alloy was also detemined as a function of alloy composition. Using the Wagne s inteaction paamete fomalism (WIPF, the specific effects of V, Ni and Mo on sulfu was detemined as the fist- and second-ode inteaction paametes as well as the secondode coss-poduct tems of two diffeent alloying elements. Using themodynamic paametes detemined in the pesent study, the sulfu distibution between a smelting slag and feo-alloy melt of vaious compositions can be pedicted to find out the optimum opeational conditions such as slag composition and toleable sulfu content in spent catalysts fo poducing low sulfu feo-alloys.. Expeimental The slag-metal equilibation expeiments wee caied out to measue the sulfu distibution atio between a CaO Al O 3 slag and cabon satuated liquid ion alloy melts containing V, Ni and Mo using an electic esistance funace 08 IIJ 408

2 IIJ Intenational, Vol. 58 (08, No. 3 heated by supe kanthal (Moi with an alumina eaction tube (OD: 70 mm, ID: 63 mm, H: 00 mm at 873 K as shown in Fig.. The eaction tempeatue was measued by a Pt/Pt-3%Rh themocouple potected with an alumina tube at the bottom of the cucible, and it was contolled within ± K using a PID contolle. The tempeatue eading of the themocouple was coected by measuing the tempeatue inside the cucible using a sepaate themocouple pio to expeiments. Two slag compositions of CaO Al O 3 (C/A=40/60 and 50/50 in mass% slags containing vaious sulfu content up to Ca satuation was pepaed by melting the eagent gade CaO, Al O 3 and Ca in a gaphite cucible using a high fequency induction funace. It was cast onto a steel plate, cushed into powde, and stoed in a desiccato until use. The maste alloys of Fe-30mass%V-mass%C-, Fe- 30mass%Mo-mass%C- and Fe-40%Ni-mass%C- wee pepaed by melting high puity electolytic ion, metallic vanadium (99.9% puity, metallic molybdenum (99.95% puity, metallic nickel (99.99% puity, Fe (99.99% puity and high puity gaphite powde in a high puity alumina cucible in an A-0%H atmosphee using a high fequency induction funace. Desied potions of maste alloys wee chaged to make an aimed melt composition fo each expeiment. Two gams of slag containing 0.3 to.5 mass% and six gams of alloys containing 0 to 0. mass% wee placed in the hole of a gaphite cucible. The gaphite cucible was tied up by Mo wie and placed in the hot zone of the funace fo 0 hous. The initial sulfu contents in slag samples wee high o low with espect to the sulfu content in equilibium with metal, and the sulfu was allowed to tansfe fom slag to metal o vice vesa. The oxygen potential was contolled by the C CO equilibium, and the CO gas was passed though the silica gel and magnesium pechloate (Mg(ClO 4 to emove moistue, ascaite to emove CO, and then blown into the eaction tube at a flow of 300 ml/min contolled by a mass flow contolle. Afte each expeiment, the cucible was pulled out of the funace and quenched apidly by a helium gas blowing. The slag and metal samples wee analyzed fo Ca, Al, V, Ni and Mo by the ICP-AE analyze (ARCO, PECTRO. ulfu and cabon contents wee analyzed by the C/ analyze (C-800, ELTRA. The sulfu content in metal samples was measued with an accuacy of ± mass ppm using the standad sample of steel containing 7 ± mass ppm sulfu. 3. Results and Discussion 3.. Themodynamic Consideations The sulfu distibution atio between a slag and liquid ion alloys at equilibium is defined as % L... ( % whee (% and [%] ae the equilibium sulfu content in mass% in slag and metal, espectively, and the sulfu distibution atio depends on the oxygen patial pessue and the themodynamic popeties of sulfu in slag and metal. The desulfuizing powe of a slag can be nomalized by the sulfide capacity defined by: 5 PO C % /... ( / P whee P O is the oxygen patial pessue at the slag-metal inteface, and P is the patial pessue of sulfu gas in equilibium with sulfu in liquid ion which can be calculated fom the themochemical data fo sulfu in the liquid ion. g... (3 6 G TJ / mol f % K 3 P /... (4 whee f is the Henian activity coefficient of sulfu in mass% standad state in liquid ion. Using Wagne s fomalism, 7 the activity coefficient of sulfu in Fe C V Ni Mo alloy melt can be expessed as the following elation using the inteaction paametes: Fig.. A schematic diagam of the expeimental appaatus. logf e % e % C % C C C i e i % i i % i VNiMo,, % i% j VNiMo,, i j... (5 whee e is the fist-ode self inteaction paamete of sulfu in liquid ion, e i and i ae the fist- and second-ode inteaction paametes of elements on sulfu in liquid ion, espectively, is the second-ode coss-poduct paamete on sulfu in liquid ion which indicates the simultaneous effect of two diffeent alloying elements (i and j on the activity coefficient of sulfu in liquid ion IIJ

3 IIJ Intenational, Vol. 58 (08, No. 3 Ishii and Fuwa 8 detemined the value of e as 0/ T+0.08 in Fe melt using the gas-metal equilibation technique at K. Ban-ya and Chipman detemined e C and C values at K in Fe C alloys containing cabon fom 0.44 mass% to 5.6 mass% (cabon satuation at 93 K as 0.4 and , espectively, using the gas-metal equilibation technique. 9 Thei data ae the ecommended values of the Japan ociety fo Pomotion of cience (JP. 0 Theefoe, the sulfide capacity of a slag, C can be obtained fom the expeimentally measued sulfu distibution between a slag and Fe-C sat - melt unde a contolled oxygen patial pessue. Convesely, fo a given slag composition with a known sulfide capacity, the values of f in Fe-C sat -i- melts (i=v, Ni and Mo can be obtained fom the L values measued fo these alloy melts. logc logl log PO logk log f... (6 3 whee the patial pessue of oxygen, P O in equilibium with cabon (a C = and CO at atm can be obtained fom Eq. (7. Cg O g COg... (7 6 G T J / mol ulfide Capacity of CaO Al O 3 lag The equilibium sulfu distibution, L between the CaO Al O 3 slags and Fe-C sat. - melt was measued at 873 K as summaized in Table. The L values wee obtained by appoaching the sulfu equilibium by tansfe of sulfu fom slag to metal and metal to slag, and they agee well with each othe. Theefoe, the sulfide capacity of a slag can be calculated fom Eqs. ( though (7 assuming that the C CO eaction (a C =, P CO = atm contols the oxygen patial pessue in the system. The f value in Fe-C sat - melt at 873 K can be calculated by Eq. (5 using the ecommended values of e, e C and C in JP 0 as discussed in the peceding section. In the pesent study, sulfu content in slag was vaied fom 0.75 mass% up to Ca satuation values of.50 and.0 mass% fo two diffeent slag compositions as shown in Table. The Ca solubility in liquid CaO Al O 3 slags was sepaately measued by contacting sinteed Ca pellets with liquid slags in a gaphite cucible as shown in Fig.. Figue 3 shows the logc values of CaO Al O 3 slags detemined in the pesent study togethe with the data epoted by othe wokes as a function of slag composition in CaO Al O 3 system at 873 K. eveal authos detemined the C values fo CaO Al O 3 slag system by diffeent expeimental techniques., Banya et al. detemined the sulfide capacity of CaO Al O 3 slag by the gas-slag equilibation technique using a CO CO O A gas mixtue unde the oxygen patial pessues contolled by CO CO gas mixtue at 873 K. They kept sulfu content in slag below 0.8 mass% in ode to avoid Ca fomation which could significantly affect the sulfide capacity of the slag. Oztuk and Tukdogan detemined the sulfide capacity of Ca satuated CaO Al O 3 slag fom the equilibium sulfu distibution between Fe Al O melts and the slag in contact with pue solid Ca unde A atmosphee at 873 K, assuming that the oxygen patial pessue was contolled by Al O deoxidation equilibium in liquid ion. As shown in Fig. 3, the C value inceased linealy with CaO content in slag, and the dissolved sulfu content in slag up to Ca satuation did not affect the sulfide capacity of the slag. The C values detemined by the slag/metal equilibation method using Fe-C sat. - melt in the pesent study ae in excellent ageement with those data detemined by diffeent expeimental techniques., This also confims that themodynamics of sulfu in Fe-C sat. - melt used in the pesent study is valid. 0 Fig.. ulfu solubility in Ca satuated CaO Al O 3 slags at 873 K. Table. Expeimental L data fo CaO Al O 3 slags and Fe-C sat.- alloys at 873 K. lag composition Melt composition (mass% [C] [] ( L logl 40%CaO-60%Al O %CaO-50%Al O : Ca satuation Fig. 3. ulfide capacity of CaO Al O 3 slag at 873 K. 08 IIJ 40

4 IIJ Intenational, Vol. 58 (08, No Themodynamics of ulfu in Fe-C sat -Ni-Mo-V Melts Using the sulfide capacity of 40%CaO-60%Al O 3 slag detemined in the peceding section, the effect of V, Ni and Mo on sulfu in Fe-C sat -i- (i=v, Ni, Mo melts can be detemined fom the sulfu distibution atios between the slag and those alloy melts unde CO atmosphee at 873 K. The expeimental esults ae summaized in Table, and the L values ae plotted as functions of V, Ni and Mo content in the melt in Fig. 4. ome expeiments wee caied out using a 40%CaO-60%Al O 3 slag satuated with solid Ca. In this case, the sulfu content in slag was assumed to be.50 mass% as detemined in the peceding section. The L values inceased linealy with inceasing Mo and V in the melt, but it deceased with Ni addition. The V, Ni and Mo contents in slag wee negligible, theefoe the effect of thei oxides on sulfide capacity was ignoed unde the pesent expeimental condition. The addition of V, Ni o Mo in liquid ion significantly affects the cabon solubility and cabon has a lage effect on sulfu in the melt as discussed in the peceding section. Figue 5 shows the vaiations of cabon solubility in alloy melts as a function of alloy content. Vanadium and molybdenum incease the cabon solubility significantly while nickel deceases it. The solid lines ae the calculated cabon solubility values using the paametes detemined in the autho s ecent study on cabon solubility in Fe V Ni Mo melts. 3 Theefoe, using the elation of Eqs. (5 and (6, the specific effect of an alloying element on sulfu in liquid ion can be obtained fom the L values measued fo Fe-C sat -i- (i =V, Ni, Mo melts with a 40%CaO-60%Al O 3 slag of the known sulfide capacity value detemined in the peceding section. Combining Eqs. (5 and (6 logf i e i % i i % i logl / log PO log K3 logc... (8 e % e % C % C C C i whee f is the inteaction coefficient of V, Ni and Mo on sulfu in liquid ion. Figue 6 shows the log f V values plotted vs. vanadium content in Fe-C sat -V- system using the elation expessed by Eq. (8 at 873 K. As shown in Fig. 4, the addition Table. Expeimental L data fo a 40%CaO-60%Al O 3 slag and Fe-C sat.-i- alloys at 873 K. ystem (Fe-C sat-i Fe-C sat-v Fe-C sat-ni Fe-C sat-mo : Ca satuation Melt composition (mass% [% i] [C] [] ( L logl Fig. 4. ulfu distibution between a 40%CaO-60%Al O 3 slag and Fe-C sat-i melts (i = V, Ni, Mo. Fig. 5. Cabon solubility in Fe V, Fe Ni and Fe Mo melts IIJ

5 IIJ Intenational, Vol. 58 (08, No. 3 Fig. 6. The elation of log f V vs. [%V] in liquid Fe V. Fig. 7. The elation of log f Ni vs. [%Ni] in liquid Fe Ni. of vanadium in Fe-C sat - melt appaently inceased the L value, and one might expect that vanadium in the melt incease the activity coefficient of sulfu in the melt. Howeve, when the effect of the cabon solubility incease with vanadium addition was consideed, the specific effect of vanadium actually deceased the activity coefficient of sulfu in the melt. The fist-ode inteaction paamete of vanadium on sulfu in Fe V system, e V, can be detemined as 0.09±0.00 by the egession analysis of data, and thee ae no significant second-ode effect of vanadium on sulfu up to 9 mass% V. Banya and Chipman 3 and Ishii et al. 4 detemined the effect of V on sulfu in liquid Fe V alloy by the gas-metal equilibation technique using H H gas mixtue, and epoted the e V values as 0.06 and 0.09 at 83 K, espectively. Examining thei data up to 5 mass% V and the data detemined in the pesent study, the V e value in liquid Fe V alloy containing vanadium up to 30 mass% can be detemined as 0.09 in the tempeatue ange fom 83 to 873 K. Using the same method, the inteaction coefficients of Ni and Mo on sulfu in liquid ion wee detemined fom the L values fo Fe-C sat -Ni and Fe-C sat -Mo alloy melts as shown in Figs. 7 and 8, espectively. The specific effect of nickel on sulfu was negligible up to 37 mass% Ni in Ni Fe-C sat -Ni- melt, and the value of e was detemined as 0± at 873 K. Banya and Chipman 3 and Ishii et al. 4 Ni also detemined the e values in Fe Ni system by the gas-metal equilibation technique as and 0, espectively, at 83 K. Examining the data shown in Fig. 7, the e Ni value in liquid Fe Ni alloy can be detemined as 0 within expeimental eos in the tempeatue ange of K. Figue 8 shows the inteaction coefficients of Mo on sulfu in liquid ion detemined in the pesent study at 873 K and compaes with the pevious esults detemined by the gas-metal equilibation technique at 83 K. 3,4 Mo The value of e can be detemined as ± at 873 K fom the pesent expeimental data up to 5 mass% Mo by the egession analysis. Thee is no second-ode effect of molybdenum on sulfu. The pesent expeimental data shows an excellent ageement with Ishii et al. data at 83 K. In ode to detemine the simultaneous effect of diffeent alloying elements on sulfu in multi-component Fe-C sat - Fig. 8. The elation of log f Mo vs. [%Mo] in liquid Fe Mo. Table 3. Expeimental L data fo a 40%CaO-60%Al O 3 slag and Fe-C sat.-v-ni-mo- alloys at 873 K. ystem (Fe-C sat-i-j-k Fe-C sat-v-ni Fe-C sat-mo-ni Fe-C sat-v-ni-mo Melt composition (mass% [V] [Ni] [Mo] [C] [] ( Ni-Mo-V alloy melts, the sulfu distibution between a 40%CaO-60%Al O 3 slag and Fe-C sat -V-Ni, Fe-C sat -Mo-Ni and Fe-C sat -V-Ni-Mo melts of vaious compositions was measued at 873 K as summaized in Table 3. In peliminay expeiments, the simultaneous additions of Mo and V inceased significantly the L value between a slag and cabon satuated alloy melts and esulted in extemely low L logl IIJ 4

6 IIJ Intenational, Vol. 58 (08, No. 3 sulfu content in metal sample. This could cause some eos in detemining sulfu content in metal samples. Theefoe, nickel was added in all expeiments since it deceased the L values as shown in Fig. 4. Using the elations shown in Eqs. (5 and (6, the secondode coss-poduct paametes on sulfu in liquid ion, can be detemined fom the expeimental esults as shown in Fig. 9. Fo Fe-C sat -V-Ni and Fe-C sat -Mo-Ni melts, it was noted that the coss-poduct effect of pai alloying elements of V Ni and Mo Ni on sulfu was negligible, and theefoe Ni, M o the values of and wee all detemined as 0 at 873 K. Then these values wee used to detemine the value as ± at 873 K fom the sulfu distibution data fo Fe-C sat -V-Ni-Mo melts as shown in Fig. 9(c. Table 4 summaizes the inteaction paametes detemined in the pesent study as well as in othe studies. 3,4 Theefoe, the sulfu distibution between a slag and multicomponent ion alloy melts of Fe-C sat -V-Ni-Mo can be pedicted fom the sulfide capacity of slag and the inteaction paametes of alloying elements on sulfu detemined in the pesent study. Combining Eqs. (5 and (6, logl C PO K e e C C C log log log % % % C Table 4. Inteaction paametes of V, Ni and Mo on in liquid ion alloys. Inteaction paametes e V e Ni e Mo i VNiM,, o i i VNiMo,, i j ( e % i % i % i % j Value... (9 Tempeatue (K Conc. Range [mass%] Ref ± V : 9 Pesent V : V : Ni : 37 Pesent Ni : Ni : ± Mo : 5 Pesent Mo : Mo : 0 3 V V : 9 Pesent Ni Ni : 37 Pesent Mo Mo : 5 Pesent Ni, Mo V : 8 Ni : 9 V : 8 Mo : 9 Ni : 9 Mo : 9 Pesent Pesent Pesent Table 5. A typical composition of spent petoleum catalyst. V Ni Mo Al O < 5 Fig. 9. Relation of Eq. (5 to detemine the value of (a, (b Mo, Ni and (c N in liquid ion. Fig. 0. Vaiation of final sulfu content in Fe-5%V-8%Ni- 5%Mo-8%C melt vs. initial (% in spent catalyst fo diffeent slag compositions at 873 K IIJ

7 IIJ Intenational, Vol. 58 (08, No. 3 Using themodynamic paametes detemined in the pesent study, a simple mateial balance calculation can be made to pedict the sulfu content in a feo-alloy melt poduced by the smelting eduction of spent petoleum catalysts. A typical composition of spent catalyst is shown in Table 5. Ion and cabon souces and lime can be added to poduce a feo-alloy of Fe-5%V-8%Ni-5%Mo-8%C and CaO Al O 3 slags of vaious compositions (C/A = 35/65 ~ 50/50. Figue 0 shows the vaiation of final sulfu content in a feo-alloy as a function of initial sulfu content in the spent catalyst fo diffeent slag compositions. Theefoe, the optimum opeational paametes such as slag/metal atio, slag composition and a toleable sulfu content in spent catalysts can be decided to poduce low sulfu feo-alloys by the smelting eduction pocess. 4. Conclusions The inteaction paametes of alloying elements on sulfu in liquid Fe-C sat -V-Ni-Mo alloys have been detemined fom the equilibium sulfu distibution between a CaO Al O 3 slag and liquid ion alloys of cabon satuated Fe, Fe V, Fe Ni, Fe Mo, Fe V Ni, Fe Mo Ni and Fe V Ni Mo melts unde CO atmosphee at 873 K. These paametes could be used to pedict the sulfu distibution between a slag and feo-alloys poduced by the smelting eduction pocess of spent catalysts. The main finding of this study can be summaized as follows. ( The fist and second-ode inteaction paametes of vanadium, nickel and molybdenum on sulfu in liquid Fe V, Fe Ni and Fe Mo melts at 873 K can be expessed as: ( The second-ode coss-poduct paametes on sulfu in liquid Fe V Ni Mo melts at 873 K can be expessed as: Ni, Mo 0 ( V 8%, Ni 9% ( V 8%, Mo 9% 0 ( Ni 9%, Mo 9% Acknowledgment This study was suppoted by the R&D Cente fo Valuable Recycling (Global-Top Envionmental Technology Development Pogam funded by the Ministy of Envionment (Poject No.: REFERENCE M. Maafi and A. tanislaus: Resou. Consev. Recycl., 5 (008, 859. M. Maafi and A. tanislaus: Resou. Consev. Recycl., 53 (008,. 3. BanYa and J. Chipman: Tans. TM-AIME, 45 (969, F. Ishii and T. Fuwa: Tetsu-to-Hagané, 67 (98, C. Finchem and F. D. Richadson: J. Ion teel Inst., 78 (954, 4. 6 E. T. Tukdogan: Physical Chemisty of High Tempeatue Technology, Academic Pess, New Yok, (980, 8. 7 C. Wagne: Themodynamics of Alloys, Addison-Wesley Pess, Cambidge, MA, (95, F. Ishii and T. Fuwa: Tetsu-to-Hagané, 67 (98, BanYa and J. Chipman: Tans. TM-AIME, 4 (968, The 9th Committee on teelmaking, The Japan ociety fo Pomotion of cience: Themodynamic Data foteelmaking, Tohoku Univesity Pess, endai, (00, 78.. Banya, M. Hobo, T. Kaji, T. Itoh and M. Hino: IIJ Int., 44 (004, 80. E. B. Oztuk and E. T. Tukdogan: Met. ci., 8 (984, D. H. Kim, M. K. Paek, T. J. Kim,. Y. Won and J. J. Pak: Mate. Tans., 55 (04, 60. e e e V Ni Mo 0. 09, 0 ( V 9% V 0, 0 ( Ni 37% Ni , Mo 0 ( Mo 5% 08 IIJ 44