Estimation of Thermodynamic Properties and Ionic Equilibria of Cobalt Chloride Solution at 298 K

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1 Materials Transactins, Vl., N. () pp. 117 t 11 # The Japan Institute f Metals Estimatin f Thermdynamic Prperties and Inic Equilibria f Cbalt Chlride Slutin at 98 K Man-seung Lee 1 and Yung-j Oh 1 Department f Advanced Materials Science & Engineering, Mkp Natinal University, Chnnam -79, Krea Metal Prcessing Research Center, Krea Institute f Science and Technlgy, P.O. Bx 11, Seul, , Krea We develped a chemical mdel t analyze inic equilibria in a cbalt chlride slutin at 98 K. The chemical mdel cnsisted f chemical equilibria, mass and charge balance equatins. The activity cefficients f slutes and water activity were calculated with Brmley equatin. Values f the equilibrium cnstants fr the frmatin f cbalt chlride cmplexes at zer inic strength and f the interactin parameters were estimated by applying Brmley equatin t the reprted equilibrium cnstants at different inic strength. The effect f and HCl cncentratins n the distributin f cbalt species was btained. The predicted ph values fr -HCl-NaOH-H O system agreed well with thse measured at 98 K. (Received January 1, ; Accepted February, ) Keywrds:, HCl, equilibrium cnstant, Brmley, ph 1. Intrductin Cbalt is a strategically imprtant metal as an allying element in superallys fr aircraft engines, magnetic allys, hard metal allys fr cutting tl and electrdepsited allys t prvide wear and crrsin-resistant metal catings. 1) In a hydrmetallurgical rute fr the prductin f cbalt, separatin f cbalt and nickel is ne f the mst difficult peratins wing t the similarities in chemical nature f the tw metals. Many studies have been perfrmed n the separatin f cbalt and nickel by emplying slvent extractin.,) Infrmatin f the distributin f cbalt and nickel species with the cmpsitin f a slutin is valuable in chsing an extractant suitable fr the separatin f cbalt and nickel. In rder t analyze the inic equilibria f the mixed slutin f and NiCl, inic equilibria f the respective slutins need t be develped. We reprted the inic equilibria analysis f NiCl slutin. ) Few studies, hwever, have been reprted n the equilibria f cbalt chlride slutin at high inic strength. In this study, inic equilibria fr the in chlride slutin were analyzed by cnsidering chemical equilibria, mass and charge balance equatins. Thermdynamic prperties, such as equilibrium cnstants fr the frmatin f cbalt chlride cmplexes at zer inic strength and interactin parameter, were estimated by applying Brmley equatin t the reprted equilibrium cnstant at different inic strength. The activity cefficient f chemical species was als calculated with Brmley equatin. ) The validity f the inic equilibria fr the -HCl-NaOH-H O system at 98 K was verified by cmparing the measured values f slutin ph with thse calculated in this study.. Experimental Cbalt chlride slutins with different cmpsitin were prepared by disslving 6H O, HCl and NaOH in distilled water. All chemicals were f reagent grade. First, knwn amunts f 6H O, HCl and NaOH were added t g f distilled water and then the mixture was stirred with a magnetic stirrer until all the chemicals were disslved. After all the chemicals were disslved, the temperature f slutin was cntrlled at 98 K by using a water bath. Once the temperature f the slutin was stable, a ph f slutin was measured with a ph meter (Orin 9A).. Results and Discussin.1 Estimatin f the equilibrium cnstant In chlride slutin, cbalt in frms varius cmplexes with chlride and hydrxide in and the cmplex frmatin reactin can be represented by C þ þ icl i ¼ CCl i ð1þ The equilibrium cnstant fr eq. (1) at a given inic strength, K I i, is related t the equilibrium cnstant at zer inic strength, K i, and t the activity cefficient rati as fllws Ki ¼ Ki I CCl i i C þð Cl Þ i ðþ By taking lgarithm n bth sides f the abve equatin, it is rearranged as lg Ki I ¼ lg Ki þ lg C þ þ i lg Cl lg CCl i ðþ i The activity cefficient f slute was calculated by the Brmley equatin. The Brmley equatin fr the activity cefficient f the catin, M, is represented by the fllwing equatins. ) lg M ¼ :18ðz MÞ I : 1 þ I : þ F M ¼ Aðz M Þ þ F M ðþ F M ¼ X X ð:6 þ :6B MX Þjz M z X j 6 1 þ 1: þ B MX 7 jz M z X j I

2 118 M. Lee and Y. Oh ðjz Mjþjz X jþ ½XŠ ðþ In the abve equatins, z is inic charge and I inic strength f slutin and B MX the interactin parameter between catin M and anin X. Substitutin f the expressin fr the activity cefficient f each species int eq. () gives lg Ki I ¼ lg Ki þði iþa ð6þ þ F C þ þ if Cl F CCl i Table 1 represents the equilibrium cnstants fr the frmatin f cbalt chlride cmplexes at different HClO cncentratin. 6) The cncentratins f C þ, Cl and i i are negligible cmpared t the HClO cncentratin in these studies. 7,8) Hence, F term fr the activity cefficient Table 1 Reprted values fr the lgarithm f equilibrium cnstant at a series f inic strength with HClO as the inert salt at 98 K. Reactin lg K I lg K I lg K I lg K I lg K I (I ¼ ) (I ¼ 7) (I ¼ 8) (I ¼ 9) (I ¼ 1) C þ +Cl = CCl þ C þ +Cl = :6 : C þ +Cl = CCl 1: : C þ +Cl = CCl :9. 1. f the anin is related nly t the catin H þ f the inic medium, while F term fr the activity cefficient f catin is related t the anin ClO f the inic medium. 7,8) In this case, F terms fr C þ,cl and CCl þ culd be represented by F C þ ¼ ð:6 þ :6B C þ,clo Þ 6 1 þ 1: þ B C þ,clo 7 I ½ClO Š ð7þ F Cl ¼ ð:6 þ :6B H þ,cl Þ ð1 þ 1:IÞ þ B H þ,cl ½Hþ Š ð8þ F CCl þ ¼ ð:6 þ :6B CCl þ,clo Þ ð1 þ 1:IÞ þ B CCl þ,clo ½ClO Š ð9þ Substitutin f eqs. (7) (9) int eq. (6) results in lg Ki I ¼ lg Ki A þ ð:6 þ :6B C þ,clo Þ 6 1 þ 1: þ B C þ,clo 7 I 9 ½ClO Šþ ð:6 þ :6B H þ,cl Þ ð1 þ 1:IÞ þ B H þ,cl ½H þ Š ð:6 þ :6B CCl þ,clo Þ ð1 þ 1:IÞ þ B CCl þ,clo ½ClO Š ð1þ Brmley reprted interactin parameters between C þ and ClO and between H þ and ClO. The values reprted by Brmley and the cncentratins f H þ and ClO were inserted int eq. (1). This peratin leaded t equatins with tw unknwns, K i and B CCl þ,clo. The equilibrium cnstant fr the frmatin f CCl þ at zer inic strength and the interactin parameter between CCl þ and ClO were estimated by least square f these equatins. Table represents the equilibrium cnstants and interactin parameters thus btained in this study. Since this methd culd nt be applied t CCl f zer charge, the equilibrium cnstant fr the frmatin f CCl was btained frm literature. 9) Table Estimated equilibrium cnstant and interactin parameter at 98 K. Reactin lg K Interactin parameter R C þ +Cl = CCl þ. B CCl þ,clo..99 C þ +Cl = CCl : B H þ,ccl..8 C þ +Cl = 9:6 B H þ, :.9 Table represents the equilibrium cnstants used in this study fr the frmatin f varius cmplexes tgether with the references. Free energy changes fr the frmatin f C þ, Cl and CCl þ reprted by Russian Academy f Science are listed in Table. 1) The equilibrium cnstant fr the frmatin f CCl þ was calculated by inserting the thermdynamic data in Table int the fllwing equatin. G ¼ RT ln K: ð11þ The lgarithm f equilibrium cnstant thus calculated was.1. This indicates that the calculated equilibrium cnstant agrees well with the value estimated in this study. The interactin parameter f CCl þ was calculated frm the B CCl þ,clo by inserting the interactin parameter f ClO reprted by Brmley int the fllwing equatin. B CCl þ,clo ¼ B CCl þ þ B ClO ð1þ Activity cefficients f electrically neutral species culd nt be calculated with the Brmley equatin. Cnsequently the activity cefficient f was assumed t be unity.

3 Estimatin f Thermdynamic Prperties and Inic Equilibria f Cbalt Chlride Slutin at 98 K 119 Table Thermdynamic equilibrium cnstant fr the frmatin f cmplexes. Reactin lg K Reference H þ +OH =H O 1. 6 C þ +Cl = CCl þ. btained in this study C þ +Cl = :9 9 C þ +Cl = CCl : btained in this study C þ +Cl = CCl 9:6 btained in this study C þ +OH = COH þ. 6 C þ +OH = C(OH) 8. 6 C þ +OH =C OH þ.7 6 C þ +OH þ =C (OH).6 6 Table Free energy change fr the frmatin f C þ,cl and CCl þ reprted by Russian Academy f Science. C þ Cl CCl þ G f (kj/ml) :6 11:6 187:19. Inic equilibria analysis Mass balance equatins fr chlride and cbalt were btained frm the abve chemical equilibria as fllws: [Cl] t ¼ [ ] t þ [HCl] t ¼½Cl Šþ½CCl þ Š þ [CCl ] þ [CCl ] þ [ ] [C] t ¼ [ ] t ¼½C þ Šþ½CCl þ Šþ½CCl Š þ½ccl Šþ½ Šþ½COH þ Š þ½c(oh) Šþ[C OH þ ] þ [C (OH) þ ] [Na] t ¼ [NaOH] t ¼½Na þ Š ð1þ ð1þ ð1þ Where subscript t represents the ttal cncentratin. The fllwing charge balance equatin was btained frm electrneutrality cnditin. ½H þ Šþ[C þ ] þ½ccl þ Šþ½COH þ Šþ[C OH þ ] þ [C (OH) þ ] þ½na þ Š ¼½Cl Šþ½CCl Šþ[ ] þ½oh Š ð16þ In -HCl-NaOH-H O system, there were 1 slutes in the equilibrium state, i.e., [Cl ], [C þ ], [CCl þ ], [ ], [CCl ], [CCl ], [COH þ ], [C(OH) ], [C OH þ ], [C (OH) þ ], [H þ ], [Na þ ], [OH ]. In rder t calculate the equilibrium cncentratins and activity cefficients f these 1 slutes and the activity f water, 7 independent equatins were needed. These equatins were btained frm 9 chemical equilibria shwn in Table, mass balance and charge balance, 1 activity cefficient equatins f slutes and activity equatin f water. These nnlinear equatins were slved by Newtn-Raphsn methd. Table shws the experimental cmpsitins f - HCl-NaOH-H O system tgether with ph values experimentally measured at C. Als ph values and the inic strength calculated in this study are shwn in Table. Bth measured Table Experimental cnditins and calculated values f ph and inic strength. (The unit f cncentratin was mlality) N [ ] t [HCl] t [NaOH] t ph ph C I C :6 : :19 : : : : : : : :18 : (N: number, ph: measured values f ph, ph C : values f ph calculated in this study, I C : values f inic strength calculated in this study) ph calc ph meas Fig. 1 Cmparisn f ph values between measured and calculated in this study. and calculated ph values are shwn in Fig. 1. Frm Table and Fig. 1, it is knwn that the experimental ph values are in gd agreement with the calculated values in the experimental ranges cnsidered in this study. This verifies that nt nly the Brmley equatin but als the thermdynamic prperties f cbalt chlride btained in this study were applicable t cbalt chlride slutins. Figures and shw the distributin f cbalt chlride and hydrxide cmplexes with cncentratin in the absence f HCl. It is seen in Fig. that mst f cbalt exist as

4 1 M. Lee and Y. Oh - - lg (mle fractin) , m / ml kg C + CCl + CCl - CCl - lg (mle fractin) HCl, m / ml kg C + CCl + CCl - CCl - Fig. Distributin f cbalt chlride cmplexes with the cncentratin f in the absence f HCl. Fig. Distributin f cbalt chlride cmplexes with HCl cncentratin. ([ ] t = 1. m) lg (mle fractin) COH + C(OH) C OH + C (OH) + lg (mle fractin) COH + C(OH) C OH + C (OH) , m / ml kg Fig. Distributin f cbalt hydrxide cmplexes with the cncentratin f in the absence f HCl HCl, m / ml kg Fig. Distributin f cbalt hydrxide cmplexes with HCl cncentratin. ([ ] t = 1. m). C þ in the cncentratin range f up t m. As the cncentratin increased, the mle fractin f CCl, CCl and greatly increased while that f CCl þ remained cnstant. The mle fractin f COH þ and C(OH) decreased with an increase in the cncentratin while that f C OH þ increased. The mle fractin f C (OH) þ increased with cncentratin and then decreased gradually with a further increase in the cncentratin after reached a maximum. By cmparing Figs. and, it is knwn that the mle fractins f COH þ and C OH þ are higher than that f CCl. Figures and shw the distributin f cbalt chlride and hydrxide cmplexes with HCl cncentratin when cncentratin was 1. m. It is seen in Fig. that mst f cbalt exists as C þ up t. m HCl cncentratin. The mle fractin f, CCl and CCl increased with HCl cncentratin while that f CCl þ remained cnstant. Frm Fig., it is knwn that the mle fractin f cbalt hydrxide cmplexes was very lw in the slutin cntaining HCl.

5 Estimatin f Thermdynamic Prperties and Inic Equilibria f Cbalt Chlride Slutin at 98 K 11 Mean activity cefficient f calculated in this study btained frm literature. Cnclusins By cnsidering chemical equilibria, mass and charge balance equatins fr -HCl-NaOH-H O system at 98 K, inic equilibira were analyzed. The equilibrium cnstants fr the frmatin f cbalt chlride cmplexes at zer inic strength and the interactin parameter were estimated by applying the reprted equilibrium cnstants at different inic strength t the Brmley equatin. The distributin f cbalt cmplexes with and HCl cncentratins was btained by applying inic equilibria. In the experimental ranges up t inic strength f 8.8 m, the measured and calculated ph values were in gd agreement. REFERENCES , m / ml kg Fig. 6 Variatin f the mean activity cefficient f with the cncentratin f. Mean activity cefficients f were calculated by the fllwing equatin frm the activity cefficient f C þ and Cl calculated with the Brmley equatin. ;CCl ¼f C þð Cl Þ g 1= ð17þ Figure 6 shws mean activity cefficients f calculated and thse btained frm literature. 11) It is seen in Fig. 6 that mean activity cefficients f experimentally measured agreed well with thse calculated in this study. 1) F. Habashi: Handbk f Extractive Metallurgy, vl. Wiley-VCH, Weinheim (1997) pp ) K. Sarangi, B. R. Reddy and R. P. Das: Hydrmetallurgy (1999) 6. ) N. B. Devi, K. C. Nathsarma and V. Chakravrtty: Hydrmetallurgy 9 (1998) ) M. S. Lee and G. S. Lee: J. f Krean Inst. f Resurces Recycling 1 () 8. ) L. A. Brmley: AIChE Jurnal 19 (197) 1. 6) E. Högfeldt: Stability cnstants f Metal-In Cmplexes: Part A. Inrganic ligands, Pergamn, Oxfrd (198) p. 9. 7) J. C. Raps, J. Sanz, G. Brge, M. A. Olazabal and J. M. Madariaga: Fluid Phase Equilibria 1 (1999) ) Y. Belaustegi, M. A. Olazabal and J. M. Madariaga: Fluid Phase Equilibria 1 (1999) ) J. Bjerrum, G. Schwarzenbach and L.G. Sillén: Stability Cnstants f Metal-in Cmplexes, Part II: Inrganic ligands, The Chemical Sciety, Lndn (197) p ) J. F. Zemaitis, D. M. Clark, M. Rafal and N. C. Scrivner: Handbk f aqueus electrlyte thermdynamics, A publicatin f the Design Institute fr Physical Prperty Data, NY (1986) p ) H. S. Harned and B. B. Owen: The Physical Chemistry f Electrlytic Slutins, Reinhld Publishing Crp., NY (19) p. 67.