The Separation of from Iron via

N. Sato1, L.R. Reyes2, M.S.M. El-Eskandarany3 and M. Nanjo1,4

1 Institute for Advanced Materials Processing, Tohoku University, Sendai 980, Japan; 2Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico; 3Graduate School, Tohoku University, Sendai 980, Japan.

(Received May 6,1993; final form May 31,1993)

ABSTRACT ppm) and very high transport efficiency (99.95%) were

obtained. The recovery of A1C13 by the reduction of

A new process for the separation of aluminium AlCl3-FeCl3 mixture with aluminium and/or iron was from iron chlorides was studied from the shown to be effective. standpoint of the recovery of aluminium from its ore and scraps. In this process, the aluminium chloride is transported from the aluminium-iron mixed chloride 1. INTRODUCTION in the presence of . The separation experiments were conducted using double cells with The combination of the Bayer process for alumina two compartments. In the case of the AlCl3-FeCl3 production and the Hall-Heroult process for system, FeCl3 tended to remain in the compartment in aluminium electrolysis in cliorite is the most complete which the mixed chloride was placed, while A1C13 was industrial process developed for aluminium transported to another compartment forming a production. Since production of aluminium is energy NaAlCl4 stable complex. Transport efficiency and consuming and strongly influenced by the price of chloride purity were investigated under several , production of aluminium in Japan is conditions. The best separation was achieved when the decreasing while imports are increasing. Recently, molar ratio of NaCl to mixed chloride and the aluminium scraps were recycled from the standpoint reaction time were 6 and 3 days, respectively. of saving energy. Transport efficiency of A1C13 increased with On the other hand, some new processes, such as increasing and became stable over the carbon reduction in a blast furnace and 200°C. The chloride purity decreased corresponding electrolysis in molten chloride, have also been to the increasing transport efficiency of FeCl3 over investigated /1-5/. When compared to the traditional 200°C. A very high separation effect was observed fluoride process, the chloride process has advantages, when the sodium chloride was used compared to the such as production of high purity aluminium and high separation result without sodium chloride. Separation current efficiency. In this process, high purity A1C13 is of aluminium became more effective when the double used in the electrowinning of aluminium in the cells were controlled at different . In the chloride bath. Since A1C13 shows high vapor pressure case of the AlClj-FeC^ system, very pure A1C13 (Fe:2 compared to A1F3, purification using distillation and/or formation of chloride complexes with other metal chloride is possible /6/. 4Died in 1989 For the recovery of aluminium from raw

299 Vol. 13, No. 4, 1994 The Separation of Aluminium from Iron via Chlorides

materials, such as bauxite, aluminium iron alloy and B. Separation Experiments scraps, the removal of iron is essential to obtain high grade aluminium. If the chloride process is applied to Experiments on the separation of aluminium

the above materials, it is important to separate chloride from AlCl3-FeCl3 and AlCl3-FeCl2 mixtures aluminium chloride from iron chloride. The effect of were performed using a Pyrex reaction cell, see Fig. 1. sodium chloride on the separation of rare metals Mixed aluminium and iron chlorides (molar ratio = containing mixed chlorides, such as niobium and 2:1) and NaCl were placed in compartment I and tantalum chlorides, has been studied /7/. In this work, compartment II of the reaction cell, respectively. The separation of aluminium chloride using sodium reaction cell was sealed off under vacuum and placed

chloride from both AlCl3-FeCl3 and AlCl3-FeCl2 in a resistance furnace. Then both compartments were mixtures obtained from the chlorination of aluminium heated up to the reaction temperature and maintained containing raw materials is studied. Selective for the reaction time. After the reaction, the content

reduction of FeCl3 to FeCl2 by aluminium and/or iron of aluminium and iron in both compartments was metal as a reducing agent is also discussed. analyzed by atomic absorption. The effect of reaction conditions, such as temperature, reaction time and amount of NaCl, on the separation of aluminium from 2. EXPERIMENTAL^ mixed chloride was determined.

A. Materials C. Reduction Experiments

A1C13 was prepared by the reaction of analytical grade aluminium powder with in a Reduction of mixed chloride by a metallic reducer reaction tube at 400 °C. FeCl3 and AlCl3-FeCl3 was examined using differential thermal analysis by mixture were prepared by the reaction of the Sato and Nanjo /8/. Reduction of FeCl^ and electrolytic iron powder and Al-Fe alloy (Al:Fe = 2:1) subsequent distillation were conducted using the same with Cl2 gas at 400°C using the same procedure as apparatus shown in Fig. 1. However, compartment II

described above. FeCl2 from the Cerac Inc. (99.99%) was empty in order to collect the distillate after the was used without further purification. Reagent grade reaction step. Mixed chlorides were placed in NaCl was dried continuously in a vacuum oven at compartment I together with Al, Fe or Al-Fe alloy as 100 "C before use. The chlorides were quantitatively reducing agents. The temperatures of the furnace weighed in an argon filled dry box due to the were set as TJ < T2 during reaction and TJ > T2 hygroscopic nature of these chlorides. during distillation. After reaction, samples were

V////A,'//////////////////,V////////,

Λ — ι Ρ Ρ > ^ ^^ ΑΙΟΙ3·ΤΘΟΙ3 J V^ICL FeCU— %V////////////// V//////y///y/////A A

Compartment II Compartment I

Fig. 1: Apparatus for separation experiments

300 Ν. Sato, L.R. Reyes, M.S.Μ. El-Eskandarany and M. Nanjo High Temperature Materials and Processes cooled at room temperature. The free energy change in Eq. 3 is written as:

AG = AG" + RT In ^Cl/PpeC!, D. Analysis v ex ex >p ' X NaFeCl4* A1C13 Aluminium and iron were determined by atomic where, assuming ideal conditions, the activities of the absorption using Seiko Electronics SAS750 type. components of the condensed phase are replaced by Reaction products and residues were identified by X- their molar concentrations, and the fugacities of the ray powder diffraction under Cu-Κα irradiation gaseous components are replaced by their partial through a nickel filter. pressures, for these calculations, the standard state of the solid phase is the pure solid at that temperature and of the gas phase the pure vapor at that tempera- 3. THERMODYNAMICS OF SEPARATION ture and a pressure of 1 atm. According to Eq. 3, if solid NaCl is exposed to a Both A1C13 and FeCl3 react with NaCl to form vapor consisting of A1C13 and FeCl3 and the system is complex chlorides, such as tetrachloroaluminate allowed to come to equilibrium, NaAlCl4 and (NaAlCl4) and tetrachloroferrate (NaFeCl4), NaFeCl4 will form, and their relative amounts may be respectively /9-11/. Eqs. 1 and 2 give the reactions: calculated using Eq. 4 when AG^ = 0. By subtracting the free energy of reaction in Eq. 1 from Eq. 2, AG^ AlCl3(g) + NaCl(s) = NaAlCl4(s,l), (1) for Eq. 3 < 0. Therefore, at equilibrium FeCl3(g) + NaCl(s) = NaFeCl;4(s,l). (2)

XNaAlCl4*PFeCl3 It was experimentally determined that for a given > 1 (5) X P alkali metal, NaAlCl4 is more stable than NaFeCl4 NaFeCl4* AlCI3 since the equilibrium constants of Eqs. 1 and 2 are When the AlCl -FeCl system is considered to be 1.2xl010 at 200°C and 1.7 at 400°C, respectively. The 3 3 ideal, the activity of each component in the condensed exchange reaction between NaAlCl and NaFeCl can 4 4 phase is equal to its mole fraction. Therefore, be written as: Ρ ·χ A1C1 A1C1 3 3 = η. AlCl3(g) + NaFeCl4(s,l) = (6) Ρ ·χ NaAiCl4(s,l) + FeCl3(g) (3) FeCI3 FeCl3 Table 1 presents the vapor pressures of the above

Table 1

Vapor Pressure of Aluminium and Iron Chlorides (mmHg)

Temperature (°C) Chlorides 100 150 200 250 300

3 4 5 A1C13 11.3 86.5 2.53xl0 * 3.52xl0 * 2.83x10 * 5 2 FeCl3 3.32xl0" 1.06xl0" 0.889 29.0 443 2 FeCl2 3.63xl0" * 3 102 1.88xl03* 3.40xl04* AlFeCL0 3.05xl0" 0.748

Extrapolated

301 Vol. 13, No. 4. 1994 The Separation of Aluminium from Iron via Chloriden

3 chlorides. Since η > 1 (n = 2.85 χ 10 at 200 °C), Temperature (°C) substituting Eq. 6 for Eq. 5, —10I 0 3010 5010 7010 901 0

Wj4^Cl3 >n>1 (?)

X X NaFeCl4* AlCl3 and thus,

X X NaAlCl4 > AIC13

X X NaFeCl4 FeCl3

Eq. 8 shows that if a mixture of A1C13 and FeCl3 is heated and the vapor equilibrated with NaCl in a closed system, the production of NaAlCl4 in excess of that of NaFeCl4 will cause the preferential depletion of AlCl^ from the AlCl^-FeCl^ mixture.

In the case of separation of A1C13 from the A1C13- FeCl2 mixture, though the thermodynamic data for the complex formation of Eq. 9 is not reported, n' = P n 6 AIC1 /Ppeo2 ( ' = 7.80x10 at 200 °C) is larger than n, and* a more effective separation should be possible. -10' ' . ' ' 300 500 700 900 1100 1300

FeCl2 + NaCl = NaFeCl3 (9) Temperature C Κ )

As for the selective reduction of ferric chloride in Fig. 2: AG° change in the reduction reactions the AlCl -FeCl mixture, the following reduction 3 3 at elevated temperatures reactions are considered:

2FeCl3 + Fe = 3FeCl2 (10) 3FeCl3 + Al = 3FeCl2 + A1C13 (11) 4. RESULTS AND DISCUSSION aici3 + Fe = A1C1 + FeCl2 (12)

aici3 + Al = 3A1C1 (13) A. Separation ofAlCl^from the AlCl^-FeCl^ System aici3 + Fe = FeCl3 + Al (14)

Preliminary tests showed that a period of three The AG" change of these reactions is calculated and days was the optimum reaction time for the shown in Fig. 2 /12/. It has been reported that FeCl is 3 equilibrium of the transport reaction of A1C13 from reduced to FeCl using aluminium /13,14/. From these 2 the AlCl3-FeCl3 mixture over 200°C. However, under results, FeCl3 can be selectively reduced to FeCl2 by 200°C, a longer reaction time is needed. Results of the iron or aluminium. When a mixture of AlCl3-FeCl3 effect of sodium chloride on the amount of transport reacts with Al-Fe alloy, Eq. 15 seems to occur: efficiency of FeCl3 and FeCl2 are shown in Fig. 3. In these and subsequent experiments, the transport

5AlCl3-FeCl3(g) + Al-Fe(s) = efficiency (η) and transferred chloride composition

6AlCl3(g) + 6FeCl2(s) (15) (e) were defined as follows:

302 Ν. Sato, L.R. Reyes, M.S.Μ. El-Eskandarany and M. Nanjo High Temperature Materials and Processes

0-3 8 FeCI3

' ^ · " ^m \ - T, = 200 °C 6 # NaCt AlClj+FeCljjj s/ __CM m : 2 or 3 „ ο Ο FeCL 4A

C- 0.1 FeClj in AICIj - FeCl^ystem

- FeClgin AlClg- FeCI3 system

8 NaCI AICI^FeClm

Fig. 3: Effect of the amount of sodium chloride on the transport of FeCl3 and FeCl2 (200 °C, t = 3 days)

λ

100 150 200 250 T1 ' T2 (°C }

Fig. 4: Effect of the temperature and sodium chloride on the transport efficiency of A1C13 and FeCl2 in the

AlCI3-FeCl3 mixture (t = 3 days, η^,/η^ρ^ = 6)

Chloride mole of Al (Fe) in compartment II The results show that the molar ratio between sodium η(%)= xlOO, (16) chloride and the AlCl3-FeClm mixture (m=2,3) is 3, Total chloride mole of Al(Fe) enough for the separation reactions.

Chloride mole of Al(Fe) in compartment II The effect of the reaction temperature on the e(%)= xlOO. (17) transport efficiency of the aluminium in AlCl3-FeCl3 Total chloride mole of Al and Fe using sodium chloride is shown in Fig. 4. The result of

303 Vol. 13, No. 4, 1994 The Separation ofAluminium from Iron via Chlorides

the separation experiment without sodium chloride, identified in compartment II /15-17/. FeCl3 remained i.e., distillation of AlCl3-FeCl3, is also shown in Fig. 6. in compartment I. Fig. 5 shows that high purity of

The purity of the transferred chloride was very high A1C13 in compartment II is obtained at temperatures when the separation was conducted without sodium around 135°C, while the amount of transported chloride; however, the transport efficiency was low. ferric chloride decreases below 200 °C. Since the It is clear that the presence of sodium chloride in transport efficiency of ferric chloride increases with compartment II achieves a high aluminium chloride increasing temperature, purity of transferred chloride transport efficiency. The transport process is decreases due to contamination of ferric chloride, see controlled by the chloride's vapor pressure which is a Fig. 5. Molar ratios of obtained A1C13 and FeCl3 in function of the temperature. Setting the same compartment II were 30-100 at 200 °C. These values temperature in both compartments, the transport are smaller than those expected from the ratio of the efficiency decreases drastically at 150 °C, below the vapor pressure of each chloride (PAici3/Ppeci = 3 6 sublimation point of A1C13 as seen in Fig. 4. Similar 2.85xl0 at 200°C). Table 1 shows that vapor vaporization behavior was observed when different pressures of NaAlCl4 and NaFeCl4 are smaller than types of the AlCl3-FeCl3 mixture were used. From the those of A1C13 and FeCl3. The interaction between result of the X-ray diffraction analysis of the product A1C13 and FeCl3 in the gaseous phase is given in Eq. given in Table 2, NaAlCl4, NaCl and A1C13 were 18/18,19/:

Table 2

X-Ray Diffraction Patterns for the Product in Compartment II after Separation of A1C13 from FeCl.

Products in NaCl NaAlCl4. A1C1, Compartment II Swanson et al. /15/ Semenenko et al. /16/ Ketelaar et al. /17/

d(A) I d(A) I d(A) I d(A) I

5.140 4 5.12 12 4.874 3 4.94 20 4.529 3 4.58 15 4.41 12 3.116 2 3.19 75 2.912 3 2.92 19

2.876 3 2.88 100 2.818 100 2.821 100 2.804 50 2.80 56 2.581 1 2.541 75 2.475 1 2.475 10 2.036 1 2.024 15 2.084 1

1.995 7 1.994 55 1.683 1 1.679 1 1.639 1 1.628 15 1.638 4 1.451 1 1.461 3 1.432 1 1.42 1

1.410 15 1.410 6 1.410 6 1.261 1 1.261 11 1.272 1

304 Ν. Sato, L.R. Reyes, M.S.M. El-Eskandarany and M. Nanjo High Temperature Materials and Processes

100 -tr· 80- AICL

NaCI AICI3+ FeCtj ~ 60- — —o— With NaCI « 40- -a-·- Without NaCI

20- FeCL

-9- 100 150 200 250

Τ, , T2 (°C )

Fig. 5: Transferred chloride composition obtained from the AlCl3-FeCl3 mixture as a function of temperature (t

= 3 days, nNaC|/nAl(Fe)Cb = 6)

100

0 τ2 i;=2oo c 80

NaCI ACI3+ FeCI3 60 ν AICI3 FeCI, 40

20

100 150 200 250 300

T2 Cc)

Fig. 6: Effect of temperature on the transport efficiency of the A1C13 and FeCl3 in the AlCl3-FeCI3 mixture (t

3 days, nNaCl/nAl(Fe)Cl3 = 6)

Al2Cl6(g) + Fe2Cl6(g) = 2AlFeCl6(g) (18) chloride vapor does not seem to be negligible. Fig. 6 shows the results of the separation of

Since the vapor pressure of AlFeClg is not so small aluminium from AlCl3-FeCl3 when the temperatures

(102 mmHg at 200 °C), the molar ratio of AlCl3/FeCl3 of compartments I and II are different and the

including the vapor pressure of the AlFeCl6 species is temperature of compartment I is fixed at 200 "C. 113 at 200 "C. As this value is close to those of the Separation is shown to be more effective when the experimental results, the influence of the mixed temperature of compartment II is set around 150°C.

305 Vol. 13, No. 4, 1994 The Separation of Aluminium from Iron via Chlorides

Under these conditions, high transport efficiency AlCl3-NaCl bath, in which the iron content is lower (—95%) and low ferric chloride content in the than 2 ppm and the reaction temperature is below transferred chlorides (< 1.5%) can be achieved. In all 200 °C. Purity of A1C13 in the transferred chlorides is experiments, ferric chloride crystallized in the low 99.95% under these conditions. temperature zone of compartment I. Subhalides or When setting the temperature of compartment I oxychlorides were not found in the chlorides during to 200 °C and changing the temperature on the sodium the experiments. chloride side, similar results were obtained below

250°C to those of the AlCl3-FeCl3 system in Fig. 6. The dependence of the melt composition on the

B. Separation ofAlCl^from the AlCl^-FeC^ Mixture temperature was not significant for the AlCl3-FeCl2 system.

Separation of A1C13 from the AlCl3-FeCl2 mixture was attempted, and the result is shown in Fig. 7. When the temperature of both compartments was C. Selective Reduction of Ferric Chloride in Mixed the same, similar behavior of the aluminium transport Chlorides was observed compared with that of the AlCl^-FeCl^ system in Fig. 4. Chlorides of aluminium and sodium Based on the above results, selective reduction of were identified by X-ray powder diffraction as ferric chloride to ferrous chloride was attempted. The presented in Table 3; iron chloride was not observed. differential thermal analysis of the ferric chloride

Since transport efficiency of FeCl2 is almost zero in reduction in the AlCl3-FeCl3 system using a metallic Fig. 7, details on this transport efficiency are shown in reducer is shown in Fig. 9. Three exothermic peaks Fig. 8 in comparison with those of ferric chloride. The were observed during the heating, showing the amount of transferred iron is very low when the occurrence of the reduction reaction. After

AlCl3-FeCl2 mixture is used. However, the iron homogenization at 260 °C for 3 days, the cooling curve content in the obtained chloride is low as can be showed two exothermic peaks at 216 and 186 °C. These expected from the vapor pressure difference between peaks correspond well to the melting (217°C) and

AlClj and FeCl2. This provides a high purity in the eutectic point (186"C) of the AlCl3-FeCl2 system,

T2 Ct)

Fig. 7: Effect of temperature on the transport efficiency of A1C13 and FeCl2 in the AlCl3-FeCl2 system (t = 3

s n /n = 6 ^y ' NaCi Aici3-Feci2 )

306 Ν. Sato, L.R. Reyes, M.S.M. El-Eskandarany and M. Nanjo High Temperature Materials and Processes

T,,T2C°C)

Fig. 8: Effect of temperature on the transport efficiency of FeCl3 and FeCl2 in the AlCl3-FeClm (m=2,3) mixture (t = 3 days, η^,/η^^ = 6)

Table 3

X-Ray Diffraction Patterns for the Product in Compartment II after Separation of AIC13 from FeCl2

Products in NaCl NaAlCl4 A1C13 Compartment II Swanson et al. /15/ Semenenko et al. /16/ Ketelaar et al. /17/

d(A) I d(A) I d(A) I d(A) I

5.88 8 5.86 100 5.15 3 5.19 25 3.254 3 3.258 13 3.15 35 3.086 4 3.09 75 2.942 3 2.948 100

2.819 100 2.821 100 2.82 31 1.994 39 1.994 55 1.625 2 1.628 15 1.411 6 1.410 6

respectively /20/. The above-mentioned results Fig. 10 shows the aluminium chloride composition in indicate that a selective reduction reaction as given in the distillate when reducing agents are used in the Eqs. 10, 11 and 15 seem to occur. Separation of mixed reduction of a mixed chloride. The reduction reactions chloride by selective reduction in the double cell was of Eqs. 10, 11 and 15 occur with the metal powders of performed with the temperatures of compartments I iron, aluminium and AI-Fe alloy, respectively. No and II at 260 °C and 320 °C, respectively. Then the difference was observed when aluminium and Al-Fe chloride distillate was collected in compartment II. alloy were used as reducing agents. Very pure AICL

307 Vol. 13, No. 4, 1994 The Separation of Aluminium from Iron via Chlorides

260 R" Al,Fe or Al-Fe alloy

240 Liq.-2AICI3FeCI2(s) + Liq. ο 1 φ Ρ 220 xz ο HXI ta 200 a> 3FeCI3(s,l) + R(s) - 3FeCI2(s) + RCI3(s,l) ο α Ε Ik . CO Φ t- 180 JZ+— ο •ο 2AICI3FeCI2(s) + Liq.-AICI3(S) + 2AICI3FeCI2(s) c ai t 60

JT* 140 DTA

AS- 0 1 2 3 4 5 6 78 79 80 8 1 82 Time Chr)

Fig. 9: Differential thermal analysis on the reduction of FeCL by metal reducing agents

100

a> a»

CO 90 •o a>

Reducing agent

a Aluminium powder _P0 80 • Iron powder Ο < • Ai-Fe alloy powder

0 0.5 I 1.5 2 2.5

Reducing agent (stoichiometric amount)

Fig. 10: Aluminium chloride purity in the distillate as a function of the stoichiometric amount of reducing agent used for the reduction of FeCl^ in the AlCl^-FeCl^ mixture

308 Ν. Sato, L.R. Reyes, Μ.SM. El-Eskandarany and Μ. Nanjo High Temperature Materials and Processes

(Fe:2 ppm) was obtained; however, the reduction Hokkaido Daigaku Kenkyu Hokoku, 48, 31 reaction with iron is low. In all cases, nearly 89% of (1968). the A1C13 was distilled. 4. L.M. Foster, A.S. Russell and C.N. Cohum, /. Amer. Chem. Soc., 72,2580 (1950). 5. B.P. Sharma, Trans. Inst. Min. Met., 84, C190 5. CONCLUSION (1975). 6. K. Reuhly and H. Wendt, Proc. 1st Int. Symp.

The separation of A1C13 from FeCl3 or FeCl2 was Molten Tech., B-103, 9 (1983). achieved using a transport reaction with sodium 7. F.N. Flengas and J.E. Dutrizac, Met. Trans. B., chloride to produce a NaAlCl4 stable complex. The 8B, 377 (1977). following conclusions were reached: 8. N. Sato and M. Nanjo, Met. Trans. Β., 16B, 639 (1985).

1. Separation of AlCl^ from FeCl3 is enhanced by 9. L.G. Boxall, H.L. Jones and R.A. Osteryoung, J.

the presence of NaCl to form NaAlCl4- Electrochem. Soc., 120,223 (1973).

2. The separation of A1C13 and FeCl3 is found to be 10. R.R. Richards and N.W. Gregory, J. Phys. effective below 200 °C. Chem., 68, 3089 (1964). 3. The transport efficiency and the purity of the 11. C.M. Cook Jr. and W.E. Dunn Jr., J. Amer. AlCLj containing product are improved when the Chem. Soc., 65,1505 (1961). temperatures of the vaporization part and 12. I. Barin, O. Kanck and O. Kubaschewski, condensation part of the process are set at 200 "C Thermodynamical Properties of Inorganic and 150 °C, respectively. Substances, Supplement, Springer Verlag, 4. Very pure AlCl3-NaCl melt (Fe:5 ppm) can be Germany (1976). obtained at temperatures below 200'C from the 13. M. Binnewies, Z. an org. allg. Chem., 487, 19 AlCl3-FeCl2 mixture. (1977). 5. Selective reduction of ferric chloride in the FeCl^- 14. B.G. Korshunov, A. Lobetskaya and A.A. Palant, AlCl^ mixture using metallic reducers is found to Zh. Neorg. Chem., 12, 203 (1967). be effective in obtaining pure aluminium chloride. 15. M. Swanson and T. Fuyat, NBS Circular 539, 2, 41 (1953). 16. M. Semenenko, Russ. J. Inorg. Chem., 14, 481 (1969). REFERENCES 17. I. Ketelaar, Ree. Trav. Chim., 66, 501 (1947). 18. R.M. Fowler and S.S. Melford, Inorg. Chem., 15, 1. S. Betty and D. Duca, J. Electrochem. Soc., 118, 473 (1976). 405 (1971). 19. E.W. Dewing, Met. Trans., 1,2169 (1970). 2. A.S. Russell, L.L. Knapp and W.E. Haupin, U.S. 20. E. Foley and F.J. Moyle, J. Appl. Chem. Patent No. 3725222 (1973). Biotechnol., 22, 867 (1972). 3. T. Narita, T. Ishikawa and R. Midorikawa,

309