Equilibria between ferrous and ferric chlorides in molten chloride salts
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were obtained. Measured values of K were in good agreement with computed ones from regression equations. The composition of the melts, the partial pressure of chlorine, and the temperature were found to have important effects on K, and the effect of dissolved iron was smaller than that of other factors. At identical other conditions, the largest values of K were observed in system 3, which suggested that the current efficiency for electrolysis of MgC12 should be lower when carnallite was used as electrolyte and that catalysis of iron species in molten salt chlorination would be better when molten salt systems containing high potassium chloride were used.
I.
INTRODUCTION
IRON species
in molten salts are harmful to electrolysis of MgC12 but play an important part as catalysts tl,21 in molten salt chlorination. Thus, equilibria between ferrous and ferric chlorides in molten salts have been studied for improving the above processes. II.
EXPERIMENTS
Experiments were carried out in a quartz reactor with a sleeve on the upper wall for cooling water and an airtight cover on the top of the reactor. There were inlets and outlets in the cover for vacuum, gases, feeding, sampling, etc. Temperature was controlled with an accuracy of + 1 K. Analytic reagents were used with the exception of anhydrous MgC12, which was the by-product of magnesiumthermic reduction of TIC14 and free from Fe, A1, Si, Ti, but which contained a trace of Mn. Iron was introduced into melts as anhydrous FeC13. Chlorine was bubbled through melts for 1.5 hours to purify and saturate the melts before FeC13 was added. During experiments at Pa2 = 1 atm, a constant flow of chlorine was retained after adding FeE13. It had been found that the decomposition of FeC13 was a rapid reaction t3~ which took place more completely when the temperature was raised. Therefore, as soon as the temperature was raised to a given value and maintained for about 1 minute, sampling was carried out for analysis of ferrous and total iron contents, and a value of K at the given temperature and total iron concentration was obtained. The total iron concentration was considered constant within a minute's time of the constant temperature. The value of K at anGUANGWEN ZHAO, Associate Professor, is with the Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK. QIUZHAN TIAN, Lecturer, and SHUZHEN DUAN, Professor, are with the University of Science and Technology Beijing, Beijing, People's Republic of China. Manuscript submitted August 3, 1988. METALLURGICALTRANSACTIONSB
other temperature and concentration was obtained by repeating the above procedure, because the total iron concentration had changed during the course of raising the temperature. Usually, four or five values of K at different temperatures and total iron concentrations were obtained in a set of experiments. When experiments at Pcl~ = 0 were carried out, melts were purified as above, but chlorine flow was stopped after adding EeC13 and the reactor was vacuated and f
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