A Phase Study of the Iron(III) Sulfate, Sodium Sulfate and Sodium Chloride System

Abstract

Abstract A phase diagram was drawn by using the results of a differential thermal analysis of the samples sealed in vicolglass and X-ray diffraction techniques undertaken in connection with the study of chlorine formation by the reaction of sodium chloride with sulfur dioxide and oxygen in the presence of iron compounds. In the two-component sodium sulfate - iron(III) sulfate system, the eutectic point was found at 562°C, the peritectic point, at 780°C, and the peritectoid point, at about 380°C. The former two values differ from those found by K. A. Bol’ shakov et al. (Zhur. Neorg. Khim., 8, 2577 (1963)). In the trigonal diagram, two eutectic points were found, one at 465°C with a composition of about 13.5 mol.% iron sulfate, 53.5 mol.% sodium chloride and 33.0 mol.% sodium sulfate, and the other at 454°C with 15.0 mol.% iron(III) sulfate on the line of sodium chloride - iron (III) sulfate. It was confirmed that the peritectic point corresponding to the Fe2(SO4)3+Na2SO4(1)=2NaFe(SO4)2 reaction shifted from 780°C on the line of sodium sulfate - iron(III) sulfate to 680°C on that of sodium chloride - iron(III) sulfate. From the diagram, the retarding tendency of the reaction rate of the final period of chlorine formation was attributed to diffusion control coming from the formation of solid phases.