THE PRECIPITATION OF IRON SULPHIDES BY THE CRYSTALLIZATION OF HALIDE MELTS IN SULPHUR ATMOSPHERE

Abstract

A new approach to a single crystals growth of the iron sulphide phases of definite structure and nonstoichiometry is developed and applied. This approach is based on the iron sulphides recrystallization from the solutions of these sulphides in the iron (II) halide melts at the fixed vapor pressure of sulphur. The recrystallization procedure is carried out in a closed non-isothermal system: the charge – the weight of iron sulphide and the solvent – the weight of iron (II) halide are located in the “hot” end of the silica ampoule at the temperature T₂ and the source of sulphur (pure S) is concentrated in the opposite “cold” end of ampoule. The vapor pressure of sulphur is controlled by the temperature of the “cold” zone (T₁). In the course of each grown experiment the temperature T₁ was unvaried (so the pressure of sulphur was unvaried too) and the temperature of the “hot” zone T₂ was decreased slowly (usually from 690 to 660 °C). Pyrite single crystals was grown using the chloride and the bromide melts as the solvents when the vapor pressure of sulphur vapor was in the range from 0.42 to 9.4 bar. The lattice constant “a” was equal to 0.5412-0.5413 nm. The mixture of pyrite (b-FeS₂) and trigonal phase of Fe_1-xS was detected when the vapor pressure of sulphur was smaller than 0.25 bar. In the experiments with the iodide melts the almost complete oxidation of ion I^- (to I₂) by sulphur and the crystallization of iron sulphides were found. This paper proposes a mechanism for the generation of the iron sulphide phases from the iron halide melts.

ACKNOWLEDGEMENTS

This work was supported by the Russian Foundation for Basic Research (project no. 15-52-61017 Egipet_a).

Keywords: iron sulphides, pyrite, pyrrhotite, iron halide, recrystallization