CRYSTALLIZATION OF THE QUASIBINARY bnss-tss EUTECTIC IN THE Cu–Fe–Ni–S SYSTEM

Abstract

In this paper we study the crystallisation processes of Cu–Fe–Ni–S quaternary system which is the basis for nickel-copper sulphide ores. Experimental sample of the initial bulk composition (% mol.): Cu = 17.19, Fe = 19.05, Ni = 19.66, S = 44.10 was synthesized using the quazi-equilibrium directional crystallization method. The results of the microscopy study have shown that the produced ingot consists of 6 zones with different phase and chemical compositions. The main part of the ingot is zone IV. The samples extracted from this zone were examined by methods of differential thermal analysis (DTA), scanning electron microscopy (SEM), and energy dispersive X-tay spectrometry (EDS). Microscopic studies suggest that the ingot in this zone is characterised by the coexistence of tenite and bornite solid solutions (tss and bnss correspondingly), but upon further cooling tss is subject to decomposition into daughter phases. The obtained data, though, can also be interpreted as the crystallization of the quaternary eutectic. The results of the DTA analysis of the samples have allowed us to determine the temperatures of the phase effects and prove the formation of a binary eutectic. The temperature of the binary eutectic (L → tss + bnss) is 578±1°C (851±1K). Liquidus temperatures increase slightly from 857±2°C till 862±2°C (1130±2K – 1135±2K). The deviation of liquidus temperatures can be accounted for by small compositional changes of the studied samples. The obtained results have also confi rmed the adequacy and consistency of the proposed technique, combining methods of directional crystallisation, differential thermal analysis and scanning electron microscopy for studying the phase equilibria of multicomponent systems.

Keywords

• Cu–Fe–Ni–S system
• phase equilibria
• eutectic
• directional crystallization
• DTA.