Chemical behavior of nickel sulfide in soda-lime-silica glass melts

Abstract

Nickel sulfide formation from nickel-containing steel residuals in the glass batch has been assumed for quite some time. Melting trials were carried out with a soda-lime-silica glass batch containing steel particles with 20 % nickel. By this the above assumption was shown to be true and the exact cascade of the reaction of the metals with the sulfate of the glass melt could be pointed out. Five steps can be distinguished: sweating out the less noble elements (chromium, manganese, carbon); formation of a mixed iron nickel sulfide phase in equilibrium with the remaining iron nickel alloy; enrichment of nickel in the alloy and the sulfide phase, until complete elimination of iron; sulfidation of the remaining pure nickel and formation of a nickel-rich sulfide; oxidation to NiS. The reaction cascade found experimentally is confirmed by the authors' own thermodynamic calculations. Literature data show that nickel sulfides containing more sulfur than the 1:1 composition are not stable in the glass melt and decompose in a small "explosion". The exact composition of an NiS stone found in glass depends on its individual temperature/time history. It consists mainly of (Ni,Fe)S, which may transform to millerite. If the former sulfide melt still contains a nickel excess, the crystalline stone may also contain minor parts of other NiySx phases such as Ni9S8 or Ni7S6.