Quantitative mineralogical characterization of roasted Ni-Cu concentrates

Hydrogen reduction of oxidized nickel concentrates

“…Since these mass changes correspond to temperatures where also O 2 is evolved, they are likely due to the decomposition of sulfates. Figure 6 gives the equilibrium constant for the decomposition of sulfates of iron, nickel, and copper according to the following reactions: [3] [4] [5] These three reactions only involve the decomposition of single compounds and as soon as the reactions become thermodynamically feasible, they will occur rapidly. As seen in Figure 6, the decomposition of Cu 2 SO 4 will take place before NiSO 4 , which again will take place before FeSO 4 .…”

“…Since these oxides form a hematite/magnetite rim, [3] it is expected that the reduction kinetics may be somewhat similar to that of hematite and magnetite. Turkdogan et al [4,5,6] studied the reduction of iron oxides by hydrogen and found that the reduction rate increased with increasing temperature up to about 650°C.…”

“…This may be possible since during roasting of pentlandite, pyrrhotite, and chalcopyrite, iron oxide rims form surrounding the sulfide cores. [3] The roasted product is fine with 100 pct less than 100 m, [1] and the reduction kinetics therefore is expected to be fast. One limitation may be the fairly low temperature of the calcine leaving the roasters.…”

Roasting of Nickel Concentrates

“…[7,[9][10][11][12][13] This result is caused either by an iron oxide coating or by a sulfate layer depending on the conditions. [7] Another important effect during sulfide oxidation is that nickel and copper tend to diffuse into the centre sulfide core, whereas iron diffuses outward to the oxide rim.…”

“…[7] Another important effect during sulfide oxidation is that nickel and copper tend to diffuse into the centre sulfide core, whereas iron diffuses outward to the oxide rim. [11][12][13] This segregation process combined with a rim of either iron oxide or sulfate makes the roasting mechanism varying and fairly complicated. A third phenomenon is the possible melting of some of the sulfide phases as the roasting temperature exceeds approximately 1073 K (800°C).…”