The aim of this study is to obtain fundamental thermodynamic and kinetic information on the process of the reduction roasting of saprolite ore, a key step in the Caron Process for nickel metal production.
Laboratory studies have been undertaken to simulate conditions occurring during the reduction roast step of the Caron Process. A number of techniques including high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM), X-ray Powder diffraction (XRD) and X-ray photoelectron spectroscopy(XPS) were used to characterise and determine the elemental reactions steps taking place during the reduction roasting process.
In the present study:
1. Systematic studies have shown that nickel recovery from serpentine ore depends on reduction temperature, time, gas composition, thermal treatment history and sulphur addition.
2. The sequence of phase and microstructure change taking place during reduction has been unambiguously determined; in particular, it has been shown that Ni-Fe alloy nano-particles are formed during the reduction roasting process.
3. The phase and microstructure changes takeing place strongly affect the kinetics of Ni reduction, the accessibility of Ni alloy by leaching, and thus the overall recovery of Ni.
Phase equilibria studies related to reduction roasting of saprolite have also been carried out in a range of temperatures and oxygen partial pressures using high temperature equilibration and quenching techniques, followed by compositional analysis using Electron Probe X-ray Microanalysis (EPMA). Particular attention has been paid to ensure the achievement of equilibrium in these multi-phase materials.
In the present study:
1. Phase equilibria in the Mg-Ni-O system have been measured from PO2 = 10-7.5-10-11.5 atm at temperatures between 1000oC and 1300oC.
2. The miscibility gap between CaO and NiO was determined between 1200oC to 1600oC in air.
3. Phase diagrams of the MgO-NiO-SiO2 system were constructed at 1400oC and 1500oC in air; tie lines and metal partitioning in (olivine + monoxide) and (pyroxene + olivine) regions have been determined.
4. Phase equilibria of the Fe-Mg-Ni-O system have been investigated at 1100oC to 1300oC in PO2 = 10-7-10-10 atm.
5. Phase equilibria of Ni-Fe alloy and Mg olivine have been investigated at 1100oC in PO2 = 10-11.2, 10-12, 10-13.2 atm.