Melting Behavior of Siliceous Nickel Ore in a Rotary Kiln to Produce Ferronickel Alloys

Abstract

Ferronickel alloys as a nickel source for high alloy steels such as stainless steels are produced from garnierite ores by means of a rotary kiln. That is basically modification of Krupp–Renn process by which clinkers, that are mixtures of ferronickel alloy particles and partially melted slag, can be extracted. It is necessary to have exact knowledge of how the ore is softening with increasing temperature because controlling this behavior is considered to be a key to stable operation.
A study has been carried out to understand the melting behavior of pelletized siliceous nickel ore samples blended with limestone and anthracite heating up to 1300°C. Microscopic observation revealed that mineralogical phases in equilibrium were 2(Mg, Fe)O·SiO₂ olivine and (Mg, Fe)O·SiO₂ enstatite. It was further found that clear formation of liquid phase composed of CaO–SiO₂–FeO–Al₂O₃–MgO system as a result of assimilation with CaO in the case of ore containing higher Al₂O₃ and CaO contents with lower MgO/SiO₂ ratio. Besides, this type of ore had ability to be molten by itself to generate primary liquid inside the ore. The primary liquid formation could promote assimilation with CaO particles to spread liquid phase causing melting of the ore. Mineralogical phases at 1300°C calculated by thermodynamic software were in good agreement with the experimental results.
In contrast, ore with lower Al₂O₃ and CaO contents with higher MgO/SiO₂ ratio could not generate liquid phase even though limestone was blended. A number of remained CaO particles were observed without assimilating with the ore. It was therefore considered that higher assimilation ability of CaO with ore enhanced liquid formation and that this property was determined mainly by Al₂O₃ and CaO contents and MgO/SiO₂ ratio of the ore.