UBC Theses and Dissertations
Sulfur deportment in nickel laterite calcination for ferronickel production via rotary kiln-electric furnace route Sarbishei, Sahand
The rotary kiln-electric furnace (RK-EF) process is a common pyrometallurgical route for ferronickel production from nickel laterite ores. Sulfur is a harmful impurity that deteriorates the mechanical properties of nickel alloys. Due to the low sulfur content of the laterites, it is believed that the majority of the sulfur in crude ferronickel is originated from the process additives such as fuel and reductant in the rotary kiln. Therefore, it is crucial to investigate the effect of the sulfur content of the fuel on the calcine composition. Reducing sulfur absorption from the fuel to the calcine is beneficial to reduce the load of the refinery. This study investigates sulfur deportment in the nickel laterite calcination to obtain a fundamental understanding of the behavior of sulfur present in the rotary kiln fuel. In this work, the main reactions that occur in the calcination stage are identified. The kinetics of the reactions are investigated by combining model-free and model-fitting methods. The sulfurization reactions in the nickel laterite calcination are identified, and the main sulfur-containing compound in the calcine is found to be pyrrhotite (Fe7S8). Using coal with higher sulfur content, employing a more aggressive reducing atmosphere in the furnace, and increasing the gas flow rate result in an increase in the sulfur content of the calcine. Increasing temperature from 600 to 700 °C leads to higher sulfur deportation from the gas phase to the calcine. However, raising the temperature above 700 °C decreases sulfur deportation due to sintering of the particles and recrystallization of the silicate compounds. A comprehensive kinetic analysis on the sulfurization reactions revealed that the sulfurization reaction is diffusion-controlled and has a low activation energy of 1.4-5.3 kJ/mol. Using CaCO3 as a sulfur absorbent leads to 70.8-91% sulfur removal in the calcine. The effect of the processing temperature and time on reducing the sulfur content of the calcine are also investigated. Increasing time from 30 to 120 min results in decreasing sulfur removal from 91 to 78.3%. Raising temperature from 700 to 800 °C promotes sulfur removal; however, sintering of additive particles at above 800 °C reduces sulfur removal.
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