Fluidized Bed Selective Oxidation and Sulfation Roasting of Nickel Sulfide Concentrate

• Main Author: Yu, Dawei
• Other Authors: Utigard, Torstein
• Language: en_ca
• Published: 2014
• Subjects: Fluidized bed; Roasting; Sulfation roasting; Nickel concentrate; Pentlandite; Leaching; TGA; DTA; Reduction; Hematite; Nickel ferrite; Kinetics; 0743
• Online Access: http://hdl.handle.net/1807/65770

Selective oxidation and sulfation roasting of nickel concentrate followed by leaching was investigated as a novel route for nickel production. In the oxidation roasting stage, the iron species in the nickel concentrate was preferentially oxidized to form iron oxides, leaving non-ferrous metals (Ni, Cu, Co) as sulfides. The roasted product was then sulfation roasted to convert the sulfides of the latter metals into water-soluble sulfates. The sulfates were then leached into solution for further recovery and separation from iron oxides. The oxidation of nickel concentrate was firstly studied by means of thermogravimetric and differential thermal analysis over a wide temperature range. A reaction scheme was deduced, in which preferential oxidation of iron sulfide species occurred over a wide temperature range up to about 700 ºC, forming a Ni1-xS core with iron oxide shell. A batch fluidized bed roaster was then constructed to study the oxidation and sulfation roasting of nickel sulfide concentrate. Oxidation roasting tests were carried out at temperatures between 650 °C and 775 °C. It was found that low temperatures (e.g. 650 °C) are favorable for the preferential oxidation of iron sulfide species while minimizing the formation of nickeliferous oxides, i.e. trevorite and NiO. Several parameters were varied in the sulfation roasting experiments, including the sulfation gas flowrate, sulfation roasting temperature, the addition of Na2SO4, sulfation roasting time, and the oxidation roasting temperature. Under optimized conditions of sulfation gas composition (95% air, 5% SO2), temperature (700 °C), Na2SO4 addition (10 wt%) and time (150 min), the conversions to sulfates were 79% Ni, 91% Cu, and 91% Co. Only 5% Fe forms water-soluble sulfate. The residue from the leaching of calcine in water contained 49% Fe and 10% Ni, which is a suitable feedstock for the production of ferronickel alloys. Therefore, further studies were also conducted to evaluate the reduction behavior of the residue with CO, H2 and graphite.