Roasting of Nickel Concentrates

Abstract

The oxidation of three nickel concentrates from two Canadian smelters was studied by thermogravimetric analysis. Concentrate samples were heated to 1223 K (950°C) in inert or oxidizing atmospheres to determine the reaction behavior. By recording the mass change as well as the SO 2 content in the outlet gas, the oxidation behaviors were quantified. Isothermal roasting tests were carried out on the concentrates over the temperature range of 673 K (400°C) to 1123 K (850°C). When heated in air, the samples gain mass as a result of sulfate formation at temperatures up to approximately 873 K (600°C) to 973 K (700°C), whereas at higher temperatures, the samples exhibit a large mass loss attributed to sulfate decomposition as well as direct SO 2 formation by oxidation. In a 4 pct O 2 gas atmosphere, significantly less sulfates were formed. Mixed reactions take place, in which some lead to mass loss and SO 2 generation, and others lead to mass gain and SO 2 consumption. The relative importance of the various reactions depends on the experimental conditions.

In–situ XRD and EDS method study on the oxidation behaviour of Ni–Cu sulphide ore

“…8 . Recently, researchers studied the isothermal oxidation behaviour of synthetic Pn in depth and proposed a novel stepwise phase–transformation mechanism 13, 14 .…”

“…Early on, the various oxidative reactions of natural Pn were deduced and summarised via thermogravimetric (TG)/mass spectroscopy (MS) analysis, differential thermal analysis (DTA), and X–ray diffraction (XRD) analysis by Dunn et al . 8 . Recently, researchers studied the isothermal oxidation behaviour of synthetic Pn in depth and proposed a novel stepwise phase–transformation mechanism 13 , 14 .…”

Sulfate Formation and Decomposition of Nickel Concentrates

“…Details of the equipment and experimental procedure have been reported previously. [11,12] After placing the sample in the TGA, the reaction chamber was evacuated and then repressurized to atmospheric pressure with the desired process gas. For the reported tests, gas flow rates of either 0.1 or 1.0 L/min were used.…”

“…[4][5][6][7] This means that the calcine being transferred to the electric furnaces consists of a mixture of unreacted sulfides in addition to various oxides and sulfates. [8][9][10][11][12] One important aspect of this is that during the subsequent heating in the calcine banks of the electric furnace, these sulfates will decompose releasing SO 2 according to reactions such as…”

“…[11,12] During the subsequent period in argon, the samples all lose weight but to varying degrees, depending on the temperature. Figure 5 shows the results for similar tests using a blend of 33 pct VBN and 67 pct A2, which was the blend that was fed to the Thompson smelter at one point in time.…”