The measurement of ignition temperatures and extents of reaction on iron and iron-nickel sulfides

Abstract

Four mineral sulfides typically found in the feed stock of a commercial nickel flash smelter, namely pyrite, violarite, pyrrhotite and pentlandite, were isolated from a primary and a supergene ore sample using magnetic separation. Relatively pure samples of pyrite, pyrrhotite and pentlandite were obtained, but violarite could only be upgraded to a 40-50% mixture with pyrite. These samples were characterized by chemical analysis, optical microscopy, Electron Probe Microanalysis (EPMA), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Thermogravimetry-Differential Thermal Analysis (TG-DTA). Each sample was split into four fractions of particle size 20--45/~m, 45-75/~m, 75-90/~m and 90-125/~m. Ignition temperatures and extents of reaction were determined using an isothermal thermogravimeter, and the products were characterized by electron microscopy. Pyrite and violarite were found to be the most reactive to ignition, followed by pyrrhotite, with pentlandite being the least reactive. This order contradicts the results of other studies and various possible causes for this are discussed. The observed trend of increasing ignition temperature with increasing particle size was in agreement with previously published reports. The extent of reaction of each mineral was measured at increasing furnace preheat temperatures. These plots were correlated with the morphology of the products formed at the ignition temperature.

Kinetics of solid-state oxidation of iron, copper and zinc sulfide mixture

“…Based on the fact of the absence of mass increase revealed by the TG method, the main processes in this temperature range can be associated with ignition and direct oxidation (burning) of sulfides with the formation of oxides [15]; the formation of sulfates is limited, or they are effectively broken by sulfide compounds. The final stage of the oxidation includes two processes accompanied by weak endothermic effects (ΔH = 49-97 and 51-113 J•g -1 , respectively), mass reduction (up to ~31 and ~21 relative %, respectively), and SO2 release; apparently, in this case, thermal decomposition of residual sulfates takes place: iron sulfates at 561-664 °C (reactions (34) and ( 35)) and copper sulfates at 743-927 °C (reactions (39) and ( 40)). This conclusion is confirmed by the literature data [19,31,57,86,87].…”

“…An important aspect of the technology is the intensity of oxidative roasting of the copper ore, which determines the specific productivity of the fluidized bed furnace and temperature and duration of the process; for its evaluation, information on the chemistry, kinetics, and mechanism of roasting is needed. A lot of publications are devoted to these questions in relation to copper-nickel ores [14], copper [15][16][17][18][19][20][21][22][23][24][25][26][27], zinc [17,28,29], nickel [30,31], and copper-cobalt [32] concentrates, as well as individual sulfide minerals which are part of them: pyrite [33][34][35][36][37][38][39][40][41][42][43][44][45][46], marcasite [47], mackinawite [48], pyrrhotite [34,36,39,[49][50][51][52][53][54], chalcopyrite [36,47,…”

Thermal metamorphism of CM chondrites: A dehydroxylation‐based peak‐temperature thermometer and implications for sample return from asteroids Ryugu and Bennu

“…Synthetic pyrrhotite and pentlandite of 45-75 μm particle size lose mass upon heating through the 500-800°C range in an oxygenated (terrestrial air) furnace atmosphere (Dunn and Mackey 1991). In nitrogen (inert) furnace atmosphere, synthetic pyrrhotites ranging in composition from Fe 0.83 S to Fe 1.00 S and grain sizes between 45 and 125 μm have decomposition temperatures of 500-700°C and lose only 1-3% of their mass by 800°C (Dunn and Chamberlin 1991;Garenne et al [2014] indicate a slightly lower temperature range of 400-650°C).…”

Thermal Analysis

“…Others studies deal with the synthesis of minerals, such as hematites produced by dehydration of synthetic goethites (251). Dunn and co-workers have studied the oxidation of pyrite in air using FT-IR spectroscopy (252) and extended the study using a wide range of techniques to include the measurement of ignition temperatures on iron and iron-nickel sulfides (253).…”