Study On Characteristics And Mechanism Of The Neogenic Pyrrhotite During Transformation Processes In Pyrite At Elevated Temperatures

Sulfide mineral is the metal cation and S2-anion combination of compounds, and the most abundant of the sulfide minerals and its occurrences are very widespread. As a rock-forming mineral, pyrite can provide a variety of important geological information; as a glob-bearing mineral, it has great significance to gold prospecting and extraction. Abroad on pyrite oxidation has been studied for many related reports, the first literature was found in1945, followed by a number of scholars have studied the oxidation of pyrite heating process, reaction kinetics and the final product. The transformation of pyrite in an oxygen-containing atmosphere proceeds through a multi-step sequential process (pyriteâ†'pyrrhotiteâ†'magnetiteâ†'hematite), some reports are (pyriteâ†'pyrrhotiteâ†'hematiteâ†'magnetite), and the others are (pyriteâ†'pyrrhotiteâ†'hematite/magnetite). Regardless of conditions in an inert gas or oxygen conditions, pyrrhotite are there, and this fact has been proven by many people, but their formation mechanism, it is quite vague. Therefore, we adopted a series of validation testing means to get new life under the experimental conditions the formation mechanism of pyrrhotite. The achievement and progress of the research are as the following.(1) The heating products of the pyrite at different temperatures between room temperature and1250℃for period of1h in air were investigated using X-ray diffraction (XRD). Pyrite present in the temperature range of room temperature-700℃. Pyrrhotite exists in the temperature range500℃-1200℃. Hematite temperature range is of300℃-1250℃. Magnetite is present in the temperature range1000℃-1200℃. (2) Neogenic pyrrhotite maximum relative content of pyrite heated to700℃. Under the condition of700℃:product heated for lOmin-lh in consistent temperature get little change in the relative content; The relative content of consistent temperature heated product for1h-3h reduced rapidly with decreasing relative content of pyrrhotite; There is only hematite existing among the consistent temperature heated product for greater than3h and all the pyrrhotite despaired. So product of pyrrhotite heated for10minutes in consistent temperature get the maximum of the relative content of pyrrhotite.(3) Pyrrhotite crystals natural characteristics that belong to hexagonal system, Pyrrhotite-3T, chemical formula Fe7S8, neogenic pyrrhotite (700℃) crystallographic characteristics are:belonging to hexagonal, Pyrrhotite-4H, chemical formula Fe1-xS, showed that newborn pyrrhotite and natural pyrrhotite still have subtle differences.(4) Whether kidney-shaped hematite or oolitic hematite with sulfur after reaction did not generate other new substances, there is no characteristic peak of pyrrhotite or hematite peaks, sulfur and oxygen in the air generated after the reaction SO2evaporate out, and hematite are not any reaction. Therefore, hematite can not react with the sulfur pyrrhotite. So through its reaction function to calculate the thermodynamic:2Fe2O3+7Sâ†'700℃4FeS+3SO2The result is thatΔG=2269.96kJ·mol-1, then at700℃when the description of the reaction can not verify the experimental results, hematite and sulfur are heated to700℃in one hour can produce temperature pyrrhotite.(5) Based on the above experiments, the generation of newborn pyrrhotite is only one path, namely the formation of thermal decomposition of pyrite pyrrhotite. Because, through the thermodynamic functions calculated reaction:FeS2+O2â†'7000℃FeS+SO2The result is thatΔG=-272.04kJ·mol-1, and indicate that at700℃the reaction can be performed.