Heating Phases Of Pyrite And Their Magnetic Property

Pyrite is the most stable iron sulphide in reducing environment, and the mostabundant of the sulphide minerals and its occurrences are very widespread. As a rockformingmineral, pyrite can provide a variety of important geological information; asa gold-bearing mineral, it has great significance to gold prospecting and extraction. Toprovide scientific basis on purification processing, industrial application andtechnological properties research of pyrite, using X-ray diffraction (XRD) , Infraredspectra(IR), Thermal analysis and so on, focus on the study of mineral compositionstructure and changes'characteristics, mineral paragenetic association, magneticchanges'characteristics and mechanism of heating transformation process in pyrite atdifferent temperatures between room temperature and 1250℃for period of 1h in air.The achievement and progress of the research are as the following,(1)The heating products of the pyrite at different temperatures between roomtemperature and 1250℃for period of 1h in air were investigated using X-raydiffraction (XRD) and the phases and their diffraction peaks were analyzed using theX'Pert HighScore software. These investigations showed that the existing temperaturerange of pyrite and its heating products are: pyrite, room temperature to700℃; 4Hpyrrhotite,500—1200℃(maximum value, 700℃); magnetite, 1000—1200℃(maximum value, 1000℃); hematite, the final product, 350—950℃(maximum value,900℃) or≥1200℃. There are seven mineral paragenetic associations during thetransformation processes: room temperature to 300℃, pyrite; 350—400℃, pyrite +hematite (trace); 500—700℃, pyrite + 4H-pyrrhotite + hematite (trace); 700—950℃,4H-pyrrhotite + hematite; 1000—1100℃, 4H-pyrrhotite+ magnetite; about 1200℃,hematite + magnetite + pyrrhotite (trace);≥1250℃, hematite. Moreover, according tothese results we discussed the possible formation pathways of pyrrhotite, magnetiteand hematite, respectively.(2) Infrared absorption spectrum of pyrite from room temperature—1250℃ (400—1800cm^-1), generate pyrite, pyrrhotite, magnetite, hematite. Pyrite(roomtemperature—700℃), absorption band of pyrite is 420cm^-1; pyrrhotite(400—1200℃), absorption band of pyrrhotite is 470cm^-1, 540cm^-1; magnetite (1000℃—1200℃), absorption band of magnetite is 565cm^-1; Hematite (≥1200℃), absorption bandof hematite is 480cm^-1, 619cm^-1, 795cm^-1, 1090cm^-1.(3) In the air condition, DTA-TG-DTG of pyrite from room temperature to 900℃, three heat-sink valley in DTA curve, with the obvious weightlessness reaction,weight loss for 33.92% in TG curve from room temperature to 900℃, with SO₂ gasescaping. There are three peaks in DTG curve, 490.0℃, 564.1℃and 605.1℃,probably because pyrite oxidation reaction, generating hematite and pyrrhotite. Inthe argon condition, DTA-TG-DTG of pyrite from room temperature to 900℃, twoheat-sink valley in DTA curve, with the obvious weightlessness reaction, weight lossfor 25.78% in TG curve from room temperature to 900℃. There are two peaks inDTG curve, 523.3℃and 673.7℃, because pyrite desulfurization reaction generatepyrrhotite and pyrite.(4) The susceptibility variation of heating products of pyrite from roomtemperature to 1250℃is asymmetrical saddle. Two peaks, the first peak appearsbetween 700 and 800℃, the second peak (magnetic maximum) appears at 1000℃.Specific change processes as follows: before 400℃, pyrite; 400℃, antiferromagnetichematite generates, magnetic susceptibility increases slightly; ferromagneticpyrrhotite generates at 550℃, magnetic susceptibility increases rapidly; the contentof pyrrhotite is the most at 700℃, reaching to relative maximum; magneticsusceptibility reaches maximum at 1000℃. In 700℃constant temperatureconditions, magnetism of pyrite is: 10min^-1h, magnetic susceptibility is the strongest,a little change; after 1h magnetic susceptibility gradually reduces; after 3h magneticsusceptibility is weak and stable. The reason is: 10min^-1h, main phases arepyrrhotite and hematite, content changes little; after 1h, pyrrhotite less, hematiteincreases; 3h, only heating product hematite exists.