Characterization of structural changes of mechanically activated natural pyrite using XRD line profile analysis

• High energy ball milling led to severe structural changes in pyrite lattice.
• The X-ray amorphization degree increased to 70% after 100 min intensive milling.
• The lattice volume of pyrite expanded due to vacancy formation.
• Crystallite size decreased and microstrain increased during mechanical activation.
• Pyrite structure is refined mainly by crystallite size rather than lattice strain.

In the present study, the X-ray diffraction line profile analysis was used for the characterization of structural changes in mechanically activated pyrite by a planetary ball mill. Applying the Williamson-Hall integral breadth and Warren-Averbach methods, comprehensive investigations were carried out on the XRD patterns in order to separate the crystallite size and microstrain contributions in XRD broadened patterns. The analysis of XRD patterns of mechanically activated pyrite indicated that no phase transformation occurred during milling operation. The results revealed that crystallite size and microstrain decreased and increased, respectively, during mechanical activation process. Volume weighted crystallite size (Dv), surface weighted crystallite size (Ds), strain (ε) and root mean square strain (RMSS) changed from 316 nm, 103.6 nm, 0.05% and 0.04% in initial pyrite to 57.73 nm, 25.1 nm, 0.224% and 0.117%, respectively, in mechanically activated pyrite for 100 min. In addition, the lattice parameter of mechanically activated pyrite increased as a function of milling time, implying that pyrite lattice volumes were expanded probably due to vacancy formation. Regarding to shape parameter study, the crystallite size broadening portion is more than the strain broadening portion on the broadened peaks in the XRD patterns of mechanically activated pyrite. This may be related to the fracture toughness of pyrite lattice, implying that pyrite structure is refined mainly by decreasing crystallite size rather than lattice strain. From surface area and particle size analysis, it can be confirmed that the agglomeration begins after 50 min mechanical activation. The X-ray amorphization degree increases to about 70% after 100 min intensive milling, reflecting the refractory nature of pyrite.

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