Effects of impurities on the structural and magnetic properties of natural iron sulphides from the lake Victoria gold field.
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Date
2002
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University of Dar es Salaam
Abstract
Three techniques, namely, X-ray Fluorescence, X-ray diffraction and Mössbauer spectroscopy were used to study the effects of impurities on the structural and magnetic properties of natural iron sulphides from the Lake Victoria gold field. Pyrite and pyrrhotite being the main component of the iron sulphide in this area were investigated. The major impurities contained in the samples ranged from 30,000 to 230,000 ppm for Silicon and Aluminum, 20,000 to 60,000 ppm for Calcium, 2,000 to 9,000 ppm for Titanium, 3,0000 to 21,000 ppm for Potassium and Cobalt 10 to 46 ppm. It was found that Aluminum and Silicon impurities decreased the inter-atomic spacing of the pyrite, the unit cell dimension decreased from 5.41 A for pure pyrite to about 5.36 A for natural pyrite. Cobalt impurities were observed to increase the inter-atomic spacing of the pyrite, and the associated unit cell dimension increased from 5.41 A for pure pyrite to about 5.43 A. However, there was no significant change observed on the crystal parameters of natural pyrrhotite. This study found that pyrite is diamagnetic at 295K and 4.2K and pyrrhotite is ferrimagnetic at both temperatures. The Aluminium and Silicon impurities were found to decrease the magnetic hyperfine fields of the pyrrhotite implying the decreasing effects on the magnetic properties of pyrrhotite. Whereas, Cobalt was found to increase the magnetic hyperfine field of pyrrhotite indicating an increasing effect of the magnetic properties of pyrrhotite. In addition, Aluminium and Silicon were found to increase the quadruple splitting of both pyrite and pyrrhotite. From these findings, it is was concluded that AI and Si decrease the crystal structure parameters of pyrite and weaken the magnetic properties of pyrrhotite, whereas Cobalt increases the crystal structure parameters and enhances the magnetic properties of pyrrhotite. Further studies, however, are recommended in order to determine the effects of other impurities on the properties of pyrite and pyrrhotite phases from the lake Victoria gold field.
Description
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF QC766.I7B34)
Keywords
Iron sulphides, Magnetic properties, Magnetic structures, Impurities
Citation
Banzi, F. P. (2002). Effects of impurities on the structural and magnetic properties of natural iron sulphides from the lake Victoria gold field. Master dissertation, University of Dar es Salaam.