Nickel sulphide (NiS) was characterised using X-ray diffraction, thermal gravimetric analysis (TG) and differential scanning
calorimetry (DSC). The 'as received' Millerite, stoichiometric NiS, observed to be slightly nickel deficient, was found to
readily decompose in a nitrogen atmosphere at elevated temperatures (450C max.) to the sulphur deficient Godlevskite, Ni7S6. DSC and X-ray measurements demonstrated that the high temperature form of the Godlevskite was readily stabilised at room
temperature. The kinetics of the α-β re-transformation in Godlevskite were then investigated using DSC and were observed to
be first order.
Authors:D. Bishop, P. Thomas, A. Ray, and P. Šimon
Toughened glass panels used as a glazing material in multistorey buildings are known to fracture prematurely when they contain
nickel sulfide inclusions as a result of the α-β phase recrystallisation in nickel sulfide. The kinetics of this recrystallisation
were studied by differential scanning calorimetry (DSC) under isothermal and non-isothermal conditions. The recrystallisation
was observed to be a two-step process with an induction period followed by the phase change. A two-stage kinetic model was
used to estimate the recrystallisation time under ambient conditions. These values were found to correlate well with the observed
time to failure for glass panels installed in multistorey buildings.
The DSC characterisation of the morphology of the metastable a phase of stoichiometric nickel sulphide was carried out using
two calorimeters; a TA Instruments 2920 MDSC and a Perkin Elmer DSC-7, and two quenching histories. Based on these quenching
histories, significant differences were observed in the heat flow curves, including the observation of a second exothermic
peak which is tentatively assigned to be a metastable phase to metastable phase transformation. The kinetic constants for
the a to b recrystallisation were determined as a function of degree of conversion using a mechanism free isoconversional
model. Variations in the values of the kinetic constants were also ascribed to the quenching histories. Although the differences
in morphology observed were ascribed to the processing history, the shift in the position of the a to b recrystallisation
peak was partially attributed to the thermal resistances of the instruments used.
The determination of ultratrace concentrations of Pt in rock samples using nickel sulphide fire assay combined with neutron activation analysis (NiS-NAA) is influenced by the presence of Te in the irradiated noble metal concentrate. Interference caused by123mTe on the 158 keV peak of199Au (produced from198Pt) is discussed with reference to a noble metal standard (Wits-1) and sedimentary rocks which generally have low Pt concentrations and high Te/Pt ratios. The importance of a rigorously controlled dissolution of the fire assay button to achieve complete removal of Te is emphasized.
Neutron activation analysis after a nickel sulphide fire assay preconcentration for platinum group elements (PGE) has been established in our laboratory. In this work, the all PGE in DZ-2, a Chinese certified ultramafic rock standard reference material, are determined for testing the accuracy and precision of the method. The experimental conditions and the blank values from reagents and detection limits for the method are also presented.
Authors:Li Xiaolin, Tong Chunhan, Zhu Jieqing, and Zhang Jiaohua
In determining the trace platinum group elements and gold in rocks and ores by the neutron activation analysis after a nickel sulphide fire assay preconcentration, there are interferences due to nuclides produced from second order nuclear reactions. This paper presents the degree of interference calculated over the ranges of long irradiation times and of reactor neutron flux from 1·1013 to 1·1015 n·cm–2·s–1. According to the results of these calculations, every one of the second order interfering reactions on the PGE+Au, except the197Au(n, )198Au(n, )199Au reaction, can be neglected under the long irradiation time or high reactor neutron flux. Special attention is given to the interference from gold in the determining platinum.
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 20–45Μm, 45–75Μm, 75–90Μm and 90–125Μm. 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.
Summary A pseudo-isothermal method for the kinetic analysis was applied to the recrystallisation of a to ß nickel sulphide based on the Ozawa model for non-isothermal crystallisation in the presence of pre-existing nuclei. The aim of the analysis was to determine the number of steps involved in the recrystallisation and, hence, determine the applicability of the kinetic equation based on a single step mechanism, as is commonly applied in the kinetic analysis of solid-state processes using thermal methods. The kinetic analysis yielded evidence of at least two processes indicating that physical and mechanistic significance should not be drawn from the use of a single step approximation of the rate equation.
the final product. Tris(ethylenediamine)nickel(II) sulphate undergoes a two stage decomposition in helium and gives a mixture of nickel and nickelsulphide as the final residues. Simultaneous TG/DTA coupled online with mass spectra (MS) in helium