An XPS study of the oxidation of pyrite and pyrites in coal

X-ray Photoelectron Spectroscopy (XPS) was used to study mineral, synthetic and coal-associated pyrites, oxidized for various time intervals at low temperatures with humid air or oxygen. This was done to find out if XPS could detect, monitor and clarify pyrite surface-oxidative changes that influence surface-dependent coal-cleaning methods such as froth flotation, and could provide a means of directly analysing coal sulphur, by determining if oxidizing conditions existed which would effectively eliminate the surface pyrite whose XPS peak may occur at the same energy as the organic sulphur peak of coal. The conditions of study were as follows: a mineral and two coals containing pyrite were exposed to air at 24 ± 3 ° C and 33 ± 8% relative humidity up to 600 h; two mineral pyrites were exposed to oxygen at 100% relative humidity and 35 ° C for up to 200 h; and the two mineral and a synthetic pyrite were exposed to oxygen at 100% relative humidity and 55 ° C for up to 300 h and at 72°C for 25 h. The results indicated that the XPS S2p pyrite peak at ≈169 eV and the surface-oxidation-product(s) peak(s) at ≈163 eV could be detected and followed with XPS, although no conclusions could be made about the oxidation mechanism. The pyrite XPS peak became small compared to that of its oxidation products when the synthetic and mineral pyrites were exposed to 55 ° C oxygen at 100% relative humidity for 300 h. These conditions may prove useful in trying to determine directly the organic sulphur in coal.     

Effect of Heat Treatment Upon the Chemical Composition of Cottonseed Meal and Upon the Reactivity of Cottonseed Condensed Tannins

The effects of heat treatment on the chemical composition of cottonseed meal (CSM), with or without the addition of cottonseed hulls (containing condensed tannins; CT), and upon reactivity of the CT were studied. Heat was applied in a forced draught oven at 100°C for 2 h. Fluorodinitrobenzene (FDNB)-available lysine, free gossypol, extractable- and bound-CT concentrations, in vitro total nitrogen (N) solubility and the in vitro rumen degradation of the two major seed proteins (52 and 48 kDa) present in cottonseed kernel (which does not contain CT) were determined. The reactivity of CT was assessed by determining N solubility and rumen degradation of cottonseed kernel proteins in the presence or absence of polyethylene glycol (PEG; molecular weight (MW) 3500), which binds and inactivates CT. Heat treatment reduced the concentrations of free gossypol and FDNB-available lysine by small amounts, reduced measurable total CT content by 13%, reduced the solubility of total N, and reduced potential degradability of the 52 and 48 kDa cottonseed storage proteins by mixed rumen microorganisms. Addition of hulls further depressed solubility of total N and ruminal degradation of the two major storage proteins in cottonseed kernel. The action of PEG in vitro indicated that only part of the depression caused by hull addition could be explained by the presence of CT in the hulls, and that the effects of CT upon N solubility and potential degradability in heated CSM were similar to that in unheated CSM. Addition of hulls also substantially reduced FDNB-available lysine. In commercially produced materials, CSM from the Brisbane mill had a lower total CT content, lower N solubility and lower ruminal protein degradation rate than CSM from the Narrabri mill, but a similar level of FDNB-available lysine. Although application of heat inactivated 13% of the total CT, such that it could no longer be extracted and detected with butanol/HCl, it did not seem to change the overall effects produced by CT in reducing N solubility and protein degradation. The effect of hull addition in reducing available lysine has considerable relevance for feeding CSM to monogastric livestock. Interactions involving heat, hulls and CT need to be further studied.