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The presence of pyrite in coal has long been known to affect the slagging propensity of the coal when burned in industrial boilers. In particular it has been found that molten pyrite bonds very well to steel furnace tubes. In addition, it has been found that the amount of chemically bound iron greatly influences the slag contact angle and stickiness on steel heat transfer tubes. The goal of this research, which is part of a larger project headed by the PSI Technology Company to study mineral matter transformations during combustion, is to explore and model the mechanisms dominating the fate of iron during combustion. To achieve this goal a well characterized suite of coals was burned in a 17kW downfired laboratory combustor. Fly ash was extracted from the flue gas and size classified. These ash samples were then subjected to a number of analytical techniques including Atomic Absorption Spectroscopy (AA), Energy Dispersive X-Ray (EDX), Computer Controlled Scanning Electron Microscopy (CCSEM), Transmission Electron Microscopy (TEM), and Mossbauer Spectroscopy to determine the ash bulk composition and morphology. Of these techniques, Transmission Electron Microscopy and Mossbauer, were instrumental in determining the iron-silicate interactions during combustion. Utilizing the information gleaned from the fly ash analysis, and work in the literature, it was possible to propose a pathway for iron interactions during combustion. A mechanistic model was then proposed to quantify the competition between processes governing iron oxidation/crystallization and those promoting iron-silicate mixing/reaction. This model described the partitioning of iron between chemically bound and physically bound phases. By utilizing kinetic parameters from the literature and fundamental transport phenomena, this model was able to successfully correlate data from several coals burned under a range of combustion conditions. The model can also be used to quantify the effect of combustion modifications and fuel property changes on iron partitioning.

A detailed study of the physical and chemical characteristics of a flue dust sample from a coal fired reverberatory furnace was carried out. The characterization studies revealed that cuprous ferrite, delafossite, is one of the major copper bearing constituents in flue dusts collected from copper reverberatory furnaces. A knowledge of the leaching characteristics of delafossite is thus essential to the development of hydrometallurgical techniques for copper recovery from flue dusts. The recovery of copper from synthetic delafossite was investigated using an ammoniacal carbonate solution. The results obtained indicate that the dissolution of delafossite in ammoniacal solution is very slow, but can be dramatically improved by a reductive roast prior to leaching. The kinetics of dissolution of delafossite has been found to strongly depend on the extent of reduction, particle size and stirring speed. It has also been found that applied oxygen pressure increases the rate of dissolution and accentuates the particle size effect. The experimental data seem to fit a film diffusion model. Limited studies have been carried out on the recovery of copper from a flue dust collected from a coal fired reverberatory furnace. Results from these studies have been compared with those obtained for synthetic delafossite.

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