Browsing by Author "Paul, Anton Dilojaan"

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    Electrocatalytically induced liberation of mineral matter from coal
    Paul, Anton Dilojaan (Virginia Polytechnic Institute and State University, 1988)
    A new method for demineralizing coal has been developed which is based on the osmotic pressures that occur when electrical double layers overlap. In this technique, coal is exposed to ferric ions in an acidic medium which causes the coal to lose electrons and become positively charged, thereby establishing ionic double layers in the vicinity of its surface. Inside the pores and crevices in which mineral matter is entrapped, the ionic double layers overlap and reduce the chemical potential of water, creating an osmotic pressure. The build-up of such pressure pushes the mineral matter out of the crevices, resulting in mineral liberation. Since the process, which is termed electro catalytically induced liberation (EIL), relies on surface-chemical reactions, the energy consumption is substantially lower than in conventional liberation processes based on comminution. Tests on several different seams of coal from varying geological locations have indicated that the process may be used to remove over 70% of the mineral matter present in coal. Mass balance studies conducted on a Wyodak coal indicate that approximately 90% of the ash removed is by the EIL mechanism, while the balance may be attributed to acid dissolution and the loss of material during handling. Scanning electron micrographs of the coal samples taken before and after treatment show morphological changes consistent with the proposed EIL mechanism. The technique has been used successfully to clean bituminous coals, low-rank coals and preparation plant refuse, and to further reduce the ash content of coals pre-cleaned by other means. A theoretical model has been developed to calculate the osmotic pressure that occurs inside a typical coal crevice during the EIL treatment. The changes in the aqueous chemical potential are calculated using semi-empirical equations derived from solution theory, while partial molar volume changes are accounted for in the final calculation of the osmotic pressure. The model indicates that pressures on the order of 4-7 atmospheres can develop inside crevices with walls 100-1000Å apart. These values are numerically consistent with those predicted by other models developed using different approaches.
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    Pretreatment of coal by anodic electrolysis of acidified coal- water slurries
    Paul, Anton Dilojaan (Virginia Polytechnic Institute and State University, 1984)
    Pretreatment of Pittsburg seam B coals to decrease its ash content and increase its solvent extractable material was investigated by anodically electrolysing acidified coal-water slurries at potentials around 1.0V SCE. The effects of the pretreatment were examined as functions of coal particle size, acid strength of the slurry, time of electrolysis and applied potential. The coal electrolysis was found to be most efficient at low acid strengths and short electrolysis times. The morphology of the coal surface changed with the conditions of the electrolysis and related to the percentage ash removal and the amount of solvent extractable material present in the coal. The anodic oxidation of the coal is suspected to occur via an electrocatalytic(EC) mechanism, whereby ferrous ions in the coal are first oxidised at the anode to the ferric state. The ferric ions migrate into the coal and accept electrons from accessible bonds in the coal micelle thereby reducing themselves back to ferrous ions and return to the anode for re-oxidation to the ferric state. The acceptance of electrons from certain bonds in the coal micelle results in the break-up of the micelle in to simpler compounds. Accordingly, the solubility of the coal in an organic solvent should increase and this was found to be so when ferrous ions were externally added to the electrolyte. The electrolytic process was also found to transfer metallic ions present in the coal into solution in the electrolyte.