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Microwave heating characteristics of pyrite and microwave assisted coal desulphurization

Uslu, Tuncay
In this study, microwave heating characteristics of pyrite mineral and desulphurization of Aşkale Lignite, by using magnetic separation after the microwave heating, were investigated. Different size of pyrite samples were heated in a microwave oven and heating characteristics of the samples were determined. It was observed that heating rates and maximum attained temperatures increased with increasing microwave power, treatment time and finer particle size. Microwave heated pyrite samples were subjected to magnetic separation and 98 % of the pyrite was removed as magnetic product. In order to study the possibilities of sulphur removal from lignites with high pyrite content, Aşkale r.o.m lignite was crushed to -19 mm and cleaned to some 111extent by sink-float process. Ash, total sulphur and pyritic sulphur contents were reduced by 14.35 %, 5.1 1 % and 7.71 % respectively. Pre-cleaned coal was subjected to magnetic separation test at 2 Tesla with different sizes and the best result was obtained for -0.15 mm particle size. Ash, total sulphur and pyritic sulphur contents were reduced by 15.79 %, 16.92 % and 22.29 %, respectively. Various size fractions of pre-cleaned coal were treated in microwave oven for different times and treated samples were subjected to magnetic separation. The increase in magnetic property of pyrite heated at 850 W and 2.45GHz, was not adequate for removing significant amount of pyrite at 2 Tesla magnetic field intensity. Nevertheless, magnetic property of pyrite increased slightly and for -0.15 mm particle size, total sulphur and pyritic sulphur contents were reduced by 32.82 % and 37.46 % respectively, by magnetic separation. Magnetite which is an excellent microwave absorbing mineral was added to the pre-cleaned coal so as to increase the microwave heating property of pyrite in coal. With 7.5 % magnetite addition, total sulphur and pyritic sulphur contents of pre-cleaned coal of -0.15 mm size were reduced by 52.05 % and 58.20 % respectively, by magnetic separation at 2 Tesla after microwave heating.