Frequency Dependence of the Dielectric Properties of Coal

Publisher Website
Google Scholar
Abstract
The dielectric properties of pulverized coal samples from identified sources were measured at 22°C over the frequency range from 1 MHz to 12 GHz and are presented graphically. Chemical composition, moisture content, bulk and particle densities, and partical distributions were also determined, Run-of-mine samples, as well as dense pyrite-bearing fractions and light fractions relatively free of pyrite, were included in the study. Dielectric constants decreased regularly with increasing frequency and were positively correlated with density. Dielectric loss factors of pyrite-bearing fractions of lower sulfur content were high at frequencies below about 50 MHz, and decreased with increasing frequency to low values at microwave frequencies. In contrast, the loss factor of a pyrite-bearing fraction with high sulfer content was low at the lower frequencies and increased with increasing frequency fo high levels at microwave frequencies. Thus, selective dielectric heating of pyrite in coal to enhance its magnetic susceptibility for possible removal by magnetic separation can probably be best accomplished at microwave frequencies for some coals and at lower dielectric healing frequencies for others