Pyrite surface characterization and control for advanced fine coal desulfurization technologies

The objective of this project is to conduct extensive studies on the surface reactivity and surface hydrophobicity of coal-pyrites using various surface characterization techniques and to correlate the alteration of the coal-pyrite surface with the efficiency of pyrite rejection in coal flotation. The flotation characteristics of coal-pyrites under various conditions was studied and compared with ore-pyrite and coal to determine the causes of pyrite rejection difficulties in coal flotation. Both the native and induced floatabilities of pyrites were investigated. It was found that both coal- and ore-pyrites, ff prepared by dry-grinding, show little or no floatability in the absence of any chemical reagents. After ultrasonic pretreatment, ore-pyrite floats effectively in the acidic to neutral pH range. Kentucky No. 9 coal-pyrite (KYPY) shows significant flotation in the pH range 7--10. With ethyl xanthate as collector, ore-pyrite floats well up to pH = 10; while coal-pyrite reveals no flotation above pH = 6. For the first time, the effect of coal collector on the floatability of coal-pyrite has been studied. It was shown that in the presence of fuel oil--a widely used collector for promoting coal flotation, coal-pyrite, particularly for the fine sizes, shows good flotation below pH = 11, whereas ore-pyrite has no or little floatability. These studies demonstrate that one of the main causes of the coal-pyrite flotation in coal separation is the oil-induced floatability due to adsorption/attachment of oil droplets on the coal-pyrite surfaces, the native'' or self-induced'' floatability of pyrite is no as profound as the oil-induced flotation