Chemical Pretreatment of Coal in a Stirred Ball Mill

Present studies on the electrochemical aspects of pyrite flotation in the presence of reducing agent C were conducted to explain the effects observed during flotation of the separated organic and mineral-rich fractions of coal independently when sodium dithionite was used as an additive during and after grinding. In addition, the electrochemical phenomena occurring on the surface of pyrites of different origin were studied to aid in explaining the differences observed in the flotation of various coal-derived pyrite samples. Potentiometric and voltammetric measurements have been conducted on electrodes prepared from natural pyrite samples of mineral and coal origin. It was shown that the rest potential of pyrite electrodes decreases very significantly with increased concentration of sodium dithionite, increased pH, and stirring of solution. Mineral pyrite displayed lower potentials than pyrites of coal origin. Voltammetric curves recorded on FeS2 electrodes indicate the presence of elemental sulfur, iron-oxy, and iron-hydroxy compounds, even on the freshly prepared surfaces. The electrochemical results observed during this investigation are very suitable as preliminary tests of individual pyrite samples and enable prediction of the behavior of pyrite in a flotation pulp containing sodium dithionite.