Studies of incipient oxidation of coal-pyrite for improved pyrite rejection. First quarterly technical progress report, October 1, 1992--December 31, 1992

Abstract

In order to foster the development of advanced coal cleaning technologies, fundamental studies of the initial stages of pyrite oxidation have been initiated. This work is being done on pyrite surfaces that are freshly fractured in an electrolyte solution. This procedure produces surfaces that are initially unoxidized, allowing the subsequent oxidation processes to be studied in detail. It is shown that freshly fractured pyrite electrodes instantaneously (at fracture) assume a rest potential several hundred millivolts more negative than the usual open-circuit potential. i i A finite, anodic photocurrent, is also observed on the fractured electrodes. Following cleavage,. the rest potential increases, indicating an oxidation reaction occurring on the electrodes. The photocurrent is relatively insensitive to this oxidation process, and to moderate anodic and cathodic polarization. However, strong cathodic polarization to about-0.76 V (SHE) at pH 9.2 causes the photocurrent to decrease to zero. No reversal in the sign of the photocurrent is observed and it is believed that the flat band potential occurs near-0.76 V, i.e., where the photocurrent goes to zero. Voltammetry indicates that pyrite also undergoes cathodic decomposition at-0.76 V. This establishes that pyrite must be cathodically decomposed to reach the flat band potential. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Referencc herein to any specific commercial product, prt'_.css,or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the ,,| United States Government or any agency thereof.