Clarification of the reaction at the solution interface of pyrite during oil agglomeration for developing desulfurization and coal cleaning efficiency

Abstract

Recently, large amounts of waste fine coals have been produced which are difficult to treat because of the high ash content and inorganic sulfuric compounds. In order to make efficient use of waste fine coal, the retrieval technique is necessary for recovery of coal combustible content from fine waste coals. Nowadays a floatation process is able to operate, but it is impractical for developing countries due to high costs. An oil agglomeration process can deal with these problems. In this study, we investigate the mechanism of the solution interface reaction on oil agglomeration in order to separate pyrite sulfur effectively from waste fine coal. For this purpose, we adjusted the pH of the solution of oil agglomeration experiments to the basic condition, which changed the surface characteristics to hydrophilicity from hydrophobicity. Furthermore, pH and dissolved oxygen changes of the solution were continually monitored and free ferric ions of the waste liquid were measured by flame atomic absorption spectrometry. These factors have a relationship with the oxidation and surface reaction of pyrite sulfur in the solution. Under high basic conditions, pyrite sulfur reduction indicated high values since the pyrite surface became hydrophilic due to covering of the surface of the pyrite sulfur by ferric hydroxide. As a result, the pyrite content did not recover together with hydrophobic carbonaceous content especially under high basic conditions.