Effect of oxidation on separation of coal and pyrite by selective oil agglomeration

The separation of coal and pyrite particles by selective agglomeration with oil can be troublesome for coals which are weakly hydrophobic or hydrophilic and, therefore, are not strongly agglomerable. The hydrophobicity of lower rank coals and other coals which have become oxidized is generally low. The problem of separating such coals from pyrite was studied by oxidizing a moderately hydrophobic coal with air at 150{degrees}C for either 8, 20, or 72 hr to systematically reduce its hydrophobicity. Samples of the raw and treated coal were subsequently mixed with aged mineral pyrite from Peru and agglomerated with heptone. Although a mixture of the raw, unoxidized coal and pyrite was largely separated by this method, it proved increasingly difficult to separate the materials as the coal became increasingly oxidized. While raw coal was agglomerated in preference to pyrite, this preference changed as the coal was oxidized. After 20 hr. of oxidation, coal and pyrite were agglomerated almost to the same extent. Finally after 72 hr. of oxidation, more pyrite was agglomerated than coal.