A selective agglomeration method to beneficiate coal

A physical process requiring a range of 10 to 30 weight percent water was investigated for the separation of mineral sulfur (pyritic) from coal. This method was based upon differences in the wettability of coal organic and mineral particles. Spray solutions containing chemicals to enhance this difference were sprayed into coal particles tumbling in a cylinder; selective pelletization of the minerals was the result. Coal particles in the size range of -80, +170 mesh containing approximately 0.86 wt.% organic sulfur and 1.16 wt. % pyritic sulfur were used.

The solutions used contained either a surface active agent (surfactant) alone or one combined with a "depressant" chemical. Anionic surfactants tested included sodium palmitate, sodium dodecyl sulfate, and ethyl xanthic acid, potassium salt. The cationic surfactant tested was hexadecyl trimethyl ammonium bromide. Depressant chemicals used were ferric sulfate and ferric chloride. In addition, the effect of varying the solution's pH was investigated over the range of 2.00 to 10.00.

Approximately 15 weight percent pellets and 85 weight percent cake was consistently produced in experimental runs regardless of the spray solution used. Cationic surfactants solutions gave results opposite of the expected. The concentration of the added chemicals, the amount of pellets produced, and the amount of spray solution added were all varied to investigate their effects on the selectivity of the sulfur in the pellets produced. The results of tests using anionic surfactants consistently showed a higher sulfur weight percent in the pellets than in the cake. However, this separation was too small under the conditions tested to be of economical significance. Also, better separation was effected at the low pHs.