Pyrite suspensions, selective

In order to ascertain that the selective dispersion effect of PAAX was truly due to the modified polymer itself and not to the associated poly-sulfides in the crude reaction, the flocculation testing was repeated with the purified PAAX solution. By using 300 mg/l of the purified PAAX solution, about 96 percent of the coal suspension flocculated in 5 minutes, while the pyrite suspension remained stable. These tests confirmed that the selective dispersion action was due to the PAAX (polyxanthate polymer) itself. 

Effect of Pyrite Particle Size on Dispersion. It was suspected that a lot of the apparently non-dispersed pyrite particles shown in Figure 2 was due to the settling of hoarse particles between 10 and 37 micrometers. Pyrite has a specific gravity of about 5 0, while that of coal is around 1.2-1.3 Therefore, a pyrite suspension having only particle size below 10 micrometers was prepared and tested. The results, which are also shown in Figure 2(b), showed that the minus 10 micrometer pyrite suspension remained very stable, with only 10 - 20% weight of the particles settled or flocculated. From these observations, it is believed that the selective dispersion of pyrite will be more effective for the smaller particle sizes. 

One of the promising new technologies for separation of very fine particles is selective flocculation. The selective flocculation process has been used effectively to separate very finely disseminated minerals from mixed ore suspensions (5.). The process is based on the preferential adsorption of an organic flocculant on the wanted minerals, thereby flocculating them, while leaving the remainder of the suspension particles dispersed. The dispersion of certain components in the suspension such as pyrite can be enhanced by using more selective or powerful dispersants. Methods for achieving selective flocculation and dispersion have been recently described by Attia (6j. 

At the end of the settling period, the suspended solids were decanted, and the settled solids were recovered. Each fraction was placed in an evaporating dish, oven dried and weighed. Selective flocculation of coal mixtures with pyrite was made on suspensions containing equal proportions of coal and pyrite, using 200 mg/l PAAX dispersant at pH 10. The flocculation procedure was the same as described above, except that the products were qualitatively analyzed by visual inspection of both fractions. The coal samples used in these experiments were anthracite coal, supplied by Wilkes-Barre, Pennsylvania, and the pyrite used was pure crystals from Wards Natural Sciences, Inc., Rochester, N.Y. 

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