Pyrite selective dispersion

Separation of Ultrafine Pyrite from High Sulfur Coals by Selective Dispersion and Flocculation... 

The key to this separation was the design and preparation of the selective dispersant for pyrite (PAAX). 

The polyxanthate dispersant, rather than improving the dispersion of pyrite, simply did not adsorb on the coal particles, thereby creating a selective dispersion action for the pyrite. These observations in Figure 2(B) were repeated and noted several times, even with purified PAAX solutions. Selective dispersion of pyrite or... 

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. 

The lower rejection ratio of 16 was accompanied by high selectivity in pyritic sulfur dispersion. This was due to the higher (10 mg/l) flocculant concentration which resulted in higher coal yield (93.1 wt) in the flocculated fraction. On the other extreme, when higher dispersant concentration (500 mg/l) was used with lower flocculant concentration (2 mg/l), much less coal was flocculated (77 wt) and more sulfur was apparently rejected (39 ). The intermediate conditions of 300 mg/l PAAX dispersant and 2 mg/l flocculant produced correspondingly intermediate results. 

A novel technique for separating ultrafine pyrite particles (minus 1 0 micrometers) from coal fines has been conceptually developed and tested. The technique involves the use of a selective polymeric dispersant for pyrite, while flocculating coal particles with a polymeric flocculant. The suspended pyrite can then be removed from the flocculated coal fines which settle preferentially by gravity. 

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. 

Given the local enrichments of arsenic locally present in pyrite of Appalachian Basin coal, enviromnental impacts are possible. Dispersal of arsenic from coal to stream sediments and soils may occur by both natural weathering and mining disturbance. Because arsenic in coal is commonly associated with iron sulfide minerals, much of the arsenic will be avoided by mining practices that favor selection of low sulfur (low pyrite) coal or that remove pyrite from the coal during coal preparation. In addition, disposal of the resulting coal or wash waste could present some concern because arsenic maybe concentrated in these materials. 

Froth Flotation. The incoming coal feed may be agitated in a controlled amount of water, air, and reagents that cause a surface froth to form, the bubbles of which selectively attach themselves to coal particles and keep them buoyant while the heavier particles of pyrite, slate, and shale remain dispersed in the water. This method can be used in cleaning smaller particles, Mo in by 0 (no minimum), particularly particles smaller than 48 mesh. 

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