Flocculation coal, selectivity

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. 

Sulfide collectors ia geaeral show Htfle affinity for nonsulfide minerals, thus separation of one sulfide from another becomes the main issue. The nonsulfide collectors are in general less selective and this is accentuated by the large similarities in surface properties between the various nonsulfide minerals (42). Some examples of sulfide flotation are copper sulfides flotation from siUceous gangue sequential flotation of sulfides of copper, lead, and zinc from complex and massive sulfide ores and flotation recovery of extremely small (a few ppm) amounts of precious metals. Examples of nonsulfide flotation include separation of sylvite, KCl, from haUte, NaCl, which are two soluble minerals having similar properties selective flocculation—flotation separation of iron oxides from siUca separation of feldspar from siUca, siUcates, and oxides phosphate rock separation from siUca and carbonates and coal flotation. 

Flotation is certainly the major separation method based on the surface chemistry of mineral particles. It is, however, not the only method. Selective flocculation and agglomeration may be mentioned as other methods used commercially to a limited extent. The former is for hematite, while the latter is for coal and finely divided metallic oxide minerals. Both processes use the same principles as described for flotation to obtain selectivity. In selective flocculation, polymeric flocculants are used. The flocculants selectively adsorb on the hematite, and the hematite floes form and settle readily. Thereby separation from the sili-... 

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

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. 

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. 

Preliminary testing of the unpurified polyxanthate dispersant mentioned earlier, during the selective flocculation of three high sulfur coals, is described here. The coal samples used for the study were Kentucky No. 9, Meigs Creek, and Ohio No. 6. The coal... 

Table 2. Material Balance for One-Step Selective Flocculation of Kentucky No. 9 Coal Using PAAX Dispersant and F1029-U Flocculant at pH 10 ( )...

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. 

Attia, Y. A., and Fuerstenau, D. W., "Feasibility of Cleaning High Sulfur Coal Fines by Selective Flocculation", Fourteenth Intern. Miner. Process Congr., Toronto, Canada, 1982. 

Fine coals in wash plant slurries Light hydrocarbon oil for selective flocculation heavy oil for balling. High intensity mixer for flocculate beneficiation, balling on a disc. 

The sequence of process operations for coal agglomeration is depicted in the generalized flow diagram of Fig. 8.2. Possible equipment for each step is also indicated. In general, equipment well-known in the chemical and mineral industries can be applied in the process. The operations consist of selective flocculation or microagglomeration, agglomerate recovery with simultaneous impurity rejection, further size enlargement of the recovered and... 

The above descriptions show the monomeric structures of starch, dextrin, cellulose, and guar gum. In reality, these polysaccharides can be extracted from different sources and the chain length and configuration, molecular weights, and the contents of impurities may vary considerably. Generally, starches have been used mainly as flocculants or flotation depressants for iron oxide minerals and phosphate minerals while the associated silica is floated. Dextrin has been mainly tested as depressants for inherently hydrophobic minerals such as talc, molybdenite, and coal [96]. Applications of polysaccharides in other mineral systems, both in the laboratory and in commercial processes, have also been frequently reported. As can be seen, the polysaccharides have been used or tested as selective depressants in practically all types of mineral systems, ranging from oxides, sulfides, salt-type, and inherently hydrophobic minerals. 

---