矿物加工煤的浮选英文文献及参考文献 第4页
oxidation can also result in the production of finer particles, which may be difficult to float.
In determining the effect of oxidation on coal floatability, the behavior of the associated mineral matter, especially pyrite, should also be taken into account. Oxidation of pyrite leads to the generation of various soluble inorganics that can adsorb on the coal surface and modify its wettability while pyrite itself was reported to show improved hydrophobicity upon oxidation [Tao et al., 1994].
2.1.3. Effect of coal particle–promoter interactions on flotation
Promoters act as surface modifiers and may alter hydrophobicity depending on the rank of coal and promoter concentration [Laskowski, 1993, Laskowski and Miller, 1984, Laskowski and Romero, 1996, Onlin and Aplan, 1987, Onlin and Aplan, 1989, Chander et al., 1994, Chander et al., 1996, Polat and Chander, 1998, Polat and Chander, 1999, Polat et al., 1994a, Polat et al., 1994b, Celik and Seyhan, 1995 and Vamvuka and Agridiotis, 2001]. A change in the surface properties of the coal particles affects their attachment and detachment characteristics with other dispersed phases in flotation pu毕业论文
http://www.751com.cn lp. In the flotation of low rank or oxidized coals with highly negative surfaces in the pH range of 3–5, the use of cationic promoters enhance flotation [Campell and Sun, 1970, Aplan, 1989, Zheng, 1997 and Vamvuka and Agridiotis, 2001]. [Bustamante and Woods, 1984] found that adsorption of dodecylammonium on non-polar parts of the coal surface decreased its hydrophobicity, while adsorption on the mineral matter caused an increase in hydrophobicity. On weathered coal where both the carbonaceous and the mineral matter were extensively negatively charged, dodecylammonium was adsorbed with the polar group interacting with surface and therefore all types of composite grains became hydrophobic.
Non-ionic surfactants and water-soluble polymers have been utilized to modify the coal surface [Harris, 1995]. [Li et al., 1992] who used a comb-like polymer found that the coal became more hydrophobic with increasing promoter concentration regardless of its original floatability. The PEO/PPO/PEO triblock co-polymers were also found to improve coal flotation and the mechanism of polymer action was a function of the coal rank [Polat and Chander, 1995, Polat and Chander, 1998, Polat and Chander, 1999, Polat et al., 1994a, Polat et al., 1994b, Polat et al., 1997 and Chander, 1997]. These reagents had double effect on flotation: they modified the coal surface and also they improved the emulsification of the oily collector. For high rank coals, which usually require relatively small amounts of the collector, the surface modifier function of the polymers was dominant over their emulsifier function. The polymer increased ash rejection in flotation primarily because the coal agglomerates, which were observed in the flotation cell, were smaller and considered to be more selective. For medium and low rank coals, where larger oil concentrations were required, the polymer acted both as an emulsifier and a surface modifier. It was suggested based on the surface tension and contact angle studies that adsorption of the block co-polymers at coal/water interface occurred by adsorption of PPO groups by hydrophobic attraction on the most hydrophobic sites, and adsorption of PEO groups by hydrogen bonding on the hydrophilic sites. The coverage of the hydrophilic sites on the surface by the promoter molecules was proposed to be the mechanism by which hydrophobicity increased. For the high rank coals, which contain a relatively small number of hydrophilic sites, the polymer adsorbed on hydrophobic sites, rendering coal less hydrophobic. This was the reason for the observed increase in selectivity for high rank coals since it caused a decrease in the size of the coal agglomerates, hence, in the amounts of ash particles entrapped in the agglomerate structure.
Even though it is common practice to float coal from the associated mineral matter, several investigators have suggested the flotation of pyrite from coal with simultaneous depression of coal. Some coal depressants used in the literature are sulphydryl collectors, natural and modified starches such as dextrines and nonionic polymers polyacrylamide and polyethylene oxide [Miller, 1973, Aplan, 1976, Aplan, 1977 and Moudgil, 1983]. Nearly all coal depressants are also pyrite depressants at a similar or somewhat higher concentration. Several pyrite depressants have been used in the literature; oxidizing agents such as potassium dichromate and sodium hypochlorite, reducing agents such as sodium sulfide and sodium thiosulfate, physically adsorbed colloids such as starches, various dyes such as congo red and nigrosine, dispersing ag本文来自辣文论文网原文请找QQ752018766ent such as sodium silicate and Aerosol OT and Quebracho, complexing agents such as citric acid and sodium cyanide, hydrolyzed ions such as various ferric and ferrous chlorides and sulfates, bacteria such as thiobacillus ferrooxidans and surface tension modifiers such as methanol and butylbenzaldehyde are some examples [Chander and Aplan, 1989]. Use of such depressants assumes that the pyrite is naturally hydrophobic floats along with the bituminous material.
In a recent paper, [Kawatra and Eisele, 1997] concluded that pyrite floats mainly in the form of entrainment with water or in the form of locked particles with coal, not because of its inherent hydrophobicity. Their data are re-plotted in Fig. 4 to establish various correlations. Combustible matter (CM), pyrite and ash-mineral recoveries are plotted as a function of water recovery in Fig. 4a. The data clearly shows that the selectivity follows the order: combustible matter>pyrite>ash-mineral up to a combustible matter recovery of 85–90%. For CM recoveries greater than 85%, flotation of locked mineral particles is indicated. Since the slope of the curves is less one (shown by a light line) in the high recovery
上一页 [1] [2] [3] [4] [5] [6] 下一页
矿物加工煤的浮选英文文献及参考文献 第4页下载如图片无法显示或论文不完整，请联系qq752018766
