| In order to investigate Hg migration and removal rules in industrial separation process and to explore the means of deep removal, we perform spot sampling in Inner Mongolia, Ningxia, Hebei, and Guizhou. Different methods were used to identify the occurrence and correlation of Hg and S(Ash) in the six coals, such as, sequential chemical extraction test, mathematical statistics, the industry analysis, elemental analysis, X-ray diffraction analysis, and X-ray fluorescence spectral analysis. The means of deep removal were studied by flotation, flotation- gravity, and flotationchemical leaching in laboratory.The results of XRD showed that silicate minerals in six coals are the main minerals. Quartz was distributed in the rest of five coals except CP1. The minerals phases found in some coal are calcite, dolomite and pyrite. SiO2/Al2O3 showed a higher degree clayzation in CP1 coal, CP3 and CP4 coal second, the rest of three coal samples contain more free silica, clayzation level is the lowest. On the basis of the TiO2/Al2O3 ratio show volcanic ash source in CP1, CP2, CP3, CP4 coals and terrigenous source in CP5 and CP6.Correlation analysis showed that good fit(R2>0.700) were obtained between Hg and S found in CP1, CP4, and CP6 coal. The correlations between Hg and S were negatively(R2=-0.828) in CP2 coal. There is a positive correlation between Hg and ash in coal country, and good fit(R2>0.900) were obtained in CP2, CP4, CP6. Regression analyses were used to establish statistical correlations between Hg and S(Ash) in some coals. Sequential leaching tests showed that the content of pyrite-Hg in coal was more than 50%, except for CP2 coal. Secondly, the content of residue-Hg is relatively low, but it is more than 20%, and the content of other bound Hg is relatively low.Mercury in coal in those samples migrates with the move of ash or sulfur in separation process. The trends to migrate with particle sizes, which depend on the dissemination characteristics, are different due to different samples. Except for few links, mercury usually enriches in gangues, tailings and coal slimes. Relatively, the removal of mercury by heavy medium separation is better than that by flotation, and the efficiency to remove mercury is different in each craft link, which ranges from 4%~75%, and it depends on the liberation degree of carrier mineral of mercury. After washing, the removal ratio of mercury ranges from 40% to 75% for clean coal in each coal preparation plant.The removal of Hg was remarkable influenced by regulation of agent in flotation test. The maximum of RHg-R in CP4 and CP2 were 37.11% and 46%, respectively, by adjusting dosage of collection and frother. The step by step releasing test show that RHg-R would increase with the released times and then reached to a critical value. The utilization of depressor for carrier minerals is good for the removal of Hg, however, adverse to the index of quantity and quality.The feasibility analysis of flotation-gravity process indicated that removal effects are associated with the distribution of Hg in density fractions. The process is appropriate to the coal in which Hg has an affinity with specific density fraction rather than the coal in which Hg is uniform distribution in different density component.Flotation-chemical leaching process which is effective in reducing the enrichment degree of Hg in both CP4 and CP2 coal samples. This process is more suitable for CP4 sample, in which the inorganic-bound Hg is dominant: reducing the content of Hg to 59.87μg /kg and the enrichment degree of Hg to 4.99, consequently, decreasing the degree of Hg enrichment from enrichment level to mild enrichment level. A reduction of Hg content of 63% can be obtained via this approach for CP4 coal sample. The Hg content and degree of Hg enrichment of CP2 coal sample can be decreased to 93μg /kg, 7.75 respectively by use of this approach with the limitation of Hg reduction of 38%, reducing the degree of Hg enrichment from High enrichment level to enrichment level. |
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