The mercury release from coal gangue
and coal slime has attracted
wide interest, because of the utilization of coal gangue and coal
slime in some power plants. In order to develop the Hg control technology,
it is necessary to gain the information on the Hg release during thermal
treatment of coal gangue and coal slime. This paper presents a study
about Hg release during thermal treatment of two coal gangues and
coal slimes under air and N2 atmosphere through the online
atomic fluorescence spectroscopy aided with the Ontario Hydro Method.
The result shows that the release profiles of Hg for the two coal
gangues and two coal slimes are similar under the same atmosphere,
respectively. Most of the Hg is released at <650 °C under
a N2 atmosphere and at<500–550 °C under
air for all of the samples. The release ratio of Hg2+ is
much lower than that of Hg0 for each sample. The release
ratio of Hg0 released under N2 is more than
that under air. Because of the high volatility of Hg, the release
ratio of total Hg is much higher than the corresponding volatile yield
in any case investigated in this study. Meanwhile, the Hg0 release profiles for the samples show two or three peaks under N2 atmosphere, suggesting that different modes of occurrence
of mercury are presented in the coal gangues and coal slimes.
The utilization of coal gangue in power plants has become a new anthropogenic discharge source of mercury and attracted much concern in China. It is crucial to obtain the information about the mercury release during thermal treatment of coal gangue. In this study, the mercury release behavior of two coal gangues selected from two power plants were studied under different thermal treatment conditions of heating rate, residence time, and atmosphere. The results of mercury release profile show that the specified release temperature ranges for the different modes of occurrence of Hg are scarcely affected by the heating rate of 10, 20, and 40 °C/min. A higher heating rate could promote the Hg release to some extent. The mercury release ratio gradually increases with the extension of residence time for both coal gangues. The oxidizing environment has a positive effect on mercury release < 600 °C and has a minor effect > 600 °C. Mercury in coal gangue is more volatile than coal gangue matrix and the mercury in GD coal gangue is more easily released out than that in ED coal gangue.
Release behaviors of arsenic (As) during pyrolysis of two Chinese coal gangues were studied in this report. The pyrolysis experiments were carried out in a temperature programmed tube furnace under N 2 atmosphere with different temperature (200-1200 °C), residence time (0-50 min), heating rate (10-50 °C min -1 ) and N 2 gas flow rate (100-500 cm 3 min -1 ). The experiment results, under different pyrolysis conditions, indicate that the release ratio of As increases with increasing temperature, as well as residence time during pyrolysis of coal gangues. Besides that, higher heating rate during pyrolysis of coal gangues can stimulate the As release from coal gangue to some extent. The release ratio of As increases to a maximum and then decreases when the N 2 gas flow rate is increased. The results imply that different modes of ocurrence of As exist in two coal gangues. The As release has positive relation with the volatile matter release. As is more easily released than coal gangue matrix during coal gangue pyrolysis.
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