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Effect of Pretreatment on Pyritic Sulphur
Reduction from Coal Biological
attack of pyrite is a potential method of reducing pyritic sulphur in coal. Integration of
such attacks with microwave pretreatment can enhance the efficiency of the process.
Alternatively, processes such as oil-agglomeration can be coupled with the biological
attack to obtain higher rates of pyritic sulphur removal. In this study desulphurization
of Indian (Assam) coal was carried out under two contrasting modes of operation, i.e.
physical (microwave) pretreatment of coal followed by biological desulphurization using Thiobacillus
ferrooxidans (method 1) and bacterial pretreatment of coal followed by physical
technique of oil agglomeration (method 2). Microwave pretreatment of coal did not show any
improvement in pyritic sulphur reduction (PSR) during subsequent biodesulphurization. On
the other hand, significant PSR in short period was observed using method 2 and the PSR
increased further by increasing the cell concentration in bacterial pretreatment liquor.
To examine the effect of bacterial metabolites, Thiobacillus ferrooxidans
membrane-filtered bacterial liquor (TMFBL) which contained no bacterial cells, was used
for pretreatment for various time periods. Even in absence of cells using TMFBL,
significant PSR (96.2%) could be achieved by 120min pretreatment. However, pretreatment of
coal with mixed bacterial liquor (MBL) did not produce substantial PSR, thus indicating
specificity of Thiobacillus ferrooxidans for pyrite removal. This study indicates
that the method 2 is a much better process for pyrite removal as compared to the method 1.
High PSR (82.7-99.1%) and cleaner coal product with increased calorific value were
obtained in short period (2.5 -120 minutes) using method 2 as compared to 76.2% PSR in
20-day period by method 1.
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