Chemical demineralization of high ash Indian coal by using alkali and acid solutions

- Adequate demineralization of high ash coal obtained by acid and alkali treatment.
- Degree of demineralization depends on coal particle size and process conditions.
- More than 50% minerals present in coal are leached out by acid/alkali treatment.
- The sodium complex formed restrict the demineralization at higher alkali solution.
- The calorific value increased with the degree of demineralization.

In the present work an attempt have been made to upgrade the low grade Indian coal to high grade coal by using caustic (NaOH) leaching followed by acid (H2SO4) treatment. The experimental works aimed at a selective attack on in situ MCL (Mahanadi Coal Limited) coal, Odisha, India with some fluxing agents like NaOH and H2SO4. The leaching experiments were carried out in a stainless steel batch reactor of 2.5 L capacity with controlled heating facility. Initially, the coal sample with −16+100 mesh particle size was leached with 50-150 g/L of NaOH solution at 100 °C for one hour and then subjected to leach further with 20% sulfuric acid. The maximum demineralization from the level of 26% ash with NaOH (100 g/L) leaching 27.5% is achieved and with combined chemical treatment method (100 g/L NaOH followed by 20% H2SO4) was obtained 48% effectively. In addition, the results showed that the percent of demineralization improved adequately by decreasing the particle size also with rise of the leaching time and temperature. Coal characterization of raw and treated coal was done by Scanning Electron Microscopy (SEM)/Energy Dispersive Spectroscopy (EDS) analysis and also showed that the calorific value of coal was increased with increase the percent of demineralization of coal.

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