Sulfur Removal Techniques in Coal Processing

Coal often contains significant quantities of sulphur in mineral and organic forms, which on combustion yield sulphur dioxide and other pollutants linked to acid rain and respiratory illness. Traditional physical beneficiation methods such as gravity separation and flotation remove coarse mineral sulphides but are less effective against finely disseminated pyrite or organically bound sulphur. Chemical routes employ acid or alkali leaching to dissolve sulphur-bearing minerals and oxidise organosulphur groups, achieving high removal yields at the expense of reagent consumption and effluent treatment. Advanced processes harness supercritical fluids—most commonly carbon dioxide and water mixtures under elevated temperature and pressure—to enhance mass transport and selectivity without generating large volumes of acidic waste. Microwave-assisted desulphurization selectively heats sulphur compounds, promoting thermal or non-thermal reactions that transform pyrite and organic sulphides into extractable species. Emerging biological treatments exploit sulphur-oxidising or reducing microorganisms to convert sulphur into water-soluble forms under mild conditions, although scale-up remains challenging. Integration of complementary methods—such as combining microwave pre-treatment with chemical leaching or supercritical extraction—can improve overall efficiency and reduce environmental impact. Globally, these techniques support cleaner coal utilisation, improved combustion efficiency and compliance with stringent emissions regulations.

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Sulfur Removal Techniques in Coal Processing publication trend

The graph below shows the total number of articles in sulfur removal techniques in coal processing across all publications each year (not limited to Nature Index journals).

Technical terms

Pyritic sulphur: Sulphur present as iron disulphide (FeS₂) mineral inclusions within coal.

Organic sulphur: Sulphur chemically bonded to the carbon matrix of coal in forms such as thiophenes and sulfides.

Leaching: The selective dissolution of mineral or organosulphur components from coal using chemical solvents.

Supercritical fluid extraction: A process utilising fluids above their critical temperature and pressure to dissolve and remove target compounds.

Microwave desulphurization: Application of microwave energy to selectively heat and transform sulphur species, facilitating their subsequent removal.

References

1. Process engineering of demineralisation of moderate to high ash Indian coals through NaOH-HCl leaching and HF leaching. International Journal of Coal Science & Technology (2024).
2. Progress of the technique of coal microwave desulfurization. International Journal of Coal Science & Technology (2014).
3. Advances in the chemical leaching (inorgano-leaching), bio-leaching and desulphurisation of coals. International Journal of Coal Science & Technology (2019).
4. Beneficiation of coal using supercritical water and carbon dioxide extraction: sulfur removal. International Journal of Coal Science & Technology (2020).
5. Effect on Combustion Properties of Coal Treated by Microwave Irradiation Combined with Sodium Hydroxide Solution. Processes (2021).