Demineralization and Desulfurization of High-Sulfur Assam Coal with Alkali Treatment

Abstract

Demineralization and desulfurization of high-sulfur coal from Assam (Makum coalfield), India, was investigated using aqueous solutions of sodium hydroxide, potassium hydroxide, and their mixtures (1:1) alone as well as followed by mild hydrochloric acid treatment. Compared to the alkali and acid alone, successive treatments with the alkali and acid resulted in significant removal of mineral matter and sulfur from the coal. Demineralization and desulfurization was found to increase with the increase in alkali concentration. Alkali treatment resulted in formation and precipitation of sodium/potassium aluminosilicates, which subsequently undergo decomposition and solubilization in the presence of acid-forming soluble salts. It is possible to remove 50-54% of the ash, total inorganic sulfur, and around 25% organic sulfur from the coal by treatment with mixtures (1:1) of 16% sodium hydroxide and potassium hydroxide solution followed by 10% hydrochloric acid.

Chemical Leaching on Sulfur and Mineral Matter Removal from Asphaltite (Harbul, SE Anatolia, Turkey)

“…Most of the pyritic and sulfate sulfur Silopi asphaltites were eliminated using the Meyers method (Hamamci et al, 1997;Doymaz et al, 2007;Saydut et al, 2008c;Duz et al, 2008;Elsamak et al, 2003). Besides this method, chemical cleaning of solid fuel and oil asphaltene has been studied using alkali solutions (Balaz et al, 2001;Mukherjee and Borthakur, 2003;Mukherjee, 2003;Gulen et al, 2005;Seferinoglu et al, 2003;Lee and Choi, 2000;Karacan et al, 1999;Saydut et al, 2007;Hicyilmaz and Altun, 2006;Bolat et al, 1998;Yaman and Kucukbayrak, 1999;Chriswell et al, 1994). During the aqueous caustic leaching of solid fuel, caustic reacts with minerals and organo sulfur compounds present in fuel to form water-soluble alkali metal salts (Ityokumbul, 1994).…”

Coal mining in northeast India: an overview of environmental issues and treatment approaches

“…Solvent extraction using dimethyl formamide (DMF) increased desulfurization of the oxidized Baragolai and Ledo coals up to 95 % and 93 % for inorganic sulfur and 31 % and 23 % organic sulfur, respectively, while the alkali treatment showed complete removal of inorganic sulfur and a maximum of 33 % and 26.4 % organic sulfur for these coals, respectively (Baruah and Khare 2007b). Alkali treatment of high sulfur Assam coal using mixtures (1:1) of 16 % sodium hydroxide and potassium hydroxide solution followed by 10 % hydrochloric acid could remove 50 %-54 % of the ash, total inorganic sulfur, and around 25 % organic sulfur (Mukherjee 2003). 9.4 % of the total organic sulfur was removed by electron transfer process (Borah and Baruah 1999).…”

Demineralization of low grade coal – A review

“…Chemical demineralization processes, either alone or following physical cleaning processes, have been extensively explored for the production of UCC. Some of the chemical demineralization processes which have been investigated, include leaching with NaOH [112], NaOH followed by mineral acids [113][114][115][116][117], KOH-acids [115,118], Na 2 CO 3 [119], Ca(OH) 2 followed by acid washing [120], mineral acids viz. HNO 3 [121][122][123], HCl [116], H 2 SO 4 [124,125], oxidizing agents viz.…”