Lignite cations

Humic acids are alkaH-extractable materials and total humic acid content is a term that refers to the humic acid content of coal that has had its carboxylate cations removed with sodium pyrophosphate. Values for some typical AustraHan brown coals range from 24—92% (13). Treatment of lignitic coals with mineral acid to release the alkaH and alkaline cations may dissolve up to 20% of the coal. The naturally moist coals are slightly acidic and have a pH of 3.5—6.5. 

Bituminous coal ash is often higher in pyritic Fe than subbituminous or lignite ashes, which are often higher in Ca and/or other basic elements. As a result of the increased content of pyritic Fe, bituminous coal ashes may form acidic solutions when mixed with water. Conversely, subbituminous and lignite coals often form basic solutions when mixed with water due to their lower content of pyrite and/or their high content of basic cations. Therefore the pH of ash leachate can range from acidic to basic values depending on coal source (see Donahoe, this volume). 

Role of Exchangeable Cations in the Rapid Pyrolysis of Lignites... 

MORGAN AND JENKINS Exchangeable Cations in Lignite Pyrolysis... 

A Montana lignite (Fort Union Seam) was utilized in this study. The major inorganic constituents present in this lignite can be classified as discrete mineral phases and ion-exchangeable cations. 

Cationic Effects During Lignite Pyrolysis and Combustion... 

A Texas lignite was acid-washed to remove its ion exchangeable cations then alkaline-earth metals (Ca,... 

Lignite Preparation. The coal chosen is a Texas lignite, PSOC-623, from the Darco seam. The coal was obtained from the PSU-DOE coal sample bank and data base. This particular coal was chosen because it has been previously well characterized ( ) and because it contains a large quantity of ion-exchangeable cations. 

The distribution of the cations on the raw coal and the quantity of each cation back exchanged on the acid-washed coal is shown in Table II. These determinations were made by atomic absorption spectroscopy. The acid-washing was fairly efficient, removing over 99% of the cations present on the raw coal. Less than 0.01 wt% cations remained on the acid-washed lignite. The predominant cations on the raw coal were Ca and Mg, these two accounting for over 90% of the total quantity. As shown in Table II, the quantity of cations back exchanged on the acid-washed coal was greater than that... 

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