Search

Influences of the factors, reaction time, temperature, nitric acid concentration and nitric acid/coal ratio were studied by factorial analysis in relation to the response in the total, hydrolysable and available nitrogen contents of the nitrohumic acids obtained when two Spanish lignites were treated with nitric acid. Correlations between the hydrolysable and the available nitrogen, and the optical properties of the nitrohumic acids have been studied to obtain a more simple and rapid index to determine the available nitrogen of the nitro-lignites.

The humic acids, HA, extracted from a Spanish lignite and the nitrohumic acids, NHA, and nitrofulvic acids, NFA, extracted from the same lignite after its nitration, are hydrolysed with 6N HCI under reflux. The α-amino acids present in the hydrolysates are determined and thirteen α-amino acids are identified. The amounts of nitrogen in the amino-acids released by the hydrolysis increase according to the sequence: NFA > NHA > HA .

Potentiometric titrations in dimethylformamide and dimethylsulphoxide have been performed in order to differentiate between the acidic groups of fulvic acids. With dimethylformamide as medium the best results have been obtained with potassium hydroxide as titrant, whereas both potassium hydroxide and tetrabutylammonium hydroxide yield good titrations in dimethylsulphoxide. The number of acidic groups differentiated depended on the solvent and titrant used; in the best case four sharp end-points were obtained. Titrations with potassium hydroxide are preferred.