We studied the humic-acid fraction isolated from a Spanish leonardite coal (Torrelapaja, Cretaceous basin belonging to the Utrillas facies) using a suite of chromatographic and spectroscopic techniques to characterize the structure of the carbon skeleton and the nature of the sulfur-containing compounds. In particular, analytical pyrolysis coupled to gas chromatography-mass spectrometry was used to gain detailed molecular information on the organic structures. Pyrolysis in the presence of a methylating agent (tetramethyl-ammonium hydroxide, TMAH) was used to characterize polar moieties. We employed non-destructive techniques, XANES and XPS, to investigate the composition of the sulfur functionalities (such as sulfide, polysulfide, thiophene, sulfoxide, sulfonate and sulfate). The combination of these different approaches allows a more complete understanding of the organic sulfur structures in the leonardite coal. In agreement with previous studies, our results show that oxidized sulfur functionalities, such as sulfonate and sulfate, represent the major forms of sulfur in leonardite coal.

a Escola Universitária Politècnica de Manresa, Av. Bases de Manresa 61 -73, E-08240 -Manresa, Catalonia, Spain b Instituto de Recursos Naturales y Agrobiología de Sevilla, Consejo Superior de Investigaciones Cienttíficas, Campus Reina de Mercedes, Apartado 1052, E-41080 Sevilla, Spain c Instituto de Catálisis y Petroquímica, Consejo Superior de Investigaciones Científicas, Campus Universidad Autónoma, Cantoblanco, E-28049 Madrid, Spain d Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973, USA

The Financial support of Spanish contract PB97-0682 and US Department of Energy support through the Office of Basic Energy Sciences, Geosciences Program to the Brookhaven National Laboratory (Contract no. DEAC02-98CH10886) are acknowledged. Murthy Vairavamurthy acknowledges support by the U.S. Department of Energy, Division of Geosciences of the Office of the Basic Energy Sciences under Contract No. DE-AC02-98CH10886 for his contribution.

Peer reviewed