Influence of extractant on quality and trace elements content of peat humic acids

Among several extractants used to isolate humic acids (HA) from terrestrial environments, sodium hydroxide (NaOH) and sodium pyrophosphate (Na4P2O7) are the most utilized. In order to evaluate the influence of these different extractant solutions on the HA quality and on their trace elements content, HA were isolated from five Sphagnum-peat samples using three different solutions: (a) 0.5 M NaOH; (b) 0.1 M Na4P2O7; (c) 0.5 M NaOH + 0.1 M Na4P2O7. The obtained HA have been analyzed with respect to ash content, elemental composition, main atomic ratios and characterized by FT-IR and total luminescence (TL) spectroscopies. In addition, both raw peat and HA have been analyzed using X-ray fluorescence in order to determine the Br, Cu, Fe, Ni, Pb and Zn contents. Results showed that HA extracted with NaOH and NaOH + Na4P2O7 are quite similar with respect to ash, elemental contents and spectroscopic characteristics, while Na4P2O7 solution, which in general reduces the extraction yield, seems to affect the nature of HA, featuring a more complex and aromatic character. With respect to the contents in the corresponding raw peat samples, the HA fractions were richer in Br, Cu and Ni, regardless of the extractant used, and poorer in Fe, Pb and Zn. Further, Br, Cu, Ni and Zn were more concentrated in HA extracted with Na4P2O7 than in those extracted with NaOH and NaOH + Na4P2O7, probably because of the greater affinity of these elements for these more aromatic humic molecules.