Abstract
PurposeTechnological progress and high market demand contributed to a significant interest in the production of fertilizers based on humic acids. The aim of this study was to evaluate the possibilities of using humic acids obtained from lignite in the production of new commercial products. For this purpose, it is necessary to determine the quality standard requirements for such material. Properties of humic acids depend on source of origin as well as method of its extraction.Materials and methodsThe humic acids were extracted from polish deposit of lignite–Sieniawa Lubuska by alkaline extraction using for this purpose six kinds of extractants: 0.1 M NaOH and 0.25 M NaOH, 0.1 M KOH and 0.25 M KOH, and 0.1 M Na4P2O7 and 0.25 M Na4P2O7. The humic samples were used in solid powder form and characterized by UV-Vis spectroscopy, 13C NMR spectroscopy, fluorescence spectroscopy, and thermal analysis.Results and discussionThe determining factor influencing a degree of humic acids extraction from lignite and their structure is type of extractant. The largest efficiency of extraction (about 50%) was obtained with the use of NaOH solutions. All examined humic acids were generally characterized by simple and heterogeneous molecularly structure with low molecular weight and low aromatic polycondensation. Therefore, it can be concluded that humic acids extracted with NaOH and KOH solutions are less condensed than those extracted with Na4P2O7 solutions. It can suggest that humic acids obtained from lignite using solutions of Na4P2O7 are characterized by a low transformation degree and greater amount of carboxyl groups.ConclusionsLow rank coal can be successfully used in agriculture as a rich source of humic acids. Reagent used in their extraction, apart from high efficiency should have a neutral impact on their structure. Studies on the physicochemical properties of humic acids can be helpful in predicting behaviors of such fertilizer components in the environment and in inventing new products taking the principles of sustainable development into consideration.
Highlights
Humic substances (HS) are known to perform many useful functions in soil and are considered to be one of the fundamental factors determining practically all properties and Responsible editor: Elżbieta Jamroz Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.J Soils Sediments (2018) 18:2868–28802002; Canellas et al 2002, 2014, 2015; Nardi et al 2016)
In order to classify lignite by type, the total moisture in the working state converted to the ash-free state (Wtraf) is used
It can suggest that humic acids obtained from lignite using solutions of Na4P2O7 are characterized by a low transformation degree
Summary
2002; Canellas et al 2002, 2014, 2015; Nardi et al 2016) For these reasons, it seems that the use of humic acids as agents which improve soil properties and affect the amount and quality of crops, it may be a perspective direction in the development of modern agriculture. It is recommended that such products should be well characterized physically and chemically This is not an easy task, even though there are many papers on examination of the structure and properties of humic compounds, not all features of these particles can be clearly specified. For this purpose, it is necessary to determine the quality standard requirements for such material
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