Purpose Technological 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 methods The 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 Na 4 P 2 O 7 and 0.25 M Na 4 P 2 O 7 . The humic samples were used in solid powder form and characterized by UV-Vis spectroscopy, 13 C NMR spectroscopy, fluorescence spectroscopy, and thermal analysis. Results and discussion The 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 Na 4 P 2 O 7 solutions. It can suggest that humic acids obtained from lignite using solutions of Na 4 P 2 O 7 are characterized by a low transformation degree and greater amount of carboxyl groups. Conclusions Low 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.

In the light of environmental law utilization lignite waste in non-energy sectors of the economy is a rational way to manage them. Lignite due to the lower degree of coalification and calorific value as well as a high content of humic substances becomes a valuable component of fertilizer. The paper presents the possibility of using lignite waste as a raw material in the process of obtaining humic acids with 0.1 M NaOH. The idea of the process combines production, environmental and economic purposes. After the extraction process of humic acids and considering the possibility of using waste formed during the process, were carried out a number of studies to assist in choosing the best solution to its management.

Granular fertilizers (especially those based on ammonium nitrate (AN)) tend to agglomerate during storage. The aims of this research were to develop effective anti-caking coatings for ammonium nitrate fertilizers while improving the quality of fertilizers and to optimize the composition of effective anti-caking coatings. The influence of the composition of the prepared organic coatings on the effectiveness of preventing the caking of fertilizers was studied by response surface methodology (RSM) using Box–Behnken design (BBD). Additionally, the effect of the developed anti-caking agents on the quality of fertilizers was determined by measuring the crushing strength of the granules. The prepared coatings included fatty amine, stearic acid, surfactant, and paraffin wax. Gas chromatography–mass spectrometry (GC–MS) was used to analyze these coatings. The morphology of the fertilizers were examined by scanning electron microscopy (SEM). Composition studies, based on statistical assessment, showed the coating components had a varying influence on preventing the caking of fertilizers after granulation and after 30 days of storage. The results demonstrated that increasing the content of fatty amines and reducing surfactant in the composition of coating had positive effects on caking prevention. In this study, more effective and economically viable anti-caking coatings were developed. In addition, the present work could serve as a basis to further improve anti-caking coatings.