Due to the positive effect on soil structure and the influence on improving the efficiency of plant roots nutrient uptake, humic acids (HA) are widely considered for fertilizer production. Especially, it seems to be particularly promising to use them as additives in technologies of mineral fertilizer production. One of the common mineral fertilizer components, due to its good water solubility and the presence of nitrogen in two forms, is ammonium nitrate (AN). The aim of this study was to determine the influence of the humic acids extracted from peat and lignite on the thermal decomposition of HA and the thermal decomposition of ammonium nitrate and humic acids mixtures. For the quality assessment of HA, spectroscopic methods (FTIR/ATR and CP/MAS ¹³C NMR) and analysis of elemental composition were used. The analysis of the spectra showed differences in the degree of humification of humic acids extracted from various raw materials. HA isolated from peat were distinguished by the presence of peptides, polysaccharides, and lignin residues. Elemental analysis showed the higher carbon and sulfur content in the extracted HA compared to the reference samples. The results of the TG-DTA-MS analysis confirmed the influence of differences in the molecular structure of humic acids, especially in the aliphatic and aromatic carbon content, on the thermal decomposition process. Total content of carboxylic and/or hydroxylic functional groups had a significant impact on the start of the decomposition temperature. Their increase visibly influenced the acceleration of the exothermic decomposition of AN.

Samples of pure ammonium nitrate (AN) and its mixtures with calcium carbonate, potassium hydrogen carbonate and potassium carbonate were investigated with the use of differential thermal analysis with mass spectrometry, powder X-ray diffraction and scanning electron microscopy. The main objective of the study was to determine the influence of selected carbonate materials on phase transitions of ammonium nitrate and to consider a possibility to use such potassium salts as fillers in fertilizer production. It was proven that all carbonate salts caused the absence of a phase transition that normally would occur at around 84–86 °C. Potassium carbonates were too reactive in systems containing AN. Based on the performed study, it was concluded that even though potassium carbonates are not fit to replace mineral fillers in the production process of fertilizers containing ammonium nitrate, they could be used in lesser amounts to remove the presence of low-temperature phase transitions of AN.

The overall effect of reactants in the form of sulfates of ammonium, calcium, copper(II), iron(III), manganese(II) and zinc on the thermal behavior of ammonium nitrate has been reported. Thermal stability assessment was performed with the use of thermogravimetric analysis and differential thermal analysis coupled with mass spectroscopy. Interestingly, sulfate anions present in the system were often not sufficient to properly inhibit the decomposition of ammonium nitrate. Sulfate ion and cation supplied with the selected compound significantly influence the studied process. Studied mixtures with ammonium sulfate and calcium sulfate were concluded to show the highest stability. Manganese and iron sulfate salts caused a significant acceleration of the initial thermal decomposition. The addition of these compounds led to visible changes in the process mechanism, which allowed them to be classified as catalysts of the decomposition of ammonium nitrate. Furthermore, small amounts of substances in the system, even those that are generally considered to be inhibitors, worsened the thermal stability of AN. Zinc and copper sulfates, under studied conditions, created double salts that were characterized by a higher thermal stability than pure ammonium nitrate. This property indicates the possibility of obtaining systems containing ammonium nitrate with significantly higher thermal stability, what could potentially have multiple useful applications.

The influence of cobalt, copper, iron(III), manganese and zinc nitrate salts on phase transitions and thermal stability of ammonium nitrate (AN) has been studied and discussed. Differential thermal analysis/differential scanning calorimetry coupled with thermogravimetry and mass spectrometry were used to evaluate the stability of analyzed systems. Each nitrate salt was appropriately mixed with ammonium nitrate to create samples with AN:salt mass ratios of 4:1, 9:1 and 49:1. It was concluded that the addition of every studied nitrate influenced phase transitions of AN. Most analyzed salts decreased the stability of AN by accelerating its exothermic decomposition process. Iron and cobalt nitrates were defined as the most hazardous additives, resulting in a creation of a highly destabilized mixture. Copper and manganese nitrates were also defined as catalysts of the AN decomposition process, lowering the initial decomposition temperature and increasing the rate of the observed process. Zinc nitrate hexahydrate was the only salt considered to be relatively neutral in such systems, especially in small amounts. The study allowed to define the influence of selected metal nitrate salts on the thermal stability of AN under conditions that are considered as potentially unsafe for such systems.