REGULATION OF THE COMPOSITION AND PROPERTIES OF HUMIC SUBSTANCES DURING ACID TREATMENT

Abstract

Introduction. Humic substances (HS) are promising natural sorbents that contain carboxyl, phenolic, hydroxyl and other functional groups, which ensures their high reactivity and tendency to complex with heavy and transition metals, influencing their migration, bioavailability and toxicity.The aim of the work is to investigate the influence of various factors on the production of humic acids from the domestic natural raw materials. Methods: standardized methods, elemental and functional analysis, IR spectroscopy, and thermogravimetry. Results and discussion. Research has been conducted on the production of humic acids (HA) by reacting sodium humate with hydrochloric acid. It has been shown that the regulation of the HCl concentration, liquid phase ratio, reaction time and temperature allows one to control the yield of HAdaf (up to 78.31%), the content of COOH and OHphen. groups (up to 1.20 and 1.62 mmol/g), the total pore volume (up to 0.58 cm3/g) and static exchange capacity (up to 21.10 mg-eq/g). The determined optimal synthesis parameters (sodium humate concentration of 3.0%, liquid phase ratio 1:1, treatment for 15 min at 20°C) ensure reproducible properties of the HA and their high efficiency in the sorption of metal ions. The elemental analysis and the calculation of the H/C and O/C atomic ratios have shown that the structure of the synthesized the HA is heterogeneous, including aromatic and aliphatic fragments. It has been found that an increase in the HCl concentration initiates an oxidative-hydrolytic destruction of the peripheral structures with a simultaneous increase in the oxygen-containing functional groups, which determine the sorption activity of the HAs. The data of the thermal analysis and IR spectroscopy confirm the preservation of the functional groups up to 350°C and are consistent with the degradation processes at higher temperatures. Conclusion. A process flow diagram for producing humic acids under the “mild” conditions has been developed. It is characterized by flexibility, low waste generation, and the ability to produce humic sorbents with a specified composition. The synthesized HA have sorption, ion exchange and other properties and are promising for practical application.