Modelling of Humic Acids Extraction Process Assisted by Low-Intensity Ultrasound with the Use of Three-Level Fractional Factorial Design.

The multitude of beneficial properties of humic acids (HA), due, among other, to the presence of numerous functional groups in their structure, determines their increasing industrial use, not only in agriculture but also as feed components or ingredients in food supplements. The continuous increase in demand for these substances determines their high market value and prompts the search for efficient methods to isolate them from natural raw materials. However, in addition to the high isolation efficiency of humic acids, the quality aspect is equally important when selecting extraction methods, and the extraction method should not cause changes within the natural structure of the macromolecules. In the present study, a complex analysis of the application of low-intensity ultrasound-assisted extraction (LI-UAE) for the isolation of humic acids from peat was presented. Based on the fractional factorial design and statistical analysis, the influence of the parameters of the LI-UAE process on the efficiency of humic acids extraction with the use of NaOH and NH₄OH solutions as extractants was described. The polynomial models, which defined the efficiency of the extraction process as a function of the most important parameters, were proposed, and the optimal extraction conditions were identified for both extactants tested. On the basis of the results, it was concluded that the use of ultrasound increases the amount of extracted humic acids, compared to the traditional process. Moreover, qualitative analysis of the products, using spectroscopic methods, did not show significant differences in the molecular structure of the humic acids, which were extracted in the processes studied. [ABSTRACT FROM AUTHOR]