# Methods for Obtaining Humus Substances: Advantages and Disadvantages
## 3 Results and Discussion
### Advantages and Disadvantages
It is caused by HA precipitation (the highest at pH < 2) and the formation of insoluble calcium salts. The content of calcium ions in HS(B) is significant and amounts to 23,800 mg/kg (Table 2). Barium salts are also insoluble. Barium content in HS(B) is 92 mg/kg (Table 2). Insoluble Si and Fe compounds can also form. Coagulation (gelation) is promoted by compensating the negative charge of the -OH and -COOH ion exchange groups with potassium cations. Their content amounts to 68,300 mg/kg (Table 2). Figure 8 shows the dependence of the turbidity of the HS(B) solution on its pH. It indicates a rapid increase in turbidity at pH < 2, caused by precipitation of HAs, which are insoluble in a strongly acidic environment. Figure 6: Particles suspended in HS(B) solution, solution concentration 0.1 g\({}_{\mathrm{DM}}\)/L: (**A**) zeta potential, (B) particle size. Figure 7: Particles suspended in HS(B) solution, solution concentration 0.1 g\({}_{\mathrm{DM}}\)/L, microscopic image: (**A**) \(\times\)40, (**B**) \(\times\)100. TOC content analysis (Table 5) showed that the HS(A) solution at a concentration of 0.1 g\({}_{\text{DM}}\)/L contained an average of 34.31 mg C/L. After precipitation of HA with HCl, it still contained an average of 34.15 mg C/L, which is 99.5% of TOC. Thus, the HS(A) solution consisted mainly of FA, which was 99.5%. On the other hand, the HS(B) solution at a concentration of 0.1 g DM./L contained 46.09 mg C/L. After the precipitation of HA with HCl, only 3.05 mg C/L was left, which was only 6.6% of the initial TOC. Thus, we can assume that the HS(B) solution contained only 6.6% of FA. The small content of fulvic acids (only 6.6%) soluble at any pH, the high content of poorly soluble HA, the presence of a solid suspension of brown coal particles (Figure 7), and the high content of mineral substances (29.59% of ash), including calcium ions forming insoluble salts, contribute to the transformation of the HS(B) sol into a gel. This is caused by the poor selection of raw material (brown coal). Brown coals are highly humidified, and contain large amounts of carbon and small amounts of oxygen. They are more aromatic and have few aliphatic functional groups. They are difficult to dissolve; therefore, they are not a good raw material for obtaining soluble humic substances. The elemental composition of HS(B) (Table 1) confirms the above. HS(B) contains 71.01% C and 20.89% O. HS(A) are different. They contain 55.33% coal and 38.15% oxygen. The \begin{table}
\begin{tabular}{c c c c} \hline  & **HS(A)** & & **HS(B)** \\ \hline
**pH** & **T [NTU]** & **pH** & **T [NTU]** \\ \hline
9.80 & 0.0 & 10.5 & 21.8 \\ \hline
8.77 & 0.0 & 8.8 & 22.7 \\ \hline
5.22 & 0.0 & 7.6 & 21.5 \\ \hline
4.20 & 0.0 & 6.5 & 22.8 \\ \hline
2.90 & 0.0 & 4.7 & 24.2 \\ \hline
0.97 & 0.57 & 3.4 & 26.2 \\ \hline
0.95 & 1.08 & 2.73 & 26.2 \\ \hline
0.84 & 0.80 & 1.5 & 40.7 \\ \hline
0.81 & 0.83 & 0.7 & 40.5 \\ \hline \end{tabular}
\end{table} 
Table 4: Turbidity of HS(A) and HS(B) solutions. Figure 8: Turbidity of HS(B) solution vs. pH. differences in values are significant and prove a high degree of humification of the HS(B) and the hydrophilic nature of HS(A). Similar dependency was obtained for hydrogen, 5.18% in HS(A) and 7.10% in HS(B), which confirms the high degree of humification of HS(B). Oxidized brown coals from the surface layer of the deposit, e.g., leonardite, lignite brown coals with a well-preserved wood structure, and earthy coals with consistency from loose to solid or shaly brown coals, are much better for the extraction of humic substances.