# Testing of Natural Sorbents for the Assessment of Heavy Metal Ions' Adsorption
## 3 The Results of the Experimental Studies and Discussion
To fix the structure of the sorbents, an Altami MET 1 digital microscope and an SNE4500M scanning electron microscope were used. The sorption properties of peat were due to the highly developed surface (Figure 3) and the presence in its composition of various functional groups, such as amine, amide, alcohol, aldehyde, carboxyl, ketone, phenolic, kinone and peptide groups. The adsorptive properties of peat were due to the presence of lignin, humic and fulvic acids [29; 30]. Figure 1: Efficiency of the sorbents (A) in relation to the grade of heavy metal ion extraction from the model solutions. It should be noted that peat takes up a special place among the effective natural sorbents of heavy metals. Peat-based sorbents are good stabilizers of heavy metal ions. These sorbents have a higher sorption capacity than other single-component sorbents [31]. Figure 3: The surface of the peat–diatomite granular sorbent (Altami MET 1 optical microscope (Altami Ltd, Russia; it has been sourced from St. Petersburg, Russia); magnification \(\times\)40). Figure 2: The total value of the degree of extraction of heavy metal ions (A) by various sorbents. On the one hand, diatomic does not contain a larger number of different functional groups than peat. On the other hand, diatomic has a high porosity (Figure 4) and corresponding adsorption properties. Vermiculite is a mineral from the hydronica group. During heat treatment, vermiculite swells and multiplies in space, which also increases the area of the adsorbing surface (Figure 5). Exfoliated vermiculite has a variety of applications, including being a sorbent for gaseous and liquid industrial waste. The study of the vermiculite's efficiency of heavy metal adsorption in comparison with other sorbents was also shown in [32], with the exception of peat-diatomic. In this research [32], [PERSON] and [PERSON] used several types of ameliorants: vermiculite, zeolite, apatite superphosphate and lime. The residual copper content in the soils after the use of vermiculite on average did not exceed 9% of the initial concentration [32]. Their results are comparable to our study. The use of peat and diatomic separately from each other was researched in [33; 34]. In [34], filter modules were used to study the processes of sorption and desorption of emission components by materials of a vermiculite-sungulite composition, obtained through the enrichment of phlogopite mining waste. The study [34] concluded that pure peat had the greatest sorption capacity. The study in [33] used diatomic rocks. The equilibrium state for the removal of heavy metals by diatomic clay was obtained by adding a constant mass of the absorbent (0.5, 1.0 and 2.0 g) to 100 mL of the initial concentrations of the prepared aqueous solution of heavy metals. The exposure time was 4 h. After that, the samples were filtered by using filter paper. The concentrations of various heavy metal ions were measured by using the ICP-MS method. It was concluded that the use of Egyptian diatomic demonstrated a significant efficiency of heavy metal adsorption [33; 34]. The results of this study show a significant increase in the adsorption efficiency when two sorbents (peat-granular diatomic) are mixed in equal proportions (Figure 2). It is remarkable that the granular physical shape increases the heavy metal adsorption. Testing other proportions of different natural sorbents with various recipes of preparation, includ  
Figure 4: The surface of diatomic (SNE 4500M microscope). ing different physical shapes, is the direction of future studies. Due to the research results, a patent has been obtained: \"Peat ameliorant for the remediation of lands contaminated with heavy metals\" RU 2 745 456, dated 9 March 2020.