# Characteristics of Removal of Lead, Cadmium and Chromium from Soil Using Biosorbent and Biochar
## 3 Result and Discussion  
### Characterizations of Materials  
The thermogravimetric analysis allowed for the measurement and recording of parameters such as sample mass (mg) and temperature (\({}^{\circ}\)C). The experimental data enabled the creation of TG and DTG profiles, which facilitated the identification of stages in the thermal degradation of biomass along with characteristic temperature ranges. The graphical representation of the thermogravimetric analysis is shown in Figure 1. Based on this, it was found that the combustion process of aspen wood sawdust occurs in three main stages: moisture evaporation, devolatilization, and combustion. The thermogravimetric curve shows that in the initial phase up to \(\sim\)100 \({}^{\circ}\)C, moisture is removed from the wood (mass loss of approximately 6.5%). The main thermal degradation process of the biomass starts above 200 \({}^{\circ}\)C and proceeds in two stages, corresponding to peaks at 317 \({}^{\circ}\)C and 444 \({}^{\circ}\)C on the DTG curve. In the first stage, the degradation of hemicellulose (\(\sim\)220 \({}^{\circ}\)C), which is less thermally stable compared to cellulose, and cellulose (\(\sim\)315 \({}^{\circ}\)C) occurs [28]. It can be assumed that the onset of cellulose thermal degradation, along with the ongoing continuous degradation of hemicellulose, generally increases the degradation rate [29]. In the second stage, a thermal effect at 444 \({}^{\circ}\)C is observed, which is most likely related to the decomposition of lignin. Due to its complex structure, lignin undergoes continuous decomposition over a wide temperature range from about 200 \({}^{\circ}\)C to 500 \({}^{\circ}\)C. This phenomenon is due to its complex and stable chemical structure, including the presence of numerous oxygen-containing functional groups that decompose at higher temperature ranges [30]. Using SEM-EDS analysis, the morphology of the surface of aspen wood, biochar derived from this wood, and activated carbon was characterized before and after the removal of the investigated heavy metals. Figure 2 illustrates the sorbent materials in their raw state and as examples after the removal of lead ions from the soil. Aspen wood sawdust before the heavy metal removal process shows a rough texture with distinct sharp edges and secondary partitions. Surface roughness refers to the irregularities and unevenness, while the sharp structure indicates the presence of prominent edges and tips on the surface of the sawdust [31]. The resulting biochar features a wrinkled, uneven, and rough surface with numerous fissures and indentations of varying sizes, indicating a high degree of porosity in the studied material [32]. Activated carbon is characterized by highly irregular surface channels that play a crucial role in the adsorption of heavy metals. These channels serve as effective sites for the adsorption of heavy metal ions. A comparison of the micrographs taken before and after the heavy metal removal process from the soil revealed that the surfaces of the studied materials became smoother and more uniform compared to the raw samples. SEM-EDS analysis detected the presence of lead, cadmium, and chromium on the surface of the applied material, confirming its ability to effectively bind these heavy metals. Based on the FTIR spectral analysis, the characteristic functional groups present on the surfaces of the studied materials were identified before and after the removal of heavy metals. The FTIR spectra, shown in Figure 3, were analyzed in terms of the relationship between transmittance and wavenumber. The spectrum shows the materials in their raw state and the materials after metal removal, illustrated using lead ions as an example. Figure 1: Thermogravimetric analysis of aspen wood sawdust. Figure 2: SEM-EDS analysis: (**A**)—aspen wood, (**B**)—biochar, (**C**)—activated carbon (**A**–**C**)—raw material, (**A\({}^{\prime}\)**–**C\({}^{\prime}\)**)—after Pb removal).