## 4 Results and Discussion
### Elemental Analysis
The biochar obtained from this material was characterized in turn by a concentration of this element in the range of 67-81% (pyrolysis at 300-800 \({}^{\circ}\)C) [57]. [PERSON] et al. (2014), when producing biochar from safflower seed cakes at 500 \({}^{\circ}\)C, achieved a total carbon content of 62.45%. Subjecting this material to chemical activation with the use of KOH and a temperature of 800 \({}^{\circ}\)C increased the content of this element to 72.09% [58]. [PERSON] et al. (2021), in a study of the pyrolysis of flax seed residues as solid waste generated during flex seed oil production, reported an increase in the total carbon content from 44.9% for unprocessed material to less than 55% for the biochars obtained [59]. Similar correlations as in our own study are reported by [PERSON] et al. (2022), noting an increase in the carbon content with the increasing flax straw pyrolysis temperatures at 400, 500 and 600 \({}^{\circ}\)C [60]. The percentage of ash increased as the temperature and time of the pyrolysis process increased. After processing the biomass into biochar, the ash content was statistically significantly different from the control sample (fennel flower--6.15%, rapeseed--5.32%, flax--6.35%, evening primrose--12%, milk thistle--99% and hemp--6.55%). After thermal processing, the ash content of the pyrolysates was statistically significantly different from the control sample and was in the following ranges: fennel flower 12.86-23.22%, rapeseed 11.21-22.09%, flax 11.06-21.91%, evening primrose 16.79-19.53%, milk thistle 15.75-17.22% and hemp 20.39-22.41%. The highest percentage of ash among all analyzed biochars, i.e., 23.22%, was recorded for fennel flower pyrolysates prepared at 500 \({}^{\circ}\)C and a temperature holding time of 15 min. [PERSON] et al. (2016), in a study on biochar produced from corn kernels, report a percentage content of ash at 18.7%, which meant a result within the range of ash content variations in the analyzed biochars from the cakes in our own study [61]. On the other hand, [PERSON] and [PERSON] (2017) report that biochar made from mahua de-oiled seed cakes has an ash content of 16.4% [62]. An inverse relationship was observed for the volatile matter, which decreased as the temperature of the pyrolysis process increased. Changes from an average content for the control samples from 73.57 to 16.36% were recorded for biochars obtained at the maximum pyrolysis parameters tested (500\({}^{\circ}\)C, 15 min). The lowest volatile matter content (13.93%) of all analyzed materials was in the biochar prepared from flax cakes (Table 5). The statistically significant value has already changed for the biochar with the smallest transformation (400 \({}^{\circ}\)C/5 min). These values were practically three times lower than the initial value for raw biomass. Similar conclusions were reached by [PERSON] and [PERSON] (2017), where the proportion of volatile matter also decreased during the conversion of biomass to biochar [53]. In a study by [PERSON] et al. (2022) on biochar from pistachio nut shells, it was reported that the volatile matter content was equal to 30.62%, giving a similar but slightly higher volatile matter content compared to the analyses in our own work [63]. In a research paper by [PERSON] et al. (2012) on rice straw, a content of volatile matter ranging from 40.2 to 13.1% was reported. The authors noted a significant decrease in the content of volatile matter as the pyrolysis temperature increased from 300 to 700 \({}^{\circ}\)C [64]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Research Material** & **General Nitrogen** & **Total Carbon** & **Hydrogen** & **Ash** & **Volatile** **Substances** \\ \cline{2-5}  & & & & & \\ \hline \multicolumn{5}{c}{**\%**} \\ \hline NC & 4.77\({}^{\text{ a}}\)\(\pm\) 0.04 & 49.55\({}^{\text{ a}}\)\(\  
According to the Duncan test results, statistically significant differences were noted in the content of carbon, hydrogen, ash and volatile substances between the control sample and biochars for all the analyzed materials.