# Characteristics of Removal of Lead, Cadmium and Chromium from Soil Using Biosorbent and Biochar
## 3 Result and Discussion
### Statistical Analysis of Results  
The significance of the data can be assessed based on their \(p\)-values, with values closer to zero indicating greater importance. For a 95% confidence level, the \(p\)-value should be less than or equal to 0.05 for an effect to be considered statistically significant [60]. Figure 7 graphically presents the absolute values of the main effects and interactions of these factors using Pareto charts. To indicate the minimum statistically significant effect size for a 95% confidence level, a vertical line is drawn on the Pareto chart. Bars that remain to the left of the reference line on the Pareto chart indicate that these variables contributed the least to predicting the effectiveness of the studied parameters. The higher the bar for a variable, the greater the impact that variable has on the dependent variable being studied. In the case of the process analysis conducted for soil containing individual metals (Figure 7A-C), it appears that all studied variables--metal type (Metal), process time (Time), sorbent concentration (Cs), and type of sorbent used (Material)--are statistically significant. Additionally, for the metal content in the soil after the removal process and removal efficiency, the interactions between Metal and Time, as well as Material and Cs, are also statistically significant. For sorption capacity, significant interactions are observed between Metal and Time, Metal and Cs, and Time and Cs. In the process of removing heavy metals from soil containing all metals (Figure 7D-F), it is observed that the only statistically significant effect influencing the process is the type of metal being removed (Metal). The approximation profile with the desirability function is a tool that enables finding the optimal solution for the analyzed issue (Figure 8). Profiling allows for displaying predicted values of dependent variables under various combinations of levels of independent variables. Additionally, it enables the determination of the desirability function for dependent variables and the establishment of a method to identify the levels of independent variables that provide the most desired response of dependent variables [61]. The desirability function, ranging from 0 to 1, estimates the degree of preference for the predicted response value at a given factor level and the average values of the remaining factors. The horizontal dashed line on the response charts illustrates the optimal values of the studied variables (lowest metal concentration in the soil, highest removal efficiency, and highest sorption capacity). Optimal conditions for removing heavy metal ions from the soil that  
Figure 7: Pareto charts of effects: (**A,D**)—Metal concentration, (**B,E**)—removal efficiency, (**C,F**)—sorption capacity ((**A–C**)—Series I and II, (**D–F**)—multi-component system). met the chosen parameters and could improve process efficiency were identified. Figure 8A shows the optimal results obtained from statistical analysis for heavy metal removal from soil in single-component systems. The horizontal line on the desirability charts indicates the highest achieved desirability. Vertical lines correspond to approximate optimal factor values (i.e., parameters that achieve the highest values for the studied variables). It is important to note that in the case of two variables, namely removal efficiency and sorption capacity, there is a mutual exclusion because increasing the amount of sorbent increases removal efficiency but decreases sorption capacity. In many publications, an optimal sorbent dose is chosen to achieve the desired removal efficiency, which is useful for the economical use of sorption materials. Therefore, individual optimal desirability values differed from those obtained for global optimal desirability. This was due to statistical conversions needed to simultaneously achieve optimal values [62]. For the three analyzed dependent variables, the individual desirability was approximately 0.61 for lead removal using BC at a concentration of 5% over 36 days.