# Characteristics of Removal of Lead, Cadmium and Chromium from Soil Using Biosorbent and Biochar
## 3 Result and Discussion
### Removal of Heavy Metals from the Soil  
Figure 4 shows the influence of the type of sorbent materials for heavy metals and the process time on the adsorption characteristics of the tested metal ions from the soil, assuming a constant sorbent amount of 10%. Figure 4A demonstrates that all three tested materials can reduce the concentration of Pb, Cd, and Cr in the soil. The concentration of metals in the soil decreased from Pb: 966.0 mg/kg, Cd: 974.7 mg/kg, and Cr: 992.7 mg/kg (without sorbents) to: AW: 783.1 mg/kg, 521.9 mg/kg; BC: 766.4 mg/kg, 483.2 mg/kg; AC: 549.6 mg/kg, 281.2 mg/kg (Pb--Series I, Series II); AW: 843.6 mg/kg, 629.5 mg/kg; BC: 805.9 mg/kg, 557.0 mg/kg; AC: 769.2 mg/kg, 457.5 mg/kg (Cd--Series I, Series II); AW: 919.4 mg/kg, 842.2 mg/kg; BC: 830.0 mg/kg, 722.6 mg/kg; AC: 739.4 mg/kg, 611.8 mg/kg (Cr--Series I, Series II). In Series I, differences in the degree of removal of individual heavy metals were observed. For lead, the values were as follows: 18.94% for AW, 20.66% for BC, and 43.10% for AC. For cadmium, the achieved values were as follows: 13.46% for AW, 17.32% for BC, and 21.08% for AC. For chromium, the values were as follows: 7.38% for AW, 16.39% for BC, and 25.52% for AC. Comparing the values obtained from Series I with those from Series II, similar relationships between the removed metal and the sorbent used can be observed. The following removal efficiency values were obtained for lead: 45.97% for AW, 49.98% for BC, and 70.98% for AC. For cadmium, the values were as follows: 35.42% for AW, 42.85% for BC, and 53.06% for AC. For chromium, the values were as follows: 15.16% for AC, 27.21% for BC, and 38.37% for AC (Figure 4B). Activated carbon demonstrated the highest sorption capacity in both Series I and II (Pb: 4.16 and 6.84 mg/g; Cd: 2.05 and 5.17 mg/g; Cr: 2.53 and 3.81 mg/g), followed by biochar (Pb: 2.00 and 4.82 mg/g; Cd: 1.69 and 4.18 mg/g; Cr: 1.63 and 2.70 mg/g) and aspen wood (Pb: 1.83 and 4.44 mg/g; Cd: 1.31 and 3.45 mg/g; Cr: 0.73 and 1.50 mg/g) (Figure 4C). Analyzing the obtained values for AW, BC, and activated carbon (the control sample), the most similar values were recorded for biochar. Aspen wood achieved slightly lower values, which also confirms the effectiveness of this material as a sorbent. The differences between Series I and Series II consist mainly of the degree of removal of metal ions by individual materials, which is directly related to the parameter that differs between these series, which is the duration of the sorption process. In the series and contact time of materials with metal ion solutions, it was shorter, which could have influenced the lower efficiency of removing metal ions. However, in Series II, with the extended contact time, higher levels of removal were observed, which indicates the importance of this parameter for the effectiveness of the sorption process. Similar observations were made by other researchers who used, among others, poplar sawdust for removing Cu, Zn, and Cd from galvanic wastewater [43], maple sawdust for removing copper ions [44], or mernati sawdust as an adsorbent for removing  
copper (II), chromium (III), nickel (II), and lead (II) [45]. The analysis of the obtained results revealed that lead was most effectively removed by all the sorbents used. [PERSON] et al., in their research, used modified activated carbon from bamboo as a cost-effective potential adsorbent for removing cadmium, copper, and lead from aqueous solutions, and the conducted experiments showed that the tested material had the highest affinity for lead ions [46]. The experiments also observed the influence of time on the degree of removal of heavy metals from the soil. The highest increase in removal efficiency was recorded for AW--163% for Cd, and the lowest for Cr and AC--50.4%. Biochar showed an increase of 142% for Pb, 147.4% for Cd, and 66% for Cr. Figure 5 shows the influence of the amount of sorption materials on the removal of heavy metals from the soil. The tested materials were added to the soil in amounts of 2%, 5%, and 10%.