# Characterization and Use of Char Produced from Pyrolysis of Post-Consumer Mixed Plastic Waste
## 3 Results and Discussion
### Application of Solids on the Adsorption of Lead from Aqueous Effluents
\begin{table}
\begin{tabular}{c c c} \hline
**Temperature** & **qe, mg/g** & **Removal \%** \\ \hline
450 \({}^{\circ}\)C & 5.26 & 37.79 \\ \hline
500 \({}^{\circ}\)C & 5.88 & 44.41 \\ \hline
550 \({}^{\circ}\)C & 7.91 & 73.48 \\ \hline \end{tabular}
\end{table} 
Table 6: Results of the lead adsorption tests in aqueous solution. Initial lead concentration = 10 mg/L; volume of solution = 50 mL; amount of solid = 0.05 g; contact time = 120 min; room temperature. The removal percentage decreases with increasing concentration (Figure 3a), varying from a value close to 90% for the lowest concentrations to a value of 65.7% for the highest concentration. This is due to the fact that, as the solid becomes saturated, the amount of metal retained with respect to the initial amount decreases. With respect to the adsorption capacity (Figure 3b), this increases as the initial concentration of lead rises, reaching a maximum value close to 26 mg/g. These results are in agreement with those reported by [PERSON] et al. (2014). The authors investigated the influence of the initial concentration of lead, varying it between 5-100 mg/L and observed a decreasing trend in lead adsorption efficiency as the initial concentration of lead increases, with 5 mg/L being the initial concentration of lead that provides the highest removal percentage. These researchers also related these results to  
Figure 3: (**a**) Removal percentages of lead at different initial lead concentrations; (**b**) Adsorption isotherms of lead. Experimental data and fit to the different models. the fact that lead at pH = 6 exists mostly as a free ion at low concentrations, but at high concentrations it has a tendency to form species based on Pb\({}_{2}\)OH\({}_{3}\)+ or Pb\({}_{3}\)OH\({}_{4}\)+, among others, which hinder the adsorption process due to their larger size. Finally, the equilibrium results present in Figure 3b have been adjusted to the different models described in Section 2.4. By means of non-linear regression, the fit parameters for each model have been obtained and are present in Table 7.  
As can be appreciated, all the models present a good fit to the data (r\({}^{2}\) > 0.99), with the Sips model being the best fit (r\({}^{2}\) = 0.995) due to the flexibility of this model, based on the previous comments. However, although the model represents the experimental results well, the value of q\({}_{\rm m}\) obtained is much higher than the experimental one, which may be due to the fact that, based on Figure 3b, equilibrium has not been reached experimentally, so it is to be expected that the solid adsorption capacity will continue to increase. The results are similar to those of [PERSON] et al. [24] where the q\({}_{\rm m}\) values of different biochars for lead adsorption vary between 2.62 to 13 mg/g. These researchers studied the arsenic, cadmium and lead adsorption capacity of biochars produced from different biomass wood wastes through pyrolysis at 400 and 450 \({}^{\circ}\)C. The researchers concluded that the biochar with the highest lead adsorption capacity is the one obtained from oak bark, being very promising for its possible industrial application, when compared to a commercial activated carbon. In addition, [PERSON] et al. [49] used two types of charcoal obtained from the carbonization at 800 \({}^{\circ}\)C of fruit seeds, which are activated by impregnation with a 25% calcium solution and their efficiency in lead and methylene blue removal from aqueous solutions is measured. They found q\({}_{\rm m}\) values of 2.058 and 47.571 mg/g.