## 4 Conclusions  
Plastics can be used as a source to prepare fuels, minimizing the impact of this waste that might otherwise end up in a landfill. The solid chars generated in the process can be considered a valuable carbonaceous source if activated for the preparation of porous materials with potential adsorption properties, such as the removal of metals in water. The original char displayed a moderate adsorption capacity (over 300 mg\(\cdot\)g\({}^{-1}\)) but displayed displayed considerable leaching of organic matter, which indicates its usefulness as a plausible adsorbent. Among the thermal chemical activation methods tested, i.e., thermal treatment in the presence of CO\({}_{2}\), NaOH, and KOH, the use of KOH resulted in the most beneficial procedure for developing a porous structure with enhanced microporosity and potential adsorption of lead in water, with a maximum adsorption capacity of ca. 700 mg\(\cdot\)g\({}^{-1}\). [PERSON]'s model fitted quite well to almost all the experimental series. The Sips model provided, in contrast, the best fitting results in all the samples. All the activated carbon materials displayed a remarkable basic character in aqueous solution; as a consequence, low lead concentrations were highly affected by the precipitation effect, especially in adsorption tests performed by SC-NaOH, which contributed to the removal of lead mostly by precipitation due to the rise in pH. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12168032/s1](https://www.mdpi.com/article/10.3390/app12168032/s1)]([https://www.mdpi.com/article/10.3390/app12168032/s1](https://www.mdpi.com/article/10.3390/app12168032/s1)), Table S1. Summary of experimental conditions used for the preparation of the different activated carbons. **Author Contributions:** Conceptualization, M.A.M.-L, G.B. and M.C. ; methodology, J.B. and G.B. ; software, R.R.S. ; validation, R.R.S., M.A.M.-L. and M.C. ; formal analysis, R.R.S., M.A.M.-L. and M.C. ; investigation, A.L., J.B. and G.B. ; resources, G.B. ; data curation, R.R.S. ; writing--original draft preparation, R.R.S., M.A.M.-L. and M.C. ; writing--review and editing, all authors; supervision, M.A.M.-L. and M.C. ; project administration, M.A.M.-L., G.B. and M.C. ; funding acquisition, M.A.M.-L. and M.C. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type of Precursor** & **Raw Material** & **Activating Agent** &
\begin{tabular}{c} **Lead Adsorption** \\ **Capacity (mg\(\cdot\)g\({}^{-1}\))** \\ \end{tabular} & **Refs.** \\ \hline \multirow{8}{*}{Biomass} & Black cumin seeds & H\({}_{2}\)SO\({}_{4}\) & 18.0 & [27] \\ \cline{2-5}  & Banana peel & — & 247.1 & [28] \\ \cline{2-5}  & Apricot stone & H\({}_{2}\)SO\({}_{4}\) & 22.9 & [29] \\ \cline{2-5}  & Potato peel & H\({}_{3}\)PO\({}_{4}\) + KOH & 9.3 & [30] \\ \cline{2-5}  & Coconut buttons & H\({}_{2}\)SO\({}_{4}\) + steam & 92.7 & [31] \\ \cline{2-5}  & Soybean oil cake & K\({}_{2}\)CO\({}_{3}\) & 476.2 & [31] \\ \cline{2-5}  & Olive stone & H\({}_{3}\)PO\({}_{4}\) & 148.8 & [32] \\ \hline \multirow{8}{*}{Tire waste} & KOH & 322.5 & [33] \\ \cline{2-5}  & \multicolumn{1}{c}{} & Physical (agent not specified) & 327.9 & [34] \\ \cline{2-5}  & KOH & 49.7 & [35] \\ \hline \multirow{2}{*}{Biomass and plastic waste} & Bamboo, sugarcane, and neem & — & NA & [10] \\ \cline{2-5}  & PET, PE, and PVC & & & \\ \hline Biomass, tire, and plastic waste & Forestry pine, used tires, and plastic wastes & — & 1.87 & [9] \\ \hline Mixture of non-recyclable plastics & Polypropylene, polystyrene & KOH & 747 & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Some published works about lead adsorption by activated carbons obtained from char of pyrolysis of different precursors materials.