# 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  
In this section, the application of the solids resulting from the pyrolysis of the non-recyclable mixed plastics from municipal solid waste for the removal of lead from aqueous solutions was studied. Figure 2: Infrared spectra of the solid pyrolysis products. The results obtained for lead adsorption capacity and percentage removal of lead for each of the solid samples used are present in Table 6.  
The results indicate that the adsorption capacity increases as the pyrolysis temperature increase, with the highest value of 7.91 mg/g for the solid obtained in the pyrolysis at 550 \({}^{\circ}\)C. The lower adsorption capacity of the solid obtained at 450 \({}^{\circ}\)C is directly related to the lower specific surface area compared to the solids obtained at higher temperatures, based on the results shown in Section 3.3.1. These results are also in agreement with those obtained in Section 3.3.3, where the elimination of polar groups is observed as the temperature increases, achieving solid residues with lower polarity and higher aromaticity, which can be an advantage in their application based on their use as adsorbent solids. Finally, as the values included in Table 5 showed an important content of lead of the solid samples and to avoid errors in the adsorption results, the possible release of lead from the solid sample was taken into account carrying out blank tests with solid in deionized water. The results showed that, although lead contents were not insignificant for solid samples obtained at 450 and 500 \({}^{\circ}\)C, they were relatively immobile under adsorption tests conditions because practically null concentration was observed in the solution in the blank tests. [PERSON] et al. [10], investigated the efficiency of the carbonaceous solid from pyrolysis of different mixtures of PVC, PET and PE waste in the adsorption of arsenic, using an arsenic initial concentration of 1000 ppm, varying pH values between 4 and 8 and char doses of 0.5 and 1.5 g. The highest percentage of retention was for the PVC/PE mixture, in the same proportions pyrolyzed at 550 \({}^{\circ}\)C. The maximum percentage of retention was between 71.6% and 99.4%. The authors observed that the solids prepared at higher temperature (550 \({}^{\circ}\)C) showed a higher arsenic adsorption capacity. Similarly, [PERSON] et al. [48] performed adsorption tests of different metals, including lead, with solid products obtained at different temperatures from walnut and peanut shells pyrolysis test. In this study, an activation treatment is carried out on the solid and the results shows that a higher pyrolysis temperature and a longer activation time increase the adsorption capacity of the solid. On the other hand, [PERSON] et al. [18] carried out lead adsorption tests in aqueous solution with a concentration of 1000 mg/L, at a temperature of 25 \({}^{\circ}\)C and varying the pH, the amount of adsorbent solid and the contact time. In this investigation, three different solids are used from the pyrolysis of different mixtures of materials (biomass, used tires and plastic waste) at a temperature of 420 \({}^{\circ}\)C. The results reveal that the highest adsorption efficiency was presented by the solid obtained from the mixture formed by 50% used tires and 50% plastic waste, reaching a retained percentage of 100%, due to its high mineral content, especially zinc, calcium and potassium, which indicates that its adsorption capacity lies in the formation of complexes with these minerals. Following, considering that the best result in terms of adsorption capacity was obtained with the solid resulting from pyrolysis at 550 \({}^{\circ}\)C (Table 6), a study of the equilibrium of the process was performed. Figure 3a,b show the results of the removal percentage and the adsorption capacity at equilibrium, qe, for each of the concentrations used.