## 3 Results and Discussion
### Pd(II) Sorption in Complex Systems
#### 3.3.2 Application to the Treatment of \"Synthesized\" Wastewaters  
To evaluate the application potential of the beads for recovering Pd(II) from industrial effluents, the sorbents were applied to two different synthesized leaching liquors from a spent catalyst and a car catalytic converter, respectively.  
Figure 9 shows the results of Pd(II) recovery from the spent catalyst leachate. Due to the presence of a high concentration of chloride ions, the sorption capacities of the beads are much less than those in a single-metal system. The sorption efficiencies of LD/PEI and CC/PEI beads are 81.2% and 97.4%, respectively, with a sorbent dose of 1 g L\({}^{-1}\). Using acidic thiourea as the desorption agent, more than 90% of the loaded Pd(II) was desorbed, contributing to a Pd(II) recovery percentage of 75% and 88% for LD/PEI and CC/PEI beads, respectively. The concentration factor (CF) was calculated as the ratio of the Pd(II) concentration in desorption agent to the initial concentration in synthesized leachate. The concentration factor is 3.76 for LD/PEI and 4.39 for CC/PEI. The photo on the right shows the sorbents after the sorption process. The sorbents are stable in the background electrolyte (2 M NaCl, 0.5 M HCl): the beads are not damaged after sorption and desorption processes.  
Figure 8: Influence of different concentrations of Pt(IV) on Pd(II) sorption using LD/PEI and CC/PEI beads (C\({}_{0}\): 0.8 mmol L\({}^{-1}\); SD: 0.25 g L\({}^{-1}\); pH: 1, adjusted by H\({}_{2}\)SO\({}_{4}\) or NaOH; Contact time: 72 h; T: 20 \({}^{\circ}\)C).  
The results of Pd(II) recovery from the leachate of the car catalyst converter are presented in Figure 10. The initial solution contains 0.38 mmol L\({}^{-1}\) of Pd(II), 0.07 mmol L\({}^{-1}\) of Pt(IV), 2.93 mmol L\({}^{-1}\) of Fe(III), 91.03 mmol L\({}^{-1}\) of Al(III), 2.47 mmol L\({}^{-1}\) of Ce(III), and 0.61 mmol L\({}^{-1}\) of Zn(II), while in the desorption solution, the concentration of Pd(II) and Pt(IV) increases to 1.37 and 0.17 mmol L\({}^{-1}\), respectively, for LD/PEI and 1.70 and 0.20 mmol L\({}^{-1}\), respectively, for CC/PEI beads. The concentration of other base metals is negligible, except for Al(III), which is close to 0.5 mmol L\({}^{-1}\) for both LD/PEI and CC/PEI beads. The recovery efficiency is close to 72% and 89% for LD/PEI and CC/PEI beads, respectively, with a sorbent dosage of 0.5 g L\({}^{-1}\). The enrichment factor (EF, calculated as the molar percentage of metal in the initial solution divided by its molar percentage in the desorption solution) of Pd(II) is 167.7 for LD/PEI and 177.5 for CC/PEI.  
Figure 10: Treatment of the synthesized leaching liquor of the autocatalytic converter using LD/PEI and CC/PEI beads: (**a**) composition of the initial leachate; and (**b**) composition of the eluate after the sorption-desorption process (Sorption step: V: 100 mL; mass: 50 mg (dry weight); time: 72 h; temperature: 20 \({}^{\circ}\)C—desorption step: 0.1 M HCl/0.2 M Thiourea solution; V: 20 mL; time: 24 h; temperature: 50 \({}^{\circ}\)C).  
Figure 9: Pd(II) recovery from synthesized leachate of spent catalysts (Sorption step: V: 100 mL; mass: 100 mg (dry weight); time: 72 h; temperature: 20 \({}^{\circ}\)C—desorption step: 0.1 M HCl/0.2 M Thiourea solution; V: 20 mL; time: 24 h; temperature: 50 \({}^{\circ}\)C). CF: concentration factor.