Activated Carbon from Pyrolysis of Plastic Waste as an Adsorbent for the Removal of Pb(II), Cd(II) and Co(II) from Aqueous Solutions

Slow pyrolysis of a plastic fraction isolated from municipal waste produced a char, which was then used as a precursor for the synthesis of activated carbon. The process involved thermal conversion at 800 °C and chemical activation using K2CO3. The resulting activated carbon was used to remove Pb(II), Cd(II), and Co(II) from aqueous solutions. Physicochemical, structural, and granulometric characterizations of the resulting adsorbent were performed. The obtained material had a specific surface area of 562 m2/g, a total pore volume of 0.328 cm3/g, and a micropore volume of 0.146 cm3/g. To determine the optimal adsorption conditions, the Box–Behnken experiment planning method was used, assuming solution pH, adsorbent mass, and initial metal ion concentration as independent variables, and the percentage removal of the contaminant as the response. Studies on sorption isotherms were conducted using a static method in a periodic system for initial metal ion concentrations ranging from 10 to 250 mg/dm3. The effect of temperature on the adsorption process was analyzed, and the kinetics sorption was investigated. Several adsorption isotherm models were used to describe the adsorption equilibrium. The maximum sorption capacity was 35.5 mg/g for Pb(II), 14.7 mg/g for Cd(II), and 11.6 mg/g for Co(II). The obtained results indicate that the plastic waste based adsorbent exhibits favorable sorption properties for the tested heavy metal ions and may be useful in water and wastewater treatment processes.