Plastic waste as a valuable resource: strategy to remove heavy metals from wastewater in bench scale application

Single-use plastic waste is gradually considered a potential material for circular economy. Ion exchange resin obtained from polystyrene waste by sulfonating with H₂SO₄ was used for heavy metal removal from electroplating wastewater. Batch mode experiments of Cu²⁺, Zn²⁺, and Cd²⁺ were carried out to determine effect of pH, initial concentration, equilibrium time, and the isotherm and kinetic parameters; the stability of the resin in continuous operation was then evaluated. Finally, the longevity of the resin after being exhausted was explored. The results indicated that at pH 6, a pseudo-second-order kinetic model was applicable to describe adsorption of studied heavy metals by sulfonated polystyrene with adsorption capacities of 7.48 mg Cu²⁺/g, 7.23 mg Zn²⁺/g, and 6.50 mg Cd²⁺/g, respectively. Moreover, the ion exchange process between sulfonated polystyrene resin and Cu²⁺, Zn²⁺, Cd²⁺ ions followed the Langmuir isotherm adsorption model with R² higher than 96%. The continuous fixed-bed column in conditions of a sulfonated polystyrene mass of 500 g, and a flow rate of 2.2 L/h was investigated for an influent solution with known initial concentration of 20 mg/L. Thomas and Yoon-Nelson models were tested with regression analysis. When being exhausted, the sulfonated polystyrene was regenerated by NaCl in 10 min with ratio 5 mL of NaCl 2 M per 1 g saturated resins. After 4 times regeneration, the heavy metal removal efficiency of sulfonated polystyrene was reduced to 50%. These aforementioned results can figure out that by sulfonating polystyrene waste to synthesize ion exchanging materials, this method is technically efficient and environmentally friendly to achieve sustainability.