Optimizing sulfonation process of polystyrene waste for hardness and heavy metal removal

Polystyrene is used widely due to their ease and convenience; however, the life cycle of this kind of plastic is really short due to the single use purpose, therefore, there are a lot of waste released into the environment annually. In this research, single use dishes made from polystyrene waste (PS) were denaturized to have capacity of ion exchanging by sulfonating process with concentrated sulfuric acid as an agent. The results showed that the sulfonated polystyrene waste (SPS) has grey black color, cation exchange capacity of 0.763 eq/L, density 1.089 g/L and no swelling; this means the functional group SO3–H+ was attached on the polymer matrix which made the polystyrene waste become ion exchange resin. Scanning electron microscopy (SEM) and X-ray energy dispersive spectrometer (EDS) analysis were also studied to prove the existence of SO3–H+ groups on the polymer chain with the increase in percentage of sulphur element from 0 to 2.24%. With the optimized sulfonating conditions such as 98% H2SO4 acid volume of 10 mL, reaction time of 10 min, temperature of 80 °C and the mass of polystyrene of 5 g, the calcium removal efficiency was 94.5% with the initial calcium concentration of 200 mg/L. The removal efficiency of heavy metal after 30 min was 98.1%, 95.5% and 98.8% for Zn2+, Cd2+ and Cu2+, respectively. After regeneration process, the sulfonated polystyrene showed the capacity of reusing for ion exchange. With the goal of waste recycling as useful material, the obtained product can be used to remove hardness and heavy metal from water, which helps to limit the exploitation of natural resources, reduce the amount of waste discharged into the environment. However, the adsorption and desorption kinetics, surface area coverage, model kinetics should be studied more to provide a more comprehensive understanding and the feasible application in the real world.