Study on coagulation effect and mechanism of polyferric sulfate on polyethylene microplastics in water
Polymerized ferric sulfate(PFS)and polyethylene(PE)microplastics were used as coagulants and removal objects,respectively.The removal performance of PFS on PE microplastics was systematically investigated in terms of coagulant dosage,microplastic particle size,solution pH,and coexisting pollutants.The coagulation mechanism was initially explored by XPS,FT-IR,SEM,and Zeta potential.The results show that the removal rate of PE microplastics increases with the increase of PFS dosage from 10 mg/L to 550 mg/L.The addition of surfactant and alkaline conditions results in better coagulation and sedimentation performance of PFS,while the excessive coagulant and acidic conditions would inhibit the removal of PE microplastics.Among the particle size of less than 500 p-m,the removal rate of PE microplastics from 50 µm to 150μm is the highest,and the removal rate can reach 98.0％when the coagulant dosing amount is 550 mg/L and pH is 8,which is better than aluminum and natural coagulants.In the coexistence system of hexavalent chromium and microplastics,the removal of microplastics is not significantly affected,while the maximum removal rate of hexavalent chromium by coagulant can reach 15.9％.The microscopic images show that the flock structure is relatively tight,and microplastics are attached or bound to the flock.The result of the Zeta potential measurement reveals that there is a strong charge neutralization effect in the reaction system.The figures of Scanning electron microscopy(SEM)illustrate that the particles are agglomerated during the coagulation process.The X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectroscopy(FT-IR)show that polymerized ferric sulfate hydrolyzes to form the hydroxyl complex,which adsorbs the microplastic particles by electrostatic attraction,and makes the microplastics settle down.The evidence from characterization techniques pointed to charge neutralization and adsorption bridging as the dominant mechanism for microplastic removal for the conditions of this study.
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