Research on the Flocculation Performance of Cysteine-Starch Flocculant for Pb(Ⅱ) Removal

Using 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) as catalyst, the natural polymer material corn starch (St) was modified by cysteine (Cy) to obtain a new flocculant cysteine-starch (Cy-St). The conditions of flocculation treatment of Pb(Ⅱ) wastewater were optimized by single-factor experiment and response surface experiment. The flocculant and floc were characterized by Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and floc fractal dimension analysis. The effect of the coexistence of common substances on the performance of Cy-St flocculation for Pb(Ⅱ) removal was investigated. The results show that the flocculant dosage is 295   mg/L, the rapid stirring time is 4   min, speed is 200   r/min, the slow stirring time is 30   min, speed is 60   r/min, the wastewater pH=5.13, and the maximum removal rate can reach 98.03%. Various functional groups such as -SH, -NH 2 , -COOH may play a role in the flocculation process, flocs also have good sedimentation performance. Flocculant Cy-St has good anti-interference to Na + , K + , Ca 2+ , Mg 2+ , SO 4 2- , turbidity, and sodium citrate, while CO 3 2- and EDTA-2Na will reduce the performance of Pb(Ⅱ) removal by flocculation.