| The preparation of a novel composite flocculant CMP-AlCl3 by combining carboxymethylpullulan (CMP) and aluminium chloride was achieved. The characterization of CMP were carried out by FT-IR, HPLC, and SEM. RSM was employed to determine the crucial factors and optimize the flocculation processes. Zeta potential measurement and Photometric Dispersion Analyzer was used to monitoring the zeta potential of coagulation and the extent of aggregation. The results of this thesis are as follows:(1) CMP has a net structure and higher molecular weight which is more favorable to coagulate colloidal particles and promote the bridging performance. It is reveal that CMP possesses better properties in water solubility and flocculating activity than pullulan.(2) The optimum treatment conditions for the composite flocculant were CMP 13.03 mg/l, AlCl3 94.87 mg/l and pH 6.50, respectively. The flocculating rate of verification test operated under optimal condition is greater than 99%.(3) The higher positive charge of Al(III) monomer could effectively modify the zeta potential and adequately destroy the stability of colloid particles which could provide a more unstable colloid suspension for the following absorption bridging, eventually resulting in significantly improved coagulation efficiency. CMP-AlCl3 produced the largest flocs with the fastest grow rate and had a wider size distribution range, when compared to the components CMP and AlCl3 used alone. The particles is aggregated to micro-flocs by charge neutralization at first, and then the micro-flocs are bridged together to form big and tenacious flocs via the bridge forming mechanism. Therefore, the predominant flocculation mechanism is the coexistence of the neutralization mechanism and the adsorption/bridge mechanism. The composite flocculant holding these two advantages obtained a favorable flocculating effect, as well as decreased secondary environment pollution. |
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