Characterization and performance of poly-silicic-cation coagulant in treatment of recycled paper wastewater

摘要

Tertiary treatment of pulp and paper wastewater has become increasingly pressing since stricter legislations were issued by the central government and some provincial governments in China. Coagulation process after biological treatment has been regarded as a techno-economically feasible technology for the high quality effluent. In this paper, a study on preparation and characterization of poly-silicic-cation coagulants (PSiCs) with different Si/(Al+Fe) molar ratios is described. X-ray diffraction, infrared spectra, ultraviolet/visible absorption scanning, and microscopic imaging were used as measures for characterization. Coagulant performance was evaluated using it in papermaking wastewater treatment. The results showed that new complex compounds had formed in the PSiC polymers and the optimal Si/(Al+Fe) molar ratio for the coagulant polymerization was about 0.9, at which the polymerization degree was highest. The content of ionic polymerized bonds and branch-like PSiC units would decrease when the molar ratio was lower or higher than 0.9. The highest efficiency appeared when PSiC0.9 was used in the wastewater treatment, rather than PSiC0.6 and PSiC1.5. The results also showed that concentrations of turbidity, COD, color, and residual aluminum in the PSiC treated effluent were lower than that from coagulation tests using traditional coagulants.