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57 results on '"Zhang, Zhongguo"'

33. Hydrolysis of polyaluminum chloride prior to coagulation: Effects on coagulation behavior and implications for improving coagulation performance

Author

Bing Yue, Yun Song, Boyu Song, Jun Wang, Zhang Zhongguo, Dan Liu, Zhao Kehui, Xiaolin Wang, and Jiuyi Li

Subjects
Environmental Engineering, Chromatography, Chemistry, Hydrolysis, Mixing (process engineering), Flocculation, Aluminum Hydroxide, 02 engineering and technology, General Medicine, 010501 environmental sciences, 021001 nanoscience & nanotechnology, 01 natural sciences, Water Purification, Tap water, Zeta potential, Polyaluminum chloride, Environmental Chemistry, Coagulation (water treatment), Turbidity, Kaolin, 0210 nano-technology, Kaolin suspension, 0105 earth and related environmental sciences, General Environmental Science
Abstract

The effects of polyaluminum chloride (PACl) hydrolysis prior to coagulation on both the coagulation zone and coagulation performance of a kaolin suspension were investigated by a novel jar test named the “reversed coagulation test”. The tests showed that PACl hydrolysis prior to coagulation decreased the performance of charge neutralization coagulation in the case of short-time slow mixing (10 min; G = 15 sec − 1 ) and increased the optimal dosage for charge neutralization and sweep coagulation. Moreover, the hydrolysis time had insignificant effects on the size and zeta potential of PACl precipitates and the residual turbidity of the raw water. However, PACl hydrolysis prior to coagulation and the size of PACl precipitates had a negligible effect on the performance of sweep coagulation. The results imply that, in practice, preparing a PACl solution with deionized water, rather than tap water or the outlet water from a wastewater treatment unit, can significantly save PACl consumption and improve the performance of charge neutralization coagulation, while preparing the PACl solution with tap or outlet water would not affect the performance of sweep coagulation. In addition, the optimal rapid mixing intensity appears to be determined by a balance between the degree of coagulant hydrolysis before contacting the primary particles and the average size of flocs in the rapid mixing period. These results provide new insights into the role of PACl hydrolysis and will be useful for improving coagulation efficiency.

Published
2017

38. Coagulation behavior of polyaluminum chloride: Effects of pH and coagulant dosage

Author

Jun Wang, Dan Liu, Wu Yue, Ning Wei, Zhang Zhongguo, and Qunhui Wang

Subjects
chemistry.chemical_classification, Environmental Engineering, Precipitation (chemistry), Chemistry, Alum, General Chemical Engineering, Inorganic chemistry, General Chemistry, Biochemistry, chemistry.chemical_compound, Wastewater, Zeta potential, Humic acid, Coagulation (water treatment), Water treatment, Turbidity
Abstract

Coagulation mechanisms of polyaluminum chloride (PACl) at various dosages were studied using a conventional jar test at different final and initial pH values during treating kaolin suspension. The optimal final pH and dosages for PACl were obtained based on residual turbidity and zeta potential of flocs. The coagulation zones at various PACl dosages and solution pH values were developed and compared with those of alum. It is found that the optimal mechanism under acidic condition is charge neutralization, while alkaline condition will facilitate the coagulation of PACl. Both charge neutralization coagulation and sweep coagulation can achieve high coagulation efficiency under the alkaline condition ranging from final pH 7.0 to 10.0. Stabilization, charge neutralization destabilization, restabilization and sweep zones occur successively with increasing PACl dosages with the final pH values fixed at 7.0 and 8.0, but restabilization zone disappears at final pH 10.0. When the final pH is not controlled and consequently decreases with increasing PACl dosage, no typical sweep zone can be observed and the coagulant efficiency decreases at high PACl dosage. It seems that the final pH is more meaningful than the initial pH for coagulation. Charge neutralization coagulation efficiency is dominated by zeta potential of flocs and PACl precipitates. The charge neutralization and sweep coagulation zones of PACl are broader in the ranges of coagulant dosage and pH than those of alum. The results are helpful for us to treat water and wastewater using PACl and to understand the coagulation process of PACl.

Published
2015

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