The aim of the present work was to produce a polyaluminium ferric silicate chloride （PAFSiC） coagulant from acidic and alkaline wastewater of purifying graphite by roasting, and subsequently to evaluate coagulation ...The aim of the present work was to produce a polyaluminium ferric silicate chloride （PAFSiC） coagulant from acidic and alkaline wastewater of purifying graphite by roasting, and subsequently to evaluate coagulation efficiency of the reagent by treating surface water from the Yellow River as well as municipal wastewater in comparison with the conventional coagulant polyaluminium chloride （PAC）. The PAFSiC coagulant was prepared by co-polymerization. The effects of （Al＋Fe）/Si molar ratio, OH/（Al＋Fe） molar ratio （i.e., γ value）, coagulant dosage and pH value of test suspension on the coagulation behavior of FAFSiC and the stability of the PAFSiC were also examined. Results showed that PAFSiC performed more efficiently than PAC in removing turbidity, chemical oxygen demand （COD）, and total phosphate （TP）. The PAFSiC with a γ value of 2.0 and （Al＋Fe）/Si ratio of 5 （PAFSiC 2.0/5） showed excellent coagulation effect for both turbidity and COD, while PAFSiC 1.0/5 was the best for TP. The optimum coagulation pH range of PAFSiC 2.0/5 was 5.0–9.0, slightly wider than that of PAC （6.0–8.0）. The process can be easily incorporated into high-purity graphite production plants, thereby reducing wastewater pollution and producing a valuable coagulant.展开更多
The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test metho...The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test method. The experimental results showed that the interaction between polysilicic acid characterized negative charge and hydrolyzed aluminum species result in a decrease of the charge neutralizing ability of PASiC, compared to PAC. The decrease has a close relationship with the basicity ( B ) and Al/Si molar ratio in PASiC. The less the B value and the Al/Si molar ratio, the lower the charge neutralizing ability of PASiC is. In contrast, the preparation technique for PASiC affects the charge-neutralization of PASiC to a smaller extent. In addition, compared with PAC, PASiC may enhance aggregating efficiency and give better coagulating effects.展开更多
Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc...Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep flocculation with polyaluminum chloride. The compensatory effect of slow-mixing on coagulation performance following inadequate or excessive rapid-mixing was also examined. It is found that slow-mixing intensity has a more marked positive effect on charge neutralization coagulation than on sweep flocculation. The optimal root-meansquare velocity gradient, G, for slow-mixing is 15s-1 for both coagulation mechanisms, and charge neutralization coagulation requires a longer slow-mixing duration. The optimal slow-mixing duration, based on residual turbidity, is longer than the time to form the largest mean flocs. The optimal product of G and mixing duration, GT, for slow-mixing during charge neutralization coagulation (13500) are higher than that during sweep flocculation (4500) and both are less than the range of values recommended by the American Water Works Association (24000-84000). The optimal GT value under various slow-mixing conditions increases with G. Appropriate extension of slow-mixing duration during charge neutralization coagulation can improve coagulation performance after an inadequate or excessive rapid-mixing duration, but during sweep flocculation, appropriate shortening of slow-mixing duration after an excessive rapid-mixing or appropriate extension of slow-mixing duration after an inadequate rapid-mixing is favorable.展开更多
The applications of natural polymeric flocculants due to their green feature has been recently received much more attention. In this work, the combined usages of a cationic starch-based coagulant and polyaluminum chlo...The applications of natural polymeric flocculants due to their green feature has been recently received much more attention. In this work, the combined usages of a cationic starch-based coagulant and polyaluminum chloride(PACl) were extensively evaluated for various addition sequences in the coagulation of both raw(surface water from the Jiuxiang River) and synthetic turbid water(two kaolin suspensions with different initial turbidities).Two typical cationic starch-based coagulants with different structures(St-G and St-E) were tried. In comparison to St-G, St-E and PACl used individually as well as St-G and St-E dosed after PACl, the combination of the starch-based coagulants fed before PACl showed higher turbidity removal efficiency, which featured not only less optimal doses of both inorganic and organic coagulants but also lower residual turbidity. On the basis of a detailed analysis of the particle size and its distribution in solution supernatants before and after coagulation by two starch-based coagulants and PACl, polymeric coagulants preferentially coagulate the small-sized colloids due to their distinct long-chain structures, but PACl preferentially coagulates the medium-sized ones. Thus, the medium-sized particles that were previously formed by the starch-based coagulants would be collectively and effectively removed by the subsequent addition of PACl. The addition sequence of the inorganic and organic coagulants in their combined usage is an important factor for improvement of the turbidity removal efficiency in practice.展开更多
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 c...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.展开更多
基金supported by the National Natural Science Foundation of China (No. 20971112)the Major Public Service Project of Henan Province (No. 101100910300)+1 种基金the Natural Science Research Pro- gram of Education Department in Henan Province (No. 2011A610012)the Science and Technology Program of Zhengzhou City (No. 10PTGG339-4)
文摘The aim of the present work was to produce a polyaluminium ferric silicate chloride （PAFSiC） coagulant from acidic and alkaline wastewater of purifying graphite by roasting, and subsequently to evaluate coagulation efficiency of the reagent by treating surface water from the Yellow River as well as municipal wastewater in comparison with the conventional coagulant polyaluminium chloride （PAC）. The PAFSiC coagulant was prepared by co-polymerization. The effects of （Al＋Fe）/Si molar ratio, OH/（Al＋Fe） molar ratio （i.e., γ value）, coagulant dosage and pH value of test suspension on the coagulation behavior of FAFSiC and the stability of the PAFSiC were also examined. Results showed that PAFSiC performed more efficiently than PAC in removing turbidity, chemical oxygen demand （COD）, and total phosphate （TP）. The PAFSiC with a γ value of 2.0 and （Al＋Fe）/Si ratio of 5 （PAFSiC 2.0/5） showed excellent coagulation effect for both turbidity and COD, while PAFSiC 1.0/5 was the best for TP. The optimum coagulation pH range of PAFSiC 2.0/5 was 5.0–9.0, slightly wider than that of PAC （6.0–8.0）. The process can be easily incorporated into high-purity graphite production plants, thereby reducing wastewater pollution and producing a valuable coagulant.
文摘The electrokinetic characteristics and coagulation behaviors of polyaluminum silicate chloride (PASiC) and polyaluminum chloride (PAC) were studied and compared by streaming current (SC) measurement and jar test method. The experimental results showed that the interaction between polysilicic acid characterized negative charge and hydrolyzed aluminum species result in a decrease of the charge neutralizing ability of PASiC, compared to PAC. The decrease has a close relationship with the basicity ( B ) and Al/Si molar ratio in PASiC. The less the B value and the Al/Si molar ratio, the lower the charge neutralizing ability of PASiC is. In contrast, the preparation technique for PASiC affects the charge-neutralization of PASiC to a smaller extent. In addition, compared with PAC, PASiC may enhance aggregating efficiency and give better coagulating effects.
基金Supported by the National High Technology Research and Development Program of China (2009AA063901)the Special Funds for Technological Development of Research Institutes from the Ministry of Science and Technology of China(2010EG111022, 2011EG111307)+1 种基金the Budding Program (2011A-12-L)the Program for Innovative Research Team(IG201204N) of Beijing Academy of Science and Technology
文摘Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep flocculation with polyaluminum chloride. The compensatory effect of slow-mixing on coagulation performance following inadequate or excessive rapid-mixing was also examined. It is found that slow-mixing intensity has a more marked positive effect on charge neutralization coagulation than on sweep flocculation. The optimal root-meansquare velocity gradient, G, for slow-mixing is 15s-1 for both coagulation mechanisms, and charge neutralization coagulation requires a longer slow-mixing duration. The optimal slow-mixing duration, based on residual turbidity, is longer than the time to form the largest mean flocs. The optimal product of G and mixing duration, GT, for slow-mixing during charge neutralization coagulation (13500) are higher than that during sweep flocculation (4500) and both are less than the range of values recommended by the American Water Works Association (24000-84000). The optimal GT value under various slow-mixing conditions increases with G. Appropriate extension of slow-mixing duration during charge neutralization coagulation can improve coagulation performance after an inadequate or excessive rapid-mixing duration, but during sweep flocculation, appropriate shortening of slow-mixing duration after an excessive rapid-mixing or appropriate extension of slow-mixing duration after an inadequate rapid-mixing is favorable.
基金supported by the National Natural Science Foundation of China(Nos.51778279 and 51438008)
文摘The applications of natural polymeric flocculants due to their green feature has been recently received much more attention. In this work, the combined usages of a cationic starch-based coagulant and polyaluminum chloride(PACl) were extensively evaluated for various addition sequences in the coagulation of both raw(surface water from the Jiuxiang River) and synthetic turbid water(two kaolin suspensions with different initial turbidities).Two typical cationic starch-based coagulants with different structures(St-G and St-E) were tried. In comparison to St-G, St-E and PACl used individually as well as St-G and St-E dosed after PACl, the combination of the starch-based coagulants fed before PACl showed higher turbidity removal efficiency, which featured not only less optimal doses of both inorganic and organic coagulants but also lower residual turbidity. On the basis of a detailed analysis of the particle size and its distribution in solution supernatants before and after coagulation by two starch-based coagulants and PACl, polymeric coagulants preferentially coagulate the small-sized colloids due to their distinct long-chain structures, but PACl preferentially coagulates the medium-sized ones. Thus, the medium-sized particles that were previously formed by the starch-based coagulants would be collectively and effectively removed by the subsequent addition of PACl. The addition sequence of the inorganic and organic coagulants in their combined usage is an important factor for improvement of the turbidity removal efficiency in practice.
基金the Special Fund for the Technical Development of Scientific Research Institutionsfinanced by the Ministry of Science and Technology of the People's Republic of China(Nos.2011EG111307 and 2012EG111122)the Program for Overseas Talents of the Beijing Academy of Science and Technology(No.OTP-2013-015)
文摘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.
