Zeolite synthesized from fly ash （ZFA） without modification is not efficient for the purification of NH4＋ and phosphate at low concentrations that occur in real effluents, despite the high potential removal capacit...Zeolite synthesized from fly ash （ZFA） without modification is not efficient for the purification of NH4＋ and phosphate at low concentrations that occur in real effluents, despite the high potential removal capacity. To develop an effective technique to enhance the removal efficiency of ammonium and phosphate at low concentrations, ZFA was modified with acid treatment and the simultaneous removal of ammonium and phosphate in a wide range of concentration was investigated. It was seen that when compared with untreated ZFA, only the treatment by 0.01 mol/L of H2SO4 significantly improved the removal efficiency of ammonium at low initial concentrations. The behavior was well explained by the pH effect. Treatment by more concentrated H2SO4 led to the deterioration of the ZFA structure and a decrease in the cation exchange capacity. Treatment by 0.01 mol/L H2SO4 improved the removal efficiency of phosphate by ZFA at all initial P concentrations, while the treatment by concentrated H2SO4 （≥0.9 mol/L） resulted in a limited maximum phosphate immobilization capacity （PIC）. It was concluded that through a previous mild acid treatment （e.g. 0.01 mol/L of H2SO4）, ZFA can be used in the simultaneous removal of NH4＋ and P at low concentrations simulating real effluent.展开更多
Discharge of wastewater containing nitrogen and phosphate can cause eutrophication.Therefore,the development of an efficient material for the immobilization of the nutrients is important.In this study,a low calcium fl...Discharge of wastewater containing nitrogen and phosphate can cause eutrophication.Therefore,the development of an efficient material for the immobilization of the nutrients is important.In this study,a low calcium fly ash and high calcium fly ash were converted into zeolite using the hydrothermal method.The removal of ammonium and phosphate that coexist in aqueous solution by the synthesized zeolites were studied.The results showed that zeolitized fly ash could efficiently eliminate ammonium and phosphate at the same time.Saturation of zeolite with Ca^(2+)rather than Na+favored the removal of both ammonium and phosphate because the cation exchange reaction by the NH_(4)^(+)resulted in the release of Ca2+into the solution and precipitation of Ca^(2+)with PO_(4)^(3−)followed.An increase in the temperature elevated the immobilization of phosphate whereas it abated the removal of ammonium.Nearly 60%removal efficiency for ammonium was achieved in the neutral pH range from 5.5 to 10.5,while the increase or decrease in pH out of the neutral range lowered the adsorption.In contrast,the removal of phosphate approached 100%at a pH lower than 5.0 or higher than 9.0,and less phosphate was immobilized at neutral pH.However,there was still a narrow pH range from 9.0 to 10.5 favoring the removal of both ammonium and phosphate.It was concluded that the removal of ammonium was caused by cation exchange;the contribution of NH3 volatilization to immobilization at alkaline conditions(up to pH level of 11.4)was limited.With respect to phosphate immobilization,the mechanism was mainly the formation of precipitate as Ca_(3)(PO_(4))_(2) within the basic pH range or as FePO_(4) and AlPO_(4) within acidic pH range.展开更多
The thermodynamic equilibrium diagrams of Mg2＋- 3-4PO - ＋4NH -H2O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from ...The thermodynamic equilibrium diagrams of Mg2＋- 3-4PO - ＋4NH -H2O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from the tungstate solution by magnesium salt precipitation were obtained. The results show that when the concentration of total magnesium increases from 0.01 mol/L to 1.0 mol/L, the optimal pH for the phosphorus removal by magnesium phosphate decreases from 9.8 to 8.8. The residual concentration of total phosphorus almost keeps the level of 4.0×10-6 mol/L in the system. MgHPO4, Mg3（PO4）2 and the mixture of Mg3（PO4）2 and Mg（OH）2 are stabilized in these system, respectively. However, increasing the total concentration of magnesium has little effect on phosphorus removal by magnesium ammonium phosphate, while it is helpful for phosphorus removal by increasing the total ammonia concentration. The calculated results demonstrate that the residual concentration of total phosphorus can decrease to 5.0×10-7 mol/L as the total concentration of ammonia reaches 5.0 mol/L and the optimal pH value is 9-10. Finally, verification experiments were conducted with home-made ammonium tungstate solution containing 50 g/L WO3 and 13 g/L P. The results show that when the dosage of MgCl2 is 1.1 times of the theoretical amount, the optimum pH for removing phosphorus is 9.5, which matches with the results of the theoretical calculation exactly.展开更多
大量陆源营养物质的输入是导致我国近岸海域富营养化问题的主要原因,传统生化法对海水中氮磷处理能力有限,天然沸石凭借较强的选择性离子交换性能已成为一种较为经济和高效的水处理材料。本研究通过穿透实验考察了天然沸石对海水中氨氮...大量陆源营养物质的输入是导致我国近岸海域富营养化问题的主要原因,传统生化法对海水中氮磷处理能力有限,天然沸石凭借较强的选择性离子交换性能已成为一种较为经济和高效的水处理材料。本研究通过穿透实验考察了天然沸石对海水中氨氮的动态吸附性能,采用磷酸铵镁(MAP)沉淀和沸石吸附组合工艺对海水中氨氮进行处理。实验结果表明,天然沸石吸附氨氮达平衡时间随过滤速度的增大而减小,随滤层高度的增加而增大,Logistic模型能较好反映天然沸石对海水中氨氮的动态吸附过程。MAP沉淀法与沸石吸附法联用可以将海水中氨氮含量降低至较低水平,适宜的滤柱过滤条件为:滤速20L/h,滤层高度100cm。通过焙烧或Na Cl浸洗处理能够恢复天然沸石对海水中氨氮的吸附能力,300℃焙烧2h和1.5mol/L Na Cl溶液浸洗24h条件下的再生率分别为99.38%和122.22%。展开更多
基金Project supported by the Chinese Ministry of Science and Technology Funding (No. 2002AA601013).
文摘Zeolite synthesized from fly ash （ZFA） without modification is not efficient for the purification of NH4＋ and phosphate at low concentrations that occur in real effluents, despite the high potential removal capacity. To develop an effective technique to enhance the removal efficiency of ammonium and phosphate at low concentrations, ZFA was modified with acid treatment and the simultaneous removal of ammonium and phosphate in a wide range of concentration was investigated. It was seen that when compared with untreated ZFA, only the treatment by 0.01 mol/L of H2SO4 significantly improved the removal efficiency of ammonium at low initial concentrations. The behavior was well explained by the pH effect. Treatment by more concentrated H2SO4 led to the deterioration of the ZFA structure and a decrease in the cation exchange capacity. Treatment by 0.01 mol/L H2SO4 improved the removal efficiency of phosphate by ZFA at all initial P concentrations, while the treatment by concentrated H2SO4 （≥0.9 mol/L） resulted in a limited maximum phosphate immobilization capacity （PIC）. It was concluded that through a previous mild acid treatment （e.g. 0.01 mol/L of H2SO4）, ZFA can be used in the simultaneous removal of NH4＋ and P at low concentrations simulating real effluent.
基金This work was supported by the National High-Tech Research and Development(863)Program of China(Grant No.2002AA601013)the Key Technologies Research and Development Program of Shanghai(Grant No.04DZ12030-2).
文摘Discharge of wastewater containing nitrogen and phosphate can cause eutrophication.Therefore,the development of an efficient material for the immobilization of the nutrients is important.In this study,a low calcium fly ash and high calcium fly ash were converted into zeolite using the hydrothermal method.The removal of ammonium and phosphate that coexist in aqueous solution by the synthesized zeolites were studied.The results showed that zeolitized fly ash could efficiently eliminate ammonium and phosphate at the same time.Saturation of zeolite with Ca^(2+)rather than Na+favored the removal of both ammonium and phosphate because the cation exchange reaction by the NH_(4)^(+)resulted in the release of Ca2+into the solution and precipitation of Ca^(2+)with PO_(4)^(3−)followed.An increase in the temperature elevated the immobilization of phosphate whereas it abated the removal of ammonium.Nearly 60%removal efficiency for ammonium was achieved in the neutral pH range from 5.5 to 10.5,while the increase or decrease in pH out of the neutral range lowered the adsorption.In contrast,the removal of phosphate approached 100%at a pH lower than 5.0 or higher than 9.0,and less phosphate was immobilized at neutral pH.However,there was still a narrow pH range from 9.0 to 10.5 favoring the removal of both ammonium and phosphate.It was concluded that the removal of ammonium was caused by cation exchange;the contribution of NH3 volatilization to immobilization at alkaline conditions(up to pH level of 11.4)was limited.With respect to phosphate immobilization,the mechanism was mainly the formation of precipitate as Ca_(3)(PO_(4))_(2) within the basic pH range or as FePO_(4) and AlPO_(4) within acidic pH range.
基金Project(2012BAB10B04)supported by the National Key Technologies R&D Program of China
文摘The thermodynamic equilibrium diagrams of Mg2＋- 3-4PO - ＋4NH -H2O system at 298 K were established based on the thermodynamic calculation. From the diagram, the thermodynamic conditions for removing phosphorus from the tungstate solution by magnesium salt precipitation were obtained. The results show that when the concentration of total magnesium increases from 0.01 mol/L to 1.0 mol/L, the optimal pH for the phosphorus removal by magnesium phosphate decreases from 9.8 to 8.8. The residual concentration of total phosphorus almost keeps the level of 4.0×10-6 mol/L in the system. MgHPO4, Mg3（PO4）2 and the mixture of Mg3（PO4）2 and Mg（OH）2 are stabilized in these system, respectively. However, increasing the total concentration of magnesium has little effect on phosphorus removal by magnesium ammonium phosphate, while it is helpful for phosphorus removal by increasing the total ammonia concentration. The calculated results demonstrate that the residual concentration of total phosphorus can decrease to 5.0×10-7 mol/L as the total concentration of ammonia reaches 5.0 mol/L and the optimal pH value is 9-10. Finally, verification experiments were conducted with home-made ammonium tungstate solution containing 50 g/L WO3 and 13 g/L P. The results show that when the dosage of MgCl2 is 1.1 times of the theoretical amount, the optimum pH for removing phosphorus is 9.5, which matches with the results of the theoretical calculation exactly.
文摘大量陆源营养物质的输入是导致我国近岸海域富营养化问题的主要原因,传统生化法对海水中氮磷处理能力有限,天然沸石凭借较强的选择性离子交换性能已成为一种较为经济和高效的水处理材料。本研究通过穿透实验考察了天然沸石对海水中氨氮的动态吸附性能,采用磷酸铵镁(MAP)沉淀和沸石吸附组合工艺对海水中氨氮进行处理。实验结果表明,天然沸石吸附氨氮达平衡时间随过滤速度的增大而减小,随滤层高度的增加而增大,Logistic模型能较好反映天然沸石对海水中氨氮的动态吸附过程。MAP沉淀法与沸石吸附法联用可以将海水中氨氮含量降低至较低水平,适宜的滤柱过滤条件为:滤速20L/h,滤层高度100cm。通过焙烧或Na Cl浸洗处理能够恢复天然沸石对海水中氨氮的吸附能力,300℃焙烧2h和1.5mol/L Na Cl溶液浸洗24h条件下的再生率分别为99.38%和122.22%。
