Dittmarite is a naturally occurring mineral which is also produced by municipal wastewater treatment processes.It contains ammonium:magnesium:phosphate in molar ratios of 1:1.25:1,respectively.Dittmarite(MgNH4PO4·...Dittmarite is a naturally occurring mineral which is also produced by municipal wastewater treatment processes.It contains ammonium:magnesium:phosphate in molar ratios of 1:1.25:1,respectively.Dittmarite(MgNH4PO4·H2O)has a very stable crystalline structure,its solubility constant(Kso)is a product of the activity coefficient(?)and the activity of the individual species that make up the compound.The conditional solubility product,PS=CT,Mg CT,NH4 CT,PO4=Kso/αMgαNH4αPO4?Mg?NH4?PO4.A theoretical plot of-log Ps vs.pH gives a pH of 10.7 for maximum dittmarite precipitation,albeit precipitation may begin at lower pH values.The pKso for dittmarite at 25°C is determined to be 13.359 from the final equilibrium pH values taking all relevant magnesium,phosphate and ammonium species into account.The geochemical speciation model,MINTEQA2 was used to verify the optimum conditions for the precipitation of dittmarite.Such theoretical predictions allow the control of phosphorus and nitrogen discharges from animal and municipal wastewaters and serve as key factors in preventing surface water eutrophication and groundwater pollution.展开更多
Increasing attention has been paid to air pollution control (APC) resi dues in China recently due to the rising proportion of waste incineration and th e hazardous characteristics of the residues, among which heavy me...Increasing attention has been paid to air pollution control (APC) resi dues in China recently due to the rising proportion of waste incineration and th e hazardous characteristics of the residues, among which heavy metal leaching to xicity plays an important role. Leaching behavior and potential risk of Pb and Z n in the APC residues from a Shanghai municipal solid waste (MSW) incinerator wa s studied, based on the leaching tests under different conditions and theoretica l calculation using a geochemical thermodynamic equilibrium model MINTEQA2. Res ults showed that, extractant species and liquid to solid (L/S) ratio predomina ntly controlled the leaching toxicity of Pb and Zn, while ionic strength, vibr ation method and leaching time had less effect on the metals release. Leachate/f inal pH determined the metal leaching behavior, which changed the speciation of heavy metals in the extraction system. The equilibrium aqueous speciation, preci pitation-dissolution of Pb and Zn was investigated according to the model comput ation, which was well in agreement with the experimental results.展开更多
文摘Dittmarite is a naturally occurring mineral which is also produced by municipal wastewater treatment processes.It contains ammonium:magnesium:phosphate in molar ratios of 1:1.25:1,respectively.Dittmarite(MgNH4PO4·H2O)has a very stable crystalline structure,its solubility constant(Kso)is a product of the activity coefficient(?)and the activity of the individual species that make up the compound.The conditional solubility product,PS=CT,Mg CT,NH4 CT,PO4=Kso/αMgαNH4αPO4?Mg?NH4?PO4.A theoretical plot of-log Ps vs.pH gives a pH of 10.7 for maximum dittmarite precipitation,albeit precipitation may begin at lower pH values.The pKso for dittmarite at 25°C is determined to be 13.359 from the final equilibrium pH values taking all relevant magnesium,phosphate and ammonium species into account.The geochemical speciation model,MINTEQA2 was used to verify the optimum conditions for the precipitation of dittmarite.Such theoretical predictions allow the control of phosphorus and nitrogen discharges from animal and municipal wastewaters and serve as key factors in preventing surface water eutrophication and groundwater pollution.
基金The Key Project of Shanghai Council of Science and Technology(No. 032312043)
文摘Increasing attention has been paid to air pollution control (APC) resi dues in China recently due to the rising proportion of waste incineration and th e hazardous characteristics of the residues, among which heavy metal leaching to xicity plays an important role. Leaching behavior and potential risk of Pb and Z n in the APC residues from a Shanghai municipal solid waste (MSW) incinerator wa s studied, based on the leaching tests under different conditions and theoretica l calculation using a geochemical thermodynamic equilibrium model MINTEQA2. Res ults showed that, extractant species and liquid to solid (L/S) ratio predomina ntly controlled the leaching toxicity of Pb and Zn, while ionic strength, vibr ation method and leaching time had less effect on the metals release. Leachate/f inal pH determined the metal leaching behavior, which changed the speciation of heavy metals in the extraction system. The equilibrium aqueous speciation, preci pitation-dissolution of Pb and Zn was investigated according to the model comput ation, which was well in agreement with the experimental results.
