EDTA (ethylenediaminetetraacceticacid) is a chelating agent and frequently found in industrial and domestic wastewater. It has an ability to form strong water soluble complexes with a variety of metal cations, is considered to be nonbiodegradable in traditional wastewater treatment processes, and th...
EDTA (ethylenediaminetetraacceticacid) is a chelating agent and frequently found in industrial and domestic wastewater. It has an ability to form strong water soluble complexes with a variety of metal cations, is considered to be nonbiodegradable in traditional wastewater treatment processes, and thus interferes with the removal of metals from wastewater. Some metal-EDTA complexes have been known to be amenable to metal-removal processes including biodegradation. And those metal-EDTA complexes that are difficult to be removed could be converted to a metal-EDTA complex that is amenable to its removal. However, it has been reported that metal exchange between some metal-EDTA complexes is not instantaneous. Therefore, metal-exchange kinetics is an important piece of information that will affect the development, design, and operation of metal-removal processes. In this study, the metal-exchange kinetics was experimentally investigated. This study was carried out in three phases. In the first phase, selected metals were reacted with EDTA to understand how fast metal-EDTA complexes are formed. EDTA complexes with the metals, Ca, Co, Cu, Fe (III), Mg, Mn, Ni, Al and Zn, were found to be formed almost instantaneously. In the second phase, the exchange kinetics between a free metal ion and a metal in its metal-EDTA complex for selected metals and metal-EDTA complexes. For each experiment, a pair of metals, whose EDTA complexes have widely different stability constants, were selected and used. The exchange between a free metal and a metal in its metal-EDTA complexes was generally fast (<30 min) when it occurred and seemed to be affected by pH. In general, a metal in its metal-EDTA complex could be replaced by a free metal, which forms a much more stable complex with EDTA than the former complex. In addition, the competition between a selected pair of metals for forming metal-EDTA complexes was studied. The higher solubility constant metal-EDTA complex dominated in concentration when two free metals were reacted with free EDAT, but at pH 10.2 lower stability constant metals shared considerable amount of EDTA. In the third phase the exchange of metals between two metal-EDTA complexes was investigated and found that no exchange of metals between the complexes was observed. Equilibrium constants for each reaction of phases one and two were calculated and compared with published values. It appeared that all reactions in this study reached equilibrium in <30 min. The results of this study would be useful to design physical/chemical/biological processes for removing metal-EDTA complexes.
EDTA (ethylenediaminetetraacceticacid) is a chelating agent and frequently found in industrial and domestic wastewater. It has an ability to form strong water soluble complexes with a variety of metal cations, is considered to be nonbiodegradable in traditional wastewater treatment processes, and thus interferes with the removal of metals from wastewater. Some metal-EDTA complexes have been known to be amenable to metal-removal processes including biodegradation. And those metal-EDTA complexes that are difficult to be removed could be converted to a metal-EDTA complex that is amenable to its removal. However, it has been reported that metal exchange between some metal-EDTA complexes is not instantaneous. Therefore, metal-exchange kinetics is an important piece of information that will affect the development, design, and operation of metal-removal processes. In this study, the metal-exchange kinetics was experimentally investigated. This study was carried out in three phases. In the first phase, selected metals were reacted with EDTA to understand how fast metal-EDTA complexes are formed. EDTA complexes with the metals, Ca, Co, Cu, Fe (III), Mg, Mn, Ni, Al and Zn, were found to be formed almost instantaneously. In the second phase, the exchange kinetics between a free metal ion and a metal in its metal-EDTA complex for selected metals and metal-EDTA complexes. For each experiment, a pair of metals, whose EDTA complexes have widely different stability constants, were selected and used. The exchange between a free metal and a metal in its metal-EDTA complexes was generally fast (<30 min) when it occurred and seemed to be affected by pH. In general, a metal in its metal-EDTA complex could be replaced by a free metal, which forms a much more stable complex with EDTA than the former complex. In addition, the competition between a selected pair of metals for forming metal-EDTA complexes was studied. The higher solubility constant metal-EDTA complex dominated in concentration when two free metals were reacted with free EDAT, but at pH 10.2 lower stability constant metals shared considerable amount of EDTA. In the third phase the exchange of metals between two metal-EDTA complexes was investigated and found that no exchange of metals between the complexes was observed. Equilibrium constants for each reaction of phases one and two were calculated and compared with published values. It appeared that all reactions in this study reached equilibrium in <30 min. The results of this study would be useful to design physical/chemical/biological processes for removing metal-EDTA complexes.
주제어
#Metal-EDTA Complex Formation Metal-Metal Exchange Metal-EDTA Complexes
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