The surface reaction on liquid-solid interface of “amino acid-Cu(II)?MnO2” system in seawater |
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| Authors: | Wang Xiulin Zhang Zhengbin Liu Liansheng |
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| Institution: | (1) Shangdong College of Oceanology, Shangdong, USA |
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| Abstract: | The results obtained from the Cu(II)%-pH curve of the system in the presence of added amino acid indicated that the added
amino acids of higher concentration can inhibit the Cu(II)-σ-MnO2 ion exchange and that their inhibiting effects decrease in the following sequence when the initial amino acid concentrations
are 20.00 ppm: histidine > cystine > glutamic acid > proline > alanine > glycine. The determination of amino acid in solution
performed with an amino acid analyser showed that added amino acids react chemically on the surface of the σ-MnO2 According to thermodynamic equilibria relations in the system, amino acids can be changed to amines because of their decarboxylation
on the surface of the σ-MnO2. Considering (1) the effect-inhibiting factor of amine FA(β, Ka, pH) representing the complex potential of amine with Cu(II) in solution and (2) the acidic constant of −NH
3
+
group in the amine molecule representing the ability of cation exchange of the amine with σ-MnO2, the inhibiting seqence of added amino acid of 20.00 ppm (Eq.(1)) is reasonable. Thus added amino acids do inhibit Cu(II)-σ-MnO2 ion exchange because (1) the amino acid and/ or amine, which is the decarboxylate of the corresponding amino acid, complex
with Cu(II) in solution and compete with σ-MnO2 for Cu(II); (2) the cation exchange of the amino acid and/or amine reduce the exchange site on the surface of the σ-MnO2. The results obtained from the isotherms indicated that the theory of interfacial stepwise ion exchange can be extended to
the Cu(II) σ-MnO2 ion exchange system in the presence of added amino acid. |
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