The effect of amino acids on copper (II)-goethite ion exchange in seawater

Abstract

In seawater, aside from metal elements and suspended particles, organic substances amount to about 500–2,000 ug carbon/l^[8], which is not neglegible in comparison with that of minor metal elements. But in the study of the interaction of the three constituents (metal elements, organics, and suspended particles), the effect of organics in seawater on the surface reaction of metal element—suspended particles has usually been neglected. Recent theoretical research^{[1, 11]} confirmed the importance of the effect of organics in seawater on the surface reaction of metal element—suspended particles. Generally, the effect of organics on the reaction of metal ions, especially Cu(II), on a solid surface is either promotive^[2] or inhibitive^{[7, 9]}. So far the fact that organics cannot affect the surface reaction of Cu(II) ions on solids has not been reported in literature. Our experimental results showed that none of the amino acids in seawater affect Cu(II)-goethite ion exchange under certain experimental condition (such as amino acid of lower concentration and lower pH). It was known that the metal ion-organics complex in a liquid competing with solids for metal ions may inhibit the surface reaction of metal ions on solids, but the mechanism of the complex reaction of metal ions competing with solids is not known yet. In fact, the decrease of surface site-exchanging due to the surface reaction of organics on solids is also inhibitive. It is also explained by the ion exchange isotherm of the “amino acid-Cu(II)-geothite” system. This result further demonstrates that the theory of interfacial stepwise ion exchange is applicable to the metal ion exchange isotherm with the presence of organic substances in the system.