Effects of Dissolved Organic Matter (DOM) on Metal Release from Solid Phases Typical for Corrosion Processes and Characterization of Interactions between DOM and Metal Cations by In Situ Spectroscopic Methods
This study examined impacts of dissolved organic matter (DOM) on copper release from copper solid model phases (tenorite and malachite) characteristic for copper corrosion in drinking water as well as characterizing interactions between DOM and metal cations (e.g., calcium, copper) by in situ spectroscopic approaches. The study focused on the role of DOM in determining metal release caused by corrosion and showed that DOM molecules with higher apparent molecular weight (AMW), higher aromaticities and contributions of protonation-active phenolic and carboxylic groups played a key role in adsorption and colloidal dispersion of the model solids. Results also showed that metal release from model phases was well correlated with a number of spectroscopic parameters characterizing DOM properties, notably SUVA254, spectral slopes of DOM absorbance, and differential absorbance at wavelength of 280 nm and 350 nm that was indicative of the contributions of carboxylic and phenolic functional groups. Treatment approaches (e.g., chlorination, ozonation) on DOM were shown to suppress the colloidal dispersion effects due to a decreased surface activity of copper solids with DOM adsorbed. Properties of DOM as well as its interactions with major cations that are typical for drinking water and affect metal release in it were also studied by in situ spectroscopic approaches. To quantify ionic strength (IS) effects on DOM and its interactions, standard DOMs of allochthonous and autochthonous origins were used. This study showed that the increase of IS from 0.001 to 0.3 mol/L was accompanied by increases of the absorbance of DOM. The absolute values of the spectral slopes of the log-processed absorbance spectra of DOM calculated for a 350 to 400 nm wavelength range decreased proportionally to the logarithm of IS values. This result was hypothesized to be indicative of the deprotonation of the DOM chromophores at increasing IS. The contribution of the latter mechanisms was supported by model calculations showing that values of the spectral slopes were nearly-linearly correlated with the extent of IS-induced deprotonation of the operationally defined phenolic groups in DOM. This in situ approach was further applied to the investigation of DOM binding of cations highly important for corrosion processes, notably copper and calcium, as well as competitive binding of calcium and copper to DOM. The competition between calcium and copper for the binding sites in DOM was tracked by examining the intensity and shapes of the differential spectra generated for the Ca2+/Cu2+/DOM system. The extent of metal binding by DOM was quantified by calculating the slopes of log-transformed absorbance spectra in the range of wavelength 350 to 400 nm and by comparing the data with predictions made using the NICA-Donnan Model. The observed effects were interpreted based on the assumption that the binding of Ca2+ and Cu2+ by DOM was accompanied by the replacement of protons bound by carboxylic and phenolic functional groups.
- Civil engineering