| dc.description.abstract | This study investigated the bonding of calcium and magnesium to specific sites in
humic acid as a function of pH, temperature, and trace metal concentrations.
Other metals were investigated but not in detail. Using a surface complexation
model with well-defined phenolic and carboxylic sites in humic acid, the fractions
of calcium/magnesium and trace metals that bond with the various sites were
quantified. These sites were also classified as monodentate or bidentate. The
goal of the study was to understand the conditions that favor calcium/magnesium
bonding to bidentate humic acid. Therefore, adsorption measurements were
performed followed by surface complexation simulations. The total metal and
labile metal ion formed in the ultrafiltrate were determined by inductively coupled
plasma mass spectrometry and square-wave anodic stripping voltammetry,
respectively. The results showed that the adsorption capacity of each metal to
humic acid was influenced by pH and metal loading. For example, zinc(II) and
copper(II) were statistically different in their adsorption capacities. The Morel and
Dzombak surface complexation models showed stronger lead and copper
interactions with monodentate sites compared to bidentate sites. The phenolic
sites were weakly involved in bonding, and the bonding capacities of calcium and
magnesium ions to phenolic or carboxylic were pH dependent. For example,
lead(II) used only 5% of bidentate carboxylic–phenolic sites at 45°C showing
95% favorable calcium/magnesium bonding to these sites in humic acid. These
results may allow substantial scale reduction. | en_US |
