Hydrous oxides of iron (HFO) and aluminum (HAO) were studied for their ability to reduce Cu to {dollar}mu{dollar}g/L levels typical of increasingly stringent wastewater discharge limits. Residual Cu was compared following adsorption (ADS), where Cu was contacted with preformed oxide flocs, and coprecipitation (CPT) where Cu was added prior to HFO or HAO precipitation. For the HAO-ADS system, residual Cu was markedly undersaturated with respect to homogeneous precipitation (PPT) of Cu(OH){dollar}sb2{dollar}(s) over the pH 6-9 range. In contrast, residual Cu was lowered by HFO-ADS for pH {dollar}<{dollar} 7.5 but comparable to PPT at higher pH. Compared to ADS, residual Cu after CPT was similar for HAO but was dramatically lower for HFO. More Cu was incorporated internal to the HFO flocs during CPT, suggesting some Cu substitution into the HFO lattice.; From the sorption isotherms, a total apparent site density of 0.425 mole Cu/mole Fe was obtained for HFO-CPT. This site density, which cannot be solely attributed to surface area effects, could be due to Cu adsorption during growth of HFO crystallites or the formation of mixed Fe,Cu hydroxy species. Isotherms suggest a Cu surface precipitate formed on HAO with solubility product lower than its HFO analogue. Therefore, HFO appears to be a better sorbent than HAO when adsorption reactions predominate; however, HAO is more effective in facilitating surface Cu precipitation. Both the pH-edge sorption data and sorption isotherms were modeled using the Generalized Two Layer Model and its extension, the Surface Precipitation Model, the latter being required for high sorbate-to-sorbent ratios.; Atomic Force Microscopy images suggest floc growth inhibition during HFO-CPT compared to HFO-ADS. X-ray diffraction analysis indicates that surface precipitation commences at a lower pH and surface coverage in the presence of HAO compared to HFO. Surface precipitation during HFO-ADS involves the presence of a discrete mixture of HFO and hydrous Cu oxide whereas a mixed Al,Cu oxide is formed during HAO-ADS.; Through a combination of macroscopic, modeling, and microscopic/spectroscopic analyses, insight was gained into the mechanisms responsible for removal of Cu from aqueous suspensions of HFO and HAO. This work has attempted to provide a fundamental understanding of the metal-oxide interactions which is essential for implementing such processes in full-scale water and wastewater treatment operations.
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