Fate of dissolved metals

As pH rises, the metal content of drainage water tends to decrease. Some metals precipitate directly from solution to form oxide, hydroxide, and oxy-hydroxide phases. Iron and aluminum are notable is this regard. They initially form colloidal and suspended phases known as hydrous ferric oxide (HFO, FeOOH H2O) and hydrous aluminum oxide (HAO, AlOOHnH2O), both of which are highly soluble under acidic conditions but nearly insoluble at nearneutral pH. 

The concentrations of other metals attenuate when the metals sorb onto the surfaces of precipitating minerals (see Chapter 8). HFO, the behavior of which is well studied (Dzombak and Morel, 1990), has a large specific surface area and is capable of sorbing metals from solution in considerable amounts, especially at moderate to high pH HAO may behave similarly. The process by which HFO or HAO forms and then adsorbs metals from solution, known as coprecipitation, represents an important control on the mobility of heavy metals in acid drainages (e.g., Chapman et al., 1983 Johnson, 1986 Davis et al., 1991 Smith et al., 1992). 

To see how this process works, we construct a model in which reaction of a hypothetical drainage water with calcite leads to the precipitation of ferric hydroxide [Fe(OH)3, which we use to represent HFO] and the sorption of dissolved species onto this phase. We assume that the precipitate remains suspended in solution with its surface in equilibrium with the changing fluid chemistry, using the surface complexation model described in Chapter 8. In our 

We do not concern ourselves with the precipitate that lines sediments in the stream bed, since it formed earlier while in contact with the drainage, and hence would not be expected to continue to sorb from solution. Smith et al. (1992), for example, found that in an acid drainage from Colorado (USA), sorption on the suspended solids, rather than the sediments along the stream bed, controls the dissolved metal concentrations. 

As the first step in the coprecipitation process, ferric hydroxide precipitates either from the effect of the changing pH on the solubility of ferric iron 

---

Low concentrations of sulfate and dissolved metals are observed in the groundwater. Higher concentrations are observed in the mined blocks, with the maximum concentrations observed in blocks that had been leached and flooded. WISMLfT plans to decommission the Konigstein mine. The fate of dissolved metals and radionuclides in the flooding water is an important factor in the development of decommissioning plans (Bain et al., 2001). 

The study of the concentration and distribution of trace metals started with the 1987-1988 expedition and at the beginning it was focused on the quantification of metals in dissolved, particulate and sediments phases. Afterwards, the work was planned in order to obtain data and information useful to understand the role and the fate of trace metals during processes, such as ice melting and biogeochemical cycles. 

Thus, it can basically be predicted under what conditions (pH, concentration of redox species) tire metal dissolution reaction (Fe Fe ) proceeds tliennodynamically. From a practical point of view, tire rate of tire reaction and tlierefore tire fate of tire oxidized species (Fe ) is extremely important tliey can eitlier be solvated, i.e., to fonn Fe (H20) complexes, and tlierefore be efficiently dissolved in tire solution, or tliey can react witli oxygen species of... 

Reduction of Ketones and Enones. Although the method has been supplanted for synthetic purposes by hydride donors, the reduction of ketones to alcohols in ammonia or alcohols provides mechanistic insight into dissolving-metal reductions. The outcome of the reaction of ketones with metal reductants is determined by the fate of the initial ketyl radical formed by a single-electron transfer. The radical intermediate, depending on its structure and the reaction medium, may be protonated, disproportionate, or dimerize.209 In hydroxylic solvents such as liquid ammonia or in the presence of an alcohol, the protonation process dominates over dimerization. Net reduction can also occur by a disproportionation process. As is discussed in Section 5.6.3, dimerization can become the dominant process under conditions in which protonation does not occur rapidly. 

In dissolving-metal ester reduction, the ester carbonyl is believed to accept an electron to form a radical oxyanion 37 (Scheme 12.12). Chelation with a lithium counterion then ensues to produce a tertiary radical 38 which then captures a second electron to become a carbanion. Protonation of 39 next yields 40, whose fate is to collapse to aldehyde 41. Another multiple electron transfer/protonation sequence subsequently yields the product alcohol 46. 

Like colloidal material, surfaces have complex-ing sites for trace elements and the same formalism as that described for colloids can be used. Understanding the partitioning of metals and more generally trace elements between water and solids is crucial for fundamental smdies on transport, bioavailability, and fate of trace elements in river systems. For example, the spatial and temporal trends of metal or radionuclide partitioning between dissolved and suspended sohds is a major issue for understanding and predicting the pathways of pollutants in the environment. As a consequence, an impressive literature focuses on experimental studies of trace-element adsorption/desorption on synthetic surfaces (mostly hydrous oxides). However, field-based studies aimed at assessing the importance... 

OVERVIEW OF PROCESSES CONTROLLING FATE OF LANDFILL LEACHATE COMPOUNDS. 5.1 Dissolved Organic Matter, Inorganic Macrocomponents, and Heavy Metals. 5.2 Xenobiotic Organic Compounds NORMAN LANDFILL (USA)... 

---