Contaminant sequestration

Mineral dissolution kinetics influence such phenomena as development of soil fertility, amelioration of the effects of acid rain, formation of karst, acid mine drainage, transport and sequestration of contaminants, sequestration of carbon dioxide at depth in the earth, ore deposition, and metamorphism. On a global basis, mineral weathering kinetics are also involved in the long-term sink for CO2 in the atmosphere ... 

Luthy RG, Aiken GR, Brusseau ML, Cunningham SD, Gschwend PM, Pignatello JJ, Reinhard M, Traina SJ, Weber WJ, Jr, Westall JC (1997) Sequestration of hydrophobic organic contaminants by geosorbents. Environ Sci Technol 31 3341-3347... 

Geologic sequestration is already being done in the North Sea. The field produces gas that is heavily contaminated with natural carbon dioxide. Before shipping the gas, the Norwegian oil company Statoil filters out the carbon dioxide and injects it into a sandstone formation half a mile... 

Another gemstone in the portfolio of rational carbon synthesis is nitrogen-doped carbons. Recently, they became the subject of particular interest to researchers due to their remarkable performance in applications such as C02 sequestration [22], removals of contaminants from gas and liquid phases [23], environmental protection [24], catalysts and catalysts supports [25], or in electrochemistry as supercapacitors [26], cells and batteries to improve stability and the loading capacity of carbon. 

So far, we have considered only the purification methods for the rapid clean up of reaction mixtures that are facilitated by sequestration of either by-products, excess reactants or spent reagents. The idea that one can used a suitably functionalized solid support to selectively capture the required product away from any contaminating impurities, filter and then re-release it in a pure form is also an important purification concept (Fig. 2.3) [31]. 

It is questionable whether or not the value obtained by bioassays or the sequestration value can be used to define contaminant-bound residues. Ageing-sequestration relationships in the subsurface, as determined through bioavailability, may provide an... 

Weber, W. J., Huang, W. L., and LeBoeuf, E. J. (1999). Geosorbent organic matter and its relationship to the binding and sequestration of organic contaminants. Colloid Surf. A151,... 

The processes responsible for contaminant removal by ZVMs and PRBs include both physical removal from solution to an immobile phase and chemical removal by reaction to form less hazardous products. In the discussion that follows, we will refer to the former as sequestration and the latter as transformation. This distinction has heuristic value, even though sequestration and transformation processes are related for many contaminants. 

For the purposes of this review, we have chosen the term sequestration to represent contaminant removal by processes that do not involve contaminant degradation. Although the term is most commonly applied to the fate of organic contaminants [54], it can also be applied to metals and other inorganic contaminants. In older literature on removal of contaminant metals, the term cementation was commonly used (e.g., Ref. 55), but this term is not used here. 

Of greater recent interest are metals that exist predominantly as soluble, hazardous oxyanions in oxic groundwaters, but that become relatively insoluble species when reduced, making them candidates for remediation by reductive immobilization. These metals include As(V), Cr(VI), Se(VI), Tc(VII), U(VI), and a few others [51,63,64], In general, a complex and variable mixture of processes is responsible for sequestration of these contaminants by Fe°. For example, Cr(VI) is at least partially reduced to Cr(III), which is then precipitated as a mixed oxyhydroxide [65-67]. 

To contrast with the term sequestration, we have chosen transformation to represent chemical reactions that convert contaminants to distinct products. The transformation of metals from one valence state to another was included in the previous section because the effect of these transformations is mainly to enhance sequestration. In contrast, there are a few nonmetal inorganic contaminants that are transformed by Fe° to soluble but comparatively innocuous products, which are discussed below. Following that,... 

Intracellular distribution of essential transition metals is mediated by specific metallochaperones and transporters localized in endomembranes. In other words, the major processes involved in hyperaccumulation of trace metals from the contaminated medium to the shoots by hyperaccumulators as proposed by Yang et al. (2005) include bioactivation of metals in the rhizosphere through root-microbial interaction enhanced uptake by metal transporters in the plasma membranes detoxification of metals by distributing metals to the apoplasts such as binding to cell walls and chelation of metals in the cytoplasm with various ligands (such as PCs, metallothioneins, metal-binding proteins) and sequestration of metals into the vacuole by tonoplast-located transporters. 

INTEX SEQUESTRANT 159 is recommended for all dyeing and scouring procedures. Some plants because of excellent quality water feel they do not need a chelate but most metal contamination is introduced by the fabric being processed and the chemicals used. 

INTEX SEQUESTRANT 259 is a general chelating agent, useful in dyeing scouring operations to prevent interference by metallic contamination. 

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