Metals immobilization mechanisms

The Chemical Stabilization Technology (CHEM-STA ) is a proprietary contaminant immobilization mechanism for treating soils, sludges, and ashes contaminated with toxic heavy metals and hydrocarbons. The three-step process can be applied either in situ or ex situ to form stable and insoluble chemical compounds. Treated wastes are usually acceptable for landfill disposal. This technology is commercially available from Environmental Solutions, Inc. (ESI). According to the vendor, CHEM-STA has the following advantages ... 

Mechanisms for metal immobilization include intracellular uptake with complexation to ligands such as sulphur-containing peptides (metallothio-neins) and carboxylic acids (citrate, malate, oxalate) (Gadd, 1993 Sarret et al., 1998, 2002 Fomina et al., 2005c). Some fungi can also precipitate... 

A number of mechanisms lead to metal immobilization. Although these can reduce the external free metal concentration, solubilization may be promoted in some circumstances because of the shift in equilibrium, which will result in the release of more metal species into solution. 

Polettini et al. (2004) investigated cement-based S/S on a mixed Cr(III)-, Cu(II)-, and Pb(II)- contaminated soil and showed that stabilization of the mixed metal(loid)-contamuiated soil was not compromized by the mixed contaminant status, which may have been related to similar immobilization mechanisms for all... 

Among the remediation technologies available for soils contaminated with heavy metals, in situ immobilization techniques are of particular interest because of their cost-effectiveness. The use of phosphorus (P) amendments has been identified as a potentially efficient in situ remediation technology. These amendments are available in various forms, and they are environmentally friendly and simple to use. Numerous studies have been conducted to demonstrate the mechanisms and effectiveness of heavy metal immobilization in soils using various P sources (Ma et al., 1993 Chen et al., 1997a Singh et al., 2001 Mavropoulos et al., 2002). 

Important mechanisms involved in phosphate-induced immobilization ofheavy metals include chemisorption and chemical precipitation. This is affected by physicochemical properties of the system, such as pH, solubility products, competitive species, chemical speciation, and complex formation. The distinction between different mechanisms is important because different mechanisms have different kinetics and efficiencies in metal immobilization. In addition, because of the uniqueness of each site, an understanding of these mechanisms serves as a basis to design an appropriate strategy when applying P amendments to contaminated sites. 

Sorption, Desorption, and Fixation Rates. A further indication that the basic immobilization mechanism for heavy metals is one of sorption and fixation by the hydrous oxides, is indicated by the slowness with which the heavy metals often become deficient after fertilization. In... 

Polymerization of 7V-vinylcarbazole catalyzed by dimethylglyoxime complexes of different metals immobilized on PVC follows the cationic mechanism. Lewis acids immobilized in a volume of swollen polymer gel catalyze cationic polymerization and oligomerization of vinyl ethers, etc. Cationic complexes of Pd(II) bound to modified PS initiate alternative copolymerization of fluorinated olefins (C F2 +i)(CH2)mCH=CH2 with carbon monoxide [112,113]. The product thus obtained was polyspiroketal rather than polyketone. 

The mechanisms resulting in dissolved metal immobilization are two stage ... 

A rather more specific mechanism of microbial immobilization of metal ions is represented by the accumulation of uranium as an extracellular precipitate of hydrogen uranyl phosphate by a Citrobacter species (83). Staggering amounts of uranium can be precipitated more than 900% of the bacterial dry weight Recent work has shown that even elements that do not readily form insoluble phosphates, such as nickel and neptunium, may be incorporated into the uranyl phosphate crystallites (84). The precipitation is driven by the production of phosphate ions at the cell surface by an external phosphatase. 

Phytostabilization (also known as in-place inactivation or phytoimmobilization) is the use of certain plant species to immobilize contaminants in the soil through absorption and accumulation by roots, adsorption onto roots, or precipitation, complexation, and metal valence reduction within the root zone. The following three mechanisms determine the fate of the contaminants within the phytostabilization process46 ... 

Recent reports describe the use of various porous carbon materials for protein adsorption. For example, Hyeon and coworkers summarized the recent development of porous carbon materials in their review [163], where the successful use of mesoporous carbons as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for protein immobilization are described. Gogotsi and coworkers synthesized novel mesoporous carbon materials using ternary MAX-phase carbides that can be optimized for efficient adsorption of large inflammatory proteins [164]. The synthesized carbons possess tunable pore size with a large volume of slit-shaped mesopores. They demonstrated that not only micropores (0.4—2 nm) but also mesopores (2-50 nm) can be tuned in a controlled way by extraction of metals from carbides, providing a mechanism for the optimization of adsorption systems for selective adsorption of a large variety of biomolecules. Furthermore, Vinu and coworkers have successfully developed the synthesis of... 

Gadd GM (2000) Bioremediation potential of microbial mechanisms of metal mobilization and immobilization. Curr Opinion Biotechnol 11 271-279... 

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