Metal immobilized

Pd metals immobilized on SBA-15 and NaY were applied as catalysts in the synthesis of amino alcohol. These catalysts afford a high level of enantioselectivity in the asymmetric hydrogenation of a-keto alcohol to corresponding amino alcohol. The large peilladium metal exhibited higher catalytic activity and enantioselectivity than well dispersed one over porous supports in the hydrogenation. 

In aquatie environments, mierobial eells attaeh to solids, ineluding metals. Immobilized eells grow, reproduee, and produee extraeellular polymers. 

This section describes catalytic systems made by a heterogeneous catalyst (e.g., a supported metal, dispersed metals, immobilized organometaUic complexes, supported acid-base catalysts, modified zeolites) that is immobilized in a hydrophilic or ionic liquid catalyst-philic phase, and in the presence of a second liquid phase—immiscible in the first phase—made, for example, by an organic solvent. The rationale for this multiphasic system is usually ease in product separation, since it can be removed with the organic phase, and ease in catalyst recovery and reuse because the latter remains immobilized in the catalyst-philic phase, it can be filtered away, and it does not contaminate the product. These systems often show improved rates as well as selectivities, along with catalyst stabilization. 

T0605 Physical Sciences, Inc., Metals Immobilization and Decontamination of Aggregate Solids (MelDAS)... 

The metals immobilization and decontamination of aggregate solids (MelDAS) technology was developed to treat organics and heavy metals in soils, sediments, and sludges. It has not progressed beyond a pilot-scale study and is not commercially available. 

The MelDAS technology is a modified incineration process in which high temperatures destroy organic contaminants in soil and concentrate metals into fly ash. Details of the metals immobilization process can vary based on the specific application, but the essential steps are to combine the toxic-metal containing material with the appropriate amount of sorbent, to form this mixture into pellets or briquets placing the metal compounds into intimate contact with the sorbent, and to heat treat the pellets causing a reaction to form nonleachable metal compounds. The MelDAS process requires a sorbent. 

In 1970s, first application of metal-chelate affinity chromatography which is later named as "immobilized-metal (ion) affinity chromatography (IMAC) was perfomed. Metal-chelate chromatography technique exploits selective interactions and affinity between transition metal immobilized on a solid support (resin) via a metal chelator and amino acid residues which act as electron donors in the protein of interest [25-26]. As well as aromatic and heterocyclic compounds, proteins such as histidine, tyrosine, tyriptophane and phenylalanine posses affinity to transition metals which form complexes with compounds rich in electrons [25,27]. 

Table 7 lists the annual masses of metals immobilized in several anthropogenic materials. Data in Table 7 take into account the concentrations of metals in these materials (Table 6) and the claimed annual production of these materials in Switzerland. For the case of our hypothetical HT material, two scenarios are taken into account. It is assumed here that the annual production of HT materials would be either 7 x 10s t/y (replacement of the 28 Swiss... 

The development of Group Vm transition metals immobilized on inorganic or polymer support continues to be an active area in the hydrosilylation reaction, mainly because of easy separation and recycling capability of these catalysts60-65. 

The incorporation of fly ash into Portland cement has been identified as one of the treatment parameters of cement composition to be evaluated. There is already an extensive experience database on the performance of fly-ash-modified Portland cement for heavy-metal immobilization and the solidification/stabilization (S/S) of radioactive waste. The United Kingdom (Wilding, 1992) and the United States (Huang et al., 1994) have used these materials, in the form of cement grouts, for the S/S of low- and intermediate-level radioactive wastes. In this section, we will review the known benefits of fly-ash-modified Portland cement over unmodified Portland cement, along with the anticipated improvements expected by the supercritical C02 treatment of modified Portland. 

The interaction of amine-modified silica with Cu2+ ion is the most documented.23,24,25 However, the retention of other transition metals as well as precious metals with dedicated modification layers has also been reported. The separation of Pd and Pt from base metals, Ir(III) and Rh(III) was effectuated by using silica-bound thioether sulfur and primary amine groups.26 A review on polymeric as well as modified silica supports for separation and preconcentration of trace metals is presented by Kantipuly.27 This metal immobilization also allows other applications such as metalion chromatography28 and heavy metal catalysis.29... 

Metal-Organics. Many organic materials also form low-solubility species with certain metals. Among these are humic acids. The most widely publicized insoluble substrate for heavy-metal immobilization has been insoluble starch xanthate (ISX). In contact with metal ions, the metal links to the sulfur group much as it would with the S-2 in inorganic sulfides ... 

In China and other countries, the application of C-rich organic materials to heavy metal-contaminated soils is a common practice. However, the potential risk of metal mobilization should not be overlooked when metal dissolution facilitated by DOM released from organic wastes exceeds metal immobilization caused by particular organic matter. Figure 10.8 demonstrates that addition of DOM derived from green manure, pig manure, peat, rice litter, and sewage sludge to a Cu-contaminated soil caused an increase in soil water-soluble Cu contents. Compared to the control (no... 

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... 

Metal immobilization in soils can be accomplished by increasing their retention in the soil matrix, which decreases their mass transfer rates. 

The main methods for the remediation of heavy metals from soils are based on three principles (a) metal immobilization (see Section 10.2), (b) electrokinetic remediation (see Section 10.4), and (c) metal extraction from the soil matrix. 

In a few studies sonochemistry was used to coat polymers with nanosized par-tides [48-50]. Of these three reports one [50] dealt with metals, more specifically with noble metals (Pt, Pd, and Au). In this research, metal colloids are adsorbed to the surface of neutral functionalized polystyrene microspheres, PSMS. The authors report on the synthesis and characterization of catalytically important noble monometallic colloids using various chemical and sonochemical methods. These metal colloids are then adsorbed onto suitably functionalized PSMS. The metal-immobilized microspheres are reacted with a linker such as 4-mercaptobutyl phosphonic acid and subsequently used to grow multilayers. 

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. 

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. 

Boisson, J., Ruttens, A., Mench, M., and Vangronsveld, J. (1999). Evaluation of hydroxyapatite as a metal immobilizing soil additive for the remediation of polluted soils, 1 Influence of hydroxyapatite on metal exchangeability in soil, plant growth and plant metal accumulation. Environ. Pollut. 104, 225-233. 

Cao, X., Ma, L. Q., Singh, S. P., Chen, M., Harris, W. G., and Kizza, P. (2003). Field Demonstration of Metal Immobilization in Contaminated Soils Using Phosphate Amendments, final report to Florida Institute of Phosphate Research, Bartow, FL. Publ. 01-148-194. 

Sugiyama, S., Ichii, T., Fujisawa, M., and Kawashiro, K. (2003). Heavy metal immobilization in aqueous solution using calcium phosphate and calcium hydrogen phosphates. J. Colloid Interface Sci. 259, 408—410. 

These biopolymers can be used for the immobilization of metal ions not only with the final objective of metal recovery (and subsequent valorization by desorption or chemical/thermal destmction of the polymer matrix) but also for elaborating new materials or designing new applications. Depending on the metal immobilized on the biopolymer, it is possible to design new sorbents (immobilization of iron on alginate [119], of molybdate on chitosan [59], for As(V) removal, of silver on chitosan for pesticide removal [120]), supports for affinity chromatography [121], antimicrobial material [122], drug release material [123], neutron capture therapy [124], and photoluminescent materials [125]. These are only a few... 

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