Minerals metal chelates

Citric acid and its citrate compounds are widely used in hundreds of applications. Global production of citric acid in 2005 was 1.6 million tons, with China producing approximately 40% of the world supply. In the United States, approximately 65% of citric acid use is in the food and beverage industry. Citric acid is used as an acidulant to impart tartness, to control pH, as a preservative and antioxidant, as a metal chelator, and to stabilize color and taste. Citrate salts can be used as mineral and metal dietary supplement for example, calcium citrate... 

Rocks colonized by lichens weather faster than uncolonized rock surfaces, as a direct result of metal chelation by lichen substances and organic acids (Fig. 15.3). Fomina et al. and Smits (Chapters 10 and 13, this volume) provide comprehensive discussions of the effects of fungi on mineral weathering processes, and therefore only a brief summary of the effects of lichens on this phenomenon will be presented here. Essentially, lichen colonization can influence the rate of silicate weathering through... 

Aqueous chemical speciation calculations (Alpers and Nordstrom, 1999 Bethke, 1996) have been used for some time to help understand the speciation of and trace metal chelation in diverse human body fluids such as plasma, wound fluids, saliva, sweat, fat emulsions, and gastrointestinal fluids (Taylor and Williams, 1995, 1998 Williams, 2000). In contrast, chemical speciation calculations have only been used infrequently in studies evaluating interactions between the human body and earth materials such as asbestos (Hume and Rimstidt, 1992 Gunter and Wood, 2000 Taunton et al., 2002 Davis et al., 1992, 1996). There are many potential uses of chemical speciation calculations in the interpretation of interactions between human body fluids and earth materials. For example, the interpretation of in vitro mineral solubility tests could be greatly improved by chemical speciation calculations on... 

Chemical reaction path calculations (Alpers and Nordstrom, 1999 Bethke, 1996) have only seen limited use as applied to fluid-mineral interactions in the human body (e.g., Davis et al., 1992). The potential further applications in this realm are intriguing, both for understanding chemical reactions between body fluids and earth materials, and in understanding potential changes in body fluid chemistry in response to physiological processes and therapeutic treatments such as toxic metal chelation therapy. 

Fe(III) maybe photoreduced to Fe (II), with the net effect of accelerated dissolution of its minerals and chelates. The reader is referred to several good reviews for a detailed description of the photoreactions involving trace metals and organometallics [31-34]. This chapter will focus on the organic photochemistry of CDOM. 

FIGURE 7.6 Inorganic chemically active adsorbent prepared by solvent deposition of chelating agents on the functionalized surface. (From N. V. Deorkar and L. L. Tavlarides. Emerging Separation Technologies for Metals II, The Minerals, Metals Materials Society, Warrendale, PA, 1996. With permission.)... 

Pradip. 1988. Applications of chelating agents in mineral processing. Miner. Metall. Process. 5 80. 

The Nernst distribution law applies to metal complexes, but their distribution ratios are determined by several interrelated equilibria. As in the case of organic acids and bases, the efficiency of extraction of metal chelates is pH dependent, and for some ion-association complexes, notably oxonium systems (hydrogen ions solvated with ethers, esters or ketones), inorganic complex ions can be extracted from concentrated solutions of mineral acids. 

Chelation can convert metal ions to less mobile forms, although with most agents, chelation has the opposite effect. A chelating agent called Tetran is supposed to form metal chelates that are strongly bound to clay minerals. The hiunin fraction of soil humic substances likewise immobilizes metal ions. 

Mediators of both the infiammatoiy and fibrotic responses have been associated with exposure to oxidants. Similarly, mediator release after incubation of cells with silica and asbestos can be the result of oxygen-based free radicals catalyzed by iron associated with the mineral oxide (Fig. 1). The increase in arachidonic acid metabolism after exposures of cells to particles and fibers can result from the eooxidation of arachidonate by metal-catalyzed oxidants. This is a lipid peroxidation that can be mediated by free radical production by the dust (83). In support of an association between metal-catalyzed oxidant generation and arachidonic acid products, the release of LTB4 by alveolar macrophages can increase with the eoneentrations of iron complexed to the surface of silica and asbestos (84). Similarly, the eellular release of eytokines postulated to participate in the infiammatory and fibrotic responses ean be associated with exposures to metal-dependent radicals (see Fig. 1). TNF-a produetion by alveolar macrophages after mineral oxide exposure can be inhibited by both the metal chelator deferoxamine and hydroxyl radical scavengers (74). The release of other cytokines pertinent to silica and asbestos exposure ean also be responsive to oxidative stress (85,86). The release of these pertinent mediators after dust exposures is likely to be controlled by oxidant-sensitive promoters such as nuclear factor (NF)-kB (87). After exposure to silica and asbestos, NF-kB can function as a promoter... 

If a neutral chelate formed from a ligand such as acetylacetone is sufficiently soluble in water not to precipitate, it may stiH be extracted into an immiscible solvent and thus separated from the other constituents of the water phase. Metal recovery processes (see Mineral recovery and processing), such as from dilute leach dump Hquors, and analytical procedures are based on this phase-transfer process, as with precipitation. Solvent extraction theory and many separation systems have been reviewed (42). 

Medical Uses. Citric acid and citrate salts are used to buffer a wide range of pharmaceuticals at their optimum pH for stabiUty and effectiveness (65—74). Effervescent formulations use citric acid and bicarbonate to provide rapid dissolution of active ingredients and improve palatabiUty. Citrates are used to chelate trace metal ions, preventing degradation of ingredients. Citrates are used to prevent the coagulation of both human and animal blood in plasma and blood fractionation. Calcium and ferric ammonium citrates are used in mineral supplements. 

Heavy metals Cation Polystyrene matrix Chelating functional groups Mineral acids... 

Acetic acid, ethylenenitrilo[(hydroxyethyl)nitrilo]tri-iron(III) complexes, 2,788 Acetic acid, hexamethylenediaminetetra-synthesis, 2,779 Acetic acid, iminodi-chelating resins mineral processing, 6,824 metal complexes, 1,554 2, 788... 

Dithiobenzoic acid metal complexes, 2, 646 colours, 2, 646 Dithiobiuret metal complexes, 2, 640 Dithiocarbamates chelating resins mineral processing, 6,826 Dithiocarbamic acid metal complexes, 2,585 amine exchange, 1,428 photographic emulsions, 6,98 nickel poisoning, 6,768 tellurium(Il) complexes photothermography, 6,121 Dithiocarbazic acid metal complexes, 2,803 Dithiocarbimic acid metal complexes, 2,588 Dithiocarbimic acid, cyano-metal complexes, 2,808 Dithiocarboxylic acids metal complexes, 2,646 Dithiodiacetic acid metal complexes, 2, 806 Dithiodiketones... 

---