Metal extraction and separation

The chemistry of hydrogen peroxide and Caro s acid can be used in many applications involving metals metal extraction and separation from ores or waste, hydrometallurgy, and surface treatment of metals and alloys. Compared to alternative treatments, the direct chemical costs are sometimes higher, but the difference is often outweighed by advantages in simplicity of operation (cost savings on equipment), and in lower overall effluent production. 

Use Metal extraction and separation, intermediate for wetting agents and detergents. 

A description of the methodologies developed in the preparation and application of SIRs on metal extraction and separation is provided in the next sections of this chipter. 

Metallurgy. The extraction and separation of metals and plating baths have involved quinoline and certain derivatives (see Electroplating Metal SURFACE TREATiffiNTs Exthaction). 

Improved selectivity at the extraction and separation of divalent metal ions such as Zn, Cd, Hg, and Ca have been found [225-229]. 

Many of the waste streams from U.S. process industries are water containing small quantities of metal ions that the law requires be removed before the wastewater is disposed of There is an economic incentive to recoup at least some of the cost of wastewater treatment by recovering and selling the metal content instead of merely disposing of the metals as sludge. Because the waste streams are dilute in desired materials, research is needed to devise efficient extraction and separation processes. 

Mhaske, A. Dhadke, P. Liquid-liquid extraction and separation of rhodium(III) from other platinum group metals with Cyanex 925. Sep. Sci. Technol. 2001, 36, 3253-3265. 

The amount of modifier required to prevent third phase formation can be determined in the following way. The aqueous and solvent phases are first contacted, and once the three phases have separated, the lower aqueous phase is drawn off and discarded. The modifier to be considered is then added from a burette in small increments to the two organic phases, and the mixture shaken after each addition. The amount of modifier required to produce a single organic phase is then used to calculate the amount required to be added to the solvent. Generally, about 2-5 vol% of modifier is needed, but more may be necessary if high concentrations of extractant are used in the solvent. Any effects of modifiers on the kinetics and equilibria of metal extraction and stripping can be determined by shakeout tests. 

Praesodymium may be recovered from its minerals monazite and bastana-site. The didymia extract of rare earth minerals is a mixture of praesodymia and neodymia, primarily oxides of praesodymium and neodymium. Several methods are known for isolation of rare earths. These are applicable to all rare earths including praesodymium. They include solvent extractions, ion-exchange, and fractional crystallization. While the first two methods form easy and rapid separation of rare earth metals, fractional crystaUization is more tedious. Extractions and separations of rare earths have been discussed in detail earlier (see Neodymium and Cerium). 

Metallurgy. The extraction and separation of metals and plating baths have involved quinoline and certain derivatives see also Electroplating. The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Dilute solutions of heavy metals such as mercury, cadmium, copper, lead, and zinc can be purified using quinoline-8-carboxylic acid adsorbed on various substrates. 

Ion exchange from organic solvents and mixed organic aqueous solvents offers interesting possibilities for the extraction and separation of metals because of the different nature of the solvation processes in these systems. Only cation solvation is significant in dipolar, aprotic, organic... 

Yakshin, V.V., Vilkova, O.N., Tsarenko, N.A. et al. 2006. Molecular design of macrocy-clic extractants for extraction and separation of alkali and alkaline-earth metals. Russ. J. Coord. Chem. 32 (2) 77-81. 

P-Diketonates. Very strong actinide complexes with p-diketones [An(acac)4 and An02(acac)2] are used in solvent extraction and separation of actinides. They are prepared by direct interaction of the metal or actinyl halide with the appropriate p-diketone in the presence of a base. Only fluorinated An(IV) diketonates produce adducts with Lewis bases, whereas common An02(acac)2 (An = Np, Pu) are stabilized by adduct formation. Fluorinated U02(hfa)2 is a very strong Lewis acid and its adducts with H20 and ROH can be sublimed without decomposition [282],... 

Addition of thiocyanate ions to chloride or perchlorate solntions of zirconium and hafnium yields complexes containing from one to eight isothiocyanate groups per metal atom. These systems are of interest because of the importance of thiocyanate complexes in the extraction and separation of the elements. IR spectroscopy indicates that M-N bonds are present in the violet (Zr) and pink (Hf) complexes [NEt4]2[M(NCS)6] analogous complexes have been obtained with alkali metal cations. In the presence of pyridine, the dodecahedral Zr(bipy)2(NCS)4 complex is produced see Ammonia N-donor Ligands). 

Ultrasound-assisted emulsification in aqueous samples is the basis for the so-called liquid membrane process (LMP). This has been used mostly for the concentration and separation of metallic elements or other species such as weak acids and bases, hydrocarbons, gas mixtures and biologically important compounds such as amino acids [61-64]. LMP has aroused much interest as an alternative to conventional LLE. An LMP involves the previous preparation of the emulsion and its addition to the aqueous liquid sample. In this way, the continuous phase acts as a membrane between both the aqueous phases viz. those constituting the droplets and the sample). The separation principle is the diffusion of the target analytes from the sample to the droplets of the dispersed phase through the continuous phase. In comparison to conventional LLE, the emulsion-based method always affords easier, faster extraction and separation of the extract — which is sometimes mandatory in order to remove interferences from the organic solvents prior to detection. The formation and destruction of o/w or w/o emulsions by sonication have proved an effective method for extracting target species. 

The materials act as separation media for molecules with radii of gyration in the range 3 to 15 nm. Thus the materials are potentially suitable for the extraction and separation of metals complexes, copolymers, micellular substances and proteins. 

Use Heavy-metal extraction and solvent separation, gasoline additives, antifoam agent, plasticizer, textile conditioner, and antistatic agent. 

Many complexing polymers have been shown to be very promising for commercial metal enrichment and separation. Among those, amine polymers such as poly(allylamine) (PAL) and poly(ethylenimine) (PEI) have been found suitable for metal extraction. The main types of the different interaction products of metal ions with functional polymers are shown in Figure 9. 

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