Solvent extraction base metals

The nature of the donor atoms in the chelating agent. Ligands which contain donor atoms of the soft-base type form their most stable complexes with the relatively small group of Class B metal ions (i.e. soft acids) and are thus more selective reagents. This is illustrated by the reagent diphenylthiocarbazone (dithizone) used for the solvent extraction of metal ions such as Pd2+, Ag+, Hg2+, Cu2+, Bi3+, Pb2+, and Zn2 +. ... 

Organic extractants facilitate the transfer of the metal ions from the aqueous phase to the organic phase in solvent extraction. Based on the nature of the organic extractant, the metal ion, and the diluent, effective separation methods can be devised. Uranium extraction into diethyl ether from nitrate medium by salting out is perhaps one of the first uses of solvent extraction for large-scale actinide processing (9). In this case, ether not only acts as the diluent, it also acts as the extractant, which works according to the solvation mechanism (discussed below). 

Kasahara, K. and Endo, M. (2001) Solvent extraction of metal ions with acyclic and macrocyclic Schiff bases, Anal. Sci, 17(Suppl.), a339-a342. 

Solvent extraction of metal ions in Inorganic Chemistry is based on the formation of an uncharged complex followed by distribution of this complex between the two concerned solvents which are immiscible in each other. The complex may be produced either by creation of coordinate covalent bonds or by solvation or by ion-pair formation. 

Liquid phases were analysed by ICP-MS for the determination of EE after both aqueous leaching and solvent extraction. Based on these analyses, the amount of extracted metals per mass of dry initial fly ash was related to the initial metal concentration of the applied fly ash as,... 

In the methods which are based on metal complex formation, the analyte reacts with either one or two reagents giving rise to a charged or neutral complex compound or an ion-association complex. The metal is then determined by AAS after filtration or solvent extraction. The metal complex formed must be very stable. Standards for calibration are prepared in the same way as the samples. Interference is caused by other anions present in the sample solution that might also be complexed with the metal cation. 

Solvent extraction of metals embodies all aspects of coordination chemistry rates, equilibria, stereochemistry, crystal field theory, covalent bonding, hard-soft acid-base theory, hydrogen bonding, steric hindrance, enthalpy and entropy. All of these basic principles can link together to produce pure metals on an industrial scale from dilute aqueous solutions — a remarkable achievement of elegant coordination chemistry. To achieve this result it is only necessary to form within the aqueous medium a neutral species containing the metal to be extracted. 

I thank my friends at the extraction plants for uranium — in Rossing, Namibia ERGO, Springs and Randfontein, Transvaal and for the base metals and platinum metals at Rustenburg, Transvaal, who showed me the real world of large-scale solvent extraction of metals. 

Due to their relevance in solvent extraction and metal recovery, the facilitated transfer of transition metal ions has been investigated by the type of electrochemical methodology described above. This electrochemical approach has in fact proven to be a valuable tool for the study of the mechanism of solvent extraction processes. Wendt et al studied the transfer of Fe, Ni, and Zn assisted by bidentate nitrogen bases, such as phenanthroline and bipyridine. Similar studies were carried out by Wang et al and by Doe and Freiser, who also studied the transfer of cadmium assisted by diphenylthiocarbazone, a weak monobasic acid. Solomon et studied terpyridine as an extractant for transition metals. An interesting result from this type of work is... 

The production of CPO is based on relatively inexpensive cycHc substances these must be derivatized, however, to meet the requirements of resistance to heat softening and suitabiUty for metallization. Metathesis polymerization is problem-prone, since relatively large amounts of catalyst (WCl, C2H AlCl2) must be removed by solvent extraction (216). In the process, the price of CPO, at small batches, is several times higher than that of BPA-PC. 

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). 

Theory. Conventional anion and cation exchange resins appear to be of limited use for concentrating trace metals from saline solutions such as sea water. The introduction of chelating resins, particularly those based on iminodiacetic acid, makes it possible to concentrate trace metals from brine solutions and separate them from the major components of the solution. Thus the elements cadmium, copper, cobalt, nickel and zinc are selectively retained by the resin Chelex-100 and can be recovered subsequently for determination by atomic absorption spectrophotometry.45 To enhance the sensitivity of the AAS procedure the eluate is evaporated to dryness and the residue dissolved in 90 per cent aqueous acetone. The use of the chelating resin offers the advantage over concentration by solvent extraction that, in principle, there is no limit to the volume of sample which can be used. 

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