Extraction of metals

Give an account of the principles underlying the extraction of metals from their oxides, illustrating your answer by specific examples. 

Extraction of metal ions Extraction processes Extraction resistance Extractive distillation... 

The overall extraction process is sometimes subdivided into two general categories according to the main mechanisms responsible for the dissolution stage (/) those operations that occur because of the solubiHty of the solute in or its miscibility with the solvent, eg, oilseed extraction, and (2) extractions where the solvent must react with a constituent of the soHd material in order to produce a compound soluble in the solvent, eg, the extraction of metals from metalliferous ores. In the former case the rate of extraction is most likely to be controUed by diffusion phenomena, but in the latter the kinetics of the reaction producing the solute may play a dominant role. 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

The reaction of chloroformates with sodium xanthates results in the formation of alkyl xanthogen formates that are useful as flotation agents in extraction of metals from their ores (48). 

Metal Extraction. As with other carboxyhc acids, neodecanoic acid can be used in the solvent extraction of metal ions from aqueous solutions. Recent appHcations include the extraction of zinc from river water for deterrnination by atomic absorption spectrophotometry (105), the coextraction of metals such as nickel, cobalt, and copper with iron (106), and the recovery of copper from ammoniacal leaching solutions (107). 

J. Stary, The S olvent Extraction of Metal Chelates, The MacmiUan Co., New York, 1964. 

The quaternary ammonium salts (QAS) are widely used as ionofores of ion-selective electrodes and extractants of metals halogenic anion complexes. The influence of the QASes nature with various methyl groups contents on the cadmium extraction from bromide media has been investigated. 

The obtained results demonstrated that in a number of cases the solid-phase multiligand systems, and in other cases - pyrazolone derivatives, improve the extraction of metal from the analyzable solution, but at that, the multiligand systems ai e not produced in solid phase. 

In the pulp and paper industry, anionic and cationic acrylamide polymers are used as chemical additives or processing aids. The positive effect is achieved due to a fuller retention of the filler (basically kaoline) in the paper pulp, so that the structure of the paper sheet surface layer improves. Copolymers of acrylamide with vi-nylamine not only attach better qualities to the surface layer of.paper, they also add to the tensile properties of paper in the wet state. Paper reinforcement with anionic polymers is due to the formation of complexes between the polymer additive and ions of Cr and Cu incorporated in the paper pulp. The direct effect of acrylamide polymers on strength increases and improved surface properties of paper sheets is accompanied by a fuller extraction of metallic ions (iron and cobalt, in addition to those mentioned above), which improves effluent water quality. 

The results of the extraction of metal cations are summarized in Table 3. The 4b showed the selectivity toward Fe " cation and cannot act as an extractant for Fe " at pH 2.2. The extraction of Fe cation with 4b was increased with increasing pH, but the Fe cation ratios at all pH decrease than that of 2b and 3b. The results suggested that the conformation of 4b and the C=0 groups in the polymer affected the extraction of Fe in this process. 

Table 3 Extraction of Metal Cations with Ligands ...

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 +. ... 

The choice of a satisfactory chelating agent for a particular separation should, of course, take all the above factors into account. The critical influence of pH on the solvent extraction of metal chelates is discussed in the following section. 

Tri-n-butyl phosphate, ( -C4H9)3P04. This solvent is useful for the extraction of metal thiocyanate complexes, of nitrates from nitric acid solution (e.g. cerium, thallium, and uranium), of chloride complexes, and of acetic acid from aqueous solution. In the analysis of steel, iron(III) may be removed as the soluble iron(III) thiocyanate . The solvent is non-volatile, non-flammable, and rapid in its action. 

Discussion. Because of the specific nature of atomic absorption spectroscopy (AAS) as a measuring technique, non-selective reagents such as ammonium pyrollidine dithiocarbamate (APDC) may be used for the liquid-liquid extraction of metal ions. Complexes formed with APDC are soluble in a number of ketones such as methyl isobutyl ketone which is a recommended solvent for use in atomic absorption and allows a concentration factor of ten times. The experiment described illustrates the use of APDC as a general extracting reagent for heavy metal ions. 

The extraction of metals by liquid amines has been widely investigated and depends on the formation of anionic complexes of the metals in aqueous solution. Such applications are illustrated by the use of Amberlite LA.l for extraction of zirconium and hafnium from hydrochloric acid solutions, and the use of liquid amines for extraction of uranium from sulphuric acid solutions.42,43... 

A K De, S M Khopkar and R A Chalmers, Solvent Extraction of Metals, Van Nostrand Reinhold, London, 1970... 

J Stary, The Solvent Extraction of Metal Chelates, Pergamon Press, Oxford, 1964... 

The extraction of metal ions from aqueous sulphate media by alkylamines. R. W. Cattrall and S. J. E. Slater, Coord. Chem. Rev., 1973,11, 227-245 (64). 

Liquid-liquid extractions of metal ions by chelating ligands. E. Uhlig, Coord. Chem. Rev., 1982, 43, 299-312 (38). 

The solvent extraction of metal ions by crown compounds. Y. Takeda, Top. Curr. Chem., 1984,... 

Analytical applications of substituted cinnamohydroxamic acids in spectrophotometry and solvent extraction of metal ions. Y. K. Agrawal and R. K. Jain, Rev. Anal. Chem., 1982, 6,49-64 (71). 

Solvent extraction of metal carboxylates. H. Yamada and M. Tanaka, Adv. Inorg. Chem. Radiochem., 1985, 29,143 (159). 

D. Extraction of Metal Ions with Sulphoxides and Sulphones.573... 

Redox reactions constitute the third of the three major classes of chemical reactions treated here. The variety of these reactions is remarkable. Many common reactions, such as combustion, corrosion, photosynthesis, the metabolism of food, and the extraction of metals from their ores, appear to be completely different. However, when we consider these changes at the molecular level with a chemist s eye, we can see that they are all examples of a single type of process. 

Liquid Liquid Extraction of Metal Ions D. F. Peppard... 

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