Extractability of iron

After aluminium, iron is the most abundant metal and the fourth most abundant of all the elements it occurs chiefly as oxides (for example haematite (FCjO,), magnetite (lodestonej (FC3O4) and as iron pyrites FeSj- Free iron is found in meteorites, and it is probable that primitive man used this source of iron for tools and weapons. The extraction of iron began several thousand years ago, and it is still the most important metal in everyday life because of its abundance and cheapness, and its ability to be cast, drawn and forged for a variety of uses. 

The mode of extraction in these oxonium systems may be illustrated by considering the ether extraction of iron(III) from strong hydrochloric acid solution. In the aqueous phase chloride ions replace the water molecules coordinated to the Fe3+ ion, yielding the tetrahedral FeCl ion. It is recognised that the hydrated hydronium ion, H30 + (H20)3 or HgO,, normally pairs with the complex halo-anions, but in the presence of the organic solvent, solvent molecules enter the aqueous phase and compete with water for positions in the solvation shell of the proton. On this basis the primary species extracted into the ether (R20) phase is considered to be [H30(R20)3, FeCl ] although aggregation of this species may occur in solvents of low dielectric constant. 

The difficulty in recognizing redox reactions is illustrated by two of the reactions that occur during the extraction of iron from iron ores, a process that we describe in detail in Chapter 20 ... 

Figure 11.1 Schematic representation of iron uptake mechanisms, (a) The transferrin-mediated pathway in animals involves receptor-mediated endocytosis of diferric transferrin (Tf), release of iron at the lower pH of the endocytic vesicle and recycling of apoTf. (b) The mechanism in H. influenzae involves extraction of iron from Tf at outer membrane receptors and transport to the inner membrane permease system by a periplasmic ferric binding protein (Fbp). From Baker, 1997. Reproduced by permission of Nature Publishing Group.

Mickler, W. Reich, A. Uhlemann, E. Extraction of iron(II) and iron(III) with 4-acyl-5-pyrazolones in comparison with long-chain l-phenyl-l,3-(cyclo) alkanediones. Sep. Sci. Technol. 1998, 33, 425-435. 

Figure 21. Duct network for extraction of iron oxide dust.

Atomic absorption spectrometry coupled with solvent extraction of iron complexes has been used to determine down to 0.5 pg/1 iron in seawater [354, 355]. Hiire [354] extracted iron as its 8-hydroxyquinoline complex. The sample is buffered to pH 3-6 and extracted with a 0.1 % methyl isobutyl ketone solution of 8-hydroxyquinoline. The extraction is aspirated into an air-acetylene flame and evaluated at 248.3 nm. 

No sulfoxide complexes of osmium have been reported. Unsymmetri-cal dialkyl sulfoxides have been utilized in extraction studies, and methyl-4,8-dimethylnonyl sulfoxide has found application in the extraction of iron (266). Extraction of ruthenium from hydrochloric acid solutions by sulfoxides has been studied (470) and comparisons of sul-fones, sulfoxides, and thioethers as extractants for nitrosoruthenium species reported (441, 443). Similar studies on the extraction of nitro-soosmium species have been reported (442). 

Ryan, J. N., and P. M. Gschwend (1991), "Extraction of Iron Oxides from Sediments Using Reductive Dissolution by Titanium(III)," Clays and Clay Minerals, in press. 

Turoff, M.L.H., and Denting, S.N. (1977), Optimization of the Extraction of Iron(Il) from Water into Cyclohexane with Hexafluoroacetylacetone and Tri-n-Butyl Phosphate, Talanta, 24, 567-571. 

Neutralization of the strip solution with hydrochloric acid gives Pd(NH3)2-CI2 as product. One of the problems that has emerged is the formation of di- -hexylsulfoxide [34] by oxidation of the sulfide. This may cause several problems including extraction of iron(III) that is strongly dependent on the HCl concentration. The iron can easily be stripped by water. There have also been indications of a buildup of rhodium in the extract phase that again can be explained by the extraction of anionic rhodium species by the sulfoxide. One benefit from the presence of the sulfoxide is that the rate of palladium extraction is increased by the presence of the protonated sulfoxide at high acidities however, this kinetic enhancement is less that found with TOA HCl, which remains protonated even at low acidities. 

The stability of iron oxide suspensions is relevant to fields as varied as the paint industry, extraction of iron from its ores, the structure of soils, hydrometallurgy and waste water treatment. The ease of homogensisation of paint, for example, is controlled by proper adjustment of the stability of the pigment suspensions. In ground waters, the settling behaviour of small iron oxide particles influences transportation of trace elements and radio-nuclides. The stability of a dispersion of magnetic particles can determine the quality of ferrofluids and magnetic tapes. 

The principles of dissolution have been reviewed by Bloom and Nater (1991), Blesa et al. (1994) and Casey (1995). The driving force for dissolution is the extent of undersaturation with respect to the oxide. Undersaturation is thus a necessity for dissolution as is supersaturation for precipitation. Other factors being equal, the rate of reaction will increase as degree of undersaturation rises. The extent of undersaturation varies from one system to the next. Dissolution of anodic Fe oxide films often takes place in nearly saturated solutions, whereas extraction of iron from its ores requires markedly undersaturated solutions in order to be efficient. In most natural systems (soils and waters) the aqueous phase is fairly dose to saturation with respect to the iron oxides and dissolution may, therefore, be extremely slow. The dissolution process can be accelerated by the presence of higher levels of electrons or chelating ligands. 

Chem. Soc. Faraday Trans. I. 71 1623-1630 Rustad, J.R. Felmy A.R. Hay, B.P. (1996) Molecular statics calculations for iron oxide and oxyhydroxide minerals Toward a flexible model of the reactive mineral-water interface. Geochim. Cosmochim. Acta 60 1553—1562 Ryan, J.N. Gschwend, P.M. (1991) Extraction of iron oxides from sediments using reductive dissolution by titanium(III). Clays Clay Min. 39 509-518... 

M. C. Yebra and A. Moreno-Cid, Continuous ultrasound-assisted extraction of iron from mussel samples coupled to a flow injection-atomic spectrometric system, J. Anal. At. Spectrom., 17(10), 2002, 1425-1428. 

It should be noted that, since the extraction of iron(III) by ort/io-hydroxyoximes shows a third-order dependence on the concentration of the extractant152... 

The extraction of uranium(VI) from sulfate media by amine sulfates of different types lies in the order tertiary > secondary > primary, whereas the extraction of iron(III) lies in the reverse order,195 206 with the result that tertiary amines are the obvious choice for the selective extraction of uranium in the presence of iron. 

An interesting property of resins impregnated with oximes or oxines is that the selectivity of, for example, copper over iron(III), approaches that of a pure solvent-extraction process only when an inert solvent is present in the pores of the resin.396 Thus, in a /S-hydroxyoxime SIR, the selectivity for copper over iron(III) improved by a factor of 20 when the solvent perchloroethylene was introduced into the SIR, and by a factor of 700 in a similar resin impregnated with 8-hydroxy-quinoline.396 This is believed to be due to kinetic and thermodynamic restrictions in the extraction of iron(III), but not of copper, at an aqueous—organic boundary.396 397... 

Calcium carbonate Extraction of iron, making cement, glass making... 

The extraction of iron is a continuous process and is much cheaper to run than an electrolytic method. 

It is true to say that almost all the reactions by which a metal is extracted from its ore are reduction reactions. Discuss this statement with respect to the extraction of iron, aluminium and zinc. 

A liquid slag is formed, which is mainly calcium silicate. More details of the extraction of iron and its conversion into steel are given in Chapter 10. 

The detection limit for gallium determination at 287.4 nm in an air-acetylene flame is only about 70 ng ml - and that by flame AFS is not much better, and sometimes even worse.1 The detection limit by flame AES at 403.3 nm is appreciably better, especially if a nitrous oxide-acetylene flame is used. This reflects the low excitation energy. These values are too low to make the direct determinations useful in environmental applications, and therefore solvent extraction is often used for pre-concentration.1 One method often used is the extraction of the anionic keto-chloro complex from strong hydrochloric acid solution (e.g. 5.5M) into 4-methylpentan-2-one.25,26 Co-extraction of iron may... 

In the extraction of iron, the oxide is reduced to metallic iron. On the other hand, the oxidation of iron to produce the brown iron oxide commonly known as rust is the opposite reaction to the production of the metal from the oxide. The extraction of iron from the oxide, must be conducted with utmost careful control of the conditions, such that the backward reaction is prevented. 

Next to aluminium, iron is the most abundant and widely distributed metal in the crust of the earth.1 It is seldom found free in nature owing to the extreme readiness with which it combines with moist air to form the hydrated oxide known as rust. Such ferruginous minerals as contain a sufficiently high percentage of iron, possess a suitable chemical composition, and occur in nature in large quantity, are termed ores and are used for the commercial extraction of iron. Owing to their economic importance the ores of iron have been studied with unusual care, and the suitability of the more important types for metallurgical purposes is discussed in Part III. of this volume. 

Exhaustive extraction involves the quantitative removal of a solute, and selective extraction, the separation of two or more solutes from each other. One classical application of an exhaustive analytical extraction is the ether extraction of iron(III) chloride from hydrochloric acid solutions. The extraction is not strictly quantitative in that a small fraction remains unextracted. Therefore the method is best suited to the removal of relatively large amounts of iron (several grams) from small amounts of such metals as nickel, cobalt, manganese, chromium, titanium, or aluminum. It is of interest that iron(II) remains unextracted. 

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