Cerium iodate

This particular experiment is designed to be an accelerated version of a standard immersion/weight loss test. This has been validated by White et al. [124] who have compared the multichannel approach with 10 channels to a standard immersion for a number of well-researched inhibitors including chromate, cerium nitrate, cerium iodate, and cerium salicylate as listed in Table 9.2. 

The standardisation of thiosulphate solutions may be effected with potassium iodate, potassium dichromate, copper and iodine as primary standards, or with potassium permanganate or cerium)IV) sulphate as secondary standards. Owing to the volatility of iodine and the difficulty of preparation of perfectly pure iodine, this method is not a suitable one for beginners. If, however, a standard solution of iodine (see Sections 10.112 and 10.113) is available, this maybe used for the standardisation of thiosulphate solutions. 

Determination of cerium as cerium(IV) iodate and subsequent ignition to cerium(IV) oxide Discussion. Cerium may be determined as cerium(IV) iodate, Ce(I03)4, which is ignited to and weighed as the oxide, Ce02. Thorium (also titanium and zirconium) must, however, be first removed (see Section 11.44) the method is then applicable in the presence of relatively large quantities of lanthanides. Titrimetric methods (see Section 10.104 to Section 10.109) are generally preferred. 

Procedure. The solution should not exceed 50 mL in volume, all metallic elements should be present as nitrates, and the cerium content should not exceed 0.10g. Treat the solution with half its volume of concentrated nitric acid, and add 0.5 g potassium bromate (to oxidise the cerium). When the latter has dissolved, add ten to fifteen times the theoretical quantity of potassium iodate in nitric acid solution (see Note) slowly and with constant stirring, and allow the precipitated cerium(IV) iodate to settle. When cold, filter the precipitate through a fine filter paper (e.g. Whatman No. 42 or 542), allow to drain, rinse once, and then wash back into the beaker in which precipitation took place by means of a solution containing 0.8 g potassium iodate and 5 mL concentrated nitric acid in 100 mL. Mix thoroughly, collect the precipitate on the same paper, drain, wash back into the beaker with hot water, boil, and treat at once with concentrated nitric acid dropwise until the precipitate just dissolves (20-25 mL... 

Cerium, D. of as oxide via iodate, (g) 453 Cerium(IV) ammonium nitrate see Ammonium cerium(IV) nitrate Cerium(IV) ammonium sulphate see Ammonium cerium(IV) sulphate Cerium(IV) hydroxide 380 preparation of, 380... 

Cerous iodates and the iodates of the other rare earths form crystalline salts sparingly soluble in water, but readily soluble in cone, nitric acid, and in this respect differ from the ceric, zirconium, and thorium iodates, which are almost insoluble in nitric acid when an excess of a soluble iodate is present. It may also be noted that cerium alone of all the rare earth elements is oxidized to a higher valence by potassium bromate in nitric acid soln. The iodates of the rare earths are precipitated by adding an alkali iodate to the rare earth salts, and the fact that the rare earth iodates are soluble in nitric acid, and the solubility increases as the electro-positive character of the element increases, while thorium iodate is insoluble in nitric acid, allows the method to be used for the separation of these elements. Trihydrated erbium iodate, Er(I03)3.3H20, and trihydrated yttrium iodate, Yt(I03)3.3H20,... 

Quadrivalent cerium salts may be volumetrically determined by arsenious acid in aqueous sulphuric acid solution using a manganese salt as catalyst, with potassium iodate present as a promoter.2 Excess of arsenious acid is used and back-titrated with permanganate. If nitric acid is present in place of sulphuric acid, an alkali chloride and a trace of iodine are used to promote the action of the manganese salt. Direct potentiometric titration with arsenious acid may also be employed. 

Potassium iodate solution white, bulky precipitate of thorium iodate, Th(I03)4. Precipitation occurs in the presence of 50 per cent by volume of concentrated nitric acid (difference from cerium(III)). 

Potassium iodate solution white precipitate of cerium(II) iodate, Ce(I03)3, in neutral solution, soluble in nitric acid (difference from cerium(IV) iodate cf. Thorium, Section VII.20, reaction 8). 

In general, lanthanides can be separated from mixtures with other elements by precipitation as oxalates or fluorides. Cerium and europium can conveniently be removed from the others, the former by oxidation to CeIV and precipitation as the iodate, and the latter by reduction to Eu2+, which can be precipitated as EuS04. 

Cerium (IV) in solution is obtained by treatment of Ce111 solutions with very powerful oxidizing agents, for example, peroxodisulfate or bismuthate in nitric acid. The aqueous chemistry of CeIV is similar to that of Zr, Hf, and, particularly, tetravalent actinides. Thus Ce gives a phosphate insoluble in 4 M HN03 and an iodate insoluble in 6 M HN03, as well as an insoluble oxalate. The phosphate and iodate precipitations can be used to separate Ce from the trivalent lanthanides. Ce is also much more readily extracted into organic solvents by tributyl phosphate and similar extractants than are the Lnm lanthanide ions. 

The classical chemical methods to separate lanthanoids were based upon the redox behavior of Ce, Sm, Eu, and Yb , Other classical methods (fractional crystallization) are essentially physical processes. Cerium is oxidized to the 4-I- state and separated from the 3+ rare earths by solvent extraction, iodate precipitation, or selective hydrolysis or precipitation of basic Ce(IV) compounds in weakly acidic solution. Europium is reduced and maintained in H2O as Eu " by Zn amalgam and precipitated as EUSO4. Sm and Yb are extracted from H2O by reduction into dilute Na or Li amalgam. 

Many of the actinoids are also separated by exploiting their redox behavior. Thorium is exclusively tetravalent and berkelium is chemically similar to cerium, so iodate precipitation of Th and extraction of Bk(IV) with bis(2-ethylhexyl)orthophos-phoric acid (HDEHP) are used to isolated these elements. The differing stabilities of the (III), (IV), (V), and (VI) states of U, Np, and Pu have be exploited in precipitation and solvent extraction separations of these elements from each other and from fission product and other impurities with which they are found. Because of its technical importance, the process chemistry to separate U and Pu in nuclear materials has been highly developed. Extraction of Bk(IV) with HDEHP is used to separate Bk from neighbouring elements. 

Colour systems suitable for use in the spectrophotometric method may also be formed in redox reactions. Some examples of such reactions are the oxidation of Mn(II) to Mn04" or Cr(III) to Cr04, oxidation of dimethylnaphthidine with vanadium(V) or chromium(VI), oxidation of o-tolidine with cerium(lV) or with chlorine. Examples of oxidation reactions are also the iodide methods, in which iodide ions are oxidized with bromine to give iodate ions which, in turn, react with the excess of iodide anions to form free iodine (see Chapter 25). A colour effect of reduction also occurs, for example, in determinations of Se and Te in the form of coloured sols produced in the reduction of Se(lV) or Te(IV) to their elementary forms. 

In 0.2 M Na2C03, the light lanthanides (cerium group) are precipitated quantitatively, while the remaining lanthanides and scandium are only partly precipitated [18). Separation of Ce(IV) as the hydroxide (pH 1) enables the separation of Ce from other REE. Ti, Zr, or Fe(III) can be used as carriers. Ce(IV) may also be precipitated as iodate. 

Thorium can be separated from rare-earth- and other metals by precipitation of the iodate, Th(I03)4, from 1 M HNO3 in the presence of tartaric acid and H2O2 [4,5]. The iodate precipitate also contains any Zr and Ce(IV) present. Mercury(II) and cerium(IV) have been used as collectors. 

Tetravalent plutonium. Solutions of tetravalent plutonium salts are generally similar to tetravalent cerium and uranium. The fluoride PUF4, potassium complex fluoride K2PUF6, iodate Pu(I03)4, and phosphate Pu3(P04)4 are insoluble. Excess soluble hydroxides precipitate Pu(OH)4. The... 

The lanthanides are separated from most other elements by precipitation of oxalates or fluorides from nitric acid solution. The elements are separated from each other by ion-exchange, which is carried out commercially on a large scale. Cerium and europium are normally first removed, the former by oxidation to Celv and removal by precipitation of the iodate which is insoluble in 6M HN03 or by solvent extraction, and the latter by reduction to Eu2+ and removal by precipitation as insoluble EuS04. 

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