Thiocyanic acid metal extraction from

Thallium, tetrakis(acetylacetone)-stereochemistry, 94 Thallium, triaquatrinitrato-structure, 97 Thermochromism, 470 Thiocyanato complexes linkage isomerism, 184 Thiocyanic acid metal extraction from, 540 Thioethers complexes chirality, 199 formation... 

In the initial thiocyanate-complex Hquid—Hquid extraction process (42,43), the thiocyanate complexes of hafnium and zirconium were extracted with ether from a dilute sulfuric acid solution of zirconium and hafnium to obtain hafnium. This process was modified in 1949—1950 by an Oak Ridge team and is stiH used in the United States. A solution of thiocyanic acid in methyl isobutyl ketone (MIBK) is used to extract hafnium preferentially from a concentrated zirconium—hafnium oxide chloride solution which also contains thiocyanic acid. The separated metals are recovered by precipitation as basic zirconium sulfate and hydrous hafnium oxide, respectively, and calcined to the oxide (44,45). This process is used by Teledyne Wah Chang Albany Corporation and Western Zirconium Division of Westinghouse, and was used by Carbomndum Metals Company, Reactive Metals Inc., AMAX Specialty Metals, Toyo Zirconium in Japan, and Pechiney Ugine Kuhlmann in France. 

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. 

Foster et al. have developed a method for determining technetium in dissolved nuclear fuel solutions. Tetrapropylammonium pertechnetate is doubly extracted from a basic medium into chloroform and the colored technetium (V) thiocyanate complex is formed in the chloroform phase by the addition of sulfuric acid, potassium thiocyanate and tetrapropylammonium hydroxide. The colored complex absorbs at 513 nm, has a molar extinction coefficient of 46,000 and is stable for several hours. Of more than 50 metals studied, none impairs measurements at ratios less than 100 to 1 mol with respect to technetium. Most anions do not disturb the determination of technetiiun. The standard deviation for a single determination is 0.09 fig over the range of 1 to 20 fig of technetium. 

While the liquid-liquid extraction of inorganic elements as coordination complexes with thiocyanate ions can be traced back to Skey (1867), the extraction from hydrochloric acid into ether of iron(III) (J. W. Rothe, 1892) or gallium (E. H. Swift, 1924) depends on the formation of solvated acido complexes derived from HMC14 extractions of metal complexes from nitric, thio-cyanic, hydrofluoric, hydrochloric and hydrobromic acids were studied exhaustively by Bock and his collaborators (1942—1956).6... 

Precipitation of Ag as chloride, or better as bromide, with a slight excess of precipitant may be a useful method of separation. Traces of Ag have been separated by thallium iodide as the collector. The precipitation can be dissolved in diluted H2SO4-H2O2 solution. A widely applicable method for the isolation of traces of Ag consists in co-precipitation with elemental tellurium formed by adding tin(II) chloride to 2 mol 1 HCl solution of the sample containing Te(IV) (see above). The extraction constant of primary Ag dithizonate is such that Ag can be extracted quantitatively from 6 mol 1 H solution by the use of 0.001%(w/v) dithizone solution in carbon tetrachloride. Anions such as halides and thiocyanates that form slightly soluble or complex Ag salts must be absent when extraction is made in mineral acid medium. Other metals extracted at high acidity are Pd, Au, and Hg. Copper will also be extracted. 

Treatment with hydrochloric acid dissolves scandium and other metals. The solution is treated with sodium thiocyanate and extracted with ether. Scandium converted to its oxide SC2O3 is separated from the solvent extract by ion exchange. 

The zirconium tetrachloride product must then be purified before reduction to metal. In particular, hafnium must be removed to less than 100 ppm Hf Zr because of the high neutron absorption cross-section it exhibits, and phosphorus and aluminum must be removed to even lower specifications due to their deleterious metallurgical impact on the final zirconium alloys. The tetrachloride product is first dissolved in water under carefully controlled conditions to produce an acidic ZrOCl2 solution. This solution is complexed with ammonium thiocyanate, and contacted with methyl isobutyl ketone (MIBK) solvent in a series of solvent extraction columns. Advantage is taken of the relative solubilities of Zr, Hf, and Fe thiocyanate complexes to accomplish a high degree of separation of hafnium and iron from the zirconium. 

Thiocyanate [2] and chloride [3-8] complexes play an important role in the extractive separation of platinum metals. They are extracted in the presence of pyridine (MIBK), TBP, phosphonium salts (ethyl acetate), DAM, DAPM (CHCI3), and TOPO (1,2-dichloroethane). Often, the extraction is carried out in hydrochloric acid media in the presence of SnCh (ligand SnClj") which plays the role of labilizing agent [8-11]. Solvent extraction is often applied in separation of platinum from other metals [3,6-8]. 

Formation constants of 3d metal ions with A-m-tolyl-p-substituted benzohydroxamic acids and of rare earths with thenoylhydroxamic acid have been determined. Formation constants of proton and metal complexes of iV-phenyl-2-thenoyl- and A-p-tolyl-2-thenoyl-hydroxamic acids have also been determined. In addition, study has been made of the mixed ligand complexes involving nicotine- and isonicotino-hydroxamic acids. A method of extraction and spectrophotometric determination of vanadium with chlorophenylmethylbenzohydroxamic acid has also been published. It may be mentioned that hydroxamic acids (in particular, the A-phenylbenzohydroxamic acid) have been widely used as analytical reagents for metal ions. Solvent extraction of titanium by benzo- or salicyl-hydroxamic acid in the presence of trioctylamine in the form of coloured complexes has been reported. A-w-Tolyl-p-methoxybenzohydroxamic acid has been used for extraction and spectrophotometric determination of Mo and W from hydrochloric acid media containing thiocyanate. 

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