Cobalt cation exchange resins

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. 

Atomic absorption spectrometry has been used to determine caesium in seawater. The method uses preliminary chromatographic separation on a strong cation exchange resin, ammonium hexcyanocobalt ferrate, followed by electrothermal atomic absorption spectrometry. The procedure is convenient, versatile, and reliable, although decomposition products from the exchanger, namely iron and cobalt, can cause interference. 

Caesium 137Cs adsorption on strong cation exchange resin ammonium hexacyano cobalt ferrate, dissolution in hydrochloric hydrofluoric acid /f counted for 137Cs lOpCi/1 [865]... 

A secondary, more subtle, effect that can be utilized in the achievement of selectivity in cation exchange is the selective complexation of certain metal ions with anionic ligands. This reduces the net positive charge of those ions and decreases their extraction by the resin. In certain instances, where stable anionic complexes form, extraction is suppressed completely. This technique has been utilized in the separation of cobalt and nickel from iron, by masking of the iron as a neutral or anionic complex with citrate350 or tartrate.351 Similarly, a high chloride concentration would complex the cobalt and the iron as anionic complexes and allow nickel, which does not form anionic chloro complexes, to be extracted selectively by a cation-exchange resin. 

An alternative method of preparing highly active zinc hexacyano-cobaltate catalyst involved the use of hexacyanocobaltic acid prepared by passing the potassium salt through cationic exchange resin (Rohm and Haas A-15). 

The ion-exchange chromatography was first applied to the separation of geometrical isomers of a cobalt(III) complex by King and Walters who separated tram- and cw-[Co(N02)2(NH3)4]. From the cation-exchange resin (Amberlite IR-120), 1 mol/ dm NaCl eluteJ the fra/w-isomer and then the c -isomer was eluted with 3 mol/dm NaCl. This difference was attributed to that the m-isomer was more firmly held because of its larger dipole moment. 

Silva, McDowell, Keller, and Tarrant have made further solvent extraction and cation-exchange studies of nobelium [57]. Its complexing ability with chloride ions was compared with that of divalent mercury, cadmium, copper, cobalt, and barium, and it was found to be most similar to the relatively weakly complexed alkaline earth. The elution behavior of nobelium was compared with the alkaline earths in a cation-exchange resin/HCl system and found to be most like Ca " ... 

A number of simple and inexpensive materials catalytically promote the cobalt-carbonylation (Reaction 2) in aqueous solution. These include ion-exchange resins, zeolites, or special types of activated carbon. Formation of the active catalyst in a separate reactor is thus economically feasible. The mechanism of this catalysis has not yet been elucidated and seems to differ for each promoter mentioned. After an induction period during which the cobalt fed to the reactor is partially retained by the promoter, fully active materials have absorbed cobalt carbonyl anion Co(CO)4 (ion exchange resins), Co2+ cation (zeolites), or a mixture of Co2+, cobalt carbonyl hydride, and cluster-type cobalt carbonyls (activated carbon). This can be shown by analytical studies (extraction, titration, and IR studies) of active material withdrawn from the reactor. 

Poly(ethyleneimine) cross-linked (CPEI) with ethylenedichloride forms stable complexes with copper (II) as well as with cobalt (II). The RC1 type of cross-linked poly(ethyleneimine) having an anion-exchange capacity of 6.8 meq g 1 retains copper from CuS04 and cobalt from 1 M aq. CoCl2 solutions [55], PEI is by itself a weak basic anion-exchange resin and forms stable complexes with anions and cations. The process is probably accompanied with chelate ring formation ... 

In order to examine more completely the above phenomenon, experiments have been carried out with both an anion and cation exchanger [14]. The resin phase chloride ion concentration levels were provided by equilibrating the AG 1-X4 with 1.84 M HCl and the Dowex 50 W-X4 with 5.4 M HCl, respectively. To obtain the resin phase absorption spectra for study, both resins were equilibrated with a 2.64 M HCl solution containing cobalt. The absorption spectra are essentially duplicated in the two exchangers (Fig 4). Once again the sizable presence of CoClj or CoCl ... 

The successful use of chelating ion exchange resins to treat metal plating baths depends upon the selective sorption properties of the resins for the ions present in the plating baths. The selectivity of the sorption can depend upon a number of factors, including the temperature, pH, and upon the type and concentration of other anions and cations present in the solution. Various competing ion effects have been noted for metals such as copper, nickel, cobalt, iron, zinc and others (4 - 8). 

In 1966, [Co(en)3] Bfj was separated into its optically active enantiomers on a colunm of anion-exchange resin, which was in advance loaded with tartrate or anti-monyltartrate ions. The resolution was partial. In the same year, Brubaker et al. achieved the total resolution of a trinuclear cobalt(III) complex, hexakis(2-amino-ethanethiolato)tricobalt(III) bromide on a column of a cation-exchange cellulose (Bio-Rad Cellex CM) by eluting with 0.1 mol/dm NaCl. 

Transition metals may also be separated via ion-pair chromatography on mac-roporous PS/DVB resins or chemically bonded silica [45]. The mobile phase contains complexing agents and a corresponding ion-pair reagent. If these columns are equilibrated with a surface-active acid such as octanesulfonic acid, metal ions such as copper, nickel, zinc, and cobalt elute in the same order as they do on surface-sulfonated cation exchangers. This suggests that in this case. 

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