Cobalt chelating 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. 

Chang et al. [952] used a miniature column packed with a chelating resin and an automatic online preconcentration system for electrothermal atomic absorption spectrometry to determine cadmium, cobalt, and nickel in seawater. Detection limits of 0.12,7 and 35 ng/1 were achieved for cadmium, cobalt, and nickel, respectively, with very small sample volume required (400-1800 xl). 

Figure 13 Comparison of absorption spectra for cobalt(II) in the IDA chelating resin A-1 phase and in the solution A Muromac A-1 (100-200 mesh, sodium form) spectrum at 27% Co loading and external pH 6.0 with 1-mm cell thickness B same as A with 2-mm cell thickness C solution spectrum for Co aqua ion D solution spectrum for Co(IDA) complex.

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 spite of the sensitivity of the determination, because of the low concentrations of cadmium in most environmental samples, the element is still often preconcentrated. For example, discrete nebulization flame AAS has been used to measure foliar cadmium after extraction of the APDC complex into chloroform.15 Cobalt was extracted at the same time. Many other solvent extraction procedures have been described.1 Alternatively resins such as a chelating polydithiocarbamate resin have been employed to concentrate cadmium prior to determination.16 Extractions onto solid phase materials for preconcentration may be made more convenient by automation, for example using flow injection methodology.17... 

R. R. Grinstead, Selective Absorption of Copper, Nickel, Cobalt and Other Transition Metal Ions from Sulfuric Acid Solutions with the Chelating Ion Exchange Resin XFS4195, Hydrometallurgy, 12, pp. 387-400 (1984). 

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). 

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