Cadmium, solvent extraction

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. 

Nogueira, C. A. Delmas, F. New flowsheet for the recovery of cadmium, cobalt and nickel from spent Ni-Cd batteries by solvent extraction. Hydrometallurgy 1999, 52, 267-287. 

Sze, Y. K. P. Lam, J. K. S. A study of a solvent extraction method for the treatment of spent electrolyte solutions generated in nickel-cadmium (Ni-Cd) battery manufacturing. Environ. Technol. 1999, 20, 943-951. 

A comparison was carried out on the results obtained using ICP-AES and AAS for eight elements in coastal Pacific Ocean water. The results for cadmium, lead, copper, iron, zinc, and nickel are in good agreement. For iron, the data obtained by the solvent extraction ICP method are also in good agreement with those determined directly by ICP-AES. In most of the results the relative standard deviations were 4% for all elements except cadmium and lead, which had relative standard deviations of about 20% owing to the low concentrations determined. 

Jagner et al. [802] used this technique to determine zinc, cadmium, lead, and copper in seawater. Their method includes computer control of the potentiometric stripping technique. They compared their results with those obtained by solvent extraction-AAS and showed that the computer-controlled potentiometric stripping technique is more sensitive, and has advantages over ASV. Computer control makes deoxygenation of the sample unnecessary. 

Kingston et al. [32] preconcentrated the eight transition elements cadmium, cobalt, copper, iron, manganese, nickel, lead, and zinc from estuarine and seawater using solvent extraction/chelation and determined them at sub ng/1 levels by GFA-AS. 

In the electrowinning of cadmium, nickel is an interfering element that has to be continuously removed from the electrolyte, a weak acidic cadmium sulfate solution. To handle the undesirable buildup of nickel contamination and at the same time obey environmental demands, the industry installed a solvent extraction kidney [8],... 

The presence of carbonate in the ammoniacal system offers a possibility of controlling the conditions for the formation of cadmium carbonate. After separation of nickel in the solvent extraction loop, cadmium is precipitated from the raffinate as carbonate. Thermal stripping reduces the ammonia concentration and some carbon dioxide will also be evaporated. Precipitation is completed by cooling the solution and by addition of... 

Alternatively, an acid route has also been reported [26], where the leaching is accomplished using a mixture of HNO3 and HF, and separation and recovery of the nickel and cadmium is performed with solvent extraction. First, in the cadmium circuit the leaching solution is adjusted to pH 3 prior to... 

Atomic absorption spectrometry with or without preliminary solvent extraction of metal has been applied extensively to the determination of cadmium in soils. 

Alonso,A.I., Urtiaga,A.M., Zamacona, S., Irabien, A. and Ortiz, I. (1997) Kinetic modelling of cadmium removal from phosphoric acid by non-dispersive solvent extraction. Journal of Membrane Science, 130, 193. 

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... 

APDC/DDDC into chloroform and back-extraction into 7.5 N HN03). Vertical profiles obtained by both techniques are shown in Figure 4. The profiles for cadmium and zinc show good agreement between the solvent extract and Chelex results, although the Chelex results are somewhat lower than those by solvent extraction concentration. The values for nickel were also lower when the Chelex technique was employed. The mean difference between the two techniques was 65 35 ng l-1. 

As a representative example, the model will be applied to the separation of Ni and Cd by nondispersive solvent extraction with the mentioned assumptions to avoid duplicate equations, the subscript i has been used, where i = 1 represents cadmium and i = 2 represents nickel. 

Dave, G., K. Andersson, R. Berglind and B. Hasselrot. Toxicity of eight solvent extraction chemicals and of cadmium to water fleas, Daphnia magna, rainbow trout, Salmo gairdneri, and zebrafish, Brachydanio rerio. Comp. Biochem. Physiol. 69C 83-98, 1981. 

Table 6.2 Distribution coefficients of copper, cadmium, and zinc ions in membrane-based solvent extraction...

O. Klinghoffer, J. Ruzicka, E.H. Hansen, Flow-injection analysis of traces of lead and cadmium by solvent extraction with dithizone, Talanta 27 (1980) 169. 

Simplicity, rapidity, and specificity have caused adoption of atomic absorption as a standard method in water analysis. Often solutions must be concentrated prior to measurement. Freezing, evaporation, ion exchange, and solvent extraction techniques have been reported. This paper describes a method for concentrating ferric iron, copper, zinc, cadmium, and lead using sodium diethyldithiocarbamate and methyl isobutyl ketone. Data shows increase in sensitivity caused by (1) concentrating effect of extraction, and (2) choice of the ketone solvent in preference to water. Recovery data on various industrial waters indicate that the method is reliable, reproducible, and accurate. 

Table IV compares the present reported limit of detectability of iron, copper, zinc, lead, and cadmium in aqueous solutions with that obtainable with the proposed solvent extraction procedure. Detectability is defined as that concentration of metal which gives a signal twice the variability of the background. Since the amount of metal recovered as shown in Table II was not 100% for most metals, the limit of detectability by this method should be increased by about 5-10%.

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