Chelation copper dissolution

EDTA can be a useful additive to an acid copper bath since it can offer some control over dissolution of the anode. In high-efficiency cyanide copper plating, the addition of EDTA can counter the harmful effects of chromate(VI). It is speculated that the chelating agent facilitates the reduction of CrVI to Crm by Cu1. 

A number of attempts have been made to understand the mechanism of the adsorption of chelates on oxide minerals. For instance, IR spectroscopic studies10 have indicated the presence of a basic monosalicylaldoximate copper complex as well as the bis-salicylaldoximate complex on the surface of malachite (basic copper carbonate) treated with salicylaldoxime. However, other workers4 have shown that the copper chelate is partitioned between the surface and dispersed within the solution, and that a dissolution-precipitation process is responsible for the formation of the chelate. Research into the chemistry of the interaction of chelating collectors with mineral surfaces is still in its infancy, and it can be expected that future developments will depend on a better understanding of the surface coordination chemistry involved. 

This method is for the determination of cadmium, cobalt, copper, iron, manganese, nickel, lead and zinc, which are solvent extracted and concentrated as their diethyldithiocarbamate chelates. After destruction of the organic complexes dissolution of the residue in dilute acid gives a solution suitable for atomic absorption analysis [13]. 

Some extremely low detection limits in chemical samples have been reported by APDC/MIBK and other dithiocarbamate extractions. Further increased concentration factors can be obtained by back-extraction into a minimum of acid. Copper in ammonium fluoride solution used in semiconductor processing has been determined down to 4.5 X 10 7% [20]. To a 40% ammonium fluoride solution (50 ml) was added ammonia solution (1ml), 50—60 /Ltg of a palladium(II) carrier solution (dissolved in 1ml) and sodium diethyldithiocarbamate (5 ml). After extraction of the copper chelate into chloroform the solvent was evaporated, the residue dissolved in concentrated nitric acid (10 drops) and water (2 ml) and this was then evaporated. The final dissolution was in concentrated hydrochloric acid (2 drops) and concentrated nitric acid (ldrop). The solution was made up to 1 ml and the determination made by standard additions using an air/ acetylene flame and the 324.7 nm copper resonance line. 

Briefly, then, these experiments suggest the use of two shghtly different precipitation procedures. One is useful for copper, nickel, and cadmium and is similar to that outhned in the methods section with the exclusion of buffer addition in order to maintain the sample near pH 1.8. The other method is useful for copper, nickel, lead, and iron and is similar to that outlined in the methods section except that a filter rinse with 3N nitric acid follows dissolution with the organic solvent. The combined organic and nitric acid washes are then evaporated to dryness over low heat, thus decomposing the chelate, and the residue is redissolved in O.IJV nitric acid prior to analysis. 

Figure 10. Dissolution of copper from plated steel in Fe(ll) chelate, 7000 ppm of Fe, at 150°F...

During copper-removal procedures that are conducted with the iron solutions of EDTA or citric acid as the reaction medium, many operators have noted that it is much easier to remove copper from plated steel in EDTAthan in ammonium citrate. The observation has been difficuit to explain since the procedures are about the same the iron solutions that remain in the boiler being cleaned are oxidized with air or air -F NaN02. These chemicals are passed through the ammoniacal chelate solution in both cases. In an attempt to understand the mechanisms of copper removal in chelate solutions, the dissolution mechanisms in chelating agents was studied in the presence and absence of iron. Two types of tests (described in detail in Reference 41) were conducted. 

For example, in the case of monosaccharide ligands, [MLnl complexes were synthesized with yields of 80-90% by electrolysis of methanol solutions of the ligands with a copper or nickel anode (M) and a platinum cathode, followed by predpitation of products with benzene. In contrast to the electrosynthesis, the chemical synthesis of the same copper chelates from cupric acetate in methanol proceeds with only a 30% yield and yields both [MLal and [M(MeC02)L], In electrosyntheses of this type the proposed reaction mechanisms involve the anodic dissolution of the metal followed by complex formation. 

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