Cyanide Systems

Cyanide is one of those rarer ligands, which stood a century-long test in functional plating. Despite their toxicity, due to their advantages, cyanide solutions have been used up to date [2]. Coatings obtained in cyanide baths are noted for their high 

As electrochemical processes are sufficiently stable, control of the composition of solutions, as well as their correction, is not compUcated. 

On the other hand, the interaction of complexes, which have a saturated coordination sphere, with the metal phase of the electrode is weak, and the activation energy is high. Therefore, the probability of reduction of such complex as CuCN is low and it should also be eliminated from the list of possible EAC. An analogous conclusion was drawn in Ref. [6]. 

Surface concentrations were used in the analysis of experimental voltammo-grams obtained for Cu electrode whose surface was mechanically renewed in the course of measurements [4]. To determine the number of ligand particles in the electrically active complex CuCNp , the following equation was suggested  

Rather controversial hterature data concerning the composition of possible EAC most likely encouraged Dudek and Fedkiw [10] to analyze the model according to which any complex may be electrically active. Reduction of each of them is described by a separate kinetic equation with individual kinetic parameters, and partial currents are summed. Regularities of mass transport are considered taking into account the fact that the components of the system participate in chemical interactions, and using the principles, which are presented in Chapter 3. 

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A striking feature of the halide systems of Cd2+ emd Zn2+ is the sudden increase of both AS and AH that takes place at a particular step in complex formation, for = 3 in the case of Cd f- and for = 2 in the case of Zn2+. As already mentioned, a similar though less marked reversal is also observed in the Zn2+ acetate system (Table 1). Among the pseudohalides hsted in Table 2, the same phenomenon occurs in the seleno-cyanate systems of both Zn2+ and Cd2+, but remarkably enough not for the closely analogous thiocyanate systems. The cyanide systems show no sign of such behavior. 

System IV is a pretreatment technology for water containing cyanide and heavy metals including chromium, nickel, zinc, lead, cadmium, and copper. The technology precipitates a range of heavy metals there is no need to install separate pieces of equipment for individual metals. A cyanide treatment system expansion option is available for waste streams that also contain cyanide. System IV is not offered commercially. 

The ring diamagnetism apparently observed for K2Ni(CN)4-H20 may be considered as experimental evidence of electron delocalization through the cyanide system. The electrons in the Osu(irb) orbital, in particular, would be expected to generate considerable ring current. ... 

Fig. 5.19. Schematic representation of the heme moiety. The x axis is taken along the metal-pyrrole II direction. The 0, angles for the four methyl groups are defined as the angles between the metal-methyl t th vector and the x axis. The

The piperidine reaction is not completely characterized. The conditions for the generation of the radical in Figure 1 have not been clearly defined, and intermediates observed during the reduction have not been identified. These difficulties have been overcome in the cyanide system, which proved to be more amenable to spectroscopic investigation. 

Since these rules were formulated from the data at hand in 1966, they have been further substantiated by recent measurements of the copper(I) and silver(I) cyanide systems (13). 

A couple of examples illustrate the issue. Consider first the catalase-cyanide system characterized by the affinity, K 2X 10 There is no doubt tha,t HCN is the reacting entity (37, 52) and that net proton release or uptake does not occur (118b). Nevertheless, FeCN appears... 

Cyanide Systems See Cyanide Complexes of the Transition Metals)... 

With terminal 1,3-dienes and either RhH(PPh3)4 or (Rh(CO)2(PPh3))2 in the presence of excess phosphine at 50-100 °C and 15 atm, selective hydrogenation of the terminal double bond is achieved (Scheme 91). Hydrogen uptake must be monitored in these reactions in order to prevent further hydrogenation of the partially reduced product. As is the case for the cobalt cyanide system, here also, substitution at the double bond inhibits the rate of hydrogenation and limits its general applicability. 

Fig. 3-67. Separation of anions derived from weak inorganic acids using a strongly basic eluent. — Separator column Wescan 269-029 eluent 0.004 mol/L NaOH + 0.0005 mol/ L sodium benzoate flow rate 1.5 mL/min detection indirect conductivity injection volume 100 pL solute concentrations 5 ppm borate (as B), 10 ppm silicate (as Si02), 10 ppm formate and sulfide, 20 ppm chloride and cyanide (system peak appears after 28 min.) (taken from [70]).

Another determination (15) of G values in the formate-ferri-ferro-cyanide system yielded results which suffer the same criticism. The... 

Transient absorption bands centered around 300-400 n.m. have been reported to be produced by the action of the hydrated electron on different metal ions. As mentioned earlier, they are ascribed to the lower oxidation states (1, 4,6). In view of the general similarity of the spectra of these ions, it has been suggested that they may be some electron adduct of the type Mn+. . . e aq (15). Evidence seems to be accumulating that these electron aducts may not occur commonly (3, 10, 18, 20, 21). Our results, on the other hand, suggest that with the gold cyanide system, at least in neutral and alkaline matrices, such a possibility does exist. 

Table V-30 Experimental equilibrium data for the Ni(ll) cyanide system.

Potentiometric measurements of the nickel(II) - cyanide system are described. The addition of Ni(CN)2, NiS04 or Ni(N03)2 to sodium cyanide solution resulted in the formation of a single nickel(II) containing species, Ni(CN)J . Its formation constant at 25°C and in 0.78 M NaCN solution was found to be log, fi = (11.83 + 0.17). The author used nickel metal as the working electrode. Since the electrode reactions involving nickel(II) are not reversible [50HUM/KOL], the reported formation constant is not reliable. 

Complex formation in the nickel(II) - cyanide system has been investigated by spectrophotometry (267.5 nm) at 24.92°C and at several ionic strengths (/ = 0.0028 to 0.1 M) using potassium perchlorate as the ionic medium, in the pH range from 5.3 to 7.7. The nickel(II) concentration was 4 x 10 M. The [Ni ]/[CN ] ratio was varied from 0.05 to 0.8 to obtain data so that the Job s method could be applied, and othenvise kept at around A. The time required for the equilibration ranged from a few days for solutions of higher pH to several weeks for those of lower pH. Acetate and phosphate buffers were used to maintain the pH, but correction was made only to account for the formation of the acetato complex. Only formation of the complex Ni(CN)4 was detected. 

Spectrophotometric measurements have been performed in the binary nickel(II)-cyanide and copper(l)-cyanide, and ternary nickel(lI)-copper(I)-cyanide systems. It was concluded that Ni(CN)4 and Ni(CN)g" form in the binary nickel system. The equilibrium constant for the reaction ... 

PER] Persson, H., The complex formation in the nickel(II)-cyanide system, Acta Chem. Scand., A25, (1971), 543-545. Cited on page 378. 

Table V-30 Experimcmal equilibrium data for the Nitll) cyanide system.228...

When silica is added to the nickel-cyanide system, the results are quite predictable as shown in Figure 16. At the lower cyanide concentration (lO M) there is enough cyanide to complex about 10% of the nickel present, so adsorption of NiOH onto silica and precipitation of Ni(OH)2(s) are affected only slightly. As would be expected, at higher cyanide concentrations the nickel is made completely soluble at all pH values studied. 

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