Cadmium deposition

The first work published in this area was that of Bigelow mentioned above [116], In 1957, monolayers of long-chain fatty acids were fonned on thin films of silver, copper, iron and cadmium deposited on glass microscope slides [43],... 

The reproducibility of test results between labs using the neutral salt spray tests has not been consistent, but the repeatability, within one lab, is better, and the test has value in comparing variations in coating systems. Correlation of hours of exposure in the salt spray test to actual performance of the plated part in service, even in marine atmospheres, is not consistent and usually avoided. A classic example is that cadmium deposits outlast zinc deposits on steel in salt spray tests and clean marine atmospheres, yet zinc outlasts cadmium when exposed to real, industrial atmospheres, because of the presence of sulfur-bearing corrodents in industrial environments. An important variable in salt spray testing is the position of the surface to be tested. Whereas the surface of test panels is specified to be 15—30° from the vertical (40), when salt spray testing chromated zinc-plated specimens, this range has appeared excessive (41). 

In 2002 anthropogenic emission of cadmium in Europe amounted to 257 t/yr that is 5% lower than in 2001. Emission caused by natural processes (natural emission and re-emission) add up 55 t/yr. Depositions to Europe in 2002 were 240 t/yr. Spatial distribution of cadmium deposition in Europe is shown in Figure 9. The regions... 

Figure 9. Spatial distribution of cadmium depositions in Europe in 2002 (Ilyin et al., 2004).

The contribution of the external European anthropogenic sources to cadmium depositions in Europe in 2002 varies from 4 to 75%. In 17 countries it exceeded 50%. The countries most affected by the trans-boundary transport of cadmium are Belarus, Ukraine, Lithuania, and Czech Republic. These countries are located close to Poland, which is a significant emitter of cadmium. Similar to lead, the lowest contributions are observed in Spain and Iceland. The contribution of the trans-boundary transport to pollution of the European Union with cadmium is about 15%. 

The highest depositions of heavy metals over the Baltic Sea can be noted in the south-western part of the Baltic Sea within the Baltic Sea and the Baltic Proper subbasins (Figure 21). Significant levels of lead and cadmium depositions can also be noted in the Gulf of Riga. The total contribution of HELCOM countries to the heavy metals deposition over the Baltic Sea in 2001 amounts to 40%. 

It was found that the competitive adsorption of 1 and AN molecules on the Cd electrode affected the kinetics of the Cd(II) electroreduction [226]. The physicochemical properties of coatings and effects of organic additives on cadmium deposition from iodide-water-AN mixtures were also studied by Kuznetsov et al. [225]. 

KC1, which bathed the CdS film. This system was also investigated by cyclic voltammetry both in the dark and under illumination. Starting at about — 0.9 V, the dark cathodic current exhibited a peak at — 1.15 V due to Cd2+ reduction and then rose to — 1.4 V as a result of hydrogen production. The observed anodic peak at — 0.85 V was attributed to the stripping of cadmium deposits in the lattice (Cd ). Cyclic voltammetry subsequent to illumination resulted in the appearance of cathodic waves at — 1.0 V and — 1.3 V, at the expense of that at — 1.15 V. The anodic peak broadened, as is indicative of photocorrosion. 

The platinum wire of the other electrode is plated with a cadmium deposit by immersing the electrode in a beaker containing a 0.1 M solution of CdS04 and a pure cadmium rod. The electrode is connected to the negative terminal of a 1.5-V dry cell, and the cadmium rod is connected to the positive terminal. Current is passed through this plating bath until a heavy deposit of cadmium is visible on the electrode. This cadmium electrode is then transferred to the cell. Handle the electrode with care to avoid flaking off any of the cadmium deposit. It is advisable to keep the electrode wet at aU times. 

The anodic process is oxygen evolution, whereas the cathodic process changes from thallium deposition to include cadmium deposition and eventually also hydrogen evolution, as the potential is gradually increased. 

AUaro-De la Torre M. C. and Tessier A. (2002) Cadmium deposition and mobility in the sediments of an acidic oligotrophic lake. Geochim. Cosmochim. Acta 66, 3549-3562. 

Figure 7 - (a) Plot of the peak potential Ep,a, for the stripping of cadmium deposited as CdS, against the charge involved in the stripping, (b) The corresponding plot for cadmium deposited as metallic Cd here, the different amounts of cadmium were obtained by depositing bulk cadmium at different times of accumulation. 

In the upcoming, fourth daughter directive to the framework directive 96/62/EG, limit values for cadmium, nickel and arsenic (especially cadmium-deposition) will have to be discussed again. 

Cadmium deposited from the atmosphere onto soil can come from a variety of natural and anthropogenic sources (Alloway and Steinnes, 1999 McArthur, 2001). It is estimated that volcanoes, the dominant natural source of atmospheric Cd, emit 520 mg of Cd into the atmosphere aimually. The dominant anthropogenic source of emission of Cd into the atmosphere is primary non-ferrous metal production, which accounts for an estimated 4721 mg of Cd emitted into the atmosphere annually. The amount of Cd emitted into the atmosphere from all anthropogenic sources is estimated to be about one order of magnitude greater than that emitted from all natural sources. 

It is worth noticing that, according to the Nernst equation, that is related to the equilibrium between cadmium oxide (Cd ) and reduced cadmium, the amount of cadmium oxide (Cd ) remaining in solution at the potential of our system set by the couple (H2/H ), should be theoretically higher than lOOOOppm (Fig. 18.36). From our results, it is obvious that the cadmium concentration in solution is decreased to ppm or even ppb level. Cadmium can then be deposited at a potential more positive than that proposed by the Nernst equation. This phenomenon has already been reported in the past with other metals and has been called underpotential deposition [236]. In fact, when cadmium is reduced, it does not build cadmium-cadmium bonds, but cadmium-nickel bonds. Therefore, the Nernst equation with standard redox potentials (Cd/Cd ) and (H2/H ) does not well represent underpotential cadmium deposition. According to Kolb [237], the potential shift observed in the underpotential deposition of a metallic ion (M +) onto a metal... 

However, if the cadmium-nickel interaction is beneficial for cadmium deposition, the cadmium-cadmium interaction has a harmful influence. It was proposed that when a metal ion M is deposited as a submonolayer, the activity of the reductant should be less than 1 and would vary with the surface coverage [238]. 

Scheme 18.20 Mechanism of cadmium deposition on a nickel nanoparticle.

Chaney RL, Stoewsand GS, Bache CA, et al. 1978. Cadmium deposition and hepatic microsomal induction in mice fed lettuce grown on municipal sludge-amended soil. J Agric Food Chem 26 992-994. 

The chemical basis of this time period may not be uniform for all of the type b metals. For mercury(II) it appears to be related to the occurrence of a minimum amount of what is literally the destruction of tissue and proteins. In the case of cadmium it appears to have a different basis at least in part. Subsequent to the injection of an otherwise lethal dose of a cadmium compound there is a relatively short period when it can be complexed and removed and the animal saved. As the interval between the cadmium injection and that of the antidote (e.g. CaEDTA or CaDTPA) increases, the cadmium becomes more and more difficult to mobilize and a point is soon reached where the antidote is without effect ( 5). In the same fashion, aged cadmium deposits are apparently resistant to mobilization by EDTA ). 

Fig. 2.8 (a) Schematic representation of the formation of an indestructible reentrant groove and the cadmium deposits obtained by deposition from 0.10 M CdS04 in 0.50 M H2SO4 onto a cadmium electrode. Deposition overpotential 50 mV. Depositirai times (b) 2 min, (c) 2 min, and (d) 10 min (Reprinted from Refs. [7, 11, 13] with kind permission from Springer and Ref. [33] with permission from Elsevier)... 

Fig. 2.14 log / as a function of time for (a) copper and (b) cadmium deposition (Reprinted from Refs. [13, 38, 43] with kind permission from Springer)... 

The r/i and //c of 260 and 660 mV for copper deposition (lower /q value) and 27 and 110 mV for cadmium deposition (larger /q value) are successfully determined using the above given procedure, being in perfect agreement with experimental findings as can be seen from Fig. 2.15 [13, 38, 43]. 

The cross sections of the copper and cadmium deposits obtained at //i < // < tjc, and // > //c are shown in Fig. 2.15a, b, respectively. It can be seen that there is no dendrite formation when t] < t, both compact and dendritic deposits are formed when rjidendritic metal is deposited when rj > This is in perfect agreement with findings of Calusaru [44] for the morphology of deposits of the same metals deposited at overpotentials corresponding to full diffusion control. 

Fig. 2.19 Cadmium deposits obtained from 1.0 M CdS04 in 0.50 M H2SO4 solution onto a copper plane electrode (a) deposition overpotential 10 mV deposition time 24 min, (b) deposition overpotential 40 mV deposition time 4 min, (c) deposition overpotential 60 mV deposition time 2 min, and (d) deposition overpotential 110 mV deposition time 80 s (Reprinted from Refs. [13, 54] with kind permission from Springer)...

Fig. 2.24 Overpotential V5. log (current density) for cadmium deposition in the presence of additive (Reprinted from Ref. [68] with permission from Elsevier and Ref. [13] with kind permission from Springer)...

Popov KI, Krstajic NV, Popov SR (1985) The morphology of cadmium deposits obtained on foreign substrates at high overpotentials. J Appl Electrochem 15 151-154... 

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