Cadmium family

Again, on the inorganic HPP side, perhaps the pigment class with the greatest likelihood of being fully replaced as a threat to human health and the environment, in favor of organic substitutes, is that of the cadmium family, which has suffered from restrictions in a number of countries But as Chap. 3 now explains, a recent scientific review for the UK authorities concludes unequivocally that this pigment family should not be considered a threat to health and the environment ... 

Pigment Systems. Most of the crystals used for ceramic pigments are complex oxides, owing to the great stability of oxides in molten silicate glasses. Table 3 fists these materials. The one significant exception to the use of oxides is the family of cadmium sulfoselenide red pigments. This family is used because the colors obtained caimot be obtained in oxide systems thus it is necessary to sustain the difficulties of a nonoxide system. 

For this purpose, the WEEE Directive has been complemented with an additional directive that limits the use of certain pollutants in these products. The EC Directive 2002/95/EC on the Restriction of the use of certain Hazardous Substances in electrical and electronic equipment (RoHS Directive) ([7], recast 2011 [9]) restricts the use of the six harmful substances/substance families lead, mercury, hexavalent chromium, polybrominated biphenyls (PBB), and polybrominated diphenyl ethers (PBDE) to 0.1% and cadmium to 0.01% w/w per homogenous material in equipment and components, but with several exemptions for a wide range of applications (Annex III and IV). 

Thomine, S., Wang, R., Ward, J. M., Crarvford, N. M., and Schroeder, J. I., 2000, Cadmium and iron transport by members of a plant metal transporter family in Arabidopsis with homology to Nramp genes, Proc. Natl. Acad. Sci. U.S.A. 97 4991-4996. 

Anion-stuffed, twinned c.c.p. 1 (CrB) cation arrays were considered in Sect. 2.4 those of twinned c.c.p. 2 (Nijin) in Sect. 2.6. But an additional example of the latter is depicted in Fig. 25 cadmium chondrodite, 2Cd2Si04 Cd(OH)2, in which the anion array is extremely distorted (from h.c.p.) although the cation array remains regular, emphasising even more strongly the point made earlier that the h.c.p. anion array description is not entirely satisfactory for this family of structures. 

Metallothionein Small molecular weight protein family, rich in cysteine, that binds strongly to divalent heavy metals. The synthesis is under the control of essential metals like zinc and copper. Other metals such as cadmium, mercury and silver can induce its concentration in cells. Volume 1(14). 

Another illustration of the potential in harnessing plant life for soil remediation is the finding20 that the fern, Pier is vittata, when grown in soil containing 6 ppm arsenic, hyper-accumulated 755 ppm of this metalloid in its fronds in only two weeks. When Pier is vittata was grown in artificially contaminated soil (1500 ppm As), the fronds took in 15,861 ppm As in the same two-week time frame. Similarly, research in both the United States and the United Kingdom has demonstrated the potential of using plants from the family Brassicacae in the remediation of soils heavily contaminated with zinc, cadmium, nickel, lead, and selenium.21... 

Copper, silver, and gold in Group I show a similarity to sodium and potassium principally in the fact that they form certain compounds of the same type, for example, M20 and MCI. Zinc, cadmium, and mercury in Group II resemble calcium, barium, and strontium in that they form compounds of the types MO, MSO4, MC12, etc. In other respects, the divergence in the properties of the elements of the A and B Families is at a maximum in these two groups. 

All further measurements in run I led to a lower cadmium activity at any composition than would be predicted by the initial curve. As the cadmium pressure increased, new curves of activity vs. composition developed. Curves of similar slopes and spacings tended to define families. After point 39 the cadmium pressure was again generally decreased. Finally at activity the CeCd 4 5 went into equilibrium with the next classical phase, presumably CeCd3 as reported by Iandelli and Ferro (8). [The technique of measurement, which is based on finding the pressure at which the two phases can be in equilibrium at this temperature, is described by Elliott and Lemons (4).]... 

The alloy was converted completely to CeCd 4 5 and measurements were continued for 2 weeks. The data define two distinct families of curves or microphases. Most of the data fell on a family of 11 equally spaced parallel lines. The separation corresponds to a difference in cadmium mole fraction of 0.000021. 

Data points were observed for each of the 11 lines of the primary family, and in six cases points obtained nonconsecutively occur on a given line. Line V was observed five separate times and seven equilibrium points were obtained however, between points 254 and 255 no equilibrium data point was recorded. The primary family disappeared and the secondary family appeared in its place three times—before points 255, 279, and 287. In each case a reconversion to the primary family occurred at a higher cadmium pressure. An effort was made to confine the system to the primary family where possible, since the object of this particular run was to demonstrate unequivocally the reversible nature of a particular family. 

In terms of the limited region covered by the experiments (approximate cadmium mole fraction range 0.813 to 0.823) some of the microphases exhibit broad solid solubility ranges. In contrast, for the family shown in Figure 3, the microphase solubility ranges were so narrow that they were not detectable within the precision of the experiments. 

The primary family of curves in Figure 2 shows a series of structures having the same cadmium activity-mole fraction relationships and separated by two-phase regions of equal width. Similar relationships are suggested for the secondary family also. 

The two-phase regions may have very similar widths in different families. The minimum two-phase gap for the Figure 3 family is very close to that observed for the Figure 2 primary family. A similarity is also apparent for the Figure 3 family and that in Figure 4. The most closely spaced microphases differ in composition by the addition of only one cadmium atom in 8000. 

Zinc efflux is mediated by a zinc exporter known as ZntA (Zn + transport or tolerance), a membrane protein which was identified through studies of bacterial strains that were hypersensitive to zinc and cadmium. Sequence inspection revealed that ZntA was a member of the family of cation transport P-type ATPases, a major family of ion-translocating membrane proteins in which ATPase activity in one portion of the protein is used to phophorylate an aspartate within a highly conserved amino acid sequence, DKTG, in another portion of the protein. The cysteine rich N-terminus of these soft metal transport proteins contains several metal-binding sites. How the chemical energy released by ATP hydrolysis results in metal ion transport is not yet known, in part because there is only partial information about the structures of these proteins. The bacterial zinc exporter also pumps cadmium and lead and is therefore also involved in protection from heavy metal toxicity (see Metal Ion Toxicity). 

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