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Cadmium

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Cadmium
Cadmium
General Info
Atomic Symbol Atomic symbol::Cd
Atomic Number Atomic number::48
Atomic Weight Atomic weight::112.4 g/mol
Chemical series Transition metal
Appearance Soft, bluish white
Cadmium-4.jpg
Group, Period, Block 12, 5, d
Electron configuration [Kr] 5s2, 4d10
Electrons per shell 2,8,18,18,2
Electron shell cadmium.png
CAS number CAS number::7440-43-9
Physical properties
Phase Solid
Density Density::8.65 g/ml
Melting point Melting point::321.07 °C
Boiling point Boiling point::767 °C
Isotopes of Cadmium
iso NA half-life DT DE (MeV) DP
106Cd 1.25% >9.5×1017 y εε2ν - 106Pd
107Cd syn 6.5 h ε 1.417 107Ag
108Cd 0.89% >6.7×1017 y εε2ν - 108Pd
109Cd syn 462.6 d ε 0.214 109Ag
110Cd 12.49% 110Cd is stable with 62 neutrons.
111Cd 12.8% 111Cd is stable with 63 neutrons.
112Cd 24.13% 112Cd is stable with 64 neutrons.
113Cd 12.22% 7.7x1015 y β- 0.316 113In
113mCd syn 14.1 y β- 0.580 113In
113mCd syn 14.1 y IT 0.264 113Cd
114Cd 28.73% >9.3×1017 y ββ2ν - 114Sn
115Cd syn 53.46 h β- 1.446 115In
116Cd 7.49% 2.9x1019 y ββ2ν - 116Sn
All properties are for STP unless otherwise stated.

Cadmium is chemical element classified as a transition metal in the periodic table of elements. Extremely toxic, it is also fairly rare in nature. It occurs most often in compounds or minerals, and is rarely found in pure form. As it is so deadly, it has almost no use in the bodily functions of either humans or animals. Even so, humans have found ways of using cadmium to our advantage, despite its lethality.

Properties

In its pure form, cadmium is very soft and has a silvery-white color. It is so incredibly soft that it can easily be cut with a knife, like an alkali metal. It is very similar to zinc in chemical properties, but it is less reactive with acids than zinc.[1]

Cadmium is very resistant to corrosion, particularly in acidic and seawater environments. It has a low melting temperature, good electrical and thermal conductivity. Compounds containing cadmium possess an amazing resistance to high stress and high temperature. They also lower ultraviolet light degradation of certain plastics. Some cadmium electronic compounds exhibit semi-conducting properties, so they are used in solar cells and many electronic appliances. Cadmium pigments produce intense yellow, orange and red colors, and are widely used in plastics, glasses, ceramics, enamels and paints.[2]

Occurrences

Cadmium Smithsonite

Cadmium is a fairly rare element. Its abundance in the lithosphere is approximately 0.5 parts per million in the earth's crust. No samples of cadmium have ever been found in large quantities, and there is no ore that is mined solely for recovering cadmium. Greenockite (cadmium sulfide) is the compound with the most significant traces of cadmium, and occurs chiefly as a yellow stain or coating on zinc sulfide. Nearly all major zinc deposits contain cadmium in varying amounts, with the concentrates containing a maximum of about 1%.[3]

Uses

Batteries that use cadmium

Uses for Cadmium
Cadmium was used as a leather tanning agent and a pigment in dye until the 1990's. It is still used in rechargeable Ni-Cd batteries, solar cells, solder alloys, some paint and plastic production, engraving, cadmium vapor lamps, some parasite treatment for farm animals, old television tubes and to electroplate other metals.[4]

By far, it is most commonly used in nickel-cadmium batteries. It is used in the form of cadmium hydroxide. The batteries themselves are commonly used in the railroad and aircraft industries for starting the vehicles, and also serve as emergency power for these. In addition, they are used in many common appliances such as cordless power tools, cell phones, camcorders, lap tops, portable household appliances and some toys. These batteries are fairly cheap and well suited for high power applications. They generally last for a long time, and when compared to other types of batteries, work very well in extreme high and low temperatures.[2]

History

Cadmium ball with a penny for size comparison

The word cadmium comes from the Latin word cadmia and the Greek word kadmeia, which are words from some of the old languages used to describe calamine (zinc carbonite).[5]

A German chemist named Friedrich Strohmeyer discovered cadmium in 1817 while studying samples of calamine (ZnCO3). When the zinc carbonite was heated, Strohmeyer noticed that some samples of the calamine gave off a yellow color, while other samples did not. After further experimentation, Friedrich determined that the samples of calamine giving off color when heated contained trace amounts of a new element. The only mineral that contains any significant amounts of cadmium is greenockite (CdS), but it is not common enough to mine for any profit. Fortunately, small amounts of cadmium can be found in zinc ores, and most of the cadmium used today is gathered as a byproduct of mining and zinc refinement.[5]

Toxicity

A Chinese man wears a mask to protect himself from cadmium poisoning.

Cadmium is one of the most toxic metals, and should be treated as such. The main method of cadmium absorption in industrial exposure is by inhalation, so industrial processes which generate cadmium dust or fumes should be extremely well ventilated. A single exposure to high concentrations of freshly generated cadmium oxide fumes can cause severe irritation and even lead to death.

Testing
Testing for cadmium can help aid in treatment for it. It can be measured in the hair, nails, blood, and urine, but the most accurate tests are urinary tests.[6]

The amount of cadmium in the blood shows any recent exposure to cadmium. But since the amount of cadmium in urine shows both your recent and your past exposure, making it the most accurate test.[6]

Effects & Symptoms
When the human body absorbs cadmium in quantities greater than ten milligrams, the effects are never good, and if exposed over a long period of time, cadmium exposure can be fatal. When absorbed, cadmium causes damage to the kidneys, cardiac tissue, bones and is thought to possibly be a cause of cancer. Symptoms of cadmium poisoning can include choking, loss of the sense of smell, vomiting, salivation, joint pain, an increased loss of small proteins in the urine, a metallic taste and some other symptoms.[4]

Treatment
Cadmium poisoning is irreversible. The cadmium stays in the body system for an extremely long time, and is eventually slowly excreted along with metallothionein. Hemodialysis has been shown to be a somewhat effective method to get rid of cadmium that has not yet been absorbed from the bloodstream, and sometimes EDTA chelation can help speed up the procedure.[4]

Gallery

References

  1. Properties Unknown author, International Cadmium Association, Accessed December 1st, 2010.
  2. 2.0 2.1 Cadmium Unknown author, International Cadmium Association, Accessed December 1st, 2010.
  3. Occurrences Unknown author, fis.uc.pt, Accessed November 19th, 2010.
  4. 4.0 4.1 4.2 Toxicity Unknown author, Toxipedia, Accessed December 1st, 2010.
  5. 5.0 5.1 Elements Thomas Jefferson National Accelerator Facility - Office of Science Education, It's Elemental, Accessed November 30th, 2010.
  6. 6.0 6.1 Cadmium and health Unknown Author, Agency for Toxic Substances and Disease Registry, Page last updated: September 1, 2010.