Description. Located in period 5 and Group 12 of the periodic table (an array of the relatedness of chemical elements), cadmium is a chemical element with the symbol Cd and atomic number 48. It is a soft, lustrous, malleable, silver-white metal with a bluish overcast.
Having a valence of 2 electrons and an incomplete inner electron shell which serves as a transitional link between the most and the least electropositive elements in a chemical series, it belongs to the d-block group of elements. Cadmium is also referred to as a transition metal, and has 8 naturally occurring isotopes as well as 34 radioactive isotopes and isomers.
Origin
While studying heated samples of calamine in 1817, Friedrich Strohmeyer, a German chemist, discovered that some of these samples glowed with a yellow color, and others did not. Puzzled with this occurrence, he did a repeat experiment, and with the obtained results, concluded that the calamine that changed color when heated, indeed, contained trace amounts of a new element. Further scientific verifications would later show that this new element was, in fact, the 48th most abundant in the world. He called it cadmium—from the word “cadmia” which, in Latin, means calamine.
Source(s)
Cadmium is contained in the mineral Greenockite (a natural mineral which occurs as massive encrustations and as six-sided pyramidal crystals with varying colors of yellow through shades of red to brown). It is usually found combined with other elements such as oxygen (cadmium oxide), chlorine (cadmium chloride) and sulfur (cadmium sulfide).
As a byproduct, it is also obtained by smelting and refining zinc, lead and copper ores.
Properties
Readily soluble in mineral acids, cadmium melts and boils at relatively low temperatures; it burns on heating to redness and releases a deep yellow, monatomic vapor. It does not react with water; but it reacts slowly with oxygen in moist air, at room temperatures, to form cadmium oxide. Its melting and boiling points are 321 and 765 degrees Celsius, respectively.
In combination with certain metals, cadmium significantly lowers the boiling point; this makes it an excellent conductor of heat and electricity.
Uses
Cadmium has various uses. In order to achieve durability and thickness, it is electroplated with steel—this helps prevent corrosion. Also, due to its ability to absorb thermal neutrons, it is used efficiently in the production of control rods for some nuclear reactors, and in the production of rechargeable batteries.
As a photosensitive material, cadmium sulfide (CdS) is used in black and white television phosphors as well as in the green and blue phosphors of color television tubes. It is also used as a yellow pigment in paints, and in photovoltaic cells to convert light energy to electrical energy.
Limitations
In spite of its attractive and unique qualities, cadmium, as well as its compounds, is carcinogenic. Although it is not readily absorbed by the skin, inordinate inhalation and ingestion can scar the lungs, irritate the digestive tract and damage the kidneys. Repeated exposures, in severe cases, can lead to death.
Unfortunately, waste streams of cadmium from factories and industries usually end up in the soil, and besides tobacco smokers, people who live close to these hazardous waste sites have the potential for cadmium poisoning.
Some of the effects and symptoms of cadmium poisoning are: diarrhea, stomach ache, severe nausea discharge, bone fracture, reproductive failure, damage to the immune system, damage to the central nervous system and psychological disorders.
In summary, cadmium indeed is a valuable metal, but safe and healthy environments are invaluable. In the last 30 years, its use as an alloy has declined by about 70 percent due to environmental concerns. More so, the European Union, in 2011, prohibited its use in the production of batteries, paints and other household electronics. It is expected that they will eventually be banned worldwide.
Albeit, with this move by the EU, and the ongoing actions to restrain its use by other nations, one question, indeed, has been left unanswered: where does cadmium go to die?
