Cadmium
Cadmium (Cd) is a metallic element that is closely related to Zinc, with which it is frequently associated. It was discovered in 1817, by Friedrich Strohmeyer in a sample of zinc carbonate, making yellow zinc oxide thought to contain arsenic. Cadmium got its name from the Latin cadmia, meaning calamine, from its being found with calamine in zinc ore.
Cadmium does not occur naturally in the uncombined state, and only one mineral is known that contains in any usable quantity, greenockite, or cadmium sulfide. Cadmium sulfide is found at Greenock, and Bishopton, Scotland, along with in Bohemia, and Pennsylvania. It is found usually in with zinc blende, and with calamine, although only in very small amounts (about 3%).
The metal was first gotten from impure zinc dusts collected in condensers, or prolongs, of a zinc retort furnace during the first three or four hours in the distillation cycle. Repeated distillations of this bluish powder (impure zinc dusts) enriched the cadmium dust in the final blue powder, which was dissolved in sulfuric or hydrochloric acid, and a high grade cadmium sponge was precipitated with the addition of metallic zinc dust. Metallic cadmium was then produced by retort distillation at about 800?C.
Most cadmium is collected during the sintering of zinc concentrates, from the dust collected from the gases leaving lead blast furnaces, and from varied purification cakes produced during the electrolytic recovery of zinc. Smaller amounts are gotten during the refining of zinc and the production and refining of lithopone, and zinc oxide.
The United States is the world’s largest producer of cadmium, with an annual output of 5,000 short tons. On an average, in the US this Cadmium sells for $4.95/lb.
The uses of cadmium are many. Including low-friction, fatigue resistant alloys, solders, dental amalgams, nickel-cadmium storage batteries, photography and photoengraving, nuclear reactor shields, in bearings, and in rustproof electroplating.
First and foremost though it is used for electroplating. About 2/3 of all cadmium produced is used in the plating of steel, iron, copper, brass, and other alloys to prevent them from corrosion. This plating works much better than a zinc plating (galvanizing) because it is deposited more quickly than zinc, and forms an even coating, even on intricate pieces. And a thinner coating of cadmium protects metal better than a thicker coating of zinc. The metal is deposited electrolytically from an alkaline cyanide bath. The cadmium oxide is dissolved in the cyanide solution; two hydroxides are freed, leaving the solution alkaline. Cadmium anodes are used to replenish the cadmium as it is deposited on the cathode, which puts out between 1 and 14 volts. Cadmium plating provides resistance to outdoor corrosion, and is comparable to zinc and superior to tin.
Bearings that contain more than 98% Cadmium are used in internal combustion engines because they withstand high speeds and high temperatures.
When Cadmium is used in copper wire or in other alloys it adds strength, especially in electrical wires.
About 1/5 of cadmium is re-dissolved and converted to pigments, the sulfides and sulfoselenides provide great yellow and red colors in many finishes, along with being used as the coloring in some stained glass.
Storage batteries using cadmium oxide in the negative plates have a much longer shelf life than those using lead elements do, and they have other advantages in respect to weight and ability to be stored in a discharged condition.
One of the most interesting uses of Cadmium is because of its high neuron absorption qualities. It is therefore used in the control rods of some nuclear reactors.
Cadmium can be described as a silver- white metal, which is capable of taking a high polish. When broken it looks like a fibrous fracture. It can be cut with a knife and is slightly harder than tin, but softer than zinc and like tin crackles when bent. It is rather malleable, and can be rolled out in sheets. The important atomic and physical properties of cadmium are shown in this table:
Atomic weight112.40
Atomic Number48
Valence Electrons2
Isotopes:
Mass:106, 108, 110, 111,112,113,114,116
Percent abundance:1.4, 1.0, 12.8, 13., 24.2, 12.3, 28., 7.3
Density, 20?C8.65g./ml.
Melting Pt. 320.9?C
Boiling Pt. 767?C
Specific Heat, 25?C0.0551cal./g./?C
Electrical Resistance, 20?C7.14 X10 -6 ohm cm.
Coefficient of linear expansion 20?C29.8 X 10 -6
Electron Structure1s,2s,2p,3s,3p,3d,4s,4p,4d,5s
2, 2, 6, 2, 6, 10, 2, 6, 10, 2
Certain Cadmium compounds are very poisonous, others seem to have little effect when present in larger quantities. The metal itself and the very fine oxide, which results from its combustion in air, appear to cause the most violent reactions when taken into the lungs. Severe lung damage is noted in fatal cases, but exposed workers are warned by such symptoms as nausea, and diarrhea before permanent damage is sustained. Soluble cadmium compounds are about as poisonous as those made of lead and arsenic and a few deaths have been ascribed to them in cases unrelated to cadmium recovery and production. Cadmium sulfide is so insoluble that it can be tolerated in relatively large amounts though.
Cadmium is a rather useful element, which can be made into many things but can also be toxic. It is a rather interesting element in this respect.