Cadmium is a periodic table Group V element of Periodic â…¡B as heavy non-ferrous metals. Element symbol Cd, atomic number 48, relative atomic mass 112.41, silver metallic luster blue vaginal discharge. In 1817, the German Stoumye discovered a new element from zinc carbonate, while Hellman and Rolf also discovered this new element from zinc oxide. Named Cadmium according to the Latin word "Cadima".
The first country to report the production of cadmium was Germany. In 1852, it produced about 100kg of cadmium. In 1918, the output exceeded 100t. In the future, the United States became a major producer of cadmium. In 1930, its output was more than 1,000 tons, and in 1940 it was close to 3,000 tons, accounting for 70% of the world's cadmium production. In 1977, the world's cadmium output reached a maximum of 19,793,000 tons. In 1989, the market economy country's refined cadmium production was 16.17 million tons, and the consumption exceeded the production volume by about 2,300 tons.
Cadmium is a ductile metal. The crystal structure is a hexagonal crystal system, and the hardness is softer than zinc. The main physical properties are listed in Table 1. Cadmium has eight natural stabilizing factors and 11 unstable artificial radioisotopes.
Table 1 Important physical properties of cadmium
nature | Numerical value | nature | Numerical value |
Melting point T/K | 593.9 | Thermal conductivity λ/(W·m -1 ·K -1 ) | 96.8 (300K) |
Boiling point T/K | 1038 | Resistivity Ï / (Ω · m) | 6.86×10 -8 (273K) |
Melting heat Q/(kJ·mol -1 ) | 6.11 | Magnetic susceptibility x / (m 3 · kg -1 ) | -2.21×10 -9 (S) |
Gasification heat Q/(kJ·mol -1 ) | 100.0 | Molar volume Vm/cm 3 | 13.00 |
Density Ï / (kg · m -3 ) | 8650 (293K) | Linear expansion coefficient α/k -1 | 29.8×10 -6 |
7996 (melting point liquid) | Electron affinity (Me-Me) A/(kJ·mol -1 ) | -26 |
The chemical properties of cadmium are similar to those of zinc. They do not react with dry air at normal temperature, slowly oxidize and lose luster in humid air, and form a brown oxide layer upon heating. The cadmium vapor burns to produce brown smoke. Cadmium is insoluble in lye, but soluble in most acids, such as sulfuric acid, hydrochloric acid and nitric acid, and produces the corresponding cadmium salt, but the dissolution rate is slower than zinc. Cadmium is extremely soluble in concentrated ammonium nitrate solution, which can be used to strip cadmium from copper and iron cadmium-plated parts. Cadmium oxide and cadmium hydroxide are different from the corresponding zinc compounds and are insoluble in excess sodium hydroxide. In acidic acid sulfate solution, cadmium ions can be replaced by metal zinc. Cadmium is in a divalent state in all stable compounds, and its ions are colorless. Cadmium can form coordination ions such as Cd(NH 3 ) 4 2 + , Cd(CN) 4 2- , and CdI 4 2 - .
Cadmium is a toxic substance, and the air polluted by cadmium is more harmful to the human body than the contaminated food. When it enters the human body, it mainly damages the human kidney and also causes bubble emphysema. It is necessary to strictly control the discharge of cadmium-containing waste gas and wastewater. The limit value of cadmium dust in air is 200 μg/m 3 , and the limit value of cadmium oxide smoke is 100 μg/m 3 . Waste water containing more than 0.5 × 10 -4 % cadmium is not allowed to be discharged.
In 1919, cadmium began to be used as an electroplating layer for iron and steel rust. By 1941 this application had become its main use. However, due to the high cost and the special treatment of toxic waste, the dosage of cadmium in electroplating is gradually decreasing. The various uses and market consumption of cadmium are shown in Table 2. The main use of cadmium is to produce nickel- cadmium batteries, and the consumption of nickel- cadmium batteries in Japan accounts for about 80% of cadmium consumption.
Table 2 Main uses and consumption of cadmium
use | Consumption | |||
1977-1980 | 1989-1990 | |||
Quality score w/% | m/t | Quality score w/% | m/t | |
battery | twenty three | 3450 | 55 | 10175 |
pigment | 27 | 4050 | 20 | 3700 |
plating | 34 | 5100 | 10 | 1850 |
stabilizer | 12 | 1800 | 10 | 1850 |
other | 4 | 600 | 5 | 925 |
total | 15000 | 18500 | ||
Cadmium is a rare element with a crust abundance between mercury and silver of 1.6 × 10 -6 %, seawater containing cadmium of 1 × 10 -8 %, and an estimated world cadmium reserve of about 540,000 tons. In cadmium sulfide minerals exist in nature, there is no separate deposits, often with symbiotic lead ore, zinc concentrate in most elected beneficiation process. Some zinc concentrates contain cadmium in the range of 1% to 2%, generally between 0.06% and 0.5%. The vast majority of metal cadmium comes from intermediate products in the zinc smelting process. Copper cadmium slag (4% to 20% cadmium) produced during the purification of zinc sulphate solution in the wet zinc smelting plant, cadmium ash (containing cadmium 10) produced during the crude zinc rectification process of the pyrometallurgical zinc plant %~30%) and some cadmium-rich dust produced by copper and lead smelters are the main raw materials for cadmium extraction. Industrial waste such as plates of nickel-cadmium and iron-cadmium batteries is often used as a secondary raw material for cadmium extraction.
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