The cadmium is a chemical element of symbol Cd and of Atomic number 48.

History

Cadmium was discovered in 1808 by Magnus Martin af Pontin, but it is into 1817 that the German Friedrich Stromeyer prepared it for the first time.

The Cadmium name comes from Latin coated with cadmium , “calamine”, old name given to zinc carbonate - cadmium was extracted from this ore around the town of Thèbes, which was founded by Cadmos, and whose citadel bears the name of kadmeia , in French Cadmée.

Properties

Cadmium is a white, soft and malleable metal. It tarnishes in contact with the air.

Physical properties

Cadmium is a silver plated white metal having physical properties close to that of zinc. It melts with 320,9 °C and boils with 767 °C. During the boiling of cadmium, it is released from the toxic yellow vapors.

Its specific mass (density) is of 8.650 kg/m ³.

It is ductile (resistance to the stretching), malleable (strength to flatness) and resists atmospheric corrosion, which in fact a coating of protection for ferrous metals.

Chemical properties

The chemical properties of cadmium are similar to those of the Zinc. The ion cadmium is moved by metal zinc in solution: it is thus nobler than zinc.

It oxidizes very little with room temperature and burns in the air by giving the anhydrous oxide CdO, insoluble in an excess of sodium hydroxide.

It reacts with the acids and the bases. Cadmium is soluble in the nitric Acid diluted and in the concentrated and hot acids hydrochloric and sulphuric.

The atomic molar mass of Cadmium (Cd) is of 112,4 g/mol.

Toxicity of cadmium

It is known since the Fifties. Very toxic in all its forms (metal, vapor, salts, made up organic), cadmium is one of the rare elements not having any function known in the human body or in the animal. It is necessary to avoid its contact with food. At the Man, it causes in particular renal problems and the increase in the tension.

History

In the years 1500, to the Japan, an acute intoxication with cadmium gave a disease of the kidneys and bones, named “ itaï-itaï ” (which means “ I have badly, I badly have ”, the sentence often repeated by the patients).
Le cadmium is concentrated by the Food chain (the Mollusque S bivalves concentrate 300.000 times cadmium, even more. This one can come by far; for example, cadmium present in excess in the Huitre S of Oléron comes from a source located very upstream (old mining waste).

Normalizes and safety

In France, the annual average quantity of cadmium introduced by anybody and per annum is estimated at 12 Mg. Absorption by digestive tract of more than 0,9 G or by respiratory tract (of dust) with concentrations larger than 200 mg/m ³ can involve serious disorders.

In France, the exposure limit value is fixed at 0,05 mg/m ³, for oxide smoke.

The consumption of Tabac can represent up to 75% of human food absorption out of cadmium daily. Today, the principal risks of intoxication are related to the exposures prolonged to low dose cadmium. Cadmium is mainly absorbed by inhalation and is fixed at 30 - 40% in the Rein S where it involves an abnormal loss of Protéine S by the Urine S (protéinurie).

Sources of exposure

Cadmium quantitatively seems absorbed initially by inhalation and moindrement by gastro-intestinal absorption. It is not absorbed by the Peau. Apart from the professional exposure, one can be exposed there via:

• smoke and the Dust S lost by certain industries (Metallurgy, recycling of the batteries to cadmium, phosphorated Manures);

• the Smoked of Cigarette (the primary source of contamination of the general population);
• the phosphorated Engrais of synthesis (or natural sometimes), which contain much of it and which pollute the ground and the tablecloths;
• the effluents and Clarification sludge urban and/or industrial épandues on the fields or in Forêt are sometimes important sources of cadmium. Two experimental cultures on field following a spreading of clarification sludge showed that these spreadings led to contents close to the authorized maximum. );
• Certain food (of which for example Mushroom S, or the bodies the such Liver and the kidneys often contain of them rates higher than the Norme S because these bodies have as a role precisely to collect and reduce the cadmium concentrations circulating in the system. The corn and certain plants (e.g spinaches) seem to be able to accumulate it more than others. Certain vegetables and the cereals can concentrate cadmium. The cereal cultures on acid grounds support the contamination of the grain, with however of the significant differences according to the planted varieties;
• ashes and residues of incineration, after combustion of objects containing of cadmium (paintings, PVC, etc) like dye, additive or catalyst;
• urban air (very high levels sometimes close to the production centres).

The Lichen S, foams and the Champignon S can accumulate of them very high amounts, even mortals, just as of others heavy metals, making these species of good indicators of the state of Pollution of the Environnement (when they survived it).

Acute intoxications

Fever of the founders

The inhalation of cadmium oxide smoke (generated when metal cadmium is brought up to high temperature). It involves symptoms similar to those of the fever of the founders (state grippal beginning). The treatment is only symptomatic.

pulmonary Attack

The exposure to higher levels can cause serious pulmonary damage even death. Cadmium oxide smoke is severe pulmonary irritants (due to the size of their particles), cadmium dust being less irritating because their particles have a greater dimension. The symptoms are types either pulmonary (clinical signs being the reflection of lesions varying irritation naso-pharyngée and bronchial with the pulmonary edema) or of headaches type, shivers, pains muscular, nauseas, vomiting, diarrhea… The fatal concentrations of smoke vary from 40 to 50 mg/m ³.

Chronic intoxications

renal Attacks

The chronic exposure to cadmium, by inhalation or ingestion, has as consequence of the renal attacks which can continue to progress even after the suspension of the exposure.

pulmonary Attack

The exposure of long life per inhalation to low levels can cause a reduction in the pulmonary function and the Emphysème.

osseous Attack

Even if absorption by ingestion is low, the chronic exposure to cadmium elevated levels in food can cause osseous disorders, including the Ostéoporose and the Ostéomalacie. Long-term ingestion, by a population Japan ease, with water and food contaminated by cadmium, was associated with a stun condition, the disease “Itai-itai” (have-have).

It is characterized by pains with the Dos and in the articulation S, of osteomalacia (adult Rachitisme), of the osseous Fracture S, and occasionally of the renal failures. This disease generally assigns the women and the risk factors are the multiparity and the food of poor quality.

Various

The other consequences of the chronic exposure to cadmium are the Anémie, the yellowish coloring of the Dent S, the Rhinite, the occasional ulceration of the nasal Septum, the damage with the olfactive nerve and the loss of the Odorat.

Residence time in the organization : Cadmium accumulates in the bodies with the length of the life for at the adult man reaching 30 to 40 milligrams, even more at those which were exposed there during their life because elimination natural (urine, excrement, and moindrement rules, ejaculation, loss of superficial body growths (nails, hair) generally does not compensate for the contributions. It accumulates temporarily in the liver before accumulating in the kidneys where beyond 200 Mg per kg in the adult, it causes irreversible lesions.

Reproductive health: the testiculaires effects were shown in the animal with strong experimental amounts. One recently showed that cadmium also interacted, with the thresholds recommended by WHO with the receivers of the estrogens in the rat. To university of Washington (the USA), Rat S females which one had removed by ablation the ovary S (so that the animal does not produce any more a Oestrogène S) were exposed in a weekly cadmium injection ata rate which is that WHO recommends not to exceed (5 and 7 micrograms per kilo and week). Four days after the 1st injection, of the hormonal pseudo effects was observed. Cadmium in blood produces in the rats females the growth of the glands mammaires, as well as an increase in the weight and size of the uterus, as well as amincicement of the uterine wall of the guinea-pigs. The pregnant females have the small ones whose puberty occurs earlier. This hormonal effect could explain some turbid osseous (Ostéoporose, fractures early…) among women in Japan at the time of the disease of Itaï Itaï described in 1967. The conclusions cannot be directly extrapolated with the Man, but the question is put. The oestrogenic effects are to be confirmed by studies on other animal models and at the Man, in particular because cadmium was injected with the rats, and that it can be present in different forms and less brutally at the man by oral or pulmonary way.

Another question is that of the Synergie or Potentialization when cadmium is absorbed - what is often the case - with other poisons. The amounts recommended by WHO 7 micrograms per kilo and week, and between 3 to 5 micrograms per liter for drink could one being day revised, as for lead.

Carcinogenesis and mutagenèse

Several inorganic compounds of cadmium cause malignant Tumeur S in the animal. The professional exposure to cadmium can be regarded as person in charge of a significant growth of the Lung cancer. The CIRC (International Research center on Cancer) determined that there are sufficient proof at the man as for the cancerogenicity of cadmium and of its compounds. It also proves that cadmium with the capacity to modify the genetic material, in particular the Chromosome S. According to the director of the research center of the foundation " live the santé" cadmium would be one of the factors of sterility.

Layers

Cadmium does not exist in a native state. Its ore, the Greenockite CdS, is very rare and unexploited.

Cadmium is present in almost all the zinc ores (the cadmium content varies from 0,01 to 0,05%), and is obtained industrially like by-product of the Métallurgie of zinc. Its production depends on that of zinc, in a variable proportion from 1,8 to 6 kg of cadmium/ton of elaborate Zn (3 zinc kg/tonne on average).

Cadmium is also present in ores of Plomb and Cuivre, like in natural Phosphate S (34 ppm for the phosphates Jordan NS, 380 ppm for the phosphates Tunisia NS).

Metallurgy

The metallurgy of cadmium is integrated into that of zinc. In all the cases, part of cadmium is recovered by filtration of gas coming from netting.

Two cases are to be studied:

• At the time of the pyrometallurgy of the Zinc: cadmium is recovered during the refining of zinc. The sponge thus obtained is refined thermically by fusion (with 450 °C) in the presence of soda to eliminate zinc and lead in the form of zincate and plumbate then by distillation with 770 °C.

• At the time of the hydrometallurgy of zinc, cadmium is in solution (0,2 to 0,3 G of Cd/l) in the bath of electrolysis. It is recovered, after exhaustion of Zn²⁺, by cementing using zinc. One obtains blue muds containing approximately cadmium 6% and copper 15% which are then attacked using sulphuric acid. The Cd²⁺ ions are again reduced out of metal by cementing by zinc. The refining takes place by leaching with the sulphuric acid and electrolysis (lead anode and aluminum cathode).

Production

Approximately 10 to 15% of the worldwide production of cadmium is done starting from recycled materials.

The table opposite gives the annual productions of various countries.

Recycling

It is carried out mainly starting from accumulators Ni-Cd and of the weldings.

It is it should be noted that in France for example, about half of the requirements out of cadmium comes from recycling (approximately 1.000 tons of cadmium recyclé/an).

Use

Cadmium has multiple uses: in particular in the screens of Television, the control rods of the nuclear reactors, them dyes (enamel, Glaze).

It enters the composition of many Alliage S at low melting point (welding S, Brasure S) and is used for manufacture of some Accumulator battery (“rechargeable batteries”).

But its principal uses are those of its compounds which relate to the anti-corrosive linings (applied in thin layer on steel by Cadmiage, cadmium protects from corrosion, in particular saltworks) or the manufacture of pigments of colors (yellow and red).

Its principal uses:

• Electric fencer (refillable “piles”) Ni-Cd: the matter constituting the anode is a pulverulent mixture of Hydroxyde of nickel and Graphite. That of cathode is cadmium with 20 to iron 25%. The active matters are placed in some 10 mm broad perforated nickel-plated steel small pockets (holes of 0,1 mm). The electrolyte is an aqueous solution of KOH: 6 to 8 moles/liter. Though currently supplanted by devices of the type Lithium-ion or metal nickel-hydride Nor-MH, accumulators Ni-Cd remain employed, in spite of their Ratchet effect, in the applications where the resistance intern must remain weak (calls of important current): electrical motors, walkie-talkies, etc

In 1992, the production of accumulators Ni-Cd was of 1,3 billion units including 60% by Japanese producers and 15% by French;

• Pigments containing cadmium sulfide (yellow with CdS, red with Cd (S,), orange by mixture of the two precedents): they were used with large scales in the plastics (helmets, glasses, ceramics…).

Van Gogh used of CdS to make the yellow of its sunflowers. The European Community adopted a directive limiting the use of the cadmium pigments to the only cases where they cannot be replaced (polymeric);

• cadmium-coating: cadmium is inalterable with the air and has a good behavior in seamen circle. Cadmium-coating is carried out by electrolysis. Used, in particular to protect the Rivet S from assembly in Aeronautical;

• alloys at low melting point: manufactured for brazings of electric drivers (Ag 50%, minor road 18%, Zn 16%, Cu 15%) and for fusible S (Bi 50%, Pb 27%, Sn 13%, minor road 10%, bottom with 70 °C);

• absorption of Neutron S: the cross Section of cadmium for the absorption of the neutrons being particularly high, cadmium is used with the realization as control rods in the nuclear reactors, and is used as a biological shielding with respect to neutron sources;

• stabilizing PVC: used in the form of cadmium sulfide.

• in combination with Gold, it belongs to the family of the Métaux " intelligents" and is thus used to manufacture unbreakable glasses, pipes in the nuclear plants…

Consumption

Table opposite watch consumption by country per year (in ton).

Table below watch importance of consumption by sector of use in the western world (en%).

Pollution by cadmium

It is in strong reduction in the seas since the years 1980, but the rates locally remain alarming, in particular in the shells and organizations top of the food Pyramide. In Europe the Belgium center is particularly touched, as well as the ex-countries of the East. The origins of the Pollution by cadmium are multiple, with in particular (in tonnes/an):

• Agricultural (total for the whole of the European Union, 545 tonnes/an):

Note : The contribution of the phosphate-enriched fertilizers is from 2 to 6 G of Cd/ha/an, that is to say in France, 82 tonnes/an. In the food chain, Cd concentrates mainly in the sheets of the plants (salads, cabbages but also tobacco).

• Atmospheric (total for the whole of the European Union, 168 tonnes/an):

Note : the Cd content in the air varies from 1 ng/m ³ in rural area, to 20 ng/m ³ in industrial park and 30 µg/m ³ close to Etna.

The risk related to the cadmium of phosphorated manures in Europe starts to be taken into account. In Europe, the Commission published several texts and decisions concerning the national provisions relating to the acceptable maximum content cadmium of manures.

• Watery (total for the whole of the European Union, 124 tonnes/an):

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