Gunnar Nordberg
Antimony is stable at room temperature but, when heated, burns brilliantly, giving off dense white fumes of antimony oxide (Sb2O3) with a garlic-like odour. It is closely related, chemically, to arsenic. It readily forms alloys with arsenic, lead, tin, zinc, iron and bismuth.
Occurrence and Uses
In nature, antimony is found in combination with numerous elements, and the most common ores are stibnite (SbS3), valentinite (Sb2O3), kermesite (Sb2S2O) and senarmontite (Sb2O3).
High-purity antimony is employed in the manufacture of semiconductors. Normal-purity antimony is used widely in the production of alloys, to which it imparts increased hardness, mechanical strength, corrosion resistance and a low coefficient of friction; alloys combining tin, lead and antimony are used in the electrical industry. Among the more important antimony alloys are babbitt, pewter, white metal, Britannia metal and bearing metal. These are used for bearing shells, storage battery plates, cable sheathing, solder, ornamental castings and ammunition. The resistance of metallic antimony to acids and bases is put to effect in the manufacture of chemical plants.
Hazards
The principal hazard of antimony is that of intoxication by ingestion, inhalation or skin absorption. The respiratory tract is the most important route of entry since antimony is so frequently encountered as a fine airborne dust. Ingestion may occur through swallowing dust or through contamination of beverages, food or tobacco. Skin absorption is less common, but may occur when antimony is in prolonged contact with skin.
The dust encountered in antimony mining may contain free silica, and cases of pneumoconiosis (termed silico-antimoniosis) have been reported among antimony miners. During processing, the antimony ore, which is extremely brittle, is converted into fine dust more rapidly than the accompanying rock, leading to high atmospheric concentrations of fine dust during such operations as reduction and screening. Dust produced during crushing is relatively coarse, and the remaining operations—classification, flotation, filtration and so on—are wet processes and, consequently, dust free. Furnace workers who refine metallic antimony and produce antimony alloy, and workers setting type in the printing industry, are all exposed to antimony metal dust and fumes, and may present diffuse miliar opacities in the lung, with no clinical or functional signs of impairment in the absence of silica dust.
Inhalation of antimony aerosols may produce localized reactions of the mucous membrane, respiratory tract and lungs. Examination of miners and concentrator and smelter workers exposed to antimony dust and fumes has revealed dermatitis, rhinitis, inflammation of upper and lower respiratory tracts, including pneumonitis and even gastritis, conjunctivitis and perforations of the nasal septum.
Pneumoconiosis, sometimes in combination with obstructive lung changes, has been reported following long-term exposure in humans. Although antimony pneumoconiosis is regarded as benign, the chronic respiratory effects associated with heavy antimony exposure are not considered harmless. In addition, effects on the heart, even fatal, have been related to long-term occupational exposure to antimony trioxide.
Pustular skin infections are sometimes seen in persons working with antimony and antimony salts. These eruptions are transient and primarily affect the skin areas in which heat exposure or sweating has occurred.
Toxicology
In its chemical properties and metabolic action, antimony has a close resemblance to arsenic, and, since the two elements are sometimes found in association, the action of antimony may be blamed on arsenic, especially in foundry workers. However, experiments with high-purity metallic antimony have shown that this metal has a completely independent toxicology; different authors have found the average lethal dose to be between 10 and 11.2 mg/100 g.
Antimony may enter the body through the skin, but the principal route is through the lungs. From the lungs, antimony, and especially free antimony, is absorbed and taken up by the blood and tissues. Studies on workers and experiments with radioactive antimony have shown that the major part of the absorbed dose enters the metabolism within 48 hours and is eliminated in the faeces and, to a lesser extent, the urine. The remainder stays in the blood for some considerable time, with the erythrocytes containing several times more antimony than the serum. In workers exposed to pentavalent antimony, the urinary excretion of antimony is related to the intensity of exposure. It has been estimated that after 8 hours exposure to 500 µg Sb/m3, the increase in concentration of antimony excreted in the urine at the end of a shift amounts on average to 35 µg/g creatinine.
Antimony inhibits the activity of certain enzymes, binds sulphydryl groups in the serum, and disturbs protein and carbohydrate metabolism and the production of glycogen by the liver. Prolonged animal experiments with antimony aerosols have led to the development of distinctive endogenous lipoid pneumonia. Cardiac injury and cases of sudden death have also been reported in workers exposed to antimony. Focal fibrosis of the lung and cardiovascular effects have also been observed in animal trials.
The therapeutic use of antimonial drugs has made it possible to detect, in particular, the cumulative myocardial toxicity of the trivalent derivatives of antimony (which are excreted more slowly than pentavalent derivatives). Reduction in amplitude of T wave, increase of QT interval and arrhythmias have been observed in the electrocardiogram.
Symptoms
The symptoms of acute poisoning include violent irritation of the mouth, nose, stomach and intestines; vomiting and bloody stools; slow, shallow respiration; coma sometimes followed by death due to exhaustion and hepatic and renal complications. Those of chronic poisoning are: dryness of throat, nausea, headaches, sleeplessness, loss of appetite, and dizziness. Gender differences in the effects of antimony have been noted by some authors, but the differences are not well established.
Compounds
Stibine (SbH3), or antimony hydride (hydrogen antimonide), is produced by dissolving zinc-antimony or magnesium-antimony alloy in dilute hydrochloric acid. However, it occurs frequently as a by-product in the processing of metals containing antimony with reducing acids or in overcharging storage batteries. Stibine has been used as a fumigating agent. High-purity stibine is used as an n-type gas-phase dopant for silicon in semiconductors. Stibine is an extremely hazardous gas. Like arsine it may destroy blood cells and cause haemoglobinuria, jaundice, anuria and death. Symptoms include headache, nausea, epigastric pain and passage of dark red urine following exposure.
Antimony trioxide (Sb2O3) is the most important of the antimony oxides. When airborne, it tends to remain suspended for an exceptionally long time. It is obtained from antimony ore by a roasting process or by oxidizing metallic antimony and subsequent sublimation, and is used for the manufacture of tartar emetic, as a paint pigment, in enamels and glazes, and as a flameproofing compound.
Antimony trioxide is both a systemic poison and a skin disease hazard, although its toxicity is three times less than that of the metal. In long-term animal experiments, rats exposed to antimony trioxide via inhalation showed a high frequency of lung tumours. An excess of deaths due to cancer of the lung among workers engaged in antimony smelting for more than 4 years, at an average concentration in air of 8 mg/m3, has been reported from Newcastle. In addition to antimony dust and fumes, the workers were exposed to zircon plant effluents and caustic soda. No other experiences were informative on the carcinogenic potential of antimony trioxide. This has been classified by the American Conference of Governmental Industrial Hygienists (ACGIH) as a chemical substance associated with industrial processes which are suspected of inducing cancer.
Antimony pentoxide (Sb2O5) is produced by the oxidation of the trioxide or the pure metal, in nitric acid under heat. It is used in the manufacture of paints and lacquers, glass, pottery and pharmaceuticals. Antimony pentoxide is noted for its low degree of toxic hazard.
Antimony trisulphide (Sb2S3) is found as a natural mineral, antimonite, but can also be synthesized. It is used in the pyrotechnics, match and explosives industries, in ruby glass manufacture, and as a pigment and plasticizer in the rubber industry. An apparent increase in heart abnormalities has been found in persons exposed to the trisulphide. Antimony pentasulphide (Sb2S5) has much the same uses as the trisulphide and has a low level of toxicity.
Antimony trichloride (SbCl3), or antimonous chloride (butter of antimony), is produced by the interaction of chlorine and antimony or by dissolving antimony trisulphide in hydrochloric acid. Antimony pentachloride (SbCl5) is produced by the action of chlorine on molten antimony trichloride. The antimony chlorides are used for blueing steel and colouring aluminium, pewter and zinc, and as catalysts in organic synthesis, especially in the rubber and pharmaceutical industries. In addition, antimony trichloride is used in the match and petroleum industries. They are highly toxic substances, act as irritants and are corrosive to the skin. The trichloride has an LD50 of 2.5 mg/100 g.
Antimony trifluoride (SbF3) is prepared by dissolving antimony trioxide in hydrofluoric acid, and is used in organic synthesis. It is also employed in dyeing and pottery manufacture. Antimony trifluoride is highly toxic and an irritant to the skin. It has an LD50 of 2.3 mg/100 g.
Safety and Health Measures
The essence of any safety programme for the prevention of antimony poisoning should be the control of dust and fume formation at all stages of processing.
In mining, dust prevention measures are similar to those for metal mining in general. During crushing, the ore should be sprayed or the process completely enclosed and fitted with local exhaust ventilation combined with adequate general ventilation. In antimony smelting the hazards of charge preparation, furnace operation, fettling and electrolytic cell operation should be eliminated, where possible, by isolation and process automation. Furnace workers should be provided with water sprays and effective ventilation.
Where complete elimination of exposure is not possible, the hands, arms and faces of workers should be protected by gloves, dustproof clothing and goggles, and, where atmospheric exposure is high, respirators should be provided. Barrier creams should also be applied, especially when handling soluble antimony compounds, in which case they should be combined with the use of waterproof clothing and rubber gloves. Personal hygiene measures should be strictly observed; no food or beverages should be consumed in the workshops, and suitable sanitary facilities should be provided so that workers can wash before meals and before leaving work.