Safety and labor protection in the production of titanium dioxide

1. Toxicity and personal protection of titanium dioxide

Pure titanium dioxide is completely non-toxic, titanium dioxide pigments can be used to paint children's toys, plastic toys, food packaging, beverage containers as well as hospitals, restaurants article. However, some pigment-grade titanium dioxide may contain trace amounts of toxic elements, which are mainly brought in by some surface treatment agents, or caused by contamination during processing and equipment wear, and the quantity is generally only a few parts per million. It is basically harmless to the human body. If titanium dioxide is used in food additives, medical drugs, and cosmetics, the United States Pharmacopoeia and the US Food and Drug Administration (FDA) have specific provisions on the content of harmful elements in titanium dioxide for the above purposes. It is recognized by many countries in the world and has the same effect. Titanium dioxide, which is usually used exclusively for food and medicine, is generally high-purity, untreated titanium dioxide.

Titanium dioxide is codenamed CAS NO. 13463-67-7 in North America. This code itself indicates that titanium dioxide is a non-toxic product. So far, there are no symptoms of acute or chronic poisoning of titanium dioxide. According to the introduction of the British Tioxide Group Science and Technology Information, the animal test results of titanium dioxide, mouse LD50 Under the test conditions of -6 titanium dioxide, there was no carcinogenic effect on both mice, except for the whitening of the skin, without any physiological influence; DuPont Company conducted a two-year animal inhalation test on the house mouse, exceeding the US Government Industrial Hygiene Conference. (ACGIH) 2 to 10 times the critical limit value, no adverse reactions in the lungs, more than 50 times, some of the rats found severe lung emptiness symptoms under the microscope; International Agency for Research on Cancer (IARC) listed titanium dioxide as Group 3, a substance that is not carcinogenic to humans, did not find evidence of the carcinogenic effects of titanium dioxide on humans. Among the organotitanium compounds, only ferrocene has been found to be carcinogenic to animals.

Titanium dioxide is an inert, insoluble (water) oxide that is chemically stable, non-flammable, non-volatile, and does not explode (of course, its packaging is often a flammable substance), only in the titanium dioxide at about 250 ° C. The organic envelope will decompose. Titanium dioxide has no biochemical activity, but because of its high hiding power and achromatic power, it can make white water even at low concentration. The activity of observing leeches in 1g of titanium dioxide solution per liter of water is not poisoned. reaction. Table 1 shows the occupational exposure regulations for titanium dioxide in the 1989 UK Health and Safety Executive Act.

Table 1 Occupational exposure limits for the UK Health and Safety Enforcement Act (1989)

project	8h long-term exposure limit / (mg / m 3 )	10min short-term exposure limit / (mg / m 3 )
Titanium dioxide Total vacuum Possible amount of dust	10 5
Other compounds Alumina Amorphous silica Total vacuum Possible amount of dust Zirconium compound	10 6 3 5	20 10

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The particles of titanium dioxide are very fine, easy to fly during production and use, and may be inhaled by the operator. Therefore, when wearing a TiO ₂ dust concentration, wear a mask and dust-proof glasses. When the fine titanium dioxide contacts the skin, it will It absorbs moisture and fat (grease) on the surface of the skin, causing dry skin, so wear gloves for long-term contacts. Generally, the titanium dioxide on the skin should be washed with water after soapy water; it can be washed with clean water or dripping with neutral eye drops; it can be taken in a small amount of titanium dioxide, which is non-toxic and will not stay in the digestive tract; Titanium dioxide only needs to leave the site without treatment.

Titanium dioxide is a raw material iron ore (especially mine as secondary; individual mine sites in India, Malaysia, Australia) sometimes contain small amounts of radioactive material (uranium, thorium), China's current domestic ilmenite used In the middle, there have been no reports of radioactive content exceeding the standard, but for the ilmenite with high monazite content, the radioactivity content should be checked when using it. A method for separating radioactive impurities from titanium-containing minerals has been described in the European Patent Application Publication No. 0 767 594 A1 (1997) by Kerr-McGee.

2. Safety precautions in the production of titanium dioxide

Titanium dioxide is a chemically very stable inorganic oxide, when using the process for producing sulfuric acid, in addition to use large quantities of corrosive sulfuric acid and a small amount of hydrochloric acid, caustic soda, phosphoric acid, most raw materials are non-toxic. It is necessary to pay attention to the protection of toxic substances, mainly formaldehyde, dimethylamine and individual organic surface treatment agents used in the modification of polyacrylamide. When using these items, they should be made according to the requirements in the instruction manual and the requirements of the factory safety regulations. Good protection work, in the whole production process, the semi-finished materials before calcination are acidic, corrosive, and wear protective equipment during operation.

Sulfuric acid is the most prone to the production of titanium dioxide poisoning post precipitation step, using antimony trioxide - when co-settling agent for the iron sulfide, iron sulfide when the process is added to the precipitation tank in hydrogen sulfide (H ₂ S Gas escapes. In the past, there were often cases of worker poisoning. When the operator added the material, he should wear a gas mask (mask) and stand in the upwind position. The state stipulates that the maximum allowable concentration of hydrogen sulfide in the air is l0mg/m ³ , and when the concentration is 0.012~0.13mg/m ³ , it can smell its special smell of stinky eggs. When the concentration is higher than 30~40mg/m ³ , the smell is odor. Instead, at 200~300mg/m ³ , due to poisoning caused by olfactory fatigue, but not feeling the taste, so most poisoned people are poisoned without consciousness, unprepared, when the concentration reaches l000mg At /m ³ , even an electric shock can cause a heartbeat to stop. Conditional units should install an automatic alarm device for hydrogen sulfide at the work site, or use a test paper impregnated with 2% lead acetate in ethanol. After exposure to air for 30 minutes, if it turns yellow-green or brown-black, the concentration of hydrogen sulfide in the environment is indicated. Higher. If poisoned, they should be immediately transferred to a fresh air zone, given oxygen or artificial respiration, and sent to the hospital for further treatment after the symptoms are relieved.

The most prone to process operation accidents in the production of titanium dioxide by sulfuric acid is acid decomposing, because the content of Fe ₂ O _{3 in the} ore powder is too high, or the ore powder is too fine, wet, contains oil, paper, grass clippings, sacks, etc. Organic matter; or the concentration of sulfuric acid, the proportion of mineral acid is not appropriate, the temperature of preheating of sulfuric acid is too high, the water content of steam is too much or the opening is too large, the acid hydrolysis reaction is too intense, and even the high temperature material containing concentrated sulfuric acid is impacted outside the tank. A “hot pot” accident occurs. Therefore, in addition to careful handling of the above matters during the acid hydrolysis operation, the operator is prohibited from staying in the vicinity of the acid hydrolysis tank during the acid hydrolysis reaction. The operator should control and understand the main acid solution through the observation window in the operation room. The progress of the reaction.

In addition calcined artillery positions firing kiln, steam superheater such as the use of coal gas, natural gas and diesel fuel, to make fire safety measures to open above the furnace, the parking operation should be carefully following the same procedures are required to do, Prevent accidental ignition or explosion accidents.

The production of chlorination method is much more dangerous than the sulfuric acid method, and the operation control is very strict. Chlorine gas (or liquid chlorine) and titanium tetrachloride in the production of chlorination process are highly corrosive and toxic gases, once leaked to the human body and the surrounding environment. They are all highly toxic. Oxygen, carbon monoxide, toluene, etc., which are up to 1000 °C in oxidation reaction, are very dangerous olefins and explosive substances. The requirements for safe operation are much stricter than those of sulfuric acid.