Oxidation smelting process and other metallurgical cupellation pyrometallurgical production of noble metal, a large amount of lead contained in the raw material is oxidized to lead oxide into the flue gas, the production of polluting workplace and its surroundings. In the hydrometallurgy of precious metals, industrial wastewater containing heavy metals such as lead is often discharged. Lead from fire and hydrometallurgy can cause lead damage.

Lead poison is mainly inhaled through the respiratory tract, and secondly enters the human body through the digestive tract. In the case of normal (non-metallurgical sites), urban residents bring about 70-750 μg of lead per day from the air (lead from the combustion of the explosion-proof agent added in gasoline), food and drinking water (including vegetables from vegetables). The intake of foods such as cereals and meat is up to about 300 μg). In the metallurgical workshops and surrounding areas, the body's intake in these areas is often many times higher than the above, due to the large amount of lead and lead dust emitted by the factory.

Respiratory intake of lead, after the body absorbed into the blood, binding to soluble lead hydrogen phosphate, lead phosphate glycerol, protein complex or in the form of lead ions, which rapidly and erythrocyte binding 90%, in each cycle being After the tissue is absorbed, part of it is excreted from the urine and feces, and the other part is transferred from the soft tissue to the bone after a few weeks, and the lead phosphate (Pb ₂ (PO ₄ ) ₂ ) which is not easily dissolved is deposited.

About 5% to 10% of the lead, which is brought into the digestive tract by food and contaminated lead fingers and utensils, is absorbed by the intestine, through the liver, part of the bile enters the intestine and is excreted in the feces, and the other part enters the bloodstream. , deposited in the epiphysis by the same route as described above.

However, lead and its inorganic compounds generally cannot penetrate through the skin.

Under normal conditions, the daily intake and discharge of lead in the human body (including the amount of accumulation) is roughly in equilibrium. It is generally believed that the amount of lead accumulated in the human body is 3 to 11 μg per day. According to 50 years, the total lead accumulated in the human body is about 51 to 205 mg. 90% to 95% of the lead accumulated in the body is present in the bone. When the amount of lead is too much, the "lead line" in the bone can be seen on the X-ray photograph.

Clinically, long-term exposure to lead poisoning produces chronic lead poisoning, often manifested as neurasthenia and indigestion. Acute poisoning of short-term intake of large amounts of lead is manifested as abdominal cramps and hepatitis. However, occupational lead poisoning is rarely severe. Signs of lead poisoning, often appear gingival line, anemia pale (lead capacity) and facial skin, angiogenesis.

International methods for the prevention and testing of lead poisoning usually use air monitoring methods and biological monitoring methods.

The air monitoring method is to install monitoring instruments in various traffic routes, industrial areas and metallurgical sites to determine the amount of lead in the air. In many countries, the critical limit of l50 μg/m ³ set by the American Industrial Hygiene Association and the 1968 International Lead Conference was adopted. Under normal circumstances, when the air lead limit is not more than 150 ~ 200μg / m ³ , the lead content (blood lead) in human blood will not exceed 70μg / 100g blood. However, since the air monitoring method uses fixed-point sampling, the geometry and installation position of the sampling head have a great influence on the sampling, and it does not reflect the actual contact between the human body and the lead poison that occurs when the operator of the metallurgical site moves back and forth during the operation. Changes, in particular, do not reflect the operator's poor work habits and personal hygiene (such as not using filter respirator, smoking at the factory, biting nails and not hygiene). It also does not reflect the inhaled lead poison. Because of its different chemical and physical properties (such as composition, particle size, humidity, solid state, etc.), the amount of dissolved by body fluids is also different, causing differences in body absorption. Therefore, the blood lead value of the human body cannot be estimated based on the amount of lead contained in the air. Nevertheless, the air monitoring method is instructive for the following purposes:

(1) indicate the need to establish a range of biological monitoring;

(2) Point out the need to establish areas to control pollution and evaluate the control methods used

Effect.

Lead levels and emission standards for air monitoring methods have been developed in all major countries of the world. The standards set by China are listed in Table 1.

Table 1 China's atmospheric and water lead content and emission standards

The biological monitoring method is a method of directly taking blood, urine, and hair samples of a human body and testing the amount of lead contained therein. Blood lead is generally considered to be the only reliable indicator of lead in human body. It not only correctly diagnoses lead poisoning, but more importantly, it can predict the possibility of lead poisoning, and take measures to prevent the occurrence of lead poisoning.

Table 2 lists the classification values ​​of lead in human blood and urine proposed by Dr. Kehoe. His classification is classified into normal, abnormal (still safe) and lead poisoning risk values ​​based on blood lead and urine lead levels. Practice has proved that the classification in the table is basically reasonable. Although some of the most sensitive people have symptoms of lead poisoning when their blood lead levels are below 80 μg/100 ml of blood, some people do not. However, exceeding this value will increase the risk of disease. Urine lead is also a useful indicator for measuring lead absorption, but its reliability is poor due to the fact that the amount of lead in urine is greater than that of blood lead. However, the urine sample is easy to pick. When it is checked that the lead value of fresh urine in a person is too high and the density is too large, the blood lead value must be checked.

Table 2 Classification of lead content in blood and urine

Table 3 lists the evaluation criteria for human lead content in China.

Table 3 Evaluation criteria for human lead content

Lead poisoning is mainly used to treat lead poisoning. At present, the drugs used to drive lead in China include disodium edetate, sodium dimercaptosuccinate, sedative (trisodium triethylenetriamine pentaacetate), penicillamine, sodium dimercaptopropane sulfonate, etc. And the test drug apple pectin, pineapple skin extract. The use of integrated Chinese and Western medicine and a variety of comprehensive therapy and Chinese medicine to drive lead, such as licorice mung bean soup, etc., also has a satisfactory effect. For acute poisoning abdominal cramps, in addition to lead-extraction therapy, intravenous injection of 10% calcium gluconate 10-20mL, intramuscular injection of atropine 0.5 ~ 1mg.

Injection with a chemical concealing agent, ethylenediaminetetraacetic acid (EDTA), a calcium salt Na ₂ [Ca(edta)] solution, can partially treat lead poisoning. This is because [edta) ^{4 - which} is decomposed by [Ca(edta)] ^{2 -} complex ions, can complex with Pb ^{2 +} in the human body, and is much more stable than [Ca(edta)] ^{2 -} [Pb (edta) )] ^{2 -} complex ions, and excreted from the human body.

The prevention of lead poisoning should be based on prevention. Since the lead poisoning in metallurgical plants is mainly from flue gas and soot containing lead oxide, and lead-containing wastewater discharged from hydrometallurgy, the main preventive measures are:

For pyrometallurgical products such as flue gas and soot containing lead oxide, dust removal and ventilation air purification measures are mainly adopted. According to the specific circumstances, it can be closed, ventilated, humidified, and dry and wet dust collection measures, or improve and simplify the process, to achieve production operation sealing, mechanization and automation, as well as harmful gas, liquid transportation pipeline, etc. Reduce operator exposure to lead poisoning. Strengthen labor protection and do a good job in personal hygiene. The floor and walls of the plant should be smooth and flat to facilitate the removal of soot. The workshop is equipped with shower and flushing water facilities to wash your face, wash your hands, rinse your mouth and eat and smoke in a special sanitation area. Work clothes contaminated with lead dust should be placed in a special closet and separated from clean work clothes. Operators should be regularly educated about the safety of lead poisoning and regular health checkups and medical custody. When it is found that the lead content of the operator exceeds the standard, administrative measures should be taken to reduce the operator's exposure to lead poisoning, medical observation and review, and if necessary, should be removed from the lead poisoning area.

The treatment of lead-containing wastewater is mostly carried out by the neutralization method and the adsorption precipitation method and then returned to the operation process. Factory output lead 6 ~ 20mg / L, arsenic 1.5 ~ 13mg / L, lead, arsenic wastewater pH6 ~ 7, and after stirring for an appropriate amount of added ferric chloride and lime milk, and the precipitate was extracted After the supernatant is filtered through the sand layer, the lead is reduced to 0.1-0.3 mg ∕L, and the arsenic is reduced to 0.03-0.08 mg ∕L. The treated wastewater is returned to the production process for use.

Sweden's "Environmental Research and Management" in the first issue of 1979 reported the National Aerospace Technology Laboratory of the National Aeronautics and Space Administration of the United States, using water hyacinth biological purification method to treat daily sewage and industrial wastewater, and achieved certain results. It has been listed by the experiment as one of the permanent facilities for treating wastewater.

Water hyacinth scientific name. It is native to Venezuela and has been passed to more than 50 countries including China. It is one of the commonly used pig green feeds in China. Because the water hyacinth has a particularly strong fecundity, at a suitable temperature, 10 water hyacinths can reproduce 600,000 trees in 8 months, and can cover a total of about 40.47 acres (one acre) of water. Water hyacinth also has a particularly strong vitality. There are no insects, viruses and natural enemies that harm its growth. Many organic substances and heavy metals cannot poison it.

Water hyacinth purifies sewage and industrial wastewater, relying mainly on its large root system to absorb substances in the water. Tests have shown that 1 kg of water hyacinth can remove 36.4 g of phenol in 72 h; remove 281 mg of chlorfenapyr in 48 h; remove 258 mg of organic sludge in 7 d. In the purification test of industrial toxic chemical wastewater, the roots of a group of water hyacinths were determined to contain 594 mg ∕kg, lead 297 mg ∕kg, silver 113 mg ∕kg, chromium 286 mg ∕kg, cadmium 164 mg ∕kg, and a large amount of mercury and nickel. Wait. This group of water hyacinths absorbed such multiple metals and did not show any signs of poisoning.

After the water hyacinth biological purification tank of the National Aerospace Technology Laboratory of the United States was put into production, they regularly harvested the water hyacinth that had reached saturation and processed it in a special basement. This basement prevents heavy metals from decaying plants from penetrating into the groundwater.

The harvested saturated plants can also be fermented by the fermentation tank to produce biogas for energy supply, and the valuable metals are recovered during the treatment.

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