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A brief overview of key harmful substances emitted in industrial production I. Fluorine (F2) Fluorine is the most reactive element, and it reacts with almost any other element at room temperature. Even gold can burn in fluorine when heated, and it can do so in nature as well when heated; however, elemental fluorine does not exist in nature. Fluorine gas is pale yellow in color and has strong irritancy and corrosiveness. Fluorine pollution in industry mainly appears in the form of hydrogen fluoride and other fluorides. Fluorine is widely distributed in nature, accounting for about two ten-thousandths of the total amount in the Earth’s crust. The heaviest fluorine minerals are fluorite (calcium fluoride, CaF2) and cryolite (Na3AlF6) ； Apatite contains about 3% fluorine, while clays contain approximately 0.02–150 million tons of fluorine; it is the largest source of fluorine in toxic gases and a key focus for air pollution control. It has a density of 2.3, is colorless, non-flammable, and possesses a strong, pungent, suffocating odor. At room temperature, it can be liquefied into a colorless liquid under four atmospheres of pressure. II. Sulfur dioxide: 57% of sulfur dioxide in the environment originates from natural sources; however, due to its dispersion, its concentration is low enough not to cause pollution. 43% comes from human activities such as industrial production, and because the sources are concentrated, the high concentration leads to air pollution. Of the anthropogenic carbon dioxide emissions, coal combustion accounts for about 70%, heavy oil combustion for 16%, the metallurgical industry for about 11%, and the refining industry for about 4%. In cities, coal used for industrial and domestic purposes is the main source of sulfur dioxide. After being emitted through tall chimneys, sulfur dioxide, influenced by wind at an altitude of 1.5 kilometers, will have more than 50% of it reach distances of over 700 kilometers within 24 hours, and it can spread to distances of 1,100 kilometers after 60 hours. Once sulfur dioxide enters the atmosphere, it can remain there for 1 to 2 weeks if the atmosphere is dry and clean ； If the atmosphere is polluted or humid, it converts into sulfur trioxide and falls to the ground. When sulfur dioxide remains in the atmosphere, it has a strong irritating effect on the eyes, nose, throat, and respiratory tract ； Harmful to the liver, kidneys, and heart. It can reduce the sense of smell and taste, and cause atrophic rhinitis, chronic bronchitis, conjunctivitis, and gastritis. Acute poisoning can lead to laryngeal edema, pulmonary edema, and even death from asphyxiation. Sulfur dioxide, along with dust and water vapor, constantly poses a threat to the environment. The Donora incident in the United States, the London smog episode in the UK, and the Yokkaichi incident in Japan are all closely related to sulfur dioxide. For people who are particularly sensitive, a sulfur dioxide concentration of 4 mg/l in the air can already be detected. Even a concentration of one part in ten million of sulfur dioxide has a significant effect on crops such as cotton, wheat, and barley. Measures to control sulfur dioxide include: 1. Reducing the sulfur content in fuels used for urban domestic and industrial purposes; where possible, gradually adopt low-sulfur coal, oil, gas, natural gas, or even electricity as a source of energy. 2. Fuel desulfurization. Such as enhancing coal washing and coal liquefaction. 3. Flue gas desulfurization. If the flue gas is washed with lime or limestone ； Using lime or dolomite mixed with coal as boiler fuel, etc. 4. Emission from tall chimneys. 5. Reform the process for comprehensive utilization. For example, sulfuric acid plants use two rotating and two absorbing stages in place of one rotating and one absorbing stage ； Sulfuric acid is produced by recovering high-concentration hydrogen sulfide from non-ferrous metallurgy exhaust gases. Wait. III. Chromium (Cr) Chromium is a metal with a silver-white luster; it is non-toxic and has very stable chemical properties. Stainless steel contains more than 12% chromium. Common chromium compounds include hexavalent chromium anhydride, potassium dichromate, sodium dichromate, potassium chromate, sodium chromate, etc ； Trivalent chromium trioxide (chromium green, Cr2O3) ； Divalent chromium(II) oxide. Among chromium compounds, hexavalent chromium is the most toxic, followed by trivalent chromium. Research shows that chromium is an essential trace element for the life and health of mammals. A lack of chromium can cause atherosclerosis. Adults need 500–700 micrograms of chromium per day, while a regular diet provides only 50–100 micrograms per day. Brown sugar, whole-grain brown rice, unrefined oils, millet, carrots, and peas contain high levels of chromium. Chromium has a stimulating effect on plant growth; trace amounts of chromium can increase plant yields ； However, slightly higher concentrations can inhibit the nitrification of organic matter in the soil. Chromic acid, dichromic acid, and their salts irritate and burn the mucous membranes and skin of humans, causing injuries and contact dermatitis. When these compounds enter the body in the form of vapor or dust, they can cause perforations of the nasal septum, gastrointestinal disorders, a decrease in white blood cells, and lung conditions similar to asthma. Skin contact with chromates can cause \"chromic ulcers\" that heal very slowly; a concentration of anhydrous chromic acid in the air of 0.15–0.31 milligrams per cubic meter can lead to perforations of the nasal septum. Trivalent chromium is also a protein coagulant. Some believe that hexavalent chromium can induce lung cancer. Furthermore, hexavalent chromium, especially chromic acid, has a strong corrosive effect on metal pipes in sewer systems; sodium dichromate at a concentration of 0.31 mg/l can already corrode such pipes. Irrigating plants with wastewater containing 3.4–17.3 mg/l of trivalent chromium can poison all plants. Chromium pollution is mainly caused by industry. Chromium compounds are released in industries such as chromium mining and smelting, the production of chromium salts, electroplating, metal processing, leather manufacturing, paints, pigments, and the printing and dyeing industry. For example, in the leather industry, when processing one ton of raw hides, 50–60 tons of wastewater containing 410 mg/l of chromium are generated ； If 10 tons of raw hides are processed per day, 72–86 tons of chromium will be discharged annually. To prevent chromium pollution, it is necessary to consider reforms to manufacturing processes and comprehensive utilization methods, such as the recovery of chromium mist from electroplating and low-chromium plating ； Production of cast stone, blue bricks, and chromium lignin from chromium slag ； Chromium-plating wastewater is recycled to recover chromium hydroxide, which is then used in processes such as Jinlu. IV. Mercury (Hg) Mercury, also known as quicksilver, is a liquid metal. Specific gravity 13.6, melting point -39.3°C, boiling point 357°C. Mercury can evaporate at room temperature; its vapor is colorless and odorless, and it is seven times denser than air. Both mercury and its compounds are highly toxic, especially the organic compounds of mercury. Fish will become poisoned when living in water with a mercury content of 0.01–0.02 milligrams per liter ； A person can die from poisoning if they consume 0.1 grams of mercury. Mercury and its compounds can enter the human body through various routes such as the respiratory tract, skin, or digestive tract. When mercury enters the body, it accumulates in organs such as the liver, kidneys, brain, heart, and bone marrow, causing neurological poisoning and damage to deep tissues. This leads to symptoms such as fatigue, dizziness, tremors, gum bleeding, hair loss, numbness in the hands and feet, and neurasthenia; in severe cases, mental confusion may occur, followed by violent convulsions that can be fatal. Organic mercury can also enter the placenta, causing congenital mercury poisoning in the fetus, leading to birth defects or dementia. The toxicity of mercury is cumulative, and it often takes several years or even a decade before its effects become apparent. Food chains have a considerable capacity to accumulate mercury. For example, the biomagnification factor for mercury in freshwater fish and phytoplankton is 1,000, in freshwater invertebrates it is 100,000, in marine plants it is 100, and in marine animals it is 200,000. Mercury has a wide range of uses, such as in barometers, pressure gauges, thermometers, mercury vacuum pumps, fluorescent lamps, rectifiers, the production of caustic soda via the mercury process, as a catalyst, in mercuric chloride disinfectants (1/1000 solution of mercurous chloride used to disinfect surgical instruments), in fulminite (mercuric fulminate, an explosive), as pigments (such as cinnabar and vermilion, which are red pigments made from mercury sulfide, as well as in ink), and in pesticides (such as Selegan and Silexan). Mercury is utilized in all these applications. Mercury pollution also comes from these sources. Severe mercury pollution can also occur during the smelting of non-ferrous metals due to mercury content in the ores (such as mercury sulfide). The problem is that waste containing mercury catalysts in the organic synthesis industry (such as mercurous chloride catalysts supported on activated carbon) also poses environmental pollution issues. V. Chlorine (Cl2) Chlorine is a highly irritating yellow-green gas that is 2.43 times heavier than air; it is soluble in water (with a volume ratio of water to chlorine of 1:2.5) and can be easily absorbed by activated carbon. At room temperature and one atmosphere pressure, it liquefies into liquid chlorine, with a specific gravity 1.56 times that of water. Chlorine has a wide range of uses, including water disinfection, pulp bleaching, the production of bromine and bleaching powder (calcium hypochlorite), BHC, rubber, ink pigments, oils, polyvinyl chloride, hydrochloric acid, pesticides, and more. Chlorination processes in the metallurgical industry, as well as the chlor-alkali industry, also result in large amounts of chlorine gas being released. For every ton of liquid chlorine produced, 9.45 kilograms of chlorine are emitted in the case of diaphragm electrolysis, while 18–72.5 kilograms are emitted in the case of mercury electrolysis. People’s stomachs contain 0.5% hydrochloric acid to aid digestion and kill bacteria. Chlorine is a highly reactive element that can combine directly with almost all common metals as well as with all non-metals except carbon, nitrogen, and oxygen (it does not react with iron in an anhydrous environment, which is why liquid chlorine is stored in steel cylinders). Low concentrations of chlorine (hydrogen chloride) in the atmosphere can irritate the eyes, nose, and throat ； Even one ten-thousandth part of chlorine in the air can severely affect human health. Inhalation of chlorine by humans can cause poisoning of the respiratory tract and skin mucous membranes. In mild poisoning, there is a burning and pressing sensation, itching in the throat, difficulty breathing, and stinging and tearing in the eyes. High concentrations of chlorine (hydrogen chloride) can cause chronic poisoning in humans, leading to conditions such as rhinitis, bronchitis, and emphysema; some people may also develop allergies, resulting in dermatitis and eczema. Chlorine is highly volatile; water vapor in the air can react with it to form hydrochloric acid mist and hypochlorous acid, which corrode materials wherever they go and pose a threat to humans as well as plants and animals. Therefore, places where chlorine is produced and used must be strictly managed, process equipment needs to be improved to prevent leaks, and comprehensive utilization of chlorine should be promoted. For chlorine-containing waste gases, when the concentration exceeds 1%, substances such as carbon tetrachloride or sulfur monochloride can be used as absorbents to absorb and concentrate them, followed by desorption for recovery ； Low and high concentrations of chlorine can be treated by absorption using water, alkaline solutions, and ferrous compounds, but attention must be paid to the issue of secondary pollution. VI. Phenols There are a wide variety of phenolic compounds, including phenol, cresol, aminophenol, nitrophenol, naphthol, chlorophenol, etc., among which phenol and cresol cause the most significant pollution. Phenol, also known as carbolic acid, is slightly acidic (corrosive); it can volatilize at room temperature, releasing a distinctive pungent odor, and turns pink in the air. The disinfectant commonly used in hospitals, “Lysol,” is a dilute solution of sodium phenolate. Cresol, also known as coal tar phenol, has similar chemical reactivity and toxicity to phenol, and is often found together with it. Phenols can be divided into monophenols and polyphenols depending on the number of hydroxyl groups directly attached to their aromatic rings ； Based on their volatility, they can be further divided into volatile phenols and non-volatile phenols. Monophenols are generally volatile (with boiling points below 230°C). Phenolic compounds are a type of prototoxin that is toxic to all living organisms. It can coagulate proteins, thus having a strong bactericidal effect. Its aqueous solution can easily cause systemic poisoning through the skin ； Its vapor, inhaled through the respiratory tract, causes greater damage to the nervous system. Prolonged inhalation of vaporized phenol or exposure to water contaminated with phenol can cause chronic cumulative poisoning ； Inhalation of high concentrations of phenol vapor or liquid, or exposure of the skin to large amounts of phenol liquid, can cause acute poisoning. If not rescued in time, death can occur within three to eight hours due to paralysis of the nervous center. Chronic phenol poisoning in its disabled form is commonly accompanied by vomiting, diarrhea, loss of appetite, dizziness, anemia, and various neurological disorders. Phenols are toxic to aquatic organisms, non-germinating microorganisms, and crops. When the phenol content in water is 0.1–0.2 mg/L, the fish meat still has an unpleasant odor but remains edible ； At levels of 6.5–9.3 mg/L, it can damage the gills and pharynx of fish, causing internal bleeding in their abdominal cavity, spleen enlargement, and even death. Direct irrigation with wastewater containing a phenol concentration above 100 mg/L can cause crop death and reduced yields. The oral lethal dose for humans of phenol is 530 mg/kg body weight. Industries such as phenol production, coking, oil refining, metallurgy, plastics, chemical fibers, insulating materials, phenolic resins, pharmaceuticals, **, pesticides, and so on all generate wastewater containing high concentrations of phenols. For example, for every ton of coke produced, 0.2 to 0.3 cubic meters of phenol-containing wastewater are generated. The approaches to dealing with phenol-containing wastewater are, first, to modify the processing processes in order to reduce the phenol concentration in the wastewater, or to recycle water in order to decrease the amount of wastewater generated and increase the phenol concentration in it, thereby facilitating recovery ； The second is recycling and treatment, with the main methods including extraction, adsorption, steam stripping, ion exchange, chemical precipitation, chemical oxidation, reverse osmosis, and biochemical treatment. Generally speaking, for wastewater with a phenol concentration of 1000 mg/L or higher, phenol recovery should be considered first, followed by destruction treatment to achieve harmless discharge. If the phenol concentration is below this level, harmless treatment must be carried out. VII. Cyanides Cyanides include cyanogen, hydrocyanic acid, sodium cyanide, potassium cyanide, ammonium cyanide, and nitriles – all of which are highly toxic! Inorganic cyanides release hydrogen cyanide when exposed to acid. Hydrocyanic acid has a specific gravity of 0.687; it is a colorless and transparent liquid with a bitter almond odor, a melting point of –14°C, a boiling point of 25.6°C, and is highly volatile. Cyanides can cause poisoning when they enter the body or come into contact with it (especially through skin wounds). In mild cases, there are headaches, dizziness, and difficulty breathing; in severe cases, there is loss of consciousness, convulsions, a drop in blood pressure, and even sudden death within two to three minutes without any warning signs. Those who have been cured from cyanide poisoning cannot suffer from any neurological sequelae such as headaches, paralysis, aphasia, epilepsy, etc. The lethal dose of hydrocyanic acid for humans is 0.06 grams, that of sodium cyanide is 0.1 gram, and that of potassium cyanide is 0.12 grams. Cyanide is highly toxic to fish; fish can die when the cyanide concentration in water is between 0.04 and 0.1 ppm. Cyanide-containing wastewater and waste gas mainly originate from industrial sectors such as electroplating, coking, metallurgy, mineral processing, chemical fibers, pharmaceuticals, plexiglass, plastics, and gas production. The main measures to eliminate its hazards are: 1. Reform the process. Such as cyanide-free or low-cyanide electroplating ； Cyanide-free mineral processing for ore processing. 2. Recycling. Recovering cyanide using methods such as evaporation concentration, ion exchange, and acid volatilization, 3. wastewater treatment. The main methods include electrolysis, oxidation, stripping and absorption, biochemical treatment, chemical treatment, etc., to destroy cyanide ions. By adding liquid chlorine, sodium hypochlorite, or bleaching powder to the waste stream, cyanide can be converted into carbon dioxide and nitrogen. Generally, activated sludge aeration tanks can be used when the cyanide concentration is less than 20 mg/L, while biological filters are suitable for concentrations between 20 and 40 mg/L, and so on. VIII. Cadmium (Cd) Cadmium is a highly toxic heavy metal, and most of its compounds are also toxic. Cadmium has a wide range of uses; it is employed in cadmium salts, cadmium vapor lamps, pigments, smoke bombs, alloys, electroplating, soldering fluxes, standard batteries, metallurgical deoxidizers, and neutron absorbers in nuclear reactors. For example, the pigment cadmium red is composed of cadmium sulfide, cadmium selenide, and barium sulfate ； Cadmium yellow is composed of cadmium sulfide and barium sulfate. Cadmium is quite rare in nature, often occurring alongside lead sulfide and zinc ores, particularly sphalerite (ZnS). The mining and smelting of metal ores, electroplating, and pigments are the main human-induced sources of cadmium pollution. Cadmium content in coarse phosphate fertilizers can reach 100 milligrams per kilogram, while that in ordinary calcium fertilizers can range from 50 to 170 milligrams per kilogram ； Cadmium is also present in vehicle exhaust. Data show that the cadmium content in the soil and grass along heavily trafficked roads is significantly higher near the roads than further away. Tobacco also contains a certain amount of cadmium. The world-shocking Japanese phenomenon of \"it hurts, it hurts\" was caused by cadmium pollution. Cadmium-containing mine wastewater contaminates river water as well as the soil and crops along the riverbanks; it enters the human body through the food chain and gradually accumulates in the kidneys and bones. It will replace the calcium in bones, causing severe softening of the bones and leading to them breaking ； Cadmium can cause gastric dysfunction, disrupt the zinc-related enzyme systems in humans and organisms, reduce the zinc-cadmium ratio, and thereby lead to an increase in hypertension. Cadmium toxicity is potential. Even at concentrations as low as 0.1 milligrams per liter in drinking water, cadmium can accumulate in human tissues (especially in women), with an incubation period of up to ten to thirty years, and it is not easily detectable in the early stages. Data indicate that the biological half-life of cadmium in the human body is 20 to 40 years. The toxicity of cadmium to human tissues and organs is multifaceted, and treatment is extremely difficult. Therefore, countries have established extremely strict regulations on cadmium in the \"three wastes\" generated by industrial activities. Japan also stipulates that rice with a cadmium content of over 1 milligram per kilogram is considered \"cadmium-contaminated rice\" and its consumption is prohibited. The Japanese Environment Agency has set 0.3 ppm as the maximum acceptable level of cadmium in rice. Since cadmium compounds exhibit varying degrees of toxicity, any method used to remove cadmium from wastewater can only change its form of existence and its location, but it cannot eliminate its toxicity. Therefore, the treatment of cadmium wastewater should be combined with recycling as much as possible. IX. Arsenic (As): Arsenic and its soluble compounds are highly toxic. For example, arsenic trioxide is what is known as white arsenic. In nature, it mainly exists in the form of compounds, occasionally as a pure element; examples include pyrithion (FeAsS), orpiment (As2S2), and realgar (As2S3). Many non-ferrous metal ores contain arsenides; therefore, during the processing of these metals (such as ore roasting), arsenides (such as white arsenic) are released. The average arsenic content in coal can reach 25 milligrams per kilogram; therefore, the burning of coal can raise the arsenic concentration in the surrounding air to 0.02 micrograms per cubic meter. Arsenides are commonly used in the manufacture of cemented carbides (such as 35% arsenic added to lead bullets), arsenate-based drugs, pesticides, and rodenticides (usually arsenic acids or arsenites), as well as as decolorants in the glass industry, depilatories and preservatives in the fur industry. Therefore, industries such as metallurgy, sulfuric acid, fertilizers, leather, and pesticides are all affected by arsenic pollution. Arsenic can enter the human body through breathing, skin contact, diet, and other means. Arsenic can bind to the thiol groups in proteins and enzymes, inhibiting many biochemical processes in the body. In particular, by binding to the thiol groups of pyruvate oxidase, it renders this enzyme inactive, leading to severe disruptions in cellular metabolism. The toxic dose of arsenic for humans is 0.01–0.052 grams, while the lethal dose is 0.06–0.2 grams. The symptoms of acute arsenic poisoning include a burning sensation in the throat, esophagus, and gastrointestinal tract, diarrhea, abdominal pain, headache, nausea, vomiting, thirst, cyanosis of the face, and a rapid drop in blood pressure; in severe cases, death can occur quickly. The effects of arsenic poisoning are also cumulative, as it can accumulate in areas affected by osteoporosis, as well as in the kidneys, liver, spleen, muscles, and keratinized tissues such as hair, skin, and nails. In recent years, it has also been found that among workers who are frequently exposed to arsenic-containing substances, the incidence of skin cancer and lung cancer is higher than in other industries ； Skin ulcers and nasal septum perforations are more common. Arsenic-containing waste gas should be subject to strict smoke and dust removal measures and recovered in the flue. Arsenic-containing waste is generally treated by adding lime, ferrous sulfate, and liquid chlorine (or bleaching powder) to precipitate the arsenic, followed by the treatment of the resulting sludge. The efficiency of various methods in removing arsenic from drinking water is as follows: lime softening can remove 85%, charcoal filtration 70%, iron sulfide filters 94%, ferric sulfate coagulation over 80%, ferric chloride coagulation over 98%, and iron hydroxide precipitation 94–96%. In cases of arsenic poisoning resulting from accidental ingestion by humans or animals, detoxification can be achieved by administering a fresh suspension of iron hydroxide, produced by vigorously mixing magnesium oxide with ferrous sulfate solution. X. Soot and dust: Apart from the dust generated in industrial processes, soot and dust are primarily products of fuel combustion. The smoke emission from industrial coal is roughly 3–18% of the weight burned, 11% for lignite, and 8–9% for anthracite. For the same ton of coal, residents generate 2 to 3 times more dust than industries do. Soot generally contains toxic gases such as oxides of sulfur, nitrogen, and carbon, as well as dust. Dust particles larger than ten micrometers will quickly settle to the ground, a phenomenon known as dust deposition ； Particles smaller than ten micrometers are known as aerosols; a significant portion of these are even smaller than bacteria, and they can remain suspended in the atmosphere for hours, or even days or years. In particular, aerosols with a diameter of 0.5 to 5 micrometers cannot be trapped by human nasal hairs or removed by respiratory mucous membranes; they can reach the alveoli directly and be carried throughout the body via the blood. Some of these airborne particles also contain benzo(a)pyrene, or they are themselves compounds of toxic metals such as chromium, beryllium, and nickel, as well as asbestos and arsenides, which can cause cancer. After entering the human body through the respiratory tract, half of these tiny dust particles adhere to lung cells, and they are a major cause of respiratory diseases in humans as well as in animals and plants. Dust can also reduce sunlight and visibility, absorbing the ultraviolet portion of sunlight that is harmful to humans, thereby increasing the incidence of rickets in children. The main measures to prevent and control smoke and dust pollution are: 1. Changing the fuel composition and combustion method. By replacing coal with pollution-free or low-pollution fuels (natural gas, city gas, refinery gas, or other energy sources such as solar, biogas, wind, tidal energy, etc.) ； Technical reforms are being implemented in existing furnaces and kilns. 2. Centralized district heating; large coal-fired power plants provide both heat and electricity, using centralized, high-efficiency boilers in place of decentralized, low-efficiency ones ； 3. Adopt various methods for removing smoke and dust. Wait. XI. Fly ash: The ash collected from the chimneys of coal-fired boilers is known as fly ash. Many thermal power plants discharge fly ash together with the sludge at the bottom of the boiler, namely fly ash slag. China’s thermal power plants emit nearly 40 million tons of fly ash and slag each year, representing an important source of pollution. It not only occupies a large amount of land, but also often discharges into rivers, causing siltation in the waterways and deteriorating the quality of the water. The main components of coal ash are silicates, aluminosilicates, silica, sulfates, etc., and it also contains a relatively high amount of iron. It does not possess hydraulic cementing properties on its own, but after being ground, it can react chemically with substances such as lime in the presence of water to form compounds with hydraulic cementing properties. Therefore, fly ash has a wide range of applications, mainly in the production of building materials. Many Western countries oppose the use of ash and slag resources as part of national policy; the United States even ranks ash and slag as the seventh type of mineral resource, with 24.1% of it (approximately 16.41 million tons) being sold as a commodity by 1978. Our country has also recently established **standards for fly ash cement, classifying it as an official product. Fly ash can also be used as an active admixture in cement, an additive in concrete, sintered fly ash granules (artificial aggregates), masonry cement (mortar cement), and materials for filling and road construction. The comprehensive utilization of fly ash requires a unified understanding among sectors such as electricity, building materials, construction, and environmental protection, in order to develop an industry for the utilization of fly ash and slag in China. By advancing dust removal technologies and dry ash discharge techniques in coal-fired power plants, as well as by promoting the resourceization of waste materials, the transformation of these materials into useful products, and the development of standardized product lines, it is possible to address the issues related to the pollution caused by fly ash and its effective utilization. XII. Pyrite slag, also known as roasting slag, is produced during the production of sulfuric acid when pyrite is roasted. Generally, about 7,000 tons of pyrite slag are produced for every 10,000 tons of sulfuric acid manufactured. Since there is still residual sulfur in the slag, discharging it into water bodies will cause severe acidification, corroding bridges and ships. The iron content in the slag is generally between 40% and 45%; after magnetic and gravity separation, this figure can be increased to 50% to 60% (with simultaneous desulfurization). It constitutes an excellent raw material for iron production – approximately 4,000 tons of iron-making material can be obtained from each 10,000 tons of pyrite slag. The residue left after separation can also be used by cement factories. In addition, the slag contains various valuable metals, so comprehensive utilization should be considered. It is worth noting that at present, in our province, most of the slag generated is not processed, with only a portion being used by cement factories. 13. Steel slag, blast furnace slag: 0.75 tons of blast furnace slag are generated for every ton of pig iron produced (in foreign countries, this amount has been reduced to 0.3 tons due to improvements in blast furnaces, their larger size, and higher grades of ore) ； For every ton of steel produced, 0.25 tons of slag are generated. The chemical composition of blast furnace slag is similar to that of cement; it has relatively stable reactivity, good wear resistance, hydration properties, and water absorption capacity. The water quenching process is well-established, making it easy to process, and its recycling is cost-effective. At present, the utilization rate of blast furnace slag in our country reaches 60 percent. Steel slag is hard, large in size, and difficult to break; moreover, the water quenching technology is not very advanced, making it hard to utilize. Blast furnace slag is generally used to produce slag cement, slag phosphate fertilizer, cast stone, slag fibers, microcrystalline glass, and so on. In basic ironmaking furnaces (such as Thomas furnaces), the steel slag, after water quenching, forms small particles of steel within it, which can be recovered through magnetic separation. Use the residual slag to produce phosphatic fertilizers and cement (whose cost is only half that of ordinary cement). Steel slag phosphate fertilizer contains phosphorus and various trace elements; it is suitable for acidic soils, can improve soil quality, and can also be used as an additive in beverages. Its effective phosphorus pentoxide content ranges from 14% to 18%. Abroad, research on the utilization of steel slag focuses on quenching it in water right at the furnace, to facilitate its granulation first ； Or the large-area layered slag breaking method (hot pouring method) can be employed. Generally, steel slag is returned to sinter or directly used in blast furnaces as a substitute for limestone as a fluxing agent. 14. Radioactive substances: The unstable atomic nuclei of certain elements undergo decay, emitting rays such as alpha (α), beta (β), and gamma (γ) – which are forms of energy – while transforming into new atoms. Such unstable elements are known as radioactive elements, and they can be natural (such as actinium, thorium, uranium, etc.) or artificial (such as plutonium, americium, curium, etc.). Substances containing radioactive elements, namely radioactive materials, hold extreme value in various fields such as industry, agriculture, medicine, and national defense. But it enters the human body through air, food, and other means, and harms human health through internal or external exposure. When the human body is exposed to radiation, mild symptoms include dizziness, fatigue, hair loss, red patches on the skin, decreased or increased white blood cell counts, and reduced platelet counts ； High-dose exposure can also cause leukemia as well as cancers of the bones, lungs, and thyroid, and even death; radiation can also lead to gene mutations and chromosomal abnormalities. Different types of radiation also pose varying levels of harm to humans; for example, radioactive substances in the form of sigma particles cause severe radiation damage to the tissues they come into contact with ； And gamma rays mainly cause harm due to external radiation ； The penetrating power of beta rays lies between the two; it can cause external radiation burns and skin damage, as well as induce internal radiation injury by penetrating through outer tissues.