Heavy Metal Pollution Prevention and Control
The Chinese government attaches great importance to the issue of heavy metal pollution. In the recent years, the State Council, the National Development and Reform Commission, and the State Environmental Protection Department continued to promulgate a series of policies and documents to strictly prevent and control heavy metal pollution. China’s “National Medium and Long-TermScientific and Technological Development Plan (2006-2020)” is focused on technologies that are related to the following: unconventional pollutant control; waste utilization; integrated product cleaning technology for pollution-intensive industries; demonstration model for establishing a circular economy. The “Non-Ferrous Metal industries Medium and Long-Term Scientific and Development Plan (2006-2020)” will also promote the important research of technologies for recycling zinc and lead from EAFD/BFD.
Lead is a toxic metal element that can accumulate in human and animal tissues and is commonly found in paint, coating, batteries, smelting waste, hardware, machinery, electroplating waste, cosmetics, hair dyes, glazed dishes, cutleries, coal, puffed food, water pipes, and so on. It enters the human body through the skin, digestive, or respiratory tract and accumulates in the internal organs. The main toxic effects of lead include anemia, neurological disorders, and kidney damage. Lead toxicity is more harmful to sensitive groups, such as children, the elderly, and immune compromised patients. The safe concentration levels of lead for aquatic organisms is defined at 0.16 mg/L. When the concentration of lead is between 0.1~4.4 mg/L in the irrigation system for rice and wheat, the lead content in crops increases significantly. The human body’s normal lead intake should not exceed 0.1 mg/L. If lead is consumed in excess, it can lead to anemia or damage the nervous system. For children, the damage will be much more serious than in adults. If lead is consumed in excess, detoxification measures should be taken immediately. Children may undergo chelation therapy to remove excessive lead.
Cadmium is not an essential element for the human. It is highly toxic and can accumulate in the human body, mainly in the kidneys, thus affecting the urinary system. Major causes of cadmium pollution include electroplating waste, mining, smelting waste, fuel, batteries, and wastewater from chemical processing. The concentration of cadmium is higher in old batteries. Cadmium also exists in fruits and vegetables, especially mushrooms, and in small amounts in dairy and cereal products. Cadmium can replace calcium in bones, causing it to be extremely fragile or even break. It can also cause gastric dysfunctions by affecting the zinc enzyme system in humans and any other living organisms, resulting in increased hypertension. Vulnerable groups include miners and immuno compromised patients. When the concentration of cadmium in water is 0.1 mg/L, it can mildly suppress the self-purification of groundwater. Safe concentrations of cadmium are defined at 0.014 mg/L. When the concentration of cadmium is 0.04 mg/L in irrigation water, soil and rice will be significantly polluted, while at 0.007 mg/L, it may also cause pollution. The normal concentration of cadmium in human blood is less than 5 mcg/L and is less than 1 mcg/L in urine.
Mercury and its compounds are highly toxic and can accumulate in the human body. Major causes of mercury pollution include instrument manufacturing, salt electrolysis, rare metals smelting, cosmetics, lightings and lamps, dental materials, fuel, and aquatic organism. Mercury in the bloodstream will accumulate in the brain, causing serious brain damage once it reaches a certain concentration. Meanwhile, mercury ions can affect the kidneys. Once the mercury has entered the human body through the food chain, inorganic mercury ions can be transformed into the even more toxic organic mercury. Vulnerable groups include women, especially pregnant mothers, and those who eat a lot of seafood. Mercury concentration exists in natural water bodies at very low concentrations, normally no more than 0.1 μg/L. The mercury content in a normal human blood should be less than 5-10 mcg/L and less than 20 mcg/L in urine. Incase of acute mercury poisoning, hepatitis and hematuria are likely to be developed.
The arsenic is nonessential to the human body. The toxicity of the element, arsenic, is rather low, while arsenic compounds are extremely toxic. Trivalent arsenic compounds are the most toxic of all arsenic compounds. Arsenic enters the body through the respiratory tract, digestive tract, and skin contact. If the intake of arsenic exceeds the excretion of it, arsenic will accumulate in the liver, kidney, lungs, uterus, placenta, bones, muscles, and other parts of the body, combining itself with enzymes and directly causing the enzyme to lose its ability for biological activity. Arsenic typically accumulates in hair or nails, which will cause chronic arsenic poisoning, leading to digestive, neurological, and skin diseases. The incubation period may be from several years up to a few decades. Arsenic is carcinogenic and can cause skin cancer. Under normal circumstances, arsenic exists in trace amounts in the soil, water, air, plants, and humans, which is not harmful. The main source of arsenic pollution is the mining, smelting, pharmaceutical, bleaching agents used by the glass industry, pesticides, rodenticides, arsenate drugs, fertilizers, and hard alloy. Vulnerable groups include farmers, housewives, and specific workers from the aforementioned industries. The arsenic content in surface water varies greatly based on different water sources and geographical conditions. Freshwater can have a concentration of 0.2 to 230 μm/L with an average of 0.5 μm/L, while in the ocean concentrations may be 3.7 μm/L. If the arsenic concentration exceeds 100 mcg/L in urine within 24 hours, neurological disorders will occur and may even cause cancer. Excessive arsenic may cause malformations in babies.
Chromium is mainly found in raw materials for cosmetics, tanning, rubber and ceramics, as well as leather preparation, metallic parts of chrome and industrial pigments. If accidentally ingested, it may cause abdominal discomfort and diarrhea, atopic dermatitis, oreczema. If inhaled, it will cause respiratory irritation and corrosion, leading to pharyngitis and bronchitis. Residents with serious chromium pollution in their water sources that are frequently exposed to or excessively intake chromium may develop rhinitis, tuberculosis, diarrhea, bronchitis, anddermatitis.
Refers to the environmental pollution caused by copper (Cu) and its compounds. The main source of this type of pollution is the mining of copper and zinc, as well as smelting, metal processing, machinery, and steel manufacturing. Smoke released from smelting are the main cause of copper pollution.
Refers to the pollution caused by nickel and its compounds. During the process of smelting nickel ore and steel, some nickel dust will enter the atmosphere. During the calcination process, nickel and its compounds are released into the air, mainly as water-insoluble nickel sulfide (NiS), nickel oxide (NiO) and metallic nickel dust. Nickel smoke from calcination reacts with hot carbon monoxide to form a volatile, highly toxic, and carcinogenic carbonyl nickel [Ni (CO)4]. Workers in the nickel refining industry have a higher chance of suffering from nasal and lung cancer. Nickel is often found in wastewater from the nickel plating, machinery manufacturing, and metal processing industries. The wastewater is treated with alkali to remove nickel hydroxide [Ni(OH)2]. Large nickel compounds particles in the at mosphere settle onto the ground over time as particulate sedimentation, increasing the concentration of nickel in the soil. Additionally, the irrigation of nickel-containing wastewater, decaying of animal and plant residues, and rock weathering also increases the concentration of nickel in the ground. Growing plants will then absorb nickel from the soil, with green vegetables and tobacco containing the highest concentration of nickel, up to 1.5 to 3 ppm. The critical concentration of nickel in rice is 20 ppm, while the maximum allowable concentration of carbonyl nickel in the atmosphere surrounding workshops is 0.001 mg/m3. The maximum allowable concentration of nickel in surface water is 0.5 mg/L.
Refers to the pollution caused by zinc and its compounds. Main pollution sources are from the zinc mining, metallurgy processing, machinery and instrument manufacturing, organic synthesis, and paper making industries. The dust that arises from the friction of car tires and coal combustion also contains zinc and zinc compounds. Meanwhile, zinc can often exist in industrial wastewater as a hydroxyl complex.
As the world’s largest steel producing country, the steel industry in China has been developing rapidly in the recent years, ranking first in the world for 14 consecutive years. However, the steel industry produces a large amount of waste each year, generating an annual volume of about 203 million tons with comprehensive utilization rate is 40.7%, posing a heavy burden to society. The solid waste produced by the steel industry including iron-containing slag, which is the most diverse and complex among all the solid waste produced by the steel industry. It is the solid waste left behind after undergoing dry and wet processing for dust removal and wastewater treatment. These include sintering dust mud, pellet dust, blast furnace dust, blast furnace sludge, steel dust, converter sludge, and electric furnace dust. The main components of steel dust are iron minerals, iron oxides, CaO, MgO, SiO2, Al2O3, Pb, Zn, Bi, Cr, Ni, and so on. Blast furnace iron smelting dust (gas sludge and ash) is one of the main solid waste produced by the steel industry. In a blast furnace smelting process, impurities from iron ore like zinc and lead are reduced to the form of steam, and removed by the blast furnace along with other fine dust like ore, coke, and flux, then captured by a blast furnace dust removal system, forming steel dust. According to statistics, the output rate of blast furnace smoke is about 1.5-2.0% of pig iron production, and the annual output from China is about 9-12 million tons.
Heavy Metal Pollution
It is known that any substance containing heavy metal can cause serious pollution if it enters the atmosphere, water, or soil. In China, heavy metals like lead, zinc, and cadmium from steel dust are causing serious environmental threats to its soil and groundwater. According to statistics, in the year 2009, ⅙ of cultivated land are at risk of heavy metal pollution. The government places great importance and concern over heavy metal pollution issues. Once the heavy metal substances enter the atmosphere, water, or soil, it will cause severe environmental pollution.
Heavy metals exist in various chemicals or chemical forms. They usually persist, accumulate, and migrate once released into the environment, and are very harmful. In recent years, heavy metal pollution incidents in China are no longer rare cases. According to statistics provided by the Ministry of Environmental Protection in 2009, 4035 people were overloaded with lead in their blood, 182 people overloaded with cadmium, causing 32 mass incidents. Heavy metal pollution has posed a tremendous threat to the people’s lives. Meanwhile, statistics in 2009 showed that 1/6 of the country’s agricultural land has been polluted by heavy metals, which includes at least 20 million hectares of soil. Heavy metal pollution brings about serious effects towards economic development, and it threatens all aspect of our lives. Thus, we must address this issue scientifically and try our best to search for a solution.