Three Waste Treatment and Radioactive Protection in Rare Earth Production Process - Overview
Outside the production process and the complexity of the diversity of the mineral composition, the rare earth metallurgical production process in addition to producing various forms of rare earth products, will be accompanied by a certain amount of "waste", i.e. gas, waste water and waste.
The exhaust gas produced in rare earth production mainly contains dusty gas and poisonous gas. Dust-containing gas sometimes has radioactive elements such as uranium and thorium , which may cause various pneumoconiosis or radioactive diseases in such a dust environment for a long time; the main harmful substances of toxic gases are HF, SiaF 4 , SO 2 and Cl 2 . Aerosols (fogs) of various acid and alkali solutions, volatiles of organic extractants and their solvents, etc. Most of the water-soluble gases of these components have a greater stimulating effect on the conjunctiva of the eyeball and the mucous membrane of the respiratory system. High concentration inhalation or long-term low concentration inhalation can cause diseases such as throat, tracheitis, pneumonia, and pulmonary edema.
The harmful components of wastewater are mainly suspended solids, acids, alkalis, fluorides, radioactive elements (uranium, thorium, radium), various inorganic salts and organic solvents. If such wastewater is directly discharged, in addition to radioactive pollution, it will also cause Soil acid-base imbalance, depletion and even salinization lead to deterioration of water quality and even extinction of aquatic organisms. For example, in the land after fluoride pollution, fluorine will enter the livestock and human body through pasture or crops, and long-term accumulation will lead to osteoporosis and bone hardening.
The waste slag is mainly tailings produced by beneficiation , smelting slag produced by pyrometallurgical smelting, insoluble slag after decomposition of concentrate, sediment slag of wet smelting, dust accumulation in dust removal system, and sediment slag after wastewater treatment. These wastes often contain radioactive elements.
It can be seen that the three wastes produced in the production of rare earths often contain substances that are harmful to living things and their living environment, and even include radioactive waste. In order to prevent the environmental pollution of such wastes, protect the natural environment on which people depend for survival, and maintain ecological balance, the “three wastes†generated in the production process must be treated to meet the prescribed sanitary standards before they can be discharged into the natural world.
The so-called health standard refers to the limit that the poison in the production environment does not cause harmful effects to humans. For our industrial waste water, waste gas, waste emissions, have been clearly defined, such as the 1974 trial of China's "industrial" three wastes "trial standards" GBJ 4 - 73, 1974 Nian Wuyue issued a "radiological protection provisions" GBJ 8 - 74, 1985 promulgated the "non-ferrous metals industrial solid waste pollution control standards" GB5085-85, etc. these standards are published in a legal form. With the continuous improvement of environmental protection requirements and the continuous advancement of science and technology, the “three wastes†emission standards for industrial production are constantly being revised and the requirements are higher and stricter. For example, from January 1, 1997, the "Integrated Emission Standard for Air Pollutants" GB16297-1996 has replaced the exhaust gases in various industrial pollutant discharge standards such as GB 4911-85, GB 4912-85, and GB 4913-85. section.
In addition to the discharge standards for the three wastes, there are also strict requirements on the working environment of the production workers to ensure the health of the workers engaged in production. Table 1 lists the hygienic standards for hazardous substances in the air of the workshop related to the production of rare earths [1 , 2 to 6 ] .
Table 1 Maximum allowable concentration of harmful substances in the air of the production workshop (partial)
Hazardous substance name | Maximum allowable concentration | Hazardous substance name | Maximum allowable concentration |
Carbon monoxide Sulfur dioxide Caustic (converted to NaOH) Sodium carbonate Hydrogen fluoride and fluoride (in terms of fluorine) ammonia Sulfuric acid and sulfur trioxide | 30mg/m3 15 mg/m3 0.5 mg/m3 6 mg/m3 1 mg/m3 30 mg/m3 2 mg/m3 | chlorine Hydrogen chloride and hydrochloric acid oxalic acid Solvent gasoline Dust containing more than 80% free silica Rare earth dust with free silica content below 10% Other dust | 1 mg/m3 15 mg/m3 2 mg/m3 300 mg/m3 1 mg/m3 5 mg/m3 10 mg/m3 |
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The maximum allowable concentration of hazardous substances in the table refers to the value that should not be exceeded in the air of workers at the workplace. The workplace is the location where workers are often or regularly stopped to observe and manage the production process. If the production operation is carried out in many different locations in the workshop, the entire workshop is counted as the work location. The maximum allowable concentration of a poison is not always constant. As people's understanding of poisons deepens, a richer practical experiment is summarized, and the standards will be revised more rationally at any time.
Therefore, understanding the harm of the three wastes to people and the natural environment is of great significance to the personnel engaged in the management, technology and production of the metallurgical industry in strengthening occupational health awareness and environmental awareness. It should be pointed out that for the treatment of the three wastes, we must earnestly implement the principle of "comprehensive planning, rational distribution, comprehensive utilization, turning harm into profit, relying on the masses, doing everything, protecting the environment and benefiting the people", and actively exploring and adopting new comprehensive management of the three wastes. Technology and new processes not only make harmless and harmless, but also recycle the useful ingredients in the treatment of the three wastes, turning waste into treasure.
The treatment of the three wastes should be specifically designed for its source, composition and emission requirements. This chapter will mainly describe the production process, composition and conventional treatment methods of the three wastes in the production of rare earths, and give a general introduction to the knowledge of radioactive protection.
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