In order to protect the safety and hygiene of production personnel and to avoid contamination of the production environment and the natural environment, the disposal of radioactive waste must comply with the national sanitary standards.
According to the "Radiation Protection Regulations" GB 8703-88, tailings sand and waste ore and related solid waste containing natural radionuclides should be built and stored when the specific strength is (2 ~ 7) × 10 4 Bq / kg. It should be properly managed to prevent resuspension and spread of pollutants. For wastes with a specific strength greater than 7×104 Bq/kg, stocks should be built.
In accordance with the Provisions for the Temporary Storage of Low-Level Level Radioactive Solid Wastes, GB 11928-89, the transportation of radioactive solid waste must use special vehicles with certain safety measures and radiological protection requirements, and implement the provisions for the safe transportation of national radioactive materials.
For radioactive solid waste, the treatment and disposal methods used for different levels of radioactivity are also different. Generally can be divided into two types of storage and curing methods. The curing method is generally suitable for treating waste slag with high radioactivity level, small amount and no recycling value. For the solid waste generated in the production of rare earths, due to its large amount and low radioactive level, it is often treated by storage.
 Storage and disposal of radioactive solid waste
It can also be seen from the Regulations on Radiation Protection GB 8703-88 that depending on the level of radioactivity, the treatment of radioactive solid waste can be divided into two types, namely, dam stacking and construction of stocks.
(1) slag dam (or slag yard) stacked apparent from Table 10-5, the output of the rare earth beneficiation tailings, rare earth smelting slag generated in the alloy, acid method of handling mixed rare earth concentrate containing uniformly slag flooding A certain amount of radioactive elements of thorium and uranium are not high in radioactivity. They are non-radioactive waste residues, but they cannot be stacked at random to prevent secondary diffusion from polluting the environment. A large amount of leaching slag generated in the treatment of ionic rare earth ore is a non-radioactive slag, but it cannot be stacked at random in order to prevent soil erosion and damage the ecological balance. According to the requirements of national standards, the dam (or slag yard) should be piled up for the above waste.
The slag dam should be selected in a large-capacity, geologically stable valley, as far as possible in an impervious rock section or an impervious substrate of an artificial building, with sufficient distance from the groundwater. The slag dam should be equipped with flood discharge facilities and isolation facilities. When the slag dam is filled, the surface must be stabilized and covered with soil, rock, slag or vegetation to prevent the waste from being spread by the wind and rain, resulting in a larger area of ​​environmental pollution.
The use of slag dams for non-radioactive solid waste is a widely used method.
(2) Establishing the storage of solid wastes in the slag storage, generally refers to temporary storage or storage in a special solid waste warehouse for long-term storage. This storage must be managed by a special person and has special for the construction and address selection of solid waste. Requirements.
In the rare earth production, the radioactive waste residue with higher specific gravity than the high-strength production, such as acid slag, high-soluble slag, radium slag and sewage slag, is a radioactive waste residue, and some waste slag has the value of recycling. Such wastes must be built and stored to meet safety and health requirements and protect the environment.
The location of the radioactive slag reservoir should be far away from the residential concentration area and the production plant area, and should be built in a remote place as much as possible; the slag reservoir should have sufficient distance from the groundwater and should be built on the downwind side of the dominant wind direction. The reservoir area must have obvious signs, and there must be a strict management system. The protection monitoring area should have a certain distance. If the waste residue contains soluble radioactive elements and acid and alkali, the material in contact with the waste residue in the slag reservoir should be made of materials with anti-corrosion and anti-leakage properties to protect the slag reservoir and prevent leakage and contaminate the groundwater.
For the transportation of radioactive waste, special vehicles with certain protective conditions shall be used, and a special garage shall be set up. The sewage of the flushing vehicles shall flow into the sewage station to be treated for proper disposal.
The completed sewage station is properly disposed of.
1 Open-air slag reservoir In the north of China, due to less rain, it can be built into an open-air slag reservoir for storing radioactive waste slag. The slag warehouse is located in a remote area about 4km away from the production plant and is rectangular in shape and built underground. The effective size in the slag bank is: length × width × depth = 30m × 20m × 2.4m, which is further divided into 6 long squares, and the effective size of each grid is: length × width × depth = 5m × 2m × 2.4 m, can hold a total of about 20,000 tons of radioactive waste residue, the service period is about 30 years.
The peripheral wall of the slag bank is made of stone blocks, and the inner and outer surfaces are covered with cement mortar. The bottom is made of gravel or bedrock, and the concrete is poured into a flat bottom. Anti-corrosion and anti-leakage treatment is carried out around the inner wall of the slag reservoir. When each slag in the slag warehouse is filled with waste slag, the reinforced concrete slab is covered, and the joint between the cover plates is sealed with linoleum and asphalt , and then filled with 0.5m thick soil and solidified.
2 Covering the slag reservoir In the south of China, due to the heavy rain, the slag warehouse needs to be covered and easy to use. The slag warehouse is built on the edge of the plant, about 0.5km from the production workshop. The slag warehouse is built in a rectangular shape on the ground, and the upper half is covered with a roof. The effective size in the slag warehouse is: length × width × depth = 20m × 15m × 2m, and the slag warehouse is divided into 20 rectangular lattices. The slag warehouse can hold about 1000 tons of radioactive waste residue, and the service period is about 25 years. Its structure is the same as that of the open-air slag.
The construction of a slag warehouse for the storage of radioactive solid waste is a commonly used method. The site selection, structure, and facilities in the warehouse can be designed according to the characteristics, types, and level of radioactive waste. It must meet the requirements of radiological protection and environmental protection, as well as safety management.
Usually, this storage method is only suitable for the case of small amount of waste. When the amount of waste slag is large, waste mines, natural caves, etc. that meet the requirements for hydrogeology of the reservoir can be selected and used as radioactive slag warehouse after renovation, but it is strictly prohibited. A slag pool is established in areas with caves.
In addition, the use of artificial caves for storage and use of rock salt pits is also a feasible method for disposal of radioactive waste.
 Other treatment methods for radioactive solid waste
As mentioned above, the radioactive solid waste generated in the production of rare earths is often treated by storage for its own characteristics. As a general understanding, the following is a brief introduction to other methods of treating radioactive solid waste.
(1) Curing method Curing method commonly used cement curing, asphalt curing, glass curing, ceramic curing, plastic curing, etc., is suitable for the curing treatment of low and medium level radioactive waste. After curing, it is conducive to the transportation and storage of radioactive waste, which is conducive to environmental protection.
1 Cement solidification The radioactive waste is incorporated into the cement to form a concrete block, and sometimes a vermiculite can be added to adsorb the radionuclide to firmly solidify it. The method is simple, economical, easy to handle and store, but the final volume is large, and the water leaching rate is high. The performance requirements of the cured body can be referred to GB 14569.1-1993.
2 Asphalt solidification The radioactive waste is uniformly mixed with the dissolved asphalt (melting temperature of about 170 ° C), and the solid waste accounts for about 40% of the total mass. After solidification, the radioactive waste is contained in the asphalt. The prepared asphalt solidified product has the advantages of small volume, water impermeability, corrosion resistance, radiation resistance, etc., and is suitable for treating highly radioactive waste, but the process and equipment of the method are complicated. The performance requirements of the cured body can be referred to GB 14569.3-1995.
â‘¢ The vitrified high-level radioactive waste mixed with the glass materials such as borax, phosphate, silica and the like, and melted at a temperature above one thousand degrees, after annealing treatment, into a stable glass body containing a large amount of fission products. These vitreous things are abandoned into the deep sea.
(2) High-temperature incineration (melting) treatment of combustible wastes that are contaminated by radioactive materials and can no longer be used, such as overalls, gloves, masks, plastics and wood products, and certain combustible radioactive solid wastes can be treated by incineration. Reducing its volume by 10 to 15 times, or even higher, is conducive to subsequent curing treatment and storage, and is an ideal treatment method for combustible waste.
Incineration is more advantageous for treatment with radioactive organisms. High temperature incineration allows high levels of radioactive waste to form stable metal oxides for storage and burial.
Incineration of combustible waste requires the construction of a dedicated incinerator. The soot and radioactive aerosol generated by incineration must be treated by an exhaust gas treatment system. The emitted gas must meet the emission requirements to avoid environmental pollution. In the case of non-incineration conditions, the combustible waste can be compressed to reduce its volume and facilitate transportation and storage.
Radioactively contaminated equipment, equipment, instruments, etc., may be scrubbed with appropriate detergents, complexing agents or other solutions to remove radioactive soil to reduce the volume of waste that needs to be treated. When necessary, the waste containing metal products can be melted in the induction furnace to consolidate the radioactive material in the melt, thereby eliminating the environmental impact.
In short, there is currently no good disposal method for the low level radioactive waste generated in rare earth production. The reason is that the radioactive element content is too low, and there is no recycling value at present; if the high-level radioactive waste is used, the disposal method is not worth the loss.
For rare earth production and even radioactive waste generated in other industries, we should first improve the process and control the amount of three wastes, and eliminate the three wastes in the production process. Secondly, strengthen the management of radioactive waste, properly dispose of or comprehensively use it, and try our best to reduce it. Emissions are also a very important part of preventing radioactive contamination.
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