There are two sources of radioactivity in rare earth production. On the one hand, rare earth elements themselves have a few radioactive isotopes that are less abundant in nature. On the other hand, it is a natural radionuclide such as uranium , thorium and radium associated with rare earth minerals. The natural radioisotope of rare earth elements has a low specific radioactivity, so the rare earth element itself is not treated as a radioactive element. Rare earth minerals associated uranium, thorium and radium and other natural radionuclides in the rare earth production is the main source of radioactivity, and the intermediate product has been distributed in the rare earth and rare earth alloy products.
The natural uranium, strontium content and specific radioactivity of some rare earth minerals, intermediate products and rare earth alloy products are listed in Table 1, Table 2 and Table 3. It can be seen from the table that the alpha specific radioactivity of the Baotou mixed rare earth ore concentrate is on the nationally controlled 7.4Ã—10 4 Bq/kg control line. When the production capacity is large, the daily operation amount may exceed the national control standard. Bastnaesite, monazite and specific radioactivity fergusonite ore concentrate were higher than the national minimum control standards. The rare earth intermediate alloy product has higher specific radioactivity, and it needs to be strengthened for storage and transportation. The radioactivity specific strength of most other products is lower than the national sanitary standard limit.
Table 1 Contents of uranium and thorium in several rare earth concentrates in China and their specific radioactivity
Rare earth concentrate ore type
Total specific radioactivity intensity / (Bq / kg)
Brown sugar mine
4.3 to 7.18
5.37Ã—10 4 to 7.77Ã—10 4
Table 2 Natural strontium content and specific radioactivity in some intermediate products produced by rare earth mixed ore
Intermediate product name
Total specific radioactivity intensity / (Bq / kg)
Mixed rare earth oxide
3.26Ã—10 4 to 7.8Ã—10 4
0.41Ã—10 4 to 1.11Ã—10 4
Table 3 Natural rare earth content and its specific radioactivity in raw materials and products of rare earth intermediate alloys
Raw material, product name
Rare earth rich slag
Rare-earth iron-silicon alloy
Rare earth magnesium alloy
Calcium rare earth alloy
Rare earth content (REO) /%
Natural strontium content /%
Total specific radioactivity intensity / (Ã—104Bq/kg)
6 to 20
Taking Baotou Mine as an example, the distribution of radioactive elements in the production process is: when alkali treatment of Baotou Mine, 96.25% of the strontium enters the slag, and less than 3.75% of the strontium enters the chlorinated rare earth product, and the rest enters the wastewater. When the concentrated sulfuric acid is used for the roasting treatment, 90% of the niobium enters the water leaching residue, and the rest is transferred to the rare earth chloride and the waste water. When the rare earth alloy is smelted in an electric furnace, almost 50% of the bismuth entering the alloy and the residue enters the dust  .
From the radiation level of each workplace in the production of rare earths, except for the slightly higher radioactivity level of uranium and plutonium recovery processes, the radioactive water in most workplaces is lower than the national allowable standard, and individual posts (such as pre-treatment processes) are slightly higher. National standards, and as the production process progresses and the uranium and uranium content of the treated materials decreases, the radioactivity level of the operating environment will decrease significantly until it is equivalent to the normal environmental level. However, since there is no clear conclusion about the long-term hazard caused by the long-term exposure of low-dose long-term exposure to the current level of knowledge, it is not possible to despise radioactive substances for human health in low-radiation posts. Harmful.
Die casting(Aluminium Die Casting) is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process. Most die castings are made from non-ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter and tin based alloys. Depending on the type of metal being cast, a hot- or cold-chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this tends to limit the process to high volume production. Manufacture of parts using die casting is relatively simple, involving only four main steps, which keeps the incremental cost per item low. It is especially suited for a large quantity of small to medium-sized castings, which is why die casting produces more castings than any other casting process. Die castings are characterized by a very good surface finish (by casting standards) and dimensional consistency.
Two variants are pore-free die casting, which is used to eliminate gas porosity defects; and direct injection die casting, which is used with zinc castings to reduce scrap and increase yield.
Aluminum Die Casting
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