Rare earth concentrate decomposition method

The product of the high rare earth grade obtained after the ore dressing of the rare earth-bearing ore containing rock is called rare earth concentrate. Listed in Table 1 are the chemical constituents of rare earth concentrates produced in China. The rare earth in the concentrate is basically the same as the rare earth in the ore rock, and is still a compound which is hardly soluble in water and inorganic acids under normal conditions. In order to make it soluble in water and inorganic acid, in order to recover rare earth therefrom, the industry has adopted a corresponding method according to the form of rare earth in the concentrate to convert the rare earth mineral into a compound which is easy to extract rare earth. Such a process of converting a rare earth mineral into a compound which is easy to extract rare earth is called concentrate decomposing, and the mass percentage of the ratio of REO to the REO of the rare earth concentrate in the rare earth compound becomes the concentrate decomposition rate.

Table 1 Main chemical constituents of rare earth concentrates

There are many methods for decomposing concentrate, which can be divided into four categories: acid decomposition method, alkali decomposition method, oxidative roasting method and chlorination method.

1. The acid decomposition method includes decomposition of sulfuric acid, hydrochloric acid and hydrofluoric acid. The sulfuric acid decomposition process is suitable for the treatment of phosphate minerals (such as monazite, xenotime) and hydrogen carbonate minerals (carboncarbonite). Hydrochloric acid decomposition method is limited applications, only suitable for treating silicate minerals (e.g. allanite, gadolinite). The hydrofluoric acid decomposition method is suitable for decomposing citrate minerals (such as brown ore and strontium ore). The acid decomposition method is characterized by strong ability to decompose minerals, and has strict requirements on the grade and particle size of concentrates. It is applicable and wide, but the selectivity is poor, the corrosion is serious, the operating conditions are poor, and the three wastes are more.

Second, the alkali decomposition method mainly includes sodium hydroxide decomposition and sodium carbonate roasting method, etc., which is suitable for the treatment of rare earth phosphate minerals and fluorocarbonate minerals. For rare earth minerals that are difficult to decompose, sodium hydroxide fusion is also used. The alkali decomposition is characterized by mature process, simple equipment and high comprehensive utilization. However, the grade and grain size of concentrates are relatively high, and the discharge of sewage is large.

Third, the oxidative roasting method is mainly used for the decomposition of hydroquinone ore. During the calcination, the hydroquinone is decomposed into gaseous compounds of rare earth oxides, oxyfluorides, carbon dioxide and fluorine, wherein the trivalent cerium oxide is simultaneously oxidized by oxygen in the air to a tetravalent oxide. The disadvantage of this method is that fluorine enters the atmosphere with the gaseous compound as the calcined tail gas, which has certain pollution to the environment. The advantage is that it is not necessary to add other roasting tail gas into the atmosphere during the roasting process, which has certain pollution to the environment. The advantage is that no additional roasting aids need to be added during the calcination process, and the chemical differences of the tetravalent europium trivalent rare earth elements are utilized. It is possible to use a double salt of sulfuric acid precipitation or a method of preferentially dissolving trivalent rare earth elements by hydrochloric acid, and to extract the cerium which accounts for about 50% of the rare earth component. This simplifies the further rare earth extraction and separation process and reduces production costs.

The sodium carbonate calcination method, the calcium oxide calcination method, and the decomposition method having the characteristics of further oxidizing the trivalent antimonide to tetravalent oxide during the calcination have the advantages of preferential separation.

Fourth, the chlorination decomposition of rare earth concentrates can be directly obtained anhydrous rare earth chloride, which can be used in the product molten salt electrowinning misch metal. Chlorination refers to the process of mixing carbon with rare earth concentrates, making agglomerates, and directly introducing chlorine gas at the high temperature of a vertical chlorination furnace. According to the difference in boiling point of different chlorides, three kinds of products can be obtained at the same time: chlorides of metals such as rare earth, calcium and barium, which flow into the chloride dissolved salt receiver in a melt state; low-boiling chlorides ( lanthanum , uranium and thorium) , bismuth, titanium , iron , silicon, etc.) are gaseous products, which are volatilized from the molten salt, collected in a condenser, and then comprehensively recovered; high-boiling components such as undecomposed concentrate and carbon slag are residues. At present, the chlorination method is difficult to solve due to the chlorine-corrosive materials of the equipment. The radioactive element lanthanum is distributed in three kinds of products, and the obtained molten salt components are complicated, and the labor conditions are poor, and the like is still adopted by the industry in China.

There are many methods for the decomposition of rare earth concentrates. In industrial production, the appropriate process is usually selected according to the following principles:

(1) According to the chemical properties of rare earth minerals in the concentrate, rare earth grades, and other non-rare earth chemical components, the decomposition method is first selected to obtain a high decomposition rate.

(2) Optimize the process to obtain high economic benefits from the product plan, the supply and price of raw materials, and the consumption situation.

(3) It is convenient for recycling valuable elements and comprehensive utilization, which is conducive to labor hygiene and environmental protection.

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