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China's weathering crust leaching rare earth ore first discovered in the late 1960s in the Longnan foot cave of Jiangxi Province, after ion-adsorption heavy rare earth ore and Xunwuling ion adsorption light rare earth ore, successively in Nanling, Fujian, Hunan, Guangdong, Guangxi, etc. The area has been found, but it is concentrated in Jiangxi. Ion-adsorbed rare earth ore is a unique new type of rare earth deposit in China that has not been reported abroad. After more than 20 years of research, it has been found that this type of mine has the characteristics of wide distribution of land, large reserves, low radioactivity, easy mining, simple process of extracting rare earth, low cost of production and good product quality. The weathered leaching type rare earth ore-bearing rare earth-bearing granite or volcanic rock is formed by weathering for many years. The ore body is shallowly covered, the ore is loose, and the particles are very fine. 80% to 90% of the rare earth elements in the ore are adsorbed on the minerals such as kaolin , halloysite and hydromica in an ionic state; the rare earth cations adsorbed on the earth's minerals are insoluble in water or ethanol, but in strong electrolytes (such as In the solution of NaC1, (NH 4 ) 2 SO 4 , NH 4 C 1 , NH 4 Ac, etc., ion exchange can occur and enter the solution and have a reversible reaction.
(1) Sodium chloride pool immersion method
The sodium chloride pool leaching process is the main method for treating weathering crust leaching rare earth ore in the 1970s. The ore transported from the mining site is sent to a rectangular cement tank, and is filled with NaC1 aqueous solution. The leaching solution is discharged from the discharge port of the filter layer at the bottom of the tank. The leaching residue is manually removed, and the leaching solution is precipitated in a saturated oxalic acid solution. The filter cake is rare earth oxalate, which is mixed with rare earth oxide by burning, water burning and re-burning.
(2) Ammonium sulfate pool immersion method
Due to many defects in the sodium chloride leaching method, the study has developed a 3% to 5% ammonium sulfate solution soaked in ore, the filtrate is oxalic acid precipitated, and the oxalic acid rare earth is once burned to obtain >90% REO mixed rare earth oxide, and the filtrate is supplemented. Ammonium sulfate is returned for reuse.
Because oxalic acid is more expensive. In the late 1980s, ammonium bicarbonate was used as a rare earth precipitant, and it has been used to produce crystalline rare earth carbonate in some factories and mines.
(3) heap leaching method
The mined ore is directly piled up, infused with (NH 4 ) 2 SO 4 solution, and the filtrate is precipitated with oxalic acid or carbon money. The rare earth oxalate or ammonium bicarbonate is once burned to obtain a mixed rare earth oxide of >90% REO.
(4) In situ leaching method
The main content of the in-situ leaching method is not to excavate the ore containing rare earth, but to drill well in the mining area or section containing the ionic rare earth ore, and to add the leaching solution through the surface injection well, through the infiltration and ion exchange, A process of selectively leaching and recovering rare earth ions in ore. The recovery of the leaching solution has a negative pressure pumping and a water seal plugging method, and the former has a wide adaptability. The leaching solution is collected and precipitated with oxalic acid or hydrogencarbonate to obtain a rare earth oxide product. The recovery rate of rare earth leaching is 70% to 75%, so that the landform, surface and vegetation are not damaged, and the in situ leaching and pool immersion are compared. The cost is low 1200 ~ 1300 yuan / t. It is now widely used.
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