Rare earth metals (rare earth metals), also known as a rare earth element, is a general term for a group â…¢B periodic table scandium, yttrium, lanthanides 17 elements, commonly represented by R or RE. Their names and chemical symbols are é’ª (Sc), é’‡ (Y), 镧 (La), 铈 (Ce), 镨 (Pr), é’• (Nd), é’· (Pm), é’ (Sm), é“• (Eu ), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu). Their atomic numbers are 21 (Sc), 39 (Y), 57 (La) to 71 (Lu).
Weathering shell ion adsorption type rare earth ore
China's weathering crust ion-adsorbed 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 Xunwuheling ion adsorption light rare earth ore, successively in Nanling, Fujian, Hunan, Guangdong, Guangxi, etc. It has been found in the region, but it is concentrated and large 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 a wide distribution of land, large reserves, low radioactivity, easy mining, simple process of extracting rare earth, low cost and good product quality. The proven industrial reserves are 1 million tons (REO) and the prospective reserves are more than 10 million tons. At present, it produces 10,000 tons (REO) of REO>60% mixed rare earth concentrate.
First, the nature of the ore
The weathering shell ion-adsorbed 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. Rare earth elements in the ore was 80% to 90% of ions adsorbed on kaolin, halloysite, mica, clay minerals, and water; adsorbed on the clay mineral rare earth cations are insoluble in water or alcohol, but strong electrolyte (e.g. Na Cl , (NH 4 ) 2 SO 4 , NH 4 Cl, NH 4 Ac, etc.) can undergo ion exchange and enter the solution and have a reversible reaction.
Second, rare earth extraction process and technical indicators
(a) sodium chloride method
After the discovery of the deposit in the late 1960s, the “Sodium Chloride Pool Immersion Process†was developed in 1970, which was the main method for treating this type of ore in the 1970s. The ore transported from the mining site is sent to a rectangular cement pool for immersion. The leachate is discharged from the discharge port of the filter layer at the bottom of the tank. The leaching residue is manually removed, and the leachate is precipitated in a saturated oxalic acid solution. The filtered cake is Rare earth oxalate, after burning, washing with water, and then burning to obtain a mixed rare earth oxide.
(2) Ammonium sulfate pool immersion method
The sodium chloride leaching method has a long leaching time, a large concentration of sodium chloride, a large consumption, and a large amount of sodium ion coprecipitation. The purity of the product can only reach 70%, and the water needs to be eluted once. Sodium, re-burning complex process, and the leaching residue (tailing) contains a large amount of sodium chloride, causing the land to be salted and polluting the environment. Immersed ore and filtrate oxalic acid precipitation with 3% to 5% ammonium sulfate solution (due to the expensive oxalic acid, ammonium bicarbonate was used as a rare earth precipitant in the late 1980s, and it has been used in some factories and mines. Crystalline rare earth carbonate). The rare earth oxalate is once burned to obtain a mixed rare earth oxide containing REO>90%, and the filtrate is added with ammonium sulfate and returned for reuse. Compared with sodium chloride, ammonium sulphate has strong leaching ability, less dosage, less ammonium ion precipitation, and is more volatile when burning, and leaching does not cause soil salinization. The process flow of chemical beneficiation is shown in Figure 1.
Figure 1 Process of ammonium sulfate-oxalic acid extraction of rare earth
(3) In situ leaching method
The pool dipping process technology and equipment are simple and easy to operate, so they develop rapidly and bloom everywhere. However, the biggest disadvantage of the pool dipping method is the production of 1t rare earth oxide. The surface area to be mined is 200-800m 2 , the mining and stripping amount is more than 1000m 3 , and the amount of tailing sand discharged is 800-1000m 3 , causing serious damage to topsoil and vegetation. Soil and water loss, environmental pollution and waste of resources, the total recovery rate of rare earth is only 30% to 40%. In order to overcome these shortcomings, as early as 1980-1985, the rare earth mine workers put forward the idea of ​​the in-situ immersion method, and later formed the more systematic process technology through the "eight-five" scientific and technological research, the main content of the in-situ immersion method. That is, the ore containing rare earth is not taken out, but the well is drilled in the mining area or section containing the ionic rare earth ore. The immersion liquid is added through the surface injection well, and the ore is selectively passed through the permeation and ion exchange. A process for leaching and recovering rare earth ions. 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 ammonium bicarbonate to obtain a rare earth oxide product. The recovery rate of rare earth leaching is 70% to 75%, so that the topography, surface and vegetation are not destroyed, and the rare earth in situ leaching and pool immersion are compared. The cost is reduced by 1200-3000 yuan / t REO. After the scientific and technological research in 1990-1995, the in-situ leaching method was successful. Ready-made has been applied in some mines such as Longnan, Jiangxi.
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