Decomposition of rare earth concentrate by sulfuric acid method

A method for decomposing rare earth concentrates from rare earth concentrates treated with sulfuric acid to produce rare earth chloride or other rare earth compounds. The method has the advantages of strong adaptability to raw materials and low production cost, and is a commonly used decomposition method in the rare earth concentrate industry, and is widely used in the fluorocarbon antimony concentrate, monazite concentrate and the Baiyun Obo mixed rare earth ore concentrate. break down. There are mainly three processes of sulfuric acid roasting-solvent extraction, sulfuric acid decomposition-double salt precipitation method, and oxidative roasting-sulfuric acid leaching method.

1. Sulfation roasting-solvent extraction

It is mainly used to decompose rare earth chlorides from the Baiyun Obo mixed rare earth ore concentrate. The Baiyun Obo mixed rare earth ore concentrate is complex and belongs to refractory ore. Its typical main components (%) are: RE ₂ O ₃ 50-55, P2.5-3.5, F7-9, Ca7-8, Ba1~ 4, Fe3 ~ 4, ThO ₂ about 0.2. Low concentrate radioactive thorium and uranium content, less demanding smelting protection, adapted for decomposing sulfated roasting method.

(a) principle

After the fine rare earth concentrate is mixed with concentrated sulfuric acid and heated and calcined to a temperature of 423 to 673 K, both the rare earth and the cerium form a water-soluble sulfate. The main reaction of bastnasite with sulfuric acid is:

2REFCO ₃ +3H ₂ SO ₄ =RE ₂ (SO ₄ ) ₃ +3HF↑+2CO ₂ +2H ₂ O

The main reactions of monazite and sulfuric acid are:

2REPO ₄ +3H ₂ SO ₄ =RE ₂ (SO ₄ ) ₃ +2H ₃ PO ₄

Th ₃ (PO ₄ ) ₄ +6H ₂ SO ₄ =3Th(SO ₄ ) ₂ +4H ₃ PO ₄

Impurities such as iron and calcium also form corresponding sulfates. The decomposition product was leached with water of 12 times the mass of the concentrate to obtain a sulfate solution containing rare earth, iron, phosphorus and cerium. By controlling the different calcination temperatures, the amount of sulfuric acid and the liquid-solid ratio of the water leaching, the decomposition effect can be changed. When the ratio of sulfuric acid to rare earth concentrate is 1.5 to 2.5, the decomposition temperature is 503 to 523 K, and the water leaching solution contains RE ₂ O ₃ 50 to 70 g/L, cerium, rare earth, phosphorus, iron, etc. enter the solution at the same time. The above calcination and leaching conditions are mainly used for the decomposition of monazite concentrate and Baiyun Obo mixed rare earth ore concentrate. When the ratio of sulfuric acid to rare earth concentrate is 1.2-1.4, the decomposition temperature is 413-433K, and the water leaching solution contains 50% of free sulfuric acid, the ruthenium mainly enters the solution, and most of the rare earth remains in the slag. When the ratio of sulfuric acid to rare earth concentrate is 1.2 to 1.4, the decomposition temperature is 573 to 623 K, and the water leaching solution contains RE ₂ O ₃ 50 g/L, the rare earth enters the solution, and bismuth and iron remain in the slag. By controlling the calcination and leaching conditions, the rare earth can be initially separated from the main associated elements.

(2) Process

From rare earth concentrates to obtaining rare earth chlorides, they are mainly subjected to sulphation roasting, leaching, removal of impurities and solvent extraction and transformation.

1. Sulfation roasting. The Baiyun Obo mixed rare earth ore concentrate and concentrated sulfuric acid are mixed in a spiral mixer and sent to a rotary kiln for sulphation roasting decomposition. Control the feed end (kiln tail) furnace gas temperature 493 ~, 523K, during the roasting decomposition process, the charge slowly moves to the high temperature zone before the kiln, and the bastnasite and monazite react with sulfuric acid to form soluble sulfuric acid rare earth. Iron, phosphorus, antimony, etc. form a phosphate that is poorly soluble in water. As the charge increases in temperature toward the high temperature zone, excess sulfuric acid is gradually evaporated. When the charge is run to the kiln discharge end of the furnace gas temperature of about 11'73K, the charge temperature reaches about 623K, and a small grain charge of 5-10 mm is formed, which is called a calcined material, and is discharged from the side end of the combustion chamber.

2. Leaching out impurities. The calcined material contains 3% to 7% of sulfuric acid, and directly falls into the water dip tank to dissolve the rare earth, and almost all of the impurities remain in the slag and are separated from the rare earth. The pure rare earth sulfuric acid solution obtained contains RE ₂ O ₃ 40 g/L, Fe 0.03 to 0.05 g/L, P about 0.005 g/L, Th < 0.001 g/L, and acid 0.1 to 0.15 mol/L. This solution is used to produce rare earth chloride.

3. Solvent extraction transformation. The process of converting rare earth sulfate into rare earth chloride by solvent extraction. This process has been used to replace the traditional sulphuric acid double salt precipitation, alkali conversion and other cumbersome transformation processes. This is a major innovation in China's rare earth extraction process in the 1980s. Solvent extraction transformation uses carboxylic acid (naphthenic acid, fatty acid) extractant, saponified with ammonia, and then directly extracts rare earth ions from rare earth sulfate solution. The rare earth supported organic phase is back-extracted with rare earth containing HCl 6mol/L solution to obtain chlorine. Rare earth solution. The extraction and stripping processes are performed by co-current extraction (see solvent extraction). The raffinate pH is 7.5-8.0, containing RE ₂ O ₃ 10 mg/L, and the rare earth extraction rate is over 99%. The hydrochloric acid stripping solution contains RE ₂ O ₃ 250-270 g/L and contains 0.1-0.3 mol/L of free acid. The stripping solution is concentrated to a rare earth chloride by a reduced pressure concentration method. The main component (mass fraction ω/%) of rare earth chloride is: RE ₂ O ₃ about 46, Fe 0.01, P 0.003, Th 0.002, SO ₄ ^{2 -} <0.01, Ca 1.25, NH ₄ ⁺ 1 ～ 2. In 1982, China used the above process to build a production line with an annual output of 6,000 tons of rare earth chloride in Gansu Rare Earth Company. After nearly ten years of production practice, the process is stable, the operation is simple, and the economic benefits are good.

The Chinese research succeeded in extracting and separating rare earth from P ₂ 0 ₄ extractant directly from the rare earth sulfate solution produced by the decomposition of Bayan Obo mixed rare earth ore concentrate by sulphating roasting, which has the separation of rare earth concentrate and single rare earth extraction. The combination of the process, namely the separation of lanthanum , cerium , lanthanum and cerium in the sulfuric acid medium and the preparation of rare earth chloride, eliminates the extraction transformation and some chemical separation processes, thereby reducing reagent consumption and reducing production costs. In 1986, four factories in China used this process to renovate the original process, and established a production line that processes 10,000 tons of mixed ore annually. The simplified process is shown in Figure 1. The ruthenium enrichment product produced by the 钐 钐 extraction group contains: Eu ₂ O ₃ 11%, Sm ₂ O ₃ 50%. The purity of the product produced by the extraction method of Na ₂ O ₃ is 99%. The rare earth chloride solution obtained by the extraction method of rare earth contains RE ₂ O ₃ 250 g/1, and the residual liquid contains RE ₂ O ₃ 0.2 to 0.4 g/L.

Fig.1 Sulfuric acid roasting of Baiyun Obo mixed rare earth ore concentrate

-P204 extraction method for the extraction and separation of rare earths

Second, sulfuric acid decomposition - double salt precipitation

Mainly used to treat monazite concentrates. Monazite is a phosphate mineral and is an important raw material for the production of rare earths and strontiums, usually containing RE ₂ O ₃ 55%, 6, ThO ₂ 3% to 10%, U ₃ O ₈ about 0.3%, and P ₂ O ₅ about 25%. In addition, it also contains a small amount of impurities such as titanium , iron, zirconium and silicon. Monazite mainly contains light rare earth elements. Medium rare earths and heavy rare earths only account for 8% to 10% of the total amount of rare earths. They are produced in Australia, India and Brazil. China produces about 2,200 tons of monazite per year. Sulfuric acid decomposition and double salt precipitation is a traditional process for extracting rare earth from monazite. The monazite concentrate and concentrated sulfuric acid are heated to 473K in a cast iron stirred tank for 2 to 4 hours, and most of the rare earth is converted into soluble sulfate. The main components of the rare earth sulfate solution obtained by leaching the decomposition product with water are:

The most common method for extracting rare earths, cerium and uranium from such leaching solutions is the sodium sulfate double salt precipitation method. The sodium sulfate double salt precipitation method is to precipitate rare earth and cerium with 3Na ₂ SO ₄ •RE ₂ (SO ₄ ) ₃ •4H ₂ O•0.09Th(SO ₄ ) ₂ double salt by using sodium sulfate or sodium chloride precipitating agent. The rare earth and cerium are then converted to hydroxides with NaOH, and then the rare earths are preferentially dissolved with hydrochloric acid. The obtained rare earth chloride solution was concentrated under reduced pressure and cooled to give a rare earth chloride (Fig. 2). The sputum enrichment is sent for handling. The sulphuric acid decomposition-separate salt precipitation process can treat monazite concentrates with lower grades, and has the advantages of strong adaptability to raw materials and low production cost. However, radioactive elements strontium and uranium are dispersed in the process and are difficult to recycle. Recently, some people have used primary amines to extract cerium from a rare earth sulfate solution, and then recover the pure rare earth by a double salt precipitation method. This method is more conducive to the extraction of rare earth and cerium.

Figure 2 Sulfuric acid process decomposition of monazite process

Third, oxidized roasting sulfuric acid leaching

It is mainly used to extract rare earth from bastnasite concentrate. China's Shandong Weishan Lake and Sichuan Suining are rich in fluorocarbon antimony ore, similar to the fluorocarbon antimony ore produced in Mountain Pass, USA. The mineral grain size is coarse and easy to be selected. RE ₂ in the concentrate. O _{3 is} about 60%, low in phosphorus and easy to extract. US molybdenum mining company (Molycorp Inc.) using a hydrochloric acid leaching roasting decomposition Bastnaesite, the production of rare earth and cerium chloride enrichment than 30 years, rare earth production accounts for more than 30% of the world's rare earth production.

During the oxidative roasting of fluorocarbon antimony ore (REFCO ₃ ) at a temperature of 773 to 873 K, CO ₂ is liberated to form rare earth oxides and oxyfluorides, and trivalent cerium is oxidized to tetravalent, insoluble fluorocarbon strontium ore. Turned into a soluble product. In the hydrochloric acid leaching process, the difference in properties between the trivalent rare earth and the tetravalent cerium can be utilized to concentrate the cerium as a fluoride and an oxide in the slag, and the CeO ₂ /RE ₂ O ₃ in the cerium-rich slag can reach 85% to 90%. . However, the slag-rich slag also contains impurities such as barite , fluorite, and monazite. When the slag is used to produce bismuth products, the process is complicated by the need to remove these impurities. U.S. molybdenum company's products are mainly europium oxide, samarium oxide, and lanthanum hydroxide A was enriched, and therefore a large amount of cerium first removed to facilitate the extraction and separation of a single rare earth.

Figure 3 Process of decomposing bastnasite by oxidizing roasting-sulfuric acid leaching

In the 1960s, the oxidized roasting-sulfuric acid leaching of the fluorocarbon antimony concentrate concentrate developed in China (Fig. 3) enabled all rare earths to enter the acid leachate. When the bastnasite is calcined at a temperature of 773 to 873 K, Ce ^{3 +} is oxidized to ce4 ⁺ . Sulfuric acid containing 1.25 ~ 1.5mol / L solution leaching roasted ore, ore roasting Ce4 ⁺ and F ^- ions form stable coordination CeF ₆ ^{2 -} into solution, Ce4 ⁺ and F ^- bound only prevents the rare earth fluoride generated The precipitate also promotes the dissolution of the rare earth fluoride in the calcined ore. When CeF ₆ ^{2 -} is present in the solution, the fluorine acts to accelerate the dissolution of the insoluble ceria. The above two effects promote each other, so that the cerium oxide and the heavy rare earth oxalate in the calcined ore are recovered and recovered, and the rare earth fluorinated rare earth, the oxyfluoride rare earth and the rare earth oxide can be quickly dissolved by the dilute sulfuric acid. The rare earth leaching rate can reach 96% to 97%. The rare earth sulfate solution prepared by the method contains about 80 g/L of RE ₂ O ₃ , about 1.5 mol/L of F8-9 g/L acid, and Fe1g/L or less, and the oxidation rate of cerium is 98% to 99%. The obtained solution is relatively pure, and the cerium oxide having a purity of 99% to 99.9% can be directly produced by the P204 extraction method, the sodium carbonate method or the sulfuric acid double salt method.

Handheld Laser Welding Machine

Better weld formation: YIHONG or STARTNOW welding head,Swing welding mode, spot width can be adjusted, welding fault tolerance is strong, make up for the disadvantage of laser welding spot small, expand the tolerance range of machining parts and weld width, get better weld forming.