1. Concentrated sulfuric acid high temperature intensification roasting method
Beijing General Research Institute for Nonferrous metals from the 1970s began the development of concentrated sulfuric acid roasting smelting Baotou mixed rare earth concentrate, have developed a first-generation, second generation, third generation sulfuric acid method, in which the high temperature concentrated sulfuric acid roasting strengthen The method ("three generations" acid method) has been put into use since the 1980s, and it has become the treatment of Baotou rare earth concentrates by high-temperature intensification roasting of concentrated sulfuric acid.
First, the concentrate is dried by an external heating rotary kiln; in the rotary kiln, the rare earth concentrate is mixed with concentrated sulfuric acid, and reacted at a certain temperature (500-600 ° C), and the rare earth concentrate is completely decomposed to form a rare earth sulfate; cold water leaching into the solution of rare earth rare earth sulfates; phosphorus acid group removing iron powder, adjusting the pH with magnesium oxide or calcite, give purer rare earth sulfate, or a rare earth transition chloride by extraction, or extraction and separation as required. Thorium generating firing at high temperatures to strengthen the water-insoluble pyrophosphates (or phosphate) remain in the slag flooding.
The advantage of the process is that the quality of the concentrate is not high, the process is continuous and easy to control, the reagent consumption is low, the running cost is low, and the mass production is easy. The disadvantage is that strontium phosphate enters the slag in the open form and cannot be recycled, resulting in radioactive pollution and waste of cesium resources; waste gas containing fluorine and sulfur and industrial wastewater polluting the environment.
The “three wastes†produced during the production of rare earths have attracted wide attention as early as the 1980s. The waste gas produced by the high-temperature enhanced roasting process of concentrated sulfuric acid is mainly acid mist containing sulfuric acid and hydrofluoric acid and a small amount of fluorosilicic acid roasting tail gas; the waste water is mainly ammonium salt wastewater generated during the process of extracting and sorting rare earth concentrate, and The main components are ammonium sulfate and ammonium chloride; the waste residue mainly contains iron, phosphorus, calcium compounds and antimony, which will cause long-term radioactive contamination. In response to these "three wastes", relevant experts have put forward some suggestions for governance. For example, Wang Junlan of Baotou City and Rare Earth Group Corporation proposed a method of splitting and dividing according to the characteristics of each major pollutant and recycling. The exhaust gas generated by roasting is treated by three-step method: purification by cooling and spray absorption, and the mixed acid solution and the leaching acid solution are mixed and concentrated by heating to obtain concentrated sulfuric acid and fluorine-containing liquid-fluorine-containing liquid. The synthetic method is used to obtain the fluorine salt, so that the exhaust gas can be discharged to the standard, and the pollution of the exhaust gas purification wastewater is also eliminated, and the cryolite required for the production of rare earth sulfuric acid and aluminum smelting industry can be obtained; for the ammonium salt wastewater, the main It is an ammonium sulfate and ammonium chloride wastewater with less impurities caused by acid rare earth smelting. It is concentrated to 12% to 14% by electrodialysis and reverse osmosis, and then qualified by conventional three-effect evaporation and cooling crystallization. The ammonium chloride and ammonium sulfate products can not only treat the ammonium salt wastewater, but also recover a large amount of ammonium sulfate and ammonium chloride. For the slag-containing waste slag, the water leaching residue and the neutralization slag are separated by low-temperature roasting to obtain enrichment. The neutralized slag of hydrazine is then converted to a cerium nitrate product by a primary amine extraction separation technique.
Second, the caustic soda method
The caustic soda method first began in India. In 1952, India first established a plant in Alwaye to decompose monazite with a design capacity of 1500 t/a. After that, the United States, Brazil, Malaysia and China began to use the caustic soda process to treat monazite. . In the 1970s, China began to use the caustic soda method to treat the monazite-fluorocarbon antimony ore mixed rare earth concentrate in Baotou. Firstly, it is soaked with acid, removes calcium by chemical beneficiation method and improves the grade of rare earth concentrate. The produced concentrate is decomposed with caustic soda to form a hydroxide which is easily soluble in inorganic acid, and fluorine and phosphate are soluble in alkali and alkali. Sodium fluoride and sodium phosphate in water are separated from the rare earth. The alkali decomposed product is washed with water, and the rare earth hydroxide is insoluble in water and separated from the impurities. The washed rare earth hydroxide is dissolved in hydrochloric acid to obtain a rare earth chloride solution, and the mixed rare earth crystal product is obtained by impurity removal and evaporation concentration; after separation, the solution is separated by extraction to obtain a single rare earth or grouped rare earth product.
The main advantage of this process is that the concentrate decomposing equipment is simple, easy to process and manufacture, and the capital investment cost is low. When the concentrate is decomposed, no fluorine-containing waste gas is generated, and the “three wastes†produced are easier to handle than the concentrated sulfuric acid high-temperature enhanced roasting method. Established factories in densely populated areas with strict environmental protection requirements. The disadvantage is that the price of caustic soda is high, the dosage is large, and the running cost is high; the rare earth, antimony and fluorine are relatively dispersed, and the rare earth yield is about 85%; in addition, it is not suitable for treating the rare earth grade (ω(REO)<50%). Mixed rare earth concentrate. Currently, only 10% of Baotou Mine is treated with this process.
Compared with the high-temperature enhanced roasting process of concentrated sulfuric acid, the caustic soda method has relatively small pollution, and the main pollutant is waste alkali liquor. Generally, it is treated by concentration-caustic method: firstly, the Na 2 CO 3 , Na 3 PO 4 and NaF crystals are precipitated, filtered, and the NaOH solution and the crystal are separated; the crystal is dissolved in water, and lime is added to cause it to be used.
3. Other processes for extracting rare earth concentrate from Baotou
(1) Concentrated sulfuric acid low-temperature roasting method
In view of the shortcomings of high-temperature enhanced roasting process of concentrated sulfuric acid, in order to reduce the "three wastes" generated during the decomposition process of Baotou rare earth ore, rare earth production enterprises and research institutes have successively carried out research on new technology of rare earth low-temperature roasting, and obtained many staged results, such as 20 In the 1970s, Beijing Nonferrous Metals Research Institute and Harbin Fushi Factory developed a low-temperature sulfuric acid roasting-double salt precipitation method for smelting mixed rare earth concentrates (first generation acid method); Changchun Institute of Applied Chemistry studied low temperature sulfuric acid roasting-water The technology of extracting bismuth by direct immersion in the leaching solution; the low-temperature static roasting of concentrated sulfuric acid in the cooperation between the Baotou Rare Earth Institute of High Technology and the Changchun Institute of Applied Chemistry - the primary ammonium extraction, the P 2 O 4 total extraction, the P 5 O 7 extraction transformation production mix Rare earth chloride process. The rare earth concentrate concentrated sulfuric acid low-temperature roasting decomposition process (patent No. ZL02144405.6) of Baotou Rare Earth Research Institute has the best effect. The process comprises mixing rare earth concentrate and concentrated sulfuric acid by mass ratio of 1:1.1 to 1:1.7 and calcining in a muffle furnace at 150-330 ° C for 2 hours, then blasting the calcine with water, and filtering to obtain an aqueous extract and Water leaching residue. The hydrazine in the aqueous extract is extracted by extraction and separated to obtain a rare earth product. The rare earth leaching rate is 95%-98%, the cerium leaching rate is greater than 95%; the rare earth mass fraction in the water leaching slag is less than 3%, the strontium mass fraction is less than 3%, the total ratio is less than 7.4 × 10 4 Bq/kg, and the slag amount Very few.
Compared with the high-temperature concentrated sulfuric acid roasting process, the process greatly reduces the discharge of waste water, waste gas and radioactive waste residue, and reduces the production cost; the rare earth leaching rate reaches over 96%, the fluorine recovery rate reaches over 95%; and the exhaust gas in the exhaust gas The volumetric mass is <2mg/m 3 , the mass fraction of bismuth in the leaching slag is <0.05%, and the specific activity is lower than the national standard (7.4×10 4 Bg/kg), which meets the requirements of industrial production. However, the process still requires dynamic testing of the mechanical roasting and equipment.
(2) Sodium carbonate roasting method
The research work on the addition of sodium carbonate roasting in Baotou rare earth concentrate began in the early 1960s. The Institute of Applied Chemistry of Changchun Institute of Applied Chemistry, Baotou Metallurgy Research Institute and Beijing Research Institute of Nonferrous Metals conducted a lot of research on sodium carbonate decomposition rare earth concentrate. Industrial tests were carried out in the 1970s.
Take a certain amount of dried Baotou rare earth concentrate, mix a certain amount of sodium carbonate, put it in a porcelain dish, put it into a muffle furnace and calcine it at 600-700 °C for 2~3h, and take it out. The calcine is ground, and the NaF, Na 3 PO 4 and unreacted sodium carbonate formed by the reaction are washed away with water, and then the salt such as calcium, magnesium or barium is washed away with dilute acid, and then leached with sulfuric acid or nitric acid to obtain a leachate. The ruthenium and osmium were separated by P 2 O 4 and TBP extraction, and the ruthenium was separated by sodium sulfate double salt precipitation method to prepare mixed rare earth chloride.
For low-grade rare earth ore, the Soviet Union used sodium carbonate + sodium sulfate roasting method, and achieved good results: high recovery rate of rare earth; good quality of three waste treatment, no radioactive waste discharge; direct extraction and separation of water and leaching liquid With a single rare earth, the obtained CeO 2 can reach 99.9%. However, its production cost is high and it is not suitable for industrial production.
(3) Chlorination method
The high-temperature chlorination process for the treatment of rare earth minerals was first used by the German company Goldsmitt for industrial production. The high-grade rare earth ore is used as raw material to produce anhydrous rare earth chloride, and then the mixed rare earth metal is prepared by electrolysis. The main disadvantages of this method are high chlorination temperature (1000-1200 °C), high energy consumption, low-boiling products and rare earth products containing radioactive element strontium. There are many imperfections, which have stopped since the 1980s. use.
In recent years, many people have been working on the treatment of rare earth ore chloride treatment. Zhang Liqing blends fluorocarbon antimony-monistite concentrate and activated carbon according to the atomic mass ratio of m(Ln):m(C)=1:3, using C+Cl 2 as reducing agent and chlorinating agent, and SiC1 4 as off Fluoride agent. The chlorination reaction is carried out in a tube furnace. The reaction tube is a blast furnace tube having an inner diameter of 25 mm and a length of 1500 mm, and the reactant is placed in the highest temperature zone of the furnace. The reactants are first heated to a specified temperature under the protection of Ar gas, and then chlorinated under a dry C1 2 atmosphere or a (Cl 2 +SiC1 4 ) atmosphere for 2 hours, finally cooled to room temperature in an Ar atmosphere, and dissolved in deionized water to chlorinate. The product causes the rare earth to enter the solution. The test results show that the carbothermal reduction chlorination reaction of bastnasite-monomite mixed concentrate can be carried out at a lower temperature (500-800 °C) in the presence of defluorination agent SiC1 4 , and its rare earth chloride ratio Up to 99%, the acid insolubles in the chlorinated product account for less than 3.5% of the added concentrate; the process is short, the equipment is simple, easy to operate; the investment is small, the effect is fast, the rare earth yield is high, the energy consumption is low, and the production cost is low. It is a better process for producing rare earth chloride. However, this process is still in the experimental stage and has not yet been put into large-scale industrial production.
Yu Xiulan's research on the use of AIC1 3 as a defluorination agent has also achieved good results. The mixed rare earth concentrate was treated by AIC1 3 defluorination-carbon thermal chlorination method, and the reaction rate was 91% at 600 °C for 2 h, and the rare earth extraction rate was 97.4% at 800 ° C for 2 h. The mixed rare earth concentrate was taken off. fluorine during the reaction, and mineral AICl 3-fluoro-decomposition reaction occurs defluorination, fluoro conversion hardly soluble AlF 3 and water left in the filter cake can promote the decomposition reaction of AIC1 3 monazite.
(4) Ammonium chloride roasting method
Selective ammonium chloride roasting decomposition method for extracting rare earth is a new process invented by Tsinghua University Nuclear Energy Technology Design and Research Institute. However, this method requires a large amount of water to wash off NaF in the calcined product. Therefore, a new method for the extraction of rare earth from ammonium fluorafluoride is proposed.
The new method requires two roastings: the first time, adding MgO and mixed rare earth concentrate to be mixed and calcined, so that the monazite and bastnasite in the mixed rare earth concentrate are decomposed into rare earth oxides and magnesium fluoride; the second time, Ammonium chloride chlorinates the rare earth oxide formed in the first calcination into a rare earth chloride. Finally, the calcine is dissolved in water to obtain a rare earth chloride. When the mass ratio of rare earth concentrate to ammonium chloride is 1:2, the recovery rate of rare earth is more than 85%, and the increase of the amount of ammonium chloride is not beneficial to the recovery of rare earth; in the range of 350-500 °C, When the reaction temperature is increased, the rare earth recovery rate is gradually increased. At 500 °C, the rare earth recovery rate is the highest; the calcine can be directly leached with water, no acid or alkali is introduced, and the rare earth conversion form is small. Good chlorination selectivity, high chlorination rate and mild chlorination conditions. In the process of chloride roasting, no harmful substances polluting the environment are produced, impurities such as Fe, Pb, etc. are reduced into the leachate, corrosion of the equipment is prevented, the operating environment is good, and the discharge of acid waste water is small, which is in line with the requirements of green chemical development. A promising method for the treatment of rare earth minerals.
(5) CaO roasting method
The conventional method for treating the Baotou rare earth concentrate is concentrated sulfuric acid high temperature roasting or alkali method. The high-temperature roasting method of concentrated sulfuric acid has a low cost, but the pollution is serious; the alkali method has a high cost due to the large amount of alkali used. Therefore, a high temperature roasting-diluted acid leaching process has been proposed. Although the process is less polluted, the rare earth leaching rate can reach more than 92%, but high temperature roasting is required, so the energy consumption is relatively high. In response to this situation, Wu Wenyuan proposed the CaO decomposition method.
The decomposition of mixed rare earth concentrate by CaO-NaCl is to enhance the decomposition of REO 4 and REFC O 3 by CaO by means of solvent NaCl. When calcined at a temperature of 600 to 900 ° C, REPO 4 and REFCO 3 are decomposed into REO and Ca 5 F(PO 4 ) 3 . Meanwhile, Ce 2 O 3 is oxidized by oxygen in the air to CeO 2 ; the calcination is washed with dilute acid After removing Ca 5 F(PO 4 ) 3 and NaCl, leaching REO, CeO 2 and ThO 2 with sulfuric acid, the rare earth recovery rate can reach above 92%, and the ThO 2 mass fraction in the leaching residue is less than 0.001 g/L, which belongs to low-level radioactive waste residue. It can be treated as general waste; the leachate is extracted by solvent extraction to extract lanthanum, cerium and non-cerium rare earth elements.
The process is a cleaning process that meets environmental requirements, but it is still in the research stage and cannot be used in production practice.
Fourth, Baotou rare earth mine development recommendations
Baotou rare earth ore is a multi-element symbiotic mine mainly composed of iron, rare earth, antimony and bismuth . However, it has been used as iron ore mining. The recycling of rare earth and antimony is less than 10%. Others such as antimony, phosphorus and manganese are not recycled. The development and utilization are unreasonable, the waste of resources is serious, and the Yellow River and Baotou areas are also at risk of being contaminated by radioactivity. Therefore, we will actively develop and introduce new technologies and new processes, continuously improve and improve the existing processes, realize the organic combination of industrial production and environmental protection, reduce the emissions of “three wastes†on the basis of comprehensive recovery of various resources, and truly achieve the significance of clean production. major.
According to the existing production process and ore composition, a large amount of rare earths in Baotou Mine will be lost, and the recovery rate of rare earth ore dressing is only 5% to 7%. A large amount of rare earths are placed in the tailings dam with the tailings. At present, the tailings reserves are about 120 million tons, and the rare earth oxides (REO) exceed 8 million tons, and they are still increasing. These resources are important resources for secondary utilization. Therefore, on the one hand, it is necessary to protect the tailings dam to prevent the loss and depletion of secondary resources; on the other hand, it is necessary to develop suitable characteristics for the low grade of resources in the tailings dam. Extraction process.
At present, the third-generation acid process used in Baotou Rare Earth Industry has an annual capacity of 50,000 tons of rare earth concentrates, and 33,000 tons of low-level waste slag is produced annually. It is necessary to build radioactive slag stocks. This treatment method not only occupies a large amount of land. It also causes waste of resources. In order to better protect the environment and recover resources, especially the resources, we should consider the following two points: on the one hand, based on the rare earth industry, research on new concentrate processing technology, comprehensive recovery of rare earth, antimony and other resources, on the other hand A suitable process was developed for the tailings produced by the high-temperature intensification roasting process of the concentrated sulfuric acid in Baotou Rare Earth Industry, and the resources such as thorium in the tailings were separated and extracted.
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