RE market is a diverse market, it is not just a product, but the 15 rare earth elements and yttrium, scandium, and various compounds of purity 46% to 99.9999% of a chloride of a single rare earth oxides and rare earth metals, Both have a variety of uses. Coupled with related compounds and mixtures, there are countless products. First, from the initial ore mining, we introduce the separation method and smelting process of rare earth one by one.
1. Rare earth beneficiation
Mineral processing is the use of different mineralization methods between the various minerals that make up the ore. Different mineral processing methods, different mineral processing techniques, different mineral processing equipment, the useful minerals in the ore are enriched to remove harmful impurities. A mechanical process that separates it from gangue minerals.
At present, rare earth ore mined in China and other countries in the world, the content of rare earth oxides is only a few percent, or even lower. In order to meet the production requirements of smelting, the ore minerals and gangue minerals will be processed before smelting. Separated from other useful minerals to increase the content of rare earth oxides to obtain rare earth concentrates that meet the requirements of rare earth metallurgy. The beneficiation of rare earth ore is generally carried out by flotation, and is often supplemented by re-election and magnetic separation to form a variety of combinations of beneficiation processes.
The rare earth deposit of the Baiyun Obo mine in Inner Mongolia is a carbonate rock deposit of iron dolomite. It is associated with rare earth minerals in the main component iron ore (in addition to fluorocarbon antimony ore, monazite, there are also several kinds of antimony and rare earth minerals). The produced ore contains about 30% iron and about 5% rare earth oxide. After the mine first crushed the large ore, it was transported by train to the concentrating plant of Baotou Iron and Steel Group Co., Ltd. The task of the concentrator is to increase the Fe2O3 from 33% to more than 55%. First, grind and classify on a conical ball mill, and then use a cylindrical magnetic separator to select a primary iron concentrate of 62 to 65% Fe2O3. The tailings continue to undergo flotation and magnetic separation to obtain a secondary iron concentrate containing 45% Fe2O3 or more. The rare earth is enriched in the flotation foam and the grade is 10-15%. The enrichment can be selected from a coarse concentrate having a REO content of 30% by a shaker, and after reprocessing by the ore dressing equipment, a rare earth concentrate having a REO of more than 60% can be obtained.
Second, rare earth smelting methods
There are two kinds of rare earth smelting methods, namely hydrometallurgy and pyrometallurgy.
Wet metallurgy metallurgy metallurgy, the whole process is mostly in solution, solvent, such as the decomposition of rare earth concentrate, rare earth oxides, rare earth compounds, single rare earth metal separation and extraction process is the use of precipitation, crystallization, redox, solvent Chemical separation process such as extraction and ion exchange. The most common application is the organic solvent extraction method, which is a general process for industrial separation of high purity single rare earth elements. The hydrometallurgical process is complex and the product purity is high.
The pyrometallurgical process is simple and has high productivity. Rare earth pyrometallurgical smelting mainly includes the preparation of rare earth alloy by silicon thermal reduction method, rare earth metal or alloy by molten salt electrolysis method, and rare earth alloy by metal thermal reduction method. The common feature of pyrometallurgy is that it is produced under high temperature conditions.
1. Decomposition of rare earth concentrate
Rare earth rare earth concentrate, generally in the form of a water-insoluble carbonates, fluorides, phosphates, oxides, silicates, or the like. The rare earth must be converted into a compound dissolved in water or inorganic acid by various chemical changes, and dissolved, separated, purified, concentrated or calcined to form various mixed rare earth compounds such as mixed rare earth chlorides as products or separations. A single rare earth raw material, such a process is called rare earth concentrate decomposition, also known as pretreatment.
There are many ways to decompose rare earth concentrates. In general, they can be divided into three categories, namely, acid method, alkali method and chlorination. The acid decomposition is further divided into hydrochloric acid decomposition, sulfuric acid decomposition, and hydrofluoric acid decomposition. Alkali decomposition is further divided into sodium hydroxide decomposition or sodium hydroxide melting or soda roasting. Generally, according to the type of concentrate, grade characteristics, product plan, easy to recycle and comprehensive utilization of non-rare earth elements, conducive to labor hygiene and environmental protection, economic and reasonable principles, select the appropriate process.
Production of rare earth carbonates and rare earth chlorides: This is the two most important primary products in the rare earth industry. Generally speaking, there are currently two main processes for producing these two products. One process is a concentrated sulfuric acid roasting process in which a rare earth concentrate is mixed with sulfuric acid and calcined in a rotary kiln. When the calcined ore is leached with water, the soluble rare earth sulfate enters the aqueous solution, which is called a leachate. Then, ammonium hydrogencarbonate is added to the leachate, and the rare earth is precipitated as a carbonate, and after filtration, a rare earth carbonate is obtained. Another process is called the caustic soda process, referred to as the alkali process. Generally, 60% of the rare earth concentrate is mixed with the concentrated alkali solution, and the reaction is melted at a high temperature. The rare earth concentrate is decomposed, the rare earth is changed into rare earth hydroxide, and the alkali cake is washed with water to remove the sodium salt and the excess alkali, and then The washed rare earth hydroxide is dissolved in hydrochloric acid, the rare earth is dissolved into a rare earth chloride solution, the acidity is removed to remove impurities, and the filtered rare earth chloride solution is concentrated and crystallized to obtain a solid rare earth chloride.
2. Separation of rare earth elements
At present, 16 rare earth elements other than Pm can be purified to a purity of 6N (99.9999%). Separating and extracting a single pure rare earth element from the mixed rare earth compound obtained by decomposing the rare earth concentrate is complicated and difficult in chemical process. There are two main reasons. First, the physical properties and chemical properties between the lanthanides are very similar. Most of the rare earth ions have a radius between adjacent two elements, which are very similar, and are stable in the aqueous solution. Rare earth ions have a large affinity with water. Due to the protection of hydrates, their chemical properties are very similar, and separation and purification are extremely difficult. Second, the mixed rare earth compounds obtained after the decomposition of rare earth concentrates have more impurity elements (such as uranium , thorium , krypton, neodymium, titanium , zirconium , iron, calcium, silicon, fluorine, phosphorus, etc.). Therefore, in the process of separating rare earth elements, not only the separation of these dozens of rare earth elements with extremely similar chemical properties but also the separation between the rare earth elements associated with the rare earth elements must be considered.
The separation method (wet production process) used in the production of rare earths now has: (1) a stepwise method (grading crystallization method, a fractional precipitation method, and a redox method); (2) an ion exchange method; and (3) a solvent extraction method.
(1) Step by step method
From the yttrium (Y) discovered in 1794 to the ruthenium (Lu) discovered in 1905, the single separation between all naturally occurring rare earth elements, as well as the radium discovered by the Curie couple, was isolated by this method. The stepwise method is carried out by separating and purifying the difference in the degree of solubility (solubility) of the compound dissolved in a solvent. The procedure of the method is as follows: a compound containing two kinds of rare earth elements is first dissolved in a suitable solvent, and then concentrated by heating, and a part of the elemental compound in the solution is precipitated (crystallized or precipitated). In the precipitate, the rare earth element having a small solubility is enriched, and the rare earth element having a larger solubility is also enriched in the solution. Since the difference in solubility between rare earth elements is small, it is necessary to repeat the operation multiple times to separate the two rare earth elements, which is a very difficult task. The single separation of all rare earth elements took more than 100 years, and the repeated operation of a single separation was as high as 20,000 times. For the chemical workers, the degree of hardship can be imagined. Therefore, a single rare earth cannot be produced in large quantities by such a method. (2) Ion exchange method
The research work on rare earth elements has also been hindered by the step-by-step method that cannot produce large amounts of single rare earths. After the Second World War, the US *** development plan, the so-called Manhattan Project, promoted the development of rare earth separation technology due to rare earth elements and Radioactive elements such as uranium and thorium are similar in nature. In order to promote atomic energy research as soon as possible, rare earth is used as a substitute. Moreover, in order to analyze the rare earth elements contained in the nuclear fission products and remove the rare earth elements in uranium and thorium, the ion exchange chromatography method (ion exchange method) was successfully studied, and the rare earth elements were separated. The principle of the ion exchange chromatography method is: first, the cation exchange resin is filled in the column, and the mixed rare earth to be separated is adsorbed at the end of the column inlet, and then the eluent is allowed to flow through the column from top to bottom. The rare earth forming the complex flows away from the ion exchange resin and flows down with the eluent. The rare earth complex decomposes during the flow and is then adsorbed onto the resin. In this manner, the rare earth ions flow toward the outlet end of the column while adsorbing and desorbing the resin. Since the stability of the complex formed by the rare earth ions and the complexing agent is different, the speed at which the various rare earth ions move downward is different, and the rare earth having a large affinity flows downward rapidly, and the result first reaches the outlet end. The advantage of the ion exchange method is that multiple elements can be separated in one operation. Moreover, high purity products can be obtained. The disadvantage of this method is that it cannot be processed continuously, the operation cycle takes a long time, and the cost of resin regeneration, exchange, etc. is high. Therefore, the main method for separating a large amount of rare earth has been retreated from the mainstream separation method. And replaced by solvent extraction. However, since the ion exchange chromatography method has the outstanding characteristics of obtaining a high-purity single rare earth product, at present, in order to prepare an ultra-high-purity single rare earth product and some heavy rare earth elements, separation by ion exchange chromatography is also required.
(3) Solvent extraction method
The method of extracting and separating the extract from an immiscible aqueous solution by using an organic solvent is called an organic solvent liquid-liquid-liquid extraction method, which is a solvent extraction method, which is a method for transferring a substance from a liquid phase to a liquid phase. Another mass transfer process in the liquid phase.
Solvent Extraction earlier application in the chemical industry, organic chemistry, pharmaceutical chemistry and analytical chemistry oil. However, in the past 40 years, due to the development of atomic energy science and technology, the need for the production of ultra-pure materials and rare elements, solvent extraction has been greatly developed in the nuclear fuel industry, rare metallurgy and other industries. China has reached a very high level in the research of extraction theory, the synthesis and application of new extractants and the extraction process of rare earth elements.
Compared with the separation method such as fractional precipitation, fractional crystallization and ion exchange, the solvent extraction method has a series of advantages such as good separation effect, large production capacity, convenient and rapid production, and easy automatic control. The main method of rare earths.
The solvent extraction method includes a mixing clarification tank, a centrifugal extractor, etc., and the extracting agent used for purifying the rare earth is: a cationic extracting agent represented by an acid phosphate such as P204, P507, an anion exchange liquid represented by an amine N1923, and Three kinds of solvent extractants represented by neutral phosphates such as TBP and P350. These extractants have high viscosity and specific gravity and are not easily separated from water. Then usually diluted with a solvent coal oil. The extraction process can generally be divided into three main stages: extraction, washing, and back extraction.
3. Preparation of rare earth metals
The production of rare earth metals is also called rare earth pyrometallurgical production. Rare earth metals are generally classified into mixed rare earth metals and single rare earth metals. The composition of the mixed rare earth metal is close to the original rare earth component in the ore, and the single metal is a metal separated and refined by each rare earth. To rare earth oxide (except samarium, europium, ytterbium, and thulium oxide) is generally used as a raw material is difficult to restore to a single metal metallurgical processes, heat is generated because of a large, high stability. Therefore, the raw materials commonly used in the production of rare earth metals are their chlorides and fluorides.
(1) molten salt electrolysis
In the industrial production of mixed rare earth metals in large quantities, molten salt electrolysis is generally used. In this method, a rare earth compound such as a rare earth chloride is heated and melted, and then electrolyzed to precipitate a rare earth metal on the cathode. The electrolysis method has two methods of chloride electrolysis and oxide electrolysis. The preparation method of a single rare earth metal varies depending on the element.é’, é“•, 镱, é“¥ are high in vapor pressure and are not suitable for electrolytic preparation, but use reduced distillation. Other elements can be prepared by electrolysis or metal thermal reduction. Chloride electrolysis is the most common method for producing metals. In particular, the process of mixing rare earth metals is simple, the cost is low, and the investment is small, but the biggest disadvantage is that chlorine gas is released and pollutes the environment. No harmful gas evolution oxide electrolysis, but the cost is slightly higher, generally more expensive production of single rare earth such as neodymium, praseodymium oxide so by electrolysis.
(2) Vacuum thermal reduction method
The electrolysis method can only prepare general industrial grade rare earth metals. For example, it is necessary to prepare a metal with low impurity and high purity, which is generally obtained by vacuum thermal reduction. Generally, the rare earth oxide is firstly made into a rare earth fluoride, which is reduced by metal calcium in a vacuum induction furnace to obtain a crude metal, and then remelted and distilled to obtain a relatively pure metal. This method can produce all the single metals. Rare earth metals, but é’, é“•, 镱, é“¥ cannot be used in this way. The redox potential of lanthanum, cerium, lanthanum, cerium and calcium only partially reduces the fluorinated rare earth. Generally, these metals are prepared by using the high vapor pressure of these metals and the low vapor pressure of the base metals. The four rare earth oxides are mixed with the crucible metal crumbs and compacted in a vacuum furnace. Active, sputum, sputum, sputum, sputum is reduced to metal by hydrazine and collected on the condenser, which is easily separated from the slag.
Third, the classification method of rare earth products
There are many types of rare earth products. According to the processing depth, we divide it into metallurgical products and application products. The former refers to rare earth concentrates produced by rare earth mines and smelting enterprises, single and mixed rare earth oxides, metals and their alloys, single and mixed rare earth salts, etc., totaling more than 300 varieties and more than 500 specifications. The latter refers to all finished products containing rare earths, such as rare earth permanent magnets, rare earth phosphors, rare earth polishing powders, rare earth micro-fertilizers, rare earth laser crystals, rare earth hydrogen storage materials, and the like. At present, there is no unified classification, there is no unified name, the boundaries are not clear, and everyone is familiar with it; mineral products, primary products (or crude products) are called upstream products; deep processing products (or single products, high-purity products) ) called midstream products; applied materials and application products (or devices) are called downstream products. The main uses of single rare earth oxides, rare earth metals, mixed rare earth oxides and mixed rare earth metals are shown in Table 1. Table 1 List of rare earth products use single rare earth oxide mixed rare earth oxide single rare earth metal mixed rare earth metal
La2O3: optical glass, ceramic capacitors, catalysts, thermal electron emitters, etc.
Ce2O3: glass decolorizer, catalyst, optical glass, polishing powder, and the like.
Pr2O3: pigment, permanent magnet, catalyst, and the like. Nd2O3: permanent magnets, glass additives, ceramic capacitors, lasers, etc. Sm2O3: permanent magnet, ceramic capacitor, catalyst. Eu2O3: red phosphor, atomic reactor control material, etc. Gd2O3: atomic reactor control material, GGG magneto-optical material, magnetic refrigeration material, optical glass. Tb4O7: high color rendering lamp, magneto-optical storage material, magnetostrictive material.
Dy2O3: permanent magnet, magnetic refrigeration material, etc. Ho2O3: pigments, lasers, etc. Er2O3: optical glass, semiconductor, optical fiber. Tm2O3: laser, etc. Polishing powder, flat glass, TV picture tube, camera lens, spectacle lens, etc. Catalyst petroleum cracking catalysis.é’‡: heat-resistant steel additives, electronic materials, nuclear reactor materials, aluminum wires.镧: hydrogen storage alloy, electron ray source, getter, aluminum alloy.镨: permanent magnet alloy, magnetic cryogenic alloy.é’•: permanent magnet alloy, magneto-optical storage material é’: permanent magnet alloy.铈: Flint alloy, metallurgical additives. é’† : atomic energy, magnetic refrigeration materials, magneto-optical storage materials.
é• : permanent magnet alloy, magneto-optical storage material, magnetic refrigeration, magnetostrictive material.é“¥: magnetostrictive materials, etc. 铽 : magnetostrictive material, magneto-optical storage material. Pyrophoric alloys, additives for steel and non-ferrous metals, hydrogen storage alloys, etc.
From the rare earth raw materials to the final product is divided into several stages, the closer to the final product, the higher the technical content, the higher the added value. From rare earth raw materials to final products, we must go through raw materials, materials, devices and products, and each key has key technologies. The closer to the final product, the higher the technical content, and of course the higher the added value. Therefore, the development of rare earth application products and high value-added products is the future hope of China's rare earths.
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