Baotou City is one of the national steel industrial base, is the world-famous hometown of rare earth, rare earth production of its main raw materials from the Bayan Obo iron ore. With the continuous expansion of the world rare earth market, the rare earth industry in Baotou City is booming, with technological routes from rare earth mining, beneficiation to rare earth smelting, separation and purification, application, and relatively complete rare earth industrial systems, which are constantly improving and prospering. The Baotou economy and the world's rare earth industry have contributed. However, there are also environmental pollution problems in the development. Especially in recent years, with the expansion of production scale, most of the products are rare earth middle and upstream products, and the pollution prevention facilities are imperfect and the pollution control technology is backward, which has produced in the production process. A large number of "three wastes" pollute the surrounding environment and the safety of drinking water, restricting the sustainable and healthy development of the rare earth industry.
1. The source of “three wastes†produced by rare earth metallurgical industry
Rare earth metallurgical industry production of "three wastes" means in addition to the production of various forms of rare earth products, accompanied by a certain amount of "waste", ie waste gas, waste water, waste residue. These wastes often contain substances that are harmful to living things. If it is discharged without treatment, it will cause pollution to the surrounding environment. Therefore, limit or reduce the spread of harmful substances in the "three wastes". By recycling the useful ingredients, you can turn harmless and harmless, turning waste into treasure.
(1) Exhaust gas in rare earth metallurgical production
Exhaust gas in rare earth production: First, dusty gas is produced through the following production processes: mining, crushing, beneficiation process, rare earth concentrate spheronization process, alkali roasting process of rare earth concentrate, rare earth pyrometallurgical process, rare earth intermediate product Or the drying, pulverizing, grinding and packaging process of the finished product. The second is radioactive gas, mainly from the dust containing uranium and thorium in the air and the aerosol of strontium and its ions. The third is toxic gas, which also produces toxic gases containing liquid particles (fog) and impurity gases. The main processes for producing such waste gas are: acid calcination of rare earth concentrate, chlorination of rare earth minerals, electrolysis of rare earth molten salt, and various chemical operations in wet smelting. Its main poisons are hydrogen fluoride, silicon tetrafluoride, sulfur dioxide, chlorine, various acids, alkali solution mist, organic extractant and solvent vapor.
(2) Waste water in rare earth metallurgical production
The wastewater in the rare earth production process mainly comes from: mineral processing wastewater, equipment and ground washing water, exhaust gas purification washing water, various waste liquids in wet smelting, cooling water, laboratory sewage and domestic sewage. Its harmful components are mainly: suspended solids, acids, alkalis, fluorides, natural radioactive elements (uranium, thorium and radium), various inorganic salts and some organic solvents. For example, concentrated sulfuric acid roasting decomposes the acidic fluorine-containing wastewater generated in the mixed rare earth concentrate smelting system, and the alkaline low-radiation wastewater generated in the alkali decomposition monazant smelting system.
(3) Waste residue in rare earth metallurgical production
The waste residue in the rare earth production process is mainly tailings after beneficiation, smelting slag in pyrometallurgical smelting, insoluble slag after acid-base decomposition, various sedimentary slag in wet smelting, dust accumulation in dust removal system and wastewater treatment Sediment. The rare earth smelter produces about 0.5t of various residues per 1t of rare earth concentrate, and some even reach 2t-4t. Some slags carry a certain amount of radioactivity.
Second, the "three wastes" treatment of rare earth metallurgical industry production
The “three wastes†discharged from rare earth production, although many varieties, are not complicated, and generally adopt appropriate treatment methods, which can meet national health standards.
(1) Waste gas treatment in rare earth metallurgical production
The purification process generally employs a condensation method, an absorption method, an adsorption method, a combustion method, and a catalytic method. At present, China uses two kinds of absorption methods and adsorption methods, which have simple process, less process equipment and better effect.
(II) Wastewater treatment in rare earth metallurgical production
The treatment of wastewater can be generally carried out by coagulation, neutralization, neutralization, adsorption, ion exchange and extraction. At present, neutralization method, neutralization precipitation method and adsorption method are commonly used. These methods are simple, effective, and low cost.
(3) Treatment of waste residue in rare earth metallurgical production
Waste residue can be divided into non-radioactive waste residue and radioactive waste residue. The former can establish the slag yard (or slag dam) stacking, the latter must establish the slag stock release, pay attention to the secondary spread to prevent pollution of the environment.
Third, the current problem of resolving the "three wastes" of rare earth metallurgical industry needs to be solved
At present, the “three wastes†produced in the production of rare earths in China have been effectively treated, but there are still problems in the overall situation, which need to be solved from the following aspects.
(1) Adopting new technology to reduce emissions of “three wastesâ€
In the process research and the selection of process technology, it is necessary to consider the emission of rare earth “three wastesâ€, eliminate the “three wastes†in the production process, try not to discharge or reduce emissions, and try to concentrate the “three wastes†within one process. To reduce the "three wastes" emissions range. In this way, the safety protection can be simplified, and the “three wastes†treatment costs and investment can be greatly reduced, thereby improving the governance level of “three wastesâ€. The School of Chemical Engineering of Inner Mongolia University of Technology and Baotou Yingjie Chemical Co., Ltd. have developed a production process for the production of ammonium hydrogen fluoride and crude white carbon by using rare earth roasting tail gas. The process can effectively utilize the tail gas acid emitted by rare earth enterprises. It can be seen that the process can not only reduce the emission of “three wastesâ€, but also achieve energy saving and emission reduction.
(2) Do a good job in the comprehensive utilization of "three wastes". Turning waste into treasure
The “three wastes†produced in the production of rare earths contain many valuable elements that can be recycled. For example, when dealing with monazite, it produces a superior slag with higher radioactivity, which contains valuable substances such as rare earth, strontium and uranium. At present, processes for producing products such as rare earth chloride, barium nitrate and ammonium diuranate have been recovered. For example, chlorine-containing waste gas can be recovered from caustic soda reagent to prepare sodium hypochlorite product.
(3) Improve the recycling rate of industrial water
At present, nearly one million tons of various waste waters are discharged from the production of rare earths in China. Although harmful strontium, uranium, fluorine, HC1 and H 2 SO 4 can be removed, they cannot be directly reused. The reuse standard for industrial water can only be achieved after further purification treatment. At present, circulating water reuse in rare earth industrial production accounts for about 20% of total water consumption, which is far lower than the 80% requirement for wastewater reuse in industrial production in general countries. The reason is that the discharged wastewater is diverse, the composition is complex, and the process is immature. In response to this problem, my research group discussed and developed a full-cycle clean production process. The process is mainly to improve the high temperature roasting process of Baotou rare earth concentrate by the third generation acid method. Change the existing roasting ore processing process. The roasting ore is based on the transformation technology, and the non-rare earth chemicals (ammonium sulfate and ammonium hydrogen sulfate) are completely recovered, and the water is purified and fully recovered. This project can make the Baotou Rare Earth Industry change the open production in history to recycling production. It can be seen that the process can not only improve the recycling rate of industrial water, but also recover non-rare earth chemicals in industrial production processes.
(4) Adhere to the "three simultaneous" policy
The state requires that the “three wastes†policy of “simultaneous design, simultaneous construction, and simultaneous production†in the construction project must be implemented to ensure that the “three wastes†emission targets reach the national health standards after the factory is completed and put into production. In the future industrial production development, the management of “three wastes†will be more strict and standardized.
Fourth, the conclusion
The “three wastes†discharged from the production of rare earth metallurgical industry in China have been largely treated, but from the aspects of the “three wastes†treatment process, equipment, operations and management, it needs to be improved, improved and improved to ensure “ The “three wastes†emissions do not pollute the environment. In addition, it is necessary to strengthen the research work on the "three wastes" governance, to improve the industrialization level of "three wastes" governance, further promote the development of China's rare earth industry, contribute our strength in the world's rare earth industry, and promote the development of the world rare earth industry.
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