Дата публикации: 27 сентября 2018
Автор: Leopold LEONTIEV →
Публикатор: Шамолдин Алексей Аркадьевич
Рубрика: ЭКОЛОГИЯ →
Источник: (c) Science in Russia, №5, 2006, C.25-29 →
Номер публикации: №1538002085 / Жалобы? Ошибка? Выделите проблемный текст и нажмите CTRL+ENTER!
Leopold LEONTIEV, (c)
The Norilsk Mining and Smelting Plant (MSP) over half a century has been a source of pollution of the environment in the Arctic regions.
The development of sulphidic platinoid-cupronickel deposits always involves high ecological hazard, but the greatest harm is caused by sulfur dioxide (SO2), which is formed in ore processing.
The high damage levels today impede further development of production.
Therefore in years to come the efforts of metallurgists will be directed to the development and introduction of technologies that make it possible to reduce emissions of sulfur dioxide. This was the subject of the interview given by the Member of the Presidium of the Russian Academy of Sciences, director of the Institute of Metallurgy of the Ural Branch of the Russian Academy of Sciences, Academician Leopold Leontiev to our correspondent Yevgeniya Sidorova.
- Leopold Igorevich, for a long time you have been engaged in the development of the technologies that reduce negative impact of the metallurgical enterprises on the environment, and you are an authority in this field. At present you make efforts for solving the nature conservancy problems of the Norilsk MSP. What are the basic indicators that evidently testifies to the gravity of the ecological problem resulting from its activity?
- Ecological conditions in the area of the Arctic branch of OAO Norilsk Nickel have been studied by many research teams, including the RAS Institute of the Global Climate and Ecology, Institutes of the RAS Siberian Branch-V. Sukachyov Forest Institute*, the Biophysics Institute, the Institute of Optics of Atmosphere, the RAS Research Institute of Far North Agriculture, the Siberian
* See: "Norilsk Project", Science in Russia, No. 4, 2005. -Ed.
Plume of combustion gas over Norilsk.
Regional Hydrometeorological Research Institute, etc. The An-30 airplane-laboratory also was involved in this work. Everything - the state of atmosphere, soil, water and vegetation - was estimated in detail. It appeared that the industrial dust covering the significant areas contains increased amounts of heavy metals, such as nickel, copper, lead. But the greatest problem is emission of sulfur dioxide. A quarter of Russian industrial emissions of SO2 accounts for the integrated iron-and-steel works working here. But it is only a restricted territory that suffers from these emissions. It is a blessing that the lands in the Arctic Circle are poorly populated. The copper and nickel plants are located on the opposite outskirts of Norilsk, and whatever the direction of the wind may be, the town is covered with a plume of emanating chimney gases.
The studies have revealed: the contours of lands with a higher sulfur level and damaged forests have here similar configuration. The scientists singled out several levels of pollution inside the exposed territory. Thus, in the southern and southeastern parts of the industrial center (with prevalence of the north-eastern wind) the wood vegetation was lost completely within the 70-kilometer zone. The sulfur content in plants exceeds the ambient level 3 - 4 times, the nickel content, 18 - 26 times, the copper content, 4 - 9.5 times. There have been detected the plots with the ambient level for copper exceeding 17 - 156 times, and for nickel, 31 - 470 times.
And only at a distance over 70 km from the town the rate of dead trunks in the wood stage decreases and there appears the cedar sensitive to technogenic impact. Further down to the mark of 80 - 100km, the features peculiar to the given bioclimatic zone become evident: dead trees comprise about 50 percent, the undergrowth and moss-grassy vegetation are not suppressed.
The scientists register a zone of weak pollution at a distance of 100 - 140 km from Norilsk. There the sulfur content in plants exceeds background indicators 1.2 - 1.7 times, nickel, 1.5 - 2.7 times, copper, 1.3 times. The rate of dead trees makes up only about 14 percent, the fur-tree and the birch-tree grow up, occasionally the larch, but strongly suppressed, can be found. The fur-tree feels better, and the birch-tree is the most resistant to the pressing of industrial discharges.
There is no degradation of vegetation at a distance over 200 km from Norilsk.
- As it follows from the scientific publications, acidity of atmospheric precipitation within the limits of the Norilsk region due to the high content of sulfur dioxide in atmosphere makes up 3.1 - 3.2 units of pH, which is destructive for plants. But, probably, the situation can be changed in future? Indeed, if the "removal" of heavy metals and the sulfur accumulated in the Taimyr soils for the years of the MSP operation, is a very difficult task today, then may be reduction of the "current" contamination of the atmosphere can be achieved?
-There are two ways for solving the problem: to enhance utilization of sulfur in exhaust gases and to learn to separate the maximum possible amounts of a sulfur-containing component of ore at the phase of its preliminary enrichment, i.e. before pyrogenic effect. So far, the first variant is used at the Norilsk MSP.
At present the amount of sulfur emitted by the enterprises of Norilsk, makes up about 1 mln tons. The methods of utilization of this gas are well-known: as a rule, foreign metallurgical companies obtain sulfuric acid on its basis. However, due to insufficient sale of sulfuric acid even in Canada, the main nickel power of the world, one of the biggest works "Copper-Cliff" emits converter gases into atmosphere. The same occurs in Finland, China, Botswana. In our case it also would make no sense to process SO2 entirely into sulfuric acid as the MSP needs it in relatively small quantities, and transportation to other consumers is impossible for lack of railway communication. In an equal
Isolines of sulfur dioxide fallout field.
measure this circumstance also prevents sale of elementary sulfur, which is obtained through the processing of sulfur dioxide, carried out by citizens of Norilsk now in view of urgent ecological problems.
By the way, this method is applied nowhere in the world, as it is very expensive, and its product is practically out of demand. Adding of sulfur as a filling agent in asphalt, its use in rubber vulcanization or for obtaining the same sulfuric acid involves significant expenses for transportation to the prospective consumer. As a result, the appropriate program of the Norilsk MSP contemplates construction of a warehouse with a capacity of 7 mm tons for long-term storage of the product, unnecessary at present.
Nowadays, elementary sulfur is obtained at the Norilsk Copper Works from sulfur dioxide by reducing the latter with the help of methane at a temperature of 1,250 - 1,300 C. Then the partially reduced portion of gas that contains hydrogen sulphide is processed by the so-called Claus method. Such method of obtaining sulfur has been developed by the Institute of Nonferrous Metals (Moscow), G. Boreskov Institute of Catalysis, the RAS Siberian Branch (Novosibirsk) and the Norilsk MSP. This technology ensures utilization of exhaust gases at a gas flow rate of 40,000 m3 per hour and 20 - 25 percent content of SO2. The total volume of production of elementary sulfur should make up 80,000 tons per year, the rate of its extraction from sulfur dioxide being 85 percent. But since processing by the Claus method is carried out in one phase, the real index is equal to 60 - 65 percent. Meanwhile, according to estimates, if the second phase of the Clause method is applied (which, by the way, is stipulated by the project) and the Sulphren type sanitary cleaning is used (successfully employed at the Astrakhan Gas-Processing Plant) not less than 99 percent of sulfur can be extracted. This method, however, is very expensive.
Today Russian scientists suggest reducing sulfur dioxide down to elementary sulfur by means of coal, not by methane. In this case both the reaction rate and the rate of extraction of sulfur, comprising approximately 98 percent, will be essentially higher than in the case of natural gas, and the cost of the process, considerably lower. True, it is necessary to develop technology and equipment, which will guarantee fire safety of the process. But the introduction of crushed coal into the zone of high temperatures of open-hearth, blast and electric furnaces in the ferrous metallurgy is a common practice. At our Institute even a small enterprise was set up, which develops and introduces devices for injection of coal-dust fuel into various metallurgical aggregates. They are successfully used at many domestic plants*.
- You have mentioned the separation of the sulfur-containing phase of the Norilsk ore at the stage of preliminary enrichment. Is it connected with any problems?
-Yes, it is. The basic part of the sulfur-containing component of the Norilsk ore - pyrrhotine (Fe1-xS) is not magnetic, since the forms with hexagonal crystal-lattice predominate in its composition. Whereas in foreign deposits monoclinic forms dominate, which makes it possible to easily separate this mineral by means of a magnet (magnet -
* See: L. Leontiev et al., "Akademichesky Center of Innovative Technologies", Science in Russia, No. 2, 2003. - Ed.
Diagram of forests damaged under effect of exhausts of Norilsk MSP: several levels of contamination are singled out.
ic separation), especially if its particles ingrained in the ore are big enough. As a result, the technology of enrichment is considerably facilitated, and losses of valuable ingredients are minimal, as a small amount of non-ferrous and precious metals is associated with the monoclinic form of the mineral. Unfortunately, the basic part of copper, nickel and cobalt, on the contrary, is concentrated in the Norilsk hexagonal pyrrhotine, which threatens with serious losses in the process of "cutting off" the sulfur-containing ingredient at the stage of pre-treatment of the ore. In addition, fine impregnations of sulphides is characteristic of our deposit.
As pyrrhotine in copper-nickel ores is a predominant mineral, the rate of its "removal" during the process of enrichment has an essential effect on the quality of obtained concentrates and on indexes of their subsequent processing. Currently, the pyrometallurgy is still the only tangible process, which ensures full extraction of precious metals.
- Are there alternative approaches to separation of pyrrhotine?
- Only the so-called hydrometallurgical methods can help in this context. Their technologies are well mastered abroad: for processing of copper-nickel sulphidic ores, concentrates and products of metallurgical productions, recourse is made to lixiviation in ammoniac, sulfuric acid, chloride and nitrogen-sulfuric-acid media. The majority of the plants, which operate according to this pattern, meet the present-day requirements to the environmental safety, though each method has its negative aspects.
Say, the defect of the ammoniac lixiviation used at the Canadian plant Fort-Saskatchewan and Australian Kwinana is low extraction of cobalt and platinum metals. The method is unacceptable for raw materials with these valuable ingredients.
Lixiviation in sulfuric acid media, a gaseous oxidizer being also involved, is widely used for processing of copper-nickel and nickel-cobalt concentrates and semi-products. For example, Finnish metallurgical company "Outokumpu" has introduced the HIKO-process, which includes sulfuric-acid lixiviation in autoclave, cleaning from admixtures, extraction separation of nickel and obtaining of its various salts. All this ensures a high rate and completeness of extraction of metals. At the Finnish enterprise in the town of Harjavalta and at South-African plants the sulfur contained in the raw material is converted into sulphate of ammonium. It can also be converted into the elementary form, as in Norilsk.
Hotmelts of sulfides of metal compounds are recycled by lixiviation in chloride media at the plants of several foreign companies (Canadian "Falkonbridge", Japanese "Sumitomo", French "Eramette"). Advantages of the method are high intensity of the process without using autoclaves, the possibility of regeneration of the basic reagents-chlorine gas or chlorides of copper and iron and a high rate of electroextraction of nickel. But its disadvantages are high aggressiveness of chloride solutions, which requires application of expensive corrosion-resistant materials.
The State Institute of Non-Ferrous Metals has offered a rather new hydrometallurgical method of processing of pyrrhotine-containing raw materials. The method consists in application of sulfur dioxide as a lixiviation reagent and can become a successful solution of some ecological and technological problems of the Norilsk MSP. In fact, with the given approach, pyrrhotine iron changes into a solution as sulphate, and sulfur of this mineral and a part of dioxide, into the elementary form. Sulphides of non-ferrous metals and platinum metals remain in the solid phase. Processing according to such pattern of the nickel concentrate with the content of the sum of nickel, copper and cobalt of about 9 percent, makes it possible to increase their content up to 30 percent after removal of elementary
Chart-scheme of damaged forests according to aerovisual examination: 1 - zone of destruction of stock of trees, 2 - zone of its severe damage.
sulfur and to conserve practically completely precious ingredients. Besides, loading of pyrometallurgical capacities and discharge of sulfur dioxide will decrease by 40 - 45 percent. The method is also good as it allows to use the existing equipment to a considerable extent. Currently, the developers need only to carry out additional kinetic studies and trial tests.
- It is well-known that the MS and OAO "Norilsk Nickel" are developing a scientific and technical program, meant to provide step-by-step decrease in discharges of sulfur dioxide down to the maximum permissible level. Will you be so kind as to tell us about this cooperation.
-Director General of OAO Norilsk Nickel Mikhail Prokhorov has appealed to the RAS to discuss this subject at the Presidium and to work out a program for solving ecological problems. It was resolved in the Company that the plant science cannot cope with fundamental studies*.
Currently, a lot of Russian (not only academic) institutes have made unique proposals on solving various MSP technological problems. I have already dealt on the technology of use of carbon for reduction of sulfur dioxide and hydrometallurgical method of processing of pyrrhotine-containing raw materials. One more interesting proposal is a transformation of pyrrhotine to troilite (FeS) and extraction from it valuable ingredients to the metal phase. The melted troilite phase in very limited quantities will dissolve nickel, copper and precious metals, thus permitting their separation from the sulfur-containing ingredient. Such process is real in the existing aggregates, but it requires creation of new technology, which is now at the laboratory stage of development.
Domestic scientists offer also methods of overcoming the ecological crisis, which make it possible to preserve the existing process patterns. One of them is a burial of sulfur dioxide with the use of natural cold. In fact in the pure state it is liquefied already at the temperature of - 10 C. For disposal of gas we can choose limy breeds, where sulfur dioxide in due course will be bound in other, harmless compounds. This approach, however, requires an analysis of the hypothetical situation, arising in the process of thawing of the permafrost as a result of predicted global warming**. We also consider the possibility of disposal of sulfur in the cavities of rocks depleted long time ago. It is expected that in this way 90 percent of this substance can be utilized.
Certainly, I have mentioned only a part of the proposals of our experts. The aim of the program, which is being developed by the Russian Academy of Sciences together with MSP Norilsk Nickel is to reveal the most original ideas. Now metallurgists and chemists are mainly involved in studies, but we are eager to attract also physicists, as they can suggest their approaches to the transformation of sulfur dioxide into more harmless production.
- But it will take some time before the program will be developed and accomplished. What is being done nowadays to decrease ecological load on the inhabitants of Norilsk?
- So far the problems of utilization of sulfur dioxides and sulfur have not been finally solved. Specialists are studying, for example, the possibility of discharging metallurgical gases from autogenous smelting furnaces through a gas pipeline beyond the residential area.
The plans of OAO Norilsk Nickel MSP envisage large-scale modernization of production of OAO Kola MSP, involving the introduction of technology of ore concentrate preparation without its sintering and a new technology of autogenous smelting, as a result of which essential reduction of discharges into the atmosphere is expected.
The total amount of investment expenses for nature protection measures in 2005 - 2015 will make up, according to the plans of the Norilsk Nickel MSP, over 30 bin rubles.
* See: Ya. Renkas, "Along the Road of Innovations and Investments," Science in Russia, No. 3, 2004. - Ed.
** See: Yu. Israel, "Threat of Climatic Catastrophe?", Science in Russia, No. 4, 2004. - Ed.
Опубликовано 27 сентября 2018 года
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