Abstract
Content
- Introduction
- 1. Zinc and its alloys
- 2. Zinc Uses
- 3. Characteristics of the sources of secondary zinc-containing raw materials
- 4. Extract zinc from ferrous metal waste
- 4.1 Processing of scrap and waste galvanized steel semi-finished products
- 4.2 Rolling dusts and sludges
- 4.3 Dust recycling with the Plasmazinc process
- Findings
- List of sources
Introduction
The world is constantly developing and improving technologies for the extraction of metals from secondary raw materials. This is due to the following economic and environmental benefits:
- reducing the volume of materials extracted from ores;
- – energy savings due to reduced mining and smelting needs;
- – reduction of soil and water pollution;
- – preservation of reserves of zinc-containing ores.
Compared with the production of primary zinc, recycling saves from 54 to 99.5% of energy costs.
1. Zinc and its alloys.
In accordance with GOST 3640–94, eight grades of zinc are produced, the chemical composition of which is listed in Table 1.1.
Table 1.1 - Stamps and chemical composition (%) GOST 3640–94 [1] Stamp designation Zn not less Pb Cd Fe Cu Sn As Al Total ЦВ00 99,997 0,00001 0,002 0,00001 0,00001 0,00001 0,0005 0,00001 0,003 ЦВ 99,99 0,005* 0,002 0,003 0,001 0,001 0,0005 0,005 0,01 ЦОА 99,98 0,01 0,003 0,003 0,001 0,001 0,0005 0,005 0,02 ЦО 99,975 0,013 0,004 0,005 0,001 0,001 0,0005 0,005 0,025 Ц1 99,95 0,02 0,01 0,01 0,002 0,001 0,0005 0,005 0,05 Ц2 98,7 1,0 0,2 0,05 0,005 0,002 0,01 0,010 1,3 Ц3 97,5 2,0 0,2 0,1 0,05 0,005 0,01 - 2,5 Zinc is used: for hot, chemical and thermal diffusion galvanizing of steel parts; in the printing industry; for the manufacture of chemical current sources; as an alloying element in alloys, primarily in brass (an alloy of the system Cu — Zn), and as the basis for zinc alloys.
Brass - was received much earlier than metallic zinc. The most ancient brass articles, made around 1500 BC Now brass alloy is denoted by the letter "L", followed by letters of the main elements forming the alloy. In the stamps of deformable brass the first two digits after the letter "L" indicates the average copper content in percent. For example, L70 is brass containing 70% Cu. When Alloyed deformable brass indicate more letters and numbers indicating the name and number of alloying element, LAZh60-1-1 means brass with 60% Cu doped with aluminum (A) in the amount of 1% and iron (W) in the amount of 1%. The content of Zn is determined by the difference from 100%. In the foundry brass average content alloy components in percents are placed immediately after the letter designating its name. For example, brass LTs40Mts1,5 contains 40% zinc (C) and 1.5% manganese (Mts).[2]
Zinc is also a part of another ancient copper-based alloy. It's about bronze. Previously, they divided clearly: copper plus tin - bronze, copper plus zinc - brass. Now, the "faces are erased." OTC-3-12-5 alloy is considered bronze, but there is four times more zinc in it than tin..
Zamak (ZAMAK, Zamac) is a family of zinc alloys alloyed with aluminum, magnesium and copper, which are very widely used in the foundry industry. Alloys of this family are distinguished by an aluminum content of about 4%. The abbreviation stands for: zink - aluminum - magnesium - kupfer, - that is, it consists of the first letters of the German designations of the metals in the alloy. The alloys of the ZAMAK family are designated by different numbers (ZAMAK-1, 2, 3, 5, 7, etc.) ), - the most common alloy ZAMAK-3. It has a Brinell hardness of 97 units, which is comparable to mild steel (~ 120 HB). The tensile strength is 268 MPa, the modulus of elasticity is 96 GPa, the melting point is 381-387 ° C, the density is 6.7 g / cm 2, the coefficient of friction is 0.07. The main field of application for alloys of the ZAMAK family is injection molding. These alloys have a low melting point (slightly higher than that of lead) and very good casting properties, while being sufficiently strong (at the level of low carbon steel), which makes it possible to obtain fairly strong parts with a very complex shape.
Table 1.2 - The chemical composition of cast zinc alloys, mass fraction,%[3] Элементы ZAMAK2 ZAMAK3 ZAMAK4 ZA8 SUPERLOY Al 3,8...4,2 3,8...4,2 3,8...4,2 8,2...8,8 6,6...7,2 Сu 2,7...3,3 ?0,03 0,7...1,1 0,9...1,3 3,2...3,8 Mg 0,035...0,06 0,035...0,06 0,035...0,06 0,02..0,035 ?0,005 Pb 0,003 0,003 0,003 0,005 0,003 Fe 0,02 0,02 0,02 0,035 0,02 Cd 0,003 0,003 0,003 0,005 0,003 Sn 0,001 0,001 0,001 0,002 0,001 Si 0,02 0,02 0,02 0,035 0,02 Ni 0,001 0,001 0,001 0,001 0,001 Throughout the world, the word Zamak has become, in fact, a synonym for zinc-aluminum alloys. In the countries of the former USSR, the abbreviation ZAM is used for similar alloys: zinc - aluminum - copper.
The list of products made from alloys of this family is very wide and includes: zippers, carburetor bodies, plumbing mixers, industrial staplers, various door handles and similar accessories, lock cases, scale models, golf clubs, art miniature, fishing reels, firearm (Hi-Point Firearms) and traumatic (Zoraki, Streamer) weapons, and much more.
The growing shortage of lead and tin made metallurgists look for recipes for new printing and antifriction alloys. Affordable, rather soft and relatively low-melting zinc naturally attracted attention in the first place. Almost 30 years of prospecting and research work preceded the emergence of zinc-based antifriction alloys. With small loads, they are noticeably inferior to babbits and bronzes, but in bearings of heavy trucks and railway cars, coal crushers and excavators, they began to replace traditional alloys. And it's not just about the relative cheapness of zinc-based alloys. These materials are prekрасно выдерживают большие нагрузки при больших скоростях в условиях, когда баббиты начинают выкрашиваться.
Typographical alloys - alloys of non-ferrous metals used in the printing industry. They have a low melting point and good casting properties. In view of the harmful effects of lead on workers' health, they began to use typographical alloys based on zinc. The characteristics of such alloys are as follows:
- Brinell hardness: up to 120 kg / cm2 (significantly higher mechanical properties than lead printing alloys);
- Melting point: 340 380 ° C
2. Zinc Uses
The world uses about 9.5 million tons of zinc. Zinc is produced and consumed mainly in the form of metal, chloride, powder, oxide and sulphate. In tab. 2.1 shows areas of zinc consumption in the world. Large consumers of this metal are China, USA, Japan and countries of Western Europe.
Table 2.1 - Zinc applications in the world,% By products By branches Galvanized steel products 41 Building 48 Brass 19 Automotive industry 23 Zinc alloys 16 Engineering 10 Powder, oxide, salts 15 Common consumption goods 10 Sheets and other semi-finished products 7 Infrastructure 9 Other 2 total 100 Total 100 The greatest amount of zinc is spent on galvanizing steel products: sheets, strips, wires, pipes, containers, bolts, nails. Another important area of zinc consumption is brass. The global demand for zinc for the production of brass is about 2.1 million tons. At the same time, the production uses 1 million tons of primary zinc, 600 thousand tons of zinc obtained from domestic waste, and 500 thousand tons of secondary raw materials. Thus, more than 50% of the zinc used in the production of brass is obtained from waste. [3]
НThe most numerous and important group of zinc alloys is casting alloys, which are used to manufacture a wide range of products - from automotive components to toys and models. Zinc oxide is used for the production of tires, rubber products, coloring pigments, ceramic glaze, carbon paper. Production of anti-corrosion coatings based on the use of zinc powders in primers and paints is growing. Anti-corrosion coatings of metal products and structures zinc filled with primers and paints are used in the automotive, shipbuilding, oil, construction and other industries. The advantage of zinc filled soils and paints is the simplicity of applying them to products of any dimensions, as well as the best protective properties. Zinc chloride is used in tinning, as a soldering flux and for dry cells of electric batteries. Zinc sulfate is used in the textile, chemical, metallurgical industries. A promising area of zinc is the production of zinc-air and alkaline batteries. Zinc-air elements are the largest density of all modern technologies. Atmospheric oxygen is used as the cathode reagent in these elements. Electrolyte in these elements is potassium hydroxide, which has a high conductivity. Best of all, such elements have proven to work for a long time in low-power devices. Methods of using zinc-air batteries in electric vehicles are currently being developed.
3.Characteristics of the sources of secondary zinc-containing raw materials
About 30% of the volume of zinc used is secondary metal. An increase in the production of zinc from secondary raw materials is not observed, since most of it is consumed for anti-corrosion coatings, from where the extraction of zinc is difficult. This also explains the lowest proportion of non-ferrous metals from the collection (from a theoretically possible) zinc waste.
Since zinc and its alloys are made into semi-finished products and products using plastic deformation and shaped casting, waste is generated at all stages of production from hydro- and pyrometallurgical to the final product.
Metal waste is represented by cutting products for rolling products, foundry production waste, die-cutting, stamping, chips. This group of zinc content is adjacent and depreciation of scrap products from zinc and zinc alloys.
In non-ferrous metallurgy, the production of primary copper, lead and tin from polymetallic ores produces zinc-containing (as oxide) slags, dust and sublimates, which can be considered as secondary raw materials for the extraction of zinc. Zinc-containing waste (slag, peeling, ash, dust) are also formed during the production of casting and rolling brass and alloys TsAM (Zn-Al-Cu-Mg system).
The resources of zinc-containing waste generated in the blast furnace smelting of iron ores containing zinc are enormous. In the reducing atmosphere of blast furnace smelting of ore, pellets or sinter, 95–98% Zn is removed from the furnace with gases in the form of sublimates, with 70% of zinc concentrated in fine dust. The zinc content in it is increased by 20-30 times compared with the content in the starting material supplied for smelting, and reaches 10%. The fineness of high-zinc dust is 0.15-0.055 mm; it is highly hygroscopic and contains 15–20% C. Zinc-containing sludges are formed by trapping dust in wet dust collectors.
4. Extraction of zinc from waste of ferrous metallurgy
4.1 Processing of scrap and waste galvanized steel semi-finished products
In the world, about 40% of consumed zinc is consumed for galvanizing steel semi-finished products and products. Consequently, due to the recycling of zinc covering the steel, it is possible to obtain significant amounts of secondary zinc raw materials.
In the process of hot-dip galvanized steel semi-finished products, zinc partially passes into izgar, removed from the surface of the bath, and into hard zinc, which settles to the bottom. Izgar is a free-flowing powder, a significant part of which (about 80%) has a particle size of more than 1 mm. The zinc content in ash is approximately 75%, with up to 30% zinc being in metallic form. The hard zinc extracted from the bottom of the bath in the form of silver or black pieces is the richest in zinc waste containing 90-95% zinc. When ammonium chloride is used as a flux, ammonia is formed — the lowest quality type of zinc-containing galvanizing waste. The life cycle of galvanizing wastes is approximately three months. New scrap is formed either in the production of galvanized sheets, or in the manufacture of automobiles and other products. Old scrap consists of used machines, electrical appliances, road barriers, street lighting poles, etc. The life cycle of a new scrap is estimated at 1.6 months, old scrap in the form of machine parts is 10-15 years old, building elements are at least 25 years old constructions - 20-100 years. The body of the modern car is made mainly of galvanized steel sheet. In Europe, the share of production of cars with galvanized body in 1980 was 10%, in 1990 - 45%, in 2000 - 70%. At the same time, requirements for the utilization of used vehicles are being tightened. The European directive on the out-of-operation vehicles obliges in 2005 to recycle 85%, in 2015 - 95% of the car's weight. The processing of galvanized scrap is usually carried out by melting in electric arc furnaces. The large amount of zinc contained in scrap can create several problems during smelting. The first one is the evaporation of zinc oxide dust accompanied by a small amount of lead and cadmium. Zinc oxide is harmful to health, so it is necessary to install the necessary equipment for its capture. About 98% of zinc goes to dust, the remaining part of the metal remains in the tank and creates a second problem. It lies in the fact that zinc vapor forms bubbles in steel. Since the zinc content in the bath gradually increases, the degree of porosity may increase up to the gaping holes, which can be observed in the cross section of the steel product. [14]
They learned how to produce useful products from zinc dusts, for example, zinc powder used in the manufacture of paint, varnish, glaze and dyeing ceramics, glass, ink, and cosmetics. Additionally, lead, cadmium, iron, and calcium are removed from the dust. Traditionally, zinc dust is treated in Waelz furnaces, which ensures a sufficiently high extraction of zinc. However, veltsevanie requires a high consumption of coke, significant capital costs associated mainly with a complex system of dust collection. The basis of other processes are not thermal, but mainly chemical processing methods. Iterpro Zinc LLC offers to add chlorine or polyvinyl chloride to the furnace, which allows to reduce the temperature of the process of galvanizing.
When zinc is removed from steel scrap, the possibility of utilizing gases generated in the steel production process is increased, and zinc is eliminated in wastewater streams. Thus, in the production of zinc, the share of the secondary metal is about 30%. The largest scrap processors are concentrated mainly in Europe and Asia.[15]
4.2 Rolling dusts and sludges
At the enterprises of ferrous metallurgy in dust and slimes of blast-furnace and steel-smelting production a significant amount of zinc accumulates. The use of dusts and sludges as working materials leads to an increase in the concentration of zinc in them, which makes it difficult to produce iron and steel.
The annual total global increase in zinc-containing dust is estimated at 10-15 million tons. Zinc content in such dust varies in a wide range: from 2 to 20%.
Existing methods of processing such dust are mostly either unprofitable or ineffective.[4], [5] There are three groups of technologies.
The first group is technologies that do not extract zinc from dust. These methods include agglomeration, followed by return to blast furnace production and stabilization with slag or cement. The advantages of both technologies include only low cost. The disadvantages of the agglomeration method include the impossibility of removing zinc from the process, which leads to its accumulation in the captured dust, and this makes this method expedient only at very low concentrations of zinc. The disadvantages of stabilization technology are the lack of extraction of valuable components and the incomplete elimination of the possibility of leaching heavy metals with atmospheric precipitation.
The second group is pyrometallurgical extraction technology. These technologies include the processes of velice, and technologies: FASTMET, FASTMELT, Oxycup, PRIMUS, PaulWurth, etc.[8]
There are also pyrometallurgical methods based on the production and distillation of zinc chloride.[9]
The third fuppa is hydrometallurgical extraction technology using various solvents. Acid and alkaline leaching can be distinguished. Acidic methods provide high zinc extraction, but the resulting solutions contain significant amounts of impurities, especially iron salts. The extraction of zinc from solutions by this technology is assumed by electrolysis, which requires a high degree of purification of the solution and will cause additional costs [6], [7]. Basically, this method uses sulfuric acid, as it is cheaper and provides a higher degree of zinc extraction than hydrochloric and nitric acid. [10]
4.3 Recycling dusts using the Plasmazinc process
he process was developed by the Swedish company SKF Steel[13] and carried out in a low shaft furnace filled with coke. A mixture of metallurgical containing non-ferrous metals and coal dust is blown into the working space of the furnace from the bottom through special devices. The mixture is fed into the oven with natural gas heated to 3500 o With a plasma torch.
The high temperatures of the process and the reducing medium ensure the complete reduction of metal oxides and the sublimation of metals having a high vapor pressure. Red-hot coke plays the role of a filter that traps dust particles and permits gas with metal vapors. The gas after the condensation of the vapor and the separation of materials from it is used for blowing in dust together with natural gas. [11]
Pilot-industrial tests of the process were carried out at an installation that provides for the production of 20 thousand tons of zinc, 4.5 thousand tons of lead and 22 thousand tons of iron from dust containing,%: 22Zn; 5Pb and 26Fe. Coke consumption per 1 ton of these metals was 0.023; 2.2; 0.285 tons, and electricity - 3300; 0.1125 and 684.4 kW / h, respectively.[12]
The recoupment of capital costs for the installation of the installation - 3 years. The process can be applied to the processing of zinc-containing powdered ferrous and non-ferrous metallurgy. The method has significant advantages over the high quality zinc-containing taps: low consumption of coca; low gas yield and low capital and operating expenses for their cleaning; the possibility of obtaining metallic zinc. However, these advantages are potential, they can be realized after the complete mastering of the “Plasmazinc” process.[13]
Findings
In metallurgy, there are two types of zinc-containing waste: in the first one, zinc is mainly in the form of non-metallic compounds, it is slag, sludge, dust, dust, izgar, etc.; the second is metal waste represented by trimming rolled products, foundry waste, die-cutting, stamping, chips.
Processing of such raw materials mainly develops in two directions:
- pyrometallurgical extraction. Basically, these technologies are reduced to the high-temperature reduction of zinc oxides by various carbon-containing reagents, with the production and subsequent distillation of zinc vapor.
- hydrometallurgical extraction using various solvents.
Acid and alkaline leaching can be distinguished. Acidic methods provide high zinc extraction, but the resulting solutions contain significant amounts of impurities, especially iron salts. The separation of zinc from solutions by this technology is assumed by electrolysis.
References
- Вышегородский Д.В. Мировой рынок: Вторичный цинк. Статья. Журнал « Уральский рынок металлов». №8. август 2003
- Сбор обработка вторичного сырья цветных металлов. Учебник или ву-зов/Колобов ГЛ., Бредихин ВН., Черновасе В.М. - М.: Металлургия. 1992. - 288 с.
- Грицай В.П., Бредихін В.М.,Червоний І.Ф.,Пожуєв В.І.,Маняк М.О.,Рабинович О.В., Шевелев О.І., Ігнатьєв В.С. Металургія кольорових металів. Металургія кольорових металів. Частина 5.Металургія важких металів. Книга 1. Технологія свинцю та цинку:підручник/ Грицай В.П., Бредихін В.М.,Червоний І.Ф.,Пожуєв В.І.,Маняк М.О.,Рабинович О.В., Шевелев О.І., Ігнатьєв В.С./За ред. д.т.н., професора Червоного І.Ф.-Запоріжжя,ЗДІА,2011.-480с.
- Валавин B.C., Юсфин Ю.С., Подгородецкий Г.С. Поведение цинка в агломерационном процессе // Сталь. 1988. №4. С. 12 - 17.
- Курунов И.Ф., Греков В.В., Яриков И.С. Производство и проплавка в доменной печи агломерата из жслсзоцинкосодсржащих шламов. // Черная металлургия. 2003. №9. С. 33-37.
- Гудим Ю.А., Голубев А.А., Овчинников С.Г., Зинуров И.Ю. Современные способы безотходной утилизации шлаков // Сталь. 2009, №7. с. 93-95.
- Комплексная переработка и использование металлургических шлаков в строительстве / B.C. Горшков, А.Е. Александров, С.И. Иващенко, В.С Горшкова. М.: Стройиздат, 1985. 272 с.
- Стовпченко Л.II., Пройдак Ю.С., Камкина Л.B. Современное состояние проблемы переработки пыли дуговой сталеплавильной печи. // III Международная конференция "Сотрудничество для решения проблемы отходов". Харьков.2009. - с. 61-63.
- Камил В., Ян С., Яна В. Отгонка цинка из сталеплавильной пыли // Операции химических технологий 2010. №21. с. 739-744.
- Оустадакис П., Тсакиридис П.E., Катслапи А., Агатзини-Леонардоу С. Гидрометаллургический процесс извлечения цинка из пыли электродуговой печи (ПЭДП), Часть 1: Характеристика и выщелачивание разбавленной серной кислотой // Журнал опасных материалов. 2010. №179. С. 5-8.
- Йан В., Стефан Я., Мичал Л. Извлечение цинка из отходов производства железа и стали традиционным выщелачиванием и с применением микроволнового излучения // Аста Монтанистиса Словаса. 2011. №16. С. 185-191.
- Худяков И.Ф., Дорошкевич А.П., Карелов С.В. Металлургия вторичных тяжелых цветных металлов. – М.: Металлургия, 1987. – 528с.
- Теслицкая М.В., Разгон Е.С. Новые способы переработки цинксодержащего сырья за рубежом. – М.:ЦНИИЭИЦМ. – Вып. 1, 1984. – 43с.
- Пинаев А.К., Мальцев В.Д., Трубачев В.И.//Цветная металлургия. Бют.НИТ. – 1982. - №19. – с.30-31.
- Медведева Л.Д, Аверина Н.Н., Сапрыгин А.Ф. / Цветные металлы. - 1981. - № 9. - С,32-33.
- Brinell hardness: up to 120 kg / cm2 (significantly higher mechanical properties than lead printing alloys);