DE2460290A1 - TREATMENT METHODS FOR DUST CONTAINING ZINC - Google Patents

Description

Dr. F. Zuf riefeln ε «η, - Dr. E. Assmann Dr. R. Koenigsberger - Dipl.-Phys. R. Holzbau ^ r - Dr. F. Zumsteln Jun.

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Ferro-Carb Agglomeration Ltd. Lake Forst, Illinois, USA

Treatment process for zinc-containing dust

waste

The invention relates to a treatment method for zinc-containing steel mill dust, which is used to control the Soiling and soiling determined in steel mills is, and in particular such a process in which the steel mill waste is recycled, the zinc and / or Contain lead.

In steelworks and foundries, pig iron is made from ore or scrap or scrap metal with coke (which are known as by-products arise) and flux produced, then find the transformation of this liquid iron to iron castings or Steel and the shaping of the steel into appropriate shapes takes place. With each of these processes, special solid waste is generated which must be removed by removing the metallic constituents

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parts are recovered for "better exploitation" the elimination has so far taken place through the sintering process, which in turn causes further pollution and contamination almost all of the carbon in the waste oxides is consumed.

If the pig iron with an open hearth, oxygen-based or When it is converted into steel in an electric furnace, high-quality iron oxide dust is produced. However, prepare these as well Difficulties in eliminating, as a large fraction of this material is sub-microscopic in particle size ', and since about 1.5 tons of this material are produced for every 100 tons of crude steel.

Piling these materials on heap is uneconomical because the metal oxides and carbon groups contained therein, valuable are. In addition, the stockpiling of such materials be prohibited by regulations or laws. Sintering has so far been the most widely used application for agglomeration Recycle found, however, since high temperatures in this process and high gas volumes occur, it causes serious air pollution. This problem resulted in ever increasing costs for the construction and operation of pollution control devices. Furthermore, in the sintering process, the oxides of zinc and lead are not recovered, and as these elements are troublesome in the iron blast furnace, the sintered products made from mixtures containing these elements cannot can be used for the known steelmaking processes. In procedures that use different types and amounts of binders provide, a slag-forming aggregate is added and all of these methods exhibit a loss of bond strength at high temperature and consequently cannot remove zinc and lead. Consequently, the agglomeration should be at carried out at low temperatures and with low gas volumes

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to get low pollution. Furthermore, the process should enable valuable ingredients, that arise in the waste products of a steelmaking plant can be recovered.

US Pat. No. 359,770 describes a process for processing waste, such as, for example, blast furnace dust, mill scale and coke, in which these are briquetted with 2 to 15%, and preferably about 3 to 8%, of a hydrocarbon binder that is one ball - and Ringerweichungspurikt below 100 ⁰ C comprises (ASTM method: e 28-58T), and in which the briquettes are heated to temperatures from 177 to 315 ° C (350 and 60O ⁰ F) 30 to 90 minutes in an atmosphere which contains at least 10% oxygen, and which are then cooled to form briquettes which can be used in iron or steel production, for example with blast furnaces, open stoves, electric furnaces and cupolas.

Difficulties are caused by steel mill waste that exceeds contain a few tenths of a percent zinc and / or lead. When such types of dust are briquetted and the briquettes to that Blast furnace are returned, the zinc and / or lead in the briquettes tends to be with the furnace lining to Feeding the blast furnace react and an early malfunction or failure due to the reaction between these metals and the furnace lining.

This problem is even more urgent than in steel production increasing amounts of automobile scrap or other galvanized iron scrap are used. Zinc content up to 35% of the dust from such steel production was found to be the mean was about 6.5%. The lead levels were generally lower, but often were in the range between 0.2 and 2.0%. In general, scrap is used in iron casting and steel production, especially

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others in the case of basic oxygen processes, such as the basic one Open hearth process or in electric arc furnace, used as an insert. Since in these processes about 1.5% of the entire metallic charge to be converted to dust in a steel blast furnace, which must be removed, is available A main task for economic exploitation is that this dust, if it contains zinc, lead and iron components, is recycled will.

The invention has for its object to provide a method in which the steel blast furnace dust, the considerable amounts Contains zinc and lead, is recovered and recycled.

According to the invention, a treatment method for steelworks dust waste containing amounts of zinc or lead or combinations thereof is characterized in that the briquetting mixture, apart from carbon, is used to reduce either all metal oxides or at least the zinc and lead oxides contained in the dust to metals 2 up to 15%, preferably 3 to 8%, of a hydrocarbon binder with a ball and ring softening point below 10O ⁰ C (ASTM method: E 28-58T) and almost free of considerable amounts of combustible, below 260 ° C (500 ⁰ F.) volatile constituents is that the briquettes are heated in a gas containing at least 10% oxygen for 30 to 90 minutes at a gas temperature between 177 and 316 ° C (350 and 60O ⁰ F), so that a selective Dehydration and oxypolymerization of the briquette binder and thus hardening of the agglomerate takes place, that thereupon the briquettes again to a tempera temperature between about 982 and 1371 ⁰ C (1800 and 2500 ⁰ F) for about 10 to 60 minutes depending on the size of the individual briquettes with a gas flow through or over the briquette body, wherein the carbon in the briquettes reacts to To reduce zinc and lead metal oxides to metallic zinc and lead, which are volatile as metals and

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deposited as such and to zinc and lead oxides in the gas stream implemented by reaction with free oxygen or carbon dioxide that the exhaust gas flow is passed through a dust collector to collect the zinc and lead oxides contained therein and that the briquettes obtained in this way are virtually zinc-free and are lead-free and contain metallic iron and iron oxides, cooled in a non-oxidizing atmosphere and be returned to iron or steel production.

Preheating with oxygen can be dispensed with if the to be briquetted Mixture 5 to 15% water (based on an anhydrous Base) is added. During the formation of briquettes, the zinc oxide acts to catalyze the reaction between the melted the pitch and the dust, leaving green briquettes result, which have sufficient strength for the direct loading of the high-temperature furnace in which zinc and. Lead to be volatilized.

In the process according to the invention, the steelworks and foundry dust, which contains zinc and lead, becomes briquettes which are free of zinc and lead, and processed valuable zinc and lead oxides. All types of steel mills are used as the starting material. and foundry waste, including coke breeze, cupoloan dust, blast furnace dust, steel furnace dust and scale, all raw materials containing a substantial amount of zinc or lead.

The greeting is mixed with the appropriate binder in known mixers (such as a kneading machine). The binder preferably contains hydrocarbons having a Ball and Ring softening point (ASTM methods: 'E-2858T) below about 10O ⁰ C (212 ⁰ C) - (for reasons of processability), and the binder is further free of major amounts of at 260 ° C (500 ⁰ F) volatile, flammable components. As such usable binders coal tar and

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Pitch, petroleum pitch residues, residues or petroleum reforming base components and the like come into consideration. For example, can tar having a softening point of 37 _f 8 ° C (10O ⁰ F) and a viscosity of 5 with respect to water and pitch locations with softening points that close to 100 ⁰ C (212 ° F) are used. Preferably, a suitable binder for the mixing temperature is chosen which does not exceed about 23.9 ⁰ C (75 ⁰ F) above its softening point. The binder only has to be liquefied in such a way that sufficient mixing with the dust can be achieved. Considerable amounts of naphthalene (or other flammable, below 260 ° C - 500 ⁰ F - volatile constituents) should not occur, since this would cause a burning process in the dehydration furnace, which causes a loss of process control.

With at least 2% as a proportion of the binder, the briquettes finally obtained have sufficient strength, but extremely high strengths of around 3 to 8% can be achieved. Up to 15% binder can be used without interference or disadvantage. If the binder content exceeds 15%, not only does the process cost increase, but the mixture tends to soften and deform in the first stage of dehydration.

The dust and the binder are, for example, mixed well in a kneading machine at such a mixing temperature that the binder is liquid, but the temperature must not exceed 23.9 ° C (75 ° F) above the softening point of the binder lie. Higher temperatures should not occur in order to prevent the raw briquettes from settling in order to avoid deformation Ensure dehydration level. The mixing can be iri 5 to 10 minutes, the time indicated depending on the composition and the system used for this purpose is.

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Carbon should be present in the briquettes in sufficient quantity to at least remove any zinc or To reduce lead oxides to the metallic state. Since the Redu-. conversion of 73.5 kg (12 lbs) zinc oxide to metal and carbon dioxide only 5.44 kg (162 lbs) of carbon are needed, and the same amount of carbon 200 kg (440 lbs) JPbo reduced, only needs a small amount of carbon even with types of dust that have a very high zinc oxide content to be. Usually the blast furnace or blast furnace contains enough dust Carbon to an equal weight of the open hearth dust, which contains zinc, reduce. In general, a steel mill produces enough carbon-containing wastes to so that the briquettes produced have enough carbon to reduce the iron oxides in the briquettes to iron in the present Process temperatures occurring as well as for the reduction of zinc and lead oxides.

The 'mixture is made by extrusion or by compression formed with a piston press or preferably by roller briquetting. The dimension of the briquette produced is determined by the special design of the return device and the use of the agglomerate. Become blast furnaces preferably charged with 5.08 cm (2 ") briquettes (e.g. with a round furnace diameter of 121 - 243 cm (4 to 8 ft.)) need larger briquettes (10 χ 10 χ5 cm (4 χ 4 χ 2 ")), while electric ovens, open stoves and basic oxygen converters Need briquettes that are slightly smaller than those for blast furnaces.

The raw briquettes are transported from the forming device to the dehydration furnace. In this furnace, the briquettes are treated in an oxygen-containing gas stream that circulates at a temperature of 177-316 ° C (350-600 ° F) until the dehydration and polymerization of the binder and the reaction between the binder and the iron contain

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tendency dust is almost complete, so that · a solid Connection forms.

All types of ovens are suitable for dehydration. For example, a chain grate, which are (12 ") uses a Brikettschicht with a height of about 30 cm, wherein heated air is introduced as the oxygen containing gas. At a gas tempera door of 177 ° C (35O ⁰ F) the reaction is very slow, but is finished after about 90 minutes at a binder content of 10% and finished after about 60 minutes at a binder content of 5%. At a gas temperature of 316 ⁰ C (600 ⁰ F) the process must be followed closely, but a high reaction rate can be achieved here be such that Preferred gas temperatures are needed in a binder content of 3% for about 30 minutes. amounted to 204-260 ° C (400 to 500 ⁰ F).

The reaction of the oxygen in the gas with the hydrogen in the binder is highly exothermic, producing about 166 to 198 kcal / kg binder. The air supply not only supplies the bed with oxygen, but this is also used for Dissipation of the heat of reaction. For a 12 "high bed, the velocity needed to dissipate the heat is between 91.4 and 304.8 cm / s (3 and 10 ft / s) i.e. below 91.4 cm / s greeting occurs, while above 304.8 cm / s the reaction occurs tends to stand still. The minimum oxygen content of the gas required for dehydration is around 10%., Although preferably an oxygen content of 15% or more is provided can be.

In the dehydrogenation, the binder is carboriert, so that a G _e paste results which has sufficient strength so that the Brikettkörper withstands the forces occurring during processing and in the final treatment. A dehydrated briquette indicates a lack of iron by at least 5% in the dust

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_ 9 -

with 3 to 8% binder on a compressive strength that is below the required value. However, since the briquettes should preferably be very strong, ie, have a drag force of approximately 56 to 352 kg / cm ² (800 to 5000 lbs / in ² ), iron is fundamental to the manufacture of the briquettes.

The partially dehydrated briquettes burn under a yellow flame, which is suitable for open hearth ovens. In this way, recycling takes place, and iron and carbon components become Recovered in the briquettes, the furnace operating conditions are more favorable, and the waste is disposed of can be done economically.

In the case of dust types containing zinc oxide, the bitumen-bound ones need Briquettes don't get partially dehydrated. If such types of dust occur in the manner described above Temperatures between 65.6 and 98.9 ° C with a water content of approximately 5 to 15? 6 (based on anhydrous basis) are briquetted, a reaction takes place during the briquetting process so that the green briquettes are strong enough to be fed directly to the zinc recovery plant without them under Oxygen to be heated. What kind of reaction took place could not be determined, but hardened briquettes could can be obtained. If zinc oxide or water is not available, the green briquettes are not strong enough to be processed further without being heated under oxygen.

However, the briquettes obtained by the process are all sufficiently strong to be commercially processed and to be fed to the high-temperature oven without decomposition. They can be used in any known oven in which they can be heated ^{to a temperature of about 982 Ms 1371 °} C (1800 to 2500 ^{° F).} In particular, muffle furnaces, hearth furnaces, continuous grate and shaft furnaces and round furnaces come into question.

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In the furnace, the zinc and lead oxides react with the carbon in the briquettes and form zinc and lead metals that evaporate. When enough carbon is available the iron oxides can also be reduced to iron. The time required for the reaction to proceed depends on the temperature and the size of the briquette. The inside of each briquette must reach the evaporation temperature of zinc; At 1371 ° C, 5 to 10 minutes are sufficient for small briquettes. in the generally 10 to 30 minutes is considered an economically reasonable time. A longer period of time becomes uneconomical, However, it is necessary for very large briquettes at low temperatures, especially when the heat transport slowly, such as in a Muffe.l oven. Here will be takes up to 60 minutes. In the case of a gas pump in the briquette bed the heat transfer can take place better, so that a shorter period of time is required.

Because the zinc vapor with the gas flow at the elevated temperatures is carried along, it oxidizes to zinc oxide by reacting either with oxygen in the stream or in the dust collectors, or by reacting with carbon dioxide in the gas stream to form zinc oxide and carbon monoxide. Preferably, however, the gas contains some oxygen, either in the atmosphere above the charge in the muffle furnace or similar furnaces, or in a gas stream, which flows through the briquette bed in a shaft furnace. In the case of a muffle furnace, air can be introduced into the space above the charge v / ground, however, preferably air tempered with the gas of about 15% oxygen or less is used to simplify the process Control used.

In the case of a shaft furnace, the gas passed through the charge represents; preferably an oxidizing furnace gas or mixtures with air in order to simplify the control. The amount of oxygen is only limited and not critical due to the control. A neutral furnace gas can also be used.

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The invention is explained in more detail below using exemplary embodiments explained.

example 1

A mixture of 1000 g, which contains the following ingredients, was put together and formed into green moldings with 1-1 / 8 "in diameter and 1" high:

250 g of coke, which is passed through a sieve with the mesh size Tyler No. 8 has happened, clear mesh size in mm 2.362

750 g open hearth dust, which contains about 10% zinc and less than 1% lead (based on the metals, although oxides of the same are contained), which have passed through a mesh sieve with Tyler No. 60, mesh size 0.25 cm 75 g coke oven tar - Carbon black pitch with a viscosity of '63 ⁰ C (145 ° F) softening point, measured by the ASTM ball and ring method.

The solid ingredients are first heated to 82.2 ° C (180 ⁰ F) and the pitch at 76.7 ⁰ C (17O ⁰ F). These were blended in a mixer for 10 minutes and then formed into the shape of a Carver press at an overpressure of 703 kg / cm (10,000 psig) as the forming force. The resulting briquettes were placed in an air circulating oven at 243 ° C (470 ° F) for 90 minutes. roasted with an oxygen concentration (air) of 21%. After 90 minutes, this air roasted form parts (F 2000 ⁰⁾ for 20 minutes annealed in a muffle furnace at 1O93 ° C, which was operated so that hot gas entered with an oxygen content of 13% in the Gasstrom.über the moldings. An exhaust gas cooling system and a solids separator made it possible to collect the raw mixture of zinc and lead oxide formed.

The air-roasted briquettes were crushed at a pressure of 210.9 kg / cm ² (3000 psig).

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The remaining, annealed pellets were cooled and could allow further processing under high forces. At the

Crushing under a pressure of 351.5 kg / cm (5000 psig) these residues formed a dense compact that was nearly was zinc and lead free.

Example 2

Example 1 was repeated, but using it a modified mixture:

500 g gout dust (100 ^ -60 Tyler, clear mesh size 0.25 mm) 500 g open hearth dust (100% -60 Tyler, clear mesh size 0.25 mm)

as in example 1,
75 g pitch as in example 1,
150 g of water.

The obtained green moldings were divided into two halves. The first half was air-roasted and calcined as in Example 1, the second half was calcined without air-roasting. The air-roasted product was air-roasted at a pressure of 288 kg / cm (4100 psig). In both cases, the crude zinc oxide was ^{recovered from the exhaust gas collected during the annealing at 1093 0} C (2000 ⁰ F) for 20 minutes, and the remaining pellets formed a zinc-free and lead-free metal compact when they were

pressure of 351 kg / cm (5000 psig).

Example 3 .

The following mixture was at 87.8 ⁰ C (190 ⁰ F) to briquettes with a dimension of 2.5 x 2.5 x 3,75cm (1 χ 1 "χ 1 1/2) with

formed in a roller press below 2270 kg / cm per 2.5 cm of roller width (5000 lbs / per linear inch):

13.6 kg of water,

68.0 kg of iron dust from a cupola furnace containing 10% zinc metal "and

V / o contains lead metal in the form of oxides, 34.0 kg gout dust,

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34.0 kg coke bones,

10.4 kg pitch, as in Examples 1 'and 2, 160 kg of total green mix.

At ambient temperature, these green briquettes withstood a compressive force of 318 kg (700 lbs) before destruction. She. could be dust-free and easy without any pulverization be transported.

Some of these moldings were annealed as in Example 2, raw Zinc oxide was recovered and the briquette residue was sintered and solidified as a whole.

The residue was air roasted as in Example 1. The air-roasted one Product was crushed with a total force of 500 kp. During the annealing as in Example 1, raw zinc oxide was obtained from the Waste gas flow collected, and the calcined residue formed a ■ -exactly shaped, sintered briquette, in which a metallic Has formed mass on the compact.

Example 4

325 parts of basic oxygen furnace dust and 350 parts of open hearth dust, which contains on average 10.2% zinc in the form of zinc oxide, were mixed with 25 parts by weight of coke breeze of -10 mesh (-1.5 mm clear mesh size). After dry blending, 6 parts of liquefied coal tar pitch (as in Example 1) were in a. Temperature of 71.1 ⁰ C (16O ° F) was added and the mixture was then stirred for 3 minutes ,. It was then air roasted as in Example 1, and the. Briquettes were heated in the furnace gas in a continuous grate furnace with a maximum temperature of 1190 ⁰ C (2175 ° F) was reached. The excited smoke gases of the zinc oxide were collected on the rear wall, and the remaining briquettes were tapped cold.

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Example 5

72 parts of open hearth dust with 17.5% zinc were mixed with 28 parts of charcoal from montana coal. The charcoal contained 80% solid carbon, 14% volatiles and 6% ash. The particle size was measured to be -20 mesh (-0.833 mm. 5 parts in the form of molten bitumen asphalt (residue from oil refining) having a Ball and Ring softening point of 71.1 ⁰ C (16O ⁰ F) was added and after a mixing in In a double kneader, which took place for 4 minutes, the mixture was briquetted with a known press to form briquettes with a dimension of "2.5 cm (1") and air-roasted as in Example 1.

The cured briquettes were then heat-treated under non-oxidizing conditions in a round kiln as a brick kiln at a maximum temperature of 1093 ^° C. (2000 ^{° F.).} The gases emerging from the round furnace were collected on a rear wall and the zinc oxide was separated out. The reduced iron briquettes were cooled and used in an electrical casting preparation process. In the treatment process for steel mill dust according to the invention, which contain zinc and / or lead oxides in addition to iron oxides, a hydrocarbon-containing binder is used together with carbon to reduce lead and zinc oxides briquetted into metal. The briquettes are preferably treated with an oxygen-containing gas at 177-560 ⁰ C (350 to 600 ⁰ F) to selectively react with the binder to obtain solid briquettes. The briquettes are then heated to a temperature between 982 and 1371 ⁰ C (1800 and 2500 ⁰ F), so that the zinc or lead contained is first reduced to metal and volatilized as metal, and then oxidized to ZnO and PbO in the gas phase, will. The zinc and lead oxides are recovered from the exhaust gas in a dust collector, while the iron-containing briquettes are cooled in a non-oxidizing atmosphere, and then as an iron charge at one. Steel or ironmaking processes can be reused.

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Claims (4)

Claims 1. Treatment process for steel mill dust and iron foundry dust to remove iron and carbon-containing waste, which also contains zinc oxide. hold on to a product that does not contain iron in the waste. Contains zinc and zinc oxide, characterized in that the waste in question is mixed with a bitumen-containing binder, which has a ball and ring softening point below 10O ⁰ C and does not contain any combustible components that are volatile at 260 ° C, carbon-containing solids in to reduce the zinc oxide contained is admixed to zinc metal in sufficient amounts so that a mixture is obtained which contains between 2 and 15% binder, that the mixture is briquetted, that the briquettes are treated to ensure sufficient strength for heating the briquettes, that the briquettes be heated at 982 to 1371 ⁰ C until the evaporation temperature of all zinc components contained therein is reached, all the zinc oxide contained is converted to zinc metal and the zinc metal is converted into zinc vapor that the zinc vapor is drawn off from the surroundings of the briquettes with a gas stream that a reactant to convert containing the zinc vapor in zinc oxide, and that the zinc oxide is recovered. 2. The method according to claim 1, characterized in that the briquettes in a gas containing at least 10% oxygen, For 30 to 90 minutes at a gas temperature of 177 to 316 ° C for selective separation of hydrogen are heated and solidified from the binder. 509827/0864 -16- 2A60290 3. The method according to claim 1, characterized in that the briquettes by an addition of 5 to 15% "water on one anhydrous base solidified to the mixture before briquetting, leaving solid briquettes without further heating develop. 4. "The method according to claim 1, characterized in that the Binder content is between 3 and 5%. 509827/0864