DE1266253B - Process for the magnetizing roasting of non-ferromagnetic iron ores - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

B 03 c

C21b

German class: lb-2

Number: 1 266 253

File number: M 67144 VI a / l b

Filing date: November 2, 1965

Open date: April 18, 1968

Modern iron ore smelting in blast furnaces aims to use richer feeds. In place of the so-called directly shipped ores which contain about 50% iron, the trend is to prepare the ore and concentrate to the iron content of 60 ° / raise to at least ₀ and the content of impurities such as silica, to a few percent in the blast furnace charges.

If the iron ore is found in naturally occurring magnetizable form, then Magnetic separators can be used for reprocessing, which are easy to use and very economical.

In order to be able to use the advantages of magnetic separation also in the processing of non-ferromagnetic iron ores, such ores were subjected to magnetizing roasting at an elevated temperature of e.g. 375 to 925 ° C in a reducing atmosphere, resulting in magnetite (FeO · Fe ₂ O ₃ ) as the end product. is obtained. Because of the higher reaction rate and better utilization of the reducing agent, relatively high temperatures have preferably been used, the z. B. between 600 and 800 ° C.

So far, the magnetizing roasting with subsequent magnetic separation was because of the pretty high temperatures, which lead to high operating costs and incipient sintering of the ore, but not used to any significant extent.

It is also known that iron oxide can also occur in another ferromagnetic form, namely as ^ -Fe ₂ O ₃ or maghemite. The two ferromagnetic iron oxides magnetite and maghemite form a complete series of solid solutions, which can be obtained from magnetite by oxidation. Hematite (a-Fe _a 0 ₃ ), on the other hand, forms ^{stable solutions with magnetite only at temperatures above 1075 °} C. in certain concentration ranges.

Surprisingly, it has now been found that it is more easily accessible through a reducing treatment and ores consisting mainly of trivalent iron, such as limonite, hematite, goethite or their mixtures, ferromagnetic end products succeed even at relatively low temperatures which consist of a solid solution of magnetite and maghemite.

The method according to the invention for the magnetizing roasting of non-ferromagnetic iron ores at elevated temperature is characterized by non-ferromagnetic hydration Iron oxides or iron hydroxides, not ferro-

Process for the magnetizing roasting of
non-ferromagnetic iron ores

Applicant:

Ministere des Richesses Naturelles, Quebec
(Canada)

Representative:

Dipl.-Chem. Dr. phil. E. Young

and Dipl.-Chem. Dr. rer. nat. V. Vossius,

Patent Attorneys, 8000 Munich 23, Siegesstr. 26th

Named as inventor:

Charles Edouard Beaulieu, Quebec (Canada)

Claimed priority:

Great Britain November 2, 1964 (44 630)

magnetic anhydrous iron oxides and their mixtures by heating in an atmosphere with reduced oxygen content to a temperature of about 225 to about 425 ° C by means of dissocitation to a strong ferromagnetic mass, which consists of a solid solution of magnetite and maghemite and a greater ratio of oxygen to iron than magnetite but a lower ratio than Has hematite, transferred.

By quenching the end product or by controlled cooling, the amount of magnetite (in solid solution) in the roasted material can be kept at a relatively high level and the heat of reaction of the oxidation of magnetite to ferric oxide can occur during the subsequent Processing used in the sintering of the pellets.

The composition of the strongly ferromagnetic roasted product can also be varied and depends on the roasting conditions. The obtained solid solutions of magnetite and maghemite show a simple cubic lattice with a lattice constant between that of magnetite (8.389 Å) and that of maghemite (8.338 Å) varies. The FeO content is preferably below 31.3%, but above 0%.

The iron ores used as starting material in the process according to the invention can lead to various Particle sizes are ground. the

809 539/39

Particle size depends on the raw material used and on the ore used away. This means that z. B. certain types of ore th reaction conditions. For example, can the product has a ferromagnetic content only to a size of less than 5.08 mm Must be milled for optimal results Solution Magnetite-Maghemite from about 20 to 85% while other ores show less than 5, the rest consists of unreacted 0.102 mm can be ground. Starting material, e.g. B. «-Hematite and gait;

The roasting process is carried out in an atmosphere when the magnetite content in solid solution is too high If the oxygen particle pressure is reduced, the roasted material tends to oxidize leads. This can be done, among other things, by adding a maghemite as soon as it is removed from the furnace Compound can be achieved that has a high affinity and comes into contact with air. This Oxyd on the other hand Having oxygen, e.g. B. a reduction also depends on the temperature and on the the gas or a solid or liquid Reduk cooling rate after removal agent. from the oven.

Carbon monoxide can be used as the reducing gas, The end product produced according to the invention can

Hydrogen, mixtures of carbon monoxide and 15 still contain a certain amount of ferrite, each hydrogen, compounds that produce hydrogen and according to the gang and other compounds that supply carbon, as well as compounds that are contained in the iron oxide. These ferrites do not provide carbon or hydrogen, and are usually magnetizable, and a mixture of such substances can be used. In every case, exert a certain influence on the purity of the concentrate, ie both when using a reducing agent and also on the recovery of iron in the case of gas as well as a suitable reducing agent, during the entire treatment process. To achieve a reduced particle pressure, it is also possible that the end product, free magnetite, can contain the oxygen particle pressure in the range that can be oxidized to maghemite. Order from about 10 ~ ¹⁵ to about 10 ~ ³⁵ at. It is clear, however, that the presence of free These values depend on the temperature and the magnetite or even the presence of ferrites in the roasting time as well as on the grain size and the present process is not required in the type of starting material. On the contrary, the formation of ferrites is possible

Avoided those used in the process of the invention in order to obtain a better concentrate. The amount of gaseous reducing agent is the particularly preferred composition of the

about 31 to 157 m ³ per ton of ore. The amount depends on the end product, which is the better recovery on the type of ore and / or on the extent of extraction of iron with the lowest cost of reduction for the purpose of extraction of ferromagne- supplies. Every type of ore must be investigated in order to obtain solid solutions. Normally 95 ° / ₀ desired precise composition can figure out or more of the reducing gas are used. and show the examples given below

The roasting time of iron ore depends on several 35 some cases. In general it can be said that the Factors, including temperature, the maghemite content should be higher than the magnetite content. Type and grain size of the material, the level of if the product manufactured according to the invention

Oxygen partial pressure as well as the type of the air to temperatures from 200 to about 400 ° C reactor or furnace, which is used for this. is heated, its magnetizable property decreases. In general, the roasting time for the iron ore 40 at room temperature can be considerably increased.
from a few seconds to several minutes This phenomenon can be exploited to advantage

vary. In a suitable atmosphere, the recovery of iron in the starting material after one minute at 350 ^° C. concentrate can be varied.

or after 15 minutes at 300 ^° C. or after 2 hours. The process according to the invention can be used in any

be converted at 250 ⁰ C. When using 45 suitable reactor type can be carried out, e.g. B. in a solid reducing agent, the reaction shaft furnace, in the fluidized bed process, etc., the temperature must generally be increased in order to obtain a comparable product for the same reaction time in the reactor using any known device. This be one that includes a facility to make the most appropriate is evident from the examples below. Adjust the atmosphere in the reactor room.

The operating temperature in the process according to the invention can, depending on the process, be generally about 225 to 375 ° C., the reactor used batchwise or, in the case of some solid reducing agents, can be carried out continuously. For economic reasons they are up to 450 ^° C., depending on the reasons used, a device is preferred which enables iron ore and the oxygen partial pressure and others to work continuously. With the advantage of the aforementioned factors. The preferred temperature 55 may be a rotary kiln are used are in soft doors between 275 and 35O ⁰ C in an at- reducing gases are introduced at the outlet end, sphere that cool a low enough oxygen to the roasted material and having the redupartialdruck. preheat decorative gases.

When using carbon monoxide as Reduk- According to the invention, the roasted material can on

tion medium, the temperature should be kept as low as possible. Avoid the reaction Bilem calcine which is not treated properly rate of this reaction is was at about 300 ⁰ C. The roast can also be low in a stream of cold air, and only about 10% of the carbon is quenched in order to use up its reoxidation to vermonoxyds for this purpose. prevent, e.g. B. if you have a dry magnetic

The type of deduction in the method according to the invention is preferred. To prevent the end products from being reoxygenated, it is important that the roasted product is made with ^;

Temperatures below about 75 ° C is maintained in the air.

The invention is further illustrated by the examples.

example 1

A sample of non-magnetizable iron ore is ground to a grain size of 0.15 mm brought. The main minerals of this ore are blue metallic hematite and martite with different amounts of goethite and limonite. Quartz is the main component of the gait. He is lying in the form of sprinkled grains of almost uniform size in front of or in the form of very fine grained ones Aggregates that are fairly evenly thinly covered with iron oxides. The iron content is 54.92%> the content of insoluble substances is 15.73%, mainly silica.

The roasting is carried out in a rotary kiln. The ore is added at the higher end and a reducing gas is fed in countercurrent to the solid material in the rotary kiln. The average temperature of the rotary kiln in the hot zone is 300 ^° C. The CO ₂ : CO ratio of the reducing gas averages 3: 1 during the process and varies between 1: 1 and 9: 1 between the inlet and outlet ends. The gas is used in an amount of about 99.1 m ³ per 907 kg of ore. The ore remains in the rotary kiln for 1 hour and there is no oxidation when it is brought into the air from the rotary kiln. The temperature of the ferromagnetic mass at the outlet end is approximately 75 ⁰ C.

After roasting, the iron content in the magnetizable concentrate is 66.47%, the gangue content is 3.23%. The percentage of iron recovered is 98 ° / ₀ · The magnetite content is about 45 ° / ₀ , the remainder is a solid solution of maghemite.

Example 2

Another type of non-magnetizable iron ore is milled to a grain size of 0.28 mm. This ore consists mainly of goethite, limonite and quartz with a small amount of aluminum oxide. The ore is very fine-grained and strong, and the quartz is generally similar to that in the previous example, but more fine-grained. The ore has an iron content of 55.62% and an insoluble matter content of 12.86%. After roasting in the rotary kiln at about 300 ^° C. and using 70.8 m ^{3 of} the reducing gas of the same composition as in Example 1 per 907 kg of ore, the iron content in the magnetizable concentrate is 62.27% and the gangue content is 7, 48%. The content of maghemite is 75% radiographically. There is no oxidation when the product is ejected from the rotary kiln and comes into contact with the air. The percentage of iron recovered is 91.5% after magnetic separation.

Example 3

The same ore as in Example 2 is used, but ground to a size of 0.20 mm.

A mixture of hydrogen and water vapor with an average Content of about 60% used. The ore is heated to 325 ° C in a shaft furnace for 1 hour. After roasting, the ferromagnetic mass is oxidized in air at room temperature. Of the The maghemite content of the product obtained by this reduction-oxidation process is 98%. The iron content in the magnetizable concentrate is 62.53%, the gangue content is 6.81%. the Recovery of iron is 98.5% after magnetic separation.

Example 4

The same material as in Example 2 is ground to a particle size of 0.28 mm and mixed with peat moss. This mixture, 9 parts of iron ore per 1 part of peat moss, is roasted for 1 hour at 380 ° C. in a closed shaft furnace without any external supply of gas.
The roasted material is stable at room temperature. The maghemite content is 85% radiographically. The magnetizable concentrate contains 61.76% iron and 5.3% insolubles. The overall process iron recovery is 75%.

Example5

The same ore as in Example 2 is ground to a particle size of 0.15 mm.
After roasting in a rotary kiln kept uniformly at 300 ° C. and treatment with 102 m ³ per 907 kg of a mixture of CO and CO ₂ in a ratio of 1: 2 for one hour, part of the ferromagnetic mass is in water at the outlet end quenched and the other part discharged and exposed to the air. The latter part oxidized itself again and gave the following analysis: FeO 0.7%, Fe ₂ O ₃ 83.8%, insoluble substances 10.8%. The part quenched with water and concentrated in a magnetic wet separator gives the following analysis:

FeO 4.5%, Fe ₂ O ₃ 81.9%, insolubles 9.07%. The iron recovery is 92% in the first case and 92.5% in the second.

The method according to the invention has, inter alia, the following advantages:

a) The work is carried out at low temperatures, preferably around 300 ^° C.

b) The reaction rate of the process is favorable even at this low temperature.

c) The conditions of the reducing atmosphere can be varied over a wide range, which leads to a favorable utilization of the reducing agent.

d) The treated material can have different grain sizes and be relatively large.

e) The formation of unwanted ferrites is at a very low level during roasting Value held.

f) The process can be carried out in a wide variety of types of ovens.

g) When the material is properly reduced and cooled, it can produce a significant amount of Contain heat of oxidation, which is later exploited during the sintering or pelletizing process can be.

h) The recovery of iron can easily be kept above 95%, when the properly roasted material is concentrated.

i) The process according to the invention is simple, economical and of various types feasible from iron ores.

Claims (7)

Claims: g 1. A method for the magnetizing roasting of non-ferromagnetic iron ores at elevated temperature, characterized in that non-ferromagnetic hydrated iron oxides or iron hydroxides, not ferro- ίο magnetic anhydrous iron oxides and their mixtures by heating in an atmosphere with reduced oxygen content to a temperature of about 225 to about 425 ^° C. by means of dissociation to a strongly ferromagnetic mass, which consists of a solid solution of magnetite and maghemite and has a higher ratio of oxygen to iron than magnetite, but a lower ratio than hematite. 2. The method according to claim 1, characterized in that the heating is carried out at a temperature from about 225 to about 375 ° C, preferably between about 275 and 350 ° C, in the presence in a reducing atmosphere. 3. The method according to claim 1 and 2, characterized in that a starting material is used which has a particle size between 5.08 and 0.102 mm has been ground. 4. The method according to claim 1 to 3, characterized in that the treatment atmosphere has an oxygen partial ^{pressure of about 10 ~ 16} to about ^{10 ~ 35} atm. 5. The method according to claim 1 to 4, characterized in that the strongly ferromagnetic The mass is heated to a temperature of about 200 to about 400 ° C in air. 6. The method according to claim 1 to 5, characterized in that the strongly ferromagnetic Quench the mass, preferably with water. 7. The method according to claim 6, characterized in that the quenching is carried out at a temperature below about 75 ⁰ C with cold air. Considered publications:
German Patent Nos. 673,402, 845181;
German patent application W6222VIb / lb (published 10/30/1952);
"Steel and Iron", 1937, no. 29, p. 806. 809 539/39 4.68 © Bundesdruckerei Berlin