Field of the Invention

The invention relates to a method for obtaining iron concentrate from metallurgical slags from steel production, for use in charges of metallurgical aggregates.

Background of the invention

Nowadays, the recycling of metallurgical slags to recover and reuse their metal content in metallurgical processes is generally known. This recycling usually consists of crushing and grinding the metallurgical slag into a fine granulate from which its metal content is separated by magnetic separation, for example in drum separators.

Within many existing patent files, such recycling of metallurgical slags by magnetic separation is known, for example, from EP 2261383, the subject matter of which is a method, apparatus and rotary drum for processing ladle slag. The method of processing the ladle slag includes steps such as emptying the residual material present in the ladle onto a bed of recycled materials, solidifying the deposited residual material at least partially, introducing the at least partially solidified material into a closed rotating drum, quenching and disintegrating the residual material within the rotating drum, and separating the powdered portion from the metallic crusts of the residual material by rotating the residual material in a closed rotating drum. The iron fraction, which is smaller in size, is then separated by magnetic separation, and the larger particles by vibratory screening.

Magnetic separation is also known from US 2015/02029798, the subject matter of which is a method and system for processing slag material to produce by-products, including an iron-rich finished product and a low fine iron content finished product. From WO 2019/054087, a method is further known of processing a slag slurry comprising crushed or powdered slag particles from steel production, carried out in a magnetic rotating drum and allowing to increase the concentration of Fe in the product obtained. From US 2015/0007696 is known the method of obtaining Fe from the slag originating during steel production, during which the slag is first heated to 1450 °C to 1600 °C, and then cooled to the temperature in the range from 1150 °C to 1250 °C, at which it is kept for at least 10 min. to allow precipitation of Fe. After rapid cooling of the slag to room temperature, the solidified slag is then crushed and the magnetic part of the slag is magnetically separated from the non-magnetic part.

The combination of magnetic separation and ultrasonic treatment of the processed material to obtain a concentrate with a relatively high content of Fe is also known, as is the case, for example, with the solution according to US 2014033867, the subject matter of which is a method for processing low-grade iron ore. This method consists in first preparing a slurry from the iron ore to be processed, which is then subjected to ultrasonic treatment and then to magnetic separation into a magnetic iron ore fraction and a residue containing the paramagnetic iron ore fraction and iron-free material. This remaining fraction is then re-treated by ultrasound and the paramagnetic fraction of the iron ore is separated magnetically.

The aim of the present invention is to use the combination of magnetic separation and ultrasonic treatment also for recycling metallurgical slags in order to obtain a concentrate with a significantly higher content of Fe, than the above-mentioned existing methods of processing these slags.

Summary of the Invention

This aim is largely addressed by the method for obtaining iron concentrate from metallurgical slags from steel production containing at least 10 mass % of Fe, including their gradual crushing and grinding to a granulate of a max. 1 .0 mm grains, and a subsequent magnetic separation of the magnetic fraction contained in the granulate according to the invention. The principle of the invention is that prior to commencing the magnetic separation, the granulate is first mixed with water in a ratio of 1 mass portion of granulate to 10 to 100 mass portions of water to obtain a well mixable slurry which, after mixing and under continuous stirring, is subjected to magnetic separation for 2 to 30 min. by effect of a magnetic field with a co-action of ultrasound with a frequency of 20 to 40 kHz. After the magnetic fraction is dried to a constant mass, an iron concentrate with a content of 20 to 80 mass % of Fe is obtained, while the remainder are the phases with a content of CaO, Si0 _2, AI ₂ O ₃ , MgO and other oxides with individual content not exceeding 40 mass %, and any other admixtures and impurities.

The principle of the invention further consists on the intensification of this method by the promotion of the formation of magnetically active particles, when the crushed and ground granulate from the steel mill slag is preferably subjected to calcination at a temperature of 600 to 1000 °C for a minimum of 60 min. before mixing it with water. The Fe content in the concentrate obtained by magnetic separation of the calcinated granulate is up to 25 % higher compared to the state with the not calcinated granulate.

This method for obtaining the iron concentrate according to the invention can be carried out using, for example, ultrasonic baths into which containers containing the prepared slurry are inserted, which are provided with stirring spindles and permanent magnets or electromagnets along their outer circumference, or using ultrasonic immersion probes. The process can also be further intensified by the use of multiple ultrasonic needles or by combining an ultrasonic bath and one or more ultrasonic needles.

The principle of the invention further consists in the fact that the remaining fraction not captured by the magnetic separation, which may still have a relatively high content of Fe, is dried, subjected to calcination again at a temperature of 600 to 1000 °C for a period of min. 60 min. and then is mixed again with water, either alone or in a mixture with new slag granulate which has been crushed, ground and possibly also calcinated, after which it is subjected to further magnetic separation by co-action of ultrasound. This method yields higher amount of magnetically separable fraction.

Examples of Invention Embodiments

Example 1

According to the first example of invention embodiment, first the ladle slag is selected with the content of 17 mass % of Fe, whereupon this slag is treated into granulate by crushing and subsequent grinding to granulometry below 0.1 mm. Then the slurry is prepared by mixing the granulate with water in the ratio of 1 mass portion of granulate to 40 mass portions of water in a cylindrical vessel fitted with a strip of neodymium magnets along its outer surface, whereupon the vessel with the slurry is placed in an ultrasonic bath or in an ultrasonic tub containing water. A spindle of overhead stirrer is immersed in the slurry vessel and stirring is initiated at a rotation speed of 250 rpm for 2 minutes.

After this initial mixing, the application of ultrasound at a frequency of 40 kHz and a power of 130 W is initiated to this slurry via an ultrasonic bath for 10 min, under continuous stirring and the application of a magnetic field induced by neodymium magnets. After this time, both the mixing and the ultrasonic action are stopped and the non-magnetic fraction in the slag granulate is removed from the vessel by pouring off the slurry.

The magnetic fraction retained on the inner walls by the neodymium magnets is then obtained by removing these magnets from the outer walls of the vessel, whereupon it is dried to constant mass for 24 hours at 70 °C to form an iron concentrate of 23 mass % of the original amount of the ladle slag, containing 31 mass % of Fe, 35 mass % of CaO, 7 mass % of Si0 ₂ , 2 mass % of Al ₂ 0 ₃ and 4 mass % of MgO, while the remainder are other admixtures and impurities.

Example 2

According to the second example of invention embodiment, first the slag from desulphurization of pig iron outside the blast furnace is selected with the content of 34 mass % of Fe, whereupon this slag is treated into granulate by crushing and subsequent grinding to a granulometry below 0.1 mm. Then the slurry is prepared by mixing the granulate with water in the ratio of 1 mass portion of granulate to 60 mass portions of water in a vessel fitted with neodymium magnets along its outer circumference, same as in Example 1. A spindle of overhead stirrer and an ultrasonic immersion probe are immersed in the suspension and stirring at a rotation speed of 250 rpm is started for 2 min.

After the initial mixing, upon continuous stirring, ultrasound with a frequency of 20 kHz and power of 360 W is initiated on this slurry by means of an ultrasonic immersion probe for 10 min. After this time, both the mixing and the ultrasonic action are stopped and the non-magnetic fraction in the slag granulate is removed from the vessel by pouring off the slurry. The magnetic fraction obtained from the inner walls of the vessel is then dried to a constant mass for 24 hours at 70 °C, yielding an iron concentrate in the amount of 60 mass % of the original amount of slag from desulphurization of pig iron outside the blast furnace, containing 52 mass % of Fe, 9 mass % of CaO, 4 mass % of S1O2 _, 1 mass % of AI2O3 and 5 mass % of MgO, while the remainder are other admixtures and impurities.

Example 3

According to the third example of invention embodiment, first the ladle slag is selected with the content of 13 mass % of Fe, whereupon this slag is treated into granulate by crushing and subsequent grinding to granulometry below 0.1 mm. The granulate thus obtained is calcinated at 1000 °C for 60 min. Then the slurry is prepared by mixing the calcinated granulate with water in the ratio of 1 mass portion of granulate to 40 mass portions of water in a cylindrical vessel fitted with a strip of neodymium magnets along its outer surface. A spindle of overhead stirrer with is immersed in the suspension and stirring at rotation speed of 250 rpm is initiated for 2 minutes.

After this initial mixing, the application of ultrasound at a frequency of 20 kHz and a power of 400 W to this slurry via an ultrasonic needle for 10 min, under continuous stirring is conducted and the application of a magnetic field induced by neodymium magnets is performed. After this time, both the mixing and the ultrasonic action are stopped and the non-magnetic fraction in the slag granulate is removed from the vessel by pouring off the slurry.

The magnetic fraction retained on the inner walls by the neodymium magnets is then obtained by removing these magnets from the outer walls of the vessel, whereupon it is dried to constant mass for 24 hours at 70 °C to form an iron concentrate in the amount of 31 mass % of the original amount of the ladle slag, containing 34 mass % of Fe, 31 mass % of CaO, 8 mass % of Si0 _2, 3 mass % of AI ₂ O ₃ and 6 mass % of MgO, while the remainder are other admixtures and impurities. Example 4

According to the fourth example of invention embodiment, first the slag from steel production in an oxygen converter is selected with the content of 21 mass % of Fe, whereupon this slag is treated into granulate by crushing and subsequent grinding to granulometry below 0.1 mm. Then the slurry is prepared by mixing the granulate with water in the ratio of 1 mass portion of granulate to 60 mass portions of water in a vessel fitted with neodymium magnets along its outer circumference, same as in Example 1. A spindle of overhead stirrer and an ultrasonic immersion probe are immersed in the suspension and stirring is started with a rotation speed of 250 rpm for 2 min.

After the initial mixing, ultrasound with a frequency of 20 kHz and power of 360 W is initiated on this slurry by means of an ultrasonic immersion probe for 10 min. After this time, both the mixing and the ultrasonic action are stopped and the non-magnetic fraction in the slag granulate is removed from the vessel by pouring off the slurry from the vessel.

The obtained slurry containing the non-magnetic fraction is subjected to vacuum filtration through filter paper to obtain a filter cake. The magnetic fraction obtained from the inner walls of the vessel and the filter cake is then dried to a constant mass for 24 hours at 70 °C. The dried filter cake is subjected to calcination at 800 °C for 60 min. Then the slurry of the calcinated filter cake is prepared by mixing with water in the ratio of 1 mass portion of dry calcinated filter cake to 40 mass portions of water in a cylindrical vessel fitted with a strip of neodymium magnets along its outer surface. A spindle of overhead stirrer is immersed in the suspension vessel and stirring with a rotation speed of 250 rpm is initiated for 2 minutes. After this initial mixing, under continuous stirring and the application of a magnetic field induced by neodymium magnets, the application of ultrasound at a frequency of 20 kHz and a power of 400 W to this slurry via an ultrasonic needle for 10 min is performed., After this time, both the mixing and the ultrasonic action are stopped and the non-magnetic fraction in the slag granulate is removed from the vessel by pouring off the slurry.

The magnetic fraction retained on the inner walls by the neodymium magnets is then obtained by removing these magnets from the outer walls of the vessel, whereupon it is dried to constant mass for 24 hours at 70 °C to form an iron concentrate. The concentrate thus prepared is combined with the concentrate prepared from the granulate.

The procedure provides an iron concentrate with the amount of 53 mass % of the original amount of slag, containing 37 mass % of Fe, 30 mass % of CaO, 4 mass % S1O2, 1 mass % of AI2O3 and 4 mass % of MgO, while the remainder are other admixtures and impurities.

Industrial Applicability

The method for obtaining an iron concentrate from metallurgical slags according to the invention can be widely used in the production of iron in a blast furnace or as an input, iron-importing raw material component in an agglomeration process in metallurgical production.