Method for recycling slag

Abstract

The invention relates to a method for separating magnetic components from a slag, having the following steps: - providing an iron-containing slag from a copper recovery process, having a grain size d95vol of less than 200 µm and comprising ferrimagnetic components comprising iron oxide and non-magnetic components comprising iron silicate, - adding a liquid medium to the slag in order to obtain a suspension, - stirring the suspension using a magnetic stirring device, and - separating the ferrimagnetic components from the non-magnetic components.

Description

[0001] Processes for the recycling of slag

[0002] The present invention relates to a process for the utilization of slag.

[0003] In metallurgy, slag refers to solidified, predominantly non-metallic accompanying phases obtained during the extraction of metals from ores. Examples include blast furnace slag, steel mill slag, metallurgical slag, etc.

[0004] Slag is widely used in the construction industry; for example, finely ground blast furnace slag is used in cement. Slag is used as aggregate in road and path construction. Other uses include fertilizer, blasting abrasives, etc.

[0005] The object of the present invention was to find further utilization possibilities for slag.

[0006] A variety of slags contain iron-containing components. A common component of slags is magnetite (FeS Cu). Iron silicates are also common components, both in pure form as fayalite (FeS Si Cu) or as mixtures with silicates of other metals such as magnesium, calcium, and aluminum, for example, magnesioferrite, olivine, and hedenbergite. These products contain significant amounts of magnetic components and can therefore be useful starting materials for various applications.

[0007] The object of the present invention was therefore to separate the iron-containing components from the slag.

[0008] The process according to the invention for separating magnetic components from a slag comprises the following steps:

[0009] - Providing a ferrous slag with a grain size d95voi less than 200 pm with magnetic and non-magnetic components

[0010] - Addition of a liquid medium to the slag to obtain a suspension

[0011] - Stirring the suspension with a magnetic stirring device to separate the magnetic components from the non-magnetic components.

[0012] According to the invention, an iron-containing slag is provided. This contains magnetic and non-magnetic components.

[0013] Typical slags are metallurgical slags, especially slags from copper production, Linz-Donawitz slags or electric furnace slags.

[0014] To extract copper, copper pyrite (CuFeS) is usually roasted with coke. This process produces not only Cu2S but also FeS and Fe2Ch. The resulting iron oxide can be slagged with silicate additives and separated. Before or after separation, the FeS can also be converted into iron oxide by blowing in air, which can then be separated as slag with silicate additives.

[0015] These slags are also called copper slags, although they contain very little copper.

[0016] The slags preferably contain at least 50 mass% Fe2Ch. Fe in any compound is determined by X-ray fluorescence analysis and calculated as Fe2Ch. The value is preferably at least 55 mass%, at least 60 mass%, or at least 65 mass%.

[0017] The slags preferably contain at least 20 mass% SiC. Si in any compound is determined by X-ray fluorescence analysis and expressed as SiO2.

[0018] The provided slag should have a grain size d95voi of less than 200 pm. d95voi means that 95% by volume of the grains have a grain size of less than 200 pm. While it is generally possible to determine such grain size distributions using a microscope, it is more common to determine them using laser diffraction and to have the grain size distributions calculated mathematically. Such methods are known to those skilled in the art. Preferably, the size d95voi is less than 150 pm, even more preferably less than 100 pm.

[0019] If necessary, the slag is first crushed. A crusher or grinder, for example, is suitable for crushing the slag.

[0020] In the next step, a liquid medium is added to the possibly crushed slag to create a suspension. In the simplest form, this is water. However, it can also be a mixture of water with other components, such as polyethylene glycols or surfactants.

[0021] The resulting suspension is then stirred. A magnetic stirrer, for example, is used to stir the suspension—a stirrer that itself possesses ferromagnetic properties. The stirring process essentially pushes the suspension particles outward, while the magnetic stirrer attracts the magnetic components toward the stirrer.

[0022] In the next step, the magnetic components are separated from the non-magnetic components. The magnetic components are preferably connected to the stirring device. For example, the stirring device can be an electromagnet or connected to an electromagnet, so that the resulting products can be easily extracted by switching off the magnet.

[0023] In a large-scale plant, the reaction can be carried out in a vessel equipped with a dosing device for adding the slag to the medium-filled vessel. A non-magnetic stirrer is then used to mix the suspension. A stationary electromagnet is located beneath the stirrer. The stirring transports the non-magnetic fraction to the edge of the vessel, where it can be extracted, for example, through an opening. An opening can be located near the electromagnet through which the electromagnet can be removed or replaced. The magnetizable fraction can then be easily separated by switching off the electromagnet.

[0024] Alternatively, the electromagnet can be mounted outside the container; during stirring, the magnetic components collect in the area of ​​the magnet. The non-magnetic components can be sucked away at the edge of the container. Once this has happened, the magnet is switched off and stirring continues. The magnetic components can then also be sucked away at the edge. In this way, it is possible to switch cyclically between two operating states.

[0025] In some embodiments of the invention, it is useful to react the slag with CO2. In a preferred form, this occurs while it is in suspension, as the liquid can then be saturated with CO2. A typical pressure for the reaction is 15 to 100 bar or 30 to 100 bar gauge pressure. The CO2 partial pressure is preferably 15 to 100 bar. The reaction with CO2 leads to a conversion of iron silicates into iron carbonates.

[0026] In some embodiments, the reaction takes place until 90 wt.% of the iron silicates present are converted into iron carbonates.

[0027] Depending on the composition of the slag, it may contain other metals, such as magnesium carbonates. These can be separated from the iron components and reused separately.

[0028] The iron carbonates can be used to produce iron. They can also be used, for example, as a "CO2 sink" to counteract the climate-damaging effects of carbon dioxide.

[0029] The resulting silicates can also be used further, for example in the cement industry or as a starting point for the production of pyrogenic silica. The invention therefore also relates to a process for the utilization of iron-containing slags, comprising the steps

[0030] - Providing an iron-containing slag with a grain size d95voi less than 200 |jm

[0031] - Conversion of the slag with CO2.

[0032] The invention is further illustrated by the following examples.

[0033] Example 1: Slag separation

[0034] A slag sample from copper mining was analyzed for its chemical and mineralogical composition using X-ray fluorescence and X-ray diffraction analysis.

[0035] Remaining 4,098

[0036] The mineral composition of the slag was as follows: Approximately 10 g of the slag with a d95voi of 100 μm were added in portions to approximately 1500 ml of water while stirring in a large beaker at room temperature for 1 hour. A magnetic stir bar was used for stirring. This stir bar was covered with a small beaker with a spout, which was inserted with the opening facing down. Despite the cover, the entire contents were set in rotation; magnetizable particles migrated through the spout to the stir bar, and non-magnetizable particles migrated to the edge of the large beaker. After stirring was stopped, the magnetic components were separated with the stir bar and mechanically separated from the stir bar, dried, and analyzed. The fraction remaining in the beaker was also dried and analyzed.

[0037] After carrying out the process according to the invention, the magnetically enriched portion was: and for the non-magnetic part:

[0038] The non-magnetic component could either be used as a CO2 sink by reacting with CO2 or be further used to extract iron. Example 2: Carbonation

[0039] Composition of the slag before treatment with CO2 (as in example 1):

[0040] After reaction in an autoclave at a CO2 partial pressure of 60 bar at a temperature of 60 °C for 2.5 weeks with a water-solid ratio of 2: 1, the following composition was obtained:

[0041] In practice, there is a quantitative conversion of the iron silicate to carbonate.

Claims

Patent claims 1. Process for separating magnetic components from a slag comprising the following steps: - Providing an iron-containing slag from copper production with a grain size d95voi of less than 200 pm with ferrimagnetic components comprising iron oxides and non-magnetic components comprising iron silicates - Addition of a liquid medium to the slag to obtain a suspension - Stirring the suspension with a magnetic stirring device - Separating the ferrimagnetic components from the non-magnetic components.

2. A method according to any one of claims 1 to 2, comprising the step of crushing an iron-containing slag from copper extraction to a grain size d95voi of less than 200 pm.

3. A method according to claim 1 or 2, wherein the comminution is carried out by means of a crusher or grinder.

4. A process according to any one of the preceding claims, wherein the iron-containing slag contains at least 30% by mass of iron silicates.

5. A process according to any one of the preceding claims, wherein the slag contains iron in an amount of at least 50 MA% FeCl.

6. A process according to any one of the preceding claims, wherein the slag contains silicon in an amount of at least 20 mass% SiC.

7. Method according to one of the preceding claims, wherein the separation of the magnetic components takes place together with the stirring device.

8. Process according to one of the preceding claims, wherein additional reaction with CO2 takes place under pressure.

9. The process according to claim 8, wherein the pressure is 15 to 100 bar.

10. The process according to claim 8 or 9, wherein the reaction takes place in the suspension.

11. A process according to any one of claims 8 to 10, wherein the reaction is carried out until at least 90% by weight of the iron silicates present have been converted into iron carbonates.

12. A process for the recycling of iron-containing slags, comprising the steps - Providing an iron-containing slag from copper production with a grain size d95voi less than 200 pm comprising iron silicates - Addition of a liquid medium to the slag to obtain a suspension - Conversion of the slag with CO2 13. The method according to claim 12, wherein the mass ratio of iron-containing slag to liquid medium is between 1:1 and 1:20, preferably 1:1 and 1:

5.

14. A method according to claim 12 or 13, comprising the step of crushing an iron-containing slag from copper extraction to a grain size d95voi of less than 200 pm.

15. A process according to any one of claims 12 to 14, wherein the slag contains iron in an amount of at least 50 mass% FeCl.

16. A process according to any one of claims 12 to 15, wherein the slag contains silicon in an amount of at least 20 mass% SiC.

17. A process according to any one of claims 12 to 16, wherein the slag is separated after the reaction into a silicate portion and an iron carbonate portion.

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