A method of reducing magnetic iron in a nickel smelter slag

Abstract

This invention discloses a method for reducing the magnetic iron content in nickel smelting slag, belonging to the field of pyrometallurgical nickel smelting technology. The method includes: detecting the magnetic iron content in the top-blown furnace slag; when the magnetic iron content is greater than 2.5%, simultaneously implementing a synergistic control operation to reduce the oxygen potential of the top-blown furnace and increase the reducing agent addition rate in the settling electric furnace; after control, detecting again; if the magnetic iron content is less than 2.5%, restoring to normal process parameters; otherwise, repeating the control until the target is met. By reducing the oxygen consumption of the top-blown furnace by 2-8 Nm³ / t concentrate, the generation of magnetic iron is reduced from the source, and the reducing agent addition rate in the settling electric furnace is controlled at 0.8%-1.6% to enhance the reduction process. This invention establishes a quantitative, closed-loop synergistic control mechanism that can stably control the magnetic iron content in the slag below 2.5%, effectively reducing the slag melting point and nickel oxide dissolution loss, promoting nickel sulfide settling, and ultimately reducing the nickel content in the slag to below 0.34%, significantly improving the metal recovery rate.

Description

Technical Field

[0001] This invention relates to the field of pyrometallurgical smelting technology for non-ferrous metal nickel, and in particular to a method for reducing the content of magnetic iron in nickel smelting slag. Background Technology

[0002] The top-blown furnace is a key piece of equipment in the smelting of nickel sulfide concentrate. Through complex physicochemical reactions between oxygen, fuel, and the concentrate, it ultimately produces low-grade nickel matte and slag. Nickel loss in the slag mainly consists of two parts: first, chemical dissolution in the slag phase as nickel oxide; and second, mechanical inclusion in the slag as nickel sulfide. The chemically dissolved nickel oxide is difficult to recover through physical sedimentation, and its content is closely related to the oxidation depth of the slag. In industrial production, the oxidation depth is usually characterized by the content of magnetic iron (Fe3O4) in the slag. A higher oxidation depth results in a higher magnetic iron content and more chemically dissolved nickel oxide, leading to a lower metal recovery rate.

[0003] The produced slag is typically discharged into a settling furnace for depletion treatment. By adding reducing agents and increasing the temperature, the aim is to reduce the magnetic iron and separate the embedded nickel sulfide particles, thereby reducing the nickel content in the slag. However, if the oxidation depth (i.e., magnetic iron content) of the slag entering the settling furnace is too high, it will not only increase the consumption of reducing agents and energy, but also severely affect the depletion effect due to the high viscosity and melting point of the slag, resulting in a persistently high nickel content in the slag, which becomes a technical bottleneck restricting the improvement of metal recovery rate.

[0004] Therefore, effectively controlling and reducing the content of magnetic iron in nickel smelting slag is of great significance for improving nickel recovery rate and reducing production costs. Summary of the Invention

[0005] To address the problem of high nickel content and low metal recovery rate in nickel smelting slag due to high magnetic iron content in existing technologies, a method is provided that can effectively reduce the magnetic iron content in the slag, thereby optimizing the depletion effect and reducing nickel loss.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for reducing the magnetic iron content in nickel smelting slag, the core of which lies in establishing a feedback control mechanism with the magnetic iron content in the slag as the key control indicator. The method includes the following steps: S1. Detect the content of magnetic iron in the slag produced by the top-blown smelting furnace; S2. When the content of magnetic iron in the slag is detected to be greater than 2.5%, a control operation is performed. When the content of magnetic iron in the slag is detected to exceed the preset threshold (2.5%), bidirectional control is immediately performed: on the one hand, at the source process - top-blown smelting furnace, the excessive oxidation of the slag is suppressed by reducing the smelting oxygen potential, thereby directly reducing the magnetic iron content and oxidation depth of the produced slag; on the other hand, at the subsequent process - settling electric furnace, the reduction ability of the generated magnetic iron is enhanced by increasing the addition rate of reducing agent.

[0007] S3. Test the slag again after adjustment. If the magnetic iron content drops below the threshold, restore the normal process parameters. If it still does not meet the standard, continue or adjust the control operation until the standard is met.

[0008] The reduction of the smelting oxygen potential in the top-blown smelting furnace is achieved by reducing oxygen consumption by 2-8 Nm³ / t·concentrate. The improvement of the reducing agent addition rate in the settling furnace refers to controlling the reducing agent addition rate within the range of 0.8% to 1.6%. The reducing agent is semi-coke with a high fixed carbon content, which is greater than 82%. The preset magnetic iron content threshold is 2.5%. This threshold is a balance point determined through practice, which can control the slag oxidation depth within a suitable range, neither over-oxidizing and increasing chemical loss, nor over-reducing and affecting the smelting process.

[0009] The mechanism of this invention lies in achieving multiple benefits by controlling the key intermediate, magnetic iron. Reducing the amount of magnetic iron directly means a shallower slag oxidation depth, resulting in less chemically dissolved nickel oxide. Simultaneously, the reduction of Fe3O4 significantly lowers the slag's melting point and high-temperature viscosity, increasing its superheat (the difference between the actual temperature and the melting point). This increased superheat improves the slag's fluidity, providing more time and favorable hydrodynamic conditions for the collision, aggregation, growth, and sedimentation separation of mechanically incorporated micro-nickel sulfide particles. This greatly enhances the depletion effect of the settling electric furnace, ultimately achieving a significant reduction in slag nickel content.

[0010] The beneficial effects of this invention are: 1. Combining source control with process enhancement: This invention does not simply involve passive reduction in the settling electric furnace stage, but innovatively moves the control point forward to the top-blown smelting furnace. By reducing the oxygen potential, it reduces the generation of magnetic iron from the source. This is supplemented by enhanced reduction in the settling electric furnace, forming a synergistic control system of "prevention first, treatment second," which has significant effects.

[0011] 2. A quantitative and closed-loop control method was established: A key process control threshold of 2.5% magnetic iron content was clearly proposed, which triggered the coordinated adjustment of the top-blown furnace and the settling electric furnace. This formed a closed-loop control logic of "detection-judgment-control-feedback", which made process control move from experience-based to precision. A complete process control closed loop was formed, which can dynamically respond to changes in raw materials or operating conditions and ensure that the slag quality is continuously and stably up to standard.

[0012] 3. Outstanding Comprehensive Benefits: By stably controlling the magnetic iron content in the slag to below 2.5%, the oxidation depth of the slag is effectively reduced, minimizing the loss of chemically dissolved nickel oxide. Simultaneously, the lower magnetic iron content lowers the melting point and viscosity of the slag, increasing its superheat and creating extremely favorable thermodynamic and kinetic conditions for the settling and separation of mechanically incorporated nickel sulfide particles, thereby significantly improving the depletion efficiency of the settling electric furnace. Practice shows that, using the method of this invention, even under high-load production conditions, the nickel content in the slag can be stably controlled below 0.34%, significantly improving the nickel metal recovery rate and resulting in significant economic benefits. Attached Figure Description

[0013] Figure 1 This is a schematic flowchart of a method for reducing magnetic iron content in nickel smelting slag, provided in an embodiment of the present invention.

[0014] Figure 2 This is a schematic diagram of the equipment for coordinated control of a top-blown furnace and a settling electric furnace according to an embodiment of the present invention. In the figure: 1-top-blown furnace spray gun, 2-top-blown furnace, 3-slag discharge chute, 4-reducing agent feed pipe of settling electric furnace, 5-settling electric furnace. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0016] like Figure 1-2 The present invention provides a method for reducing the magnetic iron content in nickel smelting slag, which involves synergistic regulation of the top-blown furnace 2 and the settling electric furnace 5 based on the detection of magnetic iron content.

[0017] In practice, samples are taken from the slag discharged from the top-blown furnace 2 or from the slag discharge trough 3 to detect the content of magnetic iron (Fe3O4) in the slag. Control threshold and logic: 2.5% is set as the critical upper limit for controlling the magnetic iron content. When the detected value > 2.5%, it is determined that the slag oxidation is too deep, and coordinated control must be implemented immediately.

[0018] Coordinated regulation and control operations: 1. Reduce the smelting oxygen potential of the top-blown furnace (source control): Reduce the smelting oxygen potential of the top-blown furnace 2 by adjusting the oxygen supply to the top-blown furnace lance 1. Specifically, this can be achieved by reducing oxygen consumption per unit, typically within the range of 2-8 Nm³ / ton of concentrate processed. This operation will moderately reduce the grade of low-grade nickel matte produced, but its core function is to reduce the oxidation depth of the smelting slag, thereby reducing the formation of magnetic iron and chemically dissolved nickel oxide from the source.

[0019] 2. Increase the reducing agent addition rate in the settling electric furnace (process intensification): Simultaneously, increase the amount of reducing agent added to the settling electric furnace 5 through the reducing agent feed pipe 4, raising the reducing agent addition rate to the range of 0.8%~1.6%. Semi-coke with good reactivity and high fixed carbon content (>82%) is preferred as the reducing agent. Increasing the reducing agent addition rate aims to enhance the reduction of magnetic iron in the slag flowing into the settling electric furnace (Fe3O4 + C → FeO + CO), further reducing its content.

[0020] Feedback and Closed Loop: After implementing the above control measures for a period of time (e.g., 4 hours, to allow the system to reach a new equilibrium), the magnetic iron content in the slag should be checked again. If the detected value is <2.5%, it indicates that the control measures have been effective, and parameters such as the oxygen potential of the top-blown furnace and the reducing agent addition rate of the settling electric furnace can be gradually restored to the normal process settings. If the detected value is still ≥2.5%, the above control operations need to be continued or strengthened (e.g., further reducing oxygen consumption or increasing the reducing agent addition rate on the basis of the adjustments already made) until the magnetic iron content stabilizes below 2.5%.

[0021] The above methods can form an effective closed-loop process control system, stabilizing the slag properties within the optimal range.

[0022] The following description uses specific examples to illustrate the point.

[0023] Example 1 The initial test showed that the magnetic iron content in the slag was 3.5%. Control measures were implemented: the oxygen consumption of the top-blown furnace was reduced by 4 Nm³ / t concentrate, while the reducing agent addition rate in the settling electric furnace was increased from 1.0% to 1.2%. After 4 hours of operation, a second test showed that the magnetic iron content in the slag had decreased to 2.3%, corresponding to a nickel content of 0.33%.

[0024] Example 2 The initial slag magnetic iron content was 2.8%. Control measures were implemented: the oxygen consumption of the top-blown furnace was reduced by 3 Nm³ / t concentrate, while the reducing agent addition rate in the settling electric furnace was increased from 0.8% to 1.1%. After 4 hours of operation, the slag magnetic iron content decreased to 2.2%, corresponding to a nickel content of 0.32%.

[0025] Example 3 The initial slag magnetic iron content was 2.6%. Control measures were implemented: the oxygen consumption of the top-blown furnace was reduced by 2 Nm³ / t concentrate, while the reducing agent addition rate in the settling electric furnace was increased from 0.8% to 0.9%. After 4 hours of operation, the slag magnetic iron content decreased to 2.4%, corresponding to a nickel content of 0.33%. Example 4 The initial slag magnetic ferrite content was 4.5%. Initial adjustment: The oxygen consumption of the top-blown furnace was significantly reduced by 8 Nm³ / t. concentrate, while the reducing agent addition rate of the settling electric furnace was increased from 0.8% to 1.2%. After 4 hours of operation, the magnetic ferrite content was 2.8%, still below the standard. Second adjustment: Based on the initial adjustment, the oxygen consumption of the top-blown furnace was further reduced by 3 Nm³ / t. concentrate, while the reducing agent addition rate of the settling electric furnace was increased from 1.2% to 1.4%. After another 4 hours of operation, the slag magnetic ferrite content decreased to 2.4%, corresponding to a nickel content of 0.33%.

[0026] The above embodiments demonstrate that the method of the present invention has a good control effect on slags with different initial magnetic iron contents. Through synergistic adjustment, the magnetic iron content can be stably controlled below 2.5%, and the excellent indicator of slag nickel content below 0.34% can be achieved.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for reducing magnetic iron content in nickel smelting slag, characterized in that, Includes the following steps: S1. Detect the content of magnetic iron in the slag produced by the top-blown smelting furnace; S2. When the content of magnetic iron in the slag is detected to be greater than 2.5%, an adjustment operation is performed. The adjustment operation includes: reducing the smelting oxygen potential of the top-blown smelting furnace to reduce the oxidation depth of the smelting slag. Increase the reducing agent addition rate in the settling furnace to reduce the magnetic iron in the slag; S3. After adjustment, the content of magnetic iron in the slag is detected again. If the content is less than 2.5%, the process parameters of the top-blown smelting furnace and the settling electric furnace are restored to normal values. If the content is still greater than or equal to 2.5%, step S2 is repeated until the content of magnetic iron in the slag is less than 2.5%.

2. The method for reducing magnetic iron content in nickel smelting slag according to claim 1, characterized in that, In step S2, the smelting oxygen potential is reduced by decreasing the oxygen consumption of the top-blown smelting furnace, with the reduction in oxygen consumption reaching 2~8 Nm³ / ton of concentrate.

3. The method for reducing magnetic iron content in nickel smelting slag according to claim 1, characterized in that, In step S2, the reducing agent addition rate of the settling furnace is controlled between 0.8% and 1.6%.

4. The method for reducing magnetic iron content in nickel smelting slag according to claim 3, characterized in that, In step S2, the reducing agent used is semi-coke with a fixed carbon content of more than 82%.

5. The method for reducing magnetic iron content in nickel smelting slag according to claim 1, characterized in that, The method reduces the content of chemically dissolved nickel oxide in the slag by decreasing the oxidation depth of the slag; and by reducing the content of magnetic iron to lower the melting point of the slag and increase the superheat of the slag, thereby promoting the sedimentation and separation of mechanically incorporated nickel sulfide in the slag, and ultimately reducing the nickel content of the slag.

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