Method for recycling nickel-copper matte by treating nickel slag through homologous vulcanizing agent

Abstract

The invention belongs to the technical field of waste residue recycling, and particularly relates to a method for recycling nickel-copper matte by treating nickel residues through a homologous vulcanizing agent. The method comprises the following steps: mixing nickel slag, limestone, a homologous vulcanizing agent and a reducing agent, heating for reduction vulcanization treatment, and cooling to obtain nickel-copper matte and depleted slag; the homologous vulcanizing agent is nickel dry concentrate, nickel sulfide and pyrite concentrate, copper sulfide and pyrite concentrate, or nickel sulfide, copper sulfide and pyrite concentrate; the mass of the homologous vulcanizing agent accounts for more than 1.5% and 1t of the mass of the nickel slag; and 8.5%. The content of Ni, Cu and Co in the depleted slag obtained through the method is far lower than the content of Ni, Cu and Co in nickel slag, and production indexes are met. The nickel-copper matte is a target product of the invention, has high Ni, Cu and Co contents, and mainly exists in the form of sulfides. According to the method, the recovery rate of valuable metal in the nickel slag is increased, and the obtained nickel-copper matte product can directly enter a nickel smelting process flow or be sold.

Description

Technical Field

[0001] This invention belongs to the field of waste residue recycling technology, specifically relating to a method for treating nickel slag with a homologous sulfiding agent to recover nickel-copper matte. Background Technology

[0002] Nickel slag is a waste product generated during nickel smelting, with approximately 6-16 tons of slag produced per ton of nickel. The accumulation of nickel slag in slag heaps not only occupies land and pollutes the environment but also represents a significant waste of metal resources. Due to its composition and resource value, smelting slag is typically classified as an ore, and its treatment and reuse usually follow mineral processing methods. According to ore classification standards, the ratio of (nickel sulfide + metallic nickel) to total nickel in nickel slag is 35.12% < 60%, classifying it as a nickel oxide ore. Because metal sulfides in ore have good floatability, flotation is the most widely used and well-developed beneficiation method for sulfide ores, recovering most of the valuable metals Ni and Cu from the nickel slag. However, nickel oxide and nickel silicate in nickel slag cannot be recovered by flotation, accounting for 64.88% of the total nickel; copper ferroate and copper oxide cannot be recovered by flotation, accounting for 11.22% of the total copper. This results in low metal recovery rates during flotation and high valuable metal content in the tailings, leading to resource waste.

[0003] In summary, due to the low metal sulfidation rate and complex ore composition and distribution in nickel slag, the recovery of valuable metals from nickel slag through flotation suffers from low flotation metal recovery rates. Summary of the Invention

[0004] The purpose of this invention is to provide a method for recovering nickel-copper matte from nickel slag by treating nickel slag with a homologous sulfiding agent. The method provided by this invention improves the recovery rate of valuable metals in nickel slag, and the resulting nickel-copper matte can be directly entered into the nickel smelting process or sold. At the same time, the method is simple and suitable for industrial application.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for treating nickel slag with a homologous sulfiding agent to recover nickel-copper matte, comprising the following steps: Nickel slag, limestone, a homologous sulfiding agent, and a reducing agent are mixed and heated for reduction sulfidation treatment. After cooling, nickel-copper matte and depleted slag are obtained. The homologous sulfiding agent includes a first sulfiding agent, a second sulfiding agent, a third sulfiding agent, or a fourth sulfiding agent. The first sulfiding agent is dry nickel concentrate or sulfur concentrate, the second sulfiding agent is nickel sulfide and sulfur concentrate, the third sulfiding agent is copper sulfide and sulfur concentrate, and the fourth sulfiding agent is nickel sulfide, copper sulfide, and sulfur concentrate. The mass percentage of the homologous sulfiding agent to the mass of the nickel slag is >1.5% and <8.5%. The reducing agent includes coke and / or pulverized coal.

[0006] Preferably, the nickel slag includes cold nickel slag and / or hot nickel slag; When the nickel slag is hot nickel slag, the mixing includes the following steps: premixing limestone, homologous sulfiding agent and reducing agent to obtain a mixture, and then mixing the hot nickel slag with the mixture by slag flushing method; When the nickel slag is cold nickel slag, the mixing includes method one or method two. Method one includes: directly mixing the cold nickel slag, limestone, homologous sulfiding agent and reducing agent. Method two includes: heating a portion of the cold nickel slag to melt to obtain molten nickel slag, premixing the remaining cold nickel slag, limestone, homologous sulfiding agent and reducing agent to obtain a premix, and mixing the premix with the molten nickel slag. The mass percentage of the portion of cold nickel slag is 60-90% of the total mass of the cold nickel slag.

[0007] Preferably, the reduction vulcanization treatment is carried out in a controllable polarity three-phase ultra-low frequency electric furnace, wherein the frequency of the controllable polarity three-phase ultra-low frequency electric furnace is 0.0001~0.1 Hz.

[0008] Preferably, the mass percentage of the homologous sulfiding agent to the mass of the nickel slag is 3-6%.

[0009] Preferably, the mass percentage of nickel sulfide in the second sulfiding agent is 0.3-0.8% of the mass of the nickel slag.

[0010] Preferably, the mass percentage of copper sulfide in the third sulfiding agent is 0.3-1% of the mass of the nickel slag.

[0011] Preferably, the mass percentage of nickel sulfide in the fourth sulfiding agent is 0.1-0.5% of the mass of the nickel slag, and the mass percentage of copper sulfide in the nickel slag is 0.2-0.6%.

[0012] Preferably, the mass percentage of the limestone is 2-8% of the mass of the nickel slag; and the mass percentage of the reducing agent is 5-15% of the mass of the nickel slag.

[0013] Preferably, the holding temperature of the reduction vulcanization treatment is 1400~1500℃, the holding time is 40~80min, the heating rate is 5~15℃ / min, and the cooling rate is 1~8℃ / min.

[0014] Preferably, the mineral phases of the nickel slag include (Mg,Fe)₂SiO₄ and Fe₂SiO₄, wherein Ni > 0.39%, Co > 0.1%, and Cu > 0.2%; the mineral phases of the nickel dry concentrate include (Ni,Fe)S₂, FeS₂, and CuFeS₂; the sulfur concentrate includes iron sulfide minerals; and the mineral phases of the nickel-copper matte include Fe 3.97 Ni 4.84 Co 0.07S8, Cu9Fe9S 16 The mineral phases of the depleted slag include Fe2SiO4 and (Fe,Mg)2SiO4, wherein Ni < 0.2%, Co < 0.05%, and Cu < 0.15%.

[0015] This invention provides a method for recovering nickel-copper matte from nickel slag using a homologous sulfiding agent, comprising the following steps: mixing nickel slag, limestone, a homologous sulfiding agent, and a reducing agent; heating to perform reduction sulfidation treatment; and cooling to obtain nickel-copper matte and depleted slag. The homologous sulfiding agent includes a first sulfiding agent, a second sulfiding agent, a third sulfiding agent, or a fourth sulfiding agent. The first sulfiding agent is dry nickel concentrate or sulfur concentrate; the second sulfiding agent is nickel sulfide and sulfur concentrate; the third sulfiding agent is copper sulfide and sulfur concentrate; and the fourth sulfiding agent is nickel sulfide, copper sulfide, and sulfur concentrate. The mass percentage of the homologous sulfiding agent relative to the mass of the nickel slag is >1.5% and <8.5%. The reducing agent includes coke and / or pulverized coal. This invention uses nickel slag as raw material and employs Ni and Cu homologous materials (i.e., homologous sulfiding agents) as sulfiding agents, while adding reducing agents and limestone. Limestone, acting as a modifier, enables the reconstruction of the molten nickel slag phases during the reduction sulfidation process. The oxide and silicate phases of Ni, Cu, and Co sulfide, generating corresponding sulfides, and the limestone also regulates the crystallization morphology of the sulfide phase grains, which is beneficial for nickel-copper-sulfur settling. The method provided by this invention results in a lean slag with significantly lower Ni, Cu, and Co contents than nickel slag, specifically below 0.1956%, 0.1225%, and 0.0678%, respectively, meeting production targets (nickel content less than 0.34% in top-blown system settling slag and less than 0.26% in flash slag). Nickel-copper matte is the target product of this invention, with high Ni, Cu, and Co contents, primarily existing in sulfide form. Calculations show that the Ni, Cu, and Co contents in the lean slag are reduced by at least 55%, 47%, and 36%, respectively, compared to nickel slag. This invention improves the recovery rate of valuable metals from nickel slag, and the resulting nickel-copper matte can be directly used in the nickel smelting process or sold. Compared with existing technologies, this invention has the following advantages: The method provided by this invention is environmentally friendly and saves on the amount of sulfiding agent: traditional sulfiding agents such as sulfur and pyrite are very easy to use in excess, leading to excessive S. 2- It easily generates SO2 gas, polluting the environment and wasting sulfurizing agents. The sulfur release process of homologous sulfurizing agents is controlled and slow, greatly reducing sulfur at the source, making operation safer and more environmentally friendly. The SO2 emission concentration in the exhaust gas of this invention is less than 35 mg / m³. 3 It meets emission standards.

[0016] The method provided by this invention enables selective sulfidation of nickel slag. Due to the significant differences in solubility products among different metal sulfides, this invention, by selecting a homologous sulfiding agent, ensures that only metals with solubility products much smaller than those of the homologous sulfiding agent are sulfided. The homologous sulfiding agent used in this invention exhibits high selectivity, resulting in high-purity metal sulfide precipitates, which is beneficial for subsequent recovery. Results from the examples show that, using the homologous sulfiding agent of this invention, when the addition amount of nickel dry concentrate is 3%~5%, the sulfidation rate of Ni is 82%~88%, the sulfidation rate of Cu is 88%~92%, and the sulfidation rate of Co is 16%~31%, while the sulfidation rate of Fe is only 3%~4%.

[0017] The method provided by this invention separates nickel-copper matte from the depleted slag: The nickel sulfide and copper sulfide in the homologous sulfiding agent used in this invention can induce newly formed nickel-copper matte in the slag to preferentially grow on the surface of the existing homologous sulfiding agent particles, forming a seed crystallization process. This results in larger, denser precipitate particles, making it easier to separate slag and sulfur through sedimentation, and achieving higher purity.

[0018] The method provided by this invention does not introduce new impurities: the first sulfiding agent used in this invention is dry nickel concentrate, which is the raw material for nickel flash furnace smelting. As a homologous sulfiding agent, it will not introduce new cations and maintains the "purity" of the product.

[0019] Furthermore, in this invention, the reduction sulfidation treatment is carried out in a controllable polarity three-phase ultra-low frequency electric furnace, the frequency of which is 0.0001~0.1 Hz. This invention uses a controllable polarity three-phase ultra-low frequency electric furnace for the reduction sulfidation treatment. Due to the very low frequency (0.0001~0.1 Hz), it is almost equivalent to DC arc smelting, thus the arc is stable, the high-temperature region is larger than that of a single-electrode DC arc furnace, and the thermal efficiency is high. When powered by the ultra-low frequency polarity controllable power supply, an electric thrust is generated between the electrode currents. Whenever the electrodes switch, the electric thrust changes from attraction to repulsion (or from repulsion to attraction), causing a stirring effect in the molten pool. This promotes a more uniform thermal temperature gradient in the furnace, accelerates the melting rate, speeds up the oxidation-reduction reaction, shortens the smelting time, thereby improving product quality and yield, while reducing power consumption. Simultaneously, the ultra-low frequency DC current generates a constant electromagnetic field during its flow, creating continuous stress on the molten slag and metal liquid, thus acting as a stirrer, accelerating mass transfer between reactants and products, and helping fine metal droplets collide, coalesce, and grow, accelerating sedimentation and separation, and making the temperature and composition within the furnace more uniform. This invention uses a controllable polarity three-phase ultra-low frequency electric furnace for the aforementioned reduction sulfidation treatment. The nickel-copper matte settled in the furnace can be directly entered into the nickel smelting process or sold, with a nickel content of less than 0.2% in the depleted slag. Furthermore, the sulfidation rate of Ni is greater than 88%, and the sulfidation rate of Cu is greater than 90%. Compared to ordinary electric furnaces, the nickel recovery rate is increased by 41.55%, and the copper recovery rate is increased by 45.23%. Attached Figure Description

[0020] Figure 1 A flowchart illustrating a method for recovering nickel-copper matte from nickel slag using a homologous sulfiding agent, provided by the present invention. Figure 2 The XRD pattern of the nickel slag in this invention; Figure 3 These are BSE images and elemental EDS surface scan images of the nickel slag in this invention; Figure 4 The XRD pattern of the dry nickel concentrate used in this invention; Figure 5 These are BSE images and elemental EDS surface scan images of the dry nickel concentrate used in this invention. Figure 6 This is a BSE image of the main minerals in a large-area SEM image of dry concentrate with a particle size >150μm, and an elemental distribution map of sulfur, nickel, copper and iron. Figure 7 These are photographs showing the different colors and morphologies of the nickel-copper matte used in this invention; Figure 8 XRD patterns of depleted slag and nickel slag, and XRD patterns of nickel-copper matte; Figure 9 SEM images and elemental surface scan images of nickel-copper matte; Figure 10 A schematic diagram of the electric arc furnace body and digital photographs of the sample; Figure 11 Photographs and XRD patterns of the upper and lower layers of the depleted slag and the nickel-copper matte layer; Figure 12 This is a physical image of an 1800kVA ultra-low frequency three-phase polarity controllable electric furnace. Figure 13 The effect of different types of sulfiding agents on the composition of slag; Figure 14 The effect of different types of sulfiding agents on the sulfidation rates of Ni, Cu, and Co in furnace slag; Figure 15 The effect of nickel dry concentrate yield on slag composition; Figure 16 The effect of nickel dry concentrate yield on the sulfidation rate of Ni, Cu, and Co in slag; Figure 17 The effect of reducing agent rate on slag composition; Figure 18 The effect of reducing agent rate on the sulfidation rate of Ni, Cu, and Co in slag; Figure 19 The effect of limestone ratio on slag composition; Figure 20 The effect of limestone ratio on the sulfidation rate of Ni, Cu, and Co in slag; Figure 21 The effect of heat preservation time on slag composition. Detailed Implementation

[0021] This invention provides a method for treating nickel slag with a homologous sulfiding agent to recover nickel-copper matte, comprising the following steps: Nickel slag, limestone, a homologous sulfiding agent, and a reducing agent are mixed and heated for reduction sulfidation treatment. After cooling, nickel-copper matte and depleted slag are obtained. The homologous sulfiding agent includes a first sulfiding agent, a second sulfiding agent, a third sulfiding agent, or a fourth sulfiding agent. The first sulfiding agent is dry nickel concentrate or sulfur concentrate, the second sulfiding agent is nickel sulfide and sulfur concentrate, the third sulfiding agent is copper sulfide and sulfur concentrate, and the fourth sulfiding agent is nickel sulfide, copper sulfide, and sulfur concentrate. The mass percentage of the homologous sulfiding agent to the mass of the nickel slag is >1.5% and <8.5%. The reducing agent includes coke and / or pulverized coal.

[0022] In this invention, unless otherwise specified, all raw materials / components are commercially available products well-known to those skilled in the art. In this invention, the nickel dry concentrate rate is the percentage of the mass of the nickel dry concentrate used as a homologous sulfiding agent relative to the mass of the nickel slag. The reducing agent rate is the percentage of the mass of the reducing agent relative to the mass of the nickel slag. The limestone rate is the percentage of the mass of limestone relative to the mass of the nickel slag.

[0023] Figure 1 This invention provides a flowchart of a method for recovering nickel-copper matte from nickel slag using a homologous sulfiding agent. The invention uses nickel slag as raw material, limestone as a modifier, and coke and / or pulverized coal as a reducing agent. A suitable homologous sulfiding agent is selected, and reduction sulfidation treatment is performed at a certain temperature to convert the silicate and oxide phases of Ni, Cu, and Co in the nickel slag into sulfide phases, generating nickel-copper matte. After holding at this temperature for a certain time, the nickel-copper matte settles in the molten nickel slag. After cooling, nickel-copper matte and depleted slag are obtained. This invention precipitates nickel and copper as sulfides to form nickel-copper matte. The homologous sulfiding agents used in this invention are dry nickel concentrate, nickel sulfide + iron sulfide, copper sulfide + iron sulfide, and nickel sulfide + copper sulfide + iron sulfide.

[0024] This invention mixes nickel slag, limestone, a homologous sulfiding agent, and a reducing agent. In this invention, the nickel slag can include cold nickel slag and / or hot nickel slag. The cold nickel slag is water-quenched nickel slag from a flash furnace (also known as flash furnace slag). The cold nickel slag is solid nickel slag; it is heated and melted to obtain molten nickel slag. The hot nickel slag is molten nickel slag.

[0025] In this invention, the mineral phase of the nickel slag preferably includes (Mg,Fe)₂SiO₄ and Fe₂SiO₄, wherein Ni > 0.39%, Co > 0.1%, and Cu > 0.2%. In embodiments of this invention, the elemental content (wt%) of the nickel slag is shown in Table 1. The XRD pattern of the nickel slag is shown below. Figure 2 As shown. The BSE photograph and elemental EDS surface scan photograph of the nickel slag are shown below. Figure 3 As shown in Table 1, the nickel slag contains approximately 35.46 wt% TFe, 37.65 wt% SiO2, 9.01 wt% MgO, and 2.40 wt% CaO, while the contents of Ni, Cu, and Co are 0.41 wt%, 0.235 wt%, and 0.125 wt%, respectively. Figure 2 and Figure 3 The images shown are the XRD pattern and SEM-EDS image of the nickel slag. Figure 2 and Figure 3 The main mineral phases of the nickel slag are (Mg,Fe)₂SiO₄ and Fe₂SiO₄. In the BSE image, the bright areas contain small amounts of aggregated Cu, S, Fe, and trace amounts of Ni and Co, indicating the presence of a small amount of Fe-Cu-Ni-Co-S type polymetallic sulfide phase in the nickel slag. However, its content is low, below the XRD detection limit. The light gray areas mainly contain Fe, Si, Mg, and O, indicating that this area is (Mg,Fe)₂SiO₄. The dark gray areas mainly contain Fe, Si, and O, indicating that this area is Fe₂SiO₄.

[0026] Table 1 Reference Chemical Composition of Nickel Slag (%)

[0027] In this invention, the mineral phases of the nickel dry concentrate (hereinafter referred to as dry concentrate) preferably include (Ni,Fe)S2, FeS2, and CuFeS2. The nickel dry concentrate used in this invention is a raw material for nickel flash furnace smelting.

[0028] In this embodiment of the invention, the main minerals and their contents in the nickel dry concentrate are shown in Table 2, and the chemical composition (wt.%) of the nickel dry concentrate is shown in Table 3. The XRD pattern of the nickel dry concentrate is shown in... Figure 4 As shown. A BSE photograph of the nickel dry concentrate is shown below. Figure 5 As shown in (a) above. The elemental EDS surface scan image of the nickel dry concentrate is shown below. Figure 5As shown in (b) to (g) of Table 3, the main components of the nickel dry concentrate are iron, nickel, copper, and sulfur. Specifically, the total iron (TFe) content is 33.86 wt%, the sulfur content is 22.18 wt%, the nickel content is 8.53 wt%, the copper content is 7.15 wt%, and the cobalt content is 0.22 wt%, indicating that the nickel dry concentrate used in this invention is mainly composed of sulfide minerals. The low content of non-metallic oxides such as CaO (1.87 wt%), MgO (8.00 wt%), and SiO2 (9.40 wt%) indicates fewer gangue impurities and higher mineral purity. Overall, the nickel dry concentrate used in this invention is a high-grade Ni-Cu-Fe sulfide concentrate.

[0029] In this invention, the particle size of the dry nickel concentrate is preferably -74μm > 80 wt%.

[0030] Depend on Figure 4 XRD analysis revealed that the nickel concentrate contained multiple phases, primarily (Ni,Fe)S2, FeS2, and CuFeS2. Further analysis... Figure 5 As can be seen in (a), various minerals are closely intergrowthed in this region. Among them, the areas enriched by Cu, Fe, and S are chalcopyrite, the brightest area of ​​Fe is magnetite grains, the areas with heavy Fe and S elements correspond to pyrite and pyrrhotite grains, the area containing Ni is nickel pyrite, and the area containing Mg and Si is talc.

[0031] Table 2. Major minerals and their contents (wt.%) in dry nickel concentrate

[0032] In this invention, the reference chemical composition of the nickel dry concentrate is shown in Table 3.

[0033] Table 3 Reference Chemical Composition of Dry Nickel Concentrate (%)

[0034] The main mineral composition and content of the nickel dry concentrate are shown in Tables 2 and 3. Tables 2 and 3 show that the main ore minerals in the nickel dry concentrate are pyrrhotite, chalcopyrite, pyrite, and pyrrhotite, with contents of 23.96%, 22.03%, 20.50%, and 10.92%, respectively, totaling 77.41%. The gangue minerals are mainly serpentine and talc, platy silicate minerals, with contents of 7.43% and 2.15%, respectively; and small amounts of magnetite and other trace minerals. When the nickel dry concentrate is used as a sulfiding agent for sulfidation, the effective sulfiding component is pyrite.

[0035] Figure 6 (a) in the image is a BSE image of the main minerals in a large-area SEM image with a particle size >150 μm in the nickel dry concentrate. Figure 6 (b) in the diagram shows the elemental distribution of sulfur, nickel, copper, and iron. Observe... Figure 6 The large-area SEM image (a) of nickel dry concentrate with a particle size greater than 150 μm shows that there are complex intergrowths of various minerals in the nickel dry concentrate. Figure 6 (b) shows the elemental distribution of sulfur, nickel, copper, and iron. S is mainly distributed in pyrrhotite, chalcopyrite, nickel pyrrhotite, and pyrite, accounting for 36% in pyrite.

[0036] In a specific embodiment of the present invention, the chemical composition (wt.%) of the sulfur concentrate is shown in Table 4.

[0037] Table 4 Chemical composition of sulfur concentrate (wt.%)

[0038] In this invention, the sulfur concentrate preferably comprises iron sulfide minerals. Table 4 shows the chemical composition analysis of the sulfur concentrate in the embodiments of this invention. As can be seen from Table 4, the sulfur concentrate has a high content of iron and sulfur, with TFe content of 33.81 wt% and S content of 37.55 wt%, indicating that the sample is mainly composed of iron sulfide minerals (such as pyrite FeS2 or pyrrhotite Fe). 1-x The composition of the concentrate is as follows: Ni, Co, and Cu are present in trace amounts of 0.03 wt%, 0.01 wt%, and 0.31 wt%, respectively. Furthermore, the MgO content is 3.61 wt%, the CaO content is 0.56 wt%, and the SiO2 content is only 0.03 wt%, indicating that the gangue impurities in this concentrate are extremely low.

[0039] In this invention, the mass percentage of the homologous sulfiding agent relative to the mass of the nickel slag is preferably 2-6%, more preferably 3-6%, and in the embodiments it can be 3%, 3.5%, 4%, 4.2%, 5%, 5.6%, 6%, or 8.4%. The mass percentage of nickel sulfide in the second sulfiding agent relative to the mass of the nickel slag is preferably 0.3-0.8%, and in the embodiments it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%, with the remainder being sulfur concentrate. The mass percentage of copper sulfide in the third sulfiding agent relative to the mass of the nickel slag is preferably 0.3-1%, and in the embodiments it can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, with the remainder being sulfur concentrate. The mass percentage of nickel sulfide in the fourth sulfiding agent relative to the mass of the nickel slag is preferably 0.1-0.5%, and in the examples it can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%; the mass percentage of copper sulfide in the fourth sulfiding agent relative to the mass of the nickel slag is preferably 0.2-0.6%, and in the examples it can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, or 0.65%, with the remainder being sulfur concentrate.

[0040] In this invention, the limestone serves as both a modifier and a flux. The particle size of the limestone can be 3-5 mm. The reference chemical composition of the limestone is shown in Table 5.

[0041] Table 5. Detection results of reference chemical composition of limestone (%)

[0042] In this invention, the mass percentage of limestone to nickel slag is 2-8%, and in the embodiments it can be 2%, 3%, 4%, 5%, 6%, 7% or 8%.

[0043] In this invention, the reducing agent is preferably pulverized coal (also known as granular coal). The particle size of the granular coal can be 1~3 mm. In this invention, the reference chemical composition (wt%) of the reducing agent is shown in Table 6.

[0044] Table 6. Detection results of reference chemical composition of reducing agent

[0045] In this invention, the mass percentage of the reducing agent to the mass of the nickel slag is preferably 5-15%, and in the embodiments it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0046] In this invention, when the nickel slag is hot nickel slag, the mixing preferably includes the following steps: premixing limestone, a homologous sulfiding agent, and a reducing agent to obtain a mixture, and then mixing the hot nickel slag with the mixture using a slag flushing method. In a specific embodiment of this invention, when the nickel slag is hot nickel slag, the mixing is carried out in a slag bag. Preferably, the limestone, reducing agent, and homologous sulfiding agent are added to the slag bag, the slag bag is placed at the tail of the slag flow channel of the nickel flash furnace, and the hot nickel slag (i.e., molten nickel slag) is placed in the slag bag using a slag flushing method.

[0047] In this invention, when the nickel slag is cold nickel slag, the mixing includes method one or method two. Method one includes directly mixing the cold nickel slag, limestone, homologous sulfiding agent, and reducing agent. Method two includes heating a portion of the cold nickel slag to melt to obtain molten nickel slag, premixing the remaining cold nickel slag, limestone, homologous sulfiding agent, and reducing agent to obtain a premix, and mixing the premix with the molten nickel slag. Preferably, the portion of cold nickel slag is heated to melt in an electric furnace, which can be a controllable polarity three-phase ultra-low frequency electric furnace. The mass percentage of the portion of cold nickel slag to the total mass of the cold nickel slag is 60-90%, and in the embodiments, it can be 3 / 4-2 / 3 or 90%. The mass ratio of the remaining cold nickel slag to the portion of cold nickel slag can be 1 / 9-1 / 3.

[0048] In this invention, the reduction sulfidation treatment is preferably performed using an electric furnace for heating. The electric furnace can be a conventional electric furnace or a controllable polarity three-phase ultra-low frequency electric furnace. In this invention, when the nickel slag is hot, the reduction sulfidation treatment can be performed in a conventional electric furnace; when the nickel slag is cold, the reduction sulfidation treatment is preferably performed in a controllable polarity three-phase ultra-low frequency electric furnace with a frequency of 0.0001~0.1 Hz. The heating is performed by electric heating.

[0049] In this invention, after the heat preservation of the reduction sulfidation treatment is completed, the heating is stopped and the temperature is lowered to room temperature; then the material in the cooled slag bag is taken out, the nickel-copper matte settles to the bottom, and the depleted slag is at the top, which can be separated by a slight tap.

[0050] In this invention, the controllable polarity three-phase ultra-low frequency electric furnace can be an 1800kVA ultra-low frequency polarity controllable electric furnace. In this invention, the electric furnace is also referred to as an electric arc furnace.

[0051] In this invention, the 1800kVA ultra-low frequency polar controllable electric furnace initially possessed the functions of a single-electrode DC electric arc furnace and an ultra-low frequency three-phase polar controllable electric furnace. After modification, it only possesses the functions of an ultra-low frequency three-phase polar controllable electric furnace. The furnace components include: a high-voltage switchgear, transformer, rectifier power supply unit, short-grid assembly, electrode lifting device, furnace body unit, furnace cover unit, cooling water unit, hydraulic station unit, compressed air unit, melt discharge metering and transfer system, melt slow cooling zone, slow cooling slag demolding zone, automatic control system, etc., equipped with... Figure 12 As shown in Table 7, the technical parameters of the project equipment are as follows.

[0052] Table 7 Technical Parameters of 1800kVA Ultra-Low Frequency Three-Phase Polarity Controllable Electric Furnace

[0053] (1) High-voltage switchgear 10KV high-voltage incoming line circuit breaker cabinet.

[0054] (2) Transformer The transformer is a dedicated electric furnace transformer for power supply, with two sets of internally sealed delta windings for low-voltage output, forming a 12-pulse output. The transformer consists of the main body, oil conservator, voltage regulating switch operating box, control cabinet, high-voltage bushing, pressure relief device, on-load tap changer, low-voltage busbar, oil-water cooler, etc.

[0055] The voltage regulation method is no-load electric voltage regulation, with a total of 9 levels. The insulation level meets the requirements of the 10kV high-voltage level. The cooling method adopts a forced oil-water circulation cooling system and is equipped with an oil-water cooler. The transformer is equipped with a remote temperature measurement device, and the oil temperature can be observed through a digital display instrument in the main control room. The transformer oil used is No. 25 oil, which is provided for initial operation.

[0056] (3) Power supply system The power supply system is a three-phase controllable polarity ultra-low frequency power supply system. The power supply system consists of a power cabinet, reactors, a pure water cooler, and a power control cabinet.

[0057] The core of the power supply system is the power cabinet. Through the combination of thyristor elements within the cabinet, the power control system controls the input-output conversion of the power cabinet, realizing the transition from an AC power supply structure to an ultra-low frequency controllable polarity power supply structure. The reactor is connected to the output side of the power cabinet to smooth fluctuations in the smelting current and balance the phase difference of the power output. The pure water cooler is a device that provides soft water cooling for the converter components, providing closed-loop circulating water for cooling the converter components. It is connected to the project equipment's cooling circulating water system through non-contact water-to-water heat exchange.

[0058] (4) Short network components The short-network assembly refers to the high-current line connecting the transformer's secondary side ultra-low frequency power supply device to the electrode cross arm and bottom electrode connection point, which transmits and outputs electrical energy. It consists of a flexible compensator, water-cooled conductive copper pipes, conductive copper busbars, and large-section water-cooled cables. The flexible compensator allows for disassembly and assembly without moving the transformer and compensates for installation errors. The short-network line support is made of stainless steel or non-magnetic steel.

[0059] Water-cooled cables, as a crucial component of short-network components, require internal water cooling, electrical conductivity, and flexible operation, necessitating a unique structure. They utilize copper stranded wire connected to copper connectors at both ends via a special process. The copper stranded wire and connector ends are externally encased in heat-resistant and wear-resistant tubing, and secured at the connector ends with stainless steel strapping to prevent internal cooling water leakage. In the design of the short-network system, two large-section water-cooled cables are used per phase to ensure that both ends of the water-cooled cables have a certain straight section when the electrode lifting mechanism reaches the top and bottom, thus extending the service life of the water-cooled cables.

[0060] (5) Electrode crossarm column system The electrode crossarm column system consists of an electrode crossarm, an electrode clamping mechanism, a lifting column, and a plunger-type hydraulic lifting cylinder.

[0061] The electrode cross arm is a product that integrates conductive and rigid structural components. Its shape is a rectangular beam structure, with conductive copper tubes connecting conductive clamps and short water-cooled cables. The electrode chuck is made of forged copper and internally water-cooled. Its internal water channel design is crucial to ensuring its service life. The electrode retainer is made of non-magnetic austenitic stainless steel with a sandwich structure and internal water cooling. The electrode release cylinder is a specialized cylinder for electrode clamping and releasing. Electrode clamping relies on the restoring force of a compressed disc spring to tighten the clamping ring and electrode chuck, thus securing the electrode. Electrode release is achieved by a piston cylinder compressing the disc spring. Reliable insulation is provided at the connection between the electrode release cylinder and the electrode clamping ring. The lifting column is a hollow steel structure with welded column guide rails. The surface of the guide rails is machined to ensure smooth and reliable lifting. There is good insulation between the column and the cross arm. A plunger-type hydraulic cylinder is installed inside the column and drives the column to rise and fall. The electrode lifting and falling is automatically adjusted by an electro-hydraulic proportional valve, and can also be controlled manually. The electrode lifting and falling is equipped with a limit switch to send a motion status signal to the electrical control system. The lifting column moves up and down in the column support guide frame. The guide frame is a two-layer guide wheel frame, and the guide wheel frame is equipped with a guide wheel device for guiding the lifting of the electrode lifting column. There are 12 guide wheels in each layer, and a total of 24 guide wheels in two layers. The water channels of the electrode cross arm and the retaining ring are connected in series, while the electrode clamp has a separate cooling water channel. This design makes the equipment simple and provides good cooling.

[0062] (6) Furnace body assembly The furnace shell is welded from steel plates, and the furnace bottom has a frustum-shaped structure with external reinforcing ribs. The furnace shell is fixedly installed to the tilting platform via pins and wedges. The tilting platform is an arc-plate cradle structure placed on two tilting tracks and is driven back and forth by a tilting cylinder to assist in unloading.

[0063] The typical tapping method involves opening the tap hole and allowing slag to flow out of the furnace. Two tap holes, one high and one low, are arranged in a line, with the lower tap hole for tapping iron and the higher tap hole for tapping slag. The height of the iron tap hole is the same as the bottom of the furnace, while the height of the slag tap hole is 205mm higher than the iron tap hole.

[0064] (7) Furnace cover assembly The furnace cover is a plate-type structure with a water-cooling ring, and a small refractory prefabricated furnace cover in the center. The small furnace cover has three electrode holes and a central charging hole. The flue gas outlet and observation port are located on the large furnace cover. The furnace cover is fixedly installed to the furnace body and moves with the furnace body when tilted. When tilting, the flue gas outlet is disconnected from the dust collection pipe.

[0065] (8) Cooling water device It provides cooling water for short grids, power sources, transformers, hydraulic stations, and crossarm devices, and consists of an inlet water distributor, a return water tank, valves, and instruments.

[0066] (9) Hydraulic station device A hydraulically driven power unit includes a hydraulic pump, hydraulic valves, and an oil tank.

[0067] (10) Compressed air device Valve stations and control boxes that provide compressed air to the equipment.

[0068] (11) Automatic control system The low-voltage control cabinet uses a Rittal-style cabinet. The complete low-voltage electrical control system consists of a low-voltage electrical power supply and distribution system, a complete set of low-voltage electrical drive equipment, an automatic electrode adjustment device, and field control and testing equipment. It mainly includes a low-voltage power cabinet, hydraulic control cabinet, PLC cabinet, main control console, furnace front control box, cooling water monitoring cabinet, field testing instruments, sensors, limit switches, and other equipment, as well as auxiliary equipment control cabinets. It performs functions such as power supply and distribution, metering and testing, various operations, and interlocking actions for the entire system.

[0069] 2. Other supporting systems (1) Melt discharge mold system Due to the low yield of nickel matte in this industrial trial, the main focus was on the reduction and sulfidation modification effect of the slag. The furnace body was equipped with only one melt discharge port (in use) 30mm above the furnace bottom. During the test, all high-temperature melt in the furnace was discharged through this discharge port. The melt discharge system was equipped with a rail-mounted ladle transfer trolley with two ladle positions. A 15t weighing sensor was installed below each ladle position to ensure that the melt discharged from each ladle did not exceed the limit weight during the test, thus ensuring the safe and stable operation of the equipment in the upstream and downstream processes during the industrial trial.

[0070] The steel ladle is placed below the slag discharge port via a transfer trolley. Two ladles are required for each furnace discharge, with each ladle discharging approximately 2.00-5.00 tons of molten material (adjusted based on the subsequent slow cooling effect). After the slag is discharged, the ladles are transferred to the slow cooling zone for 72 hours of slow cooling. After slow cooling, demolding, sampling, and testing are performed.

[0071] (2) Isolation of operating platform and equipment For convenient and safe operation, an operating platform is set up around the electric furnace equipment, which serves as the area for workers to add materials and observe the furnace conditions. The operating platform adopts a steel frame structure design and is equipped with safety railings. The operating platform also includes a working area for smelting steel plates and a high-temperature working area for laying refractory bricks.

[0072] Equipment isolation refers to the use of isolation walls to isolate electrical power supply equipment, including short-circuit power supply sections, due to the need for high voltage, high current, and clean environments.

[0073] (3) Energy medium supply system The power supply system includes high-voltage power supply, cooling water supply, softened water supply, compressed air supply, hydraulic oil supply, transformer oil supply, and other systems.

[0074] High-voltage power supply involves drawing high-voltage cables from the high-voltage power supply cabinet in the factory area and connecting them to the high-voltage cabinet of the electric furnace equipment, as well as connecting the high-voltage cables from the high-voltage cabinet of the electric furnace equipment to the transformer inlet.

[0075] Cooling water supply system, including water pump unit, 1000m 3 Water tanks and fiberglass air-cooled cooling towers provide a water source for the cooling water system of electric furnace equipment.

[0076] Compressed air is supplied by an air compressor system, which consists of an air compressor body, a dryer, an air tank, and a control box.

[0077] The hydraulic oil and transformer oil supply is for the hydraulic station and transformer, respectively using 46# hydraulic oil and 25# transformer oil.

[0078] (4) Auxiliary facilities The auxiliary facilities include: a 55KW bag filter, a 5T remote-controlled single-beam overhead crane, a 10T remote-controlled single-beam overhead crane, a 3T diesel forklift, and a 5T diesel forklift.

[0079] In this invention, the holding temperature for the reduction vulcanization treatment is preferably 1400~1500℃, and in the embodiments it can be 1400℃, 1450℃ or 1500℃. The holding time for the reduction vulcanization treatment is preferably 40~80min, and in the embodiments it can be 40min, 50min, 60min, 70min or 80min. The heating rate for the reduction vulcanization treatment is preferably 5~15℃ / min, and in the embodiments it can be 10℃ / min. The cooling rate is preferably 1~8℃ / min, and in the embodiments it can be 5℃ / min.

[0080] In this invention, the mineral phase of the nickel-copper matte preferably includes Fe. 3.97 Ni 4.84 Co 0.07 S8, Cu9Fe9S 16 And NiFe2O4. The mineral phases of the depleted slag preferably include Fe2SiO4 and (Fe,Mg)2SiO4, wherein Ni < 0.2%, Co < 0.05%, and Cu < 0.15%.

[0081] In an embodiment of the present invention, Figure 7 Photographs of different colors and morphologies of nickel-copper matte obtained in this invention: Figure 7 (a) in the text is a bluish-purple surface. Figure 7 (b) in the text is a gold-colored surface. Figure 7 (c) in the text refers to small spheres that detach when broken.

[0082] Figure 8 (a) in the figure is the XRD pattern of the depleted slag sample and the nickel slag in the embodiment of the present invention; Figure 8 (b) in the figure shows the XRD pattern of nickel-copper matte. XRD analysis was performed on the upper and lower layers of the depleted slag sample and the nickel-copper matte sample to detect different colors and morphologies. The results are shown below. Figure 8 As shown. Figure 8 In (a), the main phases of the depleted slag are Fe₂SiO₄ and (Fe,Mg)₂SiO₄, indicating that these slag samples mainly contain olivine phase, which is the same as the main phase in nickel slag. A comparison of the complexity of the diffraction patterns also shows that the depleted slag layer after reduction-sulfidation is simpler than that of nickel slag. Figure 8 (b) shows the XRD patterns of nickel-copper matte particles of different colors (small spheres, gold, purple, and nickel-copper matte). Among them, the small spheres exhibit the most obvious crystallinity. The diffraction peaks detected in all parts of the sample are the same, mainly including Fe. 3.97 Ni 4.84 Co0.07 S8, Cu9Fe9S 16 The spectral data shows that the main phase in nickel-copper matte is the sulfide phase, with a small amount of nickel-iron magnetite phase.

[0083] Figure 9 SEM images and elemental surface scan images of the nickel-copper matte prepared for embodiments of the present invention. Figure 9 The images show XEM images and elemental surface scans of nickel-copper matte. S exhibits significant elemental enrichment, indicating non-uniform phase distribution within the nickel-copper matte. Figure 9 In (c), the overall sample distribution spectrum is shown. No Si or Mg were detected, only trace amounts of Ca were present, indicating effective separation from the silicate phase. Figure 9 As shown in Figure (a), a small amount of oxide phase still exists in the nickel-copper matte, but its crystal morphology differs from that in nickel slag. Figure 9 As shown in (b) and the elemental surface scan images, the Cu distribution region overlaps with that of S and Fe. Ni, Cu, and S exhibit complementary enrichment patterns in some regions, and also overlap with Fe, indicating the precipitation of Ni-Fe alloys. Overall, the nickel-copper matte is mainly composed of Cu-Fe-S and Fe-Ni-Co-S cosulfides, with clear phase boundaries between them. The presence of a small amount of metallic phase is due to an excessive reducing atmosphere.

[0084] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0085] Example 1 (1) Add 50kg limestone, 150kg granulated coal and 50kg dry nickel concentrate to the slag bag, place the slag bag at the tail of the slag flow trough of the nickel flash furnace, and use the slag flushing method to put about 1000kg of molten nickel slag into the slag bag. Heat it to 1400℃ at a rate of 10℃ / min by induction heating, hold it for 60min, stop heating after holding, and slowly cool it to room temperature at a rate of 5℃ / min. (2) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0086] Table 8 Element content (wt%) in sample of Example 1

[0087] Table 9. Sulfidation rate and percentage of different elements in each phase in the sample of Example 1 (%)

[0088] Table 8 shows the main elements and their contents in the depleted slag and nickel-copper matte in this embodiment. As shown in Table 8, when the amount of nickel dry concentrate added is 5%, the contents of Ni, Cu, and Co in the depleted slag are much lower than those in the nickel slag. The nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents, mainly existing in the form of sulfides. The occupancy and sulfidation rate of each phase in the sample are shown in Table 9. It can be seen that the sulfidation rate of Ni and Cu is >85%, with most silicate and oxide phases transforming into sulfide phases. The sulfidation rate of Co is low, while Fe is almost non-sulfidable (<5%). Calculations show that the contents of Ni, Cu, and Co in the depleted slag are reduced by 55%, 47%, and 36%, respectively, compared to the nickel slag. Therefore, this invention uses nickel dry concentrate to treat nickel slag, effectively recovering Ni, Cu, and Co from the nickel slag in the form of nickel-copper matte. Reducing the nickel content in the nickel slag depletion process to meet production targets (nickel content less than 0.26% in flash furnace slag) improves the recovery rate of valuable metals from the nickel slag, and the resulting nickel-copper matte can be directly incorporated into the nickel smelting process. The SO2 emission concentration in the tail gas is below 31 mg / m³. 3 It meets emission standards.

[0089] Example 2 (2) Add 50kg limestone, 150kg granulated coal, and 30kg homogeneous sulfiding agent (5kg nickel sulfide + 25kg sulfur concentrate) to the slag bag. Place the slag bag at the tail of the slag flow trough of the nickel flash furnace. Using the slag flushing method, place about 1000kg of molten nickel slag in the slag bag. Heat it to 1400℃ at a rate of 10℃ / min through induction heating and hold it for 60min. After the holding period, stop heating and slowly cool it to room temperature at a rate of 5℃ / min. (3) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0090] Table 10 Element content (wt%) in samples

[0091] Table 11 Sulfidation rate and percentage of different elements in each phase in the sample (%)

[0092] Table 10 shows the main elements and their contents in the depleted slag and nickel-copper matte of this invention. As shown in Table 10, when the amount of homologous sulfiding agent (5 kg nickel sulfide + 25 kg sulfur concentrate) added is 5%, the contents of Ni, Cu, and Co in the depleted slag are much lower than those in the nickel slag. The nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents, mainly existing in the form of sulfides. The occupancy and sulfidation rate of each phase are shown in Table 11. It can be seen that the sulfidation rate of Ni and Cu is >85%, with most silicate and oxide phases transforming into sulfide phases. The sulfidation rate of Co is low, while Fe is almost unsulfidable (<5%). Calculations show that the contents of Ni, Cu, and Co in the depleted slag are reduced by 66%, 46%, and 45%, respectively, compared to nickel slag. Therefore, this invention uses dry nickel concentrate to treat nickel slag, effectively recovering Ni, Cu, and Co from the nickel slag in the form of nickel-copper matte. Reducing the nickel content in the nickel slag depletion process to meet production targets (nickel content less than 0.26% in flash furnace slag) improves the recovery rate of valuable metals from the nickel slag, and the resulting nickel-copper matte can be directly incorporated into the nickel smelting process. The SO2 emission concentration in the tail gas is below 31 mg / m³. 3 It meets emission standards.

[0093] Example 3 (1) Add 50kg limestone, 150kg granulated coal, and 30kg homogeneous sulfiding agent (5kg copper sulfide + 25kg sulfur concentrate) to the slag bag. Place the slag bag at the tail of the slag flow channel of the nickel flash furnace. Using the slag flushing method, place about 1000kg of molten nickel slag in the slag bag. Heat it to 1400℃ at a rate of 10℃ / min through induction heating and hold it for 60min. After the holding period, stop heating and slowly cool it to room temperature at a rate of 5℃ / min. (2) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0094] Table 12 Element content (wt%) in samples

[0095] Table 13 Sulfidation rate and percentage of different elements in each phase in the sample (%)

[0096] Table 12 shows the main elements and their contents in the depleted slag and nickel-copper matte of this invention. As shown in Table 12, when the amount of homologous sulfiding agent (5 kg copper sulfide + 25 kg sulfur concentrate) added is 5%, the contents of Ni, Cu, and Co in the depleted slag are much lower than those in the nickel slag. The nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents, mainly existing in the form of sulfides. The occupancy and sulfidation rate of each phase are shown in Table 13. It can be seen that the sulfidation rate of Ni and Cu is >85%, with most silicate and oxide phases transforming into sulfide phases. The sulfidation rate of Co is low, while Fe is almost unsulfidable (<5%). Calculations show that the contents of Ni, Cu, and Co in the depleted slag are reduced by 66%, 47%, and 51%, respectively, compared to nickel slag. Therefore, this invention uses dry nickel concentrate to treat nickel slag, effectively recovering Ni, Cu, and Co from the nickel slag in the form of nickel-copper matte. Reducing the nickel content in the nickel slag depletion process to meet production targets (nickel content less than 0.26% in flash furnace slag) improves the recovery rate of valuable metals from the nickel slag, and the resulting nickel-copper matte can be directly incorporated into the nickel smelting process. The SO2 emission concentration in the tail gas is below 31 mg / m³. 3 It meets emission standards.

[0097] Example 4 (1) Add 50kg limestone, 150kg granulated coal, and 30kg homogeneous sulfiding agent (2.5kg nickel sulfide + 2.5kg copper sulfide + 25kg sulfur concentrate) to the slag bag. Place the slag bag at the tail of the slag flow channel of the nickel flash furnace. Using the slag flushing method, place about 1000kg of molten nickel slag in the slag bag. Heat it to 1400℃ at a rate of 10℃ / min through induction heating and hold it for 60min. After the holding period, stop heating and slowly cool it to room temperature at a rate of 5℃ / min. (2) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0098] Table 14 Element content (wt%) in samples

[0099] Table 15 Sulfidation rate and percentage of different elements in each phase in the sample (%)

[0100] Table 14 shows the main elements and their contents in the depleted slag and nickel-copper matte of this invention. As shown in Table 14, when the amount of homologous sulfiding agent (5 kg copper sulfide + 25 kg sulfur concentrate) added is 5%, the contents of Ni, Cu, and Co in the depleted slag are much lower than those in the nickel slag. The nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents, mainly existing in the form of sulfides. The occupancy and sulfidation rate of each phase are shown in Table 15. It can be seen that the sulfidation rate of Ni and Cu is >85%, with most silicate and oxide phases transforming into sulfide phases. The sulfidation rate of Co is low, while Fe is almost unsulfidable (<5%). Calculations show that the contents of Ni, Cu, and Co in the depleted slag are reduced by 71%, 54%, and 53%, respectively, compared to nickel slag. Therefore, this invention uses dry nickel concentrate to treat nickel slag, effectively recovering Ni, Cu, and Co from the nickel slag in the form of nickel-copper matte. Reducing the nickel content in the nickel slag depletion process to meet production targets (nickel content less than 0.26% in flash furnace slag) improves the recovery rate of valuable metals from the nickel slag, and the resulting nickel-copper matte can be directly incorporated into the nickel smelting process. The SO2 emission concentration in the tail gas is below 31 mg / m³. 3 It meets emission standards.

[0101] Example 5 (1) Use an 1800kVA ultra-low frequency polar controllable electric furnace. When the furnace temperature reaches 350℃, use electrodes, coke, and water-quenched slag to start the arc for baking. Adjust the voltage level according to the furnace temperature. During the baking process, avoid the furnace temperature from rising too quickly. Normal test feeding can be carried out when the furnace temperature reaches 1200℃. Add 3 / 4 to 2 / 3 of the total amount of nickel slag for each furnace, raise the temperature to 1400℃, and melt until it reaches the molten state.

[0102] Alternatively, it can flow directly from the previous process (such as molten nickel slag from a flash furnace).

[0103] (2) After the slag in the furnace has completely melted, mix 1 / 4 to 1 / 3 of the cold nickel slag with reducing agent (granular coal), flux (limestone), and sulfiding agent (dry nickel concentrate) in a certain proportion (where the mass of limestone accounts for 7% of the mass of nickel slag, the mass of granular coal accounts for 8% of the mass of nickel slag, the mass of dry nickel concentrate accounts for 5% of the mass of nickel slag, and the mass of nickel slag is 1000 kg), and then add it to a controllable polarity ultra-low frequency electric furnace. Reheat to 1400℃ to melt the furnace charge and smelt for 35 minutes. During this process, the polarity is periodically reversed at a preset cycle of 200s to 300s.

[0104] (3) Under the combined action of heating, reduction and electromagnetic stirring, the valuable metal oxide phase and silicate phase in the nickel slag are reduced and sulfided and aggregated to form nickel-copper matte, thereby achieving the depletion of nickel slag; (4) After the depletion process is completed, the upper depleted slag (with the metal content meeting the standard) is discharged from the slag outlet. The lower layer of nickel-copper matte, which is enriched with valuable metals, is discharged from the bottom outlet. The depleted slag and nickel-copper matte are separated.

[0105] Table 16 Element content (wt%) in sample of Example 5

[0106] Example 6 Following the method in Example 5, an optimization experiment was conducted to adjust the amount of raw materials and operating parameters: 1. The effect of vulcanizing agent on reductive vulcanization (1) The effect of the type of vulcanizing agent on the industrial test of reduction vulcanization To investigate the effect of different types of sulfiding agents on the sulfidation effect of flash slag, flash slag reduction sulfidation experiments were conducted in industrial trials using two types of sulfiding agents: sulfur concentrate and dry concentrate.

[0107] In the exploratory trials, the optimal addition amount of dry nickel concentrate was 3.00%. However, considering that the dry concentrate used in the industrial trials had a lower sulfur content and contained a small amount of water than the dry concentrate used in the exploratory trials, the addition amount of dry concentrate was increased to 4.20% in the industrial trials. Experimental conditions: ① Temperature 1400℃, smelting time 35min; limestone 5%, granular coal 15%, sulfiding agent 4.20% or 5.60%; ②Temperature 1400℃, smelting time 35min; limestone 50%, granular coal 15%, sulfur concentrate 3.00% or 4.00%.

[0108] The effects of different homologous sulfiding agent ratios on the elements in slag and their sulfidation rate were investigated. The experimental results are shown in Tables 17 and 18. Figure 13 , Figure 14 As shown.

[0109] Table 17 Effect of Vulcanizing Agent Type on Slag Composition / %

[0110] Table 18 Effect of Sulfidating Agent Type on Sulfidation Rate of Ni, Cu, and Co in Slag / %

[0111] Figure 13 The figure shows the effect of the type of vulcanizing agent on the composition of slag. Figure 14The diagram illustrates the effect of different sulfiding agents on the sulfidation rates of Ni, Cu, and Co in the slag. Under otherwise identical conditions, the modified slag exhibits significant differences in valence metal content with varying sulfiding agents. The Ni and Cu content in slag using dry concentrate as the sulfiding agent is generally slightly higher than that using sulfur concentrate. This is because the Ni and Cu content in the concentrate is higher than that in the sulfur concentrate, which contains 8.53% Ni and 7.15% Cu, while the sulfur concentrate contains 0.053% Ni and 0.31% Cu. The difference in the sulfidation rate of Ni, Cu, and Co in the slag due to different sulfiding agent types is not substantial; both sulfur concentrate and dry concentrate can achieve the requirements for reductive sulfidation.

[0112] (2) Effect of the amount of vulcanizing agent added on the industrial test of reduction vulcanization Experimental conditions: temperature 1400℃, smelting time 35 min, limestone 5%, granular coal 15%. The effects of different dry concentrate ratios on the elements and sulfidation rate in the slag were investigated. The results are shown in Tables 19 and 20 below. Figure 15 , 16 As shown in Tables 21 and 22, the effects of different sulfiding agent ratios on the elements and sulfidation rate in dry concentrate and sulfur concentrate were investigated.

[0113] Table 19 Effect of Nickel Dry Concentrate Ratio on Slag Composition / %

[0114] Table 20 Effect of Nickel Dry Concentrate Ratio on Ni, Cu, and Co Sulfidation Rate in Slag / %

[0115] Figure 15 The figure shows the effect of nickel dry concentrate yield on slag composition. Figure 16 The figure shows the effect of the dry nickel concentrate ratio on the sulfidation rates of Ni, Cu, and Co in the slag. Increasing the amount of sulfiding agent is beneficial for reducing the amount of valuable metals in the modified slag; however, excessive concentrate addition will significantly impact the sulfidation rate of valuable metals in the slag, the grade of matte, and production capacity. A sulfiding agent ratio of 4.20% for the dry concentrate is recommended. Adjustments can be made appropriately based on production needs and actual conditions during subsequent engineering applications.

[0116] Table 21 Effect of Sulfurized Sand Ratio on Slag Composition / %

[0117] Table 22 Effect of sulfur concentrate ratio on the sulfidation rate of Ni, Cu, and Co in slag / %

[0118] Table 21 shows the effect of sulfur concentrate on slag composition, and Table 20 shows the effect of sulfur concentrate on the sulfidation rate of Ni, Cu, and Co in slag. Increasing the amount of sulfur concentrate added is beneficial for the sulfidation of valuable metals and reduces the content of Ni, Cu, and Co elements in the modified slag. However, because sulfur concentrate contains high levels of iron, it not only affects the grade of nickel matte but also has a significant impact on production capacity and subsequent blowing processes. Therefore, sulfur concentrate should be avoided as a sulfiding agent in industrial production whenever possible.

[0119] 2. Effect of granular coal addition amount on the results of industrial test of reduction sulfidation The effect of granular coal as a reducing agent on the reduction and sulfidation effect of flash furnace slag was mainly investigated. Experimental conditions: temperature 1400℃, smelting time 35 min; limestone 5%, dry concentrate 4.20%. The effects of different reducing agent ratios on the elements in the slag and their sulfidation rate were investigated; the results are shown in Tables 23 and 24. Figure 17 , Figure 18 As shown.

[0120] Table 23 Effect of reducing agent rate on slag composition / %

[0121] Table 24 Effect of reducing agent ratio on the sulfidation rate of Ni, Cu, and Co in slag / %

[0122] Figure 17 The figure shows the effect of reducing agent ratio on slag composition. Figure 18 The figure shows the effect of reducing agent rate on the sulfidation rates of Ni, Cu, and Co in the slag. With increasing reducing agent rate, the content of valuable metals and the sulfidation rate in the slag fluctuate within a certain range. Considering factors such as the grade of valuable metals in the slag, the grade of nickel matte, the metallization rate of nickel matte, and subsequent processing costs, a reducing agent rate of 5% is considered the most reasonable condition.

[0123] 3. Effect of limestone addition on reduction sulfidation results Experimental conditions: temperature 1400℃, smelting time 35 min; granular coal 5%, dry concentrate 4.20%. The effect of different amounts of limestone as flux on the reduction sulfidation of slag was investigated. The results are shown in Tables 25 and 26. Figure 19 , Figure 20 As shown.

[0124] Table 25 Effect of limestone ratio on slag composition / %

[0125] Table 26 Effect of limestone ratio on the sulfidation rate of Ni, Cu, and Co in slag / %

[0126] Figure 19 The figure shows the effect of limestone ratio on slag composition. As the limestone ratio increases, the content of valuable metals in the slag fluctuates within a certain range. Figure 20 The figure shows the effect of limestone ratio on the sulfidation rates of Ni, Cu, and Co in the slag. The sulfidation rates of Ni, Cu, and Co first increase and then decrease with increasing limestone ratio. The highest sulfidation rates of Ni, Cu, and Co are observed when the limestone ratio is 10%, and the content of Ni, Cu, and Co in the slag is also relatively high. Considering factors such as nickel matte grade, cost, and the grade of valuable metals in the slag, a limestone ratio of 5% is considered the most reasonable condition.

[0127] 4. Effect of holding time on reduction vulcanization Experimental conditions: temperature 1400℃, smelting time 35 min; limestone 5%, granular coal 5%, dry concentrate 4.20%. The effects of different holding times on the elements in the slag were investigated, and the results are shown in Table 27.

[0128] Table 27 Effect of holding time on slag composition / %

[0129] Figure 21 The figure shows the effect of holding time on slag composition. As the holding time increases, the content of valuable metals in the slag first decreases significantly, and then remains stable. The results indicate that a holding time of 35 min is the most reasonable, and further extending the holding time has no significant effect on the content of valuable metals in the slag.

[0130] 5. The effect of auxiliary material addition method on reduction vulcanization There are two feeding methods. One method is to add the auxiliary materials and the remaining 10.00% of the raw slag into the furnace after 90.00% of the flash slag has been added and completely melted. The auxiliary materials are then mixed and added into the furnace. After the auxiliary materials have melted, the furnace is kept at a constant temperature for 35 minutes. The other method is to mix the auxiliary materials evenly and disperse them in four bags of raw slag. The auxiliary materials are then added into the furnace along with the raw slag. After all the furnace materials have completely melted, the furnace is kept at a constant temperature for 35 minutes. The two feeding methods were tested, and the results are shown in Tables 28 and 29.

[0131] Table 28 Effect of Auxiliary Material Addition Method on Slag Composition / %

[0132] Table 29 Effect of Auxiliary Material Addition Method on the Sulfidation Rate of Ni, Cu, and Co in Slag / %

[0133] A comparison of the two feeding methods reveals that the furnace with uniformly added auxiliary materials exhibits lower slag content and a higher sulfidation rate of valuable metals. This is attributed to the more even dispersion of the auxiliary materials within the furnace during uniform addition, resulting in a longer reduction and sulfidation reaction time compared to furnaces with concentrated addition of auxiliary materials. This also aligns with the principle of "frequent, small, and uniform addition." Therefore, the uniform addition method is more conducive to the reduction and sulfidation modification of flash slag.

[0134] Comparative Example 1 (Insufficient amount of vulcanizing agent) (1) Add 50kg limestone, 150kg granulated coal and 15kg dry nickel concentrate to the slag bag, place the slag bag at the tail of the slag flow trough of the nickel flash furnace, and use the slag flushing method to put about 1000kg of molten nickel slag into the slag bag. Heat it to 1400℃ at a rate of 10℃ / min by induction heating, hold it at 60min, stop heating after holding, and slowly cool it to room temperature at a rate of 5℃ / min. (2) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0135] Table 30 Element content (wt%) in samples

[0136] Table 31 Sulfidation rate and percentage of different elements in each phase in the sample (%)

[0137] Table 30 shows the main elements and their contents in the depleted slag and nickel-copper matte of Comparative Example 1. As shown in Table 30, when the amount of nickel dry concentrate added is 1.5%, although the contents of Ni, Cu, and Co in the depleted slag are lower than those in the nickel slag, they do not meet the production targets (flame furnace slag contains less than 0.26% nickel and less than 0.20% copper). Nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents, mainly existing in the form of sulfides. The occupancy and sulfidation rate of each phase are shown in Table 31. It can be seen that the sulfidation rate of Ni and Cu is >50%, most silicate and oxide phases have not been converted into sulfidated phases, the sulfidation rate of Co is low at only 5%, and Fe is almost unsulfidable (<3%). Calculations show that the contents of Ni, Cu, and Co in the depleted slag are reduced by 36%, 8%, and 26% respectively compared to the nickel slag. Therefore, the reduction sulfidation treatment of nickel slag in Comparative Example 1 is ineffective. The SO2 emission concentration in the tail gas is below 31 mg / m³. 3 It meets emission standards.

[0138] Comparative Example 2 (Too much reducing agent) (1) Add 50kg limestone, 500kg granular coal, and 30kg homogeneous sulfiding agent (2.5kg nickel sulfide + 2.5kg copper sulfide + 25kg sulfur concentrate) to the slag bag. Place the slag bag at the tail of the slag flow channel of the nickel flash furnace. Using the slag flushing method, place about 1000kg of molten nickel slag in the slag bag. Heat it to 1400℃ at a rate of 10℃ / min through induction heating. Hold it at 60min. After the holding period, stop heating and slowly cool it to room temperature at a rate of 5℃ / min. (2) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0139] Table 32 Element content (wt%) in samples

[0140] Table 33 Sulfidation rate and percentage of different elements in each phase in the sample (%)

[0141] Table 32 shows the main elements and their contents in the depleted slag and nickel-copper matte in Comparative Example 2. As shown in Table 32, when the amount of granular coal added is 50%, the contents of Ni, Cu, and Co in the depleted slag are lower than those in the nickel slag, meeting the production targets (flame furnace slag contains less than 0.26% nickel and less than 0.20% copper). Nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents. Although mainly existing in the form of sulfides, excessive reduction produces a large amount of metallic phase, which eventually settles with the matte droplets. The occupancy and sulfidation rate of each phase are shown in Table 33. It can be seen that the sulfidation rate of Ni and Cu is >50%, some silicate and oxide phases do not transform into sulfidated phases, the proportion of each element in the metallic phase is significantly increased, the sulfidation rate of Co is low, and Fe is almost unsulfidable (<3%). Calculations show that the contents of Ni, Cu, and Co in the depleted slag are reduced by 56%, 56%, and 45%, respectively, compared to the nickel slag. Therefore, the reduction sulfidation treatment of the nickel slag in Comparative Example 1 is ineffective. SO2 emission concentration in exhaust gas is less than 31 mg / m³ 3 It meets emission standards.

[0142] Comparative Example 3 (Excessive Vulcanizing Agent) (1) Add 50kg limestone, 150kg granulated coal, and 112kg homologous sulfiding agent (10kg nickel sulfide + 10kg copper sulfide + 92kg sulfur concentrate) to the slag bag. Place the slag bag at the tail of the slag flow channel of the nickel flash furnace. Using the slag flushing method, place about 1000kg of molten nickel slag in the slag bag. Heat it to 1400℃ at a rate of 10℃ / min through induction heating and hold it for 60min. After the holding period, stop heating and slowly cool it to room temperature at a rate of 5℃ / min. (2) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0143] Table 34 Element content (wt%) in samples

[0144] Table 35 Sulfidation rate and percentage of different elements in each phase in the sample (%)

[0145] Table 34 shows the main elements and their contents in the depleted slag and nickel-copper matte of Comparative Example 3. As shown in Table 34, when the amount of homologous sulfiding agent (10 kg nickel sulfide + 10 kg copper sulfide + 60 kg sulfur concentrate) added is 8%, the contents of Ni, Cu, and Co in the depleted slag are lower than those in the nickel slag, meeting the production targets (flame furnace slag contains less than 0.26% nickel and less than 0.20% copper). Nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents. The occupancy and sulfidation rate of each phase are shown in Table 35. It can be seen that the sulfidation rate of Ni and Cu is >85%, and some of the silicate and oxide phases of Fe and Co are not converted into sulfided phases, while the sulfidation rates of Fe and Co are significantly increased. Calculations show that the contents of Ni, Cu, and Co in the depleted slag are reduced by 70%, 60%, and 55% respectively compared to the nickel slag, but the Fe content in the nickel-copper matte is increased, which is not conducive to the separation of iron in downstream processes. The SO2 emission concentration in the tail gas is higher than 110 mg / m³. 3 This does not meet emission standards. Therefore, the reduction sulfidation treatment of nickel slag in this comparative example yielded poor results.

[0146] Comparative Example 4 (Excessive Limestone) (1) Add 150kg limestone, 150kg granulated coal, and 30kg homogeneous sulfiding agent (2.5kg nickel sulfide + 2.5kg copper sulfide + 25kg sulfur concentrate) to the slag bag. Place the slag bag at the tail of the slag flow channel of the nickel flash furnace. Using the slag flushing method, place about 1000kg of molten nickel slag in the slag bag. Heat it to 1400℃ at a rate of 10℃ / min through induction heating and hold it for 60min. After the holding period, stop heating and slowly cool it to room temperature at a rate of 5℃ / min. (2) Take out the material from the cooled slag bag. The nickel-copper matte settles to the bottom, and the depleted slag is at the top. It can be separated by gently tapping.

[0147] Table 36 Element content (wt%) in samples

[0148] Table 37 Sulfidation rate and percentage of different elements in each phase in the sample (%)

[0149] Table 36 shows the main elements and their contents in the depleted slag and nickel-copper matte of Comparative Example 4. As shown in Table 36, when the limestone addition is 15%, the contents of Ni, Cu, and Co in the depleted slag are lower than those in the nickel slag, meeting the production targets (flame furnace slag contains less than 0.26% nickel and less than 0.20% copper). Nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents. The occupancy and sulfidation rate of each phase are shown in Table 37. It can be seen that the sulfidation rate of Ni and Cu is >85%, and the proportion of Fe and Co in the oxidized phase is increased. Calculations show that the Ni, Cu, and Co contents in the depleted slag are reduced by 73%, 56%, and 53% respectively compared to the nickel slag, but the Fe content in the nickel-copper matte is increased, which is detrimental to the separation of iron in downstream processes. Therefore, the reduction sulfidation treatment of nickel slag in this comparative example is ineffective. The SO2 emission concentration in the tail gas is below 31 mg / m³. 3 It meets emission standards.

[0150] As can be seen from the above examples, current technologies typically use sulfur, pyrite, etc., as sulfiding agents, which introduce impurities, result in low sulfidation rates, and lead to poor separation of nickel-copper matte from slag. Furthermore, excessive use of sulfiding agents can cause sulfur pollution. This invention uses Ni and Cu homologous materials as sulfiding agents, adding reducing agents and modifiers to pretreat nickel slag. This allows for phase reconstruction of the nickel slag, with the Ni and Cu oxide and silicate phases sulfiding to generate corresponding sulfides. The crystallization morphology of the sulfide phase grains is also regulated, which is beneficial for the precipitation of nickel, copper, and sulfur. After treatment by this invention, the Ni, Cu, and Co contents in the depleted slag are much lower than those in the nickel slag, with Ni, Cu, and Co contents below 0.1956%, 0.1225%, and 0.0678%, respectively, meeting production targets (nickel content less than 0.34% in top-blown system settling slag and less than 0.26% in flash slag). The nickel-copper matte is a product of this invention, with high Ni, Cu, and Co contents, mainly existing in the form of sulfides. Calculations show that the Ni, Cu, and Co contents in the depleted slag are reduced by at least 55%, 47%, and 36% respectively compared to nickel slag. This improves the recovery rate of valuable metals from the nickel slag, and the resulting nickel-copper matte can be directly used in the nickel smelting process or sold.

[0151] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for recovering nickel-copper matte by treating nickel slag with a homologous sulfurizing agent, characterized in that, The method comprises the following steps: The nickel slag, limestone, homologous sulfidation agent and reducing agent are mixed, and a reduction sulfidation treatment is carried out after temperature rising, and nickel copper matte and depleted slag are obtained after temperature falling; the homologous sulfidation agent comprises a first sulfidation agent, a second sulfidation agent, a third sulfidation agent or a fourth sulfidation agent, the first sulfidation agent is a nickel dry concentrate or a sulfur concentrate, the second sulfidation agent is nickel sulfide and a sulfur concentrate, the third sulfidation agent is copper sulfide and a sulfur concentrate, and the fourth sulfidation agent is nickel sulfide, copper sulfide and a sulfur concentrate; the mass percentage of the homologous sulfidation agent in the mass of the nickel slag is >1.5% and <8.5%; and the reducing agent comprises coke and / or coal powder.

2. The method of claim 1, wherein, The nickel slag comprises cold-state nickel slag and / or hot-state nickel slag; When the nickel slag is hot-state nickel slag, the mixing comprises the following steps: the limestone, homologous sulfidation agent and reducing agent are premixed to obtain a mixture, and then the hot-state nickel slag is mixed with the mixture by means of flushing slag; When the nickel slag is cold-state nickel slag, the mixing comprises mode one or mode two, the mode one comprises: the cold-state nickel slag, limestone, homologous sulfidation agent and reducing agent are directly mixed, and the mode two comprises: part of the cold-state nickel slag is heated to be in a molten state to obtain molten-state nickel slag, the remaining cold-state nickel slag, limestone, homologous sulfidation agent and reducing agent are premixed to obtain a premixed material, and the premixed material and molten-state nickel slag are mixed, and the mass percentage of the part of the cold-state nickel slag in the total mass of the cold-state nickel slag is 60-90%.

3. The method of claim 1, wherein, The reduction sulfidation treatment is carried out in a controllable-polarity three-phase ultra-low-frequency electric furnace, and the controllable-polarity three-phase ultra-low-frequency electric furnace has a frequency of 0.0001-0.1 Hz.

4. The method according to any one of claims 1 to 3, characterized in that, The mass percentage of the homologous sulfidation agent in the mass of the nickel slag is 3-6%.

5. The method of claim 4, wherein, The mass percentage of nickel sulfide in the second sulfidation agent in the mass of the nickel slag is 0.3-0.8%.

6. The method of claim 4, wherein, The mass percentage of copper sulfide in the third sulfidation agent in the mass of the nickel slag is 0.3-1%.

7. The method of claim 4, wherein, The mass percentage of nickel sulfide in the fourth sulfidation agent in the mass of the nickel slag is 0.1-0.5%, and the mass percentage of copper sulfide in the fourth sulfidation agent in the mass of the nickel slag is 0.2-0.6%.

8. The method of claim 1 or 2, wherein, The mass percentage of the limestone in the mass of the nickel slag is 2-8%, and the mass percentage of the reducing agent in the mass of the nickel slag is 5-15%.

9. The method of claim 1 or 2, wherein, The holding temperature of the reduction sulfidation treatment is 1400-1500 DEG C, the holding time is 40-80 min, the temperature rising rate is 5-15 DEG C / min, and the temperature falling rate is 1-8 DEG C / min.

10. The method of claim 1 or 2, wherein, The mineral phase of the nickel slag includes (Mg, Fe)2SiO4 and Fe2SiO4, wherein Ni > 0.39%, Co > 0.1%, and Cu > 0.2%; the mineral phase of the nickel dry concentrate includes (Ni, Fe)S2, FeS2, and CuFeS2; the sulphur concentrate includes iron sulphide minerals; the mineral phase of the nickel copper matte includes Fe 3.97 Ni 4.84 Co 0.07 S8, Cu9Fe9S 16 and NiFe2O4; the mineral phase of the lean slag includes Fe2SiO4 and (Fe, Mg)2SiO4, wherein Ni < 0.2%, Co < 0.05%, and Cu < 0.15%.

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