Vacuum carbothermic process for smelting ferrochrome dust

Abstract

The present application relates to waste resource recycling technical field, and specifically to a kind of ferrochrome smelting dust vacuum carbon thermal method, comprising the following steps: ferrochrome dust and carbonaceous reducing agent are mixed uniformly according to mass ratio 1:0.05~0.5 after being pressed into pellet;Pellet is placed in the environment with temperature 850 ℃~1050 ℃, pressure 5Pa~150Pa, and vacuum carbonization reduction reaction is carried out for 60min~180min, and product zinc and reduction slag are obtained;Reduction slag is crushed and ground, then water is added to slurry, and solid-liquid separation is carried out to obtain iron-containing slag and high-salt solution, iron-containing slag is treated by magnetic separation to obtain magnetic slag and non-magnetic slag, magnetic slag is recycled again, non-magnetic slag is used as cement plant raw material, high-salt solution is evaporated to obtain NaCl and KCl and evaporation mother liquor, and evaporation mother liquor is returned to reduction slag slurry again.The present application can effectively eliminate Cr 6+ leaching risk, and valuable elements are recycled efficiently.

Description

Technical Field

[0001] This invention relates to the field of waste resource recycling technology, specifically a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting. Background Technology

[0002] Ferrochrome alloys are produced using a closed submerged arc furnace smelting process, which generates a large amount of dust. This dust contains various elements such as Zn, Fe, Cr, Na, K, and Cl. Among them, Cr6+ is highly toxic, a strong oxidizing agent, and bioaccumulative. It is easily soluble in water to form a highly corrosive solution. Once it enters the environment, it will seriously pollute soil and water bodies and endanger human health through the food chain. Therefore, ferrochrome dust is classified as hazardous waste.

[0003] Valuable elements in ferrochrome dust originate from various raw materials, electrodes, slag-forming agents, and reducing agents used in closed submerged arc furnaces, such as coke and anthracite. Low-boiling-point elements like Zn and Pb volatilize and oxidize under high-temperature, strong reducing conditions, ultimately existing as ZnO and ZnFe₂O₄; Na and K enter the dust as chlorides. Ferrochrome, on the other hand, consists of tiny particles formed from the crushing and blasting of raw materials at high temperatures in the submerged arc furnace, which are then captured by the dust collection system to form the dust.

[0004] Traditional methods for treating ferrochrome smelting dust involve directly returning it to the batching system, but this negatively impacts the lifespan of the submerged arc furnace lining and the technical and economic indicators of smelting. Alternatively, pyrometallurgical reduction roasting using rotary kilns, rotary hearth furnaces, or vacuum carbothermal reduction methods can be employed to prepare secondary zinc oxide and Fe-rich feedstock. For example, Chinese patent CN202311293327.8 discloses a method for reducing zinc-containing dust pellets using biomass; Chinese patent CN202011075011.8 discloses a smelting device and method for zinc-containing blast furnace gas ash; Chinese patent CN202510274348.8 discloses a method for comprehensively treating zinc-containing sulfuric acid slag and blast furnace bag ash; Chinese patent CN202110733228.1 discloses a high-efficiency rotary hearth furnace direct reduction treatment process for zinc-containing dust and sludge in steel plants; and Chinese patent CN202111196615.2 discloses a zinc-containing dust treatment system for steel smelting and its usage method. The examples given here all pertain to the recovery of zinc and iron from zinc-containing materials using rotary kilns, rotary hearth furnaces, or vacuum methods. However, existing processes have significant limitations: the high chloride / fluoride ion content in zinc oxide makes it unsuitable for direct use in electrolytic Zn production and necessitates prior removal of fluoride and chloride ions, which increases energy consumption and generates secondary pollution. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a vacuum carbothermic method for collecting dust in ferrochrome alloy smelting, which can effectively eliminate Cr... 6+This treatment technology minimizes leaching risks, efficiently recovers valuable elements (such as zinc, chromium, iron, and potassium), has a short process, low energy consumption, and is environmentally friendly, generating no waste throughout the entire process.

[0006] To solve the above-mentioned technical problems, the present invention provides a vacuum carbothermic method for collecting dust from ferrochrome alloy smelting, comprising the following steps:

[0007] The ferrochrome dust and carbonaceous reducing agent are thoroughly mixed at a mass ratio of 1:0.05~0.5 and then pressed into pellets.

[0008] The pellets were placed in an environment with a temperature of 850℃ ~1050℃ and a pressure of 5Pa ~150Pa for vacuum carbonization and reduction reaction for 60min ~180min to obtain zinc product and reduction slag;

[0009] After crushing and grinding the reducing slag, water is added to form a slurry, and solid-liquid separation is performed to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag. The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation...

[0010] As a raw material for cement plants, high-salt solutions are evaporated and crystallized to obtain NaCl and KCl, as well as mother liquor. The mother liquor is then returned to the reducing slag for slurry preparation.

[0011] Vacuum carbothermal reduction is an effective way to reduce Cr. 6+ The core operation achieves a high zinc removal rate while meeting national standards. Under vacuum conditions, a carbonaceous reducing agent reacts with ferrochrome dust. On one hand, the carbon removes Cr... 6+ Reduced to low-toxicity Cr 3+ On the one hand, zinc is reduced to zinc vapor, which is then recovered through subsequent condensation to achieve a high removal rate.

[0012] The reason for limiting the mass ratio of ferrochrome dust to carbonaceous reducing agent during vacuum carbothermic reduction is that a suitable mass ratio ensures sufficient carbon participation in the reaction, thus fully reducing Cr. 6+ It can also provide sufficient reducing agent for the reduction of zinc. However, if the ratio is improper, it may lead to Cr... 6+ Insufficient reduction or decreased zinc removal rate.

[0013] The reason for the temperature limitation in vacuum carbothermal reduction is that the temperature needs to be controlled within a suitable range; if the temperature is too low, the reaction rate is slow, and Cr... 6+ Both the reduction and zinc reduction reactions are difficult to complete; excessively high temperatures may lead to energy waste and may also trigger other unnecessary side reactions, affecting product purity and reaction efficiency.

[0014] The reason for the pressure limitation in the vacuum carbothermal reduction process is that the vacuum environment (specific pressure) reduces the partial pressure of gases in the reaction system, which is conducive to the generation and escape of zinc vapor, thereby improving the zinc removal rate; at the same time, it also provides a suitable environment for Cr... 6+ The reduction creates a favorable chemical environment, promoting the reduction reaction.

[0015] The reason for limiting the holding time during vacuum carbothermal reduction is that sufficient holding time can ensure the preservation of Cr. 6+ The reduction and zinc reduction reactions must proceed fully. If the reaction time is too short, the reaction will be incomplete, resulting in insufficient Cr6+ concentration and low zinc removal rate. If the reaction time is too long, it will reduce production efficiency and increase costs.

[0016] Preferably, the carbonaceous reducing agent is semi-coke.

[0017] Preferably, the ferrochrome dust comprises 4wt%~60wt% zinc, 1wt%~50wt% iron, and 0.1wt%~10wt% chromium.

[0018] Preferably, the reducing residue and water are mixed at a solid-liquid mass ratio of 1:1 to 5.

[0019] From the perspective of reaction effect, adjusting the slurry with a solid-liquid mass ratio of 1:1 to 5 for reducing residue and water allows the reducing residue to be better dispersed and dissolved in water, making the subsequent extraction of useful components (such as iron, chromium and other related substances, or the removal of hexavalent chromium) more complete and efficient, ensuring that the target substances can be better processed or recovered.

[0020] From a practical and cost perspective, if the water volume is too small, the reduction residue may not be able to fully react with the water, affecting the treatment effect; if the water volume is too large, it will increase the energy consumption and cost of subsequent processes such as evaporation and concentration. This ratio can ensure the treatment effect while taking into account energy consumption and cost, achieving a better economic and technological balance.

[0021] Preferably, the concentration of hexavalent chromium leaching in the mother liquor is less than 0.05 ppm.

[0022] Preferably, the diameter of the pellet is 1 mm to 50 mm.

[0023] The optimal pellet diameter is 1mm to 50mm to avoid incomplete reaction or reaction defects caused by pellets that are too large or too small. The 1mm to 50mm diameter range offers optimal compatibility with existing industrial equipment, meets the processing capabilities of conventional tableting equipment, and minimizes crushing and grinding costs. Pellets within this diameter range have moderate hardness (the hardness is slightly higher after the reaction due to internal component transformation than during molding).

[0024] Preferably, the zinc content in the reducing residue is less than 0.05%, and the purity of the zinc in the product is ≥98.7%.

[0025] Preferably, after heating and evaporating the salt solution to 60%–70% of its original volume, it is cooled to room temperature to precipitate NaCl, KCl, and the mother liquor from the evaporation.

[0026] The reason for heating and evaporating the salt solution to 60%–70% of its original volume is to ensure that the concentration of the solute (such as sodium chloride, potassium chloride, etc.) in the solution reaches a suitable level. This facilitates the subsequent crystallization of the salts through cooling and other methods, while also ensuring the purity and yield of the crystals. If evaporation is excessive, the solution concentration will be too high, which may lead to the simultaneous crystallization of multiple salts in large quantities, making separation difficult and affecting product purity. If evaporation is insufficient, the solute concentration will be inadequate, resulting in a small amount of crystals and reducing production efficiency.

[0027] Furthermore, evaporating to 60%–70% of the original volume can balance energy consumption while ensuring good crystallization. Over-evaporation requires more heat, increasing energy consumption and production costs; under-evaporation may make subsequent processing steps more complicated, indirectly increasing costs as well.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention ensures sufficient carbon participation in the reaction by thoroughly mixing ferrochrome dust and a carbonaceous reducing agent at a mass ratio of 1:0.05 to 1:0.5. This allows for the complete reduction of Cr6+ and provides ample reducing agent for zinc reduction. The pellets are placed in a vacuum carbonization reduction environment at 850℃ to 1050℃ and a pressure of 5Pa to 150Pa. This ensures complete reaction between the carbonaceous reducing agent and the ferrochrome dust, avoiding side reactions, reducing the partial pressure of gases in the reaction system, and facilitating the generation and escape of zinc vapor, thereby improving the zinc removal rate. Simultaneously, it creates a favorable chemical environment for Cr6+ reduction, promoting the reduction reaction. The carbon reduces Cr6+ to less toxic forms such as Cr3+, thus lowering its concentration. Furthermore, zinc is reduced to zinc vapor, which is subsequently condensed and recovered, achieving a high removal rate. It effectively reduces the Cr6+ concentration to the national standard (0.05ppm), transforming ferrochrome dust from hazardous waste into general solid waste and eliminating the risk of leaching toxicity; the entire process is free of secondary pollution, blocking the dioxin formation pathway, while achieving a high zinc removal rate (up to 99.91%), ensuring the purity of metallic zinc meets the standards; valuable elements such as Fe and Cr are recovered and recycled through magnetic separation, achieving complete utilization of valuable elements.

[0030] The method presented in this invention features a short process flow, lower reaction temperature, and energy consumption reduced by 30%–40% compared to traditional processes. The sensible heat of the high-temperature reduction slag is used as a heat source for the multi-effect evaporator, further reducing energy consumption by 30%. The resulting zinc has high added value. Chromium is transformed from an environmentally toxic element into valuable chromite and returned to the feedstock. Furthermore, the method enables a closed-loop cycle of hazardous hexavalent chromium into valuable chromite. Trace amounts of valuable elements such as zinc, sodium, and potassium in the ore are enriched in the dust collected during the submerged arc furnace smelting process and transformed into high-purity zinc, KCl, NaCl, and other products through the process described in this invention. This aligns with the concept of sustainable development. Attached Figure Description

[0031] Figure 1 This invention provides a process path diagram for a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting. Detailed Implementation

[0032] To make the above-mentioned objectives, features, and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in Examples 1 to 13, preferred embodiments are described in this invention to avoid redundancy. However, this invention is not limited to these, but can be implemented in other ways within the scope of the technical solutions defined in the appended claims. In addition, the sublimation temperature, reduction reaction formula (such as ZnO+C→Zn↑+CO↑), and solubility properties of the substances involved in this invention are all well-known technologies in the industry; the equipment used in the process (tablet press, vacuum furnace, water-cooled crystallizer, plate and frame filter press, etc.) are conventional equipment, and their models can be adjusted according to the processing volume.

[0034] The technical solution of the present invention will be further illustrated below with specific examples. In the following embodiments, unless otherwise specified, the methods are conventional methods, and the reagents are commercially available unless otherwise specified.

[0035] Dust collected from ferrochrome alloy smelting is classified as hazardous waste, and Cr may be present during its storage. 6+ This poses a risk of environmental pollution, and existing treatment methods are costly and cannot simultaneously achieve zinc removal and Cr reduction. 6+Problems include low concentration, low resource recycling rate, and easy generation of secondary pollution; if it is directly returned to the batching, it will not only affect the service life of the lining of the electric arc furnace, but also have a negative impact on the technical and economic indicators of the electric arc furnace smelting.

[0036] This invention provides a vacuum carbothermic method for collecting dust in ferrochrome alloy smelting, which can effectively eliminate Cr... 6+ This treatment technology minimizes leaching risks, efficiently recovers valuable elements (such as zinc, chromium, iron, and potassium), has a short process, low energy consumption, and is environmentally friendly, generating no waste throughout the entire process.

[0037] The present invention provides a slurry preparation method where the reducing residue and water are mixed at a solid-liquid mass ratio of 1:1 to 5. The following is an example of a slurry preparation method where the reducing residue and water are mixed at a solid-liquid mass ratio of 1:4.

[0038] The following describes a vacuum carbothermic method for removing Cr from ferrochrome alloy smelting dust. 6+ Specific implementation examples of leaching risk mitigation and efficient recovery of valuable elements (such as zinc, chromium, iron, potassium, etc.).

[0039] Example 1

[0040] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0041] The ferrochrome dust and semi-coke were mixed at a mass ratio of 1:0.05. 20g of ferrochrome dust containing 12.76wt% zinc, 23.95wt% iron, and 3.44wt% chromium was weighed, and 1g of semi-coke was weighed. The 20g of ferrochrome dust and 1g of semi-coke were then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0042] The pellets are loaded into a high-temperature resistant reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 950°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 10Pa. The vacuum carbonization reduction reaction is carried out for 180 minutes. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0043] After crushing and grinding the reduction slag, water is added and mixed with water at a solid-liquid mass ratio of 1:4. The mixture is then slurryed and separated to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag.

[0044] The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation is used as raw material in the cement plant. The high-salt solution is heated and evaporated to 60% of its original volume. After evaporation and crystallization, 0.1087g NaCl, 0.1166g KCl, and 28.4mL of mother liquor are obtained. The mother liquor is returned to the reducing slag for slurry preparation. The obtained NaCl meets the GB / T5462-2015 standard, and the obtained KCl meets the GB / T7118-2023 standard.

[0045] The zinc removal rate of the ferrochrome dust was measured to be 91.54%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.045 ppm, the zinc content in the reduction slag was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0046] Example 2

[0047] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0048] The ferrochrome dust and semi-coke were mixed at a mass ratio of 1:0.1. 20g of ferrochrome dust containing 12.76wt% zinc, 23.95wt% iron, and 3.44wt% chromium was weighed, and 2g of semi-coke was weighed. The 20g of ferrochrome dust and 2g of semi-coke were then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0049] The pellets are loaded into a high-temperature reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 950°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 10Pa. The vacuum carbonization reduction reaction is carried out for 180 minutes. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0050] After crushing and grinding the reduction slag, water is added and mixed with water at a solid-liquid mass ratio of 1:4. The mixture is then slurryed and separated to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag.

[0051] The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation is used as raw material in the cement plant. The high-salt solution is heated and evaporated to 60% of its original volume. After evaporation and crystallization, 0.1265g NaCl, 0.1337g KCl, and 29.2mL of mother liquor are obtained. The mother liquor is returned to the reducing slag for slurry preparation. The obtained NaCl meets the GB / T5462-2015 standard, and the obtained KCl meets the GB / T7118-2023 standard.

[0052] The zinc removal rate of the ferrochrome dust was measured to be 93.45%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.033 ppm, the zinc content in the reduction residue was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0053] Example 3

[0054] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0055] The ferrochrome dust and semi-coke are mixed at a mass ratio of 1:0.5. 20g of ferrochrome dust containing 12.76wt% zinc, 23.95wt% iron, and 3.44wt% chromium is weighed, and 10g of semi-coke is weighed. The 20g of ferrochrome dust and 10g of semi-coke are then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0056] The pellets are loaded into a high-temperature resistant reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 850°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 10Pa. The vacuum carbonization reduction reaction is carried out with a holding time of 180min. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0057] After crushing and grinding the reduction slag, water is added and mixed with water at a solid-liquid mass ratio of 1:4. The mixture is then slurryed and separated to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag.

[0058] The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation is used as raw material in the cement plant. The high-salt solution is heated and evaporated to 60% of its original volume. After evaporation and crystallization, 0.1152g NaCl, 0.144g KCl, and 28.8mL of mother liquor are obtained. The mother liquor is returned to the reducing slag for slurry preparation. The obtained NaCl meets the GB / T5462-2015 standard, and the obtained KCl meets the GB / T7118-2023 standard.

[0059] The zinc removal rate of the ferrochrome dust was measured to be 99.39%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.016 ppm, the zinc content in the reduction residue was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0060] Example 4

[0061] The difference between Example 4 and Example 3 is that the mass percentage of zinc, iron, and chromium in the composition of the ferrochrome dust is different.

[0062] The ferrochrome dust and semi-coke are mixed at a mass ratio of 1:0.5. 20g of ferrochrome dust containing 4wt% zinc, 1wt% iron, and 0.1wt% chromium is weighed, and 10g of semi-coke is weighed. The 20g of ferrochrome dust and 10g of semi-coke are then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0063] The zinc removal rate of the ferrochrome dust was measured to be 99.98%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.001 ppm, the zinc content in the reduction slag was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0064] Example 5

[0065] The difference between Example 5 and Example 3 is that the mass percentage of zinc, iron, and chromium in the composition of the ferrochrome dust is different.

[0066] The ferrochrome dust and semi-coke are mixed at a mass ratio of 1:0.5. 20g of ferrochrome dust containing 60wt% zinc, 50wt% iron, and 10wt% chromium is weighed, and 10g of semi-coke is weighed. The 20g of ferrochrome dust and 10g of semi-coke are then thoroughly mixed and pressed into 30mm pellets on a tablet press.

[0067] The zinc removal rate of the ferrochrome dust was measured to be 90.12%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.049 ppm, the zinc content in the reduction slag was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0068] Example 6

[0069] The difference between Example 6 and Example 3 is that the pellets in Example 6 are granulated and compressed into 1mm pellets on a tablet press.

[0070] The zinc removal rate of the ferrochrome dust was measured to be 99.68%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.004 ppm, the zinc content in the reduction slag was less than 0.024%, and the zinc purity of the product was ≥98.7%.

[0071] Example 7

[0072] The difference between Example 7 and Example 3 is that the pellets in Example 7 are granulated and compressed into 50mm pellets on a tablet press.

[0073] The zinc removal rate of the ferrochrome dust was measured to be 95.36%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.032 ppm, the zinc content in the reduction slag was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0074] Example 8

[0075] The difference between Example 8 and Example 3 is the duration of the heat preservation reaction.

[0076] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0077] The ferrochrome dust and semi-coke are mixed at a mass ratio of 1:0.5. 20g of ferrochrome dust containing 12.76wt% zinc, 23.95wt% iron, and 3.44wt% chromium is weighed, and 10g of semi-coke is weighed. The 20g of ferrochrome dust and 10g of semi-coke are then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0078] The pellets are loaded into a high-temperature resistant reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 950°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 10Pa. The vacuum carbonization reduction reaction is carried out with a holding time of 60 minutes. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0079] After crushing and grinding the reduction slag, water is added and mixed with water at a solid-liquid mass ratio of 1:4. The mixture is then slurryed and separated to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag.

[0080] The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation is used as raw material in the cement plant. The high-salt solution is heated and evaporated to 60% of its original volume. After evaporation and crystallization, 0.1287g NaCl, 0.1566g KCl, and 29.8mL of evaporation mother liquor are obtained. The evaporation mother liquor is returned to the reducing slag for slurry preparation. The obtained NaCl meets the GB / T5462-2015 standard, and the obtained KCl meets the GB / T7118-2023 standard.

[0081] The zinc removal rate of the ferrochrome dust was measured to be 59.32%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.046 ppm, the zinc content in the reduction slag was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0082] Example 9

[0083] The difference between Example 9 and Example 3 is the duration of the heat preservation reaction.

[0084] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0085] The ferrochrome dust and semi-coke are mixed at a mass ratio of 1:0.5. 20g of ferrochrome dust containing 12.76wt% zinc, 23.95wt% iron, and 3.44wt% chromium is weighed, and 10g of semi-coke is weighed. The 20g of ferrochrome dust and 10g of semi-coke are then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0086] The pellets are loaded into a high-temperature resistant reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 950°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 10Pa. The vacuum carbonization reduction reaction is carried out for 120 minutes. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0087] After crushing and grinding the reduction slag, water is added and mixed with water at a solid-liquid mass ratio of 1:4. The mixture is then slurryed and separated to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag.

[0088] The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation is used as raw material in the cement plant. The high-salt solution is heated and evaporated to 60% of its original volume. After evaporation and crystallization, 0.1197g NaCl, 0.1358g KCl, and 28.2mL of mother liquor are obtained. The mother liquor is returned to the reducing slag for slurry preparation. The obtained NaCl meets the GB / T5462-2015 standard, and the obtained KCl meets the GB / T7118-2023 standard.

[0089] The zinc removal rate of the ferrochrome dust was measured to be 76.92%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.033 ppm, the zinc content in the reduction residue was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0090] Example 10

[0091] The difference between Example 10 and Example 3 is that the temperature inside the heating furnace is different.

[0092] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0093] The ferrochrome dust and semi-coke are mixed at a mass ratio of 1:0.5. 20g of ferrochrome dust containing 12.76wt% zinc, 23.95wt% iron, and 3.44wt% chromium is weighed, and 10g of semi-coke is weighed. The 20g of ferrochrome dust and 10g of semi-coke are then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0094] The pellets are loaded into a high-temperature resistant reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 950°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 10Pa. The vacuum carbonization reduction reaction is carried out for 180 minutes. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0095] After crushing and grinding the reduction slag, water is added and mixed with water at a solid-liquid mass ratio of 1:4. The mixture is then slurryed and separated to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag.

[0096] The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation is used as raw material in the cement plant. The high-salt solution is heated and evaporated to 60% of its original volume. After evaporation and crystallization, 0.108g NaCl, 0.1174g KCl, and 26.48mL of evaporation mother liquor are obtained. The evaporation mother liquor is returned to the reducing slag for slurry preparation. The obtained NaCl meets the GB / T5462-2015 standard, and the obtained KCl meets the GB / T7118-2023 standard.

[0097] The zinc removal rate of the ferrochrome dust was measured to be 92.78%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.048 ppm, the zinc content in the reduction slag was less than 0.05%, and the purity of the zinc in the product was ≥98.7%.

[0098] Example 11

[0099] The difference between Example 11 and Example 3 is that the temperature inside the heating furnace is different.

[0100] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0101] The ferrochrome dust and semi-coke are mixed at a mass ratio of 1:0.5. 20g of ferrochrome dust containing 12.76wt% zinc, 23.95wt% iron, and 3.44wt% chromium is weighed, and 10g of semi-coke is weighed. The 20g of ferrochrome dust and 10g of semi-coke are then thoroughly mixed and granulated into 30mm pellets on a tablet press.

[0102] The pellets are loaded into a high-temperature resistant reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 1050℃ at a heating rate of 10℃ / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 10Pa. The vacuum carbonization reduction reaction is carried out with a holding time of 180min. Then the process is ended and the product zinc and reduction slag are taken out while hot.

[0103] After crushing and grinding the reduction slag, water is added and mixed with water at a solid-liquid mass ratio of 1:4. The mixture is then slurryed and separated to obtain iron-containing slag and a high-salt solution. The iron-containing slag is then subjected to magnetic separation to obtain magnetic slag and non-magnetic slag.

[0104] The magnetic slag separated by magnetic separation is recycled back into the furnace, while the non-magnetic slag separated by magnetic separation is used as raw material in the cement plant. The high-salt solution is heated and evaporated to 60% of its original volume. After evaporation and crystallization, 0.0947g NaCl, 0.1031g KCl, and 26.9mL of evaporation mother liquor are obtained. The evaporation mother liquor is returned to the reducing slag for slurry preparation. The obtained NaCl meets the GB / T5462-2015 standard, and the obtained KCl meets the GB / T7118-2023 standard.

[0105] The zinc removal rate of the ferrochrome dust was measured to be 99.87%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.009 ppm, the zinc content in the reduction slag was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0106] Example 12

[0107] The only difference between Example 12 and Example 3 is the pressure control inside the vacuum carbonization reduction reactor.

[0108] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0109] The pellets are loaded into a high-temperature reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 950°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 5Pa. The vacuum carbonization reduction reaction is carried out for 120 minutes. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0110] The zinc removal rate of the ferrochrome dust was measured to be 99.53%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.011 ppm, the zinc content in the reduction slag was less than 0.05%, and the zinc purity of the product was ≥98.7%.

[0111] Example 13

[0112] The only difference between Example 13 and Example 3 is the pressure control inside the vacuum carbonization reduction reactor.

[0113] like Figure 1 As shown, the steps of a vacuum carbothermal method for collecting dust from ferrochrome alloy smelting are as follows:

[0114] The pellets are loaded into a high-temperature resistant reduction vessel in a heating furnace (one end of the reduction vessel is equipped with a water-cooled crystallizer). The heating furnace temperature is preset to rise from room temperature to 950°C at a rate of 10°C / min. After the furnace lid is closed, the vacuum unit is started to control the pressure inside the furnace at 150Pa. The vacuum carbonization reduction reaction is carried out with a holding time of 120min. Then the process is completed and the product zinc and reduction slag are taken out while hot.

[0115] The zinc removal rate of the ferrochrome dust was measured to be 97.35%. The chromium concentration in the washing solution was 0.024 ppm, the zinc content in the reduction slag was less than 0.024%, and the zinc purity of the product was ≥98.7%.

[0116] Comparative Example 1

[0117] The difference between Comparative Example 1 and Example 3 is that the raw material is ferrochrome dust.

[0118] The zinc removal rate of the ferrochrome dust was measured to be 97.68%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.039 ppm, the zinc content in the reduction residue was 1.41%, and the zinc purity of the product was ≥96.47%.

[0119] Comparative Example 2

[0120] The difference between Comparative Example 2 and Example 3 is that the pellets were reacted under normal pressure at a temperature of 950°C.

[0121] The zinc removal rate of the ferrochrome dust was measured to be 76.12%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.672 ppm, the zinc content in the reduction residue was 0.04%, and the zinc purity of the product was ≥98.34%.

[0122] Comparative Example 3

[0123] The difference between Comparative Example 3 and Example 3 is that the pellets were reacted in an environment of 500 Pa at a temperature of 950°C.

[0124] The zinc removal rate of the ferrochrome dust was measured to be 92.45%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.048 ppm, the zinc content in the reduction residue was 0.64%, and the zinc purity of the product was ≥93.47%.

[0125] Comparative Example 4

[0126] The difference between Comparative Example 4 and Example 3 is that the diameter of the pellets is 0.1 mm.

[0127] The zinc removal rate of the ferrochrome dust was measured to be 99.47%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.017 ppm, the zinc content in the reduction residue was 2.64%, and the zinc purity of the product was ≥86.24%.

[0128] Comparative Example 5

[0129] The difference between Comparative Example 5 and Example 3 is that the diameter of the pellet is 100 mm.

[0130] The zinc removal rate of the ferrochrome dust was measured to be 86.36%. The chromium concentration in the washing solution (evaporation mother liquor) was 0.045 ppm, the zinc content in the reduction residue was 1.45%, and the purity of the zinc in the product was ≥92.07%.

[0131] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A vacuum carbothermic process for smelting ferrochrome dust, characterized in that, The method comprises the following steps: The ferrochrome dust and the semi-coke are mixed uniformly at a mass ratio of 1:0.05-0.5, and then pressed into pellets, wherein the ferrochrome dust comprises 4wt%-60wt% zinc, 1wt%-50wt% iron and 0.1wt%-10wt% chromium; The pellets are placed in an environment with a temperature of 850-1050 DEG C and a pressure of 5-150 Pa, and subjected to vacuum carbonization reduction reaction for 60-180 min to obtain product zinc and reduction slag; The reduction slag is crushed and ground, and then added with water to form a slurry, and subjected to solid-liquid separation to obtain iron-containing slag and a high-salt solution; the iron-containing slag is subjected to magnetic separation to obtain magnetic slag and non-magnetic slag; the magnetic slag separated by the magnetic separation is recycled; the non-magnetic slag separated by the magnetic separation is used as a raw material for a cement plant; the high-salt solution is subjected to evaporation and crystallization to obtain NaCl and KCl and an evaporation mother liquor; and the evaporation mother liquor is returned to the reduction slag slurry.

2. The vacuum carbothermic process for smelting ferrochrome alloy dust according to claim 1, characterized in that, The diameter of the pellets is 1-50 mm.

3. The vacuum carbothermic process for smelting ferrochrome alloy dust according to claim 1, wherein, The zinc content in the reduction slag is less than 0.05%, and the purity of the product zinc is greater than or equal to 98.7%.

4. The vacuum carbothermic process for smelting ferrochrome alloy dust according to claim 1, wherein, The hexavalent chromium leaching concentration in the evaporation mother liquor is less than 0.05 ppm.

5. The vacuum carbothermic process for smelting ferrochrome alloy dust according to claim 1, wherein, The reduction slag is slurried with water at a solid-liquid mass ratio of 1:1-5.

6. The vacuum carbothermic process for smelting ferrochrome alloy dust according to claim 1, wherein, After the salt-containing solution is heated and evaporated to 60%-70% of the original volume, it is cooled to room temperature to precipitate NaCl, KCl and an evaporation mother liquor.

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