A method of carbothermic reduction of zinc oxide

Abstract

This invention discloses a method for carbothermic reduction of zinc oxide: (1) zinc oxide raw material, carbonaceous reducing agent, and sodium fluoride additive are mixed in a certain proportion; (2) the mixed material is subjected to a high-temperature reduction reaction under normal pressure, and zinc is reduced in the form of zinc vapor; wherein, the temperature of the reduction reaction is 1100-1250℃, and the holding time of the reduction reaction is 10-40 min. The method provided by this invention has a simple process, effectively improves the zinc reduction rate and reduces production costs, and can meet the requirements of environmentally friendly production.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy, specifically relating to a method for carbothermic reduction of zinc oxide. Background Technology

[0002] Zinc is an important strategic resource and plays a vital role in the non-ferrous metals industry. The largest use of metallic zinc is galvanizing, accounting for about 50% of total consumption. It can also be used in die casting, or in the manufacture of various grades of brass, zinc-based alloys, dry batteries, zinc oxide, building hardware, and chemical products. It is widely used in aerospace, automotive, shipbuilding, steel, machinery, construction, electronics, and daily consumer goods industries.

[0003] Modern zinc smelting methods are divided into two main categories: pyrometallurgical zinc smelting and hydrometallurgical zinc smelting. Hydrometallurgical zinc smelting is the dominant method, accounting for approximately 80% of total zinc production. Pyrometallurgical zinc smelting primarily uses closed blast furnaces, accounting for about half of the total pyrometallurgical zinc production. Its principle involves using coke as a reducing agent to heat zinc oxide to its reduction temperature inside the furnace, reducing the zinc oxide into zinc vapor. This vapor, along with a mixture of CO2 and CO in the tuyeres, enters a lead-zinc condenser, forming a lead-zinc alloy. This alloy is released from the condenser and, upon cooling, precipitates as liquid zinc.

[0004] ZnO (s) +C (s) =Zn (g) +CO (g)

[0005] However, the closed blast furnace zinc smelting process has problems such as lead dust pollution caused by the emission of lead during the sintering process and the multi-stage crushing of a large amount of returned material. It also has the disadvantages of complex supporting facilities and high investment. Therefore, some new pyrometallurgical zinc smelting methods have emerged.

[0006] CN111411230A designs a suspension smelting electrothermal reduction furnace and a method for smelting zinc concentrate. The zinc concentrate is mixed with calcium oxide and injected into the suspension smelting zone of the furnace through a material spray gun for oxidative smelting to obtain high-zinc slag. The high-zinc slag then undergoes a reduction reaction with coke or natural gas in the electrothermal reduction zone to produce zinc vapor. This process can reduce SO2 pollution, lower the zinc content in the reduction slag to 0.81%, and achieve a zinc recovery rate of 99.13%. However, because the reduction zone needs to be maintained at a high temperature of 1300–1600℃, the electric furnace consumes a large amount of energy and refractory materials.

[0007] CN112143891A proposes a highly efficient and environmentally friendly zinc smelting method. This method involves mixing zinc concentrate with flux and then adding the mixture to a smelting furnace for oxidation and desulfurization to obtain high-zinc slag. The high-zinc slag then enters a reduction zone where it reacts with a carbonaceous reducing agent to produce zinc vapor. This zinc vapor enters a condensation system where it rapidly exchanges heat with heat exchange components and condenses into metallic zinc. This method conducts the entire smelting process within a single furnace, achieving environmental protection. The zinc content in the reduction slag is less than 1%, and the zinc vapor condensation efficiency of the condensation system can reach 95%. However, the operating temperature in the reduction zone is as high as 1400–1600℃, resulting in high energy consumption and a significant consumption of refractory materials.

[0008] CN103205582A discloses a bottom-blown smelting electrothermal reduction process for lead and zinc smelting. A lead-zinc mixture and flux are added to an oxygen-enriched bottom-blown smelting furnace for smelting to obtain lead-zinc oxide melt. The lead-zinc oxide melt then flows into a submerged arc furnace for a reduction reaction to produce zinc vapor. This process uses oxygen-enriched bottom-blown smelting instead of sintering smelting, reducing environmental pollution and increasing sulfuric acid production. However, the slag contains 3%–5% zinc, reducing the direct zinc recovery rate, and further slag treatment is required to recover the zinc from the slag.

[0009] CN103451445A proposes a side-blown reduction process for lead-zinc smelting. Lead-zinc containing materials and flux are added to a smelting furnace for melting, yielding a melt containing lead-zinc oxides, or the melt flows into a side-blown reduction furnace for reduction to produce zinc-containing vapor and crude lead. Compared to using a submerged arc furnace for reducing lead-zinc materials, this process uses a side-blown reduction furnace, which improves zinc recovery, and the zinc content in the reduction slag is below 1.5%. However, the slag still needs to be treated to recover the zinc from it.

[0010] CN213266645U proposes a method for extracting metallic lead and zinc through bottom-blown oxygen-enriched autothermal smelting-electro-melting direct reduction. The method involves mixing lead-zinc sulfide ore, lead-zinc oxide ore with calcium oxide and silica to form a mixture, which is then fed into a bottom-blown oxidation furnace. High-pressure oxygen is introduced for smelting, yielding SO2 flue gas, molten lead, and oxide slag. This oxide slag is then fed into an electro-melting reduction furnace, where coal, silica, calcium oxide, and cold materials containing lead and zinc oxides are added. The furnace is then heated and reduced to obtain molten lead, reducing slag, and zinc-containing flue gas. While this process reduces environmental pollution to some extent, and the zinc content in the reducing slag can be reduced to 0.5%, it consumes a relatively high amount of energy.

[0011] The aforementioned patents propose many novel pyrometallurgical zinc smelting processes, either without additives or with calcium oxide as an additive. Although these processes meet environmental protection requirements and can achieve satisfactory zinc recovery rates, most of them suffer from high energy consumption. Summary of the Invention

[0012] The purpose of this invention is to provide a method for carbothermic reduction of zinc oxide. The method provided by this invention has a simple process, can accelerate the reduction process, significantly improve the zinc reduction rate, and reduce energy consumption.

[0013] To achieve the above objectives, the present invention provides the following technical solution:

[0014] This invention provides a method for carbothermic reduction of zinc oxide, comprising the following steps:

[0015] (1) Mix zinc oxide raw material, carbonaceous reducing agent and sodium fluoride additive in a certain proportion;

[0016] (2) The mixed materials are subjected to a high-temperature reduction reaction under normal pressure, and zinc is reduced in the form of zinc vapor; wherein the temperature of the reduction reaction is 1100~1250℃ and the holding time of the reduction reaction is 10~40min.

[0017] Preferably, in this invention, between step (1) and step (2), there is a step of granulating zinc oxide raw material, carbonaceous reducing agent and sodium fluoride additive, and the granulated pellets are placed in a vacuum drying oven for drying. Granulation can accelerate the carbothermic reduction process of zinc oxide.

[0018] Preferably, the amount of carbonaceous reducing agent added in step (1) is 2.5 to 3.5 times the theoretical ratio.

[0019] Preferably, the amount of sodium fluoride added in step (1) is 1% to 8% of the mass of the zinc oxide raw material; more preferably, it is 4% to 5%.

[0020] Preferably, the zinc content in the zinc oxide material in step (1) is ≥30%, more preferably ≥35%.

[0021] Preferably, the carbonaceous reducing agent in step (1) is coke, and the fixed carbon content in the coke is ≥85%.

[0022] Preferably, in order to improve the uniformity of mixing between materials, both the zinc oxide raw material and the carbonaceous reducing agent in step (1) are passed through a 150-mesh sieve.

[0023] Preferably, since some water is added during the granulation process, in order to facilitate a more efficient subsequent reduction reaction, the granulated material is placed in a vacuum drying oven for drying at a temperature of 150°C for 10 hours.

[0024] Preferably, the heating rate from room temperature to the reduction reaction temperature in step (2) is 3 to 5 °C / min.

[0025] In this invention, the reduction reaction in step (2) is carried out in a tubular resistance furnace. After the tubular resistance furnace is heated to the reduction temperature, the granulated and dried pellets are quickly placed into the central area of ​​the tubular resistance furnace and quickly removed after the heat preservation time is over.

[0026] The beneficial effects of this invention are:

[0027] Without additives, zinc oxide and carbon primarily undergo a solid-solid reduction reaction, resulting in low reduction efficiency. The reduction method provided by this invention uses sodium fluoride as an additive for carbothermic reduction of zinc. Sodium fluoride lowers the melting point of the material, facilitating the reduction reaction. The process flow of this invention is simple, involving reaction at atmospheric pressure and a temperature of 1100–1250°C, with a holding time of 10–40 minutes. Zinc oxide is reduced to zinc vapor, achieving a zinc reduction rate of over 95%. Compared to existing technologies, the zinc reduction rate in this invention is significantly higher than that in the control group without sodium fluoride, and the reduction reaction occurs at a lower temperature, which helps reduce energy consumption. Attached Figure Description

[0028] Figure 1 A flowchart of the carbothermic reduction of zinc oxide provided as an example of the present invention. Detailed Implementation

[0029] To further illustrate the present invention, the technical solutions provided by the present invention are described in detail below using comparative examples and embodiments. It should be noted that the descriptions of these embodiments are for the purpose of aiding understanding the present invention and do not constitute a limitation thereof. Furthermore, the technical features designed in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Example 1

[0031] according to Figure 1 The flowchart shown is for the carbothermic reduction of zinc oxide.

[0032] After crushing the zinc oxide raw material and coke, grind them to 150 mesh. Weigh 19.98g of zinc oxide raw material (dry weight), add coke with a theoretical ratio of 2.5 times, and sodium fluoride at 8% of the mass of zinc oxide raw material. Mix evenly and form into pellets with an average diameter of 8-12mm. Place them in a vacuum drying oven and dry at 150℃ for 10 hours before use.

[0033] In a specific embodiment of the present invention, the main chemical components of the zinc oxide material are (mass percentage): Zn 36.48%, Pb 17.41%, Fe 10.82%, CaO 5.88%, SiO2 4.88%, Al2O3 1.48%, S 0.93%, Cu 0.96%, Cd 0.14%, and the fixed carbon content in the coke is ≥85% (the same below).

[0034] The heating rate of the controlled tubular resistance furnace was 4℃ / min. When the temperature reached the reduction temperature of 1100℃, the dried pellets were quickly put into the furnace for reduction. The reduction time was 40 minutes. After the reduction was completed, the pellets were quickly removed. The slag contained 2.52% zinc, and the zinc reduction rate was 95.15%. Under the same conditions, the zinc reduction rate was only 85.72% without the addition of sodium fluoride.

[0035] Example 2

[0036] according to Figure 1 The flowchart shown is for the carbothermic reduction of zinc oxide.

[0037] After crushing the zinc oxide raw material and coke, grind them to 150 mesh. Weigh 20.02g of zinc oxide raw material (dry weight), add coke with a theoretical ratio of 3.0 times, and sodium fluoride at 4% of the mass of zinc oxide raw material. Mix evenly and form into pellets with an average diameter of 8-12mm. Place them in a vacuum drying oven and dry at 150℃ for 10 hours before use.

[0038] The heating rate of the controlled tubular resistance furnace was 3℃ / min. When the temperature reached the reduction temperature of 1150℃, the dried pellets were quickly put into the furnace for reduction. The reduction time was 30 minutes. After the reduction was completed, the pellets were quickly removed. The slag contained 1.73% zinc, and the zinc reduction rate was 96.16%. Under the same conditions, the zinc reduction rate was 87.63% without the addition of sodium fluoride.

[0039] Example 3

[0040] according to Figure 1 The flowchart shown is for the carbothermic reduction of zinc oxide.

[0041] After crushing the zinc oxide raw material and coke, grind them to 150 mesh. Weigh 20.11g (dry weight) of zinc oxide raw material, add coke with a theoretical ratio of 3.5 times, and sodium fluoride at 1% of the mass of zinc oxide raw material. Mix evenly and form into pellets with an average diameter of 8-12mm. Place them in a vacuum drying oven and dry at 150℃ for 10 hours before use.

[0042] The heating rate of the controlled tubular resistance furnace was 5℃ / min. When the temperature reached the reduction temperature of 1250℃, the dried pellets were quickly placed into the furnace for reduction. The reduction time was 10 minutes. After the reduction was completed, the pellets were quickly removed. The slag contained 1.62% zinc, and the zinc reduction rate was 97.23%. Under the same conditions, the zinc reduction rate was 90.36% without the addition of sodium fluoride.

[0043] Example 4

[0044] according to Figure 1 The flowchart shown is for the carbothermic reduction of zinc oxide.

[0045] After crushing the zinc oxide raw material and coke, grind them to 150 mesh. Weigh 20.03g of zinc oxide raw material (dry weight), add coke with a theoretical ratio of 3.0 times and sodium fluoride at 5% of the mass of zinc oxide raw material, mix evenly and make into pellets with an average diameter of 8-12mm. Place them in a vacuum drying oven and dry at a drying temperature of 150℃ for 10 hours before use.

[0046] The heating rate of the controlled tubular resistance furnace was 5℃ / min. When the temperature reached the reduction temperature of 1200℃, the dried pellets were quickly put into the furnace for reduction. The reduction time was 15 minutes. After the reduction was completed, the pellets were quickly removed. The slag contained 0.47% zinc, and the zinc reduction rate was 99.37%. Under the same conditions, the zinc reduction rate was 91.07% without the addition of sodium fluoride.

[0047] Example 5

[0048] according to Figure 1 The flowchart shown is for the carbothermic reduction of zinc oxide.

[0049] After crushing the zinc oxide raw material and coke, grind them to 150 mesh. Weigh 19.98g of zinc oxide raw material (dry weight), add coke with a theoretical ratio of 3.0 times, and sodium fluoride at 4% of the mass of zinc oxide raw material. Mix evenly and form into pellets with an average diameter of 8-12mm. Place them in a vacuum drying oven and dry at 150℃ for 10 hours before use.

[0050] The heating rate of the controlled tubular resistance furnace was 4℃ / min. When the temperature reached the reduction temperature of 1200℃, the dried pellets were quickly placed into the furnace for reduction. The reduction time was 20 minutes. After the reduction was completed, the pellets were quickly removed. The slag contained 0.35% zinc, and the zinc reduction rate was 99.67%. Under the same conditions, the zinc reduction rate was 93.41% without the addition of sodium fluoride.

[0051] The results of the comparative example show that adding sodium fluoride can significantly improve the reduction rate of zinc in the material.

[0052] Compared with the prior art, the advantages of the present invention are: the method is simple, it can accelerate the reduction process, shorten the reduction time, and effectively improve the zinc reduction rate.

[0053] In addition, it should be noted that using ammonium fluoride instead of sodium fluoride can also improve the zinc reduction rate.

[0054] Although the above embodiments have provided a detailed description of the present invention, they are merely some, not all, embodiments of the present invention. Various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for carbothermic reduction of zinc oxide, characterized in that, Includes the following steps: (1) Mix zinc oxide raw material, carbonaceous reducing agent and sodium fluoride additive in a certain proportion; The amount of carbonaceous reducing agent added is 2.5 to 3.5 times the theoretical ratio; the carbonaceous reducing agent is coke, and the fixed carbon content in the coke is ≥85%; The amount of sodium fluoride added is 1% to 8% of the mass of the zinc oxide raw material; (2) The mixed materials are subjected to a high-temperature reduction reaction under normal pressure. Zinc is reduced in the form of zinc vapor, and the zinc reduction rate can reach more than 95%. The temperature of the reduction reaction is 1100-1250℃, the holding time of the reduction reaction is 10-40 min, and the heating rate from room temperature to the reduction reaction temperature is 3-5℃ / min.

2. The method according to claim 1, characterized in that, Between steps (1) and (2), there is also a step of granulating zinc oxide raw material, carbonaceous reducing agent and sodium fluoride additive, and the granulated pellets are placed in a vacuum drying oven for drying.

3. The method according to claim 1, characterized in that, In step (1), the zinc oxide material contains ≥30% zinc by mass.

4. The method according to claim 1, characterized in that, In step (1), both the zinc oxide raw material and the carbonaceous reducing agent are finely ground and passed through a 150-mesh sieve.

5. The method according to claim 2, characterized in that, The drying temperature of the pellets is 150℃, and the drying time is 10 hours.

6. The method according to claim 1, characterized in that, The reduction reaction in step (2) is carried out in a tubular resistance furnace.

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