Method for efficiently recovering metal zinc in zinc slag by using rotary hearth furnace

Abstract

The invention belongs to the technical field of metallurgical waste residue recycling, and discloses a method for efficiently recycling metal zinc in zinc dross by using a rotary hearth furnace, which comprises the following steps: S1, mixing the zinc dross, a composite reducing agent, a pore forming agent, a binder and water, granulating, and drying to obtain cavity pellets; s2, the cavity pellets are fed into a rotary hearth furnace, chloride is volatilized at the low-temperature section where weak reducing atmosphere is introduced, and then zinc is reduced at the high-temperature section where strong reducing atmosphere is introduced; and S3, steam generated by reduction in the high-temperature section enters a second-stage condensation system, direct contact condensation is conducted through spraying of cooling liquid in first-stage condensation, indirect heat exchange condensation is conducted through a low-temperature wall face in second-stage condensation, and metal zinc particles are obtained. The rotary hearth furnace serves as a core platform, the high-performance composite reducing agent, the structural functionalized pellet design, atmosphere-temperature zone linkage control and graded flow guide condensation are combined, reduction efficiency, equipment durability and efficient zinc particle recycling are considered, and the method is particularly suitable for efficient resourceful treatment of zinc slag containing zinc sulfate and zinc oxide.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgical slag resource utilization, and particularly relates to a method for efficiently recovering metallic zinc from zinc slag by using a rotary hearth furnace. BACKGROUND

[0002] With the continuous development of the steel, electroplating, hydrometallurgy and other industries, a large amount of zinc-containing waste liquid is treated by using evaporation crystallization technology, and the by-product is zinc slag mainly containing zinc sulfate and mixed with zinc oxide, iron oxide and chloride and other impurities. The zinc slag has high metal content and complex particle size, and has great resource utilization potential. However, if not properly treated, it is often stored or landfilled, which not only wastes valuable metals such as zinc and iron, but also has the risk of polluting groundwater with heavy metal leachate. In recent years, the rotary hearth furnace has been gradually introduced into the treatment of zinc-containing solid waste due to its high-temperature reduction capability and wide adaptability to raw material particle size. It has the technical path basis of thermal decomposition + atmosphere reduction, but for zinc sulfate type zinc slag, the traditional process still faces the following problems: 1) insufficient reaction efficiency: zinc sulfate needs to be decomposed into ZnO first, and then reduced, the single coke reduction system has slow reaction rate and low thermal efficiency; 2) significant equipment corrosion: chlorides in zinc slag generate volatile hydrogen chloride under high temperature conditions, which corrodes the rotary hearth furnace lining and pipeline, seriously affecting the operation cycle; 3) large loss of zinc recovery: uneven release of zinc vapor limits the condensation efficiency, and submicron dust is easily escaped, making it difficult to break through 90% of the recovery rate. Therefore, it is of great significance to develop a rotary hearth furnace process with high efficiency, low corrosion and high recovery rate for realizing the resource utilization of zinc sulfate type zinc slag. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a method for efficiently recovering metallic zinc from zinc slag by using a rotary hearth furnace, which is a core platform, combined with high-performance composite reducing agent, structure-functional pellet design, atmosphere-temperature zone linkage control and graded flow condensation, taking into account the reduction efficiency, equipment durability and efficient recovery of zinc particles, especially suitable for efficient resource utilization of zinc slag containing zinc sulfate and zinc oxide.

[0004] To solve the technical problems proposed in the present application, the present application provides a method for efficiently recovering metallic zinc from zinc slag by using a rotary hearth furnace, comprising the following steps: S1, mixing zinc slag, composite reducing agent, pore former, binder and water, granulating, drying to obtain cavity pellets; S2, sending the cavity pellets into the rotary hearth furnace, first volatilizing chlorides in the low temperature section with weak reducing atmosphere, and then reducing in the high temperature section with strong reducing atmosphere; S3, the steam generated by high temperature reduction enters the secondary condensation system to obtain metallic zinc particles by condensation.

[0005] In the above scheme, the zinc sulfate content of the zinc residue is 50% to 70%, the particle size is ≤2 mm, and the water content is ≤5%.

[0006] In the above scheme, the mass ratio of the zinc residue to the composite reducing agent is 10: (3 to 4).

[0007] In the above scheme, the composite reducing agent is composed of coke and citric acid modified rice husk carbon.

[0008] Further, in the composite reducing agent, the mass percentage of coke is 60% to 70%, and the mass percentage of citric acid modified rice husk carbon is 30% to 40%.

[0009] Further, the preparation method of the citric acid modified rice husk carbon is: 1) Carbonize the rice husk under an inert atmosphere to obtain rice husk carbon; 2) Mix the rice husk carbon with a citric acid solution and heat to react, wash and dry to obtain citric acid modified rice husk carbon.

[0010] Further, in step 1), the inert atmosphere is one of nitrogen and argon.

[0011] Further, in step 1), the heating temperature for carbonization is 850 to 950°C, and the carbonization time is 0.5 to 2 hours.

[0012] Further, in step 1), the heating rate for carbonization is 5 to 15°C / min.

[0013] Further, in step 2), the mass concentration of the citric acid solution is 2% to 5%.

[0014] Further, in step 2), the mass to volume ratio of the rice husk carbon to the citric acid solution is 1g: (8 to 12) mL.

[0015] Further, in step 2), the heating temperature for the heating reaction is 70 to 90°C, and the reaction time is 4 to 8 hours.

[0016] In the above scheme, the particle size of the composite reducing agent is 50 to 150μm.

[0017] In the above scheme, the pore-forming agent is composed of urea and ammonium bicarbonate.

[0018] Further, the mass ratio of the urea to the ammonium bicarbonate is 1: (1 to 2).

[0019] In the above scheme, the particle size of the pore-forming agent is 100 to 300μm.

[0020] The adding amount of the pore-forming agent is 2-4% of the total mass of the zinc residue and the composite reducing agent.

[0021] The binder is starch or bentonite.

[0022] The particle size of the binder is ≤150 μm.

[0023] The adding amount of the binder is 3-5% of the total mass of the zinc residue and the composite reducing agent.

[0024] The adding amount of the water is such that the moisture content of the granulation material is 8-12%.

[0025] The drying temperature is 100-120°C, and the drying time is 3-4 h.

[0026] The diameter of the hollow sinter is 12-20 mm, and the sinter strength is ≥8 N.

[0027] The temperature of the low-temperature section is 600-800°C, and the residence time is 20-30 min.

[0028] The weak reducing atmosphere is a mixture of CO and N2, wherein the volume fraction of CO is 10-15%, and the volume fraction of N2 is 85-90%.

[0029] The water vapor is intermittently injected into the low-temperature section, the injection period is 2-5 min, and the injection period is the time interval from the start of one injection to the start of the next injection.

[0030] Further, the single injection amount of the water vapor is 0.08-0.12 L / min, and the single duration is 25-35 s.

[0031] Further, according to the O2 volume fraction and the CO / CO2 volume ratio in the low-temperature section system, the composition of the weak reducing atmosphere, the water vapor injection frequency and the converter speed are regulated, and a three-grade regulation mechanism is set: First grade: when the O2 volume fraction is <0.2% and the CO / CO2 volume ratio is >1.5, the volume fraction of CO in the weak reducing atmosphere is regulated to be 10-11%, the water vapor injection period is 4.5-5.5 min, and the converter speed is 0.8-1.2 r / min; Second grade: when the O2 volume fraction is 0.2-0.5% and the CO / CO2 volume ratio is 1-1.5, the volume fraction of CO in the weak reducing atmosphere is regulated to be 12-13%, the water vapor injection period is 2.5-3.5 min, and the converter speed is 1.2-1.6 r / min; The third gear: when the O2 volume fraction is greater than 0.5% and the CO / CO2 volume ratio is less than 1, the volume fraction of CO in the weak reduction atmosphere is 14-15%, the water vapor injection period is 1.5-2.5 min, and the converter speed is 1.8-2.2 r / min; When the O2 volume fraction and the CO / CO2 volume ratio are in different gears, the higher gear is executed.

[0032] This step can be realized by setting an oxygen content sensor, a CO / CO2 infrared analyzer, and a furnace speed monitoring system to form a feedback closed-loop control unit, so as to realize real-time regulation and response time < 3 s.

[0033] In the above scheme, the temperature of the high-temperature section is 1100-1200°C, and the residence time is 30-50 min.

[0034] In the above scheme, the strong reduction atmosphere is a mixture of CO and H2, and the volume ratio of CO to H2 is (1.8-2.2):1.

[0035] In the above scheme, the steam enters the secondary condensing system through a conical flow guide channel, the inlet flow rate of the steam in the conical flow guide channel is controlled to be 3-5 m / s, the outlet flow rate is 6-10 m / s, and the residence time is 2-4 s.

[0036] Further, swirl inducing vanes can be arranged on the inner wall at the junction between the outlet of the flow guide channel and the inlet of the secondary condensing system to guide the steam to form a stable rotating state, and the vane inclination angle (the angle between the vane and the axis direction of the flow guide channel) can be optimized to be 25-40° according to the flow rate and pressure conditions of the flow guide channel, so that the steam forms a stable rotation when entering the first stage of condensation, and the contact probability and condensation efficiency with the sprayed cooling liquid are improved.

[0037] In the above scheme, the first stage of condensation of the secondary condensing system is realized by directly contacting the steam with the sprayed cooling liquid, and the second stage of condensation is realized by indirect heat exchange between the low-temperature wall surface to further condense the remaining steam.

[0038] Further, the cooling liquid contact area temperature of the first stage of condensation is 250-300°C.

[0039] Further, the cooling liquid spraying flow rate of the first stage of condensation is 0.4-0.6 L / min.

[0040] Further, the condensing wall surface temperature of the second stage of condensation is 50-80°C.

[0041] In the above scheme, the condensation is carried out under micro-negative pressure or inert atmosphere to prevent Zn from being oxidized to ZnO.

[0042] Further, the micro-negative pressure is -50 to -200 Pa.

[0043] Further, the inert atmosphere is one of nitrogen and argon.

[0044] In the scheme, the average residence time of the steam in the secondary condensing system is 1-3s.

[0045] In the scheme, the particle size of the zinc metal particles is 0.1-1mm, the purity is ≥99%, and the zinc recovery rate is ≥98.7%.

[0046] The design of the present application is based on the following considerations: The present application aims at the technical difficulties existing in the high-temperature reduction process of the existing zinc slag, such as complex reaction path, insufficient release of zinc vapor, serious corrosion of chlorides and fluctuation of condensation efficiency, and constructs a multi-dimensional collaborative process taking a rotary hearth furnace as a core platform, integrating high-performance composite reducing agent, structure-functionalized pellet design, atmosphere-temperature zone linkage control and staged flow guiding condensation. The process mainly includes the following three key innovations: First, the structure-functionalized pellet design. A composite reducing agent composed of coke and citric acid modified rice husk charcoal is used, the citric acid modified rice husk charcoal provides fast reaction activity, and the coke ensures high temperature stability, which cooperatively improves the reduction efficiency of zinc and iron. By introducing different pyrolysis temperature zone pore-forming agents (urea and ammonium bicarbonate), a double-scale pore structure is constructed inside the pellet, and a small pore-main cavity distribution is formed during the pellet forming and heating process according to the temperature program, forming a gas rapid escape channel to improve the release rate and uniformity of zinc vapor. Specifically, urea starts to decompose at the pellet drying stage, forming a primary small pore channel, and ammonium bicarbonate decomposes in the subsequent rotary hearth furnace low temperature section, forming a main cavity structure for rapid release of zinc vapor. This design not only improves the reduction reaction efficiency, but also reduces the retention and loss of zinc in the solid residue.

[0047] Second, the rotary hearth furnace atmosphere-thermal field-motion three-field linkage control mechanism. A low-temperature volatilization zone and a high-temperature reduction zone are set in the rotary hearth furnace to remove chlorides first and then reduce metals, reducing equipment corrosion and optimizing the reaction process. Based on the low-temperature volatilization and high-temperature reduction partition set in the furnace, different reducing atmospheres are set in different zones, and in the low-temperature volatilization zone, the composition of the reducing atmosphere, the frequency of water vapor injection and the speed of the rotary hearth furnace are real-time controlled by combining O2 volume fraction and CO / CO2 volume ratio, realizing the coordination between reaction thermodynamics driving and kinetics rate, and at the same time, using pulse water vapor to strengthen the separation and conversion of chlorides, effectively inhibiting the diffusion of corrosion source.

[0048] Third, zinc vapor flow guide and multi-stage precision control condensing system. By setting a tapered flow channel to control the vapor flow rate and heat transfer efficiency, the cross section of which is gradually tapered to speed up the gas flow rate, while extending the effective residence time of the vapor in the high temperature zone, thereby improving the zinc vapor concentration and uniformity at the front end of the condensing zone; By setting the rotating flow induction blades on the inner wall of the junction between the outlet of the flow guide channel and the condensing cavity to induce the vapor to form a stable vortex before entering the first stage condensing zone, the gas-liquid contact probability is improved; The condensing chain formed by the temperature gradient gradually captures the Zn vapor, reduces the risk of submicron particle escape, and realizes the controllability of condensing efficiency and product particle size distribution.

[0049] Compared with the prior art, the beneficial effects of the present application are: The present application takes the rotary hearth furnace as the core platform, combines high-performance composite reducing agent, structural and functional pellet design, atmosphere-temperature zone linkage control and staged flow guiding condensation, solves the problems of low reduction efficiency, serious equipment corrosion and low zinc recovery rate of traditional rotary hearth furnace process, not only greatly improves the recovery rate, zinc recovery efficiency ≥98.7%, iron recovery rate ≥95%, zinc particle size distribution concentration improves by more than 30%, but also significantly reduces the equipment corrosion rate, prolongs the service life of the system, and the process energy consumption and pollutant emissions are further reduced, the total energy consumption of the system is ≤830kWh / t, the emissions of SO2 and dust S are reduced by more than 30%, which provides a reliable, efficient and popular solution for the high-value utilization of zinc-containing solid waste, especially for the zinc slag treatment scene in steel, electroplating and hydrometallurgy industries. DETAILED DESCRIPTION

[0050] In order to better understand the present application, the content of the present application will be further illustrated below in conjunction with examples, but the content of the present application is not limited to the following examples.

[0051] Example 1 A certain steel enterprise produces zinc slag by evaporation crystallization process, and its main components are: zinc sulfate 62%, iron oxide 14%, zinc oxide 8%, moisture 4%, and the rest is silicate impurities, particle size ≤2mm.

[0052] The metallic zinc in the zinc slag is recovered by using a rotary hearth furnace, and the steps are as follows: S1, cavity pellet preparation: ① Rice husk is heated to 900℃ at 10℃ / min under nitrogen atmosphere, and kept for 1h to obtain rice husk carbon; the obtained rice husk carbon is mixed with a citric acid solution with a mass concentration of 3.0% at 1g:9mL, and reacted at 80℃ for 7h, then washed with deionized water to neutral, and dried at 60℃ to obtain citric acid modified rice husk carbon; ② The coke and the lemon acid modified rice husk charcoal are mixed according to the mass ratio of 65:35 as the composite reducing agent, and the particle size of the composite reducing agent is 50-150 μm; the urea and the ammonium bicarbonate are mixed according to the mass ratio of 1:1 as the pore-forming agent, and the particle size of the pore-forming agent is 100-300 μm; the starch is taken as the binder, and the particle size of the binder is ≤150 μm; ③ The zinc dregs and the composite reducing agent are mixed according to the mass ratio of 10:3.5, then the pore-forming agent and the binder are added, the total mass of the pore-forming agent is 3% of the total mass of the zinc dregs and the composite reducing agent, and the total mass of the binder is 3% of the total mass of the zinc dregs and the composite reducing agent, and then the deionized water is added to control the overall water content of the granulation material at 10%, so as to obtain the granulation material; ④ The granulation material is granulated in the granulation disc (the rotating speed is 40 rpm), and the diameter of the pellet is controlled at 15 mm, the pellet is dried by hot air at 120℃ for 4 h, so as to obtain the hollow pellet; the sampling test shows that the hollow is distributed in the pellet, the average diameter of the hollow is 5 mm, and the average mechanical strength is 9.2 N; S2, hot reduction in the rotary hearth furnace ① The hollow pellet is continuously sent into the 6m-long rotary hearth furnace through the conveying device, and the furnace body is divided into a low-temperature section (0-2m) and a high-temperature section (2-6m); ② The chlorides are volatilized in the low-temperature section, the temperature of the low-temperature section is 750℃, the residence time is 25 min, the mixed gas of CO and N2 is introduced into the low-temperature section, and the water vapor is intermittently sprayed, the single spraying amount of the water vapor is 0.1 L / min, and the single spraying duration is 30 s; According to the O2 volume fraction and the CO / CO2 volume ratio in the system, the composition of the atmosphere, the water vapor spraying frequency and the rotary speed of the furnace are adjusted, and three adjustment mechanisms are set: First gear: when the O2 volume fraction is <0.2% and the CO / CO2 volume ratio is >1.5, the volume fraction of CO in the weak reduction atmosphere is adjusted to 10%, the water vapor spraying period is 5 min, and the rotary speed of the furnace is 1 r / min; Second gear: when the O2 volume fraction is 0.2-0.5% and the CO / CO2 volume ratio is 1-1.5, the volume fraction of CO in the weak reduction atmosphere is adjusted to 12%, the water vapor spraying period is 3 min, and the rotary speed of the furnace is 1.5 r / min; Third gear: when the O2 volume fraction is >0.5% and the CO / CO2 volume ratio is <1, the volume fraction of CO in the weak reduction atmosphere is adjusted to 15%, the water vapor spraying period is 2 min, and the rotary speed of the furnace is 2 r / min; When the O2 volume fraction and the CO / CO2 volume ratio are in different gears, the higher gear is executed; The real-time adjustment process is realized through the setting of the oxygen content sensor, the CO / CO2 infrared analyzer and the furnace speed monitoring system to form a feedback closed-loop control unit, and the average response time is 2.6 s; ③ Subsequently, reduction is performed in a high-temperature section, mixed gas with a volume ratio of CO and H2 of 2:1 is introduced into the high-temperature section, the temperature of the high-temperature section is 1150℃, and the residence time is 40min, to generate zinc-rich vapor and iron-rich residue, and the iron pellets are obtained by magnetic separation after the residue is cooled; S3, steam flow guiding and condensing: ① The zinc-rich vapor enters a secondary condensing system through a conical flow guiding passage, the inlet diameter of the conical flow guiding passage is 80mm, the outlet diameter is 40mm, and the length is 300mm, the inlet flow velocity of the steam in the conical flow guiding passage is 4m / s, the outlet flow velocity is 8m / s, and the residence time is about 1.5s; ② A swirl-inducing blade is arranged on the inner wall at the junction between the outlet of the flow guiding passage and the inlet of the secondary condensing system, the blade has an inclination angle (the included angle between the blade and the axis direction of the flow guiding passage) of 30°, so that the steam forms stable rotation when entering the first stage of condensation, and the contact probability and condensing efficiency of the steam with the sprayed cooling liquid are improved; ③ The first stage of condensation is achieved by directly contacting the steam with sprayed cooling liquid (deionized water), the spraying liquid flow is 0.5L / min, the cooling liquid contact area temperature is 280℃, and the condensed particles of zinc account for 83% of the total output; the second stage of condensation is achieved by indirect heat exchange between low-temperature walls to further condense the remaining steam, and the condensing wall temperature is 65℃; the above condensing is performed under a micro-negative pressure condition of-100Pa, and the average residence time is 2s.

[0053] Product analysis and system evaluation: ① The XRF detection results show that the purity of the condensed zinc particles is 99.1%, the zinc recovery rate is 98.9%, which is increased by 2.3% and 9.7% respectively compared with the comparative example; the iron content of the iron pellets is 85.4%, and the iron recovery rate is 95.2%; ② The particle size distribution of the condensed zinc particles is 0.12~0.75mm, the average particle size is 0.32mm, and the particle size concentration degree (D90 / D10) is 4.6, which is improved by about 31% compared with the comparative example (D90 / D10 is 6.7), which is more conducive to subsequent briquetting treatment; ③ The corrosion rate of the refractory lining of the hearth is 0.48mm / a, which is reduced by 56% compared with the comparative example (about 1.1mm / a); the corrosion rate is calculated by the mass difference before and after the lining and the exposure time; ④ The unit energy consumption of the whole process is 817kWh / t of zinc slag treatment, and the SO2 and dust emissions are reduced by 32% and 35% respectively compared with the comparative example.

[0054] Example 2 A certain steel enterprise produces zinc slag by evaporation crystallization process, and the main components are: zinc sulfate 58%, iron oxide 16%, zinc oxide 10%, moisture 4.5%, and the rest is silicate impurities, and the particle size is ≤2mm.

[0055] The zinc slag is recycled by a rotary hearth furnace, and the steps are as follows: S1, cavity pellet preparation: ①The rice husk is heated to 880℃ at a heating rate of 10℃ / min under a nitrogen atmosphere, and is kept for 1 hour to obtain rice husk carbon. The rice husk carbon is mixed with a 4% mass concentration citric acid solution at a ratio of 1g:10mL, and is reacted at 85℃ for 6h. After washing to neutral, drying is performed to obtain citric acid modified rice husk carbon. ②The coke and the citric acid modified rice husk carbon are mixed at a mass ratio of 60% and 40% respectively to serve as a composite reducing agent, and the particle size of the composite reducing agent is 50-150μm. Urea and ammonium bicarbonate are mixed at a mass ratio of 1:1 to serve as a pore-forming agent, and the particle size of the pore-forming agent is 100-300μm. The bentonite is taken as a binder, and the particle size is ≤150μm. ③The zinc slag is mixed with the composite reducing agent at a mass ratio of 10:4, and then the pore-forming agent is added at a mass ratio of 4% of the total mass of the zinc slag and the composite reducing agent, and the binder is added at a mass ratio of 3.5%. Deionized water is added to control the overall moisture content of the granulation material to 11% to obtain a granulation material. ④The granulation material is granulated in a disc granulator at a rotation speed of 45rpm, and the pellet diameter is controlled to be 17mm. The pellets are dried by hot air at 120℃ for 4h to obtain cavity pellets. Sampling test shows that the pellets are distributed with cavities, the average diameter of the cavities is 6mm, and the average mechanical strength is 9.6N. S2, rotary hearth furnace hot reduction: ①The cavity pellets are continuously fed into a 6m long rotary hearth furnace through a conveying device, and the furnace body is divided into a low temperature section (0-2m) and a high temperature section (2-6m). ②Chlorides are volatilized in the low temperature section, the temperature of the low temperature section is 740℃, the residence time is 28min, and the mixed gas of CO and N2 is introduced into the low temperature section, and water vapor is intermittently sprayed, the single spraying amount of water vapor is 0.1L / min, and the single duration is 30s. According to the O2 volume fraction and CO / CO2 volume ratio in the system, the composition of the atmosphere, the water vapor spraying frequency and the rotary hearth speed are adjusted to set three adjustment mechanisms: First gear: when the O2 volume fraction is <0.2% and the CO / CO2 volume ratio is >1.5, the CO volume fraction in the weak reduction atmosphere is controlled to be 11%, the water vapor spraying period is 4.5min, and the rotary hearth speed is 1.2r / min. Second gear: when the O2 volume fraction is 0.2-0.5% and the CO / CO2 volume ratio is 1-1.5, the CO volume fraction in the weak reduction atmosphere is controlled to be 12%, the water vapor spraying period is 3min, and the rotary hearth speed is 1.5r / min. Third gear: when O2 volume fraction > 0.5% and CO / CO2 volume ratio < 1, the volume fraction of CO in weak reduction atmosphere is 14%, the water vapor injection period is 1.5 min, and the converter speed is 2.2 r / min; When O2 volume fraction and CO / CO2 volume ratio are in different gears, the higher gear is executed; The real-time control process is realized by setting oxygen content sensor, CO / CO2 infrared analyzer and furnace speed monitoring system to form a feedback closed-loop control unit, and the average response time is 2.6 s; ③ Then reduce in high temperature section, pass mixed gas with CO and H2 volume ratio of 1.8:1 in high temperature section, high temperature section temperature is 1180℃, residence time is 35 min, generate zinc-rich steam and iron-rich residue, after cooling the residue is obtained by magnetic separation iron pellets; S3, steam flow guiding and condensing: ① Zinc-rich steam enters the secondary condensing system through the conical flow guiding channel, the inlet diameter of the conical flow guiding channel is 80 mm, the outlet diameter is 40 mm, and the length is 300 mm. The steam inlet flow rate in the conical flow guiding channel is 3.5 m / s, the outlet flow rate is 9 m / s, and the residence time is about 1.6 s; ② The inner wall of the junction between the outlet of the flow guiding channel and the inlet of the secondary condensing system is provided with swirl inducing blades with an inclination angle (the angle between the blade and the axis direction of the flow guiding channel) of 28°, so that the steam forms stable rotation when entering the first stage condensation, and the contact probability and condensation efficiency with the sprayed cooling liquid are improved; ③ The first stage condensation is realized by directly contacting the steam with sprayed cooling liquid (deionized water), the spraying liquid flow rate is 0.55 L / min, the cooling liquid contact area temperature is 270℃, and the condensed particles of zinc account for 82% of the total output; the second stage condensation is realized by indirect heat exchange between low temperature wall surfaces to further condense the remaining steam, and the condensing wall surface temperature is 65℃; the above condensing is carried out in N2 protective atmosphere, and the average residence time is 3 s.

[0056] Product analysis and system evaluation: ① The XRF detection results show that the purity of the condensed zinc particles is 99.0%, and the zinc recovery rate is 98.7%, which is increased by 2.2% and 9.2% respectively compared with the comparative example; the iron content of the iron-rich pellets is 84.9%, and the iron recovery rate is 94.5%.

[0057] ② The particle size range of the condensed zinc particles is 0.13~0.70 mm, the average particle size is 0.30 mm, and the particle size concentration (D90 / D10) is 4.4, which is improved by about 34% compared with the comparative example (6.7); ③ The furnace lining corrosion rate is 0.51 mm / a, which is reduced by about 54% compared with the comparative example (1.1 mm / a); ④ The unit processing energy consumption is 829 kWh / t of zinc slag, and the SO2 and dust emissions are reduced by 31% and 36% respectively compared with the comparative example.

[0058] Comparative Example A certain steel enterprise produces zinc slag by evaporation crystallization process, and its main components are: zinc sulfate 61%, iron oxide 15%, zinc oxide 9%, moisture 5%, and the rest is silicate impurities, particle size ≤2mm.

[0059] The metal zinc in the zinc slag is recovered by using the traditional rotary hearth furnace reduction + direct cooling condensation process, and the steps are as follows: S1, pellet preparation: The zinc slag and coke are mixed in a mass ratio of 10:4, deionized water is added to make the overall moisture content 12%, and then granulated in a granulating disc with a rotation speed of 40 rpm, and then dried at 120°C for 4h to obtain pellets with a diameter of 15mm; S2, rotary hearth furnace reduction: The pellets are continuously fed into a 6m long rotary hearth furnace by a conveying device, and a mixed gas with a CO volume fraction of 25% and a N2 volume fraction of 75% is introduced, the furnace temperature is gradually increased to 1150°C, and the overall residence time is 60min, the reduction reaction is completed, and zinc-containing steam and iron residue are generated, and the iron pellets are obtained after cooling and magnetic separation of the residue; S3, direct cooling condensation: The zinc steam is introduced into a cooling water jacket structure, and is condensed by heat exchange through the metal pipe wall under normal pressure and without protective gas, the metal pipe wall surface temperature is 60°C, and part of the steam is oxidized to form ZnO, forming dust loss.

[0060] Product analysis and system evaluation: ① The XRF detection results show that the purity of the condensed zinc particles is 96.8%, the zinc recovery rate is 89.2%, the iron content of the iron pellets is 81.5%, and the iron recovery rate is 89.8%.

[0061] ② The particle size of the zinc particles is 0.05~1.5mm, the average particle size is 0.43mm, and the particle size concentration (D90 / D10) is 6.7; ③ The corrosion rate of the furnace lining is 1.1mm / a; ④ The unit processing energy consumption is 923 kWh / t of zinc slag.

Claims

1. A method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace, characterized in that: The following steps are involved: S1, mixing zinc slag, a composite reducing agent, a pore-forming agent, a binder and water, granulating, and drying to obtain cavity pellets; S2. The cavity pellets are fed into a rotary hearth furnace, where chlorides are first volatilized in a low-temperature section with a weak reducing atmosphere, and then zinc is reduced in a high-temperature section with a strong reducing atmosphere; S3. The steam generated by the high-temperature reduction enters the secondary condensation system. The first stage of condensation is direct contact condensation through spraying coolant, and the second stage of condensation is indirect heat exchange condensation through the low-temperature wall to obtain metallic zinc particles.

2. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 1, characterized in that: The zinc slag has a zinc sulfate content of 50% to 70%, a particle size of ≤2 mm, and a moisture content of ≤5%; the composite reducing agent is composed of coke and citric acid-modified rice husk charcoal, with a particle size of 50 to 150 μm; the pore-forming agent is composed of urea and ammonium bicarbonate, with a particle size of 100 to 300 μm; The binder is starch or bentonite, and the particle size is ≤150 μm.

3. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 2, characterized in that: The composite reducing agent is composed of 60% to 70% by mass of coke and 30% to 40% by mass of citric acid-modified rice husk charcoal; the citric acid-modified rice husk charcoal is prepared by heating and modifying the rice husk charcoal after mixing it with a citric acid solution having a mass concentration of 2% to 5%; The pore-forming agent consists of urea and ammonium bicarbonate in a mass ratio of 1:(1-2).

4. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 1, characterized in that: The mass ratio of the zinc slag to the composite reducing agent is 10:(3~4); the added amount of the pore-forming agent is 2%~4% of the total mass of the zinc slag and the composite reducing agent; the added amount of the binder is 3%~5% of the total mass of the zinc slag and the composite reducing agent; the added amount of water makes the moisture content of the granulated material 8%~12%; the diameter of the cavity pellet is 12~20 mm, and the strength is ≥8N.

5. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 1, characterized in that: The temperature of the low-temperature section is 600~800℃, and the residence time is 20~30min; the weak reducing atmosphere is a mixture of CO and N2, wherein the volume fraction of CO is 10%~15%, and the volume fraction of N2 is 85%~90%; water vapor is intermittently sprayed into the low-temperature section, with an injection cycle of 2~5min, a single injection volume of 0.08~0.12L / min, and a single duration of 25~35s.

6. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 5, characterized in that: The composition of the weak reducing atmosphere, the frequency of water vapor injection, and the converter speed are regulated according to the O2 volume fraction and the CO / CO2 volume ratio in the low-temperature section system, and a three-speed adjustment mechanism is set: First gear: when the O2 volume fraction is less than 0.2% and the CO / CO2 volume ratio is greater than 1.5, the CO volume fraction in the weak reducing atmosphere is adjusted to 10-11%, the water vapor injection cycle is 4.5-5.5 minutes, and the converter speed is 0.8-1.2 rpm. The second gear: when the O2 volume fraction is 0.2-0.5% and the CO / CO2 volume ratio is 1-1.5, the CO volume fraction in the weak reducing atmosphere is regulated to 12-13%, the water vapor injection cycle is 2.5-3.5 minutes, and the converter speed is 1.2-1.6 rpm. The third gear: when the O2 volume fraction is greater than 0.5% and the CO / CO2 volume ratio is less than 1, the CO volume fraction in the weak reducing atmosphere is adjusted to 14-15%, the water vapor injection cycle is 1.5-2.5 minutes, and the converter speed is 1.8-2.2 rpm. When the O2 volume fraction and the CO / CO2 volume ratio are at different gears, the higher gear is used for execution.

7. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 1, characterized in that: The temperature of the high-temperature section is 1100-1200°C, and the residence time is 30-50 minutes; the strong reducing atmosphere is a mixture of CO and H2, and the volume ratio of CO to H2 is (1.8-2.2):

1.

8. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 1, characterized in that: The temperature of the coolant contact zone of the first-stage condensation is 250~300°C, and the coolant spray flow rate is 0.4~0.6L / min; the condensation wall temperature of the second-stage condensation is 50~80°C; the condensation is carried out under a slight negative pressure of -50~-200Pa or an inert atmosphere, and the total average residence time is 1~3s.

9. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 1, characterized in that: The steam enters the secondary condensation system through a tapered guide channel, and the steam inlet flow rate at the tapered guide channel is controlled to be 3-5 m / s, the outlet flow rate is 6-10 m / s, and the residence time is 2-4 s; a swirl inducing blade is provided on the inner wall of the junction between the outlet of the guide channel and the inlet of the secondary condensation system, and the blade inclination angle is 25-40 degrees, so that the steam rotates when entering the first-stage condensation.

10. The method for efficiently recovering metallic zinc from zinc slag using a rotary hearth furnace according to claim 1, characterized in that: The particle size of the metallic zinc particles is 0.1-1 mm, the purity is ≥99%, and the zinc recovery rate is ≥98.7%.