Method for simultaneously degrading thiocyanate in cyanide tailings by oxidation in suspension

Abstract

This invention discloses a method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment, belonging to the field of pollutant treatment technology in the field of precious metal beneficiation and smelting. The method includes the following steps: (1) Cyanide tailings are crushed to D90≤0.15mm, graded by vibrating screen, and the proportion of particles <0.038mm is controlled at 35%-45%; (2) Fe3O4 nanoparticles are synthesized by co-precipitation method, and then MnO2 nanosheets are epitaxially grown by hydrothermal method to obtain catalyst. Finally, the crushed cyanide tailings are mixed with the catalyst; (3) The cyanide tailings mixed with the catalyst are treated by suspension oxidation system; the temperature of the preheating section is 200℃-300℃, the temperature of the main reaction section is 450℃-550℃, and finally treated by slow cooling section to achieve gradient cooling; (4) Sodium persulfate solution is sprayed and atomized in the slow cooling section; (5) Ammonia water is recovered, wet desulfurization is performed, and the catalyst is recovered by magnetic separation. After treatment, cyanide and thiocyanate are removed from the cyanide tailings and recycled. The method of this invention enables simultaneous decyanation and degradation of thiocyanate in cyanide tailings.

Description

Technical Field

[0001] This invention belongs to the field of pollutant treatment technology in the field of precious metal beneficiation and smelting, and specifically relates to a method for simultaneously degrading thiocyanate in cyanide tailings by utilizing suspended oxidation. Background Technology

[0002] As a major gold producer, my country's annual gold output relies heavily on cyanide gold extraction technology due to its irreplaceable advantages and relatively mature process. However, the cyanide tailings produced by the cyanide process are difficult to recycle directly, leading many companies to stockpile them to save costs, resulting in resource waste and environmental pollution. The state has already enacted relevant laws and regulations; in the "Identification Standard for Solid Waste - General Rules" (GB34330-2017), cyanide tailings have been classified as hazardous waste, urgently requiring relevant technical personnel to take effective measures to address the environmental hazards caused by the large-scale stockpiling of cyanide tailings.

[0003] On March 1, 2018, the Environmental Protection Standard HJ 943-2018, "Technical Specification for Pollution Control of Cyanide Slag in the Gold Industry," was officially released and implemented. Standard HJ 943-2018 comprehensively considers cyanide removal technology with the utilization and disposal of cyanide slag, and lists various cyanide removal treatment technologies in the appendix. Currently, the treatment of cyanide tailings in China mainly refers to cyanide wastewater degradation methods, with the most widely used cyanide-breaking methods including alkaline chlorination, the INCO method, and the hydrogen peroxide oxidation method. The alkaline chlorination method utilizes chlorine-containing agents such as chlorine gas, liquid chlorine, hypochlorite, and bleaching powder to oxidize and decompose cyanide into low-toxicity or non-toxic substances under alkaline conditions. In the harmless treatment process, hypochlorite ions in the solution play a major oxidizing role. However, this method of treating cyanide consumes a high amount of chlorine, and chlorine-based oxidants are highly irritating and corrosive, posing certain risks during transportation and use. It also requires strict control of the reaction pH to maintain alkalinity to prevent the formation of toxic gases such as hydrogen cyanide and hydrogen chloride, and consumes large amounts of caustic soda and sodium hypochlorite. The INCO method oxidizes cyanide to cyanate using a mixture of SO2 and air under catalytic conditions. It is effective for treating cyanide and the reagents are inexpensive; however, the reaction with thiocyanate is slow under the same conditions, and patent fees are high. The hydrogen peroxide oxidation method utilizes the strong oxidizing properties of hydrogen peroxide under alkaline conditions to oxidize cyanide to cyanate. Ferric cyanide complexes in the solution react with dissociated zinc and copper ions to form precipitates, thus achieving removal. However, hydrogen peroxide reagent itself is expensive and transportation risks are high. Thermal treatment methods have significant effects on degrading cyanide tailings and their toxic and harmful components, offering advantages such as wide applicability, large processing capacity, and ease of operation, and have been widely discussed in the precious metal beneficiation industry. However, the application scope of this technology is relatively narrow both domestically and internationally, the corresponding technical theory still needs to be improved, and most methods have complex processing procedures and high energy consumption, making them unsuitable for the treatment of cyanide tailings in domestic gold enterprises.

[0004] In summary, due to high operating costs, complex processes, and secondary pollution from reagents, no effective technology has yet been successfully applied to the treatment of industrial cyanide tailings. Therefore, there is an urgent need for new and effective technologies for treating cyanide tailings. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for simultaneous cyanide degradation and thiocyanate reduction in cyanide tailings through suspended oxidation, thereby achieving efficient oxidative decomposition of cyanide tailings and simultaneous degradation of thiocyanate during oxidative roasting.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment includes the following steps: (1) Raw material crushing and particle size control: A vertical roller mill was used to crush the cyanide tailings to a size of D90 ≤ 0.15 mm (specific surface area ≥ 450 m²). 2 / kg), and is classified by vibrating screen, with the proportion of ultrafine powder (particle size <0.038mm) controlled at 35%-45%.

[0007] (2) Catalyst preparation and loading: First, Fe3O4 nanoparticles were synthesized using a co-precipitation method: FeCl2·4H2O and FeCl3·6H2O were dissolved in deionized water, ammonia was added to adjust the pH to 9-11, and the reaction was carried out at 55℃-65℃. Fe3O4 particles were obtained by magnetic separation. Then, MnO2 nanosheets were epitaxially grown using a hydrothermal method: Fe3O4 was dispersed in KMnO4 solution, and a hydrothermal reaction was carried out at 110℃-120℃ to form an MnO2 nanosheet coating layer, thus preparing the catalyst (Fe3O4@MnO2). Finally, the crushed cyanide tailings were mixed with the catalyst.

[0008] (3) Suspension oxidation: The cyanide tailings mixed with the catalyst are treated by a suspended oxidation system. First, an N2 atmosphere is used in the preheating section with a temperature gradient of 200℃-300℃ to suppress the pre-oxidation of FeS2 to SO2. Then, a double-layer gas distribution plate is set in the main reaction section to introduce a mixed gas of O2, water vapor and N2. Finally, the mixture is treated by a slow cooling section to achieve gradient cooling (5℃ / min). The gradient cooling method can avoid the phase change of Fe3O4 that would lead to catalyst deactivation.

[0009] In the main reaction section, the temperature is set to 450℃-550℃ (preferably 480℃-520℃), and the residence time is 30min-50min; the water vapor partial pressure is ≥0.3MPa to promote sulfur curing, and the sulfur curing rate is ≥98%. The key reactions occurring in this stage are:

[0010] In the reaction formula, Fe-Mn represents the catalyst Fe3O4@MnO2 prepared in step (2).

[0011] (4) Secondary oxidation enhancement: In the slow cooling section between 150℃ and 200℃, an ultrasonic atomizing nozzle (frequency 28kHz) is used to spray and atomize the sodium persulfate solution, utilizing the residual heat of this stage to activate the decomposition of sodium persulfate.

[0012] Meanwhile, the residual thiocyanate in the cyanide tailings is degraded via the following pathway:

[0013] (5) Product processing and resource utilization: Firstly, exhaust gas purification is implemented, using a three-stage condenser to recover ammonia water for reuse in metallurgical processes. Simultaneously, SO2 emissions from the exhaust gas are controlled through wet desulfurization with Ca(OH)2, achieving an emission concentration of <50 mg / m³. 3 Secondly, solid-phase product separation is carried out, and a permanent magnet drum separator is used to recover the catalyst. The catalyst recovery rate is ≥92%, and the activity retention rate is >85% after 15 cycles.

[0014] After treatment, cyanide and thiocyanate are removed from the cyanide tailings, thus completing the harmless disposal of the cyanide tailings. The treated cyanide tailings fully meet the pollution control technical requirements for gold ore cyanide tailings backfilling in section 8.1 of the "HJ943-2018 Standard for Pollution Control of Cyanide Slag in Gold Industry". It can be used as a substitute raw material for backfill aggregate in underground backfilling. At the same time, the cyanide tailings treated by the suspension oxidation system have enhanced activity and excellent fluidity, and can also replace some cement raw materials, further increasing the prospects for resource utilization.

[0015] In step (1), the cyanide tailings originate from hazardous waste discharged from the gold beneficiation and smelting industry, particularly from cyanide tailings produced after the adoption of whole-sludge cyanidation gold extraction technology. These cyanide tailings are derived from the "gold-bearing sulfide ore—flotation—cyanidation" process, containing a large amount of cyanide and a small amount of useful minerals. The total cyanide content in this type of cyanide tailings is 150 mg / kg-2500 mg / kg. The cyanide in the cyanide tailings is mainly complexed cyanide, accounting for 70%-80% of the total cyanide content, while simple cyanide accounts for 20%-30% of the total cyanide content. The complexed cyanides include ferric cyanide complexes, copper cyanide complexes, lead cyanide complexes, zinc cyanide complexes, etc., with ferric cyanide complexes being the most prevalent.

[0016] The mineral composition includes quartz, feldspar, mica, calcite, dolomite, pyrite, chalcopyrite, galena, and sphalerite, among which quartz, feldspar, and mica account for no less than 45% of the total mineral mass, and calcite, dolomite, and other carbonate minerals account for 0.5%-15% of the total mineral mass.

[0017] The components in the cyanide tailings, by mass percentage, are 20%-60% SiO2, 0.2%-15% S, and the balance is Fe, Al, Ca, Mg, Na, S, K, Cu and Zn. The sulfur source minerals include metallic sulfide minerals such as pyrite, chalcopyrite, galena, and sphalerite, and their degree of liberation is over 90%.

[0018] In step (1), the cyanide tailings raw material is crushed and then dehydrated by a vacuum belt dewatering machine. The moisture content of the cyanide tailings is adjusted to 8%-12% to avoid clumping during subsequent suspended transport.

[0019] In step (2), the specific steps are as follows: First, Fe3O4 nanoparticles are synthesized by co-precipitation: FeCl2·4H2O and FeCl3·6H2O are dissolved in deionized water at a molar ratio of 1:2, ammonia is added to adjust the pH to 10, and the reaction is carried out at 55℃-65℃ for 2-3 hours. Fe3O4 particles with a particle size of 50nm-80nm are obtained by magnetic separation. Then, MnO2 nanosheets are epitaxially grown by hydrothermal method: Fe3O4 is dispersed in 0.1mol / L KMnO4 solution, and the hydrothermal reaction is carried out at 110℃-120℃ for 5-6 hours to form a MnO2 nanosheet coating layer with a thickness of 5nm-10nm, thus obtaining a catalyst (Fe3O4@MnO2) with an oxygen vacancy density ≥1.2×10 15 sites / cm 2 Finally, the crushed cyanide tailings are mixed with the catalyst.

[0020] In step (2), a twin-screw mixer is used to mix the crushed cyanide tailings and the catalyst at a mass ratio of 5:1. The mixer speed is 45 r / min and the mixing time is 20 min-30 min.

[0021] In step (3), the N2 gas flow rate in the preheating section is 1.0 m / s. 3 / h-1.2m 3 / h; The main reaction section is equipped with a double-layer gas distribution plate with a central aperture of 1.5mm and an edge aperture of 2.2mm. A mixture of O2, water vapor, and N2 is introduced, with O2 accounting for 20%-25% by volume, water vapor accounting for 70%, and N2 accounting for 5%-10%, and the gas flow rate is 3.0m. 3 / h, fluidized bed density 1.2g / cm³ 3 -1.5g / cm 3 .

[0022] In step (3), the suspended oxidation system uses a suspended oxidation roasting furnace. The cyanide tailings are fed into the oxidation system from the bottom of the suspended oxidation roasting furnace to undergo oxidation reaction, and the decomposition product is NO. x It can completely oxidize and degrade substances such as N2, CO, and CO2.

[0023] In step (3), after suspension oxidation treatment, CN in the cyanide tailings - Removal rate is 99.95%-99.99%, SCN - The removal rate is 99.1%-99.6%.

[0024] In step (4), the concentration of sodium persulfate solution is 0.6 mol / L-1.2 mol / L, the droplet size is ≤20 μm, and the coverage is ≥95%.

[0025] In step (5), a three-stage condenser is used to recover ammonia water with a temperature gradient of 80℃-25℃ and the concentration of recovered ammonia water is ≥12%.

[0026] In step (5), the sulfur dioxide is removed by wet desulfurization using Ca(OH)2 with a calcium-to-sulfur ratio of 1.2:1 and an emission concentration of <50 mg / m³. 3 A permanent magnet drum magnetic separator with a magnetic field strength of 0.8T is used.

[0027] The beneficial effects of this invention are: The high cyanide content, particularly high levels of complex cyanides with high chemical stability constants, is a significant concern in gold beneficiation tailings. Current biochemical methods, operating at room temperature or low temperatures, struggle to completely remove cyanide from these tailings. Most gold processing plants currently store this cyanide tailings in tailings ponds, posing a substantial threat to the environment and human health. Furthermore, domestic and international gold companies often neglect the thiocyanates in their cyanide tailings disposal processes, leading to ineffective treatment of these compounds. This invention utilizes a suspended oxidation system to simultaneously degrade various cyanides and thiocyanates in the tailings through a thermal activation-free radical oxidation coupling mechanism at high temperatures. During the main reaction stage at 450℃-550℃, the oxygen vacancies of the Fe3O4@MnO2 catalyst activate O2 and water vapor, reducing cyanide (CN) content. - ) oxidized to CO3 2- And N2, thiocyanate (SCN) - ) oxidized to SO4 2- and NO3 - In the slow cooling section (150℃-200℃), sodium persulfate solution is sprayed to activate SO4 using residual heat. 2- Free radicals, deep degradation of residual SCN - The degradation rate was increased to 99.95% (compared to conventional pyrolysis methods that only treat CN). - SCN - (Untreated). Existing heat treatment processes easily generate SO2 from sulfur during cyanide destruction, requiring additional desulfurization equipment. This invention addresses this by controlling the atmosphere (introducing N2 in the preheating section to inhibit sulfide pre-oxidation, and introducing high-concentration water vapor (70%) in the main reaction stage to promote the conversion of sulfides into SO4). 2- And catalyst interface optimization, Fe-Mn bimetallic catalysts promote the formation of sulfur intermediates (such as S2O3) through oxygen bridging bonds (Fe-O-Mn). 2-The conversion of sulfur to stable sulfate reduces energy consumption by 37% in the sulfur oxidation pathway, achieving highly efficient sulfur solidification (solidification rate ≥98.7%). This significantly reduces the cost of tail gas desulfurization, increases enterprise profits, and the treated cyanide tailings can be used as a substitute for backfill aggregate in underground backfilling. It can also replace some cement raw materials, increasing the prospects for resource utilization. This provides a new approach for the harmless disposal of related cyanide tailings and opens up a new path for gold production enterprises to solve industry pain points. The suspended oxidation system operates well and has a large processing capacity, making it fully suitable for large-scale industrial promotion. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of a method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation according to the present invention. Figure 2 This is a SEM image of the MnO2 coated particles in this invention; Figure 3 The above are the EDS spectra of three randomly selected MnO2 coated particles in this invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments.

[0030] In the following examples, the cyanide tailings are the cyanide tailings produced after the whole-sludge cyanidation gold extraction technology.

[0031] In the following examples, the cyanide tailings were treated by pressure filtration and had a moisture content of ≤15%.

[0032] In the following examples, the raw materials used to prepare the catalysts were all commercially available industrial-grade products.

[0033] The use of a suspended oxidation system to treat cyanide tailings involves factors such as oxidation temperature, oxidation time, oxidation atmosphere, catalyst type and dosage, and can be used to treat different types and contents of cyanide tailings depending on the specific case.

[0034] Example 1 A method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment, such as... Figure 1 As shown, it includes the following steps: The cyanide tailings were derived from cyanide tailings of a gold mine in Chifeng. After sampling and analysis, the tailings contained 27% SiO2, 0.25% MgO, 2.21% Al2O3, and 0.7% CaO by mass percentage. The total cyanide content was 1175 mg / kg, and the thiocyanate content was 150 mg / kg.

[0035] (1) Raw material pretreatment: The cyanide tailings are fed into a vertical roller mill and crushed to D90≤0.15mm. They are then classified by a vibrating screen to ensure that the proportion of ultrafine powder (particle size <0.038mm) is 35%-45%. A vacuum belt dewatering machine is used to adjust the moisture content of the cyanide tailings to 8% to avoid agglomeration during subsequent suspended transport.

[0036] (2) Catalyst preparation and loading: First, Fe3O4 nanoparticles were synthesized using a co-precipitation method: FeCl2·4H2O and FeCl3·6H2O were dissolved in deionized water at a molar ratio of 1:2, ammonia was added to adjust the pH to 10, and the reaction was carried out at 60℃ for 2 hours. Magnetic separation yielded Fe3O4 particles with a particle size of 50nm-80nm. Then, MnO2 nanosheets were epitaxially grown using a hydrothermal method: Fe3O4 was dispersed in a KMnO4 solution (0.1mol / L), and the reaction was carried out hydrothermally at 120℃ for 6 hours to form a 5nm-10nm thick MnO2 nanosheet coating layer. Figures 2-3 The catalyst Fe3O4@MnO2 with an oxygen vacancy density ≥1.2×10⁻⁶ was prepared. 15 sites / cm 2 Finally, a twin-screw mixer was used to mix the crushed cyanide tailings and catalyst at a mass ratio of 5:1. The twin-screw mixer rotated at 45 r / min and the mixing time was 20 min.

[0037] (3) Suspension oxidation: The cyanide tailings mixed with catalyst are treated by a suspended oxidation system; first, the mixture is fed into a preheating section (3m high), and N2 (flow rate 1.2m) is introduced. 3 / h), with a temperature gradient of 200℃-300℃ to suppress the pre-oxidation of FeS2 to SO2; then the preheated material enters the main reaction section (8m high). The main reaction stage is equipped with a double-layer gas distribution plate with a central aperture of 1.5mm and an edge aperture of 2.2mm, through which a mixed gas of O2 (20%), water vapor (70%), and N2 (10%) is introduced at a flow rate of 3.0m. 3 / h, fluidized bed density 1.2g / cm³ 3 -1.5g / cm 3 The temperature was 520℃ and the residence time was 30min. After the main reaction, the material entered the slow cooling section (4m high) and the temperature was reduced by gradient (5℃ / min) to avoid the deactivation of the catalyst caused by the Fe3O4 phase transformation.

[0038] (4) Secondary oxidation enhancement: In the slow cooling section between 150℃ and 200℃, an acoustic atomizing nozzle (frequency 28kHz) is used to spray and atomize sodium persulfate solution (concentration 1.2mol / L, droplet size ≤20μm), achieving a coverage of ≥95% and activating free radical reactions.

[0039] (5) Product processing and resource utilization: The exhaust gas is treated in a three-stage condenser (temperature gradient 80℃-25℃) to recover ammonia water (concentration ≥12%), which is then reused in the metallurgical process; wet desulfurization using Ca(OH)2 is performed, resulting in an emission concentration <50mg / m³. 3 The catalyst was recovered using a permanent magnet drum separator (magnetic field strength 0.8T) (recovery rate ≥92%). The leaching toxicity of the tailings was: CN. - ≤0.01mg / kg, SCN - Not detected; the treated cyanide tailings were used to prepare non-fired bricks (compressive strength ≥15MPa), which meets the JC / T422-2007 standard.

[0040] Example 2 A method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment includes the following steps: The cyanide tailings originated from a gold mine in Liaoning Province, with a total cyanide content of 2150 mg / kg and a thiocyanate content of 1250 mg / kg.

[0041] (1) Raw material pretreatment: The cyanide tailings are fed into a vertical roller mill and crushed to D90≤0.15mm. They are then classified by a vibrating screen to ensure that the proportion of ultrafine powder (particle size <0.038mm) is 35%-45%. A vacuum belt dewatering machine is used to adjust the moisture content of the cyanide tailings to 10%.

[0042] (2) Catalyst preparation and loading: The catalyst preparation and loading were the same as in Example 1.

[0043] (3) Suspension oxidation: The cyanide tailings mixed with catalyst are treated by a suspended oxidation system; first, the mixture is fed into a preheating section (3m high), and N2 (flow rate 1.2m) is introduced. 3 / h), with a temperature gradient of 200℃-300℃ to suppress the pre-oxidation of FeS2 to SO2; then the preheated material is fed into the main reaction section (8m high). The main reaction stage is equipped with a double-layer gas distribution plate with a central aperture of 1.5mm and an edge aperture of 2.2mm, through which a mixed gas of O2 (20%), water vapor (70%), and N2 (10%) is introduced at a flow rate of 3.0m. 3 / h, fluidized bed density 1.2g / cm³ 3 -1.5g / cm 3 The temperature is 480℃ and the residence time is 40min. After the main reaction, the material enters the slow cooling section (height 4m) and the temperature is reduced by gradient (5℃ / min).

[0044] (4) Secondary oxidation enhancement: In the slow cooling section between 150℃ and 200℃, an acoustic atomizing nozzle (frequency 28kHz) is used to spray sodium persulfate solution (concentration 0.8mol / L, droplet size ≤20μm) with a coverage of ≥95%, activating free radical reactions.

[0045] (5) Product processing and resource utilization: The exhaust gas is treated in a three-stage condenser (temperature gradient 80℃-25℃) to recover ammonia water (concentration ≥12%); SO2 emission concentration is <50mg / m³ via Ca(OH)₂ wet desulfurization. 3 Magnetic separation recovers the catalyst, and the tailings are used as cement admixtures (replacement rate 30%).

[0046] Testing revealed that the leaching toxicity of the tailings was: CN - ≤0.03mg / kg, SCN - Not detected.

[0047] Example 3 A method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment includes the following steps: The cyanide tailings originated from a gold mine in Shandong Province, with a total cyanide content of 2230 mg / kg and a thiocyanate content of 2080 mg / kg.

[0048] (1) Raw material pretreatment: The cyanide tailings are fed into a vertical roller mill and crushed to D90≤0.15mm. They are then classified by a vibrating screen to ensure that the proportion of ultrafine powder (particle size <0.038mm) is 35%-45%. A vacuum belt dewatering machine is used to adjust the moisture content of the cyanide tailings to 11%.

[0049] (2) Catalyst preparation and loading: The catalyst preparation and loading were the same as in Example 1.

[0050] (3) Suspension oxidation: The cyanide tailings mixed with catalyst are treated by a suspended oxidation system; first, the mixture is fed into a preheating section (3m high), and N2 (flow rate 1.2m) is introduced. 3 / h), with a temperature gradient of 200℃-300℃ to suppress the pre-oxidation of FeS2 to SO2; then the preheated material is fed into the main reaction section (8m high). The main reaction stage is equipped with a double-layer gas distribution plate with a central aperture of 1.5mm and an edge aperture of 2.2mm, through which a mixed gas of O2 (25%), water vapor (70%), and N2 (5%) is introduced at a flow rate of 3.0m. 3 / h, fluidized bed density 1.2g / cm³ 3 -1.5g / cm 3The temperature is 550℃ and the residence time is 45min. After the main reaction, the material enters the slow cooling section (height 4m) and the temperature is reduced by gradient (5℃ / min).

[0051] (4) Secondary oxidation enhancement: In the slow cooling section between 150℃ and 200℃, an acoustic atomizing nozzle (frequency 28kHz) is used to spray sodium persulfate solution (concentration 1.2mol / L, droplet size ≤20μm) with a coverage of ≥95%, activating free radical reactions.

[0052] (5) Product processing and resource utilization: The exhaust gas is treated in a three-stage condenser (temperature gradient 80℃-25℃) to recover ammonia water (concentration ≥12%); SO2 emission concentration is <50mg / m³ via Ca(OH)₂ wet desulfurization. 3 Magnetic separation recovers the catalyst, and the tailings are used for road base materials.

[0053] Testing revealed that the leaching toxicity of the tailings was: CN - ≤0.02mg / kg, SCN - Not detected.

[0054] Example 4 A method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment includes the following steps: The cyanide tailings originated from the cyanide tailings of a gold mine in Chifeng, with a total cyanide content of 1755 mg / kg and a thiocyanate content of 750 mg / kg.

[0055] (1) Raw material pretreatment: The cyanide tailings are fed into a vertical roller mill and crushed to D90≤0.15mm. They are then classified by a vibrating screen to ensure that the proportion of ultrafine powder (particle size <0.038mm) is 35%-45%. A vacuum belt dewatering machine is used to adjust the moisture content of the cyanide tailings to 8%.

[0056] (2) Catalyst preparation and loading: The catalyst preparation and loading were the same as in Example 1.

[0057] (3) Suspension oxidation: The cyanide tailings mixed with catalyst are treated by a suspended oxidation system; first, the mixture is fed into a preheating section (3m high), and N2 (flow rate 1.0m) is introduced. 3 / h), with a temperature gradient of 250℃-300℃ to suppress the pre-oxidation of FeS2 to SO2; then the preheated material is fed into the main reaction section (8m high). The main reaction stage is equipped with a double-layer gas distribution plate with a central aperture of 1.5mm and an edge aperture of 2.2mm, through which a mixed gas of O2 (18%), water vapor (70%), and N2 (12%) is introduced at a flow rate of 3.0m.3 / h, fluidized bed density 1.2g / cm³ 3 -1.5g / cm 3 The temperature is 500℃ and the residence time is 35min. After the main reaction, the material enters the slow cooling section (height 4m) and the temperature is reduced by gradient (5℃ / min).

[0058] (4) Secondary oxidation enhancement: In the slow cooling section between 150℃ and 200℃, an acoustic atomizing nozzle (frequency 28kHz) is used to spray sodium persulfate solution (concentration 0.6mol / L, droplet size ≤20μm) with a coverage of ≥95%, activating free radical reactions.

[0059] (5) Product processing and resource utilization: The exhaust gas is treated in a three-stage condenser (temperature gradient 80℃-25℃) to recover ammonia water (concentration ≥12%); SO2 emission concentration is <50mg / m³ via Ca(OH)₂ wet desulfurization. 3 Magnetic separation recovers the catalyst, and the tailings are used for backfilling in the well as a substitute for aggregate.

[0060] Testing revealed that the leaching toxicity of the tailings was: CN - ≤0.01mg / kg, SCN - Not detected.

[0061] Example 5 A method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment includes the following steps: The cyanide tailings originated from a gold mine in Yunnan Province, with a total cyanide content of 2880 mg / kg and a thiocyanate content of 1800 mg / kg.

[0062] (1) Raw material pretreatment: The cyanide tailings are fed into a vertical roller mill and crushed to D90≤0.15mm. They are then classified by a vibrating screen to ensure that the proportion of ultrafine powder (particle size <0.038mm) is 35%-45%. A vacuum belt dewatering machine is used to adjust the moisture content of the cyanide tailings to 10%.

[0063] (2) Catalyst preparation and loading: The catalyst preparation and loading were the same as in Example 1.

[0064] (3) Suspension oxidation: The cyanide tailings mixed with catalyst are treated by a suspended oxidation system; first, the mixture is fed into a preheating section (3m high), and N2 (flow rate 1.2m) is introduced. 3 / h), with a temperature gradient of 200℃-300℃ to suppress the pre-oxidation of FeS2 to SO2; then the preheated material is fed into the main reaction section (8m high). The main reaction stage is equipped with a double-layer gas distribution plate with a central aperture of 1.5mm and an edge aperture of 2.2mm, through which a mixed gas of O2 (24%), water vapor (70%), and N2 (6%) is introduced at a flow rate of 3.0m. 3 / h, fluidized bed density 1.2g / cm³ 3 -1.5g / cm 3 The temperature is 530℃ and the residence time is 50min. After the main reaction, the material enters the slow cooling section (height 4m) and the temperature is reduced by gradient (5℃ / min).

[0065] (4) Secondary oxidation enhancement: In the slow cooling section between 150℃ and 200℃, an acoustic atomizing nozzle (frequency 28kHz) is used to spray sodium persulfate solution (concentration 1.1mol / L, droplet size ≤20μm) with a coverage of ≥95%, activating free radical reactions.

[0066] (5) Product processing and resource utilization: The exhaust gas is treated in a three-stage condenser (temperature gradient 80℃-25℃) to recover ammonia water (concentration ≥12%); SO2 emission concentration is <50mg / m³ via Ca(OH)₂ wet desulfurization. 3 Magnetic separation recovers the catalyst, and the tailings are used for backfilling in the mine.

[0067] Testing revealed that the leaching toxicity of the tailings was: CN - ≤0.02mg / kg, SCN - Not detected.

[0068] The above description is merely a selected embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. Equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the specification shall still fall within the scope of the present invention.

Claims

1. A method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment, characterized in that, Includes the following steps: (1) Raw material crushing and particle size control: The cyanide tailings were crushed to D90≤0.15mm and classified by vibrating screen, with the proportion of particles <0.038mm controlled at 35%-45%. (2) Catalyst preparation and loading: Synthesis of Fe3O4 nanoparticles: FeCl2·4H2O and FeCl3·6H2O were dissolved in deionized water, the pH was adjusted to 9-11, and the reaction was carried out at 55℃-65℃. Fe3O4 particles were obtained by magnetic separation. MnO2 nanosheets were epitaxially grown using a hydrothermal method: Fe3O4 was dispersed in KMnO4 solution and hydrothermally reacted at 110℃-120℃ to form an MnO2 nanosheet coating layer, thus preparing a catalyst. The crushed cyanide tailings were mixed with the catalyst. (3) Suspension oxidation: The cyanide tailings mixed with catalyst are treated by a suspended oxidation system. First, an N2 atmosphere is used in the preheating section with a temperature gradient of 200℃-300℃ to suppress the pre-oxidation of FeS2 to SO2. Then, a double-layer gas distribution plate is set in the main reaction section, and a mixed gas of O2, water vapor and N2 is introduced, with the temperature set at 450℃-550℃. Finally, the residue is treated in a slow cooling section to achieve gradient cooling. (4) Secondary oxidation enhancement: In the slow cooling section between 150℃ and 200℃, an ultrasonic atomizing nozzle is installed to spray and atomize sodium persulfate solution. The residual heat in this stage is used to activate the decomposition of sodium persulfate. At the same time, the residual thiocyanate in the cyanide tailings is degraded. (5) Product processing and resource utilization: Ammonia water is recovered using a three-stage condenser and reused in metallurgical processes; simultaneously, SO2 emissions from the tail gas are controlled through wet desulfurization with Ca(OH)2, achieving an emission concentration of <50 mg / m³. 3 Magnetic separation for catalyst recovery; After treatment to remove cyanide and thiocyanate, the cyanide tailings can be used as a substitute raw material for backfill aggregate in underground backfilling or as a cement raw material.

2. The method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment according to claim 1, characterized in that, In step (1), the cyanide tailings raw material is crushed and dehydrated, and the moisture content is adjusted to 8%-12%.

3. The method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment according to claim 1, characterized in that, In step (2), the specific steps are as follows: First, Fe3O4 nanoparticles are synthesized by co-precipitation: FeCl2·4H2O and FeCl3·6H2O are dissolved in deionized water at a molar ratio of 1:2, ammonia is added to adjust the pH to 10, and the reaction is carried out at 55℃-65℃ for 2-3 hours. Fe3O4 particles with a particle size of 50nm-80nm are obtained by magnetic separation. Then, MnO2 nanosheets are epitaxially grown by hydrothermal method: Fe3O4 is dispersed in 0.1mol / L KMnO4 solution, and the hydrothermal reaction is carried out at 110℃-120℃ for 5-6 hours to form a MnO2 nanosheet coating layer with a thickness of 5nm-10nm, thus obtaining a catalyst with an oxygen vacancy density ≥1.2×10 15 sites / cm 2 Finally, the crushed cyanide tailings are mixed with the catalyst.

4. The method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment according to claim 1, characterized in that, In step (2), a mixer is used to mix the crushed cyanide tailings with the catalyst at a mass ratio of 5:

1.

5. The method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment according to claim 1, characterized in that, In step (3), the N2 gas flow rate in the preheating section is 1.0 m / s. 3 / h-1.2m 3 / h; The main reaction section is equipped with a double-layer gas distribution plate with a central aperture of 1.5mm and an edge aperture of 2.2mm. A mixture of O2, water vapor, and N2 is introduced, with O2 accounting for 20%-25% by volume, water vapor accounting for 70%, and N2 accounting for 5%-10%, and the gas flow rate is 3.0m. 3 / h, fluidized bed density 1.2g / cm³ 3 -1.5g / cm 3 .

6. The method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment according to claim 1, characterized in that, In step (4), the concentration of sodium persulfate solution is 0.6 mol / L-1.2 mol / L, the droplet size is ≤20 μm, and the coverage is ≥95%.

7. The method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment according to claim 1, characterized in that, In step (5), a three-stage condenser is used to recover ammonia water, with a temperature gradient from 80℃ to 25℃, and the concentration of recovered ammonia water is ≥12%.

8. The method for simultaneous degradation of thiocyanate in cyanide tailings by suspension oxidation treatment according to claim 1, characterized in that, In step (5), the desulfurization is carried out by Ca(OH)2 wet process with a calcium-to-sulfur ratio of 1.2:1; a permanent magnet drum separator is used with a magnetic field strength of 0.8T.

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