Green cooperative treatment method for heavy metal gypsum residues and secondary zinc oxide smoke dust

Abstract

The invention discloses a method for green cooperative treatment of heavy metal gypsum residues and secondary zinc oxide smoke dust, and belongs to the field of solid waste resource utilization. The secondary zinc oxide smoke dust, the heavy metal gypsum residues, sodium salt and a carbonaceous reducing agent are mixed and roasted, slow cooling is conducted after roasting is completed, and roasted products containing calcium carbonate and large-size zinc sulfide crystals are obtained. In the roasting process, the volatilization rates of toxic and harmful elements of fluorine, chlorine and arsenic reach 96.66%, 96.26% and 96.44% respectively, the vulcanization rate of zinc reaches 97.87%, toxic and harmful gases of SO2 and CO2 are not generated, zinc oxide and calcium sulfate are directionally converted into large-size ZnS crystals and CaCO3 which are easy to recover through flotation, flotation separation of valuable metals is easy to realize, no solid waste or harmful gas is generated, and the method is green and environment-friendly.

Description

Technical Field

[0001] The invention relates to a method for co-processing multiple solid wastes, in particular to a method for co-processing heavy metal gypsum sludge and secondary zinc oxide smoke, and belongs to the technical field of industrial solid waste resource utilization. Background Art

[0002] For lead, zinc and other sulfide ores in the prior art, pyrometallurgical processes are mainly used for desulfurization. In the process of SO2 flue gas acid production and other processes, a large amount of dirty acid is inevitably produced, which contains heavy metal ions such as arsenic, copper, lead, cadmium and harmful components such as fluoride. At present, lime neutralization method is generally used to treat dirty acid, which will produce a large amount of heavy metal gypsum slag, i.e., dirty acid slag. Dirty acid slag and desulfurized gypsum, phosphogypsum, fluorgypsum, etc. are all industrial by-product gypsum, the main chemical component of which is calcium sulfate, and contains heavy metal elements such as As, Cu, Pb, Cd, etc. It is a hazardous solid waste and is difficult to be utilized as a resource. At present, it is mainly stored or landfilled, which occupies land resources and has a huge environmental pollution risk. If the large amount of sulfur and calcium resources contained in gypsum slag can be reasonably utilized, it can not only effectively control secondary pollution, but also replace a large amount of primary mineral resources, achieve source reduction and resource recycling, which is of great significance to improve the quality and efficiency of the circular economy. On the other hand, a large amount of secondary zinc oxide smoke will be produced during the lead-zinc smelting process, which mainly comes from the boiling roasting process of zinc concentrate, the fume volatilization process of lead-zinc smelting slag and low-grade zinc oxide ore. The main component of secondary zinc oxide is zinc oxide, and the zinc content is generally 45% to 65%. It also contains lead (1% to 10%) and a small amount of heavy metals such as arsenic, copper, cadmium, indium, and non-metallic elements such as fluorine (0.1% to 5%) and chlorine (0.01% to 10%). Although secondary zinc oxide contains abundant valuable metals, it is difficult to realize the green comprehensive utilization of resources due to its complex chemical composition, the difficulty in separating toxic elements such as fluorine and chlorine, and the extremely fine mineral particle size. The current comprehensive recovery status is not ideal. With the continuous development and increasing depletion of mineral resources, secondary zinc oxide, as an important secondary zinc resource, has important comprehensive utilization value.

[0003] As the stock of heavy metal gypsum slag and secondary zinc oxide dust in the prior art becomes increasingly large, there is no efficient, economical and green coordinated disposal solution. Therefore, it is of great significance to seek a method for realizing the comprehensive utilization of heavy metal gypsum slag and secondary zinc oxide dust and the efficient separation and recovery of valuable metals. Chinese patent CN 106755961A discloses a method for recovering lead and zinc by stepwise sulfurization roasting-flotation of difficult-to-treat zinc oxide materials; the main problems are: ① the sulfurization roasting process requires the addition of a sulfurizing agent (sulfur, pyrite), ② a large amount of carbon dioxide gas is generated during the roasting process, and ③ the general sulfurization roasting product has a small grain size and is difficult to meet the flotation requirements. Chinese patent CN 110983029 B discloses a method for co-sulfiding and roasting lead-zinc smelting slag and gypsum slag, wherein the lead-zinc smelting slag, gypsum slag and a carbonaceous reducing agent are mixed for reduction sulfiding roasting, and the gypsum slag is used as a sulfiding agent to directionally convert heavy metals such as lead and zinc in the lead-zinc smelting slag into metal sulfides that are easy to be separated by flotation, while the calcium in the gypsum slag reacts with the iron and silicon compounds in the lead-zinc smelting slag to generate calcium ferrite and calcium silicate compounds. The method has the following problems: ① a large amount of carbon dioxide gas is generated during the roasting process; ② it only obtains a sulfiding roasting product, but does not perform sulfide ore grain control; ③ the sulfiding roasting temperature is as high as 700-1000°C, and the energy consumption cost is high. Summary of the invention

[0004] In view of the technical difficulties that the sulfurization roasting-flotation technology in the prior art cannot avoid the generation of poisonous gases such as sulfur dioxide or carbon dioxide, the addition of a sulfurizing agent (sulfur, calcium sulfide, iron sulfide, etc.) is required, and the sulfurization roasting product is not conducive to subsequent flotation separation due to its small grain size, the purpose of the present invention is to provide a method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke. The method uses the idea of ​​"treating waste with waste" and uses the high content of calcium sulfate in the heavy metal gypsum slag as a sulfurizing agent. During the reduction roasting process, the elemental zinc in the heavy metal gypsum slag and the secondary zinc oxide smoke is selectively sulfurized to zinc sulfide, while calcium is directionally converted into calcium carbonate, and the poisonous elements F, Cl, and As are volatilized and separated; there is almost no release of carbon dioxide and sulfur dioxide gas in the whole process; in addition, by adding sodium salt roasting and reducing the cooling rate during the roasting process to achieve grain size control of the sulfurization product, 5-10μm grains can be obtained, providing basic conditions for subsequent flotation separation of sulfides.

[0005] In order to achieve the above technical objectives, the present invention provides a method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide dust, the method comprising: mixing and roasting secondary zinc oxide dust, heavy metal gypsum slag, sodium salt and a carbonaceous reducing agent, and slowly cooling after roasting to obtain a roasting product containing calcium carbonate and large-sized zinc sulfide crystals.

[0006] The large-sized zinc sulfide crystals of the present invention are zinc sulfide crystals with a particle size of more than 5 microns, for example, zinc sulfide crystals with a particle size in the range of 5 to 10 microns, and more preferably zinc sulfide crystals with a particle size of about 10 microns.

[0007] The present invention roasts heavy metal gypsum slag, secondary zinc oxide smoke, carbonaceous reducing agent and sodium salt. During the roasting process, poisonous elements F, Cl and As are mainly removed by volatilization, while ZnO and CaSO4 are directionally converted into ZnS and CaCO3. Then, the grain size of the sulfide product is controlled by regulating the sodium salt and reducing the cooling rate. The crystal of the sulfide ore can be grown from 5μm to 10μm, which provides a prerequisite for the subsequent flotation separation of sulfide.

[0008] It should be noted that the theoretical basis for the directional conversion of ZnO and CaSO4 into ZnS and CaCO3 in the present invention is shown in the CaSO4-ZnO-CO system phase diagram ( Figure 1 ) and the equilibrium phase composition diagram of zinc oxide sulfide ( Figure 2 ). Figure 1 It shows that when the molar ratio of CaSO4 / (CaSO4+ZnO) is in the range of 0-0.5 and the temperature is between 530℃ and 830℃, the zinc metal in the system exists in the form of zinc sulfide and the calcium exists in the form of calcium carbonate. Therefore, theoretically, by adjusting the roasting temperature and the amount of calcium sulfate, it is possible to achieve the directional conversion of calcium sulfate and zinc oxide into zinc sulfide and calcium carbonate respectively. Figure 2 It shows that when the temperature is in the range of 500℃ to 800℃, the equilibrium phases are ZnS, CaCO3 and CO2. When the temperature exceeds 800℃, calcium sulfate is preferentially reduced to form CaS, and the generated calcium carbonate also decomposes to produce CaO and CO2. This also shows that the directional conversion of ZnO and CaSO4 in heavy metal gypsum slag and zinc oxide dust into ZnS and CaCO3 is theoretically feasible.

[0009] The specific reactions of the roasting process of the present invention are: CaSO4+2C=CaS+2CO2(g)(1), ZnO+CaS=CaO+ZnS(2), NaSO4+4C=Na2S+4CO(3), NaSO4+4CO=Na2S+4CO2(4), ZnO+Na2S→ZnS+Na2O(5), CaO+CO2=CaCO3(6).

[0010] The innovations of the present invention are as follows: ① Using the innovative idea of ​​"treating waste with waste", calcium sulfate in heavy metal gypsum slag is used as the vulcanizing agent required in the vulcanization roasting process, without the need to add additional vulcanizing agent; ② During the vulcanization roasting process, elemental zinc and calcium are directional converted into zinc sulfide and calcium carbonate, respectively, providing a basis for subsequent flotation separation and purification of zinc sulfide; ③ By adding sodium salt, the viscosity of the reaction system can be effectively reduced and the vulcanization reaction can be promoted, which is beneficial to the growth of the grains of the vulcanization product and the improvement of the zinc vulcanization rate; ④ By reducing the cooling rate, the grain growth of the vulcanization product is further promoted. ⑤ No harmful gases such as sulfur dioxide and carbon dioxide are produced.

[0011] As a preferred solution, the mass ratio of the heavy metal gypsum slag to the secondary zinc oxide dust is 1 to 3. The main component of heavy metal gypsum sludge is calcium sulfate, while the main component of secondary zinc oxide dust is zinc oxide. The ratio of heavy metal gypsum sludge to secondary zinc oxide dust can be determined based on the ratio of calcium sulfate and zinc oxide contained therein. The minimum dosage of heavy metal gypsum sludge should ensure that all zinc oxide in the secondary zinc oxide dust is converted into zinc sulfide. However, excessive dosage of heavy metal gypsum sludge will lead to excessive calcium sulfide, which is not conducive to the subsequent flotation separation of zinc sulfide. The mass ratio of heavy metal gypsum slag to secondary zinc oxide dust is further preferably m (heavy metal gypsum slag): m (secondary zinc oxide dust) = 1.5 to 2. The main components and mass contents in heavy metal gypsum sludge are: CaSO4 55 to 80%, ZnO 1 to 5%, fluorine-containing compounds 1% to 5%, chlorine-containing compounds 1 to 5%, and As compounds 1 to 5%. The main components and mass contents of the secondary zinc oxide fume are: ZnO 50-70%, zinc sulfate ≤5%, fluorine-containing compounds 2%-5%, chlorine-containing compounds 1-5%, and As compounds 2-5%.

[0012] As a preferred solution, the amount of the carbonaceous reducing agent is 10% to 40% of the total mass of the heavy metal gypsum sludge and the secondary zinc oxide dust. If the mass ratio of the carbonaceous reducing agent is too high, zinc oxide will be reduced to a metal element and volatilized and lost. If the mass ratio of the carbonaceous reducing agent is too low, it will not only be unfavorable for the conversion of calcium sulfate into calcium sulfide, thereby affecting the sulfidation of zinc, but also cause the generation of sulfur dioxide. The amount of the carbonaceous reducing agent is further preferably 20% to 25% of the total mass of the heavy metal gypsum slag and the secondary zinc oxide dust. The carbonaceous reducing agent is, for example, carbon powder.

[0013] As a preferred embodiment, the sodium salt includes at least one of sodium chloride, sodium carbonate and sodium sulfate.

[0014] As a preferred solution, the amount of sodium salt is 5% to 10% of the total mass of heavy metal gypsum sludge and secondary zinc oxide dust. Sodium salt is mainly used to promote the growth of sulfidation product grains and improve the sulfidation rate of zinc. The amount of sodium salt is further preferably 6% to 9% of the total mass of heavy metal gypsum sludge and secondary zinc oxide dust. The addition of sodium salt can be converted into sodium sulfate with calcium sulfate, and sodium sulfate can produce sodium sulfide through reactions (3) and (4) during the roasting process. It can react quickly at a lower temperature (5), thereby shortening the time required for the sulfidation roasting reaction; at the same time, the introduction of sodium salt can effectively reduce the viscosity of the reaction system, which is conducive to the aggregation and growth of fine particles of sulfidation products, and then promote the subsequent flotation separation of zinc sulfide and calcium carbonate. If the amount of sodium salt is too small, it is not conducive to the full growth of sulfidation product grains and the rapid progress of sulfidation reaction. If the amount of sodium salt is too high, it is easy to cause waste of resources and is not conducive to the subsequent flotation wastewater treatment. The sodium salt is further preferably sodium sulfate.

[0015] As a preferred solution, the calcination conditions are: calcination for 60 to 180 minutes at a temperature of 600 to 800° C. under a protective atmosphere. The calcination temperature is further preferably 660 to 760° C. The calcination time is further preferably 90 to 120 minutes. As a more preferred solution, the protective atmosphere is provided by flowing nitrogen and / or inert gas, and the flow rate of nitrogen and / or inert gas is 0.2 to 3 L / min. Inert gas is, for example, argon. The flow rate of inert gas and / or nitrogen is further preferably 1 to 2 L / min. The introduction of flowing inert gas or nitrogen can not only isolate oxygen, but also facilitate the volatilization of harmful substances during the calcination process. As the calcination temperature increases, it is beneficial to the progress of reactions (1) to (3) and the volatilization of poisonous elements, but too high a calcination temperature easily leads to the decomposition of calcium sulfate and calcium carbonate to produce sulfur dioxide and carbon dioxide, which cannot fully sulfide zinc oxide and will also cause environmental pollution. Similarly, a suitable roasting time is conducive to the progress of reactions (1) to (3) and the volatilization of poisonous elements, so that calcium sulfate and zinc oxide are fully converted into calcium carbonate and zinc sulfide. However, if the roasting time is too long, it will also increase the cost and be unfavorable for production.

[0016] As a preferred solution, the slow cooling rate is 0.5℃ / min~10℃ / min. Reducing the cooling rate is conducive to the further growth of the grains of the sulfide product, thereby providing basic conditions for the subsequent flotation separation process. If the slow cooling rate is too low, it is easy to reduce production efficiency and is not conducive to production; if the slow cooling rate is too high, it is not conducive to the full growth of the grains of the sulfide product. The slow cooling rate is further preferably 0.5℃ / min~5℃ / min; most preferably 0.5℃ / min~1℃ / min

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0018] 1) The present invention proposes a synergistic sulfurization roasting process for heavy metal gypsum slag and secondary zinc oxide dust for the first time, thereby realizing the directional conversion of zinc and calcium elements in the heavy metal gypsum slag and secondary zinc oxide dust into ZnS and CaCO3, and efficiently removing the poisonous elements F, Cl, and As. At the same time, the regulation of zinc sulfide crystals is realized, which is beneficial to obtaining large-sized zinc sulfide crystal particles and facilitating the subsequent flotation separation process.

[0019] 2) The present invention can effectively avoid the generation of harmful SO2 gas and CO2 greenhouse gas during the coordinated roasting process of heavy metal gypsum slag and secondary zinc oxide smoke.

[0020] 3) The present invention utilizes the idea of ​​treating waste with waste to achieve the coordinated disposal of heavy metal gypsum sludge and secondary zinc oxide smoke, thereby realizing the resource utilization of the two solid wastes.

[0021] 4) The present invention adjusts the grain size of zinc sulfide by adding sodium salt and reducing the cooling rate to obtain large-sized zinc sulfide with a particle size of about 10 microns, which meets the requirements of flotation.

[0022] 5) The present invention shortens the sulfurization reaction time by adding sodium salt.

[0023] 6) The process of the present invention is simple, has low energy consumption and little pollution, and provides a prerequisite for subsequent flotation separation of sulfides.

[0024] In summary, the present invention proposes for the first time a "waste-to-waste" treatment scheme for heavy metal gypsum sludge and secondary zinc oxide dust. Through the sulfidation roasting process, the removal rate of poisonous elements F, Cl, and As reaches more than 96%, and the zinc and calcium elements are directionally converted into ZnS and CaCO3, respectively. The zinc sulfidation rate reaches 97.89%, and the grain size of the sulfuric acid product grows from 5μm to 10μm, which provides a prerequisite for the subsequent flotation separation of sulfides and solves the problem of resource utilization of heavy metal gypsum sludge and secondary zinc oxide dust. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The phase diagram of the CaSO4-ZnO-CO system of the present invention is the synergistic zinc sulfidation of heavy metal gypsum slag and secondary zinc oxide smoke.

[0026] Figure 2 This is the equilibrium phase composition diagram of the heavy metal gypsum slag and secondary zinc oxide smoke in the present invention in the coordinated zinc sulfidation.

[0027] Figure 3 The present invention is a process flow chart for the coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke.

[0028] Figure 4 The figure is the XRD diagram of the sulfurization roasting product of heavy metal gypsum slag and secondary zinc oxide smoke of the present invention.

[0029] Figure 5 The FTIR spectra of gas phase products during the sulfurization roasting process of heavy metal gypsum slag and secondary zinc oxide smoke at different temperatures of the present invention are shown.

[0030] Figure 6 It is the SEM of the roasting product of heavy metal gypsum slag and secondary zinc oxide smoke in the coordinated roasting process of the present invention without adding sodium salt (a) and with adding sodium salt (b).

[0031] Figure 7 The SEM images of the heavy metal gypsum slag and secondary zinc oxide fume in the co-roasting process of the present invention are taken at cooling rates of 5°C / min (a) and 1°C / min (b). DETAILED DESCRIPTION

[0032] The following will illustrate the content of the present invention in conjunction with specific embodiments, rather than limiting the protection scope of the claims of the present invention.

[0033] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. Unless otherwise specified, in the following specific embodiments, the relevant percentages refer to mass percentages.

[0034] Example 1

[0035] The vulcanizing agent used in this embodiment is the heavy metal gypsum slag produced by the neutralization and treatment of waste acid in a lead-zinc smelter. The specific composition is shown in Table 1. The main component of the slag is calcium sulfate, with a content of about 78%; the secondary zinc oxide smoke used in this embodiment is produced by a lead-zinc smelter. The specific composition is shown in Table 2. The main element in the slag is zinc, with a content of 54.59%;

[0036] Table 1 Analysis results of chemical composition of heavy metal gypsum sludge.

[0037]

[0038] Table 2 Chemical composition analysis results of secondary zinc oxide.

[0039]

[0040] according to Figure 3 The specific treatment process of heavy metal gypsum sludge and secondary zinc oxide dust includes the following steps:

[0041] S1. Firstly, the heavy metal gypsum slag and secondary zinc oxide to be treated are proportioned, and then carbon powder and sodium sulfate are added and ground evenly. Specifically, m(heavy metal gypsum slag):m(secondary zinc oxide dust)=1.6, the amount of carbon powder is 23%, and the amount of sodium sulfate is 8%.

[0042] S2, the ground mixed material was co-roasted at a temperature of 750°C, the inert gas was nitrogen, the inert gas flow rate was 1.5 L / min, and the roasting time was 100 min to obtain a sulfurized roasted product 1 ( Figure 4 ) and volatile products (a mixture of F, Cl, and As), of which the sulfidation rate of zinc reached 97.87%, and the volatility rates of F, Cl, and As reached 96.66%, 96.26%, and 96.44%, respectively. The whole process produced almost no sulfur dioxide and carbon dioxide gas ( Figure 5 ).

[0043] S3, the sulfurized roasted product 1 was slowly cooled at a cooling rate of 1°C / min, and the grain size of the final sulfurized product increased from 5μm to 10μm ( Figure 6 ).

[0044] Example 2

[0045] Example 1 was repeated, except that m(heavy metal gypsum slag):m(secondary zinc oxide dust)=1.4 in S1, and the other conditions remained unchanged. The results showed that the zinc sulfidation rate was 93.86%, indicating that increasing m(heavy metal gypsum slag) was beneficial to more fully sulfiding the zinc element during the roasting process, thereby improving the zinc sulfidation rate.

[0046] Example 3

[0047] Example 1 was repeated, except that m(heavy metal gypsum slag):m(secondary zinc oxide dust) in S1 = 1.7, and the other conditions remained unchanged. The results showed that the zinc sulfidation rate was 97.86%, indicating that further increasing m(heavy metal gypsum slag) was not very meaningful in improving the zinc sulfidation rate.

[0048] Example 4

[0049] Example 1 was repeated, except that the amount of carbon powder in S1 was 20%, and the other conditions remained unchanged. The results showed that the zinc sulfidation rate was 92.98%, indicating that the addition of carbon powder was beneficial to the progress of reactions ① to ④ during the roasting process, promoting more complete sulfidation of zinc elements, thereby increasing the zinc sulfidation rate.

[0050] Example 5

[0051] Example 1 was repeated, except that the amount of carbon powder in S1 was 25%, and the other conditions remained unchanged. The results showed that the zinc sulfidation rate was 97.88%, indicating that it was not meaningful to continue to increase the carbon powder to facilitate the progress of reactions ① to ④ during the roasting process. On the contrary, too much carbon powder could easily cause zinc oxide to be reduced to elemental zinc, and could not fully sulfidate the zinc element.

[0052] Example 6

[0053] Example 1 was repeated, except that the amount of sodium sulfate in S1 was 5%, and the other conditions remained unchanged. The results showed that the time for the zinc sulfidation rate to reach about 97% was 120 minutes, indicating that increasing the amount of sodium sulfate was conducive to promoting the rapid progress of the sulfidation reaction, so that the zinc was fully sulfided in a short time.

[0054] Example 7

[0055] Example 1 was repeated, except that the amount of sodium sulfate in S1 was 10%, and the other conditions remained unchanged. The results showed that the time for the zinc sulfidation rate to reach about 97% was 100 minutes, indicating that further increasing the amount of sodium sulfate could not further accelerate the sulfidation reaction. On the contrary, excessive sodium sulfate could easily bring negative effects to the subsequent flotation separation process of sulfides, such as the treatment of flotation wastewater was complicated and costly.

[0056] Example 8

[0057] Example 1 was repeated, except that the calcination temperature in S2 was 700°C, and the other conditions remained unchanged. The results showed that the volatilization rates of the poisonous elements F, Cl, and As were 76.32%, 72.11%, and 93.41%, respectively, and the sulfidation rate of zinc was 90.39%, indicating that appropriately increasing the calcination temperature is beneficial to the removal of the poisonous elements and increasing the sulfidation rate of zinc.

[0058] Example 9

[0059] Example 1 was repeated, except that the calcination temperature in S2 was 800°C, and the other conditions remained unchanged. The results showed that the volatilization rates of the poisonous elements F, Cl, and As reached 96.63%, 96.27%, and 96.46%, respectively, and the sulfidation rate of zinc was 97.89%, indicating that further increasing the calcination temperature was not very meaningful for removing the poisonous elements and increasing the sulfidation rate of zinc, but instead increased energy consumption.

[0060] Example 10

[0061] Example 1 was repeated, except that the calcination time in S2 was 90 min, and the other conditions remained unchanged. The results showed that the volatilization rates of the poisonous elements F, Cl, and As reached 94.24%, 94.29%, and 94.44%, respectively, and the sulfidation rate of zinc was 96.21%, indicating that extending the calcination time was beneficial to the removal of the poisonous elements and the sulfidation of zinc.

[0062] Embodiment 11

[0063] Example 1 was repeated, except that the calcination time in S2 was 120 min, and the other conditions remained unchanged. The results showed that the volatilization rates of the poisonous elements F, Cl, and As reached 96.64%, 96.29%, and 96.45%, respectively, and the sulfidation rate of zinc was 97.91%, indicating that further extending the calcination time had no significant effect on the removal of the poisonous elements and the sulfidation of zinc.

[0064] Example 12

[0065] Example 1 was repeated, except that the slow cooling rate (natural cooling rate) in S2 was 5°C / min, and the other conditions remained unchanged. The results showed that the grain size of the sulfidation product was about 5 μm ( Figure 6 a), indicating that further reducing the cooling rate is beneficial to the increase of the grain size of the sulfide product.

[0066] Embodiment 13

[0067] Example 1 was repeated, except that the slow cooling rate (natural cooling rate) in S2 was 0.5°C / min, and the other conditions remained unchanged. The results showed that the grain size of the sulfidation product was about 10 μm ( Figure 6 b), indicating that further reducing the cooling rate does not have much significance for further increasing the grain size of the sulfide product.

[0068] Comparative Example 1

[0069] Example 1 was repeated, except that sodium sulfate was not added to S1, and the other conditions remained unchanged. The results showed that the grain size of the sulfidation product was concentrated below 5 μm ( Figure 7 a) Serious particle agglomeration ( Figure 7 a) and the sulfidation rate of zinc was only 96.11%, indicating that the addition of sodium sulfate is beneficial to reduce the viscosity of the reaction system ( Figure 7 b) It is conducive to the aggregation and growth of fine particles of sulfide products ( Figure 7 b) It is also beneficial to promote the rapid occurrence of vulcanization reaction within a certain period of time.

Claims

1. A method for green synergistic treatment of heavy metal gypsum slag and secondary zinc oxide dust, Features: The secondary zinc oxide smoke, heavy metal gypsum slag, sodium salt and carbonaceous reducing agent are mixed and roasted, and then slowly cooled after the roasting is completed to obtain a roasting product including calcium carbonate and large-sized zinc sulfide crystals.

2. A method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke according to claim 1, Features: The mass ratio of the heavy metal gypsum slag to the secondary zinc oxide smoke is 1-3.

3. A method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke according to claim 1, Features: The amount of the carbonaceous reducing agent used is 10% to 40% of the total mass of the heavy metal gypsum sludge and the secondary zinc oxide smoke.

4. A method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke according to claim 1, Features: The sodium salt includes at least one of sodium chloride, sodium carbonate and sodium sulfate.

5. A method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke according to claim 1 or 4, Features: The dosage of the sodium salt is 5% to 10% of the total mass of the heavy metal gypsum sludge and the secondary zinc oxide smoke.

6. A method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke according to any one of claims 1 to 4, Features: The calcination conditions are: calcination at 600-800° C. for 60-180 min under a protective atmosphere.

7. A method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke according to claim 6, Features: The protective atmosphere is provided by flowing nitrogen and / or inert gas, and the flow rate of nitrogen and / or inert gas is 0.2-3 L / min.

8. A method for green coordinated treatment of heavy metal gypsum slag and secondary zinc oxide smoke according to claim 1, Features: The slow cooling rate is 0.5°C / min to 10°C / min.

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