Method for recovering multiple metals from smelting slag through gradient roasting

Abstract

The invention provides a method for recovering multiple metals from smelting slag through gradient roasting, and relates to the field of comprehensive utilization of solid waste resources. Mixing the smelting slag, a slag former and a reducing agent to obtain a mixture, and carrying out gradient roasting on the mixture to obtain a volatile metal-containing material; and mixing the volatilized metal-containing material with the alkaline sulfide, and carrying out alkaline leaching to obtain an alkaline-leached solution. According to the method, the follow-up extraction difficulty is lowered, leaching wastewater discharge and reagent consumption are reduced, recovery of scattered metals such as gallium and germanium in the pyrogenic process smelting slag is achieved, the recovery rate of the scattered metals is increased, the economical efficiency and environmental protection benefits of comprehensive utilization of resources are optimized, and the method is suitable for industrial production. And a feasible technical solution is provided for resourceful treatment of the pyrogenic process smelting slag which is piled up for a long time.

Description

Technical Field

[0001] This application relates to the field of comprehensive utilization of non-ferrous metal solid waste resources, and particularly relates to a method for gradient roasting and recovering multiple metals from smelting slag. Background Art

[0002] Gallium and germanium, as strategic critical minerals, play an irreplaceable role in fields such as semiconductors and optoelectronics. However, their crustal abundances are extremely low, and independent ore deposits are scarce. They mainly exist in associated forms in main ores such as zinc, aluminum, and coal, and there are significant technical challenges in their efficient extraction and separation. Currently, the production of gallium and germanium mainly relies on hydrometallurgical processes, and their raw material sources are mainly the smelting slags generated during the hydrometallurgical processes of main metals such as zinc and aluminum. They are comprehensively recovered and extracted as by-products during the hydrometallurgical process by extending the main production process. This process flow is long, the enrichment ratio is low, the process is complex, the waste water volume is large, and efficient treatment technologies for directly comprehensively recovering and utilizing rare dispersed metals such as gallium and germanium from certain smelting slags have not been fully developed and applied.

[0003] In some sulfide ores such as zinc and copper, a certain amount of gallium and germanium are also associated and have great recovery value. However, during the pyrometallurgical process, due to the strong affinity between aluminum and gallium, and silicon and germanium, most of the associated gallium and germanium elements migrate and enrich in the smelting slag, resulting in the loss and waste of key rare dispersed metal resources such as gallium and germanium. At the same time, the main element contents such as iron, silicon, and aluminum in this type of pyrometallurgical slag are relatively high, and gallium and germanium are wrapped in the high-melting-point slag phase due to their strong affinity with aluminum and silicon. Traditional wet treatment requires strong acid leaching and consumes a large amount of reagents, with poor economy.

[0004] Currently, the efficient extraction technology for rare dispersed metals in pyrometallurgical slag is not yet mature, and there is an urgent need to develop a resource utilization process with a short process flow and low cost. Summary of the Invention

[0005] Aiming at the large amount of pyrometallurgical slag of copper and zinc, the low overall component recovery value, the low recovery rates of gallium and germanium in the existing treatment processes, especially the problems of large waste water volume and high content of miscellaneous salts in wet treatment, the purpose of this application is to provide a method for recovering multiple metals from pyrometallurgical slag, which can achieve the efficient comprehensive recovery of main valuable elements in the smelting slag, reduce the consumption of acids and alkalis in subsequent treatment, has a short process flow, and is economically efficient.

[0006] To achieve the above purpose, this application provides a method for gradient roasting and recovering multiple metals from smelting slag, including:

[0007] Mixing the smelting slag, slag-forming agent, and reducing agent to obtain a mixture, and subjecting the mixture to gradient roasting to obtain a volatilized metal-containing material;

[0008] Mix the volatilized metal-containing material with an alkaline sulfide and perform alkaline leaching to precipitate and remove lead, zinc, and copper, achieving separation from rare metals. Gallium and germanium are immersed in the solution to obtain the post-alkaline leaching solution;

[0009] The smelting slag includes one or more of zinc smelting slag, lead smelting slag, and copper smelting slag.

[0010] Optionally, the method for gradient roasting and recovering multiple metals from smelting slag satisfies at least one of the following conditions:

[0011] A. The slag-forming agent includes one or more of calcium oxide, silicon oxide, magnesium oxide, calcium carbonate, and magnesium carbonate;

[0012] B. The reducing agent includes anthracite and / or coke;

[0013] C. The alkaline sulfide includes sodium sulfide and / or ammonium sulfide.

[0014] Optionally, the method for gradient roasting and recovering multiple metals from smelting slag satisfies at least one of the following conditions:

[0015] A. The fineness of the smelting slag is greater than or equal to 80 wt% at -250 mesh;

[0016] B. The mass of the slag-forming agent is 10% - 40% of the mass of the smelting slag.

[0017] Optionally, the method for gradient roasting and recovering multiple metals from smelting slag satisfies at least one of the following conditions:

[0018] A. The mass of the reducing agent is 30% - 70% of the mass of the smelting slag;

[0019] B. The fixed carbon content of the reducing agent is greater than or equal to 50%.

[0020] Optionally, the oxygen content during the gradient roasting process is 20% - 50%.

[0021] Optionally, the gradient roasting includes a first roasting and a second roasting performed in sequence;

[0022] The maximum temperature of the first roasting is 1000°C - 1300°C, and the heat preservation time is 1 h - 4 h;

[0023] The maximum temperature of the second roasting is 1200°C - 1650°C, and the heat preservation time is 1 h - 4 h.

[0024] Optionally, a reducing agent is additionally added during the second roasting process.

[0025] Optionally, the mass of the reducing agent in the second roasting process is 10%-40% of the mass of the smelting slag.

[0026] Optionally, the pH of the alkali-leached solution is adjusted using sulfuric acid to obtain a solution to be extracted;

[0027] The solution to be extracted and the extractant are mixed, and gallium and germanium are separated and purified by extraction.

[0028] Optionally, in the method for recovering multiple metals from smelting slag by gradient roasting, the pH value of the solution to be extracted is 0.5-2.5.

[0029] Compared with the prior art, the advantages of this application include:

[0030] The present application provides a method for recovering multiple metals from smelting slag by gradient roasting. By adding a slag-forming agent and a reducing agent, the melting point of the smelting slag material can be effectively increased to above 1300°C, the phenomenon of melt hardening can be suppressed, the material fluidity can be ensured, the volatilization rate and recovery rate of the target elements can be increased, and at the same time, the oxides of gallium and germanium can be avoided from being reduced to metal elements, thereby reducing the volatility. Through gradient roasting, gallium, germanium, and zinc are volatilized into smoke dust in the form of low-valent oxides and elemental lead under high temperature and weak reducing atmosphere. The smoke dust is then mixed with alkaline sulfide to generate sulfide. Zinc, lead sulfide, and copper sulfide are precipitated, thereby separating the scattered metal gallium and germanium from lead and zinc, and further enriching gallium and germanium; compared with the direct wet leaching process, the method for recovering multiple metals from smelting slag by gradient roasting provided in the present application reduces the difficulty of subsequent extraction, reduces the discharge of leaching wastewater and reagent consumption, realizes the recovery of scattered metals such as gallium and germanium in pyrometallurgical slag, improves the recovery rate of scattered metals, optimizes the economic and environmental benefits of comprehensive resource utilization, and provides a feasible technical solution for the resource recovery of long-term stored pyrometallurgical slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope of the present application.

[0032] Figure 1 This is a schematic flow chart of the method for recovering multiple metals from smelting slag by gradient roasting provided in Example 1. DETAILED DESCRIPTION

[0033] As used herein:

[0034] "Prepared by..." is synonymous with "comprising". As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or apparatus comprising the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0035] The conjunctive "consisting of" excludes any unrecited element, step or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the claim body rather than immediately following the subject, it only limits the elements described in that clause; other elements are not excluded from the claim as a whole.

[0036] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, whether or not the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise indicated, the range is intended to include its end values and all integers and fractions within the range.

[0037] In these examples, unless otherwise specified, the parts and percentages are by mass.

[0038] "Parts by mass" refers to the basic measurement unit representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1 g or 2.689 g, etc. If we say that the mass of component A is a parts by mass and the mass of component B is b parts by mass, it means the mass ratio of component A to component B is a:b. Or, it means the mass of component A is aK and the mass of component B is bK (K is any number representing a multiple factor). It should not be misunderstood that, different from the number of parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0039] "And / or" is used to indicate that one or both of the stated situations may occur. For example, A and / or B includes (A and B) and (A or B).

[0040] This application provides a method for gradient roasting and recovering multiple metals from smelting slag, comprising:

[0041] Mix the smelting slag, slag-forming agent and reducing agent to obtain a mixture, and subject the mixture to gradient roasting to obtain a volatile metal-containing material;

[0042] In some embodiments, the smelting slag is finely ground and pretreated to fully release rare dispersed elements such as gallium and germanium wrapped by the slag components, improving the recovery efficiency of subsequent processes;

[0043] Mix the volatile metal-containing material and an alkaline sulfide, and perform alkali leaching to precipitate and remove zinc, lead, and copper, and immerse gallium and germanium into the solution to obtain a solution after alkali leaching; the smelting slag includes one or more of zinc smelting slag, lead smelting slag, and copper smelting slag.

[0044] It should be noted that zinc smelting slag, lead smelting slag, and copper smelting slag all contain zinc, lead, copper, gallium, and germanium, but the contents of each element are different.

[0045] In some alternative embodiments, the method for gradient roasting and recovering multiple metals from smelting slag satisfies at least one of the following conditions:

[0046] A. The slag-forming agent includes one or more of calcium oxide, silicon oxide, magnesium oxide, calcium carbonate, and magnesium carbonate;

[0047] It should be noted that the smelting slag is mainly oxides of iron, silicon, and aluminum, and its melting point is usually around 1000°C. During the roasting process, due to the increase in temperature, phenomena such as caking and melting are likely to occur, hindering the escape of valuable elements, and easily causing phenomena such as ring formation in roasting equipment such as rotary kilns, reducing the use effect and production efficiency of the equipment; by adding the above-mentioned slag-forming agent, the temperature of the material can be effectively increased to above 1300°C, suppressing melting and caking, ensuring the fluidity of the material, and increasing the volatilization rate and recovery rate of the target elements;

[0048] B. The reducing agent includes anthracite and / or coke;

[0049] It should be noted that after pyrometallurgical smelting, the main valuable metals in the smelting slag, such as zinc, lead, copper, gallium, and germanium, exist in the form of stable oxides that are difficult to volatilize. After adding a reducing agent, the following reduction reactions mainly occur when the smelting slag is roasted:

[0050] Ga2O3 + C = GaO + CO2;

[0051] GeO2 + C = GeO + CO2;

[0052] ZnO + C = Zn + CO2;

[0053] According to thermodynamic analysis, the boiling point of germanium monoxide is about 1200 °C, the boiling point of gallium monoxide is about 1500 °C, the boiling point of elemental zinc is about 907 °C, and the boiling point of lead oxide is about 1470 °C. Under high temperature and weak reducing atmosphere, gallium and germanium volatilize into the soot in the form of low-valent oxides and can be recovered through the dust collection equipment.

[0054] C. The basic sulfide includes sodium sulfide and / or ammonium sulfide.

[0055] In some alternative embodiments, the method for gradient roasting and recovering multi-metals from smelting slag satisfies at least one of the following conditions:

[0056] A. The fineness of the smelting slag with a mesh size of -250 is greater than or equal to 80 wt%.

[0057] Optionally, the fineness of the smelting slag with a mesh size of -250 can be 80 wt%, 85 wt%, 90 wt%, 95 wt% or any value greater than or equal to 80 wt%.

[0058] B. The mass of the slag-forming agent is 10% - 40% of the mass of the smelting slag.

[0059] Optionally, the mass of the slag-forming agent can be 10%, 20%, 30%, 40% or any value between 10% - 40% of the mass of the smelting slag.

[0060] In some alternative embodiments, the method for gradient roasting and recovering multi-metals from smelting slag satisfies at least one of the following conditions:

[0061] A. The mass of the reducing agent is 30% - 70% of the mass of the smelting slag.

[0062] Optionally, the mass of the reducing agent can be 30%, 40%, 50%, 60%, 70% or any value between 30% - 70% of the mass of the smelting slag.

[0063] It should be noted that by controlling the addition amount of the reducing agent, the reducing atmosphere in the roasting process is indirectly controlled to avoid reducing the oxides of gallium and germanium to metal elements and thus reducing the volatilization rate.

[0064] B. The fixed carbon content of the reducing agent is greater than or equal to 50%.

[0065] Optionally, the fixed carbon content of the reducing agent can be 50%, 60%, 70%, 80% or any value greater than or equal to 50%.

[0066] In some alternative embodiments, the oxygen content in the gradient roasting process is 20% - 50%.

[0067] Optionally, the oxygen content during the gradient roasting process can be 20%, 30%, 40%, 50%, or any value between 20% and 50%.

[0068] It should be noted that by controlling the oxygen atmosphere during the roasting process, it is possible to prevent the re-oxidation of GaO, GeO, and Zn during the long roasting process, which affects the volatilization rate. For example, it is possible to avoid the over-oxidation of GaO and GeO into non-volatile Ga2O3 and GeO2. By controlling the oxygen concentration, it is also possible to further ensure a weakly reducing atmosphere throughout the roasting process, thereby improving the recovery rate in subsequent processing.

[0069] In some alternative embodiments, the gradient roasting includes a first roasting and a second roasting carried out in sequence.

[0070] The maximum temperature of the first roasting is 1000°C - 1300°C, and the holding time is 1h - 4h.

[0071] Optionally, the maximum temperature of the first roasting can be 1000°C, 1100°C, 1200°C, 1300°C, or any value between 1000°C and 1300°C, and the holding time can be 1h, 2h, 3h, 4h, or any value between 1h and 4h.

[0072] The maximum temperature of the second roasting is 1200°C - 1650°C, and the holding time is 1h - 4h.

[0073] Optionally, the maximum temperature of the second roasting can be 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1650°C, or any value between 1200°C and 1650°C, and the holding time can be 1h, 2h, 3h, 4h, or any value between 1h and 4h.

[0074] It should be noted that in the first roasting stage, zinc and germanium oxides are preferentially volatilized, and in the second roasting stage, gallium and lead oxides are directionally enriched. It is also possible to reduce the encapsulation of gallium and lead to improve their volatilization effect, break through the limitations of traditional single-stage roasting, and achieve multi-metal cascade separation.

[0075] In some embodiments, the volatiles obtained by two-stage roasting volatilization can be subjected to alkali leaching separately. Exemplarily, the zinc and germanium oxides obtained from the first roasting are subjected to alkali leaching with an alkaline sulfide to obtain zinc sulfide precipitate and a germanium-containing solution; the elemental lead and gallium oxides obtained from the second roasting are subjected to alkali leaching with an alkaline sulfide to obtain lead sulfide precipitate and a gallium-containing solution; it is also possible to subject the two-stage roasting products to alkali leaching together to shorten the production process.

[0076] In some alternative embodiments, a reducing agent is additionally added during the second roasting process.

[0077] In some alternative embodiments, the mass of the reducing agent in the second roasting process is 10%-40% of the mass of the smelting slag.

[0078] Optionally, the mass of the reducing agent in the second roasting process can be 10%, 20%, 30%, 40% of the mass of the smelting slag, or any value between 10%-40%.

[0079] In some alternative embodiments, the solution after alkali leaching is adjusted with sulfuric acid to mix the pH to obtain a solution to be extracted;

[0080] The solution to be extracted is mixed with an extractant, and gallium and germanium are separated and purified by extraction.

[0081] In some alternative embodiments, for the method of gradient roasting and recovering multiple metals from smelting slag, the pH value of the solution to be extracted is 0.5-2.5.

[0082] Optionally, the pH value of the solution to be extracted can be 0.5, 1, 1.5, 2, 2.5, or any value between 0.5-2.5.

[0083] In some embodiments, the extractant includes one or more of P204, P507, and YW100.

[0084] In some alternative embodiments, roasting slag is also obtained by performing the gradient roasting;

[0085] The roasting slag is subjected to acid leaching to obtain a product after acid leaching.

[0086] The following will describe the implementation schemes of the present application in detail with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0087] Example 1

[0088] This embodiment provides a method for gradient roasting and recovering multiple metals from smelting slag. The smelting slag generated by a certain zinc smelter is selected as the raw material. The main components are calculated by mass ratio, including: FeO 29%, SiO2 28%, Al2O3 6%, CaO 19%, and also contain a small amount of Ga (200 ppm) and Ge (240 ppm), and are associated with Cu (0.5%) and Zn (9%). The specific steps are as follows:

[0089] S1: After the smelting slag is fully dried, it is finely ground using a ball mill, and the particle size is controlled to be more than 90 wt% at -250 mesh;

[0090] S2: Add calcium oxide as a slag-forming agent at 30% of the weight of the smelting slag, and add anthracite (fixed carbon content of 55%) at 40% of the weight of the smelting slag as a reducing agent, and mix evenly with the smelting slag;

[0091] S3: Place the mixture in a high-temperature roasting furnace. The oxygen content during roasting is 30%, control the temperature at 1100 °C, maintain the roasting time for 3 hours, and condense the volatile phase through a volatile collection system to obtain a mixture mainly composed of elemental Zn and GeO oxides;

[0092] S4: Continue to raise the roasting temperature to 1450 °C, add anthracite as a reducing agent (mass is 10% of the mass of the smelting slag), roast for 3 hours, and condense the volatile phase through a volatile collection system to obtain a mixture mainly composed of lead oxide and GaO;

[0093] S5: Pass the metal-containing volatile components collected in Step S4 and Step S5 into a sodium sulfide solution for alkali leaching to obtain zinc sulfide and lead sulfide precipitates, and then filter to obtain a mixed solution containing gallium and germanium;

[0094] S6: Add sulfuric acid to the mixed solution containing gallium and germanium to adjust the pH value to 1.5 - 2.5, so that gallate and germanate form gallium sulfate and germanium sulfate respectively, then add an extractant P204 for extraction to achieve co-extraction of gallium and germanium, and then through back-extraction, achieve separation and purification of gallium and germanium, and finally obtain gallium and germanium back-extraction solutions.

[0095] The process for gradient roasting and recovery of multiple metals from smelting slag is as Figure 1 shown.

[0096] Example 2

[0097] The difference from Example 1 is that the slag-forming agent is magnesium oxide, with a mass of 20% of the total mass of the smelting slag, the reducing agent is coke, and the basic sulfide is ammonium sulfide solution.

[0098] Example 3

[0099] The difference from Example 1 is that during gradient roasting, the first roasting is heated to 1200 °C and the holding time is 2 h; the first roasting is heated to 1500 °C and the holding time is 2 h.

[0100] Comparative Example 1

[0101] The difference from Example 1 is that no slag-forming agent is added.

[0102] Comparative Example 2

[0103] The difference from Example 1 is that no reducing agent is added.

[0104] Comparative Example 3

[0105] The difference from Example 1 is that instead of gradient roasting, the temperature is directly raised to 1450°C.

[0106] Comparative Example 4

[0107] The difference from Example 1 is that the oxygen content during gradient roasting is 60%.

[0108] The recovery rates of gallium and germanium in the above examples and comparative examples are shown in Table 1.

[0109] Table 1 Recovery Rates

[0110] Test component Overall recovery rate of gallium Overall recovery rate of germanium Example 1 82.98％ 83.14％ Example 2 84.76％ 86.03％ Example 3 86.59％ 90.81％ Comparative example 1 67.12％ 72.38％ Comparative example 2 55.67％ 58.19％ Comparative example 3 63.65％ 57.76％ Comparative example 4 48.79％ 56.55％

[0111] Analysis:

[0112] From the above tests, it can be seen that through the collaborative optimization of the gradient roasting system design and key processes, the present technology has significantly improved the comprehensive recovery efficiency of multi-metals from lead-zinc pyrometallurgical slag containing gallium and germanium. Its technical advantages are mainly reflected in the following aspects: the directional regulation effect of the gradient roasting temperature field. Example 1 adopts the gradient roasting mode, and compared with the single-stage high-temperature roasting in Comparative Example 3, the recovery rates of gallium and germanium are significantly improved. The first-stage low-temperature roasting enables ZnO and GeO to volatilize preferentially, avoiding the premature encapsulation of PbO and GaO at high temperatures; the second-stage high temperature promotes Ga and significantly reduces the activation energy of Ga volatilization; the synergistic strengthening mechanism of the reducing agent and slag-forming agent. Adding CaO or MgO (Example 1, Example 2) improves the recovery rates of gallium and germanium compared with no slag-forming agent (Comparative Example 1). The slag-forming agent improves the metal diffusion coefficient by reducing the melt viscosity and simultaneously improves the fluidity of the system. The threshold effect of oxygen content on the volatilization efficiency. Controlling the oxygen content (Example 1) improves the recovery rates of gallium and germanium compared with (Comparative Example 4). Too high oxygen potential will inhibit the C→CO reaction, resulting in incomplete reduction of the target metal and simultaneously reducing the volatilization driving force.

[0113] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0114] In addition, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, the combination of features of different embodiments means that it is within the scope of this application and forms different embodiments. For example, in the claims above, any one of the claimed embodiments can be used in any combination. The information disclosed in this background section is only intended to deepen the understanding of the overall background of this application and should not be regarded as an admission or any form of implication that this information constitutes prior art already known to those skilled in the art.

Claims

1. A method for gradient roasting and recovering multi-metals from smelting slag, characterized in that, Including: Mixing smelting slag, slag-forming agent and reducing agent to obtain a mixed material, and subjecting the mixed material to gradient roasting to obtain a volatile metal-containing material; Mixing the volatile metal-containing material and an alkaline sulfide, and performing alkali leaching to remove zinc, lead and copper by precipitation, and gallium and germanium are immersed in the solution; The smelting slag includes one or more of zinc smelting slag, lead smelting slag and copper smelting slag.

2. The method for gradient roasting and recovering multiple metals from smelting slag according to claim 1, wherein, Satisfying at least one of the following conditions: A. The slag-forming agent includes one or more of calcium oxide, silicon oxide, magnesium oxide, calcium carbonate and magnesium carbonate; B. The reducing agent includes anthracite and / or coke; C. The alkaline sulfide includes sodium sulfide and / or ammonium sulfide.

3. The method for gradient roasting and recovering multi-metals from smelting slag according to claim 1, characterized in that Satisfying at least one of the following conditions: A. The fineness of the smelting slag greater than or equal to -250 mesh is greater than or equal to 80 wt%; B. The mass of the slag-forming agent is 10%-40% of the mass of the smelting slag.

4. The method for gradient roasting and recovering polymetals from smelting slag according to claim 1, characterized in that, Satisfying at least one of the following conditions: A. The mass of the reducing agent is 30%-70% of the mass of the smelting slag; B. The fixed carbon content of the reducing agent is greater than or equal to 50%.

5. The method for gradient roasting and recovering multiple metals from smelting slag according to claim 1, characterized in that, The oxygen content during the gradient roasting process is 20%-50%.

6. The method for gradient roasting and recovering multiple metals from smelting slag according to claim 1, wherein The gradient roasting includes a first roasting and a second roasting carried out in sequence; The highest temperature of the first roasting is 1000°C - 1300°C, and the heat preservation time is 1h - 4h; The highest temperature of the second roasting is 1200°C - 1650°C, and the heat preservation time is 1h - 4h.

7. The method for gradient roasting and recovering multi-metals from smelting slag according to claim 6, characterized in that, Reducing agent is additionally added during the second roasting process.

8. The method for gradient roasting and recovering multi-metals from smelting slag according to claim 7, characterized in that, During the second roasting process, the mass of the reducing agent is 10%-40% of the mass of the smelting slag.

9. The method for gradient roasting and recovering multiple metals from smelting slag according to any one of claims 1-8, characterized in that Adjusting the pH of the solution after alkali leaching with sulfuric acid to obtain a solution to be extracted; Mixing the solution to be extracted and an extractant, and separating and purifying gallium and germanium by extraction.

10. The method for gradient roasting and recovering multi-metals from smelting slag according to claim 9, characterized in that The pH value of the solution to be extracted is 0.5 - 2.5.

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