A method for processing gypsum residue to recover valuable metals

Abstract

The application discloses a method for processing gypsum residue to recover valuable metals, and belongs to the technical field of metallurgy, which comprises the following steps: mixing, stirring and filtering gypsum residue slurry and waste acid in a waste acid tank to obtain a pickling filtrate; introducing the pickling filtrate into a two-stage neutralization tank to mix with the gypsum residue slurry, and then performing pressure filtration by using a pressure filter to obtain a two-stage neutralization filtrate; introducing the two-stage neutralization filtrate into a three-stage adjustment tank to hydrolyze and precipitate with lime powder, and then performing pressure filtration by using a pressure filter to obtain alkali residue; and feeding the alkali residue into a rotary kiln to extract valuable metals. The method can harmlessly treat alkaline gypsum residue in a landfill, prevent landfill from causing environmental pollution, make the gypsum residue react with the waste acid to obtain valuable metal precipitates, perform secondary utilization of the waste acid, extract valuable metals from waste materials, increase the income of a factory area, and reduce wastewater discharge.

Description

Technical Field

[0001] This application belongs to the field of metallurgical technology, specifically a method for recovering valuable metals from gypsum slag. Background Technology

[0002] my country's lead and zinc smelting industry generates a large amount of wastewater and polluted acid annually. This polluted acid and wastewater exhibits significant pH fluctuations and is predominantly acidic, containing various heavy metals such as lead (Pb), zinc (Zn), and cadmium (Cd), as well as impurities like arsenic (As), fluorine (F), and chlorine (Cl). To remove these heavy metals and impurities, most non-ferrous metal smelting enterprises currently employ a combination of lime-oxidation and iron salt methods, using membrane exchange filtration systems for water treatment. The treated water is returned to the production system, while harmful impurities precipitate in the slag. The resulting gypsum slag is then disposed of through landfill.

[0003] This method results in the waste of valuable metals in the acidic wastewater, which affects the economic benefits of production and processing. At the same time, the landfilling of gypsum residue also causes certain environmental pollution. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, this invention provides a method for processing gypsum slag to recover valuable metals. The method involves slurrying and washing alkaline gypsum slag from landfills to render it harmless, thereby enriching the valuable metals in the sludge. The resulting sludge, containing various precipitated valuable metals, is then fed into a rotary kiln for extraction of the valuable metals.

[0005] In a first aspect, this application provides a method for processing gypsum slag to recover valuable metals, comprising:

[0006] First, the gypsum slag slurry and the waste acid are mixed, stirred and filtered in the waste acid tank to obtain the acid washing filtrate. The pH value of the waste acid is adjusted by the gypsum slag slurry, and the pH value of the acid washing filtrate is controlled to be 2.5. The gypsum slag slurry is obtained by using a lift pump to pass the gypsum slag in the gypsum slag storage into the integrated slurry mixing tank.

[0007] Secondly, the pickling filtrate is passed into the second-stage neutralization tank and mixed with the gypsum slurry. After being filtered by a filter press, the second-stage neutralization filtrate is obtained. The pH value in the second-stage neutralization tank is adjusted and kept constant at pH=6, and the pH value of the second-stage neutralization filtrate is controlled between 5.5 and 6.

[0008] Next, the second-stage neutralization filtrate is fed into the third-stage regulating tank to hydrolyze and precipitate with lime powder. After being filtered by a filter press, alkaline residue is obtained. The third-stage filtrate obtained from the third-stage regulating tank is then sent to a membrane system for processing.

[0009] Finally, the alkali residue is fed into a rotary kiln to extract valuable metals.

[0010] Based on the technical solution provided in the first aspect above, the following beneficial effects can be achieved: the alkaline gypsum slag in the landfill is treated to render it harmless, preventing the landfill from polluting the environment; the gypsum slag reacts with the waste acid to obtain valuable metal sludge, allowing the waste acid to be reused; the valuable metals in the waste are extracted, increasing the plant's revenue and reducing wastewater discharge.

[0011] Optionally, in some possible implementations of the first aspect, calcium fluoride, a wastewater byproduct, may be added to the waste acid and gypsum residue; the method further includes:

[0012] Wastewater is fed into a secondary neutralization tank and reacted with pickling filtrate and gypsum slurry. After being filtered by a filter press, secondary neutralization residue is obtained.

[0013] The neutralized residue from the second stage is fed into the acid pickling tank and mixed with gypsum slurry and acid. After pressure filtration, the acid pickling filtrate and calcium fluoride are obtained. The acid pickling filtrate is then fed into the second stage neutralization tank.

[0014] The acid pickling tank is located at the front end of the second-stage neutralization tank.

[0015] The wastewater consists of high-fluoride solutions from various wet scrubbing systems, including alkaline solutions from cadmium wet fluoride removal slag and desulfurization washing liquid from lead-zinc systems.

[0016] In this possible implementation, the reaction of gypsum slag slurry, waste acid, and sewage also yields calcium fluoride as a byproduct. This achieves fluorine open circuit in the system, solving the problem of difficult fluorine treatment in the lead-zinc industry. While reducing the fluorine content in the final product, alkaline slag, the sale of calcium fluoride creates new revenue for the plant, further achieving the harmless treatment of hazardous waste and realizing economic benefits.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a process for recovering valuable metals in an embodiment of this application;

[0019] Figure 2 This is a flowchart illustrating a method for recovering valuable metals in an embodiment of this application.

[0020] Figure 3 This is a schematic diagram of another processing technology for recovering valuable metals in the embodiments of this application;

[0021] Figure 4 This is another flowchart illustrating the method for recovering valuable metals in the embodiments of this application. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In the description of this application, it should be noted that the terms "vertical", "up", "down", "horizontal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0024] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] Figure 1 This is a schematic diagram of a process flow for recovering valuable metals in an embodiment of this application. Waste acid and gypsum slurry react in a waste acid tank to obtain acid washing filtrate. The acid washing filtrate and gypsum slurry react in a two-stage neutralization tank to obtain a two-stage neutralization filtrate. The two-stage neutralization filtrate is adjusted to different pH values ​​with lime powder to precipitate various valuable metals and obtain alkaline slag. The alkaline slag is sent to a rotary kiln to extract valuable metals.

[0026] Example 1: A method for recovering valuable metals from gypsum slag treated with waste acid. Figure 2 This is a flowchart illustrating a method for recovering valuable metals in an embodiment of this application.

[0027] like Figure 2 As shown, the method for recovering valuable metals from treated acid gypsum sludge in this embodiment includes:

[0028] S101. Gypsum residue slurry and waste acid are mixed, stirred and filtered in a waste acid tank to obtain acid washing filtrate.

[0029] The gypsum residue slurry and waste acid are mixed and stirred in a waste acid tank. A filtration device such as a filter screen is set up to filter the mixed liquid to obtain acid washing filtrate.

[0030] The gypsum slurry is obtained by using a lift pump to pass gypsum slag from the gypsum slag storage into a comprehensive slurry mixing tank, and then adding an appropriate amount of water to the gypsum slag and stirring to obtain the gypsum slurry.

[0031] Optionally, in one embodiment of this example, the pH value of the waste acid produced in the lead-zinc industry is 3-4. The alkaline comprehensive waste acid concentration of the gypsum slag in the landfill is fully utilized, and the pH value of the final pickling filtrate is controlled at 2.5.

[0032] S102. The pickling filtrate is fed into the second-stage neutralization tank and mixed with the gypsum slurry. After being filtered by a filter press, the second-stage neutralization filtrate is obtained.

[0033] Optionally, in one embodiment of this example, the amount of gypsum slurry added is controlled according to the acidity of the pickling filtrate, so that the pH value in the second-stage neutralization tank is kept constant at pH=6, and the pH value of the second-stage neutralization filtrate is finally controlled between 5.5 and 6. Controlling the pH at 6 in this stage can effectively inhibit the hydrolysis and precipitation of valuable metals.

[0034] S103 and the second-stage neutralization filtrate are fed into the third-stage regulating tank to hydrolyze and precipitate with lime powder. After being filtered by a filter press, alkaline residue is obtained.

[0035] In the three-stage equalization tank, the characteristics of metal hydrolysis and precipitation at different pH values ​​are utilized. By controlling the amount of lime powder introduced, metal particles are precipitated in the alkaline residue. This stage of enrichment and extraction can make the zinc content of the alkaline residue greater than 11%, while controlling the grade of water treatment sludge to not exceed 0.5%.

[0036] Optionally, in one embodiment of this example, the three-stage filtrate produced after filtration by the filter press is transported to a membrane system for treatment, and pollution-free discharge is achieved after meeting the emission standards.

[0037] S104, alkaline residue is fed into a rotary kiln to extract valuable metals.

[0038] The alkaline residue is fed into a volatilization kiln to extract valuable metals for use, achieving the harmless treatment of hazardous waste and realizing economic benefits.

[0039] The rotary kiln processing procedure is as follows: Zinc-containing materials (alkali slag in this example) are mixed with coke powder or anthracite pulverized coal in a certain proportion and fed into the rotary kiln through the kiln tail feed pipe. As the rotary kiln rotates, the material slowly rolls forward, and under forced air blowing, a high-temperature reaction zone of 1000-1200°C is formed inside the kiln. Under these conditions, the zinc metal compounds in the furnace charge come into contact with the reducing agent carbon and are reduced by C and CO to metallic zinc vapor, which enters the gas phase. In the gas phase, it is oxidized by oxygen in the air to zinc oxide dust, which is captured by the dust collection system along with the flue gas. The captured dust is the low-grade zinc oxide product. In addition, metals enriched with zinc (such as lead and indium) are also reduced and oxidized into the product, while copper and precious metals such as gold and silver remain in the kiln slag.

[0040] In this embodiment, alkaline gypsum slag in the landfill is treated to render it harmless, preventing landfill from polluting the environment. The gypsum slag reacts with waste acid to produce valuable metal sludge, allowing the waste acid to be reused. Valuable metals are extracted from the waste, increasing plant revenue and reducing wastewater discharge.

[0041] Figure 2 This is a schematic diagram of another processing flow for recovering valuable metals in an embodiment of this application. Waste acid and gypsum slurry react in a waste acid pickling tank to obtain pickling filtrate. The pickling filtrate reacts with gypsum slurry and wastewater in a two-stage neutralization tank, and is then filtered to obtain a two-stage neutralization filtrate and a two-stage neutralization residue. The two-stage neutralization residue is fed into the waste acid pickling tank to react with the waste acid and gypsum slurry, and is then filtered to obtain calcium fluoride. The two-stage neutralization filtrate reacts with lime powder in a three-stage adjustment tank. By adjusting the pH value with lime powder, various valuable metals are precipitated to obtain alkaline residue. The alkaline residue is then sent to a rotary kiln to extract valuable metals.

[0042] Example 2:

[0043] A method for recovering valuable metals from gypsum slag in acid wastewater treatment. Figure 2 This is a flowchart illustrating a method for recovering valuable metals in an embodiment of this application.

[0044] S201, gypsum slurry, waste acid, and secondary neutralization sludge waste acid are fed into the waste acid pickling tank and mixed. After pressure filtration, the pickling filtrate and the by-product calcium fluoride are obtained.

[0045] Waste acid is stored in a waste acid tank and then discharged into a waste acid pickling tank to react with gypsum slag and secondary neutralization slag. Gypsum slag slurry is obtained by using a lift pump to pass gypsum slag from the gypsum slag storage tank into a comprehensive slurry mixing tank. An appropriate amount of water is added to the gypsum slag and stirred to obtain gypsum slag slurry. Secondary neutralization slag is the filter residue obtained after reaction and filtration in the secondary neutralization tank of S202.

[0046] Calcium fluoride, with the chemical formula CaF2, is a colorless crystal or white powder that is sparingly soluble in water. It has a wide range of applications, currently mainly used in the metallurgical, chemical, and building fluorite industries, followed by light industry, optics, carving, and defense industries. Selling calcium fluoride as a by-product generates new revenue for the factory.

[0047] Optionally, in one embodiment of this example, the dirty acid pickling tank is located at the front end of the two-stage neutralization tank, so that the pickling filtrate in the dirty acid pickling tank can be input into the two-stage neutralization tank, and the two-stage neutralization residue in the two-stage neutralization tank can be input into the dirty acid pickling tank.

[0048] Optionally, in one embodiment of this example, the pH value of the waste acid produced in the lead-zinc industry is 3-4. The alkaline comprehensive waste acid concentration of the gypsum slag in the landfill is fully utilized, and the pH value of the final pickling filtrate is controlled at 2.5.

[0049] S202. The pickling filtrate is fed into the second-stage neutralization tank and mixed with gypsum slag slurry and sewage. After being filtered by a filter press, the second-stage neutralization filtrate and the second-stage neutralization residue are obtained.

[0050] The wastewater is a high-fluoride solution produced by the wet process in the lead-zinc industry, including alkaline solution of cadmium wet process defluorination slag and desulfurization washing liquid of lead-zinc system.

[0051] In the second-stage neutralization tank, the fluoride in the fluoride-containing wastewater is returned to the first stage for the production of calcium fluoride, thus achieving an open circuit of fluoride in the system and solving the difficult problem of fluoride treatment in the lead and zinc industry.

[0052] Optionally, in one embodiment of this example, the amount of gypsum slurry added is controlled according to the acidity of the pickling filtrate, so that the pH value in the second-stage neutralization tank is kept constant at pH=6, and the pH value of the second-stage neutralization filtrate is finally controlled between 5.5 and 6. Controlling the pH at 6 in this stage can effectively inhibit the hydrolysis and precipitation of valuable metals, and finally obtain a low-fluorine valuable metal solution.

[0053] S203 and the second-stage neutralization residue are fed into the acid washing tank. The second-stage neutralization filtrate is fed into the third-stage regulating tank to hydrolyze and precipitate with lime powder. After being filtered by a filter press, the alkaline residue is obtained.

[0054] The three-stage regulating tank utilizes the hydrolysis and precipitation of metals at different pH values ​​to effectively precipitate various valuable metals, including zinc. This enrichment and extraction stage can make the zinc content of the alkaline residue greater than 11%. Finally, the valuable metals are extracted and used through a volatilization kiln. The first two stages of treatment can effectively control the fluorine content of the alkaline residue in this stage to not exceed 0.5%, achieving the harmless treatment of hazardous waste and realizing economic benefits.

[0055] S204, alkaline residue is fed into a rotary kiln to extract valuable metals.

[0056] In this embodiment, it should be noted that step S204 is the same as step S104 in the previous embodiment, and its related description can be found in the description of the relevant steps in the previous embodiment. Therefore, it will not be repeated in this embodiment.

[0057] In this embodiment, alkaline gypsum slag in the landfill is treated to render it harmless, preventing landfill pollution. The gypsum slag reacts with waste acid to produce valuable metal sludge, allowing for the secondary use of the waste acid. Valuable metals are extracted from the waste, increasing plant revenue and reducing wastewater discharge. The reaction of gypsum slag slurry, waste acid, and wastewater also produces calcium fluoride as a byproduct. This achieves fluorine open circuit in the system, solving the problem of difficult fluorine treatment in the lead-zinc industry. While reducing the fluorine content in the final product, alkaline slag, the sale of calcium fluoride generates new revenue for the plant, further achieving the goal of harmless treatment of hazardous waste and realizing economic benefits.

[0058] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of this application.

Claims

1. A method for processing gypsum slag to recover valuable metals, characterized in that, include: The gypsum slag in the gypsum slag storage is fed into the integrated slurry mixing tank by the booster pump to obtain gypsum slag slurry. The gypsum slag slurry is mixed, stirred and filtered with waste acid in the waste acid tank to obtain acid washing filtrate with pH value controlled at 2.

5. The pickling filtrate is fed into the second-stage neutralization tank and mixed with the gypsum slurry. Wastewater is also introduced to adjust the pH value in the second-stage neutralization tank to a constant 6, so that the pH value of the second-stage neutralization filtrate is controlled between 5.5 and 6. After filtration by a filter press, the second-stage neutralization filtrate and the second-stage neutralization residue are obtained. The wastewater is a high-fluoride solution from various wet process systems, including alkaline solution of cadmium wet process defluorination residue and desulfurization washing liquid of lead-zinc system. The neutralized residue from the second stage is fed into the acid pickling tank and mixed with gypsum slurry and acid. After pressure filtration, acid pickling filtrate and calcium fluoride are obtained. The acid pickling filtrate is then fed into the second stage neutralization tank. The second-stage neutralized filtrate is fed into the third-stage regulating tank to hydrolyze and precipitate with lime powder. After being filtered by a filter press, alkaline residue and third-stage filtrate are obtained. The third-stage filtrate is then transported to a membrane system for treatment. The alkaline residue is fed into a rotary kiln to extract valuable metals.

2. The method as described in claim 1, characterized in that, The acid pickling tank is located at the front end of the second-section neutralization tank.

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