Method for stabilizing cobalt with bentonite and use

Abstract

The present application belongs to the technical field of wastewater treatment, and particularly relates to a method for stabilizing cobalt by bentonite and application. The present application mixes the bentonite with the cobalt-containing wastewater uniformly, adjusts the pH range, performs oscillation reaction at room temperature for a period of time, and then performs centrifugal separation, and takes the solid phase to perform steam heat reaction; the cobalt ions are combined with the bentonite through ion exchange and surface adsorption, and then in the steam heat strengthening, the cobalt ions are combined with the three-dimensional network of the polymer of the silicon-aluminum mineral in the bentonite, part of the cobalt enters the polymer structure by replacing the position of silicon atoms or aluminum atoms in the silicate, and is gradually stabilized in the polymer of the silicon-aluminum mineral bentonite. The present application realizes the fixation of the cobalt ions through ion exchange, participation in the polymerization reaction and three-dimensional network inclusion, and the leaching rate is as low as 0.01%. The process flow of the present application is simple, the reaction condition is easy to control, the operability is strong, and the present application has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method and application of bentonite-stabilized cobalt. Background Technology

[0002] Cobalt (Co) is a lustrous, steely-gray metal located in the 4th period of the periodic table, with atomic number 27. In nature, cobalt mainly exists in divalent and trivalent forms and belongs to the transition metals. Cobalt metal is hard and brittle, and ferromagnetic. It is an important raw material for the production of advanced dyes, battery materials, magnetic alloys, and various cobalt salts, and is used in fields such as circuits, aerospace, new energy batteries, metallurgy, and environmental protection. With rapid industrial development, large amounts of wastewater containing cobalt ions are inevitably generated. Large quantities of cobalt pollute soil through rainfall and infiltration, and enter groundwater and rivers with rainwater, severely polluting aquatic environments.

[0003] Cobalt salts are readily soluble, non-biodegradable, and can be distributed throughout the aqueous medium as Co. 2+ Co migrates in various forms and easily accumulates in aquatic plants and animals. It can also be bioaccumulated in the human body through the food chain. 2+ Cobalt cannot be metabolized by the body and can cause significant harm to health. When the concentration of cobalt in water exceeds the standard, it can have harmful effects on plants, such as inhibiting photosynthesis, reducing seed germination rates, and decreasing enzyme activity and chlorophyll synthesis efficiency. Cobalt poisoning can lead to difficulty breathing, dry cough, chemical pneumonia, allergic asthma, goiter, and in severe cases, cancer. Furthermore, cobalt pollutants exhibit typical characteristics of heavy metal pollution, including being difficult to degrade, easily migrating, and bioaccumulating. They can persist in water bodies and sediments for extended periods, forming persistent and delayed pollution.

[0004] Given the bioaccumulation, non-degradability, and potential toxicity of cobalt, controlling cobalt pollution in wastewater has become particularly important.

[0005] Currently, both domestic and international efforts are focused on physical adsorption, chemical adsorption, chemical precipitation, and biological adsorption to effectively remove CO from water. 2+ Adsorption is an important method for treating cobalt-containing wastewater due to its advantages of low cost, simplicity, wide applicability, and high efficiency. The main strategy of adsorption is to control process parameters and rely on adsorbents to improve the removal rate, aiming to remove easily migratable Co from the water. 2+ Methods that generate insoluble precipitates to separate and remove heavy metals mitigate their migration activity in the environment, but their stability after transfer to the solid phase has received little attention. Therefore, exploring strategies for the stabilization and solidification of heavy metals will be an effective way to avoid their environmental pollution risks. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method and application for stabilizing cobalt with bentonite. Bentonite adsorbed with cobalt ions is subjected to steam curing, which mainly achieves the stabilization and solidification of heavy metal ions through ion exchange and cell polymerization. This solves the problem of secondary pollution caused by heavy metal leaching after fixation, and realizes the stabilization and solidification of cobalt ions in wastewater.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a method for stabilizing cobalt with bentonite, comprising the following steps: Step S1: Add bentonite to cobalt-containing wastewater, adjust the pH to 7-12, and shake the reaction at room temperature; Step S2: After the reaction is complete, centrifuge to obtain a solid precipitate, and then subject the solid precipitate to a steam thermal reaction.

[0008] Furthermore, in step S1, the pH value is 12.

[0009] Furthermore, in step S1, the pH adjuster is nitric acid and sodium hydroxide.

[0010] Furthermore, the molar ratio of silicon to aluminum in the bentonite is (3~5):1.

[0011] Furthermore, the concentration of cobalt ions in the cobalt-containing wastewater is 1000~2000 mg / L, and the dosage of bentonite is 5~10 g / L.

[0012] Furthermore, in step S1, the time for the room temperature oscillation reaction is 6-8 hours.

[0013] Furthermore, in step S2, the steam thermal reaction takes 24 to 36 hours.

[0014] Furthermore, in step S2, the temperature of the steam thermal reaction is 25~200 ℃.

[0015] Furthermore, the temperature of the steam thermal reaction is 200 °C.

[0016] Furthermore, in step S2, the steam thermal reaction is carried out in a polytetrafluoroethylene reactor.

[0017] Furthermore, in step S2, the temperature of the steam thermal reaction is ensured by an electrically heated constant temperature drying oven.

[0018] Compared with the prior art, the beneficial effects of the present invention are: The steam thermal solidification of cobalt ions in bentonite is a physicochemical coupling process involving the synergistic effects of ion adsorption enrichment and hydrothermal structural modification. Montmorillonite, as the main component of bentonite, possesses a typical 2:1 layered structure and high cation exchange capacity. It can enrich cobalt ions in aqueous solution through ion exchange and surface complexation. Saturated steam thermal modification further enhances its solidification stability and inhibits the leaching and migration of cobalt ions.

[0019] The room-temperature adsorption stage serves as a preliminary foundation. The interlayer negative charge generated by isomorphous displacement of montmorillonite can replace exchangeable metal ions in the interlayer through cation exchange, achieving efficient enrichment of Co²⁺. At the same time, the silanol and aluminol hydroxyl groups on the mineral surface can undergo inner spherical surface complexation reactions with cobalt ions, and combined with electrostatic adsorption, complete the stable adsorption and immobilization of cobalt ions on the mineral surface and between layers.

[0020] Steam thermal modification is the core step in solidification and strengthening. A humid and hot environment promotes the gradual removal of interlayer hydration water and adsorbed water from bentonite, weakening its expansibility, shrinking interlayer spacing, and densifying the pore structure. This spatial confinement effect physically binds interlayer cobalt ions. Mild steam thermal action optimizes the mineral interface structure, enhances the activity of adsorption sites, strengthens the interfacial bonding between cobalt ions and the matrix, and avoids structural collapse defects caused by high-temperature dry heat.

[0021] After thermosetting, cobalt ions mainly exist in the bentonite system in stable ion-exchange and surface-complexed states. The densified mineral structure effectively seals pore permeation channels, significantly reducing the risk of cobalt ion leaching. Compared to room-temperature adsorption, steam thermal modification can significantly improve the structural stability and cobalt fixation performance of bentonite, making it an effective modification method to enhance the long-term curing effect of heavy metals in clay minerals.

[0022] Using this method, the leaching rate of cobalt ions in the solution is as low as 0.01%. The process of this invention is simple, the reaction conditions are easy to control, it is highly operable, and it has good application prospects. Attached Figure Description

[0023] Figure 1 The temperature-cobalt ion leaching efficiency is a line graph showing the temperature-cobalt ion leaching efficiency of bentonite steam thermal enhancement for fixing cobalt ions at different temperatures.

[0024] Figure 2 Line graph showing the temperature-cobalt ion leaching efficiency for the bentonite hydrothermal method at different temperatures. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0027] Example 1: A method for stabilizing cobalt in bentonite using a steam thermal method Bentonite was added to cobalt-containing wastewater (cobalt-containing wastewater is a cobalt-containing solution with a cobalt ion concentration of 1500 mg / L formed by dissolving cobalt nitrate hexahydrate in deionized water in the laboratory). The amount of bentonite added was 5 g / L, and the pH value of the solution was controlled at 7-12. After reacting in a shaker at room temperature for 6 h, the solid precipitate was obtained by centrifugation. The solid precipitate was placed in a polytetrafluoroethylene reactor and subjected to water-insulated high-temperature control at 25 ℃, 100 ℃, 150 ℃, and 200 ℃ for a steam thermal reaction time of 24 h. After cooling to room temperature, the solid in the reactor was collected. At room temperature, the obtained constant-weight solidified body was added to the extraction solvent (a solution of concentrated sulfuric acid and concentrated nitric acid in a mass ratio of 2:1, prepared in reagent water with a pH of 3.20±0.05) at a liquid-to-solid ratio of 10:1 (L / kg). The mixture was then shaken in a vortex mixer (30 r / min) for 18 h. Samples were taken, and the suspension was filtered through a 0.22 μm microporous membrane to obtain the filtrate. The concentration of residual cobalt ions was analyzed using a flame atomic absorption spectrophotometer. The cobalt leaching rate was calculated based on the amount of cobalt contained in the cobalt solidified body (calculated from the initial cobalt content in the wastewater and the cobalt content in the residual liquid after the room-temperature shaking reaction) and the amount of cobalt contained in the leaching solution. Figure 1 As shown, at pH 7, the cobalt leaching rates at temperatures of 25 ℃, 100 ℃, 150 ℃, and 200 ℃ were 4.65%, 0.49%, 0.35%, and 0.08%, respectively; under steam heat curing conditions at 200 ℃, the cobalt leaching rates at pH 7, 8, 9, 10, 11, and 12 were 0.08%, 0.07%, 0.01%, 0.01%, 0.01%, and 0.01%, respectively.

[0028] Comparative Example 1: Hydrothermal Method for Stabilizing Cobalt with Bentonite Bentonite was added to cobalt-containing wastewater (a laboratory-prepared cobalt ion solution with a concentration of 1500 mg / L, formed by dissolving cobalt nitrate hexahydrate in deionized water). The dosage of bentonite was 5 g / L, and the pH of the solution was controlled at 7-12. After reacting in a shaker for 6 h, the mixture was transferred to a polytetrafluoroethylene (PTFE) reactor and reacted at hydrothermal temperatures of 25℃, 100℃, 150℃, and 200℃ for 24 h. After cooling to room temperature, the mixture was centrifuged, and 5 ml of the resulting suspension was collected and precipitated with 0.22... The sample was filtered through a μm microporous membrane, and the cobalt ion concentration was analyzed using a flame atomic absorption spectrophotometer. The separation residue was collected, and the resulting constant-weight solidified body was added to an extraction solvent (a solution of concentrated sulfuric acid and concentrated nitric acid in a 2:1 mass ratio, prepared in reagent water at pH 3.20±0.05) at a liquid-to-solid ratio of 10:1 (L / kg) at room temperature. The mixture was shaken for 18 h using a rotary shaker (30 r / min), and a sample was taken. The suspension was filtered through a 0.22 μm microporous membrane to obtain the filtrate. The concentration of residual cobalt ions was analyzed using a flame atomic absorption spectrophotometer. The cobalt leaching rate was calculated based on the amount of cobalt contained in the cobalt solidified body (calculated from the initial cobalt content in the wastewater and the cobalt content in the residual liquid after room-temperature shaking reaction) and the amount of cobalt contained in the leaching solution. Figure 2 As shown, at pH 12, the cobalt leaching rate under hydrothermal conditions at 200 °C is 0.1%.

[0029] The test results of Example 1 and Comparative Example 1 show that bentonite adsorbs cobalt at room temperature to obtain cobalt-containing solidified material. Through steam heat treatment at 200℃, the silicon and aluminum elements in bentonite interact with the heavy metal cobalt, thereby fixing the cobalt. The bentonite solidification method used in this invention has a low leaching rate, and the effect of the steam heat strengthening method is better than that of the hydrothermal method, which can achieve the purpose of steam heat strengthening silicon and aluminum mineral solidification of heavy metals.

[0030] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for stabilizing cobalt with bentonite, characterized in that, Includes the following steps: Step S1: Add bentonite to cobalt-containing wastewater, adjust the pH to 7-12, and shake the reaction at room temperature; Step S2: After the reaction is complete, centrifuge to obtain a solid precipitate, and then subject the solid precipitate to a steam thermal reaction.

2. The method for stabilizing cobalt with bentonite according to claim 1, characterized in that, In step S1, the pH adjuster is nitric acid and sodium hydroxide.

3. The method for stabilizing cobalt with bentonite according to claim 1, characterized in that, The molar ratio of silicon to aluminum in the bentonite is (3~5):

1.

4. The method for stabilizing cobalt with bentonite according to claim 1, characterized in that, The concentration of cobalt ions in the cobalt-containing wastewater is 1000~2000 mg / L, and the dosage of bentonite is 5~10 g / L.

5. The method for stabilizing cobalt with bentonite according to claim 1, characterized in that, In step S1, the time for the room temperature oscillation reaction is 6-8 hours.

6. The method for stabilizing cobalt with bentonite according to claim 1, characterized in that, In step S2, the steam thermal reaction takes 24 to 36 hours.

7. The method for stabilizing cobalt with bentonite according to claim 1, characterized in that, In step S2, the temperature of the steam thermal reaction is 25~200 ℃.

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