Method for fixing multivalent heavy metals in microcrystalline reinforced glass body involving heavy metal residual salt

Abstract

This invention discloses a method for immobilizing multiple heavy metals in heavy metal-containing residual salts using a microcrystalline reinforced glass body, belonging to the field of hazardous waste harmless and resource-based treatment technology. This method targets residual salts containing heavy metals such as Cr, Pb, and Zn. The residual salts are mixed with silica, limestone, soda ash, and fluorite in a specific ratio, and then melted and homogenized to form a base glass with high sulfur and chlorine tolerance. Based on this, a microcrystalline reinforced glass solidified body with coexisting glass and crystalline phases is constructed through controlled crystallization treatment. This method achieves simultaneous and efficient immobilization of multiple heavy metals such as Cr, Pb, and Zn. The leaching concentrations of Cr, Pb, and Zn in the solidified product are below 0.168 mg / L, 0.207 mg / L, and 0.188 mg / L, respectively, significantly lower than the limits specified in GB / T 41015-2021, demonstrating excellent long-term environmental stability.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste treatment and resource utilization technology. Specifically, it relates to a method for simultaneously curing multiple heavy metals in residual salt using microcrystalline glass curing technology. Background Technology

[0002] Industrial waste salt mainly originates from the production processes and wastewater treatment processes of industries such as chemical, pharmaceutical, printing and dyeing, and coal chemical industries. It is a solid waste primarily composed of NaCl and Na₂SO₄, containing benzene compounds, chlorinated hydrocarbons, and heavy metals. Residual salt is the solid residue after industrial waste salt has undergone crystallization, separation, and pyrolysis, and it has a high heavy metal content. The various heavy metals Pb, Zn, and Cr in residual salt are significantly toxic to humans and can accumulate through the environment and food chain, causing damage to the nervous system, organ dysfunction, and even cancer risks, posing a serious threat to children, pregnant women, and those with occupational exposure. Therefore, how to properly handle the heavy metals in residual salt is an urgent problem to be solved.

[0003] Currently, the fixation of heavy metals in residual salts commonly employs two methods: cement solidification and glass solidification. Cement solidification involves mixing residual salts with cement for curing before rigid landfilling. However, the anions in the residual salts can disrupt the structure of cement hydration products, leading not only to salt leaching but also increasing the risk of heavy metal leaching. According to the "Standard for Pollution Control of Hazardous Waste Landfill" (GB18598-2019), the leaching concentrations of heavy metals Cr, Pb, and Zn must be below 15 mg / L, 1.2 mg / L, and 120 mg / L, respectively. Traditional cement solidification processes struggle to consistently meet these standards.

[0004] In the field of vitrification, existing patent CN111085529A discloses a method for vitrifying industrial waste salt. This method first mixes industrial waste salt with coal gangue to obtain a basic mixture, then pyrolyzes the mixture and melts the pyrolysis products to finally obtain a glassy slag. While the waste salt processed by this method has a complex composition, the resulting glass is primarily a single amorphous structure, with limited solid solution capacity for high-valence and multi-valence heavy metal ions. This makes it difficult to achieve simultaneous, efficient, and stable solidification of multiple heavy metals such as Cr, Pb, and Zn, resulting in a high risk of long-term leaching of heavy metals from the solidified product.

[0005] CN 116874183 A discloses a method for simultaneously curing rare earth waste multi-nuclides into a microcrystalline glass solidified body, wherein an R2O-CaO-SiO2-X basic glass system is constructed. The focus of this system is on forming a basic glass that is prone to "phase separation"; while this application focuses on constructing a basic glass system that can accommodate more anions and is not prone to phase separation.

[0006] CN 115672938 A discloses a method for simultaneously and stably curing multiple heavy metals in a core-shell structured glass curing body. This method involves surface crystallization treatment of the base glass to form a "core-shell" structure where crystals encapsulate an amorphous phase, thereby achieving heavy metal curing. This application, however, uses crystallization treatment to migrate heavy metals that are difficult to stably cure in the amorphous phase to the crystalline phase for curing, thus forming a partially microcrystalline-reinforced cured body with a lower crystal content than glass-ceramics.

[0007] Therefore, there is an urgent need in this field to develop a new method for vitrification that can adapt to the coexistence of multiple heavy metals, so as to achieve the harmlessness of residual salts while meeting increasingly stringent national standards and providing a reliable technical path for their large-scale treatment. Summary of the Invention

[0008] To address the common problems of poor fixation effect and insufficient long-term stability in the simultaneous curing of multiple heavy metals in existing residual salt vitrification treatment technologies, especially the difficulty in simultaneously meeting the stable curing requirements of heavy metal elements with different valence states and coordination characteristics, this invention proposes a method for fixing multiple heavy metals in heavy metal residual salts using microcrystalline reinforced glass.

[0009] This invention is applicable to the treatment of solid residues from industrial waste salt after crystallization, salt separation, and pyrolysis. Its main components include one or more of NaCl and Na2SO4, and it contains heavy metal elements such as Cr, Pb, and Zn.

[0010] The core of this invention lies in constructing a special Na2O–CaO–SiO2–X glass system with high chlorine and sulfur capacity to meet the vitrification requirements under conditions of high salt content and complex anion coexistence in residual salts. Based on this, a microcrystalline strengthening strategy is introduced. Through a controllable crystallization process, leveraging the difference in affinity between heavy metal elements and the glass phase, specific heavy metal elements (such as Cr) with weaker bonding to the glass are driven to migrate into the crystal lattice and precipitate to form stable crystals. This induces some heavy metals to enter the crystalline phase, forming a composite solidification structure where the glass and crystalline phases coexist. In this structure, the glass phase serves as the heavy metal solidification matrix, while the crystalline phase provides directional anchoring points for specific heavy metals. Their synergistic effect enhances the overall stability and leaching resistance of the solidified body, achieving efficient and simultaneous fixation of multiple heavy metals, ultimately ensuring the long-term and safe disposal of heavy metal-containing residual salts.

[0011] To achieve the above objectives, the present invention provides the following technical solution: First, residual salt is mixed with mineral raw materials such as silica, limestone, soda ash, and fluorite to form a basic batch. Then, the batch is put into a melting furnace and undergoes three stages in sequence: melting and homogenization, metastable forming, and controlled crystallization, ultimately forming a dense and stable microcrystalline reinforced glass solid.

[0012] The specific steps include: (1) Mixing: Mix the residual salt containing heavy metals with mineral raw materials such as silica, limestone, soda ash, and fluorite until uniform to form a basic batching material.

[0013] The basic batching material, by mass percentage, comprises: 1.0~10.0 wt% residual salt, 30.0~60.0 wt% silica, 15.0~30.0 wt% limestone, 10.0~20.0 wt% soda ash, and 0~10.0 wt% fluorite; the residual salt comprises one or both of NaCl and Na2SO4. (2) Melting and homogenization: The base batch is melted at 900-1400 °C for 0.5-3.0 hours to form a homogeneous glass melt.

[0014] (3) Cooling and molding: Cool the glass melt to obtain the basic glass solidified body.

[0015] (4) Controlled crystallization: The base glass curing body is heat-treated in the range of 400 to 1000 °C and held for 0.5 to 3.0 hours to induce the precipitation of microcrystalline phase and obtain microcrystalline reinforced glass curing body.

[0016] The microcrystalline reinforced glass cured body prepared by the above method is a composite material in which the glass phase and the crystalline phase coexist, enabling the simultaneous and stable curing of multiple heavy metals such as Cr, Pb, and Zn. Testing showed that the toxic leaching concentration in this cured body was significantly lower than the relevant national standard limits.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) Construct a special glass system with high sulfur and chlorine tolerance to overcome the bottleneck of traditional glass curing: This invention, through precise design of the Na2O–CaO–SiO2–X system, develops a special glass matrix structure with high chemical tolerance to sulfur and chloride ions. This system can stably solidify the sulfur and chloride components present in residual salts within the glass network structure, effectively avoiding problems such as glass phase separation, uncontrolled crystallization, or decreased chemical stability caused by anions. This provides a reliable matrix foundation for the vitrification treatment of heavy hazardous waste containing salt.

[0018] (2) Innovative microcrystalline synergistic curing mechanism to achieve simultaneous, efficient fixation and long-term stability of multiple heavy metals: The resulting microcrystalline reinforced glass curing body possesses a composite stable structure of "glass phase encapsulation + crystalline phase anchoring". The chemically inert glass network provides the bulk containment, while the structurally ordered crystalline phase precipitated through controlled crystallization provides directional anchoring points for high-valence heavy metals such as Cr. The synergistic effect of these two components locks the heavy metals within the curing body, significantly inhibiting their migration and release under service conditions, thus solving the problem of poor simultaneous curing of multiple heavy metals (especially high-valence heavy metals).

[0019] (3) The product has a stable structure and excellent environmental safety, meeting the most stringent environmental protection standards: The resulting microcrystalline reinforced glass solidified body possesses a stable composite structure of glass and crystalline phases. Heavy metals are locked within the chemically inert glass network and the structurally ordered crystalline phase, respectively, greatly inhibiting their migration and release under service conditions. Toxicity leaching tests (based on HJ / T 299-2007) show that the leaching concentrations of Cr, Pb, and Zn in the solidified body can be as low as 0.168 mg / L, 0.207 mg / L, and 0.188 mg / L, respectively, all exceeding the limits specified in the "Technical Requirements for Vitrification Products of Solid Waste" (GB / T 41015-2021) (Cr: 0.2 mg / L, Pb: 0.3 mg / L, Zn: 1.0 mg / L), demonstrating extremely high environmental safety and resource utilization potential. Attached Figure Description

[0020] Figure 1 The images are photographs of glass-cured solids containing residual salts, where a is a glass-cured solid containing NaCl, b is a glass-cured solid containing Na2SO4, and c is a glass-cured solid containing both NaCl and Na2SO4. Figure 2 Flowchart for the preparation of residual salt glass solidified body. Detailed Implementation

[0021] The technical solution of the present invention will be described in detail below with reference to specific embodiments, so as to provide a more in-depth understanding of the purpose, features and effects of the present invention. It should be noted that these embodiments are illustrative and not limiting of the present invention. Any modifications and refinements based on the concept of the present invention fall within the protection scope of the present invention.

[0022] Example 1 like Figure 2 As shown, a method for immobilizing multiple heavy metals in heavy metal residual salts using a microcrystalline reinforced glass body is provided. The method includes: (1) Mixing: Weigh 1.0 wt% of residual salt mainly composed of NaCl, 55.8 wt% of silica, 24.0 wt% of limestone (calculated as oxides), 14.4 wt% of soda ash (calculated as oxides), and 4.8 wt% of fluorite, mix them until uniform to form the basic batching material; (2) Melting and homogenization: The basic batch is put into the melting furnace and melted at 1250 ℃ for 0.5 h to form a homogeneous glass melt; (3) Metastable molding: Cooling the clarified glass melt to form a solidified base glass body; (4) Controlled crystallization: The base glass-cured body was kept at 950 ℃ for 0.5 h to obtain a partially microcrystalline strengthened residual salt glass-cured body with a crystal content of approximately 5.9%. Figure 1 As shown in 'a'; (5) The toxicity leaching test of the obtained microcrystalline reinforced residual salt glass solidified body was carried out using the solid waste leaching toxicity leaching method - sulfuric acid nitric acid method (HJ / T299-2007). The leaching concentrations of Cr, Pb and Zn were 0.134 mg / L, 0.090 mg / L and 0.079 mg / L, respectively.

[0023] Example 2 like Figure 2 As shown, a method for immobilizing multiple heavy metals in heavy metal residual salts using a microcrystalline reinforced glass body is provided. The method includes: (1) Mixing: Weigh 9.0 wt% of residual salt mainly composed of NaCl, 50.1 wt% of silica, 22.7 wt% of limestone (calculated as oxides), 13.7 wt% of soda ash (calculated as oxides), and 4.5 wt% of fluorite, mix them until uniform to form the basic batching material; (2) Melting and homogenization: The basic batch is put into the melting furnace and melted at 1250 ℃ for 0.5 h to form a homogeneous glass melt; (3) Metastable molding: Cooling the clarified glass melt to form a solidified base glass body; (4) Controlled crystallization: The base glass-cured body was kept at 950 °C for 0.5 h to obtain a partially microcrystalline strengthened residual salt glass-cured body with a crystal content of about 9.4%; (5) The toxicity leaching test of the obtained microcrystalline reinforced residual salt glass solidified body was carried out using the solid waste leaching toxicity leaching method - sulfuric acid nitric acid method (HJ / T299-2007). The leaching concentrations of Cr, Pb and Zn were 0.087 mg / L, 0.055 mg / L and 0.049 mg / L, respectively.

[0024] Example 3 like Figure 2As shown, a method for immobilizing multiple heavy metals in heavy metal residual salts using a microcrystalline reinforced glass body is provided. The method includes: (1) Mixing: Weigh 8.0 wt% of residual salt mainly composed of Na2SO4, 60.0 wt% of silica, 16.0 wt% of limestone (calculated as oxides), 11.0 wt% of soda ash (calculated as oxides), and 5.0 wt% of fluorite, mix them until uniform to form the basic batching material; (2) Melting and homogenization: The basic batch is put into the melting furnace and melted at 950 ℃ for 3.0 h to form a homogeneous glass melt; (3) Metastable molding: Cooling the clarified glass melt to form a solidified base glass body; (4) Controlled crystallization: The base glass-cured body was kept at 400 ℃ for 3.0 h to obtain a partially microcrystalline strengthened residual salt glass-cured body with a crystal content of approximately 15.2%. Figure 1 As shown in b; (5) The toxicity leaching test of the obtained microcrystalline reinforced residual salt glass solidified body was carried out using the solid waste leaching toxicity leaching method - sulfuric acid nitric acid method (HJ / T299-2007). The leaching concentrations of Cr, Pb and Zn were 0.125 mg / L, 0.083 mg / L and 0.070 mg / L, respectively.

[0025] Example 4 like Figure 2 As shown, a method for immobilizing multiple heavy metals in heavy metal residual salts using a microcrystalline reinforced glass body is provided. The method includes: (1) Mixing: Weigh 10.0 wt% residual salt mainly composed of Na2SO4, 30.0 wt% silica, 30.0 wt% limestone (calculated as oxides), 20.0 wt% soda ash (calculated as oxides), and 10.0 wt% fluorite, mix them until uniform to form the basic batching material; (2) Melting and homogenization: The basic batch is put into the melting furnace and melted at 1400 ℃ for 0.5 h to form a homogeneous glass melt; (3) Metastable molding: Cooling the clarified glass melt to form a solidified base glass body; (4) Controlled crystallization: The base glass-cured body was kept at 1000 ℃ for 0.5 h to obtain a partially microcrystalline strengthened residual salt glass-cured body with a crystal content of 7.9%; (5) The toxicity leaching test was carried out on the partially microcrystalline reinforced residual salt glass solidified body using the solid waste leaching toxicity leaching method - sulfuric acid nitric acid method (HJ / T299-2007). The leaching concentrations of Cr, Pb and Zn were 0.168 mg / L, 0.207 mg / L and 0.188 mg / L, respectively.

[0026] Example 5 like Figure 2 As shown, a method for immobilizing multiple heavy metals in heavy metal residual salts using a microcrystalline reinforced glass body is provided. The method includes: (1) Mixing: Weigh and mix the residual salt, mainly 1.0 wt% NaCl and Na2SO4, 56.0 wt% silica, 23.8 wt% limestone (calculated as oxides), 14.4 wt% soda ash (calculated as oxides), and 4.8 wt% fluorite, and mix them until uniform to form the basic batching material; (2) Melting and homogenization: The basic batch is put into the melting furnace and melted at 1250 ℃ for 0.5 h to form a homogeneous glass melt; (3) Metastable molding: Cooling the clarified glass melt to form a solidified base glass body; (4) Controlled crystallization: The base glass-cured body was kept at 950 ℃ for 0.5 h to obtain a partially microcrystalline strengthened residual salt glass-cured body with a crystal content of 5.7%. Figure 1 As shown in c; (5) The toxicity leaching test of the obtained microcrystalline reinforced residual salt glass solidified body was carried out using the solid waste leaching toxicity leaching method - sulfuric acid nitric acid method (HJ / T299-2007). The leaching concentrations of Cr, Pb and Zn were 0.137 mg / L, 0.072 mg / L and 0.053 mg / L, respectively.

[0027] Example 6 like Figure 2 As shown, a method for immobilizing multiple heavy metals in heavy metal residual salts using a microcrystalline reinforced glass body is provided. The method includes: (1) Mixing: Weigh 9.5 wt% of residual salt mainly composed of NaCl and Na2SO4, 48.9 wt% of silica, 23.1 wt% of limestone (calculated as oxides), 13.9 wt% of soda ash (calculated as oxides), and 4.6 wt% of fluorite, mix them until uniform to form the basic batching material; (2) Melting and homogenization: The basic batch is put into the melting furnace and melted at 1250 ℃ for 0.5 h to form a homogeneous glass melt; (3) Molding: Cool the clarified glass melt to form a solidified base glass body; (4) Sintering and crystallization: The base glass solidified body was kept at 950 °C for 0.5 h to obtain a partially microcrystalline strengthened residual salt glass solidified body with a crystal content of 10.3%; (5) The toxicity leaching test was carried out on the partially microcrystalline reinforced residual salt glass solidified body using the solid waste leaching toxicity leaching method - sulfuric acid and nitric acid method (HJ / T299-2007). The leaching concentrations of Cr, Pb and Zn were 0.160 mg / L, 0.094 mg / L and 0.065 mg / L, respectively.

[0028] The partially microcrystalline reinforced glass-cured body prepared by this invention has leaching concentrations of heavy metal ions such as Cr, Pb, and Zn that are far lower than the limits specified in the national standard "Technical Requirements for Vitrification Products of Solid Waste" (GB / T 41015-2021) (Cr: 0.2 mg / L, Pb: 0.3 mg / L, Zn: 1.0 mg / L). The glass-cured body can simultaneously fix multiple heavy metals such as Cr, Pb, and Zn.

[0029] The upper and lower limits of the process parameters (such as temperature, time, etc.) and the range values ​​of the present invention can all achieve this method, and examples are not listed here.

[0030] All aspects not described in detail in this invention can be covered using conventional technical knowledge in the field.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for immobilizing multiple heavy metals in heavy metal residual salts using a microcrystalline reinforced glass body, the method comprising the following steps: (1) Mixing: Mix the residual salt containing heavy metals with silica, limestone, soda ash and fluorite until uniform to form a basic batching material; The basic batching material, by mass percentage, comprises: 1.0~10.0 wt% residual salt, 30.0~60.0 wt% silica, 15.0~30.0 wt% limestone, 10.0~20.0 wt% soda ash, and 0~10.0 wt% fluorite; (2) Melting and homogenization: The basic batch is put into the melting furnace and melted at 900-1400 ℃ for 0.5-3.0 h to form a homogeneous glass melt; (3) Metastable molding: Cooling the clarified glass melt to form a solidified base glass body; (4) Controllable crystallization: The base glass solidified body is kept at 400-1000 ℃ for 0.5-3.0 h to obtain a residual salt glass solidified body that can contain some microcrystalline reinforcement; the solidified body is a composite material in which glass phase and crystal phase coexist, which can simultaneously fix the multi-element heavy metal elements in the residual salt.

2. The method according to claim 1, characterized in that: The residual salt is derived from the solid residue of industrial waste salt after crystallization, salt separation and pyrolysis treatment, and the residual salt contains one or two of NaCl and Na2SO4.

3. The method according to claim 1, characterized in that: The multi-element heavy metal includes one or at least two of Cr, Zn, and Pb.

4. The method according to claim 1, characterized in that: The residual salt vitrified body was tested according to the "Solid Waste Leaching Toxicity Leaching Method - Sulfuric Acid and Nitric Acid Method" (HJ / T 299-2007). The leaching concentration of Cr was ≤0.168 mg / L, the leaching concentration of Pb was ≤0.207 mg / L, and the leaching concentration of Zn was ≤0.188 mg / L.

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