Directional calcium removal and chlorine recovery recycling process for rare earth smelting salt-containing wastewater

Abstract

The invention relates to the field of rare earth smelting wastewater treatment, and discloses a rare earth smelting salt-containing wastewater directional calcium removal and chlorine recovery recycling process which comprises the following steps: S1, standing salt-containing wastewater to obtain supernate; s2, slowly dropwise adding sulfuric acid into the supernate, standing, and filtering to remove calcium sulfate to obtain a calcium-removed solution; s3, the calcium removal solution enters a first-stage electrodialysis system to remove part of chloride ions, and diluted hydrochloric acid is obtained; and S4, filtering the deacidified desalinized solution, feeding the filtered deacidified desalinized solution into a second-stage electrodialysis system to further remove chloride ions, returning the chlorine-containing solution to the first-stage electrodialysis system, and removing chlorine to obtain a purified solution. By adopting a method of coupling directional calcium removal with electrodialysis, efficient directional recovery of calcium ions and chloride ions is realized, and high-purity calcium sulfate and diluted hydrochloric acid are successfully obtained. The process not only solves the problems of difficult treatment, high cost, high energy consumption, poor recycling effect and the like in the traditional smelting wastewater treatment, but also remarkably improves the resource utilization efficiency.

Description

Technical Field

[0001] The invention relates to the field of rare earth smelting wastewater treatment, and in particular to a directional calcium removal and chlorine recovery resource process for rare earth smelting saline wastewater. Background Art

[0002] Rare earth elements are widely used in new energy, new materials, aerospace, electronic information and other fields due to their unique physical and chemical properties, and are known as "vitamins of industry". In particular, ion-adsorption rare earth ores have become important raw materials for the rare earth industry due to their complete rare earth distribution and high element value. However, in the smelting process of rare earths, a large amount of saline wastewater is produced. These wastewaters contain high concentrations of calcium and chloride ions, which pose a severe challenge to the environment and the sustainable use of resources.

[0003] At present, the treatment method of rare earth smelting wastewater mainly relies on adding a large amount of lime under high temperature environment to form an alkaline solution environment to promote the precipitation of calcium ions. However, although this method can remove calcium ions in wastewater, chloride ions still remain in the water, resulting in extremely high calcium and chloride ion contents in the final wastewater, forming high-alkalinity calcium chloride-containing wastewater. Due to the high salt content, this wastewater is neither allowed to be discharged nor reused in the smelting process, resulting in a waste of resources and a burden on the environment.

[0004] To solve this problem, people have researched and developed mechanical vapor recompression (MVR) technology, which treats wastewater through energy-saving evaporation. All the salt in the wastewater is converted into a solid mixture by distillation and crystallization. However, these solid wastes not only require secondary treatment, but are also difficult to recycle as resources, increasing treatment costs and environmental risks.

[0005] Based on the above technical problems, developing a wastewater treatment process that can effectively remove calcium and chlorine and realize resource utilization will help reduce the cost of wastewater treatment and reduce the impact of rare earth smelting on the environment. It has important economic and environmental significance for the rare earth smelting industry. Summary of the invention

[0006] The embodiment of the present application solves the problem of high treatment cost and difficulty in resource utilization of rare earth smelting saline wastewater in the prior art by providing a process for directional calcium removal and chlorine recovery for resource utilization of rare earth smelting saline wastewater, thereby realizing the resource utilization of rare earth smelting wastewater.

[0007] The present application provides a process for directional calcium removal and chlorine recovery of rare earth smelting saline wastewater, including the following steps: S1. Pour the salt-containing wastewater into the sedimentation tank and let it stand for 8h to 24h, wait for the insoluble matter in the water to precipitate naturally, and send the supernatant to the next step; S2: The supernatant enters the liquid phase reactor, sulfuric acid is slowly added dropwise according to a certain acid-liquid ratio to crystallize calcium sulfate, and the solution is left to stand for 8 to 24 hours after the addition, and then the calcium sulfate is filtered out and removed. The calcium sulfate removed by filtration is dried to obtain high-purity calcium sulfate, and the calcium-removed solution enters the next step; S3: The decalcified solution first enters the primary electrodialysis system to remove chloride ions to obtain dilute hydrochloric acid, and the desalinated solution enters the next step; S4: The desalinated liquid is first filtered and then enters the secondary electrodialysis system to further remove chloride ions. The chlorine-containing solution returns to the primary electrodialysis system. The solution after dechlorination is the purified liquid, and its calcium and chloride ion concentrations are reduced to the standard that can be directly reused or discharged.

[0008] As some embodiments of the present invention, the calcium ion concentration in the wastewater of step S1 is 20g / L-30g / L, the chloride ion concentration is 35g / L-70g / L, the pH is 8-12, and the total salt content is 90g / L-125g / L.

[0009] As some embodiments of the present invention, the amount of sulfuric acid added in step S2 is Ca 2+ :SO4 2- Mass ratio (0.35:1) ~ (0.45:1) (mg / L).

[0010] As some embodiments of the present invention, the purity of the high-purity calcium sulfate obtained in step S2 is >98%, reaching the level of a commercially available high-purity product.

[0011] As preferred in some embodiments of the present invention, the calcium in the decalcified solution in step S2 is 2+ <6g / L, SO4 2- <15g / L.

[0012] As some embodiments of the present invention, the concentration of dilute hydrochloric acid produced by the primary electrodialysis system in step S3 is 1 mol / L to 3 mol / L, which can be returned to the rare earth smelting process for raw material dissolution.

[0013] As some embodiments of the present invention, the hydrochloric acid content in the purified liquid after dechlorination in step S4 is less than 0.06%, which is clean purified water.

[0014] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: 1. The present invention adopts an innovative method of directional calcium removal coupled with electrodialysis to achieve efficient directional recovery of calcium ions and chloride ions, and successfully produces high-purity calcium sulfate products and dilute hydrochloric acid that can be used for rare earth smelting. This process not only solves the problems of difficult treatment, high cost, high energy consumption and poor resource utilization effect in traditional smelting wastewater treatment, but also significantly improves resource utilization efficiency.

[0015] 2. The process technology of the present invention can extract high-purity calcium sulfate with a purity of more than 98% from wastewater. This effect avoids the dependence on natural gypsum mines in the traditional wastewater treatment process for recovering calcium sulfate, greatly reduces the exploitation of natural resources, and reduces energy consumption.

[0016] 3. In the rare earth smelting process, dilute hydrochloric acid is required for the dissolution of raw materials. The dilute hydrochloric acid recovered by the process of the present invention can be directly reused in the dissolution process of raw materials, realizing the recycling of hydrochloric acid, thereby significantly reducing the purchase amount of hydrochloric acid, reducing production costs, and reducing the risks in the transportation process of hydrochloric acid.

[0017] 4. The process technology of the present invention can ensure that the salt content of the treated water is lower than 5g / L, and the hydrochloric acid content in the purified liquid is controlled below 0.06%, thereby achieving harmless treatment and resource utilization of wastewater, and contributing to environmental protection and resource conservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation of the present invention or the technical solution in the prior art, the drawings required for describing the specific implementation or the prior art will be briefly introduced below. Obviously, the drawings described below are only one implementation of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is a process flow chart for directional calcium removal and chlorine recovery of rare earth smelting saline wastewater in an embodiment of the present invention; Figure 2 This is a material change flow chart of the process for directional decalcification and chlorine recovery of rare earth smelting saline wastewater in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The embodiment of the present application discloses a process for directional calcium removal and chlorine recovery for resource utilization of saline wastewater from rare earth smelting. The process includes four steps and adopts an innovative method of directional calcium removal coupled with electrodialysis to solve the problem of resource utilization of wastewater containing calcium and chlorine in rare earth smelting. After treatment, the calcium ion concentration in the water is lower than 50 mg / L, and the hydrochloric acid content is lower than 0.06%. More than 75% of the total water volume is recyclable water, high-purity calcium sulfate with a purity of more than 98%, and 1 mol / L to 3 mol / L of dilute hydrochloric acid are produced, thereby realizing the resource utilization of rare earth smelting wastewater.

[0021] In order to better understand the above technical solution, the above technical solution is described in detail below with specific implementation methods.

[0022] Embodiment 1: The process of this embodiment is as follows Figure 1 and Figure 2As shown, the rare earth smelting saline wastewater used in the embodiment was taken from a rare earth smelting plant in the south (I), the calcium ion concentration in the saline wastewater was 30.06 g / L, the chloride ion concentration was 40.83 g / L, the pH was 11.5, and the total salt content was 102.31 g / L.

[0023] The process of the process of the present invention is as follows: S1. Pour the above-mentioned saline wastewater into a sedimentation tank and let it stand for 12 hours, wait for the insoluble matter in the water to precipitate naturally, and send the supernatant to the next step; S2: The supernatant enters the liquid phase reactor with Ca 2+ :SO4 2- Sulfuric acid is slowly added dropwise at a molar ratio of 1:1 to crystallize calcium sulfate. After the addition of sulfuric acid, the mixture is allowed to stand for 12 hours, and then the calcium sulfate is filtered out and removed. The calcium sulfate removed by filtration is dried to obtain high-purity calcium sulfate with a purity of 98.41%. The decalcified solution enters the next step; S3: The decalcified solution first enters the primary electrodialysis system to remove chloride ions to obtain 3 mol / L dilute hydrochloric acid, and the desalinated solution enters the next step; S4: The desalinated liquid is first filtered and then enters the secondary electrodialysis system to further remove chloride ions. The chlorine-containing solution returns to the primary electrodialysis system. The solution after dechlorination is the purified liquid. After testing, the total salt content in the purified liquid is reduced by 96.15% compared with the saline wastewater, meeting the discharge standard. In this embodiment, it is reused.

[0024] That is, the rare earth smelting saline wastewater treated by the process of the present invention meets the discharge standard, and at the same time, high-purity calcium sulfate with a purity of 99.78% and dilute hydrochloric acid with a concentration of 3 mol / L are obtained through resource utilization.

[0025] Embodiment 2: The process of this embodiment is as follows Figure 1 and Figure 2 As shown, the rare earth smelting saline wastewater used in the embodiment was taken from a rare earth smelting plant in the south (II). The calcium ion concentration in the saline wastewater was 26.30 g / L, the chloride ion concentration was 41.90 g / L, the pH was 12.05, and the total salt content was 96.9 g / L.

[0026] S1. Take 2000mL of the above-mentioned saline wastewater and inject it into the sedimentation tank and let it stand for 24 hours. After the insoluble matter in the water is naturally precipitated, take 1L of the supernatant and send it to the next step; S2: Inject the supernatant into the liquid phase reactor to form Ca 2+ :SO4 2- Sulfuric acid is slowly added dropwise at a molar ratio of 1:1 to crystallize calcium sulfate. After the addition of sulfuric acid, the mixture is allowed to stand for 24 hours, and then the calcium sulfate is filtered out and removed. The calcium sulfate removed by filtration is dried to obtain high-purity calcium sulfate with a purity of 99.78%. 700 mL of the calcium removal solution is taken to proceed to the next step; S3: The decalcified solution first enters the primary electrodialysis system to remove chloride ions, and 1.37 mol / L dilute hydrochloric acid is obtained after 30 minutes. The deacidified solution enters the next step; S4: The desalinated liquid is first filtered and then enters the secondary electrodialysis system to further remove chloride ions. After 1 hour of electrodialysis, the chlorine-containing solution returns to the primary electrodialysis system. The solution after dechlorination is the purified liquid. After testing, the calcium ion concentration in the purified liquid is 42.3 mg / L, the hydrochloric acid content is 0.053%, and the total salt content is 850 mg / L.

[0027] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0028] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A process for directional calcium removal and chlorine recovery from rare earth smelting saline wastewater, characterized in that: The steps include: S1. Pour the salt-containing wastewater into the sedimentation tank and let it stand for 8h to 24h, wait for the insoluble matter in the water to precipitate naturally, and send the supernatant to the next step; S2: Put the supernatant into a liquid phase reactor, then slowly add sulfuric acid to crystallize calcium sulfate. After adding sulfuric acid, let it stand for 8 hours to 24 hours, then filter to remove calcium sulfate, dry the filtered calcium sulfate residue to obtain high-purity calcium sulfate, and the decalcified solution enters the next step; S3: The decalcified solution enters the primary electrodialysis system to remove some chloride ions to obtain dilute hydrochloric acid, and the desalinated solution enters the next step; S4: The desalinated liquid is first filtered and then enters the secondary electrodialysis system to further remove chloride ions. The chlorine-containing solution returns to the primary electrodialysis system, and the solution after dechlorination is the purified liquid.

2. A process for directional calcium removal and chlorine recovery of rare earth smelting saline wastewater according to claim 1, characterized in that: The wastewater in step S1 has a calcium ion concentration of 20 g / L to 30 g / L, a chloride ion concentration of 35 g / L to 70 g / L, a pH of 8 to 12, and a total salt content of 90 g / L to 125 g / L.

3. A process for directional calcium removal and chlorine recovery of rare earth smelting saline wastewater according to claim 1, characterized in that: The amount of sulfuric acid added in step S2 is Ca 2+ :SO4 2- Mass ratio (0.35:1) ~ (0.45:1) (mg / L).

4. A process for directional calcium removal and chlorine recovery of rare earth smelting saline wastewater according to claim 3, characterized in that: The purity of the high-purity calcium sulfate obtained by drying in step S2 is >98%.

5. The process for directional decalcification and chlorine recovery of rare earth smelting saline wastewater according to claim 1, characterized in that: Step S2: Ca removal from solution 2+ <6g / L, SO4 2- <15g / L.

6. The process for directional calcium removal and chlorine recovery of rare earth smelting saline wastewater according to claim 1, characterized in that: The concentration of dilute hydrochloric acid produced by the primary electrodialysis system in step S3 is 1 mol / L to 3 mol / L.

7. The process for directional calcium removal and chlorine recovery of rare earth smelting saline wastewater according to claim 1, characterized in that: The hydrochloric acid content in the purified liquid after dechlorination in step S4 is less than 0.06%.

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