Calcium chloride wastewater resourceful treatment method

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly relates to a calcium chloride wastewater resourceful treatment method. The method comprises the following steps: (1) adding quick lime or slaked lime into the calcium chloride wastewater to adjust the pH value of a system to 10-12, then adding a flocculating agent to perform flocculation treatment, and performing solid-liquid separation to obtain a liquid phase which is an impurity-removed solution; and (2) adding an ammonium carbonate solution into the impurity-removed solution, stirring for precipitation reaction, carrying out solid-liquid separation, washing and drying a solid phase to obtain nanoscale calcium carbonate, crystallizing a liquid phase, and recovering ammonium chloride crystals. The method is simple in process and low in energy consumption, can obtain a high-whiteness nanoscale calcium carbonate product and a high-purity ammonium chloride product, and has the advantages of low cost and high resource utilization rate.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for the resource-based treatment of calcium chloride wastewater. Background Technology

[0002] In industrial processes such as chlor-alkali chemical industry, inorganic salt production, metallurgy, surface treatment, and salt pickling, large amounts of acidic wastewater containing calcium chloride are often generated. This type of wastewater is typically characterized by high acidity, high calcium salt concentration, and high content of impurity ions (such as iron, aluminum, and silicon). Direct neutralization and discharge or simple evaporation and crystallization not only result in high energy consumption but also make it difficult to achieve high-value-added resource recovery.

[0003] Existing technologies include methods that react ammonium salts (such as ammonium bicarbonate or ammonium carbonate) with calcium chloride solution to produce calcium carbonate and then recover the ammonium chloride. However, these methods generally suffer from the following shortcomings:

[0004] (1) The impact of impurity ions in acidic wastewater on the crystallization behavior of calcium carbonate and product quality was not fully considered;

[0005] (2) The calcium carbonate obtained is mostly micron-sized or agglomerated particles, which is difficult to meet the application requirements of nano calcium carbonate;

[0006] (3) Ammonia has low utilization efficiency and is easily volatilized, causing losses and secondary pollution;

[0007] (4) The recovery method of ammonium chloride has high energy consumption or insufficient crystal purity.

[0008] Therefore, there is an urgent need for a new method for the resource-based treatment of calcium chloride wastewater that can effectively remove impurities, improve the utilization efficiency of ammonia and carbon dioxide, stably prepare nano-calcium carbonate, and achieve efficient recovery of ammonium chloride. Summary of the Invention

[0009] In view of the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a method for the resource-based treatment of calcium chloride wastewater.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for resource recovery treatment of calcium chloride wastewater includes the following steps:

[0012] (1) Add quicklime or hydrated lime to calcium chloride wastewater to adjust the pH of the system to 10-12, then add flocculant for flocculation treatment, solid-liquid separation, and the liquid phase is the solution after impurity removal;

[0013] (2) Add the ammonium carbonate solution to the purified solution, stir to carry out the precipitation reaction, separate the solid and liquid phases, wash and dry the solid phase to obtain nano-sized calcium carbonate, and crystallize the liquid phase to recover ammonium chloride crystals.

[0014] Furthermore, the pH of the calcium chloride wastewater in step (1) is 1~3; the calcium ion concentration is 20000~50000ppm; and the total concentration of impurity ions iron, aluminum and silicon is 3000~5000ppm.

[0015] Step (1) By adding quicklime or its digestion product hydrated lime, the free hydrochloric acid in the wastewater is converted into calcium chloride without introducing impurity ion components, and the pH of the system is adjusted to 10~12. Under this pH condition, impurities such as iron, aluminum, and silicon in the wastewater are precipitated in the form of hydroxides or composite precipitates, which reduces the subsequent impact on calcium carbonate precipitation and improves the quality of calcium carbonate products.

[0016] Furthermore, the flocculant mentioned in step (1) is a conventional inorganic or organic flocculant, including polyaluminum chloride (PAC), polyferric chloride (PFC), polyaluminum sulfate (PAS), polyferric sulfate (PFS), polyacrylamide (PAM), and more preferably a combination of polyaluminum chloride and cationic polyacrylamide.

[0017] Furthermore, the dosage of the flocculant in step (1) is 50~150 mg / L.

[0018] Step (1) involves flocculation treatment to obtain the product after impurities are removed, using Ca. 2+ and Cl - A solution with [a certain component] as the main component.

[0019] Further, the concentration of the ammonium carbonate solution in step (2) is 0.5~2 mol / L; the ammonium carbonate solution is prepared by the following method:

[0020] Ammonia and carbon dioxide are simultaneously or sequentially introduced into the aqueous phase through a micro-nano bubble generator, allowing the ammonia and carbon dioxide to fully dissolve and react in the water to generate an ammonium carbonate solution.

[0021] Further, in step (2), the amount of ammonium carbonate solution added is controlled so that the molar ratio of ammonium carbonate to calcium ions in the solution is (1~1.2):(1~1.2), more preferably 1~1.1:1.

[0022] Furthermore, in step (2), the stirring rate for the precipitation reaction is 500~3000 rpm and the temperature is 10~35℃; the average particle size of the nano-sized calcium carbonate is 10~200 nm.

[0023] This invention enables the formation of calcium carbonate in nanoscale particles by controlling the reaction supersaturation, shear strength, and reaction temperature. To obtain nanoscale CaCO3 with even smaller particle sizes (10~200 nm), it is necessary to promote "instantaneous burst nucleation" while inhibiting crystal growth. By controlling the calcium ion concentration and the amount of ammonium carbonate added, the relative supersaturation S (relative supersaturation S = IAP / Ksp, where IAP is the ion activity product and Ksp is the CaCO3 solubility product) is controlled at 5~20, resulting in a large number of CaCO3 nuclei, which is beneficial for controlling the particle size in the nanoscale. By controlling the reaction shear strength, the corresponding stirring intensity is 500~3000 rpm, which promotes rapid mixing and uniform instantaneous nucleation. Furthermore, controlling the reaction temperature at 10~35℃ is beneficial for the formation of vaterite or small-particle calcite, thereby obtaining nanoscale CaCO3 with even smaller particle sizes (10~200 nm), meeting the application requirements for higher-quality nanoscale calcium carbonate.

[0024] Furthermore, the crystallization process described in step (2) employs cooling crystallization and / or evaporation crystallization.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] (1) The present invention can reduce the impact on calcium carbonate crystallization recovery and improve the quality of calcium carbonate products by pre-treatment to remove impurities.

[0027] (2) The method of the present invention can obtain high whiteness, nano-sized calcium carbonate products, which can meet the application requirements of nano-calcium carbonate.

[0028] (3) The method of the present invention can obtain high-purity ammonium chloride products through simple crystallization treatment, which has the advantages of simple process and low energy consumption. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0030] Example 1

[0031] (1) Take 1.0 L of acidic wastewater containing calcium chloride, with an initial pH of 2.5, a calcium ion concentration of 30,000 ppm, and a total concentration of impurity ions (iron, aluminum, and silicon) of 4,000 ppm. Add slaked lime slurry to adjust the pH to 11, stir at 800 rpm for 20 min, and let stand for 30 min. Add 100 mg / L polyaluminum chloride and 5 mg / L cationic polyacrylamide to the system for flocculation, and obtain a clear filtrate after filtration.

[0032] (2) Ammonia and carbon dioxide were introduced into the water using a micro / nano bubble generator to prepare a 1.0 mol / L ammonium carbonate solution. This ammonium carbonate solution was then added to the clarified filtrate from step (1) under stirring at 20°C and 800 rpm, with the molar ratio determined according to Ca... 2+ The ratio of (NH4)2CO3 was controlled at 1:1, and the reaction time was 10 min. Calcium carbonate precipitate was obtained by centrifugation. After washing and drying, its average particle size (D50) was measured to be 180 nm, with a purity of 98.5% and a whiteness of 97.8. The remaining solution was evaporated under reduced pressure at low temperature to crystallize ammonium chloride crystals. The ammonium chloride crystals had a purity of 98.2%, a moisture content of 0.5%, a particle size of 100–500 μm, a whiteness of 96.7, and an overall yield of 85%.

[0033] Example 2

[0034] (1) Take 1.0 L of acidic wastewater containing calcium chloride, with an initial pH of 1.5, a calcium ion concentration of 35,000 ppm, and a total concentration of impurity ions (iron, aluminum, and silicon) of 3,000 ppm. Add quicklime slurry to adjust the pH to 11.5, stir at 1200 rpm for 25 min, and let stand for 40 min. Add 120 mg / L polyaluminum chloride and 6 mg / L cationic polyacrylamide to the system for flocculation treatment, and obtain a clear filtrate after filtration.

[0035] (2) Ammonia and carbon dioxide were introduced into the water using a micro / nano bubble generator to prepare a 1.2 mol / L ammonium carbonate solution. This ammonium carbonate solution was then added to the clarified filtrate obtained in step (1) under stirring conditions at 18℃ and 1200 rpm, with the molar ratio according to Ca... 2+ The ratio of (NH4)2CO3 was controlled at 1:1.05, and the reaction time was 8 min. Calcium carbonate precipitate was obtained by high-speed centrifugation, washed, and dried at 60℃. The average particle size (D50) was measured to be 120 nm, with a purity of 99.1% and a whiteness of 98.3. The remaining mother liquor was evaporated under reduced pressure and crystallized to obtain ammonium chloride crystals. The obtained ammonium chloride had a purity of 99.3%, a moisture content of 0.4%, a particle size of 150–400 μm, a whiteness of 97.2, and an overall yield of 88%.

[0036] Example 3

[0037] (1) Take 1.0 L of acidic wastewater containing calcium chloride, with an initial pH of 2.0, a calcium ion concentration of 40,000 ppm, and a total concentration of impurity ions (iron, aluminum, and silicon) of 3,500 ppm. Add quicklime slurry to adjust the pH to 11, stir at 1500 rpm for 20 min, and let stand for 30 min. Add 110 mg / L polyaluminum chloride and 5 mg / L cationic polyacrylamide to the system for flocculation treatment, and obtain a clear filtrate after filtration.

[0038] (2) Ammonia and carbon dioxide were introduced into the water using a micro / nano bubble generator to prepare a 1.5 mol / L ammonium carbonate solution. This ammonium carbonate solution was then added to the clarified filtrate obtained in step (1) at 15℃ and 1500 rpm, with the molar ratio determined according to Ca... 2 + The ratio of (NH4)2CO3 was controlled at 1:1.1, and the reaction time was 6 min. Calcium carbonate precipitate was obtained by centrifugation, washed, and dried. Its average particle size (D50) was measured to be 85 nm, purity 99.4%, and whiteness 98.6. The mother liquor was evaporated under reduced pressure to crystallize ammonium chloride crystals. The ammonium chloride had a purity of 99.5%, moisture content of 0.3%, particle size of 200–500 μm, whiteness of 97.5, and an overall yield of 90%.

[0039] Comparative Example 1

[0040] (1) Take 1.0 L of acidic wastewater containing calcium chloride, with an initial pH of 2.0, a calcium ion concentration of 40,000 ppm, and a total concentration of impurity ions iron, aluminum, and silicon of 3,500 ppm. Without adjusting the pH with quicklime or performing flocculation and impurity removal treatment, directly filter the wastewater and use it for precipitation reaction.

[0041] (2) An ammonium carbonate solution (1.5 mol / L) was prepared under the same conditions as in Example 3, and stirred at 15°C and 1500 rpm according to Ca... 2+ The reaction was carried out at a molar ratio of (NH4)2CO3 = 1:1.1 for 6 min. After centrifugation, calcium carbonate precipitate was obtained. After washing and drying, the average particle size of calcium carbonate was measured to be D50 = 260 nm, the purity was 93.6%, and the whiteness was 88.4.

[0042] Compared to Example 3, Comparative Example 1 did not undergo alkalization and flocculation pretreatment for impurity removal, resulting in a lower Fe content in the system. 3+ Al 3+ During the formation of carbonates, co-precipitation or adsorption occurs on the crystal surface, resulting in impurity coating and a significant decrease in purity; residual colored ions significantly reduce whiteness; and impurities induce nucleation, leading to a wider particle size distribution.

[0043] Comparative Example 2

[0044] (1) After alkalization and flocculation to remove impurities according to the method of Example 3, a clear filtrate is obtained.

[0045] (2) An ammonium carbonate solution (1.5 mol / L) was prepared under the same conditions as in Example 3. The clarified filtrate was added at 15°C, with a molar ratio of Ca... 2+ The ratio of (NH4)2CO3 was 1:1.1, but the stirring speed was only 300 rpm and the reaction time was 6 min.

[0046] After centrifugation, washing, and drying, the average particle size of calcium carbonate was measured to be D50 = 2.8 μm, the particle size distribution was D90 = 5.6 μm, the purity was 99.0%, and the whiteness was 98.0%. Under low shear conditions, the system was not fully mixed, resulting in a large local supersaturation gradient. The low nucleation rate and dominant crystal growth led to significant crystal growth of calcium carbonate, forming micron-sized particles.

[0047] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for resource-based treatment of calcium chloride wastewater, characterized in that... Includes the following steps: (1) Add quicklime or hydrated lime to calcium chloride wastewater to adjust the pH of the system to 10-12, then add flocculant for flocculation treatment, solid-liquid separation, and the liquid phase is the solution after impurity removal; (2) Add the ammonium carbonate solution to the purified solution, stir to carry out the precipitation reaction, separate the solid and liquid phases, wash and dry the solid phase to obtain nano-sized calcium carbonate, and crystallize the liquid phase to recover ammonium chloride crystals.

2. The method for resource-based treatment of calcium chloride wastewater according to claim 1, characterized in that: The pH of the calcium chloride wastewater in step (1) is 1~3; the calcium ion concentration is 20000~50000ppm; and the total concentration of impurity ions iron, aluminum and silicon is 3000~5000ppm.

3. The method for resource-based treatment of calcium chloride wastewater according to claim 1, characterized in that: The flocculant used in step (1) is an inorganic or organic flocculant, including at least one of polyaluminum chloride, polyferric chloride, polyaluminum sulfate, polyferric sulfate, and polyacrylamide.

4. The method for resource-based treatment of calcium chloride wastewater according to claim 3, characterized in that: The dosage of the flocculant is 50~150 mg / L.

5. The method for resource-based treatment of calcium chloride wastewater according to claim 1, characterized in that: The concentration of the ammonium carbonate solution in step (2) is 0.5~2 mol / L.

6. The method for resource-based treatment of calcium chloride wastewater according to claim 5, characterized in that: The ammonium carbonate solution is prepared by the following method: Ammonia and carbon dioxide are simultaneously or sequentially introduced into the aqueous phase through a micro-nano bubble generator, allowing the ammonia and carbon dioxide to fully dissolve and react in the water to generate an ammonium carbonate solution.

7. The method for resource-based treatment of calcium chloride wastewater according to claim 1, characterized in that: In step (2), the amount of ammonium carbonate solution added is controlled so that the molar ratio of ammonium carbonate to calcium ions in the solution is (1~1.2):(1~1.2).

8. The method for resource-based treatment of calcium chloride wastewater according to claim 7, characterized in that: The amount of ammonium carbonate solution added is controlled so that the molar ratio of ammonium carbonate to calcium ions in the solution is 1~1.1:

1.

9. The method for resource-based treatment of calcium chloride wastewater according to claim 1, characterized in that: The stirring rate for the precipitation reaction in step (2) is 500~3000 rpm and the temperature is 10~35℃; the average particle size of the nano-sized calcium carbonate is 10~200 nm.

10. The method for resource-based treatment of calcium chloride wastewater according to claim 1, characterized in that: The crystallization process described in step (2) involves cooling crystallization and / or evaporation crystallization.