A method for treating wastewater containing trivalent cobalt

Abstract

The application discloses a treatment method of wastewater containing trivalent cobalt, and belongs to the technical field of hydrometallurgy. First, hydrochloric acid is added into the wastewater containing trivalent cobalt to adjust the pH value of the wastewater. Second, a complex breaker is added and stirred, and a primary heavy element removal is performed by using an ion exchange column. Third, hydrochloric acid is added again to adjust the pH value of the wastewater. Finally, the complex breaker is added again and stirred, and a secondary heavy element removal is performed by using the ion exchange column, so that the wastewater meeting the discharge standard is obtained. During the wastewater treatment process, no impurity element is added into the wastewater, so that the indexes of the ammonium chloride product are not affected, and the wastewater of small-size cobalt carbonate is beneficial to resource utilization.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, and specifically relates to a method for treating wastewater containing trivalent cobalt. Background Technology

[0002] In the production of small-particle cobalt carbonate, due to the characteristics of the production process, the concentration of ammonium carbonate is relatively high in the early stage of nucleation. Ammonium bicarbonate first ionizes into ammonium ions and bicarbonate ions (NH4HCO3NH4). + +HCO3-), then the ammonium ion decomposes into monohydrate and ammonia (NH4+). + Cobalt ions react with ammonia to form a 1-6 ammonia complex, namely Co(NH3·H2O). 1-6 Cl2. This complex is extremely unstable in solution and is oxidized to cobalt(II) chloride (cobalt(NH3)5Cl)Cl2, forming a trivalent cobalt-ammonium complex. This complex is deep purple, neither precipitating nor participating in the synthesis of cobalt carbonate, and remains in the mother liquor. In the early stages of nucleation, the concentration of this complex is high, approximately 400-500 mg / L, and its concentration in the mother liquor is also high. As the synthesis continues, after about 10 hours, the molar ratio of ammonium carbonate to cobalt ions in the reactor approaches 2.3 times, and the formation of the trivalent cobalt-ammonium complex ceases. When the synthesis continues for about 17-20 hours, the trivalent cobalt-ammonium complex in the mother liquor begins to overflow and continuously flows into the wastewater storage tank. As the synthesis continues and the supernatant continues to flow out, the concentration of this complex in the mother liquor gradually decreases from 400-500 mg / L to 10 mg / L.

[0003] For small-particle cobalt carbonate wastewater, it was found that the gravimetric analysis process used for large-particle cobalt carbonate wastewater could not remove cobalt. Multi-stage gravimetric analysis using resin still could not reduce the cobalt content after gravimetric analysis to less than 1 mg / L. Detection of divalent and trivalent cobalt in the small-particle cobalt carbonate wastewater revealed the presence of trivalent cobalt, which could not be removed using conventional ion exchange column resin gravimetric analysis. Summary of the Invention

[0004] The purpose of this invention is to provide a method for treating wastewater containing trivalent cobalt, aiming to solve the problems existing in the prior art described above.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for treating wastewater containing trivalent cobalt includes the following steps:

[0007] a. Add hydrochloric acid to the wastewater containing trivalent cobalt to adjust the pH value of the wastewater;

[0008] b. Add the complex-breaking agent and stir, then perform primary gravimetric removal using an ion exchange column;

[0009] c. Add hydrochloric acid again to adjust the pH value of the wastewater;

[0010] d. Add the complex-breaking agent again and stir. Use an ion exchange column for secondary gravimetric removal to obtain wastewater that meets the discharge standards.

[0011] Preferably, the complex-breaking agent in steps b and d is an aluminum-iron composite complex-breaking agent.

[0012] Preferably, in steps a and c, the pH value of the wastewater is 0.5-2.0.

[0013] Preferably, in steps a and c, the hydrochloric acid is 32% concentrated hydrochloric acid.

[0014] Preferably, the ion exchange columns in steps b and d are both sodium-type synthetic resins.

[0015] Preferably, in step b, the amount of complex-breaking agent added is 0.3-0.4 g / L.

[0016] Preferably, in step b, the amount of complex-breaking agent added is 0.1-0.15 g / L.

[0017] Preferably, in step d, the cobalt content in the wastewater that meets the emission standards is less than 1 mg / L.

[0018] Compared with the shortcomings and deficiencies of existing technologies, the present invention has the following beneficial effects:

[0019] This invention provides a method for treating wastewater containing trivalent cobalt. The method utilizes a two-stage pH adjustment process for the cobalt carbonate wastewater with small particles. After each pH adjustment, a certain amount of complex-breaking agent is added, followed by a two-stage gravimetric removal process using an ion exchange column to reduce the cobalt content in the wastewater to less than 1 mg / L, ensuring the wastewater meets discharge standards. This treatment process does not introduce impurities into the wastewater, thus not affecting the various indicators of ammonium chloride products and facilitating the resource utilization of the cobalt carbonate wastewater with small particles. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] A method for treating wastewater containing trivalent cobalt includes the following steps:

[0022] a. Add hydrochloric acid to the wastewater containing the complex to adjust the pH value of the wastewater;

[0023] b. Add the complex-breaking agent, stir, and perform primary gravimetric removal through an ion exchange column;

[0024] c. Add hydrochloric acid again to adjust the pH value of the wastewater;

[0025] d. Add the complex-breaking agent again, stir, and perform secondary gravimetric removal through an ion exchange column to obtain wastewater that meets the discharge standards.

[0026] In one embodiment, in step a, 32% concentrated hydrochloric acid is used to adjust the pH of the wastewater to between 0.5 and 2.0.

[0027] In one embodiment, in step b, 0.3-0.4 g / L of a complex-breaking agent is added. The complex-breaking agent is an aluminum-iron composite complex-breaking agent, which is an inorganic compound. It can quickly break the complex salts formed by ammonia and other complexes with metals, decompose organic matter into simple inorganic matter, and convert the complexed metal into free metal ions. After stirring for a certain period of time, the coordination bond between cobalt and ammonia is broken, and trivalent cobalt exists freely in an ionic state. However, since trivalent cobalt ions are very unstable, they cannot exist stably in solution. In a strongly acidic medium, they are quickly reduced to divalent cobalt by chloride ions. More than 95% of the trivalent cobalt is converted into divalent cobalt ions. Primary gravimetric removal is performed using an ion exchange column. Preferably, the ion exchange column uses sodium-type chelating resin, which has a removal rate of more than 98% for divalent cobalt ions.

[0028] The wastewater obtained from step b still contains trace amounts of trivalent cobalt-ammonia complexes and divalent cobalt ions. In step c, the pH of the wastewater is adjusted to 0.5-2.0 a second time using 32% concentrated hydrochloric acid.

[0029] In one embodiment, in step d, 0.1-0.15 g / L of a complex-breaking agent is added and stirred for a certain period of time to convert all trivalent cobalt in the wastewater into divalent cobalt ions. Then, a secondary gravimetric removal is performed using an ion exchange column. Preferably, the ion exchange column is a sodium-type chelating resin. The cobalt content in the wastewater obtained after the secondary gravimetric removal is less than 1 mg / L, so that the wastewater meets the discharge standards.

[0030] The advantage of this invention is that it does not increase impurity elements in the wastewater, thus not affecting the various indicators of ammonium chloride products, enabling the resource utilization of small-particle cobalt carbonate wastewater.

[0031] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0032] Example 1

[0033] Take 2L of the cobalt carbonate mother liquor synthesized for 6 hours. Sample the solution and test the concentration of divalent cobalt ions. The concentration is 85 mg / L, and the concentration of trivalent cobalt ions is 500 mg / L. Add 32% concentrated hydrochloric acid to adjust the pH of the wastewater to 0.5. Then add 0.8g of complex-breaking agent. After stirring for 5 minutes, sample the solution again. The concentration of divalent cobalt ions is 550 mg / L, and the concentration of trivalent cobalt ions is 32 mg / L. Perform primary gravimetric removal using a small ion exchange column with sodium-type chelating resin. After gravimetric removal, the concentration of divalent cobalt ions in the wastewater is 11 mg / L, and the concentration of trivalent cobalt ions is 30 mg / L. Then add 32% concentrated hydrochloric acid again to adjust the pH of the wastewater to 0.5. Add 0.3g of complex-breaking agent, stir for 3 minutes, and then perform secondary gravimetric removal using sodium-type chelating resin in an ion exchange column. After secondary gravimetric removal, the cobalt content in the wastewater is 0.83 mg / L.

[0034] Example 2

[0035] Take 2 L of the cobalt carbonate mother liquor synthesized for 15 hours. Sample the solution and test the concentration of divalent cobalt ions. The concentration of trivalent cobalt ions is 68 mg / L and 350 mg / L. Add 32% concentrated hydrochloric acid to adjust the pH of the wastewater to 0.5. Then add 0.6 g of complex-breaking agent. After stirring for 5 min, sample the solution again. The concentration of divalent cobalt ions is 401 mg / L and the concentration of trivalent cobalt ions is 20 mg / L. Perform primary gravimetric removal using a small ion exchange column with sodium-form chelating resin. After gravimetric removal, the concentration of divalent cobalt ions in the wastewater is 22 mg / L and the concentration of trivalent cobalt ions is 18.5 mg / L. Then add 32% concentrated hydrochloric acid again to adjust the pH of the wastewater to 0.5. Add 0.3 g of complex-breaking agent and stir for 3 min. Perform secondary gravimetric removal using sodium-form chelating resin in an ion exchange column. After secondary gravimetric removal, the cobalt content in the wastewater is 0.36 mg / L.

[0036] Example 3

[0037] Take 2 L of the cobalt carbonate mother liquor synthesized for 38 hours. Sample the solution and test the concentration of divalent cobalt ions. The concentration of trivalent cobalt ions is 78 mg / L, and the concentration of trivalent cobalt ions is 230 mg / L. Add 32% concentrated hydrochloric acid to adjust the pH of the wastewater to 0.5, then add 0.6 g of complexing agent. After stirring for 5 min, sample the solution again. The concentration of divalent cobalt ions is 298 mg / L, and the concentration of trivalent cobalt ions is 10 mg / L. Perform primary gravimetric removal using a small ion exchange column with sodium-type chelating resin. After gravimetric removal, the concentration of divalent cobalt ions in the wastewater is 15 mg / L, and the concentration of trivalent cobalt ions is 6.5 mg / L. Then, add 32% concentrated hydrochloric acid again to adjust the pH of the wastewater to 2.0, then add 0.2 g of complexing agent. After stirring for 3 min, perform secondary gravimetric removal using sodium-type chelating resin in an ion exchange column. After secondary gravimetric removal, the cobalt content in the wastewater is 0.56 mg / L.

[0038] Example 4

[0039] Take 2 L of the cobalt carbonate mother liquor synthesized for 50 hours. Sample the solution and test the concentration of divalent cobalt ions. The concentration of trivalent cobalt ions is 62 mg / L and 50 mg / L. Add 32% concentrated hydrochloric acid to adjust the pH of the wastewater to 0.5. Then add 0.6 g of complex-breaking agent. After stirring for 3 min, sample the solution again. The concentration of divalent cobalt ions is 110 mg / L and the concentration of trivalent cobalt ions is 3.5 mg / L. Perform primary gravimetric removal using a small ion exchange column with sodium-form chelating resin. After gravimetric removal, the concentration of divalent cobalt ions in the wastewater is 4 mg / L and the concentration of trivalent cobalt ions is 2.5 mg / L. Then add 32% concentrated hydrochloric acid again to adjust the pH of the wastewater to 2.0. Add 0.2 g of complex-breaking agent and stir for 3 min. Perform secondary gravimetric removal using sodium-form chelating resin in an ion exchange column. After secondary gravimetric removal, the cobalt content in the wastewater is 0.38 mg / L.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating wastewater containing trivalent cobalt, characterized in that, Includes the following steps: a. Add hydrochloric acid to the wastewater containing trivalent cobalt to adjust the pH value of the wastewater; b. Add the complex-breaking agent and stir, then perform primary gravimetric removal using an ion exchange column; c. Add hydrochloric acid again to adjust the pH value of the wastewater; d. Add the complex-breaking agent again and stir. Use an ion exchange column for secondary gravimetric removal to obtain wastewater that meets the discharge standards. The complex-breaking agent in steps b and d is an aluminum-iron composite complex-breaking agent; In steps a and c, the pH value of the wastewater is 0.5-2.

0. In steps a and c, the hydrochloric acid is 32% concentrated hydrochloric acid; In step b, the amount of complex-breaking agent added is 0.3-0.4 g / L; In step d, the amount of complex-breaking agent added is 0.1-0.15 g / L.

2. The method for treating wastewater containing trivalent cobalt as described in claim 1, characterized in that, The ion exchange columns in steps b and d both use sodium-type chelating resin.

3. The method for treating wastewater containing trivalent cobalt as described in claim 1, characterized in that, In step d, the cobalt content in the wastewater that meets the emission standards is less than 1 mg / L.