Resource recovery method and application of high COD nickel-cobalt-lithium-magnesium wastewater

Abstract

The present invention discloses a resource utilization method for high-COD nickel-cobalt-lithium-magnesium wastewater and its application, comprising degreasing the high-COD nickel-cobalt-lithium-magnesium wastewater, adsorbing Ni and Co ions in the degreasing liquid with a hydrogen ion resin, adsorbing Mg ions in the liquid after the primary adsorption with a sodium ion resin, and then desorbing the adsorbed sodium ion resin with an acid to obtain a magnesium salt desorption liquid, adding an organic phosphine chelating agent to the magnesium salt desorption liquid, and introducing ammonia gas to carry out a magnesium precipitation reaction, and washing the precipitate with water and dilute acid to obtain a hexagonal magnesium hydroxide solid. The wastewater after COD removal of the present invention is subjected to the combined adsorption of the hydrogen ion resin and the sodium ion resin in two stages, which is conducive to the subsequent preparation of a higher-purity hexagonal magnesium hydroxide flame retardant solid. The chelating agent can be grafted onto the surface of the generated hexagonal magnesium hydroxide solid to modify it, thereby improving thermal stability and flame retardancy.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment and metal resource recycling, and specifically relates to a resource recovery method for high-COD nickel-cobalt-lithium-magnesium wastewater and its application. Background Art

[0002] With the rapid development of my country's new energy industry, lithium-ion batteries have been widely used due to their energy storage, rapid charge and discharge, long cycle life, and environmental friendliness. Positive and negative electrode materials are the core key materials in lithium-ion batteries. The lower limit of the energy density of lithium-ion batteries depends on the positive and negative electrode materials, and the positive and negative electrode materials account for 60% to 70% of the cost of lithium-ion batteries. Therefore, accelerating the research and development of positive and negative electrode materials and improving production processes will not only help improve the overall performance of lithium-ion batteries, but also significantly reduce the current problem of excessively high battery costs.

[0003] During the hydrometallurgical smelting of ternary cathode materials, the extraction, separation, and purification of nickel, cobalt, and manganese sulfates produces a large amount of high-COD nickel, cobalt, lithium, and magnesium wastewater. Due to the high economic value of nickel, cobalt, and lithium, this wastewater has a high recycling value. The current process involves degreasing with activated carbon, then removing the nickel, cobalt, and manganese metals with sodium sulfide. The resulting filter residue is then returned to the leaching process, and sodium hydroxide is added to the sodium sulfate solution containing lithium and magnesium to produce magnesium hydroxide. After filter pressing, solid waste and liquid waste are generated, and the wastewater is then evaporated and concentrated into sodium sulfate and lithium sulfate. This process relies on chemical precipitation to remove metals, resulting in significant lithium losses and limited removal capacity. This results in a high processing load for the back-end evaporation and concentration process, which increases operating costs to a certain extent. Therefore, the current method for treating magnesium-containing wastewater containing heavy metals, high salinity, and high COD uses sodium sulfide to remove nickel and cobalt, but some magnesium is precipitated and re-enters the system. This sodium sulfide not only pollutes the environment and harms the health of workers in the workplace, but also uses sodium hydroxide to precipitate the magnesium, requiring a high amount of sodium hydroxide. The precipitation method also suffers from high lithium losses. Therefore, there is an urgent need to develop a method for treating high COD nickel-cobalt-lithium-magnesium wastewater and realize resource utilization. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a resource recovery method and application for high-COD nickel-cobalt-lithium-magnesium wastewater. While treating high-COD nickel-cobalt-lithium-magnesium wastewater, a surface-modified hexagonal magnesium hydroxide flame retardant is prepared. Nickel and cobalt are then recovered by precipitation in the concentrated liquid at the back end, achieving efficient recovery and high-value utilization of metals in wastewater and waste residue.

[0005] According to one aspect of the present invention, a method for recycling high COD nickel-cobalt-lithium-magnesium wastewater is proposed, comprising the following steps:

[0006] S1: Deoiling high COD nickel-cobalt-lithium-magnesium wastewater to obtain deoiled liquid;

[0007] S2: using a hydrogen ion resin to adsorb Ni and Co ions in the deoiled liquid to obtain a primary adsorption liquid;

[0008] S3: adsorbing Mg ions in the primary adsorption liquid with a sodium ion resin to obtain a secondary adsorption liquid, and then desorbing the adsorbed sodium ion resin with an acid to obtain a magnesium salt desorption liquid;

[0009] S4: adding an organic phosphine chelating agent to the magnesium salt desorption solution, and introducing ammonia gas to carry out magnesium precipitation reaction, aging, and solid-liquid separation. The obtained precipitate is washed with water and dilute acid to obtain hexagonal magnesium hydroxide solid.

[0010] In some embodiments of the present invention, in step S1, the COD content in the high-COD nickel-cobalt-lithium-magnesium wastewater is 1000-1500 mg / L, the nickel metal content is 30-100 mg / L, the cobalt metal content is 15-100 mg / L, the lithium metal content is 0.5-10 g / L, and the magnesium metal content is 50-150 mg / L.

[0011] In some embodiments of the present invention, in step S1, the deoiling process is as follows: first, a high-pressure CO2 aqueous solution or a high-pressure CO2 liquid is introduced into the high-COD nickel-cobalt-lithium-magnesium wastewater for flotation deoiling, and then the wastewater after flotation deoiling is subjected to adsorption deoiling through a packed column to obtain the deoiled liquid. Furthermore, the high-pressure CO2 aqueous solution is a saturated CO2 pressurized aqueous solution with a pressurization pressure of 0.5-7Mpa, and the amount of the high-pressure CO2 aqueous solution is 8-12% of the volume of the high-COD nickel-cobalt-lithium-magnesium wastewater. Furthermore, the flotation deoiling time is 2-4h. Using a high-pressure CO2 aqueous solution for flotation deoiling can utilize the process characteristics of CO2 decompression precipitation solution to gasify or cause the micro-emulsified oil substances in the wastewater to agglomerate and float, and after the high-pressure carbon dioxide is treated with deoiling adsorption, it can be reused by an air compressor, thereby reducing the consumption of auxiliary materials in the production process. The present invention combines high-pressure CO2 aqueous solution for flotation oil removal and packed column adsorption oil removal, which can effectively reduce the COD content in wastewater, reduce the pollution of oil substances to the adsorption resin in subsequent work sections, and enhance process stability.

[0012] In some embodiments of the present invention, in step S1, the CO2 after the flotation oil removal is purified by air filtration and compressed at a pressure of 0.5-1 MPa and reused in the flotation oil removal process.

[0013] In some embodiments of the present invention, in step S1, the oil removal filler of the filling column is activated carbon or ethylene-acrylonitrile copolymer gel-type oil removal resin.

[0014] In some embodiments of the present invention, in step S1, the COD content in the high-COD nickel-cobalt-lithium-magnesium wastewater after oil removal is 50-200 mg / L.

[0015] In some embodiments of the present invention, in step S2, the hydrogen ion resin is a polystyrene molecular skeleton chelate resin.

[0016] In some embodiments of the present invention, in step S2, the adsorption conditions of the hydrogen ion resin are: the resin absorption tower is filled with a height-to-diameter ratio of (2-3): 1, a flow rate of 4-5 BV / h, and the solution pH is controlled at 5-8.

[0017] In some embodiments of the present invention, step S2 further includes: desorbing and regenerating the adsorbed hydrogen ion resin with an acid to obtain a nickel-cobalt desorption solution. Furthermore, the acid used is sulfuric acid with a mass concentration of 10% to 20%, and the pH is maintained at >3 during the pickling process.

[0018] In some embodiments of the present invention, in step S3, the sodium ion resin is a styrene-divinylbenzene copolymer sulfonyl resin, a styrene-divinylbenzene cross-linked aminophosphonic acid chelate resin or a polystyrene copolymer type I quaternary amine functional resin.

[0019] In some embodiments of the present invention, in step S3, the adsorption conditions of the sodium ion resin are: the resin absorption tower is filled with a height-to-diameter ratio of (2-3): 1, a flow rate of 3-5 BV / h, and the solution pH is controlled at 7-9.

[0020] In some embodiments of the present invention, in step S3, desorption is performed using sulfuric acid with a mass concentration of 10%-20%, and the pickling flow rate is 2-4 BV / h.

[0021] In some embodiments of the present invention, in step S3, after desorption, the sodium ion resin is regenerated with a 20 wt % to 30 wt % sodium hydroxide solution at a flow rate of 2-5 BV / h for 1-2 hours.

[0022] In some embodiments of the present invention, step S3 further includes: performing MVR concentration on the secondary adsorption liquid to obtain sodium sulfate and a concentrated liquid, and subjecting the concentrated liquid to lithium precipitation with sodium carbonate to obtain crude lithium carbonate. The secondary adsorption liquid itself has a high salt content, and sodium sulfate can be obtained by concentrating it by evaporation to 1 / 5-1 / 3 of its original volume.

[0023] In some embodiments of the present invention, in step S4, the concentration of magnesium ions in the magnesium salt desorption solution is 0.5-2.5 mol / L.

[0024] In some embodiments of the present invention, in step S4, ammonia gas is introduced to maintain the pH of the solution at 10-12.

[0025] In some embodiments of the present invention, in step S4, the organic phosphine chelating agent is at least one of hexamethylenediaminetetramethylenephosphonic acid (HDTMPA), ethylenediaminetetramethylenephosphonic acid, hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylenephosphonic acid, hexylphosphonic acid or dodecylphosphonic acid.

[0026] In some embodiments of the present invention, in step S4, the amount of the organic phosphine chelating agent added is 1 wt%-5 wt% of the theoretical yield of magnesium hydroxide.

[0027] In some embodiments of the present invention, in step S4, the temperature of the magnesium precipitation reaction is 40-80°C.

[0028] In some embodiments of the present invention, in step S4, the aging time is 2-6 hours.

[0029] In some embodiments of the present invention, in step S4, the mass concentration of the dilute acid is 1%-5%. Furthermore, the dilute acid is dilute hydrochloric acid.

[0030] In some embodiments of the present invention, step S4 further includes: evaporating and concentrating the filtrate after the solid-liquid separation, recycling the evaporated ammonia gas to the magnesium precipitation operation, adding alkali to the evaporated and concentrated solution to adjust the pH value for precipitation to obtain nickel-cobalt slag. Furthermore, the nickel-cobalt slag is acid-dissolved and then returned to the hydrogen ion resin in step S2 for adsorption, desorption to obtain a nickel-cobalt desorption solution, or returned to the front-end extraction process for purification to produce a refined nickel-cobalt solution.

[0031] The present invention also provides the use of the hexagonal magnesium hydroxide solid prepared by the resource recovery method in flame retardant materials.

[0032] According to a preferred embodiment of the present invention, there are at least the following beneficial effects:

[0033] 1. The wastewater after COD removal in the present invention is subjected to the combined adsorption of hydrogen ion resin and sodium ion resin in two stages, which can increase the content of Mg ions in the magnesium salt desorption solution and reduce the content of nickel, cobalt and manganese metals, which is conducive to the subsequent acquisition of a higher purity hexagonal magnesium hydroxide flame retardant solid. Moreover, the nickel cobalt salt solution obtained by desorption can be directly reused in the front-end extraction process for purification and production of refined nickel cobalt salt products. The best experimental process at present is to first adsorb nickel cobalt and then adsorb magnesium to achieve the separation of nickel cobalt and magnesium. Since the resins on the market that adsorb nickel cobalt have stronger selectivity, magnesium will only be carried over in small amounts due to the difference in nickel cobalt and magnesium concentrations, which does not affect the adsorption capacity of nickel cobalt. If magnesium in the wastewater is adsorbed first and then nickel cobalt is adsorbed, on the one hand, when magnesium is adsorbed, nickel cobalt will be adsorbed together, affecting the resin's adsorption effect on magnesium, and on the other hand, increasing the loss of nickel cobalt.

[0034] 2. The present invention uses a special selective resin segmented adsorption process of nickel, cobalt and magnesium to achieve short-range and efficient recovery of nickel, cobalt and lithium from wastewater. The two resins have low adsorption capacity for Li ions. After the secondary adsorption, the lithium in the liquid can be concentrated to produce sodium sulfate as a by-product. The concentrated mother liquor is precipitated to obtain crude lithium carbonate, and the comprehensive recovery rate can reach 98%.

[0035] 3. Organic phosphine chelating agents can chelate with Ni, Co, Ca, and Fe metal ions in the magnesium salt solution. Under the alkaline conditions of ammonia, they will not precipitate or be trapped in the magnesium hydroxide precipitate. The chelating agent has multiple phosphate groups, and its molecular chain can be preferentially adsorbed on the (001) and (101) crystal planes of the magnesium hydroxide crystal. The (001) and (101) crystal planes are the main exposed surfaces of the regular hexagonal flakes. Therefore, the chelating agent has the function of regulating the growth direction of the magnesium hydroxide crystal form, and can obtain a hexagonal crystal structure suitable for flame retardants. In addition, the chelating agent can also be grafted onto the surface of the generated hexagonal magnesium hydroxide solid to modify it. After modification, the carbon chain increases, the thermal stability and flame retardant properties are improved, and the surface adhesion and compatibility between the magnesium hydroxide and the flame retardant matrix material can be improved, reaching the standard for adding to polymers for flame retardancy.

[0036] 4. The precipitate obtained after the magnesium precipitation reaction is washed with dilute acid to remove the complex impurity metal ions on the surface and at the same time make the phosphate groups grafted on the surface become P(OH). If it is not washed with dilute acid, it may become POM, which is not conducive to the flame retardancy of magnesium hydroxide. The use of low concentration dilute acid has less impact on the magnesium hydroxide solid. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0038] Figure 1 This is a process flow chart of Example 1 of the present invention;

[0039] Figure 2 Schematic diagram of the principle of magnesium hydroxide surface modified with hexamethylenediaminetetramethylenephosphonic acid (HDTMPA) of the present invention;

[0040] Figure 3 The SEM images of hexagonal magnesium hydroxide surface-modified with different amounts of hexamethylenediaminetetramethylenephosphonic acid (HDTMPA) added (1%, 3%, 5%) according to the present invention are shown;

[0041] Figure 4 This is an SEM image of magnesium hydroxide prepared by direct precipitation without using a chelating agent in Comparative Example 2 of the present invention;

[0042] Figure 5 DSC curves of magnesium hydroxide before (a) and after (b) modification. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0044] Example 1

[0045] A resource recovery method for high COD nickel-cobalt-lithium-magnesium wastewater, referring to Figure 1 The specific process is:

[0046] Step (1): After the high-COD nickel-cobalt-lithium-magnesium wastewater is allowed to stand, a 0.5 MPa CO2 aqueous solution is introduced to perform flotation deoiling operation for 4 hours, wherein the amount of the high-pressure CO2 aqueous solution is 10% of the volume of the high-COD nickel-cobalt-lithium-magnesium wastewater, and the high-COD nickel-cobalt-lithium-magnesium wastewater has a COD content of 1500 mg / L, a nickel metal content of 100 mg / L, a cobalt metal content of 35 mg / L, a lithium metal content of 10 g / L, and a magnesium metal content of 150 mg / L;

[0047] Step (2): The wastewater after flotation oil removal is again passed through an activated carbon column for adsorption oil removal, and the COD of the solution can be reduced to 150 mg / L;

[0048] Step (3): using a polystyrene molecular skeleton chelating resin (Xi'an Lanxiao Technology Co., Ltd. hydrogen ion resin D463 resin) to adsorb Ni and Co metal ions in the wastewater obtained in step (2); the resin absorption tower is filled with a height-to-diameter ratio of 2:1, the flow rate is 4BV / h, the solution is controlled at pH 5, and a primary adsorption liquid is obtained after the adsorption operation; using 10% sulfuric acid to analyze and regenerate the polystyrene molecular skeleton chelating resin, and the acid washing process is maintained at pH>3 to obtain a nickel-cobalt sulfate desorption solution containing 2.4 g / L nickel, 0.9 g / L cobalt, and 0.1 g / L magnesium;

[0049] Step (4): passing the primary adsorption liquid obtained in step (3) into a styrene-divinylbenzene cross-linked aminophosphonic acid chelating resin (Xi'an Lanxiao Technology Co., Ltd. aminophosphonic acid chelating resin LSC-850) for Mg metal ion adsorption, wherein the operating conditions are that the resin absorption tower is filled with a height-to-diameter ratio of 3:1, a flow rate of 5BV / h, and the solution is controlled at pH 9, and a secondary adsorption liquid is obtained after the operation; the secondary adsorption liquid is subjected to MVR concentration and crystallization to obtain sodium sulfate, and the concentrated mother liquor is subjected to lithium precipitation operation using sodium carbonate to obtain crude lithium carbonate;

[0050] Step (5): Desorbing the saturated adsorption styrene-divinylbenzene copolymer sulfonyl resin in step (4) using 10% sulfuric acid at a flow rate of 2 BV / h to obtain a magnesium sulfate desorption solution; then regenerating the styrene-divinylbenzene copolymer sulfonyl resin using 20% ​​sodium hydroxide solution at a flow rate of 5 BV / h for 2 hours;

[0051] Step (6): adding a chelating agent HDTMPA and introducing ammonia to the magnesium salt analysis solution to perform a magnesium precipitation reaction, wherein the concentration of the magnesium salt analysis solution is 0.5 mol / L, ammonia is introduced to maintain the pH of the solution at 10, the amount of chelating agent added is 1% of the theoretical yield of magnesium hydroxide, the reaction temperature is 40°C, and the precipitation aging reaction time is 2h; after aging and filtering, washing with water and then washing with 1% dilute hydrochloric acid, and finally washing with water, and drying to obtain hexagonal magnesium hydroxide solid;

[0052] Step (7): filtering the magnesium precipitate in step (6) to obtain a filtrate, evaporating and concentrating it, and returning the evaporated ammonia to step (6); adding soda ash to the concentrated mother liquor to adjust the value and precipitate it to obtain nickel-cobalt slag; dissolving the nickel-cobalt slag with low acid to obtain an acid solution, returning it to step (3) to perform nickel-cobalt metal adsorption and desorption operations for recovery.

[0053] Example 2

[0054] A resource recovery method for high COD nickel-cobalt-lithium-magnesium wastewater, the specific process is as follows:

[0055] Step (1): After the high-COD nickel-cobalt-lithium-magnesium wastewater is allowed to stand, a 3MPa CO2 aqueous solution is introduced to perform flotation deoiling operation for 3 hours, wherein the amount of the high-pressure CO2 aqueous solution is 8% of the volume of the high-COD nickel-cobalt-lithium-magnesium wastewater, and the high-COD nickel-cobalt-lithium-magnesium wastewater has a COD content of 1300mg / L, a nickel metal content of 50mg / L, a cobalt metal content of 25mg / L, a lithium metal content of 5g / L, and a magnesium metal content of 100mg / L;

[0056] Step (2): The wastewater after flotation oil removal is again passed through an activated carbon column for adsorption oil removal, and the COD of the solution can be reduced to 100 mg / L;

[0057] Step (3): using a polystyrene molecular skeleton chelating resin to adsorb Ni and Co metal ions on the wastewater obtained in step (2); the resin absorption tower is filled with a height-to-diameter ratio of 2.5:1, the flow rate is 4.5 BV / h, the solution pH is controlled at 7, and a primary adsorption liquid is obtained after the adsorption operation; using 15% sulfuric acid to perform analytical regeneration on the polystyrene molecular skeleton chelating resin, and the pH is maintained at >3 during the pickling process to obtain a nickel-cobalt sulfate desorption solution containing 2.6 g / L nickel, 1.2 g / L cobalt, and 0.15 g / L magnesium;

[0058] Step (4): passing the primary adsorption liquid obtained in step (3) into a styrene-divinylbenzene copolymer sulfonyl resin to adsorb Mg metal ions. The operating conditions are as follows: the resin absorption tower is filled with a height-to-diameter ratio of 2.5:1, the flow rate is 4BV / h, and the solution pH is controlled at 8. After the operation, a secondary adsorption liquid is obtained; the secondary adsorption liquid is subjected to MVR concentration and crystallization to obtain sodium sulfate, and the concentrated mother liquor is subjected to lithium precipitation operation using sodium carbonate to obtain crude lithium carbonate;

[0059] Step (5): Desorbing the saturated adsorption styrene-divinylbenzene copolymer sulfonyl resin in step (4) using 10% sulfuric acid at a flow rate of 2 BV / h to obtain a magnesium sulfate desorption solution; then regenerating the styrene-divinylbenzene copolymer sulfonyl resin using 20% ​​sodium hydroxide solution at a flow rate of 5 BV / h for 2 hours;

[0060] Step (6): adding a chelating agent HDTMPA and introducing ammonia to the magnesium salt analysis solution to perform a magnesium precipitation reaction, wherein the concentration of the magnesium salt analysis solution is 1.5 mol / L, ammonia is introduced to maintain the solution pH at 11, the amount of chelating agent added is 3% of the theoretical yield of magnesium hydroxide, the reaction temperature is 60°C, and the precipitation aging reaction time is 4h; after aging and filtering, washing with water and then washing with 3% dilute hydrochloric acid, and finally washing with water, and drying to obtain hexagonal magnesium hydroxide solid;

[0061] Step (7): filtering the magnesium precipitate in step (6) to obtain a filtrate, evaporating and concentrating it, and returning the evaporated ammonia to step (6); adding soda ash to the concentrated mother liquor to adjust the value and precipitate it to obtain nickel-cobalt slag; dissolving the nickel-cobalt slag with low acid to obtain an acid solution, returning it to step (3) to perform nickel-cobalt metal adsorption and desorption operations for recovery.

[0062] Example 3

[0063] A resource recovery method for high COD nickel-cobalt-lithium-magnesium wastewater, the specific process is as follows:

[0064] Step (1): After the high-COD nickel-cobalt-lithium-magnesium wastewater is allowed to stand, a 7MPa CO2 aqueous solution is introduced to perform flotation deoiling operation for 2 hours, wherein the amount of the high-pressure CO2 aqueous solution is 10% of the volume of the high-COD nickel-cobalt-lithium-magnesium wastewater, and the high-COD nickel-cobalt-lithium-magnesium wastewater has a COD content of 1000 mg / L, a nickel metal content of 30 mg / L, a cobalt metal content of 15 mg / L, a lithium metal content of 0.5 g / L, and a magnesium metal content of 50 mg / L;

[0065] Step (2): The wastewater after flotation oil removal is again passed through an activated carbon column for adsorption oil removal, and the COD of the solution can be reduced to 50 mg / L;

[0066] Step (3): using a polystyrene molecular skeleton chelating resin to adsorb Ni and Co metal ions in the wastewater obtained in step (2); the resin absorption tower is filled with a height-to-diameter ratio of 3:1, the flow rate is 5 BV / h, the solution pH is controlled at 8, and a primary adsorption liquid is obtained after the adsorption operation; using 20% ​​sulfuric acid to perform analytical regeneration on the polystyrene molecular skeleton chelating resin, and the pH is maintained at >3 during the pickling process to obtain a nickel-cobalt sulfate desorption solution containing 2.8 g / L nickel, 1.3 g / L cobalt, and 0.25 g / L magnesium;

[0067] Step (4): passing the primary adsorption liquid obtained in step (3) into a styrene-divinylbenzene copolymer sulfonyl resin to adsorb Mg metal ions. The operating conditions are as follows: the resin absorption tower is filled with a height-to-diameter ratio of 2:1, the flow rate is 3BV / h, and the solution pH is controlled at 7. After the operation, a secondary adsorption liquid is obtained; the secondary adsorption liquid is subjected to MVR concentration and crystallization to obtain sodium sulfate, and the concentrated mother liquor is subjected to lithium precipitation operation using sodium carbonate to obtain crude lithium carbonate;

[0068] Step (5): Desorbing the saturated adsorption styrene-divinylbenzene copolymer sulfonyl resin in step (4) using 10% sulfuric acid at a flow rate of 2 BV / h to obtain a magnesium sulfate desorption solution; then regenerating the styrene-divinylbenzene copolymer sulfonyl resin using 20% ​​sodium hydroxide solution at a flow rate of 5 BV / h for 2 hours;

[0069] Step (6): adding a chelating agent HDTMPA and introducing ammonia to the magnesium salt analysis solution to perform a magnesium precipitation reaction, wherein the concentration of the magnesium salt analysis solution is 2.5 mol / L, ammonia is introduced to maintain the solution pH at 12, the amount of chelating agent added is 5% of the theoretical yield of magnesium hydroxide, the reaction temperature is 80°C, and the precipitation aging reaction time is 6h; after aging and filtering, washing with water and then washing with 5% dilute hydrochloric acid, and finally washing with water, and drying to obtain hexagonal magnesium hydroxide solid;

[0070] Step (7): filtering the magnesium precipitate in step (6) to obtain a filtrate, evaporating and concentrating it, and returning the evaporated ammonia to step (6); adding soda ash to the concentrated mother liquor to adjust the value and precipitate it to obtain nickel-cobalt slag; dissolving the nickel-cobalt slag with low acid to obtain an acid solution, returning it to step (3) to perform nickel-cobalt metal adsorption and desorption operations for recovery.

[0071] Comparative Example 1

[0072] A resource recovery method for high COD nickel-cobalt-lithium-magnesium wastewater, which differs from Example 1 in that magnesium is adsorbed first and then nickel-cobalt is adsorbed. The specific process is as follows:

[0073] Steps (1) and (2) are the same as in Example 1;

[0074] Step (3): passing the wastewater obtained in step (2) into a styrene-divinylbenzene cross-linked aminophosphonic acid chelating resin to adsorb Mg metal ions. The operating conditions are as follows: a resin absorption tower with a height-to-diameter ratio of 3:1, a flow rate of 5 BV / h, and a solution pH controlled at 9. After the operation, a primary adsorption liquid is obtained;

[0075] Step (4): passing the primary adsorption liquid obtained in step (3) into a polystyrene molecular skeleton chelating resin to adsorb Ni and Co metal ions, the resin absorption tower is filled with a height-to-diameter ratio of 2:1, the flow rate is 4BV / h, and the solution is controlled at pH 5, and a secondary adsorption liquid is obtained after the operation; using 10% sulfuric acid to decompose and regenerate the polystyrene molecular skeleton chelating resin, and the pH is maintained at 3 during the pickling process to obtain a nickel-cobalt sulfate desorption solution containing 2.1 g / L nickel, 0.5 g / L cobalt, and 0.05 g / L magnesium;

[0076] Step (5): using 10% sulfuric acid at a flow rate of 2 BV / h to desorb the styrene-divinylbenzene cross-linked aminophosphonic acid chelating resin adsorbed saturated in step (3) to obtain a magnesium sulfate desorption solution; then using 20% ​​sodium hydroxide solution at a flow rate of 5 BV / h to regenerate the styrene-divinylbenzene copolymer sulfonyl resin for 2 hours;

[0077] Step (6): The secondary adsorption liquid obtained in step (4) is subjected to MVR concentration and crystallization to obtain sodium sulfate, and the concentrated mother liquor is subjected to lithium precipitation operation using sodium carbonate to obtain crude lithium carbonate.

[0078] Comparative Example 2

[0079] The difference between the styrene-divinylbenzene copolymer sulfonyl resin and Example 3 is that no chelating agent is added in the magnesium precipitation reaction. The specific process is as follows:

[0080] Steps (1) to (5) are the same as in Example 3;

[0081] Step (6): without adding a chelating agent, ammonia gas is directly introduced into the magnesium salt solution to precipitate magnesium, the concentration of the magnesium salt solution is 2.5 mol / L, ammonia gas is introduced to maintain the solution pH at 12, the reaction temperature is 80°C, and the precipitation aging reaction time is 6 hours; after aging and filtration, the solution is washed with water and dried to obtain hexagonal magnesium hydroxide solid.

[0082] Table 1 Metal element composition of magnesium sulfate desorption solution

[0083] Element content wt% Mg Ca Ni Co Fe Li Example 1 83 1 3 2 4 7 Example 2 78 2 5 4 6 5 Example 3 74 3 8 5 4 6 Comparative Example 1 62 8 12 7 5 6

[0084] Note: Element content (wt%) refers to the ratio of each metal element to the total metal elements in the magnesium sulfate desorption solution.

[0085] As can be seen from Table 1, the Mg content in the magnesium sulfate desorption solution of Comparative Example 1 is significantly reduced, while the nickel and cobalt elements are increased. This is because the styrene-divinylbenzene copolymer sulfonyl resin has insufficient selectivity for magnesium. When adsorbing magnesium, some nickel and cobalt are adsorbed together, affecting the resin's adsorption effect on magnesium. In contrast, Example 1 first adsorbs nickel and cobalt, and then adsorbs magnesium. The polystyrene molecular skeleton chelate resin has a stronger selectivity for nickel and cobalt, and only a small amount of magnesium is entrained, which does not affect the adsorption capacity of nickel and cobalt.

[0086] Table 2 Metal element composition of magnesium hydroxide solid

[0087] Element content wt% Mg Ca Ni Co Fe Li <![CDATA[BET / (m 2 / g)]]> D50 / um Example 1 98.1 0.19 0.007 0.004 0.005 0.003 11.5 2.5 Example 2 97.7 0.12 0.005 0.003 0.004 0.005 10.8 2.3 Example 3 96.4 0.07 0.004 0.002 0.007 0.006 10.1 2.1 Comparative Example 2 90.1 2.54 0.823 0.316 0.017 0.004 20.3 0.5

[0088] As shown in Table 2, the impurity elements in the magnesium hydroxide solid obtained in Comparative Example 2 are obviously more than those in Example 3. This is because after Example 3 adds a chelating agent, the chelating agent can chelate with the Ni, Co, Ca, and Fe metal ions in the magnesium sulfate stripping solution, and can not be precipitated or be sandwiched in the magnesium hydroxide precipitation, thereby improving the purity of magnesium hydroxide. The specific surface area of ​​Comparative Example 2 is also obviously higher than that of Example 3, indicating that the magnesium hydroxide crystals generated without using a chelating agent have obvious defects, and the crystal form is incomplete.

[0089] Table 3 Metal yields of Examples and Comparative Examples

[0090] Yield % nickel cobalt lithium magnesium Example 1 94.8 94.1 98.2 94.7 Example 2 95.1 97.9 97.9 93.2 Example 3 97.3 98.6 98.3 92.5 Comparative Example 1 90.4 89.3 98.8 91.9 Comparative Example 2 97.3 98.6 98.3 92.2

[0091] The nickel-cobalt-magnesium recovery rate of comparative example 1 is obviously reduced, and this is because the special effect selectivity of styrene-divinylbenzene cross-linked aminophosphonic acid chelate resin to magnesium is not strong enough. When adsorbing magnesium, part of nickel-cobalt can be adsorbed together, affecting the adsorption effect of resin on magnesium. While embodiment 1 first adsorbs nickel-cobalt, and then adsorbs magnesium. The special effect selectivity of polystyrene molecular skeleton chelate resin to nickel-cobalt is stronger, and magnesium only has a small amount of entrainment, which does not affect the adsorption capacity of nickel-cobalt. The nickel-cobalt-lithium-magnesium recovery rate of comparative example 2 is not much different from embodiment 3. This is because the chelating agent added in embodiment 3 does not affect the recovery rate of magnesium, and only has an impact on the hexagonal magnesium hydroxide crystal form. Adopting special effect selective resin segmented adsorption nickel-cobalt, magnesium combined process can increase the nickel-cobalt-lithium-magnesium recovery rate.

[0092] Figure 3 The SEM images of hexagonal magnesium hydroxide surface modified with different amounts of hexamethylenediaminetetramethylenephosphonic acid (HDTMPA) (1%, 3%, 5%). Figure 4This is an SEM image of magnesium hydroxide prepared by direct precipitation without using a chelating agent in Comparative Example 2. As can be seen from the figure, the hexagonal magnesium hydroxide prepared under the conditions of adding 1%, 3%, and 5% HDTMPA are significantly different from those without adding a chelating agent. The crystal morphology generated without using a chelating agent is different, staggered and overlapped, and the agglomeration is serious, and the crystal has obvious defects. With the addition of HDTMPA, the obtained crystal form is more complete, the arrangement is more orderly, and the agglomeration is improved. When a smaller amount of HDTMPA (1%) is added, the crystal form still has irregular, agglomerated flakes, which is due to insufficient chelating agent molecular chains. When more HDTMPA (5%) is added, the excessively long molecular chains may cause the hexagonal flakes to entangle with each other during the growth process. Adding an appropriate amount of HDTMPA (3%) can obtain more successfully modified hexagonal magnesium hydroxide.

[0093] Figure 5 The DSC curves of magnesium hydroxide before (a) and after (b) modification in Example 3 and Comparative Example 2 are shown. After the solid surface of hexagonal magnesium hydroxide is modified with HDTMPA, the carbon chain increases, the thermal stability and flame retardancy are improved, the heat absorption of the modified magnesium hydroxide increases, and the endothermic enthalpy increases. Due to the grafting of the chelating agent HDTMPA, the pyrolysis temperature increases.

[0094] While the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A resource recovery method for high COD nickel-cobalt-lithium-magnesium wastewater, characterized in that: The following steps are involved: S1: Deoiling high COD nickel-cobalt-lithium-magnesium wastewater to obtain deoiled liquid; S2: using a hydrogen ion resin to adsorb Ni and Co ions in the deoiled liquid to obtain a primary adsorption liquid; S3: adsorbing Mg ions in the primary adsorption liquid with a sodium ion resin to obtain a secondary adsorption liquid, and then desorbing the adsorbed sodium ion resin with an acid to obtain a magnesium salt desorption liquid; S4: adding an organic phosphine chelating agent to the magnesium salt desorption solution, and introducing ammonia gas to carry out magnesium precipitation reaction, aging, and solid-liquid separation. The obtained precipitate is washed with water and dilute acid to obtain hexagonal magnesium hydroxide solid.

2. The resource utilization method according to claim 1, characterized in that: In step S1, the COD content of the high-COD nickel-cobalt-lithium-magnesium wastewater is 1000-1500 mg / L, the nickel metal content is 30-100 mg / L, the cobalt metal content is 20-100 mg / L, the lithium metal content is 0.5-10 g / L, and the magnesium metal content is 50-150 mg / L.

3. The resource utilization method according to claim 1, characterized in that: In step S1, the deoiling process is: first, high-pressure CO2 liquid is introduced into the high-COD nickel-cobalt-lithium-magnesium wastewater for flotation deoiling, and then the wastewater after flotation deoiling is passed through a packed column for adsorption deoiling to obtain the deoiled liquid.

4. The resource utilization method according to claim 1, characterized in that: In step S2, the hydrogen ion resin is a polystyrene molecular skeleton chelate resin.

5. The resource utilization method according to claim 1, characterized in that: In step S3, the sodium ion resin is a styrene-divinylbenzene copolymer sulfonyl resin, a styrene-divinylbenzene cross-linked aminophosphonic acid chelate resin or a polystyrene copolymer type I quaternary amine functional resin.

6. The resource utilization method according to claim 1, characterized in that: Step S3 further includes: performing MVR concentration on the liquid after the secondary adsorption to obtain sodium sulphite and a concentrated liquid, and using sodium carbonate to precipitate lithium in the concentrated liquid to obtain crude lithium carbonate.

7. The resource utilization method according to claim 1, characterized in that: In step S4, the organic phosphine chelating agent is at least one of hexamethylenediaminetetramethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, hexylphosphonic acid or dodecylphosphonic acid.

8. The resource utilization method according to claim 1, characterized in that: In step S4, the amount of the organic phosphine chelating agent added is 1 wt% to 5 wt% of the theoretical yield of magnesium hydroxide.

9. The resource utilization method according to claim 1, characterized in that: Step S4 further includes: evaporating and concentrating the filtrate after the solid-liquid separation, recycling the evaporated ammonia gas to the magnesium precipitation operation, adding alkali to the evaporated and concentrated solution to adjust the pH value for precipitation, and obtaining nickel-cobalt slag.

10. Use of the resource recovery method according to any one of claims 1 to 9 in the preparation of flame retardant materials.

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