A method for recycling magnesium salts in the nickel-cobalt industry

Abstract

This invention discloses a method for recycling magnesium salts in the nickel-cobalt industry, relating to the treatment of wastewater containing metal ions. The method involves reacting magnesium sulfate wastewater generated after multiple extractions with medium and strong alkalis, adding trace amounts of surface treatment agents, and generating a mixed precipitate of magnesium hydroxide and sulfate. Part of the aqueous phase is filtered out using a filter press and returned to the raw material slurry. The remaining mixed slurry is pumped into a high-pressure reactor, and carbon dioxide is introduced into the reactor while maintaining a certain pressure. Simultaneously, a composite nanocatalyst, La-doped Fe3O4@SiO2, is introduced to prepare a mixed slurry of soluble magnesium bicarbonate and insoluble sulfate. After rapid filtration, the synthesized magnesium bicarbonate filtrate is used to replace the liquid alkali and saponify the blank organic phase. The carbon dioxide generated during the saponification reaction is recycled. The saponified organic phase is then sent to different extraction production lines for purification and separation of the multi-metal mixed liquid, achieving a virtuous cycle in the production system.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment containing metal ions, and to a method for recycling magnesium salts and carbon dioxide. Specifically, it relates to a method for the comprehensive recovery and recycling of magnesium sulfate waste liquid. Background Technology

[0002] The manufacture of nickel / cobalt metals and related products belongs to the hydrometallurgical industry and is an essential resource for national development. The initial processing of nickel / cobalt products mainly involves nickel-cobalt-containing ores such as crude nickel-cobalt hydroxide, nickel-cobalt carbonate, nickel-cobalt sulfide flotation feed, and high / low nickel-copper-cobalt matte. However, nickel-cobalt-rich ores, in addition to nickel and cobalt, also contain certain amounts of base metals such as calcium, magnesium, and iron. These are considered "impurities" in the production process, severely interfering with and affecting the process flow, product yield, product quality, cost control, and environmental management.

[0003] Since the manufacturing of nickel, cobalt and its derivative high-end products is based on wet production, a large amount of water is required as a reaction medium. After the reaction is completed, a large amount of saline wastewater will be generated that needs to be treated, which will lead to the waste of water resources and increase the investment in environmental protection.

[0004] Furthermore, wet production processes inevitably generate waste gas, of which carbon dioxide is a common component. Therefore, the effective recovery and recycling of industrial waste gas is a key focus of this innovative project.

[0005] In short, wastewater, waste residue, and waste gas generated during industrial production constantly affect the natural environment on which people depend for survival. We will do our utmost to promote technological progress and use the power of science and technology to utilize and overcome these challenges. Summary of the Invention

[0006] This invention proposes a novel method for the recycling of magnesium salts. The magnesium sulfate waste liquid generated by the extraction system is used as raw material. Magnesium bicarbonate generated through combination and pressurized reaction is used as saponification reagent. The saponified organic phase is then extracted and back-extracted to regenerate magnesium sulfate waste liquid and blank organic phase to be saponified. These are then returned to the precipitation process and the extraction and saponification process, respectively, for a new round of recycling, thus achieving comprehensive reuse of multiple resources.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for recycling magnesium salts and carbon dioxide, the method comprising the following steps:

[0008] (1) Take 1000 mL of magnesium sulfate waste liquid after extraction, add strong alkaline aqueous solution to make the molar ratio of magnesium sulfate to strong base 1:1-1.05, then add 3-4 mL of 10% sodium dodecylbenzenesulfonate solution and 3 g of nano activated carbon particles, react at room temperature for 2 h, and the reaction temperature is 40-60℃.

[0009] (2) After the reaction is completed, a vacuum filter is used to filter part of the slurry. The filtered aqueous phase is returned to the raw material slurry pretreatment section or step (1) for the preparation of strong alkaline aqueous solution. The filter residue and the remaining unfiltered mixed slurry are put into a high-pressure reactor. 0.1-0.5% of the total mass of the reaction system composite nano-catalyst is added. Then, CO2 gas is introduced into the reactor under stirring. The gas flow rate is 1L / min. The pressure inside the reactor is kept at 0.5-0.6MPa. The reaction is carried out for 1.5-3.5h at a temperature of 5-35℃. After the reaction is completed, solid-liquid separation is carried out. The solid is insoluble sulfate and the liquid aqueous phase is magnesium bicarbonate solution.

[0010] Furthermore, in step (1), the magnesium sulfate waste liquid in the extraction section is sourced from the mixed liquid to be extracted and the blank organic phase, which is saponified with magnesium bicarbonate solution as a saponification reagent. During saponification, the volume ratio of organic phase to water phase is 1:1.5-2, the concentration of blank organic phase is 20-25%, the saponification temperature is 20-40℃, the saponification time is 6min, and the saponification rate is 50-60%. The carbon dioxide generated during the saponification process is recovered and repressurized for reuse. The saponified organic phase and the multi-metal mixed solution enter the extraction section. The set temperature is 30-45℃, the number of extraction stages is 10, and the volume ratio of organic phase to liquid is 1:0.3-3. The magnesium sulfate wastewater is used as a raw material for the synthesis of magnesium bicarbonate and reacts with a strong alkali. The blank organic phase after back-extraction is returned to the extraction section to participate in saponification again.

[0011] Furthermore, the blank organic is P204, P507, or Cyanex272.

[0012] Furthermore, the metal composition in the metal solution includes one or more of Cu, Mn, Zn, Co, Ni, Ca, and Mg.

[0013] Furthermore, the source of the strong alkali in step (1) is: solid barium salt is washed twice with deionized water, dried at 105℃ for 2 hours, and then calcined to prepare barium oxide. Microwave assistance is added during the calcination process. The microwave power is 500-1000W, the calcination temperature is 700~750℃, and the time is 20-40min. After calcination, it is mixed with deionized water to react. The solid-liquid mass ratio is 1:3-5, and the reaction time is 2 hours. After reacting with water, a strong alkali aqueous solution is formed and recycled in the production process.

[0014] Furthermore, the magnesium content in the magnesium sulfate waste liquid mentioned in step (1) is 10-21 g / L.

[0015] Furthermore, the strong base mentioned in step (1) can be barium hydroxide or calcium hydroxide.

[0016] Furthermore, in step (2), the composite nanocatalyst is La-doped Fe3O4@SiO2, prepared as follows: 0.08-0.15 parts of carboxylated porous Fe3O4 nanoparticles are dispersed in 3 parts of deionized water, sonicated for 3 min at a power of 40 kHz, and then La(NO3)3·6H2O is added to prepare a solution with a concentration of 0.1-0.5 mol / L. Then, 50 parts of ethanol, 1 part of deionized water, and 2 parts of a solution with a concentration of 25% are added to obtain a mixed solution. % ammonium hydroxide and 0.24-0.9 μL tetraethyl orthosilicate were mixed and reacted in a water bath at 40 °C for 10-20 min. The mixture was then added, stirred at 120 rpm, and reacted at 40 °C for 8 h. The mixture was washed four times alternately with deionized water and anhydrous ethanol, the solvent was removed by rotary evaporation, and then dried at 60 °C for 12 h. The dried particles were placed in a muffle furnace and calcined at 500-600 °C for 2-4 h to form a La-doped Fe3O4@SiO2 composite nanocatalyst.

[0017] Furthermore, the porous Fe3O4 nanoparticles have a particle size of 100-500 nm.

[0018] Furthermore, the reaction speed in the high-pressure reactor described in step (2) is 200-350 rpm.

[0019] Furthermore, the magnesium content in the magnesium bicarbonate filtrate produced after the pressurized reaction in step (2) is 10-22 g / L.

[0020] Compared with existing traditional technologies, the benefits that this invention can bring are:

[0021] (1) The magnesium sulfate wastewater generated after multiple extraction is recycled and then reacted with the strong alkali generated in the cycle to undergo a metathesis reaction. During the reaction, a trace amount of surface treatment agent is added. Due to the shielding effect of the surface treatment agent ions on the hydroxyl groups of the layered crystals, the mixed precipitate of magnesium hydroxide and sulfate produced is not easy to polymerize, which increases the reaction contact area of ​​the product in the subsequent treatment, thereby improving the overall circulation efficiency. The addition of activated carbon particles can adsorb impurities in the metathesis reaction and also provides crystallization sites for the mixed precipitate, reducing the supersaturated precipitate from settling into scale on the reaction vessel wall.

[0022] (2) After the metathesis reaction is completed, a vacuum filter is used for filtration. The filtered water phase is returned to the raw material slurry in step (1) or used for strong alkali preparation. The filter residue and the remaining slurry containing magnesium hydroxide and sulfate mixed precipitate are fed into the high-pressure reactor. The recovered CO2 is introduced into the reactor and a certain pressure is maintained to synthesize a soluble magnesium bicarbonate and insoluble sulfate mixed slurry. After filtration, magnesium bicarbonate filtrate is obtained. In the high-pressure reactor, the efficiency of magnesium hydroxide reacting with CO2 to generate magnesium bicarbonate is limited by the reaction kinetics. By optimizing the amount of CO2 introduced and the synthesis temperature, the efficiency of magnesium hydroxide to magnesium bicarbonate conversion is ensured. At the same time, the composite nanocatalyst La-doped Fe3O4@SiO2 is introduced. The active sites on the catalyst surface promote the adsorption and activation of CO2 and reduce the reaction activation energy, significantly reducing the reaction time and conversion rate. The prepared magnesium bicarbonate filtrate is returned to step (1) as a saponifying agent to complete the cycle. At the same time, the rapid stirring of the high-pressure reactor makes the mixed slurry have a certain flow rate, reducing the crystallization of the product on the reactor wall and the generation of scale.

[0023] (3) Insoluble solid barium salts are calcined to prepare barium oxide and introduced into microwave-assisted calcination technology. Through the penetrating and selective heating characteristics of microwaves, the calcination temperature is significantly reduced and the calcination time is shortened. At the same time, the yield and purity of barium oxide are improved and it is recycled in the production process, further reducing the cost of waste gas treatment and realizing green and efficient regeneration of strong alkali. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] The reaction equation is as follows:

[0026] 1. Magnesium hydroxide is synthesized by reacting magnesium sulfate solution with hydroxide (calcium / barium).

[0027] MgSO4+R x (OH)₂ == Mg(OH)₂↓ + R x SO4↓ (Rx represents the symbol for calcium / barium)

[0028] 2. The generated magnesium hydroxide and other substances react with carbon dioxide gas under pressure to synthesize magnesium bicarbonate.

[0029] Mg(OH)₂ + 2CO₂ == Mg(HCO₃)₂

[0030] 3. The generated magnesium bicarbonate undergoes a saponification reaction with the organic extractant.

[0031] 2RP-OH+Mg(HCO3)2 == Mg(RP-O)2+2H2O+2CO2↑

[0032] 4. After soaping, the organic phase generates magnesium sulfate after extraction of copper / manganese / zinc / cobalt.

[0033] Mg(RP-O)2+X n SO4 == X n (RP-O)2+MgSO4

[0034] Note: In the above reaction formula 1, if calcium hydroxide is used, calcium whisker sulfate will be generated as a byproduct; if barium hydroxide is used, barium sulfate will be generated as a byproduct; however, barium sulfate and barium hydroxide can also be converted through reaction and carried out indefinitely.

[0035] 5. The reaction for preparing barium hydroxide using barium sulfate as the main raw material is as follows:

[0036] 2BaSO4 (calcined at high temperature) == 2BaO + 2SO2↑ + O2↑

[0037] BaO + H₂O == Ba(OH)₂

[0038] (Note: Adding an appropriate amount of carbon to the ingredients before calcination will allow the reaction to proceed according to the following equation.)

[0039] BaSO4 + 4C = BaS + 4CO↑

[0040] 2BaS + 2H₂O = Ba(HS)₂ + Ba(OH)₂

[0041] Example 1; (1) Using magnesium bicarbonate solution as saponification reagent, react with P204 blank organic solution for saponification. The volume ratio of organic phase to water phase during saponification is 1:2, the concentration of P204 is 20%, the saponification temperature is 30℃, the saponification time is 6min, and the saponification rate is 60%. The CO2 generated by saponification is treated by a gas recovery device and then transported to the high-pressure reaction section of step (3). After the saponification is completed, the organic phase is subjected to an extraction reaction with a multi-metal mixed solution. The multi-metal mixed solution contains: zinc 2.22g / L, copper 1.75g / L, manganese 11.08g / L, and magnesium 1.5g / L. The extraction temperature is 35℃, the extraction stage is 10 stages, and the volume ratio of organic phase to feed liquid is 1:1. The magnesium sulfate solution of the raffinate is recovered and reacted with barium hydroxide. The blank organic phase after back-extraction is returned to the extraction section for saponification again. This invention uses magnesium bicarbonate, synthesized under high pressure, as an alkaline soaping agent. The CO2 generated during the saponification process is recovered by the system and then used as a raw material for hydrocarbonation to prepare magnesium bicarbonate, which reduces carbon emissions and lowers production costs. In the saponification process, the ratio conditions are optimized to improve the saponification rate and extraction efficiency.

[0042] (2) Take 1000 mL of magnesium sulfate waste liquid after extraction, with a magnesium content of 20.34 g / L, slowly add strong alkali, the molar ratio of magnesium sulfate to strong alkali is 1:1, then add 3 mL of 10% sodium dodecylbenzenesulfonate solution and 3 g of nano activated carbon particles, react at 46℃ for 2 h to finish, filter with a vacuum filter, return the filtrate to step (1) for raw material slurrying or for strong alkali solution preparation; put the filter residue and the remaining unfiltered mixed slurry into a high-pressure reactor, add the total reaction system... 0.1% by mass of composite nanocatalyst was added, and CO2 gas was introduced into the reactor under stirring at a flow rate of 1 L / min. The pressure inside the reactor was maintained at 0.6 MPa, the stirring speed was 280 rpm, the reaction was carried out for 2 h, and the temperature was 15 °C. After the reaction was completed, solid and liquid were separated. The solid was an insoluble sulfate, and the liquid phase was a magnesium bicarbonate solution with a magnesium content of 21.3 g / L. This magnesium bicarbonate filtrate was returned to step (1) as a saponifying agent and blank organic extractant to complete the saponification cycle.

[0043] The preparation method of the composite nanocatalyst is as follows: 300 mg of porous Fe3O4 nanoparticles are weighed and dispersed in 150 mL of ethanol, and ultrasonicated for 30 min. Then, 5 mL of deionized water is added and mixed evenly. Then, 10 mL of 4-triethoxysilylbutyric acid is added and ultrasonicated for 10 min for dispersion. The mixture is placed in an oil bath and heated to 60 °C. Under 60 °C conditions, the mixture is rapidly stirred for 7 h. Then, it is washed three times with ethanol, the nanoparticles are removed, and dried to obtain carboxylated porous Fe3O4 nanoparticles. 0.08 parts of carboxylated porous Fe3O4 nanoparticles are dispersed in 3 parts of deionized water and ultrasonicated for 3 min at an ultrasonic power of 40 kWh. z, then add La(NO3)3·6H2O to prepare a concentration of 0.1-0.5mol / L to obtain a mixed solution; then mix 50 parts of ethanol, 1 part of deionized water, 2 parts of 25% ammonium hydroxide and 0.24μL of tetraethyl orthosilicate, react in a water bath at 40℃ for 10min, add the mixed solution, stir at 120rpm, react at 40℃ for 8h, wash 4 times alternately with deionized water and anhydrous ethanol, remove the solvent by rotary evaporation, and dry at 60℃ for 12h. Place the dried particles in a muffle furnace and calcine at 500℃ for 2h to form a La-doped Fe3O4@SiO2 composite nanocatalyst;

[0044] The preparation of the strong alkali is as follows: an insoluble solid barium salt is washed twice with deionized water, dried at 105°C for 2 hours, and then calcined to prepare barium oxide. Microwave assistance is added during the calcination process, with a microwave power of 500W, a calcination temperature of 700°C, and a time of 20 minutes. After calcination, it reacts with deionized water at a solid-liquid mass ratio of 1:4 for 2 hours. After reacting with water, a barium hydroxide solution is generated and recycled in the production process. Since this invention eliminates the use of liquid alkali, it may achieve a one-time input of production water and an infinite recycling of system water. Theoretically, this will not generate industrial high-sodium wastewater, and there is no need to build large-scale water treatment facilities.

[0045] Example 2; (1) Using magnesium bicarbonate solution as saponification reagent, react with P204 blank organic to saponify. The volume ratio of organic phase to water phase during saponification is 1:2, the concentration of P204 is 20%, the saponification temperature is 25℃, the saponification time is 5min, and the saponification rate is 60%. The CO2 generated by saponification is transported to the high-pressure reactor in step (3) through a gas recovery device. The saponified organic phase is subjected to an extraction reaction with the feed liquid. The feed liquid contains zinc concentration of 2.22g / L, copper concentration of 1.75g / L, manganese concentration of 11.08g / L, and magnesium concentration of 1.5g / L. The extraction temperature is 30℃, the extraction stage is 10 stages, and the volume ratio of organic phase to feed liquid is 1:1.5. After multiple extractions, the raffinate containing magnesium sulfate is combined with barium hydroxide. The blank organic phase after back-extraction is returned to the extraction section for re-saponification.

[0046] (2) Take 1000 mL of magnesium sulfate waste liquid from the extraction section. The magnesium content in the magnesium sulfate waste liquid is 20.15 g / L. Add a strong base to it. The molar ratio of magnesium sulfate to strong base is 1:1.05. Then add 3 mL of 10% sodium dodecylbenzenesulfonate solution and 3 g of nano-activated carbon particles. React at room temperature for 2 h. The reaction temperature is 50℃.

[0047] (3) After the magnesium precipitation reaction is completed, the mixture is filtered by a vacuum filter. The filtered aqueous phase is returned to step (1) for raw material slurry preparation or for strong alkali solution preparation. The filter residue and the remaining mixed slurry are combined and put into a high-pressure reactor. 0.3% of the total mass of the reaction system composite nano-catalyst is added. Then, CO2 gas is introduced into the reactor under stirring at a flow rate of 1L / min. The pressure inside the reactor is maintained at 0.5MPa, the stirring speed is 300rpm, the reaction is carried out for 2.5h, and the temperature is 19℃. After the reaction is completed, the solid and liquid are separated. The solid is insoluble sulfate, and the liquid phase is magnesium bicarbonate solution. The magnesium content in the magnesium bicarbonate solution is 20.65g / L. The magnesium bicarbonate filtrate is returned to step (1) as a saponifying agent and blank organic extractant to complete the saponification cycle.

[0048] The preparation method of the composite nanocatalyst is as follows: 300 mg of porous Fe3O4 nanoparticles are weighed and dispersed in 150 mL of ethanol, and ultrasonicated for 30 min. Then, 5 mL of deionized water is added and mixed evenly. Then, 10 mL of 4-triethoxysilylbutyric acid is added and ultrasonicated for 10 min for dispersion. The mixture is placed in an oil bath and heated to 60 °C. It is then rapidly stirred at 60 °C for 7 h. After washing three times with ethanol, the nanoparticles are removed and dried to obtain carboxylated porous Fe3O4 nanoparticles. 0.11 parts of carboxylated porous Fe3O4 nanoparticles are dispersed in 3 parts of deionized water and ultrasonicated for 3 min at an ultrasonic power of 40. kHz, then add La(NO3)3·6H2O to prepare a concentration of 0.3mol / L to obtain a mixed solution; then mix 50 parts of ethanol, 1 part of deionized water, 2 parts of 25% ammonium hydroxide and 0.56μL of tetraethyl orthosilicate, react in a water bath at 40℃ for 15min, add the mixed solution, stir at 120rpm, react at 40℃ for 8h, wash 4 times alternately with deionized water and anhydrous ethanol, remove the solvent by rotary evaporation, and dry at 60℃ for 12h. Place the dried particles in a muffle furnace and calcine at 550℃ for 3h to form a La-doped Fe3O4@SiO2 composite nanocatalyst;

[0049] The strong alkali is prepared by washing an insoluble solid barium salt three times with deionized water, drying it at 105°C for 2 hours, and then calcining it to prepare calcium oxide. Microwave assistance is added during the calcination process, with a microwave power of 750W, a calcination temperature of 725°C, and a time of 30 minutes. After calcination, it reacts with deionized water at a solid-liquid mass ratio of 1:4 for 1.5 hours. The mixture is then recycled into the production process along with magnesium sulfate wastewater.

[0050] Example 3; (1) Using magnesium bicarbonate solution as saponifying agent, react with P507 organic phase for saponification. The volume ratio of organic phase to water phase during saponification is 1:1.5, the concentration of P507 extractant is 25%, the saponification temperature is 23℃, the saponification time is 6min, and the saponification rate is 55%. The CO2 generated by saponification is transported to the high-pressure reactor in step (3) through a gas recovery device. The saponified organic phase is subjected to extraction reaction with the feed liquid. The cobalt concentration in the feed liquid is 72.52g / L, nickel is 1.67g / L, and magnesium is 0.25g / L. The extraction temperature is 34℃, the extraction stage is 10 stages, and the volume ratio of organic phase to feed liquid is 1:0.4. After further extraction to recover nickel, the wastewater containing magnesium sulfate is combined with calcium hydroxide. The blank organic phase after back-extraction is returned to the extraction section for re-saponification.

[0051] (2) Preparation of magnesium hydroxide: Take 1000 mL of magnesium sulfate waste liquid from the extraction section. The magnesium content in the magnesium sulfate waste liquid is 20.2 g / L. Add a strong base to it. The molar ratio of magnesium sulfate to strong base is 1:1.05. Then add 4 mL of 10% sodium dodecylbenzenesulfonate solution and 3 g of nano-activated carbon particles. React at room temperature for 2 h. The reaction temperature is 58℃.

[0052] (3) After the magnesium precipitation reaction is completed, the mixture is filtered by a vacuum filter. The filtered aqueous phase is returned to step (1) for raw material slurry preparation. The filter residue and the remaining mixed slurry are combined and put into a high-pressure reactor. 0.5% of the total mass of the reaction system composite nano-catalyst is added. Then, CO2 gas is introduced into the reactor under stirring at a flow rate of 1L / min. The pressure inside the reactor is maintained at 0.55MPa, the stirring speed is 265rpm, the reaction is carried out for 2.5h, and the temperature is 23℃. After the reaction is completed, the solid and liquid are separated. The solid is insoluble sulfate, and the liquid phase is magnesium bicarbonate solution. The magnesium content in the magnesium bicarbonate solution is 20.39g / L. The magnesium bicarbonate filtrate is returned to step (1) as a saponifying agent and blank organic extractant to complete the saponification cycle.

[0053] The preparation method of the composite nanocatalyst is as follows: 300 mg of porous Fe3O4 nanoparticles are weighed and dispersed in 150 mL of ethanol, and ultrasonicated for 30 min. Then, 5 mL of deionized water is added and mixed evenly. Then, 10 mL of 4-triethoxysilylbutyric acid is added and ultrasonicated for 10 min for dispersion. The mixture is placed in an oil bath and heated to 60 °C. Under 60 °C conditions, the mixture is rapidly stirred for 7 h. Then, it is washed three times with ethanol, the nanoparticles are removed, and dried to obtain carboxylated porous Fe3O4 nanoparticles. 0.15 parts of carboxylated porous Fe3O4 nanoparticles are dispersed in 3 parts of deionized water and ultrasonicated for 3 min at an ultrasonic power of 40. kHz, then add La(NO3)3·6H2O to prepare a concentration of 0.5mol / L to obtain a mixed solution; then mix 50 parts of ethanol, 1 part of deionized water, 2 parts of 25% ammonium hydroxide and 0.9μL of tetraethyl orthosilicate, react in a water bath at 40℃ for 20min, add the mixed solution, stir at 120rpm, react at 40℃ for 8h, wash 4 times alternately with deionized water and anhydrous ethanol, remove the solvent by rotary evaporation, and dry at 60℃ for 12h. Place the dried particles in a muffle furnace and calcine at 600℃ for 4h to form a La-doped Fe3O4@SiO2 composite nanocatalyst;

[0054] The strong alkali is prepared by washing the insoluble solid barium salt twice with deionized water, drying it at 105°C for 2 hours, and calcining it to prepare barium oxide. During the calcination process, microwave assistance is added, with a microwave power of 1000W, a calcination temperature of 750°C, and a time of 40 minutes. After calcination, it reacts with deionized water at a solid-liquid mass ratio of 1:4 and a reaction time of 1.5 hours. The mixture is then recycled into the production process along with magnesium sulfate wastewater.

[0055] Example 4; (1) Using magnesium bicarbonate solution as saponification reagent, react with P204 blank organic to saponify. The volume ratio of organic phase to water phase during saponification is 1:2, the concentration of P204 is 20%, the saponification temperature is 25℃, the saponification time is 5min, and the saponification rate is 60%. The CO2 generated by saponification is transported to the high-pressure reactor in step (3) through a gas recovery device. The saponified organic phase is extracted with the feed liquid. The feed liquid has a zinc concentration of 2.22g / L, a copper concentration of 1.75g / L, a manganese concentration of 11.08g / L, and a magnesium concentration of 1.5g / L. The extraction temperature is 30℃, the extraction stage is 10 stages, and the volume ratio of organic phase to feed liquid is 1:1.5. After multiple extractions, the raffinate containing magnesium sulfate combines with calcium hydroxide. The blank organic phase after back-extraction is returned to the extraction section for re-saponification.

[0056] (2) Take 1000 mL of magnesium sulfate waste liquid from the extraction section. The magnesium content in the magnesium sulfate waste liquid is 20.15 g / L. Add solid barium salt to it. The molar ratio of magnesium sulfate to solid barium salt is 1:1.05. Then add 3 mL of 10% sodium dodecylbenzenesulfonate solution and 3 g of nano-activated carbon particles. React at room temperature for 2 h. The reaction temperature is 50℃.

[0057] (3) After the magnesium precipitation reaction is completed, the mixture is filtered by a vacuum filter. The filtered aqueous phase is returned to step (1) for raw material slurry preparation. The filter residue and the remaining mixed slurry are combined and put into a high-pressure reactor. CO2 gas is then introduced into the reactor under stirring at a flow rate of 1 L / min. The pressure inside the reactor is maintained at 0.5 MPa, the stirring speed is 300 rpm, the reaction is carried out for 2.5 h, and the temperature is 19 °C. After the reaction is completed, the solid and liquid are separated. The solid is insoluble sulfate, and the liquid phase is magnesium bicarbonate solution, in which the magnesium content in the magnesium bicarbonate solution is 20.65 g / L. This magnesium bicarbonate filtrate is returned to step (1) as a saponifying agent and blank organic extractant to complete the saponification cycle.

[0058] Example of effect

[0059] Tables 1-4 below show the performance analysis results of the residual content in a single cycle using Examples 1 to 4 of the present invention.

[0060] Table 1 Comparison of metal content data before and after one cycle of extraction in Example 1

[0061]

[0062] Table 2 Comparison of residual metal content before and after one cycle of extraction in Example 2

[0063]

[0064] Table 3 Comparison of metal content data before and after one cycle of extraction in Example 3

[0065]

[0066] Table 4 Comparison of metal content before and after one cycle of extraction in Example 4

[0067]

[0068] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for recycling magnesium salts and carbon dioxide, characterized in that, The method includes the following steps: (1) The mixed liquid to be extracted contains magnesium bicarbonate solution as a saponification reagent and reacts with the blank organic phase. The volume ratio of the organic phase to the aqueous phase during saponification is 1:1.5-2, the concentration of the blank organic phase is 20-25%, the saponification temperature is 20-40℃, the saponification time is 6min, and the saponification rate is 50-60%. The carbon dioxide generated during the saponification process is recovered and repressurized for reuse. The saponified organic phase and the multi-metal mixed solution enter the extraction. The set temperature is 30-45℃, the number of extraction stages is 10, and the volume ratio of the organic phase to the liquid is 1:0.3-3. The magnesium sulfate in the raffinate wastewater is used as a raw material for the combined magnesium bicarbonate and reacts with a strong alkali. The blank organic phase after back-extraction is returned to the extraction section to participate in saponification again. (2) Take 1000 mL of magnesium sulfate waste liquid after extraction in step (1), add a strong alkaline aqueous solution to make the molar ratio of magnesium sulfate to strong alkali 1:1-1.05, then add 3-4 mL of 10% sodium dodecylbenzenesulfonate solution and 3 g of nano-activated carbon particles, react at room temperature for 2 h, and the reaction temperature is 40-60℃; wherein, the source of the strong alkaline aqueous solution is: solid barium salt is washed twice with deionized water, dried at 105℃ for 2 h, and then calcined to prepare barium oxide. Microwave assistance is added during the calcination process, the microwave power is 500-1000W, the calcination temperature is 700~750℃, and the time is 20-40 min. After calcination, it is mixed with deionized water to react, the solid-liquid mass ratio is 1:3-5, the reaction time is 2 h, and after reacting with water, a strong alkaline aqueous solution is formed, which is put into the production process for recycling; (3) After the reaction is completed, a vacuum filter is used to filter part of the slurry. The filtered aqueous phase is returned to the raw material slurry pretreatment section or step (2) for the preparation of strong alkaline aqueous solution. The filter residue and the remaining unfiltered mixed slurry are put into a high-pressure reactor. 0.1-0.5% of the total mass of the reaction system of composite nano-catalyst La-doped Fe3O4@SiO2 is added. Then, CO2 gas is introduced into the reactor under stirring. The gas flow rate is 1L / min. The pressure inside the reactor is kept at 0.5-0.6MPa. The reaction is carried out for 1.5-3.5h at a temperature of 5-35℃. After the reaction is completed, solid-liquid separation is carried out. The solid is insoluble sulfate and the liquid aqueous phase is magnesium bicarbonate solution.

2. The method for recycling magnesium salts and carbon dioxide according to claim 1, characterized in that, In step (1), the blank organic is P204, P507, or Cyanex272.

3. The method for recycling magnesium salts and carbon dioxide according to claim 1, characterized in that, The metal components in the metal solution in step (1) include one or more of Cu, Mn, Zn, Co, Ni, Ca, and Mg.

4. The method for recycling magnesium salts and carbon dioxide according to claim 1, characterized in that, The magnesium content in the magnesium sulfate waste liquid mentioned in step (2) is 10-21 g / L.

5. The method for recycling magnesium salts and carbon dioxide according to claim 1, characterized in that, The preparation method of La-doped Fe3O4@SiO2 composite nanocatalyst in step (3) is as follows: 0.08-0.15 parts of carboxylated porous Fe3O4 nanoparticles are dispersed in 3 parts of deionized water, sonicated for 3 min at a sonication power of 40 kHz, and then La(NO3)3·6H2O is added to prepare a mixture with a concentration of 0.1-0.5 mol / L. Then, 50 parts of ethanol, 1 part of deionized water, 2 parts of 25% ammonium hydroxide and 0.24-0.9 μL of tetraethyl orthosilicate are mixed and reacted in a water bath at 40 °C for 10-20 min. The mixture is added, stirred at 120 rpm, and reacted at 40 °C for 8 h. The mixture is washed 4 times alternately with deionized water and anhydrous ethanol, the solvent is removed by rotary evaporation, and then dried at 60 °C for 12 h. The dried particles are placed in a muffle furnace and calcined at 500-600 °C for 2-4 h to form La-doped Fe3O4@SiO2 composite nanocatalyst.

6. The method for recycling magnesium salts and carbon dioxide according to claim 1, characterized in that, The reaction speed in the high-pressure reactor mentioned in step (3) is 200-350 rpm.

7. The method for recycling magnesium salts and carbon dioxide according to claim 1, characterized in that, The magnesium content in the magnesium bicarbonate filtrate produced after the pressurized reaction in step (3) is 10-22 g / L.

Images