Application of ionic liquid aqueous two-phase system in heavy metal separation from high-salinity wastewater

Abstract

The application discloses application of an ionic liquid double-water phase system in heavy metal separation in high-salt wastewater, and relates to application of the ionic liquid double-water phase system in heavy metal separation in high-salt wastewater, wherein the ionic liquid double-water phase system comprises an ionic liquid, an inorganic salt and water, the ionic liquid is a quaternary phosphonium chloride ionic liquid or a quaternary ammonium chloride ionic liquid, the inorganic salt and water are from the high-salt wastewater, and the heavy metal is a heavy metal ion capable of forming a stable complex with chloride ions in the high-salt wastewater.The application of the ionic liquid double-water phase system in heavy metal separation in high-salt wastewater has the advantages of no volatilization, safety and stability and low viscosity, and the inorganic salt in the high-salt wastewater is used as a phase forming substance without additional addition of the inorganic salt.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of ionic liquids, in particular to application of an ionic liquid aqueous two-phase system to separation of heavy metals from high-salt wastewater. BACKGROUND

[0002] Traditional metal extraction processes rely on the use of a large amount of organic solvent, which is flammable, explosive and volatile, seriously affecting the safety, economy and environmental friendliness of the extraction process. Ionic liquids are a new type of solvent, which have the advantages of extremely low vapor pressure, stability, high designability, etc., and have been widely used in research in many fields. One important research direction is metal extraction. Ionic liquids are applied to metal extraction, and the first is the organic phase-water phase extraction strategy based on hydrophobic ionic liquids, which was first reported in 1999. So far, some problems have gradually emerged in this strategy, including: 1) the preparation of hydrophobic ionic liquids by introducing fluorine-containing anions (PF6 - or Tf2N - ) is expensive and has poor stability; 2) the viscosity of hydrophobic ionic liquids obtained by increasing the carbon chain length of anions and cations is large, and the mass transfer is slow; 3) the biological toxicity of hydrophobic ionic liquids is generally strong, leading to acute poisoning of aquatic plants and other phenomena.

[0003] The emergence of ionic liquid aqueous two-phase systems brings new opportunities to solve the above problems. It is a two-phase system composed of hydrophilic ionic liquids, salting-out substances and water, and the upper and lower phases are both aqueous solutions but are immiscible. Because the viscosity of this kind of hydrophilic ionic liquid is low, and the overall viscosity is greatly reduced due to the dilution of water in the system, in addition, this system also inherits the advantages of high stability and low biological toxicity of hydrophilic ions. In recent years, a variety of metal ion extraction and separation studies have been carried out using this system, including: extraction of noble metal gold, extraction of iridium; extraction of transition metal cobalt; separation of rare earth metals lanthanum / cerium, praseodymium / neodymium, neodymium / cobalt, samarium / cobalt, etc. However, the current ionic liquid aqueous two-phase system often needs to add a large amount of inorganic salt in the extraction and separation process, and there is no good solution to the recovery and recycling of these inorganic salts. SUMMARY

[0004] The purpose of the present application is to provide an application of ionic liquid aqueous two-phase system in high-salt wastewater heavy metal separation, which retains the advantages of ionic liquid aqueous two-phase system, such as no volatilization, safety and stability, and low viscosity; and uses the inorganic salt existing in high-salt wastewater as a phase-forming substance, without the need for additional inorganic salt. Therefore, the separation of heavy metals from high-salt wastewater is a very promising application scenario for ionic liquid aqueous two-phase system.

[0005] In order to achieve the above purpose, the solution of the present application is:

[0006] An application of an ionic liquid aqueous two-phase system in the separation of heavy metals from high-salinity wastewater involves applying the ionic liquid aqueous two-phase system to the separation of heavy metals from high-salinity wastewater. The ionic liquid aqueous two-phase system comprises an ionic liquid, an inorganic salt, and water. The ionic liquid is a quaternary phosphine chloride-based ionic liquid or a quaternary ammonium chloride-based ionic liquid. The inorganic salt and water are derived from the high-salinity wastewater. The heavy metals are heavy metal ions capable of forming stable complexes with chloride ions in the high-salinity wastewater.

[0007] The ionic liquid contains a total of 20 to 28 alkyl carbon atoms.

[0008] The molar concentration of chloride ions in the high-salt wastewater is at least 50 times the total molar concentration of heavy metal ions.

[0009] The inorganic salt concentration in the high-salt wastewater is 10 wt% to saturation concentration.

[0010] The heavy metal is one or more of cadmium, copper, mercury, lead, tin, cobalt, antimony and zinc, or a mixture thereof.

[0011] An application of an ionic liquid aqueous two-phase system in the separation of heavy metals from high-salt wastewater is carried out according to the following steps:

[0012] Step 1: First, add ionic liquid to the high-salt wastewater and mix thoroughly to form an ionic liquid aqueous two-phase system. After standing, the layers are separated. The upper layer is the ionic liquid phase containing heavy metals, and the lower layer is the inorganic salt water phase.

[0013] Step 2: Then, separate the upper ionic liquid phase obtained in Step 1 and mix it thoroughly with the alkali-sodium sulfate mixed solution. The heavy metals enter the alkali-sodium sulfate mixed solution from the ionic liquid phase. After standing and separating, the regenerated ionic liquid phase in the upper layer can be used for the next extraction cycle, and the separation of heavy metals is completed.

[0014] In step 1, the amount of the ionic liquid used is 0.01wt% to 1wt% of the amount of the high-salt wastewater used.

[0015] In step 2, in the alkali-sodium sulfate mixed solution, the alkali is NaOH or ammonia, the concentration of the alkali is between 0.1 wt% and the saturation concentration, and the concentration of the sodium sulfate is between 15 wt% and the saturation concentration.

[0016] In step 2, the mass ratio of the mixed solution to the ionic liquid phase is 0.2 to 1.

[0017] After adopting the above technical solution, the application of the ionic liquid aqueous two-phase system of the present invention in the separation of heavy metals in high-salt wastewater has a significant separation effect, which can achieve efficient removal of heavy metal ions in high-salt wastewater; it can improve the recovery concentration of heavy metal ions, which is convenient for further treatment and resource utilization of heavy metal ions by other technologies; it maintains the advantages of ionic liquid aqueous two-phase system, such as non-volatile, safe and stable and low viscosity; and it uses the inorganic salts that are already present in high-salt wastewater as phase-forming substances, so there is no need to add additional inorganic salts, thus avoiding the problem of inorganic salt recovery.

[0018] Furthermore, the molar concentration of chloride ions in the high-salt wastewater is at least 50 times the total molar concentration of heavy metal ions, thereby ensuring that heavy metal ions can effectively form complexes with chloride ions.

[0019] Furthermore, the mass concentration of inorganic salts in the high-salt wastewater is at least 10 wt%. If the concentration of inorganic salts in the high-salt wastewater is too low, the salting-out ability is weak, and the ionic liquid cannot form a phase.

[0020] Furthermore, the total number of alkyl carbon atoms in the ionic liquid is 20 to 28. When the total number of carbon atoms is too low, the ionic liquid is highly water-soluble and dissolves in the aqueous phase. When the total number of carbon atoms is too high, the ionic liquid is highly hydrophobic and has high viscosity, becoming an organic-aqueous phase system and losing the advantage of a two-aqueous phase system.

[0021] Furthermore, in step 1, the amount of the ionic liquid used is 0.01wt% to 1wt% of the amount of the high-salt wastewater used, to ensure effective extraction of heavy metal ions from the high-salt wastewater.

[0022] Furthermore, in step 2, the concentration of the alkali is at least 0.1 wt%, thereby ensuring that heavy metal ions can be stripped from the ionic liquid phase.

[0023] Furthermore, in step 2, the concentration of sodium sulfate is 15 wt%. If the concentration is too low, the added mixed solution cannot form a two-phase aqueous system with the ionic liquid phase, resulting in the loss of the ionic liquid.

[0024] Furthermore, the mass ratio of the mixed solution to the ionic liquid phase is 0.2 to 1. If the amount of mixed solution is too low, the ionic liquid cannot be effectively regenerated; if the amount is too high, the concentration of heavy metal ions after back-extraction will decrease, which is not conducive to subsequent processing. Detailed Implementation

[0025] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0026] An application of an ionic liquid aqueous two-phase system in the separation of heavy metals from high-salinity wastewater involves applying the ionic liquid aqueous two-phase system to the separation of heavy metals from high-salinity wastewater. The ionic liquid aqueous two-phase system comprises an ionic liquid, an inorganic salt, and water. The ionic liquid is a quaternary phosphine chloride-based ionic liquid or a quaternary ammonium chloride-based ionic liquid. The inorganic salt and water are derived from the high-salinity wastewater. The heavy metals are heavy metal ions capable of forming stable complexes with chloride ions in the high-salinity wastewater.

[0027] The ionic liquid contains a total of 20 to 28 alkyl carbon atoms.

[0028] The ionic liquid is a tributyldodecylammonium chloride ionic liquid, a tributyltetradecylammonium chloride ionic liquid, or a tributyltetradecylphosphine chloride ionic liquid.

[0029] The molar concentration of chloride ions in the high-salt wastewater is at least 50 times the total molar concentration of heavy metal ions.

[0030] The inorganic salt concentration in the high-salt wastewater is 10 wt% to saturation concentration.

[0031] The heavy metal is one or more of cadmium, copper, mercury, lead, tin, cobalt, antimony and zinc, or a mixture thereof.

[0032] An application of an ionic liquid aqueous two-phase system in the separation of heavy metals from high-salt wastewater is carried out according to the following steps:

[0033] Step 1: First, add ionic liquid to the high-salt wastewater and mix thoroughly to form an ionic liquid aqueous two-phase system. Let it stand and separate into layers to form an ionic liquid aqueous two-phase system. The upper layer is the ionic liquid phase containing heavy metals, and the lower layer is the inorganic salt water phase.

[0034] Step 2: Then, separate the upper ionic liquid phase obtained in Step 1 and mix it thoroughly with the alkali-sodium sulfate mixed solution. The heavy metals enter the alkali-sodium sulfate mixed solution from the ionic liquid phase. After standing and separating, the regenerated ionic liquid phase in the upper layer can be used for the next extraction cycle, and the separation of heavy metals is completed.

[0035] In step 1, the amount of the ionic liquid used is 0.01wt% to 1wt% of the amount of the high-salt wastewater used.

[0036] In step 2, in the alkali-sodium sulfate mixed solution, the alkali is NaOH or ammonia, the concentration of the alkali is between 0.1 wt% and the saturation concentration, and the concentration of the sodium sulfate is between 15 wt% and the saturation concentration.

[0037] In step 2, the mass ratio of the mixed solution to the ionic liquid phase is 0.2 to 1.

[0038] This invention discloses the application of an ionic liquid aqueous two-phase system in the separation of heavy metals from high-salinity wastewater. The basic principle is to utilize the formation of complexes between heavy metal ions and chloride ions in inorganic salts, followed by ion association or anion exchange reactions with the ionic liquid in the ionic liquid phase. Finally, the ionic liquid undergoes ion exchange with the regeneration solution, thereby completing the heavy metal separation process. Taking zinc ion extraction as an example, the ionic liquid is tributyltetradecylphosphine chloride ([P... 44414 Cl) ionic liquid, the specific reaction process is as follows:

[0039] Heavy metal complexation:

[0040]

[0041] Ion association extraction:

[0042]

[0043] Anion exchange extraction:

[0044]

[0045] Ionic liquid regeneration process:

[0046]

[0047] Example 1

[0048] After being concentrated by a wastewater recycling system, electroplating wastewater becomes high-salt wastewater with the following composition:

[0049] The heavy metals in the wastewater consisted of copper ions (0.002 mol / L) and cadmium ions (0.003 mol / L); the concentration of chloride ions was 0.5 mol / L; the main inorganic salts in the wastewater were sodium chloride and sodium sulfate, with a total mass concentration of 13 wt%.

[0050] Tributyltetradecylphosphine chloride ionic liquid was selected for the separation of heavy metals from this high-salt wastewater, and the following steps were followed:

[0051] Step 1: Take 1 kg of the above high-salt wastewater, add 1 g of tributyltetradecylphosphine chloride ionic liquid, stir thoroughly for 30 min, let stand for 2 hours to separate into two aqueous phases to form an ionic liquid two-phase system. The upper ionic liquid phase has a mass of 5 g, and the lower phase is an inorganic salt water phase.

[0052] Step 2: Prepare a mixed solution of sodium hydroxide and sodium sulfate, wherein the concentration of sodium hydroxide is 0.1 wt% and the concentration of sodium sulfate is 15 wt%. Take 1 g of the mixed solution and stir it thoroughly with the above ionic liquid phase for 30 min. Let it stand for 2 hours to separate the layers. The regenerated ionic liquid phase in the upper layer can be used for the next extraction and separation cycle, and the separation of heavy metals is completed.

[0053] The concentration of heavy metals in the lower inorganic brine phase obtained in step 1 was measured, and the results were calculated as follows: the removal rate of copper ions was 99.5%, and the removal rate of cadmium ions was 97.6%.

[0054] Example 2

[0055] After chemical treatment, a certain tannery wastewater contained heavy metals and was classified as high-salinity wastewater. Its composition is as follows:

[0056] The heavy metal composition of the wastewater is chromium ions (0.001 mol / L); the concentration of chloride ions is 1.0 mol / L; the main inorganic salts in the wastewater are sodium chloride and sodium sulfate, with a total mass concentration of 15 wt%.

[0057] Tributyltetradecylammonium chloride ionic liquid was selected for the separation of heavy metals from this high-salt wastewater, and the following steps were followed:

[0058] Step 1: Take 0.5 kg of the above high-salt wastewater, add 2 g of tributyltetradecylammonium chloride ionic liquid, stir thoroughly for 30 min, let stand for 2 hours to separate into two aqueous phases to form an ionic liquid two-phase system. The upper ionic liquid phase has a mass of 6 g, and the lower phase is an inorganic salt water phase.

[0059] Step 2: Prepare a mixed solution of ammonia and sodium sulfate, wherein the concentration of ammonia is 0.2 wt% and the concentration of sodium sulfate is 16 wt%. Take 2 g of the mixed solution and stir it thoroughly with the above ionic liquid phase for 30 min. Let it stand for 2 hours to separate the layers. The regenerated ionic liquid phase in the upper layer can be used for the next extraction and separation cycle, and the separation of heavy metals is completed.

[0060] The concentration of heavy metals in the lower inorganic brine phase obtained in step 1 was measured, and the calculated result was that the removal rate of chromium ions was 92.5%.

[0061] Example 3

[0062] The flue gas desulfurization wastewater, after chemical treatment, contains heavy metals and is classified as high-salinity wastewater. Its composition is as follows:

[0063] The heavy metals in the wastewater consisted of lead ions (0.004 mol / L) and mercury ions (0.005 mol / L); the concentration of chloride ions was 0.8 mol / L; the main inorganic salts in the wastewater were sodium chloride and sodium sulfate, with a total mass concentration of 13 wt%.

[0064] Tributyldodecylammonium chloride ionic liquid was selected for the separation of heavy metals from this high-salt wastewater, and the following steps were followed:

[0065] Step 1: Take 2.0 kg of the above high-salt wastewater, add 1 g of tributyldodecylammonium chloride ionic liquid, stir thoroughly for 30 min, let stand for 2 hours to separate into two aqueous phases to form an ionic liquid two-phase system. The upper ionic liquid phase has a mass of 4 g, and the lower phase is an inorganic salt water phase.

[0066] Step 2: Prepare a mixed solution of ammonia and sodium sulfate, wherein the concentration of ammonia is 0.5 wt% and the concentration of sodium sulfate is 16 wt%. Take 2 g of the mixed solution and stir it thoroughly with the above ionic liquid phase for 30 min. Let it stand for 2 hours to separate the layers. The regenerated ionic liquid phase in the upper layer can be used for the next extraction and separation cycle, and the separation of heavy metals is completed.

[0067] The concentration of heavy metals in the lower inorganic brine phase obtained in step 1 was measured, and the results were calculated as follows: the removal rate of mercury ions was 97.5%, and the removal rate of lead ions was 98.5%.

[0068] The ionic liquids used in this invention are all well-known in the art and can be purchased commercially.

[0069] The above embodiments are not intended to limit the product form and style of the present invention. Any appropriate changes or modifications made by those skilled in the art should be considered as not departing from the patent scope of the present invention.

Claims

1. An application of an ionic liquid aqueous two-phase system in the separation of heavy metals from high-salinity wastewater, characterized in that: The method involves applying the aqueous two-phase system of the ionic liquid to the separation of heavy metals from high-salinity wastewater. The aqueous two-phase system of the ionic liquid includes an ionic liquid, an inorganic salt, and water. The inorganic salt and water are derived from the high-salinity wastewater. The heavy metals are heavy metal ions that can form stable complexes with chloride ions in the high-salinity wastewater. The ionic liquid is a tributyldodecylammonium chloride ionic liquid, a tributyltetradecylammonium chloride ionic liquid, or a tributyltetradecylphosphine chloride ionic liquid.

2. The application of the ionic liquid aqueous two-phase system according to claim 1 in the separation of heavy metals in high-salt wastewater, characterized in that: The molar concentration of chloride ions in the high-salt wastewater is at least 50 times the total molar concentration of heavy metal ions.

3. The application of the ionic liquid aqueous two-phase system according to claim 1 in the separation of heavy metals in high-salt wastewater, characterized in that: The mass concentration of inorganic salts in the high-salt wastewater is 10 wt% to saturation concentration.

4. The application of the ionic liquid aqueous two-phase system according to claim 1 in the separation of heavy metals in high-salt wastewater, characterized in that: The heavy metal is one or more of cadmium, copper, mercury, lead, tin, cobalt, antimony and zinc, or a mixture thereof.

5. The application of the ionic liquid aqueous two-phase system according to claim 1 in the separation of heavy metals in high-salt wastewater, characterized in that: Follow these steps: Step 1: First, add ionic liquid to the high-salt wastewater and mix thoroughly to form an ionic liquid aqueous two-phase system. After standing, the layers are separated. The upper layer is the ionic liquid phase containing heavy metals, and the lower layer is the inorganic salt water phase. Step 2: Then, separate the upper ionic liquid phase obtained in Step 1 and mix it thoroughly with the alkali-sodium sulfate mixed solution. The heavy metals enter the alkali-sodium sulfate mixed solution from the ionic liquid phase. After standing and separating, the regenerated ionic liquid phase in the upper layer can be used for the next extraction cycle, and the separation of heavy metals is completed.

6. The application of the ionic liquid aqueous two-phase system according to claim 5 in the separation of heavy metals in high-salt wastewater, characterized in that: In step 1, the amount of the ionic liquid used is 0.01 times the amount of the high-salt wastewater used. wt %~1 wt %.

7. The application of the ionic liquid aqueous two-phase system according to claim 5 in the separation of heavy metals in high-salt wastewater, characterized in that: In step 2, the alkali-sodium sulfate mixed solution contains NaOH or ammonia solution, and the concentration of the alkali is 0.1%. wt The concentration of sodium sulfate is between % and saturation concentration, and is 15%. wt Between % and saturation concentration.

8. The application of the ionic liquid aqueous two-phase system according to claim 5 in the separation of heavy metals in high-salt wastewater, characterized in that: In step 2, the mass ratio of the mixed solution to the ionic liquid phase is 0.2 to 1.

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