Electrochemistry-assisted precipitation dechlorination method

Abstract

The invention provides a method for removing chlorine by electrochemically assisting precipitation, and belongs to the technical field of water treatment. According to the method, an aluminum electrode serves as a cathode and an anode, introduction of sodium ions can be avoided, chlorine-containing wastewater serves as electrolyte, Al < 3 + > obtained through electrolysis is hydrolyzed to obtain Al (OH) 3, the Al (OH) 3 and calcium hydroxide generated through hydrolysis of a subsequently added calcium source are subjected to a precipitation reaction to obtain Ca4Al2 (OH) 14, OH <-> in the Ca4Al2 (OH) 14 and Cl <-> are exchanged to obtain Ca4Al2Cl2 (OH) 12, and therefore chloride ions in the wastewater are removed. Results of the embodiment show that when the electrochemical dechlorination method is used for chlorine-containing wastewater, the concentration range covers 100-10000 mg / L, and the chloride ion removal rate can reach 99%.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for removing chlorine by electrochemically assisted precipitation. Background Art

[0002] Chlorine usually exists in the form of inorganic anions in industrial wastewater such as circulating cooling water. The hazards of chlorine in industrial wastewater mainly include bitter and salty drinking water, soil salinization, pipeline corrosion, difficulty in plant growth, and harm to human health. It is very important to control and reduce the content of chloride ions in industrial wastewater.

[0003] At present, the methods reported in domestic and foreign literature to remove chloride ions from industrial wastewater mainly include precipitation salt method, membrane separation method, electrosorption method, distillation method, ion exchange method, and electrochemical oxidation method. For example, the precipitation salt method recorded in "Research Progress on Chlorine Removal by Calcium Aluminum Precipitation Method and Re-application of Precipitation" generates Ca4Al2Cl2(OH) with extremely low solubility by adding CaO or Ca(OH)2 and NaAlO2 to high-chlorine wastewater. 12 (Fluorite); wherein, the addition of sodium aluminate introduces new ions, sodium ions; excess sodium aluminate will continue to react with the Fluorite, precipitating chloride ions and reducing the chlorine removal effect; and it is only suitable for high-concentration chlorine-containing wastewater, and has a low removal rate for low-concentration chlorine-containing wastewater. Summary of the invention

[0004] The object of the present invention is to provide a method for electrochemical assisted precipitation dechlorination. The electrochemical dechlorination method provided by the present invention has good dechlorination effect and can be used for Cl - Chlorine-containing wastewater with a concentration of 100 to 10,000 mg / L without introducing impurity ions.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for electrochemical assisted precipitation and dechlorination, comprising the following steps:

[0007] (1) Using aluminum electrodes as cathode and anode respectively and chlorine-containing wastewater as electrolyte, electrolysis is performed to obtain Al-containing wastewater; Al and Cl in the Al-containing wastewater are - The ratio of the amount of substance is (2-4):1;

[0008] (2) adding a calcium source to the Al-containing wastewater obtained in step (1) to perform a precipitation reaction to obtain Ca4Al2Cl2(OH) 12 precipitation.

[0009] Preferably, the thickness of the aluminum electrode in step (1) is 0.001 mm to 10 cm.

[0010] Preferably, in step (1), Cl in the chlorine-containing wastewater - The concentration is 100~10000mg / L.

[0011] Preferably, the power source for electrolysis in step (1) is a direct current power source.

[0012] Preferably, in step (1), the electrolysis current is less than 50A, and the electrolysis voltage is 1-50V.

[0013] Preferably, the calcium in the calcium source in step (2) and the Cl in the Al-containing wastewater - The ratio of the amount of substance is (6~16):1.

[0014] Preferably, the calcium source in step (2) comprises one of calcium oxide, calcium hydroxide emulsion and fly ash.

[0015] Preferably, the concentration of the calcium hydroxide emulsion is less than 0.2 mol / L.

[0016] The present invention provides a method for electrochemical assisted precipitation dechlorination, comprising the following steps: (1) using aluminum electrodes as cathode and anode respectively, and chlorine-containing wastewater as electrolyte, to electrolyze to obtain Al-containing wastewater; Al and Cl in the Al-containing wastewater are reacted with each other to form a reaction mixture; - The amount of the substance is in a ratio of (2-4):1; (2) adding a calcium source to the Al-containing wastewater obtained in step (1) to perform a precipitation reaction to obtain Ca4Al2Cl2(OH) 12 The present invention uses aluminum electrodes as the positive and negative electrodes to avoid the introduction of sodium ions, and uses chlorine-containing wastewater as the electrolyte. The Al 3+ Then, a hydrolysis reaction is carried out to obtain Al(OH)3, which reacts with calcium hydroxide generated by the subsequent hydrolysis of the calcium source to produce Ca4Al2(OH) 14 , then Ca4Al2(OH) 14 Continue with Cl - The reaction yields Ca4Al2Cl2(OH) 12 , thereby removing chloride ions from wastewater. The results of the embodiment show that the electrochemical dechlorination method of the present invention is used for Cl - The chloride ion removal rate of chlorine-containing wastewater with a concentration of 100 to 10,000 mg / L can reach 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a physical picture of the aluminum cathode and aluminum anode used in Example 1;

[0018] Figure 2 Ca4Al2Cl2(OH) prepared in Example 1 12 XRD pattern of the precipitate. DETAILED DESCRIPTION

[0019] The present invention provides a method for electrochemical assisted precipitation and dechlorination, comprising the following steps:

[0020] (1) Using aluminum electrodes as cathode and anode respectively and chlorine-containing wastewater as electrolyte, electrolysis is performed to obtain Al-containing wastewater; Al and Cl in the Al-containing wastewater are - The ratio of the amount of substance is (2-4):1;

[0021] (2) adding a calcium source to the Al-containing wastewater obtained in step (1) to perform a precipitation reaction to obtain Ca4Al2Cl2(OH) 12 precipitation.

[0022] The invention uses aluminum electrodes as cathode and anode respectively, and chlorine-containing wastewater as electrolyte to perform electrolysis to obtain Al-containing wastewater.

[0023] The present invention has no particular limitation on the source of the aluminum electrode, and any aluminum electrode known in the art can be used. In the present invention, the aluminum electrode is preferably one of aluminum foil, aluminum sheet and aluminum plate.

[0024] In the present invention, the thickness of the aluminum electrode is preferably 0.001 mm to 10 cm, more preferably 0.01 mm to 1 cm, and further preferably 0.1 mm to 0.1 cm. The present invention can further control the thickness of the aluminum electrode by limiting the thickness of the aluminum electrode. 3+ The electrolysis rate and Al 3+ The release amount of Al 3+ After Al(OH)3 is obtained through hydrolysis reaction, it undergoes precipitation reaction more fully with calcium hydroxide.

[0025] In the present invention, Cl in the chlorine-containing wastewater - The concentration of chlorine-containing wastewater is preferably 100-10000 mg / L, more preferably 500-5000 mg / L, and further preferably 1000-3000 mg / L. The present invention further ensures that the Cl in the chlorine-containing wastewater is - Can be fully removed.

[0026] The method of the present invention has no special limitation on the source of the chlorine-containing wastewater and is applicable to various chlorine-containing wastewaters known in the art. - removal.

[0027] In the present invention, the power supply for electrolysis is preferably a DC power supply. The present invention can more accurately control the voltage and current by limiting the electrolysis power supply, thereby controlling the Al 3+ dissolution rate and effective current efficiency.

[0028] In the present invention, the electrolysis current is preferably less than 50A; the electrolysis voltage is preferably 1 to 50V, more preferably 5 to 40V, further preferably 10 to 30V, and most preferably 20V. The present invention further accurately controls the Al by limiting the electrolysis current and voltage. 3+ The electrolysis rate and Al 3+ The amount of release.

[0029] In the present invention, the time of the electrolysis is preferably determined in the following manner:

[0030] 1) Determination of Cl in chlorine-containing wastewater - The mass of Al 3+ concentration;

[0031] 2) During the electrolysis process, sample the Al-containing wastewater, add acid, and monitor the Al content in the Al-containing wastewater. 3+ When the monitoring shows that the required Al concentration has been reached, the electrolysis time is reached.

[0032] The present invention has no particular limitation on the type and concentration of the acid, and can convert all Al in the Al-containing wastewater into Al 3+ That's it.

[0033] In the present invention, Cl in the chlorine-containing wastewater - The quality is preferably detected by ion chromatography.

[0034] In the present invention, the concentration of Al in the Al-containing wastewater is preferably detected by a continuous light source atomic absorption spectrometer or an inductively coupled plasma emission spectrometer.

[0035] In the present invention, the cathode preferably removes excess Al 3+ Reduced to Al element.

[0036] In the present invention, the following reactions occur during the electrolysis process:

[0037] Anode: Al-3e - =Al 3+ ---------------------------------(1)

[0038] Electrolyte Al 3+ +3H2O=Al(OH)3+3H + -------------------------(2)

[0039] Cathode: Al 3+ +3e -=Al--------------------------------(3)

[0040] In the present invention, when the aluminum anode is completely electrolyzed, the cathode is preferably reversed and reused. The present invention can achieve excess Al 3+ recovery and recycling.

[0041] In the present invention, Al and Cl in the Al-containing wastewater - The ratio of the amount of Al and Cl in the Al-containing wastewater is preferably (2-4):1, and more preferably 3:1. - The ratio of the amount of substance to ensure that the subsequent precipitation reaction is more fully carried out, and then the Cl in the chlorine-containing wastewater is more fully removed. - .

[0042] After obtaining the Al-containing wastewater, the present invention preferably turns off the power supply and stops the electrolysis.

[0043] After turning off the power supply and stopping the electrolysis, the present invention adds a calcium source to the Al-containing wastewater to perform a precipitation reaction to obtain Ca4Al2Cl2(OH) 12 precipitation.

[0044] In the present invention, the calcium source preferably includes one of calcium oxide, calcium hydroxide emulsion and fly ash. The present invention limits the type of calcium source to obtain calcium hydroxide more fully, thereby reacting with aluminum hydroxide to obtain Ca4Al2Cl2(OH) 12 .

[0045] In the present invention, the concentration of the calcium hydroxide emulsion is preferably less than 0.2 mol / L. The present invention limits the concentration of the calcium hydroxide emulsion to ensure that the calcium hydroxide in the calcium hydroxide emulsion reacts more fully with the aluminum hydroxide.

[0046] In the present invention, the mass fraction of calcium oxide in the fly ash is preferably greater than 60%. The present invention limits the mass fraction of calcium oxide in the fly ash to ensure that the calcium oxide in the fly ash reacts more fully with aluminum hydroxide after generating calcium hydroxide.

[0047] In the present invention, the calcium in the calcium source and the Cl in the Al-containing wastewater - The ratio of the amount of the substance is preferably (6-16):1, more preferably (8-12):1, and most preferably 10:1. The present invention limits the amount of calcium in the calcium source to the amount of Cl in the Al-containing wastewater. - The amount of substance is adjusted to ensure that the precipitation reaction is more complete, thereby more fully removing Cl from the chlorine-containing wastewater. - .

[0048] In the present invention, the following reaction occurs in the precipitation reaction:

[0049] CaO+H2O=Ca(OH)2-------------------------------(4)

[0050] 4Ca(OH)2+2Al(OH)3=Ca4Al2(OH) 14 -------------------(5)

[0051] Ca4Al2(OH) 14 +2Cl - =Ca4Al2Cl2(OH) 12 +2OH - ------------------(6)

[0052] In the present invention, the precipitation reaction time is preferably determined by monitoring Cl in the chlorine-containing wastewater. - The quality of Cl in the chlorine-containing wastewater is - The mass reduction is the Cl in the initial chlorinated wastewater. - When the mass of the solid is 1-5%, it is the precipitation time.

[0053] In the present invention, the monitoring of Cl in chlorine-containing wastewater - The quality instrument is preferably an ion chromatograph.

[0054] The present invention limits the precipitation reaction time to ensure that the Cl in the chlorine-containing wastewater is - More complete removal.

[0055] The present invention uses aluminum electrodes as positive and negative electrodes to avoid the introduction of sodium ions, uses chlorine-containing wastewater as electrolyte, and electrolyzes Al 3+ Then, Al(OH)3 is hydrolyzed to form Ca4Al2(OH)3, which reacts with calcium hydroxide generated by the subsequent addition of calcium source to form Ca4Al2(OH)3. 14 , then Ca4Al2(OH) 14 Continue with Cl - The reaction yields Ca4Al2Cl2(OH) 12 , thereby removing chloride ions from wastewater.

[0056] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] Example 1

[0058] A method for electrochemically assisted precipitation and dechlorination, comprising the following steps:

[0059] (1) A rectangular aluminum foil with a size of 10 cm × 3 cm and a thickness of 0.1 mm (the aluminum electrode used is as Figure 1 As shown in the figure, 2L of chlorine-containing seawater with a concentration of 110mg / L is used as the electrolyte. After electrolysis for 4min at an industrial direct current of 30A, the power supply is turned off to stop the electrolysis, and chlorine-containing wastewater containing Al(OH)3 is obtained; Al and Cl in the chlorine-containing wastewater containing Al(OH)3 - The ratio of the amount of substance is 3.7:1;

[0060] (2) Add 5.05 g of calcium oxide to the chlorine-containing wastewater containing Al(OH)3 obtained in step (1) and perform precipitation reaction for 24 min to obtain Ca4Al2Cl2(OH) 12 Precipitation; the calcium in the calcium oxide and the Cl in the chlorine-containing wastewater containing Al(OH)3 - The ratio of the amount of substance is 10:1.

[0061] The present invention uses ion chromatography to measure the removal rate of chlorine-containing wastewater in Example 1 to be 99%. By using X-ray diffraction to analyze the Ca4Al2Cl2(OH) 12 The precipitate was characterized as Figure 2 As shown in the figure, it can be seen that the precipitated product is mainly Freund's salt, which is an ionic double-layer compound, and its main characteristic peaks appear at 11.8°, 22.8°, 23.6°, 31.1°, 39.4° and 55.5°. The rest are characteristic peaks of calcium hydroxide. There are almost no impurity peaks in the entire XRD spectrum, which confirms that the synthesized Ca4Al2Cl2(OH) 12 The sample has complete crystal phase, high purity and good crystallinity. It can be seen that Example 1 of the present invention generates Ca4Al2Cl2(OH) 12 Sedimentation realizes the removal of chloride ions in chlorine-containing wastewater.

[0062] Example 2

[0063] A method for electrochemically assisted precipitation and dechlorination, comprising the following steps:

[0064] (1) A rectangular aluminum foil of 13 cm×10 cm and 0.1 mm in thickness is used as the cathode and the anode respectively, and 2 L of 760 mg / L chlorine-containing seawater circulating cooling water drainage is used as the electrolyte. After electrolysis for 25 min at an industrial direct current of 30 A, the power supply is turned off to stop the electrolysis, thereby obtaining chlorine-containing wastewater containing Al(OH)3; Al and Cl in the chlorine-containing wastewater containing Al(OH)3- The ratio of the amount of substance is 3.3:1;

[0065] (2) Add 19.2 g of calcium oxide to the chlorine-containing wastewater containing Al(OH)3 obtained in step (1) and perform precipitation reaction for 3.5 h to obtain Ca4Al2Cl2(OH) 12 Precipitation; the calcium in the calcium oxide and the Cl in the chlorine-containing wastewater containing Al(OH)3 - The ratio of the amount of substance is 8:1.

[0066] The present invention uses an ion chromatography method to measure the removal rate of chlorine-containing wastewater in Example 2 to be 95%.

[0067] Example 3

[0068] A method for electrochemically assisted precipitation and dechlorination, comprising the following steps:

[0069] (1) A rectangular aluminum foil of 16 cm×100 cm and 0.1 mm in thickness is used as the cathode and the anode respectively, and 2 L of chlorine-containing industrial wastewater with a concentration of 10000 mg / L is used as the electrolyte. After electrolysis for 200 min at an industrial direct current of 30 A, the power supply is turned off to stop the electrolysis, and chlorine-containing wastewater containing Al(OH)3 is obtained; Al and Cl in the chlorine-containing wastewater containing Al(OH)3 - The ratio of the amount of substance is 3.2:1;

[0070] (2) Add 252.39 g of calcium oxide to the chlorine-containing wastewater containing Al(OH)3 obtained in step (1) and perform precipitation reaction for 5 h to obtain Ca4Al2Cl2(OH) 12 Precipitation; the calcium in the calcium oxide and the Cl in the chlorine-containing wastewater containing Al(OH)3 - The ratio of the amount of substance is 8:1.

[0071] The present invention uses an ion chromatography method to measure the removal rate of chlorine-containing wastewater in Example 3 to be 95%.

[0072] In summary, the electrochemical dechlorination method provided by the present invention has good dechlorination effect and can be used for Cl - Chlorine-containing wastewater with a concentration of 100 to 10,000 mg / L.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for electrochemically assisted precipitation and dechlorination, comprising the following steps: (1) Using aluminum electrodes as cathode and anode respectively and chlorine-containing wastewater as electrolyte, electrolysis is performed to obtain Al-containing wastewater; Al and Cl in the Al-containing wastewater are - The ratio of the amount of substance is (2-4):1; (2) adding a calcium source to the Al-containing wastewater obtained in step (1) to perform a precipitation reaction to obtain Ca4Al2Cl2(OH) 12 precipitation.

2. The method according to claim 1, characterized in that The thickness of the aluminum electrode in step (1) is 0.001 mm to 10 cm.

3. The method according to claim 1, characterized in that In the step (1), Cl - The concentration is 100~10000mg / L.

4. The method according to claim 1, characterized in that The power source for electrolysis in step (1) is a direct current power source.

5. The method according to claim 1 or 4, characterized in that: The electrolysis current in step (1) is less than 50A and the voltage is 1-50V.

6. The method according to claim 1, characterized in that The calcium in the calcium source in step (2) reacts with the Cl in the Al-containing wastewater - The ratio of the amount of substance is (6~16):

1.

7. The method according to claim 1, characterized in that The calcium source in step (2) includes one of calcium oxide, calcium hydroxide emulsion and fly ash.

8. The method according to claim 7, characterized in that The concentration of the calcium hydroxide emulsion is less than 0.2 mol / L.

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