Method for synchronously removing calcium ions and chloride ions in wastewater

Abstract

The invention discloses a method for synchronously removing calcium ions and chloride ions in wastewater, which comprises the following steps: adding a sodium hydroxide solution into the wastewater, introducing carbon dioxide gas into an aeration hole at the bottom of a reaction device for aeration treatment, and arranging an electrode plate in the reaction device for electrochemical treatment of the wastewater, after the reaction is completed, the treated wastewater is obtained. The method is simple in technological process and high in treatment efficiency, calcium ions in the waste water can be efficiently removed, chloride ions in the waste water can be synchronously removed, the method can be suitable for treatment of waste incineration fly ash water, CaCO3 generated in the waste water removal process can be recycled, Cl2 / HClO can be used for disinfecting or oxidizing other pollutants, and the method is suitable for industrial production. And the introduced CO2 can be used for realizing carbon fixation, so that the method has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a method for synchronously removing calcium ions and chloride ions from wastewater. Background Art

[0002] The co-processing of waste incineration fly ash in cement kilns can achieve harmless treatment and resource utilization of fly ash, which can eventually be used as a raw material for cement. However, since fly ash contains a large amount of soluble chloride salts (such as sodium chloride, calcium chloride and potassium chloride), these substances will affect the cement production process. Therefore, before the fly ash enters the cement kiln, it is usually necessary to carry out water washing pretreatment, which will produce a large amount of fly ash water. Fly ash water has the characteristics of high pH value, high chloride and high calcium, and cannot be discharged directly into the sewage treatment plant. Therefore, it is crucial to research and develop a process that can effectively remove calcium ions and chloride ions in fly ash water. Summary of the Invention

[0003] This invention is based on the inventors' discovery and understanding of the following facts and problems: fly ash water cannot be discharged directly into sewage treatment plants due to its high concentrations of chloride and calcium ions. Existing wastewater treatment methods are unable to simultaneously and efficiently remove calcium and chloride ions from high-concentration fly ash water, and their treatment efficiency is low, making it difficult to meet practical engineering requirements. Therefore, there is an urgent need to develop a treatment method that can efficiently remove calcium and chloride ions from wastewater, while also ensuring corrosion-resistant equipment and stable operation.

[0004] The present invention aims to address, at least to some extent, one of the technical problems in the related art. To this end, embodiments of the present invention provide a method for the simultaneous removal of calcium and chloride ions from wastewater. This method utilizes carbon dioxide aeration, sodium hydroxide addition, and electrochemical treatment in a reaction apparatus. This method not only efficiently removes calcium ions from the wastewater, but also simultaneously removes chloride ions, effectively improving wastewater treatment efficiency.

[0005] The method for simultaneously removing calcium ions and chloride ions from wastewater according to an embodiment of the present invention comprises the following steps: adding a sodium hydroxide solution to the wastewater, introducing carbon dioxide gas through aeration holes at the bottom of a reaction device for aeration treatment, and simultaneously providing an electrode plate in the reaction device to electrochemically treat the wastewater, thereby obtaining treated wastewater after the reaction is completed.

[0006] The advantages and technical effects of the method for simultaneously removing calcium ions and chloride ions from wastewater according to the embodiment of the present invention are as follows: 1. In the embodiment of the present invention, sodium hydroxide is added to the wastewater to adjust the pH value of the solution, and the calcium ions are formed into calcium hydroxide precipitates. At the same time, carbon dioxide gas is introduced into the reaction device for aeration. CO2 aeration can not only enhance mass transfer, but also promote the conversion of Ca(OH)2 to CaCO3, thereby improving the efficiency of CaCO3 precipitation, while reducing the pH to neutral and avoiding excessive NaOH residue. 2. In the embodiment of the present invention, while adding sodium hydroxide and introducing carbon dioxide gas for aeration, an electrochemical treatment method is further coupled. Under the action of electrodes, Cl- in the wastewater can be oxidized to Cl2, hypochlorous acid (HClO) or chlorate (ClO3 - ), no external oxidant is needed, and Cl- can be converted into a recyclable chlorine product or harmlessly treated. OH- can be generated at the cathode during electrochemical treatment, which can partially replace NaOH, reduce the dosage of sodium hydroxide, and reduce costs; 3. The method of the embodiment of the present invention has a simple process flow, is easy to operate, has high treatment efficiency, can efficiently remove calcium ions in wastewater, and can simultaneously remove chloride ions. It can be applicable to the treatment of fly ash water from waste incineration. The CaCO3 generated during the wastewater treatment process can be recycled, Cl2 / HClO can be used for disinfection or oxidation of other pollutants, and the introduced CO2 can be utilized for carbon fixation, which has broad application prospects.

[0007] In some embodiments, the flow rate of the carbon dioxide gas is 50-300 mL / min. Preferably, the volume concentration of carbon dioxide in the carbon dioxide gas is not less than 50%.

[0008] In some embodiments, the concentration of the sodium hydroxide solution is 5-11 mol / L, and the dosage of the sodium hydroxide is controlled so that the molar ratio of sodium hydroxide to calcium ions in the wastewater is 0.5-6.

[0009] In some embodiments, the sodium hydroxide solution is added at intervals, and preferably, the addition cycle is 5-20 minutes.

[0010] In some embodiments, during the electrochemical treatment, a ruthenium-iridium electrode is used as the anode and a titanium plate is used as the cathode.

[0011] In some embodiments, the electrode plates are arranged in series. Preferably, the number of the electrode plates is 2-8 groups.

[0012] In some embodiments, the voltage of the electrochemical treatment is 2-5V.

[0013] In some embodiments, the distance between the electrode plates is 0.5-1 cm, and the size of the electrode plates is (3-5) cm*(8-10) cm.

[0014] In some embodiments, the reaction time is 0.5-2.5 h.

[0015] In some embodiments, the wastewater is waste incineration fly ash water, wherein the calcium ion concentration is 5000-8000 mg / L, and the chloride ion concentration is 50000-80000 mg / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1 is a flow chart of a method for simultaneously removing calcium ions and chloride ions from wastewater according to an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0018] like Figure 1 As shown, an embodiment of the present invention provides a method for simultaneously removing calcium ions and chloride ions from wastewater, comprising the following steps: adding sodium hydroxide solution to the wastewater, introducing carbon dioxide gas through the aeration holes at the bottom of the reaction device for aeration treatment, and simultaneously providing electrode plates in the reaction device to electrochemically treat the wastewater, and obtaining treated wastewater after the reaction is completed.

[0019] In the method for removing calcium ions and chloride ions from wastewater according to an embodiment of the present invention, sodium hydroxide is added to the wastewater to adjust the pH value of the solution, and the calcium ions are formed into calcium hydroxide precipitation, and carbon dioxide gas is introduced into the reaction device for aeration. CO2 aeration can not only enhance mass transfer, but also promote the conversion of Ca(OH)2 to CaCO3, thereby improving the efficiency of CaCO3 precipitation, while reducing the pH to neutral and avoiding excessive NaOH residue. In the embodiment of the present invention, while adding sodium hydroxide and introducing carbon dioxide gas for aeration, an electrochemical treatment method is further coupled. Under the action of electrodes, Cl- in the wastewater can be oxidized to Cl2, hypochlorous acid (HClO) or chlorate (ClO3 - ), no external oxidant is required, Cl- can be converted into a recyclable chlorine product or harmlessly treated, OH- can be generated at the cathode during electrochemical treatment, which can partially replace NaOH, reduce the dosage of sodium hydroxide, and reduce costs; the method of the embodiment of the present invention has a simple process flow, is easy to operate, has high treatment efficiency, can efficiently remove calcium ions in wastewater, and can simultaneously remove chloride ions, can be applicable to the treatment of fly ash water from waste incineration, the CaCO3 generated during the wastewater treatment process can be recycled, Cl2 / HClO can be used for disinfection or oxidation of other pollutants, and the introduced CO2 can be used for carbon fixation, and has broad application prospects.

[0020] In some embodiments, the flow rate of the carbon dioxide gas is 50-300 mL / min, and preferably, the volume concentration of carbon dioxide in the carbon dioxide gas is not less than 50%. In embodiments of the present invention, by controlling the flow rate of the carbon dioxide gas, the pH value of the solution can be adjusted, the removal rate of Ca ions in the wastewater can be improved, and excessive acidification or alkalization of the solution can be avoided. If the carbon dioxide flow rate is too fast, CaCO3 will dissolve, causing excessive acidification of the solution. If the carbon dioxide flow rate is too slow, the solution will be over-alkalized, resulting in waste of NaOH.

[0021] In some embodiments, the concentration of the sodium hydroxide solution is 5-11 mol / L, and the amount of sodium hydroxide added is controlled so that the molar ratio of sodium hydroxide to calcium ions in the wastewater is 0.5-6; preferably, the sodium hydroxide solution is added at intervals, and more preferably, the sodium hydroxide addition cycle is 5-20 minutes. In the method of the embodiment of the present invention, OH- is generated at the cathode during the electrochemical treatment process, which can partially replace NaOH and reduce the amount of sodium hydroxide added. Therefore, sodium hydroxide can be added at intervals in the method of the embodiment of the present invention.

[0022] In some embodiments, the electrochemical treatment uses a ruthenium-iridium electrode as the anode and a titanium plate as the cathode. In the embodiments of the present invention, the preferred electrode plate is effectively resistant to acid and alkali corrosion, preventing corrosion of the electrode plate during the electrochemical reaction, and achieving sustained and stable removal of calcium and chloride ions from wastewater.

[0023] In some embodiments, the electrode plates are arranged in series. Preferably, the number of electrode plates is 2-8 groups, wherein one anode plate and one cathode plate constitute one group. In embodiments of the present invention, the preferred number of electrode plates is used to improve the removal rate of calcium ions and chloride ions in wastewater.

[0024] In some embodiments, the electrochemical treatment voltage is 2-5V, the distance between the electrode plates is 0.5-1cm, and the electrode plate size is (3-5)cm*(8-10)cm. In the embodiments of the present invention, the preferred voltage, electrode plate distance, and electrode plate size are used to facilitate the removal of calcium and chloride ions in wastewater.

[0025] In some embodiments, the reaction time is 0.5-2.5 hours. In the embodiments of the present invention, a treatment method that couples the addition of sodium hydroxide, carbon dioxide aeration, and electrochemical treatment is adopted. The three reaction processes are operated synchronously in the chemical reaction device, and the synergistic treatment not only achieves effective removal of calcium ions and chloride ions in the wastewater, but also accelerates the treatment speed, effectively completing the wastewater treatment in a short time, and improving the treatment efficiency.

[0026] In some embodiments, the wastewater is waste incineration fly ash water, wherein the calcium ion concentration is 5000-8000 mg / L and the chloride ion concentration is 50,000-80,000 mg / L. The method of the embodiment of the present invention can simultaneously achieve effective removal of calcium ions and chloride ions in wastewater and can be used to treat waste incineration fly ash water.

[0027] The present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0028] Example 1

[0029] The supernatant of the washing liquid from the waste incineration fly ash co-processed in a cement kiln of a certain factory was collected to measure the water quality parameters of the fly ash water, as shown in Table 1. The calcium ion concentration in the fly ash water was 6071 mg / L and the chloride ion concentration was 72997 mg / L.

[0030] Table 1 Fly ash water quality parameters

[0031]

[0032] like Figure 1 As shown, fly ash water is added to a reaction device with aeration holes evenly arranged at the bottom, and 10.6 mol / L sodium hydroxide solution is added. The dosage of sodium hydroxide is controlled so that the molar ratio of sodium hydroxide to calcium ions in the wastewater is 5.6. It is added once every 15 minutes and added four times. At the same time, a mixed gas with a volume concentration of 50% carbon dioxide and 50% nitrogen is introduced into the bottom of the reaction device for aeration. The flow rate of the mixed gas is 300 mL / min. A group of electrodes is set in the reaction device, the anode is a ruthenium-iridium electrode, the cathode is a titanium plate, the electrode plate size is 4 cm*10 cm, the spacing between the plates is 0.75 cm, the control voltage is 3.3 V, and the wastewater is electrochemically treated at the same time.

[0033] The concentrations of calcium ions and chloride ions in the fly ash aqueous solution after 1 h and 2 h of reaction were measured.

[0034] The results showed that after 1 hour, the calcium ion concentration in the solution decreased by 5155 mg / L, the chloride ion concentration decreased by 7095.7 mg / L, the calcium ion removal rate in the fly ash water was 84.9%, and the chloride ion removal rate was 9.7%.

[0035] After 2 hours, the calcium ion concentration in the solution decreased by 6071 mg / L, and the chloride ion concentration decreased by 11471.5 mg / L. The calcium ion removal rate in the fly ash water was 100%, and the chloride ion removal rate was 15.7%.

[0036] Example 2

[0037] The method is the same as that of Example 1, except that three sets of electrodes connected in series are provided in the reaction apparatus.

[0038] The concentrations of calcium ions and chloride ions in the fly ash aqueous solution after reaction for 0.5 h, 1 h and 2 h were measured.

[0039] After 0.5h, the calcium ion removal rate in fly ash water was 52.2% and the chloride ion removal rate was 12.1%.

[0040] After 1 hour, the calcium ion removal rate in fly ash water was 100%, and the chloride ion removal rate was 25.1%.

[0041] After 2 hours, the calcium ion removal rate in the fly ash water was 100%, and the chloride ion removal rate was 39.8%.

[0042] Comparative Example 1

[0043] The method is the same as that of Example 1, except that only a mixed gas with a volume concentration of 50% carbon dioxide and 50% nitrogen is introduced into the reaction device, sodium hydroxide is not added, and electrochemical treatment is not performed.

[0044] The concentrations of calcium ions and chloride ions in the fly ash aqueous solution after 2 h of reaction were measured.

[0045] After 2 hours, the calcium ion removal rate in the fly ash water was 3.9% and the chloride ion removal rate was 5.1%.

[0046] Comparative Example 2

[0047] The method is the same as that of Example 1, except that the addition of sodium hydroxide solution and the introduction of mixed gas are omitted, and only electrochemical treatment is performed.

[0048] The concentrations of calcium ions and chloride ions in the fly ash aqueous solution after 2 h of reaction were measured.

[0049] After 2 hours, the calcium ion removal rate in fly ash water was 20.1% and the chloride ion removal rate was 9.3%.

[0050] Comparative Example 3

[0051] The method is the same as that of Example 1, except that the addition of sodium hydroxide solution and the introduction of mixed gas are omitted, and only electrochemical treatment is performed, and the cathode is 316L stainless steel.

[0052] The concentrations of calcium ions and chloride ions in the fly ash aqueous solution after 2 h of reaction were measured.

[0053] After 2 hours, the calcium ion removal rate in fly ash water was 14.8% and the chloride ion removal rate was 6.2%.

[0054] Comparative Example 4

[0055] The method is the same as that of Example 1, except that the addition of sodium hydroxide solution is omitted, and only mixed gas is introduced for aeration treatment, and electrochemical treatment is performed at the same time.

[0056] The concentrations of calcium ions and chloride ions in the fly ash aqueous solution after 1 h and 2 h of reaction were measured.

[0057] After 1 hour, the calcium ion removal rate in fly ash water was 22.8%, and the chloride ion removal rate was 2.1%.

[0058] After 2 hours, the calcium ion removal rate in the fly ash water was 24.6%, and the chloride ion removal rate was 8%.

[0059] Comparative Example 5

[0060] The method is the same as that of Example 1, except that the electrochemical treatment is omitted and only sodium hydroxide solution is added and mixed gas is introduced for aeration treatment.

[0061] The concentrations of calcium ions and chloride ions in the fly ash aqueous solution after 1 h and 2 h of reaction were measured.

[0062] After 2 hours, the calcium ion removal rate in the fly ash water was 63.6%, and the chloride ion removal rate was 5.9%.

[0063] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0064] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for simultaneously removing calcium ions and chloride ions from wastewater, characterized in that: The method comprises the following steps: adding sodium hydroxide solution to wastewater, introducing carbon dioxide gas through the aeration holes at the bottom of the reaction device for aeration treatment, and simultaneously arranging electrode plates in the reaction device to electrochemically treat the wastewater, and obtaining treated wastewater after the reaction is completed.

2. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, wherein: The flow rate of the carbon dioxide gas is 50-300 mL / min. Preferably, the volume concentration of carbon dioxide in the carbon dioxide gas is not less than 50%.

3. The method for synchronously removing calcium ions and chloride ions in wastewater according to claim 1, characterized in that: The concentration of the sodium hydroxide solution is 5-11 mol / L, and the dosage of the sodium hydroxide is controlled so that the molar ratio of sodium hydroxide to calcium ions in the wastewater is 0.5-6.

4. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, wherein: The sodium hydroxide solution is added at intervals, and preferably, the addition cycle is 5-20 minutes.

5. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, wherein: In the electrochemical treatment, a ruthenium-iridium electrode is used as the anode and a titanium plate is used as the cathode.

6. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, wherein: The electrode plates are arranged in series. Preferably, the number of the electrode plates is 2-8 groups.

7. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, wherein: The voltage of the electrochemical treatment is 2-5V.

8. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, wherein: The distance between the electrode plates is 0.5-1 cm, and the size of the electrode plates is (3-5) cm*(8-10) cm.

9. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, wherein: The reaction time is 0.5-2.5h.

10. The method for simultaneously removing calcium ions and chloride ions from wastewater according to claim 1, characterized in that: The wastewater is fly ash water from garbage incineration, wherein the calcium ion concentration is 5000-8000 mg / L and the chloride ion concentration is 50000-80000 mg / L.

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