A method for removing radium and / or thorium from wastewater in situ by generating hydrotalcite

Abstract

The present application relates to sewage treatment technical field, specifically to a kind of removal method of radium thorium in wastewater.The pH of wastewater is adjusted to 4~10, insoluble divalent metal source is added to carry out nucleation reaction, alkali hydroxide and soluble divalent metal source are added to carry out pre-crystallization, soluble trivalent metal source is added to carry out crystallization-adsorption complex after solid-liquid separation.The present application uses the method of in-situ hydrotalcite generation in wastewater to remove hydrotalcite, while in-situ hydrotalcite adsorption material, suitable valence complex formed by thorium radium can directly react, and in the process of directly synthesizing hydrotalcite in wastewater, thorium radium nuclide is more easily into the vacancy of hydrotalcite, and the removal rate of radium is higher.Moreover, compared with the method of preparing hydrotalcite first and then used for removing thorium radium, the method of in-situ hydrotalcite generation in wastewater provided by the present application is shorter in time consumption, wastewater treatment process is simpler, and wastewater treatment efficiency is higher.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, in particular to a method for removing radium and thorium in wastewater. BACKGROUND

[0002] In recent years, the rapid development of industry in the world, zirconium products in the national economy departments, scientific research in various fields are widely used. At present, the domestic zirconium oxychloride almost adopts "one alkali and one acid" process, namely alkali fusion decomposition (alkali burning), water washing conversion (water transfer), acidification, water solution, concentration crystallization, acid washing, centrifugal dehydration, etc. Zirconium crystallization mother liquor contains metal ions such as zirconium, titanium, hafnium and scandium, and radioactive ions such as uranium, thorium and radium. After the valuable metals are extracted by membrane separation, ion exchange, extraction and precipitation process, the last remaining solution tail liquid still contains part of thorium, radium and other radioactive substances. In order to prevent the tail liquid from causing radiation pollution to the environment, the radioactive ions in the tail liquid need to be further removed. The methods for removing radium and thorium mainly include precipitation method, adsorption method, electrochemical method, etc.

[0003] For example, Chinese patent CN102336461A discloses a method for removing metal ions in aqueous solution by using hydrotalcite, 1) dissolving soluble divalent inorganic metal salt in water to prepare salt solution A, and dissolving soluble trivalent inorganic metal salt with alkali to prepare mixed solution B, the molar ratio of divalent metal ions to trivalent metal ions is 1-4.5, the molar concentration of divalent metal ions is 0.2-2.5 mol / L, the molar concentration of trivalent metal ions is 0.1-1.25 mol / L, and the molar concentration of alkali solution is 0.1-5 mol / L; 2) adding the mixed solution B prepared in step 1) to a reaction tank, adjusting the temperature to 10-100℃, and adding solution A to the reaction tank under the stirring speed of 200-500 rpm, and then filtering to obtain hydrotalcite crude product; 3) washing the hydrotalcite crude product obtained after filtration in step 2) with water, and drying to obtain dried hydrotalcite; and then removing metal ions in aqueous solution by using the prepared hydrotalcite, wherein the metal ions include thorium and radium ions. However, the above method needs to prepare hydrotalcite first, and then remove thorium and radium ions, which is complex, and the removal rate of thorium and radium ions is only 90.5-92.3%, which is not high enough. SUMMARY

[0004] Therefore, the present application aims to provide a method for removing radium and / or thorium in wastewater by in-situ generation of hydrotalcite. The method provided by the present application has high removal rate of radium and thorium, simple process and high wastewater treatment efficiency.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a method for removing radium and / or thorium in wastewater by in-situ generation of hydrotalcite, comprising the following steps:

[0007] The pH value of the waste water is adjusted to 4-10, a source of insoluble divalent metal is added to perform nucleation reaction, then an alkali hydroxide and a source of soluble divalent metal are added to perform pre-crystallization, a source of soluble trivalent metal is added to perform crystallization-adsorption complexation, and then solid-liquid separation is performed to obtain a solid residue containing radium and / or thorium and purified water.

[0008] Preferably, the thorium content in the waste water is ≤5 mg / L, and the radium content is ≤30 Bq / L.

[0009] Preferably, the pH adjusting agent used for adjusting the pH value includes one or more of sodium hydroxide, potassium hydroxide and ammonia water.

[0010] Preferably, the divalent metal ions in the source of insoluble divalent metal include one or more of Mn 2+ , Mg 2+ , Ca 2+ , Ni 2+ , Co 2+ , Zn 2+ , Fe 2+ and Cu 2+ .

[0011] The source of insoluble divalent metal is added in an amount of 0.1-2 g / L.

[0012] Preferably, the temperature of the nucleation reaction is 20-50°C, and the time is 1-30 min.

[0013] Preferably, the divalent metal ions in the source of soluble divalent metal include one or more of Mn 2+ , Mg 2+ , Ca 2+ , Ni 2+ , Co 2+ , Zn 2+ , Fe 2+ and Cu 2+ .

[0014] Preferably, the total amount of the alkali hydroxide and the source of soluble divalent metal is 0.5-3 g / L; and the mass of the alkali hydroxide accounts for 10-30% of the total mass of the alkali hydroxide and the source of soluble divalent metal.

[0015] Preferably, the temperature of the pre-crystallization is 20-50°C, and the time is 1-30 min.

[0016] Preferably, the trivalent metal ions in the source of soluble trivalent metal include Al 3+ , Cr 3+ , Fe 3+ and Sc 3+One or more of the following: the amount of the soluble trivalent metal source added is 0.1-2 g / L.

[0017] Preferably, the temperature of the crystallization-adsorption complexation is 20-50℃, and the time is 10-60 min.

[0018] The present application provides a method for removing radium and / or thorium by in-situ generation of hydrotalcite in wastewater, comprising the following steps: adjusting the pH value of the wastewater to 4-10, adding an insoluble divalent metal source to perform nucleation reaction, then adding alkali hydroxide and a soluble divalent metal source to perform pre-crystallization, adding a soluble trivalent metal source, performing crystallization-adsorption complexation, and then performing solid-liquid separation to obtain a solid residue containing radium and / or thorium and purified water, respectively. The present application uses the method for removing hydrotalcite by in-situ generation of hydrotalcite in wastewater, and the suitable valence complex of thorium and radium can be directly reacted while the in-situ generation of hydrotalcite adsorption material, and in the process of directly synthesizing hydrotalcite in wastewater, thorium and radium nuclides are more easily entered into the vacancies of hydrotalcite, and the removal rate of radium is higher. Moreover, compared with the method of preparing hydrotalcite first and then removing thorium and radium, the method for removing radium and thorium by in-situ generation of hydrotalcite in wastewater provided by the present application is shorter in time, simpler in wastewater treatment process, higher in wastewater treatment efficiency, and lower in cost. The in-situ generation technology of hydrotalcite used in the present application can break through the single chemical reaction of the traditional precipitation method, and thorium and radium nuclides are removed by complexation in the process of hydrotalcite generation, and the reaction is rapid, and the removal and separation effect of thorium and radium is good. DETAILED DESCRIPTION

[0019] The present application provides a method for removing radium and thorium by in-situ generation of hydrotalcite in wastewater, comprising the following steps:

[0020] The pH value of the wastewater is adjusted to 4-10, an insoluble divalent metal source is added to perform nucleation reaction, then alkali hydroxide and a soluble divalent metal source are added to perform pre-crystallization, a soluble trivalent metal source is added, crystallization-adsorption complexation is performed, and then solid-liquid separation is performed to obtain a solid residue containing radium and / or thorium and purified water, respectively.

[0021] Unless otherwise specified, the materials and equipment used in the present application are commercially available in the art.

[0022] In the present application, the thorium content in the wastewater is preferably ≤5 mg / L, more preferably 0.5-5 mg / L, and further preferably 1-3 mg / L; and the radium content in the wastewater is preferably ≤30 Bq / L, more preferably 1-30 Bq / L, and further preferably 5-20 Bq / L. The present application does not have special limitations on the wastewater, and any wastewater containing radium and / or thorium known to those skilled in the art can be used, such as zirconium oxychloride waste liquid.

[0023] In the present application, the pH adjusting agent used in the pH adjustment preferably comprises one or more of sodium hydroxide, potassium hydroxide and aqueous ammonia, and more preferably sodium hydroxide and / or potassium hydroxide. The present application does not have a special limitation on the amount of the pH adjusting agent, and the pH of the wastewater can be adjusted to 4-10 (preferably 5-9, more preferably 6-8, and further preferably 6-7).

[0024] In the present application, the divalent metal ion in the insoluble divalent metal source preferably comprises one or more of Mn 2+ , Mg 2+ , Ca 2+ , Ni 2+ , Co 2+ , Zn 2+ , Fe 2+ and Cu 2+ , and more preferably Mg 2+ or Ca 2+ ; the anion in the insoluble divalent metal source preferably comprises carbonate or hydroxyl, i.e. the insoluble divalent metal source preferably comprises divalent metal carbonate and / or divalent metal hydroxide, and more preferably a mixture of divalent metal carbonate and divalent metal hydroxide, the molar ratio of divalent metal carbonate to divalent metal hydroxide in the mixture preferably being 1-2:1, more preferably 1-1.5:1, and particularly preferably comprising one or more of MgCO3-Mg(OH)2, CaCO3-Ca(OH)2. In the present application, the amount of the insoluble divalent metal source added is preferably 0.1-2 g / L, more preferably 0.2-1 g / L, and further preferably 0.15-0.5 g / L. The present application helps the formation of hydrotalcite structure and improves its stability by adding the insoluble divalent metal source as a nucleating agent.

[0025] In the present application, the temperature of the nucleation reaction is preferably 20-50°C, more preferably 25-40°C, and further preferably 25-30°C; and the time of the nucleation reaction is preferably 1-30 min, more preferably 5-20 min, and further preferably 10-15 min.

[0026] In the present application, the divalent metal ion in the soluble divalent metal source preferably comprises one or more of Mn 2+ , Mg 2+ , Ca 2+ , Ni 2+ , Co 2+ , Zn 2+ , Fe 2+ and Cu 2+ , and more preferably Mg 2+ , Mn 2+ , Ni2+ ; the anion in the soluble divalent metal source preferably comprises NO 3- , Cl - , SO4 2- or PO4 3- ; that is, the soluble divalent metal source preferably comprises one or more of divalent metal nitrate, divalent metal chloride, divalent metal sulfate and divalent metal phosphate, and particularly preferably comprises one or more of Mg(NO3)2, MgCl2, Mg3(PO4)2, MnCl2and NiCl2.

[0027] In the present application, the alkali metal hydroxide preferably comprises sodium hydroxide and / or potassium hydroxide.

[0028] In the present application, the total amount of the alkali metal hydroxide and the soluble divalent metal source is preferably 0.5-3 g / L, more preferably 1-2.5 g / L, and further preferably 1.5-2 g / L. In the present application, the mass of the alkali metal hydroxide preferably accounts for 10-30% of the total mass of the alkali metal hydroxide and the soluble divalent metal source, more preferably 10-20%, and more preferably 10-15%.

[0029] In the present application, the temperature of the pre-crystallization is preferably 20-50°C, more preferably 25-40°C, and further preferably 25-30°C; and the time of the pre-crystallization is preferably 1-30 min, more preferably 5-20 min, and further preferably 10-15 min.

[0030] In the present application, the trivalent metal ion in the soluble trivalent metal source preferably comprises one or more of Al 3+ , Cr 3+ , Fe 3+ and Sc 3+ ; the present application is not particularly limited to the specific type of the soluble trivalent metal source, and any water-soluble salt of one or more of Al 3+ , Cr 3+ , Fe 3+ and Sc 3+ known to those skilled in the art, such as one or more of sodium aluminate, ammonium aluminate and ferric chloride, can be used. In the present application, the amount of the soluble trivalent metal source is preferably 0.1-2 g / L, more preferably 0.2-1 g / L, and further preferably 0.15-0.5 g / L.

[0031] In the present application, the temperature of the crystallization-adsorption complexation is preferably 20-50°C, more preferably 30-50°C, and further preferably 40-50°C; and the time of the crystallization-adsorption complexation is preferably 10-60 min, more preferably 20-50 min, and further preferably 30-40 min. In the present application, the radium and / or thorium in the wastewater is adsorbed and complexed in situ during the crystallization-adsorption complexation process to generate hydrotalcite.

[0032] The present application is not particularly limited to the solid-liquid separation, and any solid-liquid separation method known to those skilled in the art can be used, such as filtration, suction filtration or centrifugal separation.

[0033] According to the generation mechanism and rules of hydrotalcite, the present application determines the ionic radius required for the structure generation of hydrotalcite by adjusting the ratio of ions with different valences, and screens out efficient hydrotalcite preparation materials and preparation processes to remove radioactive radium and thorium nuclides in wastewater by using the method of in-situ generation of hydrotalcite. Moreover, the present application uses the in-situ generation technology of hydrotalcite to break through the single chemical reaction of the traditional precipitation method, and the radium and thorium nuclides are complexed and removed during the generation of hydrotalcite, and the reaction is rapid and the separation effect is good.

[0034] In order to further illustrate the present application, a method for removing radium and / or thorium by in-situ generation of hydrotalcite in water is described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0035] In the following examples, the wastewater is the tail liquid of zirconium oxychloride production.

[0036] Example 1

[0037] At room temperature, the pH value of 1L wastewater containing thorium 3mg / L and radium 10Bq / L is adjusted to 6.5 by using reagent A (NaOH), reagent B is added and stirred for 5min, reagent C is added and stirred for 5min, reagent D is added, and stirred at 40°C for 40min, and then filtered to obtain a solid residue containing radium and thorium and a filtrate. The analysis results of the filtrate show that the thorium content is 0.051mg / L and the radium content is 0.5Bq / L. The types and amounts of reagents B-D are shown in Table 1. Among them, the molar ratio of MgCO3:Mg(OH)2 in reagent B is 1.5:1.

[0038] Table 1 Types and amounts of reagents B-D

[0039] B C D MgCO3:Mg(OH)2 NaOH: MgCl2 NaAlO2 0.15 g (total) 0.1 g : 0.9 g 0.15g

[0040] Comparative Example 1

[0041] Under the condition of room temperature, after adding reagent B in 1L tap water with pH value of 6.5 and stirring for 5min, reagent C is added and stirred for 5min, then reagent D is added, and stirred for 40min under the condition of 40℃, filtration is carried out, and the filter cake is dried in a vacuum drying oven under the condition of 60℃ for 8h to obtain hydrotalcite. The hydrotalcite is placed in 1L waste water containing thorium 3mg / L and radium 10Bq / L, and stirred for 40min under the condition of 40℃, filtration is carried out, and radium-thorium-containing solid residue and filtrate are obtained respectively. The analysis results of the filtrate show that the thorium is 0.096mg / L, and the radium is 1.1Bq / L. The types and adding amounts of reagents B-D are shown in Table 1. Among them, the molar ratio of MgCO3:Mg(OH)2 in reagent B is 1.5:1.

[0042] By comparing Example 1 and Comparative Example 1, it can be seen that the method for removing hydrotalcite by in-situ generation of hydrotalcite in waste water is adopted in the present application, the suitable valence complex of thorium and radium is directly reacted while the in-situ generated hydrotalcite adsorption material, and in the process of synthesis, the thorium and radium nuclides are more easily entered into the vacancy of hydrotalcite, the removal rate of radium is higher, and the time consumption is shorter, and the treatment efficiency is high.

[0043] Example 2

[0044] The pH value of 1L waste water containing thorium 3mg / L and radium 10Bq / L is adjusted to 6 by using reagent A (NaOH), then reagent B is added and stirred for 10min, reagent C is added and stirred for 10min, reagent D is added, and stirred for 30min under the condition of 50℃, filtration is carried out, and radium-thorium-containing solid residue and filtrate are obtained respectively. The analysis results of the filtrate show that the thorium is 0.023mg / L, and the radium is 0.3Bq / L. The types and adding amounts of reagents B-D are shown in Table 2. Among them, the molar ratio of MgCO3:Mg(OH)2 in reagent B is 1.5:1.

[0045] Table 2 Types and adding amounts of reagents B-D

[0046] B C D MgCO3:Mg(OH)2 NaOH: MnCl2 NaAlO2 0.15 g (total) 0.2 g : 1.2 g 0.15g

[0047] Example 3

[0048] The pH value of 1L waste water containing thorium 3mg / L and radium 10Bq / L is adjusted to 9 by using reagent A (NaOH), then reagent B is added and stirred for 5min, reagent C is added and stirred for 5min, reagent D is added, and stirred for 40min under the condition of 40℃, filtration is carried out, and radium-thorium-containing solid residue and filtrate are obtained respectively. The analysis results of the filtrate show that the thorium is 0.076mg / L, and the radium is 0.2Bq / L. The types and adding amounts of reagents B-D are shown in Table 3. Among them, the molar ratio of MgCO3:Mg(OH)2 in reagent B is 1.5:1.

[0049] Table 3 Types and adding amounts of reagents B-D

[0050] B C D MgCO3:Mg(OH)2 NaOH: MgCl2 NaAlO2 0.15 g (total) 0.1 g : 0.9 g 0.15g

[0051] Example 4

[0052] 1 L of waste water containing thorium 3 mg / L, radium 10 Bq / L was adjusted to pH 6 using reagent A (NaOH), then reagent B was added and stirred for 10 min, reagent C was added and stirred for 10 min, reagent D was added, then stirred at 50°C for 30 min, filtered, and radium-thorium-containing solid residue and filtrate were obtained respectively. The analysis results of the filtrate showed that thorium was 0.086 mg / L and radium was 0.6 Bq / L. The types and amounts of reagents B-D are shown in Table 4. Among them, the molar ratio of MgCO3:Mg(OH)2 in reagent B was 1.5:1.

[0053] Table 4 Types and amounts of reagents B-D

[0054] B C D MgCO3:Mg(OH)2 NaOH: NiCl2 FeCl3 0.15 g (total) 0.15 g : 1.2 g 0.15g

[0055] Example 5

[0056] 1 L of waste water containing thorium 3 mg / L, radium 10 Bq / L was adjusted to pH 6 using reagent A (NaOH), then reagent B was added and stirred for 10 min, reagent C was added and stirred for 10 min, reagent D was added, then stirred at 50°C for 30 min, filtered, and radium-thorium-containing solid residue and filtrate were obtained respectively. The analysis results of the filtrate showed that thorium was 0.068 mg / L and radium was 0.5 Bq / L. The types and amounts of reagents B-D are shown in Table 5. Among them, the molar ratio of CaCO3:Ca(OH)2 in reagent B was 1:1.

[0057] Table 5 Types and amounts of reagents B-D

[0058]

[0059]

[0060] Example 6

[0061] 1 L of waste water containing thorium 3 mg / L, radium 10 Bq / L was adjusted to pH 6 using reagent A (25% ammonia water), then reagent B was added and stirred for 10 min, reagent C was added and stirred for 10 min, reagent D was added, then stirred at 50°C for 30 min, filtered, and radium-thorium-containing solid residue and filtrate were obtained respectively. The analysis results of the filtrate showed that thorium was 0.055 mg / L and radium was 0.76 Bq / L. The types and amounts of reagents B-D are shown in Table 6. Among them, the molar ratio of CaCO3:Ca(OH)2 in reagent B was 1:1.

[0062] Table 6 Types and amounts of reagents B-D

[0063] B C D CaCO3: Ca(OH)2 NaOH: Mg(N03)2 [NH4AlO2] 0.15 g (total) 0.15 g : 1.2 g 0.15g

[0064] Example 7

[0065] A 1L of waste water containing thorium 3mg / L, radium 10Bq / L was adjusted to pH 6 with reagent A (NaOH), then reagent B was added and stirred for 10 minutes, reagent C was added and stirred for 10 minutes, reagent D was added, then stirred at 50°C for 30 minutes, filtered, and radium-thorium containing solid residue and filtrate were obtained respectively. The analysis result of the filtrate showed that thorium was 0.049mg / L, radium was 0.52Bq / L. The types and amounts of reagents B-D are shown in Table 7. Among them, the molar ratio of MgCO3:Mg(OH)2 in reagent B was 1.5:1.

[0066] Table 7 Types and amounts of reagents B-D

[0067] B C D MgCO3:Mg(OH)2 NaOH: Mg3(PO4)2 NaAlO2 0.15 g (total) 0.15 g : 1.2 g 0.15g

[0068] Example 8

[0069] A 1L of waste water containing thorium 3mg / L, radium 10Bq / L was adjusted to pH 6 with reagent A (NaOH), then reagent B was added and stirred for 10 minutes, reagent C was added and stirred for 10 minutes, reagent D was added, then stirred at 50°C for 30 minutes, filtered, and radium-thorium containing solid residue and filtrate were obtained respectively. The analysis result of the filtrate showed that thorium was 0.056mg / L, radium was 0.81Bq / L. The types and amounts of reagents B-D are shown in Table 8. Among them, the molar ratio of MgCO3:Mg(OH)2 in reagent B was 1.5:1.

[0070] Table 8 Types and amounts of reagents B-D

[0071] B C D MgCO3:Mg(OH)2 NaOH: Mg(N03)2 FeCl3 0.15 g (total) 0.15 g : 1.2 g 0.15 g (total) 0.15 g : 1.2 g 0.15g

[0072] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and people can also obtain other embodiments according to the embodiments of the present application without creative labor, which all belong to the protection scope of the present application.

Claims

1. A method for removing radium and / or thorium from wastewater by in-situ generation of hydrotalcite, comprising the following steps: The pH of the wastewater was adjusted to 4-10, an insoluble divalent metal source was added to carry out a nucleation reaction, then an alkali metal hydroxide and a soluble divalent metal source were added for pre-crystallization, a soluble trivalent metal source was added for crystallization-adsorption complexation, and then solid-liquid separation was carried out to obtain radium and / or thorium-containing solid slag and purified water, respectively. The wastewater contains thorium ≤5 mg / L and radium ≤30 Bq / L; The divalent metal ion in the insoluble divalent metal source is Mg. 2+ and Ca 2+ One or more of the following, wherein the insoluble divalent metal source is a divalent metal carbonate and a divalent metal hydroxide in a molar ratio of 1 to 2:1; The nucleation reaction is carried out at a temperature of 20–50°C for a time of 1–30 min. The pre-crystallization temperature is 20–50°C, and the time is 1–30 min; The crystallization-adsorption complexation is carried out at a temperature of 20–50 °C for 10–60 min.

2. The method according to claim 1, characterized in that, The pH adjustment agent used for pH adjustment includes one or more of sodium hydroxide, potassium hydroxide, and ammonia water; The amount of the insoluble divalent metal source added is 0.1–2 g / L.

3. The method according to claim 1, characterized in that, The divalent metal ions in the soluble divalent metal source include Mn. 2+ Mg 2+ Ca 2+ Ni 2+ Co 2+ Zn 2+ Fe 2+ and Cu 2+ One or more of them.

4. The method according to claim 1, characterized in that, The total amount of the alkali metal hydroxide and the soluble divalent metal source added is 0.5–3 g / L; the mass of the alkali metal hydroxide accounts for 10–30% of the total mass of the alkali metal hydroxide and the soluble divalent metal source.

5. The method according to claim 1, characterized in that, The trivalent metal ions in the soluble trivalent metal source include Al. 3+ Cr 3+ Fe 3+ and Sc 3+ One or more of the following; the amount of the soluble trivalent metal source added is 0.1 to 2 g / L.

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