Method for removing 2-ethylhexyl 2-ethylhexylphosphonate from rare earth hydrometallurgy wastewater

Abstract

The application discloses a method for removing 2-ethylhexyl 2-ethylhexyl phosphonate from rare earth wet smelting wastewater, which comprises the following steps: 1) adjusting the pH of the rare earth wet smelting wastewater to 10-12 to obtain pretreated wastewater; 2) adding a calcium chloride solution into the pretreated wastewater and stirring to obtain a reaction product containing precipitates; and 3) performing solid-liquid separation to obtain filter residue and clear liquid. The method can fully remove 2-ethylhexyl 2-ethylhexyl phosphonate in the wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for removing 2-ethylhexyl 2-ethylhexyl phosphonate from rare earth hydrometallurgy wastewater. BACKGROUND

[0002] Rare earth hydrometallurgy processes mainly include pyrometallurgy and hydrometallurgy, and ion type rare earths are usually subjected to "acid dissolution-saponification-extraction-precipitation" hydrometallurgy process. The wastewater produced by rare earth hydrometallurgy usually contains 2-ethylhexyl 2-ethylhexyl phosphonate, which can pollute the environment. It is necessary to remove it from the wastewater. 2-ethylhexyl 2-ethylhexyl phosphonate (Cas No: 14802-03-0) is a colorless or light yellow oily liquid, which is usually insoluble in water. However, after saponification of 2-ethylhexyl 2-ethylhexyl phosphonate, the water solubility is enhanced, so it is not easy to remove. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a method for removing 2-ethylhexyl 2-ethylhexyl phosphonate from rare earth hydrometallurgy wastewater, which can sufficiently remove 2-ethylhexyl 2-ethylhexyl phosphonate in the wastewater.

[0004] The present application achieves the above-mentioned purpose by adopting the following technical solutions.

[0005] The present application provides a method for removing 2-ethylhexyl 2-ethylhexyl phosphonate from rare earth hydrometallurgy wastewater, which comprises the following steps:

[0006] 1) Adjusting the pH of rare earth hydrometallurgy wastewater to 10-12 to obtain pretreated wastewater;

[0007] 2) Adding calcium chloride solution to the pretreated wastewater, stirring to obtain a reaction product containing precipitate; solid-liquid separation to obtain filter residue and clear liquid.

[0008] The present application also provides a method for removing 2-ethylhexyl 2-ethylhexyl phosphonate from rare earth hydrometallurgy wastewater, which comprises the following steps:

[0009] 1) Adjusting the pH of rare earth hydrometallurgy wastewater to 10-12 to obtain pretreated wastewater;

[0010] 2) Adding calcium chloride solution to the pretreated wastewater, stirring to obtain a reaction product containing precipitate;

[0011] 3) Adding a flocculating agent to the reaction product containing precipitate, stirring, and then solid-liquid separation to obtain solid residue and mother liquor.

[0012] According to the method of the present application, the pH of rare earth hydrometallurgy wastewater is preferably adjusted to 10-11 with hydrochloric acid.

[0013] According to the method of the present application, preferably, in step 1), the concentration of hydrochloric acid is 25-37.5 wt%.

[0014] According to the method of the present application, preferably, in step 2), the concentration of calcium chloride solution is 35-40 wt%.

[0015] According to the method of the present application, preferably, in step 2), the concentration of calcium chloride solution is 38-40 wt%.

[0016] According to the method of the present application, preferably, the volume ratio of calcium chloride solution to rare earth wet smelting wastewater is 0.28-0.4:10.

[0017] According to the method of the present application, preferably, in step 3), the flocculating agent is selected from one of polyacrylic acid sodium, anionic carboxymethyl cellulose, cationic polyvinylimine, anionic polyacrylamide, cationic polyacrylamide and non-ionic polyacrylamide.

[0018] According to the method of the present application, preferably, the flocculating agent is added in the form of a flocculating agent solution to the precipitated reaction mixture, stirred, and then solid-liquid separated to obtain solid slag and mother liquor; wherein the volume ratio of the flocculating agent solution to rare earth wet smelting wastewater is 0.4-0.6:10.

[0019] According to the method of the present application, preferably, further comprising the following step: adjusting the pH of the mother liquor obtained in step 3) to 6-7 with hydrochloric acid to obtain the wastewater to be discharged.

[0020] The method of the present application can sufficiently remove 2-ethylhexyl 2-ethylhexyl phosphonate in rare earth wet smelting wastewater by controlling the pH of the system and adding a specific reagent (calcium chloride solution), to obtain clear wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a photo of the used raw material, rare earth wet smelting wastewater.

[0022] Figure 2 It is a photo of the precipitated reaction mixture obtained in Example 1.

[0023] Figure 3 It is a photo of the sedimentation in Example 1.

[0024] Figure 4 It is a photo of the wastewater to be discharged obtained in Example 2.

[0025] Figure 5 It is a photo of the wastewater to be discharged obtained in Example 3.

[0026] Figure 6 It is a photo of the precipitated reaction mixture obtained in Comparative Example 1. DETAILED DESCRIPTION

[0027] The application will be further described in connection with specific embodiments, but the scope of the application is not limited thereto.

[0028] The present application is accomplished by controlling pH and adding calcium chloride solution to sufficiently remove 2-ethylhexyl 2-ethylhexyl phosphonate in rare earth hydrometallurgy wastewater. In some embodiments, the method of the present application comprises the following steps: 1) pH adjusting step; 2) precipitation step; 3) solid-liquid separation step; 4) neutralization step. In other embodiments, the method of the present application comprises the following steps: 1) pH adjusting step; 2) precipitation step; 3) flocculation step; 4) solid-liquid separation step; 5) neutralization step. Optionally, the method further comprises the step of preparing calcium chloride solution. The details are described below.

[0029] <PH adjusting step>

[0030] The pH of the rare earth hydrometallurgy wastewater is adjusted to 10-12 to obtain pretreated wastewater. The pH adjusting can use an acidic solution, such as hydrochloric acid. The concentration of the hydrochloric acid can be 25-37.5 wt%, preferably 30-37.5 wt%, more preferably 35-37 wt%.

[0031] According to one embodiment of the present application, the pH of the rare earth hydrometallurgy wastewater is adjusted to 10-12 using hydrochloric acid to obtain pretreated wastewater. This is conducive to more completely removing 2-ethylhexyl 2-ethylhexyl phosphonate and obtaining a clear liquid. In addition, this is also conducive to reducing the amount of calcium chloride used. The pH of the system is adjusted to 10-12, preferably 10-11.

[0032] According to one embodiment of the present application, the pH of the rare earth hydrometallurgy wastewater is adjusted to 10-12 using hydrochloric acid with a concentration of 30-37 wt% to obtain pretreated wastewater.

[0033] It is unexpectedly found that by adjusting the pH of the rare earth hydrometallurgy wastewater to a specific range and then adding calcium chloride solution to precipitate, the calcium hydroxide precipitate generated can well wrap the 2-ethylhexyl 2-ethylhexyl phosphonate oil, so that the 2-ethylhexyl 2-ethylhexyl phosphonate can be more completely removed. If the pH is less than 10, the wrapping cannot be well formed, and the 2-ethylhexyl 2-ethylhexyl phosphonate cannot be sufficiently removed. If the pH is greater than 12, the amount of calcium chloride used will be greatly increased.

[0034] <precipitation step>

[0035] The calcium chloride solution is added to the pretreated wastewater and stirred to obtain a reaction product containing precipitates. This facilitates the generated calcium hydroxide precipitate to better wrap 2-ethylhexyl 2-ethylhexyl phosphonate, so that 2-ethylhexyl 2-ethylhexyl phosphonate can be more fully removed.

[0036] In the present application, the concentration of the calcium chloride solution can be 35-40 wt%, preferably 37-40 wt%, more preferably 38-40 wt%. The volume ratio of the calcium chloride solution to the rare earth wet smelting wastewater is 0.28-0.4:10, preferably 0.30-0.4:10, more preferably 0.30-0.35:10. This facilitates the generated calcium hydroxide precipitate to better wrap 2-ethylhexyl 2-ethylhexyl phosphonate.

[0037] According to one embodiment of the present application, a calcium chloride solution with a concentration of 38-40 wt% is added to the pretreated wastewater and stirred to obtain a reaction product containing precipitates.

[0038] In the present application, the preparation of the calcium chloride solution includes the following steps: dissolving calcium chloride in water and stirring until fully dissolved. This process is an exothermic reaction, which requires slow batch addition.

[0039] In the present application, the prepared calcium chloride solution is preferably a saturated calcium chloride solution, which is ready for use.

[0040] In the present application, there are two ways to handle the obtained reaction product containing precipitates: one is to not add a flocculating agent and perform solid-liquid separation; the other is to add a flocculating agent and then perform solid-liquid separation after precipitation.

[0041] <flocculation step>

[0042] The flocculating agent is added to the reaction product containing precipitates and stirred. This can accelerate precipitation and improve efficiency.

[0043] The flocculating agent can be selected from one of sodium polyacrylate, anionic carboxymethyl cellulose, cationic polyvinylimine, anionic polyacrylamide, cationic polyacrylamide, and non-ionic polyacrylamide. Preferably, the flocculating agent is selected from one of sodium polyacrylate, anionic polyacrylamide, cationic polyacrylamide, and non-ionic polyacrylamide. More preferably, the flocculating agent is anionic polyacrylamide.

[0044] The flocculant can be used in the form of a flocculant solution. According to one embodiment of the present application, the flocculant solution is added to the precipitated reactant, stirred, and then subjected to solid-liquid separation to obtain solid residue and mother liquor; wherein the volume ratio of the flocculant solution to the rare earth wet metallurgy wastewater is 0.4-0.6:10. The volume ratio of the flocculant solution to the rare earth wet metallurgy wastewater can be 0.4-0.6:10, preferably 0.45-0.55:10, and more preferably 0.45-0.5:10. This is conducive to fully exerting the effect of the flocculant.

[0045] <solid-liquid separation step>

[0046] In some embodiments, the obtained precipitated reactant is allowed to stand and settle, and then subjected to solid-liquid separation to obtain filter residue and clear liquid. The clear liquid contains substantially no 2-ethylhexyl 2-ethylhexyl phosphonate. The filter residue mainly comprises calcium hydroxide precipitate wrapped with 2-ethylhexyl 2-ethylhexyl phosphonate.

[0047] In other embodiments, the flocculant is added to the precipitated reactant, flocculation is performed, and the precipitate containing the flocculant is subjected to solid-liquid separation to obtain solid residue and mother liquor. The mother liquor contains no 2-ethylhexyl 2-ethylhexyl phosphonate. This can obtain clear liquid containing substantially no 2-ethylhexyl 2-ethylhexyl phosphonate.

[0048] The solid-liquid separation method is not particularly limited, and filtration or centrifugal separation can be used, and filtration is preferred.

[0049] <neutralization step>

[0050] In some embodiments, the obtained clear liquid (obtained after solid-liquid separation without adding flocculant) is neutralized to pH 6-7 with hydrochloric acid to obtain clear wastewater to be discharged. The concentration of the hydrochloric acid can be 10-37 wt%, preferably 15-37 wt%, and more preferably 20-35 wt%.

[0051] In other embodiments, the obtained mother liquor (obtained after solid-liquid separation with the addition of flocculant) is adjusted to pH 6-7 with hydrochloric acid to obtain clear wastewater to be discharged. The concentration of the hydrochloric acid can be 10-37 wt%, preferably 15-37 wt%, and more preferably 20-35 wt%.

[0052] In the following examples and comparative examples, the rare earth wet metallurgy wastewater is the same batch, and the pH value is greater than 14. The flocculant used is anionic polyacrylamide.

[0053] Example 1

[0054] 100 mL of rare earth wet metallurgy wastewater (see photo Figure 1) with 3 mL of 37 wt% hydrochloric acid to pH 10 with thorough stirring to obtain pretreated wastewater.

[0055] Add 3 mL of saturated calcium chloride solution to the pretreated wastewater described above with thorough stirring to obtain a reaction product containing precipitates (see photo Figure 2 ). Allow to stand and settle, and see photo Figure 3 after settling. Separate the solid and liquid to obtain a filter residue and a clear liquid. The clear liquid is in a clear and transparent state and contains substantially no 2- ethylhexyl 2-ethylhexyl phosphonate.

[0056] Adjust the pH of the clear liquid described above to 7 with 10 wt% hydrochloric acid to obtain wastewater to be discharged.

[0057] Example 2

[0058] Dissolve 100 mL of rare earth wet metallurgy wastewater with 3 mL of 37 wt% hydrochloric acid to pH 10 with thorough stirring to obtain pretreated wastewater.

[0059] Add 3 mL of saturated calcium chloride solution to the pretreated wastewater described above with thorough stirring to obtain a reaction product containing precipitates.

[0060] Add 4 mL of 0.04 g / L flocculant solution to the reaction product containing precipitates, stir, and filter to obtain a solid residue and a mother liquor. The mother liquor contains substantially no 2-ethylhexyl 2-ethylhexyl phosphonate.

[0061] Adjust the pH of the mother liquor to 7 with 10 wt% hydrochloric acid to obtain wastewater to be discharged (see photo Figure 4 ).

[0062] Example 3

[0063] Dissolve 22.5 kg of calcium chloride in 30 L of water. This process is an exothermic reaction and requires slow stirring until complete dissolution. The supernatant is a saturated calcium chloride solution and is ready for use.

[0064] Dissolve 1000 L of rare earth wet metallurgy wastewater with 30 L of 37 wt% hydrochloric acid to pH 10 with thorough stirring to obtain pretreated wastewater.

[0065] Add 30 L of saturated calcium chloride solution described above to the pretreated wastewater described above with thorough stirring to obtain a reaction product containing precipitates.

[0066] Add 45 L of 0.04 g / L flocculant solution to the reaction product containing precipitates, stir, and pass through a plate-and-frame filter press to obtain a solid residue and a mother liquor. The mother liquor contains substantially no 2-ethylhexyl 2-ethylhexyl phosphonate. The solid residue can be treated as solid waste.

[0067] The mother liquor was adjusted to pH 7 by adding 6 L of 10 wt% hydrochloric acid to obtain the waste water to be discharged (see the photo Figure 5 ).

[0068] Comparative Example 1

[0069] The difference from Example 1 is that the pH of the rare earth wet smelting waste water is adjusted to 9 by using 37 wt% hydrochloric acid. The photo of the reaction product containing precipitate is shown in Figure 6 .

[0070] As compared with the reaction product containing precipitate of Example 1 Figure 2 and the reaction product containing precipitate of Comparative Example 1 Figure 6 , it can be seen that the pH is controlled in a specific range in the present application, which is beneficial to fully remove 2-ethylhexyl 2-ethylhexyl phosphonate to obtain clear waste water liquid.

[0071] The present application is not limited to the above-mentioned embodiments, and any modification, improvement, replacement conceived by those skilled in the art without departing from the essential content of the present application falls within the scope of the present application.

Claims

1. A method for removing 2-ethylhexyl phosphate from rare earth hydrometallurgical wastewater, characterized in that, Includes the following steps: 1) Adjust the pH of rare earth hydrometallurgical wastewater to 10-12 to obtain pretreated wastewater; 2) Add calcium chloride solution to the pretreated wastewater and stir to obtain a reactant containing a precipitate; by adding calcium chloride solution to precipitate, the generated calcium hydroxide precipitate can effectively coat 2-ethylhexyl phosphate ester oil, thereby more fully removing 2-ethylhexyl phosphate ester. 3) The flocculant is added to the reactants containing precipitate in the form of a flocculant solution, stirred, and then the solid and liquid are separated to obtain solid slag and mother liquor; wherein the volume ratio of flocculant solution to rare earth hydrometallurgical wastewater is 0.4 to 0.6:

10. The process also includes the following steps: adjusting the pH of the mother liquor obtained in step 3) to 6-7 with hydrochloric acid to obtain the wastewater to be discharged; In step 3), the flocculant is selected from one of sodium polyacrylate, anionic carboxymethyl cellulose, cationic polyethyleneimine, anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide.

2. The method according to claim 1, characterized in that, The pH of the rare earth hydrometallurgical wastewater was adjusted to 10-11 using hydrochloric acid.

3. The method according to claim 2, characterized in that, In step 1), the concentration of the hydrochloric acid is 25–37.5 wt%.

4. The method according to claim 1, characterized in that, In step 2), the concentration of the calcium chloride solution is 35–40 wt%.

5. The method according to claim 1, characterized in that, In step 2), the concentration of the calcium chloride solution is 38–40 wt%.

6. The method according to claim 1, characterized in that, The volume ratio of calcium chloride solution to rare earth hydrometallurgical wastewater is 0.28–0.4:10.

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