A method for treating waste water from production of tributyl phosphate

Abstract

The present application relates to a kind of tributyl phosphate production wastewater treatment method, belong to wastewater treatment field.The treatment method includes the following steps: by cooling to make wastewater partially freeze, then soluble ammonium salt is mixed with the wastewater that is not frozen, induce sodium chloride crystallization in the wastewater that is not frozen below 0 ℃, remove sodium chloride crystal.The present application first by cooling to make tributyl phosphate production wastewater partially freeze, form upper ice and lower solution, in the freezing process, organic matter and sodium chloride will enter lower solution, reduce the impurity content in ice, then soluble ammonium salt is added in lower solution (i.e.wastewater that is not frozen), the temperature of solution is reduced to 0 ℃ or less to make soluble ammonium salt crystallize, then induce sodium chloride in wastewater to crystallize and precipitate, so as to remove sodium chloride in wastewater.

Description

Technical Field

[0001] This invention relates to a method for treating wastewater from the production of tributyl phosphate, belonging to the field of wastewater treatment. Background Technology

[0002] Due to the "high magnesium and low lithium" characteristics of domestic salt lake brine resources, there are many process routes for lithium extraction from salt lake brine in my country, including solvent leaching, adsorption and carbonization. Among them, the commonly used method is to extract lithium salts from salt lake brine with tributyl phosphate (TBP) as the main leaching agent. Therefore, the demand for tributyl phosphate is increasing.

[0003] The preparation of tributyl phosphate utilizes a synthesis technology involving n-butanol and phosphorus oxychloride. Specifically, n-butanol and phosphorus oxychloride are added to a synthesis reactor in a specific ratio. Under stirring at room temperature, tributyl phosphate and hydrochloric acid are obtained. The reactor is then heated to convert the hydrochloric acid into hydrogen chloride gas, which is then separated. The gas is neutralized with caustic soda or sodium carbonate solution, washed with water, and further deacidified before entering a dealcoholization tank. Vacuum distillation under reduced pressure yields the product tributyl phosphate, and the butanol is recovered for reuse. However, the above preparation process generates a significant amount of wastewater. This wastewater mainly contains unreacted n-(iso)butanol, phosphorus oxychloride, incompletely separated tributyl phosphate, and sodium chloride. The COD (Chemical Oxygen Demand) is relatively high. Cr The concentration of NaCl can reach 120,000 mg / L, and the concentration of COD can reach 100,000 mg / L, meaning that the wastewater contains a high concentration of NaCl and a high content of COD. Cr (Organic matter) requires a reduction in NaCl concentration before conventional biological treatment systems can be used for wastewater treatment. Currently, the commonly used method is triple-effect evaporation desalination, but this process is energy-intensive and costly, with treatment costs reaching as high as 1600 yuan per ton of wastewater. Furthermore, the treated wastewater still contains a certain amount of COD. Cr . Summary of the Invention

[0004] The purpose of this invention is to provide a method for treating wastewater from the production of tributyl phosphate, thereby solving the problem of high energy consumption in wastewater treatment in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for treating wastewater from the production of tributyl phosphate includes the following steps: partially freezing the wastewater by cooling it down, then mixing soluble ammonium salts with the unfrozen wastewater, inducing sodium chloride crystallization in the unfrozen wastewater at a temperature below 0°C, and removing the sodium chloride crystals.

[0007] This invention first freezes a portion of the tributyl phosphate production wastewater by cooling it, forming an upper ice layer and a lower solution layer. During the freezing process, organic matter and sodium chloride enter the lower solution, reducing the impurity content in the ice. Then, soluble ammonium salts are added to the lower solution (i.e., the unfrozen wastewater), and the solution temperature is lowered below 0°C, causing the soluble ammonium salts to crystallize. This, in turn, induces the crystallization of sodium chloride in the wastewater, thereby removing sodium chloride from the wastewater. By controlling the freezing rate, the content of organic matter and sodium chloride in the upper ice layer can be kept as low as possible. After melting, the ice can be safely discharged or used for other treatments. This invention's treatment method has low energy consumption and low cost.

[0008] To improve the removal rate of sodium chloride and organic matter, the cooling rate is preferably 1-2 °C / h.

[0009] Preferably, the cooling temperature is below 0°C.

[0010] More preferably, after the wastewater partially freezes, the upper layer of ice is removed, and then a soluble ammonium salt is added to the lower layer of solution.

[0011] Preferably, the soluble ammonium salt is ammonium nitrate. The solubility of ammonium nitrate varies considerably at different temperatures, and it readily crystallizes at low temperatures.

[0012] Preferably, the sodium chloride crystallization induced in the unfrozen wastewater at below 0°C involves the crystallization of a soluble ammonium salt at below 0°C, which encapsulates the sodium chloride to form mixed crystals. To better induce sodium chloride crystallization, preferably, the amount of the soluble ammonium salt added is 2-15% of the mass of the unfrozen wastewater.

[0013] To improve reaction efficiency, preferably, the temperature below 0°C is -1 to -7°C, and the time is 1 to 2 hours.

[0014] To further remove COD from wastewater Cr To reduce impurity content, preferably, after removing sodium chloride crystals, carbon adsorbent is added to the wastewater to remove organic matter.

[0015] To improve the removal rate of organic matter in wastewater, preferably, when adding carbon adsorbent, the solution temperature is kept below 0°C, specifically -3 to -7°C, for 1 to 2 hours. At temperatures below 0°C, the wastewater can continue to partially freeze, reducing the organic matter and sodium chloride content in the ice. The organic matter content in the unfrozen wastewater is further reduced by the adsorption of the added carbon adsorbent.

[0016] To better induce the adsorption of organic matter in wastewater, preferably, the amount of carbon material adsorbent added is 0.5 to 1% of the mass of wastewater after removing sodium chloride crystals.

[0017] Preferably, the carbon adsorbent is graphene and / or biochar. These two carbon materials are more effective at treating organic matter in wastewater.

[0018] Preferably, the graphene has a particle size of 100–130 nm; and the biochar has a mesh size of 900–1000 mesh.

[0019] To reduce costs, preferably, the partially frozen wastewater is used to cool the untreated tributyl phosphate production wastewater. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0021] I. Specific embodiments of the method for treating wastewater from the production of tributyl phosphate according to the present invention are as follows:

[0022] Example 1

[0023] In this embodiment, the NaCl concentration in the wastewater from the tributyl phosphate production process was 58200 mg / L, and the COD was... Cr The mass concentration is 115000 mg / L.

[0024] The method for treating wastewater from the production of tributyl phosphate in this embodiment includes the following steps:

[0025] (1) The wastewater from the production of tributyl phosphate was cooled to make it freeze. The cooling rate was 2℃ / h, the temperature was reduced to -5℃, the residence time was 1h, and the upper layer of ice was removed. At this time, the solubility of NaCl decreased with the decrease of temperature, and the NaCl solid precipitated at the bottom was about 11180mg / L.

[0026] (2) Add 10% ammonium nitrate to the lower solution after removing the upper ice, stir, keep the temperature at -5℃ and the residence time at 1h, remove the upper ice, and then separate the crystals produced from the remaining lower solution to obtain the filtrate.

[0027] (3) The ice obtained in steps (1) and (2) was melted countercurrently, and the ice rate was 64.2%. At this time, the ice contained NaCl, and the content of the ice after melting was 1756.6 mg / L. The NaCl concentration in the filtrate obtained in step (2) was about 5402 mg / L. Based on the filtrate, the NaCl removal rate in the wastewater was 90.7% (the NaCl concentration in the filtrate was higher than that in the ice, and the NaCl removal rate after mixing the filtrate and the ice melt was definitely higher than 90.7%). The obtained ice melt was mixed with the filtrate obtained in step (2), and the COD in the wastewater was measured. Cr The concentration was 97750 mg / L, therefore, the COD in the wastewater... CrThe removal rate is 15%, and the treatment cost per ton of wastewater is approximately 260 yuan.

[0028] The countercurrent melting in step (3) refers to placing the ice obtained in this embodiment outside the pipe of the untreated tributyl phosphate production wastewater to be cooled, and achieving the initial cooling of the untreated tributyl phosphate production wastewater through countercurrent operation. Since the temperature of the untreated tributyl phosphate production wastewater that has just been produced is high, it can also play the role of melting the ice. In this way, the low temperature of the ice and the high temperature of the untreated tributyl phosphate production wastewater can be fully utilized, greatly reducing the production cost and facilitating industrial production.

[0029] Example 2

[0030] In this embodiment, the NaCl concentration in the wastewater from the tributyl phosphate production process was 55736 mg / L, and the COD was... Cr The mass concentration is 132600 mg / L.

[0031] The method for treating wastewater from the production of tributyl phosphate in this embodiment includes the following steps:

[0032] (1) Cool the wastewater from the production of tributyl phosphate to make it freeze. The cooling rate is 1.5℃ / h, the temperature is reduced to -10℃, the residence time is 1.5h, and the upper layer of ice is removed.

[0033] (2) Add 2% ammonium nitrate to the lower solution after removing the upper ice, keep the temperature at -7℃ and the residence time at 1.2h to remove the upper ice, and then separate the crystals produced from the remaining lower solution to obtain the filtrate.

[0034] (3) Add graphene (particle size 120nm) with a mass concentration of 0.5% to the filtrate obtained in step (2), keep the temperature at -5℃ and the residence time at 1h, remove the upper ice, and then separate the graphene from the remaining lower solution to obtain the filtrate.

[0035] (4) The ice obtained in steps (1), (2), and (3) was melted countercurrently, and the ice rate was summarized as 73.6%. At this time, the ice contained NaCl, and the content of the melted ice was 1271.6 mg / L. The NaCl concentration in the filtrate obtained in step (3) was about 6850 mg / L. The NaCl concentration in the filtrate was relatively high. Based on the filtrate, the NaCl removal rate in the wastewater was 87.7% (the NaCl concentration in the filtrate was higher than that in the ice, and the NaCl removal rate after mixing the filtrate with the ice melt was definitely higher than 87.7%). The obtained ice melt was mixed with the filtrate obtained in step (3), and the COD was measured. Cr The concentration was 4020 mg / L, therefore, the COD in the wastewater... CrThe removal rate was 97%, and the treatment cost per ton of wastewater was approximately 353 yuan.

[0036] Example 3

[0037] In this embodiment, the NaCl concentration in the wastewater from the tributyl phosphate production process was 56149 mg / L, and the COD was... Cr The mass concentration was 128740 mg / L.

[0038] The method for treating wastewater from the production of tributyl phosphate in this embodiment includes the following steps:

[0039] (1) Cool the wastewater from the production of tributyl phosphate to make it freeze. The cooling rate is 1℃ / h, the temperature is reduced to -4℃, the residence time is 2h, and the upper layer of ice is removed.

[0040] (2) Add 7.5% ammonium nitrate to the lower solution after removing the upper ice, keep the temperature at -4.5℃ and the residence time at 1.5h to remove the upper ice, and then separate the crystals produced from the remaining lower solution to obtain the filtrate.

[0041] (3) Add biochar (1000 mesh) with a mass concentration of 0.8% to the filtrate obtained in step (2), keep the temperature at -3.5℃ and the residence time at 1.5h, remove the upper layer of ice, and then separate the graphene from the remaining lower layer solution to obtain the filtrate.

[0042] (4) The ice obtained in steps (1), (2), and (3) was melted countercurrently, and the ice rate was summarized as 70.1%. At this time, the ice contained NaCl, and the content of NaCl after melting was 826.3 mg / L. The NaCl concentration in the filtrate obtained in step (3) was about 674 mg / L. Based on the filtrate, the NaCl removal rate in the wastewater was 98.8% (the NaCl concentration in the filtrate was higher than that in the ice, and the NaCl removal rate after mixing the filtrate with the ice melt was definitely higher than 98.8%). The obtained ice melt was mixed with the filtrate obtained in step (3), and the COD was measured. Cr The concentration was 4764 mg / L, therefore, the COD in the wastewater... Cr The removal rate was 96.3%, and the treatment cost per ton of wastewater was approximately 397 yuan.

[0043] In other embodiments, step (2) is repeated two or more times.

[0044] Example 4

[0045] The treatment method for the wastewater from the production of tributyl phosphate in this comparative example is basically the same as that in Example 1, except that the cooling rate in step (1) is set to 1℃ / h. The final removal rate of NaCl in the wastewater was 89.2%, and the COD...Cr The removal rate was 89.1%, the overall ice removal rate was 57.9%, and the treatment cost per ton of wastewater was approximately 294 yuan.

[0046] Example 5

[0047] The treatment method for the tributyl phosphate production wastewater in this comparative example is basically the same as that in Example 1, except that the cooling rate in step (1) is set to 1.5℃ / h. The final NaCl removal rate in the wastewater was 84.6%, and the COD... Cr The removal rate was 87.5%, and the treatment cost per ton of wastewater was approximately 267 yuan.

[0048] The freezing rate affects the transport of media in the solid-liquid two-phase system, thus affecting the desalination rate and the organic matter removal rate. When the freezing rate in steps (1)-(3) increases from 10% to 58%, the desalination rate decreases from 79.6% to 36.3%, and the organic matter removal rate decreases from 81.5% to 43.7%, indicating that the change in the organic matter removal rate in the upper layer of ice melt water is similar to that of the desalination rate, both decreasing with the increase of the freezing rate. This is because the formation rate of ice is greater than the mass transfer rate of salt and organic matter in water. The higher the freezing rate, the more salt and organic matter are encased in the ice, leading to a decrease in the removal rate of salt and organic matter. In this invention, the freezing rate (the water cooled and frozen into ice accounts for the total liquid volume) does not exceed 75%.

Claims

1. A method for treating waste water from production of tributyl phosphate, characterized in that, Includes the following steps: The wastewater is partially frozen by cooling, forming an upper layer of ice and a lower layer of solution. After removing the upper layer of ice, ammonium nitrate is mixed with the unfrozen wastewater. Sodium chloride crystals are induced to precipitate from the unfrozen wastewater at a temperature below 0°C. This induction of sodium chloride crystallization at 0°C involves ammonium nitrate crystallizing at a temperature below 0°C, which encapsulates sodium chloride to form mixed crystals. The sodium chloride crystals are then removed. The amount of ammonium nitrate added is 2-15% of the mass of the unfrozen wastewater. After removing the sodium chloride crystals, a carbon adsorbent is added to the wastewater to maintain the solution temperature below 0°C, thereby removing organic matter from the wastewater.

2. The treatment method of the tributyl phosphate production wastewater according to claim 1, characterized by, The cooling rate is 1~2℃ / h.

3. The treatment method of the tributyl phosphate production wastewater according to claim 1 or 2, characterized by, When inducing sodium chloride crystallization in unfrozen wastewater at a temperature below 0°C, the temperature below 0°C is -1 to -7°C, and the time is 1 to 2 hours.

4. The treatment method of the tributyl phosphate production wastewater according to claim 1, characterized by, When adding carbon adsorbent, the temperature is -3 to -7°C.

5. The treatment method of the tributyl phosphate production wastewater according to claim 4, characterized by, The time is 1 to 2 hours.

6. The treatment method of the tributyl phosphate production wastewater according to claim 4 or 5, characterized by, The amount of carbon adsorbent added is 0.5-1% of the mass of the wastewater after removing sodium chloride crystals.

7. The method for treating wastewater from tributyl phosphate production according to claim 4 or 5, characterized in that, The carbon material adsorbent is graphene and / or biochar.

8. The method for treating wastewater from tributyl phosphate production according to claim 7, characterized in that, The graphene has a particle size of 100-130 nm; the biochar has a mesh size of 900-1000 mesh.