Rare earth separation wastewater treatment process

Abstract

The invention discloses a rare earth separation wastewater treatment process which comprises the following steps: removing impurities: removing oil, organic matters and heavy metal impurities in wastewater; deamination: adding calcium hydroxide into the purified wastewater to adjust the wastewater to be alkaline, then carrying out ammonia distillation and deamination, and recycling ammonia water; performing mixed precipitation, namely performing mixed precipitation on the wastewater adjusted to be alkaline and oxalic acid, reacting calcium hydroxide in the wastewater with hydrochloric acid and oxalic acid to generate calcium chloride and calcium oxalate, and precipitating the calcium oxalate to obtain a calcium chloride solution; evaporation and concentration: the calcium chloride solution enters an evaporation device for evaporation and concentration, evaporated condensate water is recycled, and concentrated liquor obtained after evaporation and concentration enters a product production section; wastewater can be recycled while wastewater zero discharge is achieved, evaporation condensate water can be recycled to a front-end production line, and use of tap water is reduced. The calcium chloride salt is sold as a byproduct, so that the wastewater treatment cost can be greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of rare earth separation wastewater treatment technology, specifically a rare earth separation wastewater treatment process. Background Technology

[0002] Currently, rare earth extraction and separation mainly involves sodium soap, calcium soap, and ammonia soap processes, with calcium soap and ammonia soap being the mainstream. However, due to the tendency for calcium soap to cause sedimentation and scaling in the extraction tank, many rare earth separation companies have switched to the more efficient ammonia soap process. Regardless of the saponification process, both processes generate significant amounts of wastewater. Ammonia saponification or ammonium bicarbonate precipitation produces wastewater primarily composed of ammonium chloride, while oxalic acid precipitation generates wastewater primarily composed of hydrochloric acid and oxalic acid. Currently, there are no effective and low-cost methods for treating these wastewaters.

[0003] In traditional crafts, such as Figure 1 As shown, the current main treatment process involves adding excess calcium hydroxide to the ammonium chloride wastewater to adjust it to alkalinity, followed by ammonia stripping and removal. The ammonia water is then recovered and reused. The wastewater after ammonia removal is mainly composed of calcium chloride and calcium hydroxide. This wastewater is then mixed with oxalic acid precipitation wastewater. The calcium hydroxide in the oxalic acid wastewater reacts with hydrochloric acid and oxalic acid to produce calcium chloride and calcium oxalate. After calcium oxalate precipitation, the main component of the wastewater is calcium chloride, with a calcium chloride content of approximately 8-10%. The calcium chloride wastewater is then directly discharged into rivers.

[0004] However, the wastewater discharged from the above process has a high salt content, which has a significant impact on the environment and does not meet the current wastewater discharge standards. Therefore, we propose a rare earth separation wastewater treatment process to solve the problems mentioned above. Summary of the Invention

[0005] The purpose of this invention is to provide a rare earth separation wastewater treatment process to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A rare earth separation wastewater treatment process includes the following steps:

[0008] Step 1: Impurity removal, removing oil, organic matter, and heavy metal impurities from the wastewater;

[0009] Step 2: Ammonia removal. After adding calcium hydroxide to the purified wastewater to adjust it to alkalinity, ammonia is removed by steaming. The ammonia water is then recovered and reused.

[0010] Step 3: Mixing and precipitation. The wastewater, after being adjusted to alkalinity, is mixed with oxalic acid for precipitation. The calcium hydroxide in the wastewater reacts with hydrochloric acid and oxalic acid to produce calcium chloride and calcium oxalate. The calcium oxalate is then precipitated, and the wastewater after precipitation becomes a calcium chloride solution.

[0011] Step four, evaporation concentration, the calcium chloride solution into the evaporation device for evaporation concentration, the condensed water after evaporation is recycled, and the concentrated solution after evaporation concentration enters the product production section.

[0012] As a further scheme of the present application, the specific steps for removing oil, organic matter and heavy metal impurities in step one include:

[0013] Pretreatment: the wastewater is poured into a gravity oil separation tank to remove floating oil, and a demulsifier is added to remove emulsified oil, which is removed by micro-bubble adhesion and pressurized dissolved air flotation;

[0014] Organic matter degradation: the refractory organic matter and biodegradable organic matter in the wastewater are removed by advanced oxidation and biological treatment;

[0015] Heavy metal removal: the heavy metals in the wastewater are removed by chemical precipitation and activated carbon adsorption.

[0016] As a further scheme of the present application, the demulsifier is a polyether type demulsifier.

[0017] As a further scheme of the present application, the specific steps for adding calcium hydroxide to the wastewater to adjust the alkalinity in step two include: adding Ca(OH)2 to raise the pH of the wastewater to 11-12, and converting ammonium ions into free ammonia.

[0018] As a further scheme of the present application, the specific steps for ammonia stripping and deamination of the wastewater after being adjusted to alkalinity in step two include: heating the wastewater by an ammonia stripping tower, heating the wastewater to 80-95℃, blowing off the free ammonia by air or steam, condensing and recycling 10-20% ammonia water or ammonium sulfate solution by a condenser, and adjusting the pH of the wastewater to 6-9 by sulfuric acid or carbon dioxide.

[0019] As a further scheme of the present application, the specific steps for the reaction of calcium hydroxide in the wastewater with hydrochloric acid and oxalic acid to generate calcium chloride and calcium oxalate in step three include: adding hydrochloric acid to the wastewater to neutralize the calcium hydroxide, and then adding oxalic acid to the wastewater to filter and recover calcium oxalate.

[0020] As a further scheme of the present application, the specific steps for the calcium chloride solution entering the evaporation device for evaporation concentration in step four include: preheating the calcium chloride solution by a plate heat exchanger; evaporating and concentrating the preheated calcium chloride solution by an evaporation chamber, recycling the heat energy by returning the pressurized and heated secondary steam to the heating chamber after being pressurized and heated by an MVR compressor, and discharging the concentrated solution after concentration.

[0021] As a further scheme of the present application, the temperature for preheating the calcium chloride solution is 60-70℃.

[0022] As a further scheme of the present application: the temperature of the evaporation chamber is 70-90℃.

[0023] As a further scheme of the present application: the concentration of the discharged concentrated solution is 30-40%.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The rare earth separation wastewater treatment process can realize zero discharge of wastewater and resource utilization of wastewater, the evaporation condensate can be reused in the front-end production line to reduce the use of tap water, and the calcium chloride salt can be sold as a byproduct to greatly reduce the wastewater treatment cost. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a flowchart of the traditional process.

[0027] Figure 2 It is a flowchart of the improved rare earth separation wastewater treatment process of the present application. DETAILED DESCRIPTION

[0028] Example 1

[0029] In one embodiment, as shown in Figure 2 A rare earth separation wastewater treatment process includes the following steps:

[0030] Step one, impurity removal, removing oil, organic matter and heavy metal impurities in the wastewater;

[0031] Step two, ammonia removal, adding calcium hydroxide to the purified wastewater to make it alkaline, then removing ammonia by evaporation, and recycling the ammonia water;

[0032] Step three, mixing and precipitation, mixing the alkaline wastewater with oxalic acid for precipitation, the calcium hydroxide in the wastewater reacts with hydrochloric acid and oxalic acid to generate calcium chloride and calcium oxalate, the calcium oxalate is precipitated, and the precipitated wastewater is a calcium chloride solution;

[0033] Step four, evaporation and concentration, the calcium chloride solution enters the evaporation device for evaporation and concentration, the condensed water after evaporation is reused, and the concentrated solution after evaporation and concentration enters the product production section; if two water calcium chloride is needed, it enters the slicing machine for cooling and slicing to produce two water calcium chloride; if anhydrous calcium chloride is needed, it enters the drying machine or granulator to produce anhydrous calcium chloride.

[0034] The specific steps for removing oil, organic matter and heavy metal impurities in step one include:

[0035] Pre-treatment: The wastewater is poured into a gravity oil separation tank to remove floating oil, and a demulsifier is added to remove emulsified oil, which is removed by micro-bubble adhesion and pressurized dissolved air flotation;

[0036] Organic matter degradation: The refractory organic matter and biodegradable organic matter in the wastewater are removed by advanced oxidation and biological treatment;

[0037] Heavy metal removal: The heavy metals in the wastewater are removed by chemical precipitation and activated carbon adsorption;

[0038] The demulsifier is a polyether type demulsifier;

[0039] The specific steps of step two, adjusting the wastewater to alkaline by adding calcium hydroxide, include: adding Ca(OH)2 to raise the pH of the wastewater to 11, and converting ammonium ions into free ammonia;

[0040] The specific steps of step two, ammonia stripping and deamination of the wastewater after being adjusted to alkaline, include: heating the wastewater through an ammonia stripping tower, heating the wastewater to 80℃, blowing off the free ammonia by air or steam, condensing and recovering 10% ammonia water or ammonium sulfate solution through a condenser, and adjusting the pH of the wastewater to 6 by sulfuric acid or carbon dioxide;

[0041] The specific steps of step three, reaction of calcium hydroxide in the wastewater with hydrochloric acid and oxalic acid to generate calcium chloride and calcium oxalate, include: adding hydrochloric acid to the wastewater to neutralize the calcium hydroxide, then adding oxalic acid to the wastewater, and filtering and recovering calcium oxalate;

[0042] The specific steps of step four, evaporation and concentration of the calcium chloride solution in the evaporation device, include: preheating the calcium chloride solution through a plate heat exchanger; evaporating and concentrating the preheated calcium chloride solution through an evaporation chamber, recycling the heat energy by returning the pressurized and heated secondary steam to the heating chamber after being pressurized and heated by an MVR compressor, and discharging the concentrated solution after concentration;

[0043] The preheating temperature of the calcium chloride solution is 60℃; the temperature of the evaporation chamber is 70℃; and the concentration of the discharged concentrated solution is 30%;

[0044] Example 2

[0045] In one embodiment, as shown in Figure 2 a rare earth separation wastewater treatment process includes the following steps:

[0046] Step one, impurity removal, removing oil, organic matter, and heavy metal impurities in the wastewater;

[0047] Step two, deamination, adding calcium hydroxide to the purified wastewater to adjust it to alkaline, then performing ammonia stripping and deamination, and recycling the ammonia water for reuse;

[0048] Step three, mixed precipitation, the waste water after adjusting to alkaline is mixed with oxalic acid for precipitation, the calcium hydroxide in the waste water reacts with hydrochloric acid and oxalic acid to generate calcium chloride and calcium oxalate, the calcium oxalate is precipitated, and the waste water after precipitation is a calcium chloride solution;

[0049] Step four, evaporation concentration, the calcium chloride solution enters the evaporation device for evaporation concentration, the condensed water after evaporation is recycled, and the concentrated solution after evaporation concentration enters the product production section; if two water calcium chloride is needed to be produced, it enters the slicing machine for cooling and slicing to output two water calcium chloride; if anhydrous calcium chloride is needed to be produced, it enters the drying machine or the granulator to output anhydrous calcium chloride.

[0050] The specific steps for removing oil, organic matter and heavy metal impurities in step one include:

[0051] Pretreatment: the waste water is poured into a gravity oil separation tank to remove floating oil, a demulsifier is added to remove emulsified oil, and a micro-bubble adhesion pressurized dissolved gas flotation is used to remove oil;

[0052] Organic matter degradation: the biodegradable organic matter and the non-biodegradable organic matter in the waste water are removed through advanced oxidation and biological treatment;

[0053] Heavy metal removal: the heavy metal in the waste water is removed through chemical precipitation and activated carbon adsorption;

[0054] The demulsifier is a polyether type demulsifier;

[0055] The specific steps for adding calcium hydroxide to the waste water to adjust the alkalinity in step two include: adding Ca(OH)2 to increase the pH of the waste water to 11.5, and converting the ammonium ion into free ammonia;

[0056] The specific steps for ammonia stripping and deamination of the waste water after adjusting to alkalinity in step two include: heating the waste water to 87℃ through an ammonia stripping tower, blowing off the free ammonia by introducing air or steam, condensing and recycling the free ammonia into 15% ammonia water or ammonium sulfate solution through a condenser, and adjusting the pH of the waste water to 7.5 by adding sulfuric acid or carbon dioxide;

[0057] The specific steps for the reaction of calcium hydroxide in the waste water with hydrochloric acid and oxalic acid in step three include: adding hydrochloric acid to the waste water to neutralize the calcium hydroxide, and then adding oxalic acid to the waste water to filter and recover calcium oxalate;

[0058] The specific steps for the calcium chloride solution to enter the evaporation device for evaporation concentration in step four include: preheating the calcium chloride solution through a plate heat exchanger; evaporating and concentrating the preheated calcium chloride solution through an evaporation chamber, recycling the heat energy by returning the secondary steam to the heating chamber after being heated by an MVR compressor, and discharging the concentrated solution after concentration;

[0059] The temperature of the preheated calcium chloride solution is 65℃; the temperature of the evaporation chamber is 80℃; and the concentration of the discharged concentrated solution is 35%.

[0060] Example 3

[0061] In one embodiment, as shown in Figure 2 A rare earth separation wastewater treatment process includes the following steps:

[0062] Step one, impurity removal, the oil, organic matter, heavy metal impurities in the wastewater are removed;

[0063] Step two, ammonia removal, after the purified wastewater is adjusted to alkaline by adding calcium hydroxide, ammonia is removed by evaporation, and the ammonia water is recovered for reuse;

[0064] Step three, mixed precipitation, the wastewater adjusted to alkaline is mixed with oxalic acid for precipitation, calcium hydroxide in the wastewater reacts with hydrochloric acid and oxalic acid to generate calcium chloride and calcium oxalate, the calcium oxalate is precipitated, and the precipitated wastewater is a calcium chloride solution;

[0065] Step four, evaporation and concentration, the calcium chloride solution is fed into an evaporation device for evaporation and concentration, the condensed water after evaporation is reused, and the concentrated solution after evaporation and concentration is fed into a product production section; if calcium chloride dihydrate is needed, it is fed into a slicing machine for cooling and slicing to produce calcium chloride dihydrate; if anhydrous calcium chloride is needed, it is fed into a drying machine or a granulator to produce anhydrous calcium chloride.

[0066] The specific steps for removing oil, organic matter, and heavy metal impurities in step one include:

[0067] Pretreatment: the wastewater is poured into a gravity oil separation tank to remove floating oil, a demulsifier is added to remove emulsified oil, and micro-bubble adhesion and pressurized dissolved air flotation are used to remove oil;

[0068] Organic matter degradation: high-level oxidation and biological treatment are used to remove refractory organic matter and biodegradable organic matter in the wastewater;

[0069] Heavy metal removal: chemical precipitation and activated carbon adsorption are used to remove heavy metals in the wastewater;

[0070] The demulsifier is a polyether demulsifier;

[0071] The specific steps for adding calcium hydroxide to adjust the wastewater to alkaline in step two include: adding Ca(OH)2 to raise the pH of the wastewater to 12, and converting ammonium ions into free ammonia;

[0072] The specific steps of the step two of ammonia evaporation and deamination to the wastewater after adjusting to alkaline include: heating the wastewater through the ammonia evaporation tower, heating the wastewater to 95 DEG C, blowing off the free ammonia by air or steam, condensing and recycling to 20% ammonia water or ammonium sulfate solution through the condenser, and adjusting the pH of the wastewater to 9 by sulfuric acid or carbon dioxide;

[0073] The specific steps of the reaction of calcium hydroxide in the wastewater with hydrochloric acid and oxalic acid to generate calcium chloride and calcium oxalate in the step three include: adding hydrochloric acid into the wastewater, neutralizing the calcium hydroxide by the hydrochloric acid, then adding oxalic acid into the wastewater, and filtering and recycling the calcium oxalate;

[0074] The specific steps of the step four of the calcium chloride solution into the evaporation device for evaporation and concentration include: preheating the calcium chloride solution through the plate heat exchanger; evaporating and concentrating the preheated calcium chloride solution through the evaporation chamber, pressurizing and heating the secondary steam by the MVR compressor to return to the heating chamber, recycling the heat energy, and discharging the concentrated solution after concentration;

[0075] The preheating temperature of the calcium chloride solution is 70 DEG C; the temperature of the evaporation chamber is 90 DEG C; and the concentration of the discharged concentrated solution is 40%;

[0076] The same batch of rare earth separation wastewater generated in the process is divided into three equal parts, and the wastewater is treated by the process, and the water quality is shown in Table 1:

[0077] Table 1

[0078] Oil concentration Organic matter concentration Heavy metal concentration Calcium chloride solution concentration Moisture content Example 1 0.98％ 0.15％ 0.008％ 98.65％ 25.89％ Example 2 0.62％ 0.08％ 0.006％ 99.12％ 25.96％ Example 3 0.84％ 0.13％ 0.0075％ 98.24％ 25.64％

[0079] As shown in Table 1, in the wastewater treated by the treatment process in Example 2, the oil concentration, the organic matter concentration and the heavy metal concentration are the lowest, and the calcium chloride solution concentration is the highest.

[0080] The present application can realize zero discharge of wastewater and resource utilization of wastewater, the evaporation and condensation water can be reused in the front-end production line, and the use of tap water is reduced; the calcium chloride salt is sold as a by-product, which can greatly reduce the wastewater treatment cost.

[0081] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A rare earth separation wastewater treatment process, comprising the following steps: Step one, impurity removal, removing oil, organic matter and heavy metal impurities in the wastewater; Step two, deamination, adding calcium hydroxide to the purified wastewater to make it alkaline, then removing ammonia by evaporation, and recycling the ammonia water for reuse; Step three, mixing and precipitation, mixing the alkalized wastewater with oxalic acid for precipitation, the calcium hydroxide in the wastewater reacts with hydrochloric acid and oxalic acid to form calcium chloride and calcium oxalate, the calcium oxalate is precipitated, and the precipitated wastewater is a calcium chloride solution; Step four, evaporation and concentration, the calcium chloride solution is fed into an evaporation device for evaporation and concentration, the condensed water after evaporation is recycled, and the concentrated liquid after evaporation and concentration is fed into a product production section.

2. The rare earth separation wastewater treatment process according to claim 1, characterized in that, The specific steps for removing oil, organic matter and heavy metal impurities in step one include: pretreatment: removing floating oil by pouring the wastewater into a gravity oil separation tank, removing emulsified oil by adding a demulsifier, and removing oil by micro-bubble adhesion and pressurized dissolved air flotation; organic matter degradation: removing refractory organic matter and biodegradable organic matter in the wastewater by advanced oxidation and biological treatment; heavy metal removal: removing heavy metals in the wastewater by chemical precipitation and activated carbon adsorption.

3. The rare earth separation wastewater treatment process according to claim 2, characterized in that, The demulsifier is a polyether type demulsifier.

4. The rare earth separation wastewater treatment process according to claim 1, characterized in that, The specific steps for adding calcium hydroxide to the wastewater to make it alkaline in step two include: adding Ca(OH)2 to raise the pH of the wastewater to 11-12, and converting ammonium ions into free ammonia.

5. The rare earth separation wastewater treatment process according to claim 1, characterized in that, The specific steps for removing ammonia from the wastewater after it is made alkaline in step two include: heating the wastewater in an ammonia evaporation tower, heating the wastewater to 80-95℃, blowing off free ammonia by introducing air or steam, condensing and recycling the ammonia water or ammonium sulfate solution to 10-20%, and adjusting the pH of the wastewater to 6-9 by sulfuric acid or carbon dioxide.

6. The rare earth separation wastewater treatment process according to claim 1, characterized in that, The specific steps for the reaction of calcium hydroxide in the wastewater with hydrochloric acid and oxalic acid to form calcium chloride and calcium oxalate in step three include: adding hydrochloric acid to the wastewater to neutralize the calcium hydroxide, then adding oxalic acid to the wastewater, and filtering and recycling the calcium oxalate.

7. The rare earth separation wastewater treatment process according to claim 1, characterized in that, The specific steps for feeding the calcium chloride solution into an evaporation device for evaporation and concentration in step four include: preheating the calcium chloride solution through a plate heat exchanger; evaporating and concentrating the preheated calcium chloride solution in an evaporation chamber, recycling the secondary steam after being heated by a MVR compressor, and discharging the concentrated liquid after concentration.

8. The rare earth separation wastewater treatment process according to claim 7, characterized in that, The preheating temperature of the calcium chloride solution is 60-70℃.

9. The rare earth separation wastewater treatment process according to claim 7, characterized in that, The temperature of the evaporation chamber is 70-90℃.

10. The rare earth separation wastewater treatment process of claim 7, wherein, The concentration of the discharged concentrated liquid is 30-40%.

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