Method and device for continuously separating calcium and magnesium from magnesium-containing wastewater in rare earth smelting

Abstract

The invention relates to the field of water treatment and wastewater resource recovery, in particular to a continuous calcium and magnesium separation method and device for rare earth smelting magnesium-containing wastewater. The method comprises the following steps: adding a base solution into a reactor of a reaction device, adding magnesium-containing wastewater and precipitant slurry into a first-stage reactor in a parallel flow manner for reaction, after the reaction is finished, overflowing the slurry into a 2-(n-1)-stage reactor, adding precipitant slurry into the 2-(n-1)-stage reactor at the same time to react with the overflowing slurry of the previous stage, and separating the magnesium-containing wastewater and the precipitant slurry to obtain the magnesium-containing wastewater. After the (n-1)-stage slurry enters the n-stage reactor for reaction, part of the slurry flows back to the first-stage reactor from an overflow port of the reactor, the remaining slurry is discharged from the bottom of the reactor, crystal separation and solid-liquid separation are performed, calcium sulfate crystals, magnesium hydroxide precipitates and treating fluid are obtained, and n is larger than or equal to 2 and smaller than or equal to 10. According to the method, continuous and resourceful treatment of the rare earth smelting magnesium-containing wastewater is achieved, the technological process is simple, and industrialization is easy to achieve.

Description

Technical Field

[0001] The invention relates to the field of water treatment and wastewater resource recovery, and in particular to a method and device for continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting. Background Art

[0002] At present, more than 80% of mixed rare earth concentrates in industry are treated by concentrated sulfuric acid high-temperature roasting process. A large amount of magnesium-containing wastewater is generated in the process of rare earth sulfate solution being transformed into rare earth chloride solution through extraction, mainly magnesium sulfate wastewater. Due to the zero discharge requirement of wastewater in environmental protection policy, production enterprises must treat wastewater to achieve water recycling. There are two main ways to treat magnesium sulfate wastewater in industry. One is the combination of membrane concentration and evaporation crystallization. The magnesium sulfate content in the wastewater is enriched by membrane concentration, and then the wastewater is evaporated and crystallized by multi-effect or MVR. This method can obtain magnesium sulfate crystal byproducts, but due to the complex composition of wastewater, it often contains a certain amount of chloride ions, resulting in the production of byproducts containing impurities and high evaporation costs. The membrane system is blocked by fouling and does not run smoothly, thus affecting the processing volume. Another method is direct precipitation method, which uses lime to directly precipitate magnesium sulfate wastewater to produce mixed slag of calcium sulfate and magnesium hydroxide, commonly known as white slag, which is stored as solid waste. This method is simple to operate and low in cost, but the large amount of solid waste generated has limitations from the perspective of resource recycling and ecological environment. Summary of the invention

[0003] In view of this, the present invention provides a method and device for continuous separation of calcium and magnesium in magnesium-containing wastewater from rare earth smelting. The present invention adopts a multi-stage reaction device for continuous precipitation, controls the precipitation conditions, realizes the growth of calcium sulfate crystals during the precipitation process, and uses physical means to separate calcium sulfate from magnesium hydroxide through the difference in physical properties of the generated calcium sulfate and magnesium hydroxide, thereby realizing the separation and resource utilization of calcium sulfate and magnesium hydroxide.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is a method for continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting, comprising the following steps:

[0006] (1) adding a bottom liquid to each level of reactors in a reaction device, and adding magnesium-containing wastewater and a precipitant slurry into a primary reactor in parallel to react;

[0007] (2) After the reaction is completed, the slurry overflows into the 2nd to (n-1)th stage reactor, and at the same time, the precipitant slurry is added into the 2nd to (n-1)th stage reactor to react with the overflow slurry of the previous stage;

[0008] (3) After the reaction is completed, the slurry in the (n-1)-stage reactor overflows into the n-stage reactor. After the reaction, part of the slurry flows back to the first-stage reactor from the reactor overflow port, and the remaining slurry is discharged from the bottom of the n-stage reactor to perform crystal separation and solid-liquid separation to obtain calcium sulfate crystals, magnesium hydroxide precipitates and treatment liquid;

[0009] 2≤n≤10.

[0010] The second technical solution of the present invention is a device for the above-mentioned method of continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting, which is composed of n-stage reactors connected in series;

[0011] The reactor comprises an overflow port and a feed port;

[0012] The feed port extends to the bottom of the reactor, wherein the wastewater and precipitant feed ports are separated, and the overflow port is located at the upper part of the reactor;

[0013] 2≤n≤10.

[0014] The present invention discloses the following technical effects:

[0015] (1) The present invention adopts a simple one-step precipitation process, which is superior to the existing evaporation crystallization process for treating magnesium sulfate wastewater in terms of cost. At the same time, the reaction process is a one-step precipitation process, which is superior to the multi-step precipitation resource treatment process for magnesium sulfate wastewater in terms of process flow.

[0016] (2) The process flow of the method of the present invention is simple and easy to operate.

[0017] (3) The method of the present invention can make the calcium sulfate crystal size larger and easy to separate from the magnesium hydroxide, thereby obtaining magnesium hydroxide with higher purity and realizing the resource recycling of magnesium hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 The present invention is a schematic diagram of a device for continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting.

[0020] Figure 2 This is a scanning electron microscope photo of calcium sulfate on the sieve of Example 1 of the present invention.

[0021] Figure 3 A scanning electron microscope photograph of the precipitation mixture was generated for Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0024] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0025] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0026] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0027] The "%" described in the present invention, unless otherwise specified, refers to mass percentage.

[0028] The present invention provides a method and device for continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting (device such as Figure 1As shown), magnesium-containing wastewater and a precipitant are reacted in a continuous reaction device, a certain amount of bottom liquid is added to each stage of the initial reaction device, and the growth of calcium sulfate dihydrate crystals is controlled by controlling the reaction temperature, reaction time, and stirring speed in each stage of the reactor. Under the premise of differential growth of calcium sulfate dihydrate and magnesium hydroxide, a physical device is used to separate the two, and calcium sulfate dihydrate and magnesium hydroxide with higher purity are obtained respectively. Recycling of calcium sulfate dihydrate and magnesium hydroxide is achieved. The method for resource-based treatment of magnesium-containing wastewater of the present invention has low cost, simple process and easy operation, and finally realizes resource recovery.

[0029] The first aspect of the present invention provides a method for continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting, comprising the following steps:

[0030] (1) adding a bottom liquid to each level of reactors in a reaction device, and adding magnesium-containing wastewater and a precipitant slurry into a primary reactor in parallel to react;

[0031] (2) After the reaction is completed, the slurry overflows into the 2nd to (n-1)th stage reactor, and at the same time, the precipitant slurry is added into the 2nd to (n-1)th stage reactor to react with the overflow slurry of the previous stage;

[0032] (3) After the reaction is completed, the slurry in the (n-1)-stage reactor overflows into the n-stage reactor. After the reaction, part of the slurry flows back to the first-stage reactor from the reactor overflow port, and the remaining slurry is discharged from the bottom of the n-stage reactor to perform crystal separation and solid-liquid separation to obtain calcium sulfate crystals, magnesium hydroxide precipitates and treatment liquid;

[0033] 2≤n≤10.

[0034] If n=1, the crystal growth time is short, which is not conducive to the subsequent separation of the two crystals. Considering the economic factors such as site occupation, equipment investment, and energy consumption, the number of stages is controlled within 10 as much as possible.

[0035] The rate at which the magnesium-containing wastewater is added to the bottom liquid can be 0.1-1 m 3 / h.

[0036] In step (2), the rate of adding the precipitant slurry is determined by the total amount of the precipitant slurry added in 1 hour, and the sum of the amount of the precipitant added in each reactor in 1 hour is 60%-100% of the theoretical amount of sulfate added to the wastewater in 1 hour. In the present invention, the reaction process is a continuous process, the material is added all the time, and the slurry is also overflowing all the time, and the overflow amount in each reactor is consistent with the amount of material added.

[0037] The overflow port is located at the upper part of the reactor at 20% of the reactor volume from the top of the reactor.

[0038] In some embodiments of the present invention, the base liquid is at least one of water, treatment liquid, and magnesium-containing wastewater.

[0039] In some embodiments of the present invention, the amount of the bottom liquid added is 80% of the volume of the reactor.

[0040] In some embodiments of the present invention, the proportion of the precipitant slurry added is a percentage of the theoretical reaction amount of sulfate (either mass percentage or molar percentage), wherein the proportion of the precipitant slurry added to the first reactor is 40%-90%, the proportion of the precipitant slurry added to the 2nd to (n-1)th reactor is 0-60%, and the total amount of precipitant added at each stage is 60%-100% of the theoretical reaction amount of sulfate.

[0041] In some embodiments of the present invention, the slurry reflux rate of the slurry in the n-stage reactor from the reactor overflow port to the first-stage reactor is 0-20% (ie, reflux rate) of the total mass of the slurry in the n-stage reactor.

[0042] In some embodiments of the present invention, the reaction temperature in each stage of the reactor is 50-90° C., and the residence time of the reaction slurry in each stage of the reactor is 1-4 hours.

[0043] The stirring speed during the reaction or the crystal aging growth process is 100-300 rpm. In the present invention, if the stirring speed is too low, the crystal particles are easy to deposit, affecting the crystal growth, and if the stirring speed is too high, the large crystal particles will be broken, which is ultimately not conducive to crystal separation.

[0044] In some embodiments of the present invention, physical methods are used to separate crystals, such as using a screening device or a cyclone to separate crystals. After crystal separation, a slurry of large-particle calcium sulfate and small-particle magnesium hydroxide is obtained.

[0045] The second aspect of the present invention provides a device for the above-mentioned method of continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting, which is composed of n-stage reactors connected in series;

[0046] The reactor comprises an overflow port and a feed port (the overflow port of the previous reactor is connected to the feed port of the next reactor);

[0047] The feed port extends to the bottom of the reactor, wherein the wastewater and precipitant feed ports are separated, and the overflow port is located at the upper part of the reactor;

[0048] 2≤n≤10.

[0049] In some embodiments of the present invention, the bottom of the reactor is conical; a gas distributor is provided at the bottom of the reactor; and a discharge outlet valve is provided at the bottom of each stage of the reactor.

[0050] In some embodiments of the present invention, a stirring device is provided in the reactor.

[0051] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0052] The main components of the magnesium-containing wastewater used in the embodiment of the present invention are: SO4 2- :40g / L;Mg 2+ :12g / L;Cl - :4g / L.

[0053] The Ca in the precipitant slurry (calcium hydroxide slurry or calcium oxide slurry) used in the embodiment of the present invention is 2+ The concentration is 1 mol / L and the solvent is tap water.

[0054] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0055] Example 1

[0056] First, tap water is added as the bottom liquid in the reaction device (5-stage reactor), and the amount of the bottom liquid added is 80% of the reactor volume. Then, magnesium-containing wastewater and calcium hydroxide slurry are added to the first-stage reactor of the reaction device in a certain proportion and flow in parallel for reaction. The proportion of the precipitant slurry added is 60% of the theoretical reaction amount of sulfate. The reaction temperature is 60°C, and the reaction slurry stays in each reactor for 4 hours (the residence time of the reaction slurry in each reactor is determined according to the actual volume of the reactor, and the reactor volume and the feeding rate jointly determine the residence time of the slurry in the container). The reaction slurry in the first reactor overflows to the 2-5 reactors in turn for reaction. After the reaction starts, the gas distributor at the bottom of each reactor is opened to reduce the occurrence of blockage. The stirring speed in each reactor is 200r / min. The material is discharged from the bottom of the 5th stage reactor, and part of the slurry in the 5th stage reactor flows back to the 1st stage reactor with a reflux rate of 20%. A screening device is used to separate the crystals. The material on the screen is large-particle calcium sulfate dihydrate, and the slurry under the screen is magnesium hydroxide slurry mainly composed of magnesium hydroxide. The magnesium hydroxide slurry under the screen is subjected to solid-liquid separation by a centrifugal device to obtain magnesium hydroxide precipitate and treatment liquid with higher purity, which are reused in the P507 saponification step. The calcium sulfate dihydrate crystals on the screen are slurried with tap water and stirred, and the slurry is sent to a screening device for solid-liquid separation. The material on the screen is purified large-particle calcium sulfate dihydrate crystals, and the slurry under the screen can be reused for calcium sulfate slurrying. The calcium sulfate on the screen is as follows: Figure 2 Scanning electron microscope photo shows. Figure 2 It can be seen that the length of the generated calcium sulfate crystals is mostly above 200 μm and is relatively wide, which is conducive to the subsequent separation from other substances.

[0057] Example 2

[0058] First, the treatment liquid is added to the reaction device (5-stage reactor) as the bottom liquid, and the amount of the bottom liquid added is 80% of the reactor volume. Then, the magnesium-containing wastewater and the calcium oxide slurry are added to the first-stage reactor of the reaction device in a certain proportion and flow in parallel to react. The proportion of the precipitant slurry added is 60% of the theoretical reaction amount of sulfate, the reaction temperature is 90°C, and the reaction slurry stays in each stage reactor for 1h. The reaction slurry in the first-stage reactor overflows to the 2-5 stage reactors in turn for reaction. After the reaction starts, the gas distributor at the bottom of each stage reactor is opened to reduce the occurrence of material blockage. The stirring speed in each stage reactor is 200r / min. The material is discharged from the bottom of the 5-stage reactor, and part of the slurry in the 5-stage reactor is refluxed to the 1-stage reactor, and the reflux amount is 10%. A screening device is used for crystal separation. The material on the screen is large-particle calcium sulfate dihydrate, and the slurry under the screen is magnesium hydroxide slurry mainly composed of magnesium hydroxide. The magnesium hydroxide slurry under the screen is subjected to solid-liquid separation by a centrifugal device to obtain a high-purity magnesium hydroxide precipitate and treatment liquid, which are reused in the neutralization process of rare earth roasting ore water leaching liquid. The calcium sulfate dihydrate crystals on the screen are slurried with tap water and stirred, and the slurry is sent to a screening device for solid-liquid separation. The material on the screen is the purified large-size calcium sulfate dihydrate crystals, and the slurry under the screen can be reused for calcium sulfate slurrying.

[0059] Example 3

[0060] First, tap water is added as the bottom liquid in the reaction device (3-stage reactor), and the amount of the bottom liquid added is 80% of the reactor volume. Then, magnesium-containing wastewater and calcium hydroxide slurry are added to the first-stage reactor of the reaction device in a certain proportion and flow in parallel for reaction. The proportion of the precipitant slurry added is 70% of the theoretical reaction amount of sulfate. The reaction slurry continuously enters the second-stage reactor. The proportion of the precipitant slurry added in the second-stage reactor is 20% of the theoretical reaction amount of sulfate, and the total amount of the precipitant added is 90% of the theoretical reaction amount of sulfate. After the reaction of the second-stage reaction slurry, it enters the third-stage reactor for reaction. The reaction temperature is 90°C, the reaction slurry stays in each reactor for 2h, and the stirring speed in each reactor is 200r / min. After the reaction starts, the gas distributor at the bottom of each reactor is opened to reduce the occurrence of blockage. The material is discharged from the bottom of the third-stage reactor, and part of the slurry in the third-stage reactor is refluxed to the first-stage reactor, with a reflux rate of 20%. A cyclone is used for crystal separation. The material discharged from the lower part of the cyclone is a large-particle calcium sulfate dihydrate slurry, and the material discharged from the upper part of the cyclone is a magnesium hydroxide slurry mainly composed of magnesium hydroxide. The solid-liquid separation is performed separately to obtain large-particle calcium sulfate dihydrate crystals, magnesium hydroxide precipitation and recycled water.

[0061] Example 4

[0062] First, tap water is added as the bottom liquid in the reaction device (10-stage reactor), and the amount of the bottom liquid added is 80% of the reactor volume. Then, magnesium-containing wastewater and calcium hydroxide slurry are added to the first-stage reactor of the reaction device in a certain proportion and flow in parallel for reaction. The proportion of the precipitant slurry added is 40% of the theoretical reaction amount of sulfate. The reaction slurry overflows to the 2-3-stage reactor in turn. The proportion of the precipitant slurry added in the 2-3-stage reactor is 10% of the theoretical reaction amount of sulfate. After the reaction, the slurry continuously enters the 4-9-stage reactor. The proportion of the precipitant slurry added in the 4-9-stage reactor is 5% of the theoretical reaction amount of sulfate. After the reaction, the slurry overflows to the 10-stage reactor. The reaction temperature is 50°C, the reaction slurry stays in each reactor for 3h, the temperature of crystal aging growth in each reactor is 90°C, and the stirring speed is 250-200r / min. After the reaction starts, the gas distributor at the bottom of each reactor is opened to reduce the occurrence of blockage. The material is discharged from the bottom of the 10th-stage reactor, and part of the slurry in the 10th-stage reactor is refluxed to the 1st-stage reactor, with a reflux rate of 10%. A screening device is used for crystal separation. The material on the screen is large-particle calcium sulfate dihydrate, and the slurry under the screen is magnesium hydroxide slurry mainly composed of magnesium hydroxide. The magnesium hydroxide slurry under the screen is subjected to solid-liquid separation by a centrifugal device to obtain a magnesium hydroxide precipitate and a treatment liquid with a high purity, which are reused in the P507 saponification step. The calcium sulfate dihydrate crystals on the screen are slurried with tap water and stirred, and the slurry is sent to a screening device for solid-liquid separation. The material on the screen is purified large-particle calcium sulfate dihydrate crystals, and the slurry under the screen can be reused for calcium sulfate slurrying.

[0063] Comparative Example 1

[0064] A certain volume of tap water is added to a single-stage beaker as the bottom liquid. The amount of the bottom liquid added is 80% of the reactor volume. The bottom liquid is heated to 60°C, and magnesium sulfate wastewater and calcium hydroxide slurry are added (the addition ratio of magnesium sulfate wastewater and calcium hydroxide slurry is 1:0.6 in terms of the molar ratio of sulfate to calcium). After continuous addition for 2 hours, the addition is stopped. After stirring at the same temperature for 1 hour, the mixture of calcium sulfate and magnesium hydroxide is filtered to obtain a mixture. The precipitated mixture is generated as follows: Figure 3 Scanning electron microscope photo shows. Figure 3 It can be seen that most of the generated calcium sulfate is in an elongated shape with a length of about 100 μm, which is not conducive to the subsequent screening and separation of other substances.

[0065] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for continuously separating calcium and magnesium from magnesium-containing wastewater from rare earth smelting, characterized in that: The following steps are involved: (1) adding a bottom liquid to each stage of the reactor of the reaction device, and adding the magnesium-containing wastewater and the precipitant slurry into the primary reactor in parallel to react; (2) After the reaction is completed, the slurry overflows into the 2nd to (n-1)th stage reactor, and at the same time, the precipitant slurry is added into the 2nd to (n-1)th stage reactor to react with the overflow slurry of the previous stage; (3) After the reaction is completed, the slurry in the (n-1) stage reactor overflows into the nth stage reactor. After the reaction, part of the slurry flows back to the first stage reactor from the reactor overflow port, and the remaining slurry is discharged from the bottom of the nth stage reactor for crystal separation and solid-liquid separation to obtain calcium sulfate crystals, magnesium hydroxide precipitate and treatment liquid; 2≤n≤10。 2. The method for continuous separation of calcium and magnesium from magnesium-containing wastewater from rare earth smelting according to claim 1, characterized in that: The bottom liquid is at least one of water, treatment liquid and magnesium-containing wastewater; the amount of the bottom liquid added is 80% of the volume of the reactor; and the precipitant slurry is calcium hydroxide slurry or calcium oxide slurry.

3. The method for continuous separation of calcium and magnesium from magnesium-containing wastewater from rare earth smelting according to claim 1, characterized in that: The proportion of the precipitant slurry added is a percentage of the theoretical reaction amount of sulfate, wherein the proportion of the precipitant slurry added to the first-stage reactor is 40%-90%, the proportion of the precipitant slurry added to the 2nd to (n-1)-stage reactors is 0-60%, and the total amount of precipitant added at each stage is 60%-100% of the theoretical reaction amount of sulfate.

4. The method for continuous separation of calcium and magnesium from magnesium-containing wastewater from rare earth smelting according to claim 1, characterized in that: The slurry reflux rate of the slurry in the n-stage reactor flowing back to the first-stage reactor from the reactor overflow port is 0-20% of the total mass of the slurry in the n-stage reactor.

5. The method for continuous separation of calcium and magnesium from magnesium-containing wastewater from rare earth smelting according to claim 1, characterized in that: The reaction temperature in each stage of the reactor is 50 to 90° C., and the residence time of the reaction slurry in each stage of the reactor is 1 to 4 hours.

6. The method for continuous separation of calcium and magnesium from magnesium-containing wastewater from rare earth smelting according to claim 1, characterized in that: Crystal separation is performed using a screening device or a cyclone.

7. A device for the continuous separation of calcium and magnesium from magnesium-containing wastewater from rare earth smelting according to any one of claims 1 to 6, characterized in that: It consists of n-stage reactors connected in series; The reactor includes an overflow port and a feed port; The feed port extends to the bottom of the reactor, wherein the wastewater and precipitant feed ports are separated, and the overflow port is located at the upper part of the reactor; 2≤n≤10。 8. The device according to claim 7, characterized in that The bottom of the reactor is conical; a gas distributor is provided at the bottom of the reactor; and a discharge outlet valve is provided at the bottom of each stage of the reactor.

9. The device according to claim 7, characterized in that The reactor is provided with a stirring device.

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