Resourceful treatment method for magnesium sulfate wastewater from rare earth smelting

Abstract

The invention relates to the field of water treatment and wastewater resource recovery, in particular to a resourceful treatment method for magnesium sulfate wastewater in rare earth smelting. The method comprises the following steps: adding precipitant slurry and magnesium sulfate wastewater into a base solution for reaction to obtain mixed slurry containing calcium sulfate; and separating the mixed slurry containing calcium sulfate to obtain calcium sulfate crystals, magnesium hydroxide and recycled liquid. The invention provides a low-cost resourceful treatment method for rare earth smelting magnesium sulfate wastewater. The simple one-step precipitation process is adopted, the cost is superior to that of an existing magnesium sulfate wastewater evaporative crystallization treatment process, meanwhile, the reaction process is one-step precipitation, and the process is superior to that of a multi-step precipitation resourceful treatment magnesium sulfate wastewater process. The calcium sulfate crystal obtained by the method is large in size and easy to separate from magnesium hydroxide, the magnesium hydroxide and the calcium sulfate crystal with higher purity are recovered, and resource recycling of the magnesium hydroxide, the calcium sulfate crystal and the recycling liquid is realized.

Description

Technical Field

[0001] The invention relates to the field of water treatment and wastewater resource recovery, and in particular to a method for resource recovery treatment of rare earth smelting magnesium sulfate wastewater. Background Art

[0002] During the high-temperature roasting process of concentrated sulfuric acid in Bayan Obo mixed rare earth concentrate, P507 after saponification of magnesium oxide is used for the extraction and transformation of rare earth sulfate. This process produces a large amount of magnesium sulfate wastewater, and produces about 35m3 of rare earth sulfate per ton of REO. 3 Magnesium sulfate wastewater, due to environmental protection policy restrictions, wastewater can not be discharged, must be further treated to achieve water reuse. At present, there are two main treatment methods for rare earth smelting magnesium sulfate wastewater in industry, one is a combination of membrane concentration and evaporative crystallization, this method can obtain magnesium sulfate crystals and condensed water, but due to the complex composition of magnesium sulfate wastewater produced by production conditions, in addition to containing calcium, magnesium, sulfate, chloride ions and other anions and cations, it also contains certain organic matter, which will cause the fouling of the membrane in the membrane concentration process, causing the membrane system to run poorly, limiting production, in addition, because the wastewater also contains chloride ions, resulting in the output of magnesium sulfate crystals mixed with magnesium chloride, which affects the purity of magnesium sulfate crystal byproducts, and the evaporation cost is high. In order to reduce the treatment cost of wastewater, a simple lime precipitation method is used in industry for treatment, which produces a large amount of mixed precipitation of calcium sulfate and magnesium hydroxide, commonly known as white slag, which not only causes a waste of resources, but also increases the cost of wastewater treatment due to the transportation and storage of a large amount of output slag. Summary of the invention

[0003] The purpose of the present invention is to provide a method for resource-based treatment of magnesium sulfate wastewater from rare earth smelting. The present invention controls the growth of crystals in the magnesium sulfate wastewater precipitation process, selects an appropriate separation method according to the weight and particle size difference of the two crystals in the co-precipitation process, continuously separates calcium sulfate from magnesium hydroxide, and finally realizes the recycling of wastewater resources.

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

[0005] The present invention provides a method for resource treatment of rare earth smelting magnesium sulfate wastewater, comprising the following steps:

[0006] The precipitant slurry and magnesium sulfate wastewater are added to the bottom liquid for reaction to obtain a mixed slurry containing calcium sulfate;

[0007] The mixed slurry containing calcium sulfate is separated to obtain calcium sulfate crystals, magnesium hydroxide and recycled liquid.

[0008] The present invention discloses the following technical effects:

[0009] The present invention provides a low-cost method for resource-based treatment of magnesium sulfate wastewater from rare earth smelting. The present invention adopts a simple one-step precipitation process, which is more cost-effective than the current evaporation crystallization process for treating magnesium sulfate wastewater. At the same time, the reaction process is one-step precipitation, which is more cost-effective than the multi-step precipitation resource-based treatment process for magnesium sulfate wastewater.

[0010] The method of the invention can realize continuous treatment of magnesium sulfate wastewater. The calcium sulfate crystals obtained by the method of the invention are large in size and easy to be separated from magnesium hydroxide, and magnesium hydroxide and calcium sulfate crystals with higher purity are recovered, thereby realizing resource recycling of magnesium hydroxide, calcium sulfate crystals and recycled liquid, reducing solid waste accumulation and realizing resource recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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.

[0012] Figure 1 The present invention is a process flow chart of magnesium sulfate wastewater resource treatment.

[0013] Figure 2 This is a microscope photo of the calcium sulfate prepared in Example 1.

[0014] Figure 3 This is a microscope photograph of the mixture of calcium sulfate and magnesium hydroxide prepared in Comparative Example 1. DETAILED DESCRIPTION

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0020] like Figure 1 As shown, the present invention provides a method for resource treatment of rare earth smelting magnesium sulfate wastewater, comprising the following steps:

[0021] The precipitant slurry and magnesium sulfate wastewater are added to the bottom liquid for reaction to obtain a mixed slurry containing calcium sulfate (i.e., a mixed slurry of calcium sulfate with large particle size and magnesium hydroxide with small particle size);

[0022] The mixed slurry containing calcium sulfate is separated to obtain calcium sulfate crystals, magnesium hydroxide and recycled liquid.

[0023] In the present invention, the produced magnesium hydroxide can be used for the neutralization and impurity removal of rare earth roasted ore leaching solution or the P507 saponification process, the produced recycled liquid can be used in the rare earth roasted ore leaching process, and the produced calcium sulfate crystals can be used as additives in the construction, rubber and papermaking industries.

[0024] The shape of calcium sulfate crystals affects their use. Unlike granular calcium sulfate crystals that cannot be used in industries such as papermaking, whisker-shaped calcium sulfate crystals can be used in industries such as papermaking. Therefore, the resource treatment method for rare earth smelting magnesium sulfate wastewater that can prepare whisker-shaped calcium sulfate crystals has important practical application value.

[0025] In some embodiments of the present invention, the precipitant in the precipitant slurry is calcium hydroxide and / or calcium oxide; the solvent of the precipitant slurry is water; and the solid-liquid ratio of the precipitant to the solvent is 1 g:3-6 ml.

[0026] In actual production and application, the solvent of the precipitant slurry can be tap water.

[0027] In some embodiments of the present invention, the Cl in the magnesium sulfate wastewater - Content ≤10g / L.

[0028] In some embodiments of the present invention, the precipitant slurry and the magnesium sulfate wastewater Ca:SO 4 2- The molar ratio is 0.6-0.9:1.

[0029] In some embodiments of the present invention, the base liquid is water and / or recycled liquid.

[0030] In some embodiments of the present invention, the base liquid includes seed crystals; the added amount of the seed crystals is 0%-10% of the mass of calcium sulfate (ie, calcium sulfate crystals) generated from magnesium sulfate wastewater.

[0031] The amount of the base liquid added is 4-10 times the total volume of the magnesium sulfate wastewater and the precipitant slurry added in 1 hour; for example, in the actual preparation process, the flow rate of the magnesium sulfate wastewater added to the base liquid can be 0.1-1m 3 / h.

[0032] In actual production and application, the amount of the base liquid added may vary with the volume of the reaction container.

[0033] In the present invention, the role of the base liquid is to provide a lower supersaturation when the crystal nucleus is formed, because the low supersaturation will not spontaneously form the crystal nucleus, and can only grow on the original crystal nucleus (or crystal) until it grows to the required crystal size.

[0034] If the amount of base liquid added is too high, the system operation equilibrium time will be prolonged. If the amount of base liquid added is too small, it will not reduce the supersaturation of the system and will be detrimental to crystal growth.

[0035] In some embodiments of the present invention, the seed crystals are calcium sulfate crystals and / or a mixed slurry containing calcium sulfate.

[0036] In some embodiments of the present invention, the reaction temperature is 60-80°C.

[0037] In some embodiments of the present invention, the reaction time is 1-4 hours.

[0038] In some embodiments of the present invention, the separation is specifically separation by screening or separation using a cyclone, followed by solid-liquid separation.

[0039] The method of the present invention can be used for continuous production in practical application, for example, by using a screening device for continuous discharge.

[0040] The seed crystals used in the examples of the present invention are calcium sulfate crystals obtained after solid-liquid separation in the examples.

[0041] 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.

[0042] The magnesium sulfate wastewater used in the following examples is magnesium sulfate wastewater produced by a rare earth smelting and separation plant. The raw water composition of magnesium sulfate wastewater is shown in Table 1:

[0043] Table 1 Content of each component in magnesium sulfate wastewater (g / L)

[0044] index pH <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[SO 4 2- ]]> <![CDATA[Cl - ]]> Numeric 3.3 0.7 14.4 41.2 4.75

[0045] 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.

[0046] Example 1

[0047] First, calcium oxide slurry (precipitant slurry) was prepared with tap water as solvent, and the solid-liquid ratio of the prepared slurry was 1g:3ml. The prepared calcium oxide slurry was mixed with magnesium sulfate wastewater according to the ratio of Ca:SO 4 2- (molar ratio) is 0.6:1 and added to the bottom liquid containing crystal seeds, and the crystal seeds are selected from the separated calcium sulfate crystals, and the amount added is 10% of the mass of calcium sulfate generated by magnesium sulfate wastewater. The bottom liquid solvent is water, and its volume is 10 times the total volume of magnesium sulfate wastewater and precipitant slurry added in 1 hour, and the bottom liquid temperature is controlled to be 60°C. The reaction temperature is 60°C, and the growth time is 3h, to achieve differential growth of precipitation products, and obtain a mixed slurry of large-particle size calcium sulfate and small-particle size magnesium hydroxide. The mixed slurry is sieved and separated, the sieve is large-particle size calcium sulfate crystals, and the sieve slurry is magnesium hydroxide slurry. The sieve calcium sulfate and the sieve magnesium hydroxide slurry are further solid-liquid separated to obtain calcium sulfate crystals, magnesium hydroxide and recycled liquid, and the output magnesium hydroxide is used in the neutralization process of rare earth roasted ore leaching liquid, the output recycled liquid is used in the rare earth roasted ore leaching process, and the output calcium sulfate is used as an additive in the construction industry.

[0048] The microscopic image of calcium sulfate prepared in this example is as follows Figure 2 As shown by Figure 2 It can be seen that the calcium sulfate prepared in this example is in the shape of whiskers, and most of the calcium sulfate crystals are longer than 200 um.

[0049] Example 2

[0050] First, calcium hydroxide slurry (precipitant slurry) was prepared with tap water as solvent, and the solid-liquid ratio of the prepared slurry was 1g:6ml. The prepared calcium hydroxide slurry was mixed with magnesium sulfate wastewater according to the ratio of Ca:SO 4 2- (molar ratio) is 0.9:1 and added to the bottom liquid containing crystal seeds. The crystal seeds are selected from the separated calcium sulfate crystals, and the amount added is 5% of the mass of calcium sulfate generated by wastewater. The bottom liquid solvent is water, and its volume is 5 times the total volume of magnesium sulfate wastewater and precipitant slurry added in 1 hour, and the bottom liquid temperature is controlled to be 80°C. The reaction temperature is 80°C, and the growth time is 2h, to achieve differentiated growth of precipitation products, and obtain a mixed slurry of large-particle size calcium sulfate and small-particle size magnesium hydroxide. The mixed slurry is sieved and separated, the sieve is large-particle size calcium sulfate crystals, and the sieve slurry is magnesium hydroxide slurry. The sieve calcium sulfate and the sieve magnesium hydroxide slurry are further solid-liquid separated to obtain calcium sulfate crystals, magnesium hydroxide and recycled liquid, and the output magnesium hydroxide is used in the P507 saponification process, the output recycled liquid is used in the rare earth roasting ore leaching process, and the output calcium sulfate is used as an additive in the rubber industry.

[0051] Example 3

[0052] First, calcium hydroxide slurry (precipitant slurry) was prepared with tap water as solvent, and the solid-liquid ratio of the prepared slurry was 1g:5ml. The prepared calcium hydroxide slurry was mixed with magnesium sulfate wastewater according to the ratio of Ca:SO 4 2- (molar ratio) is 0.8:1 and added to the bottom liquid. The bottom liquid is a reused liquid, and its volume is 4 times the total volume of magnesium sulfate wastewater and precipitant slurry added in 1 hour, and the bottom liquid temperature is controlled to be 60°C. The reaction temperature is 60°C, and the growth time is 4h, to achieve differentiated growth of precipitation products, and obtain a mixed slurry of large-particle calcium sulfate and small-particle magnesium hydroxide. The mixed slurry is separated by a cyclone, and the upper outlet of the cyclone is a magnesium hydroxide slurry with a smaller particle size, and the lower outlet of the cyclone is a calcium sulfate slurry with a large particle size. Magnesium hydroxide, calcium sulfate crystals and reused liquid are obtained by solid-liquid separation, respectively. The produced magnesium hydroxide is used in the neutralization process of rare earth roasted ore leaching liquid, the produced reused liquid is used in the rare earth roasted ore leaching process, and the produced calcium sulfate is used as an additive in the construction industry.

[0053] Comparative Example 1

[0054] First, the precipitant calcium hydroxide and water were slurried at a solid-liquid ratio of 1g:5ml, and then added dropwise to the magnesium sulfate wastewater for reaction at room temperature. The stoichiometric ratio of calcium hydroxide to magnesium sulfate was 0.9:1. The reaction was stirred for 2h, and the precipitate was filtered to obtain a mixture of calcium sulfate and magnesium hydroxide, wherein SO 4 2- The content is 45.76%, Mg 2+ The content is 9.9%, Ca 2+The content is 17.14%. The mixture is stored as solid waste.

[0055] The microscopic photograph of the mixture of calcium sulfate and magnesium hydroxide prepared in this comparative example is as follows Figure 3 shown.

[0056] 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 recycling wastewater from rare earth smelting magnesium sulfate, characterized in that: The following steps are involved: The precipitant slurry and magnesium sulfate wastewater are added to the bottom liquid for reaction to obtain a mixed slurry containing calcium sulfate; The mixed slurry containing calcium sulfate is separated to obtain calcium sulfate crystals, magnesium hydroxide and recycled liquid.

2. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The precipitant in the precipitant slurry is calcium hydroxide and / or calcium oxide; the solvent of the precipitant slurry is water; and the solid-liquid ratio of the precipitant to the solvent is 1g:3-6ml.

3. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The Cl in magnesium sulfate wastewater - Content ≤10g / L.

4. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The precipitant slurry and Ca:SO4 in magnesium sulfate wastewater 2- The molar ratio is 0.6-0.9:

1.

5. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The base liquid is water and / or recycled liquid.

6. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The base liquid includes seed crystals; the added amount of the seed crystals is 0%-10% of the mass of the calcium sulfate crystals.

7. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The seed crystals are calcium sulfate crystals and / or a mixed slurry containing calcium sulfate.

8. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The reaction temperature is 60-80°C.

9. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The reaction time is 1-4h.

10. The method for recycling wastewater from rare earth smelting magnesium sulfate according to claim 1, characterized in that: The separation is specifically to first separate by screening or by using a cyclone, and then separate the solid and liquid.

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