Method for recovering lithium element from lithium polymer coagulation wastewater

Abstract

The invention relates to the technical field of environmental protection, and discloses a method for recovering a lithium element from lithium polymer coagulation wastewater. The method comprises the following steps: (1) pretreating the lithium polymer coagulation wastewater to remove suspended solids, colloids and small molecular organic matters in the lithium polymer coagulation wastewater; (2) carrying out reverse osmosis on the pretreated wastewater to obtain reverse osmosis concentrated water and purified water; (3) optionally, further concentrating the reverse osmosis concentrated water; and (4) precipitating the lithium element in the reverse osmosis concentrated water through a chemical precipitation method so as to separate the lithium element. The method is suitable for recovering lithium from the lithium polymer coagulation wastewater with relatively low lithium element concentration, recycling of the lithium polymer coagulation wastewater can be realized, the recovery rate of lithium is relatively high, and the obtained lithium-containing material is high in purity and small in chemical dosage.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and in particular to a method for recovering lithium elements from lithium-based polymer coagulation wastewater. Background Art

[0002] In the synthetic rubber and synthetic resin industries, there is a class of polymers that use organic lithium catalysts for polymerization. The production process of this type of polymer includes a coagulation process step, and the coagulation wastewater generated by this step is the main source of wastewater in the lithium polymer production process. The coagulation wastewater has a high temperature, and the main pollutants are small molecular organic matter and inorganic salts. The pollutant concentration is low, but it contains a small amount of lithium ions.

[0003] At present, the method for treating the condensation wastewater of synthetic rubber and synthetic resin is generally to cool the wastewater to room temperature and then send it to a wastewater treatment plant for treatment with the conventional treatment method of general industrial wastewater. Although such a treatment method is convenient, complies with national regulations and is not costly, the wastewater is discharged after treatment, which not only wastes water, but also the lithium ions contained in the water are discharged. If the recycling of wastewater can be achieved at a lower cost, the cost reduction and efficiency improvement of lithium polymer production can be achieved. Moreover, with the development of industries such as new energy, the demand for lithium salts has risen rapidly worldwide, and the output of lithium mines cannot keep up with the growth of demand, and the price of lithium salts has risen. If the lithium salts in the wastewater can be recovered at a lower cost while treating the wastewater, the production cost of lithium polymers can be further reduced and the benefits can be improved. At present, it is urgent to develop a method suitable for recovering lithium elements from the above-mentioned lithium polymer condensation wastewater. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a method for recovering lithium from lithium-based polymer condensation wastewater. The method is suitable for recovering lithium from lithium-based polymer condensation wastewater with a low lithium concentration, and can realize the resource utilization of lithium-based polymer condensation wastewater. The lithium recovery rate is high, and the obtained lithium-containing material has high purity and a small amount of chemical reagents.

[0005] In order to achieve the above object, the present invention provides a method for recovering lithium from lithium polymer coagulation wastewater, the method comprising:

[0006] (1) Pre-treating lithium polymer coagulation wastewater to remove suspended solids, colloids and small molecular organic matter therein;

[0007] (2) subjecting the pretreated wastewater to reverse osmosis to obtain reverse osmosis concentrated water and purified water, wherein the reverse osmosis conditions ensure that the water quality of the reverse osmosis concentrated water is: total organic matter ≤ 1000 mg / L, and conductivity ≥ 0.003 mS / cm;

[0008] (3) optionally, further concentrating the reverse osmosis concentrated water;

[0009] (4) Using a chemical precipitation method, the lithium element in the reverse osmosis concentrated water after the treatment in step (2) or the reverse osmosis concentrated water after the treatment in step (3) is precipitated to separate the lithium element.

[0010] Through the above technical scheme, the present invention can fully recover lithium from lithium-based polymer coagulation wastewater with low lithium element concentration, can realize the resource utilization of lithium-based polymer coagulation wastewater, and has a high lithium recovery rate. The obtained lithium-containing material has high purity and small amount of chemical reagents. DETAILED DESCRIPTION

[0011] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0012] In the present invention, the lithium polymer coagulation wastewater refers to the wastewater generated in the coagulation step of the polymerization process using an organic lithium catalyst in the synthetic rubber and synthetic resin industries.

[0013] The present invention provides a method for recovering lithium from lithium polymer coagulation wastewater, the method comprising:

[0014] (1) Pre-treating lithium polymer coagulation wastewater to remove suspended solids, colloids and small molecular organic matter therein;

[0015] (2) subjecting the pretreated wastewater to reverse osmosis to obtain reverse osmosis concentrated water and purified water, wherein the reverse osmosis conditions ensure that the water quality of the reverse osmosis concentrated water is: total organic matter ≤ 1000 mg / L, and conductivity ≥ 0.003 mS / cm;

[0016] (3) optionally, further concentrating the reverse osmosis concentrated water;

[0017] (4) Using a chemical precipitation method, the lithium element in the reverse osmosis concentrated water after the treatment in step (2) or the reverse osmosis concentrated water after the treatment in step (3) is precipitated to separate the lithium element.

[0018] It can be understood that "precipitating the lithium element in the reverse osmosis concentrated water after the treatment in step (2) or the reverse osmosis concentrated water after the treatment in step (3) to separate the lithium element" means that when step (3) is performed, the reverse osmosis concentrated water after the treatment in step (3) is treated to form a precipitate, and when step (3) is not performed, the reverse osmosis concentrated water after the treatment in step (2) is treated to form a precipitate.

[0019] The specific method of pretreatment is not particularly limited, as long as it can remove suspended matter, colloids and small molecular organic matter. Preferably, the pretreatment method is selected from at least one of grid filtration, flocculation precipitation, flotation, sand filtration, activated carbon filtration, filter cotton filtration, microfiltration and ultrafiltration. Among them, the grid used for grid filtration can be round holes or square holes, and the mesh size can be 0.2-1mm in diameter (round holes) or 0.2mm×(0.2-1)mm×1mm (square holes); the flocculants that can be used for flocculation precipitation include but are not limited to polyaluminum chloride, basic aluminum chloride, ferrous sulfate, ferric chloride, etc., and the amount of flocculant can be 300-1000g relative to 1 ton of lithium-containing wastewater; flotation can use aeration flotation or dissolved air flotation; sand filtration can use quartz sand with a particle size of 0.5-1.2mm; activated carbon filtration can use a specific surface area of ​​500-1700m 2 / g of activated carbon; filter cotton filtration can adopt synthetic fiber filter cotton with a filtration accuracy of 1-5μm (such as polypropylene synthetic fiber filter cotton, i.e. PP synthetic fiber filter cotton), non-woven filter cotton or glass fiber filter cotton; microfiltration can adopt a microfiltration membrane with an average pore size of 0.1-10μm; ultrafiltration can adopt an ultrafiltration membrane with a molecular weight cutoff of 5000-100000 (such as Koch HF series ultrafiltration membrane).

[0020] According to the present invention, preferably, the water quality of the pretreated wastewater is: total organic matter is 10-30 mg / L (for example, it can be 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L and the range formed by any two of the above values ​​and the value within the range); the conductivity is 0.005-0.3 mS / cm (for example, it can be 0.005 mS / cm, 0.01 mS / cm, 0.05 mS / cm, 0.1 mS / cm, 0.15 mS / cm, 0.2 mS / cm, 0.25 mS / cm, 0.3 mS / cm and the value within the range formed by any two of the above values); the total dissolved solid is 50-11 0mg / L (for example, it can be 50mg / L, 60mg / L, 70mg / L, 80mg / L, 90mg / L, 100mg / L, 110mg / L and the range formed by any two of the above values ​​and the value within the range); turbidity is 0-4NTU (for example, it can be 0, 1NTU, 2NTU, 3NTU, 4NTU and the value within the range formed by any two of the above values ​​and the value within the range); lithium ion concentration is 0.2-5mg / L (for example, it can be 0.2mg / L, 0.5mg / L, 1mg / L, 2mg / L, 3mg / L, 4mg / L, 5mg / L and the value within the range formed by any two of the above values ​​and the value within the range). There is no special limitation on other conditions of the water quality in the pretreated wastewater, for example, the iron ion content can be 0.05-1mg / L, the magnesium ion content can be 0.001-1mg / L, and the calcium ion content can be 0.005-1mg / L.

[0021] According to the present invention, the water quality of the reverse osmosis concentrated water obtained in step (2) is as follows: the total organic matter is 30-60 mg / L (for example, it can be 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, and the range formed by any two of the above values ​​and the value within the range); the conductivity is 0.02-0.6 mS / cm (for example, it can be 0.02 mS / cm, 0.05 mS / cm, 0.1 mS / cm, 0.2 mS / cm, 0.3 mS / cm, 0.4 mS / cm, 0.5 mS / cm, 0.6 mS / cm, and the range formed by any two of the above values ​​and the value within the range); the total dissolved solid is 220-320 mg / L (For example, it can be 220mg / L, 240mg / L, 260mg / L, 280mg / L, 300mg / L, 320mg / L, and the range formed by any two of the above values, and the value within the range); the turbidity is 4-7NTU (for example, it can be 4NTU, 5NTU, 6NTU, 7NTU, and the value within the range formed by any two of the above values); the lithium ion concentration is 0.8-2mg / L (for example, it can be 0.8mg / L, 1mg / L, 1.2mg / L, 1.4mg / L, 1.6mg / L, 1.8mg / L, 2mg / L, and the value within the range formed by any two of the above values). The iron ion concentration can be 0.1-1mg / L, the magnesium ion concentration can be 0.08-1mg / L, and the calcium ion concentration can be 0.08-1mg / L.

[0022] According to the present invention, preferably, the reverse osmosis conditions include: an operating temperature of 5-40°C, preferably 20-35°C (for example, it can be 20°C, 22°C, 25°C, 27°C, 30°C, 32°C, 35°C and the range formed by any two of the above values ​​and the value within the range); an operating pressure of 0.5-7MPa, preferably 1-5MPa (for example, it can be 1MPa, 2MPa, 3MPa, 4MPa, 5MPa and the range formed by any two of the above values ​​and the value within the range). The reverse osmosis membrane used in reverse osmosis is not particularly limited and can be any commercial anti-pollution reverse osmosis membrane, such as Hyde Energy LFC3-LD reverse osmosis membrane, Toray TML reverse osmosis membrane, etc. Under the above operating conditions, the water quality of the reverse osmosis concentrated water as described above can generally be achieved.

[0023] After the above reverse osmosis treatment, purified water that meets the reuse standards can also be obtained. The reuse standards can be found in GB / T12145-2016 "Water and Steam Quality for Thermal Power Generators and Steam Power Equipment".

[0024] According to the present invention, preferably, in step (3), the further concentration method is selected from at least one of electrodialysis, evaporation, high pressure reverse osmosis and membrane distillation. It can be understood that by further concentration, while obtaining further concentrated wastewater, another portion of relatively fresh water (which may be referred to as fresh water) can also be obtained. According to a particularly preferred embodiment of the present invention, the fresh water obtained by further concentration can be returned to step (2) for reverse osmosis treatment again.

[0025] According to the present invention, preferably, the conditions for electrodialysis include: the cation exchange membrane and the anion exchange membrane are both homogeneous membranes; the average effective membrane area per ton of wastewater is 9-20m 2 , preferably 10-15m 2 (For example, it can be 10m 2 、10.5m 2 、11m 2 、11.5m 2 、12m 2 、12.5m 2 、13m 2 、13.1m 2 、13.2m 2 、13.3m 2 、13.4m 2 、13.5m 2 、13.6m 2 、13.7m 2 、13.8m 2 、13.9m 2 、14m 2 、14.5m 2 、15m 2 and the range formed by any two of the above values ​​and the value within the range); the current density is 150-250A / m 2 (For example, it can be 150A / m 2 、160A / m 2 、170A / m 2 、180A / m 2 、190A / m 2 , 200A / m 2 , 210A / m 2 , 220A / m 2 , 230A / m 2 , 240A / m 2 , 250A / m 2 and the range formed by any two of the above values ​​and the value within the range), preferably 170-190A / m 2 (For example, it can be 170A / m 2 、171A / m 2、172A / m 2 、173A / m 2 、174A / m 2 、175A / m 2 、176A / m 2 、177A / m 2 、178A / m 2 、179A / m 2 、180A / m 2 、181A / m 2 、182A / m 2 、183A / m 2 、184A / m 2 、185A / m 2 、186A / m 2 、187A / m 2 、188A / m 2 、189A / m 2 、190A / m 2 The above homogeneous membrane refers to a film made directly from a polymer material having an ion exchange group, in which the polyelectrolyte and the film-forming polymer material are chemically combined to form a whole, or the polymer film-forming material itself has an ion exchange group to form a film-like polyelectrolyte. It is an ion exchange membrane with uniform chemical composition in the membrane, and the membrane itself has no heterogeneous structure and a uniform chemical structure. A BTE high-efficiency concentration electrodialysis system can be used.

[0026] The evaporation may be an MVR evaporation method. The MVR evaporation method, namely Mechanical Vapor Recompression, refers to an evaporation method using steam mechanical recompression technology. The volume of the further concentrated wastewater is controlled by the evaporation method to achieve the purpose of further concentration.

[0027] It is understood that the high-pressure reverse osmosis generally has an operating pressure of ≥5MPa, and the high-pressure reverse osmosis has a higher desalination rate, which can achieve further concentration. When performing high-pressure reverse osmosis, a disc-tube reverse osmosis membrane can be used. Generally, during the high-pressure reverse osmosis process, the conductivity of the concentrated water after further concentration can be monitored, and the high-pressure reverse osmosis operation can be stopped when the conductivity reaches the requirement.

[0028] According to the present invention, preferably, the water quality of the wastewater after further concentration is: total organic matter ≤ 1000 mg / L, preferably 0-200 mg / L (for example, it can be 0, 20 mg / L, 50 mg / L, 80 mg / L, 100 mg / L, 120 mg / L, 150 mg / L, 180 mg / L, 200 mg / L and the range formed by any two of the above values ​​and the value within the range); conductivity ≥ 3 mS / cm, preferably 4-200 m S / cm (for example, 4mS / cm, 10mS / cm, 20mS / cm, 50mS / cm, 80mS / cm, 100mS / cm, 120mS / cm, 150mS / cm, 170mS / cm, 200mS / cm, and a range formed by any two of the above values, and a value within the range); the turbidity is 0-10NTU, preferably 0-4NTU (for example, 0, 1NTU, 2NTU, 3NTU, 4NTU U and the range formed by any two of the above values ​​and the value within the range); lithium ion concentration ≥ 50 mg / L, preferably 120-8000 mg / L (for example, it can be 120 mg / L, 200 mg / L, 300 mg / L, 500 mg / L, 800 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, 3500 mg / L, 4000 mg / L, 4500mg / L, 5000mg / L, 5500mg / L, 6000mg / L, 6500mg / L, 7000mg / L, 7500mg / L, 8000mg / L and the range formed by any two of the above values, and the values ​​within the range); pH is 7-8.5 (for example, it can be 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.5 and the values ​​within the range formed by any two of the above values).The further concentrated wastewater may or may not contain metal elements other than lithium, such as iron ions, magnesium ions and calcium ions, and their concentrations are not particularly limited. For example, the concentration of iron ions may be 0.001-2000 mg / L (for example, 0.001 mg / L, 1 mg / L, 10 mg / L, 50 mg / L, 100 mg / L, 300 mg / L, 500 mg / L, 800 mg / L, 1000 mg / L, 1300 mg / L, 1500 mg / L, 1800 mg / L, 2000 mg / L, and the range formed by any two of the above values ​​and the value within the range), the concentration of magnesium ions may be 0.001-15 The concentration of calcium ions can be 0.001-1000 mg / L (for example, it can be 0.001 mg / L, 1 mg / L, 10 mg / L, 50 mg / L, 100 mg / L, 300 mg / L, 500 mg / L, 800 mg / L, 1000 mg / L, 1300 mg / L, 1500 mg / L, and a range formed by any two of the above values, and a value within the range).

[0029] According to the present invention, preferably, before step (4), the method further comprises: removing at least part of the metal elements other than lithium in the reverse osmosis concentrated water, wherein the metal elements are selected from at least one of magnesium, iron, aluminum and copper.

[0030] More preferably, the method for removing at least part of the metal elements other than lithium in the reverse osmosis concentrated water comprises: under the condition of pH 10-11, causing at least part of the metal elements other than lithium to form hydroxide precipitation.

[0031] Under the above conditions, magnesium, iron and other ions form corresponding hydroxide precipitates and are separated from the reverse osmosis concentrated water. Among them, the pH of the reverse osmosis concentrated water can be adjusted to the above range by adding an inorganic strong base to the reverse osmosis concentrated water, but if the pH of the reverse osmosis concentrated water itself already meets the above range, no additional alkali is required. It can be understood that in order to obtain a purer lithium-containing precipitate in step (4), the cations in the inorganic strong base added at this time preferably do not form a precipitate with the lithium element in step (4). The inorganic strong base can be sodium hydroxide and / or potassium hydroxide, and the inorganic strong base can be used in the form of its aqueous solution (the concentration of the inorganic strong base can be 0.8-1.5 mol / L).

[0032] According to the present invention, preferably, the chemical precipitation method comprises: adding anions corresponding to sparingly soluble lithium salts to the reverse osmosis concentrated water. The sparingly soluble lithium salts refer to lithium salts with a solubility of <1.5 g / 100 mL in water at room temperature (25° C.).

[0033] More preferably, the anion is selected from at least one of carbonate, phosphate and fluoride ions.

[0034] According to the present invention, preferably, step (4) is carried out under the condition of pH 5.8-8.2 (for example, it can be 5.8, 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2 and the range formed by any two of the above values ​​and the value within the range). After removing at least part of the metal elements other than lithium in the reverse osmosis concentrated water, an inorganic strong acid can be added to the reverse osmosis concentrated water to adjust it to the above range. In order to obtain a relatively pure lithium-containing precipitate, the anions in the added acid are preferably not combined with lithium ions to form salts that are not easily soluble in water. The inorganic strong acid can be at least one of hydrochloric acid, sulfuric acid and nitric acid. The inorganic strong acid can be used in the form of an aqueous solution with an acid concentration of 0.8-1.5 mol / L.

[0035] According to the present invention, preferably, the molar ratio of the amount of the anion added to the lithium content in the reverse osmosis concentrated water is (0.5-3):1.

[0036] Preferably, the anion is carbonate, and the molar ratio of the amount of carbonate added to the lithium content in the reverse osmosis concentrated water is (0.6-1):1, for example, it can be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, and a ratio range formed by any two of the above ratios and a ratio within the range. For example, sodium carbonate and / or potassium carbonate can be added to the reverse osmosis concentrated water (for example, it can be used in the form of an aqueous solution with a concentration of 0.5-2 mol / L). It can be understood that when step (3) is performed, the reverse osmosis concentrated water here refers to the reverse osmosis concentrated water treated in step (3); when step (3) is not performed, the reverse osmosis concentrated water here refers to the reverse osmosis concentrated water treated in step (2).

[0037] The operations of removing at least part of the metal elements other than lithium in the reverse osmosis concentrated water and precipitating the lithium in the reverse osmosis concentrated water can be performed in different precipitation tanks.

[0038] According to the present invention, preferably, the water quality of the lithium polymer coagulation wastewater is: total organic matter is 10-300 mg / L (for example, it can be 10 mg / L, 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L and the range formed by any two of the above values ​​and the value within the range), total dissolved solid is 20-500 mg / L (for example, it can be 20 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 250 mg / L, 300 mg / L and the range formed by any two of the above values ​​and the value within the range), 0mg / L, 300mg / L, 400mg / L, 500mg / L and the range formed by any two of the above values ​​and the value within the range), the lithium ion concentration is 0.2-5mg / L (for example, it can be 0.2mg / L, 0.5mg / L, 1mg / L, 2mg / L, 3mg / L, 4mg / L, 5mg / L and the range formed by any two of the above values ​​and the value within the range), the pH value is 4-8 (for example, it can be 4, 5, 6, 7, 8 and the value within the range). The conductivity is 0.001-0.4 mS / cm (for example, it can be 0.001 mS / cm, 0.005 mS / cm, 0.01 mS / cm, 0.05 mS / cm, 0.1 mS / cm, 0.2 mS / cm, 0.3 mS / cm, 0.4 mS / cm and the range formed by any two of the above values ​​and the value within the range), the turbidity is 22-35 NTU (for example, it can be 22 NTU, 24 NTU, 26NTU, 28NTU, 30NTU, 32NTU, 35NTU and the range formed by any two of the above values ​​and the value within the range), lithium polymer is 10-200mg / L (for example, it can be 10mg / L, 30mg / L, 50mg / L, 70mg / L, 100mg / L, 120mg / L, 150mg / L, 180mg / L, 200mg / L and the range formed by any two of the above values ​​and the value within the range). Among them, the lithium polymer coagulation wastewater may also contain or not contain other metal ions, such as at least one of iron ions, calcium ions and magnesium ions. The content of the above other metal ions is not particularly limited. For example, the content of iron ions can be 0.05-3mg / L, the content of magnesium ions can be 0.001-1.5mg / L, and the content of calcium ions can be 0.005-1.3mg / L.

[0039] In the above treatment process, the conductivity can be measured by a conductivity meter. Desktop, portable or online conductivity meters can be used. Depending on the material to be measured, conductivity meters with different ranges can be used. Concentrated wastewater with high ion concentration can use a conductivity meter with a maximum range of 200mS / cm or higher, and other wastewater conductivity generally uses a conductivity meter with a maximum range of 2mS / cm.

[0040] During the above treatment process, the pH value is measured using a pH meter. A desktop, portable or online pH meter can be used. The minimum graduation value of the pH meter can be 0.1 or less.

[0041] According to a particularly preferred embodiment of the present invention, the lithium polymer coagulation wastewater having the following water quality is treated according to the following method:

[0042] The water quality of lithium polymer coagulation wastewater is: TOC is 50-65mg / L, TDS is 270-285mg / L, lithium ion concentration is 0.4-0.5mg / L, pH value is 7-8, conductivity is 0.01-0.02mS / cm, turbidity is 27-28NTU, iron ion concentration is 0.1-0.15mg / L, magnesium ion concentration is 0.05-0.07mg / L, calcium ion concentration is 0.04-0.08mg / L, and lithium polymer is 20-50mg / L.

[0043] (1) The lithium polymer coagulation wastewater is treated by filter cotton filtration and ultrafiltration in sequence. The filter cotton uses PP filter cotton with a filtration accuracy of 1-2 μm, and the ultrafiltration membrane uses an ultrafiltration membrane with a molecular weight cutoff of 40,000-60,000.

[0044] (2) The pretreated wastewater is treated through a reverse osmosis membrane to obtain purified water and reverse osmosis concentrated water. The reverse osmosis conditions include: an operating temperature of 24-26°C and an operating pressure of 1.5-1.7 MPa.

[0045] (3) The reverse osmosis concentrate is treated with a BTE high-efficiency electrodialysis system to obtain further concentrated wastewater and fresh water. The electrodialysis conditions are: both the cation exchange membrane and the anion exchange membrane are homogeneous membranes, and the average effective membrane area per ton of wastewater is 13-14m 2 , current density is 178-182A / m 2 The fresh water is returned to step (2) for further processing.

[0046] (4) injecting the further concentrated wastewater obtained in step (3) into sedimentation tank No. 1, adding 0.9-1.1 mol / L sodium hydroxide solution until the pH value is 10-10.5, obtaining a precipitate, and separating the precipitate.

[0047] The clear liquid obtained after separation and precipitation in the sedimentation tank is injected into the buffer water tank, and hydrochloric acid (concentration 0.9-1.1 mol / L) is added until the pH value reaches between 6 and 8. The water in the buffer water tank is then injected into the No. 2 sedimentation tank, and 0.9-1.1 mol / L sodium carbonate solution is added until the molar ratio of the added amount of carbonate to the lithium content in the concentrated wastewater is (0.6-0.65):1. Solids are obtained from the bottom of the No. 2 sedimentation tank.

[0048] The present invention will be described in detail below through examples.

[0049] In the following examples, turbidity, total organic content (TOC) and total dissolved solids (TDS) were tested according to the methods specified in GB3838-2002 "Surface Water Environmental Quality Standard".

[0050] In the following examples, the concentration of lithium, calcium, magnesium, iron and other ions in water was determined by ion chromatography. The specific test method is: an ion chromatograph is equipped with a cation chromatographic column, and an aqueous solution containing 3.0mmol / L phthalic acid is used as an eluent, and the eluent flow rate is 0.8mL / min. The lithium chloride aqueous solution with a lithium ion concentration of 0.1, 0.5, 1, 5, 10, 20, 40, 60, 80, 100mg / L, and calcium chloride, magnesium chloride, and ferric chloride solutions of the same concentration are prepared, and the peak areas of lithium, calcium, magnesium, and iron ions are respectively injected into the ion chromatograph, and then the cation concentration is taken as the horizontal coordinate and the peak area is taken as the vertical coordinate, and a standard curve is obtained by linear fitting. The water sample to be measured is injected into the ion chromatograph after being filtered by a 0.45μm microporous membrane, and the peak areas of lithium, calcium, magnesium, and iron ions are respectively measured, and the corresponding standard curve equations are substituted to obtain lithium, calcium, magnesium, and iron ion concentrations. If the concentration is greater than 100 mg / L, dilute the water sample a certain number of times so that the cation concentration after dilution is less than 100 mg / L and measure again. Multiply the measured cation concentration by the dilution multiple to obtain the cation concentration in the water sample.

[0051] In the following examples, the recovery rate of lithium ions was determined by the following method: the collected lithium salt solid was fully dried and accurately weighed, and then the recovery rate of lithium ions was calculated using the following formula:

[0052]

[0053] Where R is the recovery rate, m Li is the mass of lithium salt, M S is the molecular weight of the lithium salt, n Li is the number of lithium atoms contained in each lithium salt molecule, m W is the total mass of the original wastewater, c Li is the concentration of lithium ions in the original wastewater.

[0054] In the following examples, the purity of the lithium salt product was determined by the following method: 100 mg of lithium salt was accurately weighed and added to 30 mL of 0.1 mol / L hydrochloric acid, and after it was completely dissolved, it was transferred to a 100 mL volumetric flask and diluted with water and fixed to 100 mL, and then the solution was subjected to the above-mentioned ion chromatography to determine the lithium ion concentration, and the purity of the lithium salt was calculated by the following formula:

[0055]

[0056] Where P is purity, c Li is the lithium ion concentration in the solution, M S is the molecular weight of the lithium salt, n Li The number of lithium atoms contained in each lithium salt molecule.

[0057] Example 1

[0058] The water quality of lithium polymer coagulation wastewater is: TOC is 58mg / L, TDS is 279mg / L, lithium ion concentration is 0.45mg / L, pH value is 7.5, conductivity is 0.0133mS / cm, turbidity is 27.5NTU, lithium polymer is 25mg / L, iron ion concentration is 0.112mg / L, magnesium ion concentration is 0.051mg / L, and calcium ion concentration is 0.041mg / L.

[0059] (1) The lithium polymer coagulation wastewater is treated by filter cotton filtration and ultrafiltration in sequence. The filter cotton uses PP filter cotton with a filtration accuracy of 1 μm, and the ultrafiltration membrane uses a Koch HF series ultrafiltration membrane with a molecular weight cutoff of 50,000.

[0060] The water quality parameters of the wastewater after pretreatment are: TOC is 15mg / L, TDS is 86mg / L, conductivity is 0.0127mS / cm, turbidity is 1.7NTU, lithium ion is 0.45mg / L, iron ion is 0.109mg / L, magnesium ion is 0.050mg / L, and calcium ion is 0.040mg / L.

[0061] (2) The pretreated wastewater is treated by a reverse osmosis membrane (Hydron LFC3-LD reverse osmosis membrane) to obtain purified water and reverse osmosis concentrated water. The reverse osmosis conditions include: an operating temperature of 25°C and an operating pressure of 1.6 MPa.

[0062] The water quality of the purified water obtained is: TOC is 5 mg / L, TDS is 36 mg / L, turbidity is 0.5 NTU, conductivity is 0.0054 mS / cm, and lithium ion is 0.01 mg / L.

[0063] The water quality parameters of the obtained reverse osmosis concentrated water are: TOC is 45mg / L, TDS is 267mg / L, turbidity is 5.5NTU, conductivity is 0.0385mS / cm, lithium ion is 1.36mg / L, iron ion is 0.330mg / L, magnesium ion is 0.151mg / L, and calcium ion is 0.121mg / L.

[0064] (3) The reverse osmosis concentrate was treated with a BTE high-efficiency electrodialysis system to obtain further concentrated wastewater and fresh water. The electrodialysis conditions were as follows: the cation exchange membrane (purchased from Beijing Tingrun Membrane Technology Development Co., Ltd., model number TRJCM) and the anion exchange membrane (purchased from Beijing Tingrun Membrane Technology Development Co., Ltd., model number TRJAM) were both homogeneous membranes, and the average effective membrane area per ton of wastewater was 13.7 m 2 , current density is 180A / m 2 The fresh water is returned to step (2) for further treatment. The water quality of the further concentrated wastewater is shown in Table 1.

[0065] (4) injecting the further concentrated wastewater obtained in step (3) into sedimentation tank No. 1, adding 1 mol / L sodium hydroxide solution until the pH value is 10-10.5, obtaining a precipitate, and separating the precipitate.

[0066] The clear liquid obtained after separation and precipitation in the sedimentation tank is injected into the buffer water tank, and hydrochloric acid (concentration 1 mol / L) is added until the pH value reaches between 6 and 8. The water in the buffer water tank is then injected into the No. 2 sedimentation tank, and 1 mol / L sodium carbonate solution (precipitant) is added until the molar ratio of the added amount of carbonate ions to the lithium content in the concentrated wastewater is 0.6:1.

[0067] The solid was obtained from the bottom of the No. 2 sedimentation tank, dried, weighed and the purity of lithium carbonate therein was determined.

[0068] The amounts of hydrochloric acid, sodium hydroxide and sodium carbonate added, the recovery rate of lithium and the purity of the lithium salt (lithium carbonate) are shown in Table 2.

[0069] Example 2

[0070] The method of Example 1 is used for treatment, except that in step (3), the reverse osmosis concentrated water is further concentrated by MVR evaporation method, until the volume of the reverse osmosis concentrated water after further concentration is 0.01 times that before further concentration.

[0071] Example 3

[0072] The treatment is carried out according to the method of Example 1, except that in step (3), a disc-tube reverse osmosis membrane (DTRO) is used to further concentrate the reverse osmosis concentrated water until the conductivity of the concentrated wastewater is greater than 4 mS / cm.

[0073] Example 4

[0074] The treatment is carried out in accordance with the method of Example 1, except that in step (4), no hydrochloric acid and sodium hydroxide are added. Instead, the further concentrated wastewater obtained in step (3) is directly injected into sedimentation tank No. 2, and 1 mol / L sodium carbonate solution is added until the molar ratio of the added amount of carbonate to the lithium content in the concentrated wastewater is 0.6:1.

[0075] Example 5

[0076] The treatment is carried out according to the method of Example 1, except that in step (4), the molar ratio of the amount of carbonate added to the lithium content in the concentrated wastewater is 1:1.

[0077] Example 6

[0078] The process is carried out in accordance with the method of Example 1, except that step (3) is not carried out, and the reverse osmosis concentrated water obtained in step (2) is directly carried out to step (4).

[0079] Example 7

[0080] The treatment was carried out according to the method of Example 1, except that in step (4), the precipitant added was a disodium hydrogen phosphate solution with a disodium hydrogen phosphate concentration of 1 mol / L (the obtained lithium salt was lithium phosphate), and the amount added was such that the molar ratio of the added phosphate to the lithium element in the wastewater was 0.4:1.

[0081] Example 8

[0082] The treatment was carried out according to the method of Example 1, except that in step (3), the average effective membrane area per ton of wastewater was 9.13 m 2 .

[0083] Example 9

[0084] The treatment was carried out according to the method of Example 1, except that in step (3), the average effective membrane area per ton of wastewater was 18.27 m 2 .

[0085] Example 10

[0086] The method of Example 1 was used, except that in step (3), the current density was 150 A / m 2 .

[0087] Embodiment 11

[0088] The treatment was carried out according to the method of Example 1, except that in step (3), the current density was 210 A / m 2 .

[0089] Example 12

[0090] The treatment was carried out according to the method of Example 1, except that the reverse osmosis membrane used in step (2) was Dow SW30-4040 reverse osmosis membrane.

[0091] Comparative Example 1

[0092] The process was carried out in accordance with the method of Example 1, except that step (1) was not performed. After 60 days of continuous operation, the reverse osmosis membrane was scrapped due to severe fouling.

[0093] Table 1

[0094]

[0095]

[0096] Table 2

[0097] Example No. Amount of alkali (mL) Acid dosage (mL) Precipitant dosage (mL) Lithium recovery rate (%) Lithium salt purity (%) Example 1 12.15 0.078 0.389 90.5 95.7 Example 2 514 3.30 0.389 89.3 92.3 Example 3 489 3.14 0.389 89.2 91.9 Example 4 — — 0.389 88.8 87.5 Example 5 12.15 0.078 0.648 92.4 94.8 Example 6 1012 1000 0.389 68.5 94.2 Example 7 12.15 0.078 0.259 89.9 95.2 Example 8 11.32 0.078 0.346 88.5 95.4 Example 9 12.19 0.078 0.391 90.8 95.8 Example 10 11.55 0.078 0.358 88.9 95.4 Embodiment 11 12.30 0.078 0.397 91.1 95.9 Example 12 12.06 0.078 0.385 90.3 95.6

[0098] From the above results, it can be seen that the embodiments of the method of the present invention can recover clean water and lithium salt from lithium polymer coagulation wastewater, the clean water has good water quality and can be reused, the lithium salt has a high recovery rate, the recovered lithium carbonate has a high purity, and the amount of chemicals used is small. In addition, it can be seen from Examples 1, 8-11 in Table 1 that the particularly preferred conditions of the present invention can ensure that a good effect can be fully guaranteed under lower energy consumption in further concentration.

[0099] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for recovering lithium from lithium polymer coagulation wastewater, characterized in that: The method includes: (1) Pre-treating lithium polymer coagulation wastewater to remove suspended solids, colloids and small molecular organic matter therein; (2) subjecting the pretreated wastewater to reverse osmosis to obtain reverse osmosis concentrated water and purified water, wherein the reverse osmosis conditions ensure that the quality of the reverse osmosis concentrated water is: total organic matter ≤ 1000 mg / L, and conductivity ≥ 0.003 mS / cm; (3) optionally, further concentrating the reverse osmosis concentrated water; (4) Using a chemical precipitation method, the lithium element in the reverse osmosis concentrated water after the treatment in step (2) or the reverse osmosis concentrated water after the treatment in step (3) is precipitated to separate the lithium element.

2. The method according to claim 1, wherein: The pretreatment method is selected from at least one of grid filtration, flocculation sedimentation, air flotation, sand filtration, activated carbon filtration, filter cotton filtration, microfiltration and ultrafiltration; And / or, the water quality of the pretreated wastewater is: total organic matter is 10-30 mg / L; conductivity is 0.005-0.3 mS / cm; total dissolved solid is 50-110 mg / L; turbidity is 0-4 NTU; lithium ion concentration is 0.2-5 mg / L.

3. The method according to claim 1, wherein: The water quality of the reverse osmosis concentrated water obtained in step (2) is as follows: total organic matter is 30-60 mg / L; conductivity is 0.02-0.6 mS / cm; total dissolved solid is 220-320 mg / L; turbidity is 4-7 NTU; lithium ion concentration is 0.8-2 mg / L; And / or, the reverse osmosis conditions include: an operating temperature of 5-40° C., preferably 20-35° C.; an operating pressure of 0.5-7 MPa, preferably 1-5 MPa.

4. The method according to claim 1 or 2, wherein: In step (3), the further concentration method is selected from at least one of electrodialysis, evaporation, high pressure reverse osmosis and membrane distillation.

5. The method according to claim 1 or 4, wherein: The water quality of the wastewater after further concentration is: total organic matter ≤1000mg / L, preferably 0-200mg / L; conductivity ≥3mS / cm, preferably 4-200mS / cm; turbidity is 0-10NTU, preferably 0-4NTU; lithium ion concentration is ≥50mg / L, preferably 120-8000mg / L; pH is 7-8.

5.

6. The method according to claim 1, wherein: Before step (4), the method further comprises: Removing at least part of the metal elements other than lithium in the reverse osmosis concentrated water, wherein the metal element is selected from at least one of magnesium, iron, aluminum and copper; Preferably, the method for removing at least part of the metal elements other than lithium in the reverse osmosis concentrated water comprises: under the condition of pH 10-11, causing at least part of the metal elements other than lithium to form hydroxide precipitation.

7. The method according to claim 1 or 6, wherein: The chemical precipitation method comprises: adding anions corresponding to the sparingly soluble lithium salt to the reverse osmosis concentrated water; Preferably, the anion is selected from at least one of carbonate, phosphate and fluoride; Preferably, step (4) is carried out at a pH of 5.8-8.

2.

8. The method according to claim 1, wherein: The molar ratio of the amount of the anion added to the lithium content in the reverse osmosis concentrated water is (0.5-3):

1.

9. The method according to claim 1 or 8, wherein: The anion is carbonate, and the molar ratio of the added amount of carbonate to the content of lithium in the reverse osmosis concentrated water is (0.6-1):

1.

10. The method according to claim 1 or 2, wherein: The water quality of the lithium polymer coagulation wastewater is: total organic matter is 10-300 mg / L, total dissolved solid is 20-500 mg / L, lithium ion concentration is 0.2-5 mg / L, pH value is 4-8, conductivity is 0.001-0.4 mS / cm, turbidity is 22-35 NTU, and lithium polymer is 10-200 mg / L.

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