Method for treating lithium-containing wastewater

Abstract

The invention relates to the field of chemical engineering, and discloses a method for treating lithium-containing wastewater. The method comprises the following steps: (1) concentrating the lithium-containing wastewater until the lithium ion concentration of the concentrated wastewater is greater than or equal to 4000 mg / L; (2) optionally, under an alkaline condition, forming hydroxide precipitate in the concentrated wastewater so as to remove at least part of metal elements except the lithium element; and (3) precipitating the lithium element in the concentrated wastewater treated in the step (1) or the concentrated wastewater treated in the step (2) so as to separate the lithium element. According to the method, the lithium element in the lithium-containing wastewater can be fully recycled, the cost is low, and the method is particularly suitable for wastewater which is low in salt concentration and uses a lithium catalyst.

Description

Technical Field

[0001] The invention relates to the field of chemical engineering, and in particular to a method for treating lithium-containing wastewater. Background Art

[0002] The wastewater generated by lithium battery-related industries and chemical industries that use lithium catalysts (such as synthetic rubber using lithium catalysts) often contains lithium ions. In the past, this type of wastewater was usually treated as ordinary wastewater, and the lithium ions in it were discharged and lost along with other light metal ions after treatment. With the development of new energy and other industries, the demand for lithium salts has increased rapidly around the world, but the output of lithium ore cannot keep up with the growth of demand, and the price of lithium salts has risen, making it economically valuable to recover lithium salts from wastewater.

[0003] At present, the main method for extracting lithium ions from wastewater is extraction. The advantage of the extraction method is that it can effectively separate lithium salts from other salts. The disadvantage is that it requires the use of an extractant, which is mostly an organic solvent. It is troublesome to use and subsequently treat, and the cost is also high. The salt composition in the wastewater of the lithium battery industry is relatively complex, and the extraction method has certain advantages for the wastewater of the lithium battery industry; compared with the wastewater of the lithium battery industry, the wastewater produced by the use of lithium-based catalysts has differences such as lower salt concentration, and the economic efficiency of using the extraction method is very poor. Therefore, in order to recover lithium salts in wastewater from lithium-based catalysts, a more economical new method is needed. 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 treating lithium-containing wastewater, which can fully recover the lithium element in the lithium-containing wastewater at a low cost and is particularly suitable for wastewater with a low salt concentration using a lithium-based catalyst.

[0005] In order to achieve the above object, the present invention provides a method for treating lithium-containing wastewater, the method comprising:

[0006] (1) Concentrating the lithium-containing wastewater until the lithium ion concentration of the concentrated wastewater is ≥4000 mg / L;

[0007] (2) Optionally, under alkaline conditions, forming hydroxide precipitation in the concentrated wastewater to remove at least a portion of the metal elements other than lithium;

[0008] (3) Precipitating the lithium element in the concentrated wastewater treated in step (1) or the concentrated wastewater treated in step (2) to separate the lithium element.

[0009] Through the above technical scheme, the lithium element in lithium-containing wastewater can be fully recovered, which is applicable to wastewater from the lithium battery industry and wastewater from synthetic rubber using lithium-based catalysts. However, for the treatment of wastewater from synthetic rubber using lithium-based catalysts with lower salt concentrations, the scheme of the present invention can achieve full recovery of lithium ions at a lower cost. DETAILED DESCRIPTION

[0010] 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.

[0011] The present invention provides a method for treating lithium-containing wastewater, the method comprising:

[0012] (1) Concentrating the lithium-containing wastewater until the lithium ion concentration of the concentrated wastewater is ≥4000 mg / L;

[0013] (2) Optionally, under alkaline conditions, forming hydroxide precipitation in the concentrated wastewater to remove at least a portion of the metal elements other than lithium;

[0014] (3) Precipitating the lithium element in the concentrated wastewater treated in step (1) or the concentrated wastewater treated in step (2) to separate the lithium element.

[0015] It can be understood that whether to perform step (2) can be determined based on whether the lithium-containing wastewater contains metal elements other than lithium, or based on the purity requirements for the lithium-containing precipitate obtained in step (3). When the content of metal elements other than lithium in the lithium-containing wastewater is very low, or the purity requirements for the lithium-containing precipitate obtained in step (3) are low, so that a lithium-containing precipitate that meets the quality requirements can still be obtained without performing step (2), omitting step (2) can further save costs. The phrase "precipitate the lithium in the concentrated wastewater treated in step (1) or the concentrated wastewater treated in step (2) to separate the lithium" means that when step (2) is performed, the concentrated wastewater treated in step (2) is treated to form a precipitate, and when step (2) is not performed, the concentrated wastewater treated in step (1) is treated to form a precipitate.

[0016] According to the present invention, preferably, in step (1), before concentration, the method further comprises: removing impurities from the lithium-containing wastewater to remove at least one of suspended solids, colloids and small organic molecules therein.

[0017] Among them, the impurity removal method is not particularly limited, but preferably, the impurity removal method is selected from at least one of grid filtration, flocculation precipitation, flotation, sand filtration, activated carbon filtration, filter cotton filtration, microfiltration and ultrafiltration. There are no special requirements for the specific operations of the above methods. For example, 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 in flocculation precipitation include but are not limited to polyaluminum chloride, basic aluminum chloride, ferrous sulfate, and ferric chloride. Relative to 1 ton of lithium-containing wastewater, the amount of flocculant can be 300-1000g (for example, it can be 3 00g, 400g, 500g, 600g, 700g, 800g, 900g, 1000g and the range formed by any two of the above values ​​and the value within the range), after adding the flocculant, it can be stirred for 5-10min, and then it can be left to stand for 30-50min to allow the material to fully flocculate and precipitate; flotation can be carried out by 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 (it can be a hollow fiber ultrafiltration membrane with model HF or HFM purchased from Koch).

[0018] According to the present invention, preferably, the concentration makes the water quality of the concentrated wastewater as follows: conductivity ≥ 100mS / cm, preferably 150-200mS / cm (for example, it can be 150mS / cm, 160mS / cm, 170mS / cm, 180mS / cm, 190mS / cm, 200mS / cm and the range formed by any two of the above values ​​and the value within the range); total organic matter (TOC) ≤ 1000mg / L, preferably 0-200mg / L (for example, it can be 0, 50mg / L, 100mg / L, 150mg / L, 20 0 mg / L and the value within the range formed by any two of the above values); lithium ion concentration ≥4500 mg / L, preferably 5000-8000 mg / L (for example, it can be 5000 mg / L, 5500 mg / L, 6000 mg / L, 6500 mg / L, 7000 mg / L, 7500 mg / L, 8000 mg / L and the value within the range formed by any two of the above values); pH ≥6, preferably 6.5-8 (for example, it can be 6.5, 7, 7.5, 8 and the value within the range formed by any two of the above values). Other metal contents in the concentrated wastewater may include: an iron ion concentration of 500-2000 mg / L (for example, 500 mg / L, 800 mg / L, 1000 mg / L, 1200 mg / L, 1400 mg / L, 1500 mg / L, 1600 mg / L, 1700 mg / L, 1800 mg / L, 2000 mg / L and a range formed by any two of the above values ​​and a value within the range), a magnesium ion concentration of 5-1000 mg / L (for example, 5 mg / L, 50 mg / L, 100 mg / L, 200 mg / L, 30 0mg / L, 400mg / L, 500mg / L, 600mg / L, 700mg / L, 800mg / L, 900mg / L, 1000mg / L and the range formed by any two of the above values ​​and the value within the range), the calcium ion concentration is 3-1000mg / L (for example, it can be 3mg / L, 5mg / L, 50mg / L, 100mg / L, 200mg / L, 300mg / L, 400mg / L, 500mg / L, 600mg / L, 700mg / L, 800mg / L, 900mg / L, 1000mg / L).

[0019] According to the present invention, preferably, the concentration method is selected from electrodialysis and / or high pressure reverse osmosis, more preferably electrodialysis. The operating pressure of high pressure reverse osmosis can be 5-12 MPa.

[0020] More preferably, the electrodialysis conditions 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, more 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 、13.5m 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 , more preferably 175-185A / m 2 (For example, it can be 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 ). The above-mentioned homogeneous membrane refers to a thin film directly made of a polymer material having ion exchange groups, in which the polyelectrolyte and the film-forming polymer material in the membrane are chemically combined to become one, or the polymer film-forming material itself has ion exchange groups to form a membrane-like polyelectrolyte. It is an ion exchange membrane with uniform chemical composition in the membrane. The membrane itself has no heterogeneous structure and has a uniform chemical structure. The system used for electrodialysis is not subject to special restrictions. For example, a BTE high-efficiency concentration electrodialysis system can be used. It can be understood that through electrodialysis, concentrated wastewater with a high ion concentration and water with a lower ion concentration (which can be called fresh water) can be separated.

[0021] According to the present invention, preferably, in step (2), the alkaline condition is pH ≥ 10, preferably pH 10-11.

[0022] Preferably, the alkaline condition is provided by an alkali metal hydroxide. If the pH of the concentrated wastewater itself is greater than 10, no additional alkali is required, and the pH of the concentrated wastewater is monitored during the addition of the alkali. The alkali is not particularly limited and can be any water-soluble inorganic strong base. It is understood that in order to obtain a purer lithium-containing precipitate in step (3), the cations in the inorganic strong base added in step (2) preferably do not form a precipitate together with the lithium element in step (3). More preferably, the alkaline environment is provided by sodium hydroxide and / or potassium hydroxide. The alkali metal hydroxide can be used in the form of its aqueous solution (the concentration of the alkali metal hydroxide can be 0.8-1.5 mol / L).

[0023] According to the present invention, preferably, the metal element other than lithium is selected from at least one of magnesium, iron, aluminum and copper.

[0024] According to the present invention, preferably, in step (2), the operation of removing at least part of the metal elements other than lithium element adopts at least one of static sedimentation, centrifugal separation and filtration. The hydroxide precipitate is separated by a sedimentation tank, centrifugal separation and filtration. After removing the hydroxide precipitate formed by part of the metal elements other than lithium element by using a sedimentation tank, the obtained clear liquid can be moved out of the sedimentation tank and injected into another buffer water tank.

[0025] According to the present invention, preferably, before performing step (3), the method further comprises: adjusting the pH of the concentrated wastewater to 6-8.

[0026] Preferably, an inorganic strong acid is used to adjust the pH of the concentrated wastewater. The pH value of the water can be monitored while the acid is added. The acid can be any water-soluble inorganic strong acid. It is understood that in order to obtain a relatively pure lithium-containing precipitate in step (3), the anions in the added acid preferably do not combine with lithium ions in step (3) to form a salt that is not easily soluble in water. More preferably, the inorganic strong acid is preferably 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.

[0027] According to the present invention, preferably, in step (3), the lithium element is precipitated by adding anions corresponding to a sparingly soluble lithium salt to the concentrated wastewater. The sparingly soluble lithium salt refers to a lithium salt having a solubility of less than 1.5 g / 100 mL in water at room temperature (25° C.). This operation can also be performed in a sedimentation tank.

[0028] According to the present invention, preferably, the anion is selected from at least one of carbonate, phosphate and fluoride, more preferably carbonate.

[0029] According to the present invention, in order to make the lithium element in the concentrated wastewater more fully precipitate to be separated, preferably, the molar ratio of the amount of the anion added to the lithium element content in the concentrated wastewater is (0.3-3): 1. It can be understood that when step (2) is performed, the concentrated wastewater here refers to the concentrated wastewater treated in step (2); when step (1) is not performed, the concentrated wastewater here refers to the concentrated wastewater treated in step (1).

[0030] According to the present invention, preferably, the anion is carbonate, and the molar ratio of the amount of carbonate added to the lithium content in the concentrated wastewater 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.

[0031] Among them, the anion corresponding to the sparingly soluble lithium salt can be provided by a water-soluble salt containing the anion (i.e., a precipitant used to precipitate the lithium element), and the salt can be a salt formed by the anion and an alkali metal, preferably potassium carbonate and / or sodium carbonate, and the salt can be used in the form of an aqueous solution (the concentration can be 0.5-2 mol / L).

[0032] According to the present invention, preferably, the water quality of the lithium-containing wastewater is: total organic matter is 5-1000 mg / L, total dissolved solid is 10-1000 mg / L, lithium ion concentration is 0.01-10 mg / L, pH value is 3.5-8.5, and conductivity is 0.0001-0.8 mS / cm.

[0033] More preferably, the water quality of the lithium-containing 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 20-1000 mg / L (for example, it can be 20 mg / L, 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, 300 mg / L, 350 mg / L, 400 mg / L, 450 mg / L, 500 mg / L, 600 mg / L, 700 mg / L, 800 mg / L, 900 mg / L, 1000 mg / L mg / 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, 1mg / L, 2mg / L, 3mg / L, 4mg / L, 5mg / L and the value within the range formed by any two of the above values), the pH value is 4-8 (for example, it can be 4, 5, 6, 7, 8 and the value within the range formed by any two of the above values), and the conductivity is 0.001-0.4mS / cm (for example, it can be 0.001mS / cm, 0.01mS / cm, 0.1mS / cm, 0.2mS / cm, 0.3mS / cm, 0.4mS / cm and the value within the range formed by any two of the above values). The lithium-containing wastewater may also contain or not contain metal elements other than lithium, such as magnesium, iron, aluminum and copper. Among them, the content of metal elements other than lithium is not particularly limited. The content of iron element can be 0.02-2 mg / L, the content of magnesium element can be 0.01-1 mg / L, or lower, such as <0.01 mg / L; the content of calcium element can be 0.01-1 mg / L, or lower, such as <0.01 mg / L.

[0034] According to the present invention, preferably, the lithium-containing wastewater is lithium rubber synthesis wastewater and / or lithium battery anode material production wastewater, more preferably lithium rubber synthesis wastewater, and the content of lithium rubber in the lithium rubber synthesis wastewater is preferably 10-200 mg / L (for example, it can be 10 mg / L, 30 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).

[0035] In the synthetic rubber and synthetic resin industries, some polymers are polymerized using organic lithium catalysts. The production process of such polymers includes a coagulation process step, and the coagulation wastewater generated by this step is lithium rubber synthesis wastewater, which has a low salt concentration. The method provided by the present invention is applicable to wastewater from the lithium battery industry and wastewater from synthetic rubber using lithium catalysts. However, for the treatment of wastewater from synthetic rubber using lithium catalysts with a lower lithium ion concentration, the scheme of the present invention can achieve full recovery of lithium ions at a lower cost.

[0036] In the above treatment process, the conductivity can be measured by a conductivity meter. A desktop, portable or online conductivity meter can be used. Depending on the material to be measured, a conductivity meter with different ranges can be used. Untreated lithium-containing wastewater can use a conductivity meter with a maximum range of 2mS / cm. If the fresh water part obtained after electrodialysis is measured, the above conductivity meter can also be used. The concentrated wastewater with high ion concentration can use a conductivity meter with a maximum range of 200mS / cm or higher.

[0037] 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.

[0038] According to a particularly preferred embodiment of the present invention, lithium rubber synthesis wastewater having the following water quality is treated in the following manner:

[0039] Water quality of lithium rubber synthesis wastewater: total organic matter is 40-50 mg / L, total dissolved solid is 260-275 mg / L, lithium ion concentration is 0.4-0.5 mg / L, pH value is 7-8, conductivity is 0.01-0.02 mS / cm; iron ion concentration is 0.05-0.1 mg / L, magnesium ion concentration is 0.03-0.06 mg / L, calcium ion concentration is 0.01-0.05 mg / L, and the content of lithium rubber is 25-35 mg / L.

[0040] (1) After the wastewater is filtered through a PP synthetic fiber filter with a filtration accuracy of 1-2 μm to remove suspended solids, it is treated with a BTE high-efficiency concentrated electrodialysis system to obtain fresh water and concentrated wastewater with high ion concentration. 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 13.5-13.9 m 2 , current density is 178-182A / m 2 .

[0041] (2) injecting the concentrated wastewater obtained in step (1) into sedimentation tank No. 1, adding a sodium hydroxide solution with a sodium hydroxide concentration of 0.9-1.1 mol / L until the pH value is 10-10.5, standing and settling, and separating the precipitate.

[0042] 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 6-8.

[0043] (3) injecting the water in the buffer pool of step (2) into the No. 2 sedimentation tank, adding a sodium carbonate solution with a concentration of 0.9-1.1 mol / L, and adding an amount such that the molar ratio of the added carbonate ion to the lithium element in the wastewater is (0.6-0.65):1. And obtaining a solid from the bottom of the No. 2 sedimentation tank.

[0044] The present invention will be described in detail below through examples.

[0045] In the following examples, the total organic matter content (TOC) was tested according to the method specified in GB3838-2002 "Surface Water Environmental Quality Standard".

[0046] In the following examples, the total dissolved solid and lithium rubber concentrations were determined by filtering and drying weighing method. The specific test method is: take a certain volume (V, in L) of water sample and filter it through quantitative filter paper, collect the filtrate and the solids intercepted by the filter paper respectively; dry the solids intercepted by the filter paper at 105-110°C to constant weight, record its mass m1 (in mg), and then place it in a resistance furnace at a temperature of 400-500°C to burn to constant weight, record its mass m2 (in mg); place the filtrate in an evaporating dish that has been dried to constant weight at 105-110°C. Place the evaporating dish in a boiling water bath to evaporate to dryness, and then dry the evaporating dish at 105-110°C to constant weight, and record its mass m3 (in mg).

[0047] The lithium rubber concentration c is calculated using the following formula R :

[0048]

[0049] Calculate the total dissolved solids TDS using the following formula:

[0050]

[0051] The electrodialysis adopts the BTE high-efficiency concentrated electrodialysis system manufactured by Beijing Tingrun Membrane Technology Development Co., Ltd.

[0052] In the following embodiments, the lithium, calcium, magnesium, iron and other ion concentrations in water were determined by ion chromatography, and the specific test method was: an ion chromatograph was equipped with a cation chromatographic column, and an aqueous solution containing 3.0mmol / L phthalic acid was used as an eluent, and the eluent flow rate was 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 was prepared, as well as calcium chloride, magnesium chloride, and ferric chloride solutions of the same concentration, respectively injected into the ion chromatograph to measure the peak area of ​​lithium, calcium, magnesium, and iron ions, and then with the cation concentration as the horizontal coordinate and the peak area as the vertical coordinate, a standard curve was obtained by linear fitting. The water sample to be measured was injected into the ion chromatograph after being filtered through a 0.45μm microporous membrane, and the peak area of ​​lithium, calcium, magnesium, and iron ions was respectively measured, and the corresponding standard curve equation was 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.

[0053] 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:

[0054]

[0055] 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 lithium-containing wastewater, c Li is the concentration of lithium ions in the original lithium-containing wastewater.

[0056] 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:

[0057]

[0058] 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.

[0059] In the following examples, the lithium-containing wastewater 1 to be treated is lithium rubber synthesis wastewater, and the wastewater 2 is lithium battery anode material production wastewater. The water quality is shown in Table 1.

[0060] Table 1

[0061]

[0062] Example 1

[0063] (1) After 10 tons of wastewater 1 was filtered through a PP synthetic fiber filter with a filtration accuracy of 1 μm to remove suspended solids, it was treated with a BTE high-efficiency concentration electrodialysis system to obtain fresh water and concentrated wastewater with high ion concentration. The electrodialysis conditions were as follows: the cation exchange membrane (purchased from Beijing Tingrun Membrane Technology Development Co., Ltd., model TRJCM) and the anion exchange membrane (purchased from Beijing Tingrun Membrane Technology Development Co., Ltd., model TRJAM) were both homogeneous membranes with an effective membrane area of ​​137 m 2 , current density is 180A / m 2 The water quality of the concentrated wastewater after electrodialysis is shown in Table 2.

[0064] (2) The concentrated wastewater obtained in step (1) is injected into sedimentation tank No. 1, and a sodium hydroxide solution having a sodium hydroxide concentration of 1 mol / L is added until the pH value is 10-10.5, and the solution is allowed to stand for precipitation, and the precipitate is separated.

[0065] 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 6-8. The amount of hydrochloric acid and sodium hydroxide is shown in Table 3.

[0066] (3) injecting the water in the buffer water tank of step (2) into sedimentation tank No. 2, adding a sodium carbonate solution with a concentration of 1 mol / L (as a precipitant to precipitate the lithium element), and the amount added is such that the molar ratio of the added carbonate ion to the lithium element in the 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. The amount of precipitant added, the recovery rate of lithium and the purity of lithium salt (lithium carbonate) are shown in Table 3.

[0068] Example 2

[0069] The process is carried out in accordance with the method of Example 1, except that step (2) is omitted.

[0070] Example 3

[0071] The treatment is carried out in accordance with the method of Example 1, except that in step (3), the amount of sodium carbonate added is such that the molar ratio of the added carbonate ion to the lithium element in the wastewater is 1:1.

[0072] Example 4

[0073] The treatment was carried out according to the method of Example 1, except that wastewater 2 was used, and in step (1), the filter cotton filtration was replaced by flocculation precipitation, filter cotton filtration and ultrafiltration in sequence. The flocculant used for flocculation precipitation was polyaluminium chloride (purchased from Aladdin, in accordance with the provisions of GB / T 22627-2008), the dosage was 600 mg / L lithium-containing wastewater, the stirring time was 8 min, and the wastewater was allowed to stand for 40 min. The filter cotton filtration used PP filter cotton with a filtration accuracy of 1 μm. The ultrafiltration used a hollow fiber ultrafiltration membrane with a molecular weight cutoff of 50,000 (purchased from Koch, model HFM).

[0074] Example 5

[0075] The method of Example 4 was followed, except that step (2) was omitted.

[0076] Example 6

[0077] The treatment is carried out in accordance with the method of Example 4, except that in step (3), the amount of sodium carbonate added is such that the molar ratio of the added carbonate ion to the lithium element in the wastewater is 1:1.

[0078] Example 7

[0079] The treatment is carried out according to the method of Example 1, except that in step (3), the precipitant added is a disodium hydrogen phosphate solution with a disodium hydrogen phosphate concentration of 1 mol / L, and the amount added is such that the molar ratio of the added phosphate to the lithium element in the wastewater is 0.4:1.

[0080] Example 8

[0081] The method of Example 1 was used for treatment, except that in step (1), the effective membrane area was 91 m 2 .

[0082] Example 9

[0083] The method of Example 1 was used for treatment, except that in step (1), the effective membrane area was 183 m 2 .

[0084] Example 10

[0085] The method of Example 1 was used, except that in step (1), the current density was 150 A / m 2 .

[0086] Embodiment 11

[0087] The method of Example 1 was used, except that in step (1), the current density was 210 A / m 2 .

[0088] Comparative Example 1

[0089] The treatment is carried out in accordance with the method of Example 1, except that the electrodialysis step is omitted and the wastewater after being filtered by the filter cotton is directly subjected to step (2).

[0090] Comparative Example 2

[0091] The treatment is carried out in accordance with the method of Example 4, except that the electrodialysis step is omitted and the wastewater after being filtered by the filter cotton is directly subjected to step (2).

[0092] Comparative Example 3

[0093] The treatment was carried out in accordance with the method of Example 1, except that a high-pressure reverse osmosis with an operating pressure of 10 MPa was used to concentrate the wastewater after filtering with the filter cotton to the water quality shown in Table 2.

[0094] Table 2 Water quality of concentrated wastewater after electrodialysis in various embodiments and comparative examples

[0095]

[0096]

[0097] Table 3 Amounts of alkali, acid and lithium element precipitant materials used in each embodiment and comparative example and lithium recovery index

[0098] Example No. Amount of alkali (mL) Acid dosage (mL) Precipitant dosage (mL) Lithium recovery rate (%) Lithium salt purity (%) Example 1 12.19 0.078 0.389 90.5 95.6 Example 2 — — 0.389 88.8 87.4 Example 3 12.19 0.078 0.648 92.4 94.7 Example 4 31.79 0.311 0.385 91.3 96.2 Example 5 — — 0.385 89.5 91.9 Example 6 31.79 0.311 0.642 93.0 95.3 Example 7 12.19 0.078 0.259 89.9 95.1 Example 8 11.36 0.078 0.346 88.5 95.3 Example 9 12.23 0.078 0.391 90.8 95.7 Example 10 11.59 0.078 0.358 88.9 95.3 Embodiment 11 12.35 0.078 0.397 91.1 95.8 Comparative Example 1 1012 1000 0.389 68.5 94.2 Comparative Example 2 1031 1000 0.385 72.6 94.5 Comparative Example 3 4.49 0.029 0.389 83.5 78.5

[0099] From the above results, it can be seen that the embodiment of the method of the present invention can fully recover the lithium salt in the lithium-containing wastewater, with a high recovery rate, the recovered lithium carbonate has a high purity, and the amount of chemicals used is small. For the treatment of wastewater with a lower salt concentration that is difficult to treat in conventional methods and using lithium-based catalysts to synthesize rubber, the scheme of the present invention can achieve full recovery of lithium ions at a lower cost. In addition, it can be seen from Examples 1, 8-11 that under the more preferred conditions of the present invention, it can be ensured that a better concentration effect can be obtained with lower energy consumption.

[0100] 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 treating lithium-containing wastewater, characterized in that: The method includes: (1) Concentrating the lithium-containing wastewater until the lithium ion concentration of the concentrated wastewater is ≥4000 mg / L; (2) Optionally, under alkaline conditions, forming hydroxide precipitation in the concentrated wastewater to remove at least a portion of the metal elements other than lithium; (3) Precipitating the lithium element in the concentrated wastewater treated in step (1) or the concentrated wastewater treated in step (2) to separate the lithium element.

2. The method according to claim 1, wherein: In step (1), before concentration, the method further comprises: removing impurities from the lithium-containing wastewater to remove at least one of suspended solids, colloids and small organic molecules therein; Preferably, the impurity removal method is selected from at least one of grid filtration, flocculation sedimentation, flotation, sand filtration, activated carbon filtration, filter cotton filtration, microfiltration and ultrafiltration.

3. The method according to claim 1 or 2, wherein: In step (1), the concentration makes the water quality of the concentrated wastewater: Conductivity ≥ 100 mS / cm, preferably 150-200 mS / cm; Total organic matter ≤ 1000 mg / L, preferably 0-200 mg / L; Lithium ion concentration ≥ 4500 mg / L, preferably 5000-8000 mg / L; pH ≥ 6, preferably 6.5-8.

4. The method according to claim 1 or 3, wherein: The concentration method is selected from electrodialysis and / or high pressure reverse osmosis, more preferably electrodialysis; Preferably, the electrodialysis conditions 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 , more preferably 10-15m 2 ; Current density is 150-250A / m 2 , more preferably 175-185A / m 2 .

5. The method according to claim 1, wherein: In step (2), the alkaline condition is pH ≥ 10, preferably pH 10-11; Preferably, the alkaline condition is provided by an alkali metal hydroxide, more preferably by sodium hydroxide and / or potassium hydroxide; And / or, the metal element other than lithium is selected from at least one of magnesium, iron, aluminum and copper.

6. The method according to claim 1 or 5, wherein: In step (2), the operation of removing at least part of the metal elements other than lithium is carried out by at least one of static precipitation, centrifugal separation and filtration.

7. The method according to claim 1 or 2, wherein: Before performing step (3), the method further comprises: adjusting the concentrated wastewater to a pH of 6-8; Preferably, a strong inorganic acid is used to adjust the pH of the concentrated wastewater, and the strong inorganic acid is preferably at least one of hydrochloric acid, sulfuric acid and nitric acid.

8. The method according to claim 1 or 2, wherein: In step (3), the lithium element is precipitated by adding anions corresponding to a sparingly soluble lithium salt to the concentrated wastewater; Preferably, the anion is selected from at least one of carbonate, phosphate and fluoride, more preferably carbonate.

9. The method according to claim 8, wherein: The molar ratio of the amount of the anion added to the lithium content in the concentrated wastewater is (0.3-3):1; And / or, the anion is carbonate, and the molar ratio of the added amount of carbonate to the content of lithium in the concentrated wastewater is (0.6-1):

1.

10. The method according to claim 1 or 2, wherein: The water quality of the lithium-containing wastewater is: total organic matter is 5-1000 mg / L, total dissolved solid is 10-1000 mg / L, lithium ion concentration is 0.01-10 mg / L, pH value is 3.5-8.5, and conductivity is 0.0001-0.8 mS / cm; Preferably, the water quality of the lithium-containing wastewater is: total organic matter is 10-300 mg / L, total dissolved solid is 20-1000 mg / L, lithium ion concentration is 0.2-5 mg / L, pH value is 4-8, and conductivity is 0.001-0.4 mS / cm; Preferably, the lithium-containing wastewater is lithium rubber synthesis wastewater and / or lithium battery anode material production wastewater, more preferably lithium rubber synthesis wastewater, and the content of lithium rubber in the lithium rubber synthesis wastewater is preferably 10-200 mg / L.

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