A method for preparing lithium carbonate from lithium-containing waste residues and its application

Abstract

The present invention relates to the technical field of resource recovery of lithium-containing waste. Specifically, it relates to a method for preparing lithium carbonate from lithium-containing waste residue and its application. The method for preparing lithium carbonate from lithium-containing waste residue includes the following steps: After mixing the lithium-containing waste residue, acid and oxidant, leaching treatment is carried out, and solid-liquid separation is carried out to obtain a lithium-containing leaching solution, where the leaching rate of lithium ions in the leaching solution is greater than 95%, and the leaching rate of iron ions is less than 0.05%; After the leaching solution is mixed with a impurity removal agent, calcium ions, magnesium ions and HPO4 2‑ impurities are removed, and solid-liquid separation is carried out to obtain a lithium-containing impurity removal solution; The impurity removal solution is passed through an ion exchange resin to remove residual calcium ions and magnesium ion impurities to obtain a lithium-rich solution; After the lithium-rich solution and carbonate undergo a lithium precipitation reaction, solid-liquid separation is carried out to obtain lithium carbonate. This method has the advantages of simple process flow, low production cost, high lithium recovery rate, high-efficiency recycling of lithium-containing waste residue, high resource utilization rate, high added value, and little environmental pollution.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-containing waste resource recovery, and in particular, to a method for preparing lithium carbonate from lithium-containing waste residue and its application. Background Art

[0002] In recent years, the new energy industry has developed rapidly, and lithium iron phosphate batteries have developed most rapidly due to their outstanding safety. During the production process of lithium iron phosphate, a large amount of lithium- and phosphorus-containing sewage is generated. This type of sewage has characteristics such as high COD and high phosphorus. Usually, iron-based and calcium-based flocculants are added for flocculation precipitation, and the treated sewage meets the discharge standards. The lithium-containing waste residue generated after sewage treatment, as solid waste, not only increases the cost of solid waste disposal but also causes the loss of lithium and phosphorus resources.

[0003] Generally, the recovery of lithium iron phosphate materials follows two routes: pyrometallurgy and hydrometallurgy. For example, Patent CN112111651 discloses a pyrometallurgical recovery process for waste lithium-ion battery powder. The powder, carbon-containing material, and hydrogen ion salt are mixed and roasted. The roasting is carried out in two stages; the roasted product is dissolved in an alkaline solution with a pH of 10-11, and CO2 is introduced until the pH is 8-9, followed by filtration and washing to obtain a filtrate and a filter residue; after the filtrate is heated and evaporated, lithium carbonate is obtained. Another example is Patent CN108899601, which discloses a method for recovering lithium and iron from lithium iron phosphate. The scrapped lithium iron phosphate slag is dissolved with sulfuric acid and ferric sulfate to leach iron, lithium, and phosphorus. Then, an oxidant is added, and iron reacts with phosphate to form ferric phosphate precipitation and a small amount of iron hydroxide. Lithium is converted into a water-soluble lithium sulfate solution, and the lithium sulfate solution is obtained by filtration. Sodium carbonate is added to the lithium sulfate solution to prepare lithium carbonate products.

[0004] However, the lithium-containing waste residue formed after flocculation precipitation of the lithium- and phosphorus-containing sewage generated during the above-mentioned lithium iron phosphate production process contains a large amount of calcium, magnesium, phosphorus, and iron impurities, and the lithium content is relatively low. Using pyrometallurgy to extract lithium has extremely high costs and excessive roasting waste gas, making it difficult to meet environmental protection requirements; using hydrometallurgy requires a large amount of concentrated acid, and there are many impurities, and the leachate composition is complex; using chemical methods for impurity removal has a large consumption of reagents, cumbersome steps, and a low lithium recovery rate.

[0005] Therefore, it is of great significance to provide a green and environmentally friendly preparation process for battery-grade lithium carbonate to realize the resource utilization of lithium-containing waste residue.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The first object of the present invention is to provide a method for preparing lithium carbonate from lithium-containing waste residue, aiming at solving the problems of poor recovery effect and high cost of existing lithium iron phosphate materials. This method has the advantages of simple process flow, low production cost, high lithium recovery rate, high efficient recycling of lithium-containing waste residue, high resource utilization rate, high added value, and little environmental pollution.

[0008] The second object of the present invention is to provide an application of the lithium carbonate prepared by the method for preparing lithium carbonate from lithium-containing waste residue in a lithium-ion battery.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] The present invention provides a method for preparing lithium carbonate from lithium-containing waste residue, which comprises the following steps:

[0011] The lithium-containing waste residue, an acid and an oxidant are mixed and then subjected to leaching treatment, and solid-liquid separation is carried out to obtain a lithium-containing leaching solution, wherein the leaching rate of lithium ions in the leaching solution is greater than 95%, and the leaching rate of iron ions is less than 0.05%;

[0012] The leaching solution is mixed with a impurity remover to remove calcium ions, magnesium ions and HPO4 2- impurities, and solid-liquid separation is carried out to obtain a lithium-containing impurity-removed solution;

[0013] The impurity-removed solution is passed through an ion exchange resin to remove residual calcium ions and magnesium ion impurities, and a lithium-rich solution is obtained;

[0014] The lithium-rich solution and a carbonate are subjected to a lithium precipitation reaction, and solid-liquid separation is carried out to obtain lithium carbonate.

[0015] The present invention solves the problems of environmental pollution and resource waste caused by waste residue generated in the production process of batteries. This method has the advantages of simple process flow, high lithium recovery rate, high resource utilization rate, high added value, low production cost, and little environmental pollution.

[0016] The present invention also provides an application of the lithium carbonate prepared by the above method for preparing lithium carbonate from lithium-containing waste residue in a lithium-ion battery.

[0017] The battery-grade lithium carbonate prepared by the above method for preparing lithium carbonate from lithium-containing waste residue can be used as a raw material for preparing the positive electrode material of a lithium-ion battery, which can not only avoid resource waste, but also reduce the production cost of the lithium-ion battery.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) The method for preparing lithium carbonate from lithium-containing waste residue provided by the present invention realizes the high-efficient recycling of lithium-containing waste residue, has low production cost, high lithium recovery rate, simple process, and little environmental pollution.

[0020] (2) The method for preparing lithium carbonate from lithium-containing waste residue provided by the present invention can obtain battery-grade lithium carbonate with high added value.

[0021] (3) The method for preparing lithium carbonate from lithium-containing waste residue provided by the present invention uses a small amount of acid, and iron ions are not leached during the leaching process, which saves a key step for subsequent impurity removal and reduces the consumption of reagents.

[0022] (4) The method for preparing lithium carbonate from lithium-containing waste residue provided by the present invention efficiently removes impurities such as calcium, magnesium, and phosphorus by using a combination of chemical methods and resin methods for impurity removal.

[0023] (5) The battery-grade lithium carbonate prepared by the above method for preparing lithium carbonate from lithium-containing waste residue as a raw material for preparing lithium-ion batteries can significantly reduce the production cost of lithium-ion batteries. Description of the Drawings

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is the process flow diagram of the method for preparing lithium carbonate from lithium-containing waste residue provided in Example 1 of the present invention. Detailed Embodiments

[0026] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, not all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0027] In a first aspect, to address the problem of waste of lithium resources caused by lithium, phosphorus, and iron waste residues generated after the treatment of wastewater from lithium iron phosphate production, an embodiment of the present invention provides a method for preparing lithium carbonate from lithium-containing waste residues, that is, a method for recovering lithium carbonate from lithium-containing waste residues. The lithium-containing waste residues include lithium-containing waste residues obtained after flocculation and precipitation treatment of sewage generated during the production of lithium iron phosphate. Its main components include lithium iron phosphate, as well as impurity elements such as iron, calcium, and magnesium. The content of lithium element in the lithium-containing waste residues is 2500 - 3500 mg / kg. The method for preparing lithium carbonate from lithium-containing waste residues specifically includes the following steps:

[0028] Step (1): Mix the lithium-containing waste residues, an acid, and an oxidant and perform leaching treatment to leach out the lithium element. The main reactions occurring during leaching are as follows:

[0029] 2LiFePO4 + H2SO4 + H2O2 = 2FePO4↓ + 2H2O + Li2SO4.

[0030] In the leaching process of the embodiment of the present invention, iron ions are not leached out. After the leaching is completed, solid-liquid separation is performed to obtain the leaching solution (i.e., the filtrate) and the leaching waste residue (i.e., the filter residue) respectively. The leaching solution containing lithium and not containing iron is reserved for subsequent impurity removal, which saves a key step for subsequent impurity removal and reduces the consumption of reagents. The leaching waste residue can be used for extracting and preparing iron phosphate.

[0031] Step (2): Mix the leaching solution obtained in step (1) with an impurity remover to remove calcium ions, magnesium ions, and HPO4 2- impurities, and then perform solid-liquid separation to achieve efficient separation of impurities such as calcium, magnesium, and phosphorus from the solution, obtaining the impurity-removed solution (i.e., the filtrate) and the impurity-removed waste residue (i.e., the filter residue) respectively. The impurity-removed solution is used for subsequent reactions. The content of P2O5 in the impurity-removed waste residue > 12 wt.%, which can be used for subsequent production of phosphoric acid or as a chemical fertilizer.

[0032] In the above step (2), calcium and magnesium ions are in excess relative to phosphate, and phosphate removal is relatively complete; and due to the excess of calcium and magnesium ions, step (3) is set to remove calcium and magnesium impurities by the resin method.

[0033] Step (3): After the above impurity-removed solution is passed through an ion exchange resin to remove residual calcium and magnesium ion impurities, a lithium-rich solution mainly composed of lithium ions is obtained.

[0034] Step (4): Mix the above lithium-rich solution with a carbonate and perform a lithium precipitation reaction, that is, a precipitation reaction to generate lithium carbonate. After the lithium precipitation reaction is completed, solid-liquid separation is performed to obtain lithium carbonate.

[0035] In a preferred embodiment, the lithium carbonate includes battery-grade lithium carbonate, which can be used for the preparation of lithium iron phosphate, the cathode material of lithium-ion batteries, and has a high added value.

[0036] The present invention first selectively leaches lithium from the waste residue by acid leaching, and then removes calcium ions, magnesium ions and HPO4 from the leaching solution. 2- Impurities, and then the impurity removal solution is subjected to impurity removal by resin method to further remove calcium, magnesium and phosphorus impurities to obtain a refined lithium-rich solution, and finally lithium carbonate is obtained by lithium precipitation.

[0037] The present invention solves the problems of environmental pollution and resource waste caused by the waste residue generated in the production process of the battery. The process flow of this method is simple, the production cost is low, and the lithium recovery rate is high; the efficient recovery and utilization of lithium-phosphorus-iron waste residue is realized, the resource utilization rate is high, the added value is high, the environmental pollution is small, and it is environmentally friendly.

[0038] In a preferred embodiment, in the above step (1), the acid includes concentrated sulfuric acid. The calcium content of the lithium-containing waste residue is relatively high. Because calcium sulfate is slightly soluble, a large amount of sulfate ions introduced by using sulfuric acid leaching will inhibit the dissolution of calcium ions, thereby reducing the subsequent impurity removal difficulty.

[0039] When concentrated sulfuric acid is used, during the leaching treatment process, part of the calcium impurities in the lithium-containing waste residue dissolve and react with sulfate ions to form a precipitate, that is, Ca 2+ +SO4 2- =CaSO4↓.

[0040] In a preferred embodiment, the addition amount of the acid is such that the pH of the mixed system of the lithium-containing waste residue, the acid and the oxidant is 3-4, including but not limited to the point values of any one of 3.2, 3.4, 3.5, 3.7, 3.9 or the range values between any two of them.

[0041] By adjusting the pH of the mixture during the leaching treatment process to 3-4 in the embodiment of the present invention, the leaching of iron ions can be inhibited (to avoid the harm of iron ions to the subsequent RO membrane). Under this leaching condition, the leaching rate of lithium ions can be maintained above 95%, and the leaching rate of iron ions is below 0.05%.

[0042] In a preferred embodiment, the volume ratio of the acid to the mass of the lithium-containing waste residue is 1L: 6-9 kg, such as 1L: 7 kg or 1L: 8 kg.

[0043] The main role of the acid is to regulate the pH, avoid the dissolution of iron, and provide sulfate ions to inhibit the dissolution of calcium.

[0044] The method provided by the embodiment of the present invention uses a small amount of acid, and iron ions are not leached in the leaching link, which saves a key step for the subsequent impurity removal reaction and reduces the consumption of reagents.

[0045] The structure of lithium iron phosphate is stable, and lithium is in the center of the octahedral lattice of lithium iron phosphate. The role of the oxidant is to oxidize lithium iron phosphate, destroy the lattice of lithium iron phosphate, and release the lithium in the lattice.

[0046] In a preferred embodiment, in the above step (1), the oxidant includes hydrogen peroxide solution.

[0047] Using hydrogen peroxide solution as the oxidant will not introduce other impurity ions; the lithium in the waste residue mainly exists in the form of lithium iron phosphate, and its chemical properties are particularly stable. Hydrogen peroxide can react with the iron ions in the waste residue to undergo the Fenton reaction to improve the oxidizing property, destroy the lattice of lithium iron phosphate, and thus improve the recovery rate of lithium.

[0048] In a preferred embodiment, the mass fraction of hydrogen peroxide in the hydrogen peroxide solution (referring to the aqueous solution of hydrogen peroxide, i.e., hydrogen peroxide) is 20% - 30%, such as 22%, 24%, 25%, 27% or 29%.

[0049] In a preferred embodiment, during the mixing process of the lithium-containing waste residue, acid and oxidant, water is also added, and the solid-liquid ratio (referring to the ratio of the mass of the solid phase to the volume of the liquid phase in the mixed material) is controlled to be 1:6 - 15 g / ml.

[0050] Adding water can increase the contact area between the lithium-containing waste residue, acid and oxidant, accelerate the reaction rate, and the lithium ions leach into the water, and a lithium-containing leaching solution can be obtained through filtration.

[0051] Using the solid-liquid ratio within the above range can save water consumption and energy consumption for heating the water supply. If the amount of water is too small, the stirring and reaction will be uneven; if the amount of water is too large, it will increase the water consumption and heating energy consumption.

[0052] In a preferred embodiment, the volume of the oxidant is 1% - 5% of the volume of the water added above, such as 2%, 3% or 4%.

[0053] In a preferred embodiment, in the above step (1), the temperature of the leaching treatment (i.e., the temperature of the mixed material during the leaching treatment process) is 40 - 60 °C, including but not limited to any point value of 45 °C, 50 °C, 55 °C or the range value between any two of them.

[0054] In a preferred embodiment, the time of the leaching treatment is 3 - 8 h, including but not limited to any point value of 4 h, 5 h, 6 h, 7 h or the range value between any two of them.

[0055] Adopting the above leaching temperature is beneficial to improving the leaching rate.

[0056] In a preferred embodiment, during the leaching treatment process, in order to improve the leaching efficiency, the mixed material is stirred at a rotation speed of 400 - 1000 rpm, such as 500 rpm, 600 rpm, 700 rpm, 800 rpm or 900 rpm.

[0057] In a preferred embodiment, in the above step (2), the impurity remover includes an alkali and / or an ammonia source.

[0058] In a preferred embodiment, the ammonia source includes at least one of ammonia gas, aqueous ammonia solution, ammonium carbonate solution, and ammonium bicarbonate solution.

[0059] Introducing ammonia gas and / or ammonium ions, which react with phosphorus impurities and magnesium impurities to form magnesium ammonium phosphate precipitate, achieving the purpose of removing phosphorus and magnesium impurities. Introducing carbonate ions helps to remove calcium. Since the solubility products of lithium carbonate and calcium carbonate sp differ greatly, lithium will not be lost.

[0060] In a preferred embodiment, the alkali includes at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide. More preferably, it is sodium hydroxide, which has low cost.

[0061] In a preferred embodiment, in step (2), to improve the impurity removal efficiency, the impurity remover uses an alkali and an ammonia source. The alkali is mainly used to adjust the pH so that calcium ions and magnesium ions respectively react with HPO4 2- and / or OH - to form precipitates. The ammonia source is mainly used to provide NH4 + to remove magnesium ions. The main reactions occurring during the process of removing calcium ions, magnesium ions, and HPO4 2- impurities include:

[0062] Ca 2+ +HPO4 2- =CaHPO4↓;

[0063] 3Ca 2+ +2OH - +2HPO4 2- =Ca3(PO4)2↓+2H2O;

[0064]

[0065] Ca 2+ +CO3 2- =CaCO3↓;

[0066] Mg 2+ +NH3·H2O+HPO4 2- =H2O+Mg(NH4)PO4↓;

[0067] Mg 2+ +HPO4 2- =MgHPO4↓;

[0068] Mg 2+ +2OH - =Mg(OH)2↓;

[0069] 3Mg 2+ + 2OH - + 2HPO4 2- = Mg3(PO4)2↓ + 2H2O。

[0070] In a preferred embodiment, the molar ratio of the N element (or ammonium ion) in the ammonia source to the magnesium element in the leaching solution is 0.7 - 1.5:1, such as 0.8:1, 0.9:1, 1:1, 1.2:1 or 1.4:1.

[0071] In a preferred embodiment, in the above step (2), when removing calcium ions, magnesium ions and HPO4 2- the pH of the impurity removal system is 8.5 - 9.5, including but not limited to the point values of any one of 8.7, 8.8, 9.0, 9.2, 9.4 or the range values between any two of them.

[0072] In step (2), the mixed system of the leaching solution and the impurity remover removes calcium ions, magnesium ions and HPO4 2- the pH of the impurities is 8.5 - 9.5, which can avoid the precipitation of lithium phosphate and reduce the lithium recovery rate.

[0073] In a preferred embodiment, when removing calcium ions, magnesium ions and HPO4 2- the reaction time of the impurities is 1 - 5 h, including but not limited to the point values of any one of 2 h, 3 h, 4 h or the range values between any two of them.

[0074] In a preferred embodiment, in the above step (3), in order to increase the lithium ion concentration, before the impurity removal solution is passed through the ion exchange resin to remove the residual calcium and magnesium ion impurities, it further includes a step of first concentrating the impurity removal solution.

[0075] In a preferred embodiment, in the above step (4), in order to further increase the lithium ion concentration to make the lithium precipitation reaction complete, before the lithium precipitation reaction, it further includes a step of second concentrating the lithium-rich solution.

[0076] In a preferred embodiment, the first concentration includes RO concentration (i.e., reverse osmosis concentration). The power consumption of RO concentration is about 1 / 20 of the power consumption of evaporation concentration. Therefore, using RO concentration for the first concentration can reduce the concentration cost.

[0077] In a preferred embodiment, the RO membrane used for RO concentration is a high-pressure seawater desalination membrane, and the operating pressure of RO concentration is 4 - 8 Mpa, including but not limited to the point values of any one of 5 Mpa, 6 Mpa, 7 Mpa or the range values between any two of them.

[0078] In a preferred embodiment, before RO concentration, the pH of the impurity-removing solution is adjusted to 5-6, including but not limited to the point values of any one of 5.3, 5.5, 5.8 or the range values between any two of them.

[0079] In a preferred embodiment, to enable the RO equipment to operate better and avoid calcium ion scaling from damaging the equipment, the RO concentration is carried out until the TDS (total dissolved solids) of the impurity-removing solution is 50-60 g / L, including but not limited to the point values of any one of 53 g / L, 55 g / L, 58 g / L or the range values between any two of them.

[0080] In a preferred embodiment, the second concentration includes evaporation concentration. Evaporation concentration has a high concentration efficiency, which is beneficial to obtaining a high-concentration lithium-rich solution and thus improving the lithium precipitation efficiency.

[0081] In a preferred embodiment, the evaporation concentration is carried out until the lithium element content in the lithium-rich solution is 15-30 g / L, including but not limited to the point values of any one of 20 g / L, 23 g / L, 25 g / L, 28 g / L or the range values between any two of them.

[0082] In a preferred embodiment, in the above step (3), in order to further remove residual impurity elements such as calcium, magnesium, and iron in the impurity-removing solution and improve the impurity-removing efficiency, the ion exchange resin used is a chelating ion exchange resin.

[0083] In a preferred embodiment, in the process of using the ion exchange resin to remove residual calcium ion and magnesium ion impurities, the volume of the influent water is 60-200 times the volume of the ion exchange resin, including but not limited to the point values of any one of 80 times, 100 times, 150 times, 180 times or the range values between any two of them; the influent water flow rate is 5-15 BV / h, including but not limited to the point values of any one of 8 BV / h, 10 BV / h, 13 BV / h or the range values between any two of them; the pH of the influent water is controlled at 7.0-8.5, including but not limited to the point values of any one of 7.3, 7.5, 7.8, 8.0, 8.3 or the range values between any two of them.

[0084] In a preferred embodiment, in the above step (4), the temperature of the lithium precipitation reaction (i.e., the temperature of the mixed materials during the lithium precipitation reaction) is 80-100 °C, including but not limited to the point values of any one of 85 °C, 90 °C, 95 °C or the range values between any two of them.

[0085] In a preferred embodiment, the time of the lithium precipitation reaction is 1-5 h, including but not limited to the point values of any one of 2 h, 3 h, 4 h or the range values between any two of them.

[0086] In a preferred embodiment, after the solid-liquid separation in the lithium precipitation reaction, it further includes the steps of washing and drying the obtained lithium carbonate in sequence. The lithium carbonate after washing and drying is battery-grade lithium carbonate. Among them, the washing is carried out with water at a temperature of 80-90°C, and the volume of water is 2-5 times the volume of lithium carbonate.

[0087] In a preferred embodiment, the carbonate includes at least one of sodium carbonate, potassium carbonate, and ammonium carbonate.

[0088] In a preferred embodiment, the pure water obtained after RO concentration and / or evaporation concentration can be recycled to step (1) for leaching treatment.

[0089] In the present invention, by jointly using chemical impurity removal and resin impurity removal, it is detected that this method can reduce the content of impurity elements such as calcium, magnesium, and phosphorus to below 10 ppm. The refined lithium-rich solution obtained during this period is subjected to lithium precipitation, and the battery-grade lithium carbonate standard can be achieved.

[0090] In the second aspect, the present invention provides the application of the lithium carbonate prepared by the above method for preparing lithium carbonate from lithium-containing waste residue in a lithium-ion battery.

[0091] The battery-grade lithium carbonate prepared by the above method for preparing lithium carbonate from lithium-containing waste residue can be used as a raw material for preparing the positive electrode material of a lithium-ion battery. Using the waste lithium-containing waste residue to prepare battery-grade lithium carbonate can not only avoid waste of lithium resources but also reduce the production cost of lithium-ion batteries.

[0092] Hereinafter, the embodiments of the present invention will be described in detail in conjunction with the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0093] In each of the following examples of the present invention, the content of lithium element in the lithium-containing waste residue used is about 3000 mg / kg (that is, about 3000 mg of lithium element per kilogram of lithium-containing waste residue).

[0094] Example 1

[0095] The method for preparing lithium carbonate from lithium-containing waste residue provided in this example includes the following steps:

[0096] Step (1): Add water to the lithium-containing waste residue until the solid-liquid ratio is 1:10 g / ml. Then add concentrated sulfuric acid with a mass fraction of 98% and hydrogen peroxide solution with a mass fraction of 27%. The volume ratio of concentrated sulfuric acid to the mass of the lithium-containing waste residue is 1 L:8.5 kg, and the volume of the hydrogen peroxide solution is 3% of the volume of the added water. Leaching treatment is carried out under the condition of pH 3.1. The reaction temperature of the leaching treatment is controlled at 60 °C, the stirring speed is 500 rpm. After reacting for 4 h, solid-liquid separation is carried out to obtain the leaching solution. The leaching rate of lithium ions is 96.7%, and the leaching rate of iron ions is 0.03%.

[0097] Step (2): Add ammonia water solution with a mass fraction of 22% to the leaching solution obtained in step (1) so that the molar ratio of ammonium ions in the ammonia water solution to magnesium ions in the leaching solution is 0.8:1, and add 2 mol / L sodium hydroxide solution to control its pH value at 8.9 to remove calcium ions, magnesium ions and HPO4 2- impurities. After reacting for 1 h, solid-liquid separation is carried out to obtain the impurity-removing solution.

[0098] Step (3): After adjusting the pH of the impurity-removing solution obtained in step (2) to 5.5, carry out the first concentration through an RO membrane (high-pressure seawater desalination membrane). The pressure of RO concentration is 6 Mpa to obtain the concentrated solution, and the TDS of this concentrated solution is 55.4 g / L.

[0099] Step (4): After adjusting the concentrated solution obtained in step (3) to pH 7.5, pass it through an ion exchange resin tower (the resin used is chelating ion exchange resin, specifically Duolite resin CH-90) to remove residual calcium ions and magnesium ion impurities. The volume of the influent water is 60 times the volume of the resin, and the influent water flow rate is 10 BV / h to obtain the refined lithium-rich mother liquor (i.e., lithium-rich solution). After testing, the magnesium element content in the refined lithium-rich mother liquor is 2.8 ppm, the calcium element content is 1.9 ppm, and the phosphorus element content < 3.7 ppm.

[0100] Step (5): After the refined lithium-rich mother liquor obtained in step (4) is concentrated by an evaporator (i.e., the second concentration), a refined lithium precipitation mother liquor is obtained, and the lithium element content in this refined lithium precipitation mother liquor is 16.5 g / L.

[0101] Step (6): Add sodium carbonate solution with a mass fraction of 30% to the refined lithium precipitation mother liquor obtained in step (5) so that the molar ratio of carbonate ions in the sodium carbonate solution to lithium ions in the refined lithium precipitation mother liquor is 1.1:2, carry out the lithium precipitation reaction. The reaction temperature is 90 °C, the stirring speed is 400 rpm. After reacting for 2 h, aging for 1.5 h, and then carrying out solid-liquid separation to obtain crude lithium carbonate; add 2 times the mass of 90 °C hot water to the crude lithium carbonate, carry out secondary water washing and then drying to obtain battery-grade lithium carbonate. The lithium recovery rate of this example is 83.7%.

[0102] The pure water obtained after the RO concentration in step (3) and the evaporation concentration in step (5) above are both recycled to step (1) of the next lithium carbonate preparation as the water source for leaching treatment. Moreover, the leaching waste residue obtained after the solid-liquid separation in step (1) above is recycled for extracting iron phosphate; the impurity removal waste residue obtained after the solid-liquid separation in step (2) above is used for producing phosphoric acid or as a chemical fertilizer.

[0103] The process flow diagram of the method for preparing lithium carbonate using lithium-containing waste residue provided in this embodiment is shown in Figure 1 shown.

[0104] Example 2

[0105] The method for preparing lithium carbonate using lithium-containing waste residue provided in this embodiment includes the following steps:

[0106] Step (1): Add water to the lithium-containing waste residue until the solid-liquid ratio is 1:8 g / ml, then add concentrated sulfuric acid with a mass fraction of 98% and hydrogen peroxide solution with a mass fraction of 25%. The volume ratio of the concentrated sulfuric acid to the mass of the lithium-containing waste residue is 1 L:8 kg, and the volume of the hydrogen peroxide solution is 4% of the volume of the added water. Leaching treatment is carried out under the condition of pH = 3.2. The reaction temperature of the leaching treatment is controlled at 60 °C, the stirring speed is 450 rpm, and after reacting for 4 h, solid-liquid separation is carried out to obtain a leaching solution. The leaching rate of lithium ions is 95.8%, and the leaching rate of iron ions is 0.04%.

[0107] Step (2): Add ammonia water solution with a mass fraction of 22% and ammonium bicarbonate solution with a mass fraction of 10% to the leaching solution obtained in step (1) so that the molar ratio of the total ammonium ions in the ammonia water solution and ammonium bicarbonate solution to the magnesium ions in the leaching solution is 1:1, and add 2 mol / L sodium hydroxide solution to control its pH value at 9.0 to remove calcium ions, magnesium ions and HPO4 2- impurities. After reacting for 1.5 h, solid-liquid separation is carried out to obtain an impurity removal solution;

[0108] Step (3): After adjusting the pH of the impurity removal solution obtained in step (2) to 6.0, carry out the first concentration through an RO membrane (high-pressure seawater desalination membrane). The pressure of the RO concentration is 5.8 Mpa to obtain a concentrated solution, and the TDS of this concentrated solution = 54 g / L;

[0109] Step (4): After adjusting the concentrated solution obtained in step (3) to a pH of 8.0, it passes through an ion exchange resin column (the resin used is a chelating ion exchange resin, specifically Duolite resin CH-90) to remove residual calcium and magnesium ion impurities. The volume of the influent water is 80 times the volume of the resin, and the influent flow rate is 12 BV / h, obtaining a refined lithium-rich mother liquor (i.e., lithium-rich solution). After detection, the magnesium element content in the refined lithium-rich mother liquor is 5.1 ppm, the calcium element content is 4.5 ppm, and the phosphorus element content is < 6.2 ppm;

[0110] Step (5): After the refined lithium-rich mother liquor obtained in step (4) is concentrated by an evaporator (i.e., the second concentration), a refined lithium precipitation mother liquor is obtained, and the lithium element content in this refined lithium precipitation mother liquor is 16.7 g / L;

[0111] Step (6): Add a sodium carbonate solution with a mass fraction of 20% to the refined lithium precipitation mother liquor obtained in step (5) so that the molar ratio of carbonate ions in the sodium carbonate solution to lithium ions in the refined lithium precipitation mother liquor is 1.1:2, and carry out a lithium precipitation reaction. The reaction temperature is 90 °C, the stirring speed is 450 rpm. After reacting for 2 h, aging for 1.5 h, and then performing solid-liquid separation to obtain crude lithium carbonate; Add hot water at 90 °C with a mass 3 times that of the crude lithium carbonate, carry out secondary water washing and then drying to obtain battery-grade lithium carbonate. The lithium recovery rate in this example is 81.8%.

[0112] Example 3

[0113] The method for preparing lithium carbonate from lithium-containing waste residue provided in this example includes the following steps:

[0114] Step (1): Add water to the lithium-containing waste residue until the solid-liquid ratio is 1:12 g / ml, and then add concentrated sulfuric acid with a mass fraction of 98% and hydrogen peroxide solution with a mass fraction of 27%. The volume ratio of concentrated sulfuric acid to the mass of the lithium-containing waste residue is 1 L:8.5 kg, and the volume of the hydrogen peroxide solution is 4% of the volume of the added water. Carry out leaching treatment under the condition of pH 3.4. The reaction temperature of the leaching treatment is controlled at 50 °C, the stirring speed is 500 rpm. After reacting for 4 h, perform solid-liquid separation to obtain a leaching solution. The leaching rate of lithium ions is 97.1%, and the leaching rate of iron ions is 0.03%;

[0115] Step (2): Add an ammonia water solution with a mass fraction of 22% and an ammonium carbonate solution with a mass fraction of 10% to the leaching solution obtained in step (1) so that the total ammonium ions in the ammonia water solution and the ammonium carbonate solution are in a molar ratio of 1:1 with the magnesium ions in the leaching solution, and add a 2 mol / L sodium hydroxide solution to control its pH value at 9.0 to remove calcium ions, magnesium ions and HPO4 2- impurities. After reacting for 1.5 h, perform solid-liquid separation to obtain a purified solution;

[0116] Step (3): After adjusting the pH of the impurity-removing solution obtained in step (2) to 5.5, perform the first concentration through an RO membrane (high-pressure seawater desalination membrane). The pressure for RO concentration is 5.6 Mpa to obtain a concentrated solution with a TDS of 51.5 g / L.

[0117] Step (4): After adjusting the concentrated solution obtained in step (3) to a pH of 8.5, pass it through an ion exchange resin column (the resin used is chelating ion exchange resin, specifically Duolite resin CH-93) to remove residual calcium and magnesium ion impurities. The volume of the influent is 80 times the volume of the resin, and the influent flow rate is 13 BV / h to obtain a refined lithium-rich mother liquor (i.e., lithium-rich solution). After detection, the magnesium element content in the refined lithium-rich mother liquor is 6.2 ppm, the calcium element content is 3.5 ppm, and the phosphorus element content is 4.1 ppm.

[0118] Step (5): After concentrating the refined lithium-rich mother liquor obtained in step (4) through an evaporator (i.e., the second concentration), obtain a refined lithium precipitation mother liquor with a lithium element content of 18.2 g / L.

[0119] Step (6): Add a sodium carbonate solution with a mass fraction of 20% to the refined lithium precipitation mother liquor obtained in step (5) so that the molar ratio of carbonate ions in the sodium carbonate solution to lithium ions in the refined lithium precipitation mother liquor is 1.05:2. Perform a lithium precipitation reaction at a reaction temperature of 90 °C, a stirring speed of 500 rpm. After reacting for 1.5 h, age for 2 h, and then perform solid-liquid separation to obtain crude lithium carbonate. Add hot water at 90 °C with a mass three times that of the crude lithium carbonate, perform secondary water washing and then drying to obtain battery-grade lithium carbonate. The lithium recovery rate in this example is 82.9%.

[0120] Example 4

[0121] The method for preparing lithium carbonate from lithium-containing waste residue provided in this example includes the following steps:

[0122] Step (1): Add water to the lithium-containing waste residue until the solid-liquid ratio is 1:15 g / ml, and then add concentrated sulfuric acid with a mass fraction of 98% and hydrogen peroxide solution with a mass fraction of 20%. The volume ratio of concentrated sulfuric acid to the mass of the lithium-containing waste residue is 1 L:7 kg, and the volume of the hydrogen peroxide solution is 5% of the volume of the added water. Perform leaching treatment under the condition of pH 3.6, control the reaction temperature of the leaching treatment at 40 °C, the stirring speed at 400 rpm. After reacting for 5 h, perform solid-liquid separation to obtain a leaching solution. The leaching rate of lithium ions is 95.9%, and the leaching rate of iron ions is 0.03%.

[0123] Step (2): Add an ammonia water solution with a mass fraction of 22% to the leaching solution obtained in step (1) so that the molar ratio of the total ammonium ions in the ammonia water solution and ammonium bicarbonate solution to the magnesium ions in the leaching solution is 1:1, and add a 2 mol / L sodium hydroxide solution to control its pH value at 8.9 to remove calcium ions, magnesium ions and HPO4 2- impurities. After reacting for 1.5 h, solid-liquid separation is carried out to obtain a purified solution;

[0124] Step (3): After adjusting the pH of the purified solution obtained in step (2) to 5.5, perform the first concentration through an RO membrane (high-pressure seawater desalination membrane). The pressure of RO concentration is 5.9 Mpa to obtain a concentrated solution with a TDS of 56.1 g / L;

[0125] Step (4): After adjusting the concentrated solution obtained in step (3) to a pH of 8.4, pass it through an ion exchange resin column (the resin used is a chelating ion exchange resin, specifically Duolite resin CH-93) to remove residual calcium and magnesium ion impurities. The volume of the influent water is 110 times the volume of the resin, and the influent water flow rate is 15 BV / h to obtain a refined lithium-rich mother liquor (i.e., lithium-rich solution). After detection, the magnesium element content in the refined lithium-rich mother liquor is 4.8 ppm, the calcium element content is 2.3 ppm, and the phosphorus element content is 3.7 ppm;

[0126] Step (5): After the refined lithium-rich mother liquor obtained in step (4) is concentrated by an evaporator (i.e., the second concentration), a refined lithium precipitation mother liquor is obtained, and the lithium element content in this refined lithium precipitation mother liquor is 15.9 g / L;

[0127] Step (6): Add a sodium carbonate solution with a mass fraction of 20% to the refined lithium precipitation mother liquor obtained in step (5) so that the molar ratio of the carbonate ions in the sodium carbonate solution to the lithium ions in the refined lithium precipitation mother liquor is 1.06:2 for lithium precipitation reaction. The reaction temperature is 90 °C, the stirring speed is 430 rpm. After reacting for 2 h, aging is carried out for 1.5 h, and then solid-liquid separation is carried out to obtain crude lithium carbonate; Add 3 times the mass of 90 °C hot water to the crude lithium carbonate, perform secondary water washing and then drying to obtain battery-grade lithium carbonate. The lithium recovery rate in this example is 81.9%.

[0128] Example 5

[0129] The method for preparing lithium carbonate from lithium-containing waste residue provided in this example includes the following steps:

[0130] Step (1): Add water to the lithium-containing waste residue until the solid-liquid ratio is 1:15 g / ml. Then add concentrated sulfuric acid with a mass fraction of 98% and hydrogen peroxide solution with a mass fraction of 30%. The volume ratio of concentrated sulfuric acid to the mass of the lithium-containing waste residue is 1 L:7.5 kg, and the volume of the hydrogen peroxide solution is 3.5% of the volume of the added water. Perform leaching treatment at a pH of 3.7, control the reaction temperature of the leaching treatment at 40 °C, the stirring speed at 1000 rpm. After reacting for 5.5 h, perform solid-liquid separation to obtain a leaching solution. The leaching rate of lithium ions is 96.2%, and the leaching rate of iron ions is 0.02%.

[0131] Step (2): Add ammonia water solution with a mass fraction of 22% and ammonium carbonate solution with a mass fraction of 10% to the leaching solution obtained in step (1) so that the molar ratio of the total ammonium ions in the ammonia water solution and the ammonium carbonate solution to the magnesium ions in the leaching solution is 1:1. And add 2 mol / L sodium hydroxide solution to control its pH value at 9.0 to remove calcium ions, magnesium ions and HPO4 2- impurities. After reacting for 1.5 h, perform solid-liquid separation to obtain a purified solution.

[0132] Step (3): After adjusting the pH of the purified solution obtained in step (2) to 5.3, perform the first concentration through a RO membrane (high-pressure seawater desalination membrane). The pressure of RO concentration is 6 Mpa to obtain a concentrated solution, and the TDS of this concentrated solution is 56.9 g / L.

[0133] Step (4): After adjusting the concentrated solution obtained in step (3) to a pH of 8.5, pass it through an ion exchange resin column (the resin used is a chelating ion exchange resin, specifically Duolite resin CH-90) to remove residual calcium and magnesium ion impurities. The volume of the influent water is 150 times the volume of the resin, and the influent water flow rate is 15 BV / h to obtain a refined lithium-rich mother liquor (i.e., lithium-rich solution). After detection, the magnesium element content in the refined lithium-rich mother liquor is 7.8 ppm, the calcium element content is 4.1 ppm, and the phosphorus element content is 3.4 ppm.

[0134] Step (5): After the refined lithium-rich mother liquor obtained in step (4) is concentrated by an evaporator (i.e., the second concentration), a refined lithium precipitation mother liquor is obtained, and the lithium element content in this refined lithium precipitation mother liquor is 17.5 g / L.

[0135] Step (6): Add a sodium carbonate solution with a mass fraction of 20% to the refined lithium precipitation mother liquor obtained in step (5), so that the molar ratio of carbonate ions in the sodium carbonate solution to lithium ions in the refined lithium precipitation mother liquor is 1.07:2, and carry out a lithium precipitation reaction. The reaction temperature is 85°C, the stirring speed is 460 rpm. After reacting for 1.5 h, age for 1.5 h, and then carry out solid-liquid separation to obtain crude lithium carbonate; add 4 times the mass of 90°C hot water to the crude lithium carbonate, carry out secondary water washing and then drying to obtain battery-grade lithium carbonate. The lithium yield of this example is 82.2%.

[0136] Example 6

[0137] The method for preparing lithium carbonate from lithium-containing waste residue provided in this example is basically the same as that in Example 5, except that in step (1), the leaching treatment is carried out under the condition of pH 3.8. The lithium yield of this example is 81.1%.

[0138] Example 7

[0139] The method for preparing lithium carbonate from lithium-containing waste residue provided in this example is basically the same as that in Example 5, except that in step (2), the pH value of the process of removing calcium ions, magnesium ions and HPO4 2- impurities is controlled to be 9.1. The lithium yield of this example is 82.1%.

[0140] Comparative Example 1

[0141] The method for preparing lithium carbonate from lithium-containing waste residue provided in this comparative example is basically the same as that in Example 5, except that in step (1), the leaching treatment is carried out under the condition of pH 2.0.

[0142] Comparative Example 2

[0143] The method for preparing lithium carbonate from lithium-containing waste residue provided in this comparative example is basically the same as that in Example 5, except that in step (1), hydrogen peroxide solution is not added.

[0144] In this comparative example, due to the absence of an oxidant, the leaching rate of lithium ions is reduced. The lithium yield of this comparative example is 47.1%.

[0145] Comparative Example 3

[0146] The method for preparing lithium carbonate from lithium-containing waste residue provided in this comparative example is basically the same as that in Example 5, except that in step (2), ammonia water solution and ammonium bicarbonate solution are not added.

[0147] Comparative Example 4

[0148] The method for preparing lithium carbonate using lithium-containing waste residue provided in this comparative example is basically the same as that in Example 5, except that RO concentration in step (3) and evaporation concentration in step (5) are not carried out. Since the intermediate liquor is not concentrated, the lithium concentration of the refined lithium-rich mother liquor obtained after removing residual calcium and magnesium ion impurities is low, and lithium carbonate precipitation cannot be formed during the lithium precipitation process. Therefore, battery-grade lithium carbonate is not obtained in this comparative example.

[0149] Comparative Example 5

[0150] The method for preparing lithium carbonate using lithium-containing waste residue provided in this comparative example is basically the same as that in Example 5, except that the removal of residual calcium and magnesium ion impurities in step (4) is not carried out (i.e., the concentrated liquor does not pass through the ion exchange resin column).

[0151] Comparative Example 6

[0152] The method for preparing lithium carbonate using lithium-containing waste residue provided in this example is basically the same as that in Example 5, except that in step (2), the pH of the impurity system is controlled to be 10.5 when the leaching solution is mixed with the impurity remover to remove calcium ions, magnesium ions and HPO4 2- impurities.

[0153] In this comparative example, since the pH of the impurity system is too high when the leaching solution is mixed with the impurity remover to remove calcium ions, magnesium ions and HPO4 2- impurities, lithium phosphate precipitation is formed, resulting in a reduction in the lithium carbonate yield to 69.6%.

[0154] Experimental Example 1

[0155] The impurity contents in the battery-grade lithium carbonate prepared in each of the above examples and the lithium carbonate prepared in each of the comparative examples were detected respectively, and the results are shown in Table 1.

[0156] Table 1 Impurity element contents in lithium carbonate

[0157]

[0158] As can be seen from Table 1, the impurity contents in the lithium carbonate prepared in each of the examples meet the standards of battery-grade lithium carbonate. It can be seen that the method for preparing lithium carbonate using lithium-containing waste residue provided by the present invention can obtain battery-grade lithium carbonate, with high added value and high resource utilization rate.

[0159] In Comparative Example 1, due to the too low pH during the leaching process, iron was leached out, resulting in a high iron content in the prepared lithium carbonate. In Comparative Example 3, due to the lack of ammonia source during the chemical impurity removal process, the impurity removal efficiency was low, so the calcium and magnesium impurity contents in the prepared lithium carbonate were high. In Comparative Example 5, due to the lack of resin impurity removal, the calcium and magnesium impurity contents in the prepared lithium carbonate were high.

[0160] It can be seen that the method for preparing lithium carbonate from lithium-containing waste residue provided by the present invention can efficiently remove impurities such as calcium, magnesium and phosphorus by using a combination of chemical method and resin method for impurity removal, and obtain battery-grade lithium carbonate with low impurity content and meeting the requirements.

[0161] Although the present invention has been illustrated and described with reference to specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications falling within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing lithium carbonate from lithium-containing waste residue, characterized in that, It includes the following steps: The lithium-containing waste residue, acid and oxidant are mixed and then subjected to leaching treatment. After solid-liquid separation, a lithium-containing leaching solution is obtained. The leaching rate of lithium ions in the leaching solution is greater than 95%, and the leaching rate of iron ions is less than 0.05%. The lithium-containing waste residue includes the lithium-containing waste residue obtained after the sewage generated in the production process of lithium iron phosphate is subjected to flocculation precipitation treatment, and its main component includes lithium iron phosphate. The addition amount of the acid is such that the pH of the mixed system of the lithium-containing waste residue, acid and oxidant is 3-4. The acid includes concentrated sulfuric acid. The temperature of the leaching treatment is 40-60 °C; After the leaching solution is mixed with the impurity remover, calcium ions, magnesium ions and HPO4 are removed 2- impurities, and solid-liquid separation is carried out to obtain a lithium-containing impurity-removed solution; the impurity remover includes an alkali and an ammonia source, and the ammonia source includes at least one of ammonia gas, ammonia water solution, ammonium carbonate solution and ammonium bicarbonate solution; the leaching solution is mixed with the impurity remover to remove calcium ions, magnesium ions and HPO4 2- The pH of the impurity system is 8.5 to 9.5; The impurity removal solution is passed through an ion exchange resin to remove residual calcium ion and magnesium ion impurities, obtaining a lithium-rich solution. During the process of using the ion exchange resin to remove residual calcium ion and magnesium ion impurities, the volume of the influent water is 60-200 times the volume of the ion exchange resin, the influent flow rate is 5-15 BV / h, and the influent pH is controlled at 7.0-8.5; The lithium-rich solution and carbonate are subjected to a lithium precipitation reaction, and after solid-liquid separation, lithium carbonate is obtained.

2. The method for preparing lithium carbonate from lithium-containing waste residue according to claim 1, wherein The oxidant includes hydrogen peroxide solution.

3. The method for preparing lithium carbonate using lithium-containing waste residue according to claim 1, characterized in that, The time of the leaching treatment is 3-8 h.

4. The method for preparing lithium carbonate from lithium-containing waste residues according to claim 1, characterized in that, The time for removing calcium ions, magnesium ions and HPO4 2- impurities is 1 to 5 hours.

5. The method for preparing lithium carbonate from lithium-containing waste residue according to claim 1, wherein Before the impurity removal solution is passed through an ion exchange resin to remove residual calcium ion and magnesium ion impurities, it also includes the step of performing a first concentration on the impurity removal solution.

6. The method for preparing lithium carbonate from lithium-containing waste residue according to claim 5, characterized in that, The first concentration includes RO concentration.

7. The method for preparing lithium carbonate from lithium-containing waste residue according to claim 1, characterized in that, Before the lithium precipitation reaction, it also includes the step of performing a second concentration on the lithium-rich solution.

8. The method for preparing lithium carbonate from lithium-containing waste residue according to claim 7, characterized in that, The second concentration includes evaporation concentration.

9. The method for preparing lithium carbonate from lithium-containing waste residue according to claim 1, characterized in that, The ion exchange resin includes a chelating type ion exchange resin.

10. The method for preparing lithium carbonate from lithium-containing waste residue according to claim 1, wherein, The temperature of the lithium precipitation reaction is 80-100 °C; and / or, the time of the lithium precipitation reaction is 1-5 h.

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