Method for preparing lithium carbonate by utilizing positive electrode material waste liquid

Abstract

The invention discloses a method for preparing lithium carbonate from positive electrode material waste liquid, and relates to the technical field of lithium carbonate preparation. Comprising the following steps: adding hydrogen peroxide and sulfuric acid into the positive electrode material waste liquid, and carrying out solid-liquid separation to obtain an iron phosphate / carbon black solid mixture and a lithium-containing solution; adding a flocculating agent into the lithium-containing solution to perform primary impurity removal, filtering, performing secondary impurity removal through electric descaling, and performing suction filtration to obtain a lithium-containing purified solution; heating and concentrating the lithium-containing purified solution to obtain a concentrated solution; a sodium carbonate solution is added into the concentrated solution for a lithium precipitation reaction, and crude lithium carbonate and lithium precipitation mother liquor are obtained; uniformly mixing the crude lithium carbonate with water to obtain slurry, introducing CO2, carrying out hydrogenation reaction under a supergravity condition, and filtering after the reaction is finished to obtain a lithium bicarbonate solution; and carrying out thermal decomposition reaction on the lithium bicarbonate solution under a supergravity condition, adding a nucleating agent at the same time, and after crystals are separated out, carrying out suction filtration to obtain a lithium carbonate product and crystallization mother liquor. According to the method, lithium carbonate is prepared under the supergravity condition, coating and inclusion of foreign ions in the nucleation growth process can be avoided to a great extent, and a lithium carbonate product with relatively high purity is prepared.

Description

Technical Field

[0001] The present application relates to the technical field of lithium carbonate preparation, and in particular to a method for preparing lithium carbonate using positive electrode material waste liquid. Background Art

[0002] The positive electrode material of lithium-ion batteries is part of the materials that make up lithium-ion batteries and directly affects the performance of lithium-ion batteries. A large amount of waste liquid is generated during the production process of positive electrode materials, and the treatment of positive electrode material waste liquid is extremely important. The positive electrode material waste liquid contains a large amount of lithium, and direct waste liquid treatment will cause a waste of lithium resources. The lithium in the positive electrode material waste liquid can be recovered and processed to prepare lithium carbonate / lithium hydroxide products, thereby effectively utilizing the lithium resources in the waste liquid. However, since the positive electrode material waste liquid contains more impurities, such as metal ions Fe 3+ , Fe 2+ Mg 2+ , Mn 2+ , Ca 2+ 、Na + The lithium carbonate waste liquid contains a lot of impurities, such as suspended matter, colloidal particles, etc., which are difficult to recycle, resulting in the lithium product still containing a lot of impurities. Based on this, the present application proposes a method for preparing lithium carbonate using positive electrode material waste liquid. Summary of the invention

[0003] The main purpose of the present application is to provide a method for preparing lithium carbonate using positive electrode material waste liquid, aiming to solve the technical problem that the lithium carbonate products prepared from the existing positive electrode material waste liquid contain a large amount of impurities.

[0004] To achieve the above object, the present application proposes a method for preparing lithium carbonate using cathode material waste liquid, comprising the following steps:

[0005] Adding hydrogen peroxide and sulfuric acid to the cathode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation;

[0006] Adding a flocculant to the lithium-containing solution to remove impurities once, filtering to obtain a de-impurity liquid; then performing a second de-impurity removal on the de-impurity liquid by electrostatic descaling, and filtering to obtain a lithium-containing purified liquid;

[0007] The lithium-containing purified liquid is heated and concentrated to obtain a concentrated liquid; a sodium carbonate solution is added to the concentrated liquid to perform a lithium precipitation reaction to obtain crude lithium carbonate and a lithium precipitation mother liquid;

[0008] After the crude lithium carbonate and water are mixed and slurried, CO2 is introduced and a hydrogenation reaction is carried out under supergravity conditions. After the reaction is completed, the solution is filtered to obtain a lithium bicarbonate solution;

[0009] The lithium bicarbonate solution is subjected to a thermal decomposition reaction under supergravity conditions, and a nucleating agent is added at the same time. After crystals are precipitated, they are filtered to obtain a lithium carbonate product and a crystallization mother liquor.

[0010] Optionally, in the step of adding hydrogen peroxide and sulfuric acid to the cathode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation, the amount of hydrogen peroxide used is determined according to the following relationship:

[0011] n(H2O2)=(0.55-0.65)×[C(Fe)×V]

[0012] Wherein, n(H2O2) is the molar amount of hydrogen peroxide, C(Fe) is the Fe ion concentration in the positive electrode material waste liquid, and V is the volume of the positive electrode material waste liquid;

[0013] The amount of sulfuric acid is determined according to the following relationship:

[0014] n(H2SO4)=(0.6-0.8)×[C(Li)×V]

[0015] Wherein, n(H2SO4) is the molar amount of sulfuric acid, C(Li) is the Li ion concentration in the positive electrode material waste liquid, and V is the volume of the positive electrode material waste liquid.

[0016] Optionally, the step of adding a flocculant to the lithium-containing solution to remove impurities once and filtering to obtain a de-impurity solution comprises:

[0017] Adding a flocculant to the lithium-containing solution and stirring for 8-15 minutes, leaving the solution to stand for 30-60 minutes, and filtering the solution with a multi-media filter having a filtration accuracy of 100 μm to 800 μm to obtain a decontamination solution;

[0018] Wherein, the flocculant is boron-containing polysilicon aluminum sulfate ferric, and the dosage of the flocculant is 0.5 mg / L-3 mg / L.

[0019] Optionally, in the step of performing secondary impurity removal on the impurity removal liquid by electroscaling and filtering to obtain a lithium-containing purified liquid, a stainless steel electrode is used as the cathode, a titanium-based iridium tantalum tin coating electrode is used as the anode, and the current density is set to 40A / m 2 -80A / m 2 , the reaction time is set to 0.5h-1.5h.

[0020] Optionally, the step of heating and concentrating the lithium-containing purified liquid to obtain a concentrated liquid comprises:

[0021] The lithium-containing purified liquid is evaporated and concentrated by using a triple-effect evaporator, so that the lithium ion concentration in the lithium-containing purified liquid reaches 35 g / L-55 g / L, thereby obtaining a concentrated liquid.

[0022] Optionally, in the step of adding sodium carbonate solution to the concentrated solution to carry out lithium precipitation reaction to obtain crude lithium carbonate and lithium precipitation mother liquor, the temperature of the lithium precipitation reaction is 85°C-95°C, the time of the lithium precipitation reaction is 2h-3h, and the amount of the sodium carbonate solution used is 50%-80% of the lithium content in the concentrated solution.

[0023] Optionally, the step of mixing the crude lithium carbonate with water, introducing CO2 and carrying out a hydrogenation reaction under supergravity conditions, and filtering after the reaction to obtain a lithium bicarbonate solution comprises:

[0024] The crude lithium carbonate and water are mixed and slurried at a liquid-to-solid ratio of (20-30):1, and then added into a supergravity reactor at a flow rate of 0.4L / min-0.6L / min, and CO2 is continuously introduced and hydrogenation reaction is carried out at 20°C-40°C. After the crude lithium carbonate is completely dissolved, the reaction is terminated, and the solution is filtered using a microporous filter with a filtration accuracy of 1μm-5μm to obtain a lithium bicarbonate solution;

[0025] Wherein, the hypergravity level in the hypergravity reactor is 7g-15g, the rotation speed in the hypergravity reactor is 1800rpm-3800rpm; and the flow rate of CO2 is 1.5kg / h-2.5kg / h.

[0026] Optionally, the step of subjecting the lithium bicarbonate solution to thermal decomposition reaction under high gravity conditions, adding a nucleating agent, and filtering after crystals are precipitated to obtain a lithium carbonate product and a crystallization mother liquor comprises:

[0027] The lithium bicarbonate solution is preheated to 40° C.-45° C. at a stirring speed of 100 rpm-300 rpm, and then added to the high gravity reactor at a flow rate of 0.4 L / min-0.6 L / min. At the same time, anhydrous ethanol is heated to 65° C.-75° C. and used as a heating medium, and then introduced into the high gravity reactor at a flow rate of 0.1 L / min-0.3 L / min. A nucleating agent is then added to start precipitation of lithium carbonate crystals. After all the lithium bicarbonate solution is added to the high gravity reactor, the reaction is stopped, and suction filtration is performed to obtain a lithium carbonate product and a crystallization mother liquor;

[0028] Wherein, the hypergravity level in the hypergravity reactor is 5g-10g, and the rotation speed in the hypergravity reactor is 1600rpm-2500rpm.

[0029] Optionally, the nucleating agent is battery-grade lithium carbonate powder with a particle size of 20 μm-30 μm, and the amount of the nucleating agent added is 1.5%-5% of the theoretically precipitated lithium carbonate crystals.

[0030] Optionally, the method further includes the following steps: mixing the lithium precipitation mother liquor and the crystallization mother liquor, heating to saturation at 32°C-35°C, and controlling the pH at 6.8-7.2, adding sodium sulfate seed crystals and placing the mixture in a crystallization device, controlling the bottom temperature of the crystallization device to 30°C and the top temperature to 40°C, controlling the pH at 6.8-7.2, stirring at a rate of 100rpm-300rpm, reacting until crystals are formed, filtering, separating and drying to obtain alum.

[0031] The present application firstly dissolves lithium in the positive electrode material waste liquid by adding hydrogen peroxide and sulfuric acid, and recovers iron phosphate and carbon black, then effectively separates suspended matter and colloidal substances in the positive electrode material waste liquid by a flocculant, and then performs secondary impurity removal by electroscaling to achieve the removal of metal ions such as calcium, magnesium, and manganese in the positive electrode material waste liquid, and then increases the concentration of lithium in the solution by concentration, and then uses sodium carbonate to precipitate lithium at a certain temperature to obtain crude lithium carbonate by utilizing the characteristics that lithium carbonate is slightly soluble in water and its solubility in water gradually decreases with increasing temperature, and then introduces CO2 to carry out hydrogenation reaction with crude lithium carbonate under simulated hypergravity environment conditions to enhance microscopic mixing performance and strengthen the progress of hydrogenation reaction, thereby increasing the gas-liquid-solid reaction rate and making the dioxygen The contact between the carbonized bubbles and the crude lithium carbonate solid is more complete, thereby increasing the lithium concentration in the lithium bicarbonate solution, and then the thermal decomposition reaction of the lithium bicarbonate is carried out under supergravity conditions to achieve the crystallization of lithium carbonate. Under supergravity conditions, the mass transfer and heat transfer efficiency between materials in the reaction process can be greatly improved, so that the lithium bicarbonate solution is heated more evenly, the thermal decomposition reaction rate is accelerated, and the nucleation rate is accelerated, so that a large number of crystal nuclei are generated instantly, and the reaction residence time of the lithium bicarbonate solution in the supergravity reactor is short, and it is not easy to agglomerate or agglomerate, so that the lithium carbonate crystals are more densely stacked and the crystal particle size is effectively controlled, which can greatly avoid the coating and inclusion of impurity ions in the nucleation growth process, thereby preparing a lithium carbonate product with higher purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. It is obvious that the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0033] Figure 1 This is a flow chart of the method for preparing lithium carbonate using cathode material waste liquid as described in an embodiment of the present application.

[0034] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0036] In view of the technical problems existing in the prior art, the embodiments of the present application provide a method for preparing lithium carbonate using cathode material waste liquid, such as Figure 1 As shown, the following steps are included:

[0037] Adding hydrogen peroxide and sulfuric acid to the cathode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation;

[0038] Adding a flocculant to the lithium-containing solution to remove impurities once, filtering to obtain a de-impurity liquid; then performing a second de-impurity removal on the de-impurity liquid by electrostatic descaling, and filtering to obtain a lithium-containing purified liquid;

[0039] The lithium-containing purified liquid is heated and concentrated to obtain a concentrated liquid; a sodium carbonate solution is added to the concentrated liquid to perform a lithium precipitation reaction to obtain crude lithium carbonate and a lithium precipitation mother liquid;

[0040] After the crude lithium carbonate and water are mixed and slurried, CO2 is introduced and a hydrogenation reaction is carried out under supergravity conditions. After the reaction is completed, the solution is filtered to obtain a lithium bicarbonate solution;

[0041] The lithium bicarbonate solution is subjected to a thermal decomposition reaction under supergravity conditions, and a nucleating agent is added at the same time. After crystals are precipitated, they are filtered to obtain a lithium carbonate product and a crystallization mother liquor.

[0042] The present application firstly dissolves lithium in the positive electrode material waste liquid by adding hydrogen peroxide and sulfuric acid, and recovers iron phosphate and carbon black, then effectively separates suspended matter and colloidal substances in the positive electrode material waste liquid by a flocculant, and then performs secondary impurity removal by electroscaling to achieve the removal of metal ions such as calcium, magnesium, and manganese in the positive electrode material waste liquid, and then increases the concentration of lithium in the solution by concentration, and then uses sodium carbonate to precipitate lithium at a certain temperature to obtain crude lithium carbonate by utilizing the characteristics that lithium carbonate is slightly soluble in water and its solubility in water gradually decreases with increasing temperature, and then introduces CO2 to carry out hydrogenation reaction with crude lithium carbonate under simulated hypergravity environment conditions to enhance microscopic mixing performance and strengthen the progress of hydrogenation reaction, thereby increasing the gas-liquid-solid reaction rate and making the dioxygen The contact between the carbonized bubbles and the crude lithium carbonate solid is more complete, thereby increasing the lithium concentration in the lithium bicarbonate solution, and then the thermal decomposition reaction of the lithium bicarbonate is carried out under supergravity conditions to achieve the crystallization of lithium carbonate. Under supergravity conditions, the mass transfer and heat transfer efficiency between materials in the reaction process can be greatly improved, so that the lithium bicarbonate solution is heated more evenly, the thermal decomposition reaction rate is accelerated, and the nucleation rate is accelerated, so that a large number of crystal nuclei are generated instantly, and the reaction residence time of the lithium bicarbonate solution in the supergravity reactor is short, and it is not easy to agglomerate or agglomerate, so that the lithium carbonate crystals are more densely stacked and the crystal particle size is effectively controlled, which can greatly avoid the coating and inclusion of impurity ions in the nucleation growth process, thereby preparing a lithium carbonate product with higher purity.

[0043] As an implementation method of the present application, in the step of adding hydrogen peroxide and sulfuric acid to the positive electrode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation, the amount of hydrogen peroxide used is determined according to the following relationship:

[0044] n(H2O2)=(0.55-0.65)×[C(Fe)×V]

[0045] Wherein, n(H2O2) is the molar amount of hydrogen peroxide, C(Fe) is the Fe ion concentration in the positive electrode material waste liquid, and V is the volume of the positive electrode material waste liquid;

[0046] The amount of sulfuric acid is determined according to the following relationship:

[0047] n(H2SO4)=(0.6-0.8)×[C(Li)×V]

[0048] Wherein, n(H2SO4) is the molar amount of sulfuric acid, C(Li) is the Li ion concentration in the positive electrode material waste liquid, and V is the volume of the positive electrode material waste liquid.

[0049] In the specific implementation process, theoretically, the ratio of the molar amount of hydrogen peroxide to the molar amount of Fe in the positive electrode material waste liquid is 1:2, preferably, the molar amount of hydrogen peroxide is 0.55-0.65 times the molar amount of Fe in the positive electrode material waste liquid; theoretically, the ratio of the molar amount of sulfuric acid to the molar amount of Li in the positive electrode material waste liquid is 1:2, preferably, the molar amount of sulfuric acid is 0.6-0.8 times the molar amount of Li in the positive electrode material waste liquid.

[0050] Specifically, when hydrogen peroxide and sulfuric acid are added to the cathode material waste liquid, the pH value needs to be controlled between 1.5 and 2.0, which is more conducive to the dissolution of lithium and the recovery of more lithium carbonate products. The concentration of sulfuric acid is 1 g / L-10 g / L.

[0051] As an implementation method of the present application, the step of adding a flocculant to the lithium-containing solution to remove impurities once, and filtering to obtain a de-impurity liquid comprises:

[0052] Adding a flocculant to the lithium-containing solution and stirring for 8-15 minutes, leaving the solution to stand for 30-60 minutes, and filtering the solution with a multi-media filter having a filtration accuracy of 100 μm to 800 μm to obtain a decontamination solution;

[0053] Wherein, the flocculant is boron-containing polysilicon aluminum sulfate iron, and the dosage of the flocculant is 0.5mg / L-3mg / L. Boron-containing polysilicon aluminum sulfate iron is an inorganic composite polymer flocculant, which integrates the functions of polysilicic acid, aluminum salt, and iron salt, and has multiple functions such as electrical neutralization, adsorption bridging, and net capture. The formed alum flowers are large and the sedimentation rate is fast, which improves the flocculation, decolorization, and turbidity removal effects of the flocculant, and boron can hinder the further polymerization between polysilicic acid colloid particles and improve their polymerization degree and stability. At the same time, it can also change the morphological structure of the hydrolysis polymerization product of polysilicic acid, aluminum salt and iron salt, and further improve its coagulation performance. Compared with traditional organic polymer flocculants (such as PAM) or inorganic polymer flocculants (such as polyferric sulfate), it has better flocculation performance and faster dissolution rate, and the flocs are large and fast. The flocs are not easy to break, and can effectively separate suspended matter and colloidal substances in the positive electrode material waste liquid.

[0054] As an implementation method of the present application, in the step of performing secondary impurity removal on the impurity removal liquid by electroscaling and filtering to obtain a lithium-containing purified liquid, a stainless steel electrode is used as the cathode, and a titanium-based iridium tantalum tin coating electrode is used as the anode, and the current density is set to 40A / m 2 -80A / m 2 , the reaction time is set to 0.5h-1.5h.

[0055] In order to further remove metal ions in the positive electrode material waste liquid, the present application introduces direct current for electro-descaling treatment. Under the action of the external enhanced current, a potential difference is formed between the anode and the cathode, which promotes the migration and transfer of ions in the solution in the electrolyte, forming a strong electrochemical reaction. An oxidation reaction occurs at the anode to remove part of the organic matter, and a reduction reaction occurs at the cathode to produce hydroxide flocculation, thereby removing calcium, magnesium, manganese and other ions. Impurities such as calcium and magnesium can be removed without adding other chemical agents. The treatment cost is low and no new impurities are introduced, which can ensure the stable operation of subsequent processes.

[0056] As an implementable embodiment of the present application, the step of heating and concentrating the lithium-containing purified liquid to obtain a concentrated liquid includes:

[0057] The lithium-containing purified liquid is evaporated and concentrated by using a triple-effect evaporator, so that the lithium ion concentration in the lithium-containing purified liquid reaches 35 g / L-55 g / L, thereby obtaining a concentrated liquid.

[0058] Since the lithium ion concentration in the lithium-containing purified liquid is low, it is difficult to be directly used in the subsequent preparation of lithium carbonate products. Therefore, the present application increases the lithium ion concentration to 35g / L-55g / L by evaporating and concentrating the lithium-containing purified liquid, and then uses it in the subsequent preparation of lithium products.

[0059] As an implementation method of the present application, in the step of adding sodium carbonate solution to the concentrated solution to carry out lithium precipitation reaction to obtain crude lithium carbonate and lithium precipitation mother liquor, the temperature of the lithium precipitation reaction is 85°C-95°C, the time of the lithium precipitation reaction is 2h-3h, and the amount of the sodium carbonate solution used is 50%-80% of the lithium content in the concentrated solution.

[0060] Specifically, lithium carbonate is slightly soluble in water and its solubility in water gradually decreases with increasing temperature. Lithium carbonate is obtained by precipitating lithium with sodium carbonate at a temperature of 85°C-95°C. The reaction formula is as follows:

[0061] Li2SO 4(aq) +Na2CO 3(aq) =Li2CO 3(s) ↓+Na2SO 4(aq)

[0062] Theoretically, the molar ratio of sodium carbonate to lithium in the concentrate is 1:2. To allow the lithium precipitation reaction to proceed fully, preferably, the amount of sodium carbonate solution used is 65% of the lithium content in the concentrate.

[0063] As an implementation method of the present application, the step of mixing the crude lithium carbonate with water, introducing CO2 and performing a hydrogenation reaction under high gravity conditions, and filtering after the reaction to obtain a lithium bicarbonate solution includes:

[0064] The crude lithium carbonate and water are mixed and slurried at a liquid-solid ratio of (20-30):1, and then added into a supergravity reactor at a flow rate of 0.4L / min-0.6L / min, and CO2 is continuously introduced and hydrogenation reaction is carried out at 20°C-40°C. After the crude lithium carbonate is completely dissolved, the reaction is terminated, and the solution is filtered using a microporous filter with a filtration accuracy of 1μm-5μm to obtain a lithium bicarbonate solution;

[0065] Wherein, the hypergravity level in the hypergravity reactor is 7g-15g, the rotation speed in the hypergravity reactor is 1800rpm-3800rpm; and the flow rate of CO2 is 1.5kg / h-2.5kg / h.

[0066] This application is in the hypergravity environment condition (the earth's gravity acceleration g is 9.8m / s 2 , that is, it requires an environment with a pressure of more than g) to introduce CO2 and crude lithium carbonate for hydrogenation reaction. By simulating supergravity conditions, the microscopic mixing performance is enhanced, thereby strengthening the hydrogenation reaction. On the one hand, the gas-liquid-solid reaction rate is improved, and the utilization rate of CO2 gas is improved. Under supergravity conditions, carbon dioxide bubbles can be effectively dispersed, so that the contact between carbon dioxide bubbles and crude lithium carbonate solids is more sufficient, and the hydrogenation reaction endpoint is reached faster, which promotes a significant increase in the reaction rate, thereby increasing the concentration of lithium in the lithium bicarbonate solution; on the other hand, since the reaction time is greatly shortened, the contact and reaction time between impurities such as calcium carbonate, magnesium carbonate, and manganese carbonate in crude lithium carbonate and CO2 are reduced, the dissolution of calcium, magnesium, and manganese impurities is reduced, and their participation in the hydrogenation reaction is avoided. Instead, they exist in the solution in the form of precipitation, thereby achieving the purpose of further impurity removal.

[0067] As an implementation method of the present application, the step of subjecting the lithium bicarbonate solution to thermal decomposition reaction under high gravity conditions, adding a nucleating agent, and filtering after crystals are precipitated to obtain a lithium carbonate product and a crystallization mother liquor comprises:

[0068] The lithium bicarbonate solution is preheated to 40° C.-45° C. at a stirring speed of 100 rpm-300 rpm, and then added to the high gravity reactor at a flow rate of 0.4 L / min-0.6 L / min. At the same time, anhydrous ethanol is heated to 65° C.-75° C. and used as a heating medium, and then introduced into the high gravity reactor at a flow rate of 0.1 L / min-0.3 L / min. A nucleating agent is then added to start precipitation of lithium carbonate crystals. After all the lithium bicarbonate solution is added to the high gravity reactor, the reaction is stopped, and suction filtration is performed to obtain a lithium carbonate product and a crystallization mother liquor;

[0069] Wherein, the hypergravity level in the hypergravity reactor is 5g-10g, and the rotation speed in the hypergravity reactor is 1600rpm-2500rpm.

[0070] The present application conducts a thermal decomposition reaction of lithium bicarbonate in a supergravity reactor and realizes the crystallization of lithium carbonate. Under supergravity conditions, the liquid phase can be torn into tiny liquid films, liquid filaments and droplets by shear force, which effectively increases the contact area between the liquid and liquid phases. Due to the increase in the contact area, the mass transfer and heat transfer efficiency between the materials in the reaction process is improved, the heat transfer is enhanced, and the heat transfer coefficient is effectively improved, so that the lithium bicarbonate solution is heated more evenly, the thermal decomposition reaction rate is accelerated, and the nucleation rate is accelerated, so that a large number of crystal nuclei are generated instantly. After all the lithium bicarbonate solution is added to the supergravity reactor, lithium carbonate crystals are precipitated instantly, and the reaction residence time of the lithium bicarbonate solution in the supergravity reactor is short, and it is not easy to agglomerate or agglomerate, so that the lithium carbonate crystals are more densely stacked, the crystal particle size is effectively controlled, and the coating and inclusion of impurity ions in the nucleation growth process can be avoided to a great extent, which is conducive to obtaining a lithium carbonate product with higher purity.

[0071] It should be noted that the specific type of the high-gravity reactor used in the present application is not strictly limited, and a rotating packed bed can be used to simulate high-gravity conditions.

[0072] As an implementation method of the present application, the nucleating agent is battery-grade lithium carbonate powder with a particle size of 20 μm-30 μm, and the amount of the nucleating agent added is 1.5%-5% of the theoretically precipitated lithium carbonate crystals.

[0073] As an implementable method of the present application, it also includes the steps of: mixing the lithium precipitation mother liquor and the crystallization mother liquor, heating to saturation at 32°C-35°C, and controlling the pH at 6.8-7.2, adding sodium sulfate seed crystals and placing in a crystallization device, controlling the bottom temperature of the crystallization device to 30°C and the top temperature to 40°C, controlling the pH at 6.8-7.2, and stirring at a rate of 100rpm-300rpm. After reacting until crystals are formed, filtering, separating and drying to obtain alum.

[0074] Since the lithium precipitation mother liquor and crystallization mother liquor contain more Na + and SO4 2- , in order to achieve Na + and SO4 2-In order to make full use of the lithium precipitation mother liquor and the crystallization mother liquor, the present application recycles the lithium precipitation mother liquor and the crystallization mother liquor to prepare sodium sulphate. By heating at 32°C-35°C, it is beneficial to promote the precipitation of crystals, and setting a temperature gradient to promote the uniform growth and morphology control of crystals. The pH value can control the activity of ions in the crystallization process, thereby affecting the nucleation and growth of crystals. An appropriate stirring rate can ensure that the components in the solution are evenly distributed, avoid local oversaturation or excessive aggregation, and provide good solute transfer. Preferably, the bottom temperature is 30°C, the top temperature is 40°C, the pH is controlled at 7.0, and stirring is performed at a rate of 200rpm, which is beneficial to the nucleation and growth of sodium sulfate crystals, and sodium sulphate with better crystal morphology is prepared.

[0075] The above technical solution of the present application is described in detail below in conjunction with specific embodiments.

[0076] Example 1

[0077] A method for preparing lithium carbonate using cathode material waste liquid comprises the following steps:

[0078] Adding hydrogen peroxide and sulfuric acid to the cathode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation;

[0079] Add boron-containing polysilicon aluminum sulfate ferric flocculant in an amount of 1.8 mg / L to the lithium-containing solution, stir for 11 minutes, let stand for 45 minutes, and then filter with a multi-media filter with a filtration accuracy of 450 μm to obtain a decontamination liquid; then perform secondary decontamination on the decontamination liquid by electroscaling, with a stainless steel electrode used as the cathode and a titanium-based iridium tantalum tin coated electrode used as the anode, and the current density set to 60 A / m 2 , the reaction time is set to 1h, and after filtration, a lithium-containing purified liquid is obtained;

[0080] The lithium-containing purified liquid is evaporated and concentrated by a triple-effect evaporator to make the lithium ion concentration in the lithium-containing purified liquid reach 45 g / L, thereby obtaining a concentrated liquid; sodium carbonate solution is then added to the concentrated liquid to perform a lithium precipitation reaction, wherein the temperature of the lithium precipitation reaction is 90° C. and the time of the lithium precipitation reaction is 2.5 h, thereby obtaining crude lithium carbonate and a lithium precipitation mother liquor;

[0081] The crude lithium carbonate and water are mixed and slurried at a liquid-to-solid ratio of 25:1, and then added into a supergravity reactor at a flow rate of 0.5 L / min, and CO2 is continuously introduced and hydrogenation reaction is carried out at 30° C. After the crude lithium carbonate is completely dissolved, the reaction is terminated, and the solution is filtered through a microporous filter with a filtration accuracy of 3 μm to obtain a lithium bicarbonate solution;

[0082] The hypergravity level in the hypergravity reactor is 11g, the rotation speed in the hypergravity reactor is 2800rpm, and the flow rate of CO2 is 2kg / h.

[0083] The lithium bicarbonate solution is preheated to 42° C. at a stirring speed of 200 rpm, and then added to the high-gravity reactor at a flow rate of 0.5 L / min. At the same time, anhydrous ethanol is heated to 70° C. and used as a heating medium, and then introduced into the high-gravity reactor at a flow rate of 0.2 L / min. A nucleating agent is then added to start precipitation of lithium carbonate crystals. After all the lithium bicarbonate solution is added to the high-gravity reactor, the reaction is stopped, and suction filtration is performed to obtain a lithium carbonate product and a crystallization mother liquor;

[0084] The supergravity level in the supergravity reactor is 7.5 g, the rotation speed in the supergravity reactor is 2050 rpm; the nucleating agent is a battery-grade lithium carbonate powder with a particle size of 25 μm, and the amount of the nucleating agent added is 3.2% of the theoretically precipitated lithium carbonate crystals;

[0085] The lithium precipitation mother liquor and the crystallization mother liquor are mixed, heated to saturation at 33°C, and the pH is controlled at 7.0, and then sodium sulfate seed crystals are added and placed in a crystallization device. The bottom temperature of the crystallization device is controlled to be 30°C, the top temperature is 40°C, the pH is controlled to be 7.0, and stirring is performed at a rate of 200 rpm. After reacting to form crystals, they are filtered, separated and dried to obtain glauber salt.

[0086] Example 2

[0087] A method for preparing lithium carbonate using cathode material waste liquid comprises the following steps:

[0088] Adding hydrogen peroxide and sulfuric acid to the cathode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation;

[0089] Adding boron-containing polysilicon aluminum sulfate ferric flocculant in an amount of 0.5 mg / L to the lithium-containing solution, stirring for 8 minutes, standing for 30 minutes, and then filtering with a multi-media filter with a filtration accuracy of 100 μm to obtain a decontamination liquid; then performing secondary decontamination on the decontamination liquid by electroscaling, using a stainless steel electrode for the cathode and a titanium-based iridium tantalum tin coating electrode for the anode, and setting the current density to 40 A / m 2 , the reaction time is set to 0.5h, and after filtration, a lithium-containing purified liquid is obtained;

[0090] The lithium-containing purified liquid is evaporated and concentrated by a triple-effect evaporator to make the lithium ion concentration in the lithium-containing purified liquid reach 35 g / L, thereby obtaining a concentrated liquid; sodium carbonate solution is then added to the concentrated liquid to carry out a lithium precipitation reaction, wherein the temperature of the lithium precipitation reaction is 85° C. and the time of the lithium precipitation reaction is 3 hours, thereby obtaining crude lithium carbonate and a lithium precipitation mother liquor;

[0091] The crude lithium carbonate and water are mixed and slurried at a liquid-to-solid ratio of 20:1, and then added into an ultra-gravity reactor at a flow rate of 0.4 L / min, and CO2 is continuously introduced to perform a hydrogenation reaction at 20° C. After the crude lithium carbonate is completely dissolved, the reaction is terminated, and the solution is filtered using a microporous filter with a filtration accuracy of 1 μm to obtain a lithium bicarbonate solution;

[0092] The hypergravity level in the hypergravity reactor is 7g, the rotation speed in the hypergravity reactor is 1800rpm, and the flow rate of CO2 is 1.5kg / h.

[0093] The lithium bicarbonate solution is preheated to 40° C. at a stirring speed of 100 rpm, and then added to the high-gravity reactor at a flow rate of 0.4 L / min. At the same time, anhydrous ethanol is heated to 65° C. and used as a heating medium, and then introduced into the high-gravity reactor at a flow rate of 0.1 L / min. A nucleating agent is then added to start precipitation of lithium carbonate crystals. After all the lithium bicarbonate solution is added to the high-gravity reactor, the reaction is stopped, and suction filtration is performed to obtain a lithium carbonate product and a crystallization mother liquor;

[0094] The supergravity level in the supergravity reactor is 5g, the rotation speed in the supergravity reactor is 1600rpm; the nucleating agent is a battery-grade lithium carbonate powder with a particle size of 20μm, and the amount of the nucleating agent added is 1.5% of the theoretically precipitated lithium carbonate crystals;

[0095] The lithium precipitation mother liquor and the crystallization mother liquor are mixed, heated to saturation at 32°C, and the pH is controlled at 6.8, and then sodium sulfate seed crystals are added and placed in a crystallization device. The bottom temperature of the crystallization device is controlled to be 30°C, the top temperature is 40°C, the pH is controlled to be 6.8, and stirring is performed at a rate of 100 rpm. After reacting to form crystals, they are filtered, separated and dried to obtain glauber salt.

[0096] Example 3

[0097] A method for preparing lithium carbonate using cathode material waste liquid comprises the following steps:

[0098] Adding hydrogen peroxide and sulfuric acid to the cathode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation;

[0099] Add boron-containing polysilicon aluminum sulfate ferric flocculant in an amount of 3 mg / L to the lithium-containing solution, stir for 15 minutes, let stand for 60 minutes, and then filter with a multi-media filter with a filtration accuracy of 800 μm to obtain a decontamination liquid; then perform secondary decontamination on the decontamination liquid by electroscaling, with a stainless steel electrode used as the cathode and a titanium-based iridium tantalum tin coated electrode used as the anode, and the current density set to 80 A / m 2 The reaction time was set to 1.5 h, and after filtration, a lithium-containing purified liquid was obtained;

[0100] The lithium-containing purified liquid is evaporated and concentrated by a triple-effect evaporator to make the lithium ion concentration in the lithium-containing purified liquid reach 55 g / L, thereby obtaining a concentrated liquid; sodium carbonate solution is then added to the concentrated liquid to perform a lithium precipitation reaction, wherein the temperature of the lithium precipitation reaction is 95° C. and the time of the lithium precipitation reaction is 3 hours, thereby obtaining crude lithium carbonate and a lithium precipitation mother liquor;

[0101] The crude lithium carbonate and water are mixed and slurried at a liquid-to-solid ratio of 30:1, and then added into an ultra-gravity reactor at a flow rate of 0.6 L / min, and CO2 is continuously introduced and hydrogenation reaction is performed at 40° C. After the crude lithium carbonate is completely dissolved, the reaction is terminated, and the solution is filtered using a microporous filter with a filtration accuracy of 5 μm to obtain a lithium bicarbonate solution;

[0102] The hypergravity level in the hypergravity reactor is 15g, the rotation speed in the hypergravity reactor is 3800rpm, and the flow rate of CO2 is 2.5kg / h.

[0103] The lithium bicarbonate solution is preheated to 45° C. at a stirring speed of 300 rpm, and then added to the high-gravity reactor at a flow rate of 0.6 L / min. At the same time, anhydrous ethanol is heated to 75° C. and used as a heating medium, and then introduced into the high-gravity reactor at a flow rate of 0.3 L / min. A nucleating agent is then added to start precipitation of lithium carbonate crystals. After all the lithium bicarbonate solution is added to the high-gravity reactor, the reaction is stopped, and suction filtration is performed to obtain a lithium carbonate product and a crystallization mother liquor;

[0104] The supergravity level in the supergravity reactor is 10 g, the rotation speed in the supergravity reactor is 2500 rpm; the nucleating agent is a battery-grade lithium carbonate powder with a particle size of 30 μm, and the amount of the nucleating agent added is 5% of the theoretically precipitated lithium carbonate crystals;

[0105] The lithium precipitation mother liquor and the crystallization mother liquor are mixed, heated to saturation at 35°C, and the pH is controlled at 7.2, and then sodium sulfate seed crystals are added and placed in a crystallization device, and the bottom temperature of the crystallization device is controlled to be 30°C and the top temperature is 40°C, and the pH is controlled at 7.2. At the same time, stirring is carried out at a rate of 300 rpm. After reacting to form crystals, they are filtered, separated and dried to obtain glauber salt.

[0106] Comparative Example 1

[0107] Compared with Example 1, the high-gravity reactor in the hydrogenation reaction is replaced by a conventional reaction device, and the hydrogenation reaction is not carried out under high-gravity conditions.

[0108] Comparative Example 2

[0109] Compared with Example 1, the high gravity reactor in the thermal decomposition reaction is replaced by a conventional crystallization device, and the thermal decomposition of sodium bicarbonate is not performed under high gravity conditions.

[0110] Experimental example

[0111] The main chemical components in the lithium bicarbonate solution prepared after the hydrogenation reaction in the embodiment of the present application and comparative example 1 were detected by ICP detection method, and the ICP detection method was based on the analysis method of GB / T 11064-2013. The detection results are shown in Table 1 below.

[0112] Table 1

[0113]

[0114] As can be seen from Table 1, the concentration of lithium in the lithium bicarbonate solution obtained after treatment by the method of the embodiment of the present application is significantly higher than the concentration of lithium in Comparative Example 1. The hydrogenation reaction in Comparative Example 1 is not carried out under supergravity conditions, resulting in insufficient hydrogenation of the crude lithium carbonate solid. Under the same reaction time, some crude lithium carbonate solids in Comparative Example 1 still fail to fully react with carbon dioxide, resulting in a significant decrease in the concentration of lithium in the lithium bicarbonate solution. This indicates that the present application performs a hydrogenation reaction under supergravity conditions, which can effectively disperse carbon dioxide bubbles, reach the end point of the hydrogenation reaction faster, and make the carbon dioxide bubbles more fully contact with the crude lithium carbonate solid, thereby significantly increasing the reaction rate and increasing the concentration of lithium in the lithium bicarbonate solution.

[0115] Experimental Example 2

[0116] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to detect the contents of main chemical components in the lithium carbonate products obtained in the examples of the present application and comparative example 2. The test results are shown in Table 2 below.

[0117] Table 2

[0118]

[0119]

[0120] As can be seen from Table 2, the lithium carbonate content in the lithium carbonate product prepared after treating the cathode material waste liquid by the method of the embodiment of the present application can reach more than 99%. In Comparative Example 2, the crystallization of lithium carbonate is carried out in a conventional crystallization device, and the reaction time is longer, and the heating uniformity of the lithium bicarbonate solution is lower, which makes it easier to coat and include impurity ions during the nucleation and growth of the crystals, resulting in a decrease in the purity of the lithium carbonate product. The embodiment of the present application is crystallized in a high-gravity reactor, which can make the lithium bicarbonate solution more evenly heated, and the heat transfer is enhanced. A large number of crystal nuclei are generated in an instant. The reaction residence time of the lithium bicarbonate solution in the high-gravity reactor is short, and it is not easy to agglomerate or agglomerate. The coating and inclusion of impurity ions during the nucleation and growth process can be avoided to a great extent, which is conducive to obtaining a lithium carbonate product with higher purity.

[0121] The above description is only an optional embodiment of the present application, and does not limit the patent scope of the present application. All equivalent structural transformations made by using the contents of the present application specification and drawings under the inventive concept of the present application, or direct / indirect application in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A method for preparing lithium carbonate using cathode material waste liquid, characterized in that: The following steps are involved: Adding hydrogen peroxide and sulfuric acid to the cathode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation; Adding a flocculant to the lithium-containing solution to remove impurities, and filtering to obtain an impurity-removed liquid; The impurity removal liquid is subjected to secondary impurity removal by electric descaling, and after suction filtration, a lithium-containing purified liquid is obtained; The lithium-containing purified liquid is heated and concentrated to obtain a concentrated liquid; a sodium carbonate solution is added to the concentrated liquid to perform a lithium precipitation reaction to obtain crude lithium carbonate and a lithium precipitation mother liquid; After the crude lithium carbonate and water are mixed and slurried, CO2 is introduced and a hydrogenation reaction is carried out under supergravity conditions. After the reaction is completed, the solution is filtered to obtain a lithium bicarbonate solution; The lithium bicarbonate solution is subjected to a thermal decomposition reaction under supergravity conditions, and a nucleating agent is added at the same time. After crystals are precipitated, they are filtered to obtain a lithium carbonate product and a crystallization mother liquor.

2. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: In the step of adding hydrogen peroxide and sulfuric acid to the positive electrode material waste liquid, and obtaining a solid mixture of iron phosphate / carbon black and a lithium-containing solution after solid-liquid separation, the amount of hydrogen peroxide used is determined according to the following relationship: n(H2O2)=(0.55-0.65)×[C(Fe)×V] Wherein, n(H2O2) is the molar amount of hydrogen peroxide, C(Fe) is the Fe ion concentration in the positive electrode material waste liquid, and V is the volume of the positive electrode material waste liquid; The amount of sulfuric acid is determined according to the following relationship: n(H2SO4)=(0.6-0.8)×[C(Li)×V] Wherein, n(H2SO4) is the molar amount of sulfuric acid, C(Li) is the Li ion concentration in the positive electrode material waste liquid, and V is the volume of the positive electrode material waste liquid.

3. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: The step of adding a flocculant to the lithium-containing solution to remove impurities once and filtering to obtain a de-impurity liquid comprises: Adding a flocculant to the lithium-containing solution and stirring for 8-15 minutes, leaving the solution to stand for 30-60 minutes, and filtering the solution with a multi-media filter having a filtration accuracy of 100 μm to 800 μm to obtain a decontamination solution; Wherein, the flocculant is boron-containing polysilicon aluminum sulfate ferric, and the dosage of the flocculant is 0.5 mg / L-3 mg / L.

4. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: In the step of performing secondary impurity removal on the impurity removal liquid by electroscaling and filtering to obtain a lithium-containing purified liquid, a stainless steel electrode is used as the cathode, a titanium-based iridium tantalum tin coating electrode is used as the anode, and a current density is set to 40A / m 2 -80A / m 2 , the reaction time is set to 0.5h-1.5h.

5. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: The step of heating and concentrating the lithium-containing purified liquid to obtain a concentrated liquid comprises: The lithium-containing purified liquid is evaporated and concentrated by using a triple-effect evaporator, so that the lithium ion concentration in the lithium-containing purified liquid reaches 35 g / L-55 g / L, thereby obtaining a concentrated liquid.

6. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: In the step of adding sodium carbonate solution to the concentrated solution to carry out lithium precipitation reaction to obtain crude lithium carbonate and lithium precipitation mother liquor, the temperature of the lithium precipitation reaction is 85°C-95°C, the time of the lithium precipitation reaction is 2h-3h, and the amount of the sodium carbonate solution used is 50%-80% of the lithium content in the concentrated solution.

7. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: The step of mixing the crude lithium carbonate with water, introducing CO2 and carrying out a hydrogenation reaction under supergravity conditions, and filtering after the reaction to obtain a lithium bicarbonate solution comprises: The crude lithium carbonate and water are mixed and slurried at a liquid-to-solid ratio of (20-30):1, and then added into a supergravity reactor at a flow rate of 0.4L / min-0.6L / min, and CO2 is continuously introduced and hydrogenation reaction is carried out at 20°C-40°C. After the crude lithium carbonate is completely dissolved, the reaction is terminated, and the solution is filtered using a microporous filter with a filtration accuracy of 1μm-5μm to obtain a lithium bicarbonate solution; Wherein, the hypergravity level in the hypergravity reactor is 7g-15g, the rotation speed in the hypergravity reactor is 1800rpm-3800rpm; and the flow rate of CO2 is 1.5kg / h-2.5kg / h.

8. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: The step of subjecting the lithium bicarbonate solution to thermal decomposition reaction under high gravity conditions, adding a nucleating agent, and filtering after crystals are precipitated to obtain a lithium carbonate product and a crystallization mother liquor comprises: The lithium bicarbonate solution is preheated to 40° C.-45° C. at a stirring speed of 100 rpm-300 rpm, and then added to the high gravity reactor at a flow rate of 0.4 L / min-0.6 L / min. At the same time, anhydrous ethanol is heated to 65° C.-75° C. and used as a heating medium, and then introduced into the high gravity reactor at a flow rate of 0.1 L / min-0.3 L / min. A nucleating agent is then added to start precipitation of lithium carbonate crystals. After all the lithium bicarbonate solution is added to the high gravity reactor, the reaction is stopped, and suction filtration is performed to obtain a lithium carbonate product and a crystallization mother liquor; Wherein, the hypergravity level in the hypergravity reactor is 5g-10g, and the rotation speed in the hypergravity reactor is 1600rpm-2500rpm.

9. The method for preparing lithium carbonate using cathode material waste liquid according to claim 8, characterized in that: The nucleating agent is battery-grade lithium carbonate powder with a particle size of 20 μm-30 μm, and the added amount of the nucleating agent is 1.5%-5% of the theoretically precipitated lithium carbonate crystals.

10. The method for preparing lithium carbonate using cathode material waste liquid according to claim 1, characterized in that: The method further comprises the following steps: mixing the lithium precipitation mother liquor and the crystallization mother liquor, heating to saturation at 32°C-35°C, and controlling the pH value at 6.8-7.2, adding sodium sulfate seed crystals and placing the mixture in a crystallization device, controlling the bottom temperature of the crystallization device to 30°C and the top temperature to 40°C, controlling the pH value at 6.8-7.2, stirring at a rate of 100rpm-300rpm, reacting until crystals are formed, filtering, separating and drying to obtain glauber salt.

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