Method for recovering lithium element

Abstract

The invention discloses a method for recovering lithium element, which comprises the following steps: S1, mixing lithium-containing rare earth molten salt slag, acid liquor and sodium fluoride for acid dissolution and solid-liquid separation to obtain acid dissolution slag and an acid solution; the acid liquor comprises hydrochloric acid; s2, mixing the acid solution and the caustic soda liquid, performing callback treatment, and performing solid-liquid separation to obtain callback treatment slag and callback treatment liquid; and S3, mixing the callback treatment liquid with sodium fluoride, carrying out precipitation treatment, and carrying out solid-liquid separation to obtain a lithium fluoride precipitate and fluorine-containing wastewater. According to the method for recycling the lithium element, the yield of the lithium element is high, the purity of the obtained lithium fluoride is high, meanwhile, the technological process is simple, the operation difficulty is low, and the energy consumption cost can be reduced.

Description

Technical Field

[0001] The invention relates to a method for recovering lithium elements. Background Art

[0002] Lithium is the core material of the new energy industry (such as lithium batteries). With the rapid development of electric vehicles and energy storage technology, the global demand for lithium resources has surged. Traditional lithium resources (salt lake brine, spodumene, etc.) face problems such as high mining costs, uneven geographical distribution (such as South America and Australia), and environmental pressure. There is an urgent need to develop new lithium resource channels.

[0003] Rare earth metals (such as neodymium and praseodymium) are usually produced by molten salt electrolysis. During the process, lithium-containing molten salts (such as LiF-LiCl) are used as electrolytes to lower the melting point and increase conductivity. The molten salt slag remaining after the reaction often contains unreacted lithium (in the form of LiF, LiCl or Li2O), and the lithium content is usually between 1% and 5%. Recycling lithium can reduce dependence on primary ore and reduce the carbon footprint of the new energy industry chain. If the molten salt slag is directly piled up, the fluorine, chlorine and other components in it may cause soil and groundwater pollution. Recycling lithium has both economic and environmental benefits.

[0004] Chinese patent application CN115959688A discloses a method for recycling rare earth molten salt slag to prepare high-quality lithium salt, which includes the following steps: A. ball milling and screening; B. acid leaching; C. solid fluorine precipitation of lithium; D. neutral impurity removal; E. alkalinization and impurity removal; F. evaporation and concentration; G. soda ash precipitation of lithium.

[0005] However, the above process has the following problems:

[0006] 1. Rare earths are also partially leached during the acid leaching process, resulting in rare earths in the iron slag. This part of the rare earth needs to be acid-dissolved and leached again in the subsequent recovery process, which doubles the recovery cost and affects the purity of the product;

[0007] 2. Since concentrated sulfuric acid is used for acid leaching, rare earth sulfate complex salt precipitation is easily formed in the sulfuric acid system due to the presence of rare earths. If sodium hydroxide is directly used for neutral impurity removal, sodium rare earth sulfate precipitation will be formed. This precipitate needs to be treated at high temperature before it can be separated, which is not conducive to the subsequent recovery of rare earths. Therefore, the D1 process needs to use magnesium hydroxide and calcium hydroxide to adjust the pH value in the neutral impurity removal step, so that iron ions and the like are precipitated at a specific pH value without producing dilute sulfate complex salts, thereby achieving the purpose of preliminary impurity removal. However, this method will introduce impurities such as calcium and magnesium, and the subsequent process of removing calcium and magnesium needs to be added, which is complicated to operate;

[0008] 3. The product is obtained by lithium carbonate precipitation method. Since lithium carbonate has a certain solubility in the solution, in order to improve the overall yield, the concentration of lithium needs to be increased, and a concentration process needs to be added. This process is not only difficult to operate, but also increases energy consumption. Summary of the invention

[0009] The technical problem to be solved by the present invention is that the method for recovering lithium in the prior art has the defects of complex operation, high energy consumption and cost, low yield and product purity, and provides a method for recovering lithium element. The method for recovering lithium element of the present invention has high yield of lithium element and high purity of lithium fluoride. At the same time, the process flow of the present invention is simple, the operation difficulty is low, and energy consumption cost can be saved.

[0010] The present invention adopts the following technical solutions to solve the above technical problems.

[0011] The present invention provides a method for recovering lithium, which comprises the following steps:

[0012] S1, mixing lithium rare earth molten salt slag, acid solution and sodium fluoride for acid dissolution, solid-liquid separation, to obtain acid-dissolved slag and acid solution; the acid solution comprises hydrochloric acid;

[0013] S2, mixing the acid solution and liquid alkali for callback treatment, and separating the solid and liquid to obtain callback treatment slag and callback treatment liquid;

[0014] S3, mixing the callback treatment liquid and sodium fluoride for precipitation treatment, and separating the solid and liquid to obtain lithium fluoride precipitate and fluorine-containing wastewater.

[0015] In the present invention, the lithium-containing rare earth molten salt slag is preferably rare earth reduction slag and / or rare earth molten salt slag.

[0016] Among them, rare earth molten salt slag refers to the molten salt slag produced in the process of rare earth metal production. In the process, lithium-containing molten salt is used as an electrolyte to reduce the melting point and improve conductivity. The molten salt slag remaining after the reaction often contains unreacted lithium in the form of LiF, LiCl or Li2O. It generally also includes rare earth fluorides, rare earth oxides, other metal fluorides, metal oxides (such as aluminum oxide and iron oxide) and silicon dioxide.

[0017] Among them, rare earth reduction slag refers to the reduction slag produced in the process of rare earth metal production. In the process, lithium-containing molten salt is used as an electrolyte to reduce the melting point and improve conductivity. The molten salt slag remaining after the reaction often contains unreacted lithium in the form of LiF, LiCl or Li2O. It generally also includes rare earth fluorides, rare earth oxides, other metal fluorides, metal oxides (such as aluminum oxide and iron oxide) and silicon dioxide.

[0018] In the present invention, the lithium-containing rare earth molten salt slag includes rare earth elements and lithium elements, and the rare earth elements include, for example, one or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium. In the present invention, the specific type of rare earth element in the lithium-containing rare earth molten salt slag will not affect the final lithium element yield and the purity of lithium fluoride, that is, for lithium-containing rare earth molten salt slag with a certain rare earth element content, when the contents of other components are the same, no matter the rare earth element is any one or any several of the above rare earth elements, the final lithium element yield and the purity of lithium fluoride are the same.

[0019] In the present invention, the mass content of each element in the lithium-containing rare earth molten salt slag means the mass percentage of each element in the lithium-containing rare earth molten salt slag.

[0020] In the present invention, preferably, the mass content of lithium element in the lithium-containing rare earth molten salt slag is 1%-5%, for example, 1.29%.

[0021] In the present invention, preferably, the mass content of REO in the lithium-containing rare earth molten salt slag is 10%-80%, for example, 64.57%. Wherein, REO means the oxide of rare earth elements, and the content of REO is used in the present invention to represent the content of rare earth elements. In the present invention, the method for determining the content of REO can be the oxalate weight method, specifically: mixing the lithium-containing rare earth molten salt slag and the perchloric acid solution, dissolving all the rare earth elements therein in the perchloric acid solution, and then adding an excess of oxalic acid solution to the above perchloric acid solution to convert the rare earth elements into oxalate rare earth precipitate, and burning the oxalate rare earth precipitate to obtain pure rare earth oxide, at this time, weigh the rare earth oxide, and calculate the content of the rare earth oxide, and the calculation formula is the mass of the rare earth oxide / the mass of the lithium-containing rare earth molten salt slag.

[0022] In the present invention, preferably, the lithium-containing rare earth molten salt slag also includes fluorine element.

[0023] Preferably, the mass content of fluorine in the lithium-containing rare earth molten salt slag is 3%-25%, for example, 16.28%.

[0024] In the present invention, preferably, the lithium-containing rare earth molten salt slag also includes iron element.

[0025] Preferably, the mass content of iron in the lithium-containing rare earth molten salt slag is 2%-30%, for example, 14.74%.

[0026] In certain specific embodiments of the present invention, the lithium-containing rare earth molten salt slag further includes acid-insoluble impurities, such as silicon and / or graphite. In the present invention, the specific types of acid-insoluble impurities will not affect the final lithium yield and the purity of lithium fluoride, that is, for lithium-containing rare earth molten salt slag with a certain impurity content, when the content of other acid-soluble substances is the same, whether the impurity is silicon or graphite, or both silicon and graphite, the final lithium yield and the purity of lithium fluoride are the same.

[0027] In the present invention, preferably, the mesh size of the lithium-containing rare earth molten salt slag satisfies: 90% of the lithium-containing rare earth molten salt slag passes through a mesh size of 150-300 meshes, more preferably 180-250 meshes, for example 200 meshes.

[0028] In certain specific embodiments of the present invention, the mesh size of the lithium rare earth molten salt slag can be made to meet the above conditions through particle refinement treatment.

[0029] In the present invention, step S1, for example, undergoes the following reaction:

[0030] Re2O3+6H + = Re 3+ +3H2O;

[0031] Fe2O3+6H + = Fe 3+ +3H2O;

[0032] LiF=Li + +F - ;

[0033] Li2O+2H + =2Li + +H2O;

[0034] Re 3+ +F - = ReF3↓;

[0035] In step S1, lithium, iron, aluminum and part of rare earth elements in the lithium-containing rare earth molten salt slag enter into the solution, and the rare earth elements in the solution react with sodium fluoride to produce rare earth fluoride precipitate, that is, the acid-soluble slag contains rare earth fluoride precipitate.

[0036] In the present invention, in step S1, the temperature of the acid dissolution is preferably above 95°C.

[0037] In the present invention, in step S1, the acid dissolution time is more than 4 hours.

[0038] In the present invention, in step S1, the method for preparing the acid solution comprises the following steps: mixing concentrated hydrochloric acid and water.

[0039] Wherein, the mass concentration of the concentrated hydrochloric acid is preferably 36%-38%.

[0040] The mass ratio of the concentrated hydrochloric acid to water is preferably (1-4):(4-16), for example, 1.2:4.3.

[0041] The mass ratio of the lithium-containing rare earth molten salt slag to the concentrated hydrochloric acid is preferably 1:(1-4), for example, 1:1.2.

[0042] In the present invention, in step S1, the acidity of the acid solution is preferably 0.5-1 mol / L.

[0043] In the present invention, in step S1, the concentration of REO in the acid solution is preferably below 20 ppm. REO means oxides of rare earth elements, and the content of REO is used in the present invention to represent the content of rare earth elements.

[0044] In the present invention, in step S1, the concentration of fluorine in the acid solution is preferably 0.5-2 g / L, for example 0.98 g / L.

[0045] In the present invention, in step S1, the concentration of iron in the acid solution is preferably 10-40 g / L, for example, 26.43 g / L.

[0046] In the present invention, in step S1, the concentration of lithium in the acid solution is preferably greater than 3 g / L, for example, 3.53 g / L.

[0047] In the present invention, the mass content of each component in the acid slag means the mass percentage of each component in the acid slag.

[0048] In the present invention, in step S1, the mass content of REO in the acid slag is preferably 15%-85%, more preferably 70%-80%, for example 75.96%.

[0049] In the present invention, in step S1, the mass content of fluorine in the acid slag is preferably 5%-30%, for example, 24.28%.

[0050] In the present invention, in step S1, the mass content of iron in the acid slag is preferably 0-1%, for example 0.2%.

[0051] In the present invention, in step S1, the mass content of lithium element in the acid slag is preferably 0-0.1%, for example, 0.01%.

[0052] Step S1 of the present invention can selectively leach lithium, and can drive rare earth to the subsequent processing steps, without appearing in the callback treatment slag of step S2, thereby reducing its separation cost.

[0053] In the present invention, in step S1, the amount of sodium fluoride added can be calculated according to the following formula:

[0054]

[0055] Wherein, REO (g) is the mass of rare earth oxide in lithium rare earth molten salt slag, M is the average molecular weight of rare earth, m (g) is the mass of fluorine element in lithium rare earth molten salt slag, and the unit of sodium fluoride addition is g;

[0056] Among them, the REO test method can be the oxalate weight method, which is specifically: mixing lithium-containing rare earth molten salt slag and perchloric acid solution to dissolve all rare earth elements therein in the perchloric acid solution, and then adding excess oxalic acid solution to the above perchloric acid solution to convert the rare earth elements into oxalate rare earth precipitate, and burning the oxalate rare earth precipitate to obtain pure rare earth oxide. At this time, weigh the rare earth oxide and record the mass of the rare earth oxide. This value is the mass of the rare earth oxide in the lithium-containing rare earth molten salt slag.

[0057] Among them, the calculation method of M can be: according to the weighted average of the total molecular weight of different rare earth elements in the lithium rare earth molten salt slag, the value is generally 168.

[0058] Among them, the testing method of m can be: detection using a fluoride ion meter, specifically, weighing lithium-containing rare earth molten salt slag and placing it in a three-necked flask, adding aqua regia and perchloric acid to obtain a solution; turning on the condensing water, controlling the temperature of the electric furnace to adjust the temperature of the solution for distillation, and at the same time adjusting the water vapor flow rate to receive the distillate, transferring the distilled distillate to a volumetric flask, fixing the volume, and testing the fluoride ion selective electrode.

[0059] In the present invention, the above-mentioned addition amount of sodium fluoride can further reduce the cost and improve the economic benefit.

[0060] In a specific embodiment of the present invention, the mass ratio of the added sodium fluoride to the lithium-containing rare earth molten salt slag is 0.821:6.

[0061] In the present invention, step S2, for example, undergoes the following reaction:

[0062] Fe 3+ +OH - = Fe(OH)3↓;

[0063] Al 3+ +OH - = Al(OH)3↓;

[0064] Step S2 converts the iron ions and aluminum ions in the acid solution into hydroxide precipitates.

[0065] In the present invention, the liquid alkali is a solution containing alkaline substances.

[0066] In the present invention, in step S2, the liquid alkali is preferably a sodium hydroxide solution.

[0067] In certain specific embodiments of the present invention, the solvent of the sodium hydroxide solution is water.

[0068] In the present invention, in step S2, the concentration of the liquid alkali is preferably 5-10 mol / L, for example, 10 mol / L.

[0069] In the present invention, in step S2, after mixing with the liquid alkali, the pH value of the acid solution is preferably 3-4.

[0070] In the present invention, in step S2, the temperature of the callback treatment is preferably 40-60°C, for example, 50°C.

[0071] In the present invention, in step S2, the callback processing time is preferably 2-4 hours.

[0072] In the present invention, preferably, in step S2, the concentration of lithium element in the callback treatment solution is 3-5 g / L, for example, 3.12 g / L.

[0073] In the present invention, preferably, in step S2, the concentration of REO in the callback treatment solution is 0-0.1 g / L, for example, 0.02 g / L.

[0074] In the present invention, preferably, in step S2, the concentration of fluorine element in the callback treatment solution is 0-1 g / L, for example, 0.26 g / L.

[0075] In the present invention, preferably, in step S2, the concentration of the iron element in the callback treatment solution is 0-1 g / L, for example, 0.14 g / L.

[0076] In the present invention, step S3, for example, undergoes the following reaction:

[0077] Li + +F - =LiF↓.

[0078] In the present invention, in step S3, the pH value of the callback treatment solution is preferably 7.

[0079] In certain specific embodiments of the present invention, the pH value of the adjustment treatment solution can be adjusted using a sodium hydroxide solution.

[0080] In the present invention, in step S3, the temperature of the precipitation treatment is preferably above 95°C.

[0081] In the present invention, in step S3, the precipitation treatment time is preferably 1-2 hours.

[0082] In the present invention, in step S3, the amount of sodium fluoride added can be calculated according to the following formula:

[0083]

[0084] Wherein, V (L) is the volume of the callback treatment solution, and C (mol / L) is the concentration of lithium ions in the callback treatment solution.

[0085] The concentration of lithium ions in the callback treatment solution is tested by ICP.

[0086] In the present invention, the above-mentioned addition amount of sodium fluoride can further reduce the cost and improve the economic benefit.

[0087] In the present invention, in step S3, the purity of the lithium fluoride precipitate is preferably above 99%, for example, 99.14%.

[0088] In certain specific embodiments, in step S3, the lithium fluoride precipitate further includes MgO, SiO2, Fe2O3, SO4 2- and CaO.

[0089] In certain specific embodiments, the mass content of each component in the lithium fluoride precipitate can be determined by weighing a certain amount of lithium fluoride precipitate, mixing and dissolving it with perchloric acid to obtain a solution, diluting it to a fixed volume, and subjecting the solution sample to ICP detection.

[0090] In the present invention, in step S3, the concentration of lithium element in the fluorine-containing wastewater is preferably below 0.1 g / L, for example, 0.09 g / L.

[0091] In the present invention, in step S3, the concentration of REO in the fluorine-containing wastewater is preferably below 0.1 g / L, for example, 0.02 g / L.

[0092] In the present invention, in step S3, the concentration of fluorine in the fluorine-containing wastewater is preferably below 3 g / L, for example, 2.05 g / L.

[0093] In the present invention, in step S3, the concentration of iron in the fluorine-containing wastewater is preferably below 0.1 g / L.

[0094] In the present invention, preferably, the method for recovering lithium element further comprises the following steps:

[0095] S4, mixing the fluorine-containing wastewater and calcium hydroxide, and separating the solid and liquid to obtain calcium fluoride and wastewater.

[0096] Wherein, the addition amount of the calcium hydroxide can be calculated according to the following formula:

[0097]

[0098] Where V (L) is the volume of fluoride-containing wastewater, and C (mol / L) is the concentration of fluoride ions in the fluoride-containing wastewater.

[0099] Among them, the test method for the concentration of fluoride ions in fluoride-containing wastewater can be a spike method, using a fluoride ion meter for testing.

[0100] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0101] The reagents and raw materials used in the present invention are commercially available.

[0102] The positive and progressive effects of the present invention are:

[0103] The method for recovering lithium element of the present invention has high yield of lithium element and high purity of obtained lithium fluoride; meanwhile, the process flow of the present invention is simple, the operation difficulty is low, and the energy consumption cost can be saved.

[0104] Compared with the prior art, the selective leaching of lithium and rare earth elements can be achieved, which is beneficial to the subsequent recovery of rare earth elements and can improve the purity of lithium fluoride precipitation; the present invention does not have the problem of rare earth sulfate double salt precipitation, which is beneficial to the subsequent recovery of rare earth elements; the present invention can save the evaporation and concentration process, save energy consumption costs and operation difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0105] Figure 1 This is a schematic flow chart of the method for recovering lithium element in Example 1. DETAILED DESCRIPTION

[0106] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0107] Example 1

[0108] After the molten salt slag is pre-burned, lithium-containing rare earth molten salt slag is obtained. The raw material components of the lithium-containing rare earth molten salt slag are listed in the following Table 1:

[0109] Table 1

[0110]

[0111] In Table 1, other substances remaining in the lithium-containing rare earth molten salt slag are acid-insoluble impurities such as silicon and graphite.

[0112] In Table 1, the content of REO represents the content of rare earth elements. The content is determined by the oxalate weight method, specifically: mixing lithium-containing rare earth molten salt slag and perchloric acid solution, dissolving all rare earth elements therein in the perchloric acid solution, and then adding excess oxalic acid solution to the above perchloric acid solution to convert the rare earth elements into oxalate rare earth precipitate, and burning the oxalate rare earth precipitate to obtain pure rare earth oxides, at which time the rare earth oxides are weighed, and the content of the rare earth oxides is calculated, and the calculation formula is the mass of the rare earth oxide / the mass of the lithium-containing rare earth molten salt slag. Rare earth elements include one or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium.

[0113] The lithium rare earth molten salt slag is sent to the abrasive system for particle refinement treatment, so that the mesh size of the lithium rare earth molten salt slag meets the following requirements: 90% of the lithium rare earth molten salt slag passes through a mesh size of 200 meshes.

[0114] The schematic flow diagram of the method for recovering lithium element in Example 1 is as follows Figure 1 , specifically including the following steps:

[0115] Mixing concentrated hydrochloric acid with a mass concentration of 36%-38% with water to prepare a hydrochloric acid solution, wherein the mass ratio of concentrated hydrochloric acid to water is 1.2:4.3;

[0116] S1. Place 6 kg of lithium-containing rare earth molten salt slag in the above hydrochloric acid solution (the mass ratio of lithium-containing rare earth molten salt slag to concentrated hydrochloric acid is 1:1.2), add sodium fluoride thereto and dissolve it in acid at a temperature of 95°C for 4 hours, separate the solid and the liquid, and obtain acid-dissolved slag and 251 L of acid solution;

[0117] Among them, the mass of added sodium fluoride is calculated according to the following formula:

[0118]

[0119] Wherein, REO (g) is the mass of rare earth oxide in lithium rare earth molten salt slag, M is the average molecular weight of rare earth, m (g) is the mass of fluorine element in lithium rare earth molten salt slag, and the unit of sodium fluoride addition is g;

[0120] Among them, the REO test method is the oxalate weight method, which is specifically: mixing lithium-containing rare earth molten salt slag and perchloric acid solution to dissolve all rare earth elements therein in the perchloric acid solution, and then adding excess oxalic acid solution to the above perchloric acid solution to convert the rare earth elements into oxalate rare earth precipitate, and burning the oxalate rare earth precipitate to obtain pure rare earth oxide. At this time, weigh the rare earth oxide and record the mass of the rare earth oxide. This value is the mass of the rare earth oxide in the lithium-containing rare earth molten salt slag.

[0121] Among them, M is counted as 168.

[0122] Among them, the testing method of m is: detection using a fluoride ion meter, specifically, weighing lithium-containing rare earth molten salt slag and placing it in a three-necked flask, adding aqua regia and perchloric acid to obtain a solution; turning on the condensing water, controlling the temperature of the electric furnace to adjust the temperature of the solution for distillation, and at the same time adjusting the water vapor flow rate to receive the distillate, transferring the distilled distillate to a volumetric flask, fixing the volume, and testing the fluoride ion selective electrode.

[0123] According to the above formula, the mass of sodium fluoride added is 821g.

[0124] The acidity of the acid solution is 1 mol / L, the concentration of REO in the acid solution is 20 ppm, and the components and contents of the acid slag and the acid solution are listed in Table 2 below:

[0125] Table 2

[0126]

[0127] The test method for the mass content of the components of the acid slag is as follows: a certain amount of acid slag is taken once, and it is completely dissolved with perchloric acid. The content of REO is determined and calculated by the oxalate weight method, and the concentration of other elements is determined by ICP and converted into mass fraction.

[0128] The test method for the concentration of the components of the acid solution is as follows: the content of REO is determined and calculated by the oxalate weight method, and the concentration of other elements is determined by ICP.

[0129] S2. Take 500mL of the above acid solution and place it in a water bath heating beaker, slowly add 10mol / L sodium hydroxide aqueous solution to mix (the pH value of the acid solution after mixing is 4), and perform adjustment treatment at 50°C for 2h, separate the solid and liquid, and obtain adjustment treatment residue and adjustment treatment liquid; among which, the composition and content of the adjustment treatment liquid, the content of REO is determined and calculated by the oxalate weight method, and the rest is tested by ICP.

[0130] The composition and content of the callback treatment solution are listed in Table 3 below:

[0131] Table 3

[0132]

[0133] S3. The pH value of the above-mentioned callback treatment liquid is adjusted to 7 with sodium hydroxide solution, 500 mL of the callback treatment liquid is placed in a water bath heating beaker, sodium fluoride is slowly added, and precipitation treatment is carried out at 95° C. for 1 hour, and solid-liquid separation is performed to obtain lithium fluoride precipitate and fluoride-containing wastewater; the lithium fluoride precipitate is dried at 60° C. for 8 hours, and its composition and content are determined.

[0134] Wherein, the amount of sodium fluoride added is calculated according to the following formula:

[0135]

[0136] Wherein, V (L) is the volume of the callback treatment solution, and C (mol / L) is the concentration of lithium ions in the callback treatment solution.

[0137] Among them, after the above calculation, the amount of sodium fluoride added is 5g.

[0138] Among them, the composition and content of lithium fluoride precipitate are listed in the following Table 4:

[0139] Table 4

[0140]

[0141] The other components in Table 4 are some inevitable impurities. The mass content of each component in Table 4 is determined by weighing a certain amount of lithium fluoride precipitate, mixing and dissolving it with perchloric acid to obtain a solution, diluting it to a fixed volume, and subjecting the solution sample to ICP detection.

[0142] Among them, the composition and content of fluoride-containing wastewater are listed in the following Table 5:

[0143] Table 5

[0144]

[0145] The concentration of lithium in the fluoride-containing wastewater in Example 1 is 0.09 g / L, and the yield of lithium element is 94.68%. The mass of the lithium fluoride precipitate is 5.51 g, and the purity of the lithium fluoride precipitate is 99.14%, which meets the requirements of industrial-grade lithium fluoride.

[0146] The calculation method of the yield of lithium element is:

[0147] In the 251L acid solution formed by S1, the mass of lithium is 6kg*1.29%=0.774kg;

[0148] The mass of lithium in S3 lithium fluoride precipitate is 5.51g*99.14%*(6.9 / 25.9)=1.46g;

[0149] S3 takes 500mL of callback treatment solution, that is, its scaling ratio is 251L / 500mL=502; among which, the change in solution volume from S2 to S3 can be ignored;

[0150] The yield of lithium element is: 1.46g*502 / 0.774kg=94.68%.

[0151] The yield of lithium element in step S3 was calculated as follows: 1-[(0.09 g / L*500mL) / (3.12 g / L*500mL)]=97%.

[0152] Comparative Example 1

[0153] The lithium rare earth molten salt slag of Comparative Example 1 is the same as that of Example 1.

[0154] In the method for recovering lithium element of Comparative Example 1, except that sodium fluoride is not added in step S1, other conditions are the same as those of Example 1.

[0155] The acidity of the acid solution formed in Comparative Example 1 is 1 mol / L, the concentration of REO in the acid solution is 2670 ppm, and the components and contents of the acid slag and the acid solution are listed in Table 6 below:

[0156] Table 6

[0157]

[0158] According to the above table, comparative example 1 does not use sodium fluoride, resulting in a large amount of rare earth elements remaining in the acid solution. These rare earth elements will enter the subsequent steps S2 and S3, which is not conducive to improving the recovery rate of rare earths and the purity of lithium fluoride precipitation.

[0159] Comparative Example 2

[0160] The lithium rare earth molten salt slag of Comparative Example 2 is the same as that of Example 1.

[0161] In the method for recovering lithium element of Comparative Example 2, in step S3, the addition of sodium fluoride is replaced by the addition of sodium carbonate, and the other conditions are the same as those in Example 1.

[0162] Comparative Example 2 obtained lithium carbonate precipitate and fluorine-containing wastewater, the composition and content of the fluorine-containing wastewater are listed in the following Table 7:

[0163] Table 7

[0164]

[0165] The concentration of lithium in the fluoride-containing wastewater in Comparative Example 2 is 1.15 g / L, and the yield of lithium element in step S3 is 63%.

[0166] The specific calculation is: 1-[(1.15 g / L*500mL) / (3.12 g / L*500mL)]=63%.

[0167] It can be seen from the above data that the use of sodium carbonate instead of sodium fluoride in Comparative Example 2 is not conducive to the yield of lithium element in step S3, and thus is not conducive to the yield of lithium element in the entire process.

Claims

1. A method for recovering lithium, characterized in that: It includes the following steps: S1, mixing lithium rare earth molten salt slag, acid solution and sodium fluoride for acid dissolution, solid-liquid separation, to obtain acid-dissolved slag and acid solution; the acid solution comprises hydrochloric acid; S2, mixing the acid solution and liquid alkali for callback treatment, and separating the solid and liquid to obtain callback treatment slag and callback treatment liquid; S3, mixing the callback treatment liquid and sodium fluoride for precipitation treatment, and separating the solid and liquid to obtain lithium fluoride precipitate and fluorine-containing wastewater.

2. The method for recovering lithium element as claimed in claim 1, characterized in that: The lithium-containing rare earth molten salt slag includes rare earth elements and lithium elements, and the rare earth elements include, for example, one or more of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium; And / or, the lithium-containing rare earth molten salt slag is rare earth reduction slag and / or rare earth molten salt slag; And / or, the mass content of lithium element in the lithium-containing rare earth molten salt slag is 1%-5%, for example, 1.29%; And / or, the mass content of REO in the lithium rare earth molten salt slag is 10%-80%, for example, 64.57%; And / or, the lithium-containing rare earth molten salt slag further includes fluorine element, wherein, preferably, the mass content of fluorine element in the lithium-containing rare earth molten salt slag is 3%-25%, for example, 16.28%; And / or, the lithium-containing rare earth molten salt slag further includes iron, wherein, preferably, the mass content of iron in the lithium-containing rare earth molten salt slag is 2%-30%, for example, 14.74%; And / or, the mesh size of the lithium-containing rare earth molten salt slag satisfies: 90% of the lithium-containing rare earth molten salt slag passes through a mesh size of 150-300 meshes, preferably 180-250 meshes, for example 200 meshes.

3. The method for recovering lithium element as claimed in claim 1, characterized in that: In step S1, the temperature of the acid dissolution is preferably above 95°C; And / or, in step S1, the acid dissolution time is more than 4 hours; And / or, in step S1, the method for preparing the acid solution comprises the following steps: mixing concentrated hydrochloric acid and water; Wherein, the mass concentration of the concentrated hydrochloric acid is preferably 36%-38%; The mass ratio of the concentrated hydrochloric acid to water is preferably (1-4): (4-16), for example, 1.2:4.3; The mass ratio of the lithium-containing rare earth molten salt slag to the concentrated hydrochloric acid is preferably 1:(1-4), for example, 1:1.

2.

4. The method for recovering lithium element as claimed in claim 1, characterized in that: In step S1, the acidity of the acid solution is 0.5-1 mol / L; and / or, in step S1, the concentration of REO in the acid solution is less than 20 ppm; And / or, in step S1, the concentration of fluorine in the acid solution is 0.5-2 g / L, for example, 0.98 g / L; And / or, in step S1, the concentration of iron in the acid solution is 10-40 g / L, for example, 26.43 g / L; And / or, in step S1, the concentration of lithium element in the acid solution is greater than 3 g / L, for example, 3.53 g / L.

5. The method for recovering lithium element as claimed in claim 1, characterized in that: In step S1, the mass content of REO in the acid slag is 15%-85%, preferably 70%-80%, for example 75.96%; And / or, in step S1, the mass content of fluorine in the acid slag is 5%-30%, for example, 24.28%; And / or, in step S1, the mass content of iron in the acid slag is 0-1%, for example, 0.2%; And / or, in step S1, the mass content of lithium element in the acid slag is 0-0.1%, for example, 0.01%; And / or, in step S1, the amount of sodium fluoride added is calculated according to the following formula: Wherein, REO (g) is the mass of rare earth oxide in the lithium-containing rare earth molten salt slag, M is the average molecular weight of rare earth, m (g) is the mass of fluorine element in the lithium-containing rare earth molten salt slag, and the unit of the amount of sodium fluoride added is g.

6. The method for recovering lithium element as claimed in claim 1, characterized in that: In step S2, the liquid alkali is a sodium hydroxide solution; And / or, in step S2, the concentration of the liquid caustic soda is preferably 5-10 mol / L, for example, 10 mol / L; and / or, in step S2, after mixing with the liquid alkali, the pH value of the acid solution is 3-4; And / or, in step S2, the temperature of the callback treatment is preferably 40-60° C., for example, 50° C.; And / or, in step S2, the callback processing time is 2-4 hours.

7. The method for recovering lithium element as claimed in claim 1, characterized in that: In step S2, the concentration of lithium in the callback treatment solution is 3-5 g / L, for example, 3.12 g / L; And / or, in step S2, the concentration of REO in the callback treatment solution is 0-0.1 g / L, for example, 0.02 g / L; And / or, in step S2, the concentration of fluorine in the callback treatment solution is 0-1 g / L, for example, 0.26 g / L; And / or, in step S2, the concentration of iron in the callback treatment solution is 0-1 g / L, for example, 0.14 g / L.

8. The method for recovering lithium element as claimed in claim 1, characterized in that: In step S3, the pH value of the callback treatment solution is 7; and / or, in step S3, the temperature of the precipitation treatment is above 95°C; And / or, in step S3, the precipitation treatment time is 1-2h; And / or, in step S3, the amount of sodium fluoride added can be calculated according to the following formula: Wherein, V (L) is the volume of the callback treatment solution, and C (mol / L) is the concentration of lithium ions in the callback treatment solution.

9. The method for recovering lithium element as claimed in claim 1, characterized in that: In step S3, the purity of the lithium fluoride precipitate is above 99%, for example, 99.14%. And / or, in step S3, the concentration of lithium in the fluorine-containing wastewater is less than 0.1 g / L, for example, 0.09 g / L; And / or, in step S3, the concentration of REO in the fluorine-containing wastewater is less than 0.1 g / L, for example, 0.02 g / L; And / or, in step S3, the concentration of fluorine in the fluorine-containing wastewater is less than 3 g / L, for example, 2.05 g / L; And / or, in step S3, the concentration of iron in the fluorine-containing wastewater is below 0.1 g / L.

10. The method for recovering lithium element according to claim 1, characterized in that: The method for recovering lithium element further comprises the following steps: S4, mixing the fluorine-containing wastewater and calcium hydroxide, and performing solid-liquid separation to obtain calcium fluoride and wastewater; Wherein, the addition amount of the calcium hydroxide can be calculated according to the following formula: Where V (L) is the volume of fluoride-containing wastewater, and C (mol / L) is the concentration of fluoride ions in the fluoride-containing wastewater.

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