Iron phosphate adsorbent and use thereof in pre-concentration of low-concentration lithium-containing solution

Abstract

The present invention provides an iron phosphate adsorbent used in pre-concentration of a low-concentration lithium-containing solution. The iron phosphate adsorbent is a mixture of ferric phosphate and a calcium compound, and the mass ratio of the mixture is: ferric phosphate:calcium compound=1:(0.1-1). The present invention further provides a use of an iron phosphate adsorbent in pre-concentration of a low-concentration lithium-containing solution. The adsorbent of the present invention has low cost and simple preparation method, and preliminary concentration of a low-concentration lithium-containing solution can be achieved without adding an organic matter and using the technical means of evaporation for concentration, thereby avoiding organic pollution and reducing energy consumption.

Description

Phosphorus iron salt adsorbent and application thereof in pre-concentration of low-concentration lithium-containing solution TECHNICAL FIELD

[0001] The present application belongs to the field of lithium adsorbent, and particularly relates to a phosphorus iron salt adsorbent and application thereof in pre-concentration of low-concentration lithium-containing solution. BACKGROUND

[0002] At present, evaporation is often used to concentrate the solution with low lithium concentration. Obviously, this not only consumes a lot of energy, but also the impurities in the solution will be concentrated together with lithium, resulting in low purity of the product obtained by subsequent lithium precipitation. Subsequently, an extraction method is developed, in which N523 and TBP are used as extractants to separate lithium from the solution, which plays a good purification role. However, the extractants are all organic substances, and flammable substances such as sulfonated kerosene are often used as diluents in the production process, which has high safety requirements. In addition, since the organic substances will be partially dissolved in the solution system, forming organic wastewater, which will increase the difficulty of wastewater treatment. Therefore, the current research direction is more active in inorganic adsorbents. The reported inorganic adsorbents include aluminum-based adsorbents, manganese-based adsorbents, titanium-based adsorbents, etc. Among them, the aluminum-based adsorbent has been widely used in large-scale industrial applications. Other adsorbents have not been popularized due to the reasons of difficult preparation, high price, high solution loss rate, etc. However, the aluminum-based adsorbent has a fatal defect, that is, it only has a separation function for lithium and has very limited enrichment capacity. In order to achieve further concentration, evaporation is still needed. How to economically and efficiently enrich the low-concentration lithium-containing solution is still a big problem in the industry.

[0003] After searching, the existing adsorbents and methods for enriching low-concentration lithium-containing solution are as follows:

[0004] CN117999120A discloses a preparation method of a granular lithium adsorbent, which comprises the following steps: mixing a lithium adsorbent or a precursor powder thereof, a plurality of polymers, a pore former and an organic solvent under normal pressure and at a temperature of 10-190 DEG C, stirring for 1-120 min to obtain a uniform mixture; dropping the uniform mixture into a solution, or crushing the extruded uniform mixture to obtain a granular lithium adsorbent after washing.

[0005] CN117999120A discloses a preparation method and application and device of an aluminum salt lithium adsorbent, belonging to the field of new materials and salt lake chemical technology, the preparation method comprising the following steps: washing lithium carbonate with pure water to remove water-soluble impurities, and preparing lithium carbonate slurry from the filter cake at a certain ratio; introducing CO2 gas into the lithium carbonate slurry to perform a hydrogenation reaction, and obtaining hydrogenated liquid after filtering the reaction slurry; introducing the hydrogenated liquid into an ion exchange resin column to perform a refining and impurity removal process, and obtaining refined hydrogenated liquid; performing a precipitation reaction on the refined hydrogenated liquid and an aluminum salt solution, and obtaining a powdery aluminum salt lithium adsorbent after filtration; and mixing the powdery aluminum salt lithium adsorbent, an adhesive, and a solvent in a mixing device, and obtaining the same through an extrusion granulation process, and simultaneously providing a method and device for preparing battery-grade lithium carbonate based on the aluminum salt lithium adsorbent.

[0006] The above adsorbents have complex compositions and high costs, and it is of great significance to develop an adsorbent and method which are simple in technical scheme, low in cost, and free of evaporation and lithium enrichment. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a phosphorus iron salt adsorbent and its application in low-concentration lithium-containing solution pre-enrichment, which is low in cost, simple in preparation method, free of organic matter addition, and can realize the preliminary enrichment of low-concentration lithium-containing solution without using evaporation and concentration technical means, thereby avoiding organic pollution and saving energy consumption.

[0008] The method of the present application is mainly used for lithium-containing solutions with a lithium ion concentration of less than 1 g / L. Low-concentration lithium-containing solutions are generally derived from two sources: one is a lithium-containing salt lake, which generally contains 50-600 mg / L of lithium, and a high amount of sodium, potassium and other salts, and some salt lakes also contain a high amount of magnesium ions; the other is an intermediate solution generated during the lithium extraction process, such as an intermediate solution containing 100-300 mg / L of lithium generated after the use of sodium carbonate to precipitate lithium and the subsequent use of phosphate to precipitate. The above solutions can obtain relatively pure low-lithium solutions after separation by aluminum-based adsorbents, but only impurities can be removed, and good enrichment cannot be achieved.

[0009] To achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0010] The present application provides a phosphorus iron salt adsorbent for low-concentration lithium-containing solution pre-enrichment, which is a mixture of iron phosphate and calcium compounds, and the mass ratio of the mixture is iron phosphate: calcium compound = 1: (0.1-1); the calcium compound includes one or more of calcium chloride, calcium oxide, calcium hydroxide, and calcium nitrate; and the phosphorus iron salt adsorbent is used for low-concentration lithium-containing solution pre-enrichment.

[0011] Preferably, the mass ratio of the mixture is: iron phosphate: calcium compound = 1: (0.1-0.5).

[0012] Preferably, the primary nucleation particle size of the iron phosphate is less than 2000 nm. Controlling the particle size in this range can improve the adsorption effect of the adsorbent.

[0013] Preferably, the primary nucleation particle size of the iron phosphate is less than 1000 nm. Further preferably, the primary nucleation particle size of the iron phosphate is less than 200 nm.

[0014] The application also provides the use of the phosphorus iron salt adsorbent in the pre-concentration of low-concentration lithium-containing solutions. The phosphorus iron salt adsorbent is iron phosphate, or the phosphorus iron salt adsorbent described above.

[0015] Preferably, the use of the phosphorus iron salt adsorbent in the pre-concentration of low-concentration lithium-containing solutions specifically includes the following steps:

[0016] (1) 1-200 g of the adsorbent described in claim 5 is added to 1 L of a low-concentration lithium-containing solution, the pH is adjusted to 8-13 using an alkaline substance, and the mixture is reacted at 0-100 ℃ for 10 min-12 h. The liquid and solid are then separated, and the adsorption is completed. The low-concentration lithium-containing solution has a lithium ion concentration of less than 1 g / L.

[0017] (2) The adsorbent after adsorbing lithium is washed several times with water, and then acid is added to adjust the pH to 1-5. The mixture is reacted at 0-100 ℃ for 10 min-12 h, the liquid and solid are separated, and the desorption is completed. A lithium-containing pre-concentration solution and a filter cake are obtained, and the filter cake is washed to obtain a regenerated adsorbent.

[0018] Preferably, the low-concentration lithium-containing solution has a lithium ion concentration of less than 1 g / L, and preferably a lithium ion concentration of 10-600 mg / L.

[0019] Preferably, the alkaline substance includes one or a combination of sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide, and ammonia.

[0020] Preferably, the acid includes one or a combination of sulfuric acid, hydrochloric acid, and nitric acid.

[0021] Preferably, the pH in step (1) is adjusted to 10-12. The method for using the adsorbent of the application needs to be controlled in an alkaline environment. If it is in an acidic environment, the adsorbent of the application cannot enrich lithium.

[0022] Preferably, step (2) obtains a lithium-containing pre-concentration solution with a concentration greater than 1 g / L, and preferably a lithium-containing pre-concentration solution with a concentration of 1.5-6 g / L.

[0023] Preferably, the water washing in step (2) is 1-3 times of hot water washing at 40ºC-100ºC. The mass of water has no fixed requirement, and 1-2 times of the mass of the filter cake obtained after lithium adsorption and filtration can be used for hot water washing.

[0024] Preferably, the filter cake is washed with an acid solution with pH=2~6 until the lithium content in the filtrate is ≤0.5mg / L to obtain the regenerated adsorbent; further preferably, the acid solution has pH=2~3.

[0025] Further preferably, step (1) is 20~100g of adsorbent for 1L of low-concentration lithium-containing solution.

[0026] Further preferably, step (1) is 1~8h of reaction at 20℃~ 80℃.

[0027] Further preferably, step (2) is 1~8h of reaction at 20℃~ 80℃.

[0028] The present application is further explained and described below

[0029] In an alkaline environment, the surface of iron phosphate will be hydroxylated and negatively charged, while lithium ions are positively charged, so they can be adsorbed on the surface of iron phosphate by electrostatic attraction; at the same time, the surface of iron phosphate has a large number of phosphorus-containing groups, and since lithium ions have a tendency to form precipitates with phosphate ions, they can be strongly attracted by these surface phosphorus-containing groups. From the microscopic level, the similarities and differences in the structure and morphology of particles are the key factors that determine the arrangement and density of active sites on the surface, thereby affecting the capture of target particles. This study found that the addition of calcium compounds during the adsorption process can significantly improve the adsorption effect of iron phosphate on lithium. This study further found that the primary nucleation particle size of iron phosphate particles has a great influence on their adsorption performance, so by controlling or selecting the primary particle characteristics of iron phosphate, iron phosphate with different adsorption capacities can be obtained. At present, many academic papers and patents have studied the preparation of iron phosphate, and the related technology is relatively mature, and the main use is as a precursor of lithium iron phosphate, but this application has found another new use of iron phosphate.

[0030] The primary nucleation particle size (also called primary particle size, primary particle, and original particle size) in the present application refers to the particle size of a single fine crystal grain produced in the chemical crystallization process. The secondary particle size (secondary particle) refers to the particle size of the agglomerated particles. The present application only limits the primary particle size (primary nucleation particle size) and does not limit the secondary particle size, because we have found through experimental research that as long as the primary particle size is within the control range of the present application, even if the secondary particle size is large (several hundred microns), the present application can still be realized.

[0031] Due to the existence of agglomeration, the secondary particle size is usually obtained by using a laser particle size analyzer, and only under the observation of analysis equipment such as a scanning electron microscope (SEM), a transmission electron microscope (TEM) and a tunnel scanning electron microscope (STM), the morphology and particle size (i.e. primary particle size) of primary grains can be observed. For amorphous particles, there also exist primary particles and agglomerated particles.

[0032] Compared with the prior art, the advantages of the present application are:

[0033] 1. The phosphorus iron salt adsorbent has low cost, simple preparation and use method, does not add organic matter, and can realize preliminary enrichment of low-concentration lithium-containing solution without using evaporation concentration technical means, thereby avoiding organic pollution and saving energy consumption.

[0034] 2. The phosphorus iron salt adsorbent can enrich lithium-containing solution with a concentration less than 1 g / L to lithium-containing pre-enriched solution with a concentration of 1.5-6 g / L, thereby changing waste into treasure, changing raw materials or intermediates that are difficult to utilize in the prior art into raw materials that can be further processed, and having good enrichment effect.

[0035] 3. The phosphorus iron salt adsorbent can be regenerated and reused in the application process.

[0036] The detailed structure of the present application is further described below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0037] Fig. 1 is an XRD pattern of the adsorbent prepared in Example 1;

[0038] Fig. 2 is an SEM pattern of the adsorbent prepared in Example 1;

[0039] Fig. 3 is an XRD pattern of the adsorbent prepared in Example 7;

[0040] Fig. 4 is an SEM pattern of the adsorbent prepared in Example 7;

[0041] Fig. 5 is an SEM pattern of the adsorbent used in Example 9;

[0042] Fig. 6 is an XRD pattern of the adsorbent used in Example 10;

[0043] Fig. 7 is an SEM pattern of the adsorbent used in Example 10;

[0044] Fig. 8 is an XRD pattern of the adsorbent used in Comparative Example 1;

[0045] Fig. 9 is an SEM pattern of the adsorbent used in Comparative Example 1;

[0046] Fig. 10 is an XRD pattern of the adsorbent used in Comparative Example 4;

[0047] Figure 11 is an SEM image of the adsorbent used in Comparative Example 4. DETAILED DESCRIPTION Example 1

[0048] Preparation of iron phosphate: a 5 L solution containing 0.5 mol / L of phosphorus (sodium phosphate dodecahydrate as phosphorus source) was prepared, and the pH was adjusted to 2 using sulfuric acid. 2.5 mol of ferrous sulfate heptahydrate was added, and after complete dissolution, 1.5 mol of hydrogen peroxide was added under stirring. The solution was heated to boiling and reacted for 2 h. The product was filtered, washed thoroughly with water, and dried to obtain iron phosphate.

[0049] Figure 1 is an XRD characterization image of the adsorbent prepared in Example 1, which shows no complete peaks and is amorphous. Figure 2 is an SEM image of the adsorbent prepared in Example 1. As can be seen from Figure 2, the particles are aggregates of primary fine particles with irregular shapes. The particle sizes of the primary fine particles are extremely small, and the particle sizes of 10 randomly marked particles were between 37 and 63 nm using the software Nano Measurer. Other primary fine particles are mostly similar.

[0050] 20 g of the above iron phosphate was added to a 1 L solution containing 505 mg / L of lithium. The main other components in the solution were sodium sulfate 50.23 g / L, and the pH of the solution was 6.84. The pH of the solution was adjusted to 10 using sodium hydroxide, and the solution was reacted for 2 h at 30 °C under stirring. The product was filtered to obtain 41.43 g of lithium-containing adsorbent (water content 50.64%), and the adsorbed solution was obtained at the same time. The lithium concentration of the adsorbed solution was reduced to 358.16 mg / L, and the lithium adsorption capacity was 7.34 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent was washed three times with hot water at 60 °C, 50 mL of water was added, and the system was stirred uniformly. The pH of the system was adjusted to 3 using sulfuric acid, and the system was reacted for 2 h at 30 °C under stirring. The product was filtered to obtain a lithium-containing solution and a filter cake. The lithium content in the solution was 2.02 g / L, which achieved the purpose of pre-concentration.

[0051] The filter cake was washed with a sulfuric acid solution with a pH of 2-3 until the lithium content in the filtrate was ≤0.5 mg / L to obtain a regenerated adsorbent. The regenerated adsorbent was operated according to the procedure of Example 1, and the adsorption capacity could still reach 7.29 mg / g.

[0052] Example 2: Mixed adsorbent I

[0053] Take 20 g of iron phosphate prepared in Example 1 and 6 g of calcium chloride, and then put them into 1 L of a solution containing 505 mg / L of lithium. The other main components in the solution are mainly sodium sulfate 50.23 g / L. The pH of the solution is 6.84. The pH of the solution is adjusted to 12 by sodium hydroxide. The solution is stirred at 20 °C for 1 h. Filtration is performed to obtain 43.18 g of lithium-containing adsorbent (moisture content 49.94%) and a solution after adsorption. The lithium concentration in the solution after adsorption is reduced to 201.59 mg / L. The lithium adsorption capacity is 15.17 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed with 95 °C hot water three times. 50 mL of water is added, and the system is stirred uniformly. The pH of the system is adjusted to 2 by hydrochloric acid. The solution is stirred at 30 °C for 1 h. Filtration is performed to obtain a lithium-containing solution. The lithium content in the solution is 4.11 g / L, which achieves the purpose of pre-concentration.

[0054] Example 3 Mixed adsorbent II

[0055] Take 30 g of iron phosphate prepared in Example 1 and 6 g of calcium oxide, and then put them into 1 L of a solution containing 443.4 mg / L of lithium (the pH of the original solution is 5.66). The other main components in the solution are mainly sodium sulfate 10.11 g / L and potassium sulfate 1.58 g / L. The pH of the solution after the adsorbent is put in is 12.79. The solution is stirred at 20 °C for 5 h. Filtration is performed to obtain 62.78 g of lithium-containing adsorbent (moisture content 48.33%) and a solution after adsorption. The lithium concentration in the solution after adsorption is reduced to 1.31 mg / L. The lithium adsorption capacity is 14.74 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed with 95 °C hot water once. 70 mL of water is added, and the system is stirred uniformly. The pH of the system is adjusted to 2 by sulfuric acid. The solution is stirred at 20 °C for 3 h. Filtration is performed to obtain a lithium-containing solution. The lithium content in the solution is 4.25 g / L, which achieves the purpose of pre-concentration.

[0056] Example 4 High-salt solution containing magnesium

[0057] Take 20 g of iron phosphate prepared in Example 1 and 4 g of calcium oxide, mix them, and then put them into a 2 L solution containing 511.4 mg / L of lithium. The other main components in the solution are mainly sodium sulfate 101.3 g / L and magnesium sulfate 52.3 g / L. After the calcium oxide is put into the solution containing lithium, the pH increases to 11.5. Under stirring, the reaction is carried out at 25 °C for 1 h, and then filtration is performed. As a result, 40.1 g of lithium-containing adsorbent (with a water content of 50.35%) is obtained, and at the same time, the solution after adsorption is obtained. It is determined that the lithium concentration in the solution after adsorption is reduced to 439.76 mg / L, and it can be seen that the lithium adsorption amount is 7.16 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed with 95 °C hot water three times, 50 mL of water is added, and the system is stirred uniformly. Hydrochloric acid is used to adjust the pH of the system to 2. Under stirring, the reaction is carried out at 25 °C for 1 h, and then filtration is performed. As a result, a lithium-containing solution is obtained. It is determined that the lithium content in the solution is 1.98 g / L, which achieves the purpose of pre-concentration.

[0058] Example 5 Lithium-containing solution with ultra-low concentration

[0059] Take 20 g of iron phosphate prepared in Example 1 and 8 g of calcium hydroxide, mix them, and then put them into a 10 L solution containing 10.24 mg / L of lithium. After the calcium hydroxide is put into the solution containing lithium, the pH increases to 12. Under stirring, the reaction is carried out at 25 °C for 1 h, and then filtration is performed. As a result, 41.23 g of lithium-containing adsorbent (with a water content of 51.11%) is obtained, and at the same time, the solution after adsorption is obtained. It is determined that the lithium concentration in the solution after adsorption is reduced to 0.053 mg / L, and it can be seen that the lithium adsorption amount is 5.09 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed with 95 °C hot water once, 50 mL of water is added, and the system is stirred uniformly. Sulfuric acid is used to adjust the pH of the system to 2. Under stirring, the reaction is carried out at 25 °C for 2 h, and then filtration is performed. As a result, a lithium-containing solution is obtained. It is determined that the lithium content in the solution is 1.38 g / L, which achieves the purpose of pre-concentration.

[0060] Example 6 Comparison of adsorption capacity of mixed adsorbent in high-salt solution

[0061] Take 20 g of the adsorbent prepared in Example 1, 4 parts, 1 part alone, and the other 3 parts mixed with calcium-containing additives (additive dosage is based on the amount of calcium, all containing calcium 2.86 g), of which 1 part is mixed with 4 g of calcium oxide (containing calcium about 2.86 g), 1 part is mixed with 10.52 g of calcium chloride dihydrate (containing calcium about 2.86 g), and 1 part is mixed with 16.87 g of calcium nitrate tetrahydrate (containing calcium about 2.86 g). Then put into 2 L of lithium-containing solution 487.12 mg / L, the main components of the solution are sodium sulfate 100 g / L, adjust the pH of the solution to 12 with sodium hydroxide (the adsorbent mixed with calcium oxide does not need to be adjusted, after being put into the lithium-containing solution, the pH rises to 12.08), then react for 1 h at 25°C under stirring, filter, measure the lithium content in the filtrate, and calculate the lithium adsorption amount (calculated on the basis of iron phosphate dry). Table 1 is the adsorption effect comparison of Example 6. As can be seen from Table 1, under the same conditions, the adsorption effect of adding calcium salt additives is obviously better than that of using the adsorbent alone, and the adsorption amount of using the adsorbent alone is only 2.78 mg / g, which is difficult to resolve to more than 1 g / L.

[0062] Table 1 Comparison of the effects of different additives and iron phosphate adsorbent alone

[0063] Additive No calcium chloride calcium nitrate Filtrate concentration Lithium adsorption amount 459.34 mg / L 415.12 mg / L 413.5 mg / L 416.22 mg / L 2.78 mg / g 7.2 mg / g 7.36 mg / g 7.09 mg / g

[0064] Example 7

[0065] Preparation of iron phosphate: prepare 5 L of a solution containing 0.2 mol / L of phosphorus (sodium phosphate dodecahydrate as phosphorus source), adjust the pH to 2 with sulfuric acid, heat to 80°C, then add 5 L of a solution containing 0.2 mol / L of iron (ferric chloride hexahydrate as iron source) under stirring, react for 2 h, filter, wash thoroughly with water, and dry to obtain iron phosphate.

[0066] Figure 3 is the XRD pattern of the adsorbent prepared in Example 7, which has no complete peak and is amorphous. Figure 4 is the SEM pattern of the adsorbent prepared in Example 7, which can be seen that the primary particles are similar to spherical shape, and there is a clear boundary between adjacent ones, and the particle size is much larger than that of Example 1, the mark 10 in the figure is in the range of 510-810 nm, and the particle sizes of other primary particles are also mostly similar to this.

[0067] Take 20 g of the above iron phosphate into 1 L of a solution containing lithium 505 mg / L, the other main components in the solution are mainly sodium sulfate 50.23 g / L, the solution pH is 6.84, adjust the solution pH to 12 with sodium hydroxide, under stirring conditions at 20 °C for 1 h, filter, get lithium-containing adsorbent 41.17 g (water content 49.84%), at the same time get the adsorbed solution, by measuring, the lithium concentration of the adsorbed solution is reduced to 393.12 mg / L, the lithium adsorption capacity is 5.59 mg / g (calculated on the dry basis of iron phosphate). The lithium-containing adsorbent is washed with 90 °C hot water three times, add 60 mL of water, stir evenly, adjust the system pH to 3 with sulfuric acid, under stirring conditions at 80 °C for 1 h, filter, get the lithium-containing solution, by measuring, the solution contains lithium 1.27 g / L, reaching the purpose of pre-concentration.

[0068] Example 8 In this embodiment, the lithium concentration of the lithium-containing solution is lower, and the adsorbent dosage is larger

[0069] Take 50 g of the iron phosphate prepared in Example 7 and 10 g of calcium oxide, and put them into 1 L of a solution containing lithium 241.9 mg / L (the original solution pH is 6.76), the other main components in the solution are mainly sodium sulfate 5.23 g / L, the solution pH after putting in the adsorbent is 12.11, under stirring conditions at 20 °C for 1 h, filter, get lithium-containing adsorbent 101.86 g (water content 49.74%), at the same time get the adsorbed solution, by measuring, the lithium concentration of the adsorbed solution is reduced to 0.44 mg / L, the lithium adsorption capacity is 4.83 mg / g (calculated on the dry basis of iron phosphate). The lithium-containing adsorbent is washed with 95 °C hot water once, add 100 mL of water, stir evenly, adjust the system pH to 2 with sulfuric acid, under stirring conditions at 20 °C for 1 h, filter, get the lithium-containing solution, by measuring, the solution contains lithium 1.54 g / L, reaching the purpose of pre-concentration.

[0070] Example 9

[0071] Select the existing iron phosphate as the adsorbent (purchased from Changsha Shenghua Scientific Research Institute), its XRD characterization is similar to that of Example 1, which is amorphous. Figure 5 is the SEM characterization of the iron phosphate used in Example 9, it can be seen that the primary particles are also spherical, there are obvious boundary lines at the agglomeration, the particle size is larger than that of Example 6, basically reaching the micron level, the mark 10 in the figure is in the range of 1.1-1.9 μm, and the particle sizes of other primary particles are also mostly similar to this.

[0072] Take 20 g of the above iron phosphate and 4 g of calcium oxide, and put them into a 2 L solution containing 503.34 mg / L of lithium. The other main components in the solution are mainly sodium sulfate 11.88 g / L (the pH of the solution is 7.13). After the adsorbent is put in, the pH of the solution is 11.79. Under stirring, the solution is reacted at 40°C for 1 h, and then filtered. 40.54 g of lithium-containing adsorbent (with a water content of 49.83%) is obtained, and at the same time, the solution after adsorption is obtained. It is determined that the lithium concentration of the solution after adsorption is reduced to 392.44 mg / L, and the lithium adsorption capacity is 11.09 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed with 95°C hot water for three times, 50 mL of water is added, and the system is stirred uniformly. The pH of the system is adjusted to 2 with sulfuric acid, and under stirring, the system is reacted at 30°C for 6 h. After filtration, a lithium-containing solution and a filter cake are obtained. It is determined that the lithium content in the solution is 3.11 g / L, which achieves the purpose of pre-concentration.

[0073] Example 10

[0074] Preparation of iron phosphate: 5 L of a solution containing 0.5 mol / L of phosphorus (sodium phosphate dodecahydrate as the phosphorus source) is prepared, and the pH is adjusted to 2 with sulfuric acid. 5 L of a solution containing 0.5 mol / L of iron (ferric sulfate as the iron source) is prepared. The solution containing phosphorus is heated to boiling, and the solution containing iron is added. The reaction is carried out for 4 h, and then the product is filtered, washed with water, and dried to obtain iron phosphate.

[0075] Figure 6 is an XRD pattern of the adsorbent used in Example 10, and obvious crystal diffraction peaks can be seen, which is crystalline iron phosphate;

[0076] Figure 7 is an SEM image of the adsorbent used in Example 10. Some fine primary grains can be seen, and there is an obvious boundary between adjacent fine grains. Finally, irregular secondary particles are formed. The software Nano Measurer is used to mark the primary grains at 24 different positions, and it is determined that the primary grains are distributed between 50 nm and 170 nm.

[0077] Take 20 g of the above iron phosphate, and put it into a 1 L solution containing 259.6 mg / L of lithium. The other main components in the solution are mainly sodium sulfate 12.49 g / L, and the pH of the solution is 5.84. The pH of the solution is adjusted to 10 with sodium hydroxide. Under stirring, the solution is reacted at 20°C for 5 h, and then filtered. 39.39 g of lithium-containing adsorbent (with a water content of 49.13%) is obtained, and at the same time, the solution after adsorption is obtained. It is determined that the lithium concentration of the solution after adsorption is reduced to 98.24 mg / L, and the lithium adsorption capacity is 8.07 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed with 60°C hot water for three times, 50 mL of water is added, and the system is stirred uniformly. The pH of the system is adjusted to 2 with nitric acid, and under stirring, the system is reacted at 30°C for 1 h. After filtration, a lithium-containing solution and a filter cake are obtained. It is determined that the lithium content in the solution is 2.32 g / L, which achieves the purpose of pre-concentration.

[0078] Example 11

[0079] Take 20 g of iron phosphate used in example 10 and 6 g of calcium chloride mixed, put into 1 L of solution containing lithium 325.61 mg / L, the other main components in the solution are mainly sodium sulfate 67.53 g / L, the solution pH is 6.22, adjust the solution pH to 11 with sodium hydroxide, get lithium-containing adsorbent 41.12 g (moisture content 50.11%), at the same time, the adsorbed solution is reduced to 109.24 mg / L, and the lithium adsorption capacity is 10.82 mg / g. The lithium-containing adsorbent is washed with 95°C hot water three times, 50 mL of water is added, stirred uniformly, the system pH is adjusted to 3 with sulfuric acid, under stirring at 30°C for 2h, filtration, get lithium-containing solution and filter cake, by determination, the lithium content in the solution is 2.99 g / L, reaching the purpose of pre-concentration.

[0080] Example 12

[0081] Select the existing iron phosphate as adsorbent (purchased from Macklin reagent), which is similar to the characterization of iron phosphate used in example 10, the particle size distribution of primary particles is less than 200 nm.

[0082] Take 20 g of the above iron phosphate and 5 g of calcium oxide, put into 2 L of solution containing lithium 503.34 mg / L, the other main components in the solution are mainly sodium sulfate 11.88 g / L (solution pH is 7.13), after putting in the adsorbent, the solution pH is 12.24, under stirring at 30°C for 4h, filtration, get lithium-containing adsorbent 41.33 g (moisture content 49.22%), at the same time, the adsorbed solution is obtained, by determination, the lithium concentration of the adsorbed solution is reduced to 351.98 mg / L, the lithium adsorption capacity is 15.14 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed with 95°C hot water once, 50 mL of water is added, stirred uniformly, the system pH is adjusted to 2 with hydrochloric acid, under stirring at 30°C for 1h, filtration, get lithium-containing solution and filter cake, by determination, the lithium content in the solution is 4.22 g / L, reaching the purpose of pre-concentration.

[0083] Example 13

[0084] Select the existing iron phosphate as adsorbent (purchased from Luo En reagent), which is also similar to the characterization of iron phosphate used in example 10, the particle size distribution of primary particles is less than 200 nm.

[0085] Take 20 g of the above iron phosphate, put into 1 L solution containing lithium 467.24 mg / L, the other main components in the solution are mainly sodium sulfate 23.14 g / L, the solution pH is 8.62, adjust the solution pH to 10 with ammonia water, under stirring conditions at 30 °C for 2 h, filter, get lithium-containing adsorbent 40.04 g (moisture content 49.59%), at the same time get the adsorbed solution, by determination, the lithium concentration of the adsorbed solution is reduced to 318.88 mg / L, the lithium adsorption capacity is 7.42 mg / g (calculated on the basis of dry iron phosphate). The lithium-containing adsorbent is washed twice with 95 °C hot water, add 50 mL water, stir evenly, adjust the system pH to 2 with sulfuric acid, under stirring conditions at 20 °C for 1 h, filter, get lithium-containing solution and filter cake, by determination, the lithium content in the solution is 2.08 g / L, reaching the purpose of pre-concentration.

[0086] Comparative Example 1 (primary particle size of iron phosphate is too large):

[0087] Take the existing iron phosphate (purchased from Aladdin Reagent), Figure 8 is the XRD characterization diagram of the iron phosphate used in Comparative Example 1, there are obvious crystal diffraction peaks. Figure 9 is the SEM characterization of the iron phosphate used in Comparative Example 1. From the SEM, it can be seen that the particles have obvious crystal structure, but some particles are in sheet structure (indicated as 1 and 2 in the figure), and there are relatively complete crystal grains (indicated as 3 and 4 in the figure). Whether it is a sheet grain or a block grain, the surface is relatively smooth, which is a primary nucleation of original particles, so the primary particle size is larger than 2 microns.

[0088] Take 20 g of the above iron phosphate, operate according to Example 1, and measure that the adsorbed solution is only reduced to 477.22 mg / L, and the lithium adsorption capacity is only 1.39 mg / g, that is, the adsorption capacity is very weak, and there is basically no enrichment effect.

[0089] Comparative Example 2:

[0090] Take 20 g of the iron phosphate of Comparative Example 1 instead of the iron phosphate of Example 2, operate according to Example 2, and measure that the adsorbed solution is only reduced to 485.58 mg / L, and the lithium adsorption capacity is only 0.97 mg / g, basically no enrichment effect (calcium chloride has no promoting effect).

[0091] Comparative Example 3:

[0092] Take 30 g of the iron phosphate of Comparative Example 1 instead of the iron phosphate of Example 3, operate according to Example 3, and measure that the adsorbed solution is only reduced to 394.56 mg / L, and the lithium adsorption capacity is only 1.63 mg / g, basically no enrichment effect (calcium oxide has no promoting effect).

[0093] Comparative Example 4:

[0094] The existing iron phosphate (purchased from Changsha Fumao Chemical Material Co., Ltd.) was used to replace the iron phosphate of Example 1, and Figure 10 is an XRD characterization diagram of the iron phosphate used in Comparative Example 4, and there are obvious crystal diffraction peaks. Figure 11 is an SEM characterization diagram of the iron phosphate used in Comparative Example 4. It can be seen from the diagram that there are obvious crystal grains, some of which are relatively regular (indicated as 1 and 2 in the diagram), and some of which are disordered (indicated as 3 and 4 in the diagram), but it can be seen that the particle size of most primary crystal grains is relatively large, reaching more than 5 microns.

[0095] 20 g of the above iron phosphate was taken, and the operation of Example 1 was performed, and it was measured that the adsorbed solution was only reduced to 487.54 mg / L, and it can be known that the lithium adsorption amount is only 0.873 mg / g, that is, the adsorption capacity is very weak, and there is basically no enrichment effect.

[0096] The above is a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change, combination (such as multi-stage adsorption and desorption to improve the recovery rate, etc.) according to the technical scheme and concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the claims of the present application.

Claims

1. A phosphorus iron salt adsorbent for pre-concentration of low concentration lithium containing solutions, characterized in that, The phosphorus iron salt adsorbent is a mixture of iron phosphate and calcium compound, the mass ratio of the mixture is: iron phosphate: calcium compound = 1: (0.1-1); the calcium compound includes one or several of calcium chloride, calcium oxide, calcium hydroxide, calcium nitrate; the phosphorus iron salt adsorbent is a phosphorus iron salt adsorbent for pre-enrichment of low-concentration lithium-containing solution.

2. The ferrophosphorus salt adsorbent according to claim 1, characterized in that The mass ratio of the mixture is: iron phosphate: calcium compound = 1: (0.1-0.5).

3. The ferrophosphorus salt adsorbent according to claim 1 or 2, characterized in that, The primary nucleation particle size of the iron phosphate is less than 2000 nm.

4. The ferrophosphorus salt adsorbent according to claim 3, characterized in that The primary nucleation particle size of the iron phosphate is less than 1000 nm, and further preferably the primary nucleation particle size of the iron phosphate is less than 200 nm.

5. Application of a phosphorus iron salt adsorbent in pre-enrichment of low-concentration lithium-containing solution, the phosphorus iron salt adsorbent is iron phosphate, or the phosphorus iron salt adsorbent is the phosphorus iron salt adsorbent according to any one of claims 1-4.

6. The use of the phosphorus iron salt adsorbent according to claim 5 for pre-concentration of low concentration lithium-containing solutions, characterized in that, The application specifically includes the following steps: (1) 1-200 g of the adsorbent in claim 5 is added to 1 L of low-concentration lithium-containing solution, the pH is adjusted to 8-13 with an alkaline substance, and the mixture is reacted at 0-100 ℃ for 10 min-12 h, then liquid-solid separation is performed to complete adsorption; the low-concentration lithium-containing solution is a lithium-containing solution with a lithium ion concentration of less than 1 g / L; (2) the adsorbent after adsorbing lithium is washed with water several times, then an acid solution is added to adjust the pH to 1-5, and the mixture is reacted at 0-100 ℃ for 10 min-12 h, then liquid-solid separation is performed to complete desorption, and a lithium-containing pre-enrichment solution and a filter cake are obtained, and the filter cake is washed to obtain regenerated adsorbent.

7. Use according to claim 6, characterized in that, The low-concentration lithium-containing solution is a lithium-containing solution with a lithium ion concentration of less than 1 g / L, preferably a lithium ion concentration of 10-600 mg / L.

8. Use according to claim 6, characterized in that, The alkaline substance includes one or a combination of sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide, and ammonia.

9. Use according to claim 6, characterized in that, The acid includes one or a combination of sulfuric acid, hydrochloric acid, and nitric acid.

10. Use according to claim 6, characterized in that, Step (2) obtains a lithium-containing pre-enrichment solution with a concentration of more than 1 g / L, and preferably a lithium-containing pre-enrichment solution with a concentration of 1.5-6 g / L.

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