Method for improving lithium yield in process of producing lithium hydroxide by sulfuric acid method

Abstract

The invention relates to the field of lithium hydroxide production, in particular to a method for improving the lithium yield in the process of producing lithium hydroxide through a sulfuric acid method. The method comprises the following steps: step 1, mixing crude lithium phosphate with an acid solution for reaction to obtain a re-dissolution material solution; 2, the re-dissolution feed liquid in the step 1 is subjected to precise filtration treatment, and filtrate is obtained; step 3, adding a calcium source into the filtrate obtained in the step 2, and removing phosphate radicals in the filtrate to obtain feed liquid containing precipitates; and 4, filtering the material liquid containing the precipitate in the step 3 to obtain filter residues and filtrate. And 5, merging the filtrate obtained in the step 4, and feeding the merged filtrate into a production system for producing lithium hydroxide monohydrate. The invention aims to primarily purify the crude lithium phosphate obtained by recovering the residual lithium resource from the production process and then return to the production system for continuously producing the lithium hydroxide, the whole process flow is short, the operation is simple and convenient, the effect of improving the lithium yield in the production process is obvious, and the industrial production can be quickly realized.

Description

Technical Field

[0001] The invention relates to the field of lithium hydroxide production, and in particular to a method for improving lithium yield in the process of producing lithium hydroxide by a sulfuric acid method. Background Art

[0002] The sulfuric acid method for preparing lithium hydroxide monohydrate is a common industrial method, and the main steps include leaching, purification, separation, etc. The existing production method usually produces a large amount of lithium-containing mother liquor with more impurities. For this part of lithium resources, the general factory produces it in the form of lithium carbonate, lithium phosphate, etc., so that it forms other lithium salt removal systems. For example, the patent with publication number CN 117776233 A records that the lithium resources in the mother liquor are converted into lithium carbonate for sale; the patent with publication number CN 118084020 A records that the lithium in the mother liquor is converted into lithium phosphate and further used to purify the lithium sulfate solution; or the lithium resources are recovered by adsorption, for example, the patent with publication number CN 111533145 A records the use of adsorbents to treat low-concentration lithium resource mother liquors.

[0003] All of the above processes involve the problem of discharging lithium resources from the existing system for re-development and utilization. The overall process flow is long and the processing cost is high, and it cannot effectively increase the production capacity of lithium hydroxide monohydrate.

[0004] Therefore, it is of great significance to develop a method to quickly and concisely return trace lithium resources in the system to the main system for the production of lithium hydroxide. Summary of the invention

[0005] The present invention provides a method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method. The method is to mix the crude lithium phosphate separated in the production process with acid solution for reaction and dissolution, and obtain a return solution and insoluble matter after precise filtration, wherein the return solution is mixed with a calcium source for reaction to remove phosphate, and a lithium-containing solution is obtained after filtration after preliminary purification, and then the lithium-containing solution is returned to the production system for the production of lithium hydroxide monohydrate. The lithium resources recovered by the present invention can be directly returned to the system for the production of lithium hydroxide, the process flow is simple, and the overall lithium yield is significantly improved.

[0006] In order to achieve the above invention object, the specific technical scheme of the present invention is as follows:

[0007] A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method, comprising the following steps:

[0008] Step 1: crude lithium phosphate is mixed with acid solution to react to obtain a re-dissolving solution;

[0009] Step 2: The re-dissolved liquid in step 1 is subjected to precision filtration to obtain insoluble matter and filtrate;

[0010] Step 3: adding a calcium source to the filtrate of step 2 to remove phosphate;

[0011] Step 4: Filter the feed liquid containing the precipitate in step 3 to obtain filter residue and filtrate; the filtrate is the preliminary purified liquid.

[0012] Furthermore, a method for improving lithium yield in the process of producing lithium hydroxide by the sulfuric acid method may also include step 5: combining the filtrate in step 4 into a production system for producing lithium hydroxide monohydrate.

[0013] Furthermore, a method for improving lithium yield in the process of producing lithium hydroxide by sulfuric acid method also includes step 6: returning the insoluble matter obtained in step 2 and the filter residue obtained in step 4 to the main system for pulping together with the acidified ore.

[0014] Furthermore, a method for improving the lithium yield in the process of producing lithium hydroxide by the sulfuric acid method also includes step 7: filtering the slurry obtained in step 6 to obtain leaching residue and leaching liquid, and mixing the leaching liquid with the preliminary purified liquid in step 4 for deep purification for preparing lithium hydroxide.

[0015] Preferably, the lithium concentration in the re-dissolving solution prepared in step 1 is 5-20 g / L.

[0016] Preferably, the acid solution added in step 1 is sulfuric acid, and the amount added is 2-3 times the molar amount of crude lithium phosphate.

[0017] Preferably, the temperature range of the re-dissolution process in step 1 is from room temperature to 90°C.

[0018] Preferably, in step 2, one of the common material precision filters such as meltblown filter element filter, wire wound filter element filter, pleated filter element filter, pleated filter element filter, activated carbon filter, ceramic filter, etc. is used. The purpose of filtering is to filter out the insoluble matter remaining in the re-dissolution process and reduce the loss caused by the entrainment and adsorption of lithium by the insoluble matter in the subsequent steps.

[0019] Preferably, the calcium source in step 3 is CaO, Ca(OH) 2 、CaCO 3 A mixture of one or more of.

[0020] Preferably, the amount of calcium source added in step 3 is based on the system pH = 6.5-8.5, and more preferably, the amount of calcium source added is based on the system pH = 7-8.

[0021] Preferably, the precipitation reaction temperature in step 3 ranges from room temperature to 90°C.

[0022] Preferably, the filtration section in step 4 adopts two-stage filtration, wherein the first stage is plate and frame filtration and the second stage is precision filtration.

[0023] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0024] (I) According to the method of the present invention, crude lithium phosphate is dissolved by acid, phosphate radicals are removed, and insoluble matter is filtered out, which can be directly returned to the main system to produce lithium hydroxide monohydrate. The entire process flow is simple, and a small number of auxiliary sections can be branched out from the main system to quickly increase the lithium yield in the main process. The economic value is obvious and industrialization is easy to achieve.

[0025] (ii) This method has no restriction on the lithium phosphate content in the crude lithium phosphate. It only needs to adjust the amount of sulfuric acid to ensure a good dissolution effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart of a method for increasing lithium yield in the process of producing lithium hydroxide by sulfuric acid method provided in Example 1;

[0027] Figure 2 A flow chart of a method for increasing lithium yield in the process of producing lithium hydroxide by sulfuric acid method provided in Example 3;

[0028] Figure 3 This is a schematic diagram of the process flow of the main production system of lithium hydroxide using the sulfuric acid method. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0031] The technical solution of the present invention is further described in detail and completely below in conjunction with the embodiments.

[0032] The composition analysis of the crude lithium phosphate used in the following examples is shown in Table 1.

[0033] Table 1:

[0034]

[0035] Example 1

[0036] A method for increasing the lithium yield in the process of producing lithium hydroxide by sulfuric acid method, the flow chart of which is as follows Figure 1 As shown, the following steps are included:

[0037] Step 1: Mix crude lithium phosphate and 2.5 times the molar amount of sulfuric acid (the specific preparation process here is: first accurately weigh a certain mass of crude lithium phosphate and prepare it into a suspension, weigh 2.5 times the molar amount of lithium phosphate and add concentrated sulfuric acid with a mass fraction of 98% to the above-prepared suspension, and then add water according to the required lithium concentration of 10g / L) under the condition that the lithium concentration after complete dissolution is 10g / L) and stir the reaction at 40°C for 30min to obtain a re-dissolving liquid;

[0038] Step 2: Filter the re-dissolved liquid obtained in step 1 through a ceramic precision filter to obtain a filtrate;

[0039] Step 3: After stirring and heating the filtrate obtained in step 2 to 40° C., CaO is slowly added thereto until the pH of the system reaches 7 to obtain a slurry;

[0040] Step 4: The slurry obtained in step 3 was stirred and reacted at 40° C. for 30 minutes, and then filtered once using a plate and frame filter. The obtained filtrate was filtered once again through a ceramic precision filter to obtain a filtrate, i.e., a preliminary purified solution (lithium concentration of 9.6 g / L);

[0041] Step 5: Return the preliminary purified liquid obtained in step 4 to the main system (leaching liquid step) for the production of lithium hydroxide monohydrate. The purified liquid only needs to be put into the feed liquid with similar properties in the main system for subsequent deep purification and lithium salt separation, and can be returned to the main system for the production of lithium hydroxide monohydrate without additional treatment, and will not affect the product quality.

[0042] The lithium yield in the preliminary purified liquid obtained in this example is 95.51%, and the residual phosphate rate in the preliminary purified liquid is 1.84%.

[0043] Example 2

[0044] A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method is implemented according to the method described in Example 1, except that:

[0045] In the step 1, the crude lithium phosphate is mixed and dissolved with 2.0 times the molar amount of sulfuric acid;

[0046] In step 3, Ca(OH) is slowly added thereto. 2 , until the system pH = 7.5.

[0047] The lithium yield in the preliminary purified solution obtained in this example was 80.54%, and the residual phosphate rate was 1.18%.

[0048] Example 3

[0049] A method for increasing the lithium yield in the process of producing lithium hydroxide by sulfuric acid method, the flow chart of which is as follows Figure 2 As shown, the following steps are included:

[0050] Step 1: Mix the crude lithium phosphate with 2.5 times the molar amount of sulfuric acid under the condition that the lithium concentration after complete dissolution is 10 g / L, and stir and react at 40° C. for 30 minutes to obtain a re-dissolving solution;

[0051] Step 2: Filter the re-dissolving liquid obtained in step 1 through a ceramic precision filter to obtain lithium-containing insoluble matter and a filtrate;

[0052] Step 3: After stirring and heating the filtrate obtained in step 2 to 40° C., CaO is slowly added thereto until the pH of the system reaches 7 to obtain a slurry;

[0053] Step 4: The slurry obtained in step 3 was stirred and reacted at 40° C. for 30 minutes, and then filtered once using a plate and frame filter. The obtained filtrate was filtered once through a ceramic precision filter to obtain a filter residue (containing lithium calcium phosphate) and a liquid (preliminary purified liquid) (lithium concentration is 9.6 g / L);

[0054] Step 5: returning the lithium-containing insoluble matter obtained in step 2 and the lithium-containing calcium phosphate obtained in step 4 to the main system (water leaching step) for pulping with the acidified ore;

[0055] Step 6: filtering the slurry obtained in step 5 to obtain leaching residue and leaching liquid;

[0056] Step 7: The leaching solution obtained in step 6 is mixed with the preliminary purified solution obtained in step 4 for deep purification, and then lithium hydroxide is prepared.

[0057] In this embodiment, the lithium yield in the crude lithium phosphate is 98.25%, and the residual phosphate rate in the preliminary purified liquid is 1.04%.

[0058] Example 4

[0059] A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method is implemented according to the method described in Example 3, except that:

[0060] Step 1: Reverse dissolution is performed under the condition that the lithium concentration after complete dissolution is 20g / L.

[0061] The lithium yield in the crude lithium phosphate of this example is 97.84%, and the residual phosphate rate in the preliminary purified liquid is 0.72%.

[0062] Comparative Example 1

[0063] A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method is implemented according to the method described in Example 1, except that:

[0064] In the step 1, the crude lithium phosphate is mixed and dissolved with 1.0 times the molar amount of sulfuric acid.

[0065] The lithium yield in the preliminary purified solution obtained in this comparative example is 40.74%, and the residual phosphate rate in the preliminary purified solution is 28.14%. The amount of sulfuric acid used in this comparative example is lower than that in the embodiment, resulting in incomplete dissolution of the crude lithium phosphate, a significant reduction in the lithium yield, and due to insufficient residual acid in the return solution, the introduced calcium source is insufficient to react completely with the phosphate, resulting in an increase in residual phosphate.

[0066] Comparative Example 2

[0067] A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method is implemented according to the method described in Example 1, except that:

[0068] In step 3, CaCO is slowly added thereto. 3 , CaO mixture until the system pH = 9.

[0069] The lithium yield in the preliminary purified liquid obtained in this comparative example was 82.67%, and the residual phosphate rate in the preliminary purified liquid was 0.22%. The pH controlled when removing phosphate in this comparative example was higher than that in the example, resulting in the reprecipitation of part of the lithium phosphate, but the removal effect of phosphate was better than that in the example.

[0070] Comparative Example 3

[0071] A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method is implemented according to the method described in Example 3, except that:

[0072] In step 3, Ca(OH) is slowly added thereto. 2 , until the system pH = 5.5.

[0073] The lithium yield of the crude lithium phosphate in this comparative example is 98.41%, and the residual phosphate rate is 24.75%. The pH controlled during the precipitation of phosphate in this comparative example is lower than that in the example, resulting in incomplete precipitation of phosphate.

[0074] Comparative Example 4

[0075] A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method is implemented according to the method described in Example 3, except that:

[0076] Step 1: Reverse dissolution is performed under the condition that the lithium concentration after complete dissolution is 30g / L.

[0077] The lithium yield in the crude lithium phosphate of this comparative example is 88.27%, and the residual phosphate rate in the preliminary purified solution is 1.65%. The lithium concentration of the return solution configured in this comparative example is higher than that of the embodiment, resulting in excessive lithium entrainment loss during phosphate precipitation, and lithium-containing calcium phosphate cannot be effectively recovered when it returns to the main system for pulping.

[0078] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0079] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A method for improving the lithium yield in the process of producing lithium hydroxide by sulfuric acid method, characterized in that: The following steps are involved: Step 1: mixing crude lithium phosphate with acid solution to obtain a re-dissolving solution; Step 2: The re-dissolved liquid in step 1 is subjected to precision filtration to obtain insoluble matter and filtrate; Step 3: adding a calcium source to the filtrate obtained in step 2 to remove phosphate therein, thereby obtaining a feed solution containing a precipitate; Step 4: Filter the feed liquid containing the precipitate in step 3 to obtain filter residue and filtrate, and the filtrate is the preliminary purified liquid.

2. The method for improving lithium yield in a process of producing lithium hydroxide by sulfuric acid method according to claim 1, characterized in that: The method further comprises step 5: combining the filtrate in step 4 into a production system for producing lithium hydroxide monohydrate.

3. The method for improving lithium yield in a process of producing lithium hydroxide by sulfuric acid method according to claim 1, characterized in that: The method also includes: the insoluble matter obtained by filtration in step 2 is lithium-containing insoluble matter, and the filter residue obtained in step 4 is lithium-containing calcium phosphate; the lithium-containing insoluble matter and the lithium-containing calcium phosphate are returned to the main system for pulping together with the acidified ore, and after the pulping is completed, the leaching residue and the leachate are obtained by filtering.

4. The method for improving lithium yield in a process of producing lithium hydroxide by sulfuric acid method according to claim 3, characterized in that: The leachate is deeply purified together with the preliminary purified liquid in step 4 and then used to prepare lithium hydroxide.

5. The method for improving lithium yield in a process of producing lithium hydroxide by sulfuric acid method according to claim 1, characterized in that: The crude lithium phosphate described in step 1 is the product of recovering trace lithium resources in the production system; the acid solution is sulfuric acid, and the amount of sulfuric acid input is 2-3 times the molar amount of crude lithium phosphate based on the amount of crude lithium phosphate input; the lithium concentration in the re-dissolving solution is 5-20g / L.

6. The method for improving lithium yield in a process of producing lithium hydroxide by sulfuric acid method according to claim 1, characterized in that: In step 2, the precision filtration adopts any one of the melt-blown filter element filter, wire-wound filter element filter, pleated filter element filter, pleated filter element filter, activated carbon filter, and ceramic filter; the precision filtration removes the insoluble matter remaining in the re-dissolution process.

7. The method for improving lithium yield in a process of producing lithium hydroxide by sulfuric acid method according to claim 1, characterized in that: The calcium source in step 3 refers to a mixture of any one or more of CaO, Ca(OH)2, and CaCO3.

8. The method for improving lithium yield in the process of producing lithium hydroxide by sulfuric acid method according to claim 7, characterized in that: The amount of calcium source input is based on the pH of the reaction system, and the pH value is controlled at 6.5-8.

5.

9. The method for improving lithium yield in a process of producing lithium hydroxide by sulfuric acid method according to claim 1, characterized in that: In step 4, the filtration is divided into primary plate and frame filtration and secondary precision filtration.

10. The method for improving lithium yield in the process of producing lithium hydroxide by sulfuric acid method according to claim 1, characterized in that: In step 5, the filtrate is returned to the existing production system for back-end processing.

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