Abstract:
The present disclosure provides a method of preparing highly pure lithium carbonate from brine. The method includes adding an adsorbent to the brine, from which the magnesium ions Mg 2+  have been removed, to adsorb lithium ions Li +  to the adsorbent, followed by providing the adsorbent having the lithium ions Li +  adsorbed thereto to a strong acid solution to desorb the lithium ions Li +  from the adsorbent; enriching the strong acid solution in which the lithium ions Li +  are desorbed from the adsorbent; and obtaining lithium carbonate Li 2 CO 3  through chemical reaction between the lithium ions Li +  in the enriched solution and a carbonate precursor.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a method of preparing lithium carbonate Li 2 CO 3  used for lithium secondary batteries, and more particularly to a method of preparing highly pure lithium carbonate from brine. 
         [0003]    2. Description of the Related Art 
         [0004]    With a recent increase in demand for lithium secondary batteries, lithium carbonate Li 2 CO 3  for a positive electrode material has also been increasingly demanded. 
         [0005]    Lithium carbonate can be prepared in various ways. Recently, many studies have been conducted to prepare lithium carbonate from lithium contained in brine. 
         [0006]    Brine contains many ionic components such as lithium ions, magnesium ions, sodium ions, chlorine ions, and the like. 
         [0007]    In order to prepare lithium carbonate from brine, a conventional process includes preparing a lithium solution by separating other components from the brine except for lithium components, followed by enrichment of the prepared lithium solution. 
         [0008]    However, the process of preparing the lithium solution through separation of other components except for the lithium components is complicated and requires a long process time. 
       BRIEF SUMMARY 
       [0009]    The present invention provides a method of preparing lithium carbonate having a high purity of 99% from brine through a simple process within a short period of time. 
         [0010]    In accordance with an aspect of the invention, a method of preparing lithium carbonate includes: removing magnesium ions Mg 2+  from brine; adding an adsorbent to the brine, from which the magnesium ions Mg 2+  have been removed, to adsorb lithium ions Li 30   to the adsorbent, followed by providing the adsorbent having the lithium ions Li +  adsorbed thereto to a strong acid solution to desorb the lithium ions Li +  from the adsorbent; enriching the strong acid solution in which the lithium ions Li +  are desorbed from the adsorbent; and obtaining lithium carbonate Li 2 CO 3  through chemical reaction between the lithium ions Li +  in the enriched solution and a carbonate precursor. 
         [0011]    In accordance with another aspect of the invention, a method of preparing lithium carbonate includes: removing magnesium ions Mg 2+  from brine; adding an adsorbent to the brine, from which the magnesium ions Mg 2+  have been removed, to adsorb lithium ions Li +  to the adsorbent, followed by providing the adsorbent having the lithium ions Li +  adsorbed thereto to a strong acid solution to desorb the lithium ions Li +  from the adsorbent; and obtaining lithium carbonate Li 2 CO 3  through chemical reaction between the desorbed lithium ions Li +  in the enriched solution and a carbonate precursor. 
         [0012]    As such, according to exemplary embodiments of the invention, the method of preparing lithium carbonate from brine may prepare highly pure lithium carbonate through simple processes including a process of removing magnesium ions, a process for adsorption/desorption of lithium ions Li + , an enrichment process and a process of obtaining lithium carbonate. 
         [0013]    Further, the method of preparing lithium carbonate from brine according to the embodiments of the invention does not need a process for removing impurities except for magnesium, thereby reducing process time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0014]    The above and other aspects, features, and advantages of the invention will become apparent from the following detailed description of exemplary embodiments in conjunction with the accompanying drawing, in which: 
           [0015]      FIG. 1  is a flowchart of a method of preparing lithium carbonate from brine in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawing. It should be understood that the present invention is not limited to the following embodiments and may be embodied in different ways, and that the embodiments are given to provide complete disclosure of the invention and to provide thorough understanding of the invention to those skilled in the art. The scope of the invention is limited only by the accompanying claims and equivalents thereof. Like components will be denoted by like reference numerals throughout the specification and the accompanying drawing. 
         [0017]    Hereinafter, a method of preparing lithium carbonate from brine in accordance with an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawing. 
         [0018]      FIG. 1  is a flowchart of a method of preparing lithium carbonate from brine in accordance with an exemplary embodiment of the present invention. 
         [0019]    Referring to  FIG. 1 , the method of preparing lithium carbonate from brine in accordance with the exemplary embodiment includes a magnesium removal operation S 110 , a lithium adsorption/desorption operation S 120 , an enrichment operation S 130 , and a lithium carbonate obtaining operation S 140 . 
         [0020]    Magnesium Removal 
         [0021]    In the magnesium removal operation S 110 , magnesium ions Mg 2+  are removed from brine. 
         [0022]    The magnesium ions Mg 2+  have a smaller size than lithium ions Li +  Thus, the magnesium ions Mg 2+  also tend to be adsorbed together with the lithium ions Li +  upon adsorption of the lithium ions as described below, and there is a need for previous removal of the magnesium ions Mg 2+  from the brine before adsorption of the lithium ions Li + . 
         [0023]    Removal of the magnesium ions Mg 2+  may be performed by settling precipitates of the magnesium ions Mg 2+  in the form of magnesium hydroxide, magnesium oxalate, magnesium carbonate, and the like. 
         [0024]    Table 1 shows a removal rate of magnesium ions Mg 2+  and a co-precipitation rate according to a method of removing magnesium ions Mg 2+ . 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Kind 
                 Hydroxide 
                 Oxalate 
                 Carbonate 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Mg removal rate (%) 
                 99.9 
                 99.9 
                 99.9 
               
               
                   
                 Li co-precipitation rate 
                 4.7 
                 15.3 
                 12.2 
               
               
                   
                 (%) 
               
               
                   
                   
               
             
          
         
       
     
         [0025]    Referring to Table 1, the removal rate of magnesium ions Mg +  is 99.9% in any precipitate form of magnesium hydroxide, magnesium oxalate and magnesium carbonate. 
         [0026]    However, the co-precipitation rate of lithium ions Li +  varies depending on the form of magnesium precipitate. More specifically, since the co-precipitation rate of lithium ions Li +  is lower in the precipitate form of magnesium hydroxide than in the precipitate forms of magnesium oxalate and magnesium carbonate, it is desirable that the magnesium ions Mg 2+  be removed in the precipitate form of magnesium hydroxide. 
         [0027]    When the magnesium ions Mg +  are removed in the precipitate form of magnesium hydroxide, NaOH, KOH, CaO and the like may be used for precipitation of magnesium hydroxide. 
         [0028]    Particularly, CaO may be used in terms of economic feasibility. 
         [0029]    Lithium Adsorption/Desorption 
         [0030]    Next, in the lithium adsorption/desorption operation S 120 , lithium ions Li +  are adsorbed to an adsorbent for a predetermined period of time (lithium desorption) by adding the adsorbent to the brine from which the magnesium ions Mg +  have been removed in the magnesium removal operation S 110 . Then, the adsorbent to which the lithium ions Li +  are adsorbed is supplied to a strong acid solution such as hydrochloric acid HCl to desorb the lithium ions Li +  from the adsorbent (lithium desorption). 
         [0031]    Adsorption of the lithium ions Li +  may be achieved using manganese oxide or aluminum oxide. 
         [0032]    Table 2 shows adsorption amounts of lithium ions and other ions per unit weight according to the kind of adsorbent. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 (unit: mg/g) 
               
             
          
           
               
                   
                 Kind 
                 Li 
                 Mg 
                 Na 
                 K 
                 Ca 
                 B 
               
               
                   
                   
               
               
                   
                 Mn oxide 
                 17.3 
                 0 
                 0.3 
                 0.1 
                 1.1 
                 0.05 
               
               
                   
                 Al oxide 
                 12.5 
                 0 
                 0.1 
                 0.1 
                 0.8 
                 0.02 
               
               
                   
                   
               
             
          
         
       
     
         [0033]    Referring to Table 2, it can seen that, when manganese oxide is used as the adsorbent, the adsorption rate of the lithium ions Li +  is higher than in the case of using aluminum oxide. Thus, manganese oxide may be used as the adsorbent in order to increase the adsorption rate of the lithium ions Li + . 
         [0034]    In desorption of the lithium ions Li + , a strong acid solution such as a hydrochloric acid solution, a nitric acid solution, a sulfuric acid solution, or the like may be used. 
         [0035]    After the lithium adsorption/desorption operation S 120  or the enrichment operation S 130  as described below, the method may further include a process of neutralizing the strong acid solution. 
         [0036]    Enrichment 
         [0037]    In the enrichment operation S 130 , the strong acid solution in which the lithium ions Li +  are desorbed is subjected to an enrichment process. 
         [0038]    The enrichment process may be performed to enrich the strong acid solution such that the lithium ions Li +  may be present in a concentration of 4 wt % or more therein, and preferably 6±0.5 wt %. If the concentration of lithium ions Li +  does not reach 4 wt % after the enrichment process, an increase in concentration of lithium ions Li +  by the enrichment process can be considered insufficient. Although the concentration of lithium ions Li +  may increase with increasing number of times of performing the enrichment process, the time and cost for enrichment also increase thereby. Thus, the enrichment operation may be performed to have a concentration of lithium ions Li +  of about 6 wt %. 
         [0039]    The enrichment operation may be performed using sunlight. 
         [0040]    In this embodiment, the brine may be natural brine. Alternatively, the brine may be synthetic brine which contains lithium ions, magnesium ions, sodium ions, potassium ions, chlorine ions and boron ions, as shown in Table 3. 
         [0041]    Table 3 shows one example of compositions of synthetic brine. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Kind 
                 Li 
                 Mg 
                 Na 
                 K 
                 Cl 
                 B 
               
               
                   
               
             
             
               
                 Concentration 
                 500 
                 10,000 
                 100,000 
                 20,000 
                 200,000 
                 50 
               
               
                 (ppm) 
               
               
                   
               
             
          
         
       
     
         [0042]    Table 4 shows the amount of lithium ions and other ions after the enrichment operation, in which synthetic brine containing components as shown in Table 3 is subjected to removal of magnesium ions Mg +  in the precipitate form of magnesium hydroxide, adsorption and desorption of lithium ions using a hydrochloric acid solution, and enrichment using sunlight. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 (unit: ppm) 
               
             
          
           
               
                   
                 Kind 
                 Li 
                 Mg 
                 Na 
                 K 
                 B 
               
               
                   
                   
               
             
          
           
               
                   
                 Mn oxide 
                 1040 
                 0 
                 16 
                 4.8 
                 2 
               
               
                   
                 Al oxide 
                 760 
                 0 
                 5.2 
                 4.8 
                 0.8 
               
               
                   
                   
               
             
          
         
       
     
         [0043]    Referring to Table 4, it can seen that, when manganese oxide is used as the absorbent of the lithium ions, the concentration of lithium ions Li +  is higher even after desorption and enrichment of the lithium ions Li +  than in the case of using aluminum oxide, and that the lithium-enriched solution has a significantly reduced concentration of impurities with respect to any adsorbent. 
         [0044]    Although the enrichment operation S 130  is not an essential process for the method according to this embodiment, the content of lithium ions Li +  may be increased through the enrichment operation, thereby increasing the amount of lithium finally obtained. 
         [0045]    Yield of Lithium Carbonate 
         [0046]    In the lithium carbonate obtaining operation S 140 , the lithium ions Li +  contained in the enriched solution are chemically reacted with a carbonate precursor to obtain lithium carbonate Li 2 CO 3 . 
         [0047]    The carbonate precursor may include carbon dioxide CO 2 . 
         [0048]    The lithium carbonate has a high purity of 99%, when prepared by the method described above, that is, through removal of magnesium ions Mg 2+ , adsorption/desorption of lithium ions, enrichment, and yield of lithium carbonate. Accordingly, the method according to the embodiment of the present invention may produce lithium carbonate having a high purity of about 99±1wt %. 
         [0049]    As such, the method according to the embodiment of the invention may produce highly pure lithium carbonate from brine through a simple process and does not need a process of removing impurities except for magnesium, thereby reducing processing time. 
         [0050]    Although some embodiments have been described herein, it should be understood by those skilled in the art that these embodiments are given by way of illustration only, and that various modifications, variations, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be limited only by the accompanying claims and equivalents thereof.