Abstract:
A process for the preparation of potassium sulfate, sodium bicarbonate and sodium carbonate. The process involves the treatment of potash brines by the reaction of sodium chloride and potassium chloride with calcium sulfate and sodium sulfate. Syngenite precipitate (CaSO 4 .K 2 SO 4 χH 2 O) is produced and a first filtrate containing sodium chloride and potassium chloride. The syngenite precipitate is reacted with ammonium bicarbonate at between 70° C. and 100° C., with the result being calcium carbonate precipitate and a second filtrate containing ammonium sulfate and potassium sulfate. The second filtrate is cooled to a temperature of between 20° C. and 50° C. and treated with potassium chloride. A potassium sulfate precipitate results. The sodium bicarbonate is precipitated from the first filtrate by the addition of ammonium bicarbonate to the first precipitate. The sodium bicarbonate may be calcined to form sodium carbonate.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for formulating potassium sulfate, sodium bicarbonate and sodium carbonate and more particularly, the present invention relates to a method for formulating such compounds from spent potash brine. 
     BACKGROUND OF THE INVENTION 
     In a typical potash plant approximately between 85% and 90% of potassium chloride is recovered. The residual is lost due to washing with water sodium chloride from the sodium chloride during purification procedures. A second cause of the losses is occlusion of the potassium chloride in the sodium chloride tailings. 
     Tailing ponds are used to collect the excess brine of saturated sodium chloride and potassium chloride with the brine usually being deep well injected for disposal. As an example, for every 1,000,000 tonnes of potassium chloride produced, between 80,000 and 100,000 tonnes of potassium chloride is disposed of by deep well injection. 
     Generally known techniques are deficient in any clear teachings regarding the methodology set forth above having the following commercial and industrial advantages: 
     a) production of useful salts from material typically discarded; 
     b) avoidance of the requirement for deep well injection; 
     c) use of a nominal amount of energy to synthesize product; 
     d) use of common equipment widely employed in chemical engineering unit operations; and 
     e) environmentally friendly protocol devoid of operations which generate pollutants or otherwise adversely affect the soil or air. 
     There is, therefore, a clear need for a process having these desirable properties; the present invention addresses these needs in an elegant and environmentally conscious manner. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide an improved method for formulating useful alkali salts from waste potassium chloride. 
     A further object of one embodiment of the present invention is to provide a method for forming potassium sulfate from potash brines, comprising the steps of: 
     providing a source of sodium chloride and potassium chloride in a first step; 
     reacting the sodium chloride and potassium chloride with calcium sulfate and sodium sulfate; 
     forming a syngenite precipitate and a first filtrate; 
     treating the syngenite precipitate with ammonia and carbon dioxide at between 60° C. and 100° C.; 
     forming calcium carbonate precipitate and a second filtrate; 
     cooling the second filtrate to a temperature of between 0° C. and 40° C.; 
     treating the second filtrate with potassium chloride crystals; and 
     forming potassium sulfate precipitate and a third filtrate. 
     A further object of one embodiment of the present invention is to provide a method for forming potassium sulfate and sodium bicarbonate from potash brines, comprising the steps of: 
     forming potassium sulfate in a first phase and sodium bicarbonate in a second phase, the first phase, comprising the steps of: 
     providing a source of sodium chloride and potassium chloride in a first step; 
     reacting the sodium chloride and potassium chloride with calcium sulfate and sodium sulfate; 
     forming a syngenite precipitate and a first filtrate; 
     treating the syngenite precipitate with ammonia and carbon dioxide at between 50° C. and 100° C.; 
     forming calcium carbonate precipitate and a second filtrate; 
     cooling the second filtrate to a temperature of between 0° C. and 40° C.; 
     treating the second filtrate with potassium chloride solid; 
     forming potassium sulfate precipitate and a third filtrate, said second phase comprising the steps of: 
     treating the first filtrate with ammonia or ammonium ions and carbon dioxide; and 
     forming sodium bicarbonate precipitate. 
     Having thus described the invention, reference will now be made to the accompanying drawing illustrating preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an overall schematic representation of the method according to one embodiment of the present invention; and 
     FIG. 2 is a detailed schematic of FIG.  1 . 
    
    
     Similar numerals employed in the text denote similar elements. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, shown is an overall schematic representation of the process according to one embodiment. All amounts are expressed on a percentage by weight basis unless otherwise indicated. 
     In the embodiment shown, approximately 20% sodium chloride and 10% potassium chloride are added to a mixer  10  together with hydrated calcium sulfate and sodium sulfate. The mixture is filtered in filter  12 , with the filtrate  14  undergoing subsequent treatment (discussed herein after). The precipitate  16  comprises syngenite, CaSO 4 —K 2 SO 4 xH 2 O, and is reacted in vessel  18  with ammonia and carbon dioxide, as an example. The syngenite may also be reacted with ammonium bicarbonate. The reaction preferably is conducted at a temperature of between 30° C. and 100° C. and most desirably at 90° C. The mixture is filtered in filter  20 , with the precipitate comprising calcium carbonate high grade having a brightness of at least +80. The calcium carbonate is subsequently treated by further unit operations to be discussed herein after. 
     The filtrate from filter  20  is cooled to a temperature of between 20° C. and 40° C. and most desirably at 30° C. Once cooled, the filtrate is reacted in vessel  22  with potassium chloride and filtered in filter  24  to provide a potassium sulfate precipitate and a filtrate containing potassium chloride and ammonium chloride. 
     Referring now to FIG. 2, the filtrate containing potassium chloride and ammonium chloride is concentrated in an evaporator  26  and filtered in filter  28 . The precipitate comprising potassium chloride is recycled to vessel  10  and the filtrate comprising approximately 25% ammonium chloride is passed into vessel  28 . Calcium carbonate from the filtration step at filter  20  is calcined to yield lime and added to vessel  28 . Ammonia gas formed is recycled to ammonium bicarbonate and the mixture is filtered in filter  30 . The precipitate of calcium sulfate is reused and the filtrate, comprising calcium chloride (25%) is disposed of by, for example, deep well injection. 
     The filtrate from filter  12  (approximately 28% sodium chloride and 2% potassium chloride) is reacted with ammonium bicarbonate (ammonia and carbon dioxide) in vessel  32  and filtered in filter  34 . The result is a precipitate of sodium bicarbonate and ammonium chloride filtrate. The sodium bicarbonate is, for example, calcined to yield sodium carbonate. 
     As a illustration of the efficacy of the technology set forth herein, the following is representative of the quantitative result. 
     EXAMPLE 
     Sample Calculation                    Feed                   Brine              @             21      %                 NaCl                           10      %                 Kcl           }                     At                 1.24                 5.6                                                  
     Basis: One (M) 3  of Feed Brine            ∴         tonnes                 of                 NaCl         =           1   ×   1.24   ×   0.21     =     0.260                 t                             tonnes                 of                 KCl         =           1   ×   1.24   ×   0.10     =     0.124                 t                             tonnes                 of                   H   2        O         =             0.856                 t                  _                         Total       =           1.24                 t                                             
     Reaction with CaSO 4 .2H 2 O+Na 2 SO 4 +KCl→Ca 2 SO 4 .K 2 SO 4 .x+H 2 O+NaCl0.1 t KCl enter into the reaction            ∴             CaSO   4     ·   2          H   2        O                 required         =             0.1     74        (   2   )         ×   172     =       0.116                 t     _                               Na   2          SO   4                   required         =             0.1     74        (   2   )         ×   142     =       0.096                 t     _                                  
     Syngenite produced: (as) Ca 2 SO 4 K 2 SO 4 .4H 2 O            0.1     74        (   2   )         ×   382     =         0.258                 t     _                   of                 wet                 cake                                        The                 filtered                 exit                 brine                 contains        :             0.024                 t                 KCl                           0.338                 t                 NaCl                 %                 NaCl     =   27.7               0.856                 t     _                     H   2        O                 %                 KCl                =              2.0             1.218   _                  _          t   _                                   
     Syngenite conversion @+90° C.          0.258                 t                     CaSO   4     ·     K   2              SO   4     ·   4                     H   2                   O     +                NH   3     +                    CO   2                            +     H   2          O                       
                     CaCO   3     ↓     +       (     NH   4     )     2              SO   4       +       K   2          SO   4       +       H   2        O                       NH   3                   required     =         0.258   382     ×     (   2   )     ×   17     =     0.023                 t                       CO   2                   required     =         0.258   382     ×   44     =     0.030                 t                     CaCO3                 produced     =         0.258   382     ×   100     =       0.067   _                   t                         (     NH   4     )     2          SO   4                   produced     =         0.258   382     ×   132     =       0.089   _                   t                       K   2          SO   4                   produced     =         0.258   382     ×   174     =       0.137   _                   t                                    
     Filtered Solution          ∴     0.137   0.18       =     0.761   |                of                                      H   2        O     _                         Brine                 make        -        up                 is     =                0.137                 t                   K   2          SO   4                                0.089                 t                     (     NH   4     )     2          SO   4                                  0.761   _                   t                   H   2        O                              0.987                 t                 Brine                   %                   K   2          SO   4       =                13.88      %                   %                     (     NH   4     )     2          SO   4       =                  9.00   _        %                   Total                 salts     =                22.88      %                                  
     Conversion of (NH 4 ) 2 SO 4  to K 2 SO 4    
     The solution is cooled to 30° C. 
     KCl that reacts with (NH 4 ) 2 SO 4 =0.100 t 
     This makes 0.070 t NH 4 Cl. 
     Solubility of Cl salts @ 25° C. is 24% 
     7.09% is NH 4 Cl, 17% needs to added.                  Solid                 KCl                 addition                 1     )                   0.010                 t                 for                 reaction                 2   )                       0.168                 t     _                   for                 common                 ion                 crystallization               Total   =                0.178                 t                 KCl                                  
     K 2 SO 4  Crystallization        Brine                 Composition                 at                 Exit                 0.168                 t                 KCl               0.070                 t                   NH   4        Cl               0.020                 t                   K   2          SO   4                     0.761                 t                   H   2       _          O   _                 1.019                 t                 Brine                                
     K 2 SO 4  Production 
     0.137 t+0.118−0.02=0.235 t 
     Recovery of KCl from (NH4)Cl brine          at                 30      %                   NH   4        Cl     ,         KCl                 is                 1      %          
     ∴                  0.07                 t       (     0.761   -   x     )         =   0.30             0.07   =     0.2283   -     0.3      x                 x   =   0.527                                       
     Therefore: 0.527 tonnes of H 2 O is to evaporated for every 0.237 t of K 2 SO 4  production. 
     Evaporative hood 2.22 tonnes H 2 O per tonne of K 2 SO 4    
     KCl solid is recycled to the K 2 SO 4  production step. 
     The ammonium chloride is now reacted with lime. (CaO) 
     0.07 t NH 4 Cl+0.038 t CaO→0.074 t CaCl 2 +0.023 t NH 3 ↑ 
     0.023 t of NH 3  gas is recycled and a 30% brine of CaCl 2  is sold or disposed of. 
     The CaCO 3  precipitated from this process maybe washed and sold as high grade precipitated CaCO 3  for paper coatings or recycled by drying and calcining to produce CaO. The CO 2  may be recovered and recycled using conventional amines.                The                 exit                 brine                 from                 the                 syngenite                 conversion     ,     namely                 the        :               27.7      %                 NaCl                   S   .   G   .                1.218              @              25          °                   C   .                                         2.0      %                 KCl     _                                  
     Solid NaCl may be added to upgrade saturation, but this is not critical. 
     This brine is cooled to between 0 and 10° C. and reacted with NH 3  and excess CO 2  or NH 4 HCO 3 . 
     The process will react with about 90% of the NaCl.          ∴     27.7   ×   0.9       =     24.93      %                 NaCl                 reacts                 to                 produce        :                       1.218   ×   0.2493     58     ×   84     =     0.440                 t                   NaHCO   3                                           
     Solubility of NaHCO 3  @ 0° C. is 5%. 
     ∴ 1.218×0.05=0.061 t NaHCO 3  (liquid)                yield                 of                   NaHCO   3                   crystals     =     0.44   -   0.061                 =       0.379                 t                   NaHCO   3       _                       NaHCO   3                   yield     =         0.379   0.44     ×   100     =       86.1      %     _                              
     Ammonium Chloride Brine Produced                    1.218   ×   0.2493     58     ×   52     =                0.272                 t                   NH   4        Cl                   1.218   ×   0.0277     =                0.034                 t                 NaCl                   1.218   ×   0.02     =                0.024                 t                 KCl                   1.218   ×   0.05     =                0.061                 t                   NaHCO   3                                    0.827                 t                   H   2       _          O   _                                1.218                   t   _                                    
     Lime required                1   )                   for                   NH   4        Cl             0.272     53        (   2   )         ×   56         =             0.144                 t     _                   lime                 2   )                   for                   NaHCO   3               0.061       (   84   )          (   2   )         ×   56         =             0.020                 t     _                   lime                         Total       =           0.164                 t                 lime     _                             CaCl   2                   brine                 produced     _     =                0.282                 t                   CaCl   2                   =                0.076                 t                 NaCl                 =                0.024                 t                 KCl                   23.3      %                   CaCl   2       =                    0.827                 t     _                     H   2        O                                1.209                 t     _                                  
     This brine can be combined with the exit from the KCl recovery step and further processed to sell CaCl 2  or disposed of. 
     Ammonia Recycled            0.272   53     ×   17     =     0.0872                 t                   NH   3                              
     The requirements for CO 2  can be made up by recovering CO 2  from calcining CaCO 3  or by using amine stripping units to recover CO 2  from exhaust gas streams. 
     Key Numbers for Processing        One                     (   m   )     3                   of                 1.24                   S   .   G   .              brine                   of                 saturated                 KCl                 and                 NaCl                     K   2          SO   4                   produced     =                0.235                 t                     NaHCO   3                   produced     =                0.379                 t                   Lime                 used                 as                 CaO     =                0.202                 t                   as                   CaCO   3       =                  0.361                 t     _                     Evaporative                 load                 2.2                 t                   H2O   _                                       t                   K   2          SO   4                   Recycle                   NH   3       =     0.157                 t                                         
     Although embodiments of the invention have been described above, it is not limited thereto and it will be apparent to those skilled in the art that numerous modifications form part of the present invention insofar as they do not depart from the spirit, nature and scope of the claimed and described invention.