Abstract:
Improved potassium sulfate/potassium nitrate salt products in both solid particulate and liquid form are provided which exhibit enhanced salt solubility in water. The products include potassium nitrate and potassium sulfate, in combination with a surfactant and mixed together in water. The aqueous mixture is heated to a maximum reaction temperature in the range of about 100-°210° F., and will retain enhanced water solubility in either a heated or cooled condition.

Description:
This application is a continuation of application Ser. No. 08/310,487, filed Sep. 22, 1994 and now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with improved potassium sulfate/potassium nitrate salt products having enhanced water solubility permitting them to be used with greater efficiency as liquid, spray-on fertilizer products. More particularly, it is concerned with such improved potassium products, as well as a method of producing the same, wherein treated potassium sulfate and potassium nitrate (a surfactant may optionally be added) are mixed with water and subjected to heating to a temperature of 100°-210° F.; the solution, when cooled, exhibits a significantly increased potassium solubility (measured in terms of K 2  O solubility), as compared with either untreated potassium sulfate or potassium nitrate solutions individually. 
     2. Background 
     Potassium sulfate (K 2  SO 4 ), potassium chloride (KCl) and potassium nitrate (KNO 3 ) are all used as fertilizer products to a greater or lesser degree. Potassium chloride is the most widely used potassium salt, but is inapplicable for chloride and/or salt-sensitive crops such as tobacco, fruits, vegetables and turfs. However, KCl has a significant water solubility on the order of 14-16% (measured as K 2  O), and therefore this salt is often applied as a liquid. 
     Potassium sulfate (commonly referred to in the trade as sulfate of potash or SOP) is a premium fertilizer product. Certain grades of SOP, particularly those manufactured from the brine of the Great Salt Lake, are especially valuable products because they are essentially free of chlorides. Therefore, such products are admirably suited for use on chloride and/or salt-sensitive crops and the like. A drawback of SOP, however, is that in its natural state it is significantly less soluble in water than KCl, having an ambient temperature solubility of about 4-6 wt % as K 2  O. This relatively low water solubility has inhibited the use of K 2  SO 4  as a liquid fertilizer product, despite its otherwise significant advantages. 
     Potassium nitrate is more soluble than SOP, normally about 9-11 wt % as K 2  O, but is a very expensive product as compared with KCl or K 2  SO 4 . Nevertheless, it has achieved some commercial utility as a liquid fertilizer source, owing at least in part to its low salt index. 
     The water solubility of potassium sulfate salt products may be enhanced to ≧8% (as K 2  O) by use of the method taught in U.S. Pat. No. 5,298,050 (the teachings of which are incorporated herein by reference), wherein potassium sulfate is mixed with water and an appropriate surfactant and optional defoamer, hereinafter referred to as &#34;enhanced soluble potash&#34; (hereinafter referred to as or &#34;ESP&#34;). 
     It will of course be appreciated that the further enhancement of the solubility of potassium sulfate salts would represent a significant advance. Such an improvement would mean that more concentrated solutions could be prepared and applied, thereby lessening preparation, storage and transportation costs associated with the liquids. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems outlined above, and provides improved potassium sulfate products (both solids and liquids) which exhibit materially improved water solubilities. The invention is predicated upon the discovery that improved aqueous compositions having enhanced potassium solubilities can be formulated through the use of a mixture of ESP with potassium nitrate in water. In particular, the improved composition of the instant invention exhibits significantly increased potassium solubility, as compared to either untreated potassium sulfate or potassium nitrate solutions, individually or in combination. 
     As described in U.S. Pat. No. 5,298,050, ESP broadly includes potassium sulfate products supplemented with an appropriate surfactant and optional defoamer. In preparative procedures, the potassium sulfate and surfactant are present in water solution, which solution is heated to a temperature in the range of 100° to 210° F. ESP may also be formulated by means of particulate potassium sulfate with a surfactant and optional defoamer applied onto the surface thereof. As disclosed in the &#39;050 patent, the surfactant is present at a level of at least about 0.1 wt %, or preferably at least 0.25 wt %, and most preferably from about 0.30-0.50 wt %, based upon the weight of the nominally dry potassium sulfate. 
     The preferred surfactants for use in the instant invention, and as described in the &#39;050 patent, are selected from the group consisting of the disulfonate and oxyalkylated alcohol-carboxylic acid adduct surfactants. In former class, the alkly diphenyl ether disulfonates are preferred, wherein the alkly group contains from about 8-22 carbon atoms, and more particularly from about 10-18 carbon atoms, moreover, the alkyl group of the disulfonate is preferably linear. The second class of preferred surfactants are those selected from the group consisting of surfactants having the general formula: ##STR1## wherein R is a C 8  -C 22  hydrophobe, X and Y are individually selected from the group consisting of CH 3  and a succinic acid radical, and n ranges from about 1-8. Particularly preferred are the succinic acid derivatives wherein the hydrophobe has a carbon number of from about 9-16. 
     As yet further disclosed in the &#39;050 patent, in a further aspect of ESP, aqueous potassium sulfate solutions are provided which comprise water, dissolved potassium sulfate and a surfactant of the type and in the amounts described previously; a defoamer may also optionally be used. 
     The method of increasing potassium solubility in the present invention comprises the steps of mixing together quantities of water, potassium sulfate, a surfactant and optional defoamer of the types and the amounts specified in connection with the particular products, and potassium nitrate. 
     The mixture is then heated to a reaction temperature of 100°-210° F., preferably with agitation or stirring. In this respect, it has been found that increasing the reaction temperature has a positive effect upon solubility. However, for overall reasons of ease of processing and handling, and fuel economy, it is believed that a solution having ≧14% potassium solubility (measured as K 2  O) is commercially feasible. These types of solutions can readily be produced using a maximum reaction temperature on the order of 100°-140° F. 
     After the maximum reaction temperature is achieved, it may be held at this maximum temperature for a short time (e.g., 5 minutes) whereupon the solution is allowed to cool, again with at least occasional agitation or stirring, to approximately room temperature (i.e., 68°-75° F.). 
     The ESP and potassium nitrate reagents can be individually stored and shipped to a remote location in proximity to a point of use. Thereupon, the ESP/potassium nitrate reagents can be dissolved in hot water, or placed in cold water and heated to a minimum reaction temperature and cooled to about ambient. This liquid is then eminently suited for spray application onto a crop or turf grass, or direct application to the soil. The dissolved salt content as K 2  O will not significantly decrease over time, and little or no salting out or precipitation should occur. 
     To give a specific example, a 100 pound sample of K 2  SO 4  can be sprayed with 0.5 wt % of a preferred disulfonate surfactant, which will adequately adhere to the K 2  SO 4  without drying or other steps. This amount of ESP can then be dissolved with 233 pounds of potassium nitrate in 90 gallons of water and heated to a temperature of 110°-120° F. The product will then have a minimum of 14% solubility as K 2  O, with a surfactant content on the order of 460 ppm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a graphical representation illustrating comparative tests with KNO 3  and K 2  SO 4  at ambient temperature (about 71°-74° F.), and showing the effect of formulating a solution with KNO 3  and K 2  SO 4  treated with surfactant, followed by heating. 
     FIG. 2 is a graphical representation illustrating comparative tests with KNO 3  and K 2  SO 4  at a temperature of about 50° F., and showing the effect of formulating a solution with KNO 3  and K 2  SO 4  treated with surfactant, followed by heating. 
     FIG. 3 is a graphical representation illustrating comparative tests with KNO 3  and K 2  SO 4  at different temperatures. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following examples are illustrative of the present invention. It should be understood, however, that these examples are to be taken by way of illustration only and nothing therein should be considered as a limitation upon the overall scope of the invention. 
     As indicated above, one preferred class of surfactants for use in the present invention is the disulfonates, and particularly the alkyl diphenyl ether disulfonates. Two particular products which have been found to be useful are the Poly-Tergent 2A1-L anionic surfactant and the Poly-Tergent 3B2 anionic surfactant, both of which are commercialized by Olin Chemicals of Stamford, Conn. 
     The 2A1-L surfactant is a linear dodecyl diphenyl ether sodium disulfonate, having a freezing point of 32° F., a boiling of 212° F., a specific gravity of 1.16, a bulk density of 9.15 lb/gal., a pH at 25° C. of greater than 9, and a vapor pressure at 25° C. of 23.7 mm Hg. This product is further defined in an Olin Product Data Sheet entitled &#34;Poly-Tergent 2A1 Acid and Poly-Tergent 2A1 Artionic Surfactant&#34;, and the associated Material Safety Data Sheets, all of which are incorporated by reference herein. 
     The Poly-Tergent 3B2 anionic surfactant is a decyl diphenyl ether sodium disulfonate having essentially the same physical properties as the 2A1-L surfactant. The 3B2 surfactant is described in an Olin Product Data Sheet entitled &#34;Poly-Tergent 3B2 Acid and Poly-Tergent 3B2 Artionic Surfactant&#34;, and the associated Material Safety Data Sheets; these publications are incorporated by reference herein. 
     Another disulfonate of interest is the Poly-Tergent 4C3 anionic surfactant commercialized by Olin Chemical. This is the sodium salt of hexadecyl diphenyl ether disulfonic acid. Its physical data vary slightly as compared with the 2A1-L and 3B2 surfactants. This product is described in an Olin Product Data Sheet entitled &#34;Poly-Tergent 4C3 Artionic Surfactant&#34; and the related Material Safety Data Sheets, and these materials are incorporated by reference herein. 
     One type of the oxyalkylated alcohol-carboxylic acid adduct surfactants preferred for use in the invention is the Poly-Tergent C-series surfactants commercialized by Olin Chemical. This series is a family of 9 polycarboxylated surfactants having the formula described previously. Particularly preferred members of this class are the succinic acid derivative products, with hydrophobes having an average carbon length ranging from C 9  -C 16 . This class of surfactants is described in an Olin Product Data Sheet entitled &#34;Poly-Tergent C-Series Polycarboxylated Multi-functional Surfactants&#34;, and the related Material Safety Data Sheets, all of which are incorporated by reference herein. 
     In some instances, it may be advisable to add a very minor amount of a defoamer to the potassium sulfate salt products of the invention, in order to minimize foaming during heating and stirring. One suitable defoamer is a product commercialized under the name &#34;Foam Ban Co&#34; by Ultra Additives, Inc. of Patterson, N.J. This proprietary product contains polyalkylene glycol as well as an oxyalkylene polymer, and is known to be useful as an anti-foam/defoamer agent. 
     The potassium sulfate and potassium nitrate of the invention can be derived from virtually any commercial source. However, the use of the Soluble Fine grade of potassium sulfate sold by Great Salt Lake Mineral Corporation is particularly preferred. This material is in itself a premium product which is free of KCl. Therefore, this K 2  SO 4  is especially suited for applications where significant chloride ion presence cannot be tolerated. 
     In all the examples discussed below, ingredients were weighed into a 600 ml beaker equipped with a magnetic stirring bar. The mixtures of liquid and solid were then brought up to the temperature indicated while stirring. The resulting solutions were then placed into a constant temperature bath and then cooled. Each sample was allowed sufficient time to reach equilibrium temperature and to allow crystallization to occur. Each beaker was also stirred periodically to break any supersaturation. 
     Example 1 
     In this series of tests, samples of reagent grade K 2  SO 4  and KNO 3  were treated with the surfactant Poly-Tergent 3B2 and a magnesium compound to determine the resulting enhancement of potassium solubility. In each test, water containing 0.16 wt % 3B2 surfactant and 2.13 wt % MgSO4 was added to solid K 2  SO 4  to form ESP with a constant Mg and surfactant content. Solid KNO 3  was added to the mixture and the mixture was then heated to 160° F. and allowed to cool to ambient temperature. Each test sample was then filtered and the clear solution analyzed for salt and ingredient content. Table 1 sets forth the results of these test runs. 
     
                                           TABLE 1__________________________________________________________________________(Solid ESP and KNO.sub.3 with Water and with Added Surfactant 3B2 and MgIon to Maintain Constant HigherLevels of Mg and Surfactant)Sample    Starting Weights.sup.1           Solid Mix                Temp                    Analyzed                         Weight percent in Solution                                       Surfactant#   Liquid   K.sub.2 SO.sub.4       KNO.sub.3           % ESP                Deg F.                    K.sub.2 O.sup.3                         Mg SO.sub.4                               NO.sub.3 *.sup.4                                   H.sub.2 O*.sup.5                                       ppm__________________________________________________________________________561 287     135      74  12.23                         0.32                            1.54                               15.7                                   72.3                                       1088562 340 16  144 10   74  12.99                         0.29                            3.42                               14.2                                   71.4                                       1088563 340 24  136 15   74  13.56                         0.32                            4.25                               14.0                                   70.2                                       1088565 340 40  120 25   74  15.02                         0.33                            5.02                               15.0                                   67.2                                       1088566 340 48  112 30   74  14.59                         0.31                            5.04                               14.3                                   68.3                                       1088567 340 64   96 40   74  13.88                         0.34                            5.48                               12.9                                   69.7                                       1088569 340 96   64 60   74  11.47                         0.35                            5.93                               9.2 75.0                                       10885610    340 112  48 70   74  10.43                         0.36                            6.41                               7.3 77.3                                       1088__________________________________________________________________________ .sup.1 Weights are in grams .sup.2 Weight percent of solid ESP in the solids used (ESP + KNO.sub.3) .sup.3 K.sub.2 O is a calculated value determined by the equation K.sub.2 O = (% K) × (1.2046) .sup.4 The NO.sub.3 content was calculated from the molecular balance after analyzing for the other ions. .sup.5 The water weight percent was calculated as the difference between 100% and the sum of the ions in weight percent. *Calculated 
    
     The data appearing in Table 1 demonstrates the significant increase in potassium solubility derived from the addition of ESP, potassium nitrate and water, and heating in accordance with the present invention. The advantageous results are particularly evident where the initial weight ratio of ESP (measured as wt % K 2  SO 4 ) to KNO 3  is 30% (at which level potassium concentration is 14.59 (measured as K 2  O). This value far exceeds the theoretical potassium concentration which can be achieved if only potassium sulfate and potassium nitrate are mixed in water at the same initial weight ratio of 30%. For 30% K 2  SO 4  /70% KNO 3 , the theoretical K 2  O content is calculated as follows: 
      K 2  O!=(wt % K 2  SO 4 ) K 2  O from 100 wt % K 2  SO 4  Theo!+(wt % KNO 3 ) K 2  O from 100 wt % KNO 3  Theo! 
     where: 
     wt % K 2  SO 4  =30% 
     K 2  O from 100 wt % K 2  SO 4  at 71° F.=5.57 wt % KNO 3  =70% 
     K 2  O from 100 wt % KNO 3  at 71° C.=11.77  K 2  O!=(0.30)(5.57)+(0.07)(11.77)=9.91 
     The following Table 2 sets forth K 2  O values for various ESP/KNO 3  /water systems, as well as giving the known solubilities for potassium nitrate and potassium sulfate. 
     
                       TABLE 2______________________________________ESP-KNO3-Water Systems       Weight %Start       K.sub.2 O in Solution at Temperature                          Surfactant#    Solids**   71 F.  60 F.                       50 F.                            40 F.                                 30 F.                                      (ppm)______________________________________55    30% ESP.sup.1           14.18  11.93                       10.56                            9.36 6.69 46054    70% ESP   9.71   9.65 8.65 7.79 7.17 750Theo 100% KNO.sub.3.sup.2           11.77  9.76 8.05 6.43 5.29  071   100% ESP   8.55   7.84 6.78 6.20 5.12 967Theo 100% K.sub.2 SO.sub.4.sup.3           5.57   5.03 4.59 4.16 3.62  0______________________________________ **Mixtures are ESP with KNO.sub.3 .sup.1 ESP was prepared according to Example 3, Table 5 in U.S. Pat. No. 5,298,050 (GSL Production ESP (Sprayed K.sub.2 SO.sub.4)) .sup.2&amp;3 The theoretical KNO.sub.3 and K.sub.2 SO.sub.4 concentrations were from Lange&#39;s Handbook of Chemistry (McGrawHill Publishing) and Seidell Solubility Tables (American Chemical Society, 1965) 
    
     Contrasting the theoretical potassium concentration calculated above (i.e.,  K 2  O!=9.91) with the actual potassium concentration achieved when practicing the invention as taught by Example 1 (i.e.,  K 2  O! actual=14.59, 74° F., 30 wt % ESP), it can be appreciated that there is a significant increase in potassium concentration as a result of the composition of the instant invention. 
     Example 2 
     In this test, a number of runs were carried out to determine the effect of allowing the Mg content to decrease while the surfactant level in the composition was maintained having 500 ppm in one series and a constant 1000 ppm in another series. The major objective was to obtain additional cooling data between 5-95% ESP in the solid mix, and to determine whether the Mg and surfactant levels needed to be maintained. In each test, water containing 0.03 wt % 3B2 surfactant was added to solid ESP (obtained from Great Salt Lakes Minerals Production, Ogden, Utah) to form adjusted ESP and maintain the surfactant level above 500 ppm and at a constant 1000 ppm in the solution. Solid KNO 3  was then added and the mixture heated to 160° F. and allowed to cool to ambient temperature. Each sample was then filtered and the clear solution analyzed. Each solution was then progressively cooled and sampled. Tables 3 and 4 set forth the results of these test runs. 
     The data presented in Table 3 and 4 also demonstrate the significant increase in potassium solubility derived from the addition of KNO 3  ( K 2 )!=13.44, 40 wt % ESP, 72° F.) even where  MgSO 4  ! is reduced in the composition and surfactant level below those in Example 
     
                                           TABLE 3__________________________________________________________________________(Solid Protection ESP With KNO.sub.3 and Water with Surfactant 3B2 Addedto Assure the PPM Level wasabove 500)Starting Weights.sup.1          Solid Mix               Temp                   Weight percent in Solution                                       Surfactant#  Liquid  ESP KNO.sub.3          % ESP.sup.2               Deg F.                   K.sub.2 O.sup.3                      Mg Cl SO.sub.4                               NO.sub.3 *.sup.4                                   H.sub.2 O*.sup.5                                       ppm__________________________________________________________________________21 410 81   9  90   72  8.50                      0.16                         0.48          81222 402 78  20  80   72  9.81                      0.18                         0.46          78323 392 75  32  70   72  10.60                      0.16                         0.49          75424 380 72  48  60   72  11.36                      0.16                         0.45          71825 368 66  66  50   72  12.36                      0.15                         0.45          65926 354 58  88  40   72  13.44                      0.13                         0.41          585271   413 83   4  95   74  8.97                      0.19                         0.54                            8.64                               0.7 82.5                                       826281   406 80  14  85   74  9.59                      0.17                         0.53                            8.37                               1.8 81.2                                       795291   397 77  26  75   74  10.13                      0.18                         0.43                            8.07                               3.1 79.8                                       7752101   387 74  40  65   74  10.34                      0.18                         0.44                            7.36                               4.3 79.2                                       7362111   375 69  56  55   74  11.30                      0.16                         0.44                            6.72                               6.2 77.1                                       6892121   362 62  76  45   74  11.70                      0.14                         0.38                            5.80                               8.0 76.0                                       623          % ESP212   Cooled #&#39;s 21-2121          90   50  7.16                      0.18                         0.45                            7.07                               0.4 85.9                                       812222            80   50  8.54                      0.19                         0.44                            6.94                               2.5 82.9                                       783232            70   50  9.00                      0.18                         0.49                            6.65                               3.3 81.9                                       754242            60   50  10.46                      0.16                         0.42                            6.16                               5.9 78.7                                       718252            50   50  11.46                      0.15                         0.40                            5.75                               7.7 76.5                                       659262            40   50  10.66                      0.14                         0.38                            5.51                               7.0 78.2                                       585273            95   50  7.00                      0.21                         0.51                            7.30                               -0.0                                   86.2                                       826283            85   50  8.01                      0.20                         0.48                            7.14                               1.5 84.0                                       795293            75   50  8.75                      0.21                         0.45                            6.93                               2.9 82.3                                       7752103           65   50  9.58                      0.19                         0.42                            6.78                               4.1 80.6                                       7362113           55   50  11.12                      0.18                         0.48                            6.35                               6.5 77.2                                       6892123           45   50  10.84                      0.16                         0.36                            5.83                               6.9 77.7                                       623__________________________________________________________________________ *Calculated .sup.1 Weights are in grams .sup.2 Weight percent of solid ESP in the solids used (ESP + KNO.sub.3) .sup.3 K.sub.2 O is a calculated value determined by the equation K.sub.2 O = (% K) × (1.2046) .sup.4 The NO.sub.3 content was calculated from the molecular balance after analyzing for the other ions. .sup.5 The water weight percent was calculated as the difference between 100% and the sum of the ions in weight percent 
    
     
                                           TABLE 4__________________________________________________________________________(Solid Production ESP With KNO.sub.3 and Water with Surfactant 3B2 Addedfor a Constant PPM Level)Starting Weights.sup.1          Solid Mix               Temp                   Weight percent in Solution                                       Surfactant#  Liquid  ESP KNO.sub.3          % ESP.sup.2               Deg F.                   K.sub.2 O.sup.3                      Mg Cl SO.sub.4                               NO.sub.3 *.sup.4                                   H.sub.2 O*.sup.5                                       ppm__________________________________________________________________________313   349 53   98 35   73  12.62                      0.13                         0.37                            4.86                               10.4                                   73.8                                       1000314   346 46  108 30   73  12.99                      0.11                         0.34                            4.53                               11.2                                   73.0                                       1000315   341 40  119 25   73  11.40                      0.11                         0.30                            4.25                               9.6 76.3                                       1000316   348 30  122 20   73  13.08                      0.07                         0.25                            3.57                               12.5                                   72.7                                       1000317   355 22  123 15   73  12.59                      0.05                         0.18                            2.66                               13.1                                   73.6                                       1000318   366  7  127  5   73  12.12                      0.06                         0.19                            1.41                               14.1                                   74.2                                       1000          % ESP3132   Cooled #&#39;s 313-318          35   50  10.42                      0.13                         0.31                            5.07                               7.3 78.5                                       10003142           30   50  10.41                      0.15                         0.31                            4.87                               7.6 78.4                                       10003152           25   50  10.31                      0.17                         0.32                            4.68                               7.8 78.4                                       10003162           20   50  9.95                      0.11                         0.25                            3.85                               8.3 79.3                                       10003172           15   50  9.40                      0.08                         0.21                            2.94                               8.6 80.4                                       10003182            5   50  8.31                      0.08                         0.20                            1.15                               9.5 82.2                                       1000__________________________________________________________________________ *Calculated .sup.1 Weights are in grams .sup.2 Weight percent of solid ESP in the solids used (ESP + KNO.sub.3) .sup.3 K.sub.2 O is a calculated value determined by the equation K.sub.2 O = (% K) × (1.2046) .sup.4 The NO.sub.3 content was calculated from the molecular balance after analyzing for the other ions. .sup.5 The water weight percent was calculated as the difference between 100% and the sum of the ions in weight percent 
    
     Example 3 
     In this example, a number of runs were carried out to determine the effect of using non-adjusted ESP in formulating composition. In each test, water was added to solid ESP (obtained from Great Salt Lake Minerals Production). Solid KNO 3  was then added to the mixture, and the mixture was heated to 160° F. and allowed to cool to ambient temperature. Each sample was then filtered and the clear solution was analyzed. Each sample was then progressively cooled and further analyzed. Table 5 sets forth the results of these test runs. 
     
                                           TABLE 5__________________________________________________________________________(Solid Production ESP with KNO.sub.3 and Water, No Other Additives)Starting Weights.sup.1          Solid Mix               Temp                   Weight percent in Solution                                       Surfactant#  H2O ESP KNO.sub.3          % ESP.sup.2               Deg F.                   K.sub.2 O.sup.3                      Mg Cl SO.sub.4                               NO.sub.3 *.sup.4                                   H.sub.2 O*.sup.5                                       ppm__________________________________________________________________________52 410 81   9  90   71  8.75                      0.20                         0.44                            8.40                               0.9 82.8                                       81053 402 78  20  80   71  9.55                      0.18                         0.44                            8.14                               2.2 81.1                                       78054 393 75  32  70   71  9.71                      0.20                         0.41                            7.32                               3.6 80.4                                       75055 346 46  108 30   71  14.18                      0.13                         0.28                            4.63                               12.9                                   70.3                                       46056 348 30  122 20   71  13.49                      0.10                         0.23                            3.98                               12.7                                   71.8                                       30057 361 14  125 10   71  12.80                      0.03                         0.18                            1.55                               14.7                                   72.9                                       140          % ESP522   Cooled #&#39;s 52-57          90   50  6.99                      0.19                         0.48                            6.46                               1.0 86.1                                       810532            80   50  7.63                      0.19                         0.45                            6.44                               1.9 84.7                                       780542            70   50  8.65                      0.18                         0.44                            6.17                               3.6 82.5                                       750552            30   50  10.56                      0.12                         0.36                            4.61                               7.9 78.2                                       460562            20   50  9.84                      0.07                         0.32                            3.51                               8.2 79.7                                       300572            10   50  8.78                      0.09                         0.20                            1.79                               9.4 81.3                                       140__________________________________________________________________________ *Calculated .sup.1 Weights are in grams .sup.2 Weight percent of solid ESP in the solids used (ESP + KNO.sub.3) .sup.3 K.sub.2 O is a calculated value determined by the equation K.sub.2 O = (% K) × (1.2046) .sup.4 The NO.sub.3 content was calculated from the molecular balance after anlyzing for the other ions. .sup.5 The water weight percent was calculated as the difference between 100% and the sum of the ions in weight percent 
    
     The data in Table 5 demonstrate that a composition can be advantageously prepared without adjusting the composition of the ESP, under which conditions the potassium concentration is significantly higher than theoretical ( K 2  O! actual=14.18, 30 wt % ESP, 71° C. compared to  K 2  O! theoretical=9.91 (as calculated above)). 
     Example 4 
     In this example, a number of runs were carried out to determine the effect of using K 2  SO 4  rather than ESP. In each test, water was added to reagent grade. K 2  SO 4  meeting American Chemical Society specifications for reagent grade (obtained from Fisher Scientific Company). Solid KNO 3  was then added and the mixture heated to 160° F. The mixture was then allowed to cool to ambient temperature. Each sample was next filtered and the clear solution was then analyzed. Each solution was then progressively cooled and thereafter analyzed at the cooler temperature. The data in Table 6 sets forth the results of these test runs. 
     
                                           TABLE 6__________________________________________________________________________(Reagent Grade K.sub.2 SO.sub.4, KNO.sub.3 and H.sub.2 O, No OtherAdditives)Starting Weights.sup.1          Solid Mix                Temp                    Weight percent in Solution#  H2O K.sub.2 SO.sub.4      KNO.sub.3          % K2SO4.sup.2                Deg F.                    K.sub.2 O.sup.3                       SO.sub.4                          NO.sub.3 *.sup.4                              H.sub.2 O*.sup.5__________________________________________________________________________91 356 14  130 10    73  11.56                       1.84                          12.8                              75.792 375 25  100 20    73  12.36                       2.80                          12.7                              74.393 398 31   71 30    73  9.97                       3.43                          8.7 79.694 422 39   39 50    73  7.76                       4.31                          4.6 84.695 434 46   20 70    73  6.66                       4.82                          2.5 87.196 441 53   6  90    73  5.95                       4.94                          1.5 88.7971   355 22  123 15    73  10.53                       2.97                          10.0                              78.3981   389 28   84 25    73  10.85                       2.97                          10.5                              77.6991   412 36   54 40    73  8.65                       3.67                          6.6 82.59101   430 42   28 60    73  6.97                       4.58                          3.3 86.49111   437 51   13 80    73  6.32                       5.13                          1.7 87.99121   443 55   3  95    73  5.64                       5.30                          0.6 89.4          % K2SO4912   Cooled #&#39;s 91-9121          10    50  8.79                       1.86                          9.2 81.7922            20    50  9.25                       2.51                          8.9 80.9932            30    50  8.43                       Lost942            50     0  6.50                       Lost952            70    50  5.52                       3.66                          2.5 89.2962            90    50  4.65                       4.13                          0.8 91.2973            15    50  9.76                       2.93                          9.1 79.9983            25    50  9.29                       2.73                          8.7 80.9993            40    50  8.00                       3.09                          6.5 83.79103           60    50  6.06                       3.5O                          3.5 88.09113           80    50  5.17                       4.02                          1.6 90.19123           95    50  4.57                       4.40                          0.3 91.5__________________________________________________________________________ *Calculated .sup.1 Weights are in grams .sup.2 Weight percent of K.sub.2 SO.sub.4 in the solids used (K.sub.2 SO.sub.4 + KNO.sub.3) .sup.3 K.sub.2 O is a calculated value determined by the equation K.sub.2 O = (% K) × (1.2046) .sup.4 The NO.sub.3 content was calculated from the molecular balance after analyzing for the other ions. .sup.5 The water weight percent was calculated as the difference between 100% and the sum of the ions in weight percent 
    
     The highest K 2  O value attainable using the method of this example was 12.36 (20 wt % K 2  SO 4 , 73° F.), which is still substantially less than that attainable using the method taught by the instant invention (i.e.,  K 2  O!=15.02, see Example 1 and Table 1). 
     FIG. 1 illustrates in graphical form the effect of using the various compositions of Examples 1 through 4, the data presented corresponding to temperatures in the range of 71°-74° F. FIG. 1 also includes published solubility data for K 2  SO 4  /KNO 3  water systems as contained in Linke, Solubilities, Inorganic and Metal-Organic Compounds, American Chemical Society (4th Ed., 1965). Likewise, FIG. 2 illustrates in graphical form the effect of using the various compositions of Examples 1 through 4 at the lower temperature of about 50° F. 
     FIG. 3 is a graphical illustration of the data presented in Table 2, showing the effect upon the various solutions by lowering temperature.