Abstract:
Metal complexes having high bulk density and a process for the production of the same without the generation of heavy metal-contaminated effluents are disclosed. Solid complexes of EDTANaFe and EDTAKFe having high bulk densities are formed by reaction with mixed metal solutions containing low chromium levels, followed by total drying of the resulting mixture in the same processing equipment without the prior separation of the sulfate salts formed. The amounts of the various metals in any given formulation can be preselected.

Description:
This application is a continuation-in-part of U.S. application Ser. No. 07/958,376 filed Oct. 8, 1992, now U.S. Pat. No. 5,274,151. 
    
    
     BACKGROUND OF THE INVENTION 
     Conventional processes for the production of solid Fe(III) chelates for agricultural and other uses generate waste crystal liquors with high concentrations of iron and heavy metals, particularly chromium. Such heavy metals are problematic from an environmental standpoint. The economic implications of properly disposing of such streams are significant, and are often prohibitive. In addition, the waste liquor can contain some soluble product. Although disposal of the waste liquors without recovering the product results in yield loss, recovery of contained product is not economical. 
     A conventional process for producing the complexes involves reacting chelating agents, such as EDTNa 4  or DTPANa 5 , with ferric chloride solution, followed by filtration, washing and drying. However, one major source of chromium contamination is the ferric chloride used as the ferric iron source. Where low cost grade ferric chloride derived from scrap iron is used, the chromium concentration of the waste streams produced is on the order of 30 ppm. Higher grade ferric chloride can be used, which can reduce the chromium concentration in the waste streams to about 2-3 ppm; however, this higher grade ferric chloride is more expensive. A further drawback of ferric chloride is the highly corrosive properties of the slurries and liquors produced from the chelating agent/ferric chloride reactions. 
     Prior art drying processes include spray drying and drum drying. However, the resulting product is often very dusty, which creates handling problems. Accordingly, there is a need to find an alternative production process which reduces or eliminates the generation of high heavy metal effluents without adding significant cost. 
     Fertilizer formulations often contain secondary nutrients or micronutrients. These are metals, usually in the form of metal complexes. EDTA is the most commonly used chelating agent and the major micronutrient metals are iron, copper, manganese and zinc. Several other metals are also used as micronutrients in such formulations, including boron, molybdenum and cobalt. Secondary nutrients are calcium and magnesium. The major components of fertilizer formulations are potash, phosphate and nitrogen compounds. To prepare these formulations, the components are blended. This operation requires adding to the blender the major components plus very small amounts of two or more micronutrients or secondary nutrients, each of which must be precisely weighed and thoroughly blended. The blending operation could be simplified and made more efficient if a single mixture of all the micronutrients and secondary nutrients were available as a single blend. One object of this invention is to provide such a blend. 
     SUMMARY OF THE INVENTION 
     The problems of the prior art have been solved by the instant invention, which provides solid complexes having high bulk density and a process for the production of the same without the generation of heavy metal-contaminated effluents. In particular, the present invention relates to the production of blends of metal chelates of EDTA and non-complexed metals in any desired ratio, the blends having high bulk densities. Solutions of metal sulfates and other inorganic salts or oxides are reacted with solutions of EDTANa 4  or EDTAK 4 , followed by total drying of the resulting mixture without the prior separation of the sulfate salts formed. The reaction, mixing and drying processes are carried out in the same processing equipment. By eliminating the separation step and drying the total reaction product, no waste liquor is generated, and a uniform blend of micronutrients is produced. The product loss of prior art processes due to the presence of some soluble product in the waste liquor is thereby eliminated. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention concerns a total drying process for preparation of blends of metal complexes and the resulting products formed thereby. Preferably, the equipment used is a jacketed vessel which is a combinationof a high-torque mixer or reactor and a vacuum dryer, such that the mixing or reaction and the subsequent drying are carried out in the same equipment chamber. Scrapers or ploughshares mounted on the agitator shaft create a mechanically fluidized action to agitate the particles to be dried and to free the heat transfer surface of dried material. In addition, high shear choppers reduce large agglomerate masses to promote thoroughly dried particle interiors. Preferably, the equipment utilizes a hydraulic drive and should be constructed of stainless steel, preferably 316 stainless steel. Such equipment is available from Littleford Bros, Inc., Florence, Ky. 
     In accordance with the present invention, prior to drying, a solution of metal sulfates and other inorganic salts or oxides in predetermined ratiosis produced. To the solution, an equivalent amount of EDTANa 4  or EDTAK 4  solution is added which has been previously acidified with acid to just neutralize the contained free alkali. The reaction is illustrated for EDTANa 4  and ferric, copper, manganese and zinc sulfates as follows: 
     
         EDTANa.sub.4 +0.5Fe.sub.2 (SO.sub.4).sub.3 →EDTANaFe+1.5Na.sub.2 SO.sub.4 
    
     
         EDTANa.sub.4 +CuSO.sub.4 →EDTANa.sub.2 Cu+Na.sub.2 SO.sub.4 
    
     
         EDTANa.sub.4 +MnSO.sub.4 →EDTANa.sub.2 Mn+Na.sub.2 SO.sub.4 
    
     
         EDTANa.sub.4 +ZnSO.sub.4 →EDTANa.sub.2 Zn+Na.sub.2 SO.sub.4 
    
     After drying, the product is a uniform blend of EDTANa x  or EDTAK x metal complexes plus non-complexed metals (such as borate and MoO 4 ) and sodium or potassium sulfate. Exact blends of micronutrients can be produced by preselecting appropriate amounts of reactants and non-reactivemetal compounds. 
     Any metal can be incorporated into the product by using the process disclosed herein. It is not necessary that the metal be complexed with theligand; the total drying process creates a blend of all of the ingredients that have been incorporated as part of the formulation. Particularly suitable metals include iron, copper, manganese, zinc, boron, molybdenum, magnesium, cobalt, and any other metals suitable as micro or secondary nutrients in fertilizer formulations or that may be desired in the formulation to provide some effect. 
     An important feature of the present invention is the ability to preselect the ratio of metals depending upon the desired application. For example, possible micronutrient formulations may be comprised of the following micronutrients in the ratios stated: 
     
         ______________________________________        Parts Metal/100 PartsMicronutrient        Total Metal______________________________________FORMULA 1Fe           47.9Cu           22.3Mn           12.1Zn           17.7FORMULA 2Fe           79.8Mn           20.2FORMULA 3Fe           57.1Cu           16.2Mn           9.0Zn           17.7______________________________________ 
    
     Upon preselecting the desired ratios of metals in the formulation, the necessary quantity of the source of the metal and the chelating agent (e.g., EDTA) to arrive at that desired amount can be readily ascertained by those skilled in the art. 
     Other salts of the chelating agents can be used, such as the potassium salts. The pH-adjusted chelating agent is prepared by neutralizing free alkali metal (e.g., sodium or potassium) hydroxide with the acid chelate, or with a mineral acid, such as 50% or 93% sulfuric acid. Suitable chelating agents are available from Hampshire Chemical Corp. as Hamp-ene® 100S or Hamp-ene® K 4  100 and are one of the feedstocks to the reactor/dryer. Other chelating agents can be used as long as the physical properties of the metal complexes thereof do not cause the mix, when it goes through a &#34;mud stage&#34;, to become too viscous for the processing equipment. A slurry is then formed by reacting the chelating agent with the solution of metal compounds at about 40°-50° C. Preferably the chelating agent is as concentratedas possible in order to reduce the evaporative load on the drying equipmentutilized. In the same piece of equipment, the resulting slurry is vacuum dried to a blend of the alkali metal salts of the metal chelates, alkali metal sulfate, and non-complexed metal compounds such as borate. In contrast to conventional spray drying processes, the instant vacuum dryingemploys relatively long residence times which depend upon the steam pressure and the vacuum applied. 
     Since the entire product is vacuum dried without separation of the alkali metal sulfate salt formed, no effluent is produced and the yield is 100% (less any physical losses that occur). Although the metal content of the final product is lower than the prior art products from which the salt hasbeen separated, a significant savings results from the absence of any effluent and the said 100% yield of product. 
     One surprising aspect of the instant process is the high bulk density of the resulting product formed. A comparison of the total iron content and bulk densities of the products formed in accordance with the instant invention with that of the iron chelate formed from a prior art process (wherein the alkali metal chloride salt (NaCl) has been separated) is illustrated in Table 1: 
     
                       TABLE 1______________________________________                    BULK DENSITYPRODUCT          % Fe    LB/Cu Ft______________________________________EDTANaFe (prior art)            12.6    37.1EDTANaFe/Na.sub.2 SO.sub.4            8.73    62.1EDTAKFe/K.sub.2 SO.sub.4            7.80    61.8______________________________________ 
    
     The very high bulk densities of the instant products is a further advantagewhich offsets the slightly lower iron content of the products due to the presence of the alkali metal sulfate. 
     The total dried product may be milled to remove any gritty material. For commercial applications, it may be desirable to have 100% of the material pass through a 25 mesh sieve. A sieve analysis has demonstrated that about7% of EDTANaFe/Na 2  SO 4  is greater than 25 mesh and therefore requires milling to meet the desirable specifications. 
     It would be obvious to those skilled in the art that the disclosed process should be generally applicable to preparation of metal complexes of ligands other than EDTA. 
     The following examples will serve to illustrate various embodiments of the instant invention. The processes of Examples 1 and 2 were carried out in asmall commercial reactor/dryer. 
     EXAMPLE 1 
     Production of EDTANaFe/Na 2  SO 4   
     The equipment used was a Littleford reactor/dryer model MR5. EDTANa 4  solution was charged to a hold tank and free alkali therein was neutralized with 93% sulfuric acid. As the iron source, 50% Fe 2  (SO 4 ) 3  was used. The Fe 2  (SO 4 ) 3  was charged to the reactor/dryer and warmed to about 40° C. The neutralized chelate was then added in an amount of 3% excess over iron, and the resulting slurry was vacuumed dried to a blend of EDTANaFe and Na 2  SO 4 . The data are provided in Table II. 
     EXAMPLE 2 
     Production of EDTAKFe/K 2  SO 4   
     The reaction and drying were carried out as in Example 1, except that the chelating agent was EDTAK 4  solution. The data are provided in Table III. 
     
                                           TABLE II__________________________________________________________________________Preparation of EDTANaFe/Na2SO4 in MR5 Reactor/Dryer at the 1.0 Lb MoleScale          % Active                Molecular                      Lb  Pounds at          Ingredient                Weight                      Moles                          100% A.I.                                Actual A.I.__________________________________________________________________________Hamp-ene 100S (EDTANa4)          38.0% 380.2 1.030                          392   1031Free NaOH in H-100S          1.5%  40.0  0.386H2SO4 (to neutralize NaOH)          93.0% 98.0  0.193                           19    20Fe2(SO4)3      50.0% 399.9 0.500                          200    400Total                                1451PRODUCT        % FeEDTANaFe             367.1 1.000                          367Na2SO4               142.0 1.693                          240Total Anhydrous Product          9.2%            608Total Product at 8.7% Fe          8.7%            642__________________________________________________________________________Note:the 8.7% Fe value was the Fe content of product produced from the MR5 Reactor/Dryer 
    
     
                                           TABLE III__________________________________________________________________________Preparation of EDTAKFe/K2SO4 IN MR5 Reactor/Dryer at the 1.0 Lb MoleScale          % Active                Molecular                      Lb  Pounds at          Ingredient                Weight                      Moles                          100% A.I.                                Actual A.I.__________________________________________________________________________Hamp-ene K4 100S (EDTAK4)          44.4% 444.6 1.030                          458   1031Free KOH in H-K4 100S          1.5%  56.1  0.276H2SO4 (to neutralize KOH)          93.0% 98.0  0.138                           14    15Fe2(SO4)3      50.0% 399.9 0.500                          200    400Total                                1446PRODUCT        % FeEDTAKFe              383.2 1.000                          383K2SO4                174.3 1.638                          285Total Anhydrous Product          8.4%            669Total Product at 8.7% Fe          7.8%            716__________________________________________________________________________Note:the 7.8% Fe value was the Fe content of product produced from the MR5 Reactor/Dryer 
    
     EXAMPLES 3-5 
     The process used to prepare these samples was designed to simulate the commercial reactor/dryer process equipment. 
     The free NaOH of EDTANa 4  (Hamp-ene® 100S) was neutralized with sulfuric acid and the Ca chelation value (assay) of this solution was determined. To a stainless steel beaker on a stirring hot plate was charged 50% ferric sulfate, 12% Zn solution (as ZnSO 4 ), dry CuSO 4  monohydrate and/or dry MnSO 4  monohydrate, the amounts of each depending upon the specific blend of micronutrients in Formulas 1, 2,and 3 above. The raw material formulas are listed below in Table IV. The actual laboratory charges to produce these formulations are set forth in Table V. The mixture of metal compounds was heated to approximately 65° C. or until a clear solution was obtained. This solution was transferred to a 1 liter round bottom vacuum flask which was then mounted on a rotary evaporator and rotated in a 60° C. bath. A slight vacuum was pulled and the neutralized EDTANa 4  was added over a periodof about 20 minutes. Crystallization occurred when about half of the EDTANa 4  had been added. Full vacuum was applied and the mixture was dried to a moist solid. (The vacuum was occasionally interrupted to scrapematerial off the walls of the flask.) The moist solid was then removed and drying was finished in a 105° C. oven. No tackiness was observed and adhesion to the walls was minimal. All samples dried to a crumbly moist cake, indicating that the products would process well in the commercial reactor/dryer equipment. The dried products were weighed and ground to pass a 20 mesh screen. The 5% pH was measured and found to be 6.56, 6.37 and 6.56 for Formulations 1, 2 and 3, respectively. 
     
                       TABLE IV______________________________________Raw Materials for Preparation of ChelatedMixed Micronutrients for Examples 3-5                        % MetalMolecular Weights        Source of Metal or EDTANa4______________________________________Fe       55.85   50% Fe2(SO4)3   12.5%Cu       63.55   CuSO4.H2O       35.7%Mn       54.94   MnSO4.H2O       29.5%Zn       65.38   ZnSO4 Solution  12.0%EDTANa4  380.18  H-100S (neutralized)                            37.9%______________________________________ 
    
     
                       TABLE V______________________________________Charges for Laboratory Preparations for Examples 3-5             Laboratory Preparations   Desired Metal Ratio               Grams of   Ratioed to   Weight Mole     Raw Material                              Capacity of   Ratio  Ratio    Source     1L Flask______________________________________FORMULA NO. 1Fe        117.5    2.104    940.8    94.9Cu        54.7     0.861    153.2    15.5Mn        29.7     0.541    100.7    10.2Zn        43.3     0.662    360.8    36.4Total Moles        4.168             0.0H-100S             4.376    4389.7   443.0Total Grams                 5945.1   600.0FORMULA NO. 2Fe        117.5    2.104    940.8    147.5Mn        29.7     0.541    100.7    15.8Total Moles        2.645             0.0H-100S             2.777    2785.4   436.7Total Grams                 3826.9   600.0FORMULA NO. 3Fe        60.5     1.083    484.4    110.4Cu        17.2     0.271    48.2     11.0Mn        9.5      0.173    32.2     7.3Zn        18.8     0.288    156.7    35.7Total Moles        1.814             0.0H-100S             1.905    1911.1   435.6Total Grams                 2632.6   600.0______________________________________ 
    
     EXAMPLES 6-7 
     The process used to prepare these samples was designed to more closely simulate the reactor/dryer process equipment than Examples 3-5. The raw materials used for these examples are shown in Table VI. The free alkali in a 38% EDTANa 4  solution (sold commercially as Hamp-ene® 100S) and a 54% EDTAK 4  solution were neutralized with 98% H 2  SO 4 .The amount of acid needed in terms of g 98% H 2  SO 4  /g mole of EDTANa 4  was 14.8 g/M, and in terms of g 98% H 2  SO 4  /g mole of EDTAK 4  was 10.6 g/M. The metal salts in the amounts shown in TableVII were charged to a 1 L round bottom vacuum flask in the following order to obtain a clear solution of the metal salts: thirty grams of water plus the borax was mixed until dissolved; the 50% ferric sulfate was added and mixed until the crystals formed nearly all dissolved; the ZnSO 4  solution was added; the MgSO 4   was added and mixed until dissolved; then the CuSO 4 , MnSO 4  and NaRMoO 4  were added in that order with mixing between each addition until dissolved. The flask was mounted on a rotary evaporator and rotated without vacuum in a 65° C. bath until a clear solution was obtained. A slight vacuum was then applied and the neutralized EDTA solution was sucked into the flask via an addition tube over ˜1 hour. Full vacuum was then applied and the bath temperature was raised to &gt;90° C. Each was stripped to a paste, andthe paste was quantitatively transferred to a tared glass tray and placed in an oven. Each product was dried to constant weight at 105° C. The product was weighed and then ground to pass a 20 mesh screen. The calculated compositions of the dry product are shown in Table VIII. The sodium salt had a 1% solution pH of 9.13, a density of 1.153 g/cc (72.0 lb/ft 3 ) and was a greyish powder. The potassium salt had a 1% solution pH of 7.18, a density of 1.279 g/cc (79.8 lb/ft 3 ) and was a greenish powder. 
     
                       TABLE VI______________________________________Raw Materials for Preparation of Chelated Mixed Micronutrientsfor Examples 6 &amp; 7Molecular                      % Metal orWeights       Source of Metal or Ligand                          EDTAM4______________________________________Fe      55.85     50% Fe2(SO4)3 Solution                              12.5%Cu      63.55     CuSO4.H2O        35.7%Mn      54.94     MnSO4.H2O        29.5%Zn      65.38     ZnSO4 Solution   12.0%B       10.81     Na2B4O7.10H2O    11.3%Mo      95.94     Na2MoO4.2H2O     39.6%Mg      24.31     MgSO4 (anhydrous)                              20.2%EDTANa4 380.18    Hamp-ene 100S Neut.                              37.9%EDTAK4  444.61    Hamp-ene K4 100 Neut.                              53.6%______________________________________ 
    
     
                                           TABLE VII__________________________________________________________________________Formulas for Laboratory Preparations for Examples 6 &amp; 7                       Charges Actually Used                  Grams of                       For Total Charge of 600 gMetal or Weight Ratios    Raw  for Na Salt                                 for K SaltLigand      × 100            Moles Material                       Moles Grams                                 Moles Grams__________________________________________________________________________Fe    0.15  15.0 0.269 120.0                       0.126 56.21                                 0.146 65.29Cu    0.07  7.0  0.110 19.6 0.052 9.18                                 0.060 10.67Mn    0.05  5.0  0.091 16.9 0.043 7.94                                 0.050 9.22Zn    0.06  6.0  0.092 50.0 0.043 23.42                                 0.050 27.20B     0.02  2.0  0.185 17.6 0.087 8.26                                 0.101 9.60Mo    0.0005       0.05 0.0005                  0.13 0.00024                             0.059                                 0.00028                                       0.07Mg    0.06  6.0  0.247 29.7 0.116 13.91                                 0.134 16.16Total moles of metal =            0.994      0.466     0.541Total grams of metal salts =                  254.0EDTANa4          1.024 1026.9                       0.480  481.01EDTAK4           1.024 848.8          0.557 461.8Total grams to produce Na Salts =                  1280.9     600.00Total grams to produce K salts =                  1102.8               600.0__________________________________________________________________________ 
    
     
                       TABLE VIII______________________________________Calculated Compositions of Dry Products of Examples 6 &amp; 7 andProperties of the Dry Products______________________________________            Sodium Potassium            Salt   Salt______________________________________Estimation of Sulfate Content            Moles of SulfateFrom H2SO4         0.071    0.059From Fe2(SO4)3     1.189    0.219From CuSO4         0.052    0.060From MnSO4         0.043    0.050From ZnSO4         0.043    0.050From MgSO4         0.116    0.134Total              0.513    0.572Calculated Grams of Contained Sulfate            Na2SO4 K2SO4            72.80  99.66Calculated Grams of Contained MetalFe                 7.026    8.161Cu                 3.279    3.808Mn                 2.342    2.720Zn                 2.811    3.264B                  0.937    1.088Mo                 0.023    0.027Mg                 2.811    3.264Estimated EDTA ContentMoles              0.480    0.557gEDTAH2Na2         160.3gEDTAH2K2                   204.1Total Calculated Grams =              252.3    326.1Calculated Composition of Dry Products            Composition Wt. %Na2SO4             28.86%K2SO4                       30.57%Fe                 2.79%    2.50%Cu                 1.30%    1.17%Mn                 0.93%    0.83%Zn                 1.11%    1.00%B                  0.37%    0.33%Mo                 0.01%    0.01%Mg                 1.11%    1.00%*EDTAH2Na2         63.52%*EDTAH2K2                   62.59%Total              100.00%  100.00%*Free + complexed______________________________________Measured Properties of Dry Products              Na Salt  K Salt______________________________________pH of 1% Solution  9.13     7.18Density, g/cc      1.153    1.279Density, lb/cu. ft 72.0     79.8Appearance of powder              grey     greenish______________________________________