AU8909598A - Compositions comprising iron chelates - Google Patents

Description

WO 99/08982 PCT/US98/16994 COMPOSITIONS COMPRISING IRON CHELATES Field of the Invention The present invention is generally about solubilization of iron ions in aqueous systems. A specific implementation of the invention is in preparing 5 solubilized chelated iron to crops in an easily manageable form. Background of the Invention The use of synthetic phenolic chelating agents for solubilizing iron is a well known practice in aqueous systems buffered to pH values higher than neutral. In the environments of hard water being buffered by carbonates or bicarbonates, 10 a constant value of pH above 7.5 is maintained. For agricultural purposes, application of iron chelates to soils being buffered by carbonates causes fast removal of the iron ions from the chelating agent, thus rendering the iron ion prone to precipitation in the form of sparingly soluble ferric hydroxide (Chen and Barak, Iron nutrition of plants in calcareous soils, 1982, Advances in Agronomy, 15 35: 217-240). The commercial phenolic chelating agents EDDHA (ethylene diamine di- o- hydroxy phenylacetic acid) and EDDHMA (ethylene diamine di o- hydroxy phenyl methyl acetic acid) effectively bind ferric ions up to pH values well above those occurring in soils and thus favoring the use of said phenolic chelating agents in agriculture in the most demanding conditions occurring in 20 soils. However, the phenolic chelates suffer from two main shortcomings: (a) their high prices and (b) handling difficulty associated with the need to spend time and effort on solubilizing dry commercial preparation in the fertilizing tank. 1 WO 99/08982 PCT/US98/16994 To deliver liquid iron chelate to the consumer would be beneficial due to the fact that modem fertilizing schemes tend to prefer using ready made soluble mixes of liquid fertilizers to dispersion of granular forms of fertilizers in the fields or orchards. A product overcoming the shortcomings indicated above to an 5 appreciable extent, would constitute an improvement in the delivery and consumption of iron chelates. However, saving the cost of drying in the manufacturing process requires that the extent that the remaining water, by raising the cost of transportation, should not compromise the above saving. Consequently, the solution should be as concentrated as possible in order to 10 become more cost efficient. Summary of the Invention The present invention provides a means for the production of high concentrations of soluble chelated iron capable of being easily distributed to plants. By one of its aspects a product made according to the invention is an 15 aqueous solution characterized in having a high pH value, containing solubilized iron ions chelated by at least one ligand comprising a plurality of hydroxyl groups, in such a manner that pouring said solution into water delivers into the water the chelated iron without the need for any effort other than the pouring action itself, said water being characterized in that its pH value may be between 3 to 12, such 20 that the new mixture formed with said water is stable over periods extending above at least two days. According to another aspect of the invention, there is provided a method for processing iron chelated with phenolic, ethylene diamine based ligands such 2 WO 99/08982 PCT/US98/16994 that an aqueous solution is obtained comprising adding a ligand having a plurality of hydroxyl groups, in high pH environment, said solution characterized in providing a source of chelated iron stable over a wide range of pH values. Description of the Invention 5 Sequestrene T M , which is a ferric ion chelate with EDDHA by Ciba-Geigy, containing 6% chelated iron, was mainly used to demonstrate the method according to the invention. Example 1. Ten grams of SequestreneTM were mixed with 300 ml of tap water. The slurry was stirred thoroughly and after 30 minutes all the solubles 10 were dissolved. Example 2. Ten grams of SequestreneTM were mixed with 70 ml water in a beaker. After stirring the slurry, a clear solution formed with some undissolved granules left on the bottom of the beaker. In a separate beaker, 8 grams of tartaric acid and 18 grams of KOH were mixed with 50 ml water. The mixture, having a 15 high pH value, was stirred until settling and clearing. After cooling down the clear solution, it was poured with stirring into the beaker containing the SequestreneTM. Immediately a dark clear solution formed, with all granules dissolved except for slight light-brown residue remaining on a Whatman no. 1 filter paper after filtering. 20 Example 3. Eight grams of tartaric acid (food grade) and 18 grams of KOH were slowly dissolved in 50 ml water and the high pH mixture formed was stirred until completely clear and left to cool. Then 10 grams of SequestreneTM were introduced into the solution, stirring thoroughly until the mixture became 3 WO 99/08982 PCT/US98/16994 clear. Only a minor light-brown residue remained on a Whatman no. 1 filter paper after filtering. Example 4. Eight grams of KOH were slowly dissolved in 50 ml water in a beaker. The solution cleared and was left to cool down. Ten grams of 5 SequestreneTM were consequently introduced into the beaker and mixed thoroughly with the clear solution. The high pH solution became turbid with a light-brown slurry forming, which turned into a thick brown residue, indicating disruption of the chelate. The supernatant above the residue was very dark indicating the existence of chelated iron there. 10 Example 5. Eight grams of tartaric acid (food grade) and 18 grams of KOH were slowly dissolved in 25 ml water and the high pH mixture formed was stirred until completely clear, then allowed to cool down. Consequently, 10 grams of SequestreneTM were introduced into the solution, stirring throughly until the mixture became clear. In this case the dissolving action required a considerably 15 longer time than in Example 3, without some of the chelate being dissolved. However, no light-brown slurry was formed as in Example 4, indicating no disruption of the chelate. Example 6. Eight grams of KOH and 10 grams of mannitol were slowly dissolved in 50 ml water in a beaker. The high pH solution cleared and was left 20 to cool down. Ten grams of SequestreneTM were introduced into the solution and stirred thoroughly. A clear dark solution formed with only a slight light-brown residue left on the Whatman no. 1 filter paper after filtering. 4 WO 99/08982 PCT/US98/16994 Example 7. To 500 ml solution of 0.5 Molar EDDHMA were added 75 grams of tartaric acid (food grade). While mixing, 130 grams KOH were added, forming a clear solution. After cooling, 0.5 Moles of FeCl3.6H20 were added while stirring, forming a dark slurry. Upon further addition of 80 grams KOH a 5 quick solubilization response was induced, producing a dark high pH solution, with no apparent disruption of the chelate. Further addition of 300 ml water kept the solution stable without the formation of residue. 5

Claims (10)

1. aims 1. An aqueous solution characterized in having a high pH value, containing solubilized iron ions chelated by at least one ligand having a plurality of hydroxyl groups, in such a manner that pouring said solution into water delivers into the water the chelated iron without the need for any effort other than the pouring action itself, said water being characterized in that its pH value may be between about 3 to 12.5, such that the new mixture formed with said water is stable over periods extending above at least two days.
2. 2. A solution as in claim 1 having a pH value exceeding 12.
3. 3. A solution as in claim 1 containing EDDHA.
4. 4. A solution as in claim 1 containing EDDHMA.
5. 5. A solution as in claim 1 containing polyhydroxy acid.
6. 6. A solution as in claim 1 containing polyhydroxy alcohol.
7. 7. A solution as in claim 1 containing at least a half percent in weight of iron, in chelated form.
8. 8. A method for processing iron chelated with phenolic, ethylene diamine based ligands such that an aqueous solution is obtained comprising adding a ligand having a plurality of hydroxy groups, in a high pH environment, said solution characterized in providing a source of chelated iron stable over a large range of pH values.
9. 9. A method as in claim 8 used for supplying stably chelated iron to aqueous environments having pH values ranging between 3 to 9.
10. 10. A method as in claim 8 used for supplying stably chelated iron to aqueous environments having pH values ranging between about 5 to 12.