WO1994000405A1 - A process for modifying particulate solids and particulate solids prepared thereby - Google Patents
A process for modifying particulate solids and particulate solids prepared thereby Download PDFInfo
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- WO1994000405A1 WO1994000405A1 PCT/GB1993/001370 GB9301370W WO9400405A1 WO 1994000405 A1 WO1994000405 A1 WO 1994000405A1 GB 9301370 W GB9301370 W GB 9301370W WO 9400405 A1 WO9400405 A1 WO 9400405A1
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- water soluble
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
- B01J2/006—Coating of the granules without description of the process or the device by which the granules are obtained
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- C—CHEMISTRY; METALLURGY
- C05—FERTILISERS; MANUFACTURE THEREOF
- C05G—MIXTURES OF FERTILISERS COVERED INDIVIDUALLY BY DIFFERENT SUBCLASSES OF CLASS C05; MIXTURES OF ONE OR MORE FERTILISERS WITH MATERIALS NOT HAVING A SPECIFIC FERTILISING ACTIVITY, e.g. PESTICIDES, SOIL-CONDITIONERS, WETTING AGENTS; FERTILISERS CHARACTERISED BY THEIR FORM
- C05G5/00—Fertilisers characterised by their form
- C05G5/30—Layered or coated, e.g. dust-preventing coatings
Definitions
- the present invention relates to water soluble inorganic salts having substantially water insoluble coatings and to processes for the preparation thereof. More particularly the present invention relates to the water soluble fertilizers provided with substantially water insoluble coatings for slow/sustained release thereof.
- Water soluble salts are of extensive use in aqueous solutions.
- Tne first approach involves the preparation of low solubility compounds such as: urea formaldehyde (Hasegawa and Onishi, JP63, 134,593, Stajer, Glaser, Vidensky and Vosolsobe (CS 2588147), syngemte (Von Maessennausen, Czikkely and Jung, DE 3,518,369) and magnesium ammonium phosonate (JP 82 67,089); or water soluble salts granulated, pressed or sintered with other compounds such as gypsum (Koike JP 61,295,294), coal (Fujimori BR 88 03,282), coal ash (Oshikata, JP 60,239,381) and silicates (JP 59 04,397).
- Coatings of soluble salts comprise polymers (Hansen, US 3,223,518, Showa, JP 60,103,093; U.S. 3,223,518), sulfur, wax (Eibner, DE 3,321,053), pitch (Zou, CM 1,030,745), soybean formulation (NL 84 03,505), salts of fatty acids (Pipko, Manor and Ziv, EP 276,179), sodium silicate ( Komissarov and Panfileva SU 1,353,767), iron phospnate (Eibner DE 3,321,053), magnesium ammonium phosphate (Ninon JP 81,164,090) and gypsum or cement (JP 59,50,086).
- coating witn a polymer is complex, multistage operations which involve elements from polymer processing such as the use of a solvent which may cause safety and environmental difficulties and which has to be evaoorated and recovered, curing, cross-linking and condensation.
- These operations are expensive, require know-how and equipment wnicn is strange to the fertilizer industry and in some cases, incompatible with the fertilizer due, e.g., to relatively high temperatures or to formation of explosive compositions with HN 4 NO 3 containing fertilizers.
- Current processes of coating witn inorganic materials are also tedious, require several stages and may require binders.
- coating with MgNH 4 PO 4 comprises spraying of H 3 PO 4 solution followed by dusting with MgO and SiO 2 and then spraying NH 4 OH solution or ammomation with gaseous ammonia.
- the surface of the water soluble, inorganic salt particles can be converted through reaction with suitable reagents into a water insoluble coating thereby decreasing the dissolution of the water soluble salt. It was surprisingly found that such coating can be formed even when the reagent is applied in aqueous solution.
- the present invention provides a process for modifying a particulate solid comprising a water soluble inorganic salt, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, so as to decrease the rate of dissolution of said salt in aqueous solution, said process comprising contacting said salt with at least one reagent which reacts with one or more ions of said salt to form a reaction product which coats said salt, said reaction product containing at least one ion of said water soluble inorganic salt as a component thereof and having a water solubility not more than half that of the original uncoated organic salt.
- particulate solids as used herein concerns particulate solids that range from soluble salts only to compositions that contain at least one water soluble salt as one constituent amongst others that may be water soluble or water insoluble.
- particulate table salt consisting of 100% sodium chloride is included in the present invention as is a particulate dry soup containing about 10% sodium chloride.
- particulate solid for the purposes of the present invention, several fertilizer materials are listed below. These were chosen since controlling the rate of dissolution of particulate fertilizer is a major, though by no means exclusive, object of this invention.
- granulated "triple super phosphate” which is made from phosphate rock and wet process acid and contains soluble monocalci urn phospnate as the main constituent and may contain some 20% of insoluble solids originating in the rock (silica, iron oxide%) and in clay used as a binder for the granulation process;
- the water soluble salts present in the particulate solids to which this invention refers are halides, sulfates, nitrates and phosphates. Naturally, when anions of these salts report to an aqueous solution an equivalent amount of cations do so.
- the invention also provides a particulate solid comprising a water soluble inorganic salt, said salt being selected from the group consisting of halioes, nitrates, phosphates and sulfates, and said salt having a substantially water insoluble coating, said coating having been formed by contacting said salt with at least one reagent which reacts with one or more ions of said water soluble salt to form a reaction product which coats said salt, said reaction product containing at least one ion of said water soluble organic salt as a component thereof and having a water solubility not more than half that of the original uncoated organic salt.
- the invention provides a particulate solid comprising a water soluole inorganic salt, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, and optionally including cations of K, NH 4 , Fe, Mn, Cu, Co, Mo and Zn, said salt having a substantially water insoluble coating, said coating having been formed by contacting said salt with at least one reagent which reacts with one or more of said ions to form a reaction product which coats said salt, said reaction product containing at least one of said ions as a component thereof and having a water solubility not more than half that of the original uncoated organic salt.
- a water soluole inorganic salt said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, and optionally including cations of K, NH 4 , Fe, Mn, Cu, Co, Mo and Zn, said salt having a substantially water in
- a surface active agent which is added to the reagent or applied at a subsequent stage.
- Such agent might be selected, for example, from those used for anticaking of crystals or for flotation (e.g. amines).
- the polar side of the surface active agent (surfactant) interacts with the reaction product in the particulate cover, while the hydrophobic end decreases interaction with water and thereby affects solubility.
- This hydrophobic end also provides for further coating of the particle by hydrophobic solvents as hydrocarbons.
- the above method suffers from the disadvantages that it requires the introduction and use of both an organic acid or salt and a metal oxide or carbonate to interreact with each other to form a coating around the fertilizer particles as opposed to the present invention in which water soluble fertilizer particles themselves actively interact with the reagent and ions of said water soluble fertilizer form an integral component of the formed water insoluble coating.
- the reagent can be chosen to also add micro-nutrients to the fertilizer.
- micro-nutrients e.g, Zn(HN 4 ) 2 (SO 4 ) 2 or cobalt ammonium nitrate are suitable insoluble coatings of ammonium salts.
- preferred embodiments of the present invention will include the nutrients N, P or K as a component of the reaction product and especially preferred embodiments of the present invention will also incorporate one or more micronutrients selected from Fe, Mn, Cu, Co, Mo and Zn in said coating.
- soluble calcium phosphates or Ca(NO 3 ) 2 can be coated with insoluble salts such as CaCO 3 , CaF 2 , Ca laurate, Ca oxalate, Ca 3 (PO 4 ) 2 and Ca tartarate; water soluble phosphate can be coated with water insoluble phosphates such as FePO 4 and water soluble sulfates with water- insoluble sulfates such as CaSO 4 and BaSO 4 .
- Particles coated in the process of this invention can be further coated by other coating materials such as wax.
- the reagent is introduced in an organic solvent.
- organic solvents such as those defined in Israel
- the treated granules were separated from the solution, washed and introduced into water in w/w ratio of 1:20 respectively. Strong shaking was applied in a mechanical shaker at ambient temperature. Potassium nitrate dissolution could be visually followed as the coating formed is partially transparent. About eight hours were required for substantial dissolution of the potassium fluosilicate coated potassium nitrate. After 16 hours only the coating remains in solution.
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Abstract
The invention provides a process for modifying a particulate solid comprising a water soluble inorganic salt, the salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, so as to decrease the rate of dissolution of the salt in aqueous solution, the process comprising contacting the salt with at least reagent which reacts with one or more ions of the salt to form a reaction product which coats the salt, the reaction product containing at least one ion of the water soluble inorganic salt as a component thereof and having a water solubility not more than half that of the original uncoated water soluble inorganic salt.
Description
A PROCESS FOR MODIFYI NG PARTI CULATE SOLI DS AND PARTI CULATE SOLIDS PREPARED
THEREBY
The present invention relates to water soluble inorganic salts having substantially water insoluble coatings and to processes for the preparation thereof. More particularly the present invention relates to the water soluble fertilizers provided with substantially water insoluble coatings for slow/sustained release thereof.
Water soluble salts are of extensive use in aqueous solutions.
Especially salts selected from the group consisting of halides, nitrates, phosphates and sulfates are of extensive use in the fertilizer industry. Such salts often contain cations of Li, Na, Mg and Ca and preferably contain cations which also serve as nutrients and micronutrients e.g., K, NH4, Fe, Mn, Cu, Co, Mo and Zn. In certain cases, however, slow release of the salt into the aqueous solution is required. An important example is slow release fertilizers. Use of slow release fertilizers instead of direct application of the fertilizer as a soluble salt provides many advantages such as:
increased efficiency, reduced number of applications, reduced soil toxicity, reduced nutrient losses and thereby lower contamination of underground water.
In the prior art literature there are described two basic approaches for the preparation of slow release salts, i.e., the preparation of. low solubility formulations or the coating of a water soluble salt.
Tne first approach involves the preparation of low solubility compounds such as: urea formaldehyde (Hasegawa and Onishi, JP63, 134,593, Stajer, Glaser, Vidensky and Vosolsobe (CS 2588147), syngemte (Von Maessennausen, Czikkely and Jung, DE 3,518,369) and magnesium ammonium phosonate (JP 82 67,089); or water soluble salts granulated, pressed or sintered with other compounds such as gypsum (Koike JP 61,295,294), coal (Fujimori BR 88 03,282), coal ash (Oshikata, JP 60,239,381) and silicates (JP 59 04,397). The main disadvantage of low-solubility compounds or formulations is the high cost of raw materials and/or manufacturing.
Coatings of soluble salts comprise polymers (Hansen, US 3,223,518, Showa, JP 60,103,093; U.S. 3,223,518), sulfur, wax (Eibner, DE 3,321,053), pitch (Zou, CM 1,030,745), soybean formulation (NL 84 03,505), salts of fatty acids (Pipko, Manor and Ziv, EP 276,179), sodium silicate (Komissarov and Panfileva SU 1,353,767), iron phospnate (Eibner DE 3,321,053), magnesium ammonium phosphate (Ninon JP 81,164,090) and gypsum or cement (JP 59,50,086).
Current coating material and processes involve many disadvantages such as low resistance to moisture penetration, explosivity with certain fertilizers, high cost raw materials, introducing into the soil of non-degradable materials and difficulties in achievement of well adhering complete coatings. The main disadvantages, however, relate to complicated and expensive coating processes, to reduction of
nutrient content, to addition of oalast and to reduced freedom in tailoring fertilizer compositions.
As is known, even the preferred prior art processes of coating witn a polymer are complex, multistage operations which involve elements from polymer processing such as the use of a solvent which may cause safety and environmental difficulties and which has to be evaoorated and recovered, curing, cross-linking and condensation. These operations are expensive, require know-how and equipment wnicn is strange to the fertilizer industry and in some cases, incompatible with the fertilizer due, e.g., to relatively high temperatures or to formation of explosive compositions with HN4NO3 containing fertilizers. Current processes of coating witn inorganic materials are also tedious, require several stages and may require binders. Thus, coating with MgNH4PO4 comprises spraying of H3PO4 solution followed by dusting with MgO and SiO2 and then spraying NH4OH solution or ammomation with gaseous ammonia.
With current coating materials and processes, consiaerable amounts of coating are required (up to 50% of fertilizer's weight). Nutrient content thus decreases and expensive raw-materials are consumed, balast such as polymers, sodium silicate and calcium stearate, making uo a substantial component of the coated materials. Cost of raw materials and of coating processes, toxicity and coating builcup in the soil thus limit the use of coated fertilizers.
With this state of the art in mind, it is an object of the present invention to provide a process for modifying a particulate solid comprising a water soluble inorganic salt, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, so as to decrease the rate of dissolution of such salts in water.
It is another object of the present invention to provide a new and simpler method of coating which is compatible with the fertilizer industry, enables the utilization of low-cost raw materials, decreases the reduction in nutrient content and addition of balast and enables the preparation of tailor made fertilizers.
In accordance with the present invention it has now been found that the surface of the water soluble, inorganic salt particles can be converted through reaction with suitable reagents into a water insoluble coating thereby decreasing the dissolution of the water soluble salt. It was surprisingly found that such coating can be formed even when the reagent is applied in aqueous solution.
Thus, the present invention provides a process for modifying a particulate solid comprising a water soluble inorganic salt, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, so as to decrease the rate of dissolution of said salt in aqueous solution, said process comprising contacting said salt with at least one reagent which reacts with one or more ions of
said salt to form a reaction product which coats said salt, said reaction product containing at least one ion of said water soluble inorganic salt as a component thereof and having a water solubility not more than half that of the original uncoated organic salt.
The term particulate solids as used herein concerns particulate solids that range from soluble salts only to compositions that contain at least one water soluble salt as one constituent amongst others that may be water soluble or water insoluble. Thus, particulate table salt consisting of 100% sodium chloride is included in the present invention as is a particulate dry soup containing about 10% sodium chloride. For further clarification of the term "particulate solid" for the purposes of the present invention, several fertilizer materials are listed below. These were chosen since controlling the rate of dissolution of particulate fertilizer is a major, though by no means exclusive, object of this invention. In this connection it is appropriate to mention that the term "rate of dissolution" is commonly used loosely with respect to the interaction of particulate commercial materials with aqueous solutions; the implication being that as the truly water soluble constituents dissolve, the particle disintegrates. This clearly applies to particulate fertilizer that frequently contains insoluble constitutents.
Thus examples of particulate solids which can be modified according to the above process include:
a) muriate of potash, which is over 95% KCl and the remainder of which is mainly NaCl, both of which are fully water soluble:
b) granulated "triple super phosphate" which is made from phosphate rock and wet process acid and contains soluble monocalci urn phospnate as the main constituent and may contain some 20% of insoluble solids originating in the rock (silica, iron oxide...) and in clay used as a binder for the granulation process;
c) granulated NPK made of ammonium phosphate, muriate of potash arid phosphate rock, which may contain over 50% of the water insoluble rock.
As stated hereinbefore, the water soluble salts present in the particulate solids to which this invention refers are halides, sulfates, nitrates and phosphates. Naturally, when anions of these salts report to an aqueous solution an equivalent amount of cations do so.
As explained hereinafter said reagent can react with either said anion or its companion cation.
In a preferred embodiment of the present invention there is provided a process for modifying a particulate solid comprising a water soluble inorganic salt, so as to decrease the rate of dissolution of said salt in aqueous solution, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates and optionally including cations of K, MH4, Fe, Mn, Cu, Co, Mo and Zn, said process comprising contacting said salt with at least
one reagent which reacts with one or more ions of said salt to form a reaction product which coats said salt, said reaction product containing at least one of said ions as a component thereof and having a water solubility not more tnan half that of the original uncoated organic salt.
In an especially preferred embodiment of the present invention there is provided a process for modifying a particulate solid comprising a water soluble inorganic salt, said process comprising contacting particles of said particulate solid with at least one reagent which reacts with one or more ions of said salt to form a reaction product which coats said particles.
The invention also provides a particulate solid comprising a water soluble inorganic salt, said salt being selected from the group consisting of halioes, nitrates, phosphates and sulfates, and said salt having a substantially water insoluble coating, said coating having been formed by contacting said salt with at least one reagent which reacts with one or more ions of said water soluble salt to form a reaction product which coats said salt, said reaction product containing at least one ion of said water soluble organic salt as a component thereof and having a water solubility not more than half that of the original uncoated organic salt.
In especially preferred embodiments the invention provides a particulate solid comprising a water soluole inorganic salt, said salt
being selected from the group consisting of halides, nitrates, phosphates and sulfates, and optionally including cations of K, NH4, Fe, Mn, Cu, Co, Mo and Zn, said salt having a substantially water insoluble coating, said coating having been formed by contacting said salt with at least one reagent which reacts with one or more of said ions to form a reaction product which coats said salt, said reaction product containing at least one of said ions as a component thereof and having a water solubility not more than half that of the original uncoated organic salt.
The invention also provides a particulate solid according to the present invention comprising a water soluble inorganic salt wherein particles of said particulate solid are provided with a substantially water insoluble coating, said coating on said particles having been formed by contacting said salt with at least one reagent which reacts with one or more of said ions to form a reaction product which coats said particles, said reaction product containing at least one of said ions as a component thereof and having a water solubility not more than half that of the original uncoated organic salt.
In an especially preferred embodiment of the present invention said reaction product has a water solubility less than 10% of that of the original uncoated water soluble inorganic salt.
In a preferred embodiment, the reagent is applied in a combination with at least one of the group comprising surfactants, viscosity, modifiers, water-repellants and binders, to improve mechanical strength, adhesivity to the particle and to further reduce solubility in water.
In another preferred embodiment, additional operations are effected for further improvement of the solid particulate properties.
One example is treatment by a surface active agent (which is added to the reagent or applied at a subsequent stage). Such agent might be selected, for example, from those used for anticaking of crystals or for flotation (e.g. amines). The polar side of the surface active agent (surfactant) interacts with the reaction product in the particulate cover, while the hydrophobic end decreases interaction with water and thereby affects solubility. This hydrophobic end also provides for further coating of the particle by hydrophobic solvents as hydrocarbons.
Other treatments may include thermal treatment for affecting the coating's characteristics (e.g., converting gypsum dihydrate to hemi-hydrate), a second treatment by the same reagent or treatment by a second reagent (e.g., treatment by a base to convert CaHPO4 in the coating to the less soluble Ca,(PO4)2), etc.
In EPA publication No. 276179 there is described and claimed a method for the manufacture of physically prepared slow-release fertilizers, wherein the fertilizer particles are coated by at least one layer of a substantially water insoluble metal salt of an organic acid containing from 6 to 30 cabon atoms, particularly between 12 and 20 carbon atoms, or of water insoluble metal salts of a mixture of two or more such organic acids,, the metal salt(s) coating being formed in-situ from the organic salt(s) and metal oxide or carbonate.
As will be realized, nowever, the above method suffers from the disadvantages that it requires the introduction and use of both an organic acid or salt and a metal oxide or carbonate to interreact with each other to form a coating around the fertilizer particles as opposed to the present invention in which water soluble fertilizer particles themselves actively interact with the reagent and ions of said water soluble fertilizer form an integral component of the formed water insoluble coating.
Furthermore, the present invention assures that the reaction to form the water insoluble coating takes place on the surface of the water soluble salt, since in the present invention this salt functions as one of the reactants, which is not the case with said prior art process. This further assures that loss of reagent due to precipitation away from the surface of the salt does not take place.
Although the process of the present invention can be applied to all kinds of water soluble salts, the following description concentrates on the treatment of water soluble fertilizers in order to modify these into fertilizers with slow release properties.
Thus, as in said European application the fertilizer to be coated according to the present invention, may be selected from the well known water scluole fertilizers such as: potassium nitrate, potassiu-sulfate, ammonium nitrate, monopotassium phosohate, ammonium ohosonates, mixtures of N. P.K. fertilizers, etc.
The main nutrients provided tnrough fertilizers are N, P and K. Micro-nutrients consist of Fe, Mn, Cu, Co, Mo, In, etc. N is provided as ammonium salts (e.g., (NH4)2SO4), NO3- salts (e.g., Ca(NO3)2, NaNC3) and urea. K is provided in its soluble salts such as KCl andK2SO4 and P as pnosonates. Of higher value are fertilizers in which both the amon and the cations comprise a nutrient, e.g. KNO, (NH4)2HPO4, KH2PO4 and NH4NO3.
Reagents forming water insoluble salts with the anion or the cation of the water soluble salts are suitable for the process. Thus, e.g., on reacting K2SO4 particles witn H2SiF6, the surface of the particle is converted according to the reaction: K2SO4 + H2SiF6 > K2SiF6 + H2SO4.
The modified particle thus comprises K2SO4 coated with K2SiF6 with substantially no decrease of nutrient content. However, even on reaction with the other ion, nutrient replacement is low and the replaced nutrient can oe recovered as in the reaction:
K2SO4 + Ca(NO3)2 > CaSO4 + KNO3.
In another preferred embodiment the reagent can be chosen to also add micro-nutrients to the fertilizer. Thus, e.g, Zn(HN4)2(SO4)2 or cobalt ammonium nitrate are suitable insoluble coatings of ammonium salts.
Thus, preferred embodiments of the present invention will include the nutrients N, P or K as a component of the reaction product and especially preferred embodiments of the present invention will also incorporate one or more micronutrients selected from Fe, Mn, Cu, Co, Mo and Zn in said coating.
Reagents for the process are those forming water insoluble salts with at least one of the ions comprising the fertilizer. A person versed in the art can choose reagents according to solubility data and according to crystalographic know-how. According to the present invention, it will now be realized that, e.g., K salts can be coated with K2Ca(SO4)2, K3Co(NO2)6 and K2SiF6; NH4 + salts form insoluble coatings such as NH4CaPO4, NH4CoPO4, NH4MgPO4 and NH4MnPO4;
soluble calcium phosphates or Ca(NO3)2 can be coated with insoluble salts such as CaCO3, CaF2, Ca laurate, Ca oxalate, Ca3(PO4)2 and Ca tartarate; water soluble phosphate can be coated with water insoluble phosphates such as FePO4 and water soluble sulfates with water- insoluble sulfates such as CaSO4 and BaSO4.
In carrying out the process of the present invention, reagents may be applied in vapor phase (NH3, SiF4), in non-aqueous liquid, as a dispersion, emulsion or even in aqueous solution. The reagent may also be sprayed over the solid particles.
It has thus been found that on introducing particles comprising a water-soluble salt into gently mixed, relatively concentrated solution
of the reagent at about ambient temperature, a water insoluble coating is immediately formed on the surface of the salt particles which prevents considerable losses of the soluble salt through dissolution in the aqueous solution.
The rate of release of the water soluble salt is dependent on coating thickness, which can be affected by parameters of reagent application. Thus in using the reagent in an aqueous solution, concentration of the aqueous solution, contact time and temperature. pH, reagent nature and additives to the solution, affect coating thickness and thereby the rate of release of the soluble salt.
The rate of release is also affected by solubility of the coating wherein less soluble coatings provides for slower release.
Unlike in other processes of coating water soluble particles, elevated temperatures are not required. The process is thus suitable for coating particles of unstable compounds such as HN4NO3.
Particles coated in the process of this invention can be further coated by other coating materials such as wax.
Modified particulate solids obtained according to the invention, having a low rate of dissolution in aqueous solutions, provide excellent starting material for additional treatments for further improvement of their properties, i.e., improvement of mechanical strength, further reduction of rate of dissolution, etc. Such additional treatment may, for example, use components such as surfactants, binders and polymeric materials dissolved or dispersed in aqueous solution. Such option is, in fact, impractical with unmodified water-soluble particulate solids, as it would lead to the dissolution of a major part of the unmodified particulate. The reaction product of low water solubility that coats the soluble salt in the modified particulate solid may, in some cases, perform as a low-cost filler in other coatings formed cocurrently with, or subsequently to, it.
The large variety of reagents suitable for modifying the solubility of water soluble particles according to the present invention allows freedom in choosing the reagents and adjusting them
to requirements such as addition of micronutrients, adjustability to acid/base properties of the soil and low cost.
The latter point is of high importance as slow release fertilizers formed by current processes are relatively expensive due to high cost of raw material and of processing. Using the present invention thus allows the use of low cost reagents such as H2SiF6 solutions. More specifically, it has now been found that introducing granules of KNO3 into gently mixed H2SiF6 solution at ambient temperature results in their coating with water insoluble K2SiF6, which changes the solubility of the coated fertilizer. H2SiF6 is a very low cost reagent. In fact, in the neighborhood of wet process acid (WPA) production it may even have a negative value. Fluoride present in phosphate rock in the form of fluoroapatite results in fluosilicic acid in the phosphoric acid. On concentration of the WPA
SiF4 evaporates and on scrubbing in water H2SiF6 reforms according to the reaction:
2SiF2 + H2O > H2SiF6 + Sio2.
Since the coating is formed on reaction with the soluble salt particle and includes at least one of its ions, good adhesion to the particle is ootained avoiding the need of binders and improving the ability to affect the coating of less spherical particles.
Formation of inorganic coating reduces the danger of flammability and of formation of explosive materials.
The process of the invention allows using reagents in vapor phase, in non-aqueous liquid, as an emulsion or even in aqueous solution. Melting of reagents is not required. In addition reaction of the reagent with the water soluble particle is spontaneous requiring no energy introduction. The process thus does not require energy input or temperature elevation. In fact in most cases low temperature is favorable, which is advantageous for coating of temperature-sensitive compounds such as HN4NO3.
In another preferred embodiment the reagent is introduced in an organic solvent. Thus, amine solvents such as those defined in Israel
Patent 57024 corresponding to U.S. Patent No. 4,291,007, the teachings of which are incorporated herein by reference, bind H2SiF6 to form the fluosilicate of the amine according to the reaction
RnNH3-n + H2SiF6 > RnNH4-nHSiF6 or (RnNH4-n)2SiF6.
wherein n = 1, 2 or 3.
Reacting this organic phase with a solid particle containing KNO3 for example, results in a reaction of forming a water insoluble coating on the particle according to the reaction
(RnNH4-n)2SiF6 + 2KNO3 > 2R4NH4-nNO3 + K2SiF6.
Introduction of the reagent in the presence of an organic solvent provides several advantages such as:
1. Reaction may be affected and controlled by the properties of the solvent, e.g., it is known that amines prefer nitric acid over
fluosilicic acid thereby providing a driving force for the reaction;
2. the solvent may be used to extract a reagent from its aqueous solution thereby permitting the use of reagents formed as by-products even if in dilute solutions (e.g., H2SiF6 formed on scrubbing SiF6 in phosphoric acid industry); and
3. the solvent may be chosen so as to form the required organic coating on the top of the insoluble salt which is formed.
The extensive know-how in the field of crystalization, and in benaviour of saturated and of super-saturated solutions can be utilized for adjusting coating's properties. Small amounts of additives may affect the habit of coating and improve product properties.
As both fertilizers and soil are inorganic and as fertilizer release and utilization are dependent on water presence, the process of the invention provides for higher compatibility with fertilizer production and utilization.
While the invention will now be described in connection with certain preferred embodiments in the following examples so that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary. it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following
examples wnich include preferred embodiments will serve to illustrate the practice of tms invention, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of formulation procedures as well as of the principles and conceptual aspects of the invention.
Comparative Example A
Potassium nitrate granules with sizes ranging between about 1 mm and 5 mm were introduced into water in w/w ratio of 1:20 respectively. Strong shaking was applied in a mechanical shaker at ambient temperature. Complete dissolution was observed after about 3 minutes. (No insoluble matter was left in the solution).
Example 1
Potassium nitrate granules from the batch used in Comparative Example A were introduced into 36% w/w aqueous solution of fluosilicic acid and gently stirred in a mechanical shaker at ambient temperature for a period of about five hours to effect the coating thereof. No indication of potassium nitrate dissolution was found and it is assumed that any potassium nitrate exiting from the coated granules was immediately reacted with the fluosilicic acid still in solution and adds to the coating. Independent precipitation of K2SiF6 was not
ooserved thus strengthening the assumption that K2SiF6 was formed solely as a coating on the granules and not independent thereof.
The treated granules were separated from the solution, washed and introduced into water in w/w ratio of 1:20 respectively. Strong shaking was applied in a mechanical shaker at ambient temperature. Potassium nitrate dissolution could be visually followed as the coating formed is partially transparent. About eight hours were required for substantial dissolution of the potassium fluosilicate coated potassium nitrate. After 16 hours only the coating remains in solution.
This example shows that coating potassium nitrate with potassium fluosilicate slows its dissolution by a factor of 2 orders of magnitude.
Having illustrated the principals of the present invention and the carrying out thereof in the above example it will now be simple for men skilled in the art to carry out the present invention with other ions simply by consulting any handbook and noting the comparative solubility of soluble and substantially insoluble salts.
Thus, e.g., from The Handbook of Chemistry and Physics, Chemical Rubber Co. the following listing of solubilities of a gram of salts per 100 gram H2O in cold water can be found, which listings are presented hereinafter for eacn ion, first with regard to water soluble
salts and then with regard to less soluble salts which can serve as the reaction product coating for the first batch of water soluble salts.
In the following lists, "i" stands for insoluble.
Sodium salts Cold water
Sodium nitrate 92.1
Sodium hydrogen oxalate 1.7 Sodium phosphate 1.5 Sodium fluosilicate 0.65
Lithium salts
Lithium nitrate 90
Lithium laurate 0.15 Lithium phosphate 0.04 Lithium fluoride 0.27
Magnesium salts
Magnesium nitrate hexahydrate 125
Magnesium phosphate
Magnesium fluoride 0.008 Magnesium laurate 0.007 Magnesium oleate 0.024 Magnesium oxalate 0.07
K. salts
Potassium sulfate 12
Potassium chloride 34.7
Potassium nitrate 13.3
Potassium dihydrogen phosphate 33
Dipotassium hydrogen phosphate 167
Potassium hydrogen oxalate 2.5
Potassium hydrogen tartarate 0.37
Potassium fluosilicate 0.12 Potassium calcium sulfate
(syngenite) 0.25
Calcium salts
Calcium dihydrogen phosphate 1.8 Calcium nitrate 121
Calcium sulfate 0.2
Calcium carbonate 0.001
Calcium fluoride 0.002
Calcium laurate 0.004
Calcium oxalate 0.0007
Calcium phosphate 0.002
Calcium tartrate 0.03
Ammonium salts
Ammonium sulfate 70.6
Ammonium nitrate 118.3
Ammonium dihydrogen phosphate 22.7
Ammonium hydrogen phosphate 57.5
Ammonium calcium phosphate i
Ammonium magnesium phosphate 0.02
Ammonium cobalt phosphate i
Ammonium manganese phosphate 0.003
Ammonium zinc sulfate 7
Cobalt ammonium nitrate 1.7
Cobalt ammonium sulfate 1.4
Cobalt ammonium chloride 0.4
Iron Salts
Fe(III) chloride 74.4
Fe(III) nitrate 104
Fe(III) oleate i
Fe(III) oxalate i
Fe(III) phosphate i
Magnanese Salts
Manganese chloride 72.3
Manganese nitrate 426
Manganese fluoride 0.66
Manganese oxalate i
Manganese phosphate i
Copper salts
Copper chloride 70.6
Copper nitrate 98
Cu(NH3)2Cl2 i
Cu oleate i
Cu oxalate 0.003
Cu phosphate i
Cobalt Salts
Cobalt chloride 38
Cobalt nitrate 134
Cobalt citrate 0.8
Cobalt oxalate i
Cobalt phosphate i
Zinc Salts
Zinc chloride 432
Zinc nitrate 114
Zinc oleate i
Zinc oxalate 0.0008
Zinc phosphate i
Phosphates
Potassium dihydrogen phosphate 33 Ammonium dihydrogen phosphate 22.7
Iron (III) phosphate i
Cobalt (II) phosphate i
Copper (II) phosphate i
Zinc phosphate i
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims
1. A process for modifying a particulate solid comprising a water soluble inorganic salt, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, so as to decrease the rate of dissolution of said salt in aqueous solution, said process comprising contacting said salt with at least one reagent which reacts with one or more ions of said salt to form a reaction product which coats said salt, said reaction product containing at least one ion of said water soluble inorganic salt as a component thereof and having a water solubility not more than half that of the original uncoated water soluble inorganic salt.
2. A process for modifying a particulate solid comprising a water soluble inorganic salt, as claimed in claim 1, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, and optionally including cations of K, NH4, Fe, Mn, Cu, Co, Mo and Zn, so as to decrease the rate of dissolution of said salt in aqueous solution, said process comprising contacting said salt with at least one reagent which reacts with one or more ions of said salt to form a reaction product which coats said salt, said reaction product containing at least one of said ions as a component thereof and having a water solubility not more than half that of the original uncoated water soluble inorganic salt.
3. A process according to claim 1 wherein said particulate solid is contacted with an aqueous medium containing said reagent.
4. A process according to claim 1 for modifying a particulate solid comprising a water soluble inorganic salt, said process comprising contacting particles of said particulate solid with at least one reagent which reacts with one or more ions of said salt to form a reaction product which coats said particles.
5. A particulate solid comprising a water soluble inorganic salt, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, and said salt having a substantially water insoluble coating, said coating having been formed by contacting said salt with at least one reagent which reacts with one or more ions of said water soluble salt to form a reaction product which coats said water soluble salt, said reaction product containing at least one ion of said water soluble inorganic salt as a component thereof and having a water solubility not more than half that of the original uncoated water soluble inorganic salt.
6. A particulate solid as claimed in claim 5 comprising a water soluble inorganic salt, said salt being selected from the group consisting of halides, nitrates, phosphates and sulfates, and optionally containing cations of K, NH4, Fe, Mn, Cu, Co, Mn and Zn, said salt having a substantially water insoluble coating, said coating having been formed by contacting said salt with at least one reagent which reacts with one or more of said ions to form a reaction product which coats said salt, said reaction product containing at least one of said ions as a component thereof and having a water solubility not more than half that of the original uncoated water soluble inorganic salt.
7. A particulate solid according to claim 5 wherein said reaction product has a water solubility less than 10% of that of the original uncoated water soluble inorganic salt.
8. A particulate solid according to claim 5 wherein said reaction product is selected from K2Ca(SO4)2, K3Co(NO2)6 and K2SiF6.
9. A particulate solid according to claim 5 wherein said reaction product is selected from calcium sulfate, calcium carbonate, calcium fluoride, calcium laurate, calcium oxalate, calcium phosphate and calcium tartrate.
10. A particulate solid according to claim 5 wherein said reaction product includes nitrogen, phosphorus or potassium as a component thereof.
11. A particulate solid according to claim 5 wherein said reaction product further includes a micronutrient selected from Fe, Mn, Cu, Co, Mo and Zn as a component thereof.
12. A particulate solid according to claim 5 comprising a water soluble inorganic salt, wherein particles of said particulate solid are provided with a substantially water insoluble coating, said coating on said particles having been formed by contacting said salt with at least one reagent which reacts with one or more ions of said waster-soluble salt to form a reaction product which coats said particles, said reaction product containing at least one ion of said water-soluble inorganic salt as a component thereof and having a water solubility not more than half that of the original uncoated water-soluble inorganic salt.
13. A particulate solid according to claim 5, wherein said water-soluble inorganic salt is KNO3.
14. A particulate solid according to claim 13, wherein said reaction product is K2SiF6.
15. A particulate solid according to claim 1, further comprising a surfactant.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU45071/93A AU4507193A (en) | 1992-06-30 | 1993-06-30 | A process for modifying particulate solids and particulate solids prepared thereby |
| EP93914848A EP0648198A1 (en) | 1992-06-30 | 1993-06-30 | A process for modifying particulate solids and particulate solids prepared thereby |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IL102,370 | 1992-06-30 | ||
| IL10237092A IL102370A (en) | 1992-06-30 | 1992-06-30 | Process for modifying particulate solids and particulate solids prepared thereby |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO1994000405A1 true WO1994000405A1 (en) | 1994-01-06 |
Family
ID=11063777
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/GB1993/001370 WO1994000405A1 (en) | 1992-06-30 | 1993-06-30 | A process for modifying particulate solids and particulate solids prepared thereby |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0648198A1 (en) |
| AU (1) | AU4507193A (en) |
| IL (1) | IL102370A (en) |
| WO (1) | WO1994000405A1 (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1997017868A1 (en) | 1995-11-16 | 1997-05-22 | Goettfert Johann | Kitchen apparatus |
| CN1040096C (en) * | 1995-08-17 | 1998-10-07 | 郑州乐喜施磷复肥技术研究推广中心 | Releasion controlled fertilizer |
| FR2787799A1 (en) * | 1998-12-23 | 2000-06-30 | Rhodia Chimie Sa | COMPOSITION COMPRISING AN INORGANIC BARK AND A CORE COMPRISING AT LEAST ONE POLYHYDROXYL COMPOUND |
| US6163336A (en) * | 1994-12-13 | 2000-12-19 | Richards; Angus Duncan | Tracking system for stereoscopic display systems |
| FR2801810A1 (en) * | 1999-12-07 | 2001-06-08 | Rhodia Food S A S | CAPSULE COMPRISING AT LEAST ONE MINERAL BARRIER CONSISTING OF A SINGLE CHEMICAL COMPOUND AND A CORE COMPRISING AT LEAST ONE POLYHYDROXYL COMPOUND |
| DE102014100026A1 (en) * | 2014-01-02 | 2015-07-02 | Chemische Fabrik Budenheim Kg | Mixed-metallic crystalline orthophosphates for the time-controlled release of trace elements in rhizodermal and epidermal areas of plants |
| WO2024105570A1 (en) * | 2022-11-14 | 2024-05-23 | SABIC Agri-Nutrients Company | Method for multi-phase preparation of complex mineral fertilizer from phosphate rock and nitric acid |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102013013377A1 (en) | 2013-08-10 | 2015-02-12 | Advanced Acoustic Sf Gmbh | Decentral structure of a wave field synthesis system |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3378363A (en) * | 1965-02-23 | 1968-04-16 | Shell Oil Co | Method of imparting hardness on water-soluble particles |
| US5152821A (en) * | 1988-02-01 | 1992-10-06 | Hi-Fert Pty. Ltd. | Addition of supplemental macro & micro nutrients to granular phosphatic fertilizers |
-
1992
- 1992-06-30 IL IL10237092A patent/IL102370A/en not_active IP Right Cessation
-
1993
- 1993-06-30 AU AU45071/93A patent/AU4507193A/en not_active Abandoned
- 1993-06-30 EP EP93914848A patent/EP0648198A1/en not_active Ceased
- 1993-06-30 WO PCT/GB1993/001370 patent/WO1994000405A1/en not_active Application Discontinuation
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3378363A (en) * | 1965-02-23 | 1968-04-16 | Shell Oil Co | Method of imparting hardness on water-soluble particles |
| US5152821A (en) * | 1988-02-01 | 1992-10-06 | Hi-Fert Pty. Ltd. | Addition of supplemental macro & micro nutrients to granular phosphatic fertilizers |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6163336A (en) * | 1994-12-13 | 2000-12-19 | Richards; Angus Duncan | Tracking system for stereoscopic display systems |
| CN1040096C (en) * | 1995-08-17 | 1998-10-07 | 郑州乐喜施磷复肥技术研究推广中心 | Releasion controlled fertilizer |
| WO1997017868A1 (en) | 1995-11-16 | 1997-05-22 | Goettfert Johann | Kitchen apparatus |
| FR2787799A1 (en) * | 1998-12-23 | 2000-06-30 | Rhodia Chimie Sa | COMPOSITION COMPRISING AN INORGANIC BARK AND A CORE COMPRISING AT LEAST ONE POLYHYDROXYL COMPOUND |
| WO2000038829A1 (en) * | 1998-12-23 | 2000-07-06 | Rhodia Chimie | Composition comprising an inorganic coating and a core comprising at least a polyhydroxyl compound |
| US6689467B1 (en) | 1998-12-23 | 2004-02-10 | Rhodia Chimie | Composition comprising an inorganic coating and a core comprising at least a polyhydroxyl compound |
| FR2801810A1 (en) * | 1999-12-07 | 2001-06-08 | Rhodia Food S A S | CAPSULE COMPRISING AT LEAST ONE MINERAL BARRIER CONSISTING OF A SINGLE CHEMICAL COMPOUND AND A CORE COMPRISING AT LEAST ONE POLYHYDROXYL COMPOUND |
| WO2001041914A1 (en) * | 1999-12-07 | 2001-06-14 | Rhodia Chimie | Capsule comprising at least a mineral coating consisting of a single chemical compound and a core comprising at least a polyhydroxylated compound |
| DE102014100026A1 (en) * | 2014-01-02 | 2015-07-02 | Chemische Fabrik Budenheim Kg | Mixed-metallic crystalline orthophosphates for the time-controlled release of trace elements in rhizodermal and epidermal areas of plants |
| DE102014100026A8 (en) * | 2014-01-02 | 2016-03-24 | Chemische Fabrik Budenheim Kg | Mixed metallic crystalline orthophosphates for the timed release of trace elements in the rhizodermal and epidermal region of plants |
| WO2024105570A1 (en) * | 2022-11-14 | 2024-05-23 | SABIC Agri-Nutrients Company | Method for multi-phase preparation of complex mineral fertilizer from phosphate rock and nitric acid |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0648198A1 (en) | 1995-04-19 |
| IL102370A (en) | 1995-03-30 |
| IL102370A0 (en) | 1993-01-14 |
| AU4507193A (en) | 1994-01-24 |
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