OA17455A - Fertiliser coating containing micronutrients. - Google Patents

Abstract

A single-step method for preparing a freeflowing, non-dusting micronutrient-coated particulate solid fertiliser material, the method comprising applying a single fluid onto particulate solid fertiliser material at ambient temperature without chemical reaction or chelation, said single fluid comprising a suspension of one or more micronutrient materials in an oil.

Description

Plant nutrients can be divided into three main classes:

Primary or macronutrients: nitrogen (N), phosphorus (P) and potassium (K).

Secondary nutrients: calcium (Ca), magnésium (Mg), sulphur (S), sodium (Na).

Micronutrients: boron (B), copper (Cu), iron (Fe), manganèse (Mn), molybdenum (Mo), zinc (Zn).

Partîculate solid forms of inorganic fertiliser such as granules or prills represent the most common type of fertiliser used in agriculture, incorporating at least the primary or macronutrients (the so-called NPK-fertilizers), and often secondary nutrients. Partîculate solid fertilisers are commonly applied to the soil in order to provide the growing crop with the bulk of its requirement for primary and secondary nutrients.

There is often a requirement to also include micronutrients in partîculate solid fertiliser products in order to meet the agronomie requirements of the crop.

This can be achieved by incorporating micronutrients during the prilling or granulation process. Altematively, WO 9915480 (Norsk Hydro, 1999) describes how micronutrients can be coated onto partîculate fertilisers by application of an

-2 aqueous solution of an acid and a minerai base. However, practical considérations in high volume production operations imply that it is difficult to satisfy the widely different nutrient requirements of different crops and different soi! types using any of the aforementioned approaches. Furthermore, the use of an aqueous solution on an hygroscopic material such as calcium ammonium nitrate and ammonium nitrate fertiliser is not recommended.

Physical blending of powdered or granular micronutrient components with solid fertîlîsers offers more flexibility in terms of manufacture but the end product suffers from several disadvantages. The différences in particle size and density between the different components can lead to ségrégation during storage and handling which can resuit in uneven application to the soil and crop. Another disadvantage, particularly where powdered micronutrients are used, is the dusting that can occur during transfer and application. This not only leads to uneven application but also présents a potential environmental or health and safety risk.

WO 03071855 (Ade & Company, 2003) teaches a method by which a fertiliser can be coated with micronutrient applied in the form of a fine, dry powder which is claimed to produce a low dusting product. However, if the original fertiliser substrate is itself naturally dusty, this method offers no possibility of reducing the inhérent dustiness.

These problems can be reduced to a certain extent by applying an oil, surfactant or binding polymer during the blending process, e.g. by spraying, but this adds a further step to the process and thereby increases the complexity of the blending operation.

Micronutrients may be added to solid fertiliser by coating the granules using an aqueous slurry or suspension of the micronutrient components. This method can resuit in a low dusting product with an even distribution of micronutrient. However, the introduction of water using this technique (albeit a very small the amount) can compromise the storage stability of the solid fertiliser by increasing its tendency to cake or by reducing the strength of the prills or granules, especially with nitrate based solid hygroscopic materials such as calcium ammonium nitrate and ammonium nitrate, and with urea. Furthermore, it is easy to ,

-3make a mîstake by adding more of the aqueous slurry or suspension to the solid fertilizer than necessary, which has a detrimental effect on the whole batch în terms of swelling and caking tendency.

It has been proposed in US 3,692,529 (Rychman, 1972) to treat solid carrier particles wîth an adhering oil, and a pigment or colouring compound. Subsequently, the thus oiled carrier particles are blended with granular solids to provide a free-flowîng non-segregating, homogeneous composition. The function of the oiled carrier particles is to provide free-flowing properties to the granular solids composition which would otherwise be non-free flowing. The granular solids are liable to give off dust, and may require further processing steps to suppress dusting.

Other approaches hâve required spécial apparatus to add components separately and create chemical or chélation reactions in situ , in particular between the particulate solid fertilizer material and the components, and/or the use of elevated températures. Examples are: US 2005/076687, CN102603431, WO 2011/080764, US 4,657,576, GB 954,555 and CN 102358710.

Hence, there is a need for a better method to post-treat solid fertilizer particles to at least party overcome the problems from the prior art.

SUMMARY OF THE INVENTION

Aspects of the invention are specified in the independent claims. Preferred features are specified in the dépendent claims.

By using a pre-prepared suspension of one or more micronutrient components in an oil, coating of the solid fertiliser can be carried out in a simple single-stage blending or coating operation using standard fertiliser blending equipment at ambient températures (herein defîned as 0°C or greater, typically 10°C or greater; and 40°C or less, typically 30°C or less). The method according to the invention results in an evenly coated fertiliser which is non-dusting and has excellent storage characteristics. The use of an oil-based suspension not only prevents the micronutrients from dusting but also suppresses dust présent in the

-4granular fertiliser itself. No additional non-aqueous liquid or other anti-dusting agent is required during blendîng. Furthermore, we hâve found that the application of the oil-based suspension can hâve an additional bénéficiai effect on storage and handlîng characteristics of the final product by reducing the caking tendency.

The micronutrient suspension is prepared by blendîng a suitable source of micronutrient in the form of a finely ground powder with an oil.

Suitable micronutrient sources are any suitable compounds of the micronutrient éléments boron, copper, iron, manganèse, molybdenum and zinc, such as but not limited to salts, for instance sulphates, oxysulphates, nitrates, borates, chlorides, oxychlorides and phosphates; minerais; métal chelates, for instance EDTA, HEDTA, DTPA, EDDHA; oxides, carbonates or hydroxides.

We hâve found that the best results in terms of coverage and low dusting are obtained when the particles in the micronutrient material hâve sizes substantially in the range of 0.1 to 100 pm, more preferably between 0,1 and 50 pm, even more preferably to hâve 90% of particles between 0.1 and 50 pm, ideally to hâve 90% of particles between 0.1 and 20 pm. Such a fine particle size may be obtained by milling.

The oil can be any suitable natural, minerai or synthetic oil, such as a minerai white oil, but preferably an environ me ntally acceptable oil such as a vegetable oil is used. Suitable vegetable oils include rapeseed oil, soya oil, sunflower oil, linseed oil, castor oil, or other similar vegetable oils. Other oils, such as methylated oils or modified vegetable oils could also be used, but not watermiscible materials.

Surprisingly, vegetable oil turned out to be a much better oil for dispersing said particles, in particular zinc oxide particles, than minerai white oil.

It is advantageous to achieve as high a loading of the micronutrient in the suspension as possible, as this allows a sufficiently high addition of micronutrient onto the solid fertiliser without over-loading the fertiliser with oil which can make the final product sticky and difficult to handle.

In a preferred embodiment, a solids loading of 30 to 80 weight%, more

-5preferably a solids loading of 50 to 80 weight% should be achieved. The loading dépends on the type of carrier oil, the type of dispersant, etc. As an example, it can be mentioned that rapeseed oil with 60 weight% zinc oxide was pumpable and could be used to coat fertiliser. However, rapeseed oil with 70 weight% zinc oxide turned out to be too thick to be pumped, but by adding a dispersion agent, the amount could be increased to 70 weight% without increasing the viscosity of the resulting dispersion. It is an inventive aspect of the invention that it has been found possible to produce a dispersion with 65 to 70 weight% zinc oxide to coat a fertilizer product such that it contains 0,5 weight% Zn, which is an agrîculturally relevant amount, yet without using too much oil such that the fertilizer product does not become sticky and prone to caking.

It is also advantageous to achieve a mobile liquid form such that the micronutrient suspension can be easily pumped and dosed into the fertiliser blend. In order to achieve a liquid suspension at this high solids loading a dispersing agent may need to be incorporated into the formulation. Suitable dispersing agents may be natural or synthetic and include fatty acids, mono- and diglycerides, polycondensed fatty acids, polymerized fatty acid esters, fatty acid modified polyesters, non-ionic block copolymers.

It is also désirable for the micronutrient suspension to hâve good stability to allow for storage so it is necessary to prevent rapid settlement of the micronutrient from the suspension. Accordingly, the formulation may include any one or a combination of dispersion agents, rheology agents, thickeners and anti-settle agents. Suitable rheology agents, thickeners and anti-settling agents include clays such as sepiolite, bentonite, attapulgite, hectorite, palygorscite and organically modified clays; polyuréthanes; polyurea; hydrophilic fumed silica; hydrophobie fumed silica; fumed mixed oxides.

An advantage of using an oil as dispersant is that it may disperse both water-soluble and non-water soluble particles in the same way. An example of a water-soluble material is zinc sulphate (ZnSO₄). If water is used as a coating medium, it will dissolve the water-borne particles and disperse the non-waterbome particles, giving a different and undesired coating behaviour.

-6A colorant, either dye or pigment, may be added to the formulation in order to aid monitoring of the coating process and to enhance the physîcal appearance of the final fertiliser product. Examples of suitable pigments classes include, but are not limited to, Phthalocyanine Blues (for example, C.l. Pigment Blues 15, 15:1, 15:2, 15:3, 15:4) and Aluminium Chlorophthalocyanine (for example, C.l. Pigment Blue 79); Ultramarine Blue; red, yellow and green iron oxides.

The oil containing the dispersed micronutrients can be added to the particulate solid fertiliser by any conventional means, such as spraying the oil dispersion on to the particulate fertiliser during blendîng in a drum blender, or spraying on to the particulate fertiliser after which the product is blended in a drum blender, or spraying on to the particulate fertiliser on a moving conveyor belt.

The invention will now be further described with reference to the following examples. In Examples 1 and 2, the dispersant used was Decal FD (Devine Chemicals) hydroxystearic acid polymer and the blue pigment dispersion was Dispers Blue LS6900 (BASF) Pigment Blue 15:1.

Example 1

The following example shows the formulation required to make 1 kg of an oilbased suspension of zinc oxide containing 50 weight% Zn (zinc oxide obtained from Umicore, Belgium, having an average particle size of approximately 0.5 pm, 90 % of particles less than 2 pm).

Rapeseed Oil	0.3320 kg
Dispersant	0.0300 kg
Blue Pigment Dispersion	0.0150 kg
Zinc Oxide	0.6230 kg

1.0000 kg

-7The above components are added in the order listed into a stirred beaker and mixing continued for 30 minutes. The résultant product is a fluid suspension with a viscosity of 4220 cPs at 20 °C as measured on a Brookfield

LVD viscometer using spindle 3 at 12 rpm.

Samples of the product were subjected to storage testing under various conditions. A sample stored at ambient température for a period of 4 months remained stable and fluid with no significant seulement of the suspended solids.

The zinc oxide suspension described above was coated onto prilled urea at 20 °C using a rate équivalent to 5 litres per tonne of urea using the following method:

kg of prilled urea was added to a iabscale drum blender and the blender started. 5 ml of the zinc oxide suspension was introduced via a syringe and blending continued for 2 minutes. The résultant product was evenly coated with micronutrient (équivalent to 0.47 weight% Zn), dust-free and free flowing.

The suspension described in Example 1 was also coated onto two types of granular fertiliser, NPK 27-4-4 and calcium ammonium nitrate (CAN) (both obtained from Yara) at 20 °C. Samples of both fertiliser grades (finished products obtained from the production plant and already treated with an anti-caking coating) were treated with the zinc oxide suspension using a rate to achieve a coating équivalent to 0.81 weight% on to the fertiliser. The résultant samples were tested for caking tendency compared against uncoated control samples of each fertiliser (that is, without the normal anti-caking coating) and samples ofthe normal finished fertiliser. The tests were carried out at 25 °C with 60 % Relative Humidity and the results are shown in Table 1 below. The lower figures for the coated samples indicate less tendency to cake than the untreated samples and demonstrates the improvement conferred by the treatment.

	Caking Index (gf)
Uncoated NPK 27-4-4	3017
NPK 27-4-4 finished product from plant	1175
NPK 27-4-4 finished product + coated with Example 1	917
Uncoated CAN	975
CAN finished product from plant	583
CAN finished product + coated with Example 1	350

Table 1 : Caking index for various ferfilizers according to Example 1

The suspension described in Example 1 was also coated onto urea, calcium ammonium nitrate and an NPK blend in factory conditions with an ambient température of 30 °C at rates ranging from 2.1 litres per metric tonne of granular fertiliser to 4.2 litres per metric tonne of fertiliser. The résultant coated fertiliser was well-coated and free-flowing with low dust levels.

Example 2

The following example shows a formulation to make 1 kg of an ollbased suspension of colemanite, a boron-containing minerai with the chemical formula CaBjO^OHJa ^O, containing about 7 weight% boron. (colemanite obtained from Eti Holdings AS, Turkey; ground to achieve a particle size spécification of 90 % < 50 pm - the particle size distribution of the actual batch used was 90 % < 13 pm; 50 % < 7 pm). The clay thickener was Pangel B5 (Toisa

S.A.) Sepiolite clay.

Rapeseed Oil	0.3988 kg
Dispersant	0.0357 kg
Blue Pigment Dispersion	0.0107 kg
Clay thickener	0.0054 kg
Colemanite	0.5494 kg

-91.0000 kg

The above components are added in the order listed into a stirred beaker and mixîng contînued for 30 minutes. The résultant product is a fluid suspension with a vîscosity of 3180 cPs at 20 °C measured on a Brookfield LVD viscometer using spindle 3 at 12 rpm.

The suspension described in Example 2 was coated onto prilled urea at 8 °C using a rate équivalent to 5 litres per metric tonne of granular fertiliser. The résultant coated fertiliser was well-coated with micro-nutrient (équivalent to 0.05 weight% of boron) and free-flowing with low dust levels

Example 3

The following example shows a formulation to make 1 kg of an oilbased suspension of cuprous oxide, chemical formula Cu^O, containing about 86 weight% copper and with a particle size spécification of 99 % < 5 pm; 80 % < 2 pm (obtained from Nordox industries AS, Norway). The dispersant was Synthro Pon 9TD (Synthron) and the clay thickener was Pangel B5 (Toisa S.A.) Sepiolite clay.

Methylated Rapeseed Oil	0.1570 kg
Dispersant	0.0400 kg
Clay thickener	0.0030 kg
Cuprous Oxide	0.8000 kg
	1.0000 kg

The above components are added in the order listed into a stirred beaker and mixing continued for 30 minutes. The résultant product is a fluid suspension with a vîscosity of 2900 cPs at 20 °C measured on a Brookfield LVD viscometer using spindle 3 at 12 rpm.

The suspension described in Example 3 was also coated onto prilled urea

-10at 15 °C using a rate équivalent to 5 litres per metric tonne of granular fertiliser.

The résultant coated fertiliser was well-coated with micro-nutrient and free-flowing with low dust levels

Example 4

The following example shows a formulation to make 1 kg of an oilbased suspension of manganèse carbonate chemical formula MnCOa, containing about 44 weight% of manganèse (obtained from Erachem Comilog S.A.). The manganèse carbonate used was micronized to achieve a particle size spécification of 100 % < 50 pm; 90 % < 15 pm; 50 % < 5 pm. The dispersant was Decal FD (Devine Chemicals) and the fumed silica was Aerosil R812 (Evonik Industries AG). Methylated Rapeseed Oil 0.2991 kg

Dispersant 0.0290 kg

Blue Pigment Dispersion 0.0029 kg

Manganèse Carbonate 0.6603 kg

Fumed Silica 0.0087 kg

1.0000 kg

The above components are added in the order listed into a stirred beaker and mixing continued for 30 minutes. The résultant product is a fluid suspension with a viscosity of 2500 cPs at 20 °C measured on a Brookfield LVD viscometer using spindle 3 at 12 rpm.

The suspension described in Example 4 was also coated onto granular calcium nitrate (which was already treated with an anti-caking coating) at 24 °C using a rate équivalent to 5 litres per metric tonne of granular fertiliser. The résultant coated fertiliser was well-coated with micro-nutrient and free-flowing with low dust levels

It will be understood that the invention is not limited to the exempiified dispersing agent, and that any suitable natural and/or synthetic dispersant may be

-11 used. Suitable dispersing agents include, but are not limited to: fatty acids (FA), mono- and diglycerides, polymeric fatty acid dérivatives such as Afcona 6226,

Atlox LP1 and Decal FD and others.

It will also be understood that the C.l. Pigment Blue 15:1 used in the examples is non-limiting and that other colorants known to those skilled in the art may be used. Examples include: Phthalocyanine blue ( C.l. Pigment Blue 15, 15:1, 15:2, 15:3, 15:4), Aluminium Chlorophthalocyanine (C.l. Pigment blue 79). Other pigments than blue pigments may, of course, also be used.

SUMMARY

The invention provides a method for the préparation and use of oil-based dispersions of plant micronutrients for coating solid granular, prilled or blended fertilisers.

Benefits of the invention include:

1) Greater production flexibility than incorporation of micronutrients during the granulation or prilling process.

2) Superior coverage and the élimination of ségrégation and dusting compared to dry blending processes.

3) Simple one step (single-step) application process of applying only a single fluid (eliminating the need to add oil separately) without chemical or chélation reactions occurring during the process, in particular between the particulate solid fertilizer material and the single fluid comprising a suspension of one or more micronutrient materials in an oil.

4) Reduces the caking tendency of the final solid fertiliser when compared with aqueous-based Systems.

5) Application at ambient températures provides a simple, robust process that does not require use of an external source of heat.

Claims (23)

1. Single-step method for preparing a free-flowing, non-dusting micronutrientcoated particulate solid fertiliser material, the method comprising applying a single fluid onto particulate solid fertiliser material at ambient température without chemical reaction or chélation, said single fluid being pumpable at ambient température and comprising a suspension of one or more micronutrient materials in an oil; wherein 90% of the micronutrient particles in the suspension hâve sizes in the range of 0.1 to 50 pm.

2. The method according to claim 1, wherein the suspension has a solids Ioading in the range 30 to 80 weight%, more preferably 50 to 80 weight%.

3. The method according to claim 1 or claim 2, wherein the 90% of micronutrient particles in the suspension hâve sizes between 0.1 and 20 pm.

4. The method according to any one ofthe preceding claims, wherein the micronutrient suspension has a viscosity in the range 500 to 6000 cPs at 20 °C, preferably 2000 to 5000 cPs at 20 °C measured on a Brookfield LVD viscometer using Spindle 3 at 12 rpm.

5. The method according to any one ofthe preceding claims, wherein the suspension is blended with the fertiliser material in a ratio in the range 1 to 10 litres, preferably 2 to 6 litres per tonne of fertiliser material.

6. The method according to any one ofthe preceding claims, wherein the micronutrient comprises at least one compound of an element selected from boron, copper, iron, manganèse, molybdenum, zinc, or mixtures thereof. ys

7. The method according to any one of the preceding claims, wherein the oil is a vegetable oil.

8. The method according to any one of the preceding claims, wherein the suspension includes a dispersing agent.

9. The method according to any one of the preceding claims, wherein the suspension includes a rheology agent, thickener or anti-settling agent,

10. The method according to any one of the preceding claims, wherein the suspension includes a colorant material.

11. The method according to any one of the preceding claims, further comprising preparing the suspension by blending an oil with particles of a compound containing the micronutrient material; wherein 90% of the micronutrient particles in the suspension hâve sizes in the range of 0.1 to 50 pm.

12. The method according to any one of the preceding claims, wherein at least one of said one or more micronutrient materials is water soluble.

13. The method according to claim 12, wherein said at least one water soluble micronutrient material is zinc sulphate, manganèse sulphate, sodium borate, boric acid, iron sulphate, iron EDTA, iron EDDHA, copper sulphate or sodium molybdate.

14. Oil-based suspension of particles of a micronutrient material, comprising at least one compound of an element selected from boron, copper, iron,

-14manganese, molybdenum, zinc, or mixtures thereof; wherein 90% ofthe particles in the micronutrient material hâve sizes between 0.1 and 50 pm, notably 90% of particles between 0.1 and 20 pm and the suspension has a solids loading in the range 30 to 80 weight%, more preferably 50 to 80 weîght% and is pumpable at ambient température.

15. The oil-based suspension of a micronutrient material according to claim 14, wherein the micronutrient material is a sait, such as a sulphate, oxysulphate, nitrate, borate, chloride, oxychloride, phosphate ; a minerai ; a métal chelate ; an oxide, carbonate or hydroxide ; and the oil is a vegetable oil.

16. The oil-based suspension of a micronutrient material according to claim 14, wherein the micronutrient material is colemanite, boric acid, sodium borate, copper oxide, copper hydroxide, copper carbonate, copper sulphate, copper oxychloride, iron sulphate, iron EDTA, iron EDDHA, manganèse carbonate, manganèse sulphate, sodium molybdate, zinc oxide or zinc sulphate, and the oil is a vegetable oil.

17. Method of preparing an oil-based suspension of a micronutrient material for use in the method of claim 1, in particular according to any one of claims 14 to 16, the method comprising blending an oil with particles of a compound containing the micronutrient material to produce a suspension which is pumpable at ambient température; wherein 90% ofthe particles in the micronutrient material hâve sizes between 0.1 and 50 pm, notably 90% of particles between 0.1 and 20 pm.

18. The method according to claim 17, further comprising adding a dispersant to the oil prior to or during formation of the suspension.

19. The method according to claim 17 or 18 , further adding a rheology agent, </17455

-15thîckener or anti-settling agent to the oil prior to or during formation of the suspension.

20. The method according to any one of claims 17 to 19, further comprising adding a colorant to the oil.

21. The method according to any one of claims 17 to 20 wherein the suspension has a viscosity in the range 500 to 6000 cPs at 20 °C, preferably 2000 to 5000 cPs at 20 °C measured on a Brookfield LVD viscometer using spindle 3 at 12 rpm.

22. Free-flowing, non-dusting micronutrient-coated particulate solid fertiliser material obtainable by the method according to any one of claims 1 to 13; wherein 90% of the particles in the micronutrient material hâve sizes between 0.1 and 50 pm, notably 90% of particles between 0.1 and 20 pm.

23. Use of an oil-based suspension of a micronutrient material according to any one of claims 14 to 16, or an oil-based suspension of a micronutrient material prepared by the method according to any one of claims 17 to 21, for coating a particulate solid fertiliser material.