NZ299160A - High analysis, granular fertiliser and its production - Google Patents

Description

New Zealand No. International No. 299160 PCT/ TO BE ENTERED AFTER ACCEPTANCE AND PUBLICATION Priority dates: 11.08.1995; Complete Specification Filed: 12.08.1996 Classification:^) C05G5/00; C05B19/00; C05G3/00 Publication date: 27 May 1998 Journal No.: 1428 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION Title of Invention: Method of coating high analysis granular fertilisers Name, address and nationality of applicant(s) as in international application form: GRAHAM MICHAEL SHIELDS, an Australian citizen of Glenvar, Wongan Hills, Western Australia 6063, Australia 299160 Patents Form No. 5 Patents Act 1953 COMPLETE SPECIFICATION METHOD OF COATING HIGH ANALYSIS GRANULAR FERTILISERS I, GRAHAM MICHAEL SHIELDS, an Australian citizen of Glenvar, Wongan Hills, Western Australia 6063, Australia hereby declare the invention, for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: PT06A71907 299160 The present invention relates to a method of coating high analysis granular fertilisers with micronutrients. In particular, the invention relates to a method of coating a granular phosphatic fertiliser with a micronutrient such as elemental sulphur to produce a dry, relatively free-flowing product with good slow-release properties. The invention also relates to apparatus for use with the method, together with a product made by the method.

With very few exceptions, soils require regular inputs of most plant nutrients to enable sustainable agriculture. Nutrient input is required to balance the loss of nutrients caused by product removal, leaching of soluble nutrients, erosion and fixation by soil.

With regard to volume, the most important nutrients required for plant production are nitrogen (N), phosphorus (P) and potassium (K). For many farming situations, the plant requirements for these elements are met by application of fertilisers. Artificial inorganic t materials are the most efficient and effective fertilisers, examples of which include triple superphosphate (TSP), diammonium phosphate (DAP), monoammonium phosphate (MAP), potassium nitrate, ammonium sulphate and potassium chloride. Urea (46% N) is an example of the few organic materials that can also be considered as an inexpensive effective fertiliser.

The majority of these nutrients are advantageous as most are water soluble, making them very efficient forms of fertiliser as the nutrients can be taken up directly by plant roots. Also, the high nutrient content greatly reduces bulk, which is desirable for transportation over long distances and for application by farm machinery. The materials are also generally of a uniform composition, exhibit high stability, and are suitable for long term storage.

Sulphur is another plant nutrient required in moderately large amounts. In low input farming systems, sulphur fertilisers are often not required as the plant's sulphur requirements can be met by sulphur present in rainfall (from seawater and by combustion of fossil fuels) and by efficient recycling of sulphur decomposing plant residues. However, in high rainfall situational ^considerably 299160 amounts of sulphur can be lost by leaching. To maintain productivity, these losses must be supplemented by application of sulphur-containing fertilisers. The most important sulphur fertilisers are elemental sulphur, superphosphate, gypsum (calcium sulphate) and potassium sulphate.

Sandy soils of the high rainfall areas of the south-west of Western Australia and parts of South Australia and western Victoria are often sulphur deficient. Such soils require careful fertiliser management as both phosphorus and sulphur can be lost by leaching, often leading to algal pollution in rivers and lakes. These soils require slow-release fertilisers to best match their phosphorus and sulphur requirements.

Extensive field trials have shown that superphosphate and triple superphosphate are generally unsuitable fertilisers for sandy soils in high rainfall areas. Triple superphosphate is unsatisfactory as the phosphorus is too soluble, and it contains low levels of sulphur. Superphosphate is more effective, but requires relatively high application rates to provide sufficient sulphur (present as gypsum) throughout the growing season. The use of superphosphate at such high rates is not sustainable as large concentrations of phosphorus are lost by leaching, with the subsequent potential for environmental damage.

The direct use of sulphate salts such as potassium and ammonium sulphate, may be costly for large scale agricultural use. While the sulphate ions would be immediately available for plant uptake, they would be quickly leached from the soil. Alternatively, elemental sulphur is an excellent source of sulphur, although two conditions must be met for it to be effective. Firstly, it must be present in a finely divided state, and secondly there must be a high activity of soil bacteria such as Thiobaclllus sp. to oxidise the elemental sulphur to sulphate.

Unfortunately, the use of finely divided elemental sulphur as a fertiliser poses several problems. The flammable nature of finely divided sulphur presents major storage and transportation hazards, and it is an eye irritant. It also Dissents application problems due to its fine nature, it does not flow hKrodJ^ M / I- I \ 1 5 OCT a, * f r- c spreading machines at the very low rates required, and it can be blown away if applied on windy days. 299100 ate the sulphur in aw An attractive solution to these problems would be to incorporate the sulphur coating phase of a high analysis phosphatic fertiliser. Such a fertiliser would have 5 improved slow-release characteristics for both sulphur and phosphorus and should be more efficient and environmentally friendly. Also, such a fertiliser should overcome the problems associated with the use of finely-divided elemental sulphur described above.

Indeed, coated fertilisers have previously been attempted in the agricultural 10 industry. For example, polyolefin and bitumen coated ureas, having improved slow-release characteristics over an un-coated product, have been developed. A process which converts elemental sulphur into pellets, making it safer and easier to store, transport and apply, has also been developed. In this process, other micronutrients may also be incorporated by mixing them with the sulphur prior to 15 the addition of water, clay and a wetting agent. The res» iltant paste is then extruded, dried and crushed, giving the desired pellets.

The term "high analysis", as used herein, refers to fertilisers having a phosphate content of about 18 percent. This distinguishes those fertilisers from traditional fertilisers such as superphosphate which has a phosphate content of about 9 percent.

The coating of high analysis granular fertilisers such as TSP, MAP or DAP has also been described. US patent 3580715 describes the use of mineral oil and calcium lignosulphonate as bonding agents to coat granules with elemental 20 sulphur, other micronutrients and pesticides. However, the sequence of the steps in the method of that patent is critical and involves the initial addition of mineral oil to the granules while they are in a rotating drum, the subsequent addition of calcium lignosulphonate and the final addition of the fertiliser supplements. The process is complete when all the granules are uniformly coated.

( This method requires a high degree of fineness of its components for a successful outcome, which means the sulphur would be rapidly oxidised and subsequently lost by leaching, indeed, sulphate ions are particularly mobile in sandy soils and so this product would not be a very effective source of sulphur in, for example, much of the coastal plain and high rainfall areas of Western 30 Australia. 299160 for example, much of the coastal plain and high rainfall areas of Western Australia.

Another method for the incorporation of elemental sulphur and other fertiliser supplements to high analysis granular fertilisers has been described in Australian patent 601099. This method involves the initial wet-mixing of the base fertiliser with elemental sulphur and/or other micronutrients, together with the addition of an aqueous solution of ammonium and/or potassium salts of sulphate and/or phosphate.

It is an object of the present invention to provide a method of coating high analysis, granular fertilisers with micronutrients, such as elemental sulphur, in a simple and effective manner.

The invention provides a method of coating a high analysis, granular fertiliser, the method comprising the steps of: a) the dry mixing of a granular base fertiliser, powdered triple superphosphate (TSP), a primary binding agent and a micronutrient; b) the subsequent addition of water; and c) the addition of quicklime to dry the product and to produce a coated, high analysis granular fertiliser.

The method of the invention is preferably operated continuously in an inclined rotating drum. The rotating drum may be of dimensions in the order of 2 to 4 metres in diameter (preferably about 2.4 metres in diameter), and in the order of 6 to 9 metres in length, having a feed end and a discharge end. Preferably, the three step method of the invention is implemented at three separate areas in the rotating drum such that the dry mixing occurs at or towards the feed end of the drum, the water is added in a central region of the drum, while the quicklime is added at or towards the discharge end of the drum. However, the water may also be added near the feed end of the drum. % -6 299160 In this preferred form, the speed of rotation of the drum, the angle of inclination of the drum, and the feed rates of all required components may be determined and controlled so as to provide a suitable residence time for mixing and reaction. Additionally, the location of the water supply will also determine residence times during the dry mixing and reaction phases of the method. It will be appreciated that suitable residence times will vary for different material and volume requirements.

The base fertiliser used in the method of the invention may be selected from the group comprising ammonium and calcium orthophosphates such as triple superphosphate (TSP), monoammonium phosphate (MAP) and diammonium phosphate (DAP), while the micronutrients used in the method of the invention may be selected from the group comprising elemental sulphur, the sulphate salts of copper (Cu2+), zinc (Zn2+), ammonium (NH4+) and manganese (Mn2+), molybdate salts (Mo042")p and any mixtures thereof. Elemental sulphur is usually the preferred micronutrient.

The primary binding agent Is preferably ferrous sulphate (FeS04), although it may alternatively be calcium lignosulphonate or urea formaldehyde. In general, the use of FeS04 is preferred as its use does not necessitate the use of an additional drying stage.

The size of the particles of the various solid additives is important to the proper operation of the method of the invention. The granules of the base fertiliser are preferably uniform in size and shape are in a size range of 95% being 1 to 5mm. The powdered TSP, the micronutrients and the primary binding agent are all preferably at least 90% passing 250 micron, although are ideally 100% passing 250 micron.

However, where elemental sulphur is used as the micronutrient, it has been found that particle sizes between about 250 and 500 micron may also be suitable, although only in conjunction with secondary binding agents used in thejjfyiflt: step with the primary binding agent. In particular, and where tffe" preferred0 299160 primary binding agent, ferrous sulphate, is in use, it has been found that copper sulphate and zinc sulphate are suitable secondary binding agents.

Indeed, it is envisaged that there may be some instances where the altered micronutrient profile of the final product, which results from the use of the secondary binding agents, is preferred. Thus, in some instances, it will be preferred to use coarser sized elemental sulphur as the micronutrient.

With regard to the nature of the final product, the chemical reactions that occur after the addition of the water are believed to be between the surface of the granules and the binding agents, and thus the final coating is not simply a surface coating but is an integral part of the granule. Indeed, the addition of the powdered TSP is seen as particularly beneficial due probably to the additional orthophosphate surface area which is available for reaction and cross-linking.

The reactions of phosphates with metal cations are very complex and often result in the formation of mixed cation phosphate salts. Generally, the phosphates of the alkali metals (Na+, K* etc) and of ammonium are soluble in water, as are the primary salts (H2P04) of the alkaline earth metals (Ca2+ etc). All of the phosphates of the other metals (Fe, Cu, Zn etc) and the secondary (HP042") and tertiary (PO/") phosphates of the alkaline earth metals are sparingly soluble or insoluble in water.

The following reaction pathways are those envisaged to be occurring and provide a basis for understanding some of the processes that are occurring. where X can be Fe, Cu, Zn or Mn TSP - triple superphosphate (or monocalciumphosphate) - Ca(H2P04)2.1H20 Ca(H2P04)2.1H20 + XS04 + (n+1)H20 - X(H2P04)2 nH20 + CaS04.2H20 V 1 5 ctf ,538 V 299160 MAP - monoammoniumphosphate - NH4H2P04 2NH4H2P04 + XS04 + nH20 - X(H2P04)2.nH20 + (NH4)2S04 DAP - dlammoniumphosphate - (NH4)2HP04 (NH4)2HP04 + XS04 + nH20 - XHP04.nH20 + (NH4)2S04 Molybdate If Mo042" is added the complex salt PMo^O^3* forms.

However, it is envisaged that what is actually happening is far more complex. Indeed, triple superphosphate Is not pure Ca(H2P04)2.1H20 as it also contains considerable quantities (6-10%) of relatively insoluble CaHP04 and unreacted apatites. Also, any ferrous phosphate (Fe(H2P04)2) that is formed is rapidly oxidised to ferric phosphate as per: 4Fe(H2P04)2 + 02 4FeP04 + 4H3P04 + 2H20 Following is a list of other salts that are likely to form under these reaction conditions.

Zn(NH4)HP04(H2P04).H20 ZnNH4P04.H20 ZnHP04.H20 Zn3(P04)2.nH20 where n = 2,4,5,6 or 8 Cu3(P04)2.3H20 (Ca,Fe)3(P04)2.4H20 299160 The addition of quicklime in the final step of the method of the invention plays a significant role In the cementation process. The major reaction Is believed to be the formation of CaHP04.2H20 from Ca(H2P04).H20 as follows: CaO + Ca(H2P04)2.1H20 - 2CaHP04.2H20 It also assists with removal of excess water, thus serving to "detackify" and dry the final product as per: CaO + H20 -> Ca(OH)2 The quicklime also promotes the formation of insoluble phosphates of Cu, Fe, and Zn by neutralising the phosphoric acid (H3P04) formed in the double decomposition reactions: X(H2P04)2 - XHP04 + H3P04 3X(H2P04)2 - X3(P04)2 + 4H3P04 All the initial additives are preferably water soluble, or slightly soluble, and are at least partially dissolved on the addition of water, allowing the multiple reactions to proceed. Generally, the final product will have a higher degree of hydration than the starting products. This increase in hydration, and the slightly exothermic nature of the process (the self-generated operating temperature is around 50°C), ensures that substantially all the water added to, and generated by, the process is absorbed as water of hyriration or driven off by the reaction temperature. The final product is also generally more insoluble and less hygroscopic than the starting products, and so the converted granules are easier to store, transport and apply, and have improved slow release properties.

It .J also believed that the elemental sulphur does not react with any of the other components, but is incorporated within the cementitous nature of the end ^ products of the reactions. - % ... 299160 The method of the invention doet, >t require the pre-mixing of bonding agents with water prior to their addition to, and coating of, the base fertiliser granules. The method merely requires the addition and mixing of the components in a dry form prior to the addition of the water. Furthermore, the addition of a relatively small amount of quicklime at the final stage of the process converts the somewhat tacky, coated granules into a dry, relatively free-flowing product that is smooth, and is uniformly and strongly coated and which Is easily stored, transported and applied to soils. The product also has a reasonably long shelf-life.

Thus, it will be apparent that the apparatus for use with the method of the invention is reasonably simple and indeed may advantageously be constructed as a portable unit, allowing location at the agricultural area where the product is required. The product may then be varied in its composition depending upon local requirements, it also being more economic to deliver the starting materials to regional distribution centres than to deliver them to a central manufacturing site for subsequent transport of the final product over large distances.

The invention will now be described in relation to an example as Illustrated in the accompanying flow diagram of Figure 1. However, the following description is not to limit the generality of the above description.

The flow diagram of Figure 1 illustrates a granulator in the form of a rotary drum 10. As Indicated earlier, the drum is preferably in the order of 2.4 metres in diameter and 9 metres in length, rotating at about 10 rpm and having an angle of inclination of 1° to 3°. The drum is preferably configured, together with the relevant feed flowrates, to give a residence time of about 3 minutes and to produce about 35 tonnes of product per hour.

In this respect, the solid feed 11 is introduced at the feed end 12 of the drum 10, the water 13 is introduced at a point near the feed end 12 (preferably about 1 metre from the feed end 12), and the quicklime 15 is added at the discharge end 16 of the drum 10, while product 17 is removed from the drum lO^ak discharge end 16. i- 299160 The product is preferably passed to a screen 18 having a 10mm aperture size to provide a final product 20 to be stockpiled, and an oversize product 22.

In this example, the micronutrient is elemental sulphur milled to be in the size range of 250 to 500 micron, thus requiring the use of the secondary binding agents CuS04 and ZnS04. The primary binding agent is the preferred FeS04. However, and with regard to primary binding agents, it is possible, although not preferred, to alternatively use calcium lignosulphonate or urea formaldehyde. These alternatives are not preferred as they necessitate the addition to the process of a further drying phase.

The flow rates of the components used In the example flow diagram in Figure 1 are as follows: Component Base fertiliser - triple superphosphate Powdered triple superphosphate Micronutrient - milled elemental sulphur - Na2Mo04 Primary binding agent - FeS04 Secondary binding agents - CuS04 ZnS04 Water Quicklime (CaO) Rate -30 t/hr 0.5 -1.0 t/hr 2 -4 t/hr 50- 100kg/hr 0.25 -0.5 t/hr 0.1 - 2.0 t/hr 0.1 - 0.7 t/hr 10- 18litre/min 0.1 - 0.3 t/hr Size 1 to 5 mm less than 250 ixm 250 (im to 500fxm 250 nm to 500|*m less than 250 urn less than 250nm less than 250 i*m less than 250(im Additionally, and as a specific example of preferred proportions of components which are suitable for the method of the present invention, in 1000kg of feed components the following preparations may be used, together with 30 kg of water: 299160 Option 1 (kgs) Option 2 (kgs) Base TSP 874 870 Ground TSP 20 20 Elemental sulphur 91 (fine) 89 (coarse) Ferrous sulphate 10 10 Copper sulphate - 3 Zinc sulphate - 3 Quicklime 5 5 1000 kgs 1000 kgs Finally, it will be appreciated that there may be other variations and modifications to the matters described above which are also within the scope of the present invention.

Claims (7)

WHAIXWE CLAIM IS:> 13- 299160

1. A method of coating a high analysis, granular fertiliser, the method comprising the steps of: 5 a) the dry mixing of a granular base fertiliser, powdered triple superphosphate (TSP), a primary binding agent and a micronutrient; b) the subsequent addition of water; and c) the addition of quicklime to dry the product and to produce a coated, 10 free flowing high analysis granular fertiliser.

2. A method according to claim 1, wherein the method is operated continuously in an inclined rotating drum. 15

3. A method according to claim 1 or claim 2, wherein the three step method is implemented at three separate areas in the rotating drum.

4. A method according to claim 3, wherein the drum has a feed end and a discharge end, and the dry mixing occurs at the feed end of the drum, the water is 20 added near the feed end of the drum, and the quicklime is added at or near the discharge end of the drum.

5. A method according to any one of claims 2 to 4, wherein the drum is inclined at an angle in the range of 1° to 3° from horizontal. 25

6. A method according to any one of claims 2 to 5, wherein the drum is about 6 to 9 metres in length, about 2.4 to 4 metres in diameter, rotates at about 10 rprr , and has a residence time of about 3 minutes. 30

7. A method according to any one of claims 1 to 6, wherein the base fertiliser is selected from the group comprising ammonium and calcium orthophosphates, such as triple superphosphate (TSP), monoammonium phosphate (MAP) and diammonium phosphate (DAP). 299160

8. A method according to any one of claims 1 to 7, wherein the primary binding agent is ferrous sulphate.

9. A method according to any one of claims 1 to 7, wherein the primary binding agent is calcium lignosulphonate or urea formaldehyde.

10. A method according to any one of claims 1 to 9, wherein the micronutrient is selected from the group comprising elemental sulphur, the sulphate salts of copper (Cu2+), zinc (Zn2+), ammonium (NH4+) and manganese (Mnz+), molybdate salts (Mo042"), and any mixtures thereof.

11. A method according to any one of claims 1 to 10, wherein the granules of the base fertiliser are uniform in size and shape, and are in a size range of 95% being 1 to 5 mm.

12. A method according to any one of claims 1 to 11, wherein the powdered TSP, the micronutrient, and the primary binding agent are all at least 90% passing 250 micron.

13. A method according to claim 12, wherein the micronutrient is elemental sulphur.

14. A method according to any one of claims 1 to 11, wherein the micronutrient is elemental sulphur in a size range of 250 to 500 micron, and wherein the method includes the additional step of incorporating a secondary binding agent in the dry mixing step.

15. A method according to claim 14, wherein the primary binding agent is ferrous sulphate and the secondary binding agent is copper sulphate, zinc ulphate, or a combination of both. -15- 299160

17. A method according to claim 1 substantially as herein described in relation to Figure 1.

18. A method according to claim 1 substantially as herein described in relation to the Example.

19. A high analysis, granular fertiliser according to claim 16 substantially as herein described in relation to Figure 1.

20. A high analysis, granular fertiliser according to claim 16 substantially as herein described in relation to the Example. 299160 ABSTRACT A method of coating a high analysis, granular fertiliser, the method comprising the 5 steps of: a) the dry mixing of a granular base fertiliser, powdered triple superphosphate (TSP), a primary binding agent and a micronutrient; b) the subsequent addition of water; and 10 c) the addition of quicklime to dry the product and to produce a coated, high analysis granular fertiliser.