NZ286023A - Production of nutrient-coated urea fertilizer granules by tumbling coating with minimal water present - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £86023 A 286023 Patents Form 5 Priority Date(s): Complete Specification FiLd: Class: (6)C.oSC9.|.OQ; CftS&.dfo.Q, .. jBo.I xzf.m+.iht.

Publication Date: /.$.JR.&£fLli8S.....?.Xt..P.r P.O. Journal No: wan N.Z. No.

NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION ADDITION OF NUTRIENTS OF GRANULAR UREA FERTILIZER We, HI-FERT PTY LTD., a Company incorporated under the laws of the State of South Australia of, 168 Greenhill Road, Parkside, South Australia, Australia, do hereby declare the invention, for which we 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:- \ vrS \ - 1 - (Followed by J A) 2 0 » -" 28 6 0 2 3 r "ADDITION OF NUTRIENTS TO GRANULAR ORE A FERTILIZER" This invention relates generally to a process for the addition of micromitrients as veil as secondary nutrients to granular urea fertiliser, and more particularly to a coating process which relies upon chemical reactions between the micronutrient and a chemical compound, and not an aqueous hinder and subsequent drying process, for the establishment of a tenaciously adhering coating system carrying micro aad/ or secondary nutrients. In common terminology, "secondary nutrients" are S, Kg and Ca (the "primary nutrients" being N, F and K).

In the last five decades or so, the addition of artificial nitrogenous fertilizers to the soil has had an enormous beneficial effect in terms of increased crop production.

On certain soil types, similar increases in crop production have been obtained by the addition of micronutrients and secondary nutrients to the soil. These types of nutrients perform primarily a catalytic role in the enzyme systems of the plant cells and can vary from weak ionic effects to the formation of highly specific compounds known as metalloenzymes, or participate in the formation of proteins and other organic compounds. as HV»> Gut, Go, While all plants require generally such micronutrients fend .2>> FtL qnd Nla> ana ^Or^cX Cq, A secondary nutrients as 5, •£», Kg// Hn, Cu» Co, B, re and Nay the addition of these nutrients is only required when these types of nutrients are either absent from the soil or are in a less available form, thereby causing depressions in crop production..

Since the designation "secondary nutrients" for S, Kg and Ca could imply that the role of these nutrients is secondary in comparison with the primary nutrients N# F and K or the micronutrients, it is now more or less customary to combine-the three primary nutrients with the three secondary nutrients and use the tern "macronutrients • for these six nutrients. - jA- 9 FEB '96 11:50 FROM MADDERNS TO PAGE.005 286023 Since it is a wall established fact that improving conditions for maximum crop or pasture production by the addition of a single nutrient fertilizer can be negated if another macro-or nlcrontxtrlent 1s limiting, it is absolutely essential that none of the other essential macro- or micronutrients are limiting.

Over the last 30 years or so, most sacronutrient carrying fertilizers (N, P or K) have been in closely-sized granular foCTis, which can be blended with each other without causing any problems of segregation. Zn comparison with macro nutrient fertilizers, the quantities of micronutrients required are considerably less. Thus, the micronutrient-carrying materials have to have a considerably smaller grain size than the xaacronutrient in order for an even distribution throughout the granular macronutrient fertilizer to be achieved. This means, however, that the extreme differences in particle si zings between the granular macronutrient fertilizer and the powdery micronutrient will lead to problems of segregation during the blending of these two types of fertilizers. There can be little doubt that an even distribution of the micronutrient fertilizer through the macronutrient carrier is of utmost importance if patchlness in the field is to be avoided. Patchlness in the field may not only be due to the absence of a micronutrient in the applied blended fertilizer, but also to the toxic effects of the micronutrient as a result of excessive application caused by segregation in the blend.

While a number of patents teach the incorporation of micronutrients in phosphatic fertilizers, the incorporation of micronutrients into granular urea has so far received very little attention.

The following patents describe the incorporation of micronutrients into phosphatic fertilizers:- Otis D Fhilen, Julius Silverberg and Melvin M Morton, OS IS FEB '96 11:51 FROM MADDERNS TO 28'C07 Patent 3423199; Jan 21, 1969; "Adding Micronutrients to Granular Fertilizers" 0 D Philen, J Silvarberg and M X Norton, OS Patent 3520651; July 14, 1970; "Fertilisers Containing Micro- and Macronutrient* • G 0 Cicco, US Patent 3360192; Feb 2, 1971; "Micronutrient Enriched Granular Fertilizers" Ralph Miller, US Patent 3961932; June 8, 1976; "Coating Granular Fertilizers with Chelated Micronutrients" R B Walter, Australian Patent 354749; March 15, 1985; 15 "Production of Granular Trace Element Fertilizer" K H Walter, as Patent 5152821; Jan 27; 1989; "Addition of Supplemental Macro & Micro Nutrients to Granular Phosphatic Fertilizers".

Micronutrient-carrying compounds can be evenly dispersed throughout molten urea before the congelation of the molten urea droplets in a prilling tower or the spraying of the molten urea onto a bed of tumbling solids in a conventional granulation device, which leads to particle size enlargement by a surface layering mechanism. However, this approach ^ poses many problems in regard to storage. This is due to the ^ fact that the requirements for a particular micronutrient 30 vary with the soil, the climate and typ« of crop ta be grown. Thus different mixtures are needed.

G L Tucker and S L Blanton teach in tJS Patent 3981713; Sept 21, 1976; entitled "Urea-Zinc Oxide Composition and Process* 35 the homogeneous dispersion of ZnO in molten urea at 104"C -168°C, which has a maximum H^O content of 0.3 wt%. The resulting dispersion is subsequently solidified by a conventional process of congelation in a prilling tower or granulating equipment. 19 FEB '36 11:51 FROM MADDERNS TO PAS£.007 28 6 0 2 Sine* the main aim of an adeguate program of fertilizer application is to supply all essential plant nutrients during ^ the growing season to the plant and since, in contrast to phosphatic or potassic fertilizers, the chance of losing 5 nitrogen by leaching or volatilization after denitrifieation is considerable, the application of nitrogenous fertilizers has to be split throughout the growing season,.

I Because phosphorus and potassium fertilizers move very little in a soil/ a number of soils still have an adequate supply of phosphorus or potassium and do not have to be fertilized with either a phosphorus or a potassium fertilizer. This means that it is impossible at present to correct any micronutrient imbalance- in these soils during the application of a nitrogenous fertilizer.

From the many nitrogenous fertilizers which can be applied to a crop/ urea (NHj-CO-NS^) represents not only the cheapest source per unit of nitrogen, but has the highest nitrogen content of any solid nitrogen fertilizer. Unfortunately, the physical properties of urea in regard to its solubility as well as hygrascopicity do not make it am ideal carrier for the addition of micronutrients by coating.

This is clearly shown by the solubility of urea in water at different temperatures/ which varies as followsi- Temp. of Solution Urea Dissolved in lOOg Solution £ c/iOOg 0 41.0 40 62.2 80 SO.6 100 88.3 120 ?5.5 130 99.2 4 19 FEB ' 9G 11:51 FROM MflDDERNS TO .PAGE-. 0&S 286023 This In practice that, at 100"C, 11.7g water will dissolve 88.3g urea. While it weald be possible to establish a coating system with subsequent drying, this approach would lead to an increase in the biuret content o£ the area.

Biuret is a very undesirable phytotoxic impurity in fertilizer-grade urea. Its concentration varies normally between 0.3 and 2.0 wt%. Biuret is formed at atmospheric pressure at temperatures >100°C by the combination of two molecules of urea with the release of ammonia according tax- 0 OHO * | ■ 2(NH2 - C - NH2) > (NHj - C - N - C - HHj) + NHj [1] >10Q*C Urea Biuret or in a semi structural form: £ 2 CO-tNHjJj > (NHj-CO-KH-CO'NHJ) + NHj (1] >100«C Urea Biuret Since it is almost impossible to avoid localised overheating in an industrial drying process, the drying of coated urea would lead to a higher biuret content and is for this reason not a practical proposition.

It is the object of the present invention to provide a method for the coating of granular urea with such micronutrients as Zinc (Zn), Copper (Cu), Manganese (Ma}, Boron (B) etc, as well as the macronutrients Mg and S (which were previously designated as secondary nutrients}, for the establishment of a nutrient coating on the surface of urea. 19 FEB '36 11:52 FROM MADDERNS TO PAGE-. 009 286023 It has been found that area, which can be considered to be either an amide of carbamic acid [SH2 COOH] or the diamide of carbonic acid [S^CO^J, ha* certain properties which can be utilised in the establishment of a tenaciously adhering nutrient coating. in the presence of certain oxides# as well as. hydroxides, urea is hydrolysed as follows x- CO*(NH2)2 + Me20 + 2H20 ^ 2 NH3 + C02 + 2 He OH [2J (Me =■ Na, Zn/2, Ca/2, Mg/Z) with strong acids, urea acts as a monobasic substance and 15 forms adducts, as illustrated below: - CO«(!lH2)2 + H2S04 ^ CCO'fNHjJj'HjSO^] or t3a] CO-(NH2)2 + H3P04 > CC0.(NH2)2-H3F04] [3b] These are easily decomposed into their ammonium salts and carbon dioxide according to:- [C0-(NH2)2'H2S04] + H20—>(NH4)2 S04 + C02 or [4a] tC0.(NH2)2.H3P04] + H20—^(NH4)2 H P04 + C02 [4b] Furthermore, it forms with a great number of metallic salts relatively stable addition products having the general 30 formula CO*(NH2)2»Me R.

(Me R = CaS04, ZnS04, CuS04, NH^Cl, Na2S04, etc.) The present invention provides a amitinutrient-carrying, granular urea fertilizer/ and a process for its production. 35 The nu:rient(s) may be, for example, elemental sulphur, optionally together with one or more compounds of Zn, Kg, Ma, Cu, Co and/or B. Suitable compounds of these metals ares zinc oxide, sine sulphate, zinc carbonate, basic sine 19 FEB '36 11:52 FROM MfiDDERNS TO _ PAGE.010 286023 sulphate, magnesium oxi.de/ magnesium hydroxide/ magnesium carbonate/ magnesium sulphate/ manganese oxide, manganese sulphate, manganese carbonate, basic manganese sulphate/ copper oxide, copper sulphate, basic copper sulphate, cobalt sulphate/ cobalt carbonate, cobalt hydroxide, orthoboric acid (H3BOj), metaboric acid (HB02), tetraboric acid (H2B207), boric oxide (B^O^)/ calcium metaborate and calcium tetraborate. It should be noted that this list is illustrative/ and not restrictive, of nutrients which may be 10 utilized in the product and process of the present invention.

More particularly, this invention provides a multinutrient-coated/ granular urea fertilizer comprising between about 0.1% and 20% by weight of the total composition of the 15 zmtrient(s). The coated fertiliser is produced by placing granular urea into a conventional granulating or coating device, wetting the tumbling bed of granules with sufficient water (generally, less than 2.5 wt%) and/or concentrated sulphuric acid to produce a tacky surface, and cheli "WWII 20 the nutrient(s), either with or without coating agent(s). In the case of urea, establishment of a tacky surface takes a place almost instantaneously/ on addition of the water or the sulphuric acid. If the nutrient to be coated on the granules is capable of reacting with the water or sulphuric acid at 25 ambient temperatures, then a coating agent is unnecessary. Accordingly, a coating agent will not be required if the nutrient is a metal oxide having a lower electronegativity ^ than iron (eg ZnO/ MgO or MnO). Otherwise, if the nutrient is incapable of reacting with the water or sulphuric acid at 30 ambient temperatures/ a coating agent will be required.

Suitable coating agent(s) are e.g. (a) oxides or hydroxides of metals having a lower electronegativity than iron; (b) oxides or hydroxides which form basic salts with the micronutrient(s); (c) sulphates of metals; (d) phosphates of 35 ammonia; (e) carbonates; and mixtures thereof. In particular/ the coating agent(s) may comprise magnesium oxide, zinc oxide, sodium hydroxide, magnesium hydroxide, zinc hydroxide, magnesium sulphate# ammonium dihydrogen 12 FEB '9S 11:52 FROM MfiDDERNS TO PAGE.011 286023 phosphate, di-ammonium hydrogen, phosphate and/or sodium carbonate.

^ Coating agents will only be required if the nutrient(s) will 5 neither hydrolyse urea according to equation (2] nor form adducts as shown in equations [3], which in turn decompose as indicated in equations [4].

^ The actual coating operation will be performed in equipment 10 normally employed in agglomerative granulation processes^ The most widely used general types of granulation device are the rolling drum and the inclined disk or pan gremulator, while we prefer a rolling drum equipped with annular rings, 15 an inclined disk or pan granulator can be successfully employed for this coating operation as long as the inclined disk diameter to disk rim height ratio is <2.

Our preference for the rolling drum is entirely due to the 20 fact that the effects of such disk design parameters as angle of disk inclination, disk diameter, rotational speed and ^ residence time upon the quality of the coated product or, in ^ the case of granulation, upon the finished granule are not well understood and make the scale-up of disk coating devices a very semi-empirical procedure.

^ As far as the coating drum is concerned/ we have found that a device meeting the following design parameters will be well suited for the coating operation disclosed in this 30 specification- Drum Length / Drum Radius Ratio * 2.4:1 Annular Ring / Drum Radius Ratio » >0.30:1 Angle of Decline of Drum = <1.5" Residence Time of Granule in Device «► >12 min.

Rotational Speed of Drum * >40% <60% of Critical Speed 8 19 H EB '96 11:53 FROM MADDERNS TO PAGE.012 286023 Critical speed Ncs is defined as the speed at which the centrifugal force on the granule in the rotating device equals, in the zenith of rotation, the gravitational force on the said granule. That is achieved when g " r»2? g being —2 the acceleration due to gravity- (9.81 m sec ); 2 r being the diameter of the rotating drum in metres and Co the angular velocity in radians per second.

The critical speed is given by* - N__ «= A3.317 rpm c9 v?2r This critical speed applies only to dry materials in smooth 15 as well as clean drums. Wet and sticky materials will have a somewhat lower critical speed than dry materials.

A coating drum meeting these design parameters will produce a tumbling bed of granules, which will have excellent mixing 20 action ensuring maximum collisions between the granules and the particles of the nutrient(s) to be coated onto the surface of the granules and thus generating ideal conditions for producing a very dense coating by chemical reaction between the tacky surface of urea and the nutrient(s), as 25 well as any additive which might be employed.

The chemical reactions occurring during the actual coating operation are considerably more complex than the equations written in this specification which are, for this reason, probably uot a true representation of the many reactions which occur . Reaction products fanned during the coating operation comprise or include one or more sulphates, hydroxides, phosphates or carbonates of the nutrient(s), or a mixture thereof. In particular, the reaction products may 35 includes (a) struvite; (b) one or more sulphates of calcium, copper, zinc, magnesium or manganese, or a mixture thereof; (c) one or more basic sulphates of copper, manganese, magnesium, zinc or cobalt, or a mixture thereof; (d) one or i 9 FEB '96 11:53 FROM MfiDDERNS TO ~ PAGE. 0 1 286023 more complex metal ammonium hydroxides; (e) one or more ^ complex metal ammonium sulphates; (£) one or more complex ^ metal ammonium carbonates; and/or (g) one or more carbonates or basic carbonates of copper, magnesium, sine, manganese or 5 cobalt:, or a mixture thereof.

The use of a coating additive will be required if the ™ nutrients to be coated on will not react with urea as shown in equation [ 2 ]. This means that the nutrient oxides of 10 metals can be coated onto area without a coating additive only if they readily react with water, forming hydroxides of the relevant metals.

We found that only those metal oxides having an 15 electronegativity lower than that of iron can be coated without the use of a coating additive. Metals having a higher electronegativity than iron, as well as nutrients in a salt form, require either a coating additive or respective oxide to get the coating reactions going.

Multinutrient coating of urea can be performed by the 0 following methods 1) MICRONUTRIENTS AS METAL OXIDES ONTO UREA WITHOUT COATING 25 AP.QITIVSS £ Magnesium, zinc and divalent pure MnO can be coated onto urea with water as a coating liquid. This is due to the fact that these oxides form, in the presence of water, the following hydroxides * - 2IHC ZnO + RjO > Zn(OH)2 [5] MAGNESIUM MgO * > Mg(0H)2 [6] flftflSftKSSE MnO 4- HjO Mn(OH)2 [7] - 13 ffcB -ato 11:54 FROM MfiDDERNS TO PfiGE.014 286023 Since most commercially available manganous oxides are easily oxidized to Hn^O^ (tri-manganese-tetroxide) , freshly manufactured manganous oxide can. be employed for coating of urea. Even the purest KnO, having an extremely fine crystallite size, will be. deactivated by the formation of an inactive film of Mn^O^ on the surface of MnO.

We have found that for this reason the use of manganous oxide as a coating agent on its own is not a practical proposition, especially if we consider that the higher oxides of manganese (Mn^O^ and Mn203) which are formed during the oxidation of manganous oxide are not very available to plants.

As far as the coating of urea with zinc or manganese is concerned, we have found that the following reactions will occuri- ZTNC: CO-(NH2)2 + ZnO + nH20 ^ 2NH3 + CG2 + Zn(0H)2 + (n-2)H20 JSJ C0*(MH2)2 + Zn(OH)2 >2NH3 + ZnC03 (9J ^ SZn(OH)2 * 2C02 + HjO—^ [2ZnC03* 32ri(OH) 2-3H20] [10J The zinc hydroxide formed from amorphous zinc oxide according to this reaction [S] is very reactive, and readily adsorbs water as well as gaseous . The ammonia evolved during the reaction can only be noticed during the start of the reaction. The freshly precipitated Zn(0fi)2 is in its status nascendi a very 35 plastic thixotropic mass, which will set: hard in a short period of time.

IS FEB '96 11:54 FROM MfiDDERNS TO PfiGE.015 286023 Adsorbed will not form an ammonium zincate vlth the zinc hydroxide, but will adhere very strongly to the surface of the zinc hydroxide.

Similar reactions are applicable to manganese. jjAGWgSTtJMi Tha reactions occurring during the coating of urea with magnesium oxide will be very similar to the reactions with zinc.

+ KgO ♦ HjO 2NH3 * COj + Hg(OH)2 + (a^Z'j^O [HJ CO*(US2)2 + Mg(0H)2 + nHjO 2NH3 * MgCOj• 3HjO + (n-SjHjO C12] MgC03 + Mg(0H)2 + nH20 MgC03'Mg(0H)2-3H20 + (n-3)H-,0 (13] The magnesium oxide used in this coating operation has to be a low temperature amorphous MgO, which is very 25 reactive. Calcined or high temperature MgO cannot be employed in this coating operation. 2) MICRONUTRIENTS A3 METAL 0X108S. ELEMENTAL S ANO BORIC ACID ONTO PRgA WITH COATINS ADDITIVES All metal oxides having a higher electronegativity than iron will not be able to react with water at ambient temperatures forming their respective hydroxides, and thus require a coating agent. We have found that any 35 oxide or hydroxide of a metal having a lower electronegativity than iron (2n, Ca, Mg, Na, Li, Al, K> can be used as a coating additive, for the incorporation of unreactive metal oxide and boron compound nutrients 12 - IS FEB '96 11:54 FROM MfiDDERNS TO PAGE.01G 2860 as well as elemental S, according to the following general formula jie1 • Na, K, Li, *ff/2, Ca/2, 2n/2 or Al/3 CO(NK2)2 + oHjO ^ 2NS3 + MeX2 C03 + (it-lJH^O [14] m CO[tm2)2 +■ 2M®1 OH + nH20 > 2NH3 + Me12 C03 + nH20 [15] while copper as well as manganese could be coated onto urea with the aid of these coating aids, the oxidation of MnO to the less agronomically available Ka^O^ would 15 considerably reduce the effectiveness of the manganese coating as a source of Mn for plants. As far as copper is concerned, the following reactions will most likely occur during the coating operation. coppers £ CO(NH2)2 + Ca(0H)2 + nHjO ^ 2NH3 CaC03 + nHjO £16} CuO +4NH3 + hHjO ^ [CU(NH3)4] «-(OH)2 + (n-l)S20 £17] [cu(nh3)4]-(oh)2 + coj ^£cu(h83)4i.c03 * hjo [18] The coating produced by these reactions will consist of unreacted CuO, CaC03, [Cu(NH3)4].(OE)2, [Cu(NH3)4]-C03 and most likely some basic copper carbonate, which will be formed as follows CuO +• [Cu(HH3)4]*C03 + rifijO > CUC03-CU(OH)2-*H20 + 4NH3 + [»-(*+!) 1^0 [1*1 While the resulting copper coating adheres strongly onto the urea granules, we found that using a salt of copper or mixture of a copper salt with copper oxide will produce a more strongly adhering capper coating. 19 FEB * 9G 11:55 FROM MfiDDERNS TO ** <-k.P^E'01L 286023 RT.RMftWTAL SUT.Pmmi ^ w were able to demonstrate that MgO as well as ZnO can be eaployed for the coating of 0.1% to 20% by weight of the total composition of elemental sulphur onto urea.

The coating mechanism is most likely the one described in reactions [8] to t13J* » A better adhering and less hygroscopic sulphur- containing coating can be established by the formation of struvite during the coating operation. Struvite, which has the formula MgNH4P04* SHjO, occurs widely in guano as well as in dung deposits and is found as a constituent of human urinary calculi, it is formed in the soil in the presence of di-hydrogen phosphate, ammonium and magnesium ions. The high water of crystallisation content, as well as its low solubility (O.OSg by weight in lOOg of water), make these additives ideal coating agents for the incorporation of elemental sulphur.

^ The reactions occurring during this coating operation can be described as follows i MgO + HjO >Mg(OH)2 [S] Mg(OH) 2 + NH4H2l»04 + 4H20 ^ MgNH4P04* 6H20 C20] ^ The elemental 5 to be incorporated by these methods has to be ground to such a degree that at least 75% by weight of all ground particles will be smaller than 150 yxm.

BORON: RjBO^ or orthoboric acid is, in contrast to many other inorganic acids, a very weak acid, having a very low solubility in water (3.9% by weight at 30°C). in its - 14' - 19 FEB '96 11:55 FROM MfiDDERNS TO PflGE-.01« 286023 pure form, it is a white crystalline solid. Wto have found that crystalline orthoboric acid can be coated onto urea if reactive MgO is employed as a coating additive, as long as the orthoboric acid is in a fine state of division. We found that crystalline orthoboric acid in which at least 60% of all particles are smaller than 150^ua can be coated onto urea. Since reactive MgO reacts readily with water, as shown in equation [26], we can assume that part of the Mg(OH)2 formed during this 10 reaction will react with orthoboric acid forming relatively complex borates which in turn, together with Mg(OH) 2, will cement any unreacted H^BO^ onto the urea •particles. Since the complex borates formed during these reactions will take up water of crystallisation and possibly of constitution, and since Kg(0H)2 can absorb relatively high quantities of water, the resulting coat is dry and will adhere onto the urea.

Furthermore, we have found that boron trioxide (BjO^), boric acids and any other hard-to-bond nutrients are easily coated onto urea with the help of Kg and ammoniumphosphate ions. The presence of these two ions will lead, as is shown in equation £20], to the formation of struvite crystals, which will become 2 5 interlocked with the slightly soluble boron compound or any other less reactive nutrient compound, thereby F incorporating said compound into the coating. The fact that struvite contains 6 moles of water will make the use of coating-watar less critical in regard to the overwetting of the coated product. 3) METAL SALTS OP M1CROWTFPRIENTS ONTO URSA WITH OXIDES ft HYDROXIDES AS COATING ADDITIVES With the exception of the nutrient zinc, we have found that the best adhering coating systems are based on nutrients in a salt forts. The reactions occurring 19 FEB '36 11:55 FROM MfiDDERNS TO PAGE.019 286023 during those coating operations can be represented as follows s- 17 COATING ADDITIVES ARE Cu(OH)2, 2nO, Zn(0H)2, MgO, Mg(OH)2, NaOH, KOH NOTRIENT He1X - Cu, Ma, Mg, Zn C0(NH2)2+«eltS04+Ca(0H)2+nH20 « CaC03+(NH4)2SO4+MeII(0H)2-H(a-2)H2O £21] CO(NS2)2+M«lrS04+nH20 — > C02+Heri(OH)2>(NH4)2S04+(n-3)H20 [22] aMoI^SO4+bMeII(0H)2+nH2O > alte"s04»bMeri(0H)2«xH20+(n-x)H20 £23] MeI3:S04-t-(NH4)2S04>nH20 > Me S04* (NH4)2s04»xH20+(n-x)H2° C24* Me^1 (OH)2+COj > M*ZZC03+K^O [25] ^ The basic salts formed during these reactions always have a higher state of hydration than the raw materials 25 employed in the coating operations, which means that drying of the coat is achieved by the removal of free ^ water from the system as water o£ constitution as well as water of hydration.

Basic salts are well-defined chemical compounds, which can be famed from polyacid bases, such as Cu, Zn, Kg, Fe, Al etc., and contain two or more negatively charged ions of which at least one is a hydroxide ion.

The following basic salts have been described in the literature s- 19 FEB '9G 11:56 FROM MfiDDERNS TO 8t?o<d3 COPPER? CuS04-4Cu(0H)2*nHj0 (n-l-S) CuS04'3Cu(QH)2*% HjO 2CuS04*5Cu( OH) 2*42^0 CuSO4»3Cu(0H)2 CttS04*3Cu(OH)2*2220 CttS04*2Ctt(0H)2 CuS04*3Cu(0H)2»IH20 CuS04*Cu(0H)2 In contrast to copper oxide, magnesium oxide reacts readily with water, forming magnesium hydroxide, according tox- MgO Mg(OH)2 C26J This freshly precipitated hydroxide of magnesium forms with such magnesium salts as MgCl2, MgSO^ and Mg(N03)2 colloidal solutions, which harden on ageing (sorel cement) . The structure of these solid solutions is not very well understood and it appears that the hardened cement consists of basic magnesium sulphate containing varying quantities of water of hydration. Xn addition, it appears that the presence of ammonium sulphate formed in reaction [22] will lead to the very stable double salt MgS04* (NH4)2S04*SH20 as indicated in equation [24]. aQRQNi We were able to demonstrate anhydrous partially dehydrated calcium tetraborate (CaB^O^) as well as calcium metaborate (Ca(BC2)2) coated onto urea employing sulphuric acid as a coating agent. During this operation, the following reactions will most likely take place: 17 19 FEB '36 11:56 FROM MfiDDERNS TO PfiGE.021 286023 Calcium tetraborate Cafi407 + HjSO^ +■ 7HjO > CaSO^* 2^0 + 4H3BC>3 Calcium aetaborata Ca(802)2 + H2S04 + 2H20—>CaS04*2H20 + 2HBOz MAJTGANESgz The chemistry of the basic manganese sulphate has not 10 been very well investigated. Existing literature on such compounds is often confusing, which could be due to the fact that MnO is readily oxidised to Mn^O^ and that manganese sulphate forms a whole range of rather complex sulphate aquo complexes. T£ urea is coated with 15 manganese by this method, it is advisable to incorporate at least 2% of finely ground elemental sulphur, which will considerably retard the oxidation of the manganous ion to the manganese (Il-t-III) oxide according tot- 5Mn304 + 2S + 14HJ0 >14Mn(OH)2 + MnSjOg [27] ^ We have found that the addition of elemental sulphur to manganese compounds will considerably improve the agronomic effectiveness of the manganese coating.

?.IN£: The amphoteric nature of zinc suggests that sine aquo or aquato ions are easily formed. This means that many zinc compounds will be able to incorporate water molecules into their crystalline structure. This could explain the phenomenon that ZnO can adsorb much more water than is stoichiometrically required for its conversion to Zn(0B)2 according to equation [5] and thus 19 FEB '96 11:57 FROM MFIDDERNS TO PPGE.022 286023 can be coated very easily as an oxide onto tiraa or can be employed as a coating additive in such nixed coatings as those containing copper and zinc or manganese and zinc.

S The presence of these aqua ions could also be responsible for the fact that the literature on basic ^ zinc sulphates is rather complex and often " contradictory. There can be no doubt however that/, during the coating operation with ZnS04, a number of hydrated zinc oxy sulphates will be formed. 4) METAL SALTS OF NPTRIgMTS ONTO UREA WITH SOPrtm fltt POTASSIUM CARBONATE AS A COATING AGENT.

We have found that tho coating of copper sulphate is easily performed with the help of either sodium or potassium carbonate as a coating agent.

The reactions occurring during this coating operation are again rather complex and can be expressed as follows: - C0(NH2)2 + CuS04-1H20 + Na2C03 nH20 Cu(OH)2 + C02 + Na2S04 + (NH4)2 C03 + (n-2)H20 C2*l CUS04*1H20 + (NH4)2 C03 + Cu(0H)2 + nH20 CuC03•Cu(OH)2*xHjO + (NH4)2 S04 * (n+l-x) HjO [29J 2 CuS04«1H20 +2(»H4)2 C03 + Cu(0H)2 + nH20 ^ 2CuC03*Cu{0H)j'xHjO -»-2(NS4)2 S04 * (n+2-x) HjO [30] The basic carbonate obtained by reaction £29] is a di-copper dihydroxide carbonate, which according to the literature can contain up to 4 moles af water. This basic carbonate is naturally occurring as the mineral malachite. 19 FEB '96 11:57 FROM MfiDDERNS TO 2SW23 The basic carbonate formed in reaction [30] occurs in natur« as the mineral arurite.

Both these compounds will hydrate easily* As far as the coating of boron is concerned/ we have found that boric acid can be coated onto, urea with the aid of a hydroxide as a coating additive according to i- 2 H3B03 + (NH4)2 S04 + Ca(OH)2 + nHjO > 2 NH4«H2B03 + CaS04*2H20 + nH20 [31] These reactions talcing place daring the various .<coating operations will always yield crystalline or 15 microcystalline compounds/ which often exist in different states of hydration.

The existence of different st^tec of hydration for the sane compound is most likely responsible for the fact that coated urea products have a much lower tendency to show signs of wetness during storage than uncoated urea.

The crystals formed during the reactions of the coating operation, as well as the crystals formed during changes 25 in the state of hydration of the reaction products, will interlock with each other and hold unreacted portions of the raw material in the coating.

The raw materials to be used in these coating operations should be free flowing solids, in a state of fine division. The particles of the micronutrient, as well as the coating additives, should always be smaller than 250jum and meet the raw material specifications in Table I. Salts of micronutrients should be either anhydrous 35 or contain not more than 1 mole H^O. Alternatively, at least part of the nutrient(s) or of the coating agent(s) may be added in the form of saturated aqueous solutions. lb btt) 'ab 11:57 FROM MfiDDERNS TO PfiGE . 024 286023 The process of this invention is further illustrated in the following examplesi- EXAMPLES 1 In a number of production runs, we used a coating drum with the following specifications: DRUM DIAMETER DRUM RADIUS 2500 sua 1250 ma DRUM-LENGTH 3000 mm ANNULAR RING HEIGHT 595 mm ANGLE OF DRUM DECLINE 1.97' SPEED OF ROTATION NUMBER OF SPRAT DEVICES x 13 rpra * 48*6% of Critical Speed 2 only LOCATION OF SPRAY DEVICES: At Feed Inlet and 1/3 Downstream Orea is wetted by means of a spray jet, which is located more or less in the falling stream of urea from the feed conveyor belt into the drum. In view of the relatively large size of the urea granules, the size of the droplets produced by this jet is not very critical. Generally speaking, the droplet size for the wetting of dry powders should always be equal to or less than the dried powder particle size. We found that the minute quantities of coating water required make it imperative that the size of the droplets should be larger than 100 fun. A small droplet size will ensure an even 19 FEB 196 11:58 FROM MfiDDERNS TO PAGE.025 28 6 0 wetting operation and avoid localised overwetting.

Overwetting or nan-uniform distribution of coating water wili lead to an unacceptable uneven coat.

While misting jets, which produce droplet sizes smaller than 10 jbm, will ensure an even wetting, the drift of the mist droplets poses a serious problem in regard to the wetting of equipment outside the coating drum.

Since the state o£ hydration, as well as the moisture content of all raw materials, will vary from one batch to another, the quantity of coating water required is not constant and will have to be adjusted for each new production run.

Table II illustrates the different coating procedures, which were employed in the production of the different products. All percentages quoted are on a w/w basis and are based on the total dry solids fed into the granulation system, and include for this reason water of hydration and any moisture in the raw materials.

The coating water is expressed as % of the total solids employed in the coating operation- In regard to the nomenclature employed, the name ZINC COTE, COPPER COTE or MANGANESE COTE is a trademark owned by Hi-Fert Pty Ltd for a range of coated products, which have been coated with one of these nutrients.

The terminology in regard to the finished product grade is based upon the internationally accepted fertilizer terminology, which expresses the % of total nitrogen, % of available phosphorus and % of soluble potassium in numerals. Urea, which has a total nitrogen content of 46%N and does not contain any phosphorus or potassium, is thus described as 45-Q-Q. If 5% sine is coated onto urea, this fertilizer will be represented by the following grade ratios: 42-0-0-ZnS. 22 13 FEB '36 11:58 FROM MfiDDERNS TO 23W23 The raw materials employed in these test runs were as follows:- TABLE Is COMPOSITION OF RAW IALS CONTAINTNG NOTOYgMTS • COMPOUND FORMULA NUTRIENT MINIMUM" SIZINGS UREA CO'{NH2)2 46% N CUPRIC OXIDE CuO 75-78% Cu 40% - 75f» COPPER SULPHATE MONO HYDRATE COS04*1H20 24-25% Cu 90% -ISO^m ZINC OXIDE ZrtO 62-68% Zn 100% -2S0^u& ZINC SULPHATE MONO HYDRATE ztiso4* is2o 34-35.9% Zn 50% - 75^m MAGNESIUM OXIDE MgO 55-59% Mg 90% - 75^m A KIESERITE MgS04•1H20 19-20% Mg 100% —lOOjt^n 9 MAGNESIUM CARBONATE MgC03 26.7% Mg 75% — 75^m MANGANOUS OXIDE MnO 62% Mn 98% —250pjB MANGANOUS SULPHATE A HO NO HYDRATE MrS04* IHjO 31-32% Mn 99% -ISOyim 9 SULPHUR s 98-99.9% S 92% -ISO^a BORON OXIDE a:°3 28-31% B 75% -lSO^m BORIC ACIDS ORTHO H3303 16-17.5% B 75% -150^a KETA H902 22-24-5% B 75% -lSO^m TETRA a2B4°7 -27% B 75% -15<Jn» CALCIUM BORATE Ca(B02)2 16-17% a 75% -150^m CALCIUM TETRABORATE CaB.O- 4 7 -22% B 75% -150^m 23 FEB '96 11:58 FROM MfiDDERNS TO — PAGE.027 20602 1 2 a 1 a* J u s -t fs * 33 w o 3 «s g 3 u VI 1 if W1 if G *5 «j it i £ <3 * * 5 * 1 3 . —» i m i S O O ^ e o " a ^ • • i ^ • £ A v « « t t i 31 ^ brt S 7 • I « « , T S 3 * » S R £ J5 * s 8 z. « s 2 ft • 4) « » • « • I i n e M I I • « I 4 II • < I I I • • • f I * SO i » • • t vn «M » I • • ♦ I » * > • I «A oJ N Sk O *1 •a* cri I w ja* ^ 1*1* 1* 1*« flails Hftafi ffMl! in m 0 01 m <N O M 24 • • Tafrlg .ITBi Various Prftti»cU9n Parameters .of Exafflplfig Procedure No, Composition of Nutrient Salta with Addltivea Salts with Carbonates Product Names "Urea Cote* 2n 5% Cu 5% Hn 51 B 2% Mn 51 Mn 5% Cu 3.61 Example Mo 11 12 13 14 16 Grade N- 41- 41- 40- 38- 37- 38- 39- P- 0 0 0 0 0 0 0 K- 0 0 0 0 0 0 0 2n S Cu Mn 2 B * Mn Mn 4 Cu RAW MATERIALS Urea 69.40 89.20 86.20 83.20 79.80 82.70 84.70 Sulphur H3BO3 Ca(B02)2 znO NH4H2PO4 MgO MgS04•IH2O 2nS04.lH20 CuO CUS04•1H20 MnO MnS04*1H20 Ca(0H)2 NaoCOi H2SO^ Coating HjO Production flats 11.a 7.0 4.a .0 0.8 JUL 0.6 JUL 4.0 7.8 2.0 0.9 ^JL .0 0 _SUS_ .4 3.8 2.0 .Q .4 1.9 2.0 £±Sl 14.24 1.06 1.0 JUL 19 CEB '9G 11:59 FROM MfiDDERNS TO imwi The coatings produced by these various operating methods were dry, stable and adhered strongly to the urea granules, thus providing a simple and inexpensive approach for the supply of micro and secondary nutrients to crops while fertilizing with urea.

It must also be appreciated that this invention is of ^ particular value in supplying micro- and secondary nutrient:.? with urea as a side dressing to plants at a time when there 10 exists a great need for these materials, i.e. the growing season.

The methods provided in this invention are well suited for the incorporation of micronutrients into granular urea 15 without an artificial drying process, which would lead to an increase in the rather toxic biuret content of urea. Furthermore, they allow the incorporation of such materials as finely ground sulphur, which does not react with urea, to urea.

While the present invention has been described in terms of preferred embodiments in order to facilitate better understanding of the invention/ it should be appreciated that 25 various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope. 26 " 23 6 0

Claims (1)

1. WHAT WE CLAIM IS: 1. A process for the production of a nutrient-coated urea fertiliser by the addition of one or more micronutrient(s) and/or secondary nutrient(s) to particulate urea fertiliser, wherein the particulate urea is tumbled in ^conventional coating device in the presence ,o£ quantities ef water J W> t- tender "toe. surface, guavjuies i-ocky 'together with the* particulate micronutrient(«) and/or secondary nutrients(s) and/or chemical compound(s) added as coating additive(s) to assist the coating and bonding mechanism, thereby forming a nutrient-containing coating comprising one or more hydrated reaction products on the particulate urea, in the absence of either an aqueous binder or subsequent drying step.;2. A process according to claim 1, wherein the particulate urea is produced by either the congelation of molten urea droplets in a prilling tower or the spraying of the molten urea onto a bed of tumbling solids in a conventional granulation device.;3. A process according to claim 1 or 2, wherein the nutrient material comprises one or more compounds of Cu, Zn, Mg, Mn, 8 and/or Co.;4. A process according to claim 1 or 2, wherein the nutrient material is elemental sulphur.;5. A process according to claim 3/ wherein the nutrient material comprises a capper compound selected from copper oxide, copper sulphate, basic copper sulphate and mixtures thereof.;5. A process according to claim 3, wherein the nutrient material comprises a zinc compound selected from zinc oxide/, zinc sulphate, zinc carbonate, basic zinc sulphate and mixtures thereof.;3 FEB 'SB 12:00 FROM MfiDDERNS;TO;e:n;0;10;7. a process according to claim 3/ wherein the nutrient material comprises a magnesium compound selected from magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium sulphate and mixtures thereof.;8. A process according to claim 3, wherein the nutrient material comprises a manganese compound selected from manganese oxide, manganese sulphate, manganese carbonate, basic manganese sulphate and mixtures thereof. "";9. A process according to claim 3, wherein the nutrient material comprises a compound of boron selected from orthoboric acid (H^BO^), metaboric acid (HB02), tetraboric acid boric oxide calcium metaborate,;15 calcium tetraborate and mixtures thereof.;10. A process according to claim 3, wherein the nutrient material comprises a compound of cobalt selected from cobalt sulphate, cobalt carbonate, cobalt hydroxide and mixtures;20 thereof.;m;^ 11. A process according to any one of claims 1 to 10, wherein the coating additive(s) comprise one or more compounds selected from: oxides and hydroxides of metals 2 5 having an electronegativity lower than that of iron,;sulphates of metals, phosphates of ammonia, carbonates, ™ sulphuric acid and mixtures thereof.;12. A process according to claim IX, wherein the coating 30 additive(s) comprise one or more compounds selected from sodium hydroxide, magnesium hydroxide and zinc hydroxide.;13. A process according to claim ll, wherein the coating additive(s) comprise one or more compounds selected from;35 magnesium oxide and zinc oxide.;- 28 -;la htH -ab 1 c;:uu f-KOH riflDDERNS TO;2arD02;14. A process according to claim 11/ wherein the coating additive(s) comprise sodium carbonate.;15. A process according to claim 11, wherein the coating additive(s) comprise ammonium dihydrogen phosphate, di-ammoniua hydrogen phosphate or a mixture thereof mixed with magnesium hydroxide, magnesium oxide, magnesium sulphate or a mixture thereof.;10 16. A process according to claim 11, wherein the coatixig additive (s) comprise sulphuric acid.;17. a process according to any one o£ claims 1 to 16,;wherein the reaction pcoducts formed during the coating;15 operation comprise or include one or more sulphates,;hydroxides, phosphates or carbonates of the nutrient(s), or a mixture thereof.;18. A process according to claim 17, wherein the reaction 20 products include struvite (MgNH^PO^* (JHjO). 19. A process according to claim 17, wherein the reaction ™ products include one or more sulphates of calcium, copper, zinc, magnesium or manganese, or a mixture thereof. 25 20. A process according to claim 17, wherein the reaction products include one or more basic sulphates of copper, w manganese, magnesium, zinc or cobalt, or a mixture thereof. 30 21. A process according to claim 17, wherein the reaction products include one or more complex metal ammonium hydroxides. 35 22. A process according to claim 17, wherein the reaction products include one or more complex metal ammonium sulphates. - 29 - 2 8 6 0 2 3 r 23. A process according to claim 17, wherein the reaction products Include one or more complex metal ammonium carbonates. 24. A process according to claim 17, wherein the reaction products include one or more carbonates or basic carbonates of copper, magnesium, zinc, manganese or cobalt, or a mixture thereof. 25. A process according to any one of claims 1 to 24, wherein the whole or part of the nutrient(s) is added in the form of a solid. 26. A process according to any one of claims 1 to 24, wherein the whole or part of the nutrient(s) is added in the form of a saturated aqueous solution. 27. A process according to any one of claims 1 to 24, wherein the whole or part of the coating additive(s) is added in the form of a saturated aqueous solution. 28. A process according to any one of claims 1 to 27, substantially as herein described and with reference to any one of the Examples. 29. A nutrient-coated urea fertilizer produced by the process of any one of claims 1 to 28. 30. A process according to claim 1 substantially as herein described or exemplified. 31.—Any novel feature -or novol combination of footuroo diooloood hcrain HI-FERT PTY LTD By Their Attorneys HENRY HUGHES 30