CALCIUM NITRATE BASED FERTILIZER

Abstract: Homogeneous calcium nitrate based fertilizers containing sulphur, and method for their preparations. Solid gypsum and/or a slow reacting sulphate mineral is mixed with melted calcium nitrate fertilizer at a temperature of 90-110 DEG C and kept at this temperature for 3-15 minutes and subsequently particulated at a temperature of 80-110 DEG C. The particulation by prilling is performed at 95-110 DEG C and the particulation by granulation is performed at 90-110 DEG C. The fertilizer is a homogeneous composition of a calcium nitrate fertilizer and gypsum and/or a slow reacting sulphate mineral comprising 0.1-5.0 weight % SO4-S, 14-19 weight % water soluble calcium and 16-21 weight % total calcium, and 0-3.0 weight % water soluble magnesium. The fertilizer may contain microamounts of Se and/or Co, and/or micronutrients like Mn, Cu, B and Zn.

Description: Calcium nitrate based fertilizer The present invention relates to calcium nitrate based fertilizers containing sulphur and a process for making such fertilizers. Calcium nitrate is widely used within horticulture and as a dry product on open fields. There are two major types of calcium nitrate, one made from acidulation of calcium carbonate by nitric acid and one obtained as a by-product from nitrophosphate fertilizer processes. The latter normally contains 75-81 weight% Ca(NO 3 ) 2 , 5-9 weight% NH 4 NO 3 and 12-14 weight% water of crystallization. This type is usually called NH-CN (Norsk Hydro Calcium Nitrate). In the following the abbreviation CN will be used for both these types of fertilizer. Over the last years there has been an ever increasing demand for sulphur in fertilizers in general, even for special applications of CN-fertilizers sulphur has been required. For some markets and crops there has also been a demand for CN-fertilizers containing Mg, Se, Co and some micronutrients in addition to sulphur. In order to meet the demands for new fertilizers the simplest solution seemed to be blending various S-containing fertilizers like ammonium sulphate or potassium sulphate, but when other ingredients like Mg, Se etc. should be added, segregation problems would inherently arise. Another criteria will of course be the price of the various components and it would be advantageous to use cheap sulphur sources like gypsum, kieserite and langbeinite, but again segregation problems were experienced. Preparation of homogeneous CN-based fertilizers by particulation of melts or solutions of CN and sulphur sources like ammonium- or potassium sulphate did however prove to be most difficult due to the low ability to tie up water of crystallization possessed by these two sulphur sources Possible application of gypsum and/or kiesente for making homogeneous fertilizers was then investigated From Japanese patent application J54085957 it is known preparation of a fertilizer comprising mixing calcium nitrate, gypsum and superphosphate of lime and then granulating the mixture Mixing is performed at 100-120°C and the molten mixture is extruded, cut to a size of 2-3 mm and cooled and dried The amount of superphosphate of lime is 50-70% of the calcium nitrate Firstly, this fertilizer contains large amounts of phosphate and no magnesium Secondly, the particulation process is most uneconomical Further it is known from J53027564 to coat CN-fertilizers with gypsum during the spraying of CN melt in cooling air containing gypsum powder This fertilizer is stated to have a prolonged effect Its sulphur content will however be far too low to meet the requirements which the present invention has to meet It is also known to add minor amounts of CN to granulated ammonium sulphate as a binder and to add minor amounts of ammonium sulphate and calcium nitrate to ammonium nitrate to improve its crushing strength, but none of these publications solve the problems related to making homogeneous CN-based fertilizers The main object of the present invention was to arrive at a homogeneous CN-based fertilizer containing sulphur and optionally magnesium, selenium, cobalt and micronutπents Another object was to arrive at a cost effective continuous process for making homogeneous sulphur containing CN-based fertilizers which could be par- ticulated. A further object was to arrive at a process for making homogeneous sulphur containing CN-based fertilizers containing magnesium and optionally selenium, cobalt and micronutrients. Application of normal S-sources like ammonium sulphate and potassium sulphate were first investigated. It was then found that when these sources are mixed with CN melt the following reactions will take place: 1. (NH 4 ) 2 SO 4 + Ca(NO 3 ) 2 => CaSO 4 + NH 4 NO 3 2. K 2 SO 4 + Ca(NO 3 ) 2 => KNO 3 + CaSO 4 The formation of gypsum consumes calcium nitrate and the melt loses its ability to solidify due to less power to tie up water of crystallization. Accordingly, the two S-sources were found to be too difficult to apply in CN-based fertilizers. Gypsum (CaSO 4 1/2 H 2 O) was expected to not react with CN melt and should therefore constitute a cheap S-source. Even though gypsum is not water soluble, several agronomical examinations have shown that gypsum is readily available to plants. Different gypsum sources can be utilized, such as dead burned gypsum and gypsum with hydrate water up to dihydrate, the hemi hydrate form is however preferred. Kieserite (MgSO 4 H 2 O) is both a Mg- and S-source which is considered to be water soluble. By mixing this salt into a CN melt the following reaction was found to take place: 3. MgSO 4 H 2 O + Ca(NO 3 ) 2 => CaSO 4 + Mg(NO 3 ) 2 + H 2 O It was further found that if the Mg(NO 3 ) 2 content became too high, solidification problems would occur. However, trials carried out revealed surprisingly that reaction no. 3 did not take place at a significant rate. During further laboratory tests at which kieserite was thoroughly mixed into CN melt for several minutes it was confirmed that said reaction did not result in solidification problems. The investigations also showed that reaction 3 indeed did take place at the surface of each kieserite crystal, but the gypsum formed a thin coating that protected the crystals from further attack by the CN melt. This formation of gypsum coating and the slow dissolving time of the kieserite mineral in general seemed to give possibilities for homogeneous distribution of fine kieserite crystals in the CN melt prior to solidification and thereby make it possible to utilize this for making a homogeneous CN-based fertilizer containing both sulphur and magnesium. Based on the results from the above investigations, several tests were performed in a pilot plant. It was then confirmed that by using gypsum and slow reacting sulphate minerals like kieserite, langbeinite etc. together with a CN melt it would be possible to make homogeneous S-containing fertilizers which met the above stated objects of the invention. Thus, according to the invention, solid gypsum and/or a slow reacting sulphate mineral could be mixed with melted calcium nitrate fertilizer at a temperature of 90-110°C and kept at this temperature for 3-15 minutes and subsequently particulated at a temperature of 80-110°C. The particulation by prilling should be performed at 95-110°C and the granulation at 90-110°C. Microamounts of Co and/or Se and/or micronutrients like Mn, Cu, B, and Zn could be added as solutions of their salts to the mixture prior to particulation. One preferred method comprises mixing 4-23 weight% gypsum, based on the total composition, with a melted calcium nitrate fertilizer at 103-106°C during stirring and keeping the mixture at this temperature for 5-10 minutes and then particulate the thus formed slurry. Another preferred method comprises mixing 4-23 weight% kieserite during stirring with a melted calcium nitrate fertilizer for 6-12 minutes and subsequently particulate the thus formed slurry. Fertilizers according to the invention comprise a homogeneous composition of a calcium nitrate fertilizer and gypsum and/or a slow reacting sulphate mineral comprising 0.1-5.0 weight% SO 4 -S, 14-19 weight% water soluble calcium and 16-21 weight% total calcium and 0-3.0 weight% water soluble magnesium Preferably said new fertilizer contains 1.0-3.0 weight% SO 4 -S. The preferred content of magnesium is 0.1-4.0 weight%. The scope and special features of the invention are as stated in the attached claims. The invention is further explained by the following examples and the comments to these examples: Example 1 This example relates to formation of prilled homogeneous CN-based fertilizer by mixing 12 weight% kieserite crystals into NH-CN melt at 105°C during stirring at this temperature for about 10 minutes and then spraying the slurry through a nozzle. The formed droplets solidified as they fell through cooling air. The product thus formed had a homogeneous composition and had the following analysis: 15.0 % N 2.6 % SO 4 -S 2.0 % Mg (water soluble) 16.8 % Ca (water soluble) Example 2 This example shows drum granulation of a homogeneous CN-based fertilizer. 7 weight% kieserite crystals were mixed into 93 weight% NH-CN melt at 105°C and stirred for about 6 minutes. The slurry was then sprayed into a drum containing fines from example 1. Hard homogeneous granules were formed with the following composition: 15.2% N 1.5% NH 4 -N 13.7% NO 3 -N 1.5% SO 4 -S 1.1 % Mg (water soluble) 17.5% Ca (water soluble) Example 3 This example shows granulation of homogeneous CN-based fertilizer containing sulphur 11 5 weιght% calcium sulphate hemi hydrate (22 1 %S) was mixed with 88 5 weιght% NH-CN melt at about 105°C and stirred for about 5 minutes and subsequently sprayed into a rotating drum containing NH-CN fines The thereby formed product had the following analysis 15 0% N 2 5% SO 4 -S 16 8% Ca (water soluble) 20 0% total Ca Example 4 This example shows preparation of homogeneous CN-based fertilizer containing sulphur and magnesium and in addition selenium 7 weιght% kieserite and some droplets of a 25 weιght% Na 2 SeO 4 solution were mixed into a NH-CN melt at about 105°C and stirred for about 5 minutes The melt was solidified as in example 2 The formed product had the following analysis 15 2% N 1 5% NH 4 -N 13 7% NO 3 -N 1 5% SO 4 -S 1 1 % Mg (water soluble) 17 5% Ca (water soluble) 25 ppm Se Cobalt can be incorporated in the same way as selenium by addition of droplets of a CoSO 4 solution giving 0 02% of Co Example 5 This example shows preparation of homogeneous CN-based fertilizer containing both sulphur and magnesium 4 weιght% gypsum (calcium sulphate hemi hydrate) and 6 weιght% kieserite were thoroughly mixed into 90 weιght% of NH-CN melt at about 105°C for about 4 minutes The thereby formed slurry was then sprayed into a granulating drum containing fines Hard, homogeneous granules were formed with the following composition 15.1 % N 2.2% SO 4 -S 1.0% Mg 16.7% water soluble Ca 17.8% total Ca The main advantages attained by using both gypsum and kieserite for making such fertilizers are that gypsum is a cheaper sulphur source than kieserite and that the product is somewhat less hygroscopic than a product using only kieserite as sulphur and magnesium source. From the above examples it can be seen that it is possible to prepare homogeneous S-contaming fertilizers based on CN-fertilizers and a S-source The new fertilizer can be particulated, for instance by prilling or granulation, both pan granulation and drum granulation Further tests showed that a rather wide range of such fertilizers could be prepared It was then found that the various components should be within the following ranges SO 4 -S 0.1-5.0 weight% preferably: 1.0-3.0 weight% Mg (w.s) 0-4.0 weight% preferably: 0-2.3 Ca (w.s) 14-19 weight% preferably: 16-19 Ca (total) 16-21 weight% In addition fertilizers of the above type can contain microamounts of cobalt and selenium, and the usual fertilizer micronutrients like manganese, copper zinc, boron etc. Preparations of the above new fertilizers can be performed at the following conditions: Recommended mixing temperature: 90-110°C Recommended retention time : 3-15 minutes Recommended particulation temperatures Prilling 100-110°C Granulation: 80-100°C The products of examples 1 and 2 were bagged and stored at a pressure of 1 kg/cm 2 for three months and there were no signs of caking. Also the rate of water absorption was tested for these new fertilizers and compared with conventional CN-fertilizers. The rate of absorption was measured at 60% relative humidity and 25°C. The recorded values are listed in the below table: Table 1 From these data it can be seen that fertilizers based on CN and kieserite had somewhat higher hygroscopicity compared to pure CN-fertilizer. The increase is very modest and due to the formation of some Mg(NO 3 ) 2 . The increase of water absorption can be compensated by increasing the amount of coating applied. By the present invention the inventors have managed to arrive at a method for making a new type of fertilizer being a homogeneous fertilizer based on calcium nitrate and containing the required amount of sulphur. Said new fertilizer may also contain magnesium and microamounts of Se and Co and micronutrients like Mn, Cu, B, Zn etc.

Claims: Claims 1. A method for making calcium nitrate based fertilizers containing sulphur, characterized in that solid gypsum and/or a slow reacting sulphate mineral is mixed with melted calcium nitrate fertilizer at a temperature of 90-110°C and kept at this temperature for 3-15 minutes and subsequently particulated at a temperature of 80-110°C. 2. A method according to claim 1 , characterized in that 4-23 weight% gypsum, based on the total composition, is mixed with a melted calcium nitrate fertilizer at 103-106°C during stirring and kept at this temperature for 5-10 minutes and that the thus formed slurry is particulated by prilling or granulation. 3. A method according to claim 1 , characterized in that 4-23 weight% solid kieserite is mixed during stirring with a melted calcium nitrate fertilizer for 6-12 minutes and that the thus formed slurry is subsequently particulated. 4. A method according to claim 1 , characterized in that the particulation by prilling is performed at 95-110°C and that the particulation by granulation is performed at 90-110°C. 5. A method according to claim 1 , characterized in that selenium, cobalt, and the micronutrients like manganese are added as solutions of their salts into the mixture prior to particulation. 6. A calcium nitrate based fertilizer containing sulphur, characterized in that the fertilizer is a homogeneous composition of a calcium nitrate fertilizer and gypsum and/or a slow reacting sulphate mineral comprising 0.1-5.0 weight% SO 4 -S, 14-19 weight% water soluble calcium and 16-21 weight% total calcium, and 0-3.0 weight% water soluble magnesium. 7. A fertilizer according to claim 6, characterized in that the fertilizer contains 1.0-3.0 weight% SO 4 -S. 8. A fertilizer according to claim 6, characterized in that the fertilizer contains 0.1-4.0 weight% water soluble magnesium. 9. A fertilizer according to claim 6, characterized in that the fertilizer contains microamounts of Se and/or Co, and/or micro¬ nutrients like Mn, Cu, B and Zn.

Inventors: LEGARD TORBJOERN, OBRESTAD TORSTEIN, ROEDSVIK JOHANNE, LEGARD, TORBJOERN, OBRESTAD, TORSTEIN, ROEDSVIK, JOHANNE
Applicants: LEGARD TORBJOERN, NORSK HYDRO AS, OBRESTAD TORSTEIN, ROEDSVIK JOHANNE, LEGARD, TORBJOERN, NORSK HYDRO ASA, OBRESTAD, TORSTEIN, ROEDSVIK, JOHANNE
Application year: 1997
Main classification: C05C5
IPC codes: C05C5, C05G1