Method for producing calcium superphosphate using in-situ fluorine sequestration

Abstract

Disclosed is a method for producing calcium superphosphate granules using in-situ fluorine sequestration, comprising performing a calcium superphosphate production process. The calcium superphosphate manufacturing process includes reacting a phosphate source and an acid in a reactor stage to form a reaction mixture, the phosphate source comprising fluorine, converting the reaction mixture to a product mixture, and granulating the product mixture in a granulation stage to form calcium superphosphate granules. A metal oxide is introduced into at least one stage of the calcium superphosphate production process, the metal oxide, the phosphate source and the acid forming a net production composition. In the calcium superphosphate production process, at least a portion of the fluorine of the phosphate source is bound to the metal oxide as fluorine bound to the metal oxide.

Description

[0001] Related Applications

[0002] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 399,382, filed on August 19, 2022, entitled “Method for Producing Superphosphate with In Situ Fluorine Sequestration,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to a method for producing superphosphate. Specifically, the present application relates to a method for producing superphosphate using in-situ fluorine sequestration. Background Art

[0004] The standard method for producing superphosphate was first developed in 1840, which involved the chemical processing of phosphate ore and produced monocalcium phosphate as the main product. This method led to superphosphate being called the first chemical fertilizer.

[0005] While the complexity of production varies by location, the general production method, known as "run-of-the-pile" or "disintegrated," involves feeding ground phosphate rock to a combined conical mixer and pug mill system, where the phosphate rock is introduced into concentrated sulfuric acid (65–75% w / w) or phosphoric acid (40–55% w / w P2O5). When treated with sulfuric acid, the resulting material is known as ordinary superphosphate (normalsuperphosphate, single superphosphate) ( Figure 1 When phosphate rock is treated with phosphoric acid, the resulting material is known as triple superphosphate ("TSP") ( Figure 2 ). The material stays in the reaction vessel for about 30 minutes. The reaction with the acid results in the production of a semi-solid material, which is placed in a kiln (den) for several hours to cool and steam the product. The material treated in the kiln is then usually transported to a storage site where it is cured for an additional few weeks. After the curing process, the material has hardened sufficiently for agricultural use. Typically, the cured superphosphate is then fed to a drum granulator through a clod breaker to form a uniform product. After granulation, the particles undergo a drying and cooling process and are then sieved to the desired size. Granular ordinary superphosphate and granular TSP are both common commercial fertilizer products.

[0006] In addition, in another method called "slurry-type granulation", the curing process is omitted and superphosphate is produced by a slurry-type granulation method. This manufacturing method is most commonly used for granular TSP products, but it can also be used to produce ordinary superphosphate.

[0007] Particulate and gaseous emissions are common throughout the SSP manufacturing process, particularly fluorine emissions in the form of silicon tetrafluoride, hydrogen fluoride, and agglomerated fluorine and phosphate particulates. Fluorinated greenhouse gases include some of the longest-lasting and most potent greenhouse gases emitted by human activities. Due to health and environmental toxicity, regulatory agencies require that fluorine emissions be monitored during SSP manufacturing and that ongoing efforts be made to reduce the amount of fluorine emitted per ton of SSP produced.

[0008] Table 1. Emission factors for the production of ordinary calcium phosphate according to Inorganic Chemical Industry: Emission Factors 8.5.1

[0009]

[0010] a Factors used to estimate emissions from a baghouse with a collection efficiency of 99% b JMNyers et al., Source Assessment: Phosphate Fertilizer Industry, EPA-600 / 2-79-019c, US Environmental Protection Agency, Cinncinnati, OH, May 1979.

[0011] c Taken from the Atmospheric Measurement Information Retrieval System (AIRS) list of criteria air pollutants

[0012] d Factor used to control emissions from a wet scrubber that is said to be 97% efficient

[0013] e Uncontrolled

[0014] Although fluoride is emitted at all stages of the superphosphate manufacturing process, the emissions are balanced throughout the process (see Table 1). Ore unloading and feeding produce significant particulate emissions, but the greatest emissions of gaseous and particulate fluoride occur during the superphosphate curing stage. On average, about 0.2 weight percent of the P2O5 produced is emitted as fluoride, meaning that one ton (2,000 lbs) of P2O5 produces about 4 lbs of gaseous fluoride emitted to the atmosphere. To reduce these emissions, superphosphate production and granulation facilities are equipped with advanced scrubber systems; however, relatively high levels of fluoride still enter the air surrounding phosphate production facilities. It would be desirable in the art to further reduce these emissions without adversely affecting the efficiency of superphosphate fertilizer in the field. Summary of the invention

[0015] In an exemplary embodiment, a method for producing superphosphate particles using in-situ fluorine sequestration includes performing a superphosphate manufacturing process. The superphosphate manufacturing process includes reacting a phosphate source and an acid to form a reaction mixture in a reactor stage, the phosphate source comprising fluorine, converting the reaction mixture to a product mixture, and granulating the product mixture in a granulation stage to form superphosphate particles. A metal oxide is introduced into at least one stage of the superphosphate manufacturing process, the metal oxide, the phosphate source, and the acid forming a net production composition. In the superphosphate manufacturing process, at least a portion of the fluorine of the phosphate source is combined with the metal oxide as metal oxide-bound fluorine.

[0016] Other aspects of the disclosed subject matter are provided by:

[0017] A method for producing superphosphate granules using in situ fluoride sequestration comprises conducting a superphosphate manufacturing process, the superphosphate manufacturing process comprising reacting a phosphate source and an acid to form a reaction mixture in a reactor stage, the phosphate source comprising fluorine, converting the reaction mixture to a product mixture, and granulating the product mixture to form superphosphate granules in a granulation stage, introducing a metal oxide into at least one stage of the superphosphate manufacturing process, the metal oxide, the phosphate source and the acid forming a net production composition, and combining at least a portion of the fluorine of the phosphate source with the metal oxide during the superphosphate manufacturing process as metal oxide-bound fluorine.

[0018] Process according to any of the preceding items, wherein the conversion of the reaction mixture into the product mixture is carried out in a kiln stage between the reactor stage and the granulation stage.

[0019] A method according to any of the preceding clauses, further comprising curing the product mixture in a curing stage between the kiln stage and the granulation stage.

[0020] A method according to any of the preceding clauses, wherein the kiln stage comprises cooling and steaming the reaction mixture.

[0021] A method according to any of the preceding clauses, wherein the metal oxide is introduced to constitute from about 0.5 wt % to about 50 wt % of the net production composition.

[0022] A method according to any of the preceding clauses, further comprising a mixing stage, wherein the phosphate source and the acid are mixed together prior to the reactor stage, and wherein the metal oxide is introduced into the mixing stage together with the phosphate source and the acid.

[0023] A method according to any preceding clause, wherein the mixing stage comprises at least one of a conical mixer or a mud mill.

[0024] A process according to any of the preceding clauses, wherein a metal oxide is introduced into the reactor stage.

[0025] A method according to any of the preceding clauses, wherein the metal oxide is introduced into the granulation stage.

[0026] Process according to any of the preceding items, wherein the conversion of the reaction mixture into the product mixture is carried out in a kiln stage between the reactor stage and the granulation stage, and the metal oxide is introduced into the kiln stage.

[0027] A method according to any of the preceding clauses, further comprising curing the product mixture in a curing stage between the reactor stage and the granulation stage, and introducing the metal oxide into the curing stage.

[0028] Method according to any of the preceding clauses, wherein the superphosphate manufacturing process comprises at least one scrubber stage and the metal oxide is introduced into at least one scrubber stage.

[0029] A method according to any of the preceding clauses, wherein the metal oxide is introduced independently at various stages of the superphosphate manufacturing process.

[0030] The method according to any of the preceding items, wherein the superphosphate particles are ordinary superphosphate particles.

[0031] A method according to any of the preceding items, wherein the superphosphate particles are TSP particles.

[0032] A method according to any of the preceding clauses, wherein the phosphate source is phosphate rock.

[0033] The method according to any of the preceding items, wherein the superphosphate manufacturing process is a slurry-type granulation process.

[0034] The method according to any one of the preceding items, wherein the superphosphate manufacturing process is a stockpile-type granulation process.

[0035] A method according to any of the preceding clauses, wherein the fluorine is initially present in the phosphate source in the form of silicon tetrafluoride, hydrogen fluoride, aggregated fluorine and phosphate particles or a combination thereof.

[0036] A method according to any of the preceding clauses, wherein metal oxide bound fluorine is mixed with superphosphate particles.

[0037] A method according to any preceding clause, wherein the metal oxide bound fluorine comprises at least 50 wt% phosphate derived fluorine.

[0038] A method according to any of the preceding items, wherein the superphosphate is a bonded dispersible particle comprising at least one metal oxide domain comprising metal oxide and fluorine associated with the metal oxide, and at least one phosphate domain comprising superphosphate, wherein the at least one metal oxide domain and the at least one phosphate domain are present in the bonded dispersible particle as distinct domains coherently agglomerated together such that the bonded dispersible particle has a particle-to-particle variability in the metal oxide:phosphate weight ratio of ±40% and a bonded dispersible particle crush strength of at least 3 lbf.

[0039] The method according to any of the preceding items, wherein the metal oxide comprises at least one metal oxide selected from the group consisting of aluminum oxide, α-alumina, β-alumina, γ-alumina, δ-alumina, bauxite, alumina trihydrate, alumina monohydrate, boehmite, pseudoboehmite, gibbsite, iron oxide, hematite, hematite, magnetite, goethite, iron hydroxide, calcium oxide, calcium hydroxide, copper oxide, magnesium oxide, manganese oxide, manganese dioxide, nickel oxide, silicon dioxide and zinc oxide and combinations thereof.

[0040] A method according to any preceding clause, wherein the metal oxide comprises an activated metal oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] These and other features, aspects and advantages of the present subject matter will become better understood when the following detailed description is read with reference to the accompanying drawings, in which:

[0042] Figure 1 The present invention is a process flow chart of a method for taking material from a stockpile for manufacturing common superphosphate.

[0043] Figure 2 is a flow chart of a method for producing TSP by slurry-type granulation.

[0044] Figure 3is a graph comparing fluorine concentrations in the effluent from the initial feed reactors of TSP and TSP containing bauxite, according to one embodiment of the present disclosure.

[0045] Figure 4 is a graph comparing the fluorine emission flow rates of the initial feed reactors of TSP and TSP containing bauxite according to one embodiment of the present disclosure.

[0046] Figure 5 is a graph comparing fluorine concentrations in the effluent of a rotary granulator of TSP and TSP containing bauxite, according to one embodiment of the present disclosure.

[0047] Figure 6 is a graph comparing the fluorine emission flow rates of a rotary granulator for TSP and TSP containing bauxite according to one embodiment of the present disclosure. DETAILED DESCRIPTION

[0048] Disclosed herein is a method for producing superphosphate using in-situ fluorine sequestration. Compared to a method lacking one or more features disclosed herein, embodiments of the present disclosure have reduced fluorine emissions, reduced greenhouse gas emissions, increased process efficiency, reduced costs, or a combination thereof.

[0049] As used herein, "about" means a deviation of up to 10% from the value so modified. All values ​​modified with "about" are also intended to convey the unmodified value as an alternative, thus, for example, "about 10 μm" discloses a range of 9-11 μm as well as specifically 10 μm.

[0050] As used herein, "bonded" dispersible particles are distinguished from "agglomerated" dispersible particles in that "agglomerated" refers to particles formed by mechanically agglomerating at least two types of preformed particles together, while "bonded" refers to particles formed by agglomerating one type of preformed particles with a second material domain formed simultaneously. The structural differences between bonded dispersible particles and agglomerated dispersible particles include, but are not limited to, greater particle crush strength, improved wear resistance, reduced moisture content, greater moisture stability, less inter-grain variability in the metal oxide:phosphate weight ratio, greater contact surface area between metal oxide and phosphate domains resulting in more tightly bonded, increased metal oxide surface area, reduced binder bonding, greater degree of mixed domains, or a combination thereof.

[0051] In one embodiment, a method for producing superphosphate particles using in-situ fluorine sequestration includes carrying out a superphosphate manufacturing process and introducing a metal oxide into at least one stage of the superphosphate manufacturing process. The superphosphate manufacturing process includes reacting a phosphate source and an acid to form a reaction mixture in a reactor stage. The phosphate source contains fluorine. The reaction mixture is converted into a product mixture, and the product mixture is granulated in a granulation stage to form superphosphate particles. The metal oxide, the phosphate source, and the acid together constitute a net production composition. During the superphosphate manufacturing process, at least a portion of the fluorine of the phosphate source is combined with the metal oxide as metal oxide-bound fluorine. The formation of metal oxide-bound fluorine represents in-situ sequestration of fluorine. The metal oxide-bound fluorine can remain mixed with the superphosphate particles produced by the superphosphate manufacturing process, or can be separated from the superphosphate particles produced by the superphosphate manufacturing process. In one embodiment, wherein the particle size of the product mixture formed is greater than the desired particle size of the superphosphate particles, the granulation stage is an inverted granulation, wherein the product mixture is at least one of ground or crushed, and then optionally sieved. As used herein, "granulation stage" includes granulation and reverse granulation.

[0052] The metal oxide may constitute any suitable proportion of the net production composition, including but not limited to about 0.1 wt % to about 75 wt %, or about 0.5 wt % to about 50 wt %, or about 0.5 wt % to about 10 wt %, or about 5 wt % to about 15 wt %, or about 10 wt % to about 20 wt %, or about 15 wt % to about 25 wt %, or about 20 wt % to about 30 wt %, or about 25 wt % to about 35 wt %, or about 30 wt % to about 40 wt %, or about 35 wt % to about 45 wt %, or about 40 wt % to about 50 wt %, or any combination or sub-range thereof. In one embodiment, the metal oxide is a powdered metal oxide. The powdered metal oxide may have any suitable particle size, including but not limited to -30 mesh. In another embodiment, a metal oxide suspension having a suspended powder is used, the particle size of the powder being less than 100 μm, or less than 75 μm, or less than 50 μm, or less than 25 μm, or 1 μm to 50 μm.

[0053] In one embodiment, the conversion of the reaction mixture into the product mixture is carried out in a kiln stage between the reactor stage and the granulation stage. In another embodiment, the product mixture is solidified in a solidification stage between the kiln stage and the granulation stage. The kiln stage may include cooling and steaming the reaction mixture.

[0054] In one embodiment, the phosphate source and acid are mixed together in a mixing stage before the reactor stage, and the metal oxide is introduced into the mixing stage together with the phosphate source and acid. In another embodiment, the phosphate source and acid are mixed together in a mixing stage before the reactor stage, and the metal oxide is introduced into the mixing stage after the phosphate source and acid. The mixing stage may include a cone mixer, a mud mill, or both.

[0055] The metal oxide may be introduced into any stage, any combination of stages, or all stages of the process for producing superphosphate particles, including but not limited to the mixing stage, the reactor stage, the kiln stage, the granulation stage, the curing stage, or the scrubber stage.

[0056] The superphosphate granules produced by the superphosphate manufacturing process may be ordinary superphosphate granules or TSP granules.

[0057] The phosphorus source used in the phosphate manufacturing process can be any suitable phosphate source, including but not limited to phosphate rock, struvite, avian litter, or combinations thereof.

[0058] The superphosphate manufacturing process can be a slurry-type granulation process or a windrow-type process. In another embodiment, a slurry-type granulation process can be used for the production of TSP granules.

[0059] The fluorine may be present in the phosphate source in any form including, but not limited to, silicon tetrafluoride, hydrogen fluoride, aggregated fluorine and phosphate particles, or combinations thereof. The method for producing superphosphate particles using in-situ fluorine sequestration can sequester any suitable proportion of fluorine from a phosphate source in the form of fluorine bound to metal oxides, including but not limited to at least 25% of the fluorine from a phosphate source, or at least 30% of the fluorine from a phosphate source, or at least 35% of the fluorine from a phosphate source, or at least 40% of the fluorine from a phosphate source, or at least 45% of the fluorine from a phosphate source, or at least 50% of the fluorine from a phosphate source, or at least 55% of the fluorine from a phosphate source, or at least 60% of the fluorine from a phosphate source, or at least 65% of the fluorine from a phosphate source, or at least 70% of the fluorine from a phosphate source, or at least 75% of the fluorine from a phosphate source, or at least 80% of the fluorine from a phosphate source, or at least 85% of the fluorine from a phosphate source, or at least 90% of the fluorine from a phosphate source, or at least 95% of the fluorine from a phosphate source, or at least 98% of the fluorine from a phosphate source, or at least 99% of the fluorine from a phosphate source.

[0060] The metal oxide can be any suitable metal oxide, including but not limited to aluminum oxide, alpha-alumina, beta-alumina, gamma-alumina, delta-alumina, bauxite, trihydrated aluminum oxide, monohydrated aluminum oxide, boehmite, pseudo-boehmite, gibbsite, iron oxide, hematite, maghemite, magnetite, goethite, iron hydroxide, calcium oxide, calcium hydroxide, copper oxide, magnesium oxide, manganese oxide, manganese dioxide, nickel oxide, silicon dioxide and zinc oxide and any of the aforementioned active metal oxide forms and combinations thereof. The metal oxide can be activated by calcination, acid treatment or a combination thereof. As used herein, "metal oxide" is understood to include metal oxide hydrates and metal oxide hydroxides.

[0061] The superphosphate particles can be agglomerated dispersible particles or bonded dispersible particles. The bonded dispersible particles can have a bonded dispersible particle crushing strength greater than the agglomerated dispersible particles. In one embodiment, the bonded dispersible particles have a bonded dispersible particle crushing strength of at least 3 lbf, or at least 3.5 lbf, or at least 4 lbf, or at least 4.5 lbf, or at least 5 lbf.

[0062] In one embodiment, the superphosphate particles are bonded dispersible particles comprising at least one metal oxide domain comprising a metal oxide and fluorine associated with the metal oxide, and at least one phosphate domain comprising superphosphate, wherein the at least one metal oxide domain and the at least one phosphate domain are present in the bonded dispersible particles as distinct domains bonded together such that the bonded dispersible particles have a particle-to-particle variability in the metal oxide:phosphate weight ratio of ±40% and a bonded dispersible particle crush strength of at least 3 lbf.

[0063] The at least one metal oxide domain and the at least one phosphate domain may be distributed uniformly or non-uniformly within the superphosphate granule.The at least one metal oxide domain and the at least one phosphate domain of the soil conditioning dispersible granule may be distributed uniformly or non-uniformly between the granules in the superphosphate granule.

[0064] In one embodiment, each of the at least one metal oxide domain is at least 50% surrounded by at least one phosphate domain, or is at least 60% surrounded, or is at least 70% surrounded, or is at least 80% surrounded, or is at least 90% surrounded, or is at least 95% surrounded, or is at least 99% surrounded, or is completely surrounded.

[0065] The superphosphate particles may include at least one of a water-soluble binder, a suspending agent or an emulsifier. In one embodiment, the superphosphate particles include 1-40% by weight, or 5-35% by weight, or 5-15% by weight, or 10-20% by weight, or 15-25% by weight, or 20-30% by weight, or 25-35% by weight, or any sub-range or combination thereof of a water-soluble binder. Suitable water-soluble binders include, but are not limited to, calcium lignin sulfonate, ammonium lignin sulfonate, or a combination thereof. Suitable suspending agents include, but are not limited to, polysaccharides, inorganic salts, carbomers, or a combination thereof. Suitable emulsifiers include, but are not limited to, plant derivatives such as acacia, tragacanth, agar, pectin, carrageenan or lecithin, animal derivatives such as gelatin, lanolin or cholesterol, semi-synthetic agents such as methylcellulose or carboxymethylcellulose, synthetic agents such as benzalkonium chloride, benzethonium chloride, alkaline soaps (including sodium oleate or potassium oleate), amine soaps (including triethanolamine stearate), detergents (including sodium lauryl sulfate, dioctyl sodium sulfosuccinate or docusate sodium), sorbitan esters, polyethylene oxide derivatives of sorbitan esters, glycerides, or combinations thereof.

[0066] In one embodiment, the superphosphate granules include 1-60 wt% metal oxide domains, 30-95 wt% phosphate domains, and optionally, 0-50 wt% water-soluble binder, or 30-40 wt% metal oxide domains, 30-40 wt% phosphate domains, and 20-40 wt% water-soluble binder, or 35 wt% metal oxide domains, 35 wt% phosphate domains, and 30 wt% water-soluble binder, or any sub-ranges or combinations thereof. In another embodiment, the superphosphate granules include 5-70 wt% metal oxide domains, 10-70 wt% phosphate domains, up to 50 wt% water-soluble binder, and up to 20 wt% surfactant and emulsifier combination, or consist of 5-50 wt% metal oxide domains, 10-50 wt% phosphate domains, up to 50 wt% water-soluble binder, and up to 5 wt% surfactant and emulsifier combination.

[0067] The superphosphate particles can have any suitable size (measured by diameter based on the median value within the sample). Suitable sizes of superphosphate particles can include, but are not limited to, about 0.4 mm to about 4.0 mm, or about 0.4 mm to about 1.2 mm, or about 0.9 mm to about 1.5 mm, or about 1.2 mm to about 1.8 mm, or about 1.5 mm to about 2.1 mm, or about 1.8 mm to about 2.4 mm, or about 2.1 mm to about 2.7 mm, or about 2.4 mm to about 3.0 mm, or about 2.7 mm to about 3.3 mm, or about 3.0 mm to about 3.6 mm, or about 3.3 mm to about 4.0 mm, or about 0.4 mm, or about 0.5 mm, or about 0.6 mm, or about 0.7 mm, or about 0.8 mm, or about 0.9 mm, or about 1.0 mm, or about 1.1 mm, or about 1.2 mm, or about 1.3 mm. In one non-limiting example, golf greens may use superphosphate particles of about 0.5 mm to about 0.8 mm. In another non-limiting example, corn can use superphosphate particles of about 2.4 mm by broadcast application. In a third non-limiting example, any crop applied with a strip tiller can use superphosphate particles of about 1.5 mm. In one embodiment, suitably, for example, for application as a suspension, the superphosphate particles are micronized and have a particle size of less than about 200 μm, or less than about 150 μm, or less than about 100 μm, or less than about 75 μm, or less than about 1 μm, or less than about 1 μm, or less than about 50 μm, or less than about 25 μm, or less than about 10 μm, or less than about 5 μm, or less than about 2 μm, or less than about 1 μm, or less than about 0.75 μm, or less than about 0.5 μm, or less than about 0.25 μm, or less than about 0.1 μm, or less than about 0.05 μm, or less than about 0.01 μm measured by the maximum particle size.

[0068] The weight ratio of metal oxide:phosphate in the superphosphate particles can be any suitable weight ratio, including but not limited to a weight ratio of 20:1 to 1:20, or 10:1 to 1:10, or 8:1 to 1:8, or 7:1 to 1:7, or 6:1 to 1:6, or 5:1 to 1:5, or 4:1 to 1:4, or 3:1 to 1:3, or 2:1 to 1:2, or 3:1 to 1:1, or 1:1 to 1:3, or about 2:1, or about 1:1, or about 1:2, or any sub-range or combination of ranges thereof.

[0069] Example

[0070] method

[0071] A study was conducted in which granulated TSP was produced by slurry-type granulation in a large-scale pilot plant at the International Fertilizer Development Center ("IFDC"). First, TSP was produced under standard procedures. Next, bauxite was added to the process. In both cases, fluorine emissions were monitored at two locations within the plant. The process is detailed below.

[0072] Superphosphate production

[0073] use A solid feeder feeds phosphate rock into the reactor. A peristaltic pump is used to feed the defoamer solution into the reactor. When bauxite is used, a second A solid feeder feeds it into the reactor. The flow rates of phosphate rock, defoamer and bauxite are manually checked every 30 minutes using a balance and a stopwatch. The commercial grade phosphoric acid ("MGA") used is stored in two 4,150L stainless steel conical bottom storage tanks. A centrifugal pump is used to recirculate the MGA in the storage tanks to keep the insoluble solids suspended. The MGA used to produce TSP is transferred from the storage tanks to a 1,300L stainless steel feed tank. The MGA in the feed tank is recirculated to prevent solid precipitation. A centrifugal pump is used to transfer the MGA from the feed tank to the reactor. The MGA flow rate is measured by using a magnetic flowmeter and manually checked and confirmed every 30 minutes using a balance and a stopwatch.

[0074] The reactor used was 61 cm in diameter and 201 cm high with a shallow conical bottom of 9 cm. A constant liquid level was maintained in the reactor by using an overflow port located 74 cm above the cone. The reactor was equipped with a variable speed agitator equipped with three axial flow thrust turbines. The slurry overflowed into a pump surge tank from which it was transferred to a drum granulator using a progressive-cavity variable speed pump. The pump speed was changed to maintain a constant liquid level in the surge tank. The reactor slurry spray was discharged through a drilled pipe onto a rolling material bed in the granulator.

[0075] An exhaust fan is used to force the reactor gas through a spray scrubber to clean the gas before it is discharged into the atmosphere. Water is used as the scrubbing medium. The exhaust fan and scrubber system are coated with fluorine-resistant reinforced polyester.

[0076] Large Scale Test Equipment The granulator was 92 cm in diameter and 180 cm long. A 15 cm retaining dam was located 25.4 cm from the discharge end of the granulator. The granulator was operated at an angle of 1.5 degrees from the horizontal towards the discharge direction.

[0077] The gas extracted from the granulator is treated in a direct current venturi type scrubber. The scrubbing system uses water as the scrubbing medium. The scrubbing system consists of a reinforced polyester venturi type scrubber, a reinforced polyester recirculation seal tank, a centrifugal recirculation pump and a carbon steel fan. The scrubbing liquid is not returned to the process but is discharged to an on-site effluent detention pond.

[0078] The moist granular material is discharged from the granulator by gravity into a rotary drum dryer. The dryer has a diameter of 92 cm and a length of 7.3 m. The dryer operates with a co-current airflow which is heated by a burner burning natural gas in a combustion chamber located at the inlet (material feed end) of the dryer. The operating temperature of the dryer is indirectly controlled by measuring the temperature of the material discharged from the dryer and adjusting the air-gas ratio of the combustion chamber to maintain the desired operating temperature. The dryer operates at an angle of 2.0 degrees from the horizontal towards the discharge direction. The dryer is equipped with a set of four hammers, each weighing 7.7 kilograms (kg).

[0079] The cyclone dust collector is located in the process air duct between the dryer discharge and the dryer fan. The dryer cyclone dust collector is rated at 6,797 actual cubic meters per hour (Am 3 / h). The dryer fan exhaust duct is connected to the DynaWave scrubber.

[0080] The dust collected in the dryer cyclones is not returned to the process; it is weighed before being disposed of. The gas extracted from the dryer, after passing through the dryer cyclones, is treated in a wet scrubber before being discharged to the atmosphere. The scrubbing system uses water as the scrubbing medium and consists of a 316L stainless steel fan. The airflow through the dryer ranges from 3,600 to 3,800 m 3 / hr. The scrubbing liquid produced is not returned to the process but is sent to a cesspool.

[0081] A centrifugal bucket elevator is used to transfer the material from the dryer to an inclined double-layer mechanical vibrating screening system. The screen housing is equipped with a Ty-Rod 4.00mm oversize screen and a Ty-Rod 2.36mm undersize screen to produce products in the size range of 2.36 to 4.00mm. The oversize material from the screening system is conveyed to the chain mill. The crushed material discharged from the chain mill is returned to the screening system. If necessary, the undersize material from the screening system is returned (recirculated) to the granulator along with the controlled part product size material to maintain granulation control. The product size portion from the screening system is transferred to the product cooler, which operates with a downstream airflow discharged to the fugitive dust collection system. The product cooler operates at a rotation speed of 10rpm. The product size material is discharged from the product cooler into 1 metric ton bags.

[0082] The test facility is equipped with a fugitive dust collection system. The system consists of a network of collection ducts connected to a cyclone dust collector. The dust collector receives dust from the elevator, screening system, and conveyor. The velocity of the fugitive dust cyclone is 6,797Am 3 / h. A 316L stainless steel centrifugal fan exhausts the air into the atmosphere.

[0083] All process units in the large-scale granulation pilot plant, with the exception of the Venturi-type scrubber, reactor, auxiliary tank, dryer, elevator and DynaWave scrubber, are made of mild steel. The exterior of the mild steel components is coated with zinc epoxy corrosion resistant resin. The interior of the units is uncoated.

[0084] Composite samples of the product are taken from each test and evaluated at the IFDC laboratory to determine the chemical composition and selected physical properties. Samples are also taken from other selected process streams during each test and submitted to the IFDC laboratory for chemical analysis.

[0085] IFDC subcontracted Alliance Technology Group to monitor the fluorine content in selected gas streams. The gas streams monitored were the reactor and pelletizer outlets. In two production runs (TSP and TSP with bauxite), the system was operated long enough to reach steady state and provide reliable data. The fluorine emission assessment method is detailed below.

[0086] Fluorine emission monitoring

[0087] The emission testing procedures were conducted according to the test methods listed in Table 2. A description of the methods is provided below.

[0088] Table 2. Source test methods

[0089]

[0090] US EPA Reference Test Methods 1 and 2 - Volume Flow

[0091] The sampling locations and number of lateral (sampling) points were selected based on U.S. EPA Reference Test Method 1. To determine the minimum number of lateral points, the upstream and downstream distances were equated to equivalent diameters and compared to the values ​​in U.S. EPA Reference Test Method 1. Figure 1-1 Make a comparison.

[0092] Full velocity traverses were conducted to determine average flue gas velocity pressure, static pressure, and temperature according to U.S. EPA Reference Test Method 2. The velocity and static pressure measurement system included a pitot tube and tilting manometer. Flue gas temperature was measured with a K-type thermocouple and a pyrometer.

[0093] For molecular weight and volume flow calculations, O2 and CO2 concentrations were assumed to be ambient concentrations.

[0094] During each test run, stack gas dynamic pressure and temperature readings were recorded. The collected data were used to calculate volume flow rate according to the U.S. EPA Reference Test Method 2.

[0095] US EPA Reference Test Method 4 - Moisture Content

[0096] Flue gas moisture content ("BWS") was determined according to U.S. EPA Reference Test Method 4. The gas conditioning train consisted of a series of cooled impingers. Prior to testing, each impinger was loaded with a known amount of water or silica gel. Before and after each test, each impinger was gravimetrically analyzed on the same balance to determine the amount of condensed moisture.

[0097] US EPA Reference Test Method 13B-Fluorine

[0098] Total fluoride ("TF") testing was performed according to U.S. EPA Reference Test Method 13B. The sampling system consisted of a polytetrafluoroethylene nozzle, a heated stainless steel liner, a quartz filter, a gas conditioning system, a pump, and a calibrated dry gas meter. The gas conditioning system included four cooled impactors. The first two impactors contained 100 mL of deionized ("DI") water, the third was empty, and the fourth contained 200-300 g of silica gel. Throughout the test, the probe liner heating system was maintained at 120°C ± 14°C and the impactor temperature was maintained at 20°C or less.

[0099] After each test run, the sampling system was leak checked and the moisture gain of the impinger contents was measured at a vacuum pressure greater than or equal to the highest vacuum pressure observed during the run. The contents of impingers 1–3 were collected in sample container 1. The filter was removed and placed in sample container 1. The nozzle, probe liner, impingers 1-3, and all connected glassware were rinsed with DI water. This rinse was added to sample container 1. All containers were sealed, labeled, and marked with liquid levels for shipment to designated laboratories for analysis.

[0100] result

[0101] Table 2. Chemical analysis of raw materials

[0102] Chemical analysis Phosphoric acid Phosphate rock Bauxite <![CDATA[Total P2O5]]> 52.4 31.1 ---- Total Sulfur 3.1 2.3 ---- CaO 0.0 45.0 ---- Fluoride ---- 3.2 ---- <![CDATA[Al2O3]]> 0.5 1.0 44.1 <![CDATA[Fe2O3]]> 0.6 0.6 ---- <![CDATA[K2O]]> 0.2 0.3 ---- MgO 1.1 0.7 ---- <![CDATA[Na2O]]> 0.1 0.5 ---- <![CDATA[CO2]]> ---- 3.3 ---- <![CDATA[H2O]]> ---- 0.6 1.2

[0103] *Chemical analyses were performed according to AOAC International methods, except for total nitrogen and sulfur, which were determined using a combustion analyzer. *“----” indicates not analyzed.

[0104] Table 3. Overview of general manufacturing parameters during the production of granular triple superphosphate and granular triple superphosphate containing bauxite.

[0105]

[0106]

[0107] *Viscosity was measured using a Brookfield Ametek Dial Reading Viscometer Model LVT.

[0108] Referring to Table 3, the manufacturing conditions did not change significantly despite the addition of solid powder material. The similar recycle ratios between the two runs indicated that there was no significant difference in manufacturing efficiency after the addition of bauxite.

[0109] refer to Figure 3, presents the fluorine concentration in the effluent from the initial feed reactor. Although the solution in the reactor during the bauxite-TSP run was higher than during the TSP run, no statistical difference was observed between the two runs. The lack of difference between the two runs was expected because phosphoric acid must first dissolve the phosphate rock in the reactor to release gaseous fluorine. Since the bauxite has not had sufficient time to react with the fluorine in this environment, it is not expected that a statistical difference would be observed. The lack of statistical difference proves that the effluent readings and fluorine concentration analysis were accurate during the test.

[0110] refer to Figure 4 , presents the fluorine emission fluxes from the initial feed reactor for manufacturing runs of TSP and TSP containing bauxite. Although the solution in the reactor during the bauxite-TSP run was higher than during the TSP run, no statistical difference was observed between the two runs. The total emissions during the bauxite-TSP run were lower than those during the TSP run, resulting in Figure 3 and Figure 4 The lack of a difference between the two runs was expected because phosphoric acid must first dissolve the phosphate rock in the reactor to release gaseous fluorine. Since the bauxite does not have sufficient time to react with the fluorine in this environment, no statistical differences are expected to be observed. The lack of a statistical difference proves that the emission readings and fluorine concentration analysis were accurate during the test.

[0111] refer to Figure 5 , presents fluorine concentrations in the effluent from a rotary granulator. Despite only minor changes to manufacturing and granulator conditions, large statistical differences between the two runs were observed. Overall, a 94% reduction in fluorine concentration in the effluent was observed in the bauxite-TSP run compared to the TSP run. The difference between the two runs was unexpected as it suggests that bauxite actively sequesters gaseous fluorine as it is produced by acid dissolution of phosphate rock during the manufacturing process.

[0112] refer to Figure 6 , presents fluorine emission flows from a rotary granulator during manufacturing runs of TSP and TSP containing bauxite. Despite only minor changes to manufacturing and granulator conditions, large statistical differences between the two runs were observed. Overall, a 94% reduction in fluorine emissions was observed in the bauxite-TSP run compared to the TSP run. Total emissions were the same between the two runs. The difference in fluorine emissions between the two runs was unexpected as it suggests that bauxite actively sequesters gaseous fluorine as it is produced by acid dissolution of phosphate rock during the manufacturing process.

[0113] Table 4. Physical properties of granules produced during TSP and TSP containing bauxite granulation runs.

[0114]

[0115]

[0116] Referring to Table 4, despite the addition of bauxite, no adverse effect on pellet quality was observed.

[0117] Although the foregoing description illustrates and describes exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope of the present invention. In addition, many modifications may be made to adapt specific situations or materials to the teachings of the present invention without departing from the basic scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed as the best mode for carrying out the present invention, and the present invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method for producing superphosphate particles using in-situ fluorine sequestration, comprising: A superphosphate manufacturing process is carried out, the superphosphate manufacturing process comprising: reacting a phosphate source and an acid in a reactor stage to form a reaction mixture, the phosphate source comprising fluorine; converting the reaction mixture into a product mixture; and granulating the product mixture in a granulation stage to form superphosphate granules; introducing a metal oxide into at least one stage of said superphosphate manufacturing process, the metal oxide, phosphate source and acid constituting a net production composition; and During the superphosphate manufacturing process, at least a portion of the fluorine from the phosphate source is combined with the metal oxide as metal oxide-bound fluorine.

2. The process according to claim 1, wherein the conversion of the reaction mixture into a product mixture is carried out in a kiln stage between the reactor stage and the granulation stage.

3. The method of claim 2, further comprising curing the product mixture in a curing stage between the kiln stage and the granulation stage.

4. The method of claim 2, wherein the kiln stage comprises cooling and steaming the reaction mixture.

5. The method of claim 1 wherein the metal oxide is introduced to constitute from about 0.5 wt. % to about 50 wt. % of the net production composition.

6. The process of claim 1 further comprising a mixing stage wherein a phosphate source and an acid are mixed together prior to the reactor stage, and wherein the metal oxide is introduced into the mixing stage along with the phosphate source and the acid.

7. The method of claim 6, wherein the mixing stage comprises at least one of a cone mixer or a mud mill.

8. The process of claim 1 wherein the metal oxide is introduced into the reactor stage.

9. The process of claim 1, wherein the metal oxide is introduced into the granulation stage.

10. The process according to claim 1, wherein the conversion of the reaction mixture into a product mixture is carried out in a kiln stage between the reactor stage and the granulation stage, and the metal oxide is introduced into the kiln stage.

11. The method of claim 1 further comprising curing the product mixture in a curing stage between the reactor stage and the granulation stage and introducing the metal oxide into the curing stage.

12. The method of claim 1, wherein the superphosphate manufacturing process comprises at least one scrubber stage and the metal oxide is introduced into at least one scrubber stage.

13. The method of claim 1, wherein the metal oxide is introduced independently at multiple stages of the superphosphate manufacturing process.

14. The method of claim 1, wherein the superphosphate particles are superphosphate particles.

15. The method of claim 1, wherein the superphosphate particles are triple superphosphate particles.

16. The method of claim 1, wherein the phosphate source is phosphate rock.

17. The method of claim 1, wherein the superphosphate manufacturing process is a slurry-type granulation process.

18. The method of claim 1, wherein the superphosphate manufacturing process is a windrow type granulation process.

19. The method of claim 1, wherein the fluorine is initially present in the phosphate source in the form of silicon tetrafluoride, hydrogen fluoride, aggregated fluorine and phosphate particles, or a combination thereof.

20. The method of claim 1 wherein the metal oxide bound fluorine is mixed with the superphosphate particles.

21. The method of claim 1 wherein the metal oxide bound fluorine comprises at least 50 weight percent phosphate derived fluorine.

22. The method of claim 1, wherein the superphosphate is a cohesive dispersible granule comprising: at least one metal oxide domain comprising said metal oxide and fluorine associated with said metal oxide; and comprising at least one phosphate domain of said superphosphate, wherein the at least one metal oxide domain and the at least one phosphate domain are present in the bonded dispersible particles as distinct domains cohesively agglomerated together such that the bonded dispersible particles have a particle-to-particle variability in the metal oxide:phosphate weight ratio of ±40% and a bonded dispersible particle crush strength of at least 3 lbf.

23. The method of claim 1, wherein the metal oxide comprises at least one metal oxide selected from the group consisting of aluminum oxide, alpha-alumina, beta-alumina, gamma-alumina, delta-alumina, bauxite, alumina trihydrate, alumina monohydrate, boehmite, pseudoboehmite, gibbsite, iron oxide, hematite, maghemite, magnetite, goethite, iron hydroxide, calcium oxide, calcium hydroxide, copper oxide, magnesium oxide, manganese oxide, manganese dioxide, nickel oxide, silicon dioxide and zinc oxide, and combinations thereof.

24. The method of claim 1, wherein the metal oxide comprises an activated metal oxide.

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