A method for producing a full-element fertilizer by using bulk solid waste such as desulfurization gypsum and / or phosphogypsum

Abstract

The application discloses a method for producing a full-element fertilizer by using bulk solid wastes such as desulfurization gypsum and / or phosphogypsum. Industrial gypsum solid wastes are reacted with industrial-grade ammonium carbonate to generate calcium carbonate and ammonium sulfate. The former calcium carbonate can form a three-component reaction system with potassium ore, desulfurization gypsum and / or phosphogypsum, and a fluxing agent is added to prepare a potassium-calcium-silicon fertilizer intermediate. The latter ammonium sulfate can form a struvite reaction system with phosphoric acid, anhydrous magnesium chloride and the like. The reaction product is precipitated into struvite crystals and magnesium sulfate by adjusting the pH value with ammonia water. Then, trace element accessories such as ferric ammonium citrate, zinc sulfate, sodium selenite and borax are added, and the potassium-calcium-silicon fertilizer intermediate is stirred together. After water evaporation, granulation, drying and packaging, a full-element composite fertilizer is obtained. The product has the characteristics of weak alkalinity and can provide crops with abundant macroelements, mesoelements and trace elements. The method greatly improves the utilization efficiency of industrial gypsum solid wastes.

Description

Technical Field

[0001] This invention relates to the field of agricultural resource utilization of industrial gypsum-based solid waste. Specifically, it relates to a method for producing all-element fertilizers using bulk solid wastes such as desulfurized gypsum and / or phosphogypsum. Background Technology

[0002] The limestone-gypsum method is currently the most widely used flue gas desulfurization method in coal-fired power plants. Its working principle involves a gas-liquid absorption reaction between limestone emulsion and sulfur dioxide in the flue gas within the desulfurization tower, producing calcium sulfite. This calcium sulfite is then aerated with air to generate gypsum dihydrate, which is subsequently aged, filtered, washed, and dried to become a desulfurization gypsum byproduct. It is a large-volume industrial solid waste generated from wet flue gas desulfurization, its main component being calcium sulfate dihydrate (CaSO4·2H2O), with a free water content generally around 10% or even higher, resulting in poor fluidity. As of 2025, my country's annual production of desulfurization gypsum reached 120 million tons, with thermal power plants accounting for over 85%. Production areas are mainly concentrated in East China, North China, Central China, and provinces with relatively concentrated coal resources. Currently, the comprehensive utilization of desulfurized gypsum in my country is relatively limited, mainly used as a cement retarder and in the production of new wall materials such as gypsum board and gypsum blocks. Simultaneously, its application is gradually being promoted in the production of gypsum-based dry-mixed mortar and high-strength gypsum. However, with the decline of my country's real estate industry, the consumption of gypsum in the building materials industry has decreased year by year, further compressing profit margins.

[0003] Phosphogypsum is an industrial byproduct of high-concentration phosphate fertilizer production, primarily composed of calcium sulfate dihydrate (CaSO4•2H2O). Producing 1 ton of phosphoric acid generates 4.8-5.0 tons of phosphogypsum. Phosphogypsum is grayish-white or grayish-black, typically containing 10.0-30.0% water, with a pH of 1.9-5.3, a fluorine content ≤0.5%, and a particle diameter generally 5-50 μm. The product also contains residual organic phosphorus, inorganic phosphorus, fluorides, and impurities such as silicon, aluminum, potassium, sodium, and iron. The phosphogypsum production in 10 provinces in my country—Yunnan, Hubei, Guizhou, Shandong, Anhui, Chongqing, Jiangsu, Sichuan, Guangdong, and Shaanxi—accounts for 91.5% of the country's total phosphogypsum production. However, its comprehensive utilization rate is currently very low, necessitating effective treatment and resource utilization.

[0004] Potassium ore comprises aluminosilicate minerals such as potassium feldspar, illite, muscovite, leucite, potassium nepheline, and glauconite. It generally requires a K₂O content of ≥8% and encompasses various types including volcanic rocks, volcanic sedimentary rocks, sedimentary rocks, and metamorphic rocks. These ores are widely distributed throughout most of my country. It is estimated that my country's total reserves of insoluble potassium-rich ore are at least 20 billion tons (in terms of K₂O), far exceeding the country's water-soluble potassium reserves of 82.916 million tons. Because the K₂O in insoluble potassium-rich ore is fixed within the aluminosilicate lattice, it is difficult for plants to directly absorb it under natural conditions. Therefore, how to utilize potassium ore to produce potash fertilizer under profitable conditions has become a global challenge.

[0005] Since the early 1960s, my country has successively carried out research on the production of potash fertilizer from potassium ore. The production methods can be broadly categorized into: sintering, high-temperature melting, hydrothermal, blast furnace smelting, and low-temperature decomposition methods, among others. However, to date, only the sintering method has achieved industrial application. Its reaction principle involves using limestone and coal as auxiliary materials, mixing them with potassium ore, and then crushing, pelletizing, and calcining them to convert large-molecule potassium feldspar into smaller-molecule potassium silicate, potassium carbonate, and other potash fertilizer products. This method is now widely used by enterprises, such as Shanxi's "Fulibang" and Shaanxi's "Rongchang." This method has the advantages of low production cost and the ability to extract silicon from potassium feldspar and calcium from limestone, converting them into potassium-calcium-silicon fertilizer with weak alkaline properties. It is beneficial for the comprehensive utilization of various mineral nutrients in the ore, and the product has a good market prospect. It has a significant effect on improving acidic soil. However, it also has problems such as high calcination temperature (generally above 1200 degrees Celsius), low water solubility of the product (not exceeding 15%), and the product's hydraulic properties, similar to cement, which can easily cause soil compaction. Summary of the Invention

[0006] To address the current state of resource utilization of bulk solid wastes such as industrial gypsum and the existing problems in potassium extraction technology from potassium ore, this invention proposes a method for producing all-element fertilizers using bulk solid wastes such as desulfurized gypsum and / or phosphogypsum. By employing wet desulfurized gypsum and / or phosphogypsum, which currently have low utilization rates, a metathesis reaction is carried out with an industrial-grade ammonium carbonate aqueous solution to produce calcium carbonate precipitate and ammonium sulfate solution. The former can be activated with potassium ore, industrial gypsum, flux, etc., to produce potassium-calcium-silicon fertilizer intermediates. The latter can be coupled with phosphoric acid, magnesium chloride, and trace elements such as iron, zinc, boron, and selenium to produce struvite + trace element fertilizer with citrate-soluble characteristics. The two intermediate products are then mixed, dehydrated, granulated, dried, cooled, weighed, and packaged to produce an all-element fertilizer product. This enables the efficient utilization of bulk solid waste resources such as industrial gypsum in agriculture, solving the environmental pollution problems caused by the large-scale accumulation of these bulk solid wastes. At the same time, the produced all-element fertilizer products can also make up for the deficiency of micronutrients (such as calcium, magnesium, sulfur, silicon, zinc, iron, boron, and selenium), improve the quality of agricultural products, and achieve efficient utilization in agriculture.

[0007] A method for producing all-element fertilizer using bulk solid waste such as desulfurized gypsum and / or phosphogypsum includes the following steps: (1) Desulfurized gypsum and / or phosphogypsum are used as reactants and reacted with another reactant, industrial grade ammonium carbonate, in an aqueous solution system to produce calcium carbonate precipitate and ammonium sulfate solution. After liquid-solid separation, washing and drying, filter residue calcium carbonate powder and ammonium sulfate filtrate are obtained. (2) In the calcium carbonate powder of the filter residue in step (1), potassium ore, desulfurized gypsum and / or phosphogypsum are added to form a potassium ore-calcium carbonate-gypsum three-phase reaction system, and flux is added thereto. After material compatibility, mixing, drying, activation, cooling and pulverization, the reactants are converted into potassium sulfate, dicalcium silicate, tricalcium aluminate and carbon dioxide gas, thereby converting the reactants into potassium calcium silicon fertilizer intermediates; (3) Add phosphoric acid to the ammonium sulfate filtrate prepared in step (1), then add anhydrous magnesium chloride, and add ferric ammonium citrate, zinc chloride, sodium selenite, and borax solution. Stir and adjust the pH of the mixture with ammonia water. This will convert the ammonium sulfate mixture into a mixture of struvite (MgNH4PO4) precipitate, magnesium sulfate, and trace elements iron, zinc, selenium, boron, and chloride solution. (4) The potassium-calcium-silicon fertilizer intermediate prepared in step (2) is thoroughly mixed with the struvite (MgNH4PO4), magnesium sulfate and trace elements iron, zinc, selenium, boron and chlorine solution prepared in step (3). After dehydration, granulation and drying, a complete element fertilizer can be obtained. This fertilizer product not only contains the macro-elements nitrogen, phosphorus and potassium, but also the medium-element elements calcium, magnesium, sulfur and silicon, as well as the trace elements iron, zinc, selenium, boron and chlorine. It is a very cost-effective weak alkaline complete element fertilizer with a complete range of nutrients.

[0008] Furthermore, in step (1), Desulfurized gypsum is a byproduct of wet flue gas desulfurization, while phosphogypsum is a byproduct of wet phosphate fertilizer production. Generally, a calcium sulfate dihydrate content greater than 90% is required (after drying at 105℃ for 6 hours). Industrial-grade ammonium carbonate generally requires an (NH4)2CO3 content ≥95%, a moisture content ≤2.0%, and chloride ≤0.01%. The precipitate calcium carbonate (the product of the reaction between gypsum and ammonium carbonate) after metathesis reaction requires a CaCO3 content ≥91.0% (after drying at 105℃ for 6 hours). The liquid / solid ratio in the aqueous solution system is between 1.2 and 10.5:1.

[0009] Furthermore, in step (2), Potassium ore includes potassium feldspar, illite, muscovite, leucite, potassium nepheline, glauconite, and other potassium-containing aluminosilicate minerals. Generally, a K2O content of ≥8.0% is required. Potassium ore types cover igneous rocks, volcanic sedimentary rocks, sedimentary rocks, and metamorphic rocks.

[0010] This invention requires that the particle size of the three raw and auxiliary materials (gypsum, calcium carbonate, and potassium ore) be greater than 200 mesh, and the weight ratio of the three is: desulfurized gypsum and / or phosphogypsum: 5%-80%, calcium carbonate: 5%-80%, and potassium ore: 5%-70%. A small amount of flux is added, including any two of the following four types: sodium chloride, sodium sulfate, potassium chloride, and potassium sulfate. The amount added is 3.0%-5.0% of the total mass of the other three raw and auxiliary materials. After thorough mixing and drying, the mixture is granulated when the moisture content reaches 5.0%-8.0%. The granules are dried again until the moisture content is below 2.0%, and then activated and calcined at a temperature of 850-1050℃ for 0.5-2.0 hours. After cooling to below 40℃, they are pulverized a second time, and the powder becomes the intermediate of potassium-calcium-silicon fertilizer.

[0011] Furthermore, in step (3), Add industrial-grade phosphoric acid, anhydrous magnesium chloride, and auxiliary materials such as ferric ammonium citrate, zinc chloride, sodium selenite, and borax to the ammonium sulfate filtrate, according to the following mass percentages (unit: by mass percentage, wt.%): 25%-60%, 15%-35%, 1%-5%, 0.5%-3.5%, 0.3%-1.5%, 0.3%-1.5%. Phosphoric acid must have a purity of ≥85%, and the main content (excluding water) of other auxiliary materials must be ≥98.0%. Maintain the Mg:P molar ratio at 1.2-1.5:1. Stir at 85-175 rpm for 30-60 minutes. Through the wetting and dissolving action of water, the various compounds fully dissolve, react, and chelate with each other. Adjust the pH of the mixture to 8.5-9.5 with ammonia (25% purity) to obtain intermediates such as struvite. Furthermore, in step (4), The potassium-calcium-silicon fertilizer intermediate prepared in step (2) is mixed with the struvite (MgNH4PO4), magnesium sulfate, and trace elements iron, zinc, selenium, boron, and chlorine solution prepared in step (3) at a mass ratio of 0.5-4.5 (struvite):1.0 (potassium-calcium-silicon fertilizer). After thorough mixing, the mixture is evaporated, cooled, and then granulated in a disc. The particle size is controlled at 3.0-15.0 mm. The granules are dried with hot air, weighed, and packaged into bags. This product is a complete element fertilizer product.

[0012] The aforementioned all-element fertilizer product contains nitrogen (N) of 3.0%-15.0%, phosphorus (as P2O5) of 3.0%-35.0%, potassium (as K2O) of 0.5%-7.0%, citrate-soluble calcium (as CaO) of 15.0%-28.0%, citrate-soluble magnesium (as MgO) of 3.0%-28.0%, available sulfur (as SO3) of 4.5%-20.5%, and available silicon (as SiO2) of 3.0%-13.5%. It also contains trace elements such as iron, zinc, selenium, boron, and chlorine. The total available nutrients are ≥80%, and the pH value is 9.0-12.0. It is an all-element fertilizer product with weak alkaline properties.

[0013] The beneficial technical effects of the present invention are as follows: 1. The method provided by this invention mainly uses desulfurized gypsum produced from flue gas desulfurization and / or phosphogypsum produced during phosphoric acid production, industrial-grade ammonium carbonate, and potassium-containing aluminosilicate minerals—potassium ore, etc. These materials are widely available, have low production costs, and simultaneously turn waste into treasure, aligning with my country's concept of sustainable development.

[0014] 2. This invention couples the calcium carbonate filter residue from the metathesis reaction and the ammonium sulfate filtrate into the preparation system of potassium-calcium-silicon fertilizer and struvite, respectively. It employs a nutrient-type binary compound flux such as sodium chloride, and precisely controls the pH of the struvite reaction and the mixing ratio of the two intermediates using ammonia. This eliminates the energy-intensive process of ammonium sulfate concentration and crystallization, reduces the calcination temperature of potassium ore from over 1200℃ to 850-1050℃, while ensuring a struvite precipitation rate of over 95% and zero loss of trace elements. It also improves the citric acid solubility of potassium. The aforementioned raw material combination, process coupling, and parameter range are all unconventional techniques in this field, and the technical effects are difficult to predict through simple derivation using existing technologies.

[0015] 3. The all-element fertilizer prepared by the method of this invention is weakly alkaline, which can neutralize soil acidity, and can also provide crops with abundant macro-, meso-, and micronutrients. It will be a powerful supplement for addressing soil acidification, nutrient imbalance, and improving the quality of agricultural products. At the same time, the method of this invention significantly improves the utilization efficiency of industrial gypsum, turning waste into treasure and promoting the healthy and sustainable development of the circular economy. Attached Figure Description

[0016] The technical solution of the present invention will be further described in detail below with reference to specific implementation cases and accompanying drawings, but the scope of protection and implementation of the present invention are not limited thereto.

[0017] Figure 1 The conversion route for industrial gypsum (desulfurized gypsum / phosphogypsum).

[0018] Figure 2 This describes the preparation process route for intermediates in potassium-calcium-silicon fertilizers.

[0019] Figure 3 Process route for preparing intermediates such as struvite.

[0020] Figure 4 The process route for preparing all-element fertilizer products. Detailed Implementation

[0021] like Figure 1 The diagram shown illustrates the transformation of industrial gypsum (desulfurized gypsum / phosphogypsum), and is described in detail below: Wet desulfurization gypsum and / or phosphogypsum and industrial-grade ammonium sulfate are used as raw materials. Water and other materials are added, and the filter residue—calcium carbonate powder and ammonium sulfate solution—is obtained through material compatibility, mixing, stirring, aging and filtration.

[0022] Figure 1Industrial gypsum, including desulfurized gypsum and / or phosphogypsum, generally requires a calcium sulfate dihydrate content greater than 90% (after drying at 105℃ for 6 hours). Industrial-grade ammonium carbonate generally requires an (NH4)2CO3 content ≥95%, a moisture content ≤2.0%, and a chloride content ≤0.01%. The precipitate calcium carbonate (the product of the reaction between gypsum and ammonium carbonate) after the metathesis reaction requires a CaCO3 content ≥91.0% (after drying at 105℃ for 6 hours). The amount of water added is 2.0-13.0:1 of the total solid mass (i.e., liquid / solid ratio) to ensure complete dissolution of ammonium carbonate and its conversion into calcium carbonate. Sulfate ions combine with ammonium ions to form an ammonium sulfate solution.

[0023] like Figure 2 The diagram shows the preparation process route for potassium-calcium-silicon fertilizer intermediates, described in detail below: use Figure 1 The filtered residue, calcium carbonate powder, is added to industrial gypsum, including desulfurized gypsum and / or phosphogypsum, as well as potassium ore powder. Through metering, stirring, drying, granulation, activation, and cooling, potassium-calcium-silicon fertilizer intermediates are produced.

[0024] Figure 2 The activation temperature is 850-1050℃ and the activation time is 0.5-1.5 hours, which transforms the reactants into potassium-calcium-silicon fertilizer intermediates. The intermediates to be prepared—silicon-calcium-potassium-magnesium fertilizers—are mainly composed of silicon, calcium, potassium, magnesium, etc.

[0025] like Figure 3 The diagram shows the process route for preparing intermediates such as struvite, and the detailed description is as follows: use Figure 1 The filtered ammonium sulfate solution is mixed with industrial-grade phosphoric acid, anhydrous magnesium chloride and other auxiliary materials. Ammonia water is used to adjust the pH of the solution and trace elements such as ferric ammonium citrate, zinc chloride, sodium selenite, and borax are added. Through mixing, stirring, adjusting and evaporating, intermediates such as struvite are produced.

[0026] In the preparation of intermediates such as struvite, phosphoric acid with a purity ≥85% needs to be added, followed by anhydrous magnesium chloride (purity ≥98%), maintaining a Mg:P molar ratio of 1.2-1.5:1. Ferric ammonium citrate, zinc chloride, sodium selenite, and borax (all with a content ≥98%) solutions are also added. The pH of the mixed solution is adjusted to between 8.5 and 9.5 using an appropriate amount of ammonia water (ammonia content ≥25%). The stirring speed is 85-175 rpm, and the stirring time is 30-60 minutes. This process converts the ammonium sulfate mixture into a mixture of struvite (MgNH4PO4) precipitate, magnesium sulfate, and aqueous solutions of trace elements iron, zinc, selenium, boron, and chloride. After evaporation, the intermediates such as struvite are obtained.

[0027] like Figure 4The diagram shows the process flow chart for preparing all-element fertilizer products, described in detail below: use Figure 2 The obtained potassium-calcium-silicon fertilizer intermediate, and Figure 3 The obtained intermediates, such as struvite, are used to produce all-element fertilizer products through steps such as metering, stirring, granulation, drying, weighing, and packaging. Will Figure 2 The prepared potassium-calcium-silicon fertilizer intermediate, and Figure 3 The prepared struvite (MgNH4PO4), magnesium sulfate, and trace elements iron, zinc, selenium, boron, and chlorine are thoroughly mixed and stirred at a mass ratio of 0.5-4.5 (struvite):1.0 (potassium, calcium, and silicon fertilizer). After dehydration, granulation, drying, weighing, and packaging, a complete element fertilizer product is obtained. This product not only contains the macroelements nitrogen, phosphorus, and potassium, but also the medium elements calcium, magnesium, sulfur, and silicon, as well as trace elements iron, zinc, selenium, boron, and chlorine, etc. It is a complete fertilizer with a wide range of nutrients and is a cost-effective, weakly alkaline complete element fertilizer product.

[0028] The following describes in detail a method for producing all-element fertilizer using desulfurized gypsum and / or phosphogypsum, calcium carbonate, potassium ore and other raw and auxiliary materials, with specific embodiments.

[0029] Example 1 A coal-fired power plant in Shandong Province used the limestone-gypsum method for flue gas desulfurization, generating a large amount of desulfurized gypsum. Sampling and analysis revealed that the desulfurized gypsum contained more than 93.45% calcium sulfate dihydrate (after drying at 105℃ for 6 hours). One ton of industrial-grade ammonium carbonate was purchased, with (NH4)2CO3 content ≥96.12%, moisture content ≤1.37%, and chloride content ≤0.01%. 1.8428 tons of dried desulfurized gypsum dihydrate was weighed and reacted with one ton of industrial-grade ammonium sulfate in a double decomposition reaction. 60% of the total mass of tap water was added, and the mixture was stirred at a rate of 105 rpm for 55 minutes. After stirring, the mixture was filtered, and the filter residue was washed twice with approximately 20% of the total mass of clean water, yielding calcium carbonate filter residue and ammonium sulfate filtrate. The net weight of dried calcium carbonate was 1.0012 tons, and the net weight of ammonium sulfate was 1.3216 tons. 0.4% of the dried calcium carbonate filter residue was added to the filtrate. 683 tons of potassium feldspar produced in Yantai (containing 14.35% K₂O, 66.59% SiO₂, and 17.16% Al₂O₃, with approximately 2% Na₂O and Fe₂O₃), 0.1316 tons of desulfurized gypsum dihydrate (containing 93.45% CaSO₄·2H₂O, dried at 105℃ for 6 hours), and fluxes NaCl and K₂SO₄ in a 1:1 mass ratio were added. The amount added was 3.5% of the total mass of the other three raw materials, approximately 56.9 kJ. 4 kg of the above five materials were thoroughly mixed and dried at 105°C until the moisture content of the mixture reached 7.5%. Granulation was then carried out, with granules having a diameter of 15 mm. The mixture was dried again until the moisture content was reduced to 2%, and then calcined. The calcination temperature was controlled at 950°C for 115 minutes. Afterward, it was cooled to room temperature (approximately 25°C) and then pulverized, passing through a 100-mesh (0.15 mm) sieve to obtain approximately 1.1832 tons of potassium-calcium-silicon fertilizer intermediate. In the separated ammonium sulfate filtrate (net weight of ammonium sulfate 1.3216 tons), [the following was added]... The product contains industrial-grade phosphoric acid and magnesium chloride, with 2.3087 tons of industrial-grade phosphoric acid (85% purity), 1.2352 tons of industrial-grade anhydrous magnesium chloride (98.0% purity), and 2.5%, 0.50%, 0.35%, and 0.40% by weight of trace element additives such as ferric ammonium citrate, zinc chloride, sodium selenite, and borax, respectively. All these additives are required to have a main content (excluding water) ≥98.0%. This produces 4.6630 tons of a mixture including struvite; which is then mixed with 1.1832 tons of potassium-calcium-silicon fertilizer intermediates. These materials are thoroughly stirred at a stirring speed of 135 rpm for 35 minutes. Through the wetting and dissolving effects of water, the various compounds are fully dissolved and reacted. The mixture is then granulated using a disc granulator, with the particle size controlled at 9.0 mm. After hot air drying, the granules are weighed and packaged into bags. This product is a complete element fertilizer.The product contains 4.79% nitrogen (N), 24.84% phosphorus (P2O5), and 0.81% potassium (K2O), 4.05% citrate-soluble silica, 7.08% available calcium oxide, 20.71% citrate-soluble magnesium oxide, and 15.26% available sulfur. It also contains trace elements such as iron, zinc, selenium, and boron. The total available nutrients are over 80%, and the pH value is 9.85. It is a complete fertilizer product with weak alkaline properties.

[0030] Example 2 A coal-fired power plant in Hebei Province uses the limestone-gypsum method for flue gas desulfurization, which also produces a large amount of desulfurized gypsum. Analysis showed that the calcium sulfate dihydrate content in the desulfurized gypsum was 90.05% (after drying at 105℃ for 6 hours). One ton of this desulfurized gypsum (after drying) was weighed and mixed with 0.5241 tons of industrial-grade ammonium carbonate ((NH4)2CO3 content 96.01%). 60% of the total mass of the two substances was then added to tap water, and the mixture was stirred at a rate of 95 rpm for 55 minutes. After stirring, the mixture was filtered, and the filter residue was washed twice with approximately 20% of the total mass of clean water, yielding calcium carbonate filter residue and ammonium sulfate filtrate. The net mass of the obtained product was approximately 0.5241 tons of calcium carbonate and 0.6918 tons of ammonium sulfate. Locally produced potassium feldspar ore (K2O content 9.18%, purity 54) was added to the calcium carbonate filter residue. 0.3832 tons of 32% desulfurization gypsum (CaSO4·2H2O content 90.05%, dried at 105℃ for 6 hours) and 0.0715 tons of dihydrate desulfurization gypsum (CaSO4·2H2O content 90.05%, dried at 105℃ for 6 hours) were added, along with flux KCl and Na2SO4 in a 1:1 mass ratio. The amount added was 4.5% of the total mass of the other three raw materials, approximately 44.05 kg. After thorough mixing, the five materials were dried at 105℃ until the moisture content of the mixture reached 6.5%. Granulation was then performed, with granules having a diameter of 1 mm. The powder was dried again to a moisture content of 2%, then calcined. The calcination temperature was controlled at 1050℃ for 75 minutes. After cooling to room temperature (approximately 35℃), it was pulverized and passed through a 100-mesh (0.15mm) sieve to obtain approximately 0.7716 tons of potassium-calcium-silicon fertilizer intermediate. One-quarter of the ammonium sulfate filtrate (net weight of ammonium sulfate 0.6918 tons), or 0.1729 tons, was extracted and mixed with industrial-grade phosphoric acid and industrial-grade magnesium chloride. The amount of acid added is 0.3020 tons (85% purity), industrial-grade anhydrous magnesium chloride 0.1616 (98% purity), and auxiliary materials such as ferric ammonium citrate, zinc chloride, sodium selenite, and borax, with a total mass of 4.5%, 1.50%, 1.00%, and 1.40% respectively. All these auxiliary materials are required to have a main content (excluding water) ≥98.0%, yielding 0.6374 tons of products such as struvite. Then, 0.7716 tons of potassium-calcium-silicon fertilizer intermediate are mixed with it, resulting in a total product mass of approximately 1.4090 tons. These materials are thoroughly stirred at a stirring speed of 105 rpm for 25 minutes. Through the wetting and dissolving effects of water, the various compounds are fully dissolved and reacted. The mixture is then granulated using a disc granulator, with the particle size controlled at 7.5 mm. After the granules are dried with hot air, weighed, and packaged into bags, this product is a complete element fertilizer.The product contains 2.60% nitrogen (N), 13.48% phosphorus (P2O5), and 2.19% potassium (K2O), 9.86% citrate-soluble silica, 19.17% available calcium oxide, 11.24% citrate-soluble magnesium oxide, and 11.65% available sulfur. It also contains trace elements such as iron, zinc, selenium, and boron. The total available nutrients are over 80%, and the pH value is 10.54. It is a complete fertilizer product with weak alkaline properties.

[0031] Example 3 A wet-process phosphoric acid production plant in Guizhou Province produced a large quantity of phosphogypsum. Analysis revealed that the phosphogypsum contained 90.15% calcium sulfate dihydrate (after drying at 105℃ for 6 hours). The plant purchased 0.5170 tons of industrial-grade ammonium carbonate, with (NH4)2CO3 content ≥97.33%, moisture content ≤1.09%, and chloride content ≤0.01%. One ton of dried phosphogypsum dihydrate was weighed and reacted with 0.5170 tons of industrial-grade ammonium sulfate in a double decomposition reaction. Tap water, accounting for 60% of the total mass of the two substances, was added, and the reaction was stirred. The stirring rate was 85 rpm, and the stirring time was 60 minutes. Then, the mixture was filtered. The filter residue was washed twice with approximately 20% of the total mass of water to obtain calcium carbonate filter residue and ammonium sulfate filtrate. The net mass of calcium carbonate was 0.5241 tons, and the net mass of ammonium sulfate was 0.6918 tons. To the calcium carbonate filter residue, 0.3490 tons of illite (K₂O content 10.08%, purity 59.64%) from Guizhou Fuquan potassium ore and 0.0703 tons of phosphogypsum (calcium sulfate dihydrate content greater than 91.55%, 105℃) were added. (Calculation results after 6 hours of drying), then add the flux potassium chloride and potassium sulfate in a 1:1 mass ratio. The amount added is 4.75% of the total mass of the other three raw materials, approximately 44.81 kg. After thoroughly mixing the five materials, dry them until the moisture content reaches 7.5%. Granulate the mixture to a diameter of 20 mm, then dry it again until the moisture content is as low as 2%. Then calcine at 1000℃ for 75 minutes. After cooling to room temperature (approximately 35℃), pulverize the pulverized material through a 100-mesh sieve (0.15 mm). The potassium-calcium-silicon fertilizer intermediate was obtained by sieving through a (mm) sieve. Industrial-grade phosphoric acid and industrial-grade anhydrous magnesium chloride were added to the separated ammonium sulfate filtrate. The amount of industrial-grade phosphoric acid added was 1.2085 tons (85% purity), and the amount of industrial-grade magnesium chloride added was 0.6466 tons (98% purity). Auxiliary materials such as ferric ammonium citrate, zinc chloride, sodium selenite, and boron were added at a total mass of 1.0%, 0.5%, 1.5%, and 1.4%, respectively. The main content (excluding water) of these auxiliary materials was required to be ≥98.0%. The materials were thoroughly stirred at a stirring speed of 100 rpm for 45 minutes. Through the wetting and dissolving effects of water, the various compounds were fully dissolved and reacted. The mixture was then granulated using a disc granulator, with the particle size controlled at 5.0 mm. The granules were dried with hot air, weighed, and packaged into bags. This product is a complete element fertilizer product. The product contains 4.79% nitrogen (N), 24.81% phosphorus (P2O5), and 0.9% potassium (K2O), 4.56% citrate-soluble silica, 8.19% available calcium oxide, 20.68% citrate-soluble magnesium oxide, and 15.69% available sulfur. It also contains trace elements such as iron, zinc, selenium, and boron. The total available nutrients are over 87%, and the pH value is 11.05. It is a complete fertilizer product with weak alkaline properties.

[0032] Example 4 A chemical plant in Zhanjiang City, Guangdong Province, produces phosphoric acid from phosphate rock. During the production process, a large amount of phosphogypsum (CaSO4·2H2O) is generated. The phosphogypsum is dried to a moisture content of 5.50% and a dihydrate gypsum content of 93.86%. The potassium ore is sourced from potassium feldspar granite surrounding the production plant. After sorting, the rock contains 8.02% potassium oxide, 75.65% silicon dioxide, and 13.68% aluminum oxide. Weigh 1 ton of dried phosphogypsum. Based on the double decomposition reaction calculation, 0.5468 tons of industrial-grade ammonium carbonate are required, with (NH4)2CO3 content ≥95.80%, moisture content ≤1.00%, and chloride content ≤0.01%. Weigh 1.00 ton of dried dihydrate phosphogypsum and carry out a double decomposition reaction with 0.5468 tons of industrial-grade ammonium carbonate. Add tap water equal to 60% of the total mass of the two, stir and react at a stirring speed of 110 rpm for 45 minutes. Then filter, and wash the filter residue twice with approximately 20% of the total mass of clean water to obtain calcium carbonate filter residue and ammonium sulfate filtrate, with a net mass of 0.5385 tons of calcium carbonate and a net mass of 0.7109 tons of ammonium sulfate. Add 0.4507 tons of surrounding potassium feldspar granite (containing 8.02% potassium oxide, 75.65% silicon dioxide, and 13.68% aluminum oxide) to the calcium carbonate filter residue. Add 0.0705 tons of phosphogypsum (calcium sulfate dihydrate content greater than 93.86%, calculated after drying at 105℃ for 6 hours), followed by flux sodium sulfate and potassium chloride in a 1:1 mass ratio. The amount added is 3.15% of the total mass of the other three raw materials, approximately 33.38 kg. After thoroughly mixing all five materials, dry them until the moisture content reaches 6.5%, then granulate to a particle diameter of 15 mm. Dry again until the moisture content is as low as 2%, then calcine at 1035℃ for 80 minutes. Afterward, cool to room temperature (approximately 37.5℃) before proceeding with further processing. The mixture was pulverized and passed through a 100-mesh (0.15 mm) sieve to obtain 0.6981 tons of potassium-calcium-silicon fertilizer intermediate. Industrial-grade phosphoric acid and industrial-grade magnesium chloride were added to the separated ammonium sulfate filtrate. The amount of industrial-grade phosphoric acid added was 1.2418 tons (85% purity), and the amount of industrial-grade anhydrous magnesium chloride was 0.6644 tons (98% purity). Auxiliary materials such as ferric ammonium citrate, zinc chloride, sodium selenite, and borax were added at total mass of 2.5%, 1.75%, 0.95%, and 0.90%, respectively. The main content (excluding water) of all these auxiliary materials was required to be ≥98.0%. The above materials were thoroughly stirred at a stirring speed of 105. The stirring speed is 100 rpm, and the stirring time is 37.5 minutes. Through the wetting and dissolving effect of water, various compounds are fully dissolved and reacted to obtain a mixture of 2.3655 tons of struvite, magnesium sulfate and trace elements. 20% of this mixture, namely 0.4731 tons, is taken out and mixed evenly with 0.6981 tons of potassium-calcium-silicon fertilizer intermediate. Then, it is granulated by disc granulation, and the particle size is controlled at 9.0 mm. After the granules are dried with hot air, they are weighed and packaged into bags. This product is a complete element fertilizer product.The product contains 2.56% nitrogen (N), 8.19% phosphorus (P2O5), and 2.39% potassium (K2O), 11.95% citrate-soluble silica, 20.92% available calcium oxide, 11.07% citrate-soluble magnesium oxide, and 6.71% available sulfur. It also contains trace elements such as iron, zinc, selenium, and boron. The total available nutrients are over 83%, and the pH value is 10.92. It is a complete fertilizer product with weak alkaline properties.

Claims

1. A method for producing a total-element fertilizer using bulk solid waste such as desulfurization gypsum and / or phosphogypsum, characterized by, Includes the following steps: (1) Desulfurized gypsum and / or phosphogypsum are used as reactants and reacted with another reactant, industrial grade ammonium carbonate, in an aqueous solution system to produce calcium carbonate precipitate and ammonium sulfate solution. After liquid-solid separation, washing and drying, filter residue calcium carbonate powder and ammonium sulfate filtrate are obtained. (2) In the calcium carbonate powder of the filter residue in step (1), potassium ore, desulfurized gypsum and / or phosphogypsum are added to form a three-phase reaction system of potassium ore-calcium carbonate-gypsum. Flux is added, and after material compatibility, mixing, drying, activation, cooling and pulverization, the reactants are transformed into potassium calcium silicon fertilizer intermediates. (3) Add phosphoric acid to the ammonium sulfate filtrate prepared in step (1), then add magnesium chloride, then add iron ammonium citrate, zinc chloride, sodium selenite, borax and other trace element additives, stir, and use ammonia water to adjust the pH of the mixture to convert it into a mixture of struvite precipitate, magnesium sulfate and trace element iron, zinc, selenium, boron and chloride water. (4) The potassium-calcium-silicon fertilizer intermediate prepared in step (2) is thoroughly mixed with the mixture of struvite, magnesium sulfate and trace elements iron, zinc, selenium, boron and chlorine solution prepared in step (3), and then dehydrated, granulated and dried to obtain the full-element fertilizer.

2. The method of claim 1, wherein, In step (1), the desulfurization gypsum is a byproduct generated during the wet flue gas desulfurization process; the phosphogypsum is a byproduct generated during the wet phosphate fertilizer production process; the industrial grade ammonium carbonate has a (NH4)2CO3 content ≥95%, a moisture content ≤2.0%, and a chloride content ≤0.01%; the liquid / solid ratio in the system is between 1.2 and 10.5:

1.

3. The method according to claim 1, characterized in that, In step (2), the potassium ore is a potassium-containing aluminosilicate mineral with a K2O content ≥ 8.0%.

4. The method according to claim 1, characterized in that, The particle size of desulfurized gypsum and / or phosphogypsum, industrial-grade calcium carbonate, and potassium ore is all greater than 200 mesh. The weight ratio of the three is: desulfurized gypsum and / or phosphogypsum: 5%-80%, calcium carbonate: 5%-80%, and potassium ore: 5%-70%.

5. The method according to claim 1, characterized in that, In step (2), the flux includes any two of the following four materials: sodium chloride, sodium sulfate, potassium chloride, and potassium sulfate, and the amount added is 3.0%-5.0% of the total mass of the other three materials.

6. The method according to claim 1, characterized in that, In step (2), the calcination temperature of the activation process is 850-1050℃, and the calcination time is 0.5-2.0 hours.

7. The method according to claim 1, characterized in that, In step (3), the industrial grade phosphoric acid, anhydrous magnesium chloride, ferric ammonium citrate, zinc chloride, sodium selenite, and borax are in the following mass percentages: 25%-60%, 15%-35%, 1%-5%, 0.5%-3.5%, 0.3%-1.5%, and 0.3%-1.5%, respectively. The phosphoric acid is required to have a purity of ≥85%, and the other auxiliary materials are required to have a content ≥98.0%.

8. The method according to claim 1, characterized in that, In step (3), the stirring rate is 85-175 rpm and the stirring time is 30-60 minutes; the pH of the mixture is adjusted to 8.5-9.5 with ammonia.

9. The method according to claim 1, characterized in that, In step (4), the mass ratio of the potassium-calcium-silicon fertilizer intermediate to the mixture of struvite, magnesium sulfate, and trace elements iron, zinc, selenium, boron, and chlorine solution is 0.5-4.5:1.

0.

10. The method according to any one of claims 1-9, characterized in that, The prepared all-element fertilizer contains 3.0%-15.0% nitrogen, 3.0%-35.0% phosphorus, 0.5%-7.0% potassium, 15.0%-28.0% citrate-soluble calcium, 3.0%-28.0% citrate-soluble magnesium, 4.5%-20.5% sulfur, and 3.0%-13.5% silicon. It also contains trace elements such as iron, zinc, selenium, boron, and chlorine. The total effective nutrients are ≥80%, and the pH value is 9.0-12.

0. It is an all-element fertilizer with weak alkaline properties.

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