A method for producing acidic soil conditioner using phosphogypsum and pyrite

Abstract

The present invention provides a method for producing an acidic soil conditioner by using phosphogypsum and pyrite, wherein the pyrite and coal blocks are crushed, effectively mixed with the phosphogypsum filter cake, added to a calcining kiln, and superheated steam is introduced to reduce and decompose the phosphogypsum and remove fluoride, and humic acid, citric acid, plant ash, etc. are added to the solid product, mixed and crushed, and the acidic soil conditioner is obtained after granulation. The method overcomes the major drawbacks of low pH and high fluorine content when phosphogypsum is used as a soil conditioner, and while obtaining a conditioner for acidic soil, efficient utilization of sulfur and calcium resources is achieved, providing a new way for the comprehensive utilization of phosphogypsum solid waste.

Description

Technical Field

[0001] The invention belongs to the field of phosphorus-containing solid waste resource utilization and relates to a method for producing an acidic soil conditioner by utilizing phosphogypsum and pyrite. Background Art

[0002] The area of ​​acidic soil in China reaches 2.03 million km 2 , accounting for 21% of China's total cultivated land, and has become the main factor restricting the growth of crops in the soil. The soil types in southern China are mainly brick red soil and purple soil, most of which are acidic soils, and more than 60% of the soils are severely acidified (pH <5.5). The degree of heavy metal pollution in southern soil is particularly severe among heavy metal pollution in the country, among which Cd, Cr, Cu, Ni, Pb, and Zn exceed the standard rate at a high level. The reasons include: (1) my country's heavy metal mining areas are mainly distributed in the south, and the waste generated by heavy metal mining and smelting contains a large amount of heavy metals. For example, cadmium mines are mainly distributed in the south, and the typical red soil in the south has the strongest adsorption capacity for Cr compared to yellow-brown soil and black soil. Therefore, cadmium pollution in southern my country is much higher than in the north; (2) There are differences in soil types and soil parent materials between the north and the south. Ni, The fact that the content of heavy metals such as Pb and Zn is higher in the south and lower in the north is closely related to the high background value of the soil in the south. The heavy metals brought by atmospheric deposition in the south are also higher than those in the north. (3) Waste discharged from industrial production and people's daily life can also cause heavy metal pollution in the land near industrial areas and suburban farmland. (4) In agricultural production, people blindly pursue output and use pesticides and fertilizers without restraint. Most of the parts that are not used by crops accumulate in the soil. The use of sewage containing excessive heavy metals for irrigation also causes excessive heavy metal content in the soil.

[0003] At present, the most efficient way to improve soil is to directly add soil conditioners, and use their adsorption and precipitation effects on heavy metals to passivate the active state of heavy metals in the soil that are easily absorbed and migrated by crops into stable precipitation or ions to change their biological effectiveness and mobility. Currently, the commonly used soil conditioners mainly include lime, phosphate, organic matter and some large industrial solid wastes, such as red mud, phosphogypsum, desulfurized gypsum, dolomite tailings, etc. Heavy metal ions are active in the acidic soil environment in the south. Studies have shown that adding alkaline soil conditioners such as lime and calcium sulfide to increase its pH value will reduce the corresponding heavy metal elements such as Cd, Cr, and Ni in plants.

[0004] Phosphogypsum, a byproduct of wet phosphoric acid, is a gray or white powdery granular substance, the main component of which is CaSO 4 ·2H 2 O, rich in calcium and sulfur, two soil nutrients, and has many types of impurities, including free phosphate, P 2 O 5, phosphates, acid insolubles, fluorides, alkali metal salts, organic matter and SiO 2 Phosphorus, silicon, potassium, manganese, etc. are also nutrients needed by the soil, which can promote the growth of crops, increase crop yields and disease and drought resistance, etc. Phosphogypsum is acidic, with a pH value between 1.5-4.5, and can be used to improve soil structure and reduce salt content, especially in saline-alkali land, with obvious effects. There is a certain amount of free Ca in phosphogypsum 2+ , which and CO in alkaline soil 3 2- , HCO 3 - The reaction produces CaCO 3 , Ca(HCO 3 ) 2Precipitation reduces soil alkalinity, improves soil compaction, and reduces the harm of carbonate to crops. Among them, CN 113502164A (a method and product for producing mineral soil conditioner using desulfurized gypsum, phosphogypsum and potash ore) prepares a mineral soil conditioner intermediate by mixing desulfurized gypsum, phosphogypsum, potash ore, additives and water, filtering, drying, calcining, cooling and crushing the materials; then zinc sulfate, sodium selenite and borax are added, and water is added and stirred thoroughly, and then granulated, and the granules are dried to obtain a mineral soil conditioner. CN 113337295B discloses a method and product for producing soil conditioner by using bulk industrial solid waste. The method comprises: using alkali-making white mud, desulfurized gypsum, phosphogypsum, potassium ore, additives and water, and preparing active mineral soil conditioner intermediate by material mixing, drying, roasting, cooling and crushing; then adding potassium humate, zinc sulfate, iron sulfate, sodium selenite and borax auxiliary materials, adding water and stirring together, granulating, drying and packaging the mixture, and obtaining a mineral soil conditioner. The product has good effects and promotion functions for improving acidic soil, preventing soil compaction and supplementing missing soil minerals. my country has promulgated the standard "HG / T 4219-2011 Phosphogypsum Soil Conditioner", striving to expand the application scale of phosphogypsum in soil improvement and conditioning. However, although phosphogypsum can improve soil or be made into fertilizer to supplement soil nutrients, there are still many problems: (1) Phosphogypsum is highly acidic, generally between 1.5 and 4.5. It is advantageous for improving saline-alkali soil, but it is not ideal for acidic soil in the south and may have a counter-effect. The production areas of phosphogypsum are basically in southern regions such as Sichuan, Yunnan and Hubei, and transportation problems are extremely prominent; (2) Phosphogypsum contains 0.2-0.5% fluorine, most of which is insoluble fluorine, but there is also water-soluble fluorine. Once it enters the soil, it will cause great harm; (3) Some phosphogypsum contains radioactive nuclides such as uranium-238, radium-226, thorium-232, and potassium-40. Although the radioactivity of phosphogypsum in my country is not high, the types and contents of radioactive nuclides in different production areas are different, which deserves attention and requires radioactive reduction treatment steps. Otherwise, it will enter the soil and cause endless troubles. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for producing an acidic soil conditioner using phosphogypsum and pyrite, wherein the method uses pyrite, coke and coal powder as reducing agents, and in a water vapor atmosphere, a portion of the phosphogypsum is reduced to calcium sulfide at low temperature. With the help of a high-temperature calcination environment, the radioactivity of the phosphogypsum is reduced, the hydroxyl radicals generated by superheated water vapor will eliminate the fluorine in the phosphogypsum, and the hydrogen fluoride produced in the gas phase can be recovered. The solid product obtained is a mixture of calcium sulfide, calcium oxide, phosphogypsum, iron oxide, etc., which has a certain alkalinity. Humic acid, citric acid, plant ash, etc. are compounded to obtain a soil conditioner for acidic soil. The soil conditioner prepared by the method is an alkaline substance rich in sulfide, which can effectively fix the sulfides of heavy metals existing in the soil, such as cadmium, chromium and other toxic pollutants, and can simultaneously adjust the pH value and provide nutrients and the ability to adsorb and fix heavy metals to the soil in combination with iron oxide, humic acid, citric acid, wood ash, etc.; the method utilizes water vapor and high-temperature calcination to achieve the removal of fluoride ions in phosphogypsum; after the high-temperature process, the radioactivity of phosphogypsum is greatly reduced, and at the same time, the efficient utilization of sulfur and calcium resources is achieved, providing a new way for the comprehensive utilization of phosphogypsum, a large amount of solid waste.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for producing an acidic soil conditioner by using phosphogypsum and pyrite, the method comprising the following steps:

[0008] (1) pulverizing pyrite and coal lumps separately, and effectively mixing them with phosphogypsum filter cake in a crushing mixer to obtain a mixture;

[0009] (2) Add the mixture obtained in step (1) into a calcining kiln, introduce superheated steam, and set the kiln at a calcining temperature of 900 to 1000° C. to reduce and decompose the phosphogypsum.

[0010] (3) The gas phase reduced and decomposed in step (2) is rich in hydrogen fluoride, which is recovered by absorbing the hydrogen fluoride in the gas phase with water. The gas phase contains a certain amount of sulfur dioxide, which is desulfurized by adding lime, and the tail gas is finally discharged in compliance with the emission standards.

[0011] (4) The solid product obtained by calcining in step (2) is added with humic acid, citric acid, wood ash, etc., mixed and crushed, and then granulated to obtain an acidic soil conditioner.

[0012] As a preferred technical solution of the present invention, the pyrite and coal blocks described in step (1) are crushed separately and effectively mixed with the phosphogypsum filter cake in a crushing mixer.

[0013] Preferably, in step (1), the ratio of pyrite: coal powder: phosphogypsum filter cake is 1-3 parts: 1-3 parts: 4-8 parts.

[0014] Preferably, the pyrite in step (1) has an effective sulfur content of 30-35 wt% and is crushed to a size below -100 mesh.

[0015] Preferably, the coal in step (1) has an ash content of 10-15 wt% and is crushed to a size below -100 mesh.

[0016] Preferably, the phosphogypsum filter cake in step (1) has a water content of 30-35 wt% and a fluorine content of 0.3-0.5 wt%.

[0017] As a preferred technical solution of the present invention, the mixture obtained in step (2) is added to a calcining kiln, superheated steam is introduced, and the calcining temperature of the kiln is 900-1000°C to carry out reduction decomposition of phosphogypsum.

[0018] Preferably, the temperature of the superheated steam in step (2) is 500-600°C. The steam with a slight positive pressure of 5-10kPa is reheated by heat exchange with the high-temperature gas of the calcining kiln to obtain superheated steam. The purpose of maintaining slight pressure increase is to ensure that the superheated steam can enter the calcining kiln more easily and the calcining kiln space is filled with superheated steam. Superheated steam produces a large amount of hydroxyl free radicals in a high-temperature environment and has extremely strong oxidizing properties. It can rapidly gasify the coal and other media in the material to obtain reducing gases such as carbon monoxide and hydrogen, which can greatly reduce the decomposition temperature of phosphogypsum.

[0019] Preferably, the calcining kiln described in step (2) can be a calcining equipment such as a fluidized bed or a rotary kiln, and the calcining temperature is 900-1000°C.

[0020] Preferably, the phosphogypsum decomposition reaction time in step (2) is 60-120 min.

[0021] As a preferred technical solution of the present invention, the gas phase produced by reduction decomposition in step (3) is rich in hydrogen fluoride, which is absorbed by water, and the subsequent sulfur dioxide is absorbed and removed by lime.

[0022] Preferably, the gas phase in step (3) contains HF, SO 2 wait.

[0023] Preferably, the gas phase in step (3) contains HF at a content of 1000-2000 ppm, and the HF content in the flue gas after removal is less than 5 ppm.

[0024] Preferably, the gas phase in step (3) contains SO 2 The content is 2000-4000ppm, and the SO in the flue gas after removal2 The content is less than 30ppm.

[0025] As a preferred technical solution of the present invention, the solid product obtained by calcining in step (4) is added with humic acid, citric acid, wood ash, etc., mixed and crushed, and then granulated to obtain an acidic soil conditioner.

[0026] Preferably, the solid product in step (4) comprises: 40-50wt% calcium sulfide; 5-10wt% calcium oxide; 5-10wt% iron oxide; 30-40wt% gypsum; 2-5wt% silicon dioxide; the fluorine content is reduced to below 0.005wt% and there is no water-soluble fluorine.

[0027] Preferably, the humic acid in step (4) accounts for 10-20% of the mass of the soil conditioner.

[0028] Preferably, the citric acid in step (4) accounts for 2-5% of the mass of the soil conditioner.

[0029] Preferably, the wood ash in step (4) accounts for 2-5% of the mass of the soil conditioner.

[0030] As a preferred technical solution of the present invention, the method comprises the following steps:

[0031] (1) Pyrite with an effective sulfur content of 30-35 wt% and coal blocks with an ash content of 10-15 wt% are crushed to below -100 mesh and effectively mixed with phosphogypsum filter cake in a crushing mixer to obtain a mixture in which the ratio of pyrite: coal powder: phosphogypsum filter cake is 1-3 parts: 1-3 parts: 4-8 parts.

[0032] (2) adding the mixture obtained in step (1) into a calcining kiln, which may be a fluidized bed, rotary kiln or other calcining equipment, and introducing superheated steam, wherein the superheated steam temperature is 500-600°C, the pressure is a slightly positive pressure of 5-10 kPa, the calcining temperature of the kiln is 900-1000°C, and the phosphogypsum is reduced and decomposed, and the decomposition reaction time is 60-120 min.

[0033] (3) The gas phase reduced and decomposed in step (2) is rich in hydrogen fluoride, with a content of 1000-2000 ppm. The hydrogen fluoride is recovered by water absorption, and the HF content in the flue gas after removal is less than 5 ppm; the flue gas after hydrogen fluoride removal contains SO 2 , the content is 2000-4000ppm, lime is added for desulfurization, and the SO in the flue gas after removal 2 The content is lower than 30ppm, and the final exhaust gas meets the emission standards.

[0034] (4) The solid product obtained by calcining step (2) comprises: 40-50wt% calcium sulfide; 5-10wt% calcium oxide; 5-10wt% iron oxide; 30-40wt% gypsum; 2-5wt% silicon dioxide; the fluorine content is reduced to below 0.005wt% and there is no water-soluble fluorine. Humic acid accounting for 10-20% of the mass of the soil conditioner, citric acid accounting for 2-5% of the mass of the soil conditioner and wood ash accounting for 2-5% of the mass of the soil conditioner are added, the mixture is mixed and crushed, and then granulated to obtain an acidic soil conditioner.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention uses pyrite and coal powder as reducing agents, and in a water vapor atmosphere, reduces a portion of phosphogypsum to calcium sulfide at low temperature, and compounding with nutrients such as humic acid to form a soil conditioner that is an alkaline substance rich in sulfide, which can effectively fix the sulfides of heavy metals such as cadmium, chromium and other toxic pollutants existing in the soil. In combination with iron oxide, humic acid, citric acid, wood ash, etc., it can simultaneously adjust the pH value and provide nutrients to the soil and the ability to adsorb and fix heavy metals.

[0037] (2) The present invention utilizes high-temperature calcination in a superheated steam atmosphere to achieve the removal of fluorine ions in phosphogypsum and a significant reduction in the radioactivity of phosphogypsum.

[0038] (3) The present invention overcomes the major drawbacks of phosphogypsum as a soil conditioner, such as low pH and high fluorine content, and provides a new approach for the comprehensive utilization of this large amount of solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The present invention provides a process flow diagram of a method for producing an acidic soil conditioner using phosphogypsum and pyrite. DETAILED DESCRIPTION

[0040] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail with specific implementation methods below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0041] The main raw materials involved in the present invention include phosphogypsum, pyrite and coal blocks, all of which are from a domestic enterprise. The main components of each raw material are shown in Tables 1 to 3.

[0042] Table 1 Main components of phosphogypsum

[0043] Element <![CDATA[CaSO 4 ]]> <![CDATA[H 2 The]]> <![CDATA[SiO 2 ]]> <![CDATA[P 2 THE 5 ]]> F <![CDATA[Al 2 THE 3 ]]> <![CDATA[Fe 2 THE 3 ]]> MgO Composition (wt%) 58-66 30-38 1.5-3.0 0.7-1.1 0.3-0.5 0.4-0.6 0.3-0.5 0.1-0.3

[0044] Table 2 Main components of pyrite

[0045] Element Fe S Mg Ca Si Al Composition (wt%) 26-30 30-35 0.4-0.5 0.5-0.6 1.5-1.6 0.3-0.4

[0046] Table 3 Main components of coal blocks

[0047] Element <![CDATA[M ad ]]> <![CDATA[V daf ]]> <![CDATA[A d ]]> <![CDATA[FC ad ]]> S Calorific value KJ / Kg Composition (wt / %) 2.03 21.78 12.36 63.28 1.32 25671

[0048] The following are typical but non-limiting embodiments of the present invention:

[0049] This embodiment provides a method for producing an acidic soil conditioner using phosphogypsum and pyrite. The process flow diagram of the method is shown in FIG. Figure 1 The method comprises the following steps:

[0050] (1) Pyrite with an effective sulfur content of 30-35 wt% and coal blocks with an ash content of 10-15 wt% are crushed to below -100 mesh and effectively mixed with phosphogypsum filter cake in a crushing mixer to obtain a mixture in which the ratio of pyrite: coal powder: phosphogypsum filter cake is 1-3 parts: 1-3 parts: 4-8 parts.

[0051] (2) adding the mixture obtained in step (1) into a calcining kiln, which may be a fluidized bed, rotary kiln or other calcining equipment, and introducing superheated steam, wherein the superheated steam temperature is 500-600°C, the pressure is a slightly positive pressure of 5-10 kPa, the calcining temperature of the kiln is 900-1000°C, and the phosphogypsum is reduced and decomposed, and the decomposition reaction time is 60-120 min.

[0052] (3) The gas phase reduced and decomposed in step (2) is rich in hydrogen fluoride, with a content of 1000-2000 ppm. The hydrogen fluoride is recovered by water absorption, and the HF content in the flue gas after removal is less than 5 ppm; the flue gas after hydrogen fluoride removal contains SO 2 , the content is 2000-4000ppm, lime is added for desulfurization, and the SO in the flue gas after removal 2 The content is lower than 30ppm, and the final exhaust gas meets the emission standards.

[0053] (4) The solid product obtained by calcining step (2) comprises: 40-50wt% calcium sulfide; 5-10wt% calcium oxide; 5-10wt% iron oxide; 30-40wt% gypsum; 2-5wt% silicon dioxide; the fluorine content is reduced to below 0.005wt% and there is no water-soluble fluorine. Humic acid accounting for 10-20% of the mass of the soil conditioner, citric acid accounting for 2-5% of the mass of the soil conditioner and wood ash accounting for 2-5% of the mass of the soil conditioner are added, the mixture is mixed and crushed, and then granulated to obtain an acidic soil conditioner.

[0054] Example 1

[0055] This embodiment provides a method for producing an acidic soil conditioner using phosphogypsum and pyrite. The process flow diagram of the method is shown in FIG. Figure 1 shown.

[0056] 100 kg of pyrite containing 35% effective sulfur and 100 kg of coal blocks with 10% ash content were crushed to -100 mesh respectively, and then added into a crushing mixer together with 800 kg of phosphogypsum filter cake containing 35% water, and mixed thoroughly and effectively to obtain a mixture. The mixture was added into a fluidized bed kiln, and superheated steam with a temperature of 600°C and a slight positive pressure of 10 KPa was introduced. The phosphogypsum was reduced and decomposed at a kiln temperature of 900°C for 120 minutes. The gas phase generated during the decomposition process contained HF, the content of which was 1000 ppm. It was absorbed and removed with water, and the HF content in the gas phase after defluorination was reduced to 4.5 ppm. The gas phase also contained SO 2 , its content is 2000ppm, desulfurization is carried out with lime, and SO in the gas phase after desulfurization 2 The content is reduced to 25ppm, and the exhaust gas meets the emission standards. The solid after calcination and decomposition in the kiln is 390Kg, of which the calcium sulfide content is 50wt%, the calcium oxide content is 3wt%, the iron oxide content is 5wt%, the gypsum content is 40wt%, the silicon dioxide content is 2wt%, the fluorine content is 0.004wt%, and there is no water-soluble fluorine. Take 112Kg humic acid, 28Kg citric acid, and 11.2Kg wood ash, add them to the above calcined and decomposed solids, mix and crush them into granules, and obtain 560Kg of acidic soil conditioner, of which humic acid accounts for 20% of the mass of the conditioner, citric acid accounts for 5% of the mass of the conditioner, and wood ash accounts for 2% of the mass of the conditioner.

[0057] Comparative Example 1

[0058] 100 kg of pyrite containing 35% effective sulfur and 100 kg of coal blocks with 10% ash content were crushed to -100 mesh respectively, and then added into a crushing mixer together with 800 kg of phosphogypsum filter cake containing 35% water, and mixed thoroughly and effectively to obtain a mixture. The mixture was added into a fluidized bed kiln, and superheated steam with a temperature of 450°C and a slight positive pressure of 10 KPa was introduced, and then the phosphogypsum was reduced and decomposed at a kiln temperature of 900°C for 120 minutes. The gas phase generated during the decomposition process contains HF, the content of which is 800 ppm. It is absorbed and removed with water, and the HF content in the gas phase after defluorination is reduced to 4.5 ppm. The gas phase also contains SO 2 , its content is 1600ppm, desulfurization is carried out with lime, and SO in the gas phase after desulfurization 2The content is reduced to 25ppm, and the exhaust gas meets the emission standards. The solid after calcination and decomposition in the kiln is 430Kg, of which the calcium sulfide content is 30wt%, the calcium oxide content is 2.4wt%, the iron oxide content is 3.8wt%, the gypsum content is 55wt%, the silicon dioxide content is 1.8wt%, the fluorine content is 0.01wt%, and there is no water-soluble fluorine. Compared with the introduction of 600℃ superheated steam, the defluorination efficiency is reduced, the decomposition rates of phosphogypsum and pyrite are reduced, and the calcium sulfide generation is reduced. Although the calcined decomposition material can also be prepared into an acidic soil conditioner, the resource utilization rate of sulfur and calcium is greatly reduced.

[0059] Comparative Example 2

[0060] 100 kg of pyrite containing 35% effective sulfur and 100 kg of coal blocks with 10% ash content were crushed to -100 mesh respectively, and then added into a crushing mixer together with 800 kg of phosphogypsum filter cake containing 35% water, and mixed thoroughly and effectively to obtain a mixture. The mixture was added into a fluidized bed kiln, and the phosphogypsum was reduced and decomposed at a kiln temperature of 900°C without passing superheated steam, and the decomposition time was 120 minutes. The gas phase generated during the decomposition process contained HF, the content of which was 800 ppm, which was absorbed and removed with water, and the HF content in the gas phase after defluorination was reduced to 4.5 ppm. The gas phase also contained SO 2 , its content is 1500ppm, desulfurization is carried out with lime, and SO in the gas phase after desulfurization 2 The content is reduced to 25ppm, and the exhaust gas meets the emission standards. The solid after calcination and decomposition in the kiln is 470Kg, of which the calcium sulfide content is 30wt%, the calcium oxide content is 1wt%, the iron oxide content is 3wt%, the gypsum content is 50wt%, the silicon dioxide content is 1.5wt%, the fluorine content is 0.15wt%, and there is no water-soluble fluorine. This shows that without the introduction of superheated steam, the defluorination is not thorough, the decomposition of gypsum and pyrite is not thorough, the production of calcium sulfide is greatly reduced, and it is difficult to achieve full circulation of calcium sulfate. Although it can be prepared into an acidic soil conditioner, the resource utilization rate is greatly reduced.

[0061] Comparative Example 3

[0062] 100 kg of pyrite containing 35% effective sulfur and 100 kg of coal with 10% ash content were crushed to -100 mesh respectively, and then added to the crushing mixer together with 800 kg of phosphogypsum filter cake containing 35% water, and mixed fully and effectively to obtain a mixture. The mixture was added to the fluidized bed kiln, and the temperature was 500 ° C and the flow rate was 1m 3 / min of superheated air, and the phosphogypsum was reduced and decomposed at a kiln temperature of 900℃ for 120min. The gas phase produced during the decomposition process contained HF, with a content of 600ppm. It was absorbed and removed by water, and the HF content in the gas phase after defluorination was reduced to 4.5ppm. The gas phase also contained SO 2 , its content is 1000ppm, desulfurization is carried out with lime, and SO in the gas phase after desulfurization 2 The content is reduced to 25ppm, and the exhaust gas meets the emission standards. The solid after calcination and decomposition in the kiln is 510Kg, of which the calcium sulfide content is 20wt%, the calcium oxide content is 10wt%, the iron oxide content is 2.5wt%, the gypsum content is 65wt%, the silicon dioxide content is 1.3wt%, the fluorine content is 0.12wt%, and there is no water-soluble fluorine. It shows that when superheated air is introduced, the defluorination is not thorough, and the decomposition of gypsum and pyrite is not thorough. Because the coal powder vaporizes very quickly under oxygen-rich conditions, there is no time to decompose the calcium sulfate in the gypsum, and the production of calcium sulfide is greatly reduced. Therefore, it is difficult to achieve full circulation of calcium sulfate in calcium sulfate. Although it can be prepared into an acidic soil conditioner, the resource utilization rate is greatly reduced.

[0063] Example 2

[0064] This embodiment provides a method for producing an acidic soil conditioner using phosphogypsum and pyrite. The process flow diagram of the method is shown in FIG. Figure 1 shown.

[0065] 100 kg of pyrite containing 30% effective sulfur and 100 kg of coal blocks with 15% ash content were crushed to -100 mesh respectively, and then added into a crushing mixer together with 800 kg of phosphogypsum filter cake containing 30% water, and mixed thoroughly and effectively to obtain a mixture. The mixture was added into a fluidized bed kiln, and superheated steam with a temperature of 500°C and a slight positive pressure of 5KPa was introduced. The phosphogypsum was reduced and decomposed at a kiln temperature of 1000°C for 60 minutes. The gas phase generated during the decomposition process contained HF, the content of which was 2000 ppm. It was absorbed and removed with water, and the HF content in the gas phase after defluorination was reduced to 4.8 ppm. The gas phase also contained SO 2 , its content is 4000ppm, desulfurization is carried out with lime, and SO in the gas phase after desulfurization 2The content is reduced to 28ppm, and the exhaust gas meets the emission standards. The solid after calcination and decomposition in the kiln is 400Kg, of which the calcium sulfide content is 40wt%, the calcium oxide content is 10wt%, the iron oxide content is 10wt%, the gypsum content is 30wt%, the silicon dioxide content is 5wt%, the fluorine content is 0.003wt%, and there is no water-soluble fluorine. Take 50Kg humic acid, 50Kg citric acid, and 25Kg wood ash, add them to the above calcined and decomposed solids, mix and crush them into granules, and obtain 500Kg of acidic soil conditioner, of which humic acid accounts for 10% of the mass of the conditioner, citric acid accounts for 10% of the mass of the conditioner, and wood ash accounts for 5% of the mass of the conditioner.

[0066] Example 3

[0067] This embodiment provides a method for producing an acidic soil conditioner using phosphogypsum and pyrite. The process flow diagram of the method is shown in FIG. Figure 1 shown.

[0068] 100 kg of pyrite containing 32% effective sulfur and 100 kg of coal blocks with 12% ash content were crushed to -100 mesh respectively, and then added into a crushing mixer together with 800 kg of phosphogypsum filter cake containing 32% water, and mixed thoroughly and effectively to obtain a mixture. The mixture was added into a fluidized bed kiln, and superheated steam with a temperature of 560°C and a slight positive pressure of 7 KPa was introduced. The phosphogypsum was reduced and decomposed at a kiln temperature of 950°C for 90 minutes. The gas phase generated during the decomposition process contained HF, the content of which was 1600 ppm. It was absorbed and removed with water, and the HF content in the gas phase after defluorination was reduced to 4.6 ppm. The gas phase also contained SO 2 , its content is 3200ppm, desulfurization is carried out with lime, and the SO in the gas phase after desulfurization 2 The content is reduced to 26ppm, and the exhaust gas meets the emission standards. The solid after calcination and decomposition in the kiln is 405Kg, of which the calcium sulfide content is 45wt%, the calcium oxide content is 7wt%, the iron oxide content is 8wt%, the gypsum content is 35wt%, the silicon dioxide content is 3wt%, the fluorine content is 0.004wt%, and there is no water-soluble fluorine. Take 78Kg humic acid, 41.6Kg citric acid, and 20.8Kg wood ash, add them to the above calcined and decomposed solids, mix and crush them into granules, and obtain 520Kg of acidic soil conditioner, of which humic acid accounts for 15% of the mass of the conditioner, citric acid accounts for 8% of the mass of the conditioner, and wood ash accounts for 4% of the mass of the conditioner.

[0069] Example 4

[0070] This embodiment provides a method for producing an acidic soil conditioner using phosphogypsum and pyrite. The process flow diagram of the method is shown in FIG. Figure 1 shown.

[0071] 100 kg of pyrite containing 33% effective sulfur and 100 kg of coal block with 11% ash content were crushed to -100 mesh respectively, and then added into a crushing mixer together with 800 kg of phosphogypsum filter cake containing 31% water, and mixed thoroughly and effectively to obtain a mixture. The mixture was added into a fluidized bed kiln, and superheated steam with a temperature of 570°C and a slight positive pressure of 8 KPa was introduced. The phosphogypsum was reduced and decomposed at a kiln temperature of 920°C for 100 minutes. The gas phase generated during the decomposition process contained HF, the content of which was 1500 ppm. It was absorbed and removed with water, and the HF content in the gas phase after defluorination was reduced to 4.4 ppm. The gas phase also contained SO 2 , its content is 3000ppm, desulfurization is carried out with lime, and SO in the gas phase after desulfurization 2 The content is reduced to 25ppm, and the exhaust gas meets the emission standards. The solid after calcination and decomposition in the kiln is 410Kg, of which the calcium sulfide content is 42wt%, the calcium oxide content is 6wt%, the iron oxide content is 7wt%, the gypsum content is 38wt%, the silicon dioxide content is 2wt%, the fluorine content is 0.003wt%, and there is no water-soluble fluorine. Take 95.4Kg humic acid, 37.1Kg citric acid, and 15.9Kg wood ash, add them to the above calcined and decomposed solids, mix and crush them into granules, and obtain 530Kg of acidic soil conditioner, of which humic acid accounts for 18% of the mass of the conditioner, citric acid accounts for 7% of the mass of the conditioner, and wood ash accounts for 3% of the mass of the conditioner.

[0072] It can be seen from the above embodiments that the present invention uses phosphogypsum and pyrite as raw materials, coal blocks as reducing agents, and superheated steam as atmosphere to partially decompose the phosphogypsum and remove fluorine at the same time, converting the acidic phosphogypsum into alkaline, and adding soil nutrient components such as humic acid, citric acid and wood ash to obtain an acidic soil conditioner. This method overcomes the major drawbacks of using phosphogypsum as a soil conditioner, such as low pH and high fluorine content. While obtaining a conditioner for acidic soil, it achieves efficient utilization of sulfur and calcium resources, providing a new way for the comprehensive utilization of phosphogypsum solid waste.

[0073] The applicant declares that the present invention illustrates the method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned methods, that is, it does not mean that the present invention must rely on the above-mentioned methods to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the method of the present invention, addition of auxiliary devices and components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for producing an acidic soil conditioner using phosphogypsum and pyrite, characterized in that: The method comprises the following steps: (1) crushing pyrite and coal blocks respectively, and effectively mixing them with phosphogypsum filter cake in a crushing mixer to obtain a mixture; the ratio of pyrite: coal powder: phosphogypsum filter cake is 1-3:1-3:4-8; (2) Adding the mixture obtained in step (1) into a calcining kiln, introducing superheated steam and then calcining in the kiln, wherein the superheated steam is superheated water steam, and reducing and decomposing the phosphogypsum to obtain an acidic soil conditioner; the superheated steam temperature is 500-600°C, the pressure is a slightly positive pressure of 5-10 kPa, and the calcining temperature is 900-1000°C; the reduction and decomposition reaction time is 60-120 min.

2. The method according to claim 1, characterized in that In step (1), the pyrite and coal blocks are crushed separately and effectively mixed with the phosphogypsum filter cake in a crushing mixer; The pyrite in step (1) has an effective sulfur content of 30-35 wt%, and is crushed to a size of less than -100 mesh; The coal block in step (1) has an ash content of 10-15 wt % and is crushed to a size of less than -100 mesh; The water content of the phosphogypsum filter cake in step (1) is 30-35wt%, and the fluorine content is 0.3-0.5wt%.

3. The method according to claim 2, characterized in that The calcining kiln described in step (2) includes a fluidized bed or a rotary kiln calcining device.

4. The method according to claim 3, characterized in that After the reduction decomposition in step (2), a gas phase is obtained, wherein the gas phase contains HF and SO2; The gas phase contains HF content of 1000-2000 ppm, and the HF content in the flue gas after removal is less than 5 ppm; The gas phase contains 2000-4000 ppm of SO2, and the SO2 content in the flue gas after removal is less than 30 ppm; The gas phase uses water to absorb the hydrogen fluoride, and the sulfur dioxide is absorbed and removed by lime.

5. The method according to any one of claims 1 to 4, characterized in that: The acidic soil conditioner prepared by the method includes the following components: 40-50wt% calcium sulfide, 5-10wt% calcium oxide, 5-10wt% iron oxide, 40-50wt% gypsum, 2-5wt% silicon dioxide, the fluorine content is reduced to 0.005wt%, and there is no water-soluble fluorine.

6. A method for preparing an acidic soil conditioner composition, characterized in that: The method comprises the following steps: (1) crushing the pyrite and coal and mixing them with the phosphogypsum filter cake in a crushing mixer to obtain a mixture, wherein the ratio of the pyrite: coal powder: phosphogypsum filter cake is 1-3:1-3:4-8; (2) adding the mixture obtained in step (1) into a calcining kiln, the calcining kiln comprising a fluidized bed and a rotary kiln calcining device, introducing superheated steam, wherein the superheated steam is superheated water steam, the superheated steam temperature is 500-600° C., and the pressure is a slightly positive pressure of 5-10 kPa; then calcining in the kiln, the calcining temperature is 900-1000° C., performing reduction decomposition of phosphogypsum, and the reduction decomposition reaction time is 60-120 min, to obtain an acidic soil conditioner; (3) Add 10-20% of humic acid, 2-5% of citric acid, and 2-5% of wood ash to the acidic soil conditioner obtained by calcining in step (2), mix and grind, and then granulate to obtain an acidic soil conditioner composition.

7. The method for preparing the acidic soil conditioner composition according to claim 6, characterized in that: The pyrite in step (1) has an effective sulfur content of 30-35 wt%, and is crushed to a size of less than -100 mesh; The coal block in step (1) has an ash content of 10-15 wt % and is crushed to a size of less than -100 mesh; The water content of the phosphogypsum filter cake in step (1) is 30-35wt%, and the fluorine content is 0.3-0.5wt%.

8. The method for preparing the acidic soil conditioner composition according to claim 6, characterized in that: After the reduction decomposition in step (2), a gas phase is obtained, wherein the gas phase contains HF and SO2; The gas phase contains HF content of 1000-2000 ppm, and the HF content in the flue gas after removal is less than 5 ppm; The gas phase contains 2000-4000 ppm of SO2, and the SO2 content in the flue gas after removal is less than 30 ppm; The gas phase uses water to absorb the hydrogen fluoride, and the sulfur dioxide is absorbed and removed by lime.

9. The method for preparing the acidic soil conditioner composition according to claim 6, characterized in that: The acidic soil conditioner comprises the following components: 40-50wt% calcium sulfide; 5-10wt% calcium oxide; 5-10wt% iron oxide; 40-50wt% gypsum; 2-5wt% silicon dioxide; the fluorine content is reduced to 0.005wt% and there is no water-soluble fluorine.

Images