Preparation method and application of soil conditioner based on saline gypsum

Abstract

The invention belongs to the technical field of salt manufacturing systems, and relates to a preparation method and application of a saline gypsum-based soil conditioner. According to the invention, a low-carbon green process route is established, the salty gypsum is taken as a raw material, firstly, the salty gypsum is subjected to resource desalination by adopting a three-stage countercurrent circulation elution process, and multi-stage washing water is recycled and finally returns to a salt production system for industrial salt production, so that internal circulation and zero emission of wastewater are realized; then adopting a desalted gypsum-ammonium bicarbonate-phase transfer catalyst reaction system to generate a mixed solution containing light calcium carbonate microcrystals through a phase transfer catalytic reaction; finally, the mixed liquid is settled and stood, separated supernatant liquid is used as a next batch of base solution after the catalyst is supplemented, consumption of the catalyst and raw materials is reduced, light calcium carbonate and ammonium sulfate are recycled from lower-layer slurry, potassium chloride is compounded, and the novel soil conditioner is obtained. The gap diameter of soil is enlarged, and the soil improvement effect is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of salt production systems, and particularly relates to a method for preparing and applying a soil conditioner based on saline gypsum. Background Technology

[0002] Salt-containing gypsum is a type of gypsum produced during the salt-making industry or seawater concentration in salt fields. Currently, my country's annual salt-containing gypsum production is approximately 1 million tons. A large amount of this gypsum is not effectively utilized and is instead stockpiled in slag dumps, occupying vast amounts of land, posing significant environmental risks, and resulting in enormous resource waste. Therefore, deeply exploring the potential value of salt-containing gypsum and establishing technical solutions for its effective utilization within the salt-making industry's production system is of great practical significance.

[0003] my country is one of the countries with the largest area of ​​soil salinization in the world, with an existing area of ​​about 100 million hectares of saline-alkali land, of which about 7.6 million hectares of saline-alkali arable land and about 2.67 million hectares of saline-alkali wasteland (grassland) are suitable for development. This has a huge impact on agricultural and forestry development, and the importance of saline-alkali land improvement is gradually becoming apparent.

[0004] Adding soil conditioners is a common chemical improvement method used in coastal areas. Based on principles of ion exchange and acid-base neutralization, specific chemical substances are added to the soil to lower its pH and salinity. Since the salt content in coastal saline-alkali land is primarily sodium chloride, calcium-based conditioners are commonly used. 2+ Replacing Na+ increases soil permeability and salt leaching efficiency, increases soil organic matter, alkaline nitrogen, available phosphorus and available potassium, and reduces soil salinity.

[0005] Traditional soil conditioners include substances such as gypsum, zeolite, and sulfur. However, gypsum easily causes soil compaction and solidification, blocking the soil's micropores, reducing soil looseness, and decreasing the penetration and transformation capacity of other beneficial components in the soil. Therefore, the soil improvement effect is not ideal. As a result, the need to develop a new type of soil conditioner that can effectively reduce sodium without causing soil compaction is becoming increasingly prominent. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, the present invention provides a method for preparing a soil conditioner based on saline gypsum and its application.

[0007] The technical solution adopted by the present invention to solve this problem is as follows:

[0008] A method for preparing a soil conditioner based on saline gypsum includes the following steps:

[0009] (i) Raw material washing and desalination process

[0010] A three-stage circulating elution process is used to clean and desalinate saline gypsum raw materials. The wash water generated from the first stage of elution is recycled to the salt production system as a raw material for salt production. The wash water generated from the second stage of elution is used for the first stage of elution of the next batch of raw materials. The wash water generated from the third stage of elution is used for the second stage of elution of the next batch of raw materials. This cycle is repeated to achieve zero wastewater discharge from the elution process.

[0011] (ii) Catalytic reaction process

[0012] Solid-liquid phase catalytic reaction is carried out using a phase transfer catalyst as a medium, wherein: an 80% ammonia solution and an equivalent amount of ammonium chloride are used as the base liquid, and the gypsum raw material treated in step (i) is prepared into a gypsum slurry with a solid-liquid ratio of 1:1 and a 60% ammonium bicarbonate solution are added countercurrently to the reactor containing the base liquid to carry out a solid-liquid phase catalytic conversion reaction to generate a reaction mixture containing light calcium carbonate;

[0013] (iii) Separation and compounding process

[0014] After sedimentation and static separation, the mixture is recycled and compounded. Specifically, the reaction mixture obtained in step (ii) is sedimented and separated to obtain an upper clear liquid and a lower slurry. Part of the catalyst is recovered from the upper clear liquid and recycled as the bottom liquid in the next batch of step (ii). The reaction product calcium carbonate and ammonium sulfate in the reaction liquid are recovered from the lower slurry. Potassium chloride is compounded as an auxiliary material to obtain a new type of soil conditioner.

[0015] In the above technical solution, ammonia water with a concentration of 80% and ammonium chloride in an equivalent ratio are used as preferred. The molar ratio of ammonium chloride to ammonia water is 1:1. As a phase transfer catalyst for the reaction, the addition ratio is 25% of the main raw material (desalinated gypsum). The reaction temperature is 25℃-30℃, the reaction time is 3-5 hours, and the stirring speed of the reaction vessel is 300r / h.

[0016] In the above technical solution, the compounded potassium chloride additive accounts for 15%-30% of the dry basis weight of the lower slurry (adjusted according to the soil salinity in the region).

[0017] In the above technical solution, the compounded potassium chloride auxiliary material comes from salt production by-products.

[0018] The second objective of this invention is to provide a soil conditioner prepared by the above-described method, wherein the active ingredient is light calcium carbonate microcrystals, and the light calcium carbonate microcrystals are loaded with potassium and nitrogen elements.

[0019] In the above technical solution, the calcium carbonate microcrystals have a particle size of 50um-100um and a crystal form of microspheres.

[0020] The third objective of this invention is to provide an application of a soil conditioner prepared by the above-described method in improving soil compaction, reshaping soil aggregate structure, expanding soil pore diameter, and improving the nutrient environment of deep soil.

[0021] In the above technical solution, the active ingredient of the soil conditioner is light calcium carbonate microcrystals loaded with nutrients, which reshape the soil aggregate structure and expand the soil pore diameter by utilizing the soil permeability of the microcrystals.

[0022] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows:

[0023] 1. This invention establishes a low-carbon and green process route. Using saline gypsum as raw material, a three-stage countercurrent circulation elution process is first used to desalinate the saline gypsum for resource recovery. The multi-stage wash water is recycled and eventually returned to the salt production system for industrial salt production, realizing the internal circulation and zero discharge of wastewater. Then, a reaction system of desalinated gypsum-ammonium bicarbonate-phase transfer catalyst is used to generate a mixed liquid containing light calcium carbonate microcrystals through phase transfer catalysis. Finally, the mixed liquid is allowed to settle and stand. The supernatant after separation is used as the reaction base liquid in the next batch step (ii) for recycling, supplementing part of the phase transfer catalyst and reducing the consumption of catalyst and raw materials.

[0024] 2. The novel soil conditioner prepared by this invention, using saline gypsum as raw material, is transformed into lightweight calcium carbonate through efficient catalytic synthesis using a phase transfer catalyst as a medium. The microcrystalline soil permeability reshapes the soil aggregate structure, expands the soil pore diameter, and improves soil looseness, thus solving the problem of soil compaction and solidification when gypsum is used as a soil conditioner in traditional soil improvement.

[0025] 3. This invention uses saline gypsum as raw material to form light calcium carbonate through a phase transfer reaction. The resulting calcium carbonate crystals have a particle size of 50um-100um and are microspherical. The light calcium carbonate has drug loading capacity. The beneficial elements such as potassium and nitrogen loaded in the calcium-based crystal loading agent can reach deep into the soil, effectively solving the problem of gypsum compaction and solidification as a soil conditioner and effectively improving the soil improvement effect.

[0026] 4. This invention is applied in the salt production industry, where desalination wash water enters the salt production system for secondary salt production, with no "three wastes" emissions.

[0027] 5. This invention establishes a three-dimensional model for soil improvement based on resource recycling, providing practical space for the promotion of this technology in other provinces of China. This invention achieves the recycling of desalination wash water and reaction liquid, and utilizes potassium chloride raw materials derived from salt production byproducts, reducing costs and maximizing the comprehensive utilization of resources, thus possessing significant practical value.

[0028] 6. The novel soil conditioner prepared in this invention can effectively adjust the pH value of low-salt-alkali land, increase the total nitrogen content of the soil, and increase the looseness of the soil, showing significant advantages compared with similar products.

[0029] In addition, the inventive step evidence for this invention is also reflected in the following important aspects:

[0030] 1. The expected benefits and commercial value of the technical solution of this invention after transformation are as follows: In salt production enterprises, the disposal cost of saline gypsum as solid waste is RMB 2,000-4,000 per ton. The resource utilization to synthesize a new type of soil conditioner has an annual output value of RMB 40,000 per ton and an expected benefit of RMB 5 million per year, which has huge market potential and commercial value.

[0031] 2. The technical solution of this invention fills a technical gap in the domestic and international industries: This invention uses saline gypsum from the salt production industry as raw material to establish a three-dimensional model for soil improvement through resource recycling. It effectively solves the problem of gypsum compaction and solidification as a soil conditioner with a low-cost technical solution, improves the soil improvement effect, and provides practical feasibility for the promotion and application of this technology in many provinces in China with its excellent economic efficiency, filling the technical gap in the synthesis of new soil conditioners from saline gypsum.

[0032] 3. The technical solution of this invention solves a long-standing but unresolved technical problem: traditional soil conditioners use gypsum as the main raw material. Wet gypsum has extremely high viscosity, easily causing soil to clump together and lacking looseness. Air-dried gypsum hardens and solidifies, blocking soil micropores, reducing soil permeability, and decreasing the penetration and transformation capacity of other beneficial components in the soil. Therefore, the soil improvement effect is not ideal. This invention uses saline gypsum as a raw material, forming light calcium carbonate through a phase transfer reaction. The resulting calcium carbonate crystals have a particle size of 50-100 μm, are microspherical, and have good dispersibility. Simultaneously, light calcium carbonate has drug loading capacity, effectively loading elements such as potassium and nitrogen to reach deep into the soil, effectively solving the problem of gypsum hardening and solidification as a soil conditioner, and improving the soil improvement effect. Attached Figure Description

[0033] Figure 1 This is a process flow diagram of soil conditioner preparation technology based on saline gypsum;

[0034] Figure 2 These are SEM scan images of light calcium carbonate products;

[0035] Figure 3 This is the XRD pattern of a light calcium carbonate product. Detailed Implementation

[0036] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0038] Example:

[0039] Traditional soil conditioners use gypsum as the main raw material. Wet gypsum has extremely high viscosity, easily causing soil to clump together and lack looseness. Air-dried gypsum hardens and solidifies, blocking soil micropores, reducing soil permeability, and decreasing the penetration and transformation capacity of other beneficial components in the soil. Therefore, the soil improvement effect is not ideal. Meanwhile, saline gypsum, a product of the salt industry or seawater concentration in salt fields, is not effectively utilized, not only occupying large amounts of land but also causing huge resource waste.

[0040] Based on this, the present invention designs a method for preparing a soil conditioner that can overcome the bottleneck of traditional gypsum amendment leading to compaction, and can combine the resource utilization of saline gypsum, a byproduct of the salt-making industry, with soil improvement.

[0041] 1. A method for preparing a soil conditioner based on saline gypsum, comprising the following steps:

[0042] (i) Raw material washing and desalination process

[0043] A three-stage circulating elution process is used for raw material cleaning and desalination. Specifically, the first-stage wash water is returned to the salt-making system as raw material; the second-stage wash water is used for the first washing of the next batch of raw materials; and the third-stage wash water is used for the second washing of the next batch of raw materials, thus creating a cycle and achieving zero wastewater discharge in the elution process. This process employs a three-stage counter-current circulating elution and zero-discharge design, reusing multi-stage wash water for the salt-making system and the next batch of washing, achieving internal wastewater recycling and zero discharge.

[0044] (ii) Catalytic reaction process

[0045] Solid-liquid phase catalytic reaction is carried out using a phase transfer catalyst as a medium. Specifically, an 80% ammonia solution is used as the base liquid, and a 60% ammonium bicarbonate solution and gypsum slurry with a solid-liquid ratio of 1:1 are countercurrently introduced into the reactor to carry out a solid-liquid phase conversion reaction. This process employs a reaction system of desalinated gypsum-ammonium bicarbonate-phase transfer catalyst. Through phase transfer catalytic reaction, light calcium carbonate and a reaction completion liquid are obtained (wherein, the main components of the reaction completion liquid are ammonium sulfate and catalyst; in step (iii), a portion of the reaction completion liquid is mixed with the light calcium carbonate product and compounded with a soil conditioner; the remaining reaction completion liquid is reused as the catalyst for the next batch of reaction).

[0046] (iii) Separation and compounding process

[0047] The reaction solution is then allowed to settle and separate. The supernatant and the lower slurry are separated. A portion of the supernatant is used to replenish the catalyst and is recycled as the base liquid for the next batch of reaction. The lower solution is used to recover light calcium carbonate and ammonium sulfate, and then compounded with potassium chloride to obtain a novel soil conditioner. In this process, the supernatant after settling and separation is used as the phase transfer catalyst in the next batch of step (ii), and a portion of the base liquid is recycled, which reduces the consumption of catalyst and raw materials.

[0048] In this embodiment, saline gypsum is used as raw material, and a three-stage countercurrent circulation elution process is employed to desalinate the saline gypsum through resource recovery, achieving zero wastewater discharge. Using ammonia water as the base liquid, in the presence of a phase transfer catalyst, the gypsum slurry undergoes a solid-liquid phase catalytic reaction with ammonium bicarbonate, forming light calcium carbonate through a phase transfer reaction. Figure 3 As shown, qualitative analysis of the obtained product using XRD detection reveals from the peak positions that the product is calcium carbonate; Figure 2 As shown, SEM scanning of the obtained product revealed calcium carbonate crystals with a particle size of 50-100 μm and a microspherical crystal form, which significantly improves soil looseness. Simultaneously, the lightweight calcium carbonate possesses drug loading capacity, capable of adsorbing and loading various nutrients such as nitrogen and potassium. This function has been effectively verified in the pharmaceutical field. By fully utilizing the loading capacity of calcium carbonate in the soil conditioner, the soil permeability of beneficial elements is increased, reaching deep into the soil and ensuring nutrients reach the root zone, thus enhancing the soil amendment effect and effectively solving the problem of compaction and solidification associated with gypsum as a soil conditioner.

[0049] This invention realizes the high-value utilization of saline gypsum. The light calcium carbonate microcrystals in the prepared soil conditioner can effectively penetrate the soil, break up compaction, reshape the aggregate structure, and carry nutrients (nitrogen, potassium, etc.) to the depths of the soil, significantly improving soil improvement efficiency and resource utilization, integrating improvement, nutrition and environmental protection into one.

[0050] 2. Application Testing

[0051] (1) Application Test 1:

[0052] A periodic soil improvement experiment was conducted on slightly saline soil. The experiment consisted of three groups, each containing 100 kg of saline-alkali soil. The soil was tested using gypsum, a self-made soil conditioner (HJ-t), and a purchased soil conditioner (SDL), respectively. Sampling was conducted every fifteen days at a depth of 0.15 m for three consecutive cycles. Soil testing was performed according to the standard CJT340-2016 for greening planting soils. The test results are shown in the table below.

[0053] Table 1. Test results of soil conditioner application effects.

[0054]

[0055] The results show that:

[0056] ①. Soil improvement tests were conducted using gypsum, homemade soil conditioner, and purchased soil conditioner. Through three testing cycles, all three agents were effective in adjusting soil pH, with HJ-t and SDL showing more significant effects.

[0057] ②. In the total nitrogen test, it was found that HJ-t had the most obvious effect on soil nitrogen supplementation, mainly because the compound components in HJ-t amendment played a key role in ammonia nitrogen conversion.

[0058] ③. In the aeration porosity test, it was found that the soil compaction was the highest when gypsum was used as a conditioner. During the 45-day test, the gypsum gradually solidified, and the soil compacted rapidly. When HJ-t was used as a conditioner, the porosity was improved. During the process of the soil drying out completely, the porosity was finally maintained at 15.2%, which effectively improved the soil looseness. When SDL was used as a conditioner, the porosity was improved most significantly. However, since the porosity of the dried soil reached 16.9%, the porosity was too high, which could easily cause soil erosion during irrigation.

[0059] In summary, the homemade soil conditioner (HJ-t) can effectively adjust the pH value of low-salt-alkali land, increase the total nitrogen content of the soil, and increase soil looseness, showing significant advantages compared with similar products.

[0060] (2) Application Test 2:

[0061] Soil composition tests were conducted at different depths using slightly saline soil as the subject. A self-made soil conditioner (HJ-t) and gypsum were used for testing. Soil samples were taken at depths of 0.15m, 0.30m, and 0.45m. Soil testing was performed according to the standard CJT340-2016 for greening planting soils. The test results are shown in the table below:

[0062] Table 2 Soil Permeability Test Table

[0063]

[0064] The results show that:

[0065] ①. Soil permeability tests were conducted using gypsum and a self-made soil conditioner (HJ-t). Because gypsum has low levels of water-soluble nitrogen and readily available potassium, these two components were not effectively replenished in the soil during the test. In contrast, HJ-t contains ammonium sulfate and potassium chloride in proportion, and both components are present in soil layers at different depths with ideal content. The load-bearing capacity of the calcium carbonate microcrystals in the conditioner also plays a crucial role in soil penetration.

[0066] ②. Soil permeability tests were conducted using gypsum and a self-made soil conditioner (HJ-t). The available sulfur content in soil layers at different depths showed that gypsum had poor soil permeability due to its available sulfur content, and the sulfur content in the soil layers decreased very quickly. In contrast, using HJ-t as a soil conditioner resulted in a more ideal available sulfur content in deeper soil layers. This is mainly because gypsum, as a soil conditioner, caused a certain degree of soil compaction, resulting in poor soil permeability. Furthermore, the sulfur in calcium sulfate exists in a slightly water-soluble solid form, which has poor soil absorption. In contrast, the sulfur in HJ-t exists in the form of ammonium sulfate, which is easily soluble in water and has good soil permeability.

[0067] ③. Soil permeability tests were conducted using gypsum and a self-made soil conditioner (HJ-t). The effective calcium content of gypsum decreased rapidly during soil penetration, mainly because the platy crystal structure of gypsum is not conducive to soil penetration. In contrast, the effective calcium content of HJ-t remained relatively stable at different soil depths, mainly because the spherical crystal structure of calcium carbonate has soil penetration power, thus improving the efficiency of soil improvement.

[0068] Conclusion: The self-made soil conditioner (HJ-t) can effectively increase the content of water-soluble ammonia, available potassium, available sulfur and available calcium in deep soil, and has a good soil improvement effect. It also shows that using light calcium carbonate as a loading agent has excellent soil penetration ability.

[0069] Application example:

[0070] In traditional agricultural pesticide synthesis, the treatment of "three wastes" (waste gas, wastewater, and solid waste) is a major technical challenge. This invention establishes a low-carbon and green process route. This invention is implemented in the salt-making industry, where desalination wash water enters the salt-making system for secondary salt production, resulting in zero emissions of "three wastes."

[0071] In the field of agricultural technology, economic costs are crucial to the promotion and application of technology. This invention establishes a three-dimensional model for soil improvement based on resource recycling, realizing comprehensive resource utilization and providing practical space for the promotion of this technology in other provinces. This invention achieves the recycling of desalination wash water and reaction liquid, and utilizes the compounded potassium chloride raw material derived from by-products of the salt industry, maximizing comprehensive resource utilization, reducing costs, and possessing significant practical value.

[0072] The above description is merely a preferred embodiment of the present invention. It should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments, but can be used in various other combinations, modifications, and environments. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing a soil conditioner based on saline gypsum, characterized in that: Includes the following steps: (i) Raw material washing and desalination process A three-stage circulating elution process is used to clean and desalinate saline gypsum raw materials. The wash water generated from the first stage of elution is recycled to the salt production system as a raw material for salt production. The wash water generated from the second stage of elution is used for the first stage of elution of the next batch of raw materials. The wash water generated from the third stage of elution is used for the second stage of elution of the next batch of raw materials. This cycle is repeated to achieve zero wastewater discharge from the elution process. (ii) Catalytic reaction process A solid-liquid phase catalytic reaction is carried out using a phase transfer catalyst as a medium. Specifically, a base liquid is formed by mixing 80% ammonia water with an equivalent proportion of ammonium chloride as a phase transfer catalyst. The gypsum raw material treated in step (i) is prepared into a gypsum slurry with a solid-liquid ratio of 1:1 and a 60% ammonium bicarbonate solution are added countercurrently to the reactor containing the base liquid to carry out a solid-liquid phase catalytic conversion reaction, generating a reaction mixture containing light calcium carbonate. (iii) Separation and compounding process After sedimentation and static separation, the mixture is recycled and compounded. Specifically, the reaction mixture obtained in step (ii) is sedimented and separated to obtain an upper clear liquid and a lower slurry. The upper clear liquid is supplemented with a phase transfer catalyst and then recycled as the bottom liquid in the next batch of step (ii). The lower slurry is used to recover light calcium carbonate and ammonium sulfate and is compounded with potassium chloride to obtain a new type of soil conditioner.

2. The method for preparing the soil conditioner based on saline gypsum according to claim 1, characterized in that: In step (ii), ammonia water with a concentration of 80% and ammonium chloride in an equivalent ratio are mixed as a phase transfer catalyst for the reaction, with an addition ratio of 25% of the main raw material.

3. The method for preparing the soil conditioner based on saline gypsum according to claim 1, characterized in that: In step (ii), the reaction temperature is 25℃-30℃, the reaction time is 3-5 hours, and the stirring rate of the reactor is 300r / h.

4. The method for preparing the soil conditioner based on saline gypsum according to claim 1, characterized in that: In step (iii), the compounded potassium chloride additive accounts for 15%-30% of the dry basis mass of the lower layer slurry.

5. The method for preparing the soil conditioner based on saline gypsum according to claim 4, characterized in that: The compounded potassium chloride auxiliary material comes from salt production byproducts.

6. A soil conditioner prepared by the method according to any one of claims 1-5, characterized in that: Its active ingredient is light calcium carbonate microcrystals, which are loaded with potassium and nitrogen elements.

7. The soil conditioner according to claim 6, characterized in that: The calcium carbonate microcrystals have a particle size of 50µm-100µm and are microspherical crystals.

8. The application of a soil conditioner prepared by any one of claims 1-5 in improving soil compaction, reshaping soil aggregate structure, expanding soil pore diameter, and improving the nutrient environment of deep soil.

9. The application according to claim 8, characterized in that: The active ingredient of the soil conditioner is potassium- and nitrogen-loaded light calcium carbonate microcrystals, which reshape the soil aggregate structure and expand the soil pore diameter through the soil permeability of the microcrystals.

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