Preparation and application of titanium gypsum-plant ash composite soil conditioner embedded pellets

Abstract

The invention discloses a preparation method of titanium gypsum-plant ash composite soil conditioner embedded pellets, which comprises the following steps: step 1, mixing titanium gypsum and plant ash to obtain a titanium gypsum-plant ash composite soil conditioner; step 2, soaking sodium alginate in ultrapure water, adding the titanium gypsum-plant ash composite soil conditioner, and continuously stirring to obtain a mixed solution; and step 3, pumping out the mixed solution into a CaCl2 aqueous solution to enable the mixed solution to form small balls, and standing to obtain the titanium gypsum-plant ash composite soil conditioner embedded small balls. The titanium gypsum-plant ash composite soil conditioner embedded pellets have good improvement performance and plant growth promoting performance on soil with different degrees of acidification, the pH of the soil can be restored to be close to 7.0, the plant height of oat grass can be increased to about 1.5 times of the original plant height, the dry weight can be increased to about 2 times of the original plant height, and the yield of the oat grass can be increased to about 2 times of the original plant height. Meanwhile, the activity of soil urease and dehydrogenase can be promoted to be improved by about 1.7 times.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation. More specifically, the present invention relates to the preparation and application of an embedded ball of a titanium gypsum - plant ash composite soil conditioner. Background Art

[0002] Soil acidification can activate heavy metals in the soil solid phase and release them into the soil solution, thereby causing toxic effects on the roots of crops. At the same time, soil acidification will accelerate the loss of soil nutrients, resulting in a decline in soil fertility. Secondly, soil acidification will also lead to an increase in the harm degree of heavy metal pollution. In addition, soil acidification will also cause an aggravation of plant diseases, affecting the local plant diversity and soil microbial diversity. Therefore, it is urgent to take effective measures to improve acidified farmland soil and at the same time curb the continuous acidification of the soil. In particular, it is necessary to maintain the soil acidity in the tropical and subtropical regions of southern China at a low level and carry out relevant research to provide a theoretical basis for soil acidification improvement and food safety production.

[0003] Applying a soil conditioner is an effective measure to alleviate soil acidification. Using industrial solid waste processed products for soil acidification improvement can not only expand agricultural cultivated land but also reduce the stock of solid waste. Titanium gypsum is a solid industrial gypsum produced by using alkaline limestone or carbide slag to neutralize acidic waste liquid during the production of titanium dioxide by the sulfuric acid method. Its main component is dihydrate gypsum (CaSO 4 ·2H 2 O). In recent years, some scholars have utilized the characteristics of titanium gypsum containing components such as calcium source and sulfur source, and applied it to the remediation of cadmium - contaminated soil. As a soil conditioner to repair cadmium pollution in the soil, it can not only reduce the bio - availability of cadmium in the soil but also promote crop growth. Some scholars have also used titanium gypsum to prepare calcium sulfate compound fertilizer, fully utilizing secondary resources for soil improvement, which not only meets the soil's demand for calcium and sulfur but also promotes the growth of plant roots.

[0004] Plant ash is an alkaline ash formed after the combustion of firewood and straw. Its main component is potassium carbonate, and almost all the mineral elements contained in plants are present in plant ash, which can be used as a quick - acting potassium fertilizer. As an inorganic farmyard manure with a wide source and low cost, plant ash has been widely used in agricultural production and life. Chen Jie et al. selected plant ash obtained by burning agricultural rice straw as a passivator and studied its passivation effect on copper, lead, and chromium in contaminated soil. Xiang Xiao used different combinations of plant ash, lignite, and peat to passivate and repair heavy - metal - contaminated farmland soil and optimized the addition amount of this soil conditioner for the passivation efficiency of available heavy metals.

[0005] Although certain progress has been made in the research on using titanium gypsum as a soil conditioner, the exploration of using a composite soil conditioner that combines plant ash and titanium gypsum to improve acidified soil and plant growth is still insufficient. Summary of the Invention

[0006] One object of the present invention is to solve at least the above problems and / or deficiencies and to provide at least the advantages described hereinafter.

[0007] To achieve these objects and other advantages of the present invention, there is provided a method for preparing a titanium gypsum-plant ash composite soil conditioner, including: mixing titanium gypsum and plant ash powder in a mass ratio of 1-2:1-2 to obtain the titanium gypsum-plant ash composite soil conditioner.

[0008] A method for preparing an embedded ball of a titanium gypsum-plant ash composite soil conditioner includes the following steps:

[0009] Step 1: Mix titanium gypsum and plant ash to obtain a titanium gypsum-plant ash composite soil conditioner;

[0010] Step 2: Add sodium alginate to ultrapure water, and then add the titanium gypsum-plant ash composite soil conditioner, and continuously stir to obtain a mixed solution;

[0011] Step 3: Pump out the mixed solution into a CaCl 2 aqueous solution to form balls of the mixed solution, and let it stand to obtain the embedded balls of the titanium gypsum-plant ash composite soil conditioner.

[0012] Preferably, in the step 1, the mass ratio of titanium gypsum to plant ash is 1-2:1-2.

[0013] Preferably, in the step 2, the mass of sodium alginate is 2-5 wt% of the mass of ultrapure water.

[0014] Preferably, in the step 2, the mass ratio of sodium alginate to the titanium gypsum-plant ash composite soil conditioner is 1-3:1.

[0015] Preferably, in the step 2, continuously stir for 10-16 h.

[0016] Preferably, in the step 3, the concentration of the CaCl 2 aqueous solution is 3-5 wt%.

[0017] Preferably, in the step 3, let it stand at 3-5 °C for 10-16 h.

[0018] Preferably, when preparing the embedded balls of the titanium gypsum-plant ash composite soil conditioner, use modified titanium gypsum to replace titanium gypsum; the method for preparing the modified titanium gypsum includes the following steps:

[0019] S1. Mix titanium gypsum and sepiolite powder evenly at a mass ratio of 1:0.1 - 0.5, and calcine at 300 - 600 °C for 1 - 3 h to obtain a calcined product;

[0020] S2. Add the calcined product obtained in step one to a potassium carbonate solution with a concentration of 0.01 - 0.1 mol / L, stir for 30 - 60 min under microwave assistance, filter by suction, dry, grind, and sieve through a 30 - 100 mesh sieve to obtain modified titanium gypsum; wherein, the microwave power is 200 - 400 W; the mass - to - volume ratio of the mixed powder and the potassium carbonate solution is 1 g:30 - 60 mL.

[0021] Application of a titanium gypsum - plant ash composite soil conditioner prepared by the preparation method as described above in the remediation of acidified soil.

[0022] Application of a titanium gypsum - plant ash composite soil conditioner prepared by the preparation method as described above in promoting plant growth.

[0023] Application of a titanium gypsum - plant ash composite soil conditioner prepared by the preparation method as described above in enhancing the activities of soil dehydrogenase and urease.

[0024] Application of the embedded pellets of a titanium gypsum - plant ash composite soil conditioner prepared by the preparation method as described above in the remediation of acidified soil.

[0025] Application of the embedded pellets of a titanium gypsum - plant ash composite soil conditioner prepared by the preparation method as described above in promoting plant growth.

[0026] Application of the embedded pellets of a titanium gypsum - plant ash composite soil conditioner prepared by the preparation method as described above in enhancing the activities of soil dehydrogenase and urease.

[0027] Preferably, in the application as described above, the addition amount of the titanium gypsum - plant ash composite soil conditioner is 3 - 7 wt% of the soil mass.

[0028] Preferably, in the application as described above, the addition amount of the embedded pellets of the titanium gypsum - plant ash composite soil conditioner, based on the mass of the titanium gypsum - plant ash composite soil conditioner, is 3 - 7 wt% of the soil mass.

[0029] The present invention has at least the following beneficial effects: The present invention designs and prepares titanium gypsum-plant ash composite soil conditioners and their embedded pellets with different mixing ratios using industrial by-product titanium gypsum and plant ash, explores their improvement performance on acidified soil and growth promotion effect on plants, and explores the changes in soil enzyme activity. The results show that the embedded pellets of the titanium gypsum-plant ash composite soil conditioner of the present invention have good improvement performance and plant growth promotion performance for soils with different degrees of acidification. The embedded pellets of the composite soil conditioner with a specific mixing ratio can restore the pH of acidified soil to close to 7.0, and can increase the plant height of oat grass to about 1.5 times the original, and increase the dry weight to about 2 times the original. At the same time, it can promote the activity of soil urease and dehydrogenase to increase by about 1.7 times. The present invention provides new ideas and theoretical guidance for the industrial solid waste reuse and acidified soil improvement practice.

[0030] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Brief Description of the Drawings

[0031] Figure 1 Plant height and dry weight of oat grass at 30 days after the titanium gypsum-plant ash composite soil conditioner prepared in Examples 1 to 3 was used to improve soils with different pH values; wherein, A-C: plant height of oat grass when the initial soil pH was 4.5, 5.5, and 6.5 respectively; D-F: dry weight of oat grass when the initial soil pH was 4.5, 5.5, and 6.5 respectively;

[0032] Figure 2 Plant height and dry weight of oat grass at 30 days after the titanium gypsum-plant ash composite soil conditioner prepared in Examples 4 to 6 was used to improve soils with different pH values; wherein, A-C: plant height of oat grass when the initial soil pH was 4.5, 5.5, and 6.5 respectively; D-F: dry weight of oat grass when the initial soil pH was 4.5, 5.5, and 6.5 respectively;

[0033] Figure 3 Dehydrogenase activity and urease activity of soil at 30 days after the titanium gypsum-plant ash composite soil conditioner prepared in Examples 4 to 6 was used to improve soils with different pH values; wherein, A-C: dehydrogenase activity of soil when the initial soil pH was 4.5, 5.5, and 6.5 respectively; D-F: urease activity of soil when the initial soil pH was 4.5, 5.5, and 6.5 respectively. Detailed Description of the Embodiments

[0034] The following further describes the present invention in detail with reference to the drawings, so that those skilled in the art can implement it according to the description in the specification.

[0035] It should be understood that terms such as "having", "comprising", and "including" as used herein do not preclude the presence or addition of one or more other elements or combinations thereof.

[0036] Preparation of the test soil and source of raw materials used in the following examples:

[0037] The original soil was sourced from the farmland soil on the back hill of Southwest University of Science and Technology (Mianyang, Sichuan Province, China) (104°31′E, 31°32′N). After air-drying the soil, it was ground in a mortar, passed through a 20-mesh soil sieve, and the initial pH of the soil was measured to be 7.28 ± 0.02. Three pH levels of 4.5, 5.5, and 6.5 were designed in the present invention. By adding different concentrations of H 2 SO 4 to the quantitative soil, the soil was brought to the required initial pH value. The titanium gypsum was sourced from Panzhihua vanadium-titanium tailings, and the titanium gypsum used in the experiment was the aged titanium gypsum. The plant ash was purchased from Jinan Shengyuan Chemical Fertilizer Co., Ltd., and it was dried and ground for standby.

[0038] Example 1

[0039] A preparation method of a titanium gypsum-plant ash composite soil conditioner, comprising: mixing titanium gypsum and plant ash powder in a mass ratio of 1:2 to obtain a titanium gypsum-plant ash composite soil conditioner.

[0040] Example 2

[0041] This example is basically the same as Example 1, except that the mass ratio of titanium gypsum to plant ash in this example is 1:1.

[0042] Example 3

[0043] This example is basically the same as Example 1, except that the mass ratio of titanium gypsum to plant ash in this example is 2:1.

[0044] Example 4

[0045] A preparation method of an embedded ball of a titanium gypsum-plant ash composite soil conditioner, comprising the following steps:

[0046] Step 1: Mix titanium gypsum and plant ash powder in a mass ratio of 1:2 to obtain a titanium gypsum-plant ash composite soil conditioner;

[0047] Step 2: Soak 3 g of sodium alginate in 100 mL of ultrapure water, add 1.5 g of the titanium gypsum-plant ash composite soil conditioner, and continuously stir with a mechanical stirring table for 12 h to obtain a mixed solution;

[0048] Step 3: Pump out the mixed solution through a peristaltic pump into 4 wt% CaCl 2In an aqueous solution, the mixture is formed into small balls, which are left standing at 4°C for 12 h for crosslinking. After the crosslinking is completed, titanium gypsum - plant ash composite soil conditioner - embedded small balls are obtained and stored in a refrigerator at 4°C for later use.

[0049] Example 5

[0050] This example is basically the same as Example 4, except that the mass ratio of titanium gypsum to plant ash in this example is 1:1.

[0051] Example 6

[0052] This example is basically the same as Example 4, except that the mass ratio of titanium gypsum to plant ash in this example is 2:1.

[0053] Example 7

[0054] In this example, modified titanium gypsum is used to replace titanium gypsum, and the remaining steps are the same as those in Example 6;

[0055] The preparation method of the modified titanium gypsum includes the following steps:

[0056] Step 1: Mix titanium gypsum and sepiolite powder evenly according to a mass ratio of 1:0.3, and calcine at 400°C for 2 h to obtain a calcined product;

[0057] Step 2: Add the calcined product obtained in Step 1 to a 0.05 mol / L potassium carbonate solution, stir for 40 min under 300 W microwave assistance, filter by suction, dry, grind, and pass through a 50 - mesh sieve to obtain modified titanium gypsum; wherein, the mass - to - volume ratio of the calcined product to the potassium carbonate solution is 1 g:50 mL.

[0058] Example 8

[0059] In this example, modified titanium gypsum is used to replace titanium gypsum, and the remaining steps are the same as those in Example 6;

[0060] The preparation method of the modified titanium gypsum includes the following steps:

[0061] Step 1: Calcinate titanium gypsum at 400°C for 2 h to obtain a calcined product;

[0062] Step 2: Add the calcined product obtained in Step 1 to a 0.05 mol / L potassium carbonate solution, stir for 40 min under 300 W microwave assistance, filter by suction, dry, grind, and pass through a 50 - mesh sieve to obtain modified titanium gypsum; wherein, the mass - to - volume ratio of the calcined product to the potassium carbonate solution is 1 g:50 mL.

[0063] Comparative Example 1

[0064] A preparation method of plant ash - embedded small balls includes the following steps:

[0065] Step 1: Soak 3 g of sodium alginate in 100 mL of ultrapure water, add 1.5 g of plant ash, and continuously stir with a mechanical stirring table for 12 h to obtain a mixed solution.

[0066] Step 2: Pump out the mixed solution through a peristaltic pump into an aqueous solution of 4 wt% CaCl 2 to form small balls, and let them stand at 4 °C for 12 h for crosslinking. After the crosslinking is completed, plant ash-embedded small balls are obtained and stored in a refrigerator at 4 °C for later use.

[0067] Applications of the titanium gypsum-plant ash composite soil conditioner and its embedded small balls prepared in Examples 1-8 in improving acidified soil and promoting plant growth include:

[0068] Pot experiment

[0069] Select oat grass that grows rapidly and has low requirements for soil fertility. During the entire soil experiment, no fertilizers or other nutrients are added except for the tested soil conditioner. According to the orthogonal experimental design, the titanium gypsum-plant ash composite soil conditioner is uniformly added to the acidified soil with an initial pH adjusted to 4.5, 5.5, or 6.5 at an addition amount of 3 wt%, 5 wt%, or 7 wt% respectively. Each pot of different initial pH soil is 100 g, and three parallel replicates are set for each group. The experimental period is 30 days. During this period, the greenhouse temperature is maintained at 25 ± 2 °C, the humidity is maintained at 80% ± 2%, and watering is carried out every 3 days. After 30 days, plant growth indicators such as the plant height and dry weight of oat grass are measured, and soil samples are collected, passed through a 2 mm sieve, and after being divided into portions, part is used to measure the soil pH, and the other part is used to measure the soil enzyme activity.

[0070] Measurement of soil pH

[0071] Before measuring the soil pH, first calibrate the pH meter. Then, add ultrapure water to the soil to be tested, and the mass ratio of the soil to be tested to the ultrapure water is 1:2.5. Subsequently, stir the system with a magnetic stirrer for 2 h, and then measure the pH value of the soil suspension through the pH meter.

[0072] Measurement of plant growth indicators

[0073] Carefully take out the oat grass and its roots, and measure the plant height of the oat grass. Gently wash away the impurities attached to the surface of the oat grass roots with distilled water, and then measure the dry weight of the oat grass after being fully dried in an oven.

[0074] Measurement of soil enzyme activity

[0075] Dehydrogenase (S-DHA) activity: 100 μL of 2,3,5-triphenyltetrazolium chloride (TTC) was mixed with 0.05 g of soil, and the reaction was carried out on a shaker at 120 rpm and 37 °C for 24 h. Thereafter, 900 μL of methanol was added, and the reaction was carried out on a shaker at 120 rpm and 25 °C for 60 min. After centrifugation, the supernatant was taken for colorimetric determination, and the dehydrogenase activity at 485 nm was quantified by a microplate analyzer.

[0076] Urease (S-UE) activity: 20 μL of toluene was added to 0.05 g of soil, and after thorough mixing, it was allowed to stand at room temperature for 15 min to disrupt the cell walls of soil microorganisms. After enzymatic hydrolysis, 90 μL of urea and 190 μL of buffer were added, and the reaction was carried out at 37 °C for 24 h. After centrifugation and staining, the urease activity at 578 nm was quantified by a microplate analyzer.

[0077] Data analysis

[0078] The data such as soil pH, enzyme activity, and plant growth indicators measured in this experiment were statistically analyzed using IBM SPSS Statistics 27 and plotted using Origin 2018.

[0079] Results and discussion

[0080] (1) Effects of adding the titanium gypsum-plant ash composite soil conditioner prepared in Examples 1 to 3 on soil pH

[0081] As shown in Table 1, Table 2, and Table 3, the CK group represents the pH values of soils with different initial pH values without adding soil conditioners. The results show that the acidity and alkalinity of the tested soils do not change significantly within 30 days. The addition of alkaline plant ash and titanium gypsum will significantly increase the soil pH. The effect of plant ash is stronger in strongly acidic soils (Table 1), the effect of titanium gypsum is stronger in weakly acidic soils (Table 2), and in soils close to neutral, the effects of plant ash and titanium gypsum are comparable (Table 3). This indicates that both soil conditioners have a certain improvement effect on acidified soils. By adjusting the mixing ratio of titanium gypsum and plant ash, in soils close to neutral, the soil improvement performance of the plant ash - titanium gypsum composite soil conditioner is similar to that of the single conditioner (Table 3); in weakly acidic soils, the appropriate introduction of plant ash (such as 1:1 / 2:1) can synergistically enhance the effects of both with titanium gypsum, which originally has stronger soil improvement performance. However, when there is more plant ash (such as 1:2), the soil acidification improvement performance of the composite soil conditioner decreases instead, and is even slightly weaker than that of single titanium gypsum, showing the dominant role of titanium gypsum in the improvement of weakly acidic soils (Table 2); in strongly acidic soils, the introduction of plant ash, which originally has stronger soil improvement performance, does not significantly enhance the soil acidification improvement performance of the composite soil conditioner compared to single plant ash. Even the introduction of a small amount of titanium gypsum (1:2) makes its effect weaker, but it is still stronger than single titanium gypsum, and with the increase of titanium gypsum, the improvement performance slightly increases, showing the important influence of titanium gypsum on the composite soil conditioner in strongly acidified soils (Table 1). In addition, when the addition amount of the soil conditioner is 5wt%, generally the soil acidification improvement performance of each soil conditioner is the best. Lower or higher addition amounts may lead to a certain degree of weakening of its improvement performance, which may involve the complex biochemical interactions among soil conditioners - soil microorganisms - plants. In summary, the titanium gypsum - plant ash composite soil conditioner is more suitable for the improvement of weakly acidic soils (pH 5.5), and titanium gypsum plays a key role. When the addition ratio of titanium gypsum - plant ash is 2:1 and the addition amount is 5wt%, the soil acidification improvement performance is generally the best. Therefore, subsequent experiments are carried out with a 5wt% addition amount of the soil conditioner.

[0082] Table 1 pH change of soil with an initial pH of 4.5 after being improved by soil conditioner at 30 days

[0083]

[0084] Table 2 pH change of soil with an initial pH of 5.5 after being improved by soil conditioner at 30 days

[0085]

[0086]

[0087] Table 3 pH change of soil with an initial pH of 6.5 after being improved by soil conditioner at 30 d

[0088]

[0089] Note: CK represents the control group without adding soil conditioner; C represents plant ash; T represents titanium gypsum. 3%, 5%, and 7% represent the addition amounts of various soil conditioners.

[0090] (2) Effects of adding the titanium gypsum - plant ash composite soil conditioner prepared in Examples 1 - 3 on the plant height and dry weight of oat grass

[0091] As Figure 1 shown, the plant height and dry weight of oat grass were measured at 30 d after adding the soil conditioner. The results showed that the introduction of single plant ash could improve the plant height and dry weight of oat grass to a certain extent, and the improvement effect of single titanium gypsum on the plant height and dry weight of oat grass was generally stronger, indicating that plant ash and titanium gypsum could effectively promote the growth of oat grass, and the growth - promoting performance of titanium gypsum was stronger. After adding the two soil conditioners in a certain proportion, it was found that the appropriate introduction of the composite soil conditioner could increase the plant height of oat grass, but the effect was similar to that of single titanium gypsum. At the same time, the appropriate introduction of the composite soil conditioner could effectively increase the dry weight of oat grass, and the effect was stronger than that of single titanium gypsum. And in the weakly acidic soil (pH = 5.5), when the addition amount of the composite soil conditioner was 5 wt% and the mixing ratio was 1:2, the promotion effect of the soil conditioner on the dry weight of oat grass was the strongest, which once again confirmed the conclusion that titanium gypsum was more suitable for improving weakly acidic soil, showing its outstanding potential in improving plant biomass. Generally, when the addition amount of the soil conditioner was 5 wt%, the promotion effect on the dry weight and plant height of oat grass was the best. Lower or higher addition amounts might lead to a certain degree of weakening of its growth - promoting performance. The growth - promoting performance of the soil conditioner was affected by its complex chemical components and its soil acidification improvement performance, and might change the soil microbial community structure, thus affecting plant growth. In summary, the titanium gypsum - plant ash composite soil conditioner had the strongest plant growth - promoting performance in the weakly acidic soil (pH = 5.5), and when the addition amount of the soil conditioner was 5 wt%, the growth - promoting performance on plants was the strongest in general. Therefore, subsequent experiments were carried out with a 5 wt% addition amount of the soil conditioner.

[0092] (3) Effects of adding the titanium gypsum - plant ash composite soil conditioner - embedded pellets prepared in Examples 4 - 6 on soil pH

[0093] To obtain a soil conditioner with slow release and longer-lasting effects, the present invention further explored the influence of embedding treatment on the performance of the conditioner. Composite soil conditioner embedding pellets were prepared from titanium gypsum and plant ash in a mixing ratio of 1:2, 1:1, or 2:1 through sodium alginate, and their soil acidification improvement performance was tested 30 days after addition, with an addition amount of 5 wt% (based on the mass of the titanium gypsum-plant ash composite soil conditioner, the same hereinafter). As shown in Table 4, in the CK group, no conditioner was added to the soil with different initial pH values, and the results showed that the soil acidity and alkalinity did not change significantly within 30 days. After adding the embedding pellets of plant ash and the composite soil conditioner prepared by mixing plant ash and titanium gypsum in a certain ratio to the soil for 30 days, the pH values of the soil with different initial pH values all increased significantly, and the effects of the embedding pellets of the composite soil conditioner in Examples 4 to 6 were significantly better than those of the single plant ash embedding pellets in Comparative Example 1. For soils with different acidities, the mixing ratio of titanium gypsum and plant ash can be adjusted to repair the acidified soil to make its pH close to neutral to the greatest extent. For example, in a strongly acidic soil (pH = 4.5), a mixing ratio of 2:1 can restore the pH of the acidified soil to 6.87 ± 0.19; in a weakly acidic soil (pH = 5.5), mixing ratios of 1:2 or 1:1 can restore the pH of the acidified soil to 7.06 ± 0.25 or 6.96 ± 0.34 respectively; in a soil close to neutral (pH = 6.5), a mixing ratio of 1:1 can restore the soil pH to 7.15 ± 0.23. After making the embedding pellets from plant ash and titanium gypsum in a specific ratio and adding them to the soil, the soil acidification improvement performance equivalent to that of directly adding the composite soil conditioner can be achieved in weakly acidic soils; at the same time, the embedding pellets of the composite soil conditioner can obtain better soil acidification improvement performance compared with directly adding the composite soil conditioner in strongly acidic soils, improving the acidified soil improvement of the composite soil conditioner under strongly acidic conditions; for soils close to neutral, the effect of the embedding pellets of the composite soil conditioner is more moderate compared with directly adding the composite soil conditioner, so as to avoid excessive increase in soil alkalinity due to the addition of the soil conditioner. In summary, making the embedding pellets from plant ash and titanium gypsum in a specific ratio can not only improve the soil acidification improvement performance of the composite soil conditioner but also expand its application in the improvement of soils with different degrees of acidification.

[0094] Table 4 pH changes of soils with different initial pH values 30 days after being improved by soil conditioner embedding pellets

[0095]

[0096]

[0097] Note: CK represents the control group without adding soil conditioner; 1:2\1:1\2:1 represent the mixing ratios of titanium gypsum and plant ash in the embedded pellets; C represents plant ash; Q represents the soil conditioner embedded pellets. Oat grass was planted in each group.

[0098] (4) Effects of adding the titanium gypsum-plant ash composite soil conditioner embedded pellets prepared in Examples 4-6 on the plant height and dry weight of oat grass

[0099] As Figure 2 shown, the plant height and dry weight of oat grass were measured 30 days after adding the soil conditioner embedded pellets. The results showed that the introduction of single plant ash embedded pellets could slightly increase the plant height and dry weight of oat grass, while the titanium gypsum-plant ash composite soil conditioner embedded pellets had a stronger effect on increasing the plant height and dry weight of oat grass. Moreover, compared with directly adding the composite soil conditioner, the plant growth-promoting performance of the composite soil conditioner embedded pellets was significantly superior, indicating that sodium alginate embedding effectively improved the plant growth-promoting performance of the soil conditioner. In addition, different from Figure 1 the conclusion that the obtained composite soil conditioner had the strongest plant growth-promoting performance in weakly acidic soil, the embedded composite soil conditioner also achieved good plant growth-promoting performance in strongly acidic soil (pH = 4.5) and near-neutral soil (pH = 6.5). Even in strongly acidic soil (pH = 4.5), the plant height of oat grass was higher after adding the composite soil conditioner embedded pellets prepared in a 2:1 ratio than in weakly acidic soil (pH = 5.5), and the plant height and dry weight of oat grass were the highest after adding the composite soil conditioner embedded pellets prepared in a 1:2 ratio in near-neutral soil (pH = 6.5). This was similar to the effect of sodium alginate embedding on the soil acidification improvement performance of the composite soil conditioner, that is, it improved the plant growth-promoting performance of the composite soil conditioner under strongly acidic and near-neutral conditions, and once again proved from the perspective of plant growth-promoting performance that sodium alginate embedding could not only improve the excellent performance of the composite soil conditioner but also expand its application in soil improvement with different degrees of acidification.

[0100] (5) Effects of adding the titanium gypsum-plant ash composite soil conditioner embedded pellets prepared in Examples 4-6 on soil enzyme activity

[0101] Dehydrogenase present in the soil can act as an intermediate carrier of hydrogen and catalyze the dehydrogenation reaction of soil organic matter such as sugars, organic acids, and amino acids, which can reflect the metabolic activity of soil microorganisms to a certain extent; urease in the soil can catalyze the decomposition of urea into ammonia, which can promote the absorption and utilization of nitrogen in the soil by plants and can reflect the nitrogen fertility of the soil to a certain extent. The activities of soil dehydrogenase and urease were measured 30 days after adding the soil conditioner embedded pellets. As Figure 3As shown, the introduction of single plant ash-embedded pellets can slightly enhance the activities of soil dehydrogenase and urease, while the enhancement effect of the composite soil conditioner-embedded pellets is significantly stronger. This is consistent with the conclusion that the composite soil conditioner-embedded pellets are superior to the single plant ash-embedded pellets in terms of soil acidification improvement performance and plant growth promotion performance described above. The composite soil conditioner-embedded pellets have a better effect on improving soil enzyme activity. The composite soil conditioner-embedded pellets prepared in a specific proportion have a significant enhancing effect on the enzyme activities of soils with different degrees of acidification, and the application range is relatively wide. In soils with relatively strong relevant enzyme activities, the growth and metabolism of plants will be more vigorous, and the excellent effect of the composite soil conditioner-embedded pellets on enhancing soil enzyme activity can, to a certain extent, explain its excellent plant growth promotion performance.

[0102] This invention conducts research on the solid waste recycling of industrial by-product titanium gypsum and plant ash, mixes the two materials in a specific proportion to prepare a composite soil conditioner, and embeds it with sodium alginate to prepare pellets, explores the improvement effects on soils with different degrees of acidification and plant growth promotion performance under different addition amounts and different mixing ratios, and characterizes the enzyme activities of the improved soils to comprehensively evaluate the application potential of the titanium gypsum-plant ash composite soil conditioner in acidified soil improvement. The main conclusions are as follows:

[0103] (1) The titanium gypsum-plant ash composite soil conditioner-embedded pellets have good soil acidification improvement performance in soils with different degrees of acidification.

[0104] Single plant ash is suitable for strongly acidic soils, single titanium gypsum and the titanium gypsum-plant ash composite soil conditioner are suitable for weakly acidic soils, and their effects are equivalent in soils close to neutral. Titanium gypsum plays a key role in the soil acidification improvement performance of the composite soil conditioner. Embedding the titanium gypsum-plant ash composite soil conditioner with sodium alginate can not only improve its soil acidification improvement performance but also expand its application range, enabling it to achieve good soil acidification improvement performance in the improvement of soils with different degrees of acidification.

[0105] (2) The titanium gypsum-plant ash composite soil conditioner-embedded pellets have good plant growth promotion performance in soils with different degrees of acidification.

[0106] Wood ash and titanium gypsum can effectively promote the increase in the plant height and dry weight of oat grass. Among them, titanium gypsum has stronger plant growth-promoting properties. The single titanium gypsum and the titanium gypsum-wood ash composite soil conditioner have stronger plant growth-promoting properties in weakly acidic soils. Titanium gypsum has great potential in improving plant biomass. Encapsulating the titanium gypsum-wood ash composite soil conditioner with sodium alginate can not only enhance the plant growth-promoting properties of the composite soil conditioner but also expand its application in soil improvement under different degrees of acidification, making it still have good plant growth-promoting properties in strongly acidic and near-neutral soils.

[0107] (3) The encapsulated pellets of the titanium gypsum-wood ash composite soil conditioner have good effects on enhancing soil enzyme activities in soils with different degrees of acidification.

[0108] The introduction of the encapsulated pellets of single wood ash can slightly enhance the activities of soil dehydrogenase and urease, while the enhancement of soil enzyme activities by the encapsulated pellets of the composite soil conditioner is more obvious. The encapsulated pellets of the composite soil conditioner prepared in a specific proportion have significant enhancement effects on the enzyme activities of soils with different degrees of acidification and have a wide range of applications. The effective enhancement of soil enzyme activities by the encapsulated pellets of the titanium gypsum-wood ash composite soil conditioner is beneficial to promoting plant growth and further improving acidified soils.

[0109] (4) When the addition amount of the soil conditioner is 5 wt%, its soil acidification improvement performance and plant growth-promoting performance are the strongest.

[0110] When the addition amount of the soil conditioner is 5 wt%, generally, the soil acidification improvement performance of each soil conditioner is the best, and at the same time, the promotion effects on the dry weight and plant height of oat grass are also the best. Lower or higher addition amounts may cause a certain degree of weakening of its soil acidification improvement performance and growth-promoting performance, which involves complex soil conditioner-soil microorganism-plant biochemical interactions.

[0111] In summary, the embedded pellets designed in the present invention, which are prepared according to a specific mixing ratio, have good soil acidification improvement performance, plant growth promotion performance, and soil enzyme activity enhancement effect. Different mixing ratios can be adopted for soils with different degrees of acidification to achieve soil improvement suitable for soils with different degrees of acidification. In the acidified soil improvement by the titanium gypsum - plant ash composite soil conditioner embedded pellets, the embedding effect of sodium alginate effectively improves the action mode and application effect of the titanium gypsum - plant ash composite soil conditioner. To a certain extent, this benefits from the improvement effect of sodium alginate gel pellets on the soil structure. On the one hand, the gel - like structure helps to evenly distribute plant ash and titanium gypsum in the soil, enhancing their interaction with the soil, effectively improving soil air permeability, water retention, and fertilizer retention, and promoting the activities of soil microorganisms. On the other hand, sodium alginate can embed plant ash and titanium gypsum inside the gel, enabling their slow release to achieve a slow - release effect, thereby achieving long - term soil improvement. In addition, the sodium alginate - embedded titanium gypsum - plant ash composite soil conditioner can be directly spread on the soil surface or mixed into the soil, effectively reducing the flying loss of the soil conditioner and improving the application efficiency.

[0112] In order to further improve the acidified soil improvement performance and plant growth promotion effect of the titanium gypsum - plant ash composite soil conditioner embedded pellets, in Example 7 of the present invention, modified titanium gypsum is used to replace titanium gypsum. By mixing sepiolite powder with excellent adsorption and dispersion properties with titanium gypsum and calcining them, and then treating them in a potassium carbonate solution, its dispersibility and stability can be improved, its activity can be enhanced, the repair performance for acidified soil can be improved, and at the same time, it can fix the available nutrients in the soil and promote plant growth. As shown in Table 5, 30 days after adding the composite soil conditioner embedded pellets made by mixing plant ash and modified titanium gypsum in a mass ratio of 2:1 into the soil, the soil pH values of soils with different initial pH values all increased significantly. Compared with Example 6, the repair effects of Examples 7 - 8 are better. As shown in Table 6, the titanium gypsum - plant ash composite soil conditioner embedded pellets prepared in Examples 7 - 8 have better plant growth promotion performance. Compared with Example 6, the oat grass plant height in Examples 7 - 8 is higher.

[0113] Table 5 pH changes of soils with different initial pH values 30 days after being improved by soil conditioner embedded pellets

[0114] Initial pH CK Example 6 Example 7 Example 8 4.5 4.62±0.27 6.87±0.19 7.03±0.17 6.98±0.20 5.5 5.36±0.16 6.27±0.31 6.74±0.24 6.55±0.26 6.5 6.43±0.25 7.38±0.25 7.28±0.23 7.35±0.29

[0115] Table 6 Oat grass plant height 30 days after the composite soil conditioner embedded pellets improve soils with different pH values

[0116]

[0117] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those skilled in the art, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. A method for preparing titanium gypsum-wood ash composite soil conditioner embedded beads, characterized in that: The following steps are involved: Step 1: Mix titanium gypsum and wood ash to obtain a titanium gypsum-wood ash composite soil conditioner; Step 2: Add sodium alginate to ultrapure water, then add titanium gypsum-wood ash composite soil conditioner, and continue stirring to obtain a mixed solution; Step 3: Pump the mixed solution into a CaCl2 aqueous solution to form small balls, and let the mixed solution stand to obtain titanium gypsum-wood ash composite soil conditioner embedded small balls.

2. The method for preparing a titanium gypsum-wood ash composite soil conditioner embedded pellet according to claim 1, characterized in that: In the step 1, the mass ratio of titanium gypsum to wood ash is 1-2:1-2.

3. The method for preparing a titanium gypsum-wood ash composite soil conditioner embedded pellet according to claim 1, characterized in that: In the step 2, the mass of sodium alginate is 2-5 wt % of the mass of ultrapure water.

4. The method for preparing a titanium gypsum-wood ash composite soil conditioner embedded pellet according to claim 1, characterized in that: In the step 2, the mass ratio of sodium alginate to titanium gypsum-wood ash composite soil conditioner is 1 to 3:

1.

5. The method for preparing a titanium gypsum-wood ash composite soil conditioner embedded pellet according to claim 1, characterized in that: In the step 2, stirring is continued for 10 to 16 hours.

6. The method for preparing a titanium gypsum-wood ash composite soil conditioner embedded pellet according to claim 1, characterized in that: In the step 3, the concentration of the CaCl2 aqueous solution is 3-5 wt%; and the step of standing is standing at 3-5°C for 10-16 hours.

7. The method for preparing a titanium gypsum-wood ash composite soil conditioner embedded pellet according to claim 1, characterized in that: In the step 1, modified titanium gypsum is used to replace titanium gypsum; wherein the preparation method of the modified titanium gypsum comprises the following steps: S1. Titanium gypsum and sepiolite powder are uniformly mixed in a mass ratio of 1:0.1-0.5, and calcined at 300-600° C. for 1-3 h to obtain a calcined product; S2. Add the calcined product obtained in step 1 to a 0.01-0.1 mol / L potassium carbonate solution, stir for 30-60 min under microwave assistance, filter, dry, and grind through a 30-100 mesh sieve to obtain modified titanium gypsum; wherein the microwave power is 200-400 W; and the mass volume ratio of the mixed powder and the potassium carbonate solution is 1 g:30-60 mL.

8. Use of titanium gypsum-wood ash composite soil conditioner embedded beads prepared by the preparation method according to any one of claims 1 to 7 in acidified soil remediation.

9. Use of titanium gypsum-wood ash composite soil conditioner embedded beads prepared by the preparation method according to any one of claims 1 to 7 in promoting plant growth.

10. Use of titanium gypsum-wood ash composite soil conditioner embedded beads prepared by the preparation method according to any one of claims 1 to 7 in enhancing soil dehydrogenase and urease activities.

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