Soil heavy metal passivator with fertilizer characteristics as well as preparation process and application of soil heavy metal passivator

Abstract

The invention belongs to the cross technical field of material application and fertilizer application, and discloses a soil heavy metal passivator with fertilizer characteristics as well as a preparation process and application of the soil heavy metal passivator. The preparation process comprises the following steps: uniformly mixing an equal amount of alkaline substance and plant biomass, controlling the water content of the material to be 55-65%, and premixing and reacting for a certain period of time under the conditions of compaction and room temperature; the method comprises the following steps: uniformly mixing a wet solid material with equivalent or 1 / 2 equivalent CS2 under a spraying condition after the alkalization reaction of the plant biomass, and carrying out a yellowing reaction for a period of time under the conditions of continuously keeping the water content of the material at 55-65% and room temperature to obtain a plant biomass xanthate product; and spreading the product, naturally air-drying, and then drying at 50-60 DEG C. The product prepared by the invention is a heavy metal passivator and a novel fertilizer, and is particularly suitable for being applied to acidic soil which is heavily polluted by heavy metals.

Description

TECHNICAL FIELD

[0002] The present application belongs to the technical field of material application and fertilizer application, and particularly relates to a soil heavy metal passivator with the characteristics of supplying crop nutrient elements and a preparation process and application thereof. BACKGROUND

[0003] Xanthates are easy to form insoluble substances with heavy metals, and are often used in heavy metal flotation, precious metal recovery and other industrial applications, such as heavy metal ion copper, nickel and other collectors. With the development of environmental science, chemical-based xanthates are derived into biomass-based xanthates to remove heavy metals from heavy metal contaminated water. Insoluble agrobased xanthates are used for copper removal in wastewater (document 1: Saswati Chakraborty, Vinod Tare, 2006. Role of various parameters in synthesis of insoluble agrobased xanthates for removal of copper from wastewater. Bioresource Technology 97:2407-2413) and sugarcane bagasse cellulose-based sodium xanthate for adsorption of heavy metal ions in water (document 2: Ke Min, Yang Lianmin, Chen Yuanxia, Chen Wenna, 2006. Preparation and application of sugarcane bagasse cellulose xanthate. Chemical Technology and Development, 35(6): 1-4). However, these xanthate preparation processes, although using different plant biomasses such as crop straw, or sugarcane bagasse, or eichhornia crassipes cellulose (with a pre-extraction step) as the basic raw material, cannot be separated from the basic characteristics of preparing xanthates in aqueous solution. In these xanthate preparations, the ratio of the amount of raw material to the amount of mother liquor (waste liquid) is 30 (g) : 480 (mL) for the former and 3 (g) : 45 (mL) for the latter, and 480 mL and 45 mL of waste liquid are produced at the end of the preparation, respectively. As a result, the large amount of waste liquid produced hinders the large-scale preparation of plant biomass-based xanthates and their practical application in environmental governance. SUMMARY

[0004] To overcome the shortcomings of preparing plant biomass xanthates in aqueous solutions and the practical problem that such xanthates cannot be prepared in large quantities, thus hindering their application in the environment, this invention aims to provide a soil heavy metal passivating agent with fertilizer properties, along with its preparation process and application. To accelerate the chemical reaction without increasing the amount of water requiring mechanical separation after the reaction, this invention designs the material reaction ratio based on the water content of moist straw and the stoichiometric dosages of alkalizing and xanthizing agents for the reaction with free hydroxyl groups in general straw. Based on this, plant biomass xanthates and plant biomass hemihydroxy salt hemixanthates are prepared as soil heavy metal passivating agents. The invention also provides results on the adsorption capacity of these agents for heavy metals and pot experiments verifying their passivation of soil heavy metals and their fertilizer-like effects.

[0005] To achieve the above objectives, the present invention provides the following technical approach: A preparation process for a soil heavy metal passivating agent that also possesses fertilizer properties includes the following steps: S1. Pre-reaction process: Alkaline substances are mixed evenly with plant biomass, and the moisture content of the material is controlled at 55% to 65%. The pre-mixing reaction is carried out for a certain period of time under compaction and room temperature conditions. S2, xanthation reaction process: The pre-reacted wet solid material is uniformly mixed with CS2 under spraying conditions, and the reaction is carried out for a period of time while maintaining the material moisture content of 55% to 65% and room temperature to obtain the reaction product plant biomass xanthate. S3. Two-step drying process: After the product is laid flat and air-dried naturally, it is then dried at 50-60℃ to obtain a soil heavy metal passivating agent.

[0006] Optionally, in step S1, an equivalent amount of KOH solution, CaO powder, or MgO powder and a measured amount of water are added to the plant biomass powder according to the active hydroxyl content of 17%, and then the mixture is thoroughly stirred with the plant biomass powder to make the overall material moisture content 55% to 65%.

[0007] Optionally, in step S2, the material obtained in step S1 is transferred to the main reactor, and 1.0 mol CS2 / 100 g plant biomass is added to the main reactor to carry out the xanthation reaction, based on the active hydroxyl content of 17% in the plant biomass.

[0008] Optionally, in step S2, the material obtained in step S1 is transferred to the main reactor, and 0.5 mol CS2 / 100 g plant biomass is added to the main reactor according to half the amount of 17% active hydroxyl groups in the plant biomass to carry out the xanthation reaction.

[0009] Furthermore, in step S1, after the material is thoroughly mixed, it is compacted and placed by pressing or squeezing. The compaction is an intermittent operation, during which the material is turned over 1 to 2 times before being compacted again.

[0010] Furthermore, in step S1, the reaction time is 48 hours and the reaction temperature is room temperature.

[0011] Furthermore, in step S2, the material is sprayed at a uniform speed while being turned and tossed until it is uniform, then compacted and set aside.

[0012] Furthermore, in step S2, the compaction and resting is an intermittent operation, during which the material is turned over 1 to 2 times and then compacted and rested, with an operation time of 24 hours and a reaction temperature of room temperature.

[0013] Preferably, the plant biomass is one of rice straw powder, sugarcane bagasse powder, corn stalk powder, and wheat straw powder.

[0014] The aforementioned soil heavy metal passivating agent is used for passivating heavy metals in soil and simultaneously as a crop fertilizer.

[0015] Compared with the prior art, the present invention has the following technical effects: The core technology of this invention overcomes the shortcomings of preparing xanthates in aqueous solutions. It eliminates the classic, cumbersome processes involved in the preparation of xanthates from excessive alkalizing and xanthating agents, aqueous solution preparation, solid-liquid separation of the product, and treatment of the mother liquor (waste liquor). Instead, it utilizes a method of preparing plant biomass xanthates under moist plant biomass conditions and stoichiometric ratios. Specifically, under moist conditions, the plant biomass undergoes an alkalization reaction with an equimolar amount of alkali (KOH, CaO, or MgO) to react with the biomass, followed by a xanthation reaction with an equimolar amount or half an equimolar amount of CS2. This yields potassium xanthate, calcium xanthate, magnesium xanthate, or hemihydroxypotassium hemixanthate, hemihydroxycalcium hemixanthate, and hemihydroxymagnesium hemixanthate. The applicant defines this as an alternative preparation process or method for plant biomass xanthates.

[0016] The structure of xanthates from plant biomass reveals that the thiogroup (-S-) on xanthic acid carries a negative charge and serves as an exchange site for cations. Upon application to the soil, this exchange site encounters heavy metal cations in the soil. The heavy metal ions exchange with the base ions on the thiogroup, and the heavy metal ions transferred to the thiogroup further react with the thiogroup to undergo precipitation, resulting in passivation of the heavy metal ions. Furthermore, since the free hydroxyl groups on plant biomass and the thiogroups on xanthic acid can coordinate to chelate and precipitate heavy metal ions, the xanthating agent can be halved during the xanthation process to prepare hemihydroxy salts and hemixanthates from plant biomass. The chelation-precipitation effect of these salts on heavy metal ions in the soil also constitutes a passivation effect.

[0017] Based on the above principles, this invention measures the adsorption capacity of plant biomass xanthate and plant biomass hemihydroxy salt hemixanthate for Cd prepared by the process of this invention, and conducts biological verification on their significant reduction of soil heavy metal absorption by potted crops and increase of crop yield. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the preparation process and effect testing of plant biomass xanthate of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0020] A preparation process for a soil heavy metal passivating agent that also possesses fertilizer properties is described in [reference]. Figure 1 This includes the following steps: S1. Pre-reaction (alkalization reaction) process: Use an equivalent amount of alkaline substance (solution or solid) to mix evenly with plant biomass, control the moisture content of the material at 55% to 65% (mass percentage), and premix and react for a certain time under compaction and room temperature conditions; S2, Main Reaction (Xanthanation Reaction) Process: The wet solid material after the pre-reaction of alkaline substances and plant biomass is uniformly mixed with an equivalent or 1 / 2 equivalent of CS2 under spraying conditions. The reaction is carried out for a period of time while maintaining the material moisture content of 55% to 65% and room temperature to obtain the reaction product plant biomass xanthate. S3. Two-step drying process of the reaction product: The product is spread out to air dry naturally, and then dried at 50-60℃ to obtain soil heavy metal passivating agent.

[0021] Specifically, corresponding to step S1 are the material conveying equipment and feeding system, including: raw material end 1: plant biomass feeding; raw material end 2: alkaline solution (KOH) feeding; raw material end 3: alkaline powder (CaO or MgO) feeding; raw material end 4: water supplement feeding during powder feeding; CS2 sampling device (raw material end 5) corresponding to step S2; the downstream process of step S3 is the crushing and inspection of the product, and the adsorption capacity of the product for heavy metals is determined after the product is crushed to 100 mesh.

[0022] As a preferred technical solution of the present invention: In step S1, 100 g (laboratory small-dose experiment) or 23 kg (large-dose shed experiment) of rice straw powder with an active hydroxyl content of 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter) is added to a pre-reactor. Correspondingly, 235 mL or 52.5 L of 4.3 mol / L KOH solution is added and thoroughly mixed with the rice straw powder, compacted, and the material moisture content is maintained at 55%–65% (mass concentration). The alkalization reaction is carried out at room temperature, and the material is compacted by pressing or squeezing. Compaction is an intermittent operation, with the material turned over 1–2 times before compaction. The operation time of step S1 is 48 h, and the reaction temperature is room temperature. In practical applications, the active hydroxyl groups in plant biomass can be 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter). The amount of plant biomass and the amount of 4.3 mol / L KOH solution can be adjusted according to the same stoichiometric ratio to maintain the moisture content of the material at 55% to 65% (mass concentration).

[0023] As a preferred technical solution of the present invention: In step S1, 100 g (laboratory small-dose experiment) of rice straw powder is added to a pre-reactor according to the active hydroxyl content of 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter). Then, 28 g of CaO powder and 207 mL of water are added, and the mixture is thoroughly stirred and compacted, maintaining a material moisture content of 55%–65% (mass concentration). The reaction is carried out under alkalization conditions at room temperature, compacted by pressing or squeezing, and left to stand. Compaction is an intermittent operation, with the material turned over 1–2 times before compaction. The operation time for S1 is 48 h, and the reaction temperature is room temperature. In practical applications, the active hydroxyl content of the plant biomass can be based on 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter), and the amount of plant biomass, CaO, and water can be adjusted according to equal stoichiometric ratios to maintain a material moisture content of 55%–65% (mass concentration).

[0024] As a preferred technical solution of the present invention: In step S1, 100 g (small-scale laboratory experiment) of rice straw powder is added to a pre-reactor based on the active hydroxyl content of 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter). Then, 20.2 g of MgO powder and 195 mL of water are added, and the mixture is thoroughly stirred and compacted, maintaining a material moisture content of 55%–65% (mass concentration). The reaction is carried out under alkalization conditions at room temperature, compacted by pressing or squeezing, and then left to stand. Compaction is an intermittent operation, with the material turned over 1–2 times before compaction. The operation time for S1 is 48 h, and the reaction temperature is room temperature. In practical applications, the active hydroxyl content of the plant biomass can be based on 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter), and the amount of plant biomass, MgO, and water can be adjusted according to equal stoichiometric ratios to maintain a material moisture content of 55%–65% (mass concentration).

[0025] As a preferred technical solution of the present invention: After step S1 is completed, step S2 is performed to complete the preparation of plant biomass potassium xanthate, or plant biomass calcium xanthate, or plant biomass magnesium xanthate. Specifically, the pre-reacted material is uniformly mixed with an equivalent amount of CS2. That is, after adding 100 g of rice straw powder, 235 mL of 4.3 mol / L KOH solution is added to complete the pre-reaction, or after adding 28 g of CaO powder and 207 mL of water is added to complete the pre-reaction, or after adding 20.2 g of MgO powder and 195 mL of water is added to complete the pre-reaction, 60 mL of CS2 is added to the pre-reacted material and mixed uniformly. The material is compacted and placed under the conditions of maintaining a moisture content of 55% to 65% and room temperature. The compaction and placement is an intermittent operation, during which the material is turned over 1 to 2 times and then compacted and placed. The operation time of step S2 is 24 h, and the reaction temperature is room temperature. In practical applications, the active hydroxyl groups in plant biomass can be 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter). The amount of plant biomass, 4.3 mol / L KOH solution, CaO and water, MgO and water, and CS2 can be adjusted proportionally to maintain the material moisture content at 55%–65% (mass concentration).

[0026] As a preferred technical solution of the present invention: After step S1 is completed, step S2 is performed to complete the preparation of plant biomass hemihydroxy potassium hemixanthate, or plant biomass hemihydroxy calcium hemixanthate, or plant biomass hemihydroxy magnesium hemixanthate. Specifically, the material after the pre-reaction is uniformly mixed with 1 / 2 equivalent of CS2. That is, after adding 100g of rice straw powder and 235 mL of 4.3 mol / L KOH solution to complete the pre-reaction, or after adding 28g of CaO powder and 207 mL of water to complete the pre-reaction, or after adding 20.2g of MgO powder and 195 mL of water to complete the pre-reaction, 30 mL of CS2 is added in 1 / 2 equivalent and uniformly mixed with the material after the pre-reaction. The material is compacted and placed under the conditions of maintaining a moisture content of 55% to 65% and room temperature. The compaction and placement is an intermittent operation, during which the material is turned over 1 to 2 times and then compacted and placed. The operation time of step S2 is 24 hours, and the reaction temperature is room temperature. In practical applications, the active hydroxyl groups in plant biomass can be 17% (dry matter basis, i.e., 1.0 mol -OH / 100 g dry matter). The amount of plant biomass, 4.3 mol / L KOH solution, CaO and water, MgO and water, and CS2 can be adjusted according to the same stoichiometric ratio to maintain the moisture content of the material at 55% to 65% (mass concentration).

[0027] The aforementioned soil heavy metal passivating agents are plant biomass potassium xanthate, plant biomass calcium xanthate, plant biomass magnesium xanthate, and plant biomass semi-hydroxy potassium hemi-xanthate, plant biomass semi-hydroxy calcium hemi-xanthate, and plant biomass semi-hydroxy magnesium hemi-xanthate.

[0028] Optionally, the compaction and resting time of the products in steps S1 and S2 pre-reaction and main reaction is controlled to a moderate time. In actual production, the reaction time can be appropriately extended according to the preparation conditions in order to coordinate the entire production process.

[0029] Optionally, in step S1, in addition to rice straw powder, plant biomass can also be replaced by sugarcane bagasse powder, corn stalk powder, wheat stalk powder, or other gramineous crop straw powder.

[0030] The study investigated the adsorption capacity of a soil heavy metal passivating agent for heavy metals and verified its passivation of soil heavy metals and improvement of fertilizer efficiency through pot experiments. The study also examined the adsorption capacity of pulverized plant biomass xanthate products for heavy metals, the reduction of soil heavy metal Cd in rapeseed, Chinese cabbage, and rice under pot conditions, and the fertilizer effect of the product on the relevant crops.

[0031] For ease of comparison and operation, the technical specifications of the relevant literature and this application are listed in Table 1, taking the plant bio-xanthate sodium in Reference 1 and Reference 2 and the plant biomass xanthate potassium prepared in this application as examples.

[0032] The specific steps for preparing the plant biomass potassium xanthate in this application are as follows: 56 g of KOH is dissolved in 235 mL of water and stirred until homogeneous. The KOH solution is gradually sprayed into 100 g of rice straw powder (< 1 mm) using a plastic bottle while stirring until all the KOH solution is added to the rice straw powder. The mixture is continuously turned until all the powder is evenly mixed, compacted, and reacted at room temperature for 48 h, turning 1-2 times during this period. After the above pre-reaction is completed, the material is turned with a glass rod, and 60 mL of CS2 (i.e., 76 g of CS2) is sprayed onto the material using a stainless steel spray bottle while stirring evenly. This xanthation process takes 24 h at room temperature to obtain wet material. The wet material is then air-dried. During this process, depending on the dryness of the material, lumps are gradually broken into fine pieces or even powder. After air-drying, the material is dried in a 60℃ drying oven for 4 h to obtain the plant biomass potassium xanthate sample. The sample is then pulverized and passed through a 100-mesh sieve for later use.

[0033] Table 1. Main technical indicators of sodium (potassium) xanthate from plant biomass Note: * The alkalizing agent used in References 1 and 2 is NaOH, while that used in this application is KOH; ** Waste liquid volume generated from the preparation of plant biomass xanthate from 100 g of plant biomass.

[0034] Meanwhile, to facilitate the preparation of the plant biomass xanthate series and plant biomass hemihydroxy salt hemixanthate series involved in this application, 100 g of crop straw powder (i.e., which provides 1.0 mol of hydroxyl groups) was used as the reactant. The main technical indicators of these two series are listed in Table 2.

[0035] Table 2. Dosage of alkalizing and xanthating agents for preparing xanthates from 100 g of straw Note: * Potassium salts refer to potassium xanthate from plant biomass, and hemipotassium salts refer to potassium hydroxyl and potassium hemixanthate from plant biomass; calcium salts refer to calcium xanthate from plant biomass, and hemicalcium salts refer to calcium hydroxyl and calcium hemixanthate from plant biomass; magnesium salts refer to magnesium xanthate from plant biomass, and hemimagnesium salts refer to magnesium hydroxyl and magnesium hemixanthate from plant biomass.

[0036] The adsorption capacity of the product obtained in this application was determined by isothermal adsorption. The procedure involved using plant biomass xanthate or plant biomass hemihydroxy salt hemixanthate, sieved through a 100-mesh sieve, at a dosage of 0.1000 g. The adsorbate was Cd. 2+ Pb 2 + Cu 2+Ionic solution, initial adsorbate concentration 0–2000 mg / L, adsorption medium 0.02 mol / L CaCl2 solution (pH 7.0), volume 25 mL, adsorption temperature 25 °C. 1℃. At 180 The device was subjected to reciprocating vibration at a speed of 5 r / min for 1 h. The formula for calculating the adsorption capacity is as follows: X = (C0 - C)×V / m (1) In equation (1), X is the adsorption capacity of the adsorbent (mg / g); C0 and C are the initial concentration and equilibrium concentration of the adsorbate (mg / L), respectively; V is the volume of the adsorption medium (L); and m is the amount of adsorbent used (g).

[0037] The isothermal adsorption equation is: X = X m K L C / (1+K L C) (2) In equation (2), X and X m The adsorption capacity (mg / g) and maximum adsorption capacity (mg / g) of the adsorbent; K L is the adsorption constant (L / g), and C is the equilibrium concentration of the adsorbate (mg / L).

[0038] Table 3 shows the maximum adsorption capacity and adsorption constant of heavy metal ions by the plant biomass xanthates or plant biomass semi-hydroxy salt semi-xanthates prepared in this application, and the adsorption capacity of heavy metal ions by plant biomass xanthates measured under certain conditions in the references.

[0039] Table 3 Comparison of adsorption parameters of heavy metal ions by xanthates from plant biomass (25℃) Note: *The adsorption solution volume is 1 L with 120 mL acetate buffer (ionic strength 1 mol / L, pH 5.0), Cu 2+ The adsorption amount was obtained by oscillating at 20 rpm for 240 min with an initial concentration of 20 mg / L and an adsorbent dosage of 0.125 g or 0.75 g, without specifying the adsorption temperature. **Test conditions were: solution volume 50 mL, Cu 2+ The initial concentration of Pb was 10 mg / L. 2+ The initial concentration was not mentioned, the amount of adsorbent used was not specified (a certain amount), the pH of the adsorption solution was 7.0, and the adsorption time and temperature were not specified. a The results were obtained by fitting the Langmuir isotherm adsorption equation.

[0040] It should be noted that the Cu used in Reference 12+ The initial concentration of the solution was 20 mg / L; Reference 2 used Cu 2+ The initial concentration of the solution was 10 mg / L, Pb 2+ The solution concentration was not specified, but judging from the range of heavy metal ion concentrations used in the experiments in this literature, the Pb concentration is likely high. 2+ The initial concentration of the solution may be between 5 and 10 mg / L. Furthermore, neither Reference 1 nor Reference 2 conducted isothermal adsorption experiments on the tested heavy metal ions; therefore, there is no Kg. L It is worth mentioning.

[0041] This application uses biological testing methods to verify the product's reduction effect on soil heavy metals and its yield-increasing effect on related crops. The biological testing method employs pot experiments under natural temperature conditions. The tested soil is approximately 1 mg / kg Cd-contaminated brown-red soil (sampling point: 114°21'E). 29°59'N The soil Cd level was between the pollutant screening value and the control value, falling within the risk assessment range (suitable soil under safe conditions). 8 kg of soil was used per pot, with 5 replicates. Irrigation was done with deionized water, and the soil was protected from rain by a transparent rainproof canopy. In the pot experiment from 2021 to 2024, the tested crops were: first round, rice (variety: Huanghuazhan) and Chinese cabbage (variety: Heiye Wuyueman); second round, rice (variety: Huanghuazhan); and third round, rice (variety: Huanghuazhan) and rapeseed (variety: Fengyou 520).

[0042] The potassium salt used in the first and second rounds of potted rice and bok choy cultivation was potassium xanthate, a plant biomass. Its preparation process involved dissolving 56 g of KOH in 235 mL of water and stirring thoroughly. The KOH solution was then gradually sprayed into 100 g of rice straw powder (< 1 mm) using a plastic sprayer, stirring continuously until all the KOH solution was incorporated. The mixture was then constantly turned until all the powder was evenly mixed, compacted, and allowed to react at room temperature for 48 hours, turning 1-2 times during this period. After the pre-reaction, the material was turned with a glass rod, and 60 mL of CS2 (76 g of CS2) was sprayed onto the material using a stainless steel sprayer, stirring constantly. This xanthation process took 24 hours at room temperature, yielding a wet material. The wet materials are air-dried until dry. During this process, depending on the dryness of the materials, the lumpy materials are gradually broken into fine pieces or even powder. After air-drying, the materials are dried in a drying oven at 60℃ for 4 hours to obtain a sample of potassium xanthate from plant biomass. The sample is then pulverized and passed through a 100-mesh sieve for later use. The potassium salts, hemipotassium salts, calcium salts, hemicalcium salts, magnesium salts, and hemimagnesium salts used in the third round of rice and rapeseed production refer to potassium xanthate, potassium hemihydroxy potassium hemixanthate, calcium xanthate, calcium hemihydroxy calcium hemixanthate, magnesium xanthate, and magnesium hemihydroxy magnesium hemixanthate from plant biomass. The chemical parameters involved in the preparation process are shown in Table 2. The operation process is as follows: 100 g of rice straw powder is mixed evenly with an alkaline solution (KOH) or alkaline powder is mixed evenly with rice straw powder first and then water is added and mixed evenly. The mixture is compacted and reacted at room temperature for 48 hours, turning it 1-2 times during the reaction. After the above pre-reaction was completed, the material was turned with a glass rod, and CS2 was sprayed onto the material with a stainless steel sprayer while stirring evenly to carry out the xanthation reaction. The xanthation reaction took 24 hours at room temperature to obtain wet material. The wet material was air-dried and then dried in a drying oven at 60℃ for 4 hours to obtain plant biomass xanthate samples. The samples were pulverized and passed through a 100-mesh sieve for later use. Pot experiments were conducted from 2021 to 2024 to obtain the passivation effect of the plant biomass xanthate or plant biomass hemihydroxy salt hemixanthate prepared in this application on the heavy metal Cd in the test soil (quantitatively expressed as the heavy metal uptake of the test crop). The results are shown in Table 4.

[0043] Table 4. Passivation effect of plant biomass xanthate products on heavy metal Cd As shown in Table 4, the passivation rate of plant biomass xanthates prepared in this application for cadmium in soil averages 73% for rice, 31% for rapeseed, and 36% for Chinese cabbage in similar soils. This indicates that the plant biomass xanthates of this invention have a better passivation effect on cadmium in paddy fields than in dry land. This may be because during rice growth, waterlogging facilitates the movement of chemical substances, increasing the binding frequency of plant biomass xanthates and heavy metal ions, thus strengthening their interaction. Therefore, macroscopically, the plant biomass xanthates of this invention exhibit a better passivation effect on cadmium in paddy fields than in dry land.

[0044] In addition to reducing the content of active heavy metals in the soil and promoting crop growth, plant biomass xanthates or plant biomass hemihydroxy salts / hemixanthates, which contain essential plant nutrients such as S, K, Ca, or Mg, as well as organic matter, can improve the soil's fertility and promote crop growth. The fertilizer properties of plant biomass xanthates or plant biomass hemihydroxy salts / hemixanthates, and the resulting yield increases for potted crops in the current season, are shown in Table 5. Table 5 shows that after passivation of cadmium in soil, the plant biomass xanthates prepared in this application resulted in an average yield increase of 70.0% for rice in the first round, 48.8% in the second round, and 9.6% in the third round in similar soils. The yield increase rate for potted rice in the third round was relatively lower because the heavy metal hazard in the soil had been significantly reduced after the first two rounds of passivation. Table 5 also shows that after passivation of cadmium in soil, plant biomass xanthates resulted in an average yield increase of 58% for rapeseed, an average increase of 32% in the number of rapeseed pods, and a 75% increase in the yield of bok choy.

[0045] Table 5. Yield-increasing effects of plant biomass xanthates on crops. It is worth noting that when treating potted crops with potassium xanthate or potassium hemihydroxy-2-xanthate from plant biomass, to ensure that the potassium application rate of these two treatments is consistent with the control (CK), the amount of potassium carried by the treatments themselves is taken into account; that is, when used as fertilizer, a corresponding amount of potassium is applied less. Under these circumstances, the crops planted in these two treatments still yielded more than the control, further demonstrating that the fertilizer effect of potassium xanthate or potassium hemihydroxy-2-xanthate from plant biomass is superior to that of potassium chloride fertilizer. Other plant biomass xanthates in Table 5, compared with the CK, all showed varying degrees of yield-increasing effects, indicating that these substances are also novel calcium and magnesium fertilizers. Therefore, the plant biomass xanthates prepared in this invention are both a type of heavy metal passivating agent and a novel fertilizer. Since plant biomass xanthates are alkaline substances (pH ~ 10), they are particularly suitable for application in acidic soils with heavy heavy metal pollution or in acidic soils.

[0046] The above description is merely a specific embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A preparation process for a soil heavy metal passivating agent that also possesses fertilizer properties, characterized in that, Includes the following steps: S1. Pre-reaction process: Alkaline substances are mixed evenly with plant biomass, and the moisture content of the material is controlled at 55% to 65%. The pre-mixing reaction is carried out for a certain period of time under compaction and room temperature conditions. S2, xanthation reaction process: The pre-reacted wet solid material is uniformly mixed with CS2 under spraying conditions, and the reaction is carried out for a period of time while maintaining the material moisture content of 55% to 65% and room temperature to obtain the reaction product plant biomass xanthate. S3. Two-step drying process: After the product is laid flat and air-dried naturally, it is then dried at 50-60℃ to obtain a soil heavy metal passivating agent.

2. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 1, characterized in that, In step S1, an equivalent amount of KOH solution, CaO powder, or MgO powder and a measured amount of water are added to the plant biomass powder according to the active hydroxyl content of 17%, and then the mixture is thoroughly stirred with the plant biomass powder to make the overall material moisture content 55% to 65%.

3. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 1, characterized in that, In step S2, the material obtained in step S1 is transferred to the main reactor, and 1.0 mol CS2 / 100 g plant biomass is added to the main reactor to carry out the xanthation reaction, based on the active hydroxyl content of 17% in the plant biomass.

4. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 1, characterized in that, In step S2, the material obtained in step S1 is transferred to the main reactor, and 0.5 mol CS2 / 100 g plant biomass is added to the main reactor according to half the amount of 17% active hydroxyl groups in the plant biomass to carry out the xanthation reaction.

5. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 1 or 2, characterized in that, In step S1, after the material is thoroughly mixed, it is compacted by pressing or squeezing and then placed on the ground. The compaction is an intermittent operation, during which the material is turned over 1 to 2 times and then compacted again.

6. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 5, characterized in that, In step S1, the reaction time is 48 h.

7. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 3 or 4, characterized in that, In step S2, the material is sprayed at a constant speed while being turned and tossed until it is uniform, then compacted and set aside.

8. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 7, characterized in that, In step S2, the compaction and resting is an intermittent operation, during which the material is turned over 1 to 2 times and then compacted and rested. The operation time is 24 hours and the reaction temperature is room temperature.

9. The preparation process of the soil heavy metal passivating agent with fertilizer properties according to claim 1, characterized in that, The plant biomass is one of rice straw powder, sugarcane bagasse powder, corn stalk powder, or wheat straw powder.

10. The application of the soil heavy metal passivating agent according to claim 1 in the passivation of heavy metals in soil and simultaneously as a crop fertilizer.

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