A passivating agent for iron-modified biomass power plant ash and its preparation method

Abstract

This invention provides an iron-modified biomass power plant ash passivating agent and its preparation method, relating to the field of soil remediation technology. The passivating agent comprises the following raw materials: biomass power plant ash, ferric chloride, ferric citrate, sodium alginate, and tea polyphenols. This iron-modified biomass power plant ash passivating agent exhibits excellent adsorption and solidification effects on heavy metals Cd and As in the soil, effectively realizing the resource utilization of biomass power plant ash, while also being more efficient and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, specifically to an iron-modified biomass power plant ash passivating agent and its preparation method. Background Technology

[0002] Heavy metal pollution in soil occurs because heavy metals such as mercury, cadmium, lead, and copper cannot be decomposed by soil microorganisms, leading to their gradual accumulation and consequently reduced soil fertility, decreased soil quality, and impaired vegetation growth. To address heavy metal pollution in soil, remediation is necessary. The principles of heavy metal remediation mainly include reducing the total amount of heavy metals in the soil and altering their bioavailability. During soil remediation, passivating agents can reduce the bioavailability of heavy metals by changing their form, thereby reducing their harmfulness to organisms. Commonly used passivating agents include organic passivating agents, inorganic passivating agents, microbial passivating agents, and composite passivating agents.

[0003] Among the many types of passivating agents, biomass power plant ash is currently being widely studied due to its advantages such as low cost and high efficiency. Biomass power plant ash is the ash produced by burning biomass to generate electricity in biomass power plants. It is divided into fly ash and ash residue, both of which can be used as raw materials for passivating agents. The combustion compositions of various types of biomass are relatively similar, with the main components including silicon, aluminum, sulfur, calcium, potassium, and phosphorus, which have good adsorption and passivation effects on heavy metals such as Cd and As.

[0004] Existing research on biomass power plant ash as a passivating agent includes:

[0005] Reference: Song Le, Han Zhantao, Zhang Wei, et al. Study on the long-term effect of modified biomass power plant ash passivation in the remediation of cadmium-contaminated soil in southern China [J]. China Environmental Science, 2019, 39(1):9. Ash from biomass power plants in southern my country was selected as raw material and modified by physical and chemical methods to prepare a heavy metal passivating agent. The final BFA type passivating agent can adsorb more than 16 mg / g of Cd in water.

[0006] Reference: Song Le, Han Zhantao, Lü Xiaoli, et al. Experimental study on passivation remediation of Cd contaminated soil in northern China using modified biomass power plant ash [J]. Journal of Agricultural Environmental Science, 2018, 037(007):1484-1494. Using ash from biomass power plants in northern my country as raw material, a heavy metal passivating agent was prepared by modification. Isothermal adsorption test, pot experiment and in-situ remediation test were carried out. The final passivating agent showed higher adsorption performance for Cd in water than fly ash, with a maximum adsorption capacity of more than 10 mg·g-1; and under neutral conditions, the contribution rate of precipitation to the total adsorption capacity was less than 30%.

[0007] Reference: Li Xiongguang. Application of modified biomass power plant ash for remediation of Cd contaminated soil [D]. Hebei University of Geosciences. Biomass power plant ash was modified by adding magnesium oxide and polyphenol-reduced nano-iron to improve its adsorption performance for Cd. The results showed that the modified biomass power plant ash with polyphenol-reduced nano-iron had the highest Cd adsorption capacity at an iron-to-ash ratio of 0.3:1, with a maximum adsorption capacity of 38.39 mg / g.

[0008] Reference: Zhang Chi. Study on passivation and remediation of cadmium and arsenic co-polluted soil by iron-modified biomass power plant ash [D]. Hebei University of Geosciences. Using biomass power plant ash as a carrier and ferrous sulfate as a modifier, and using ultrasonic and pH adjustment methods, iron-modified biomass power plant ash (FeBFA) was made capable of simultaneously passivating cadmium and arsenic in the soil.

[0009] Another patent, CN110157442A, discloses a passivation material and its combined agronomic approach for remediating cadmium-copper contaminated soil. The passivation material has a pH of 10-13 and a particle size of 1-3 mm, and is formulated from biomass power plant ash, lime, apatite, and organic fertilizer. This passivation material and its combined remediation method can effectively promote the transformation of soil heavy metals Cd and Cu from a usable state to a potentially usable or unusable state. While stabilizing / solidifying heavy metals Cd and Cu, it promotes plant growth and biomass accumulation, thereby improving land productivity and economic benefits.

[0010] However, to date, biomass power plant ash still suffers from problems such as excessive usage and weak passivation effect on heavy metals other than Cd. The current modification methods also suffer from problems such as high consumption of modifiers and high pollution. Therefore, it is essential to find an environmentally friendly, low-consumption, and highly effective iron-modified biomass power plant ash passivating agent and its preparation method. Summary of the Invention

[0011] This invention addresses the problems existing in the prior art by providing an iron-modified biomass power plant ash passivating agent and its preparation method. This iron-modified biomass power plant ash passivating agent has a good adsorption and solidification effect on heavy metals Cd and As in soil.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] This invention provides a passivating agent comprising the following raw materials: biomass power plant ash (existing in the form of fly ash and ash residue, with fly ash being used directly and ash residue being used after being ground by a ball mill), ferric chloride, ferric citrate, sodium alginate, and tea polyphenols.

[0014] Furthermore, the passivating agent, by weight, comprises: 180-224 parts biomass power plant ash, 1-3 parts ferric chloride, 1-2 parts ferric citrate, 0.8-2 parts sodium alginate, and 0.8-2 parts tea polyphenols.

[0015] Preferably, the passivating agent comprises, by weight, 200 parts biomass power plant ash, 2 parts ferric chloride, 1 part ferric citrate, 1 part sodium alginate, and 1 part tea polyphenols.

[0016] Further, the weight ratio of the biomass power plant ash to ferric chloride and ferric citrate is 180-224:1-3:1-2. Preferably, the weight ratio of the biomass power plant ash to ferric chloride and ferric citrate is 200:2:1.

[0017] Further, the weight ratio of the biomass power plant ash to sodium alginate and tea polyphenols is 180-224:0.8-2:0.8-2. Preferably, the weight ratio of the biomass power plant ash to sodium alginate and tea polyphenols is 200:1:1.

[0018] Further, the weight ratio of ferric citrate, sodium alginate, and tea polyphenols is 1-2:0.8-2:0.8-2. Preferably, the weight ratio of ferric citrate, sodium alginate, and tea polyphenols is 1:1:1.

[0019] Furthermore, the present invention provides a method for preparing the above-mentioned passivating agent, comprising the following steps: mixing ferric chloride, ferric citrate, sodium alginate, tea polyphenols and water, heating in a water bath, adding biomass power plant ash, impregnating, and drying to obtain the passivating agent.

[0020] Furthermore, the water bath heating temperature is 60-70℃.

[0021] Furthermore, the soaking time is 18-24 hours.

[0022] Furthermore, the raw materials also include one or more of lignin, zeolite powder, fly ash, and activated carbon.

[0023] Furthermore, the present invention provides a method for preparing the above-mentioned passivating agent, comprising the following steps: mixing ferric chloride, ferric citrate, sodium alginate, tea polyphenols, and water, heating in a water bath, adding biomass power plant ash, impregnating, drying, and then adding one or more of lignin, zeolite powder, fly ash, and activated carbon.

[0024] Grind it to obtain the product.

[0025] The technical effects achieved by this invention are:

[0026] 1. Compared with ferrous sulfate modification, ferric chloride modification in this invention has a superior effect. Combined with ferric citrate, it can achieve the loading of iron species with a low dosage, effectively modifying biomass power plant ash and realizing the resource utilization of biomass power plant ash. At the same time, it is more efficient and environmentally friendly.

[0027] 2. In this invention, after the biomass power plant ash is impregnated in a mixture of ferric chloride, ferric citrate, sodium alginate, and tea polyphenols, some components are dissolved, increasing the specific surface area of ​​the biomass power plant ash and facilitating the full adsorption of iron species into the surface pores of the biomass power plant ash. Simultaneously, the iron species complex with various groups in sodium alginate and tea polyphenols, working in conjunction with the biomass power plant ash to facilitate the effective adsorption and solidification of heavy metals Cd and As in the soil by the final passivating agent.

[0028] 3. This invention has found that, compared to some researchers who use ferric chloride, green tea extract, biomass power plant ash, and alkaline solutions together, this invention, by introducing sodium alginate and ferric citrate, can effectively achieve a synergistic effect. Without the need to add alkaline solutions, iron species can achieve good adsorption and, combined with a high specific surface area, also have a good passivation effect on other heavy metals besides Cd, such as As. Detailed Implementation

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention.

[0031] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] It is worth noting that the biomass power plant ash used in this invention comes from the biomass power plant in Jinzhou City, Hebei Province. In addition, biomass from biomass power plants in Guangzong County, Yuanshi County, Wuqiao County, Nanpi County, Gucheng County, Hebei Province, as well as Hengyang City, Linli County, Longhui County, and Shuangfeng County, Hunan Province, can also be supplied with corresponding biomass power plant ash. The remaining raw materials are all ordinary commercially available products, so their sources are not specifically limited.

[0033] The table below shows the content of available heavy metals in the biomass power plant ash used in this invention:

[0034] Table 1. Content of available heavy metals in biomass power plant ash used in this invention.

[0035]

[0036] In the following examples, bottom ash was used for the experiment. Biomass power plant ash (bottom ash) was ground and passed through a 200-mesh sieve. The sieved fine ash was used as raw material for subsequent experiments.

[0037] Example 1

[0038] A method for preparing an iron-modified biomass power plant ash passivating agent includes the following steps: mixing 1 part ferric chloride, 1 part ferric citrate, 0.8 parts sodium alginate, 0.8 parts tea polyphenols with water, heating in a water bath at 60°C, adding 180 parts biomass power plant ash, soaking for 18 hours, and drying to obtain the agent.

[0039] Example 2

[0040] A method for preparing an iron-modified biomass power plant ash passivating agent includes the following steps: mixing 3 parts ferric chloride, 2 parts ferric citrate, 2 parts sodium alginate, and 2 parts tea polyphenols with water, heating in a water bath at 70°C, adding 224 parts biomass power plant ash, soaking for 24 hours, and drying to obtain the final product.

[0041] Example 3

[0042] A method for preparing an iron-modified biomass power plant ash passivating agent includes the following steps: mixing 2 parts of ferric chloride, 1 part of ferric citrate, 1 part of sodium alginate, and 1 part of tea polyphenols with water, heating in a water bath at 65°C, adding 200 parts of biomass power plant ash, soaking for 24 hours, and drying to obtain the final product.

[0043] Comparative Example 1

[0044] A method for preparing an iron-modified biomass power plant ash passivating agent includes the following steps: mixing 2 parts of ferric chloride, 3 parts of ferric citrate and water, heating in a water bath at 65°C, adding 200 parts of biomass power plant ash, soaking for 24 hours, and drying to obtain the agent.

[0045] Comparative Example 2

[0046] A method for preparing an iron-modified biomass power plant ash passivating agent includes the following steps: mixing 2 parts of ferric chloride, 3 parts of sodium alginate with water, heating in a water bath at 65°C, adding 200 parts of biomass power plant ash, soaking for 24 hours, and drying to obtain the agent.

[0047] Comparative Example 3

[0048] A method for preparing an iron-modified biomass power plant ash passivating agent includes the following steps: mixing 2 parts ferric chloride, 3 parts tea polyphenols with water, heating in a water bath at 65°C, adding 200 parts biomass power plant ash, soaking for 24 hours, and drying to obtain the agent.

[0049] Comparative Example 4

[0050] A method for preparing an iron-modified biomass power plant ash passivating agent includes the following steps: mixing 1 part ferric chloride, 1 part ferric citrate, 0.5 parts sodium alginate, 4.1 parts tea polyphenols with water, heating in a water bath at 60°C, adding 177 parts biomass power plant ash, soaking for 18 hours, and drying to obtain the agent.

[0051] I. Using the passivating agent of this invention to reduce the Cd content in soil caused by Chinese cabbage. 2+ absorption

[0052] Test method:

[0053] (1) Preparation of Cd 2+ Contaminated soil

[0054] Soil samples were collected from wheat fields at a depth of 0-20 cm, transported back to the laboratory, spread out indoors to dry, and then crushed into larger particles in a mortar and pestle. The crushed soil was passed through a 20-mesh sieve to remove plant residues and stored in containers for later use. A 100 mg / L solution of Cd was prepared by weighing the dried soil. 2+ Add 10L of solution to the soil using a water sprayer, stirring thoroughly. If it is not moist enough, add more water until it is both moist and loose. Cover with plastic film and pile for 15 days to allow the Cd to settle. 2+ It is fully absorbed in the soil.

[0055] (2) Take 16 5L flowerpots, add soil, passivating agent, and base fertilizer according to Table 2, and mix thoroughly (two flowerpots were used for the background group and the other example groups). Sow three Chinese cabbage seeds in each pot and place them in a cold light source plant climate chamber for 40 days. Apply the same nitrogen, phosphorus, and potassium fertilizer to each pot according to the general Chinese cabbage planting method. Set the temperature to 15-25 degrees Celsius and maintain the humidity at around 60%.

[0056] At harvest, the bok choy is first gently dug out, the roots are washed with deionized water, and then dried in an oven at 75℃ until constant weight. The dry weight is then measured separately. The bok choy is then separated into roots and leaves, and the Cd content is measured. 2+Content. Three plants per pot constitute one replicate. Cd content was determined in the roots and leaves after microwave digestion using ICP-AES. 2+ content.

[0057] Table 2. Passivating agents reduce the Cd content in soil from bok choy. 2+ Absorption Comparison Table

[0058]

[0059] As shown in Table 2, Cd in the roots and leaves of bok choy 2+ The content was significantly lower than that of the background sample, and the yield of Chinese cabbage with added passivating agent increased by more than 25%, showing obvious adsorption, repair and yield-increasing effects.

[0060] II. Utilizing the passivating agent in this invention to reduce the impact of rice on As in the soil 3+ absorption

[0061] 1. Preparation of As 3+ Contaminated soil

[0062] Soil samples were collected from wheat fields at a depth of 0-20 cm, transported back to the laboratory, spread out indoors to dry, and then crushed into larger particles in a mortar. The crushed soil was passed through a 20-mesh sieve to remove plant residues and stored in containers for later use. A 100 mg / L solution of As was prepared. 3+ 10L of solution was sprayed onto the soil using a water sprayer and thoroughly mixed. If it was not moist enough, more water was added until it reached a state that was both moist and loose. The soil was then covered with plastic film and left to stand for 15 days to allow the As... 3+ It is fully absorbed in the soil.

[0063] 2. Planting Experiment

[0064] Take 16 5L flowerpots (two flowerpots for each of the background group and other example groups), add soil, passivating agent, and base fertilizer according to Table 3, and mix thoroughly.

[0065] Move the sample containers into a greenhouse, fill them with water, and submerge them for 7 days. Prepare the rice seeds indoors beforehand, ensuring they are free of As. 3+ Seedlings are raised in soil for 15 days, then transplanted into pots of 3 seedlings each. These are placed in a cold-light plant climate chamber and cultivated for approximately 120 days, keeping the soil submerged during this period. Each pot is fertilized with the same nitrogen, phosphorus, and potassium fertilizers as usual for rice cultivation. The temperature is set at 20-30 degrees Celsius, and the humidity is maintained at around 60%.

[0066] Rice was first washed with deionized water and dried at 75°C to constant weight. The dry weight was then measured separately, and the rice plants were separated into roots and grains to determine the aspergillin content. 3+ Content. Three plants per pot constitute one replicate. Roots and seeds after microwave digestion were analyzed by ICP-AES for As content. 3+ content.

[0067] Table 3. Passivating agents reduce the susceptibility of rice to As in the soil. 3+ Absorption Comparison Table

[0068]

[0069] As shown in Table 3, the content of As in rice roots and grains... 3+ The content was significantly lower than that of the background sample, and the yield of rice with added passivating agent increased by more than 20%, showing obvious adsorption, repair and yield-increasing effects.

[0070] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A passivating agent, characterized in that: By weight, it is made from the following raw materials: 200 parts biomass power plant ash, 2 parts ferric chloride, 1 part ferric citrate, 1 part sodium alginate, and 1 part tea polyphenols. The method for preparing the passivating agent includes the following steps: mixing ferric chloride, ferric citrate, sodium alginate, tea polyphenols and water, heating in a water bath at 60-70°C, adding biomass power plant ash, impregnating, and drying to obtain the passivating agent.

2. The method for preparing the passivating agent as described in claim 1, characterized in that: Includes the following steps: The mixture of ferric chloride, ferric citrate, sodium alginate, and tea polyphenols with water is heated in a water bath, then biomass power plant ash is added, impregnated, and dried to obtain the final product.

3. The preparation method according to claim 2, characterized in that: The water bath heating temperature is 60-70℃.

4. The preparation method according to claim 2, characterized in that: The soaking time is 18-24 hours.

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