阅读说明：本技术 一种缓释型重金属固定剂及其制备方法和在重金属污染农田土壤修复中的应用 (Slow-release heavy metal fixing agent, preparation method thereof and application thereof in remediation of heavy metal contaminated farmland soil ) 是由 文波 王豪 李栎 雷国建 史勇 刘朝 马英才 于 2021-09-23 设计创作，主要内容包括：本发明公开了一种缓释型重金属固定剂及其制备方法和在重金属污染农田土壤修复中的应用。将生物质原料在保护气氛下进行热处理后,得到生物质炭材料；将生物质炭材料置于碱液中,再向碱液中通入含氧气体进行活化处理,得到活化生物质碳材料；将海泡石、生石灰及活化生物质碳材料混合后,进行振荡处理,在振荡过程中喷洒海藻酸钠溶液,得到颗粒状缓释型重金属固定剂。该重金属固定剂能够有效稳定和固定重金属污染农田土壤中有效态重金属,大大降低重金属在农作物中富集,同时该重金属固定剂能够缓慢、稳定释放固定重金属的活性成分,使得固定重金属的能力长期稳定有效,达到重金属农田土壤持续修复的目的。(The invention discloses a slow-release heavy metal fixing agent, a preparation method thereof and application thereof in remediation of heavy metal contaminated farmland soil. Carrying out heat treatment on the biomass raw material under a protective atmosphere to obtain a biomass charcoal material; putting the biomass carbon material into an alkali liquor, and introducing oxygen-containing gas into the alkali liquor for activation treatment to obtain an activated biomass carbon material; mixing sepiolite, quicklime and an activated biomass carbon material, oscillating, and spraying a sodium alginate solution in the oscillating process to obtain the granular slow-release heavy metal fixing agent. The heavy metal fixing agent can effectively stabilize and fix the effective heavy metal in the heavy metal polluted farmland soil, greatly reduces the enrichment of the heavy metal in crops, and can slowly and stably release the active ingredients for fixing the heavy metal, so that the capability of fixing the heavy metal is stable and effective for a long time, and the aim of continuously repairing the heavy metal farmland soil is fulfilled.)

1. A preparation method of a slow-release heavy metal fixing agent is characterized by comprising the following steps: the method comprises the following steps:

1) carrying out heat treatment on the biomass raw material under a protective atmosphere to obtain a biomass charcoal material;

2) putting the biomass carbon material into an alkali liquor, and introducing oxygen-containing gas into the alkali liquor for activation treatment to obtain an activated biomass carbon material;

3) mixing sepiolite, quicklime and an activated biomass carbon material, oscillating, and spraying a sodium alginate solution in the oscillating process to obtain the granular slow-release heavy metal fixing agent.

2. The preparation method of the slow-release heavy metal fixing agent according to claim 1, characterized in that: the biomass raw material comprises at least one of straw, rice hull and wood chips.

3. The preparation method of the slow-release heavy metal fixing agent according to claim 1, characterized in that: the conditions of the heat treatment are as follows: the temperature is 400-600 ℃, and the time is 0.5-2 h.

4. The preparation method of the slow-release heavy metal fixing agent according to claim 1, characterized in that: the conditions of the activation treatment are as follows: the liquid-solid ratio is 3-5 mL:1g, the alkali liquor is a sodium hydroxide solution with the mass percentage concentration of 1-3%, and the oxygen-containing gas is air with the air supply volume of 1-5 m³The activation time is 0.5-2 h per min.

5. The preparation method of the slow-release heavy metal fixing agent according to claim 1, characterized in that: the mass ratio of the sepiolite to the quicklime to the activated biomass material is 3-15: 2-5: 80-95.

6. The preparation method of the slow-release heavy metal fixing agent according to claim 1, characterized in that: the mass percentage concentration of the sodium alginate solution is 2-5%.

7. The preparation method of the slow-release heavy metal fixing agent according to claim 1, characterized in that: the spraying amount of the sodium alginate solution is 2-6% of the total mass of the sepiolite, the quicklime and the activated biomass carbon material, wherein the mass of the sodium alginate solution is measured by the mass of the sodium alginate contained in the sodium alginate solution.

8. The preparation method of the slow-release heavy metal fixing agent according to claim 1, characterized in that: the conditions of the oscillation treatment are as follows: the temperature is 60-80 ℃, the oscillation frequency is 300-400 rpm, and the time is 1-3 h.

9. A slow-release heavy metal fixing agent is characterized in that: the preparation method of any one of claims 1 to 8.

10. The use of the slow-release heavy metal fixing agent as claimed in claim 9, wherein: the method is applied to the remediation of the heavy metal polluted farmland soil.

Technical Field

The invention relates to a heavy metal fixing agent, in particular to a slow-release heavy metal fixing agent, and also relates to a preparation method of the slow-release heavy metal fixing agent and application of the slow-release heavy metal fixing agent in heavy metal polluted farmland soil remediation, belonging to the technical field of heavy metal polluted farmland soil remediation.

Background

With the continuous improvement of industrial development and urbanization degree, land resources are increasingly tense, and the world is suffering from various environmental problems. The soil environment condition of China is not optimistic overall, soil pollution is serious in part of areas, and the soil environment quality of cultivated land is great. Due to the development of human activities and industrial and agricultural industries, heavy metal substances are brought into farmland soil, so that soil hardening, soil fertility reduction and agricultural product yield reduction are caused, and the sustainable development of agriculture in China is severely restricted. In addition, heavy metals in the soil are absorbed by crops and finally enter human bodies through food chains to cause harm to human health.

The farmland heavy metal polluted soil restoration technology mainly comprises a biological restoration technology, a chemical restoration technology, a physical restoration technology, an agricultural improvement measure, a multi-technology combined restoration technology and the like according to the principle. At present, the repair technology of single heavy metal polluted soil has more researches, but the researches on the multiple metal composite polluted soil are relatively few, most of the researches only exist in the laboratory research field, and the industrial application is difficult to realize really due to the reasons of production cost, raw material toxicology, application complexity and the like. Moreover, as crops are planted in the farmland, the farmland soil polluted by heavy metals is treated in a mild mode so as to retain the basic functions of the farmland to the maximum extent.

Chinese patent document (CN201510838665.4) discloses a preparation method of a multifunctional repairing agent for heavy metal contaminated soil treatment, which takes agricultural biomass wastes and clay minerals as raw materials, and generates a biomass charcoal clay complexing agent loaded with struvite in a nitrogen-phosphorus solution after magnesium salt modification and roasting, and can be used for efficient in-situ repair of farmland and other industrial heavy metal contaminated soil. Has the advantages of simple preparation method, quick response and low cost. However, a large amount of clay minerals are required to be added into the biomass charcoal clay complexing agent prepared by the method, most of the clay minerals have strong water absorption, and are easy to absorb a large amount of water in soil when used for farmland restoration, a large amount of water needs to be irrigated in practical application to keep farmland water, and medicament loss is easily caused in the irrigation process.

Chinese patent document (CN201710425905.7) discloses mixed biomass charcoal for improving degraded soil and a preparation method thereof, the method mixes black fungus chaff, chicken manure and corn straw and then prepares the biomass charcoal through cracking and oxidation, and the biomass charcoal has the functions of soil carbon fixation, nutrient substance slow release, heavy metal fixation and the like, thereby improving the degraded soil and repairing the heavy metal contaminated soil. However, the biomass has a general effect of reducing heavy metal accumulation of plants, and has fewer raw materials, so that large-scale industrial production is not easy to realize.

Disclosure of Invention

Aiming at the defects in the prior art, the first purpose of the invention is to provide a slow-release heavy metal fixing agent, which can effectively stabilize and fix the effective heavy metal in the farmland soil polluted by the heavy metal, greatly reduce the enrichment of the heavy metal in crops, and slowly and stably release the active ingredients for fixing the heavy metal, so that the heavy metal fixing ability is stable and effective for a long time, and the aim of continuously repairing the heavy metal farmland soil is fulfilled.

The second purpose of the invention is to provide a preparation method of the slow-release heavy metal fixing agent, which adopts cheap raw materials, is simple to operate, has short flow and is beneficial to large-scale production.

The third purpose of the invention is to provide the application of the slow-release heavy metal fixing agent, the slow-release heavy metal fixing agent can be added into the heavy metal polluted farmland soil to effectively reduce the effective heavy metal in the farmland soil, reduce the enrichment of the heavy metal in crops, simultaneously realize the lasting and stable restoration of the heavy metal polluted farmland soil, is convenient to apply and small in damage to the soil, can also finely adjust the pH value to prevent the soil from being acidified, improves the soil fertility, and is favorable for popularization and application.

In order to achieve the technical purpose, the invention provides a preparation method of a slow-release heavy metal fixing agent, which comprises the following steps:

1) carrying out heat treatment on the biomass raw material under a protective atmosphere to obtain a biomass charcoal material;

2) putting the biomass carbon material into an alkali liquor, and introducing oxygen-containing gas into the alkali liquor for activation treatment to obtain an activated biomass carbon material;

3) mixing sepiolite, quicklime and an activated biomass carbon material, oscillating, and spraying a sodium alginate solution in the oscillating process to obtain the granular slow-release heavy metal fixing agent.

As a preferred scheme, the biomass raw material comprises at least one of straw, rice hull and wood chip. The preferable biomass raw material is common agricultural solid waste and is easy to obtain, and resource utilization can be achieved in the technical scheme of the invention.

As a preferable mode, the heat treatment conditions are: the temperature is 400-600 ℃, and the time is 0.5-2 h. The biomass charcoal material generated by the biomass raw material can be ensured to have the characteristics of rich pore structure and rich polar groups by carrying out heat treatment under a proper temperature condition, if the temperature is too low, the high-temperature activation effect is difficult to achieve, if the temperature is too high, the generation of the pore structure can be reduced, and most polar groups can be removed, so that the adsorption activity of the biomass charcoal material on heavy metal ions is reduced. The protective atmosphere in the heat treatment process is nitrogen or inert gas.

As a preferred embodiment, the conditions of the activation treatment are: the liquid-solid ratio is 3-5 mL:1g, the alkali liquor is a sodium hydroxide solution with the mass percentage concentration of 1-3%, and the oxygen-containing gas is air with the air supply volume of 1-5 m³The activation time is 0.5-2 h per min. After the activation treatment, the specific surface area and the micropore content of the biomass carbon material can be further improved, so that the adsorption capacity of the biomass carbon material on heavy metal ions is improved.

As a preferable scheme, the mass ratio of the sepiolite to the quicklime to the activated biomass material is 3-15: 2-5: 80-95. The lime can improve the pH environment of the soil, thereby promoting the precipitation and separation of heavy metals. Quicklime can reduce the migration of heavy metals by improving the pH value of soil, and the activated biomass material has a porous structure and is rich in polar groups, so that the water retention of the soil can be increased, the soil fertility of farmlands is improved, the growth of crops is promoted, the yield is improved, the abundant functional groups of the activated biomass material can be utilized to perform ion exchange with the heavy metals, the effective state content of the heavy metals is reduced, and the accumulation of the heavy metals in the crops is reduced. The sepiolite is a magnesium silicate clay mineral, has strong adsorption performance and good water retention performance, and the low-mobility heavy metal is adsorbed and wrapped by the sepiolite with high adsorbability to prevent the sepiolite from being released into soil again. Sepiolite, quick lime and activated biomass material are combined according to appropriate proportion and used, and can combine together through multiple mode of action such as physical adsorption, chemical precipitation, physics parcel, reach the effect of heavy metal ion in the fixed soil in coordination, and the proportional control of three is in suitable within range, not only can keep higher performance of adsorbing the heavy metal, can prevent in the soil moisture loss moreover, and lead to local caking, reduce medicament and contaminated soil effective contact. Meanwhile, after the sepiolite is compounded with the quick lime and the activated biomass material, the activated biomass carbon material and the lime can enter the inner gap of the sepiolite to play a certain slow release effect.

As a preferable scheme, the mass percentage concentration of the sodium alginate solution is 2-5%. On one hand, sodium alginate plays a role in binding, powder materials such as sepiolite, quicklime, activated biomass carbon materials and the like can be bound and agglomerated into larger particles, and meanwhile, sodium alginate is rich in polar groups such as carboxylate radicals and the like, and can adsorb and enrich free heavy metal ions in soil through a chemical bonding effect.

As a preferable scheme, the spraying amount of the sodium alginate solution is 2-6% of the mass of the sepiolite, the quicklime and the activated biomass carbon material, wherein the mass of the sodium alginate solution is measured by the mass of alginic acid contained in the sodium alginate solution. If the dosage of sodium alginate is too high, the slow release effect cannot be achieved, and if the dosage is too low, the sodium alginate is difficult to bond and form, and the slow release effect cannot be achieved.

As a preferable mode, the conditions of the oscillation treatment are as follows: the temperature is 60-80 ℃, the oscillation frequency is 300-400 rpm, and the time is 1-3 h. The material can be mixed more uniformly through high-frequency oscillation, the physical and chemical properties of soil are prevented from being influenced by the fact that the medicament is added into a farmland and is locally contacted with a single high-concentration medicament, meanwhile, part of biomass carbon materials and lime enter gaps inside sepiolite, and the slow-release effect can be exerted to a certain degree.

The biomass raw material is subjected to grinding and crushing pretreatment, and the crushing granularity is 50-200 meshes.

The sepiolite, the quicklime and the activated biomass carbon material are uniformly mixed and then ground and crushed to 100-300 meshes.

The granular slow-release heavy metal fixing agent is placed in a constant-temperature oven at the temperature of 60-80 ℃ and dried to constant weight.

The invention also provides a slow-release heavy metal fixing agent which is prepared by the preparation method.

The invention also provides application of the slow-release heavy metal fixing agent, which is applied to remediation of heavy metal contaminated farmland soil.

Compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:

1) the slow-release heavy metal fixing agent provided by the invention can be added into heavy metal farmland polluted soil to effectively reduce the concentration of heavy metals such as effective cadmium, mercury and the like in the heavy metal farmland polluted soil, and if the content of the effective cadmium in the restored heavy metal farmland polluted soil is less than 1.5mg/kg, the content of the effective cadmium mercury in the restored heavy metal farmland polluted soil is less than 2 mg/kg.

2) The slow-release heavy metal fixing agent provided by the invention has the functions of slow-release heavy metal curing agent and pH regulation, most of the farmland soil polluted by cadmium and mercury is weakly acidic, the slow-release heavy metal fixing agent can slowly release alkaline substances and has the effect of micro-regulating the pH of the soil, meanwhile, the mobility of heavy metals in the farmland is reduced through precipitation, the heavy metal adsorption material can be slowly released, and the heavy metals are further fixed through adsorption and wrapping effects, so that the content of the effective heavy metals in the soil is greatly reduced, the soil polluted by the heavy metals is maintained to be repaired effectively for a long time and durably, the physical and chemical properties of the farmland soil and the microbial environment are effectively prevented from being damaged due to the fact that a large amount of chemical preparations are put into the farmland soil at one time, the growth of crops is not facilitated, the damage to the soil can be greatly reduced through a slow-release mode, and the original properties of the soil are kept, belongs to an environment-friendly fixing agent.

3) The slow-release heavy metal fixing agent provided by the invention can slowly release organic matters into soil, improves the soil fertility to a certain extent, and is beneficial to the growth of crops.

4) The slow-release heavy metal fixing agent provided by the invention is granular, does not generate dust in the farmland application process, avoids medicament waste and simultaneously does not pollute the air quality.

5) The slow-release heavy metal fixing agent provided by the invention is cheap in preparation raw materials, simple in process and capable of realizing industrial application.

Drawings

FIG. 1 is a flow chart of a preparation process of a slow-release heavy metal fixing agent.

Detailed Description

The present invention will be described in further detail with reference to the following drawings and specific examples. The following examples are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of the claims of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The instruments, reagents and the like used in the following examples are all available by conventional commercial means unless otherwise specified.

Example 1

(1) Grinding and crushing the straws to 50 meshes, transferring the straws into a heating furnace, heating the straws for 2 hours at 400 ℃ in a helium environment, and naturally cooling the straws to room temperature in the helium environment. Then, according to the liquid-solid ratio of 3 mL:1g of sodium hydroxide solution with the mass concentration of 1 percent is added, the mixture is stirred for 0.5h by air, and the air supply rate is 4m³And/min. Filtering and drying the filter cake in a constant-temperature oven at 95 ℃ to constant weight to obtain the activated biomass carbon material.

(2) Uniformly mixing 3 parts of sepiolite, 5 parts of quicklime and 92 parts of activated biomass carbon material, grinding and crushing to 200 meshes, transferring to a shaking table, and vibrating for 1h at constant temperature with the vibration frequency of 400rpm and the temperature of 60 ℃.

(3) 2 percent (mass percentage) of sodium alginate solution is slowly sprayed while shaking, and the spraying amount of the sodium alginate is 5 percent of the mass of the sepiolite, the quicklime and the activated biological mixed material.

(4) And (3) drying the obtained particles in a constant-temperature oven at 60 ℃ to constant weight to obtain the slow-release heavy metal fixing agent.

Example 2

(1) Grinding and crushing the rice hulls to 100 meshes, transferring the rice hulls into a heating furnace, heating the rice hulls for 1h at 600 ℃ in a helium environment, and naturally cooling the rice hulls to room temperature in the helium environment. Then, according to the liquid-solid ratio of 4 mL: adding 3% sodium hydroxide solution into 1g, stirring with air for 1.5 hr with air supply rate of 2m³And/min. Filtering and drying the filter cake in a constant-temperature oven at 100 ℃ to constant weight to obtain the activated biomass carbon material.

(2) Mixing 10 parts of sepiolite, 2 parts of quicklime and 88 parts of activated biomass carbon material uniformly, grinding and crushing to 100 meshes, transferring to a shaking table, and shaking for 2 hours at constant temperature with the shaking frequency of 300rpm and the temperature of 75 ℃.

(3) 4 percent (mass percentage) of sodium alginate solution is slowly sprayed while shaking, and the spraying amount of the sodium alginate is 3 percent of the mass of the sepiolite, the quicklime and the activated biological mixed material.

(4) And (3) drying the obtained particles in a constant-temperature oven at 70 ℃ to constant weight to prepare the slow-release heavy metal fixing agent.

Comparative example 1

(1) Grinding and crushing the straws to 50 meshes.

(2) Uniformly mixing 3 parts of sepiolite, 5 parts of quicklime and 92 parts of straws, grinding and crushing to 200 meshes, transferring to a shaking table, and vibrating for 1h at constant temperature with the vibration frequency of 400rpm and the temperature of 60 ℃.

(3) And 2 percent (mass percentage) of sodium alginate solution is slowly sprayed while shaking, and the spraying amount of the sodium alginate is 5 percent of the mass of the sepiolite, quicklime and straw mixture.

(4) And (3) drying the obtained particles in a constant-temperature oven at 60 ℃ to constant weight to obtain the slow-release heavy metal fixing agent.

Comparative example 2

(1) Grinding and crushing the straws to 50 meshes, transferring the straws into a heating furnace, heating the straws for 2 hours at 400 ℃ in a helium environment, and naturally cooling the straws to room temperature in the helium environment. Then, according to the liquid-solid ratio of 3 mL:1g of sodium hydroxide solution with the mass concentration of 1 percent is added, the mixture is stirred for 0.5h by air, and the air supply rate is 4m³And/min. Filtering and drying the filter cake in a constant-temperature oven at 95 ℃ to constant weight to obtain the activated biomass carbon material.

(2) Grinding and crushing 100 parts of activated biomass carbon material to 200 meshes, transferring to a shaking table, and oscillating for 1h at constant temperature, wherein the oscillating frequency is 400rpm, and the temperature is 60 ℃.

(3) 2 percent (mass percentage) of sodium alginate solution is slowly sprayed while shaking, and the spraying amount of the sodium alginate is 5 percent of the mass of the sepiolite, the quicklime and the activated biological mixed material.

(4) And (3) drying the obtained particles in a constant-temperature oven at 60 ℃ to constant weight to obtain the slow-release heavy metal fixing agent.

Comparative example 3

(1) Grinding and crushing the straws to 50 meshes, transferring the straws into a heating furnace, heating the straws for 2 hours at 400 ℃ in a helium environment, and naturally cooling the straws to room temperature in the helium environment. Then, according to the liquid-solid ratio of 3 mL:1g of sodium hydroxide solution with the mass concentration of 1 percent is added, the mixture is stirred for 0.5h by air, and the air supply rate is 4m³And/min. FiltrationAnd drying the filter cake in a constant-temperature oven at 95 ℃ to constant weight to obtain the activated biomass carbon material.

(2) Uniformly mixing 3 parts of sepiolite, 5 parts of quicklime and 92 parts of activated biomass carbon material, grinding and crushing to 200 meshes, transferring to a shaking table, and vibrating for 1h at constant temperature with the vibration frequency of 400rpm and the temperature of 60 ℃.

(3) Slowly spraying a proper amount of distilled water while shaking.

(4) And (3) placing the obtained mixture in a constant-temperature oven at 60 ℃ to dry to constant weight, thus obtaining the slow-release heavy metal fixing agent.

Examples 1 and 2 and comparative examples 1 to 3 were tested in the release cycle investigation of 5 kinds of sustained-release heavy metal fixing agents:

(1) example 1 release test of the prepared sustained-release heavy metal fixing agent:

adding 0.5cm of distilled water into a vessel, wetting 5 pieces of absorbent paper, stacking the wetted absorbent paper in the vessel, spreading 0.2cm of slow-release heavy metal fixing agent, covering the wetted absorbent paper with the wetted absorbent paper, spreading 0.2cm of slow-release heavy metal fixing agent, wetting 5 pieces of absorbent paper, covering the wetted absorbent paper with the wetted absorbent paper, sealing and storing the wetted absorbent paper in the shade, and storing the wetted absorbent paper in the cool place. Properly spraying distilled water according to the water content in the vessel, measuring the pH value of the water content in the vessel after 1d, and measuring once every 5d for 1 month.

(2) Example 2, comparative example 1, comparative example 2, and comparative example 3 the slow release heavy metal fixing agent release test:

the slow release heavy metal fixing agents prepared in example 2, comparative example 1, comparative example 2 and comparative example 3 were tested according to the test method of example 1.

(3) Results and analysis of the experiments

TABLE 1 examination of release period of slow-release heavy metal fixing agent

As can be seen from Table 1, after the sodium alginate solution is sprayed on the surface of the fixing agent, the pH of the system rises smoothly, while the sustained-release heavy metal fixing agent prepared in comparative example 3 without spraying sodium alginate diffuses into the system within one day, so that the pH of the system increases rapidly. Therefore, the slow-release heavy metal fixing agent prepared by the method has a good slow-release effect.

Examples 1 and 2 and comparative examples 1 to 3 are 5 slow-release heavy metal fixing agents and heavy metal fixing effect test tests:

the method comprises the steps of selecting cadmium and mercury compound contaminated farmland soil in Jiangxi as a test material, detecting the cadmium content in the soil by taking the soil according to a graphite furnace atomic absorption spectrophotometry (GB/T17141-1997) for detecting lead and cadmium in soil quality, detecting the mercury content in the soil according to an atomic fluorescence method (GB/T22105.1-2008) for detecting total mercury, total arsenic and total lead in soil quality, detecting the effective cadmium content in the soil according to a DTPA leaching-inductively coupled plasma emission (HJ804-2016) for detecting 8 effective elements in the soil, and detecting the effective mercury content in the soil according to an atomic fluorescence method (DB35/T1459-2014) for detecting the effective arsenic and the effective mercury in acid soil.

Through detection, the cadmium content in the soil is 0.98mg/kg, the mercury content is 0.37mg/kg, the effective cadmium content is 0.352mg/kg, and the effective mercury content is 0.017 mg/kg.

(1) Example 1 test of heavy metal fixation effect of the slow-release heavy metal fixative:

taking soil to be tested into a reaction container, spraying a small amount of distilled water to keep the soil in a wet state, adding the slow-release heavy metal fixing agent prepared in the example 1 according to 0.5% of the mass of the soil, uniformly stirring, maintaining, sampling and detecting the content of effective cadmium and effective mercury in the test soil after 1d of maintenance, measuring every 5d, and properly spraying a small amount of distilled water according to the soil state to keep the soil moisture in the period of half a month.

(2) Example 2, comparative example 1, comparative example 2, and comparative example 3

The slow release heavy metal fixing agents prepared in example 2, comparative example 1, comparative example 2 and comparative example 3 were tested according to the test method of example 1.

(3) Results and analysis of the experiments

TABLE 2 heavy metal fixation effect test of slow-release heavy metal fixation agent

Note: "ND" means not detected, i.e., less than 0.002mg/kg of the detection limit of the method.

As can be seen from table 2, it is found that the slow-release heavy metal fixing agent prepared directly without activation in comparative example 1 has far less effect of fixing heavy metal cadmium mercury than the slow-release heavy metal fixing agent prepared in example 1 in comparative example 1. The activated biomass has larger specific surface area, stronger adsorbability to the fixed heavy metal and important effect on reducing the content of the effective heavy metal in the polluted soil. Compared with the example 1 and the comparative example 2, the slow release heavy metal fixing agent prepared by the comparative example 2 without adding the sepiolite and the quicklime has the lower fixing effect on the heavy metal cadmium and mercury than the slow release heavy metal fixing agent prepared by the example 1. The quick lime has the effect of improving the pH value of the soil and promoting the precipitation of the heavy metal, the sepiolite has strong adsorbability on the heavy metal, and the heavy metal concentrate is adsorbed and wrapped by the high adsorbability of the activated biomass, so that the content of the effective heavy metal in the polluted soil can be greatly reduced, and the quick lime has more excellent effect than a single biomass. It can be clearly seen from comparison of comparative example 3 with examples 1 and 2, comparative example 1 and comparative example 2 that the slow-release heavy metal fixing agent sprayed with sodium alginate has a better slow-release effect.