CN110591728B - Conditioner for mercury-polluted soil and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of farmland soil remediation, and particularly discloses a conditioner for remediation and treatment of mercury-contaminated soil and a preparation method thereof. The conditioner for mercury contaminated soil remediation is prepared from the following five raw materials in percentage by weight (%): 10-15 parts of bentonite, 30-40 parts of quicklime, 10-20 parts of sepiolite powder, 30-35 parts of humic acid and 5-10 parts of chitosan. The conditioner disclosed by the invention is simple in raw material composition, wide in source, low in price, simple in preparation method, low in repair cost and suitable for large-area popularization; but also can realize the reduction of the mercury content in various forms.

Description

Conditioner for mercury-polluted soil and preparation method thereof

Technical Field

The invention belongs to the field of farmland soil remediation, and particularly relates to a conditioner for remediation and treatment of mercury-contaminated soil and a preparation method thereof.

Background

Mercury is an environmental poison seriously harming human health, mercury pollution has the characteristics of durability, easy migration, high biological enrichment, strong toxicity and the like, mercury in any form in the environment can be converted into highly toxic methyl mercury under certain conditions, and particularly after the mercury enters soil, the health and safety of crops are directly threatened. According to investigation, the Guizhou, Jilin, Shaanxi, Hubei, Liaoning, Chongqing and other places in China are polluted by mercury, wherein the Guizhou area is the most serious, and the excess elevation of part of the Guizhou area reaches 50 times.

Some agents for remedying mercury-contaminated soil have appeared at present, for example, chinese patent application (application No. 201910627786.2) discloses a mercury-contaminated soil passivation conditioner and a preparation method thereof, which comprises the following main raw materials in parts by weight: 50-70 parts of attapulgite, 10-20 parts of modified fly ash, 15-20 parts of humic acid, 7-10 parts of plant ash, 10-13 parts of phosphate tailing powder, 20-30 parts of sodium thiosulfate, 5-10 parts of ferrous oxide, 5-8 parts of calcium hydroxide and 100-130 parts of water. The invention can effectively reduce the effectiveness of mercury in soil, reduce the absorption and enrichment of mercury by crops and improve the physical and chemical properties of soil. Chinese patent application (application number: 201910281046.8) discloses a mercury-contaminated soil remediation agent and a preparation method thereof, and the agent is composed of the following raw materials: 20-30 parts of diopside, 3-8 parts of sodium dimethylthiocarbamate, 10-18 parts of lime, 15-25 parts of chitosan, 5-10 parts of sodium thiosulfate, 10-22 parts of sepiolite, 8-15 parts of pig manure, 5-10 parts of plant ash and 4-8 parts of pig bone ash. The soil remediation agent can reduce the mercury concentration in soil to meet the national second-level soil quality standard concentration, and can improve the organic matters in the soil.

However, these products still have the following problems:

(1) most raw materials are complex in composition, and part of raw materials are narrow in source range, so that the method is not beneficial to large-area popularization and use.

(2) The raw materials contain phosphorus, thiosulfate and other components, the long-term use of the phosphorus-containing material can make the soil strongly alkaline and induce water eutrophication, and the use of thiosulfate can cause secondary release of mercury.

(3) Most products can reduce the concentration of mercury in soil to a certain extent, but the production method of the products is complex and the repair cost is high.

(4) Most products can reduce the content of one form of mercury, but it is difficult to achieve reduction of the content of multiple forms of mercury. The effective mercury in the mercury form is easily absorbed by crops, and the iron-manganese oxidation state and the organic combination state have potential effectiveness and can be converted into the effective state under the condition of changing soil environment and then absorbed by the crops.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a soil conditioner which can effectively repair mercury-polluted soil, has simple raw materials and lower repair cost, and a preparation method thereof.

The invention achieves the above purpose through the following technical scheme:

a mercury-polluted soil conditioner is prepared from five raw materials in percentage by weight:

raw material weight percent (%)

10-15 parts of bentonite

30-40 portions of quicklime

Sepiolite powder 10-20

Humic acid 30-35

5-10 parts of chitosan;

the sum of the weight percentages of the five raw materials is 100 percent;

preferably, the mercury-polluted soil conditioner is prepared from the following five raw materials in percentage by weight: raw material weight percent (%)

Bentonite 12

Quicklime 33

Sepiolite powder 15

Humic acid 34

Chitosan 6

The calcium oxide content in the quicklime is more than or equal to 85 percent by mass, and the calcium oxide is powder obtained by calcining and crushing limestone raw ore and then sieving the calcined limestone raw ore with a 60-100-mesh sieve.

The sepiolite powder is the powder of milled sepiolite raw ore, the purity is more than or equal to 20 percent, and the sepiolite powder is the powder of air-dried and crushed sepiolite raw ore which is sieved by a sieve with 60 to 100 meshes.

The bentonite is sodium bentonite, the alkalinity coefficient is more than 1, the montmorillonite content is more than or equal to 85 percent, and the bentonite is powder obtained by air drying and crushing raw ore and sieving the crushed raw ore with a 60-100-mesh sieve.

The humic acid is humic acid raw powder, the organic matter is more than or equal to 85 percent, and the grain diameter is less than or equal to 0.20 mm.

The chitosan is chitosan raw powder, the effective component is more than or equal to 99 percent, the deacetylation degree is more than or equal to 70 percent, and the particle size is less than or equal to 0.20 mm.

The moisture content and the heavy metal content of the five raw materials of bentonite, quicklime, sepiolite powder, humic acid and chitosan all meet the following requirements: the mass percentage content of water is less than or equal to 3 percent, the mercury content is less than or equal to 2mg/kg, the arsenic content is less than or equal to 10mg/kg, the cadmium content is less than or equal to 3mg/kg, the lead content is less than or equal to 50mg/kg and the chromium content is less than or equal to 50 mg/kg.

A preparation method of the mercury-contaminated soil conditioner comprises the following steps:

(1) and (3) uniformly mixing: taking five raw materials of bentonite, quicklime, sepiolite powder, humic acid and chitosan according to the weight parts, mixing and stirring uniformly.

(2) Heating and drying: drying the uniformly mixed raw materials at the temperature of 60-70 ℃.

(3) Processing and grinding: and (3) after the mixture is dried, grinding the mixture to ensure that more than 95 percent of the mixture can pass through a standard sieve of 100 meshes to obtain the mercury-polluted soil conditioner.

Further, the method can also comprise the step (4) of cooling and packaging: and (5) packaging when the temperature of the finished product is reduced to below 40 ℃.

Further, the time required for uniform mixing in the step (1) is 3 hours or more.

Further, the time required for adding and drying in the step (2) is more than 1 hour.

Compared with the prior art, the invention has the advantages and beneficial effects that:

(1) the conditioner disclosed by the invention is simple in raw material composition, wide in source and low in price, can well control the production cost, and is beneficial to large-area popularization and use. Bentonite, quicklime, humic acid and the like are common commodities in various places; sepiolite is a natural ore with a large amount of deposits in Hunan province and is low in price; chitosan is widely available in nature and is easily purchased.

(2) The conditioner uses a certain amount of quicklime, on one hand, the quicklime contains calcium ions and can compete for exchange sites on the surface of a plant rhizosphere with trace mercury ions; on the other hand, after the quicklime is dissolved in water, the pH value reaches 10-13, the quicklime is strong in basicity, the pH value of the soil can be improved by 0.2-0.4 unit, the activity of mercury in the soil is reduced, and meanwhile, the soil acidification problem can be relieved.

(3) The conditioner disclosed by the invention can effectively reduce the content of mercury in soil, and can also increase the fertilizer efficiency, improve the use efficiency of a chemical fertilizer and improve the biomass and quality of crops. The bentonite, as a natural clay mineral, reduces the bioavailability of heavy metals mainly through adsorption; ca (OH) generated by reaction after quicklime is applied into soil₂The pH value of the soil can be increased, and the soil can form an antagonistic action with mercury to block the absorption of the mercury by crops; the sepiolite has rich microporous structure and strong adsorption capacity, and can adsorb free molecules or ions in the fertilizerIn the pore canal, the slow release prolongs the fertilizer efficiency by more than one time, greatly improves the utilization rate of the fertilizer, and can also have strong adsorption capacity to mercury through complexation, ion exchange and the like; humic acid is beneficial to HgCl₂The mercury is converted into organic combined mercury, on the other hand, the mercury can also play a fixing role on atmospheric mercury and can absorb mercury vapor to form the organic combined mercury, and the organic combined mercury can become a form which can not be utilized in the microbial activity, so that the opportunity that the microbes reduce the ionic mercury into elemental mercury is reduced, and the volatilization of the soil mercury is prevented; the chitosan as an organic substance can increase beneficial bacteria such as actinomycetes in soil, reduce harmful bacteria such as fusarium and nematodes and the like, enhance the fertilizer capacity of the soil, and reduce the effectiveness of mercury because active groups containing amino, hydroxyl and the like are easy to perform complexation or chelation reaction with mercury to generate a stable product.

(4) The conditioner is environment-friendly and does not cause secondary pollution. Can adapt to various soil qualities, aims at various forms of mercury, and can assist in solidifying (stabilizing) heavy metals such as cadmium, lead and the like in soil.

Detailed Description

In the following examples 1 to 5, raw quicklime, which is provided by a lime plant in Hunan Tan county, Hunan province and has a calcium oxide content of not less than 85% by mass, was prepared by calcining and pulverizing limestone raw ore and sieving the pulverized limestone raw ore with a 80-mesh sieve; the raw materials of bentonite and sepiolite are prepared by air drying and crushing corresponding raw ores and sieving the crushed raw ores through a 80-mesh sieve, wherein the two raw ores are provided by a certain ore powder plant in Ningxiang county of Hunan province; humic acid is humic acid raw powder, and organic matter is more than or equal to 85 percent and is provided by Jinan Hongyang cultural engineering limited company; the chitosan is raw chitosan powder, the effective component is more than or equal to 99 percent, the deacetylation degree is more than or equal to 70 percent, and the chitosan is provided by Shaanxi Yuan plant Biotechnology Limited.

The soil pH determination method comprises the following steps: taking water as a leaching agent, collecting a small amount of soil, and mixing the soil and water according to a water-soil ratio of 2.5: 1, and measured by a potentiometric method (see NY/T1377-2007).

Example 1:

a conditioner for restoring soil polluted by mercury is prepared from five raw materials in percentage by weight as follows:

raw material weight percent (%)

Bentonite 12

Quicklime 33

Sepiolite powder 15

Humic acid 34

Chitosan 6

The preparation method of the conditioner for restoring soil polluted by mercury comprises the following steps:

(1) and (3) uniformly mixing: taking various raw materials such as bentonite, quicklime, sepiolite powder, humic acid, chitosan and the like according to the weight percentage, mixing the raw materials and stirring uniformly.

(2) Heating and drying: and (3) drying the uniformly mixed raw materials at 65 ℃.

(3) And (3) processing and grinding, drying the mixture, and grinding to enable more than 95% of the mixture to pass through a standard sieve of 100 meshes to obtain the mercury-polluted soil conditioner.

Examples 2 to 5: a conditioner for restoring soil polluted by mercury is prepared from the following five raw materials in percentage by weight (unit:%):

examples	2	3	4	5
					Bentonite clay	10	10	12	15
Quick lime	40	30	30	34
					Sepiolite powder	12	18	20	10
Humic acid	33	32	30	35
					Chitosan	5	10	8	6

Examples 2-5 preparation of a conditioner for remediation of soil contaminated with mercury was the same as in example 1.

The plot test for the mercury contaminated soil conditioner prepared in example 1 is as follows:

dividing a certain mercury-polluted pepper planting base into 9 cells of 2m multiplied by 5m, planting 40 peppers in each cell, and arranging protection rows of 1m in width around a test area. The fertilization level is completely consistent with other field management measures.

Treatment 1: blank (CK), conventional fertilization without any conditioner;

and (3) treatment 2: conventional fertilization plus 150 kg/acre basal application of the conditioner prepared in example 1;

and (3) treatment: conventional fertilization + 250 kg/mu basal application of the conditioner prepared in example 1;

on the basis of conventional fertilization, the conditioner is uniformly spread on the field surface 6 days before ploughing by adopting a manual spreading mode, ploughing by using a rotary cultivator for 2 times to uniformly mix the conditioner with soil, and watering sufficient water for stable curing. During the growth period of the pepper, weeding, fertilizing, pesticide spraying, irrigating and the like are carried out according to a local production management mode.

The peppers are harvested after about 45 days of growth. And randomly collecting 3-5 pepper plants which are 35-45cm away from the ground and face the same direction in each cell as a mixed sample in each cell, wherein each cell is processed by 3 mixed samples respectively for detecting the fresh weight of a single pepper and the mercury content in a dried pepper sample, and finally picking off the pepper corresponding to each cell for field production measurement. Collecting 1 soil sample in each cell, wherein the collection depth of the soil sample is 0-20cm, removing impurities such as surface garbage, residual leaves and the like, selecting 1kg of soil by a five-point sampling method, and treating 3 soil samples in each cell for detecting the mercury form and the effective mercury content in the soil.

Sample treatment and analysis:

1. treatment mode for measuring weight of single fruit of crop and mercury content in crop

And washing the crop sample with tap water, then washing with deionized water, naturally drying the surface water, and weighing the fresh weight of the single pepper. And after weighing the fresh weight, placing the weighed fresh weight in a constant-temperature drying oven at 60 ℃ for drying for 72 hours until the fresh weight is constant, recording the dry weight of the sample, and crushing the sample by using a plant sample crusher for measuring the mercury content in the dry sample.

2. Processing mode for determining crop yield

And washing the sample of the crop in the residential area with tap water, then washing the sample with deionized water, and weighing the total amount of the pepper after the surface moisture is naturally dried.

3. Treatment mode for determining soil sample

And naturally drying the soil sample at room temperature, and sieving the ground soil sample with a 80-mesh sieve.

The mercury content in crops, the total mercury in soil and the like are measured by a cold atom absorption spectrometry. And (3) measuring various forms of mercury in the soil by adopting a continuous chemical leaching method.

Main results and analysis:

1. basic physicochemical properties of soil

The physicochemical properties of the soil tested were as follows: the pH value of the soil is 6.3; the organic matter content of the soil is 17 g/kg; the total mercury content is 7.54mg.kg^-1The soil to be tested belongs to moderate mercury-polluted soil. Wherein the available mercury is 0.023mg.kg^-1The content of mercury in the iron-manganese oxidation state is 0.12mg^-1The content of organic combined mercury is 6.86mg.kg^-1The content of mercury in residue state is 0.61mg.kg^-1。

The mercury content is measured by mercury element.

2. Effect of different treatments on quality of individual Pepper fruits

The effect of different treatments on the quality of individual pepper fruits is shown in table 1. From the test results, it was found that the mass of the single fruit in treatment 1(CK) was only 31.6 g/piece, and the mass of the single fruit in treatment 2 and treatment 3 was increased by 1.6 g/piece and 4.9 g/piece, respectively, as compared with that in treatment 1(CK), and the increase was 5.06% and 15.51%, respectively. This shows that the conditioner prepared in example 1 can effectively improve the quality of the single pepper fruits, and further improve the quality and commodity rate of the pepper fruits.

TABLE 1 Effect of different treatments on the quality of individual Pepper fruits

3. Effect of different treatments on Mercury content in Capsicum annuum

The effect of the different treatments on the mercury content of the peppers is shown in table 2. According to the test results, the mercury content in the pepper treated by the method 2 is 0.009mg/kg, which is reduced by 0.013mg/kg and 59.09% compared with the method treated by the method 1; the mercury content in the pepper treated by the treatment 3 is 0.004mg/kg, which is reduced by 0.018mg/kg and 81.82% compared with that in the pepper treated by the treatment 1. This shows that the application of the conditioner prepared in example 1 can effectively reduce the mercury content in the pepper, and both treatments can make the pepper reach the pollutant limit in national food Standard for food safety (GB 2762-2017) (total mercury is less than or equal to 0.01 mg/kg).

TABLE 2 Effect of different treatments on Mercury content of Capsicum annuum

4. Influence of different treatments on pepper acre yield

The effect of different treatments on the per mu yield of pepper is shown in table 3. From the test results, the acre yield of the treatment 1(CK) is only 406 kg/acre, and the acre yields of the treatment 2 and the treatment 3 are respectively increased by 137 kg/acre and 215 kg/acre compared with the treatment 1(CK), and the increase ranges are respectively 33.74 percent and 52.96 percent. This shows that the application of the conditioner prepared in example 1 can effectively increase the acre yield of the pepper, and further greatly increase the pepper planting benefit, on one hand, the conditioner contains nutrient elements, and on the other hand, the heavy metal activity is inhibited, so that the toxicity of the heavy metal to crops is reduced.

TABLE 3 influence of different treatments on the acre yield of capsicum annuum

5. Effect of different treatments on Mercury content in soil

The effect of different treatments on the mercury content of the soil is shown in table 4. The test results show that the mercury content in the soil treated 1 is 7.54mg/kg, which exceeds the soil pollution risk control standard (GB 15618-; the mercury content in the soil treated by the method 3 is 1.03mg/kg, which is reduced by 6.51mg/kg and 86.33% compared with the soil treated by the method 1. This demonstrates that the application of the conditioner prepared in example 1 is effective in reducing the mercury content of the soil.

TABLE 4 Effect of different treatments on soil Mercury content

6. Effect of different treatments on Mercury morphology in soil

The contents of organic combined mercury, residual mercury, iron-manganese oxidized state and soil available state mercury (including dissolved state and exchangeable state mercury and special adsorbed state mercury) before and after remediation are measured by using a continuous chemical leaching method, and the influence of different treatments on the mercury state is shown in table 5. After the treatment 1, the organic combined mercury, the residual mercury, the iron-manganese oxidized mercury and the effective mercury are all reduced to a certain degree. Wherein, the mercury in the organic combination state and the iron-manganese oxidation state is a potential bioavailable state, can be absorbed by plants under certain conditions, and can obviously reduce the content of the mercury in the organic combination state and the iron-manganese oxidation state after being treated 2 and 3. The conditioner is added to change the soil environment such as pH, oxidation-reduction potential and the like, and physical and chemical reactions such as complexation are generated to change the chemical form and occurrence state of mercury elements in the soil, so that the activity of the soil mercury is reduced.

TABLE 5 Effect of different treatments on soil Mercury morphology

Claims (2)

1. The mercury-polluted soil conditioner is characterized by being prepared from the following components in percentage by weight: 10-15% of bentonite, 30-40% of quicklime, 10-20% of sepiolite powder, 30-35% of humic acid and 5-10% of chitosan; the bentonite is sodium bentonite, and the content of montmorillonite is more than or equal to 85 percent; sieving bentonite, quicklime, sepiolite powder, humic acid and chitosan with 60-100 mesh sieve; the preparation method of the conditioner comprises the following steps:

(1) and (3) uniformly mixing: taking five raw materials of bentonite, quicklime, sepiolite powder, humic acid and chitosan, mixing and stirring uniformly;

(2) heating and drying: drying the uniformly mixed raw materials at the temperature of 60-70 ℃;

(3) processing and grinding: and (3) after the mixture is dried, grinding the mixture to ensure that more than 95 percent of the mixture can pass through a standard sieve of 100 meshes to obtain the mercury-polluted soil conditioner.

2. The mercury-contaminated soil conditioner according to claim 1, characterized by being prepared from the following components: 12% of bentonite, 33% of quicklime, 15% of sepiolite powder, 34% of humic acid and 6% of chitosan.