CN114437732B - Compound leaching agent for arsenic-polluted soil and method for repairing arsenic-polluted soil - Google Patents

Abstract

The invention discloses a compound leaching agent for arsenic-polluted soil and a method for repairing the arsenic-polluted soil. The compound eluent consists of sodium dithionite and tartaric acid, arsenic-polluted soil and the compound eluent are uniformly mixed, and arsenic in the soil can be effectively removed by oscillation leaching. The invention utilizes the combination and the compounding of the sodium dithionite and the tartaric acid, can effectively reduce the content of arsenic in polluted soil, has the arsenic removal rate of more than 80 percent, has simple components of the leaching agent, obvious effect and low cost, and has good application prospect.

Description

Compound leaching agent for arsenic-contaminated soil and remediation method for arsenic-contaminated soil

Technical field

The invention relates to the technical field of arsenic-contaminated soil treatment and remediation, and specifically to a compound leaching agent for arsenic-contaminated soil and a remediation method for arsenic-contaminated soil.

Background technique

Arsenic is a toxic and carcinogenic metalloid element. It is one of the five major poisons in environmental pollution. It is listed as the first type of pollutant in environmental protection standards. Domestic arsenic pollution mainly comes from waste from the mining and smelting process of arsenic-containing ores and industrial waste residue from arsenic production enterprises, and shows the characteristics of wide range of pollution, deep pollution degree, and serious harm. According to the "National Soil Pollution Situation Survey Bulletin" issued by the Ministry of Environmental Protection and the Ministry of Land and Resources in 2014, the total exceedance rate of soil pollution nationwide was 16.1%, and heavy metal pollution accounted for a large proportion, of which the arsenic site exceedance rate was 2.7%. . The survey found that the overall soil environmental situation across the country is not optimistic, with serious soil pollution problems in some areas, worrying soil environmental quality in cultivated land, and prominent soil environmental problems in abandoned industrial and mining lands. Red soil soil in China is mainly distributed in the low mountainous and hilly areas south of the Yangtze River, including most of Jiangxi and Hunan provinces, Guangdong and other southern China regions. Red soil is called ferro-aluminous soil, mainly because the main reason why red soil is formed is through the process of desilicate-rich iron-aluminization. In this type of soil, the iron and aluminum content is very high, while silicon, calcium, magnesium, sodium and other elements are low. According to surveys, arsenic pollution accounts for a large proportion of heavy metal pollution in soil in southern China, which causes arsenic to form stable oxides with iron and aluminum in red soil soil after entering the soil. The high iron, aluminum and arsenic-contaminated soil in southern my country has become a typical type of arsenic-contaminated soil with wide distribution and uniqueness. There are five main forms of arsenic in soil. In red loam soils with high iron and aluminum content, arsenic is mainly in the form of amorphous and poorly crystalline hydrated oxides of iron and aluminum, and well-crystallized hydrated oxides of iron and aluminum. Form exists. In these two forms, arsenic and iron and aluminum form iron and aluminum oxides with good stability, so it is more difficult to remediate this type of arsenic-contaminated soil. In addition, arsenic accumulated in this type of contaminated soil is difficult to eliminate through dilution and self-purification, and cannot be decomposed by soil microorganisms; on the contrary, organisms can enrich arsenic, often causing it to gradually accumulate in the soil environment, Arsenic can even be converted into more toxic compounds in the soil, and some can accumulate in the human body at harmful concentrations through the food chain, seriously endangering human health. Excessive intake of such heavy metals can cause varying degrees of damage to bones and nerves. damage and increase the risk of cancer. Therefore, the remediation of arsenic-contaminated soil in southern red loam soil is of great significance.

Current methods for remediating arsenic-contaminated soil mainly include physical, chemical and biological methods. The physical method mainly uses certain engineering techniques and means to remediate contaminated soil, including the guest soil method, the soil replacement method and other methods. Chemical methods mainly include in-situ passivation method, in-situ leaching method and ex-situ leaching method, mainly by adding certain chemical reagents or amendments, in order to directionally change the existence form of arsenic in the soil, through separation, adsorption, transformation, etc. The action reduces the bioavailability of arsenic, or promotes the dissolution of pollutants in the soil through leaching agents or accelerates migration, causing arsenic in the soil to migrate into the leaching agent and flow out with it. Biological methods mainly include animal remediation, phytoremediation, and microbial remediation, which are methods that use natural or genetically engineered microorganisms or plants and some specific animals to remove arsenic from the soil, improve soil quality, and restore soil functions.

Compared with other technologies, soil ex-situ leaching technology has become one of the main technologies currently used to study the remediation of soil arsenic pollution due to its short remediation cycle, high removal efficiency, and stable effect. The key to leaching and remediating arsenic-contaminated soil is to find an economical and efficient leaching agent. At the same time, different leaching agents must be selected according to the presence of arsenic in the soil and the characteristics of the soil. In the remediation of arsenic-contaminated soil, various forms of arsenic need to be remediated, especially the most abundant form, so as to achieve a greater degree of removal of arsenic in the soil.

Aiming at the remediation of arsenic-contaminated soil that is mainly combined with iron and aluminum oxides, the Korean invention patent with publication number KR2015073289 (A) discloses a method for remediating iron- and aluminum-rich arsenic-contaminated soil. This method has been published under acidic conditions. Sodium oxalate is used as an eluent to extract arsenic bound to iron or aluminum amorphous oxides through contact with arsenic-contaminated soil. This method mainly uses sodium oxalate to extract arsenic from most amorphous iron and aluminum oxides in the soil, but it has great limitations for the extraction of other forms of soil with high arsenic content.

The Chinese invention patent with publication number CN111957731A discloses a sulfur-induced stabilization treatment method for iron-rich arsenic-contaminated soil. The method discloses the use of sodium sulfide solution induction to accelerate the conversion of amorphous iron oxides in the soil into stable iron ore. It allows the arsenic initially adsorbed on the surface of iron oxide to enter the stable iron mineral structure, thereby improving the stability of arsenic in the soil and reducing the mobility and toxicity of arsenic in arsenic-contaminated soil. This invention stabilizes iron-rich arsenic-contaminated soil and transfers the originally unstable arsenic into stable iron ore. However, this method does not remove the total arsenic content in the soil from the root cause. As time and the environment change, Changes in the stability of arsenic-containing iron minerals will decrease, which will lead to the re-release of arsenic inside, which will again cause secondary pollution of arsenic and increase environmental risks.

According to surveys, in current cases of leaching and remediation of iron-rich and aluminum-rich arsenic-contaminated soils in southern red loam soils, most of the leaching agents used in the remediation of contaminated soils are less effective and fail to achieve the expected results. Therefore, it is very necessary to develop a compound leaching agent and its application method for remediating arsenic-contaminated soil in southern red loam soil.

Contents of the invention

The purpose of the present invention is to achieve the remediation of arsenic-contaminated soil and provide a compound leaching agent and an application method for remediating arsenic-contaminated soil in southern red loam soil. In this method, sodium dithionite and tartaric acid are first prepared into a single eluent solution, and then the two solutions are combined into a compound eluent according to different concentrations and volumes; the arsenic-contaminated soil undergoes preparatory steps such as air-drying, impurity removal, grinding, and sieving. Treatment, mix evenly with a certain amount of compound eluant and then put it into a oscillator for oscillation elution experiments. The present invention selects a compound combination of two eluents, sodium dithionite with reducing properties and tartaric acid with complexing properties. Sodium dithionite extracts arsenic in contaminated soil by reducing and dissolving iron oxide related to arsenic. Adding tartaric acid can dissolve the arsenic. The iron that comes out forms a complex, which greatly enhances the extraction of reduced arsenic. On the one hand, it prevents the precipitation of new iron oxide phases. On the other hand, it can enhance the dissolution of iron oxide through the non-reducing dissolution pathway. In addition, the addition of tartaric acid will also It has the effect of removing other forms of arsenic in the soil. The combined leaching of the two eluants will increase the leaching amount of arsenic in the red soil soil. The present invention is aimed at remediating arsenic-contaminated soil in southern red soil. By adding a compound eluant, the iron oxide form with strong stability in arsenic-contaminated soil is extracted. The compound eluant is effective in elucidating and repairing arsenic pollution in southern red soil. Soil has better results.

The invention provides a method for remediating arsenic-contaminated soil, which is characterized in that it includes the following steps:

1) Mix the compound eluant and arsenic-contaminated soil evenly, and perform oscillation elution; the compound eluent is obtained by mixing sodium dithionite and tartaric acid solutions;

2) Separate the soil from solid and liquid after oscillation and elution, remove the elution waste liquid, add clean water, and continue oscillation and elution;

3) Perform solid-liquid separation on the soil washed with clean water and remove the clean water to obtain the repaired soil.

Preferably, in terms of molar concentration, the compound eluent consists of the following components: 0.1~0.3mol/L sodium dithionite: 30%~80% volume; and 0.05~0.6mol/L tartaric acid: 20%~70% capacity.

Preferably, the solid-liquid ratio of the composite eluent and contaminated soil in step 1) is: 1g:10~20mL; preferably, the arsenic-contaminated soil is southern red loam. Further preferably, the oscillation elution time described in step 1) is 6 to 8 hours;

In a specific implementation, the oscillation and elution are carried out in the oscillator described in steps 1) and 2), and the rotation speed is 180~200r/min;

Preferably, the oscillation elution time described in step 2) is 0.5~1h;

In a specific embodiment, the solid-liquid ratio of the clean water in step 3) and the arsenic-contaminated soil after leaching is 1g:5~10mL;

The invention also provides a compound leaching agent for repairing arsenic-contaminated soil, which is characterized in that it is obtained by mixing sodium dithionite and tartaric acid solution.

Preferably, in terms of molar concentration, the eluent in S1 consists of the following components: 0.1~0.3mol/L sodium dithionite: 30%~80% volume part; and 0.05~0.6mol/L tartaric acid: 20 %~70% capacity.

The present invention further provides the application of the compound eluant in repairing arsenic-contaminated soil, especially arsenic-contaminated soil in southern red soil.

Compared with the existing technology, the present invention has the following beneficial effects: the present invention achieves enhanced extraction of arsenic bound to amorphous and crystalline iron oxides by combining sodium dithionite and tartaric acid into a compound eluent.

Sodium dithionite has a good dissolving effect on arsenic-containing crystalline iron oxides, but the research of the present invention found that arsenic will be re-adsorbed by the newly formed iron oxide phase in the soil, so the extraction effect of sodium dithionite on arsenic is not obvious; Tartaric acid has a better extraction effect on arsenic combined with amorphous iron oxides. The simultaneous use of sodium dithionite and tartaric acid effectively removes arsenic bound to amorphous and crystalline iron oxides by inducing a synergistic effect. It also reduces new minerals and increases the removal of the main forms of arsenic in red soil. This further improves the remediation effect on arsenic pollution in red loam soils in the south.

The present invention further selects the appropriate eluent concentration, volume ratio and elution process parameter range by changing the volume ratio and molar concentration of sodium dithionite and tartaric acid as well as the elution process parameters. The composite compound configured under such conditions The eluent effectively reduces the formation of secondary minerals and improves the removal rate of arsenic in the soil, effectively reducing the arsenic content in the soil.

The leaching process of the present invention is simple and the processing time is short, which further shortens the operation time and greatly reduces the processing cost. The tartaric acid in the compound eluent is a biodegradable organic acid, which has little impact on the physical and chemical properties and structure of the soil, reducing secondary pollution of the soil. It can also compensate for some nutrients in the soil and is suitable for promotion and use.

Detailed ways

In order to better present the technical content, implementation objectives and effects of the present invention, further description will be given below with reference to specific embodiments. Obviously, the embodiments described below are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Unless otherwise stated, the test methods used in the examples are conventional methods; unless otherwise stated, the materials and reagents used are commercially available reagents and materials.

Example 1

Collected from an actual contaminated site in the south, dried naturally, removed impurities, and then pulverized and passed through a 60-mesh sieve. The basic physical and chemical properties and heavy metal content of soil are shown in Table 1.

Table 1 Basic physical and chemical properties of soil and heavy metal content

Moisture content(%) Soil type As(mg/kg) Fe(mg/kg) Al(mg/kg) Mn(mg/kg) 10.55 red soil 70 20042.65 26071.25 283.45

1. Weigh sodium dithionite, dissolve tartaric acid in water in different containers and mix evenly to obtain 0.1mol/L sodium dithionite solution and 0.6mol/L tartaric acid solution;

2. Mix the 0.1 mol/L sodium dithionite solution with a volume of 40% and the 0.6 mol/L tartaric acid solution with a volume of 60% to obtain a compound eluent;

3. At room temperature, according to the solid-liquid ratio (g:ml) of 1:10, mix the compound eluent and 3g of arsenic-contaminated soil evenly, and shake and elute in a oscillator at 180 r.min ^-1 6h;

4. Separate the liquid and solid of the soil after oscillation and elution, collect the elution waste liquid, add clean water to the container according to the solid-liquid ratio (g:ml) of 1:5, and continue oscillation and elution in the oscillator for 0.5h;

5. Separate the liquid and solid of the soil washed with clean water, and remove the clean water to obtain the repaired soil.

After the reaction, the arsenic concentration in the leaching waste liquid was measured by atomic fluorescence emission spectrometry; the arsenic content remaining in the soil after leaching was determined in accordance with the "Determination of Mercury, Arsenic, Selenium, Bismuth, and Antimony in Soil and Sediment Microwave Digestion" /Atomic Fluorescence Method" (HJ 832~2017), to determine the content of residual arsenic in soil.

After remediation using the above methods, the arsenic content of the original arsenic-contaminated soil was reduced from 70mg/kg to 21.98mg/kg, with a removal rate as high as 68.6%. The content of the contaminated soil after remediation reached the second-level national soil environmental quality standard.

Example 2

1. Weigh sodium dithionite, dissolve tartaric acid in water in different containers and mix evenly to obtain 0.2mol/L sodium dithionite solution and 0.5mol/L tartaric acid solution;

2. Mix the 0.2 mol/L sodium dithionite solution with a volume of 50% and the 0.05 mol/L tartaric acid solution with a volume of 50% to obtain a compound eluent;

3. At room temperature, according to the solid-liquid ratio (g:ml) of 1:15, mix the compound eluent and 3g of the same arsenic-contaminated soil as in Example 1 evenly, and mix in a oscillator at 180 r.min ^-1 Elute with shaking for 8 hours;

4. Separate the soil from solid and liquid after oscillation and elution, collect the elution waste liquid, add clean water to the container according to the solid-liquid ratio (g:ml) of 1:10, and continue oscillation and elution in the oscillator for 1 hour;

5. Separate the soil from solid and liquid after washing with water, and remove the water to obtain the repaired soil.

After the reaction, the arsenic concentration in the leaching waste liquid was measured by atomic fluorescence emission spectrometry; the arsenic content remaining in the soil after leaching was determined in accordance with the "Determination of Mercury, Arsenic, Selenium, Bismuth, and Antimony in Soil and Sediment Microwave Digestion" /Atomic Fluorescence Method" (HJ 832~2017), to determine the content of residual arsenic in soil.

After remediation using the above methods, the arsenic content of the original arsenic-contaminated soil was reduced from 70mg/kg to 13.055mg/kg, with a removal rate as high as 81.35%. The content of the contaminated soil after remediation reached the first-level national soil environmental quality standard.

Example 3

An actual contaminated site in Guangzhou was collected, air-dried naturally, impurities removed, pulverized, and passed through a 60-mesh sieve. The basic physical and chemical properties and heavy metal content of soil are shown in Table 2.

Table 2 Basic physical and chemical properties of soil and heavy metal content

Moisture content(%) Soil type As(mg/kg) Fe(mg/kg) Al(mg/kg) Mn(mg/kg) 8.8 red soil 134 18874.5 29559.45 282.16

1. Weigh sodium dithionite, dissolve tartaric acid in water in different containers and mix evenly to obtain 0.2mol/L sodium dithionite solution and 0.05mol/L tartaric acid solution;

2. Mix the 0.2 mol/L sodium dithionite solution with a volume of 80% and the 0.4 mol/L tartaric acid solution with a volume of 20% to obtain a compound eluent;

3. At room temperature, according to the solid-liquid ratio (g:ml) of 1:10, mix the compound eluent and 3g of arsenic-contaminated soil evenly in the container, and mix in a oscillator at 200 r.min ^-1 Shake and rinse for 6 hours;

4. Separate the soil from solid and liquid after oscillation and elution, collect the elution waste liquid, add clean water to the container according to the solid-liquid ratio (g:ml) of 1:10, and continue oscillation and elution in the oscillator for 1 hour;

5. Carry out solid-liquid separation of the soil washed with water and remove the water to obtain the repaired soil.

After the reaction, the arsenic concentration in the leaching waste liquid was measured by atomic fluorescence emission spectrometry; the arsenic content remaining in the soil after leaching was determined in accordance with the "Determination of Mercury, Arsenic, Selenium, Bismuth, and Antimony in Soil and Sediment Microwave Digestion" /Atomic Fluorescence Method" (HJ 832~2017), to determine the content of residual arsenic in soil.

After remediation using the above methods, the arsenic content of the original arsenic-contaminated soil dropped from 134mg/kg to 41.5mg/kg, with a removal rate as high as 69.03%. The content of the contaminated soil after remediation reached the second-level national soil environmental quality standard.

Example 4

1. Weigh sodium dithionite, dissolve tartaric acid in water in different containers and mix evenly to obtain 0.3mol/L sodium dithionite solution and 0.2mol/L tartaric acid solution;

2. Mix the 0.3 mol/L sodium dithionite solution with a volume of 30% and the 0.2 mol/L tartaric acid solution with a volume of 70% to obtain a compound eluent;

3. At room temperature, according to the solid-liquid ratio (g:ml) of 1:20, mix the compound eluant and 3g of the same arsenic-contaminated soil as in Example 3 evenly, and mix in a oscillator at 200 r.min ^-1 Elute with shaking for 8 hours;

4. Shake and rinse the soil, collect the elution waste liquid, add clean water to the container at a solid-to-liquid ratio (g:ml) of 1:10, and continue shaking and leaching in a horizontal oscillator for 1 hour;

5. Carry out solid-liquid centrifugal separation of the soil washed with clean water and remove the clean water to obtain the repaired soil.

After the reaction, the arsenic concentration in the leaching waste liquid was measured by atomic fluorescence emission spectrometry; the arsenic content remaining in the soil after leaching was determined in accordance with the "Determination of Mercury, Arsenic, Selenium, Bismuth, and Antimony in Soil and Sediment Microwave Digestion" /Atomic Fluorescence Method" (HJ 832~2017), to determine the content of residual arsenic in soil.

After remediation using the above methods, the arsenic content in the original arsenic-contaminated soil dropped from 134 mg/kg to 35.6 mg/kg, with a removal rate as high as 73.42%. The arsenic content in the contaminated soil after remediation reached the second-level national soil environmental quality standard.

Comparative ratio

The leaching effect of a single eluent on arsenic-contaminated soil:

Comparative Example 1: An eluent for arsenic-contaminated soil. The eluant is a 0.2mol/L sodium dithionite solution.

Comparative Example 2: An eluent for arsenic-contaminated soil. The eluant is a 0.05 mol/L tartaric acid solution.

Comparative Example 3: A leaching agent for arsenic-contaminated soil. The leaching agent is a 0.4mol/L oxalic acid solution.

Comparative Example 4: A leaching agent for arsenic-contaminated soil. The leaching agent is a 0.4mol/L phosphoric acid solution.

The above arsenic-contaminated soil leaching agent is used for arsenic-contaminated soil remediation. The specific operations are as follows:

It was collected from an actual contaminated site in Guangzhou. It was naturally air-dried. After removing impurities, it was pulverized and passed through a 60-mesh sieve. The measured arsenic content was 134mg/kg. The specific steps to explore the elution effect under the condition of a single eluent are as follows: The prepared eluant solution is based on a solid-liquid ratio (g:ml) of 1:10, and 30ml of arsenic-contaminated soil is added to a container containing 3g of arsenic-contaminated soil. For a single eluent, shake in a oscillator at 200 r.min ^-1 for 6 hours, then perform solid-liquid separation, and take the supernatant for measurement. Among them, the arsenic concentration in the leaching waste liquid was measured by atomic fluorescence emission spectrometry; the arsenic content remaining in the soil after leaching was determined in accordance with the "Determination of Mercury, Arsenic, Selenium, Bismuth, and Antimony in Soil and Sediment Microwave Digestion/Atomic Fluorescence"Law" (HJ 832~2017), to determine the content of residual arsenic in soil. After repair using the above method, the arsenic removal rates in Comparative Examples 1 to 4 of the present invention are: 7.99%, 6.83%, 21.31%, and 24.78% respectively.

Based on the above-mentioned Examples 1 to 4 and Comparative Examples 1 to 4, it can be seen that compared with a single eluent, the compound eluant provided by the present invention is more effective in repairing high iron-aluminum arsenic pollution in southern red soil. Compared with the original method, it has been greatly improved, and the removal rate of arsenic in contaminated soil has been significantly improved.

As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present invention, but the implementation of the present invention is not limited by the above embodiments; although the present invention has been described in detail with reference to the foregoing embodiments, ordinary skill in the art Personnel should understand that any other changes, modifications, substitutions, combinations and simplifications that do not deviate from the spirit and principles of the present invention shall be equivalent substitutions and shall not deviate from the essence of the corresponding technical solutions of the present invention. spirit and scope of the technical solutions of the embodiments.

Claims (5)

1. A method for remediation of arsenic contaminated south red soil comprising the steps of:

1) Uniformly mixing the compound eluent with arsenic-polluted soil, and carrying out oscillation leaching; wherein the compound eluent is obtained by mixing sodium dithionite and tartaric acid solution; wherein, the eluent is composed of the following components: 0.1-0.3 mol/L sodium dithionite: 30% -80% of a volume part; and 0.05 to 0.6mol/L tartaric acid: 20% -70% of a volume part;

2) Performing solid-liquid separation on the soil after the oscillation leaching, removing leaching waste liquid, adding clear water, and continuing the oscillation leaching;

3) Carrying out solid-liquid separation on the soil washed by the clear water, and removing the clear water to obtain the repaired soil;

wherein, the solid-liquid ratio of the composite eluent to the polluted soil in the step 1) is 1g to 10-20 mL.

2. The method of claim 1, wherein the oscillation leaching time in step 1) is 6-8 hours.

3. The method according to claim 1, wherein the oscillators in step 1) and step 2) are used for rinsing at a rotational speed of 180-200 r/min.

4. The method of claim 1, wherein the oscillation rinse time in step 2) is 0.5 to 1 hour.

5. The method of claim 1, wherein the solid-to-liquid ratio of the clean water to the arsenic-contaminated soil after leaching in step 3) is 1 g/5-10 ml.