CN112251236B

CN112251236B - Preparation and application method of plant-derived soil multi-metal eluting agent

Info

Publication number: CN112251236B
Application number: CN202011039405.8A
Authority: CN
Inventors: 刘星; 吴颖欣; 吴文成; 刘晓文; 宋清梅; 吴嘉慧
Original assignee: South China Institute of Environmental Science of Ministry of Ecology and Environment
Current assignee: South China Institute of Environmental Science of Ministry of Ecology and Environment
Priority date: 2020-09-28
Filing date: 2020-09-28
Publication date: 2022-04-29
Anticipated expiration: 2040-09-28
Also published as: CN112251236A

Abstract

The invention discloses a preparation method of a plant source soil multi-metal eluting agent, which comprises the following steps: mixing the walnut green seedcase with a solvent according to the solid-liquid ratio of 1: 5-100, leaching and filtering to obtain a leaching solution which is a plant source soil multi-metal eluting agent. The invention relates to a soil heavy metal pollution treatment technology, in particular to a leaching remediation method for heavy metals Cd, Pb and Zn in soil. In the existing leaching remediation methods, chemical agents are mostly used for leaching remediation, and because most of the chemical agents can stably exist in soil, new pollutants can be introduced, or the basic properties of the soil are negatively affected, so that the reutilization of the remedied soil is influenced. Aiming at the problem, the eluting agent prepared from the walnut green husks does not cause secondary pollution to soil on the premise of ensuring better eluting effect, has better environmental safety and is beneficial to recycling of restored soil.

Description

Preparation and application method of plant-derived soil multi-metal eluting agent

Technical Field

The invention belongs to a soil heavy metal pollution treatment technology, and relates to a preparation method and a use method of a walnut green husk-based material for leaching heavy metals Cd, Pb and Zn in soil.

Background

Common soil heavy metal pollution remediation methods include a soil-moving method, a ploughing method, a solidification and stabilization method, a plant extraction method, a chemical leaching method and the like. Wherein, the soil-dressing method has huge engineering quantity, high economic cost and difficult large-scale implementation; the plowing method is to mix surface soil and deeper soil to reduce the heavy metal content of the plough layer, but the heavy metal in the soil is not removed, and the possibility of reaching the risk threshold value again after the restoration is high; the passivant is applied in the process of curing and stabilizing, so that the content of the effective state of the heavy metal in the soil can be reduced, but some defects still exist, such as the environmental risk of the passivant, the long-term stability of the repair and the like; the phytoremediation technology is an effective measure for remedying the heavy metal contaminated soil, but the factors of long remediation period, large environmental influence on the enrichment effect and the like are difficult to overcome.

As a mature soil remediation technology, a chemical leaching method has a plurality of application examples, which mainly comprises in-situ leaching and ex-situ leaching, and the method has the advantages of realizing the removal of heavy metals in soil in a real sense, along with good removal effect and quick response, but is very important for the selection of leaching agents. The conventional eluting agent has various problems, such as that EDTA is not easily degraded by soil microorganisms due to too long retention time in soil, and the percolation of Ca and Mg ions in the soil can be increased; GLDA has a good leaching effect, but is expensive, and the application and popularization of the GLDA are limited. Aiming at the problems, the invention adopts natural organic walnut green seedcase as a raw material to prepare the soil heavy metal eluting agent of biological source.

China is a big walnut producing country, and the cultivation area and the preservation quantity are the first in the world. With the annual increase of the walnut yield, the green husks of walnuts are used as agricultural wastes, the influence on the environment is more and more large, and the walnut peeling can be mechanized in the production process and is accompanied with the generation of a large amount of waste water and waste residues, so that the environmental problems caused by the mechanical peeling are widely concerned.

The walnut green seedcase contains a large amount of phenolic hydroxyl, carboxyl, carbonyl and lipid substances, the functional groups have good activation effect on heavy metals in soil, and the walnut green case solution is acidic, so that the heavy metals are more easily resolved from the soil. The walnut green seedcase is used as a natural organic matter, is easy to decompose in the environment, cannot cause secondary pollution to soil and water, and is beneficial to safe utilization of soil; the walnut green seedcase is used as agricultural waste, the raw materials are easy to obtain, the collection is convenient, the price is low, the recycling of the walnut green seedcase and the treatment and restoration of the polluted soil can be simultaneously realized by the method, and the purpose of treating wastes with processes of wastes against one another is achieved.

Disclosure of Invention

The invention provides an environment-friendly soil heavy metal eluting agent, which at least solves the problem of secondary pollution caused by residue of the eluting agent in the soil after remediation in the prior art. The agricultural waste walnut green seedcase is used as the eluting agent, so that the problems of negative influence of the eluting agent on the soil environment and high eluting cost in the prior eluting technology are solved under a good eluting effect.

The invention provides a preparation method of a plant source soil multi-metal eluting agent, which comprises the following steps: mixing the walnut green seedcase with a solvent according to the solid-liquid ratio of 1: 5-100, leaching and filtering to obtain a leaching solution which is a plant source soil multi-metal eluting agent.

Further, the walnut green seedcase is dried walnut green seedcase, and specifically dried walnut green case powder can be selected.

Further, the solvent is water.

Further, the leaching time is 12-24h, and the temperature is 20-45 ℃.

Further, the filtration is performed by using 300-mesh gauze.

Further, pH adjustment is needed after the filtration, and the pH of the leaching liquor after the pH adjustment is 4.

The invention also provides a plant source soil multi-metal eluting agent prepared by any one of the preparation methods.

The invention provides a use method of the plant source soil multi-metal eluting agent, which comprises the following steps: adding a plant source soil multi-metal eluting agent into soil, oscillating for 10-18h at room temperature, and centrifugally separating soil and eluate to simultaneously remove various heavy metals such as cadmium, lead, zinc and the like in the soil.

Further, the liquid-solid ratio of the plant source soil polymetallic eluting agent to the polluted soil is 20 mL: 1 g.

Further, the oscillation time is 12 h.

Compared with the prior art, the preparation method is simple, the raw materials are cheap and easy to obtain, various heavy metals in the soil can be removed simultaneously, and the high leaching efficiency is achieved.

Compared with the prior art, the plant-derived eluting agent has the characteristics of simple preparation method, higher removal efficiency of heavy metals such as cadmium, lead, zinc and the like in soil, and capability of simultaneously eluting a plurality of heavy metals at one time. Meanwhile, the eluting agent of the invention can not cause secondary pollution to soil and water after soil remediation; on the contrary, the organic matter content of the soil can be increased, so that the fertility of the soil is increased, the soil is restored, the effect of improving the soil is achieved, and the soil after restoration can be recycled. In addition, the raw materials of the eluent used in the invention are agricultural wastes, the raw materials are easy to obtain and low in price, the influence of the walnut green husks on the environment is reduced, the active ingredients are efficiently utilized, the resources are fully utilized, and the aim of treating wastes with processes of wastes against one another is fulfilled.

Drawings

FIG. 1 shows the extraction efficiency of three heavy metals with different concentrations of leaching solution in the embodiment of the present invention;

FIG. 2 shows the extraction efficiency of three heavy metals for different leaching pH values in the examples of the present invention;

FIG. 3 shows the extraction efficiency of three heavy metals for different leaching times in the examples of the present invention;

FIG. 4 shows the leaching effect of an activator on Cd in soil according to an embodiment of the invention;

FIG. 5 shows the leaching effect of the activator of the embodiment of the invention on Pb in soil;

FIG. 6 shows the leaching effect of the activator of the embodiment of the invention on Zn in soil.

Detailed Description

In order to make the technical solutions of the present invention better understood by those skilled in the art, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments.

The soil to be tested was collected from a contaminated agricultural land in Guangdong province, and the soil contamination conditions are shown in Table 1.

TABLE 1 test soil heavy Metal content

The preparation method of the eluting agent comprises the following steps: the dried walnut green seedcase and water are leached for 24 hours at room temperature by a turnover mixer according to the solid-to-liquid ratio and then filtered by 300-mesh gauze, the pH of the filtrate is 4.63, the pH of the filtrate is adjusted to a specified value, and the prepared water extract of the walnut green case is the plant-source heavy metal eluting agent stock solution of the embodiment of the invention.

The research method of the embodiment of the invention adopts a single-factor experiment and an orthogonal experiment, and the experimental design tables are shown in tables 2 and 3. Wherein the pH is adjusted with 1M nitric acid solution or sodium hydroxide solution. As shown in Table 2, the concentration gradients of 0.01g/mL, 0.03g/mL and 0.05g/mL were used in the orthogonal experiments, because as shown in FIG. 1, the leaching agent concentration of 0.05g/mL can ensure the higher leaching efficiency of 3 heavy metals, and the extraction efficiency reaches the inflection point at the concentration of 0.1 g/mL. This concentration gradient is chosen in view of the poor storage of the activator liquid at higher concentrations, the need for more raw materials, the poor organoleptic properties, the impact on the user experience to balance the various advantages and disadvantages.

The leaching process is as follows: adding an eluting agent into the soil, oscillating for 12h at room temperature, and centrifugally separating the soil and the eluate to simultaneously remove various heavy metals such as cadmium, lead, zinc and the like in the soil. The liquid-solid ratio of the eluting agent to the polluted soil is 20 mL: 1 g.

TABLE 2 Single factor experiment design Table

The concentration of the leaching liquor is expressed by the extraction ratio of the dried walnut green husk powder to water.

TABLE 3 orthogonal experimental design Table

The experimental results are as follows:

the extraction efficiency of three heavy metals for different leaching liquor concentrations is shown in figure 1, the extraction efficiency of three heavy metals for different leaching pH values is shown in figure 2, and the extraction efficiency of three heavy metals for different leaching time is shown in figure 3. According to the result of a single-factor test, the extraction efficiencies of Cd, Pb and Zn can respectively reach 7.703-77.505%, 1.475-19.522% and 3.531-47.694%.

According to the orthogonal test result (figure 4), the response relation of the leaching effect of Cd, Pb and Zn to each condition can be obtained by using a response surface analytical method model and Design-Expert software as follows.

Cd: the extraction rate was 31.34+8.97 × A-5.94 × B-1.47 × C-3.15 × A × B +0.82 × A × C +3.08 × B × C-8.32 × A²-2.41×B²-9.20×C²；R²＝0.9867；

Pb: the extraction rate was 14.06+2.27 × A-1.49 × B +1.77 × C-0.88 × A × B-0.7 × B × C-2.47 × A²-0.7×B²-4.01×C²；R²＝0.9791；

Zn: the extraction rate is 11.87+2.87 × A-0.96 × B +0.48 × C-0.48 × A × B +0.38 × A × C-0.15 × B × C-0.63 × A²-0.18×B²-0.71×C²；R²＝0.9919；

The above-mentioned R2 represents the ratio of the coefficient of determination (coefficient of determination) that can be occupied by the independent variable interpretation part in the variation of the dependent variable in statistics, so as to determine the interpretation power of the statistical model.

Wherein A represents eluent concentration, B represents eluent pH, C represents extraction time, and A x B represents interaction of eluent concentration and pH on leaching rate; b × C represents the interaction of eluent pH and extraction time on leaching rate, A × C represents the interaction of eluent concentration and extraction time on leaching rate; a. the²Is the square of the concentration, B²Is the square of the pH of the eluent, C²The square of the eluent extraction time. The absolute value of each parameter coefficient in the polynomial represents the contribution degree of the parameter to the leaching rate.

According to the response relationship, the preferable leaching conditions of Cd, Pb and Zn are shown in Table 4.

TABLE 4 preferred heavy metal elution conditions

Respectively preparing two leachates with leaching liquor concentration of 0.1g/mL and 0.05g/mL, mixing the two leachates with the soil according to the proportion of 20mL to 1g, leaching, and analyzing the change of Cd, Pb and Zn in the soil.

As can be seen from FIG. 4, the eluents with two concentrations have better leaching effect on Cd in the soil. The Cd in exchangeable state, carbonate combined state and organic state are reduced in different degrees, especially the content of iron and manganese in oxidation state is reduced to maximum, the concentrations of the Cd are reduced by 90.26% and 90.89%, respectively, and reduced to 0.044 mug/kg and 0.048 mug/kg, and the total amount of Cd in the soil is reduced by 32.44% and 31.48% by using the eluents with two concentrations. The two groups of information show that the eluent of the embodiment of the invention has higher elution efficiency on Cd-polluted soil, reduces the environmental risk of heavy metals in the leached soil, and is beneficial to reutilization or harmless treatment of the soil.

FIG. 5 shows that the leaching effect of the leachables of two concentrations on Pb is better, and the reduction of Pb content in the residue Pb is most obvious in 4 forms except the organically bound Pb, and the leachables of two concentrations reduce Pb content in the residue Pb from 27.25mg/kg to 14.33mg/kg, and reduce Pb content in the residue Pb content in 11.88mg/kg by 47.4% and 56.422%, respectively.

In the figure 6, the leaching effect of the activating agent on Zn in soil is mainly reflected in the conversion of a carbonate combined state and an iron-manganese oxidation state, the organic combined state and a residue state are not changed greatly, and the leaching efficiency of Zn can reach 20.88% when the concentration is 0.1 g/mL. As can also be seen from FIG. 1, the leaching effect of Zn in soil is obviously improved with the increase of the concentration of the leaching agent.

Finally, it should be noted that the above-mentioned embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above-mentioned embodiments, it should be understood by those skilled in the art that the modifications and equivalents of the specific embodiments of the present invention can be made by those skilled in the art after reading the present specification, but these modifications and variations do not depart from the scope of the claims of the present application.

Claims

1. The application method of the plant-derived soil multi-metal eluting agent is characterized by comprising the following steps: adding a plant source soil multi-metal eluting agent into soil, oscillating for 10-18h at room temperature, and centrifugally separating the soil and the eluate to simultaneously remove various heavy metals such as cadmium, lead and zinc in the soil;

the preparation method of the plant source soil multi-metal eluting agent comprises the following steps: mixing walnut green seedcase with a solvent according to a solid-to-liquid ratio of 1: 5-100, leaching and filtering to obtain a leaching solution;

after the filtration, the pH value of the leaching liquor is adjusted to be 4;

mixing the leaching liquor with the adjusted pH value with a solvent again to obtain a multi-metal eluting agent, wherein the concentration of the leaching liquor is 0.05-0.1 g/mL; the walnut green seedcase is dried walnut green seedcase; the solvent is water.

2. The use according to claim 1, wherein the leaching time is 12-24h and the temperature is 20-45 ℃.

3. The method of use of claim 1, wherein said filtering is with 300 mesh gauze.

4. The use method according to claim 1, wherein the liquid-solid ratio of the plant-derived soil polymetallic eluting agent to the contaminated soil is 20 mL: 1 g.

5. The use of the method according to claim 1, wherein the oscillation time is 12 h.