CN113020234A

CN113020234A - Environment-friendly chemical leaching method for Cd-polluted soil

Info

Publication number: CN113020234A
Application number: CN202110001572.1A
Authority: CN
Inventors: 乔显亮; 栾雪
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2021-01-04
Filing date: 2021-01-04
Publication date: 2021-06-25

Abstract

The invention belongs to the field of soil remediation, and provides an environment-friendly chemical leaching method for Cd-polluted soil, which comprises the following steps: the method comprises the steps of determining the optimal concentration and the optimal pH value of Cd in the soil by oscillating extraction, eluting Cd contaminated soil by using an oscillating extraction concentration and pH value-determined GLDA solution column, washing the eluted soil by using water in order to reduce the risk of reactivating heavy metals by GLDA remained in the soil after elution, analyzing the residual condition of GLDA by determining soluble organic carbon, and determining the content of Cd by using an atomic absorption spectrophotometer. According to the invention, the biodegradable chelating agent is used, and the column is washed with water after leaching, so that the residue of the chelating agent in the soil is reduced while the higher Cd removal efficiency is maintained, the influence on the ecological environment of the soil is reduced, and a reference is provided for GLDA in-situ chemical leaching restoration of Cd-polluted soil.

Description

Environment-friendly chemical leaching method for Cd-polluted soil

Technical Field

The invention relates to an environment-friendly remediation technology for leaching Cd-polluted soil by using a biodegradable chelating agent GLDA column, which can reduce the residue of a chelating agent in the soil while keeping a high removal rate, and belongs to the field of soil remediation.

Background

The national soil pollution condition survey bulletin issued in 2014 shows that the national soil total standard exceeding rate is 16.1%, the pollution type is mainly inorganic type, the number of the inorganic pollutant standard exceeding points accounts for 82.8% of all standard exceeding points, and the standard exceeding rate of cadmium pollution is up to 7.0%. Heavy metals are concealed, durable and nondegradable in soil, can not be restored through soil self-purification, and only are converted among various forms. Heavy metal pollution affects soil physicochemical properties and ecological structural functions, destroys microbial community structures, and may harm human health through food chain enrichment. The action plan for soil pollution control issued in 2016 emphasizes the practical enhancement of soil pollution control and the gradual improvement of soil environment quality. How to repair heavy metal contaminated soil and reduce the harm caused by heavy metal contamination has become an important work in the field of environment.

According to different remediation process principles, the technology for remediating the heavy metal contaminated soil is mainly divided into a physical method, a chemical method and a biological method. Among the repair technologies, chemical leaching transfers heavy metals from soil to liquid phase by using the dissolution, chelation, and desorption of various leaching agents. The method is considered to be a repair technology with application prospect due to the advantages of thorough heavy metal removal, short period, simple process and the like. Leaching materials have been reported to include inorganic solutions, chelating agents, natural organic acids, surfactants, and the like, as well as complex leachates combining two or more leachates. Inorganic acid/salt and other inorganic solutions have the advantages of good effect, high speed, low cost and the like, but the inorganic acid/salt damages the soil structure, increases the risk of soil salinization, corrodes leaching equipment and the like, and limits the use of the inorganic acid/salt in practical engineering. EDTA is capable of extracting potential toxic metals from all non-silicate bonding phases in Soil and is considered to be one of the most effective chelating agents for removing heavy metals from Soil, but EDTA is not easy to degrade, and the document "Soil Biology and Biochemistry,2009,41(10): 2214-2221" reports that EDTA is decomposed by only 14% within 20 days, can leach into underground water to cause secondary pollution, and even with low doses of EDTA, the growth of plants and rhizosphere microorganisms of Soil is inhibited. Citric acid is a natural organic acid, and has better biodegradability compared with EDTA (ethylene diamine tetraacetic acid), but the citric acid has weaker chelating ability at low concentration, and has poor effect of removing Pb, Cd and Cu in polluted soil.

Glutamic acid N, N-diacetic acid (GLDA) is a new generation of biodegradable environment-friendly chelating agent, belongs to aminocarboxylic acid chelating agents with EDTA, has higher heavy metal chelating capacity, but is different from the condition that a carbon source used for producing EDTA is a fossil raw material, the carbon source for producing GLDA is mainly a biological source, the degradation rate is more than 60 percent within 28 days, and GLDA is expected to become an environment-friendly EDTA substitute for soil leaching. In order to achieve a good leaching repair effect, a corresponding leaching method needs to be established for GLDA. Furthermore, in order to reduce the risk of GLDA remaining, it is necessary to investigate the remaining GLDA in the soil after washing.

Aiming at the problems, the invention establishes an environment-friendly remediation technology for chemically leaching Cd-polluted soil by using a biodegradable chelating agent GLDA. Oscillating and extracting to determine leaching parameters of the GLDA for leaching the Cd-polluted soil, simulating a repairing effect of the GLDA in-situ leaching the Cd-polluted soil by using a column leaching method, finally washing the soil leached by the column with water, inspecting the residual condition of the GLDA, and providing a reference for the in-situ chemical leaching repairing of the Cd-polluted soil by using the biodegradable chelating agent GLDA.

Disclosure of Invention

The method comprises the steps of determining leaching parameters of column leaching by oscillation extraction, leaching Cd-polluted soil by using a biodegradable chelating agent GLDA column, investigating the remediation efficiency of the GLDA in-situ chemical leaching-polluted soil, measuring the Cd content in a supernatant by using an atomic absorption spectrometry, and further washing the leached soil by water so as to reduce the risk caused by re-activation of metals in the soil by a residual chelating agent.

The technical scheme of the invention is as follows:

an environment-friendly chemical leaching method for Cd-polluted soil comprises the following steps:

(1) oscillatory extraction for determining concentration of GLDA eluted Cd

Mixing the GLDA solution with the polluted soil screened by a 2mm sieve according to a solid-to-liquid ratio of 1: 5, mixing the solution at a constant speed of 150rpm under the original pH condition of the solution for 240min, centrifuging the suspension at 4000rpm for 10 min, filtering, and measuring the concentration of Cd in the supernatant by using a flame atomic absorption spectrophotometer;

(2) oscillatory extraction for determining pH of GLDA eluted Cd

Mixing GLDA solutions with different pH values with the polluted soil screened by a 2mm sieve according to a solid-to-liquid ratio of 1: 5, mixing, oscillating, centrifuging, filtering and measuring according to the operation of the step (1);

(3) leaching Cd-polluted soil by using GLDA (solvent-soluble data acquisition) column with determined concentration and pH (potential of hydrogen)

Feeding the GLDA solution with determined concentration and pH into a leaching column filled with the polluted soil through a peristaltic pump, collecting leaching liquid every 50ml until the total leaching liquid reaches 700ml, and measuring the concentration of Cd in the leaching liquid by using a flame atomic absorption spectrophotometer;

(4) analysis of residual GLDA in soil washed by water washing column

In order to reduce the risk of heavy metal reactivation caused by GLDA remaining in soil after leaching, ultrapure water is used according to a solid-to-liquid ratio of 1: 1, washing the soil after leaching by a column; because the soil leachate has complex components, a GLDA quantitative analysis method which is simple to operate and low in cost is not available at present, the method is used for measuring the content of soluble organic carbon (TOC) of GLDA solutions with different concentrations, establishing a standard curve of the TOC and GLDA concentrations, and quantitatively analyzing the GLDA by measuring the TOC content of the soil leachate.

The invention has the beneficial effects that:

according to the invention, the Cd-polluted soil is restored by using the biodegradable chelating agent GLDA, the optimal concentration and pH of the GLDA eluted soil are determined through oscillation extraction, the influence on the ecological environment of the soil is reduced while the higher Cd removal efficiency is ensured, the restoration effect of the GLDA in-situ eluted Cd-polluted soil is simulated through column elution, and the secondary risk caused by the residual chelating agent is reduced through water washing.

Drawings

Fig. 1 is a result of chemical leaching experiment of environment-friendly Cd-contaminated soil, wherein fig. 1A shows that Cd removal efficiency varies with GLDA concentration, fig. 1B shows that Cd removal efficiency varies with GLDA pH, fig. 1C shows that Cd leaching rate varies with leachate volume, and fig. 1D shows that GLDA removal efficiency varies with water washing frequency.

Detailed Description

The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.

(1) In order to determine the change of Cd removal efficiency with the concentration of GLDA, a GLDA solution with a certain concentration range of 0.5-100mmol/L is used, an oscillation extraction experiment is carried out at the original pH value of the solution, and a flame atomic absorption spectrophotometer is used for measuring the Cd concentration in the supernatant. As shown in the attached figure 1A, when the concentration of GLDA exceeds 10mmol/L, the Cd removal efficiency is not increased along with the increase of the concentration of GLDA any more, and the optimal concentration of GLDA eluting Cd is determined to be 10 mmol/L.

(2) In order to determine the change of Cd removal efficiency along with the pH value of the GLDA solution, the GLDA solution with a certain pH value range of 3-10 is used for carrying out an oscillation extraction experiment, and a flame atomic absorption spectrophotometer is used for measuring the Cd concentration in the supernatant. As can be seen from the attached figure 1B, different pH values have little influence on the removal efficiency of Cd, and the optimal pH value for eluting Cd by GLDA is determined to be the soil pH value of 6.1 in consideration of the influence of elution on soil as small as possible.

(3) Eluting Cd contaminated soil by a GLDA solution column with the concentration of 10mmol/L and the pH value of 6.1, and collecting eluate every 50ml by adopting a column elution mode. As shown in FIG. 1C, the final leaching rate of Cd is 61.66%.

(4) In order to reduce the risk of heavy metal reactivation caused by GLDA remaining in soil after leaching, ultrapure water is used according to a solid-to-liquid ratio of 1: 1 washing the washed soil. The residual situation of GLDA in the soil is analyzed by measuring the content of soluble organic carbon (TOC) in soil leachate, and after the soil leachate is washed for five times by water, the removal rate of GLDA reaches 98 percent.

Claims

1. An environment-friendly chemical leaching method for Cd-polluted soil is characterized by comprising the following steps:

(1) oscillatory extraction for determining concentration of GLDA eluted Cd

(2) oscillatory extraction for determining pH of GLDA eluted Cd

(4) analysis of residual GLDA in soil washed by water washing column

In order to reduce the risk of heavy metal reactivation caused by GLDA remaining in soil after leaching, ultrapure water is used according to a solid-to-liquid ratio of 1: 1, washing the soil after leaching by a column; because the soil leachate has complex components, a GLDA quantitative analysis method which is simple to operate and low in cost is not available at present, the method is used for determining the content of soluble organic carbon of GLDA solutions with different concentrations, establishing a standard curve of TOC and GLDA concentrations, and quantitatively analyzing GLDA by determining the TOC content of the soil leachate.