CN104550224A - Method for removing lead from contaminated soil by virtue of taro leaf or achyranthes bidentata leaching - Google Patents

Abstract

The invention relates to the technical field of remediation of contaminated soil in the environment, and particularly relates to a method for removing lead from contaminated soil by virtue of taro leaf or achyranthes bidentata leaching. The method comprises the following steps: (1) preparing biomass leachate: washing a biomass material taro leaves with tap water, rinsing the taro leaves with distilled water, air-drying the taro leaves at a naturally-ventilated place, grinding the taro leaves by virtue of a crusher, sieving the taro leaves with a 2mm sieve, adding a proper amount of distilled water, performing oscillatory extraction on the mixed liquor for 12h, and performing filtration to obtain the leachate; (2) leaching the contaminated soil: adding the leachate obtained in step (1) into the lead-contaminated soil, regulating the pH value of the mixed solution to 4.4 to 5.0 by virtue of diluted hydrochloric acid and a sodium hydroxide solution, and performing oscillatory leaching. Achyranthes bidentata can be used instead of the biomass material taro leaves. The method is convenient and simple, an obvious leaching effect on the lead-contaminated soil is played, and secondary contamination to the environment is avoided.

Description

A method for removing lead in polluted soil by leaching taro leaves or hyssopia

technical field

The invention relates to the technical field of remediation of polluted soil in the environment, in particular to a method for removing lead in polluted soil by leaching with taro leaves or achyranthes bidentata.

Background technique

Soil heavy metal pollution is one of the serious environmental problems facing the world today. Lead is a non-essential nutrient element for organisms. When its concentration exceeds a certain threshold, it will produce severe toxicity to organisms, and it is often transmitted through the food chain to cause various diseases in the human body. Mining, smelting, electroplating, sewage irrigation, chemical fertilizer and pesticide abuse are the main sources of lead pollution. With the development of industry and agriculture and urbanization in my country, the spread of heavy metal lead pollution in soil is gradually deepening. Therefore, the remediation of lead-contaminated soil has become an urgent problem to be solved in our country.

At present, heavy metal contaminated soil is mainly remediated by physical, chemical and biological methods. Physical methods mainly include soil improvement, electric restoration and heat treatment, which are suitable for soil with a small and lightly polluted area. Fertility and other defects; bioremediation mainly includes phytoremediation, animal remediation and microbial remediation. Among them, phytoremediation is to plant hyper-accumulative plants on polluted soil, and reduce the heavy metal content in the soil through the enrichment of plants. Economic, environmental protection and other advantages, but the repair period is long and the efficiency is low; chemical repair technology mainly includes soil leaching method, solidification-stabilization method, etc., which have the advantages of high efficiency and easy operation in practical application.

Soil leaching technology is a kind of chemical remediation method. It utilizes the interaction between the leaching agent and the heavy metal in the soil solid phase to form soluble heavy metal ions or metal complexes, which are transferred to the eluate and then collected. The washing solution recovers heavy metals. Therefore, the selection of a suitable leaching agent is a key part of soil leaching technology. At present, the main leaching agents used for soil lead leaching restoration are inorganic acids, salts, surfactants, chelating agents and organic acids. Inorganic acids such as HCl have a leaching rate of 56% for soil cadmium, but only 35% for soil lead under the same conditions; salts such as CaCl ₂ and KCl are suitable for leaching acidic and neutral polluted soils respectively. However, the residual ^Cl in the soil is likely to cause soil salinization pollution; the efficiency of the chelating agent EDTA and the surfactant saponin to wash the lead in the polluted soil can reach 68.95%, but some studies have shown that EDTA is easy to damage the soil structure. The soil causes secondary pollution, and the cost of using surfactants such as saponin is high; although some low-molecular-weight organic acids such as citric acid and malic acid have a high leaching rate of soil cadmium, the research by Wang et al. shows that 0.2 The leaching efficiency of mol/L citric acid and malic acid on soil lead is low, only about 50% removal rate, and it is easy to cause soil acidification and nutrient loss. Therefore, it is urgent to find a low-cost, non-polluting, high-efficiency leaching agent.

Biomass material is a renewable or recyclable organic substance formed by biological action, which has the advantages of wide source, large output and environmental friendliness. The KCl extract of watermelon rind powder can remove 72.35% of cadmium in the polluted soil, indicating that biomass materials have certain potential in removing heavy metals in soil. However, due to the different properties of different types of heavy metals, the KCl extract of watermelon peel powder, which is very effective in removing cadmium in soil, has a low leaching removal rate of lead in soil, which is difficult for practical application in engineering. Therefore, it is of great practical significance to screen new bioleaching agent materials for lead in soil.

To sum up, the existing technology has problems such as secondary pollution, high cost, or low efficiency, so it needs to be improved to screen out leaching materials that are environmentally friendly, low-cost, and high in leaching efficiency.

Contents of the invention

The purpose of the present invention is to address the above technical problems, to provide a method that is convenient and simple, has an obvious leaching effect on lead-contaminated soil, and does not cause secondary pollution to the environment. method.

Concrete technical scheme of the present invention is:

A kind of method that utilizes taro leaf or achyranthes bidentata leaching to remove lead in polluted soil, this method comprises the following steps:

(1) Preparation of biomass material eluent:

The biomass material taro leaves were washed with tap water, rinsed with distilled water, and then placed in a naturally ventilated place to air-dry. They were ground through a 2mm sieve with a pulverizer, an appropriate amount of distilled water was added, and the mixed solution was oscillated to extract for 12 hours and then filtered to obtain the Washing solution: the oscillation rate of the extraction mixture in the shaking rinse is 180r/min, and the concentration of the washing solution is 30-50g/L.

(2) Washing of contaminated soil

Add the eluent obtained in step (1) into the lead-contaminated soil of the farmland, adjust the pH value of the mixed solution to the range of 4.4-5.0 with dilute hydrochloric acid and sodium hydroxide solution, and then carry out oscillating leaching;

The biomass material taro leaves are replaced by Achyranthes knuckles, and the method for removing lead in polluted soil by rinsing Achyranthes bidentata is the same as the method for leaching and removing lead in polluted soil by taro leaves.

As a preference, the soil for testing is lead-contaminated soil near a lead-zinc mine in Hanyuan, and the measured lead content in the soil is 700.42 mg/kg.

The volume ratio of the polluted soil and the eluent of the biomass material is selected as 1:20.

The present invention selects taro leaf or Achyranthes bidentata, a biomass material with a wide range of sources and is easy to collect, as the leaching material, which has low cost, strong operability, and strong scalability; it is also developed for the leaching and removal of heavy metal lead-contaminated soil new biomass materials.

Compared with prior art, the beneficial effect of the present invention is:

(1), the leaching process of the present invention is convenient and simple to operate, and the leaching effect on lead-contaminated soil is obvious.

(2) Compared with the distilled water itself, the distilled water extract of taro leaf powder has a greater ability to remove lead from contaminated soil. After three times of leaching, the taro leaf eluate with a concentration of 30g/L and 50g/L has a greater effect on soil lead. The total leaching rates were 94.19% and 97.74%.

(3) The content of lead in the soil after leaching in the present invention complies with the national soil environment standard, the residual lead in the eluate can be recovered by methods such as biomass adsorption, and the leaching waste liquid can reach the national discharge standard.

Detailed ways

The present invention is further described below in conjunction with embodiment, but does not limit the scope of the present invention.

Example 1:

1. Preparation of contaminated soil eluent

Wash taro leaves, achyranthes bidentata, white clover and watermelon peel with tap water respectively, rinse with distilled water, place them in a naturally ventilated place to air dry, and use a grinder to grind them through a 2mm sieve.

Add 10g, 20g, 60g and 100g of taro leaf powder to 2000ml of distilled water, vibrate and extract at a speed of 180r/min for 12h and then filter, so that the taro leaf powder and distilled water are fully contacted and mixed. The eluents with concentrations of 5g/L, 10g/L, 30g/L and 50g/L of taro leaves were prepared respectively. The preparation method of distilled water extraction eluate with the concentration of 5g/L, 10g/L, 30g/L and 50g/L of Achyranthes bidentata, white clover and watermelon rind is the same as that of taro leaf eluate.

, leaching of contaminated soil

According to distilled water, distilled water + 5g/L taro leaf eluent, distilled water + 10g/L taro leaf eluent, distilled water + 30g/L taro leaf eluent, distilled water + 50g/L taro leaf eluent; distilled water + 5g/L Achyranthes bidentata eluate, distilled water+10g/L Achyranthes bidentata eluent, distilled water+30g/L Achyranthes bidentata eluent, distilled water+50g/L Achyranthes bidentata eluent; distilled water+5g/L white clover Eluent, distilled water + 10g/L white clover eluent, distilled water + 30g/L white clover eluent, distilled water + 50g/L white clover eluent; distilled water + 5g/L watermelon rind eluent 17 treatments including distilled water + 10g/L watermelon rind eluent, distilled water + 30g/L watermelon rind eluent, distilled water + 50g/L watermelon rind eluent, etc. were used to wash lead-contaminated soil respectively. For each treatment, the polluted soil is leached in the following manner: Weigh 10.000 g of the polluted soil with a lead concentration of 700.42 mg/kg, add 200 ml of the prepared leaching solution to the soil each time, and then wash it with dilute hydrochloric acid and sodium hydroxide solution to adjust the pH of the mixed solution to the range of 4.4-5.0, and shake and rinse at a speed of 250r/min for 2h. After rinsing, let the mixture stand for 5 minutes, pour the upper liquid into a centrifuge tube and centrifuge, pour out the supernatant and filter it for measurement on the machine, continue to add 200ml of the same amount of eluent to the remaining soil, and repeat three times. The waste liquid after rinsing is recovered and treated with Houttuynia cordata powder. For specific treatment methods, please refer to the research on the absorption of heavy metal lead by Houttuynia cordata powder. (Note: In specific engineering applications, the soil-liquid separation part can be omitted. The purpose of using this step in this study is to reduce the statistical error of the leaching rate in the process of multiple leaching, and it does not participate in practical applications.)

The supernatant was taken, and the lead content in the eluate was measured with an atomic absorption spectrometer (AAS) (Table 1).

Table 1 Efficiency of biomass material leaching to remove lead in polluted soil

Note: The concentration of the eluting agent is the extraction concentration of taro leaf, hyssop, white clover and watermelon rind; each treatment was repeated 3 times, and the data in the table are the average value of 3 repetitions.

After analysis, with the increase of the concentration of added biomass materials, the leaching removal rate of lead-contaminated soil is also gradually increasing, especially in the treatment of distilled water + 30g/L and distilled water + 50g/L taro leaf eluent. The leaching removal rate of contaminated soil can reach 59.19% and 65.23% respectively under the conditions of this embodiment, and the total leaching rate can reach 94.19% and 97.74% after three times of rinsing, and the total rinsing rate of three times can reach 59.19% and 97.74% respectively, and the total rinsing rate of three times is higher than that of Achyranthes bidentata treated with the same concentration. , white clover and watermelon rind were 48.84%, 68.78% and 79.93% higher and 35.68%, 61.38% and 78.48% higher. In addition, under the treatment conditions of distilled water + 50g/L, the total leaching rate of Achyranthes bidentata can reach 62.06% after three leaching, which is 25.70% and 42.80% higher than that of white clover and watermelon rind under the same concentration treatment.

Example 2:

1. Preparation of taro leaf and Achyranthes knuckle lotion

Wash the taro leaves and Achyranthes bidentata respectively with tap water, place them in a naturally ventilated place to air-dry, and use a grinder to grind them.

Add 0.5kg, 1kg, 3kg and 5kg of taro leaf powder to 100L tap water, oscillate and extract at a speed of 180r/min for 12h, and then filter with gauze to obtain solutions with taro leaf concentrations of 5g/L, 10g/L, 30g/L and 50g/L eluent. Achyranthes bidentata concentrations of 5g/L, 10g/L, 30g/L and 50g/L tap water eluents were prepared in the same way as taro leaf eluents.

, leaching of 500g contaminated soil

According to tap water, tap water + 5g/L taro leaf rinse, tap water + 10g/L taro leaf rinse, tap water + 30g/L taro leaf rinse, tap water + 50g/L taro leaf rinse; tap water + 5g/L Achyranthes bidentata eluate, tap water+10g/L Achyranthes bidentata eluate, tap water+30g/L Achyranthes bidentata eluate, tap water+50g/L Achyranthes bidentata eluent, etc. were used to wash lead-contaminated soil respectively.

Each treatment carries out leaching to the polluted soil in the following manner: Weigh 500g of polluted soil with a lead concentration of 700.42mg/kg, add 10L of the above-mentioned prepared leaching solution into the soil each time, and then use concentrated hydrochloric acid and The lime powder solution adjusts the pH of the mixed solution to the range of 4.4-5.0, shakes and rinses for 2 hours. After rinsing, let the mixed solution stand for 5 minutes, pour out the supernatant and wait for recovery, and continue to add 10L of the same amount of eluent to the remaining soil for rinsing, and repeat three times. The waste liquid after rinsing is recycled with Houttuynia cordata powder.

Take the supernatant, and measure the lead content in the eluate with atomic absorption spectrometer (AAS) (Table 2). Comparing the data in Table 1, it can be seen that the leaching removal rate of lead-contaminated soil with larger soil samples in the treatment of tap water + 30g/L and tap water + 50g/L taro leaf and Achyranthes bidentata eluate is the same as that of distilled water + 30g/L and distilled water + 50g /L taro leaf and Achyranthes knuckle treatment, the total leaching rate of lead was similar after three leaching of small soil samples.

Table 2 Efficiency of leaching large soil samples of taro leaves and Achyranthes bidentata to remove lead in polluted soil

Note: The concentration of the eluent is the extraction concentration of taro leaves and Achyranthes bidentata; each treatment was repeated 3 times, and the data in the table are the average values of 3 repetitions.

In summary, taro leaf and Achyranthes bidentata have outstanding effects as bioleaching materials for remediating lead-contaminated soil.

It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should belong to the protection scope of the appended claims of the present invention.

Example 3:

The preparation method of the leaching agent and the rinsing steps of the polluted soil are kept consistent with the conditions in the examples, only the volume ratio parameters of the polluted soil and the eluent of the biomass material are changed, and the test is performed under different ratio conditions. Changes, see Table 3 for specific data.

Table 3 Efficiency of four biomass materials to remove lead from polluted soil under different soil-liquid ratio conditions

Note: The concentration of the eluting agent is the extraction concentration of taro leaf, hyssop, white clover and watermelon rind; each treatment was repeated 3 times, and the data in the table are the average value of 3 repetitions.

It can be seen from Table 3 that under the same conditions, the leaching agents prepared by using biomass materials taro leaves, hyssopia, white clover and watermelon rinds respectively, under the same concentration conditions of leaching agents, the contaminated soil and biomass materials were leached. The volume ratio of the washing solution also plays an important role. It can be clearly seen that when the volume ratio of the contaminated soil and biomass material eluting solution is 1:20-30, the leaching effect on the contaminated soil is obviously better, but from Considering the economic cost, the preferred volume ratio of contaminated soil and eluent of biomass material is 1:20.

Claims (4)

1. utilize taro leaf or root of bidentate achyranthes drip washing to remove a method plumbous in contaminated soil, it is characterized in that the method comprises following step:

(1) preparation of biological material leacheate:

Cleaned by biological material taro leaf running water, be placed on gravity-flow ventilation place air-dry with distilled water rinse, use pulverizer by its milled 2mm sieve, add appropriate distilled water, vibration mixed liquor lixiviate 12h refilters, obtained leacheate;

(2) drip washing of contaminated soil:

The leacheate obtained in step (1) is added in lead-contaminated soil, regulates after within the scope of mixed solution pH value to 4.4-5.0 with watery hydrochloric acid and sodium hydroxide solution and carry out vibration drip washing;

The described biological material taro leaf root of bidentate achyranthes substitutes.

2. the method utilizing taro leaf or root of bidentate achyranthes drip washing to remove lead in contaminated soil according to claim 1, is characterized in that: the concentration of described leacheate is 30-50g/L.

3. the method utilizing taro leaf or root of bidentate achyranthes drip washing to remove lead in contaminated soil according to claim 1, is characterized in that: in described vibration drip washing, the oscillation rate of lixiviate mixed liquor is 180r/min.

4. the method utilizing taro leaf or root of bidentate achyranthes drip washing to remove lead in contaminated soil according to claim 1, is characterized in that: the volume ratio of described contaminated soil and biological material leacheate is 1:20.