Remediation method for tailing heavy metal contaminated soil

Abstract

The invention relates to the technical field of heavy metal contaminated soil remediation, in particular to a tailing heavy metal contaminated soil remediation method which comprises the following steps: leaching contaminated soil with ferric chloride leacheate, then plowing, transplanting sedum alfredii hance from September to November, performing conventional field management, and performing whole-plant harvesting on the sedum alfredii hance in April. According to the method, chemical remediation and biological remediation are combined, the removal effect of cadmium in the soil is remarkably improved, the soil is improved within a short time, the soil can be used for farming and is suitable for remediation and reutilization of tailing contaminated soil, and in addition, the method is low in cost, high in feasibility and free of the risk of secondary pollution.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal contaminated soil remediation, and in particular to a method for remediating soil contaminated by heavy metals from tailings. Background Art

[0002] While the development and application of mineral resources have promoted social and economic development, it has also brought a series of problems to the local ecological environment, destroying regional vegetation, soil, water resources and ecosystems, leading to a series of ecological and environmental problems such as land subsidence, non-point source pollution, soil erosion, and air pollution.

[0003] Tailings are solid waste generated during the mineral processing process. They are usually piled up in large quantities around mining areas, causing huge pollution problems in the soil, air and water, and seriously threatening soil ecology and water source safety. The types of pollution caused by tailings are related to the heavy metal pollutants they contain, generally zinc, copper, cadmium and lead pollution. Among them, cadmium and lead pollution are the most harmful to the soil. It is of great significance to repair the ecological environment of tailings soil. In addition, heavy metal tailings can cause soil acidification and salinization. The pH of strongly acidified soil is generally between 1 and 3. When the pH is less than 3, various enzymes in the bodies of most acid-resistant plants are inactivated, the cell membrane is damaged, and they cannot maintain normal growth and die.

[0004] Existing ecological restoration technologies are mainly divided into chemical restoration and biological restoration. Chemical restoration refers to the use of chemical reagents such as eluents and passivators to produce chemical reactions to achieve the purpose of leaching, passivation or removal of heavy metal pollutants. Chemical restoration has a high pollution restoration efficiency, but the added chemicals usually also change the soil pH, organic matter content, and cation exchange capacity, causing secondary pollution. Ferric chloride solution is a commonly used soil elution solution, which can not only effectively remove heavy metals in the soil, but also has good biodegradability, and can replenish nutrients lost from the soil during the elution process. It has broad application prospects in engineering restoration. However, it is reported that although ferric chloride elution can effectively remove heavy metals, it will also cause severe soil acidification, so that the soil needs to be neutralized and repaired before it can be put into use.

[0005] Bioremediation is generally done by planting resistant plants on contaminated soil, which absorb heavy metal pollutants through plant roots and then volatilize them through leaves. Bioremediation has low costs and does not cause secondary pollution, but its remediation efficiency is poor.

[0006] It can be seen that there is currently a lack of an effective method for remediating heavy metal pollution in tailings. This application is committed to combining chemical remediation with biological remediation to provide a method for remediating soil contaminated by heavy metals in tailings with low pollution and high efficiency, so as to effectively reduce the cadmium content in the soil without causing secondary pollution. Summary of the invention

[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for at least achieving the effect of high cadmium removal rate and low cost.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] A method for repairing soil contaminated by heavy metals from tailings comprises the following steps:

[0010] The contaminated soil was leached with ferric chloride solution, and then the land was prepared. From September to November, Sedum austriatum was transplanted and conventional field management was carried out. In April, the whole plant of Sedum austriatum was harvested.

[0011] Furthermore, the ferric chloride eluent is a 10-15 mM ferric chloride solution.

[0012] Furthermore, the ferric chloride eluent is added at a liquid-to-solid ratio (L / kg) of 1:4-6.

[0013] Furthermore, the land preparation includes tilling the soil, forming ridges and applying base fertilizer.

[0014] Furthermore, the conventional field management includes fertilization and watering;

[0015] The fertilizers used for fertilization are compound fertilizer and quicklime;

[0016] The amount of fertilizer applied is 15-20 kg per mu, and top dressing is performed every 15-20 days.

[0017] Furthermore, the transplanted Sedum alfredii uses Sedum alfredii seedlings with a growth period of 4 to 5 months.

[0018] It is worth noting that the principle of this method for soil remediation is that the H+ produced by the hydrolysis of FeCl3 reduces the soil pH value, making it easier for Cd in the contaminated soil to be leached out. 3+ and H produced by hydrolysis + Cd can be eluted through ion exchange. FeCl3 is cheap and is a commonly used eluting agent. It has a good removal effect on cadmium in the soil, but it will cause soil acidification. The soil after elution cannot be used directly for farming. The eluate after elution also needs to be treated uniformly, which is costly.

[0019] Sedum austriatum is a hyperaccumulator that can effectively absorb Cd in the soil, especially after FeCl3 leaching, the Cd in the soil is eluted into the elution solution and is in a free state, which is more conducive to the absorption of Sedum austriatum. It has been found through experiments that Sedum austriatum still has a high Cd absorption activity in an acidic soil environment. In the growth process of Sedum austriatum, in addition to conventional fertilizers, quicklime is added as a soil conditioner and calcium source, which can neutralize the soil pH and improve the soil flora on the one hand, and promote the survival rate of Sedum austriatum on the other hand. After the implementation of this method, Sedum austriatum can be pulled out and used as an ornamental flower during its flowering period. At this time, the soil pH is close to neutral and can be used for the cultivation of other conventional crops.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention combines chemical remediation with biological remediation, significantly improving the removal effect of cadmium in the soil, and improving the soil in a short time so that it can be used for farming. It is suitable for the repair and reuse of tailings contaminated soil.

[0022] 2. The method of the present invention has low cost, high feasibility and no risk of secondary pollution. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described in detail below, but the protection scope of the present invention is not limited to the following.

[0024] Example 1

[0025] A soil sample (soil type: mountain red mud) was taken from the Majiatian tailings area in Panzhihua for a remediation experiment. The cadmium content in the soil was 0.257 mg kg -1 , pH was 3.2, and the soil samples were pretreated by screening and removing impurities before the experiment.

[0026] Experimental method: In September, 5 soil samples were taken and placed in potted flower pots, with 15 cm of soil spread. According to the solid-liquid ratio of 1:5, 10 mM sodium chloride solution was added for leaching. After leaching, the Southeast Sedum seedlings and flower pots were transplanted and routinely cultivated with ordinary potassium sulfate fertilizer and quicklime as fertilizers. In April of the following year, the Southeast Sedum plant was pulled out, and then the soil pH and cadmium content were tested. The sampling was carried out at five points, and the detection method was graphite furnace atomic absorption spectrophotometry. After testing, the cadmium content in the five groups of soils was 0.026, 0.035, 0.041, 0.028, and 0.032 mg kg, respectively. -1 The cadmium removal rate was 84-90%, and the measured pH was 6.2.

[0027] Comparative Example 1

[0028] In order to compare the effects of chemical leaching and biological restoration of Sedum alfredii, a comparative experiment was carried out simultaneously. The difference from Example 1 is that no transplanting of Sedum alfredii was performed. The specific scheme is as follows:

[0029] Take a soil sample and place it in a potted flowerpot, cover the soil with 15 cm, add 10 mM sodium chloride solution at a solid-liquid ratio of 1:5 for leaching, drain the water, and then test the cadmium content and pH in the soil.

[0030] The cadmium content in the soil was 0.108 mg kg -1 , the cadmium removal rate reached 58.0%, and the pH was 3.0.

[0031] Comparative Example 2

[0032] In order to compare the effects of chemical leaching and biological restoration of Sedum alfredii, a comparative test was carried out simultaneously, which differed from Example 1 in that no chemical restoration was carried out. The specific scheme is as follows:

[0033] In September, a soil sample was taken and placed in a potted flower pot, with 15 cm of soil spread. The Sedum australis seedlings were transplanted into the pots and cultivated with ordinary fertilizers. In April of the following year, the entire Sedum australis plant was removed, and then the soil pH and soil cadmium content were tested. The cadmium content in the soil was 0.182 mg kg -1 , the cadmium removal efficiency was 29.1% and the measured pH was 4.5.

[0034] It can be seen that the cadmium removal rate was significantly improved after combining ferric chloride chemical leaching with Sedum southeasternense chemical remediation. According to Comparative Example 2, although the cadmium remediation effect of Sedum southeasternense is not as good as that of ferric chloride leaching, it still has a certain pH regulating effect without using the soil conditioner quicklime.

[0035] Example 2

[0036] A field restoration experiment was conducted in the Majiatian tailings area in Panzhihua. The experimental method is as follows:

[0037] 1) In September, the test area (10m×10m) of the selected polluted farmland area was prepared, and then ridges were made every 1.5 meters, with a ridge height of 15-20cm. Then 10kg of potassium sulfate compound fertilizer (purchased from Hubei Aoteer Chemical Co., Ltd.) was evenly applied as base fertilizer.

[0038] 2) Calculate the amount of elution solution (based on a soil depth of 15 cm), prepare 600 L of 15 mM ferric chloride solution, and leach the test area five times.

[0039] 3) When the soil surface is basically dry, transplant the Sedum australis seedlings, one plant at a distance of 20 cm, and then carry out regular watering and pest control. Fertilize once every 20 days by mixing 3kg of compound fertilizer and 1kg of quicklime.

[0040] 4) In April of the following year, transplant the entire plant of Sedum alfredii into an ornamental pot and test the cadmium content and pH of the soil in the test area.

[0041] According to the test, the average cadmium content in the soil is 0.05 mg kg -1 The cadmium removal rate is about 80%, and the pH is 6-6.3.

[0042] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for remediating soil contaminated by heavy metals from tailings, characterized in that: The following steps are involved: The contaminated soil was leached with ferric chloride solution, and then the land was prepared. From September to November, Sedum austriatum was transplanted and conventional field management was carried out. In April, the whole plant of Sedum austriatum was harvested.

2. The repair method according to claim 1, characterized in that: The ferric chloride eluent is a 10-15 mM ferric chloride solution.

3. The repair method according to claim 2, characterized in that: The ferric chloride eluent is added in an amount according to a liquid-to-solid ratio of 1:4-6.

4. The repair method according to claim 1, characterized in that: The conventional field management includes fertilization and watering.

5. The repair method according to claim 4, characterized in that: The fertilization includes applying compound fertilizer and quicklime.

6. The repair method according to claim 1, characterized in that: The transplanted Sedum alfredii uses Sedum alfredii seedlings with a growth period of 4 to 5 months.