CN109967513B

CN109967513B - Leaching method for repairing cation type and anion type composite heavy metal polluted soil

Info

Publication number: CN109967513B
Application number: CN201910231676.4A
Authority: CN
Inventors: 曹梦华; 涂书新; 熊双莲; 张娥; 侯耀宗
Original assignee: Huazhong Agricultural University
Current assignee: Huazhong Agricultural University
Priority date: 2019-03-25
Filing date: 2019-03-25
Publication date: 2020-12-08
Anticipated expiration: 2039-03-25
Also published as: CN109967513A

Abstract

The invention discloses a leaching method for repairing cation type and anion type composite heavy metal polluted soil, which comprises the steps of adopting polyphosphate as a leaching agent to simultaneously desorb cation type and anion type heavy metals in the polluted soil, then adjusting the pH value of the leaching agent after solid-liquid separation to 2-4, adding ferrous sulfide to simultaneously remove the cation type and anion type heavy metals in the leaching agent, wherein the polyphosphate is one or a combination of more of sodium tripolyphosphate, sodium tetrapolyphosphate, potassium tripolyphosphate and potassium tetrapolyphosphate. The method overcomes the defect that most of the existing chemical leaching is only suitable for single type heavy metal pollution, is simple to operate, adopts the medicament which has the advantages of low price, environmental friendliness, small damage to soil matrix and the like, and can give consideration to both economic benefits and environmental benefits in the application of repairing the composite heavy metal polluted soil.

Description

Leaching method for repairing cation type and anion type composite heavy metal polluted soil

Technical Field

The invention belongs to the field of soil pollution remediation, and particularly relates to a method for leaching soil polluted by cationic and anionic composite heavy metals.

Background

With the growth of population and the rapid development of economic society in China, the heavy metal pollution of soil is increasingly serious due to the discharge of solid wastes, the excessive use of agricultural chemicals, mining, sewage irrigation and the like, which seriously threatens the human health and the ecological environment, and the effective restoration is urgently needed. Most heavy metal contaminated soils have a complex contamination profile comprising cationic heavy metals (such as cadmium, lead and copper, etc. present in the soil medium predominantly in the cationic form) and anionic heavy metals (such as chromium and arsenic present in the soil medium predominantly in the form of oxoanions).

The main repair technologies of the composite heavy metal contaminated soil commonly used at present comprise phytoremediation, chemical stabilization/immobilization and chemical leaching. The chemical leaching remediation technology is to transfer heavy metals from a soil medium to a water phase medium by utilizing the interaction between a leaching agent and the heavy metals, and then thoroughly remove the heavy metals in the soil through solid-liquid separation. Compared with chemical stabilization/immobilization repair technology, chemical leaching can effectively avoid the risk of re-leaching of heavy metals. Compared with phytoremediation, the chemical leaching can rapidly remediate heavy metal contaminated soil with different concentrations, and is less affected by environmental factors.

The chemical leaching of the soil mainly comprises two parts of selection of the leaching solution and post-treatment of the leaching solution. The selection of the eluting agent is the core of the chemical leaching of the soil, and the removal efficiency of the heavy metals in the soil is directly influenced. At present, the chemical leaching of soil mainly aims at single type of heavy metal, for example, the common heavy metal leaching agent EDTA can only effectively desorb cationic heavy metal in soil, and the heavy metal leaching agent phosphate can only effectively desorb anionic heavy metal arsenic. Therefore, an eluting agent capable of simultaneously desorbing cationic and anionic heavy metals in contaminated soil needs to be found. In addition, the post-treatment of the leacheate is also an important link of the chemical leaching of the soil. At present, the post-treatment of the leacheate mainly adopts a precipitation method. The precipitation method generally uses soda lime to adjust the pH of the leacheate to alkalinity, so that cationic heavy metals in the leacheate are converted into hydroxide precipitates to be removed, but the alkaline condition promotes dissolution of anionic heavy metal arsenic instead. Therefore, there is a need to find a treatment method that can remove both cationic and anionic heavy metals from the leacheate.

Disclosure of Invention

The invention aims to provide a leaching method for repairing cation type and anion type composite heavy metal polluted soil, which comprises the steps of simultaneously desorbing cation type and anion type heavy metals in the polluted soil by adopting polyphosphate as a leaching agent, and then adding ferrous sulfide into the leaching agent after solid-liquid separation to simultaneously remove the cation type and anion type heavy metals in the leaching agent.

The technical principle of the invention is as follows: the polyphosphate radical can form a stable dissolved complex with cationic heavy metal so as to promote desorption of cationic heavy metal in the polluted soil, and can promote desorption of anionic heavy metal arsenic and chromium in the soil in a mode of competing adsorption sites on soil particles with arsenate radicals and chromate radicals. Adding ferrous sulfide into the leacheate after solid-liquid separation, wherein the ferrous sulfide can release sulfur ions and ferrous ions under an acidic condition, the sulfur ions and cationic heavy metals form sulfide precipitates to remove the cationic heavy metals in the leacheate, the pH value of the leacheate is gradually increased along with the consumption of hydrogen ions, the ferrous ions are gradually converted into ferric oxyhydroxide, and the ferric oxyhydroxide removes anionic heavy metals in the leacheate in a coprecipitation mode.

In order to achieve the purpose, the invention adopts the following technical scheme:

a leaching method for repairing cation type and anion type composite heavy metal polluted soil comprises the following steps: and (3) adopting polyphosphate as an eluent to simultaneously desorb cationic and anionic heavy metals in the polluted soil, then adjusting the pH value of the eluent after solid-liquid separation to 2-4, and adding ferrous sulfide to simultaneously remove the cationic and anionic heavy metals in the eluent.

Furthermore, the cationic heavy metal contaminated soil contains one or more of copper, lead, zinc and cadmium, and the anionic heavy metal contains one or two of arsenic and chromium.

Further, the polyphosphate is one or a combination of more of sodium tripolyphosphate, sodium tetrapolyphosphate, potassium tripolyphosphate and potassium tetrapolyphosphate, and the polyphosphate solution passes through a column filled with the polluted soil, or is mixed with the polluted soil by adopting a mechanical stirring or oscillation mode.

Further, ferrous sulfide is added into the leacheate, and the leacheate is mechanically stirred or oscillated for 4 to 8 hours, so that the compound heavy metals in the leacheate are fully removed.

Further, inorganic acid is selected to adjust the pH value of the leacheate, and the inorganic acid is hydrochloric acid, sulfuric acid or nitric acid.

The invention can optimize and adjust the parameters of the polyphosphate and the ferrous sulfide, such as the adding amount, the stirring speed, the reaction time and the like according to the different concentrations of the composite heavy metal in the polluted soil.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the chemical leaching method provided by the invention can effectively repair cation type and anion type composite heavy metal polluted soil, and overcomes the defect that most of the existing chemical leaching is only suitable for single type heavy metal pollution.

(2) The chemical leaching method provided by the invention is simple to operate, and the adopted medicament has the advantages of low price, environmental friendliness, small damage to soil matrix and the like, and can give consideration to both economic benefits and environmental benefits in the actual application process.

Detailed Description

Example 1

The method comprises the steps of collecting composite heavy metal contaminated soil from the periphery of a certain mining area in the large smelting city, wherein the concentration of lead is 355.5mg/kg, the concentration of copper is 591.9mg/kg, and the concentration of arsenic is 86.8 mg/kg. Mixing 0.2mol/L sodium tetrapolyphosphate (pH is adjusted to 7.0) and polluted soil in a glass tube according to a mass ratio of 1:10, placing the glass tube in a constant temperature oscillator, oscillating at a speed of 120r/min at a temperature of 25 ℃, oscillating at a constant temperature for 72h, and then performing mud-water separation by using a high-speed centrifuge. The concentrations of lead, copper and arsenic in the leached soil are respectively 38.4, 43.8 and 18.5mg/kg, and the removal rates of the three heavy metals in the corresponding soil are respectively 89.2%, 92.6% and 78.7%. The concentrations of lead, copper and arsenic in the leacheate were 31.7, 54.8 and 6.83mg/L, respectively. Under the same reaction conditions, the removal rate of lead, copper and arsenic in the soil by a common heavy metal eluting agent EDTA (initial concentration is 0.2mol/L, initial pH is 7.0) is 91.4%, 88.9% and 18.4% respectively. The result shows that the desorption efficiency of the sodium tetraphosphate to cationic heavy metals (lead and copper) is basically equivalent to that of EDTA (ethylene diamine tetraacetic acid), but the desorption efficiency of the sodium tetraphosphate to anionic heavy metal arsenic is obviously higher than that of EDTA, and the desorption efficiency of the sodium tetraphosphate to arsenic is 4.3 times that of EDTA.

To 100mL of the soil leacheate was added 1g of ferrous sulfide and the pH of the leacheate was adjusted to 2.5 with dilute sulfuric acid. Mechanically stirring and mixing the leacheate and the ferrous sulfide at the rotating speed of 300r/min for 8 hours, and measuring the concentrations of heavy metals of lead, copper and arsenic in the supernatant to be 0.3, 1.5 and 0.4mg/L respectively after centrifugation, wherein the removal rates of the three heavy metals in the corresponding leacheate are 99.1%, 97.2% and 94.1% respectively.

Example 2

The method comprises the steps of collecting the composite heavy metal contaminated soil from the vicinity of a sewage discharge ditch of a certain electroplating plant in Wuhan, wherein the cadmium content is 26.8mg/kg, the lead content is 69.8mg/kg, and the chromium content is 96.8 mg/kg. Mixing 0.1mol/L sodium tetrapolyphosphate (pH is adjusted to 7.0) and polluted soil in a glass tube according to a mass ratio of 1:10, placing the glass tube in a constant temperature oscillator, oscillating at a speed of 120r/min at a temperature of 25 ℃, oscillating at a constant temperature for 72h, and then performing mud-water separation by using a high-speed centrifuge. The concentrations of cadmium, lead and chromium in the leached soil are respectively 3.7, 5.1 and 9.8mg/kg, and the removal rates of the three heavy metals in the corresponding soil are respectively 86.2%, 92.7% and 89.9%. The concentrations of cadmium, lead and chromium in the leacheate were 2.3, 6.5 and 8.7mg/L, respectively. Under the same reaction conditions, the removal rate of cadmium, lead and chromium in the soil by a common heavy metal eluting agent EDTA (initial concentration is 0.1mol/L, and initial pH is 7.0) is 82.4%, 89.9% and 23.7% respectively. The results show that the desorption efficiency of sodium tetrapolyphosphate to cationic heavy metals (cadmium and lead) is slightly higher than that of EDTA. Meanwhile, the desorption efficiency of the sodium tetrapolyphosphate to the anion type heavy metal chromium is obviously higher than that of EDTA (ethylene diamine tetraacetic acid), and the desorption efficiency of the sodium tetrapolyphosphate to the chromium is 3.8 times that of the EDTA.

To 100mL of the soil leacheate was added 0.2g of ferrous sulfide and the pH of the leacheate was adjusted to 2.5 with dilute sulfuric acid. Mechanically stirring and mixing the leacheate and the ferrous sulfide at the rotating speed of 300r/min for 4 hours, and measuring the concentrations of heavy metals cadmium, lead and chromium in the supernatant to be 0.1, 0.2 and 0.6mg/L respectively after centrifugation, wherein the removal rates of the three heavy metals in the corresponding leacheate are 95.7%, 96.9% and 93.1% respectively.

Claims

1. A leaching method for restoring cation type and anion type composite heavy metal polluted soil is characterized in that polyphosphate is used as a leaching agent to simultaneously desorb cation type and anion type heavy metals in the polluted soil, then the pH value of the leaching agent after solid-liquid separation is adjusted to 2-4, and ferrous sulfide is added to simultaneously remove the cation type and anion type heavy metals in the leaching agent.

2. The leaching method according to claim 1, wherein the cationic heavy metal of the contaminated soil is one or more of copper, lead, zinc and cadmium, and the anionic heavy metal is one or both of arsenic and chromium.

3. The leaching method according to claim 1, wherein the polyphosphate is one or more of sodium tripolyphosphate, sodium tetrapolyphosphate, potassium tripolyphosphate and potassium tetrapolyphosphate.

4. The leaching process according to claim 1, wherein ferrous sulfide is added to the leaching solution and mechanically agitated or shaken for 4 to 8 hours to substantially remove complex heavy metals from the leaching solution.

5. The elution method according to claim 1, wherein the inorganic acid is selected to adjust the pH of the elution liquid, and the inorganic acid is hydrochloric acid, sulfuric acid or nitric acid.