CN110560474B - Method for removing total chromium pollutants in chromium-polluted soil by water removal - Google Patents
Method for removing total chromium pollutants in chromium-polluted soil by water removal Download PDFInfo
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- CN110560474B CN110560474B CN201910834898.5A CN201910834898A CN110560474B CN 110560474 B CN110560474 B CN 110560474B CN 201910834898 A CN201910834898 A CN 201910834898A CN 110560474 B CN110560474 B CN 110560474B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/02—Extraction using liquids, e.g. washing, leaching, flotation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/08—Reclamation of contaminated soil chemically
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Abstract
The invention relates to a method for removing total chromium pollutants in chromium-polluted soil by water removal, which comprises the following steps: (1) and reduction and transformation: mixing organic acid, water and chromium-contaminated soil, and fully and uniformly stirring to form slurry; adding the seaweed extract into the slurry, uniformly stirring, and standing for 24-36 hours to form a reactant; (2) soaking and washing: adding water into the reactant, stirring and soaking for 2 hours, and dehydrating by using centrifugal or filter pressing dehydration equipment to form dehydration water; soaking and washing for many times according to the above mode, and mixing the washing water obtained by soaking and washing for many times; (3) precipitation: adding quicklime into the dewatering and washing water to precipitate out trivalent chromium in the dewatering and washing water, and regulating the pH value of the supernatant for recycling or direct discharging. The method can remove total chromium pollutants in the chromium-polluted soil, and does not damage and cause secondary pollution to the soil.
Description
Technical Field
The invention belongs to the technical field of soil treatment, and relates to a method for removing pollutants in soil, in particular to a method for removing total chromium pollutants in chromium-polluted soil by water removal.
Background
In the past, because the environmental protection is not paid enough attention and the aspects of supervision and the like have loopholes, the soil in a plurality of regions has chromium pollution.
At present, for the remediation and treatment of chromium-contaminated soil, the basic idea is to reduce hexavalent chromium with strong toxicity into trivalent chromium by a reduction and stabilization method and reduce the mobility of chromium in the soil by a stabilization and immobilization method. However, this method can only reduce the highly toxic hexavalent chromium to trivalent chromium, but the total chromium content in the soil is not reduced, and under certain environmental conditions, trivalent chromium may be re-oxidized to hexavalent chromium. Moreover, the total chromium content in the soil is not reduced, and the soil cannot be used as normal soil.
There is also a method of removing chromium contamination in soil by leaching using inorganic acid or organic acid in combination with chelating agent as a leaching agent. However, in the existing leaching technology, acid liquor and other chemical agents are required to be used as leaching liquid, and hexavalent chromium and total chromium in soil cannot be removed by 100%. In addition, the eluate and the leached soil need to be further repaired and treated, so that the treatment cost is actually increased.
In view of the above technical defects in the prior art, there is an urgent need to develop a novel method for removing total chromium pollutants in chromium-polluted soil.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a method for removing total chromium pollutants in chromium-polluted soil by water removal, which greatly reduces the total chromium content in the chromium-polluted soil by a water washing mode, so that the total chromium content in the chromium-polluted soil reaches the national relevant soil total chromium content standard and the normal soil use function is recovered.
In order to achieve the above purpose, the invention provides the following technical scheme:
a method for removing total chromium pollutants in chromium-polluted soil by water removal is characterized by comprising the following steps:
(1) and reduction and transformation of
Mixing organic acid, water and chromium-contaminated soil, and fully and uniformly stirring to form slurry, wherein the adding amount of the organic acid is 5-10% of the mass of the chromium-contaminated soil, and the adding amount of the water is 40-50% of the mass of the chromium-contaminated soil; then, adding the seaweed extract into the slurry, uniformly stirring, standing for 24-36 hours to form a reactant, reducing hexavalent chromium in chromium-polluted soil into trivalent chromium at one time in the standing reaction process, and converting the trivalent chromium into a complex which is easily dissolved in water, wherein the volume of the added seaweed extract is 0.1-1.5% of the volume of the slurry;
(2) soaking and washing
Adding water into the reactant, stirring and soaking for 2 hours, wherein the adding amount of the water is 2 times of the mass of the reactant, and then dehydrating by using a centrifugal or filter pressing dehydration device to form dehydrated washing water; soaking and washing for many times according to the above mode, and mixing the washing water obtained by soaking and washing for many times;
(3) precipitation out of the precipitate
Adding quicklime into the dewatering and washing water to precipitate trivalent chromium in the dewatering and washing water, adjusting the pH value of supernatant and recycling or directly discharging, wherein the amount of the added quicklime needs to be preset by taking a water sample, and the specific method comprises the following steps: and taking 5 liters of the dewatering water, averagely dividing the dewatering water into 10 beakers of 600 milliliters, adding quicklime according to the amount of 5g, 7.5g, 10g, 12.5g, 15g, 17.5g, 20g, 22.5g, 25g and 27.5g respectively, fully stirring and dissolving, standing for 24 hours, taking supernate to determine the total chromium content, and taking a sample with the lowest quicklime adding amount in all water samples with the total chromium content lower than 1.5mg/L in the supernate as the adding proportion.
Further, the organic acid in the step (1) is citric acid, and the seaweed extract is a composite seaweed active enzyme liquid.
Further, wherein the slurry formed in step (1) is acidic.
Still further, wherein the slurry formed in step (1) has a PH of 4.5.
On the other hand, the soaking and washing times in the step (2) are not less than 3.
Further, in the step (2), after each dehydration, the moisture content of the dehydrated reactant is less than 100%.
And (3) adjusting the pH value of the supernatant in the step (3) by using dilute hydrochloric acid or dilute sulfuric acid.
Further, wherein the pH value of the supernatant in the step (3) is adjusted to 6.5-7.5.
Compared with the prior art, the method for removing the total chromium pollutants in the chromium-polluted soil by water removal has the following beneficial technical effects:
1. the reductive leaching agent adopted by the invention can convert most trivalent chromium in soil into a complex state which is easy to dissolve in water, so that the chromium substances can be leached and separated by using common tap water under a neutral condition.
2. The invention adopts organic acid and seaweed extract as reducing immersion cleaning agent, compared with the prior reducing technology and leaching technology, the invention does not add metal preparation, inorganic acid and damage or secondary pollution to soil.
3. The invention greatly reduces the total chromium content in the chromium-polluted soil by a water washing mode, so that the total chromium content reaches the national relevant soil total chromium content standard, and the normal soil use function is recovered.
Drawings
FIG. 1 is a flow diagram of the water-stripping process of the present invention for removing total chromium contaminants from chromium contaminated soil.
Detailed Description
The present invention is further described with reference to the following drawings and examples, which are not intended to limit the scope of the present invention.
FIG. 1 shows a flow diagram of the water-stripping process of the present invention for removing total chromium contaminants from chromium-contaminated soil. As shown in figure 1, the method for removing the total chromium pollutants in the chromium-polluted soil by water removal comprises the following steps:
first, a reductive transformation is performed.
Unlike the prior art, in the present invention, organic acids and seaweed extracts are used as the reducing pickling agent. Organic acids are generally not capable of reducing hexavalent chromium, however, in the present invention, the addition of seaweed extract may catalyze the reduction of hexavalent chromium by organic acids.
When the reduction conversion is carried out, the organic acid, the water and the chromium-polluted soil are mixed and fully and uniformly stirred to form slurry. Wherein, the adding amount of the organic acid is 5-10% of the mass of the chromium-polluted soil, and the adding amount of the water is 40-50% of the mass of the chromium-polluted soil. Preferably, the addition amount of the organic acid is adjusted so that the formed slurry is slightly acidic. More preferably, the pH of the slurry formed is adjusted to 4.5 by adjusting the amount of the organic acid added. Thus, the reductive conversion is more convenient to carry out.
Then, adding the seaweed extract into the slurry and stirring uniformly, and then standing and reacting for 24-36 hours to form a reactant. During the standing reaction process, hexavalent chromium in the chromium-polluted soil can be reduced into trivalent chromium at one time, and the trivalent chromium is converted into a complex which is easy to dissolve in water. Wherein the volume of the added seaweed extract is 0.1-1.5% of the volume of the slurry.
Preferably, the organic acid is citric acid. The seaweed extract is a composite seaweed active enzyme liquid. In this way, hexavalent chromium in the chromium-contaminated soil can be reduced into trivalent chromium at one time through reduction and conversion, and the trivalent chromium is converted into a chromium citrate complex which is easily soluble in water.
The seaweed extract is seaweed dry powder obtained by acidifying with 35% sulfuric acid and drying at low temperature, and is composite seaweed active enzyme liquid obtained by leaching with 35% sodium hydroxide solution. This technique for obtaining a liquid of complex seaweed active enzyme is prior art and is not central to the present invention, and therefore, it is not described in a critical way. The seaweed extract used by the inventors is the complex seaweed active enzyme liquid purchased from the market.
Secondly, soaking and washing.
Unlike the prior art which uses acidic eluting agents, in the present invention, a repeated process of soaking and eluting is performed using ordinary city tap water.
Specifically, first, water was added to the reactant after the standing reaction and immersed for 2 hours with stirring. Where the amount of water added is 2 times the mass of the reactants, e.g. 1 ton of reactants, then 2 tons of water need to be added. Thereafter, dehydration is carried out using a centrifugal or filter-press dehydration apparatus to form the dehydrated water. In order to effectively strip the chromium citrate complex from the reaction mass, multiple soaking strips are generally required. That is, after dehydration, 2 times of tap water is added again and stirred and soaked for 2 hours, and then, dehydration is performed using a centrifugal or filter-press dehydration apparatus to form a dehydrated washing water. And soaking and washing for many times according to the above mode, and mixing the washing water obtained by soaking and washing for many times.
Preferably, after each dehydration, the moisture content of the dehydrated reactant is less than 100%. In the present invention, the water content is a ratio of a water content in the reactant to a dried product of the reactant after drying.
In the present invention, the number of repetition of soaking and elution needs to be set in accordance with the target elution rate. For example: the target removal rate was 90%, that is, if 90% of the chromium contaminants in the soil were to be removed, the number of repetitions was set to 3.
After soaking and washing, the total chromium pollutants in the soil are dissolved in the washing water, and the treated soil reaches the national relevant soil total chromium content standard, so that the normal soil use function is recovered.
Thirdly, precipitating.
Adding quicklime into the dewatering and washing water to precipitate out trivalent chromium in the dewatering and washing water, and adjusting the pH value of supernatant for recycling or directly discharging.
Wherein, the amount of the added quicklime needs to be preset by taking a water sample. The specific method comprises the following steps: and taking 5 liters of the dewatering water, averagely dividing the dewatering water into 10 beakers of 600 milliliters, adding quicklime according to the amount of 5g, 7.5g, 10g, 12.5g, 15g, 17.5g, 20g, 22.5g, 25g and 27.5g respectively, fully stirring and dissolving, standing for 24 hours, taking supernate to determine the total chromium content, and taking a sample with the lowest quicklime adding amount in all water samples with the total chromium content lower than 1.5mg/L in the supernate as the adding proportion.
For example, if 7.5g, 10g, 12.5g, or 15g of quicklime is added to the supernatant so that the total chromium content in the supernatant is less than 1.5mg/L, then 7.5g of quicklime is added to 500ml of the dehydration water to precipitate out.
Adding 15g, 17.5g, 20g, 22.5g and 25g of quicklime can ensure that the total chromium content in the supernatant is lower than 1.5mg/L, and adding the quicklime into the dehydration water according to the amount of adding 15g of quicklime into every 500ml of the dehydration water for precipitation.
In the present invention, preferably, the supernatant is adjusted in pH with dilute hydrochloric acid or dilute sulfuric acid. More preferably, the pH of the supernatant is adjusted to 6.5-7.5.
The invention adopts organic acid and seaweed extract as reducing immersion cleaning agent, compared with the prior reducing technology and leaching technology, the invention does not add metal preparation, inorganic acid and soil damage or secondary pollution. The organic acid can not reduce hexavalent chromium, and the seaweed extract can catalyze the organic acid to reduce the hexavalent chromium.
Meanwhile, a large amount of acid eluting agents are required to be used in the common eluting technology to keep the pH value of the soil under a strong acid condition, so that trivalent chromium compounds in the soil can be eluted in a soluble state, secondary pollution of the soil is increased, and the treatment process and cost are increased. The reductive leaching agent adopted by the invention can convert most trivalent chromium in soil into a complex state which is easy to dissolve in water, so that the chromium substances can be leached and separated by using common tap water under a neutral condition.
The above examples of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. Not all embodiments are exhaustive. All obvious changes and modifications which are obvious to the technical scheme of the invention are covered by the protection scope of the invention.
Claims (8)
1. A method for removing total chromium pollutants in chromium-polluted soil by water removal is characterized by comprising the following steps:
(1) and reduction and transformation of
Mixing organic acid, water and chromium-contaminated soil, and fully and uniformly stirring to form slurry, wherein the adding amount of the organic acid is 5-10% of the mass of the chromium-contaminated soil, and the adding amount of the water is 40-50% of the mass of the chromium-contaminated soil; then, adding the seaweed extract into the slurry and uniformly stirring; then standing for 24-36 hours to form a reactant, reducing hexavalent chromium in the chromium-contaminated soil into trivalent chromium at one time in the standing reaction process, and converting the trivalent chromium into a complex which is easy to dissolve in water, wherein the added seaweed extract accounts for 0.1-1.5% of the volume of the slurry;
wherein the seaweed extract is dried seaweed powder obtained by acidification with 35% sulfuric acid and low-temperature drying, and then is extracted with 35% sodium hydroxide solution to obtain composite seaweed active enzyme liquid;
(2) soaking and washing
Adding water into the reactant, stirring and soaking for 2 hours, wherein the adding amount of the water is 2 times of the mass of the reactant; then, dewatering by using centrifugal or filter pressing dewatering equipment to form dewatering and washing water; soaking and washing for many times according to the above mode, and intensively mixing the washing water obtained by soaking and washing for many times;
(3) precipitation out of the precipitate
Adding quicklime into the dewatering and washing water to precipitate trivalent chromium in the dewatering and washing water, adjusting the pH value of supernatant and recycling or directly discharging, wherein the amount of the added quicklime needs to be preset by taking a water sample, and the specific method comprises the following steps: and taking 5 liters of the dewatering water, averagely dividing the dewatering water into 10 beakers of 600 milliliters, adding quicklime according to the amount of 5g, 7.5g, 10g, 12.5g, 15g, 17.5g, 20g, 22.5g, 25g and 27.5g respectively, fully stirring and dissolving, standing for 24 hours, taking supernate to determine the total chromium content, and taking a sample with the lowest quicklime adding amount in all water samples with the total chromium content lower than 1.5mg/L in the supernate as the adding proportion.
2. The method for removing total chromium pollutants by washing with water according to claim 1, wherein the organic acid in the step (1) is citric acid.
3. A method for removing total chromium contaminants from soil contaminated with chromium by water scrubbing according to claim 2, wherein the slurry formed in step (1) is weakly acidic.
4. A method for removing total chromium contaminants from soil contaminated with chromium by water removal according to claim 3, wherein the slurry formed in step (1) has a PH of 4.5.
5. The method for removing total chromium pollutants by water stripping in chromium-polluted soil according to claim 3, wherein the soaking and stripping in the step (2) are not less than 3 times.
6. The method for removing total chromium pollutants by water removal and washing in chromium-polluted soil according to claim 3, wherein in the step (2), after each dehydration, the moisture content of the dehydrated reactants is lower than 100%.
7. The method for removing total chromium pollutants by water removal and washing in chromium-polluted soil according to claim 5, wherein the pH value of the supernatant in the step (3) is adjusted by using dilute hydrochloric acid or dilute sulfuric acid.
8. The method for removing total chromium pollutants by water removal and washing in chromium-polluted soil according to claim 6, wherein the pH value of the supernatant in the step (3) is adjusted to 6.5-7.5.
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