CN106699237B

CN106699237B - Resource utilization method of straws produced after phytoremediation of soil heavy metal pollution

Info

Publication number: CN106699237B
Application number: CN201710057862.1A
Authority: CN
Inventors: 曾清如; 葛一陈; 周细红; 陈梦莹
Original assignee: Hunan Agricultural University
Current assignee: Hunan Agricultural University
Priority date: 2017-01-23
Filing date: 2017-01-23
Publication date: 2020-06-05
Anticipated expiration: 2037-01-23
Also published as: CN106699237A

Abstract

The invention relates to a resource utilization method of straws produced by plants after soil heavy metal pollution remediation. The method comprises the steps of firstly placing crushed straws in a tubular furnace to be calcined into biochar at low temperature, then extracting heavy metals from the biochar containing high-concentration heavy metals in an acidic solution by a liquid phase extraction principle, and separating the heavy metals from the filtered solution by adding an alkaline solution for precipitation reaction. The invention effectively provides a new solution and approach for the subsequent treatment of the heavy metal pollution of the phytoremediation soil, so that the phytoremediation technology is efficiently and continuously developed, and a new approach is provided for the plant resource recovery.

Description

Resource utilization method of straws produced after phytoremediation of soil heavy metal pollution

Technical Field

The invention relates to a method for effectively treating straws containing heavy metals produced after the heavy metal pollution of soil is repaired by plants and recycling the heavy metals to obtain a liquid fertilizer containing high potassium.

Background

Frequent human activities have caused serious heavy metal pollution to soil for a long time, especially heavy metal pollution to farmland soil. Heavy metal pollutants cannot be chemically or biologically degraded, are easy to accumulate in plants, animals and human bodies through a food chain way, have high toxicity, and pose serious threats to the ecological environment, food safety and human health. The treatment of heavy metal pollution in soil is carried out by physical methods such as leaching method, soil-filling method and adsorption-immobilization method, and chemical methods such as biological reduction method and complex leaching method. However, these methods are expensive in investment, most of them can only temporarily relieve the harm of heavy metals, and can also cause secondary pollution, and the pollution problem of heavy metals cannot be fundamentally solved; phytoremediation belongs to an environment-friendly, safe and low-cost heavy metal pollution treatment measure compared with other remediation methods such as chemistry, physics and the like, and is applied to the treatment of heavy metal pollution and site pollution in mining areas. However, researches show that the plant repair also has some limitations, such as slow repair speed, and most of plants which can be used for repair have no economic value. Tobacco, peanut, oil sunflower and the like belong to plants which are easy to absorb and enrich heavy metals, and simultaneously contain high-concentration nutrient elements such as potassium, but a large amount of biomass such as straws and the like can be left after the tobacco is mature and harvested, the content of the heavy metals in the tobacco straws is higher, and secondary pollution can be caused if the biomass is not well treated, so that a large amount of dry matters such as biological straws and the like obtained in the soil heavy metal pollution treatment process can not be effectively treated or recycled at present, which is the bottleneck of the current plant restoration technology.

The common treatment methods for plants mainly include incineration method, pyrolysis method, ashing method, liquid phase extraction method and the like to extract metals. The above-mentioned disposal techniques are mainly characterized in that the plants after restoration are disposed of as garbage or dangerous waste, rather than being comprehensively utilized.

Disclosure of Invention

The invention aims to provide a resource utilization method of straws produced by plants after soil heavy metal pollution remediation.

In order to achieve the purpose, the invention relates to a resource utilization method of straws produced after heavy metal pollution of plants in soil, which comprises the following steps:

1) harvesting straws after the plant in the mature period restores the heavy metal pollution of the soil, cleaning the straws, and drying the straws;

2) weighing dried straws, crushing the straws by a crusher, placing the crushed straws in a tubular furnace into which high-purity nitrogen is introduced, and firing the straws at a low temperature of 300-350 ℃ for 2 hours in an absorption liquid of 0.1mol/L nitric acid to obtain biochar, metal and other element ash. So that the low-temperature firing has less volatilization of cadmium with low melting point and higher yield of the biochar;

3) after the step 2), putting the fired biochar into clean water, regulating the pH value of the biochar to be 1-3 by using nitric acid, stirring for 3 hours, extracting heavy metals, and washing residual acid in the biochar by using clean water for filtering or a centrifugal dehydration mode;

4) collecting the solution extracted in the step 3) in a centralized manner, regulating the pH value to 9-11 by using a potassium hydroxide or potassium carbonate solution to precipitate heavy metals, separating, filtering and recovering the heavy metals to obtain the liquid fertilizer containing high potassium. The straws of the plants in the mature period after the heavy metal pollution of the soil are high-potassium-content tobacco straws, oil sunflower straws, sesame straws or peanut straws.

The method comprises the steps of firing straws produced after the plants in the mature period restore the heavy metal pollution of the soil into biochar in a tubular furnace at low temperature, extracting the heavy metal in the biochar by low-concentration nitric acid, finally regulating the pH value to 9-11 to precipitate and recycle the heavy metal in the extract liquor, removing the heavy metal in the biochar while changing the straws into valuables, recycling the heavy metal, and enabling the remaining extract liquor to have high content of nutrient elements and be used as an alkaline liquid potash fertilizer.

The invention provides a new solution and approach for the subsequent treatment of the straws produced by the heavy metal pollution of the phytoremediation soil, so that the phytoremediation technology can be developed efficiently and continuously, and a new approach is provided for the resource utilization of plants.

Detailed Description

Example 1:

1) harvesting tobacco straws after the plant in the mature period restores the heavy metal pollution of the soil, cleaning the tobacco straws, and drying the tobacco straws in an oven at 60 ℃;

2) weighing dried tobacco straws, crushing the tobacco straws by using a crusher, weighing 10g of the dried tobacco straws, placing the crushed tobacco straws into a clean quartz boat, then placing the quartz boat into a tubular furnace into which high-purity nitrogen is introduced for firing, setting the temperature to be 300-350 ℃, setting the time to be 2 hours, and setting the absorption liquid to be 0.1mol/L nitric acid to obtain biochar;

3) after the step 2) is finished, weighing the fired biochar, measuring the yield of the biochar, then weighing 10g of the fired biochar, putting the baked biochar into a clean beaker, adding 300ml of clean water, regulating the pH value of the biochar to be 1 by using nitric acid, stirring for 3h, extracting heavy metals, and washing residual acid in the biochar by using clean water for filtering or a centrifugal dehydration mode;

4) collecting the solution extracted in the step 3) in a centralized manner, regulating the pH value to 9-11 by using a potassium hydroxide or potassium carbonate solution to precipitate heavy metals, separating, filtering and recovering the heavy metals to obtain the liquid fertilizer containing high potassium.

Experiments prove that the heavy metal and nutrient element change in the process of preparing the biochar, and the content of the heavy metal is reduced and the K element is increased in the process of separating the heavy metal.

Experiment one: 10g of dried tobacco straw is put into a tubular furnace and is fired by introducing nitrogen, the firing time is 2h, the dried tobacco straw is taken out after being cooled at the equal temperature and is subjected to digestion and detection on a machine, and the test result is shown in the table I.

Table one: the heavy metal and nutrient element changes of the tobacco straw when the tobacco straw is baked at 300 and 350 DEG C

Experiments show that the heavy metals in the tobacco straws start to obviously volatilize at 400 ℃, cadmium is completely volatilized when the temperature reaches 600 ℃, and the carbon-based dry yield is reduced along with the increase of the temperature; and the content of heavy metal is changed and is reduced by a certain amount, the cadmium volatilization amount is small at 300 ℃, the yield of the biochar is high, and the change of other nutrient elements is not large, so that the biochar is fired at 300 ℃ in the subsequent extraction experiment.

Experiment two, weighing 10g of biochar fired at 300 ℃, placing the biochar into a beaker, adding 300ml of clean water, placing the beaker on a magnetic stirrer, stirring for 20 minutes, fully and uniformly stirring, regulating the pH to 1 by using nitric acid, stirring for 3 hours, filtering, collecting filtrate into the beaker in a centralized manner, stirring, regulating the pH to 9, 10 and 11 by using potassium hydroxide or potassium carbonate solution, fully stirring, taking 5ml of solution from each point to one point, and filtering for detection on a machine; the results are shown in Table II.

Table two: change of heavy metals and nutrient elements of 350 ℃ biochar at different pH (unit: ug;/"is not detected)

From the second table, it is known that the total amount of elements in the solution decreases when the pH is adjusted to be alkaline, wherein the heavy metal elements Pb, Zn, Cu, and Cd are not detected when the pH is 9, which indicates that the heavy metal is chemically reacted to generate precipitate under the alkaline condition, and the total amount of potassium is increased because the potassium hydroxide or potassium carbonate solution is added when the pH is adjusted.

Claims

1. A resource utilization method of high-potassium-content straws produced after heavy metal pollution of soil remediation by plants is characterized by comprising the following steps:

1) harvesting tobacco straws, oil sunflower straws, sesame straws or peanut straws after the heavy metal pollution of the plant restoration soil in the mature period, cleaning and drying;

2) weighing dried straws, crushing the straws by using a crusher, placing the crushed straws in a tubular furnace into which high-purity nitrogen is introduced, and firing the straws at a low temperature, wherein the temperature is set to be within the range of 300-350 ℃, the time is set to be 2 hours, and the absorption liquid is 0.1mol/L nitric acid to obtain biochar;

3) after the step 2), putting the fired biochar in clean water, regulating the pH value of the biochar to be 1-3 by using nitric acid, stirring for 3 hours, dissolving out heavy metals, and washing residual acid in the biochar by using clean water for filtering or a centrifugal dehydration mode;