CN110749488B

CN110749488B - Soil treatment method and method for detecting heavy metals in soil

Info

Publication number: CN110749488B
Application number: CN201911235861.7A
Authority: CN
Inventors: 谢连科; 张永; 吴中杰; 张兆波; 侯亚琴; 巩泉泉; 刘国强; 张燕
Original assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd
Current assignee: State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Shandong Electric Power Co Ltd
Priority date: 2019-12-05
Filing date: 2019-12-05
Publication date: 2022-05-10
Anticipated expiration: 2039-12-05
Also published as: CN110749488A

Abstract

The invention provides a soil treatment method, which comprises the following steps: (1) drying, grinding and sieving the sampled soil sample; (2) calcining a soil sample; and (3) mixing the calcined soil sample with hydrochloric acid to form a suspension, and carrying out ultrasonic treatment on the suspension. In the step (2), the soil sample is subjected to two-stage heating type calcination, and the temperature of the second stage calcination is higher than that of the first stage calcination. The invention also provides a method for detecting the heavy metal in the soil, which comprises the following steps: (1) treating a soil sample by using the soil treatment method disclosed by the invention to obtain a soil suspension; (2) preparing a solution to be detected containing heavy metals by using the soil turbid liquid; (3) and detecting the content of heavy metal in the soil by using the solution to be detected. The soil treatment method does not involve the use of strong oxidizing acid, and improves the safety in the operation process on the basis of keeping the accuracy of the analysis result.

Description

Soil treatment method and method for detecting heavy metals in soil

Technical Field

The invention belongs to the field of soil heavy metal detection, and particularly relates to a soil treatment method for detecting heavy metal content and a method for detecting the heavy metal content.

Background

Along with the development of industries such as batteries, electroplating and the like, more and more soil is polluted by heavy metals, the heavy metals in the soil can cause great pollution to animals, plants and underground water, and can finally enter the human body through a biological circulation ring to cause irreversible damage to the human body, particularly, the heavy metals such as mercury, lead and the like, and trace heavy metals can cause great damage to the human body and are difficult to recover. Therefore, the detection of the heavy metals is an extremely important work, the condition that the soil is polluted by the heavy metals can be effectively indicated, the subsequent soil treatment work is guided, and the damage of the heavy metals to the human body is avoided.

The general processes of soil analysis comprise collection, pretreatment, digestion, test and result analysis, and the collection, pretreatment and other processes are demonstrated for a long time and are easy to realize. The digestion process aims to destroy the soil structure, destroy the lattice structure in the soil and completely release heavy metals in the soil, and the soil is usually treated by strong oxidizing acids such as perchloric acid, nitric acid and the like at high temperature and finally prepared into clear and transparent aqueous solution suitable for instrument detection. Still need stir or vibrate in order to prevent to explode to solution in the heating process, still corrode the hot plate when solution explodes and boils, cause equipment to damage, all have strict experience requirements to acid addition amount, acid sequence, acid adding opportunity etc. simultaneously, therefore soil analysis process not only is consuming time, moreover because uses multiple strong oxidizing property acid, there are many unsafe factors in the test procedure.

Therefore, with the increase of the requirement and range of soil detection, a method for digesting soil with no or little strong acid is required to be selected for detecting soil, and the accuracy and the high efficiency of the detection method are ensured. The soil digestion aims at destroying the structure of the soil, so that the soil is mineralized, and various heavy metals in the soil are released into the solution to be detected. Various dispersion processes and modification processes can be adopted to replace the application of various strong acids, the problems of bumping, acid mist and the like in the current strong acid using process are solved, the heavy metal in the soil is dispersed into the solution to be detected, and the high-efficiency and accurate detection of the content of the heavy metal in the soil is realized.

Disclosure of Invention

In one aspect, the invention aims to provide a soil treatment method for detecting heavy metal content, which comprises the following steps: (1) drying, grinding and sieving the sampled soil sample; (2) calcining a soil sample; and (3) mixing the calcined soil sample with hydrochloric acid to form a suspension, and carrying out ultrasonic treatment on the suspension.

Preferably, in the step (1), the temperature of the drying is not lower than 100 ℃.

Preferably, in step (1), the dried soil sample is ground and sieved using a 100 mesh screen.

Preferably, in step (2), the soil sample is subjected to two-stage isothermal calcination, wherein the temperature of the second stage calcination is higher than the temperature of the first stage calcination.

Preferably, the temperature of the first-stage calcination is increased from room temperature to 300-400 ℃, the temperature increase rate is not higher than 7 ℃/min, and the constant temperature time is not lower than 3 h; the temperature of the second stage of calcination is increased from the temperature of the first stage of calcination to 800-1000 ℃, the temperature increase rate is not higher than 5 ℃/min, and the constant temperature time is not lower than 1 h.

Preferably, the temperature of the first stage of calcination is raised from room temperature to 350 ℃, the temperature raising rate is 5 ℃/min, and the constant temperature time is 5 h.

Preferably, the temperature of the second stage of calcination is increased from the temperature of the first stage of calcination to 900 ℃, the temperature increase rate is 3 ℃/min, and the constant temperature time is 3 h.

Preferably, in the step (3), the calcined soil sample is mixed with hydrochloric acid with the mass fraction of 30%, the mixture is shaken by an air bath shaker for 24 hours at 60 ℃ after sealing, and then the mixture is subjected to ultrasonic treatment under the conditions that the power is 2000Hz and the temperature is 60-90 ℃.

Preferably, the time of sonication is not less than 3 h.

Preferably, the temperature of the ultrasonic treatment is 80 ℃ and the treatment time is 5 h.

Preferably, in the step (3), the calcined soil sample is mixed with hydrochloric acid with the mass fraction of 30% according to the proportion of 0.5g of soil sample to 30ml of hydrochloric acid, after sealing, the mixture is shaken by an air bath shaking table at 60 ℃ for 24 hours, and then the mixture is subjected to ultrasonic treatment under the conditions that the power is 2000Hz and the temperature is 60-90 ℃.

On the other hand, the invention also provides a method for detecting heavy metals in soil based on the soil treatment method, which comprises the following steps: (1) treating a soil sample by using the soil treatment method to obtain a soil suspension; (2) preparing a solution containing the heavy metal to be detected by using the soil turbid liquid; and (3) detecting the content of heavy metal in the soil by using the solution to be detected.

Preferably, the method for detecting the heavy metal content in the soil can be used for measuring heavy metals including Ni, Zn, Cu, Cr, Pb, Cd and Co.

Preferably, in the method for measuring the content of heavy metals in soil, in the step (2), the process of preparing the solution containing the heavy metals to be measured by using the soil suspension comprises the following steps: the soil suspension was centrifuged at 11000rpm for 15min, the supernatant after centrifugation was transferred to a volumetric flask, the soil precipitate was washed by resuspending and centrifuging at 11000rpm for 15min using demineralized water, the centrifuged supernatant was transferred to the volumetric flask, and then 10% ammonium chloride solution was added to the volumetric flask and a predetermined volume was fixed with 1% nitric acid solution.

Preferably, in the method for measuring the heavy metal content of soil, the washing in the step (2) is performed three times.

The soil treatment method does not involve the use of strong oxidizing acids, and replaces the digestion process of soil by strong acid by the steps of superfine grinding, high-temperature calcination and ultrasonic treatment. On the basis of keeping the accuracy of the analysis result, the method eliminates serious consequences such as human body injury, equipment corrosion and the like possibly caused by strong oxidizing acid, and improves the safety of the operation process. Meanwhile, due to the fact that the current procedure for purchasing the strong oxidizing acid is complex, the soil treatment method greatly reduces the complexity of soil treatment of the content of the heavy metal to be detected, simultaneously greatly reduces the potential danger of operation in the analysis process of the content of the heavy metal in the soil, and basically can minimize the influence of the detection process of the content of the heavy metal in the soil on human bodies and detection equipment.

Drawings

FIG. 1 shows a flow chart of the soil treatment method and the method of detecting heavy metal content of the present invention.

Detailed Description

The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings, and the embodiments are merely illustrative of the technical solutions of the present invention, and the scope of the present invention is not limited thereto.

The heavy metals in the soil are detected, firstly, the soil to be detected needs to be processed, the soil structure is damaged, so that various heavy metals in the soil are fully released and converted into a soluble state to be dissolved in a solution to be detected.

The soil treatment method provided by the invention mainly destroys the soil structure by calcining and ultrasonic treatment. The calcination changes the lattice structure of the soil, removes the adsorption of the soil to heavy metals, eliminates organic matters in the soil, makes the soil inorganic, ensures that the heavy metals can be fully dissolved in the solution to be detected, and ensures the accuracy of the detection.

The soil suspended in the hydrochloric acid is subjected to ultrasonic treatment, so that heavy metals in the soil can be released more fully, the contact between the soil and the hydrochloric acid can be promoted, carbonate in the soil is fully eliminated, and the heavy metals in the soil are further fully converted into a soluble state and dissolved in a solution to be detected.

The soil treatment method avoids using a large amount of strong oxidizing acids such as nitric acid, perchloric acid and the like, and can meet the requirement of detecting the content of heavy metals in the soil.

Fig. 1 shows a flow chart of the soil treatment method of the present invention and its subsequent method for detecting heavy metal content, wherein steps S1 to S3 are the main steps involved in the soil treatment method.

As shown in fig. 1, step S1 is a step of sampling, drying, grinding and sieving a soil sample. Selecting a proper soil collecting tool, sampling according to the principle of random, equivalent and multipoint mixing, then performing air drying, crushing, screening and other steps, sampling by a quartering method, and dividing the soil into a sample to be detected and a reserved standby sample to be detected. And fully drying the soil in a drying box, wherein the drying temperature is preferably 100 ℃, and grinding the dried soil until all soil samples can pass through a 100-mesh screen.

Step S2 is a step of subjecting the soil sample to calcination treatment. The soil sample is preferably calcined in a muffle furnace. The calcination is preferably a two-stage, elevated calcination in which the temperature of the second stage is higher than the temperature of the first stage. Preferably, the temperature of the first stage of calcination is increased from room temperature to 300-400 ℃, the temperature increase rate is not higher than 7 ℃/min, and the constant temperature holding time is not less than 3 h. The temperature of the second stage of calcination is continuously increased from the temperature of the first stage of calcination to 800-1000 ℃, the temperature increase rate is not higher than 5 ℃/min, and the constant temperature holding time is not lower than 1 h.

Step S3 is a step of subjecting the soil sample to ultrasonic treatment. First, a soil suspension was prepared in hydrochloric acid. Mixing the calcined soil sample and hydrochloric acid in a glass container according to the proportion of 0.5g of the soil sample to 30ml of hydrochloric acid (the mass fraction is 30%), sealing the opening of the container, and shaking the mixture in an air bath shaker at 60 ℃ for 24 hours to obtain a fully and uniformly mixed soil suspension. And then, carrying out ultrasonic treatment on the soil suspension under the conditions that the ultrasonic power is 2000Hz and the temperature is 60-90 ℃. The time of the ultrasonic treatment is preferably not less than 3 hours. In the ultrasonic treatment process, attention is paid to noise isolation so as to reduce the harm of noise to operators.

After the soil sample is processed in steps S1 to S3, the process proceeds to steps S4 to S5.

In step S4, a solution containing the heavy metal to be measured is prepared using the soil suspension obtained after the above soil treatment. First, the soil suspension was centrifuged at not less than 9000rpm for at least 10min, and the centrifuged supernatant was transferred to a volumetric flask. Next, the soil precipitate is washed with demineralized water by resuspending and centrifuging at a rotation speed of not less than 9000rpm for at least 10min, and the centrifuged supernatant is transferred to the above volumetric flask, preferably washing is repeated three times. And then adding a 10% ammonium chloride solution into the volumetric flask containing the centrifugal supernatant, and fixing the volume to a preset volume by using a 1% nitric acid solution to obtain a solution, namely the solution containing the heavy metal to be detected. The amount of the desalted water used per washing is preferably 5mL per 0.5g of soil sample, and accordingly, the amount of 10% ammonium chloride used is preferably 1 mL. The rotation speed of the centrifugation is preferably 11000rpm, and the centrifugation time is preferably 15 min.

The solution containing the heavy metal to be detected prepared in the step S4 is suitable for detecting the contents of Ni, Zn, Cu, Cr, Pb, Cd and Co.

After the solution containing the heavy metals to be detected is prepared, the method of the present invention proceeds to step S5, i.e., the content of each target heavy metal is detected. And analyzing various heavy metals in the solution by using an inductively coupled plasma analyzer. Firstly, determining a standard curve of the relation between the absorbance and the content of the corresponding heavy metal under a characteristic spectral line by using standard solutions of various heavy metals to be detected, and then deducing and calculating the content of the corresponding heavy metal in the soil according to the absorbance of the solution to be detected under the characteristic spectral line.

The digestion of soil samples in the existing various standardized methods usually involves the use of strong acids such as hydrofluoric acid, perchloric acid and the like, the acids have strong corrosivity and irritation and great harm to human bodies, and the acids belong to strong-control acids, and the procedures for obtaining and using the acids are very strict, so that the corresponding heavy metal detection means are not convenient enough. The soil treatment method can replace the soil sample digestion process in the national standard method, and can relatively more freely implement corresponding operation because the use of strong acid such as hydrofluoric acid, perchloric acid and the like is not involved.

In addition, various standardized methods often include a silicon flying step. The silicon-on-fly step forms volatile SiF₄Gas, formed SiF₄The gas is toxic and corrosive, and easily stimulates the respiratory system. The silicon flying process needs to shake the crucible regularly, which easily causes scalding of operators. The soil treatment process of the present invention does not involve a silicon fly step, sinceThis is more secure and reliable.

Although the soil treatment method relates to the use of hydrochloric acid, the acid solution does not need to be boiled when the hydrochloric acid is used for dissolving heavy metals in the soil, and the container is sealed in the operation process, so that on one hand, the damage of acid mist to operators can be avoided, and on the other hand, the corrosion of devices such as a heating plate caused by the overflow of the acid can be avoided.

In the soil treatment method, the steps of calcining in a muffle furnace, ultrasonic treatment and the like can simultaneously treat a plurality of samples, and the treatment efficiency is obviously improved compared with the conventional standardized method.

According to the soil treatment method, special materials such as a polytetrafluoroethylene crucible are not needed, various strong acids are avoided, the soil detection efficiency is improved, and the soil detection cost is reduced.

Several specific examples of the present invention are provided below to aid in understanding the present invention.

Example 1

Soil polluted by a lead-acid storage battery in a certain converter station in Shandong and Jinan is taken as a treatment object.

Firstly, sampling is carried out according to the principle of random, equivalent and multipoint mixing, then sampling is carried out by a quartering method through the steps of air drying, crushing, screening and the like, and a soil sample to be detected is determined.

And then, fully drying the soil by using an oven, wherein the temperature in the drying process is 100 ℃, and grinding the dried soil until all the soil can pass through a 100-mesh screen.

And transferring the ground and sieved soil sample into a muffle furnace, wherein the temperature is increased from room temperature to 350 ℃ in the first stage at the temperature increasing rate of 5 ℃/min for 5h at the constant temperature, and the temperature is continuously increased to 900 ℃ in the second stage at the temperature increasing rate of 3 ℃/min for 3h at the constant temperature.

Weighing 0.5g of calcined soil sample, adding 30ml of hydrochloric acid with the mass fraction of 30%, sealing, and shaking at 60 ℃ for 24h to obtain a fully and uniformly mixed soil suspension. And then carrying out ultrasonic treatment on the soil suspension in an ultrasonic instrument, wherein the ultrasonic power is set to 2000Hz, the temperature is set to 80 ℃, and the ultrasonic treatment time is 5 h.

And then, preparing a solution to be detected containing the heavy metal elements by using the ultrasonically treated soil suspension. First, the soil suspension was centrifuged at 11000rpm for 15min by a high-speed centrifuge, and the supernatant was transferred to a volumetric flask. The soil sediment was washed three times with 5mL of demineralized water by resuspending and centrifuging for 15min at 11000rpm, the centrifuged supernatant during washing was transferred to the same volumetric flask, and finally 1mL of 10% ammonium chloride solution was added and the volume was fixed with 1% nitric acid solution.

Next, the solution to be measured was analyzed by an inductively coupled plasma spectrometer (ICP-AES, Thermal Fisher, USA). And detecting the absorbance of the solution to be detected under the characteristic spectral line by establishing a standard curve of the relationship between the absorbance and the content of various heavy metals under the characteristic spectral line, and deducing and calculating the content of various heavy metal elements in the soil under the standard curve based on the value of the absorbance.

Soil samples treated according to local standard DB65/T3974-2017 soil determination of heavy metal elements inductively coupled plasma Mass Spectrometry were used simultaneously as controls.

Table 1 shows the results of analysis of the heavy metal content of the soil after treatment in example 1 and standard DB65/T3974-2017 method.

TABLE 1

Example 2

The soil outside a waste battery workshop of a certain storage battery manufacturer in Shandong Jinan area is taken as a treatment object.

And then, preparing a solution to be detected containing the heavy metal elements by using the ultrasonically treated soil suspension. First, the soil suspension was centrifuged at 11000rpm for 15min by a high-speed centrifuge, and the centrifuged supernatant was transferred to a volumetric flask. The soil sediment was washed three times with 5mL of demineralized water by resuspending and centrifuging for 15min at 11000rpm, the centrifuged supernatant during washing was transferred to the same volumetric flask, and finally 1mL of 10% ammonium chloride solution was added and the volume was fixed with 1% nitric acid solution.

Table 2 shows the results of analysis of the heavy metal content of the soil after example 2 and treatment according to the standard DB65/T3974-2017 method.

TABLE 2

Example 3

Soil outside a certain circuit board cleaning workshop in the Shandong Jinnan region is taken as a treatment object.

And then, fully drying the soil by using an oven at the temperature of 100 ℃ in the drying process, and grinding the dried soil until all the soil can pass through a 100-mesh screen.

And then, preparing a solution to be detected containing the heavy metal elements by using the ultrasonically treated soil suspension. First, the soil suspension was centrifuged at 11000rpm for 15min by a high-speed centrifuge, and the supernatant was transferred to a volumetric flask. Washing the soil sediment with 5mL of demineralized water by resuspending and centrifuging for 15min at the rotating speed of 11000rpm, washing three times, transferring the centrifugal supernatant during washing into the same volumetric flask, finally adding 1mL of 10% ammonium chloride solution, and fixing the volume with 1% nitric acid solution.

Table 3 shows the results of analysis of the heavy metal content of the soil after example 3 and treatment according to the standard DB65/T3974-2017 method.

TABLE 3

The soil treatment method provided by the invention replaces a method for dissolving heavy metals in soil by boiling strong acid in a standard method through calcination and ultrasonic treatment processes, avoids the harm of acid mist and volatile silicon to operators on the basis of ensuring the stability and high efficiency of the test, and eliminates a great amount of potential threats in the soil test process.

Simultaneously using the in-process of hydrochloric acid solution heavy metal in the soil, need not to boil acid solution, and the overall process is sealed, can avoid acid mist to operating personnel's stimulation on the one hand, on the other hand can avoid overflowing of acid and cause devices such as hot plate to corrode in operation process. From the test result, the soil treated by the process can completely release heavy metals in the soil into the liquid to be tested. Compared with the standard method, the test result is accurate, the process can be used for replacing the national standard method for testing, and the interference caused by using other optical instruments for testing and the danger caused by using strong acid in the national standard method are avoided.

The foregoing detailed description and drawings are merely illustrative of the present invention for the purpose of facilitating a better understanding of the concepts of the invention, and are not intended to limit the scope of the invention. Variations of the invention may be made by those skilled in the art without departing from the spirit of the invention. Any modification or variation made without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A soil treatment method for detecting heavy metal content, which is characterized by comprising no operation of digesting soil by using strong oxidizing acid and comprises the following steps:

(1) drying, grinding and sieving the sampled soil sample;

(2) performing two-stage heating type calcination on the soil sample, wherein the temperature of the second stage of calcination is higher than that of the first stage of calcination; and the number of the first and second groups,

(3) mixing the calcined soil sample with hydrochloric acid to form a suspension, and carrying out ultrasonic treatment on the suspension.

2. A soil treatment method as claimed in claim 1, wherein:

in the step (1), the drying temperature is not lower than 100 ℃.

3. A soil treatment method as claimed in claim 1, wherein:

in step (1), the dried soil sample was ground and subjected to the sieving with a 100 mesh screen.

4. A soil treatment method as claimed in claim 1, wherein:

the temperature of the first stage of calcination is increased from room temperature to 300-400 ℃, the temperature increase rate is not higher than 7 ℃/min, and the constant temperature time is not lower than 3 h;

the temperature of the second stage of calcination is increased from the temperature of the first stage of calcination to 800-1000 ℃, the temperature increase rate is not higher than 5 ℃/min, and the constant temperature time is not lower than 1 h.

5. A soil treatment method as claimed in claim 1, wherein:

the temperature of the first stage of calcination is raised from room temperature to 350 ℃, the temperature raising rate is 5 ℃/min, and the constant temperature time is 5 h.

6. A soil treatment method as claimed in claim 4, wherein:

the temperature of the second stage of calcination is increased from the temperature of the first stage of calcination to 900 ℃, the temperature increase rate is 3 ℃/min, and the constant temperature time is 3 h.

7. A soil treatment method as claimed in claim 1, wherein:

in the step (3), the calcined soil sample is mixed with hydrochloric acid with the mass fraction of 30%, the mixture is subjected to shaking for 24 hours at 60 ℃ by using an air bath shaking table after being sealed, and then the mixture is subjected to ultrasonic treatment under the conditions that the power is 2000Hz and the temperature is 60-90 ℃.

8. The soil treatment method as set forth in claim 7, wherein:

the ultrasonic treatment time is not less than 3 h.

9. A soil treatment method as claimed in claim 7 or 8, wherein:

the temperature of ultrasonic treatment is 80 ℃, and the treatment time is 5 h.

10. A soil treatment method as claimed in claim 1 or 7, wherein:

in the step (3), the calcined soil sample is mixed with hydrochloric acid with the mass fraction of 30% according to the proportion of 0.5g of soil sample to 30ml of hydrochloric acid, the mixture is subjected to shaking for 24 hours at 60 ℃ by using an air bath shaking table, and then the mixture is subjected to ultrasonic treatment under the conditions that the power is 2000Hz and the temperature is 60-90 ℃.

11. A method for detecting heavy metals in soil, comprising the steps of:

(1) treating a soil sample using the soil treatment method of any one of claims 1 to 10 to obtain a soil suspension;

(2) preparing a solution to be detected containing heavy metals by using the soil turbid liquid;

(3) and detecting the content of heavy metal in the soil by using the solution to be detected.

12. The method for detecting heavy metals in soil according to claim 11, wherein: the heavy metals detected include Ni, Zn, Cu, Cr, Pb, Cd, and Co.

13. The method for detecting heavy metals in soil according to claim 11, wherein:

in the step (2), the process of preparing the solution containing the heavy metal to be detected by using the soil suspension liquid comprises the following steps: the soil suspension was centrifuged at 11000rpm for 15min, the supernatant after centrifugation was transferred to a volumetric flask, the soil precipitate was washed by resuspending and centrifuging at 11000rpm for 15min using demineralized water, the centrifuged supernatant was transferred to the volumetric flask, and then 10% ammonium chloride solution was added to the volumetric flask and a predetermined volume was fixed with 1% nitric acid solution.

14. The method for detecting heavy metals in soil according to claim 13, wherein: in step (2), the washing is performed three times.