CN113640236A - Method for detecting heavy metal cadmium in farmland soil - Google Patents
Method for detecting heavy metal cadmium in farmland soil Download PDFInfo
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Abstract
The invention relates to a detection method of heavy metal cadmium in farmland soil, belonging to the technical field of heavy metal detection methods. The invention provides a detection method of heavy metal cadmium in farmland soil, which aims to solve the problem that the specific distribution conditions of different forms of cadmium in farmland soil cannot be accurately mastered only by paying attention to the total amount of cadmium or the detection of active cadmium in the existing detection method of heavy metal cadmium in soil. The method can respectively detect the contents of water-soluble cadmium, exchange cadmium, carbonate cadmium and ferro-manganese oxide combined cadmium in the farmland soil, accurately master the specific distribution conditions of different forms of cadmium in the farmland soil, and provide a reference basis for pertinently treating cadmium pollution in the farmland soil. The invention avoids the damage of acid-base solution to soil samples, simplifies the sample treatment steps, and has the advantages of simple experimental method, high detection speed, high stability, low analysis cost and the like.
Description
Technical Field
The invention belongs to the technical field of heavy metal detection methods, and particularly relates to a detection method of heavy metal cadmium in farmland soil.
Background
Cadmium is an element harmful to human body, belongs to carcinogenic substance, can enter into human body through respiratory system and digestive system, and can accumulate in human skeleton, kidney and liver, etc., finally induce orthopedic diseases, such as osteomalacia, osteoporosis, humeral pain, etc., and also induce renal tubule absorption function decline.
The sources of cadmium in soil include natural sources, which are background values derived from rocks and soil, and man-made sources, which are due to the increasingly widespread use of cadmium in electroplating, pigment, plastic stability, nickel cadmium batteries, television picture tube manufacture. With the continuous development of mining, smelting and electroplating industries, a large amount of cadmium-containing wastewater is discharged into rivers, thereby polluting the atmosphere, water and soil. The cadmium pollution of the soil is mainly distributed in the developed regions of the heavy industry and on the two sides of roads and railways, and the cadmium pollution of the farmland soil in the developed irrigation regions of agriculture is also serious. The main ways for generating cadmium pollution in the farmland soil are as follows: the sedimentation of cadmium in the atmosphere, the use of pesticides, fertilizers and plastic films, sewage irrigation, sludge fertilization, the accumulation of waste containing heavy metals, the pollution of acidic wastewater of metal mines and the like.
Heavy metal cadmium has different forms in farmland soil, and has different migration and transformation characteristics, pollution properties and ecological hazard degrees. However, the existing detection of the cadmium content in the soil usually only focuses on the total amount of cadmium or the detection of active cadmium, and neglects the morphological distribution characteristics of cadmium, particularly the distribution of the water-soluble state, the exchange state, the carbonate state and the iron-manganese oxide combination state of the cadmium. Because the specific distribution conditions of different forms of cadmium in a complex system of soil-water-crops cannot be accurately mastered, an effective method for treating heavy metal cadmium in soil cannot be provided, and therefore a detection method capable of detecting different forms of heavy metal cadmium in farmland soil is urgently needed in the field.
Disclosure of Invention
The invention provides a method for detecting heavy metal cadmium in farmland soil, aiming at solving the problem that the existing method for detecting heavy metal cadmium in soil only focuses on the detection of the total amount of cadmium or active cadmium and cannot accurately master the specific distribution conditions of different forms of cadmium in farmland soil.
The technical scheme of the invention is as follows:
a detection method of heavy metal cadmium in farmland soil comprises the following steps:
firstly, sampling cultivated land soil:
randomly collecting soil samples in a to-be-detected farmland area, and uniformly mixing the farmland soil samples collected in the same batch to serve as mixed farmland soil samples for later use;
step two, soil sample pretreatment of cultivated land:
air-drying, grinding and sieving the mixed cultivated land soil sample collected in the step one at room temperature for later use;
step three, carrying out soil sample leaching treatment on cultivated land:
(1) adding deionized water into the soil pretreatment sample I obtained in the step two according to a certain mass-volume ratio, oscillating, centrifuging, and collecting supernatant, namely the water-soluble cadmium solution to be detected;
(2) washing the soil sample precipitate obtained by centrifuging in the step (1) with deionized water to obtain a soil sample II, and adding CaCl into the soil sample II according to a certain mass-volume ratio2Oscillating and centrifuging the solution, and collecting supernatant to obtain exchangeable cadmium solution to be detected;
(3) washing the soil sample precipitate obtained by centrifuging in the step (2) with deionized water to obtain a soil sample III, and adding NH into the soil sample III according to a certain mass-volume ratio4Oscillating and centrifuging the OAc solution, and collecting supernatant to obtain carbonate cadmium solution to be detected;
(4) washing the soil sample precipitate obtained by centrifuging in the step (3) with deionized water to obtain a soil sample IV, adding a hydroxylamine hydrochloride solution into the soil sample IV according to a certain mass-volume ratio, oscillating, centrifuging, and collecting supernatant to obtain the solution to be detected, namely the iron-manganese oxidized cadmium;
step four, detecting by a graphite furnace-atomic absorption spectrometer:
(a) making a standard curve: respectively diluting the cadmium standard mother liquor to obtain cadmium standard solutions with gradient concentrations, respectively measuring the absorbance values of the cadmium standard solutions with different concentrations by using a graphite furnace-atomic absorption spectrometer, and taking the absorbance values as vertical coordinates and the cadmium concentration of the cadmium standard solutions as horizontal coordinates to obtain a standard curve;
(b) and (3) determining a sample to be tested: under the same detection condition as the step (a), sequentially injecting the solutions to be detected obtained in the step three into a graphite tube of a graphite furnace-principle absorption spectrometer, and detecting the absorbance value of each solution to be detected after atomization;
(c) and (c) substituting the absorbance values of the solutions to be detected measured in the step (b) into the standard curve in the step (a) for quantitative analysis, and calculating to respectively obtain the contents of water-soluble cadmium, exchangeable cadmium, carbonate cadmium and iron-manganese oxidized cadmium in the soil sample.
Further, in the step one, randomly collecting soil is uniformly and randomly sampling 10-20 parts in a zigzag or snake-shaped distribution in a to-be-detected ploughing area, and the distribution range of the samples is not less than 3 mu; and continuously collecting soil samples in a full-layer column shape with the depth of 0-20cm in a plough layer, wherein the weight of each soil sample is 1kg, a plastic inner pipe soil sampler is used during sampling, the collected soil samples are placed into a plastic bag for storage, and the collection place, the depth and the collection time are marked.
Further, the weight of the soil sample of the mixed cultivated land in the second step is 5.00-10.00 g, and the soil sample of the mixed cultivated land is air-dried at room temperature of 20-30 ℃ until the water content is less than 2%; the grinding and sieving are grinding in an agate mortar and sieving by a 200-mesh sieve.
Further, the mass-to-volume ratio of the soil pretreatment sample I to deionized water in the step three (1) is 1g:4mL, and the oscillation treatment is carried out at 150-200 rpm for 1-3 h; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
Further, the deionized water cleaning treatment in the step three (2) is to shake and clean the soil sample precipitate obtained by centrifuging in the step (1) by using 10mL of deionized water, centrifuge at 4000rpm for 20min, and collect the soil sample precipitate to obtain a soil sample II; the soil sample II is mixed with CaCl2The mass volume ratio of the solution is 1g to 4mL, and the CaCl is2The concentration of the solution is 0.05 mol/L; the oscillation treatment is carried out for 1-3 h at 150-200 rpm; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
Further, the deionized water cleaning treatment in the third step (3) is to shake and clean the soil sample precipitate obtained by centrifuging in the step (2) by using 10mL of deionized water, centrifuge at 4000rpm for 20min, and collect the soil sample precipitate to obtain a soil sample III; the soilSample III and NH4The mass-to-volume ratio of the OAc solution is 1g to 4mL, and the NH is4The concentration of the OAc solution is 1 mol/L; the oscillation treatment is carried out for 1-3 h at 150-200 rpm; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
Further, the deionized water cleaning treatment in the step three (4) is to shake and clean the soil sample precipitate obtained by centrifuging in the step (3) by using 10mL of deionized water, centrifuge at 4000rpm for 20min, and collect the soil sample precipitate to obtain a soil sample IV; the mass volume ratio of the soil sample IV to the hydroxylamine hydrochloride solution is 1g:4mL, and the concentration of the hydroxylamine hydrochloride is 0.5 mol/L; the oscillation treatment is carried out for 1-3 h at 150-200 rpm; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
Further, in the fourth step (a), the concentration of the cadmium standard mother liquor is 500 mug/mL, and the concentration of the cadmium standard solution with gradient concentration is 0 mug/L, 0.8 mug/L, 1.5 mug/L, 3 mug/L and 5 mug/L in sequence.
Further, in the optical parameters of the graphite furnace-atomic absorption spectrometer in the step four (a), the detection wavelength is 228.8nm, the slit width is 0.7nm, and the lamp current is 4.0 mA.
Further, the atomization temperature of the graphite furnace-atomic absorption spectrometer in the step four (a) is 1500 ℃, and the atomization time is 5 s; the burning residual temperature is 2450 ℃ and the burning residual time is 3 s; high-purity argon is used as the protective gas of the graphite furnace, and the gas flow is 1.8L/min.
The invention has the beneficial effects that:
the detection method of the heavy metal cadmium in the farmland soil provided by the invention can respectively detect the contents of water-soluble cadmium, exchange cadmium, carbonate cadmium and iron manganese oxide combined cadmium in the farmland soil, accurately master the specific distribution conditions of different forms of cadmium in the farmland soil and provide a reference basis for pertinently treating cadmium pollution in the farmland soil.
The method for processing the soil sample avoids the damage of the acid-base solution to the soil sample and the damage of different forms of cadmium, simplifies the sample processing steps and reduces the possibility of sample loss or pollution. The method uses graphite furnace atomic absorption spectrometry, and has the advantages of simple experimental method, high analysis sensitivity, high detection speed, high stability, low analysis cost and the like.
Detailed Description
The technical solutions of the present invention are further described below with reference to the following examples, but the present invention is not limited thereto, and any modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention. The process equipment or apparatus not specifically mentioned in the following examples are conventional in the art, and if not specifically mentioned, the raw materials and the like used in the examples of the present invention are commercially available; unless otherwise specified, the technical means used in the examples of the present invention are conventional means well known to those skilled in the art.
Example 1
The embodiment provides a detection method of heavy metal cadmium in farmland soil, which comprises the following steps:
firstly, sampling cultivated land soil:
uniformly and randomly sampling 10-20 parts in a zigzag or snake-shaped distribution in the ploughing area to be detected, wherein the distribution range of the samples is not less than 3 mu; continuously collecting soil samples in a full-layer column shape with the depth of 0-20cm in a plough layer, wherein the weight of each soil sample is 1kg, a plastic inner tube soil sampler is used during sampling, the collected soil samples are put into a plastic bag for storage, the collection place, the collection depth and the collection time are marked, and the soil samples of the cultivated land collected in the same batch are uniformly mixed to be used as soil samples of mixed cultivated land for later use;
step two, soil sample pretreatment of cultivated land:
taking 5.00-10.00 g of the mixed farmland soil sample collected in the step one, air-drying the mixed farmland soil sample at the room temperature of 20-30 ℃ until the water content is less than 2%, grinding the mixed farmland soil sample in an agate mortar, and sieving the mixed farmland soil sample with a 200-mesh sieve for later use;
step three, carrying out soil sample leaching treatment on cultivated land:
(1) taking 5.00g of the soil pretreatment sample I obtained in the second step, adding 20mL of deionized water, oscillating at 150rpm for 2h, centrifuging at 4000rpm for 20min, and collecting supernatant, namely the water-soluble cadmium solution to be detected;
(2) washing the soil sample precipitate obtained by the centrifugation in the step (1) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample II, adding 20mL of CaCl with the concentration of 0.05mol/L into the soil sample II2Oscillating the solution at 150rpm for 5h, centrifuging the solution at 4000rpm for 20min, and collecting supernatant to obtain exchangeable cadmium solution to be detected;
(3) washing the soil sample precipitate obtained by the centrifugation in the step (2) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample III, and adding 20mL of NH with the concentration of 1mol/L into the soil sample III4Oscillating the OAc solution at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant as carbonate cadmium solution to be detected;
(4) washing the soil sample precipitate obtained by the centrifugation in the step (3) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample IV, adding 20mL of hydroxylamine hydrochloride solution with the concentration of 0.5mol/L into the soil sample IV, oscillating at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant to obtain the solution to be detected of the iron-manganese oxidized cadmium;
step four, detecting by a graphite furnace-atomic absorption spectrometer:
(a) making a standard curve: respectively diluting the cadmium standard mother liquor with the concentration of 500 mu g/mL to obtain cadmium standard solutions with gradient concentrations of 0 mu g/L, 0.8 mu g/L, 1.5 mu g/L, 3 mu g/L and 5 mu g/L in sequence, respectively measuring the absorbance values of the cadmium standard solutions with different concentrations by using a graphite furnace-atomic absorption spectrometer, and obtaining a standard curve by using the absorbance values as ordinate and the cadmium concentration of the cadmium standard solution as abscissa;
in the optical parameters of the graphite furnace-atomic absorption spectrometer in the embodiment, the detection wavelength is 228.8nm, the slit width is 0.7nm, and the lamp current is 4.0 mA; the atomization temperature is 1500 ℃, and the atomization time is 5 s; the burning residual temperature is 2450 ℃ and the burning residual time is 3 s; taking high-purity argon as the protective gas of the graphite furnace, wherein the gas flow is 1.8L/min; the drying temperature is 100 ℃, the drying time is 25s, the ashing temperature is 500 ℃, and the ashing time is 20 s; zeeman corrected for background, peak area was measured and the amount of sample was 20. mu.L.
Under the working conditions of the apparatus of this example, a standard curve was drawn, the measurement was repeated 10 times for the blank solution, and 3 times the standard deviation of the measurement results was taken as the detection limit and 10 times as the measurement lower limit. The detection limit of cadmium was 0.05mg/kg, and the measurement lower limit was 0.12 mg/kg.
(b) And (3) determining a sample to be tested: under the same detection condition as the step (a), sequentially injecting the solutions to be detected obtained in the step three into a graphite tube of a graphite furnace-principle absorption spectrometer, and detecting the absorbance value of each solution to be detected after atomization;
(c) and (c) substituting the absorbance values of the solutions to be detected measured in the step (b) into the standard curve in the step (a) for quantitative analysis, and calculating to respectively obtain the contents of water-soluble cadmium, exchangeable cadmium, carbonate cadmium and iron-manganese oxidized cadmium in the soil sample.
Example 2
In the embodiment, the method provided by the embodiment 1 is used for detecting the cadmium content in the farmland soil in different forms.
Firstly, sampling cultivated land soil:
the farmland soil sample of the embodiment is taken from a farmland area containing cadmium in irrigation water, 20 parts of farmland soil are randomly sampled in a sawtooth distribution within a sampling range of 5 mu, and the specific sampling method comprises the following steps: continuously collecting soil samples in a full-layer column shape with the depth of 0-20cm in a plough layer, wherein the weight of each soil sample is 1kg, a plastic inner tube soil sampler is used during sampling, the collected soil samples are put into a plastic bag for storage, the collection place, the collection depth and the collection time are marked, and the soil samples of the cultivated land collected in the same batch are uniformly mixed to be used as soil samples of mixed cultivated land for later use;
step two, soil sample pretreatment of cultivated land:
taking 10.00g of the soil sample of the mixed cultivated land collected in the first step, air-drying the soil sample of the mixed cultivated land at the room temperature of 20-30 ℃ until the water content is less than 2%, grinding the soil sample in an agate mortar, and sieving the ground soil sample with a 200-mesh sieve for later use;
step three, carrying out soil sample leaching treatment on cultivated land:
(1) taking 5.00g of the soil pretreatment sample I obtained in the second step, adding 20mL of deionized water, oscillating at 150rpm for 2h, centrifuging at 4000rpm for 20min, and collecting supernatant, namely the water-soluble cadmium solution to be detected;
(2) step (1) washing with 10mL deionized water by oscillationCentrifuging at 4000rpm for 20min to obtain soil sample precipitate, collecting the soil sample precipitate to obtain soil sample II, adding 20mL of 0.05mol/L CaCl into the soil sample II2Oscillating the solution at 150rpm for 5h, centrifuging the solution at 4000rpm for 20min, and collecting supernatant to obtain exchangeable cadmium solution to be detected;
(3) washing the soil sample precipitate obtained by the centrifugation in the step (2) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample III, and adding 20mL of NH with the concentration of 1mol/L into the soil sample III4Oscillating the OAc solution at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant as carbonate cadmium solution to be detected;
(4) washing the soil sample precipitate obtained by the centrifugation in the step (3) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample IV, adding 20mL of hydroxylamine hydrochloride solution with the concentration of 0.5mol/L into the soil sample IV, oscillating at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant to obtain the solution to be detected of the iron-manganese oxidized cadmium;
step four, detecting by a graphite furnace-atomic absorption spectrometer:
(a) making a standard curve: respectively diluting the cadmium standard mother liquor with the concentration of 500 mu g/mL to obtain cadmium standard solutions with gradient concentrations of 0 mu g/L, 0.8 mu g/L, 1.5 mu g/L, 3 mu g/L and 5 mu g/L in sequence, respectively measuring the absorbance values of the cadmium standard solutions with different concentrations by using a graphite furnace-atomic absorption spectrometer, and obtaining a standard curve by using the absorbance values as ordinate and the cadmium concentration of the cadmium standard solution as abscissa;
in the optical parameters of the graphite furnace-atomic absorption spectrometer in the embodiment, the detection wavelength is 228.8nm, the slit width is 0.7nm, and the lamp current is 4.0 mA; the atomization temperature is 1500 ℃, and the atomization time is 5 s; the burning residual temperature is 2450 ℃ and the burning residual time is 3 s; taking high-purity argon as the protective gas of the graphite furnace, wherein the gas flow is 1.8L/min; the drying temperature is 100 ℃, the drying time is 25s, the ashing temperature is 500 ℃, and the ashing time is 20 s; correcting background by Zeeman, measuring peak area, and sampling amount is 20 mu L;
(b) and (3) determining a sample to be tested: under the same detection condition as the step (a), sequentially injecting the solutions to be detected obtained in the step three into a graphite tube of a graphite furnace-principle absorption spectrometer, and detecting the absorbance value of each solution to be detected after atomization;
(c) and (c) substituting the absorbance values of the solutions to be detected measured in the step (b) into the standard curve in the step (a) for quantitative analysis, and calculating to respectively obtain the content of water-soluble cadmium of 0.72mg/kg, the content of exchangeable cadmium of 0.31mg/kg, the content of carbonate cadmium of 0.135mg/kg and the content of iron-manganese oxidized cadmium of 0.173mg/kg in the soil sample.
The precision of the method is continuously measured for 10 times by the method of the embodiment on the soil sample of the same cultivated land, the relative standard deviation (RSD, n is 10) of cadmium is 2.3 percent, and the precision is better.
Example 3
In the embodiment, the method provided by the embodiment 1 is used for detecting the cadmium content in the farmland soil in different forms.
Firstly, sampling cultivated land soil:
the method for sampling the farmland soil sample is characterized in that the farmland soil sample is taken from a cadmium-containing farmland area near a mining area, 20 parts of farmland soil sample are randomly sampled in a snake-shaped distribution within a sampling range of 3 mu, and the specific sampling method comprises the following steps: continuously collecting soil samples in a full-layer column shape with the depth of 0-20cm in a plough layer, wherein the weight of each soil sample is 1kg, a plastic inner tube soil sampler is used during sampling, the collected soil samples are put into a plastic bag for storage, the collection place, the collection depth and the collection time are marked, and the soil samples of the cultivated land collected in the same batch are uniformly mixed to be used as soil samples of mixed cultivated land for later use;
step two, soil sample pretreatment of cultivated land:
taking 10.00g of the soil sample of the mixed cultivated land collected in the first step, air-drying the soil sample of the mixed cultivated land at the room temperature of 20-30 ℃ until the water content is less than 2%, grinding the soil sample in an agate mortar, and sieving the ground soil sample with a 200-mesh sieve for later use;
step three, carrying out soil sample leaching treatment on cultivated land:
(1) taking 5.00g of the soil pretreatment sample I obtained in the second step, adding 20mL of deionized water, oscillating at 150rpm for 2h, centrifuging at 4000rpm for 20min, and collecting supernatant, namely the water-soluble cadmium solution to be detected;
(2) washing the soil sample precipitate obtained by the centrifugation in the step (1) by 10mL of deionized water in a vibration mode, centrifuging for 20min at 4000rpm, and collecting the soil sample precipitateThe precipitate is a soil sample II, 20mL of CaCl with the concentration of 0.05mol/L is added into the soil sample II2Oscillating the solution at 150rpm for 5h, centrifuging the solution at 4000rpm for 20min, and collecting supernatant to obtain exchangeable cadmium solution to be detected;
(3) washing the soil sample precipitate obtained by the centrifugation in the step (2) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample III, and adding 20mL of NH with the concentration of 1mol/L into the soil sample III4Oscillating the OAc solution at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant as carbonate cadmium solution to be detected;
(4) washing the soil sample precipitate obtained by the centrifugation in the step (3) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample IV, adding 20mL of hydroxylamine hydrochloride solution with the concentration of 0.5mol/L into the soil sample IV, oscillating at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant to obtain the solution to be detected of the iron-manganese oxidized cadmium;
step four, detecting by a graphite furnace-atomic absorption spectrometer:
(a) making a standard curve: respectively diluting the cadmium standard mother liquor with the concentration of 500 mu g/mL to obtain cadmium standard solutions with gradient concentrations of 0 mu g/L, 0.8 mu g/L, 1.5 mu g/L, 3 mu g/L and 5 mu g/L in sequence, respectively measuring the absorbance values of the cadmium standard solutions with different concentrations by using a graphite furnace-atomic absorption spectrometer, and obtaining a standard curve by using the absorbance values as ordinate and the cadmium concentration of the cadmium standard solution as abscissa;
in the optical parameters of the graphite furnace-atomic absorption spectrometer in the embodiment, the detection wavelength is 228.8nm, the slit width is 0.7nm, and the lamp current is 4.0 mA; the atomization temperature is 1500 ℃, and the atomization time is 5 s; the burning residual temperature is 2450 ℃ and the burning residual time is 3 s; taking high-purity argon as the protective gas of the graphite furnace, wherein the gas flow is 1.8L/min; the drying temperature is 100 ℃, the drying time is 25s, the ashing temperature is 500 ℃, and the ashing time is 20 s; correcting background by Zeeman, measuring peak area, and sampling amount is 20 mu L;
(b) and (3) determining a sample to be tested: under the same detection condition as the step (a), sequentially injecting the solutions to be detected obtained in the step three into a graphite tube of a graphite furnace-principle absorption spectrometer, and detecting the absorbance value of each solution to be detected after atomization;
(c) and (c) substituting the absorbance values of the solutions to be detected measured in the step (b) into the standard curve in the step (a) for quantitative analysis, and calculating to respectively obtain the content of water-soluble cadmium of 0.246mg/kg, the content of exchangeable cadmium of 0.558mg/kg, the content of carbonate cadmium of 0.321mg/kg and the content of iron-manganese oxidized cadmium of 0.483mg/kg in the soil sample.
The soil samples of the embodiment are respectively added with water-soluble cadmium with equal concentration, the method is used for measuring, the recovery rate of the method reaches 103.5 percent, and the method is proved to be more reasonable in accuracy.
Example 4
In the embodiment, the method provided by the embodiment 1 is used for detecting the cadmium content in the farmland soil in different forms.
Firstly, sampling cultivated land soil:
the method for sampling the farmland soil samples in the embodiment is that the farmland soil samples are taken from farmland areas containing cadmium near industrial areas, 20 parts of farmland soil samples are randomly sampled in a snake-shaped distribution within a sampling range of 3 mu, and the specific sampling method comprises the following steps: continuously collecting soil samples in a full-layer column shape with the depth of 0-20cm in a plough layer, wherein the weight of each soil sample is 1kg, a plastic inner tube soil sampler is used during sampling, the collected soil samples are put into a plastic bag for storage, the collection place, the collection depth and the collection time are marked, and the soil samples of the cultivated land collected in the same batch are uniformly mixed to be used as soil samples of mixed cultivated land for later use;
step two, soil sample pretreatment of cultivated land:
taking 10.00g of the soil sample of the mixed cultivated land collected in the first step, air-drying the soil sample of the mixed cultivated land at the room temperature of 20-30 ℃ until the water content is less than 2%, grinding the soil sample in an agate mortar, and sieving the ground soil sample with a 200-mesh sieve for later use;
step three, carrying out soil sample leaching treatment on cultivated land:
(1) taking 5.00g of the soil pretreatment sample I obtained in the second step, adding 20mL of deionized water, oscillating at 150rpm for 2h, centrifuging at 4000rpm for 20min, and collecting supernatant, namely the water-soluble cadmium solution to be detected;
(2) washing the soil sample precipitate obtained by the centrifugation in the step (1) with 10mL of deionized water in an oscillating way, centrifuging for 20min at 4000rpm, collecting the soil sample precipitate to obtain a soil sample II, and adding the soil sample II into the soil sampleAdding 20mL of CaCl with the concentration of 0.05mol/L into the II2Oscillating the solution at 150rpm for 5h, centrifuging the solution at 4000rpm for 20min, and collecting supernatant to obtain exchangeable cadmium solution to be detected;
(3) washing the soil sample precipitate obtained by the centrifugation in the step (2) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample III, and adding 20mL of NH with the concentration of 1mol/L into the soil sample III4Oscillating the OAc solution at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant as carbonate cadmium solution to be detected;
(4) washing the soil sample precipitate obtained by the centrifugation in the step (3) with 10mL of deionized water in an oscillating way, centrifuging at 4000rpm for 20min, collecting the soil sample precipitate to obtain a soil sample IV, adding 20mL of hydroxylamine hydrochloride solution with the concentration of 0.5mol/L into the soil sample IV, oscillating at 150rpm for 5h, centrifuging at 4000rpm for 20min, and collecting supernatant to obtain the solution to be detected of the iron-manganese oxidized cadmium;
step four, detecting by a graphite furnace-atomic absorption spectrometer:
(a) making a standard curve: respectively diluting the cadmium standard mother liquor with the concentration of 500 mu g/mL to obtain cadmium standard solutions with gradient concentrations of 0 mu g/L, 0.8 mu g/L, 1.5 mu g/L, 3 mu g/L and 5 mu g/L in sequence, respectively measuring the absorbance values of the cadmium standard solutions with different concentrations by using a graphite furnace-atomic absorption spectrometer, and obtaining a standard curve by using the absorbance values as ordinate and the cadmium concentration of the cadmium standard solution as abscissa;
in the optical parameters of the graphite furnace-atomic absorption spectrometer in the embodiment, the detection wavelength is 228.8nm, the slit width is 0.7nm, and the lamp current is 4.0 mA; the atomization temperature is 1500 ℃, and the atomization time is 5 s; the burning residual temperature is 2450 ℃ and the burning residual time is 3 s; taking high-purity argon as the protective gas of the graphite furnace, wherein the gas flow is 1.8L/min; the drying temperature is 100 ℃, the drying time is 25s, the ashing temperature is 500 ℃, and the ashing time is 20 s; correcting background by Zeeman, measuring peak area, and sampling amount is 20 mu L;
(b) and (3) determining a sample to be tested: under the same detection condition as the step (a), sequentially injecting the solutions to be detected obtained in the step three into a graphite tube of a graphite furnace-principle absorption spectrometer, and detecting the absorbance value of each solution to be detected after atomization;
(c) and (c) substituting the absorbance values of the solutions to be detected measured in the step (b) into the standard curve in the step (a) for quantitative analysis, and calculating to respectively obtain the content of water-soluble cadmium of 0.12mg/kg, the content of exchangeable cadmium of 0.629mg/kg, the content of carbonate cadmium of 0.292mg/kg and the content of ferro-manganese cadmium in an oxidation state of 0.521mg/kg in the soil sample.
Claims (10)
1. A detection method of heavy metal cadmium in farmland soil is characterized by comprising the following steps:
firstly, sampling cultivated land soil:
randomly collecting soil samples in a to-be-detected farmland area, and uniformly mixing the farmland soil samples collected in the same batch to serve as mixed farmland soil samples for later use;
step two, soil sample pretreatment of cultivated land:
air-drying, grinding and sieving the mixed cultivated land soil sample collected in the step one at room temperature for later use;
step three, carrying out soil sample leaching treatment on cultivated land:
(1) adding deionized water into the soil pretreatment sample I obtained in the step two according to a certain mass-volume ratio, oscillating, centrifuging, and collecting supernatant, namely the water-soluble cadmium solution to be detected;
(2) washing the soil sample precipitate obtained by centrifuging in the step (1) with deionized water to obtain a soil sample II, and adding CaCl into the soil sample II according to a certain mass-volume ratio2Oscillating and centrifuging the solution, and collecting supernatant to obtain exchangeable cadmium solution to be detected;
(3) washing the soil sample precipitate obtained by centrifuging in the step (2) with deionized water to obtain a soil sample III, and adding NH into the soil sample III according to a certain mass-volume ratio4Oscillating and centrifuging the OAc solution, and collecting supernatant to obtain carbonate cadmium solution to be detected;
(4) washing the soil sample precipitate obtained by centrifuging in the step (3) with deionized water to obtain a soil sample IV, adding a hydroxylamine hydrochloride solution into the soil sample IV according to a certain mass-volume ratio, oscillating, centrifuging, and collecting supernatant to obtain the solution to be detected, namely the iron-manganese oxidized cadmium;
step four, detecting by a graphite furnace-atomic absorption spectrometer:
(a) making a standard curve: respectively diluting the cadmium standard mother liquor to obtain cadmium standard solutions with gradient concentrations, respectively measuring the absorbance values of the cadmium standard solutions with different concentrations by using a graphite furnace-atomic absorption spectrometer, and taking the absorbance values as vertical coordinates and the cadmium concentration of the cadmium standard solutions as horizontal coordinates to obtain a standard curve;
(b) and (3) determining a sample to be tested: under the same detection condition as the step (a), sequentially injecting the solutions to be detected obtained in the step three into a graphite tube of a graphite furnace-principle absorption spectrometer, and detecting the absorbance value of each solution to be detected after atomization;
(c) and (c) substituting the absorbance values of the solutions to be detected measured in the step (b) into the standard curve in the step (a) for quantitative analysis, and calculating to respectively obtain the contents of water-soluble cadmium, exchangeable cadmium, carbonate cadmium and iron-manganese oxidized cadmium in the soil sample.
2. The detection method of the heavy metal cadmium in the cultivated land soil according to claim 1, characterized in that the randomly collected soil in the step one is uniformly and randomly sampled 10-20 parts in a zigzag or snake-shaped distribution in the cultivated area to be detected, and the distribution range of the samples is not less than 3 mu; and continuously collecting soil samples in a full-layer column shape with the depth of 0-20cm in a plough layer, wherein the weight of each soil sample is 1kg, a plastic inner pipe soil sampler is used during sampling, the collected soil samples are placed into a plastic bag for storage, and the collection place, the depth and the collection time are marked.
3. The detection method of the heavy metal cadmium in the farmland soil according to claim 1 or 2, characterized in that the soil sample of the mixed farmland in the second step is 5.00-10.00 g in weight, and the soil sample of the mixed farmland is air-dried at room temperature to a water content of less than 2% under the condition of 20-30 ℃ of air-drying; the grinding and sieving are grinding in an agate mortar and sieving by a 200-mesh sieve.
4. The method for detecting the heavy metal cadmium in the cultivated land soil according to claim 3, wherein in the third step (1), the mass-to-volume ratio of the soil pretreatment sample I to the deionized water is 1g:4mL, and the oscillation treatment is 150-200 rpm for 1-3 h; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
5. The method for detecting the heavy metal cadmium in the cultivated land soil according to claim 4, wherein the deionized water washing treatment of the third step (2) is to shake and wash the soil sample precipitate obtained by centrifugation of the step (1) with 10mL of deionized water, centrifuge at 4000rpm for 20min, and collect the soil sample precipitate to obtain a soil sample II; the soil sample II is mixed with CaCl2The mass volume ratio of the solution is 1g to 4mL, and the CaCl is2The concentration of the solution is 0.05 mol/L; the oscillation treatment is carried out for 1-3 h at 150-200 rpm; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
6. The method for detecting the heavy metal cadmium in the cultivated land soil according to claim 5, wherein the deionized water washing treatment of the third step (3) is to shake and wash the soil sample precipitate obtained by centrifugation of the step (2) with 10mL of deionized water, centrifuge at 4000rpm for 20min, and collect the soil sample precipitate to obtain a soil sample III; the soil sample III and NH4The mass-to-volume ratio of the OAc solution is 1g to 4mL, and the NH is4The concentration of the OAc solution is 1 mol/L; the oscillation treatment is carried out for 1-3 h at 150-200 rpm; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
7. The method for detecting the heavy metal cadmium in the cultivated land soil according to claim 6, wherein the deionized water washing treatment of the third step (4) is to shake and wash the soil sample precipitate obtained by centrifugation of the step (3) with 10mL of deionized water, centrifuge at 4000rpm for 20min, and collect the soil sample precipitate to obtain a soil sample IV; the mass volume ratio of the soil sample IV to the hydroxylamine hydrochloride solution is 1g:4mL, and the concentration of the hydroxylamine hydrochloride is 0.5 mol/L; the oscillation treatment is carried out for 1-3 h at 150-200 rpm; the centrifugation is carried out at 3000-4000 rpm for 15-20 min.
8. The method for detecting the heavy metal cadmium in the cultivated land soil according to claim 7, wherein the concentration of the cadmium standard mother liquor in the fourth step (a) is 500 μ g/mL, and the concentration of the cadmium standard solution with the gradient concentration is 0 μ g/L, 0.8 μ g/L, 1.5 μ g/L, 3 μ g/L and 5 μ g/L in sequence.
9. The method for detecting the heavy metal cadmium in the cultivated land soil according to claim 8, wherein in the optical parameters of the graphite furnace-atomic absorption spectrometer in the fourth step (a), the detection wavelength is 228.8nm, the slit width is 0.7nm, and the lamp current is 4.0 mA.
10. The method for detecting the heavy metal cadmium in the cultivated land soil according to claim 9, wherein in the fourth step (a), the atomization temperature of the graphite furnace-atomic absorption spectrometer is 1500 ℃, and the atomization time is 5 s; the burning residual temperature is 2450 ℃ and the burning residual time is 3 s; high-purity argon is used as the protective gas of the graphite furnace, and the gas flow is 1.8L/min.
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