CN110813233A - Method for adsorbing heavy metal ions in soil by coconut shell charcoal - Google Patents

Abstract

The invention discloses a method for adsorbing heavy metal ions in soil by coconut shell charcoal. The coconut shell charcoal is prepared by carbonizing the coconut shell; and then, mixing the coconut shell biochar in the soil uniformly to adsorb heavy metal ions. The addition of 5% by mass coconut shell charcoal in the soil can improve the adsorption rate of the soil to heavy metals by 11.6% -20.0%, and the adsorption of metal ions in the soil is irreversible, so that the soil has obvious hysteresis effect. The coconut shell charcoal applied to the soil can effectively restore heavy metal pollution in the soil, thereby reducing the harm of heavy metal ions to agricultural soil.

Description

A method for adsorbing heavy metal ions in soil by utilizing coconut shell biochar

technical field

The invention belongs to the field of analysis and detection, and in particular relates to a method for adsorbing heavy metal ions in soil by utilizing coconut shell biochar.

Background technique

Biochar is a highly aromatic and refractory substance produced by carbonization of plant biomass through high-temperature pyrolysis under completely anoxic conditions. It exists widely in the natural environment and has a multi-level pore structure and huge specific surface area , large pore volume, high thermal stability and CEC, the application of biochar in soil can change the physical and chemical properties of soil, greatly improve soil water retention, fertilizer retention and soil aggregate stability; Carbon emission reduction and utilization of agricultural waste resources. In recent years, due to the great advantages and potential of biochar in mitigating climate change, improving soil quality and remediating environmental pollution, biochar can effectively promote the solidification of free heavy metal ions into the soil and reduce the entry of heavy metal ions into crops, thereby reducing The pollution of heavy metal ions to crops and human body. The use of biochar to alleviate and control organic pollution and heavy metal pollution in soil has become a current research hotspot. There have been reports on biochar adsorption of lead, cadmium, arsenic, etc. in soil. However, there is no relevant report on the effect of biochar fired from tropical and subtropical agricultural waste resources as precursor materials on heavy metal adsorption in agricultural soils in Guangdong.

SUMMARY OF THE INVENTION

The object of the present invention is to remediate and treat the problem of heavy metal pollution in Guangdong agricultural soil by using the biochar fired with tropical and subtropical agricultural waste resources coconut shell precursor materials in the prior art, and provide a kind of coconut shell biological Charcoal and method for adsorbing heavy metal ions in soil by using coconut shell biochar.

The present invention provides a kind of coconut shell biochar, which is characterized in that, it is prepared by the following method:

The coconut shell is air-dried and pulverized, the particle size is controlled below 3mm, filled into a porcelain crucible, sealed with a lid, and then fired in a muffle furnace, and heated to 200°C at a heating rate of 10°C/min, and pre-carbonized at a constant temperature of 2h; Then, the temperature was heated to 600°C for 3 hours at a heating rate of 10°C/min, and then cooled and ground through a 100-mesh sieve to obtain coconut shell biochar.

The present invention also provides a method for utilizing coconut shell biochar to absorb heavy metal ions in soil, which is characterized in that the method comprises the following steps:

The coconut shell biochar is mixed in soil to adsorb heavy metal ions.

Preferably, according to the mass ratio of 1-20 parts of coconut shell biochar: 80-99 parts of soil, the coconut shell biochar is mixed into the soil.

More preferably, according to the mass ratio of 5 parts of coconut shell biochar: 95 parts of soil, the coconut shell biochar is mixed into the soil.

Preferably, the heavy metal ions are Cd ²⁺ , Co ²⁺ and/or Cu ²⁺ .

The coconut shell biochar and Guangdong soil of the present invention have better removal rates in terms of removing Cd ²⁺ , Co ²⁺ and/or Cu ²⁺ in the solution, and the highest removal rate exceeds 75%, which is superior to the previously reported utilization of biological The removal rate of heavy metal ions by charcoal shows that coconut shell biochar has a good application prospect in the removal of heavy metal ions in wastewater in combination with Guangdong soil in addition to the effective remediation of heavy metal pollution in soil.

The invention uses coconut shell, a waste resource of tropical fruit, as a precursor material to burn into biochar, has a large specific surface area and strong adsorption performance after testing, and has a good application prospect in soil remediation. By applying coconut shell charcoal in subtropical agricultural soil—Guangdong typical paddy soil, it was found that its passivation and remediation ability to the available heavy metals in the soil, temperature, pH value and biochar addition amount all affect the adsorption rate of coconut shell biochar.

Through method optimization, the present invention establishes an optimal method for removing heavy metal ions in Guangdong soil with coconut shell biochar. The invention provides a reliable and efficient method for adsorbing and removing heavy metal ions in soil with coconut shell biochar, thereby reducing the pollution of heavy metal ions to agricultural soil and promoting the development of healthy agriculture and green agriculture.

Description of drawings

Fig. 1 is the surface morphology and energy spectrum of coconut shell biochar: A) before adsorption of heavy metal ions; B) after adsorption of heavy metal ions;

Fig. 2 is the adsorption equilibrium diagram of several heavy metal ions under the condition of adding and not adding coconut shell biochar: A) without adding biochar; B) adding biochar;

Fig. 3 is the adsorption and desorption isotherm diagram of several heavy metal ions under the condition of adding coconut shell biochar: A) adsorption isotherm diagram; B) desorption isotherm diagram;

Figure 4 is a graph of the adsorption rate of heavy metal ions under the conditions of different temperatures, pH and coconut shell biochar addition: A) at different temperatures; B) with different coconut shell biochar additions.

Detailed ways

The following examples are further illustrations of the present invention, rather than limitations of the present invention.

Example 1: The effect of adding coconut shell biochar on soil adsorption of heavy metal ions in Guangdong

1. Preparation of coconut shell biochar, Guangdong soil and heavy metal ion solution

The coconut shell is produced in Hainan. The coconut shell is air-dried and then pulverized. The particle size is controlled to be less than 3 mm. It is filled into a porcelain crucible, sealed with a lid, and burned in a muffle furnace. The temperature rises to 200 °C at a heating rate of 10 °C/min. , 2h constant temperature to achieve pre-carbonization. Then, the temperature was raised to 600 °C for 3 hours at the same heating rate, and after cooling, it was ground through a 100-mesh sieve (the particle size was less than 0.15 mm) to test the specific surface area, surface morphology and element composition of coconut shell biochar, which was sealed and stored at room temperature for later use. .

Stock solution S-1: Weigh 0.01g of cadmium chloride hemi (pentahydrate), 0.01g of cobalt chloride hexahydrate and 0.1g of copper chloride dihydrate into a 50mL volumetric flask, dissolve and dilute with 0.01mol/LCaCl2 solution To the mark, make up the stock solution S-1.

Stock solution S-2: Weigh 0.2g cadmium chloride hemi (pentahydrate), 0.2g cobalt chloride hexahydrate and 2g cupric chloride dihydrate in a 100mL volumetric flask, dissolve with 0.01mol/LCaCl ₂ solution and dilute to volume To the mark, make up the stock solution S-2. Pipette 2.5mL, 5.0mL, 10.0mL, 15.0mL, and 20.0mL of stock solution S-2 into a 50mL volumetric flask, dilute to the mark with 0.01mol/L CaCl ₂ solution, and prepare stock solution S-2-1 in turn. , S-2-2, S-2-3, S-2-4 and S-2-5 for adsorption and desorption isotherm tests.

Under the above carbonization conditions, as shown in Fig. 1A, the surface morphology of coconut shell biochar is mainly dominated by fine granular and sheet-like structures, showing many irregular pores formed by stacking of amorphous structures of different sizes. The constituent elements are biomass matrix elements. The surface morphology of biochar after adsorbing heavy metals is shown in Figure 1B. The main elements are the elements that make up the biomass matrix, the Ca and Cl elements in the test solution, and the Cu element added during the test; the addition of Co and Cd elements The concentration was relatively low, below the detection limit of the spectrometer and not detected.

The nitrogen adsorption isotherm of coconut shell biochar is a typical mesoporous material adsorption isotherm. The adsorption linear equation using BET test is y=26.61x-0.2796, and the specific surface area is 132.264m ² /g.

2. The effect of adding coconut shell biochar on the adsorption of heavy metal ions in Guangdong soil

The Guangdong soil used was collected from paddy soil in the experimental field of South China Agricultural University.

Weigh 1.00g of soil into a 50mL plastic centrifuge tube, add 22.5mL of 0.01mol/LCaCl ₂ solution (pre-experiment determines the water-soil ratio to be 1g soil: 25mL water), and continuously shake at 165r/min and 25℃±1℃ Carry out water and soil balance for about 16 hours, add 2.5mL of heavy metal stock solution S-1, as the test group without adding biochar; weigh 0.95g of soil into a 50mL plastic centrifuge tube for water and soil balance, add 2.5mL of heavy metal stock solution S-1 and 0.05g coconut shell charcoal was used as the biochar test group. At the same time, no soil blank control and soil blank control were made. The centrifuge tube was continuously shaken at 165r/min and 25℃±1℃, and the soil suspension was taken out at 2h, 16h, 25h, 41h and 48h, and centrifuged at 8000r/min for 5min. , separate the supernatant, sample and measure the concentration of the supernatant, and analyze the actual concentration of the test substance in the blank control group and the soil-free control group at the same time.

Under the condition of not adding coconut shell biochar, the adsorption characteristics of several heavy metal ions are shown in Figure 2A; under the condition of adding 5% biochar to the soil, the adsorption characteristics of several heavy metal ions are shown in Figure 2B. Shell biochar and Guangdong soil have better removal rates of Cd ²⁺ , Co ²⁺ and/or Cu ²⁺ in the solution, and the highest removal rate exceeds 75%; Biochar can increase the adsorption rate of Cd ²⁺ by 17.9%, the adsorption rate of Co ²⁺ by 11.6%, and the adsorption rate of Cu ²⁺ by 20%. The main reason is that adding biochar to the soil can change the soil The chemical properties of biomass char and the improvement of soil CEC, the huge specific surface area of biomass char and its improved soil properties can enhance the adsorption of compounds, element conversion and ion exchange.

Under the condition of 5% biochar addition, the adsorption strength of several heavy metal ions in soil is 1/n<1, which belongs to L-type adsorption isotherm. The nonlinearity of adsorption isotherm is stronger than that of relatively flat desorption isotherm. There is a significant difference between them, which indicates that the desorption process is not a reversible process of adsorption, and the desorption process has obvious hysteresis effect. According to the hysteresis coefficient HI formula, the desorption of Cd ²⁺ , Co ²⁺ and Cu ²⁺ in soil was calculated The lag coefficients are: 33.838, 1.347 and 0.972, respectively. There are significant differences in hysteresis. The hysteresis will affect the mobility and bioavailability of metal ions in soil. The weaker the hysteresis, the easier the desorption and release of ions in the solid medium. The ease of desorption of the three metal ions in soil is: Cu ²⁺ >Co ²⁺ >Cd ²⁺ . This desorption hysteresis can lead to the short-term accumulation of metal ions in the soil and reduce the diffusion of heavy metal pollution, but there are also potential ecological and environmental risks. The adsorption and desorption isotherms of soil for several different concentrations of heavy metal ions are shown in Figure 3.

Example 2: Effects of different temperatures, pH and biochar addition on soil adsorption of heavy metal ions

Different metal ions have different pH precipitation values. The precipitation pH values of Cd ²⁺ , Co ²⁺ and Cu ²⁺ at 20 °C are 11, 9 and 5.5, respectively, namely Cd ²⁺ >Co ²⁺ >Cu ²⁺ , For the test solutions with different pH values (3-9), the adsorption rates of Co ²⁺ and Cu ²⁺ increased significantly near the pH precipitation value, and the adsorption rate of Co ²⁺ was higher than that of the adsorption pH=3. 11.0%, the adsorption rate of Cu ²⁺ increased by 13.5% compared with the adsorption rate of pH=3, the pH precipitation value of Cd ²⁺ was higher than the highest pH value set in the experiment, and its adsorption rate also increased gradually with the increase of pH value. High, because some metal ions form hydroxide precipitation, the metal ion concentration in the solution becomes lower, and the adsorption rate is different.

When the adsorption equilibrium is reached under different temperature conditions, the adsorption rate of several heavy metal ions in soil is shown in Figure 4A. Within the test temperature range, with the increase of temperature, the adsorption rate of several metal ions increases. trend with good linearity. The results show that the adsorption process of several metal ions in the biochar soil is an endothermic reaction, and increasing the temperature can improve the adsorption rate of the metal ions on the biochar. The influence of temperature factors on several heavy metals is: Cu﹥Cd﹥Co.

Under the conditions of 0%, 1%, 5%, 10%, 15%, and 20% biochar addition, the pH values of the test solutions were 4.74, 4.85, 5.01, 5.23, 5.33 and 5.52, respectively. Adding biochar can increase the pH value of soil solution, especially in acidic soil, thereby improving the status of heavy metal pollution in acidic soil. When the adsorption equilibrium is reached, the adsorption rates of several heavy metal ions in soil are shown in Fig. 4B. With the increase of biochar addition, the adsorption rates of several heavy metal ions all increase with good linearity. The effect of carbon addition on the adsorption rate of several heavy metals from large to small is: Cd﹥Cu﹥Co.

The results showed that the adsorption equilibrium time of several heavy metals in the soil was 25h, the desorption equilibrium time was 30h, and the addition of coconut shell biochar with a mass concentration of 5% could improve the soil adsorption rate of heavy metals by 11.6%-20.0%, Cd ²⁺ The adsorption of metal ions of , Co ²⁺ and Cu ^{2 +} in the soil with coconut shell biochar is irreversible and has obvious hysteresis effect. The desorption hysteresis coefficients of Cd ²⁺ , Co ²⁺ and Cu ²⁺ are: 33.838, 1.347 and 0.972. Under the test conditions, the pH value of the soil solution increased with the increase of carbon content, and the effect of temperature and carbon content on the adsorption rate showed a good linear relationship, R>0.9508. It shows that the application of coconut shell biochar in the soil can effectively repair the heavy metal pollution in the soil.

Claims (5)

1. a coconut shell biochar, is characterized in that, is prepared by the following method: The coconut shell is air-dried and pulverized, the particle size is controlled below 3mm, filled into a porcelain crucible, sealed with a lid, and then fired in a muffle furnace, and heated to 200°C at a heating rate of 10°C/min, and pre-carbonized at a constant temperature of 2h; Then, the temperature was heated to 600°C for 3 hours at a heating rate of 10°C/min, and then cooled and ground through a 100-mesh sieve to obtain coconut shell biochar. 2. a method for utilizing coconut shell biochar to absorb heavy metal ions in soil, is characterized in that, comprises the following steps: The coconut shell biochar of claim 1 is mixed in soil to adsorb heavy metal ions. 3. method according to claim 2 is characterized in that, is by mass ratio 1-20 part coconut shell biochar: 80-99 part soil ratio, coconut shell biochar is mixed in soil. 4. method according to claim 2 is characterized in that, is by mass ratio 5 parts of coconut shell biochar: 95 parts of soil ratio, coconut shell biochar is mixed in soil. 5. The method according to claim 2, wherein the heavy metal ions are Cd ²⁺ , Co ²⁺ and/or Cu ²⁺ .

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