GREENHOUSE GAS EMISSION REDUCTION METHOD FOR HEAVY METAL CONTAMINATED SOIL

Abstract

The present disclosure provides a greenhouse gas emission reduction method for a heavy metal contaminated soil, falling within the technical field of emission reduction of greenhouse gas nitrous oxide. Specifically, hydroxyapatite (HAP) is added to a soil to effectively reduce the emission of nitrous oxide in the soil, and at the same time, the treatment of heavy metal contamination is realized, which is very suitable for the promotion and use of nitrous oxide emission reduction in the contaminated soil.

Claims

1. A greenhouse gas emission reduction method for a soil, hydroxyapatite (HAP) being used to reduce the emission of a nitrogen-containing gas in a soil, the nitrogen-containing gas being nitrous oxide, and an amount of HAP being 1-5% of a mass of a dry soil.

2. The greenhouse gas emission reduction method for a soil according to claim 1, wherein the soil is a heavy metal contaminated soil.

3. The greenhouse gas emission reduction method for a soil according to claim 1, wherein HAP is prepared by a sol-gel method using calcium nitrate and phosphoric acid as raw materials.

4. The greenhouse gas emission reduction method for a soil according to claim 3, wherein a preparation method for HAP comprises the steps of: mixing a calcium nitrate solution with a phosphoric acid solution, adding aqueous ammonia at 40-50? C. to adjust a pH to 9-11, and continuing to react 30-50 min, followed by ageing to obtain a colloid; washing the colloid with water, followed by performing suction filtering to obtain a filter cake; and drying the filter cake, calcining the dried filter cake, and continuing to grind and sieve the calcined filter cake to prepare HAP.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a graph showing dynamic changes of rates of nitrous oxide in soils under different emission reduction treatments;

[0015] FIG. 2 is a graph showing the effect of different emission reduction treatments on average emission rates of nitrous oxide in the soils;

[0016] FIG. 3 is a graph showing dynamic changes of cumulative emissions of nitrous oxide in soils under different emission reduction treatments;

[0017] FIG. 4 is a graph of the effect of different emission reduction treatments on the cumulative emissions of nitrous oxide in the soils;

[0018] FIG. 5 is a graph showing functional gene copy numbers of nitrous oxide-producing microorganisms in the soils under different emission reduction treatments;

[0019] FIG. 6 is a graph showing the effect of HAP on the availability of cadmium in a blank test soil; and

[0020] FIG. 7 is a graph showing the effect of HAP on the availability of a cadmium-contaminated soil.

[0021] In the figures, a control refers to a blank test soil, and HAP refers to a blank test soil added with HAP; and the difference between a and b is significant, and the difference between A and B is significant.

DETAILED DESCRIPTION

[0022] Hereinafter, the preferred mode of the present disclosure will be described in further detail with reference to the attached drawings.

[0023] HAP of the present disclosure is self-made or commercially available, and is not limited to the protection scope of the present disclosure.

Example 1

[0024] HAP was mainly prepared by a sol-gel method using calcium nitrate and phosphoric acid as raw materials. The main operation steps were as follows. [0025] 1. A 0.025 mol/L Ca(NO.sub.3).sub.2 solution and a 0.3 mol/L H.sub.3PO.sub.4 solution were prepared. The Ca(NO.sub.3).sub.2 solution was poured into a three-neck flask, and then the H.sub.3PO.sub.4 solution was added under stirring (a volume ratio of the Ca(NO.sub.3).sub.2 solution to the H.sub.3PO.sub.4 solution being 2:1), and a temperature of a system was maintained at 40-50? C. [0026] 2. A pH of the mixed solution was adjusted to 10.00 by adding aqueous ammonia. After the completion of the dripping, the reaction was continued for 40 min and then aging was performed for 24 h. [0027] 3. The colloid obtained after the completion of the reaction was washed with distilled water for 3 times, followed by performing suction filtering to obtain a filter cake, and the filter cake was dried in a drying oven at 80? C. [0028] 4. The dried filter cake was ground, then calcined in a muffle furnace for 12 h (heating to 600? C. at room temperature within 3 h, and calcining at 600? C. for 9 h), and ground again after the completion of calcination to obtain HAP powder; and the HAP powder was stored after being sieved with a 180-mesh sieve.

[0029] The HAP powder was added to a soil for use in an input amount of 3 wt %.

Example 2

[0030] 1. A 0.025 mol/L Ca(NO.sub.3).sub.2 solution and a 0.3 mol/L H.sub.3PO.sub.4 solution were prepared. The Ca(NO.sub.3).sub.2 solution was poured into a three-neck flask, and then the H.sub.3PO.sub.4 solution was added under stirring (a volume ratio of the Ca(NO.sub.3).sub.2 solution to the H.sub.3PO.sub.4 solution being 2:1), and a temperature of a system was maintained at 40-50? C. [0031] 2. A pH of the mixed solution was adjusted to 9.00 by adding aqueous ammonia. After the completion of the dripping, the reaction was continued for 40 min and then aging was performed for 36 h. [0032] 3. The colloid obtained after the completion of the reaction was washed with distilled water for 4 times, followed by performing suction filtering to obtain a filter cake, and the filter cake was dried in a drying oven at 80? C. [0033] 4. The dried filter cake was ground, then calcined in a muffle furnace for 12 h (heating to 600? C. at room temperature within 3 h, and calcining at 600? C. for 9 h), and ground again after the completion of calcination to obtain HAP powder; and the HAP powder was stored after being sieved with a 180-mesh sieve.

[0034] The HAP powder was added to a soil for use in an input amount of 1 wt %.

Example 3

[0035] 1. A 0.025 mol/L Ca(NO.sub.3).sub.2 solution and a 0.3 mol/L H.sub.3PO.sub.4 solution were prepared. The Ca(NO.sub.3).sub.2 solution was poured into a three-neck flask, and then the H.sub.3PO.sub.4 solution was added under stirring (a volume ratio of the Ca(NO.sub.3).sub.2 solution to the H.sub.3PO.sub.4 solution being 2:1), and a temperature of a system was maintained at 40-50? C. [0036] 2. A pH of the mixed solution was adjusted to 11.00 by adding aqueous ammonia. After the completion of the dripping, the reaction was continued for 40 min and then aging was performed for 24 h. [0037] 3. The colloid obtained after the completion of the reaction was washed with distilled water for 5 times, followed by performing suction filtering to obtain a filter cake, and the filter cake was dried in a drying oven at 80? C. [0038] 4. The dried filter cake was ground, then calcined in a muffle furnace for 12 h (heating to 600? C. at room temperature within 3 h, and calcining at 600? C. for 8 h), and ground again after the completion of calcination to obtain HAP powder; and the HAP powder was stored after being sieved with a 180-mesh sieve.

[0039] The HAP powder was added to a soil for use in an input amount of 5 wt %.

[0040] HAP prepared in the above Example 1 was tested on soils, and test operation steps were specifically as follows. [0041] 1. Test soils were air-dried to obtain dry soils, and a maximum water-holding capacity of the dry soil was determined. [0042] 2. HAP and the dry soil were thoroughly mixed in a mass ratio of 3:100, 30 g of the dry soil was taken, and a soil moisture content was adjusted to 60% of the maximum water-holding capacity. The soils were set as: a heavy metal contaminated soil treated with a cadmium chloride solution (cadmium chloride being prepared into a solution and added into the soil, and an addition amount of cadmium ion being 30 mg/kg), a blank test soil, a heavy metal contaminated soil added with HAP and a blank test soil added with HAP. [0043] 3. The above samples were put into a constant temperature and humidity incubator for cultivation for 2 months, a temperature of the incubator was maintained at 25? C., and a humidity was maintained at 60%. [0044] 4. On 3th, 6th, 9th, 13th, 16th, 18th, 22th, 26th, 33th, 38th, 43th, 48th, 53th, and 59th days, emission rates of nitrous oxide were determined for each of soils using equipment of Agilent 7890B, Santa Clara, CA, USA; and cumulative emissions of greenhouse gas nitrous oxide were calculated. [0045] 5. Functional genes of microorganisms (ammonia-oxidizing archaea (AOA) and nirS, a nitrifying bacteria, indicating an emission mechanism of nitrous oxide from the soil) were determined on the 38.sup.th day, and an available cadmium content in the soil was determined after the completion of the cultivation. (The total DNA of soil was extracted from 0.5 g of tested soil using FastDNA SPIN Kit equipment, and then N.sub.2O functional genes were quantitatively detected, specifically in Shanghai Baile Biotechnology Co. Ltd.) [0046] (1) A calculation formula of an emission rate of nitrous oxide is as follows:

[00001]$F=P?V?\frac{?c}{?t}?\frac{1}{RT}?M?\frac{1}{m}$

[0047] where F represents an emission rate of nitrous oxide in a soil, P and V represent the standard atmospheric pressure and a volume of a headspace bottle, ?c/?t represents the change of a mass concentration of nitrous oxide per unit time, R is a universal gas constant, T represents an air temperature, M is a molecular mass of nitrous oxide in the soil, and m is a mass of dry soil in the cultivated soil. [0048] (2) A calculation formula of a cumulative emission of nitrous oxide is as follows:

[00002]$E=\underset{i=1}{\overset{n}{.Math.}}\frac{\left(F_i-F_{i+1}\right)}{2}?\left(t_{t+1}-t_i\right)?24$

[0049] where F represents an emission rate of nitrous oxide, i represents the gas collection performed for an i.sup.th time, (t.sub.t+1?t.sub.i) represents the number of days between two sampling, and n represents the number of times of gas collection.

[0050] In addition, physical and chemical property tests were performed on a blank test soil and a blank test soil added with HAP. The test results are shown in the table below.

TABLE-US-00001 TABLE 1 Study on physical and chemical properties of soil Ammonium Nitrate Organic Total nitrogen nitrogen matter nitrogen pH mg/kg mg/kg mg/g mg/g Control 5.45 ? 0.02 217.95 ? 6.72 12.10 ? 0.28 10.33 ? 0.18 0.75 ? 0.04 HAP 9.59 ? 0.01 18.76 ? 1.19 2.20 ? 0.20 9.53 ? 0.10 0.73 ? 0.05

[0051] Note: in the table, the control refers to the blank test soil, and HAP refers to the blank test soil added with HAP.

[0052] As can be seen from Table 1, ammonium nitrogen and nitrate nitrogen reduce significantly in the blank test soil added with HAP compared to the blank test soil, indicating that the addition of HAP in the soil can reduce ammonium nitrogen and nitrate nitrogen in the soil.

[0053] In addition, emission rates of nitrous oxide in the blank test soil and the blank test soil added with HAP on different days were tested, as shown in FIG. 1. The effect on an average emission rate of nitrous oxide in the blank test soil and the soil added with HAP is shown in FIG. 2. It can be seen from FIGS. 1 and 2 that the emission rate of the nitrous oxide in the soil added with HAP is lower than that in the blank test soil without addition, indicating that HAP can inhibit the emission rate of nitrous oxide in soil; and it can also be seen from FIG. 2 that the average emission rates of nitrous oxide between the two are significantly different.

[0054] Cumulative emissions of nitrous oxide on different days and a cumulative emission of nitrous oxide on the 59.sup.th day in the blank test soil and the blank test soil added with HAP were tested, as shown in FIGS. 3 and 4, respectively. It can be seen from the figures that the cumulative emission of nitrous oxide in the blank test soil without HAP is much larger than that in the blank test soil added with HAP, and the cumulative emission of nitrous oxide becomes more and more obvious with the increase of days.

[0055] Functional gene copy numbers of nitrous oxide-producing microorganisms in the soil on the 38.sup.th day in the blank test soil and the blank test soil containing HAP were tested, as shown in FIG. 5. It can be seen from FIG. 5 that AOA and nirS in the soil added with HAP are significantly lower than those in the blank test soil, inhibiting the emission of nitrous oxide and reducing the loss of N element in the soil, thus having a fertilizer-preserving effect. Therefore, this may be the main reason why HAP inhibits the emission of nitrous oxide.

[0056] Effects of HAP on available cadmium in a blank test soil and a heavy metal contaminated soil were tested. Specific test values are shown in FIGS. 6 and 7. It can be seen from FIGS. 6 and 7 that the cadmium contents in the blank test soil and heavy metal contaminated soil added with HAP are lower than that in the blank test soil without HAP. The possible reason is that HAP has adsorption and ion exchange properties to adsorb and replace cadmium ions, thus reducing the cadmium content in the soil.

[0057] Therefore, by adding HAP to soils in the present disclosure, the emission of nitrous oxide in the soil is effectively reduced, and the treatment of heavy metal contamination is realized at the same time, which is very suitable for the promotion and use of the nitrous oxide emission reduction in the contaminated soil. On the premise of no conflict, those skilled in the art can freely combine and superimpose the above additional technical features.

[0058] What has been described above is only the preferred implementation of the present disclosure, and all technical solutions that realize the objects of the present disclosure by basically the same means are within the protection scope of the present disclosure.