Preparation method of modified rock debris material for farmland soil As immobilization

Abstract

The invention discloses a preparation method of a modified rock debris material for farmland soil As immobilization, which comprises the following steps: (1) oil-based rock debris modification: collecting pyrolyzed oil-based rock debris powder as a basis of a modified material, carrying out preliminary cleaning, uniformly grinding the rock debris powder, then heating to remove moisture interference, putting 6.00 g of treated rock debris into a 250 mL beaker, and carrying out ultrasonic treatment for 20-30 min; the rock debris is soaked in 1 mol / L oxalic acid for 24 h and then centrifugally separated to remove supernate, the oxalic acid modified rock debris is washed with pure water for multiple times, and oxalic acid modified rock debris is obtained after freeze drying; (2) oxalic acid modification: mixing the oxalic acid modified rock debris with humic acid HA and hexadecyl trimethyl ammonium bromide HDTMA according to a mass ratio of 3: 1: 1 to form a solid material with an aggregate structure. The adsorbent has the advantages that the adsorbent can be used as an As adsorbent, has a carbon sequestration effect, reduces the toxicity of As in soil, and promotes soil fertility.

Description

Technical Field

[0001] The invention belongs to the technical field of farmland heavy metal soil pollution remediation, and particularly relates to a method for preparing a modified rock chip material for farmland soil As fixation. Background Art

[0002] Heavy metal pollution in farmland soil is an environmental issue of great concern in my country. With the rapid development of industrialization and urbanization, the problem of heavy metal pollution has become increasingly prominent. Heavy metal pollution in farmland soil includes arsenic. Heavy metal pollution in farmland soil mainly includes elements such as mercury (Hg), cadmium (Cd), lead (Pb), chromium (Cr), arsenic (As), copper (Cu) and nickel (Ni). These heavy metal elements cannot be decomposed by soil microorganisms, easily accumulate in the soil, and enter the human body through the food chain, causing harm to human health. Excessive heavy metal content in farmland soil leads to a decrease in soil fertility and a reduction in crop yields, which in turn affects the sustainable development of the agricultural economy. Developing green economic soil pollution remediation materials and their applications is an important technical method to ensure the quality of farmland soil.

[0003] The development of shale gas is an important part of promoting the development of my country's energy industry. However, various heavy metal pollutants generated during the mining process can enter the surrounding farmland soil through various channels. The preparation method of farmland soil heavy metal remediation materials mainly selects carbonaceous materials, clay minerals or synthetic materials with adsorption capacity for heavy metals, and prepares adsorbents or curing agents by a technical method of solid phase mixing in a certain proportion. However, the existing preparation and application technology may consume additional mineral or organic carbon resources on the one hand, resulting in low utilization rate of solid waste. On the other hand, in the process of repairing heavy metal pollution, previous technologies often ignore the restoration or improvement of soil fertility. The present invention uses the rock cuttings generated in the shale gas mining process as the basic material, mixes it with decomposed fertilizer (HS) on the basis of acid modification, and forms a new type of remediation material for adsorbing and curing soil heavy metals by adding biosurfactant (BS). The application of this material can achieve the technical improvement of soil fertility and soil structure by reducing the activity of heavy metals in the soil, which is of great significance to agricultural environmental ecological protection and agricultural sustainable development. Summary of the invention

[0004] The above technical objectives of the present invention are achieved through the following technical solutions: A modified rock chip material for fixing As in farmland soil and a preparation method thereof, comprising the following steps:

[0005] (1) Modification of oil-based rock chips: Collect the oil-based rock chip powder after pyrolysis as the basis of the modified material and perform preliminary cleaning. Grind the rock chip powder evenly and heat it to remove moisture interference. Put the treated rock chips in a beaker, soak them with oxalic acid and centrifuge to remove the supernatant. Rinse the oxalic acid-modified rock chips with pure water several times and freeze-dry them to obtain oxalic acid-modified rock chips.

[0006] (2) Oxalic acid modification: The oxalic acid-modified rock chips were mixed with humic acid HA and hexadecyltrimethylammonium bromide HDTMA in a mass ratio of 3:1:1 to form a solid material with an aggregate structure.

[0007] Furthermore, in step (1), the rock cuttings powder is ground uniformly and then heated at 105° C. for 240 minutes.

[0008] Furthermore, 6.00 g of the processed cuttings were placed in a 250 mL beaker, soaked in 1 mol / L oxalic acid for 24 h, and then centrifuged to remove the supernatant.

[0009] Furthermore, the humic acid in step (2) is obtained from decomposed fertilizer.

[0010] The modified rock cuttings material for fixing As in farmland soil provided by the present invention is prepared by the above method.

[0011] In summary, the present invention has the following beneficial effects: 1. The pore structure and reaction activity of the rock chips after preliminary modification with oxalic acid are optimized and improved. The double-layer flaky structure of the rock chips after mixed modification is more complete, and the carbon content of the modified material is significantly increased. New elements Al and Fe are also produced during the modification process. They have high surface activity and can fix organic carbon through coordination exchange, cation bridging, etc.

[0012] 2. The surface potential of the mixed modified cuttings increased under different pH conditions compared with that of the oxalic acid modified cuttings. At the same time, under acidic conditions, it can be used as an adsorbent for As.

[0013] 3. Oxalic acid-modified rock cuttings have an activation effect on soil As. HDTM A and HA in the mixed modified rock cuttings can form stable complexes with As, increasing the soil's ability to adsorb and fix As, thereby reducing the concentration of exchangeable As.

[0014] 4. The addition of HDTMA and HA during the mixed modification process enhanced the oxidizability of soil As, which was beneficial to reducing the toxicity of As in the soil, and also significantly reduced the mobility of As.

[0015] 5. The HDTMA and HA attached to the mixed modified cuttings can occupy the original negative potential points on the surface, reduce the exchange between As and other cations or anions in the soil solution, and thus enhance the fixation of As.

[0016] 6. Mixed modified rock cuttings can improve soil fertility. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Scanning electron microscope and X-ray energy spectrum analysis of cuttings before and after preliminary modification with oxalic acid;

[0018] Figure 2 This is a comparison of the surface morphology of cuttings modified with pure oxalic acid and mixed oxalic acid;

[0019] Figure 3 This is the EDX analysis comparison of the cuttings modified by oxalic acid alone and mixed oxalic acid;

[0020] Figure 4 This is a comparison of the zeta potential of the cuttings surface after modification with oxalic acid alone and with that after modification with mixed oxalic acid + HDTMA + HA;

[0021] Figure 5 The infrared spectra of the cuttings after modification with oxalic acid alone and mixed oxalic acid + HDTMA + HA;

[0022] Figure 6 This is a graph showing the effect of adding cuttings modified by different methods into the soil on the exchangeable As in the soil;

[0023] Figure 7 The results of the effects of adding rock chips modified by different methods into the soil on the distribution characteristics of soil As forms;

[0024] Figure 8 This is a comparison chart of the effects of oxalic acid-modified and mixed-modified rock cuttings on soil physical and chemical properties;

[0025] Fig. 9 This is a comparison chart of the effects of oxalic acid-modified and mixed-modified rock cuttings on soil nutrient content;

[0026] Fig.10 This is a comparison chart of the effects of different modified rock cuttings on soil fertility;

[0027] Fig.11 This is the result diagram of the microbial symbiotic network. DETAILED DESCRIPTION

[0028] The following is combined with Figure 1-Figure 11 The present invention is further described in detail with the following embodiments:

[0029] Production:

[0030] (1) Modification of oil-based cuttings:

[0031] The oil-based rock chip powder after pyrolysis was collected as the basis of the modified material and was preliminarily cleaned. After the rock chip powder was evenly ground, it was heated at 105°C for 240 minutes to remove moisture interference. 6.00 g of the treated rock chip was put into a 250 mL beaker, soaked in 1 mol / L oxalic acid for 24 hours, and then centrifuged to remove the supernatant. The oxalic acid-modified rock chip was rinsed with pure water several times and freeze-dried to obtain oxalic acid-modified rock chip.

[0032] (2) Oxalic acid modification

[0033] The oxalic acid-modified rock chips are mixed with humic acid (HA) and hexadecyltrimethylammonium bromide (HDTMA) in a mass ratio of 3:1:1 to form a solid material with an aggregate structure. The humic acid is obtained from decomposed fertilizer.

[0034] The following are various analyses of the modified rock cuttings material for As fixation in farmland soil obtained by the present invention:

[0035] (1) Characterization and analysis of rock cuttings using scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS)

[0036] In order to determine the morphological changes of the cuttings and the content and distribution of elements in each part, the cuttings were characterized and analyzed using scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Figure 1 As shown in the figure, the attachment of C, O, N, and S elements in the cuttings after oxalic acid modification has increased significantly and the distribution is more uniform. The increase of C and O elements is the most obvious, and the number of pores in the SEM spectrum has increased by about 21% compared with before modification. In addition, after the cuttings are modified, the content of active groups such as C=C and -OH increases by about 11.3%, and the specific surface area increases by 17%. The above results show that the cuttings after preliminary modification with oxalic acid have been optimized and improved in terms of pore structure and reaction activity.

[0037] (2) Comparison of SEM and EDX between oxalic acid modification and mixed modification

[0038] The HDTMA and HA molecules used in the experiments can be adsorbed on the outer surface of the cuttings to form a structurally complete bilayer or a sheet-like bilayer. Figure 2 (a) Simple oxalic acid modification and Figure 2 (b) The comparison of the surface morphology of the cuttings after mixed oxalic acid + HDTMA + HA modification shows that the double-layered flaky structure of the cuttings is more complete after mixed modification (oxalic acid + HDTMA + HA). Figure 3 EDX analysis of the cuttings (c) and (d) shows that the carbon content of the modified material increased significantly, which was mainly caused by the addition of HA. In addition, Br replaced Cl, which was because HDTMA itself contained Br, which together led to the increase of carbon and Br on the cuttings after loading. New elements Al and Fe were also produced during the modification process.

[0039] (3) Comparison of Zata potential and infrared spectra of oxalic acid-modified and mixed-modified cuttings

[0040] The comparison of the zeta potential of the cuttings after modification with oxalic acid alone and with the mixed oxalic acid + HDTMA + HA showed that the surface potential of the cuttings after the mixed modification was higher than that after the oxalic acid modification under different pH conditions ( Figure 4 ). This is because the cationic part of the surfactant occupies the negatively charged surface position, making the surface of the cuttings less negatively charged. When the pH is about 4, the surface of the mixed modified cuttings is positively charged, which is conducive to the adsorption of As. It can be considered that under acidic conditions, it can be used as an As adsorbent.

[0041] The changes of surface functional groups of cuttings by two modification methods are as follows Figure 5 As shown. The most obvious change in the absorption peak is in the range of 600-800 cm-1, where the absorption peak of C-Cl on the cuttings after surfactant modification has shifted, indicating that Br- replaces Cl. Compared with the unmodified cuttings, the spectral intensity corresponding to hydroxyl (-OH) in the modified cuttings increased by 10.5%, which is due to the increase in the content of hydroxyl functional groups caused by the addition of HA.

[0042] (4) Effects of oxalic acid-modified and mixed-modified rock cuttings on exchangeable As and Cd in soil

[0043] Effects of different modification methods of cuttings added into soil on soil exchangeable As Figure 6 The results showed that compared with no rock chips added at all (CK), the concentration of exchangeable As in the soil after adding 5% and 10% by mass oxalic acid-modified rock chips (B5, B10) was 9.7%, 11.3% and 3.2% higher than that in the soil treated with CK during the 30-day, 60-day and 90-day incubation period, respectively, indicating that oxalic acid-modified rock chips had an activation effect on soil As. However, after adding mixed modified rock chips (HB5, HB10), the concentration of extractable As in the soil was significantly reduced by 25.3%, 21.4% and 20.5% compared with the simple oxalic acid modification treatment during the 30-day, 60-day and 90-day incubation period. This is mainly because HDTMA and HA in the mixed modified rock chips can form stable complexes with As, which increases the adsorption and fixation capacity of the soil for As, thereby reducing the concentration of exchangeable As.

[0044] (5) Comparison of the changes in soil As morphological distribution characteristics between oxalic acid-modified and mixed-modified rock chips

[0045] Figure 7The results of the effects of adding rock chips modified by different methods into the soil on the distribution characteristics of soil As morphology show that compared with no rock chips added at all (CK), after adding oxalic acid-modified rock chips, the reducible As in the soil decreased by 27.6% with the increase in the amount of addition, but the exchangeable As proportion increased by 8.3%, and the proportion of residual As did not change significantly compared with CK. This further shows that the addition of oxalic acid-modified rock chips has a potential activation risk for soil As. Compared with oxalic acid-modified rock chips, the addition of mixed modified rock chips reduced the exchangeable As by 58.5% and significantly increased the oxidizable As proportion by 47.3%, indicating that the addition of HDTMA and HA in the mixed modification process enhanced the oxidizability of soil As, which is beneficial to reducing the toxicity of As in the soil, and also significantly reduced the mobility of As.

[0046] (6) Effects of oxalic acid-modified and mixed-modified rock chips on soil physical and chemical properties

[0047] Depend on Figure 8 It can be seen that the soil pH underwent a natural acidification process within 90 days, and the addition of oxalic acid modification and mixed modified rock chips increased the soil pH from the original 4.03 to 5.47 and 5.21, respectively. Figure 8 (a)]. The EC value of the CK group on the 30th day was 1230μs cm-1. Except for the B10 treatment group, which had a maximum EC value of 1547μs cm-1, the EC values ​​of the other treatment groups decreased to varying degrees on the 30th day, but there was no significant difference compared with the CK group; and the EC value of each treatment group was the highest on the 60th day and decreased on the 90th day. Figure 8 (b)]. Mixed modification can reduce impurities on the surface of rock chips, thereby reducing the salt content in the soil, resulting in a decrease in EC value at 90 days. The SOM of soils with oxalic acid-modified and mixed modified rock chips increased with increasing dosage and incubation time. Figure 8 (c)]. Compared with the blank treatment (CK), the SOM content increased by 27.80-465.72%. With the increase of the dosage of rock chips or modified rock chips. The changes in the content of soil CEC showed that in the first 60 days, there was no significant change in the CEC of the soil modified by oxalic acid or mixed modified rock chips. Figure 8 (d)]. However, at 90 days, the CEC of the soil treated with mixed modified rock chips was significantly reduced by 15.32%. The HDTMA and HA attached rock chips in the mixed modified rock chips can occupy the original negative potential points on the surface, reduce the exchange of As with other cations or anions in the soil solution, and thus enhance the fixation of As.

[0048] (7) Comparison of the effects of oxalic acid-modified and mixed-modified rock cuttings on soil nutrients

[0049] Effects of oxalic acid modified rock chips and mixed modified rock chips on soil K, Ca, and Mg after application Fig. 9 As shown in the figure, the application of both modified rock chips increased the content of K, Ca and Mg in the soil, and the increase in the content of K, Ca and Mg in the soil after applying the mixed modified rock chips was greater than that in the soil after applying the oxalic acid modified rock chips, indicating that the mixed modified rock chips have a more obvious effect on promoting soil fertility.

[0050] Depend on Fig.10 It shows that mixed modified rock chips have a promoting effect on soil fertility; the promoting effect of modified rock chips on soil fertility can be analyzed from the characteristics of soil microbial diversity and microbial symbiotic network after adding rock chips with different modification methods. First, compared with CK (no rock chips added), the soil microbial diversity showed a significant increase after adding oxalic acid modified and oxalic acid + HDMTA + HA modified rock chips. After adding oxalic acid + HDMTA + HA modified rock chips, the average values ​​of the Shannon index and Chao index of soil microorganisms increased by 11.5% and 7.3% respectively compared with the treatment of only oxalic acid modified rock chips. It shows that the effect of composite modified (oxalic acid + HDMTA + HA) rock chips on improving soil microbial diversity is more significant. At the same time Fig.11 The results of the microbial symbiotic network also further showed that the complexity of the soil microbial network after adding mixed modified rock chips showed a significant increase in concentration compared with CK, with the highest increase of 72.4%. It was higher than the complexity of the soil microbial network after adding oxalic acid modified rock chips (55.3%). Soil nutrients are released as a result of microbial mineralization. The above results show that the improvement of soil fertility by mixed modified rock chips is mainly achieved by strengthening the diversity of soil microorganisms.

[0051] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A method for preparing a modified rock material for fixing As in farmland soil, characterized in that: The following steps are involved: (1) Modification of oil-based rock chips: Collect the oil-based rock chip powder after pyrolysis as the basis of the modified material and perform preliminary cleaning. Grind the rock chip powder evenly and heat it to remove moisture interference. Put the treated rock chip in a beaker, soak it with oxalic acid and centrifuge it to remove the supernatant. Rinse the oxalic acid-modified rock chip with pure water for several times and freeze-dry it to obtain oxalic acid-modified rock chip. (2) Oxalic acid modification: The oxalic acid-modified rock chips were mixed with humic acid HA and hexadecyltrimethylammonium bromide HDTMA in a mass ratio of 3:1:1 to form a solid material with an aggregate structure.

2. The method for preparing a modified rock chip material for fixing As in farmland soil according to claim 1, characterized in that: In the step (1), the rock cuttings powder is ground uniformly and then heated at 105°C.

3. The method for preparing a modified rock chip material for fixing As in farmland soil according to claim 1, characterized in that: The heating time in step (1) is 240 minutes.

4. The method for preparing a modified rock chip material for fixing As in farmland soil according to claim 1, characterized in that: In step (1), 6.00 g of the processed rock chips were placed in a 250 mL beaker, soaked in 1 mol / L oxalic acid for 24 h, and then centrifuged to remove the supernatant.

5. The method for preparing a modified rock chip material for fixing As in farmland soil according to claim 1, characterized in that: The humic acid in step (2) is obtained from decomposed fertilizer.

6. A modified rock material for fixing As in farmland soil, characterized in that: The modified rock chip material is prepared by the method for preparing the modified rock chip material for As fixation in farmland soil as described in any one of claims 1 to 4.

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