Hydroxypropyl starch-chitosan complex-coated manganese-based microspheres, method for preparing the same, and use thereof

Abstract

The application discloses a kind of hydroxypropyl starch-chitosan composite coated manganese-based microspheres and its preparation method and application.The manganese-based microspheres include inner core, and the inner core surface is sequentially coated with chitosan layer and hydroxypropyl starch layer from inside to outside;The particle size of the manganese-based microspheres is 150-300 μm.By introducing manganese-based microspheres with oxidizing property and three consecutive treatments, the iron components in the soil can be effectively controlled, and the arsenic availability can be reduced.

Description

TECHNICAL FIELD

[0001] The application relates to the field of soil pollution remediation and environmental regulation, and particularly relates to a manganese-based microsphere coated with hydroxypropyl starch-chitosan and a preparation method and application thereof. BACKGROUND

[0002] Due to the special physiological characteristics, the arsenic pollution problem in paddy soil drives a series of redox reactions in the soil during the seasonal flooding and drainage of the paddy field. Under the flooding and reduction condition, iron oxides as the main arsenic adsorption medium are prone to reduction and dissolution, which leads to a large amount of arsenic release into the water phase, increases the migration and bioavailability of arsenic in the soil, and thus threatens the absorption of rice.

[0003] Current research attempts to stabilize the arsenic form and fixation capacity by applying iron, manganese, calcium, silicon and other conditioners. Among them, manganese oxides are considered to indirectly regulate the redox environment of the soil due to their strong oxidizing property. Slow-release materials are also widely used in soil, and some slow-release materials can control the release of oxygen, water or nutrients, thereby regulating the key environmental parameters such as rhizosphere pH and redox potential. At present, there are many methods to reduce the release of soil arsenic, but most of the researches only stay at the level of phenomenon description of element application and arsenic form change, especially the mechanism of inhibiting the reduction and dissolution of iron oxides is still unclear. Due to the flooding condition of paddy soil, the redox potential of the soil is unstable, but the research on controlling the redox potential and applying materials to jointly inhibit the reduction of iron oxides and then affect the release of arsenic is still unclear. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and provide a manganese-based microsphere coated with hydroxypropyl starch-chitosan and a preparation method and application thereof. By introducing manganese-based microspheres with oxidizing property and three consecutive treatments, the iron components in the soil can be effectively regulated, and the arsenic availability can be reduced.

[0005] To achieve the above purpose, the technical scheme designed by the present application is as follows:

[0006] The present application provides a manganese-based microsphere coated with hydroxypropyl starch-chitosan, the manganese-based microsphere comprises an inner core, and the inner core surface is sequentially coated with a chitosan layer and a hydroxypropyl starch layer from inside to outside;

[0007] The inner core is prepared from nano-manganese dioxide and potassium permanganate, and the mass ratio of the nano-manganese dioxide and the potassium permanganate is 1:0.1-2;

[0008] The raw materials of the chitosan layer are chitosan, acetic acid solution, citric acid and sodium tripolyphosphate solution, wherein the mass ratio of chitosan, the inner core and citric acid is 1:0.3-1:0.01-0.02, the mass-volume ratio of the inner core and the sodium tripolyphosphate solution is 1:5-20 mg / mL; the mass-volume ratio of chitosan and acetic acid solution is 0.01-0.02:1 mg / mL;

[0009] The raw materials of the hydroxypropyl starch layer are hydroxypropyl starch solution and calcium chloride solution, and the mass ratio of the inner core and the hydroxypropyl starch in the hydroxypropyl starch solution is 1:9-50, and the volume ratio of the hydroxypropyl starch solution and the calcium chloride solution is 1:0.2-0.5.

[0010] Further, the particle size of the manganese-based microspheres is 150-300 μm;

[0011] The mass ratio of the nanometer manganese dioxide and potassium permanganate is 1:1;

[0012] The mass ratio of the chitosan, the inner core and citric acid is 1:0.5:0.015, the mass-volume ratio of the inner core and the sodium tripolyphosphate solution is 1:15 mg / mL, and the mass-volume ratio of chitosan and acetic acid solution is 0.015:1 mg / mL;

[0013] The mass ratio of the inner core and the hydroxypropyl starch in the hydroxypropyl starch solution is 1:15, and the volume ratio of the hydroxypropyl starch solution and the calcium chloride solution is 1:0.3.

[0014] Further, the concentration of the acetic acid solution is 1-2%, the concentration of the sodium tripolyphosphate solution is 0.5-5%, the concentration of the hydroxypropyl starch solution is 3-8%, and the concentration of the calcium chloride solution is 2-8%.

[0015] Further, the concentration of the acetic acid solution is 1%, the concentration of the sodium tripolyphosphate solution is 2%, the concentration of the hydroxypropyl starch solution is 5%, and the concentration of the calcium chloride solution is 6%.

[0016] The application also provides a preparation method of the manganese-based microspheres.

[0017] (1) The nanometer manganese dioxide and potassium permanganate are mixed according to the mass ratio, and the inner core is obtained after ball milling;

[0018] (2) The chitosan and citric acid are added to the acetic acid solution according to the mass-volume ratio of chitosan and acetic acid solution and the mass ratio of chitosan, the inner core and citric acid, and a chitosan solution is obtained;

[0019] (3) The chitosan solution and the inner core are mixed, the sodium tripolyphosphate solution is added dropwise according to the mass-volume ratio of the inner core and the sodium tripolyphosphate solution, and a primary coated microsphere is obtained by centrifugation.

[0020] (4) according to the mass-volume ratio of the above-mentioned primary coated microspheres and the hydroxypropyl starch solution, the primary coated microspheres are dispersed in the hydroxypropyl starch solution, the calcium chloride solution is added dropwise according to the volume ratio of the above-mentioned hydroxypropyl starch solution and the calcium chloride solution, and after drying, sieving is performed to obtain manganese-based microspheres coated by hydroxypropyl starch-chitosan.

[0021] Further, in the step (2), the concentration of the acetic acid solution is 1-2%;

[0022] In the step (3), the concentration of the sodium tripolyphosphate solution is 0.5-5%;

[0023] In the step (4), the concentration of the hydroxypropyl starch solution is 3-8%, and the concentration of the calcium chloride solution is 2-8%.

[0024] The application further provides a use of the manganese-based microspheres in repairing heavy metal contaminated soil.

[0025] The application further provides a method for regulating iron components in soil and reducing the availability of arsenic in soil by using the manganese-based microspheres, comprising the following steps:

[0026] S1: weighing the heavy metal contaminated soil to be repaired in an anaerobic culture bottle, adding water and 1 manganese-based microspheres;

[0027] S2: first, anaerobic culture is performed, and on the 10th-11th day of anaerobic culture, peroxide is added to the heavy metal contaminated soil;

[0028] S3: on the 20th-22nd day of anaerobic culture, air is started to be introduced, and the air is introduced every 3-5 days, and the culture is performed to 40-42 days, and the anaerobic culture is ended;

[0029] S4: finally, aerobic culture is performed for 20-22 days, and the iron components in the soil are regulated and the availability of arsenic in the soil is reduced.

[0030] Further, in the step S1, the basic physicochemical properties of the heavy metal contaminated soil are as follows: pH=6-7, total iron 18-20 g / kg, total manganese 130-140 mg / kg, and total arsenic 30-45 mg / kg;

[0031] The mass-volume ratio of the heavy metal contaminated soil and deionized water is 1:2-3 g / mL;

[0032] The application amount of the manganese-based microspheres in the heavy metal contaminated soil is 1.93-19.3 g / kg, and after the manganese-based microspheres are applied, the molar ratio of Mn and Fe in the heavy metal contaminated soil is 0.05-0.5.

[0033] Further, in the step S2, the mass ratio of the manganese-based microspheres and the peroxide is 1:0.1-2;

[0034] The peroxide is a combination of calcium peroxide and urea peroxide, wherein the mass ratio of the calcium peroxide and the urea peroxide is 1:0.5-2;

[0035] In the step S3, when the air is introduced, the introduction speed of the air is 40-45 mL / min, and the air is introduced in an intermittent manner, each time for 30-32 minutes, and stopped for 8-10 minutes, for 6 hours.

[0036] Principle of the present application:

[0037] The manganese-based microspheres are double-wrapped by hydroxypropyl starch-chitosan in the present application, and the dual functions of rapid oxidation and long-term stability are realized through the synergistic effect of the inner and outer layers, which solves the technical problem that the traditional single-layer material cannot balance rapid response and long-term repair, and significantly improves the arsenic pollution repair efficiency and environmental adaptability.

[0038] In the present application, nano-manganese dioxide and potassium permanganate are used as composite core materials, potassium permanganate has strong oxidizing property, and manganese dioxide has high specific surface area and surface active sites, and efficient arsenic pollution repair is realized through the synergistic effect of the two. Hydroxypropyl starch solution can balance cold water solubility, film strength and slow release performance through molecular modification, and is an ideal choice for the wrapping layer of manganese-based microspheres, especially suitable for soil remediation scenarios that require precise controlled release and complex environmental adaptation.

[0039] Advantages of the present application:

[0040] 1、The present application stabilizes the change of the oxidation-reduction potential in the soil through three continuous treatments, enhances the effect of the applied manganese-based microspheres, and better inhibits the reduction and dissolution of iron oxides, thereby significantly reducing the release and activation of arsenic in the soil. The method has clear scientific principles, strong adaptability and environmental friendliness, and provides a new idea and path for the treatment of arsenic pollution in rice fields.

[0041] 2、Different from the traditional focus on oxidation-reduction regulation or adsorption-desorption mechanism, the present application innovatively uses the slow release performance of the material, regulates the oxidation-reduction potential, and simultaneously performs multiple treatment steps, thereby inhibiting the reduction and dissolution of iron oxides from the source, and further reducing the release of arsenic.

[0042] 3、The manganese-based microspheres used in the present application are widely available, and can be selected from natural or industrial materials. The manganese-based microspheres are environmentally friendly, slow-release, have long-term treatment effect, do not introduce harmful chemicals, and are easy to obtain, and are suitable for the remediation of arsenic pollution in wet soils such as rice fields.

[0043] 4、The application is simple to operate, can be directly applied to farmland by manganese-based microspheres, does not require complex equipment or processing procedures, and has good field operability and sustainability. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 Figure 4 is a graph of the change in soil redox state over time under different Mn / Fe molar ratio treatments;

[0045] wherein CK-1 is Comparative Example 3, CK-2 is Comparative Example 4, CK-3 is Comparative Example 5, Mn / Fe = 0.05 is Example 3, Mn / Fe = 0.1 is Example 4, and Mn / Fe = 0.5 is Example 5;

[0046] Figure 2 Figure 5 is a graph of the change in soil pH over time under different Mn / Fe molar ratio treatments;

[0047] wherein CK-1 is Comparative Example 3, CK-2 is Comparative Example 4, CK-3 is Comparative Example 5, Mn / Fe = 0.05 is Example 3, Mn / Fe = 0.1 is Example 4, and Mn / Fe = 0.5 is Example 5;

[0048] Figure 3 Figure 6 is a graph of the change in dissolved Fe over time under different Mn / Fe molar ratio treatments; 2+

[0049] wherein CK-1 is Comparative Example 3, CK-2 is Comparative Example 4, CK-3 is Comparative Example 5, Mn / Fe = 0.05 is Example 3, Mn / Fe = 0.1 is Example 4, and Mn / Fe = 0.5 is Example 5;

[0050] Figure 4 Figure 7 is a graph of the change in soil amorphous Fe over time under different Mn / Fe molar ratio treatments;

[0051] wherein CK-1 is Comparative Example 3, CK-2 is Comparative Example 4, CK-3 is Comparative Example 5, Mn / Fe = 0.05 is Example 3, Mn / Fe = 0.1 is Example 4, and Mn / Fe = 0.5 is Example 5;

[0052] Figure 5 Figure 8 is a graph of the change in dissolved As over time under different Mn / Fe molar ratio treatments;

[0053] wherein CK-1 is Comparative Example 3, CK-2 is Comparative Example 4, CK-3 is Comparative Example 5, Mn / Fe = 0.05 is Example 3, Mn / Fe = 0.1 is Example 4, and Mn / Fe = 0.5 is Example 5;

[0054] Figure 6 ​The figure of the change of the effective arsenic with time under the treatment of different Mn / Fe molar ratios is shown in the following figure:

[0055] In the figure, CK-1 is Comparative Example 3, CK-2 is Comparative Example 4, CK-3 is Comparative Example 5, Mn / Fe=0.05 is Example 3, Mn / Fe=0.1 is Example 4, and Mn / Fe=0.5 is Example 5.

[0056] Figure 7 The figure of the change of the soil amorphous iron adsorbed arsenic with time under the treatment of different Mn / Fe molar ratios is shown in the following figure:

[0057] In the figure, CK-1 is Comparative Example 3, CK-2 is Comparative Example 4, CK-3 is Comparative Example 5, Mn / Fe=0.05 is Example 3, Mn / Fe=0.1 is Example 4, and Mn / Fe=0.5 is Example 5. DETAILED DESCRIPTION

[0058] The application will be further described in detail below with reference to specific examples so as to be understood by those skilled in the art.

[0059] Material Description

[0060] 1. The degree of deacetylation of chitosan is greater than or equal to 70%.

[0061] 2. The content of hydrogen peroxide in the urea peroxide is 35-45%, and the total content of urea and hydrogen peroxide is greater than or equal to 95%.

[0062] 3. The content of active ingredients in the calcium peroxide is 60-75%.

[0063] 4. The heavy metal contaminated soil for testing is a heavy metal arsenic contaminated soil in a certain place in Hubei Province, and the basic physicochemical properties of the soil are as follows: pH=6.5, total iron 18.05 g / kg, total manganese 130 mg / kg, and total arsenic 45.38 mg / kg. According to the Soil Environmental Quality Risk Control Standard for Agricultural Land (Trial) (GB 15618-2018), the content of As in the soil is between the soil screening value and the risk control value.

[0064] Example 1

[0065] Preparation method 1 of hydroxypropyl starch-chitosan composite coated manganese-based microspheres 1

[0066] The hydroxypropyl starch-chitosan composite coated manganese-based microspheres of the application comprise an inner core, and the surface of the inner core is sequentially coated with a chitosan layer and a hydroxypropyl starch layer from inside to outside.

[0067] 1. Mix nano manganese dioxide and potassium permanganate according to a mass ratio of 1:0.1-2, and ball mill to uniformly disperse to obtain the inner core.

[0068] 2. Dissolve chitosan in 1-2% acetic acid solution at a ratio of 0.01-0.02:1 mg / mL, the mass ratio of chitosan to the inner core is 1:0.3-1, add citric acid to help dissolve, the mass ratio of chitosan to citric acid is 1:0.01-0.02, to obtain a chitosan solution.

[0069] 3. Mix the chitosan solution with the inner core, and drop 0.5-5% sodium tripolyphosphate solution to solidify, the mass volume ratio of the inner core to the sodium tripolyphosphate solution is 1:5-20 mg / mL, centrifugal collect the microspheres, to obtain the primary coated microspheres.

[0070] 4. Disperse the primary coated microspheres in 3-8% hydroxypropyl starch solution, the mass ratio of the inner core to the hydroxypropyl starch in the hydroxypropyl starch solution is 1:9-50, drop 2-8% calcium chloride solution to crosslink, the volume ratio of the 3-8% hydroxypropyl starch solution to the 2-8% calcium chloride solution is 1:0.2-0.5, sieve after drying, to obtain 150-300 μm particles, that is, the hydroxypropyl starch-chitosan composite coated manganese-based microspheres 1.

[0071] Example 2

[0072] Preparation method of hydroxypropyl starch-chitosan composite coated manganese-based microspheres 2

[0073] 1. Mix nano manganese dioxide and potassium permanganate at a ratio of 1:1, ball mill to uniformly disperse, to obtain an inner core.

[0074] 2. Dissolve chitosan in 1% acetic acid solution at a ratio of 0.015:1 mg / mL, the mass ratio of chitosan to the inner core is 1:0.5, add citric acid to help dissolve, the mass ratio of chitosan to citric acid is 1:0.015, to obtain a chitosan solution.

[0075] 3. Mix the chitosan solution with the inner core, and drop 2% sodium tripolyphosphate solution to solidify, the mass volume ratio of the inner core to the 2% sodium tripolyphosphate solution is 1:15 mg / mL, centrifugal collect the microspheres, to obtain the primary coated microspheres.

[0076] 4. Disperse the primary coated microspheres in 5% hydroxypropyl starch solution, the mass ratio of the inner core to the hydroxypropyl starch is 1:15, drop 6% calcium chloride solution to crosslink, the volume ratio of the 5% hydroxypropyl starch solution to the 6% calcium chloride solution is 1:0.3, sieve after drying, to obtain 150-300 μm particles, that is, the hydroxypropyl starch-chitosan composite coated manganese-based microspheres 2.

[0077] Example 3

[0078] Method for regulating iron components in soil and reducing arsenic availability in soil 1

[0079] This example uses the hydroxypropyl starch-chitosan complex coated manganese-based microspheres 2 prepared in Example 2 to repair the soil, which specifically includes the following steps:

[0080] 1. Dry and sieve the heavy metal contaminated soil to be repaired.

[0081] 2. Weigh the heavy metal contaminated soil to be repaired into an anaerobic culture bottle, and add deionized water, the mass-volume ratio of the heavy metal contaminated soil to be repaired and deionized water is 1:2 g / mL, at the same time, add the hydroxypropyl starch-chitosan complex coated manganese-based microspheres 2 prepared in Example 2, the amount of manganese-based microspheres 2 added in the heavy metal contaminated soil is 1.93 g / kg, so that the molar ratio of Mn and Fe in the soil is 0.05.

[0082] 3. First, anaerobic culture is carried out, which is divided into three different treatment methods in succession, and the anaerobic culture is carried out in a 25°C biochemical incubator, which is specifically as follows:

[0083] (1) After adding the hydroxypropyl starch-chitosan complex coated manganese-based microspheres 2, anaerobic culture is carried out for 10 days;

[0084] (2) On the 10th day of anaerobic culture, peroxide is added to the heavy metal contaminated soil for culture, the mass ratio of the hydroxypropyl starch-chitosan complex coated manganese-based microspheres and peroxide is 1:0.1-2, the peroxide is a combination of calcium peroxide and urea peroxide, and the mass ratio of calcium peroxide and urea peroxide is 1:0.5-2.

[0085] (3) On the 20th day of anaerobic culture, air is started to be introduced, and the air is introduced every 3 days, when the air is introduced, an air pump is used to inject air into the soil (the air introduction speed is 40 mL / min), and an intermittent introduction method is adopted, the air is introduced for 30 minutes each time, and stopped for 10 minutes, and the process is continued for 6 hours. Better maintain the high oxidation-reduction potential of the soil under the flooded condition until the end of the 40-day anaerobic culture.

[0086] 4. Then, aerobic culture is carried out for 20 days (the total length of anaerobic culture and aerobic culture is 60 days), and the aerobic culture is carried out in a 25°C constant temperature shaking incubator, the bottle opening is opened, and a porous membrane is sealed to slowly introduce oxygen.

[0087] 5. During the whole culture process, destructive sampling is carried out at 1, 3, 5, 7, 14, 25, 40 and 60 days. At different sampling times, before destructive sampling, the oxidation-reduction potential of the soil is measured. After destructive sampling, the soil sample is fully shaken and centrifuged to obtain pore water and soil solid phase. The pH and dissolved Fe2+ Determination of dissolved As. Soil solid phase was air-dried, ground and sieved, and the effective Fe, effective As, amorphous Fe and amorphous Fe-adsorbed As were determined. The effective Fe of soil was extracted by DTPA, the amorphous Fe and amorphous Fe-adsorbed As were extracted by ammonium oxalate, and the effective As of soil was extracted by NaHCO3.

[0088] Example 4

[0089] Method 2 for regulating iron components in soil and reducing the availability of arsenic in soil

[0090] This example uses the hydroxypropyl starch-chitosan composite coated manganese-based microspheres 2 prepared in Example 2 to repair the soil. The method of this example is the same as that of Example 3, the difference is that in step 2, the hydroxypropyl starch-chitosan composite coated manganese-based microspheres 2 are applied, and the amount of manganese-based microspheres 2 applied in the heavy metal contaminated soil is 3.86 g / kg, so that the molar ratio of Mn and Fe in the soil is 0.1.

[0091] Example 5

[0092] Method 3 for regulating iron components in soil and reducing the availability of arsenic

[0093] This example uses the hydroxypropyl starch-chitosan composite coated manganese-based microspheres 2 prepared in Example 2 to repair the soil. The method of this example is the same as that of Example 3, the difference is that in step 2, the hydroxypropyl starch-chitosan composite coated manganese-based microspheres 2 are applied, and the amount of manganese-based microspheres 2 applied in the heavy metal contaminated soil is 19.3 g / kg, so that the molar ratio of Mn and Fe in the soil is 0.5.

[0094] Comparative Example 1

[0095] Preparation method of chitosan single-layer coated manganese-based microspheres

[0096] 1. Mix nano-manganese dioxide and potassium permanganate in a mass ratio of 1:1, ball mill to uniform dispersion, and obtain the inner core.

[0097] 2. Dissolve chitosan in a 1% acetic acid solution at a mass-volume ratio of 0.015:1 mg / mL, the mass ratio of chitosan to inner core is 1:0.5, add citric acid to help dissolution, the mass ratio of chitosan to citric acid is 1:0.015, and obtain a chitosan solution.

[0098] 3. Mix the chitosan solution with the inner core, add a 2% sodium tripolyphosphate solution dropwise for solidification, the mass-volume ratio of the inner core to the 2% sodium tripolyphosphate solution is 1:15 mg / mL, centrifuge to collect the microspheres, and obtain chitosan single-layer coated manganese-based microspheres.

[0099] Comparative Example 2

[0100] Method for preparing manganese-based microspheres coated with a single layer of hydroxypropyl starch

[0101] 1. Mix nano-manganese dioxide and potassium permanganate in a mass ratio of 1:1, and ball mill until uniformly dispersed to obtain an inner core.

[0102] 2. Disperse the inner core in a 5% hydroxypropyl starch solution, with the mass ratio of inner core to hydroxypropyl starch being 1:15, and add a 6% calcium chloride solution dropwise for cross-linking, with the volume ratio of 5% hydroxypropyl starch solution to 6% calcium chloride solution being 1:0.3. After drying, sieve to obtain 150-300 μm particles, i.e. manganese-based microspheres coated with a single layer of hydroxypropyl starch.

[0103] Comparative Example 3

[0104] Method for repairing soil 1

[0105] The repair method of this comparative example is the same as that of Example 3, except that in step 2, no manganese-based microspheres 2 coated with a hydroxypropyl starch-chitosan composite are applied.

[0106] Comparative Example 4

[0107] Method for repairing soil 2

[0108] The repair method of this comparative example is the same as that of Example 4, except that in step 2, manganese-based microspheres coated with a single layer of chitosan prepared in Comparative Example 1 are used instead of manganese-based microspheres 2 coated with a hydroxypropyl starch-chitosan composite.

[0109] Comparative Example 5

[0110] Method for repairing soil 3

[0111] The repair method of this comparative example is the same as that of Example 4, except that in step 2, manganese-based microspheres coated with a single layer of hydroxypropyl starch prepared in Comparative Example 2 are used instead of manganese-based microspheres 2 coated with a hydroxypropyl starch-chitosan composite.

[0112] Analysis of results

[0113] The results are shown in Table 1. Figures 1-7

[0114] Figure 1 and Figure 2 ​The redox potential (Eh) and pH change trends of different treatments in the culture stage are shown respectively. With the extension of the culture time, the Eh value gradually decreases, and in the comparative example group, it decreases to about-200 mV, while in the example group of the manganese-based microspheres 2 wrapped by hydroxypropyl starch-chitosan composite, the decreasing trend of Eh is significantly inhibited, and the higher the Mn / Fe molar ratio, the higher the Eh tends to be, which shows that the manganese-based microspheres wrapped by hydroxypropyl starch-chitosan composite have the ability to maintain the oxidizing environment in the soil, and the effect is better than that of the single-layer wrapped manganese-based microspheres.

[0115] Figure 3 and Figure 4 The dissolved Fe 2+ and amorphous iron content change trends with time are shown respectively. In Comparative Example 3, Fe 2+ concentration continuously increases and amorphous iron content decreases, indicating that the iron oxide undergoes obvious reduction and dissolution process; while after adding the manganese-based microspheres wrapped by hydroxypropyl starch-chitosan composite, the accumulation of dissolved Fe 2+ and the transformation of amorphous iron are significantly inhibited, and the effect is enhanced with the increase of the Mn / Fe molar ratio.

[0116] Figures 5-7 Reflect the dynamic change trends of different forms of arsenic (dissolved state, available state and amorphous iron adsorption state). The results show that in the manganese-based microspheres wrapped by hydroxypropyl starch-chitosan composite example group, the dissolved and available arsenic concentrations are significantly lower than those of the control group, and the decrease amplitudes are 20.60-44.01% and 2.6-17.09% respectively, and the decrease of amorphous iron combined arsenic is inhibited, so the availability of arsenic is significantly inhibited.

[0117] In summary, the introduction of the slow-release manganese-based microspheres with oxidation and the continuous treatment measures can effectively regulate the soil iron components and significantly reduce the availability of arsenic in the soil. Among them, the slow-release manganese-based microspheres are mechanically mixed, which is simple to operate, economical in cost, and can be widely promoted and replicated. Combined with the continuous treatment measures, a new regulation mechanism is provided for farmland pollution control, and a new way is provided for the prevention and control of arsenic contaminated soil and agricultural products heavy metals.

[0118] The other parts not specifically described are prior art. Although the above examples make a detailed description of the present application, it is only a part of the examples of the present application, not all examples, and other examples can be obtained under the premise of no creativity according to the present examples, which all belong to the protection scope of the present application.

Claims

1. Hydroxypropyl starch-chitosan complex-coated manganese-based microspheres, characterized in that: The manganese-based microspheres comprise an inner core, and the surface of the inner core is sequentially coated with a chitosan layer and a hydroxypropyl starch layer from inside to outside; The inner core is prepared from nano-manganese dioxide and potassium permanganate, and the mass ratio of the nano-manganese dioxide to the potassium permanganate is 1:0.1-2; The raw materials of the chitosan layer are chitosan, an acetic acid solution, citric acid and a sodium tripolyphosphate solution, and the mass ratio of the chitosan, the inner core and the citric acid is 1:0.3-1:0.01-0.02, and the mass-volume ratio of the inner core to the sodium tripolyphosphate solution is 1:5-20 mg / mL; and the mass-volume ratio of the chitosan to the acetic acid solution is 0.01-0.02:1 mg / mL. The raw materials of the hydroxypropyl starch layer are a hydroxypropyl starch solution and a calcium chloride solution, and the mass ratio of the inner core to the hydroxypropyl starch in the hydroxypropyl starch solution is 1:9-50, and the volume ratio of the hydroxypropyl starch solution to the calcium chloride solution is 1:0.2-0.

5.

2. The manganese-based microspheres of claim 1, wherein: The particle size of the manganese-based microspheres is 150-300 μm. The mass ratio of the nano-manganese dioxide to the potassium permanganate is 1:

1. The mass ratio of the chitosan, the inner core and the citric acid is 1:0.5:0.015, the mass-volume ratio of the inner core to the sodium tripolyphosphate solution is 1:15 mg / mL, and the mass-volume ratio of the chitosan to the acetic acid solution is 0.015:1 mg / mL. The mass ratio of the inner core to the hydroxypropyl starch in the hydroxypropyl starch solution is 1:15, and the volume ratio of the hydroxypropyl starch solution to the calcium chloride solution is 1:0.

3.

3. The manganese-based microspheres of claim 1, wherein: The concentration of the acetic acid solution is 1-2%, the concentration of the sodium tripolyphosphate solution is 0.5-5%, the concentration of the hydroxypropyl starch solution is 3-8%, and the concentration of the calcium chloride solution is 2-8%.

4. The manganese-based microspheres of claim 3, wherein: The concentration of the acetic acid solution is 1%, the concentration of the sodium tripolyphosphate solution is 2%, the concentration of the hydroxypropyl starch solution is 5%, and the concentration of the calcium chloride solution is 6%.

5. A method of preparing the manganese-based microspheres of claim 1, characterized by: The method comprises the following steps: (1) The nano-manganese dioxide and the potassium permanganate are mixed according to the mass ratio, and the inner core is obtained after ball milling; (2) The chitosan and the citric acid are added to the acetic acid solution according to the mass-volume ratio of the chitosan to the acetic acid solution and the mass ratio of the chitosan, the inner core and the citric acid, and a chitosan solution is obtained; (3) The chitosan solution and the inner core are mixed, the sodium tripolyphosphate solution is added dropwise according to the mass-volume ratio of the inner core to the sodium tripolyphosphate solution, and a primary coated microsphere is obtained by centrifugation; (4) The primary coated microsphere is dispersed in the hydroxypropyl starch solution according to the mass ratio of the inner core to the hydroxypropyl starch in the hydroxypropyl starch solution, the calcium chloride solution is added dropwise according to the volume ratio of the hydroxypropyl starch solution to the calcium chloride solution, and a manganese-based microsphere coated with a hydroxypropyl starch-chitosan composite is obtained after drying and sieving.

6. The method of claim 5, wherein: In the step (2), the concentration of the acetic acid solution is 1-2%; In the step (3), the concentration of the sodium tripolyphosphate solution is 0.5-5%; In the step (4), the concentration of the hydroxypropyl starch solution is 3-8%, and the concentration of the calcium chloride solution is 2-8%.

7. Use of the manganese-based microspheres according to claim 1 for the remediation of heavy metal contaminated soils, characterized in that: The heavy metal contaminated soil is arsenic contaminated soil.

8. A method for regulating iron fraction in soil and reducing arsenic availability in soil using the manganese-based microspheres of claim 1, characterized in that: The method comprises the following steps: S1: taking the heavy metal contaminated soil to be repaired, adding water and the manganese-based microspheres of claim 1; S2: first anaerobic culture, on the 10th-11th day of anaerobic culture, adding peroxide to the heavy metal contaminated soil; S3: on the 20th-22nd day of anaerobic culture, starting to pass in air, passing in once every 3-5 days, culturing to 40-42 days, ending anaerobic culture; S4: finally, carrying out aerobic culture for 20-22 days, which can regulate iron components in the soil and reduce arsenic availability in the soil.

9. The method of claim 8, wherein: In the step S1, the basic physicochemical properties of the heavy metal contaminated soil are: pH = 6-7, total iron 18-20 g / kg, total manganese 130-140 mg / kg, and total arsenic 30-45 mg / kg; The mass-volume ratio of the heavy metal contaminated soil and water is 1:2-3 g / mL; The application amount of the manganese-based microspheres in the heavy metal contaminated soil is 1.93-19.3 g / kg, and after applying the manganese-based microspheres, the molar ratio of Mn and Fe in the heavy metal contaminated soil is 0.05-0.

5.

10. The method of claim 8, wherein: In the step S2, the mass ratio of the manganese-based microspheres and peroxide is 1:0.1-2; The peroxide is a composition of calcium peroxide and urea peroxide, wherein the mass ratio of calcium peroxide and urea peroxide is 1:0.5-2; In the step S3, when passing in air, the passing-in speed of air is 40-45 mL / min, and the intermittent passing-in mode is adopted, passing in for 30-32 minutes each time, stopping for 8-10 minutes, and continuing for 6 hours.

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