Method for passivating trivalent arsenic in farmland soil by using iron-sulfur minerals

Abstract

The invention discloses a method for passivating trivalent arsenic in farmland soil by using iron-sulfur minerals, and belongs to the technical field of soil pollution remediation. The method is applied to farmland soil, iron-sulfur minerals, hyposulfate and the like commonly existing in the soil are added, and the conversion and passivation mechanism of trivalent arsenic (As (III)) after the components are coupled is studied. The hyposulfate can generate a series of free radicals after being easily coupled and activated by metal minerals in a water body, the free radicals are main driving force for oxidizing As (III), the iron-sulfur minerals and the hyposulfate serve as electron donors in the reaction, and oxygen serves as an electron acceptor. Meanwhile, the efficiency of fixing pentavalent arsenic (As (V)) can be remarkably improved by a coupling substance generated after oxidation. Therefore, the invention provides a new thought for prevention and control of arsenic pollution of farmland soil, and shows a wide application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of soil pollution remediation, and in particular to a method for passivating trivalent arsenic in farmland soil by using iron-sulfur minerals. Background Art

[0002] Arsenic can enter the land and water environment through geological movement and human movement, and human movement makes the concentration of arsenic in the local environment significantly higher than the natural background value. Geological movement includes rock weathering and volcanic eruption; human movement mainly includes industrial and agricultural production, such as mining, metal smelting, arsenic-containing pesticides, insecticides, wood preservatives, etc. Arsenic enters the soil and water through these pathways, causing arsenic pollution, which is particularly serious in mining areas. It has been reported that the average arsenic content in groundwater is about 1~2mg / L, but in areas containing sulfide deposits, the average arsenic content in groundwater can be as high as 3mg / L.

[0003] Since arsenic usually coexists with pyrite, the environmental chemical behavior of pyrite will also affect the migration and transformation of arsenic. Studies have shown that FeS will undergo oxidative dissolution, and the As(III) released under acidic and neutral conditions will also undergo a synergistic oxidation reaction with Fe(II) and adsorb on the surface of the newly generated iron oxide. When the concentration of As(III) increases, the synergistic oxidation of As(III) and Fe(II) can also occur under neutral and alkaline conditions, and finally arsenate precipitation is generated instead of iron hydroxide colloid. At the same time, when pyrite comes into contact with oxygen, a small amount of active oxygen species such as H2O2, ·OH, etc. will be produced. These active oxygen species can also oxidize As(III) in the system to As(V). Therefore, the development of a remediation technology based on pyrite and arsenic pollution has great environmental significance and application prospects. However, only a few domestic patents disclose the application of microorganisms or artificially added oxidants to repair arsenic pollution. For example, Chinese invention CN202410188116.6 discloses a detoxification and mineralization method for arsenic-contaminated neutralized slag; Chinese invention CN202410278456.8 discloses a method for reducing the risk of environmental arsenic pollution. Most of the above methods focus on the effects of microorganisms and artificially added oxidants on arsenic, and do not involve the contribution of low-sulfate salts coupled with iron-sulfur ores, which are ubiquitous in the environment and easily associated with arsenic, to arsenic conversion and passivation.

[0004] Therefore, there is an urgent need to develop a technology for remediating As pollution in farmland soil based on the coupling of iron-sulfur minerals / low-sulfate salts. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for passivating trivalent arsenic in farmland soil by using iron-sulfur minerals, which can effectively passivate trivalent arsenic in farmland soil and has good universality.

[0006] In order to solve the above technical problems, a technical solution adopted by the present invention is: to provide a method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals, and to passivate trivalent arsenic in farmland soil using iron-sulfur minerals and low-sulfate particle coupling components.

[0007] In a preferred embodiment of the present invention, the iron-sulfur minerals are pyrite and makinoite.

[0008] Furthermore, the content of the iron-sulfur mineral is 0.1-1 g / L.

[0009] In a preferred embodiment of the present invention, the low sulfate salt is sodium bisulfite or potassium bisulfite.

[0010] Furthermore, the content of the oligosulfate is 0.2-2 mM.

[0011] In a preferred embodiment of the present invention, the initial pH of the As(III) contaminated soil in farmland is controlled within the range of 6.0-8.0.

[0012] In a preferred embodiment of the present invention, the reaction temperature of the passivation treatment is 25 ± 2 °C.

[0013] In a preferred embodiment of the present invention, the As pollution concentration in the farmland soil is 0.5-10 ppm.

[0014] The present invention occurs in farmland soil, adds iron-sulfur minerals and oligosulfates commonly present in the soil, and studies the conversion passivation mechanism of trivalent arsenic (As(III)) after coupling of the above components. Oligosulfates are easily coupled and activated by metal minerals in water to generate a series of free radicals, which are the main driving force for the oxidation of As(III). Iron-sulfur minerals and oligosulfates act as electron donors in the reaction, and oxygen acts as an electron acceptor. At the same time, the coupling products produced after oxidation can significantly improve the efficiency of pentavalent arsenic (As(V)) fixation. Therefore, the present invention provides new ideas for the prevention and control of arsenic pollution in farmland soil and shows broad application prospects.

[0015] The beneficial effects of the present invention are: (1) The present invention is based on the oxidation and fixation of As(III) in farmland soil by iron-sulfur minerals. During the treatment process, it was found that when the pH was 6.0 and the ratio of the added concentration of pyrite and makinoite to the concentration of low-sulfate salt was 1:5, the system could quickly and effectively oxidize and remove As(III), and it was mainly fixed on the FeS surface in the form of As(V); (2) In the present invention, As(V) generated by oxidation of As(III) is co-precipitated with trivalent iron generated instantaneously in the solution, without the need to add additional adsorbents and curing agents; (3) The present invention is simple to operate, low in cost, and suitable for the passivation treatment of trivalent arsenic in farmland soil, and has good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 (a) is a schematic diagram of the effect of quenching agent on the oxidation of As(III) in the system; (b) FeS / SO3 2- EPR spectra of the system at different reaction times; Figure 2 (a) Schematic diagram of As(III) oxidation under different initial pH conditions; (b) As(III) oxidation at an initial pH of 10; (c) The form of sulfite at different pH values; (d) Removal of total As in solution under different initial pH conditions; Figure 3 (a) Schematic diagram of the effect of different FeS concentrations on the oxidation removal of As(III); (b) Schematic diagram of the effect of different sulfite concentrations on the oxidation removal of As(III); (c) pH change curve of different sulfite and FeS coupling systems. DETAILED DESCRIPTION

[0017] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0018] The embodiments of the present invention include: Embodiment 1: The present invention provides a method for passivating trivalent arsenic in farmland soil by using iron-sulfur minerals, the method comprising: taking an appropriate amount of farmland As(III) contaminated soil (0.5-10 ppm), controlling the initial pH in the range of 6.0-8.0, adding iron-sulfur minerals and low-sulfate particles to start the reaction. The reaction system is placed in a dark environment and vigorously stirred with a magnetic stirrer, and the reaction temperature is (25±2)°C. 1 mL of the suspension is taken out at a specific reaction time and mixed with 1 mL of methanol to quench the reaction. The reaction solution uses sodium hydroxide as a pH regulator. The quenched sample is filtered with a 0.22 μm PTFE filter membrane for determining the arsenic concentration in the aqueous solution.

[0019] Embodiment 2: In order to study the contribution of each free radical in the system to the oxidation of As(III), a free radical quenching experiment was performed with an initial pH of 6.0. · OH has a good quenching effect, up to 99.75%, on SO4 ·- The quenching effect of SO4 is only 55.13%, so the system with TBA can show that SO4 ·-contribution of 50 mmol / L ethanol (EtOH) to SO4 ·- and · The quenching effect of OH is very good, all above 95%, which can be reflected in the system containing TBA. · The contribution of OH to As(III) oxidation; due to SO5 ·- The reaction rate constants of the reaction with TBA and EtOH are small, and the system with EtOH can also indirectly reflect the SO5 ·- The contribution to As(III) oxidation is shown in Figure 1 (a) is shown. In addition, EPR analysis revealed that the sulfite radical signal in the system increased significantly with the extension of reaction time, indicating that a large number of sulfite radicals were generated in the system, thereby accelerating the oxidation of As(III). Figure 1 (b) shown.

[0020] After adding 50 mmol / L TBA, · OH was effectively quenched, and the apparent rate constant of As(III) increased from 0.6731 min in the system without quencher to 0.6731 min in the system without quencher. -1 Reduced to 0.0453 min -1 , the rate has slowed down, · Quenching of OH or SO4 ·- However, it can still rapidly oxidize As(III) within 30 min of reaction, indicating that · OH contributes less to the oxidation of As(III). When 50 mmol / L EtOH is added, · OH and SO4 ·- All of them were effectively quenched, and As(III) was almost not oxidized and removed. The removal efficiency was only 6.6% after 30 min of reaction, indicating that SO4 ·- It plays a major role in As(III) oxidation. Because EtOH cannot effectively quench SO5 ·- From the results, we can get SO5 ·- The contribution to As(III) oxidation is minimal, and the reduction of As(III) is due to the removal of As(III) fixed on the surface of iron-sulfur minerals.

[0021] Embodiment 3: In order to explore the effect of the initial pH value of the reaction on the oxidation of As(III) by the system, experiments were conducted under different initial pH conditions (pH range 3-9), with the addition of 0.1 g / L of iron-sulfur minerals, the initial concentration of oligosulfate was 0.5 mmol / L, the initial concentration of As(III) was 500 μg / L, and the reaction time was 60 min. At the end of the reaction, only the pH values ​​of the systems with initial pH of 5.0 and 6.0 decreased, which was the generation of SO4·- H + The results of As(III) oxidation under different pH conditions are shown in Figure 2. Figure 2 a. As the initial pH value gradually increased to an alkaline environment, the apparent reaction rate increased significantly from 0.46 min -1 Increased to 3.17 min -1 , and when the pH of the reaction system was 9, As(III) was no longer detected after 3 min of reaction, indicating that the reaction proceeded rapidly at pH = 9, and As(III) was oxidized to As(V). In order to verify that the oxidation rate of As(III) increases with the increase of alkalinity, the system with an initial pH of 10.0 was investigated, and the reaction time was 5 min. The results are as follows Figure 2 As shown in Figure b, no significant oxidation removal of As(III) occurred in the first 5 min of the reaction, and only 7.9% of As(III) was oxidized. When the pH of the system dropped to about 3.0, oligosulfate began to escape in the form of SO2 (e.g. Figure 2 c), resulting in a decrease in the concentration of oligosulfate in the system, thereby reducing the oxidation rate of the system (when the initial pH was 3.0, the oxidation rate of As(III) was reduced to 0.22 min -1 ).

[0022] In order to further explore the effect of initial pH on the arsenic fixation of the system, the removal kinetics of total As in systems with different initial pH values ​​were determined. Figure 2 d. When the pH is between 4-6, the total As is basically completely fixed on the iron-sulfur mineral particles within 30 minutes of reaction, and is completely removed from the solution at 60 minutes of reaction; when the initial pH of the reaction is 3.0, only 41.8% of the total As is fixed and removed by FeS at 60 minutes of reaction, and when the initial pH of the reaction is 7.0, only 13.3% of the total As is fixed and removed by iron-sulfur minerals, and when the initial pH of the reaction is 9.0, only 13.2% of the total As is removed. The adsorption effect of the oxidation product As(V) on the FeS surface is poor, mainly through the reaction with FeS formed in the solution. 3+ co-precipitate is removed from solution, therefore, Fe 3+ The precipitation rate is the key control step. When the pH is around 4, Fe 3+ The precipitation begins, and an amorphous Fe(OH)3 precipitate is formed on the FeS surface. As the pH increases, the precipitation rate accelerates. When the pH increases to 7, the Fe(II) on the surface is oxidized to Fe(III) and precipitates rapidly, making it difficult to combine with As(V) to achieve the purpose of co-precipitation. When the pH in the system is 3, Fe 3+Precipitation has not yet begun, so the rate at which it is fixed on the surface of iron-sulfur minerals has been greatly slowed down.

[0023] Embodiment 4: In order to explore the effect of different iron-sulfur mineral contents on the oxidation of As(III) in the system, the system was designed with an initial pH of 6.0, iron-sulfur mineral contents of 0.05 g / L, 0.1 g / L, 0.2 g / L, 0.5 g / L and 1.0 g / L, low sulfate concentration of 0.5 mmol / L, and initial As(III) concentration of 500 μg / L. The oxidation results of As(III) are shown in Figure 2. Figure 3 The effect of FeS concentration on As(III) oxidation can be divided into two stages. In the first stage, the concentrations of FeS were 0.05, 0.1, and 0.2 g / L, respectively. In these systems, As(III) was completely removed within 30 min of reaction, and the apparent reaction rate constant increased with the increase of FeS concentration, from 0.29 min at 0.05 g / L FeS to 0.10 min at 0.25 g / L FeS. -1 0.69min when increased to 0.2 g / L FeS -1 , and reached the highest at 0.2 g / L iron-sulfur mineral. It is speculated that this result occurs because as the concentration of iron-sulfur minerals increases, more Fe(II) sites can be provided to combine with sulfite anions to produce more free radicals, and the active sites of S(-II) also increase, accelerating the Fe(II) / Fe(III) cycle. In the second stage, when the concentration of iron-sulfur minerals increased to 0.5 g / L and 1.0 g / L, the As(III) removal efficiency dropped sharply from 100% to 21.13% and 25.8% within 30 minutes, respectively. This phenomenon is because the concentration of iron-sulfur minerals is too high, and the reaction system can instantly produce a large amount of SO3 ·- , and these free radicals undergo mutual quenching reactions; this is also because as the concentration of iron-sulfur minerals increases, the dissolved Fe 2+ The concentration also increases through the SO4 ·- Reaction, quenching SO4 ·- , thereby reducing the concentration of free radicals that oxidize As(III), thereby reducing the oxidation removal efficiency of As(III).

[0024] In order to explore the effect of different oligosulfate concentrations on the oxidation of As(III) in the system, the system was designed with an initial pH of 6.0, oligosulfate concentrations of 0.1 mmol / L, 0.5 mmol / L, 1.0 mmol / L and 2.0 mmol / L, the dosage of iron-sulfur minerals was 0.1 g / L, the initial concentration of As(III) was 0.5 ppm, and the oxidation results of As(III) were as follows: Figure 3b. When the concentration of oligosulfate was 0.1 mmol / L, the As(III) removal efficiency was only 12.5% ​​after 30 min of reaction. However, when the concentration of oligosulfate increased to 0.5 and 1 mmol / L, the As(III) removal efficiency reached 100% within the first 10 min of reaction, indicating that SO4 ·- The yield increased and the oxidation rate of As(III) was improved. As the concentration of oligosulfate increased to 2 mmol / L, the oxidation rate of As(III) decreased, and the apparent rate constant increased from 0.47 min-1 to 0.53 min-2 in the 1 mmol / L system. 1 Reduced to 0.24 min -1 .

[0025] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0026] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals, characterized in that: The trivalent arsenic in farmland soil was passivated using a coupling component of iron-sulfur minerals and low-sulfate particles.

2. The method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals according to claim 1, characterized in that: The iron-sulfur minerals are pyrite and makinoite.

3. The method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals according to claim 2, characterized in that: The content of the iron-sulfur mineral is 0.1-1 g / L.

4. The method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals according to claim 1, characterized in that: The low sulfate salts are sodium bisulfite and potassium bisulfite.

5. The method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals according to claim 2, characterized in that: The content of the hyposulfate is 0.2-2 mM.

6. The method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals according to claim 1, characterized in that: The initial pH of As(III) contaminated soil in farmland was controlled in the range of 6.0-8.

0.

7. The method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals according to claim 1, characterized in that: The reaction temperature of the passivation treatment is 25 ± 2 ℃.

8. The method for passivating trivalent arsenic in farmland soil using iron-sulfur minerals according to claim 1, characterized in that: The As pollution concentration in the farmland soil is 0.5-10 ppm.

Images