Method for passivating soil arsenic by using ferrous sulfide and sulfite conjugate

Abstract

The invention discloses a method for passivating soil arsenic by using a ferrous sulfide and sulfite conjugate, and belongs to the technical field of soil pollution remediation. The method is carried out in a heterogeneous system, a ubiquitous sulfur conversion intermediate product sulfite (SO32-) is taken as a research object, and a passivation mechanism of the sulfite to trivalent arsenic (As (III)) after the sulfite is coupled with ferrous sulfide is researched. The kinetic process of oxidizing and passivating As (III) under the coexistence of FeS and sulfite is analyzed, and after As (III) is oxidized into pentavalent arsenic (As (V)) in the process, the pentavalent arsenic (As (V)) is adsorbed and passivated on the surface of FeS, so that the removal of total arsenic in the soil is realized. As (V) mainly exists in a form of forming coprecipitation with Fe ions on the surface of FeS, the passivation long-term effect is relatively good, and the As (V) is not easily activated again. Therefore, a new thought is provided for research and development of farmland soil arsenic pollution control measures, and wide application prospects are shown.

Description

Technical Field

[0001] The invention relates to the technical field of soil pollution remediation, and in particular to a method for passivating soil arsenic by utilizing ferrous sulfide and sulfite coupling products. 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 As(III) concentration increases, the synergistic oxidation of As(III) and Fe(II) can also occur under neutral and alkaline conditions, and ultimately produce arsenate precipitates rather than iron hydroxide colloids. At the same time, a small amount of active oxygen species, such as H 2 O 2 , ·OH, etc. 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 neutralization slag; Chinese invention CN202410278456.8 discloses a method for reducing the risk of environmental arsenic pollution. Most of the above methods mainly focus on the effects of microorganisms and artificially added oxidants on arsenic, and do not involve the contribution of sulfites coupled with pyrite, which is ubiquitous in the environment and easily associated with arsenic, to the passivation of arsenic conversion.

[0004] Therefore, there is an urgent need to develop a technology for controlling As pollution in farmland soil based on the coupling of ferrous sulfide and sulfite. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for passivating soil arsenic based on ferrous sulfide and sulfite coupling, 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 soil arsenic using ferrous sulfide and sulfite coupling products, and to passivate soil trivalent arsenic by using the coupling process of sulfite and ferrous sulfide.

[0007] In a preferred embodiment of the present invention, the sulfite is sodium bisulfite or potassium bisulfite.

[0008] Furthermore, the content of the sulfite is 0.5-5 mM.

[0009] In a preferred embodiment of the present invention, the content of ferrous sulfide is 0.1-5 g / L.

[0010] In a preferred embodiment of the present invention, the initial pH of the soil is controlled within the range of 6.0-8.0.

[0011] In a preferred embodiment of the present invention, the As-contaminated soil to be treated is paddy field soil.

[0012] Furthermore, the soil As pollution concentration was 0.5-10 ppm.

[0013] In a preferred embodiment of the present invention, the reaction temperature of the passivation treatment is 25 ± 2 °C.

[0014] The principle of the present invention is as follows: iron ions and sulfite ions can couple to produce SO 4 ·- and · OH, thereby achieving rapid oxidation of trivalent arsenic. The specific reaction process is shown in formulas 1 to 10. First, the surface structural iron Fe(II) or the Fe dissolved in the solution 2+ Combines with sulfite to form >Fe(II)-SO 3 2- or FeHSO 3+ complex; then combined with oxygen, an oxidation reaction occurs to convert >Fe(II)-SO 3 2- and FeHSO 3+ The complexes are oxidized to >Fe(III)-SO 3 2- and FeSO 3+ complex, which subsequently decomposes into >Fe(II) and Fe 2+ with SO 3 ·- . SO 3 ·- It has a certain oxidizing property, and its redox potential E(SO 3 ·- / SO3 2- ) is 0.74 V at pH 5.2 and 0.63 V at pH 10, which can selectively oxidize some organic matter. The redox potential of As (As(III) / As(V)) is 0.17 V at pH 5.2 and -0.33 V at pH 10, both of which are lower than E(SO 3 ·- / SO 3 2- ), therefore, SO will occur 3 ·- Under aerobic conditions, SO 3 ·- It will further react with oxygen to form SO 5 ·- , and the reaction rate is relatively high. The generated SO 5 ·- With the remaining HSO 3- Reaction to generate SO 4 ·- and · OH, through formula (11)~(13), quickly oxidizes As(III) to As(V), and adsorption passivation of As(V) occurs.

[0015] The beneficial effects of the present invention are: (1) The present invention is based on the oxidation and passivation of As(III) by the iron-sulfur coupling system. During the treatment process, it was found that at a pH of 6.0, the FeS dosage concentration and the sulfite concentration (SO 3 2-) is 1:5, the system can quickly and effectively oxidize and remove As(III), and it is mainly passivated on the FeS surface in the form of As(V). Therefore, this method has a strong conversion and passivation ability for trivalent arsenic; (2) In the present invention, As(V) generated by oxidation of As(III) reacts with trivalent iron (Fe 3+ ) co-precipitation, no need to add additional adsorbent and curing agent; (3) The present invention is simple to operate, low in cost, and suitable for the prevention and control of trivalent arsenic pollution in soil, and has good universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The changes of arsenic concentration in different systems: (a) water-soluble As(III), (b) water-soluble total As; (c) changes of sulfite concentration; (d) concentration diagram of various forms of arsenic on the FeS surface; Figure 2 (a) Dissolved iron concentrations in different systems; (b) Oxidation diagram of As(III) by different concentrations of dissolved iron and goethite-activated sulfite; Figure 3 (a) As(V) adsorption on the FeS surface; (b) Zeta potential diagram of the FeS surface under different pH conditions. 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 soil arsenic by using ferrous sulfide and sulfite coupling products, the method comprising: taking an appropriate amount of As-contaminated paddy field soil, and controlling the initial pH within the range of 6.0±0.1. The system reaction contains a specific concentration of bisulfite and As(III). Ferrous sulfide particles are added to start the reaction, and the content of ferrous sulfide in the reaction system is 0.1 g / L. The reaction system is placed in a dark environment and vigorously stirred with a magnetic stirrer, and the reaction temperature is room temperature ((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 and used to determine the concentrations of arsenic, dissolved iron and sulfite in the soil solution.

[0019] Embodiment 2: The kinetics of FeS-coupled sulfite conversion of As(III) in aqueous solution was investigated at an initial pH of 6.0 and a reaction temperature of 25°C. The FeS dosage was 0.1 g / L and the sulfite concentration was 0.5 mmol / L. Figure 1 As shown. Single SO 3 2- In the As(III) system, there is no significant change in As(III) during the entire reaction process, indicating that in SO 3 2- Under the action of oxygen, As(III) cannot be directly oxidized. In the FeS system alone, the concentration of As(III) decreased by only 21.1% after 60 minutes of reaction, while the total As decreased by only 14.1%, indicating that FeS has a certain adsorption and oxidation effect on As(III). In this process, 7% of As(III) is converted into As(V) and then re-adsorbed and passivated on the FeS surface. The main reason is that FeS will also produce a small amount of hydroxyl radicals during the direct oxidation of oxygen, which can quickly degrade As(III) and oxidize it to As(V), and As(V) can be passivated on the FeS surface. In addition, direct electron transfer after As(III) contacts the FeS surface will also lead to the oxidation of As(III). For example, Fe-O-As complex will be formed on the FeS surface, and electron transfer between Fe and As will cause a small amount of As(III) to be oxidized to As(V), and then As(V) and As(III) will be partially adsorbed, which will eventually lead to a decrease in total As.

[0020] In FeS / SO 3 2- In the system, As(III) was completely removed within the first 10 min of reaction, and the total As in the system was completely removed within the first 30 min of reaction. 3 2- / N 2 After 60 min of reaction time, the concentrations of As(III) and total As decreased by only 27.4% and 13.3%, respectively, which further illustrates the important role of oxygen in this process. In order to further explore the form of As adsorbed and passivated on the FeS surface, 6 mol / L HCl was used to dissolve the arsenic adsorbed on the surface. The results are shown in Figure 2. Figure 1 As shown in (d). The ratios of As(III) and As(V) on the FeS surface are 9.3% and 90.7%, respectively, indicating that FeS can adsorb a small amount of As(III) and a large amount of As(V). 3 2- / N 2 The main reason for the decrease in As(III) concentration in the system is the adsorption of As(III) by FeS.

[0021] Embodiment 3: Firstly, the FeS system alone and the FeS / SO 3 2- The dissolved iron concentration in the system is as follows: Figure 2 As shown in (a), it can be found that only Fe dissolved in the FeS system 2+ The concentration increased rapidly in the first 10 min of the reaction, and then gradually decreased in the next 50 min; Fe 3+ No trace was detected in the first 30 min, and only a small amount was detected in the last 60 min. 3 2- In the system, Fe 2+ The concentration increased rapidly within the first minute of the reaction, then increased slowly and began to decrease gradually after 10 minutes of reaction. This phenomenon was mainly due to the 3 ·- With the participation of Fe 2+ The oxidation rate is greater than that of Fe 2+ This result indirectly illustrates the dissolution rate of FeS / SO 3 2- Fe in the system 2+ The oxidation rate of FeS alone is greater than that of Fe 2+ oxidation rate.

[0022] Figure 2 As shown in (b), after 60 min of reaction, 10 μmol / L Fe 2+ In the system, the removal rate of As(III) was only 14.1%. 2+ In the system, the removal rate of As(III) was 31.0%. 3+ In the system with 30 μmol / L Fe 3+ In the system with 0.1 g / L goethite, the As(III) removal rate reached 62.5%, and in the system with 0.1 g / L goethite, the As(III) removal rate was 27.4%. 3 2- The As(III) removal rate of the system was 100.0% after 60 min of reaction. The direct interaction between the iron ions dissolved by FeS and sulfite was not the driving force for As(III) oxidation. 3 2- The main factor for the system to activate sulfite to produce free radicals is the direct action of structural iron and sulfite.

[0023] Embodiment 4: In order to further explore the passivation mechanism of As(V) on the FeS surface, the adsorption process of As(V) on the FeS surface under different environmental conditions was studied. Figure 3 As shown in (a), it was found that only 6.1% of As(V) was adsorbed on the FeS surface after 30 min of reaction, which was significantly lower than that of FeS / SO 3 2- The system (100% removal of As(V) in 30 min) indicates that the passivation mechanism of As(V) on the FeS surface is not mainly adsorption passivation. The main reason is that in the absence of sulfite, iron ions are almost not dissolved and cannot coprecipitate with As(V). Another reason is that the different pH of the system leads to changes in the form of As(V), which causes differences in adsorption. It was also found by measuring the Zeta potential of the FeS surface that Figure 3 As shown in (b), when the pH is 6.0, the FeS surface is negatively charged, and under this pH condition, As(V) is in the form of H 2 AsO 4 - It exists in the form of and is easily affected by electrostatic repulsion and is not easy to be adsorbed. 2+ As(V) was adsorbed in the system, and 41.6% of As(V) was adsorbed at 60 min of reaction.

[0024] In As(V) / Fe 3+ and As(V) / SO 3 2- In the system, As(V) is rapidly adsorbed on the FeS surface and is completely adsorbed within the first 10 min. 3+ The adsorption rate of the system is higher than that of As(V) / SO 3 2- system, indicating that Fe 3+ In the formation of amorphous Fe(OH) 3 When in colloid form, it can coprecipitate with As(V) and passivate on the FeS surface. 2+ The slow rate of As(V) adsorption in the system is presumably due to the fact that coprecipitation needs to occur on the Fe 3+ Between As(V), Fe 2+ Oxidized to Fe 3+ The rate of As(V) adsorption determines the adsorption capacity. At pH 6.0, Fe 2+ Slowly oxidized to Fe 3+ , resulting in the slow precipitation removal of As(V); while in As(V) / SO 3 2- There is no Fe in the original system 3+ , mainly through the dissolution of Fe 2+inFeS / SO 3 2- The free radical SO generated in the system 4 ·- and · Rapidly oxidized to Fe 3+ , resulting in the adsorption rate of As(V) on FeS being slightly lower than that of As(V) / Fe 3+ system.

[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 soil arsenic using ferrous sulfide and sulfite coupling products, characterized in that: Utilizing the coupled process of sulfite and ferrous sulfide to passivate soil trivalent arsenic.

2. The method for passivating soil arsenic using ferrous sulfide and sulfite coupling according to claim 1, characterized in that: The sulfite is sodium bisulfite or potassium bisulfite.

3. The method for passivating soil arsenic using ferrous sulfide and sulfite coupling according to claim 2, characterized in that: The content of sulfite is 0.5-5 mM.

4. The method for passivating soil arsenic using ferrous sulfide and sulfite coupling according to claim 1, characterized in that: The content of ferrous sulfide is 0.1-5 g / L.

5. The method for passivating soil arsenic using ferrous sulfide and sulfite coupling according to claim 1, characterized in that: The initial pH of the soil is controlled within the range of 6.0-8.

0.

6. The method for passivating soil arsenic using ferrous sulfide and sulfite coupling according to claim 1 or 5, characterized in that: The As-contaminated soil treated was paddy field soil.

7. The method for passivating soil arsenic using ferrous sulfide and sulfite coupling according to claim 6, characterized in that: The concentration of As pollution in soil is 0.5-10 ppm.

8. The method for passivating soil arsenic using ferrous sulfide and sulfite coupling according to claim 1, characterized in that: The reaction temperature of the passivation treatment is 25 ± 2 ℃.

Images