Method for simultaneously removing trivalent arsenic and pentavalent arsenic in sewage by in-situ generation of nanoscale iron-manganese-sulfur composite colloid

Abstract

The application discloses a method for removing trivalent and pentavalent arsenic in sewage by in-situ generation of iron-manganese sulfide, and belongs to sewage treatment technology, and is characterized by comprising the following operation steps: (1) adding soluble divalent manganese salt, soluble ferrous salt, sulfur ions and phosphate into a reactor containing sewage containing trivalent arsenic and pentavalent arsenic, and mixing; (2) stirring the reaction system, producing nanometer iron-manganese sulfur composite colloid material, and promoting the produced nanometer iron-manganese sulfur composite colloid material to form a precipitate with trivalent arsenic and pentavalent arsenic ions; and (3) performing solid-liquid separation on the precipitate, and the supernatant is sewage from which arsenic elements are removed. The technology has the advantages of simple technological process, low cost, good arsenic removal effect and obvious advantages in practical application, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to sewage treatment technology, and in particular to a method for simultaneously removing trivalent arsenic and pentavalent arsenic in sewage by in-situ generation of nanoscale iron-manganese-sulfur composite glue. BACKGROUND

[0002] As a highly toxic heavy (similar) metal element, arsenic exists widely in the environment, with a content of about 5 mg / kg in the earth's crust. Industrial activities such as non-ferrous metal smelting, sulfuric acid production and mineral processing often discharge large amounts of strong acid wastewater containing high concentrations of arsenic, which not only poses a serious threat to water bodies and the surrounding ecological environment, but also can directly endanger human health. Arsenic and its compounds are recognized as carcinogens by the International Agency for Research on Cancer (IARC), and have the "three effects" of mutagenicity, teratogenicity and carcinogenicity. Among them, the toxicity of trivalent arsenic is 25 ~ 60 times that of pentavalent arsenic. The World Health Organization and the "Drinking Water Health Standards" of China have clearly stipulated that the arsenic content in drinking water shall not exceed 10 μg / L, therefore, efficient treatment of arsenic-containing wastewater is particularly important.

[0003] Currently, the common method for treating trivalent arsenic and pentavalent arsenic complex pollution in sewage is the oxidation-adsorption / precipitation two-step method. This method usually oxidizes trivalent arsenic to less toxic pentavalent arsenic by injecting oxidizing agents (such as hydrogen peroxide, ozone or chlorine), and then adds chemical precipitants (such as lime, manganese dioxide, iron sulfate, etc.) to make pentavalent arsenic form insoluble precipitates (such as iron arsenate, manganese arsenate or arsenic sulfide). Although this method can reduce the concentration of arsenic in water under certain conditions, it has multiple defects in practical application. First, the process requires frequent adjustment of acid-base conditions to meet the requirements of oxidation and precipitation reactions, resulting in long treatment period, large amount of chemical reagents, and thus significantly increasing the treatment cost. Second, the excessive use of oxidizing agents and precipitants may lead to secondary pollution risk, and even make the adsorbed / precipitated arsenic re-release. In addition, the oxidation and precipitation steps are carried out separately, making it difficult to achieve simultaneous removal of trivalent arsenic and pentavalent arsenic. These problems seriously restrict the popularization and application of the oxidation-adsorption / precipitation method in practical engineering.

[0004] Iron, manganese sulfides show good application potential in arsenic-containing wastewater remediation due to their green economy. Under anaerobic conditions, sulfur ions in sulfides can react with trivalent arsenic to generate arsenic sulfide precipitates, effectively reducing the concentration of trivalent arsenic, while iron sulfide (such as pyrite) and manganese sulfide can combine with pentavalent arsenic through adsorption and complexation, further reducing the mobility of pentavalent arsenic. Under aerobic conditions, iron, manganese sulfides produce hydrogen peroxide and hydroxyl radicals (ROS) through oxidation reaction, rapidly oxidizing trivalent arsenic to pentavalent arsenic, while the surface of iron, manganese oxides produced by oxidation of iron, manganese sulfides easily combines with pentavalent arsenic ions to form a strong complex, thereby reducing the concentration and mobility of arsenic in water.

[0005] However, the existing iron and manganese sulfide materials still have many limitations in the practical application of sewage remediation, and it is difficult to meet the demand of efficient treatment. First, the preparation cost of such materials is high. In order to improve the migration of the material in the sewage, it needs to be broken into micron / nano-sized small particles and mixed before being injected into the sewage, and there is a disadvantage of easy blockage during injection, so the application cost is high. However, this granulation treatment significantly increases the cost, and in the actual injection process, it is easy to block the sewage penetration channel, thereby affecting the treatment efficiency. In addition, the adaptability of these materials under different pH conditions is low, especially in the complex and variable sewage environment, the removal efficiency of arsenic pollution is often difficult to stabilize. SUMMARY

[0006] Based on the above needs or problems in the field, the present application provides a new method for removing trivalent arsenic and pentavalent arsenic in arsenic-containing sewage, especially a new method for in-situ generation of nano-state iron-manganese sulfur colloidal composite material for rapid and synchronous removal of trivalent arsenic and pentavalent arsenic in sewage. The method has a wide pH adaptation range, can synchronously and efficiently remove trivalent arsenic and pentavalent arsenic in sewage, has low cost and no secondary pollution. The method has strong adaptability to different arsenic pollution characteristics of sewage, has simple process flow, easy operation, low cost, high removal efficiency for trivalent arsenic and pentavalent arsenic composite pollution, stable effluent water quality, and obvious advantages in practical application. The specific scheme is as follows:

[0007] A method for in-situ generation of iron-manganese sulfur composite colloid for synchronous removal of trivalent arsenic and pentavalent arsenic in sewage, characterized in that it comprises the following operation steps:

[0008] (1) adding soluble divalent manganese salt, soluble ferrous salt, sulfur ion and phosphate into a reactor containing sewage to be treated containing trivalent arsenic and pentavalent arsenic and mixing;

[0009] (2) stirring the reaction system to generate nano-state iron-manganese sulfur composite colloid material, and promoting the generated iron-manganese sulfur composite colloid material to form a precipitate with trivalent arsenic and pentavalent arsenic ions;

[0010] (3) solid-liquid separation of the precipitate, and the supernatant is the sewage from which arsenic elements are removed;

[0011] The soluble divalent manganese salt is selected from manganese sulfate and / or manganese chloride; the soluble ferrous salt is selected from ferrous sulfate and / or ferrous chloride; and the sulfur ion is from sodium sulfide and / or potassium sulfide.

[0012] Preferably, the method is characterized in that when the molar ratio of trivalent arsenic to pentavalent arsenic in the sewage to be treated containing trivalent arsenic and pentavalent arsenic is less than 0.5, step (2) does not need to additionally introduce oxygen for stirring reaction for 20-60 minutes, so that the iron-manganese sulfur composite colloid removes arsenic through adsorption and precipitation.

[0013] Preferably, the method is characterized in that, when the molar ratio of trivalent arsenic to pentavalent arsenic in the wastewater containing trivalent arsenic and pentavalent arsenic to be treated is greater than or equal to 0.5, in step (2), the reaction system is aerated with an oxygen-containing gas under stirring to remove arsenic through oxidation, adsorption and precipitation by the iron-manganese-sulfur composite colloid. Preferably, the aeration time is 15-45 min, the oxygen-containing gas is air, and the aeration rate is 5-40 m 3 / h. 3 / h.

[0014] Preferably, the method is characterized in that the pH value of the wastewater containing trivalent arsenic and pentavalent arsenic to be treated is adjusted to be within the range of 3.0-7.5, and the concentration of arsenic is adjusted to be within the range of 0.1-60.0 mg / L.

[0015] Preferably, the method is characterized in that the phosphate is potassium dihydrogen phosphate, and the mass ratio of the potassium dihydrogen phosphate to the nano-state iron-manganese-sulfur composite colloid is 0.5%-1.5%.

[0016] Preferably, the method is characterized in that the soluble divalent manganese salt is manganese sulfate, the soluble ferrous salt is ferrous sulfate, and the sulfur ions come from sodium sulfide.

[0017] Preferably, the method is characterized in that the temperature in the reactor is 10℃-40℃.

[0018] Preferably, the method is characterized in that the molar ratio of the divalent manganese ions, ferrous ions and sulfur ions added into the reactor is 0.3-0.8:0.5-1.2:1.

[0019] Preferably, the method is characterized in that the ratio of the sum of the moles of the divalent manganese ions and ferrous ions added into the reactor to the sum of the moles of trivalent arsenic and pentavalent arsenic in the water is 0.6-3.5.

[0020] The present application has at least the following beneficial technical effects:

[0021] The invention directly injects divalent manganese ions, ferrous ions and sulfur ions into the contaminated water body, so that they combine in real time in the reaction system to generate nanoscale iron-manganese-sulfur composite colloids. This process can simultaneously complete the formation of colloids and the removal of arsenic pollutants, avoiding the passivation problem of surface active sites that may occur in pre-prepared colloids, while ensuring uniform distribution and high adsorption of colloids in the water body. Compared with the conventional ex situ preparation-dosing method, the in situ generation technology of the invention can achieve efficient arsenic removal without excessive addition of reagents, thereby reducing treatment cost and improving arsenic removal efficiency. Under anaerobic conditions, the in situ generated iron-manganese-sulfur composite colloids react with trivalent arsenic and pentavalent arsenic through adsorption, complexation and precipitation to form stable arsenic precipitates, thereby reducing the arsenic concentration in the water body. Under aerobic conditions, the colloids can catalyze dissolved oxygen to generate hydrogen peroxide and hydroxyl radicals, oxidize trivalent arsenic to pentavalent arsenic, and further remove pentavalent arsenic through adsorption and precipitation, thereby exhibiting stable arsenic removal capacity under different environmental conditions. In addition, the technology is applicable to a wide pH range (acidic to neutral) without the need for additional adjustment of water body pH, and has significantly better adaptability than traditional methods.

[0022] Compared with commonly used composite metal oxide arsenic removal precipitants, the invention has obvious advantages in chemical mechanism, reaction efficiency and cost control. First, existing multi-component composite metal oxides usually exist in the form of particles with large particle size, and their reaction activity is much lower than that of nanoscale iron-manganese-sulfur composite colloids. The manganese sulfide colloids used in the invention have higher specific surface area and more active sites, and can achieve efficient arsenic removal through multiple mechanisms such as interfacial oxidation, adsorption, surface complexation, chelation and sedimentation. Second, the reaction activity of manganese sulfide colloids is much higher than that of metal oxides, so the dosage of reagents is significantly reduced. In addition, the iron-manganese-sulfur composite colloids of the invention can exist stably in acidic, neutral and even weakly alkaline environments and maintain high arsenic removal capacity, while traditional metal oxide materials usually work best under specific pH conditions, with limited application range. At the same time, iron-manganese-sulfide can effectively remove arsenic pollutants under aerobic and anaerobic conditions, overcoming the defect of unstable arsenic removal efficiency caused by fluctuation of dissolved oxygen concentration in traditional technology.

[0023] The process of the invention is simple, and the colloids are generated in situ in the contaminated water body by liquid precursors, avoiding the loss of active sites during the storage and transportation of pre-prepared materials, and without the need for additional addition of oxidizing agents or precipitants, reducing the secondary pollution risk caused by excess reagents. Compared with traditional methods, the invention breaks through the limitations of ex situ dosing technology and has obvious advantages in efficient arsenic removal, wide adaptability and low cost operation, providing an efficient, economical and environmentally friendly solution for arsenic pollution control of sewage and industrial wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1is the scanning electron microscope image of the iron-manganese-sulfur composite colloidal material in the application;

[0025] Figure 2 is the EPR qualitative analysis result of in-situ generated iron-manganese-sulfur composite colloidal activated oxygen generating hydroxyl radicals in the application.

[0026] Figure 3 is the amount of hydroxyl radicals generated by the iron-manganese-sulfur composite colloidal material under different pH conditions in the application.

[0027] Figure 4 is the removal effect diagram of different valence arsenic by the iron-manganese-sulfur composite colloidal material under anoxic conditions in the application.

[0028] Figure 5 is the removal effect diagram of different valence arsenic by the iron-manganese-sulfur composite colloidal material under aerobic conditions in the application.

[0029] Figure 6 is the pH change trend of the solution in the process of removing arsenic by the iron-manganese-sulfur composite colloidal material under different conditions in the application. DETAILED DESCRIPTION

[0030] The technical solutions of the application are described in detail below by means of specific embodiments in combination with the drawings, which are more helpful for the public to understand the application.

[0031] Example 1. Preparation of nano-state iron-manganese-sulfur composite colloidal material and its application steps

[0032] A soluble divalent manganese salt, a soluble ferrous salt, a sulfur ion and a phosphate are added to a reactor containing wastewater containing trivalent arsenic and pentavalent arsenic, and a nano-state iron-manganese-sulfur composite colloidal material is generated by stirring in the reactor, and the generated iron-manganese-sulfur composite colloidal material forms a precipitate with trivalent arsenic and pentavalent arsenic ions; after solid-liquid separation of the precipitate, the supernatant is wastewater from which arsenic elements are removed.

[0033] Among them: the soluble divalent manganese salt is selected from manganese sulfate and / or manganese chloride; the soluble ferrous salt is selected from ferrous sulfate and / or ferrous chloride; the sulfur ion is from sodium sulfide and / or potassium sulfide.

[0034] The steps of in-situ generating nano-state iron-manganese-sulfur composite colloidal material for treating wastewater in the application are as follows:

[0035] Step 1. Introduce wastewater containing trivalent arsenic and pentavalent arsenic to be treated into a reactor and measure the molar concentration of trivalent arsenic and pentavalent arsenic therein;

[0036] Step 2. Add manganese sulfate, ferrous sulfate and sodium sulfide

[0037] The manganese sulfate, ferrous sulfate and sodium sulfide are added in a molar ratio of 0.3-0.8:0.5-1.2:1, preferably in a molar ratio of 0.3:0.7:1;

[0038] Meanwhile, the total molar amount of divalent manganese ions and ferrous ions is in a molar ratio of 0.6-3.5 to the total arsenic in water, preferably 1.0-2.5;

[0039] Step 3. The temperature in the reactor is controlled at 10-37°C, preferably 15-35°C, and is uniformly stirred to generate nanoscale iron-manganese-sulfide composite colloids in the wastewater to be treated; at the same time, phosphate is added to the reaction system to promote the dispersibility and stability of the colloidal particles.

[0040] By precisely controlling these addition conditions, the precursor ions react in water to generate iron-manganese-sulfide composite colloids with good stability and adsorption performance, thereby efficiently removing trivalent arsenic and pentavalent arsenic in wastewater.

[0041] In this embodiment, the phosphate is selected as potassium dihydrogen phosphate, and is added to the reactor in an amount of 0.5%-1.5% of the total mass of the soluble divalent manganese salt, the soluble ferrous salt and the sulfur ions. The anions in the phosphate are adsorbed on the surface of the iron-manganese-sulfide composite colloidal particles through electrostatic attraction, increasing the surface charge between the particles, thereby effectively reducing the van der Waals attraction between the particles and inhibiting the aggregation and sedimentation of the particles. In addition, the addition of phosphate can also form a stable chemical protective layer on the surface of the colloids, improving the dispersibility of the colloids and the contact area with arsenic ions in water. This modification significantly enhances the adsorption efficiency of the iron-manganese-sulfide composite colloids, providing a strong guarantee for the subsequent removal of trivalent arsenic and pentavalent arsenic in water through adsorption, complexation and precipitation. At the same time, the improvement of colloidal dispersion also reduces the local concentration difference, improving the uniformity and treatment efficiency of the reaction system.

[0042] The reactor is used to generate nanocolloidal iron-manganese sulfide in situ, and can be a reactor with a magnetic stirrer or a mechanical stirrer to ensure that the reaction process is sufficient and uniform, and to improve the generation efficiency and dispersion effect of the colloidal material. Users can choose different types of stirring equipment according to actual needs, for example, a magnetic stirrer is suitable for small-scale reactions or fine control scenarios, while a mechanical stirrer is more suitable for large-scale treatment or complex system mixing requirements. It can be understood that if the construction environment allows, the user can also directly stir in the current natural environment without the need to introduce an additional reactor.

[0043] In step 2, when the molar ratio of trivalent arsenic to pentavalent arsenic in the sewage to be treated is less than or equal to 0.5, the iron-manganese-sulfur composite colloid is stirred in an anoxic environment for 15 to 60 minutes to adsorb arsenic and form a precipitate, and after standing, solid-liquid separation is performed, and the pH of the supernatant is adjusted to 6.5 to 8.5 before being discharged, completing the sewage treatment.

[0044] In practical applications, since the sewage is in a closed environment, the anoxic environment refers to the completion of the arsenic removal reaction without additional stirring. However, in open reaction containers or laboratory conditions, in order to maintain an anoxic state, the water body should be as little as possible to be directly exposed to air. Generally, the reaction can be carried out in a sealed container with relatively low oxygen content to prevent the interference of oxygen on the oxidation reaction of trivalent arsenic.

[0045] When the molar ratio of trivalent arsenic to pentavalent arsenic in the sewage to be treated is greater than or equal to 0.5, oxygen-containing gas is introduced into the water body, and aeration is carried out under stirring conditions for at least 10 minutes, so that the iron-manganese-sulfur composite colloid removes arsenic through adsorption, complexation, oxidation and precipitation. After standing, solid-liquid separation is performed, and the pH of the supernatant is adjusted to 6.5 to 8.5 before being discharged, completing the sewage treatment.

[0046] Specifically, the oxygen-containing gas is air, and the aeration time is controlled to be 5 to 25 minutes, and the aeration rate per 1 cubic meter of sewage is 2 to 30 m³ / h.

[0047] The principle of the above process is that in the solution, ferrous ions, manganese ions and sulfur ions are quickly combined to form a precipitate through electrostatic attraction to generate positively charged iron-manganese sulfide colloid; this colloid can enhance the adsorption capacity of pentavalent arsenic anions.

[0048] The reaction chemical formula is:

[0049] Fe 2+ +S 2− → FeS (iron sulfide precipitate) ;

[0050] Mn 2 + +S 2− → MnS (manganese sulfide precipitate) ;

[0051] Under anoxic conditions, the generated iron-manganese sulfide colloid combines with trivalent arsenic and pentavalent arsenic in the water through adsorption and complexation to form a precipitate:

[0052] 2As 3 + +3S 2− → As2S3 (arsenic sulfide precipitate) ;

[0053] FeS / MnS + H2AsO4 − → adsorption complex;

[0054] Under aerobic conditions, iron sulfide and manganese sulfide react with oxygen to generate hydrogen peroxide and hydroxyl radicals and other active oxygen substances:

[0055] FeS + O2 + H2O → Fe 3 + + H2O2;

[0056] MnS + O2 + H2O → Mn 4 + + H2O2;

[0057] The generated active oxygen can rapidly oxidize trivalent arsenic to pentavalent arsenic:

[0058] As 3 + + H2O2 → H3AsO4;

[0059] At the same time, the oxidized iron (such as ferric ions) and manganese oxides on the surface have active sites, which combine with pentavalent arsenic to generate insoluble arsenic compounds (such as ferric arsenate or manganese arsenate):

[0060] Fe 3 + + H2AsO4 − → FeAsO4 (ferric arsenate precipitate);

[0061] Mn 4+ + H2AsO4 − → MnAsO4 (manganese arsenate precipitate);

[0062] In summary, the iron-manganese sulfide provided by the present application can simultaneously remove trivalent arsenic and pentavalent arsenic pollution in wastewater under anaerobic and aerobic conditions through coupling oxidation, adsorption and complexation, thereby significantly reducing the concentration and mobility of arsenic in water.

[0063] The performance of the nano-state iron-manganese sulfur composite colloid is researched, characterized and verified as follows

[0064] Experimental Example 1: Characterization of nano-state iron-manganese sulfur composite colloid

[0065] Preparation of nano-state iron-manganese sulfur composite colloid: Add divalent manganese ions, ferrous ions and sulfur ions to the wastewater reactor containing 20 mg / L trivalent arsenic and 20 mg / L pentavalent arsenic, wherein the molar ratio of the three is 0.3:0.7:1, add 0.7% potassium dihydrogen phosphate, and mix and stir for 5 min to quickly generate nano-state iron-manganese composite colloid.

[0066] Performance test:

[0067] The generated nano-state iron-manganese sulfur composite colloid is characterized by scanning electron microscopy (SEM), as shown in Figure 1As shown, the nano-sized iron-manganese-sulfur composite colloid exhibits a spherical structure with a relatively small surface area. The small particle size and nanoscale appearance, combined with a large specific surface area, indicate that this nano-sized iron-manganese-sulfur composite material possesses high reactivity. The random orientation of its surface defects increases the number of active sites for catalytic reactions, which is beneficial for the electron transfer processes of its structural iron, divalent manganese, and sulfur ions.

[0068] Experimental Example 2: Nanoscale iron-manganese-sulfur composite colloids activate oxygen to generate hydroxyl radicals.

[0069] The catalytic reaction of nano-sized iron-manganese-sulfur composite colloids (obtained in Example 1) in wastewater was detected using electron paramagnetic resonance (EPR) technology. Figure 2 As shown in the EPR spectrum, under aerobic conditions, the active substance catalyzing the dissolved oxygen generation of the nano-iron-manganese-sulfur composite material produced a characteristic peak of 1:2:2:1 with DMPO, indicating that hydroxyl radicals were generated in the system.

[0070] Hydroxyl radicals are strong oxidants that can rapidly oxidize trivalent arsenic to pentavalent arsenic. Pentavalent arsenic is readily adsorbed by iron sulfide and manganese sulfide. Therefore, the generated hydroxyl radicals are beneficial for the simultaneous and rapid removal of trivalent and pentavalent arsenic compound pollutants in wastewater.

[0071] Experimental Example 3: Comparison of hydroxyl radical production under different pH conditions

[0072] According to the comparative application test of the present invention, the pH of the solution significantly affects the ability of nano-sized iron-manganese-sulfur composite colloids to activate oxygen and generate hydroxyl radicals.

[0073] like Figure 3 As shown, when the mass concentration of the iron-manganese-sulfur composite colloid (obtained in Experiment 1) was 1 g / L and the pH of the wastewater solution was 3.0, the production of hydroxyl radicals reached a peak of 350 μM, exhibiting extremely high oxidizing power.

[0074] As the solution pH increases, the production of hydroxyl radicals gradually decreases. For example, when the pH increases to 5.0, the production drops to 250 μM; at pH 7.0 (triangular labeling curve), the production of hydroxyl radicals remains at 171 μM, exhibiting strong oxidizing ability; however, at pH 8.0 (inverted triangular labeling curve), the production of hydroxyl radicals significantly decreases to 30 μM. Although it still possesses some oxidizing ability, the effect is significantly weakened. This directly leads to a decrease in the efficiency of oxidizing trivalent arsenic to pentavalent arsenic, which in turn affects the subsequent removal of pentavalent arsenic, thus weakening the overall arsenic removal effect.

[0075] Notably, the nanometer-state iron-manganese-sulfur composite colloid of the present application can efficiently activate oxygen to generate hydroxyl radicals under acidic to neutral conditions (pH 3.0-7.5), which plays an important role in rapidly oxidizing trivalent arsenic to pentavalent arsenic in wastewater. Especially under alkaline conditions (pH>7), although most iron sulfides and manganese oxides are difficult to react with dissolved oxygen to generate active oxygen species, the nanometer-state iron-manganese-sulfur composite material of the present application can still generate about 30 μM of hydroxyl radicals, which provides technical support for expanding the application range of the material in the treatment of alkaline arsenic-containing wastewater.

[0076] Experimental Example 4: Experimental results of nanometer-state iron-manganese-sulfur composite colloid removing different forms of arsenic under anoxic conditions

[0077] According to the application test of the present application, as shown in Figure 4 When the total mass concentration of the nanometer-state iron-manganese-sulfur composite colloid (obtained in Experimental Example 1) in the reactor is 1 g / L, the concentrations of trivalent arsenic and pentavalent arsenic in the solution are 20 mg / L respectively, and the pH value is 4.0, the nanometer-state iron-manganese-sulfur composite colloid in the reactor can quickly remove trivalent arsenic and pentavalent arsenic in the solution, and the total arsenic removal rate is close to 60% at 60 minutes, and the total arsenic removal rate is more than 90% at 2 hours. Under anoxic conditions, since no active oxygen (ROS) is produced in the system, the removal of arsenic mainly depends on chemical adsorption, precipitation and surface reaction.

[0078] The surface of the nanometer-state iron-manganese-sulfur composite colloid is rich in sulfur and metal ions, and these functional groups can combine with arsenic ions to form stable complexes, especially under anoxic conditions, which is more likely to form stable complexes. The surface of the colloid also has negatively charged active sites, which can adsorb positively charged trivalent arsenic ions through ion exchange mechanism. In addition, the colloid can also react with arsenic to generate insoluble iron arsenide or manganese arsenide precipitate, further reducing the concentration of arsenic in water.

[0079] In this process, the sulfide crystal structure of the colloid may be restructured to generate new reactive sites, further enhancing its adsorption capacity for arsenic.

[0080] In summary, under anoxic conditions, the nanometer-state iron-manganese-sulfur composite colloid forms complex interactions with trivalent arsenic and pentavalent arsenic through chemical adsorption, precipitation and crystal restructuring, etc., effectively achieving efficient removal of arsenic.

[0081] Experimental Example 5: Trend of nanometer-state iron-manganese-sulfur composite colloid removing different forms of arsenic under aerobic conditions

[0082] According to the application test of the present application, as shown in Figure 5As shown, when the mass concentration of the nano-sized iron-manganese-sulfur composite colloid (obtained in Experimental Example 1) in the reactor is 1 g / L, the concentrations of trivalent arsenic and pentavalent arsenic in the solution are 30 mg / L and 20 mg / L, respectively, and the pH value is 4.0, the total arsenic removal rate reaches 80% after 60 minutes of treatment and 95% after 120 minutes of treatment.

[0083] like Figure 5 As shown, under aeration conditions, the nano-sized iron-manganese-sulfur composite colloid removes pentavalent arsenic at a faster rate than trivalent arsenic under aeration conditions. This can be mainly attributed to the following reasons: Pentavalent arsenic, as arsenic with a higher oxidation state, has higher chemical reactivity and reacts more readily with the nano-sized iron-manganese-sulfur composite colloid than trivalent arsenic. Under aeration conditions, the redox properties of the reactants make the removal of pentavalent arsenic more effective. The precipitation rate of pentavalent arsenic with the nano-sized iron-manganese-sulfur composite colloid is faster than that of trivalent arsenic. In addition, under aeration conditions, iron oxides and manganese oxides are generated on the surface of the nano-sized iron-manganese-sulfur composite colloid, which helps to increase the contact with pentavalent arsenic and accelerate the reaction. Therefore, the faster reaction rate of pentavalent arsenic with manganese sulfide under aeration conditions compared to trivalent arsenic is mainly due to the reactivity of the oxidation state, precipitation formation, interfacial reaction kinetics, and the influence of environmental conditions.

[0084] Experimental Example 6: pH Changes During Arsenic Removal by Iron-Manganese-Sulfur Composite Colloid under Different Manganese / Iron Ratios

[0085] According to the comparative test of the present invention, the concentrations of trivalent arsenic and pentavalent arsenic in the solution were 20 mg / L, and the initial pH value was 6.

[0086] like Figure 6 As shown, under different manganese / iron ratios, the pH of the solution increased to varying degrees during the removal of trivalent arsenic by the iron-manganese-sulfur composite colloid. This phenomenon is closely related to the multiple chemical reaction mechanisms of iron-manganese sulfides in the removal of arsenic.

[0087] First, the iron-manganese sulfide reaction may remove acidic substances (such as free hydrogen ions) from the solution. These acidic substances are related to the ionic state of arsenic, and their removal leads to a decrease in the concentration of hydrogen ions in the solution, thereby increasing the pH value. Furthermore, when the sulfide reacts with an oxidizing agent (such as dissolved oxygen), it may generate volatile gases such as hydrogen gas or hydrogen sulfide, further reducing the concentration of acidic substances in the system and causing the pH to rise.

[0088] Secondly, the dissolution of iron and manganese sulfides may release iron and manganese ions. These cations combine with hydroxide ions in the water to form soluble metal hydroxides, thereby increasing the alkalinity of the solution. Under aerobic conditions, the precipitates formed by the oxidation of iron and manganese will further consume hydrogen ions, leading to an increase in pH.

[0089] In addition, in the process of removing arsenic, the iron-manganese sulfide may remove surface adsorbed substances (such as arsenic complexes). The release of these adsorbed substances may be accompanied by the generation of hydroxyl ions, further enhancing the alkalinity of the solution. At the same time, cation exchange reactions may occur on the surface of the iron-manganese sulfide, adsorbing hydrogen ions and releasing hydroxyl ions, also causing the solution to deviate towards alkalinity; the operator should pay attention to the change of the liquid pH value during water treatment, and complete discharge after qualification.

[0090] The above experimental results prove that the iron-manganese sulfide colloid provided by the present application can achieve rapid removal of trivalent arsenic and pentavalent arsenic under a wide range of pH conditions; whether under anaerobic or aerobic conditions, the iron-manganese sulfide colloid particles can achieve simultaneous removal of trivalent arsenic and pentavalent arsenic; the process flow is simple, the cost is low, the arsenic removal effect is good, the advantages are obvious in actual application, and it has a wide application prospect, providing experimental basis for arsenic-containing wastewater remediation practice.

Claims

1. A method for in-situ generation of nanoscale iron-manganese-sulfur composite colloid for simultaneous removal of trivalent arsenic and pentavalent arsenic from wastewater, characterized in that, The method comprises the following steps: (1) adding soluble divalent manganese salt, soluble ferrous salt, sulfur ions and phosphate into a reactor containing wastewater containing trivalent arsenic and pentavalent arsenic, and mixing; (2) stirring the reaction system to generate nanometer iron-manganese-sulfur composite colloidal material, and to form a precipitate of the nanometer iron-manganese-sulfur composite colloidal material and trivalent arsenic and pentavalent arsenic ions; (3) performing solid-liquid separation on the precipitate, and the supernatant is wastewater from which arsenic elements are removed; The soluble divalent manganese salt is selected from manganese sulfate and / or manganese chloride; The soluble ferrous salt is selected from ferrous sulfate and / or ferrous chloride; The sulfur ions are from sodium sulfide and / or potassium sulfide.

2. The method of claim 1, wherein, When the molar ratio of trivalent arsenic to pentavalent arsenic in the wastewater containing trivalent arsenic and pentavalent arsenic to be treated is less than 0.5, the stirring reaction in step (2) is performed for 20-60 minutes, and no additional oxygen is introduced, so that the iron-manganese-sulfur composite colloidal material removes arsenic through adsorption and precipitation.

3. The method of claim 1, wherein, When the molar ratio of trivalent arsenic to pentavalent arsenic in the wastewater containing trivalent arsenic and pentavalent arsenic to be treated is greater than or equal to 0.5, an oxygen-containing gas is introduced into the reaction system under stirring in step (2), so that the iron-manganese-sulfur composite colloidal material removes arsenic through oxidation, adsorption and precipitation.

4. The method of claim 1, wherein, The pH value of the wastewater containing trivalent arsenic and pentavalent arsenic to be treated is adjusted to be in the range of 3.0-7.5, and the concentration of arsenic elements is adjusted to be in the range of 0.1-60.0 mg / L.

5. The method of claim 1, wherein, The phosphate is potassium dihydrogen phosphate; The mass ratio of the potassium dihydrogen phosphate to the nanometer iron-manganese-sulfur composite colloidal material is 0.5%-1.5%.

6. The method of claim 1, wherein, The soluble divalent manganese salt is manganese sulfate, the soluble ferrous salt is ferrous sulfate, and the sulfur ions are from sodium sulfide.

7. The method of claim 1, wherein, The temperature in the reactor is 10-40℃.

8. The method according to any one of claims 1 to 7, characterized in that, The molar ratio of the divalent manganese ions, ferrous ions and sulfur ions added into the reactor is 0.3-0.8:0.5-1.2:

1.

9. The method according to any one of claims 1 to 7, characterized in that, The ratio of the sum of the molar amounts of the divalent manganese ions and ferrous ions added into the reactor to the sum of the molar amounts of trivalent arsenic and pentavalent arsenic in the water is 0.6-3.

5.

10. The method of claim 3, wherein, wherein the aeration time is 15 ~ 45 min, the oxygen-containing gas is air, and the aeration rate is 5 ~ 40 m 3 / h per 1 m 3 of the wastewater.

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