Method for synchronously removing trivalent arsenic and pentavalent arsenic in sewage through in-situ generation of nano-state iron-manganese-sulfur composite colloid

Abstract

The invention discloses a method for removing trivalent and pentavalent arsenic in sewage by generating iron and manganese sulfide in situ, which belongs to a 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 to be treated containing trivalent arsenic and pentavalent arsenic, and uniformly mixing; (2) stirring the reaction system to promote the production of the nano-state iron-manganese-sulfur composite colloid material and promote the generated nano-state iron-manganese-sulfur composite colloid material to form precipitates with trivalent arsenic and pentavalent arsenic ions; (3) carrying out solid-liquid separation on the precipitate, wherein supernate is sewage without arsenic element; the technology is simple in technological process, low in cost, good in arsenic removal effect and obvious in advantages in practical application, and has wide application prospects.

Description

Technical Field

[0001] The present application relates to sewage treatment technology, and in particular to a method for in-situ generation of nano-iron-manganese-sulfur composite colloid to simultaneously remove trivalent arsenic and pentavalent arsenic in sewage. Background Art

[0002] Arsenic, as a highly toxic heavy (class) metal element, is widely present in the environment, and its content in the earth's crust is about 5 mg / kg. Industrial activities such as non-ferrous metal smelting, sulfuric acid production and mineral processing often discharge a large amount of highly acidic wastewater containing high concentrations of arsenic. These wastewaters not only pose a serious threat to water bodies and the surrounding ecological environment, but may also directly endanger human health. Arsenic and its compounds are identified as carcinogens by the International Agency for Research on Cancer (IARC), with "trivalent effects" of mutagenicity, teratogenicity and carcinogenicity. Among them, the toxicity of trivalent arsenic is 25 to 60 times that of pentavalent arsenic. The World Health Organization and my country's "Standards for Drinking Water Hygiene" both clearly stipulate that the arsenic content in drinking water shall not exceed 10 μg / L. Therefore, it is particularly important to efficiently treat arsenic-containing wastewater.

[0003] At present, the common method for treating the combined pollution of trivalent arsenic and pentavalent arsenic in sewage is the two-step oxidation-adsorption / precipitation method. This method usually oxidizes trivalent arsenic to pentavalent arsenic with lower toxicity by injecting an oxidant (such as hydrogen peroxide, ozone or chlorine), and then adds a chemical precipitant (such as lime, manganese dioxide, iron sulfate, etc.) to form a difficult-to-dissolve precipitate (such as iron arsenate, manganese arsenate or arsenic sulfur). Although this method can reduce the arsenic concentration 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 a long treatment cycle and a large amount of chemical reagents, thereby significantly increasing the treatment cost. Secondly, the excessive use of oxidants and precipitants may lead to the risk of secondary pollution, and even re-release the adsorbed / precipitated arsenic. In addition, the oxidation and precipitation steps are carried out separately, making it difficult to achieve the simultaneous removal of trivalent arsenic and pentavalent arsenic. These problems seriously restrict the promotion and application of oxidation-adsorption / precipitation methods in practical engineering.

[0004] Iron and manganese sulfides show good application potential in the remediation of arsenic-containing wastewater due to their green economy. Under anaerobic conditions, the sulfur ions in sulfides can react with trivalent arsenic to form arsenic sulfide precipitates, effectively reducing the concentration of trivalent arsenic, while iron sulfides (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 and manganese sulfides produce hydrogen peroxide and hydroxyl radicals (ROS) through oxidation reactions, quickly oxidizing trivalent arsenic to pentavalent arsenic, and the surfaces of iron and manganese oxides produced by the oxidation of iron-manganese sulfides are very easy to combine with pentavalent arsenic ions to form a strong complex, thereby reducing the concentration and mobility of arsenic in water.

[0005] However, the practical application of existing iron and manganese sulfide materials in sewage remediation still has many limitations, and it is difficult to meet the needs of efficient treatment. First of all, the preparation cost of this type of material is relatively high. In order to improve the mobility of the material in sewage, it needs to be broken into micron-scale / nano-scale small particles and mixed before it can be injected into the sewage. In addition, there is the disadvantage of easy clogging during the injection process, so its application cost is relatively high; however, this granulation treatment significantly increases the cost, and it is easy to clog the sewage infiltration channel during the actual injection process, thereby affecting its treatment efficiency. In addition, these materials have low performance adaptability under different pH conditions, especially in complex and changeable sewage environments, and their efficiency in removing arsenic pollution is often difficult to stabilize. Summary of the invention

[0006] Based on the needs or existing problems in the above-mentioned fields, the present invention provides a new method for removing trivalent arsenic and pentavalent arsenic from arsenic-containing wastewater, particularly a new method for in-situ generation of nano-iron-manganese-sulfur colloidal composite materials to quickly and synchronously remove trivalent arsenic and pentavalent arsenic from wastewater. This method has a wide pH adaptability range, can simultaneously and efficiently remove trivalent arsenic and pentavalent arsenic from wastewater, has low cost and no secondary pollution. This method has strong adaptability to wastewater with different arsenic pollution characteristics, a simple process flow, convenient operation, low cost, high removal efficiency for trivalent arsenic and pentavalent arsenic composite pollution, stable effluent water quality, and obvious advantages in practical applications. The specific scheme is as follows:

[0007] A method for in-situ generation of iron-manganese-sulfur composite colloid to simultaneously remove trivalent arsenic and pentavalent arsenic in sewage, characterized by comprising the following steps:

[0008] (1) adding a soluble divalent manganese salt, a soluble ferrous salt, sulfide ions and phosphate into a reactor containing wastewater containing trivalent arsenic and pentavalent arsenic to be treated and mixing them uniformly;

[0009] (2) stirring the reaction system to promote the production of nano-iron-manganese-sulfur composite colloidal materials and to promote the formation of precipitation between the generated iron-manganese-sulfur composite colloidal materials and trivalent arsenic and pentavalent arsenic ions;

[0010] (3) separating the precipitate into solid and liquid, and the supernatant is the wastewater from which arsenic has been removed;

[0011] Wherein, 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 sulfide ion comes 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 wastewater containing trivalent arsenic and pentavalent arsenic to be treated is ≤0.5, in step (2), the reaction is stirred for 20 to 60 minutes without the need for additional oxygen introduction, so that the iron-manganese-sulfur composite colloid removes arsenic by 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 conditions, so that the iron-manganese-sulfur composite colloid removes arsenic through oxidation, adsorption and precipitation. Preferably, the aeration time is 15 to 45 minutes, and the oxygen-containing gas is air. The aeration time is 15 to 45 minutes. The ... 3 The corresponding aeration rate for arsenic-containing wastewater is 5 to 40 m 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 a range of 3.0 to 7.5, and the arsenic concentration is adjusted to a range of 0.1 to 60.0 mg / L.

[0015] Preferably, the method is characterized in that the phosphate is potassium dihydrogen phosphate; the mass ratio of the potassium dihydrogen phosphate to the nano-iron-manganese-sulfur composite colloid is 0.5% to 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 sulfide ions come from sodium sulfide.

[0017] Preferably, the method is characterized in that the temperature in the reactor is 10°C to 40°C.

[0018] Preferably, the method is characterized in that the molar ratio of divalent manganese ions, ferrous ions and sulfide ions added to 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 divalent manganese ions and ferrous ions added to the reactor to the sum of the moles of trivalent arsenic and pentavalent arsenic in the water is 0.6 to 3.5.

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

[0021] The present invention directly injects divalent manganese ions, ferrous ions and sulfide ions into the polluted water body, so that they are combined in real time in the reaction system to generate nano-scale iron-manganese-sulfur composite colloids. This process can simultaneously complete the formation of the colloid and the removal of arsenic pollutants, avoiding the problem of surface active site passivation that may occur in the prefabricated colloid, while ensuring the uniform distribution and efficient adsorption of the colloid in the water body. Compared with the conventional ex situ preparation-addition method, the in situ generation technology of the present invention can achieve efficient arsenic removal effect without excessive addition of reagents, thereby reducing processing costs and improving arsenic removal efficiency. Under anaerobic conditions, the in situ generated iron-manganese-sulfur composite colloid reacts with trivalent arsenic and pentavalent arsenic through adsorption, complexation and precipitation to form a stable arsenide precipitate, thereby reducing the arsenic concentration in the water body. Under aerobic conditions, the colloid 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 showing a stable arsenic removal ability under different environmental conditions. In addition, this technology is applicable to a wide pH range (acidic to neutral) without the need for additional adjustment of the water pH, and its adaptability is significantly better than traditional methods.

[0022] Compared with the commonly used composite metal oxide arsenic removal sedimentation agent, the present invention has obvious advantages in chemical mechanism, reaction efficiency and cost control. First, the existing multi-component composite metal oxides usually exist in the form of particles, with a large particle size and a reaction activity far lower than that of nano-iron manganese sulfur composite colloids. The manganese sulfide colloid used in the present invention has a higher specific surface area and more abundant active sites, and can achieve efficient arsenic removal through various mechanisms such as interface oxidation, adsorption, surface complexation, chelation and sedimentation. Secondly, the reaction activity of manganese sulfide colloid is much higher than that of metal oxides, so the dosage of the agent is significantly reduced. In addition, the iron manganese sulfur composite colloid of the present invention can stably exist in acidic, neutral and even weakly alkaline environments, and maintain a high arsenic removal ability, while traditional metal oxide materials usually play the best role under specific pH conditions, and the scope of application is limited. At the same time, iron manganese sulfide can effectively remove arsenic pollutants under both aerobic and anoxic conditions, overcoming the defect of unstable arsenic removal efficiency caused by fluctuations in dissolved oxygen concentration in traditional technologies.

[0023] The process of the present invention is simple, and the colloid is directly generated in situ in the polluted water body through the liquid precursor, thereby avoiding the loss of active sites during the storage and transportation of the prefabricated materials, and no additional oxidant or precipitant is required, thereby reducing the risk of secondary pollution caused by excessive reagents. Compared with the traditional method, the present invention breaks through the limitations of the ex situ dosing technology, and shows significant advantages in terms of efficient arsenic removal, wide adaptability and low-cost operation, providing an efficient, economical and environmentally friendly solution for the treatment of arsenic pollution in sewage and industrial wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is a scanning electron microscope image of the iron-manganese-sulfur composite colloidal material of the present invention;

[0025] Figure 2 This is the EPR qualitative analysis result of the in-situ generation of iron-manganese-sulfur composite colloid to activate oxygen to generate hydroxyl radicals in the present invention.

[0026] Figure 3 It is the yield of hydroxyl radicals generated by the iron-manganese-sulfur composite colloid under different pH conditions.

[0027] Figure 4 This is a diagram showing the removal effect of iron-manganese-sulfur composite colloid on arsenic in different valence states under anoxic conditions in the present invention.

[0028] Figure 5 This is a diagram showing the removal effect of arsenic in different valence states by the iron-manganese-sulfur composite colloid under aerobic conditions in the present invention.

[0029] Figure 6 It is the pH change trend of the solution during the process of removing arsenic by the iron-manganese-sulfur composite colloid under different conditions in the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in detail below through specific implementation modes in combination with the accompanying drawings, which is more helpful for the public to understand the present invention.

[0031] Example 1. Preparation and application steps of nano-iron-manganese-sulfur composite colloid

[0032] Soluble divalent manganese salt, soluble ferrous salt, sulfide ions and phosphate are added to a reactor containing wastewater containing trivalent arsenic and pentavalent arsenic to be treated, and nanometer iron-manganese-sulfur composite colloid material is generated by stirring in the reactor. At the same time, the generated iron-manganese-sulfur composite colloid forms a precipitate with trivalent arsenic and pentavalent arsenic ions; after the precipitate is separated from the solid and liquid, the supernatant is the wastewater with the arsenic element removed.

[0033] Wherein: 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 sulfide ion comes from sodium sulfide and / or potassium sulfide.

[0034] The steps of in-situ generation of nano-iron-manganese-sulfur composite colloids for sewage treatment in the present invention are as follows:

[0035] Step 1. introducing wastewater containing trivalent arsenic and pentavalent arsenic to be treated into a reactor and measuring the molar concentrations of trivalent arsenic and pentavalent arsenic therein;

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

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

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

[0039] Step 3. Control the temperature in the reactor at 10°C to 37°C, preferably 15°C to 35°C, and stir evenly to react in the wastewater to be treated to generate nano-iron-manganese-sulfur composite colloid; at the same time, add phosphate to the reaction system to promote the dispersibility and stability of the colloid particles.

[0040] By precisely controlling these dosing conditions, the precursor ions react in water to generate iron-manganese-sulfur composite colloids with good stability and adsorption properties, 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% to 1.5% of the mass ratio of the total mass of soluble divalent manganese salt, soluble ferrous salt and sulfide ion to potassium dihydrogen phosphate. The anions in the phosphate are adsorbed on the particle surface of the iron-manganese-sulfur composite colloid through electrostatic action, 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 colloid, improving the dispersibility of the colloid and the contact area with arsenic ions in water. This modification significantly enhances the adsorption efficiency of the iron-manganese-sulfur composite colloid, and provides a strong guarantee for the subsequent removal of trivalent arsenic and pentavalent arsenic in water by adsorption, complexation and precipitation. At the same time, the improvement of colloid dispersion also reduces local concentration differences and improves the uniformity and treatment efficiency of the reaction system.

[0042] The reactor is used to generate nano-colloidal iron-manganese sulfide in situ, and can be a reactor containing a magnetic stirrer or a mechanical stirrer to ensure that the reaction process is sufficient and uniform, while improving 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 processing or mixing requirements of complex systems. It is understandable that if the construction environment permits, users can also stir directly 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 wastewater to be treated is less than or equal to 0.5, the reaction is stirred in an anaerobic environment for 15 to 60 minutes to allow the iron-manganese-sulfur composite colloid to adsorb arsenic to form a precipitate. After standing, solid-liquid separation is performed, and the pH of the supernatant is adjusted to 6.5 to 8.5 before being discharged to complete the wastewater treatment.

[0044] In practical applications, since the sewage is in a closed environment, anoxic environment means that the arsenic removal reaction is completed without additional stirring. In open-air reaction vessels or laboratory conditions, in order to maintain anoxic conditions, the water body should be avoided from being directly exposed to the air as much as possible. Usually, the reaction can be carried out in a closed container with relatively less oxygen to prevent oxygen from interfering with the trivalent arsenic oxidation reaction.

[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 aerated for at least 10 minutes under stirring conditions to allow the iron-manganese-sulfur composite colloid to remove arsenic through adsorption, complexation, oxidation and precipitation. After standing, solid-liquid separation is carried out, and the pH of the supernatant is adjusted to 6.5 to 8.5 before being discharged to complete the sewage treatment.

[0046] Specifically, the oxygen-containing gas is air, the aeration time is controlled at 5 to 25 minutes, and the aeration rate is 2 to 30 m3 per cubic meter of sewage. 3 / h.

[0047] The principle of the above process is: in the solution, ferrous ions, manganese ions and sulfur ions quickly combine through electrostatic attraction to form a precipitate, generating a 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 precipitation);

[0050] Mn 2+ +S 2- →MnS (manganese sulfide precipitation);

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

[0052] 2As 3+ +3S 2- →As 2 S 3 (Arsenic sulfide precipitation);

[0053] FeS / MnS+H 2 AsO 4- → Adsorption complex;

[0054] Under aerobic conditions, iron sulfide and manganese sulfide react with oxygen to produce reactive oxygen species such as hydrogen peroxide and hydroxyl radicals:

[0055] FeS+O 2 +H 2 O→Fe 3+ +H 2 O 2 ;

[0056] MnS+O 2 +H 2 O→Mn 4+ +H 2 O 2 ;

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

[0058] As 3+ +H 2 O 2 →H 3 AsO 4 ;

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

[0060] Fe 3+ +H 2 AsO 4- →FeAsO 4 (ferric arsenate precipitation);

[0061] Mn 4+ +H 2 AsO 4- →MnAsO 4 (Manganese arsenate precipitation);

[0062] In summary, the iron-manganese sulfide provided by the present invention can simultaneously remove trivalent arsenic and pentavalent arsenic pollution in sewage through coupled oxidation, adsorption and complexation under both anoxic and aerobic conditions, and significantly reduce the concentration and mobility of arsenic in water.

[0063] The following is a study, characterization and verification of the performance of nano-iron-manganese-sulfur composite colloids.

[0064] Experimental Example 1 Characterization of Nano-state Iron-Manganese-Sulfur Composite Colloid

[0065] Preparation of nano-iron-manganese-sulfur composite colloid: Add divalent manganese ions, ferrous ions and sulfur ions into a sewage 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, mix and stir for 5 minutes to quickly produce nano-iron-manganese composite colloid.

[0066] Performance Test:

[0067] The generated nano-iron-manganese-sulfur composite colloids were characterized by scanning electron microscopy (SEM). Figure 1 As shown in the figure, the nano-iron-manganese-sulfur composite colloid presents a spherical structure, and the surface is relatively small. The particle size is small, presents a nano state, and has a large specific surface area, indicating that the nano-iron-manganese-sulfur composite material has high reactivity. The random orientation combination of its surface defects increases the number of active sites for the catalytic reaction, which is beneficial to the electron transfer process of its structural ferrous iron, divalent manganese and sulfur ions.

[0068] Experimental Example 2 Nano-iron-manganese-sulfur composite colloid activates oxygen to produce hydroxyl radicals

[0069] The catalytic reaction of the nano-iron-manganese-sulfur composite colloid (obtained in Experimental Example 1) in sewage was detected by electron paramagnetic resonance (EPR) technology. Figure 2 As shown, the EPR spectrum shows that under aerobic conditions, the active substances generated by the nano-iron-manganese-sulfur composite material catalyzed the generation of dissolved oxygen and DMPO produced a characteristic peak of 1:2:2:1, indicating that hydroxyl radicals were generated in the system.

[0070] Hydroxyl radicals are a strong oxidant that can quickly oxidize trivalent arsenic to pentavalent arsenic. Pentavalent arsenic is easily adsorbed by iron sulfide and manganese sulfide. Therefore, the generated hydroxyl radicals are beneficial to the simultaneous and rapid removal of trivalent arsenic and pentavalent arsenic complex pollutants in wastewater.

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

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

[0073] like Figure 3 As shown, when the mass concentration of the iron-manganese-sulfur composite colloid (obtained in Experimental Example 1) is 1 g / L and the pH of the sewage solution is 3.0, the production of hydroxyl radicals reaches a peak value of 350 μM, showing extremely high oxidation ability.

[0074] As the pH of the solution increases, the production of hydroxyl radicals gradually decreases. For example, when the pH increases to 5.0, its production drops to 250 μM. At pH 7.0 (triangle marked curve), the production of hydroxyl radicals remains at 171 μM, showing strong oxidation ability. At pH 8.0 (inverted triangle marked curve), the production of hydroxyl radicals significantly decreases to 30 μM. Although it still has a certain oxidation ability, the effect is significantly weakened. This directly leads to a decrease in the efficiency of trivalent arsenic oxidation to pentavalent arsenic, which in turn affects the subsequent removal of pentavalent arsenic, and the overall arsenic removal effect is therefore weakened.

[0075] It is worth noting that the nano-iron-manganese-sulfur composite colloid of the present invention can efficiently activate oxygen to generate hydroxyl radicals under acidic to neutral conditions (pH3.0-7.5), which plays an important role in quickly oxidizing trivalent arsenic in sewage to pentavalent arsenic. 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 nano-iron-manganese-sulfur composite material of the present invention can still generate about 30μM hydroxyl radicals, providing technical support for expanding the application scope of the material in the treatment of alkaline arsenic-containing sewage.

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

[0077] According to the application test of the present invention, Figure 4 As shown, when the total mass concentration of the nano-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 nano-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% in 60 minutes, and the total arsenic removal rate exceeds 90% in 2 hours. Under anaerobic conditions, since no reactive oxygen species (ROS) are generated in the system, the removal of arsenic mainly depends on chemical adsorption, precipitation and surface reaction.

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

[0079] During this process, the colloidal sulfide crystal structure may be reconstructed to generate new reactive active sites, further enhancing its adsorption capacity for arsenic.

[0080] In summary, nano-iron-manganese-sulfur composite colloids form complex interactions with trivalent arsenic and pentavalent arsenic through multiple mechanisms such as chemical adsorption, precipitation and crystal reconstruction under anaerobic conditions, effectively achieving the efficient removal of arsenic.

[0081] Experimental Example 5 The trend of removing different forms of arsenic by nano-iron-manganese-sulfur composite colloid under aerobic conditions According to the application test of the present invention, Figure 5 As shown, when the mass concentration of the nano-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 the removal rate reaches 95% after 120 minutes of treatment.

[0082] like Figure 5 As shown in the figure, under aeration conditions, the rate at which nano-iron-manganese-sulfur composite colloid removes pentavalent arsenic is faster than trivalent arsenic under explosive oxygen conditions, which can be mainly attributed to the following reasons: pentavalent arsenic, as arsenic with a higher oxidation state, has a higher chemical reaction activity and is easier to react with nano-iron-manganese-sulfur composite colloid than trivalent arsenic. Under explosive oxygen conditions, the redox characteristics of the reactants make the removal of pentavalent arsenic more effective. The rate at which pentavalent arsenic precipitates with nano-iron-manganese-sulfur composite colloid is faster than that of trivalent arsenic. In addition, under aeration conditions, iron oxides and manganese oxides will be produced on the surface of nano-iron-manganese-sulfur composite colloids, which help to increase contact with pentavalent arsenic and accelerate the reaction. Therefore, the rate at which pentavalent arsenic reacts with manganese sulfide under explosive oxygen conditions is faster than that of trivalent arsenic, mainly due to the reactivity of the oxidation state, the formation of precipitation, the kinetics of interfacial reaction and the influence of environmental conditions.

[0083] Experimental Example 6 pH changes during arsenic removal by iron-manganese-sulfur composite colloid under different manganese / iron ratios

[0084] According to the comparative test of the present invention, the concentrations of trivalent arsenic and pentavalent arsenic in the solution are 20 mg / L respectively, and the initial pH value is 6.

[0085] like Figure 6 As shown in the figure, 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 various chemical reaction mechanisms of iron-manganese sulfide in removing arsenic.

[0086] First, iron-manganese sulfide may remove acidic substances (such as free hydrogen ions) in the solution during the reaction. These acidic substances are related to the ionic state of arsenic, and their removal will lead to a decrease in the concentration of hydrogen ions in the solution, thereby increasing the pH value. In addition, when sulfide reacts with oxidants (such as dissolved oxygen), volatile gases such as hydrogen or hydrogen sulfide may be generated, further reducing the concentration of acidic substances in the system, leading to an increase in pH.

[0087] Secondly, the dissolution of iron-manganese sulfide may release iron and manganese ions, which combine with hydroxide ions in water to form soluble metal hydroxides, thereby increasing the alkalinity of the solution. Under aerobic conditions, the precipitation generated by the oxidation reaction of iron and manganese will further consume hydrogen ions, leading to an increase in pH.

[0088] In addition, during the process of removing arsenic from iron-manganese sulfide, surface adsorbed substances (such as arsenic complexes) may be removed. The release of these adsorbed substances may be accompanied by the generation of hydroxide ions, further enhancing the alkalinity of the solution. At the same time, cation exchange reactions may occur on the surface of iron-manganese sulfide, adsorbing hydrogen ions and releasing hydroxide ions, which will also cause the solution to be alkaline; operators should always pay attention to changes in liquid pH when performing water treatment, and complete discharge after it is qualified.

[0089] The above experimental results prove that the iron-manganese sulfide colloid provided by the present invention can realize the rapid removal of trivalent arsenic and pentavalent arsenic under a wide range of pH conditions; the iron-manganese sulfide colloid particles can realize the simultaneous removal of trivalent arsenic and pentavalent arsenic under both anoxic and aerobic conditions; the process is simple, the cost is low, the arsenic removal effect is good, the advantages are obvious in practical applications, and the broad application prospects provide an experimental basis for the practice of arsenic-containing wastewater remediation.

Claims

1. A method for in-situ generation of nano-iron-manganese-sulfur composite colloids to simultaneously remove trivalent arsenic and pentavalent arsenic from wastewater, characterized in that: The steps include: (1) adding a soluble divalent manganese salt, a soluble ferrous salt, sulfide ions and phosphate into a reactor containing wastewater containing trivalent arsenic and pentavalent arsenic to be treated and mixing them uniformly; (2) stirring the reaction system to promote the production of nano-iron-manganese-sulfur composite colloidal materials, and promoting the formation of precipitation between the generated nano-iron-manganese-sulfur composite colloidal materials and trivalent arsenic and pentavalent arsenic ions; (3) separating the precipitate into solid and liquid, and the supernatant is the wastewater from which arsenic has been 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 sulfide ions are derived from sodium sulfide and / or potassium sulfide.

2. The method according to claim 1, characterized in that When the molar ratio of trivalent arsenic to pentavalent arsenic in the wastewater to be treated containing trivalent arsenic and pentavalent arsenic is ≤0.5, the reaction is stirred for 20 to 60 minutes in step (2) without the need for additional oxygen introduction, so that the iron-manganese-sulfur composite colloid removes arsenic by adsorption and precipitation.

3. The method according to claim 1, 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 oxygen-containing gas under stirring conditions, so that the iron-manganese-sulfur composite colloid removes arsenic through oxidation, adsorption and precipitation.

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

5. The method according to claim 1, characterized in that The phosphate is potassium dihydrogen phosphate; The mass ratio of the potassium dihydrogen phosphate to the nano-iron-manganese-sulfur composite colloid is 0.5% to 1.5%.

6. The method according to claim 1, characterized in that The soluble divalent manganese salt is manganese sulfate, the soluble ferrous salt is ferrous sulfate, and the sulfide ion comes from sodium sulfide.

7. The method according to claim 1, characterized in that The temperature in the reactor is 10°C to 40°C.

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

5.

10. The method according to claim 3, characterized in that: The aeration time is 15 to 45 minutes, and the oxygen-containing gas is air. 3 The corresponding aeration rate for arsenic-containing wastewater is 5 to 40 m 3 / h.

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