WO2015109899A1

WO2015109899A1 - Method for quickly and effectively removing heavy metals in water body

Info

Publication number: WO2015109899A1
Application number: PCT/CN2014/093606
Authority: WO
Inventors: 郭学军
Original assignee: 北京师范大学
Priority date: 2014-01-21
Filing date: 2014-12-11
Publication date: 2015-07-30
Also published as: CN104276646A; CN104276646B

Abstract

A method for removing heavy metals in a water body, characterized in that the surface of zero-valent iron is oxidized and activated using the common oxidizing agents in water treatment such as hydrogen peroxide, sodium hypochlorite, potassium permanganate, etc., so as to continuously generate the active constituents of fresh iron (III) / (II) (hydro) oxide, etc., and the heavy metals including As, Hg, Cd, Pb, Cr, Se, Sb, Cu, Zn etc. in the water body are removed quickly and effectively by way of adsorption, precipitation, redox, etc.

Description

Method for quickly and efficiently removing heavy metals in water

Technical field

The invention belongs to the technical field of water treatment, in particular to activating a surface of a zero-valent iron by using a common oxidant for water treatment, and continuously producing fresh iron (III)/(II) (hydrogen) oxide by adsorption, precipitation, oxidation reduction, etc. A method for quickly and efficiently removing heavy metals from water.

Background technique

With the rapid development of the economy, China's water pollution has become more and more serious, especially heavy metal pollution, and the heavy metal pollution rate of river, lake and reservoir is as high as 81%. The results of the survey on the water environment of the seven major river systems in China show that in 2003, the pollution levels of heavy metals exceeding the standard sections of the Yellow River, Huaihe River, Songhua River and Liaohe River were all super-V. As pollution in China's water bodies is also very serious, including As pollution cases in more than 30 counties in Taiwan, Xinjiang, Inner Mongolia and Shanxi. Heavy metals are mostly non-essential elements of the human body. Excessive intake can cause various acute and chronic toxic effects on the human body, and can accumulate in the human body for a long time, thus posing a great threat to human health. The acute manifestation of heavy metal poisoning is vomiting, fatigue, coma and even death. Chronic symptoms are long-term low immunity, and various malignant tumors and chronic diseases occur frequently. Therefore, cost-effectively repairing water bodies contaminated by heavy metals and ensuring the safety of drinking water has always been the goal pursued in the field of water treatment.

Methods for removing heavy metals in water include coagulation sedimentation, electrolysis, ion exchange, membrane filtration, and adsorption. The coagulation sedimentation method adds lime, carbonate, iron-aluminum salt and the like to the water, and removes heavy metals in the water body by precipitation and adsorption. The coagulation sedimentation method is widely used and is a relatively mature process, but the treatment effect is affected by many factors. When the concentration of heavy metals is low, the removal effect is poor, and a large amount of sludge containing heavy metals is difficult to dispose, which is easy to cause twice. Pollution. Electrolytic technology consumes a large amount of energy and has a small amount of water treatment, which is not suitable for treating low-concentration heavy metal-containing water bodies. The ion exchange method utilizes an ion exchange agent to exchange heavy metals in a polluted water body, and exchanges heavy metals from the water body for the purpose of treatment. After ion exchange treatment, heavy metal ions in the water are transferred to the ion exchange resin, and after regeneration, they are transferred from the ion exchange resin to the regeneration waste liquid. This type of method has the characteristics of high removal rate and good selectivity. The disadvantages are high cost, limited application range, and high concentration of heavy metal wastewater when the resin is regenerated, which may cause secondary pollution due to poor management. In addition, the side containing heavy metal water treatment The method also has a membrane separation method such as reverse osmosis, but the above methods all have disadvantages such as high cost, high energy consumption, and difficulty in operation. The adsorption method is reliable, economical than the membrane method, and relatively small amount of sludge generated by the coagulation-filtration method, and has been widely used for the treatment and repair of heavy metal water bodies.

The adsorbents on which the adsorption method depends include metal oxides, activated carbons, natural adsorbents, etc., wherein iron oxides are widely used for adsorption removal of various heavy metals because of their excellent performance and low cost. A large number of studies have been reported on the adsorption and removal of As by various iron oxides such as goethite, hematite and amorphous ferric hydroxide. However, these oxides do not have a good pore structure and are difficult to apply to a fixed bed. A German patent improves the preparation process of traditional iron hydroxide particles (GEH). The traditional method is to add iron salt and alkali one by one. The improvement method is to add at the same time. The granules obtained by granulation are more GFH. It has better porosity than (GEH) and is widely used in fixed bed removal As process. However, GFH has low mechanical strength, is not resistant to abrasion, and is prone to agglomeration during filtration and blocks the column. Guo et al. (2005) used cotton cellulose spheres as a carrier to carry iron hydroxide on cotton cellulose spheres to prepare iron-loaded spherical cotton cellulose. The adsorption activity of iron on the carrier is good, the content is high, several times to ten times that of other related adsorbents, and the adsorption performance is good. Both the batch experiment and the column experiment show that the adsorbent has good As ability and good. Strength and wear resistance. However, the process of spheronization and iron loading of cotton fibers is complicated, which leads to an increase in the preparation cost of the adsorbent, which limits its large-scale application.

Zero-valent iron has low cost, wide source and environmental friendliness, and is very promising in water remediation applications. The mechanism by which zero-valent iron removes heavy metals can be roughly summarized as reduction, precipitation and adsorption. A large number of studies have confirmed that zero-valent iron can efficiently remove heavy metals such as Cd, Cr, Pb, As, Ni, and Zn from water and soil. Although zero-valent iron can efficiently remove various pollutants in water bodies at low cost, there are still some shortcomings and shortcomings. A significant problem faced by zero-valent iron technology is the surface passivation of zero-valent iron, and the resulting low surface activity, which is very slow to remove contaminants. The passivation of zero-valent iron is carried out as the reaction progresses. The iron surface gradually forms a dense layer of iron oxyhydroxide, which prevents the internal iron from coming into contact with external pollutants, thereby reducing the reactivity of iron and reducing the service life of iron.

A series of improved attempts have been made for the passivation problem, such as adding a magnetic field outside the reactor, preparing nano-zero-valent iron, forming a bimetallic system, and supporting nano-zero-valent iron. One of our previous inventions utilized a zero-valent iron/oxidant/zeolite synergistic system to effectively address the passivation of zero-valent iron and the use of this synergistic system to remove nitrate from water. The invention is commonly used by treating an appropriate amount of water An oxidizing agent, such as hydrogen peroxide, potassium permanganate, sodium hypochlorite, etc., oxidizes the passivation layer on the surface of the zero-valent iron, and the zero-valent iron electrons are efficiently transferred to the external nitrate electron acceptor to maintain high reducing activity. The nitrate is reduced to ammonia; the high selectivity of the zeolite to ammonia is utilized, and finally the nitrogen-containing contaminants are removed.

A reinforcement ZVI As recently disclosed other methods (CN103342410A), may be understood as a Fenton-like reaction principle, the principle and the synergistic agent is a persulfate catalyzed generation SO4 · ZVI ^- radical will As(III) in As-contaminated water is oxidized to As(V) which is easily removed by zero-valent iron. However, persulfate decomposition may produce secondary pollutants such as sulfur dioxide and sulfate ions. Sulfate ions compete with As for adsorption sites, which affects the removal effect of As. The use of persulfate is prone to safety problems, inherently toxic, environmentally friendly, and relatively expensive. Under strong acidic conditions, the hydrogen peroxide/zero-valent iron Fenton reaction utilizes the chain catalysis of Fe(II) to oxidatively degrade a variety of refractory organic wastewaters, which have been widely used for many years. A method for treating strong heavy metal complex wastewater (CN102351349A) is to first oxidize an organic ligand by using a hydrogen peroxide/zero-valent iron-like Fenton reaction (pH 2.4-2.6), and then adjust the pH to 9.5-11 by adding a base. The coagulated Fe in the system is coagulated and precipitated to remove the heavy metal in the organic complex state. Different from the technical principle, implementation method and treatment object of the previous "zero-valent iron/oxidant/zeolite synergistic system for removing nitrate", the present invention utilizes the oxidation activity of common water treatment oxidants such as hydrogen peroxide, sodium hypochlorite, potassium permanganate and the like. It activates zero-valent iron and continuously forms iron (hydrogen) oxide on the surface of zero-valent iron to remove heavy metals from water by precipitation, adsorption and reduction. The oxidant continuously oxidizes the internal Fe ⁰ layer of zero-valent iron, which can continuously produce fresh iron (hydrogen) oxide active components on the surface, and continuously and efficiently remove heavy metals such as As, Hg, Cd, Pb, Cr, Se, Sb, Cu, Zn, etc. can also remove phosphate, pathogenic microorganisms and organic pollutants in water. The present invention will provide a rapid, efficient and inexpensive method for water weight metal removal and repair.

Summary of the invention

The invention provides a method for removing water and body weight metal which is environmentally friendly, fast and efficient, low cost and practical. It is characterized in that the surface of the zero-valent iron is activated by using a common oxidant for water treatment, and the active component of iron (III) / (II) (hydrogen) oxide, that is, the oxide of divalent or trivalent iron, divalent or trivalent, is continuously produced. Iron hydroxide, which quickly and efficiently removes heavy metals from water by adsorption, precipitation, redox, etc. method.

The invention does not need to limit the pH of the system.

The zero-valent iron according to the present invention may be zero-valent iron powder, zero-valent iron particles or iron filings, and the type of zero-valent iron is not limited, and the size range of zero-valent iron is not limited.

In the present invention, the zero-valent iron is an iron source for generating iron oxides or iron hydroxides, and the zero-valent iron exhibits a remarkable reduction effect on heavy metals, especially high-valent heavy metals in the present invention, unlike the Fenton-like system. The action of iron as a catalyst and catalytic oxidant to generate free radical oxidation to remove contaminants.

The oxidizing agent used in the present invention is a common oxidizing agent for water treatment, such as potassium permanganate, hydrogen peroxide/sodium/potassium, ozone, chlorine, chlorine dioxide, hypochlorous acid, sodium hypochlorite/calcium, perchlorate, chlorate. (ClO ₃ ^- ), high iron (VI) acid salt.

The above oxidizing agents may be used singly or in combination of two or more.

In the present invention, the role of the oxidizing agent is to rapidly oxidize and etch zero-valent iron, and react with zero-valent iron to form iron oxide or iron hydroxide, which is significantly different from the effect of the oxidant in the Fenton-like system to provide free radicals. The iron oxide or hydroxide removes heavy metals by adsorption and precipitation, and the principle is significantly different from the zero-valent iron in the Fenton-like system as a catalyst, catalyzing hydrogen peroxide to generate hydroxyl radicals OH under acidic conditions, or catalyzing Persulfate produces the sulfate radical SO4 ^· -, the principle of the action of removing pollutants from water by oxidation. Therefore, in the present invention, the oxidizing agent may be selected from an oxidizing agent which generates a hydroxyl radical·OH, such as hydrogen peroxide/sodium/potassium, ozone, etc., and other commonly used oxidizing agents such as permanganate and ferrate may be used. A chlorine-based oxidizing agent such as hypochlorite, chlorate or perchlorate; and a preferred oxidizing agent of the present invention is sodium hypochlorite or potassium permanganate.

The oxidizing agent of the present invention activates the surface of the zero-valent iron, and the oxidizing agent may be added in advance, intermittently added or continuously added in the water treatment process (heavy metal removal), and the above activation modes may be combined in combination, or several combinations; the oxidizing agent may be added. The water to be purified can also be directly added to the zero-valent iron system. The order of addition of zero-valent iron, oxidant, and water to be purified is not limited. The concentration of the oxidizing agent in the reaction system ranges from 0.001 mM to 10 M; and the activation temperature ranges from -20 to 100 °C.

The oxidizing agent of the present invention activates the surface of the zero-valent iron, and adsorbs the heavy metal with the activated iron oxide or iron hydroxide, either simultaneously or in the same time period in the reactor, or in different The time period and the reactor are carried out independently. In most polluted waters containing heavy metals, other reducing substances may exist at the same time, especially reducing substances with higher chemical oxygen demand. Because these substances react with oxidants, they consume oxidants, resulting in zero-valent iron. Can not be fully activated. Because the nature of Fenton and Fenton-like reactions is that oxidants generate strong oxidative free radicals under the catalysis of iron, oxidatively removes pollutants, and the lifetime of free radicals in water is milliseconds and nanoseconds, so the process of generating free radicals It must be carried out in the same reactor at the same time as the removal of contaminants, and the consumption of oxidizing agents by reducing substances with high chemical oxygen demand in the water body cannot be avoided. In the solution provided by the present invention, the step of oxidizing the surface of the zero-valent iron by the oxidant and the step of adsorbing the heavy metal by the iron oxide or iron hydroxide formed after activation may be carried out simultaneously or separately; in some embodiments of the present invention The oxidizing agent can be used to activate the zero-valent iron, and then the activated iron oxide or iron hydroxide can be used to adsorb the heavy metal, thereby avoiding the negative effects caused by high chemical oxygen demand pollutants and ensuring the removal efficiency of heavy metals.

The invention solves the technical problems and can generally adopt two implementation modes: a batch processing method, a stable bed, a fluidized bed, a filter column or a filter wall method can be adopted. Other auxiliary media, adsorption or filtration media such as activated carbon, magnesia, bauxite, clay, montmorillonite, zeolite, kaolin, sand, ore, ceramsite may be incorporated into the system, but are not limited thereto.

The implementation of the batch processing method includes: an appropriate amount of zero-valent iron, an oxidizing agent, and a heavy metal-containing water body are stirred in a reaction vessel, and the reducing activity of the zero-valent iron and the generated iron (hydrogen) oxide are used to remove heavy metals in the water body. Subsequent solid-liquid separation can be carried out by gravity sedimentation, centrifugation, magnetic separation, etc. The suspension can be cleaned by sand filtration, granule filtration, membrane filtration, etc. The concentration of iron powder or iron particles in the batch process may range from 1 mg/L to 1000 g/L, the concentration of the oxidant in the reactor ranges from 0.001 mM to 10 M, and the temperature ranges from -20 to 100 ° C; the dosage mode, sequence, The mixing mode and the stirring rate are not limited; the remaining zero-valent iron and the iron (III)/(II) (hydrogen) oxide produced by oxidation can be used continuously for a plurality of times, and the lost iron can be added.

Specifically, the batch processing method may include the following steps: adding a zero-valent iron powder to a water body containing a heavy metal and an oxidizing agent, stirring, and fully reacting to obtain a suspension, and after separating the solid and liquid, the water body of the heavy metal is removed; The iron powder can continue to be mixed with the water to be purified and reused.

In the batch mode, oxygen or air can be supplied while stirring; oxygen or air can be combined with The oxidant works synergistically to oxidize the iron and save the amount of oxidant.

Examples of stable bed, fluidized bed, filter column or filter wall: a small amount of oxidant is used to mature (initialize) a test column and a filter bed containing zero-valent iron to pre-form a layer of iron (hydrogen) oxide on the surface of the iron particle, so that Each of the iron particles becomes a filter carrier having an iron (hydrogen) oxide supported on its surface. Then, the heavy metal-containing water body passes through the experimental column at a certain flow rate and residence time, and relies on the reduction activity of zero-valent iron and the precipitation and adsorption of iron (hydrogen) oxide to remove heavy metals in the water body. A small amount of oxidant may be added to the heavy metal containing water to ensure the continuous formation of the fresh adsorption layer of iron (hydrogen) oxide during the continuous removal of heavy metals. It is also possible not to adopt an initialization process, the oxidant activates zero-valent iron and zero-valent iron to remove heavy metals in the water at the same time, and the removal of heavy metals can be stable and efficient after running for a period of time. The concentration of the oxidant in the reaction system ranges from 0.001 mM to 10 M, and the temperature ranges from -20 to 100 ° C; the oxidizing agent can be added to the water to be purified, or can be directly added to the zero-valent iron bed system. The zero-valent iron bed system, that is, the zero-valent iron system, is a reaction system for generating an active component such as iron (III) / (II) (hydrogen) oxide on the surface of zero-valent iron by an oxidant.

Stabilized bed, fluidized bed, filter column or filter wall method, can add alkaline solution to stabilize ferrous iron, prevent ferrous iron leakage, or remove residual ferrous iron in water by subsequent oxidation, characterized in that alkali reagent includes sodium hydroxide and hydroxide Potassium, ammonia, calcium hydroxide, magnesium hydroxide, etc.; concentration range of 1 mM-10M; alkali solution can be added beforehand, intermittently added or continuously added in water treatment; subsequent oxidation to remove residual ferrous iron in water, oxidant is a common water treatment oxidant, Such as air, chlorine, chlorine dioxide, sodium hypochlorite / calcium, potassium permanganate, ozone, hydrogen peroxide. When the head loss is too large and the filter column is clogged, it can be backwashed with water or removed by column. It can replenish the zero-valent iron that consumes the loss and repack the column.

Specifically, the filter column treatment method may include the steps of: filling zero-valent iron particles into the filter column, introducing a solution containing an oxidant from the top of the filter column, activating zero-valent iron, and then introducing a water body containing heavy metals and an oxidant. The water body flowing out from the bottom end of the filter column is collected, that is, the water body of the heavy metal is removed.

The method for removing heavy metals in a water body provided by the invention can treat water bodies including sewage, industrial and agricultural wastewater, drinking water and ground water, and can remove heavy metals in the water body, including As, Hg, Cd, Pb, Cr, Se, Sb, Cu, Zn and the like.

During the removal process, most of the heavy metals are adsorbed onto the activated iron oxide or iron hydroxide, and removed by adsorption and precipitation; some As(V) is reduced to As(III), Se(VI) and other water-soluble. The large, high-valence heavy metal is partially reduced by zero-valent iron into a low-solution form such as Se(IV) with very low solubility, and is removed by precipitation.

The first feature of the present invention is that if a heavy metal water body is treated by a batch process, the zero-valent iron powder or iron particles can be used repeatedly, until the Fe ^{0 is} consumed, and the lost iron can be added. Subsequent solid-liquid separation is very easy. Zero-valent iron has high density and magnetic properties. It can be gravity sedimented, centrifuged, magnetically separated, etc. The supernatant containing a small amount of suspended solids can be passed through sand filtration, granule filtration, membrane filtration, etc. Get clean water. The exfoliated iron (III) / (II) (hydrogen) oxide will remain in the filter column and still have the ability to remove heavy metals. In our case, the batch method reacted extremely quickly, and it took only 10-30 minutes to remove heavy metals efficiently, and it could be reused many times.

The second feature of the present invention is that if the water-weight metal is removed by a fixed bed method, since the filter bed composed of the iron particles itself has the filtering ability, the precipitate and the exfoliate generated during the removal of the heavy metal are filtered by the filter bed itself. The cleanliness and chroma of the effluent are better. The invention is more commendable in that no significant head loss is found in the filter column, and no column plugging problem occurs; although there is a ferrous leakage phenomenon, it can be easily solved by the alkali solution stabilization treatment.

The third feature of the present invention is that the cost is low and the operation is simple. The filter column is activated by an oxidizing agent, and the surface of the iron particles is shaped like iron (hydrogen) oxide by using an oxidizing agent, so that each iron particle becomes a surface-loaded iron (hydrogen) oxide. The adsorption carrier of the material, when the heavy metal containing water flows through the filter column, relies on the reduction of iron, the precipitation of iron (hydrogen) oxide, and the adsorption to remove heavy metals in the water. The required chemicals are only zero-valent iron and water treatment common oxidants, the price is low, and the dosage of the oxidant is very low, so the method is extremely low in cost compared with the conventional adsorbent, and the treatment steps are simple.

The fourth characteristic of the present invention is that the iron loading rate of the adsorbent is much higher than that of the other adsorbents, because the main adsorbent active component in the present invention is an iron (hydrogen) oxide layer formed by oxidation of iron or iron powder. The core Fe ⁰ acts as a carrier, and as the outer iron (hydrogen) oxide layer continuously adsorbs heavy metals, it is penetrated, saturated, or peeled off by the water jet erosion, and the zero-valent iron exposed by the inner core is oxidized. A new iron (hydrogen) oxide layer is formed, which continuously supplies fresh iron (III) / (II) (hydrogen) oxide adsorption layer, so the iron loading rate is theoretically 100%, that is, the entire iron particle can be It is regarded as an adsorbent, so the penetration capacity is extremely large. At the same time, the iron particles themselves are carriers, and the adsorption medium and the filter medium composed of the iron core and the porous iron (III)/(II) (hydrogen) oxide adsorption layer produced by oxidation have good porosity and mechanical strength, and overcome one by one. The conventional adsorbent has the defects of poor porosity and low mechanical strength.

The method for removing heavy metals in water by the zero-valent iron/oxidant synergistic system of the invention can effectively solve the passivation problem faced by the current zero-valent iron removal heavy metal technology and the high cost, complicated operation, poor porosity and other adsorbents Low mechanical strength and other issues. The invention has the advantages of high removal rate of heavy metal, low cost, simple equipment demand, easy operation and low energy consumption, and can be applied to treatment of heavy metal-containing wastewater, drinking water and groundwater, and simultaneously removes pathogenic microorganisms and organic substances in the above water body. Contaminants.

The beneficial effects of the present invention are that the zero-valent iron used in the invention, that is, ordinary iron particles, iron sand, iron filings or iron powder, has no strict requirements on purity and particle size. Oxidants are oxidants commonly found in the field of water treatment, and are widely produced as industrial products at low cost. In the examples, we can use iron/sodium hypochlorite, iron/potassium permanganate, iron/hydrogen peroxide to form iron (hydrogen) oxide, which can be successfully used for the removal of heavy metals in water. The invention utilizes the oxidation activity of common oxidants, activates zero-valent iron, continuously forms iron (hydrogen) oxide on the surface of zero-valent iron, and removes heavy metals in the water by precipitation, adsorption, reduction and the like. The oxidant continuously oxidizes the internal Fe ⁰ layer of zero-valent iron, which can continuously produce fresh iron (hydrogen) oxide active components on the surface, and continuously and efficiently remove heavy metals such as As, Hg, Cd, Pb, Cr, Se, Sb, Cu, Zn, etc. can also simultaneously remove phosphates, pathogenic microorganisms, organic pollutants, etc. in water. The present invention provides a rapid, efficient and inexpensive method for water weight metal removal and repair. The implementation process is carried out at normal temperature, the reaction rate is fast, the pH value of the water body is not high, and no other equipment such as a magnetic field or a light source is required, and the invention has the advantages of low cost and simple operation. The method is novel, simple, environmentally friendly, extremely low cost and easy to implement, and has a good application prospect for the removal of heavy metals in water.

DRAWINGS

Figure 1 Column experiment of removing As(V) from zero-valent iron/H ₂ O ₂ ;

Fig. 2 Column experiment of simultaneous removal of As, Sb, Cd and Hg by zero-valent iron/NaClO;

Fig. 3 Column experiment of zero-valent iron/KMnO ₄ simultaneously removing As, Sb, Cd and Hg;

Figure 4 is a column experiment result of removing As(V) by zero-valent iron/H ₂ O ₂ under a treatment volume of 40000 BV;

Figure 5, under the condition of treatment volume 40,000 BV, zero-valent iron / NaClO simultaneously removes As, Sb, Column experimental results of Cd and Hg;

Figure 6. Column test results of simultaneous removal of As, Sb, Cd, and Hg by zero-valent iron/KMnO ₄ under a treatment volume of 20000 BV.

detailed description

Example 1: Zero-valent iron/H ₂ O ₂ filter column to remove As

The removal of As (V) was carried out in an 18 x 400 mm plexiglass column. 100 g of iron sand (particle size 1 mm) was filled in a glass column (the bottom of the column was filled with 1 cm glass wool), and then ₂₀₀ ml of 10 mM H ₂ O ₂ solution was quickly introduced from the top. This step was the initialization of the experiment, and then the introduction of As (V) was carried out. Raw water, the As-containing (V) solution in the experiment uses tap water as the raw water background, and the sodium arsenate is added to adjust the As(V) concentration to 200 μg/L, and hydrogen peroxide (H ₂ O ₂ ) is added to adjust to As ( V) The concentration of H ₂ O ₂ in water was 0.1 mM, and the influent water inflowed from the top of the adsorption column was about 7.5 empty bed volume (BV) / hour, and the empty bed contact time (HRT) was 8 min. A certain volume of effluent was taken at regular intervals to determine As (V), iron effluent concentration and effluent pH. As (V) removal and effluent pH values are shown in Figure 1.

According to the experiment, according to the World Health Organization and China's drinking water As standard 10μg / L, the experimental column did not appear As breakthrough after continuous removal of 3600 times empty bed volume of As (V) water, and the As concentration of effluent is basically Below 1μg/L, it is far superior to the national drinking water As standard. The pH of the effluent is stable within the range of 7.8 ± 0.2, which meets the requirements of the national drinking water for pH. With the extension of the column time, the problem of ferrous leakage occurred during the operation. The column was washed with 50 mM NaOH solution, and the iron leakage problem was effectively solved. The total effluent concentration of the effluent was less than 0.1 mg/L, which reached the national drinking iron standard. At the same time, the NaOH solution washes the column and causes the As (V) concentration and pH value of the effluent to rise temporarily, but it is still within the national drinking water sanitation standard and quickly returns to normal level. During the operation of the experimental column, the average removal rate of As(V) is higher than 99.9%. The effluent pH value and total iron concentration are in line with national drinking water standards. The whole process shows that the zero-valent iron/H ₂ O ₂ system has extremely high As. Removal capacity.

Further column experiments demonstrated that even though the treatment volume reached 40,000 BV, there was no penetration; the removal of Cd and Pb remained efficient and stable (Figure 4).

In this example, the zero-valent iron/H ₂ O ₂ filter column is always in a reducing environment, and X-ray absorption near-edge expanded structure (XANES) analysis indicates that 21.5% of the raw water As (V) is reduced to As (III).

Example 2: Zero-valent iron/NaClO filter column simultaneously removes As, Sb, Cd, Hg

Heavy metal (As, Sb, Cd, Hg) removal of heavy metal contaminated water in the experiment using tap water as the raw water background, respectively, adding sodium arsenate, potassium pyroantimonate, cadmium chloride, mercury chloride to a concentration of 200μg / L. The filling and initialization of the reaction column were the same as in Example 1. Then, a contaminated water body containing heavy metals was introduced, sodium hypochlorite (NaClO) was added to the liquid solution at a concentration of 0.5 mM, and the flow rate of water was the same as in Example 1. A certain volume of the effluent was taken at regular intervals to measure four heavy metals, iron concentration and pH. value. The removal of heavy metals and the pH of the effluent are shown in Figure 2. As and Hg maintain a very high removal rate, the removal rate reaches 99-100%. After the effluent volume reaches 3000BV, there is no sign of penetration; the removal effect of Cd is also Very good, only in the short-term stage after the alkali treatment stabilizes the ferrous iron, the hygienic standard is occasionally higher; the pollution of Sb in the water body is less common, and the removal effect of Sb is second, but it is maintained above 85%.

Further column experiments show that even if the treatment volume reaches 40,000 BV (the concentration of NaClO drops to 0.1 mM during 3000-40000 BV), arsenic still does not penetrate; the removal rate of Cd and Pb is 98-99%, and remains stable (Figure 5 Shown).

In this embodiment, the zero-valent iron/NaClO filter column is always in a reducing environment, and the X-ray absorption near-edge expansion structure (XANES) analysis indicates that 17.4% As (V) in the raw water is reduced to As (III).

Example 3: Zero-valent iron/KMnO ₄ filter column simultaneously removes As, Sb, Cd, Hg

The filling, initialization, raw water arrangement, and influent flow rate of the filter column were the same as in Example 2. The influent KMnO ₄ concentration was 0.5 mM. The heavy metal removal effect and the effluent pH value are shown in FIG. Similar to the zero-valent iron/H ₂ O ₂ , zero-valent iron/NaClO filtration system, As and Hg always maintain a very high removal rate of 99-100%, and there is no sign of penetration after the outflow volume reaches 1000 BV; The removal effect of Cd was also kept good, and the removal effect of Sb was second, and it was maintained at about 75%.

Further column experiments showed that even though the treatment volume reached 20000 BV (the concentration of KMnO ₄ decreased to 0.1 mM during 1000-20000 BV), arsenic did not penetrate; the removal of Cd and Pb remained stable (Figure 6).

In this embodiment, the zero-valent iron/KMnO ₄ filter column is always in a reducing environment, and the X-ray absorption near-edge expanded structure (XANES) analysis indicates that part of As (V) is reduced to As (III).

Example 4: Simultaneous removal of water bodies As, Sb, Cd, Hg using a zero-valent iron batch process alone

Removal of heavy metals (As, Sb, Cd, Hg) was carried out in a 250 ml three-necked flask. Come by Water is used for drinking water containing heavy metals. The initial concentrations of As, Sb, Cd and Hg are 1000, 200, 200, 200μg/L, 200ml per treatment, 1.0g iron powder is added, and the reaction is stirred for 30min. The stirring speed is 400rpm. The reaction temperature is room temperature (about 25 ° C). The amount of four heavy metals is determined by taking an appropriate amount of suspension every 10 minutes. After the reaction for 30 minutes, the suspension was poured off, but the residual iron powder was retained, and then 200 ml of new sewage was added, and the reaction was carried out for 30 minutes, and the zero-valent iron was repeatedly used three times. The heavy metal removal effect is shown in Table 1.

The results show that the use of zero-valent iron alone without oxidizing agent for the removal of four heavy metals such as As, Sb, Cd and Hg, but the removal effect is not ideal. After 30min, the concentration of heavy metal in effluent is still high, and the removal effect of As and Hg is slightly better, the removal rate is 75-80% and 56-70%, respectively, while the removal effect of Sb and Cd is poor, only 22-32% respectively. , 49-56%. It shows that the single use of zero-valent iron has low surface activity, which is not conducive to the removal of heavy metals in water.

Table 1: Removal of multiple batches of heavy metal containing water using zero-valent iron alone

Example 5: Zero-valent iron/NaClO batch process simultaneously removes water bodies As, Sb, Cd, Hg

The raw water containing heavy metal was the same as in Example 4. The NaClO concentration in the system was 0.5 mM, and the zero-valent iron was repeatedly used ten times. The poured suspension contains a small amount of ferrite, which can be cleaned by sand filtration or membrane filtration. The heavy metal removal effect is shown in Table 2.

The results show that compared with the use of zero-valent iron to remove heavy metals, NaClO is added to the system, and the removal of four heavy metals such as As, Sb, Cd and Hg by zero-valent iron is greatly improved, and As and Cd are removed very quickly, 10min. The inside is almost completely removed, Hg also reaches 100% removal rate within 30min, and the removal effect of Sb is relatively poor, 70-86%, but still much higher than the pure zero-valent iron system. With the increase of the number of uses, the removal effect of zero-valent iron on heavy metals remained stable, and there was no significant decrease, indicating that NaClO significantly increased the surface activity of zero-valent iron, inhibited zero-valent iron passivation, and ensured fresh iron ( III) / (II) Continuous formation of (hydrogen) oxides.

Table 2: Zero-valent iron/NaClO removal of multiple batches of heavy metal containing water results

Example 6: Zero-valent iron/KMnO ₄ batch process simultaneously removes water bodies As, Sb, Cd, Hg

The raw water containing heavy metal was the same as in Example 4. The concentration of KMnO _{4 in the} system is 0.5 mM, and the zero-valent iron is repeatedly used ten times. The suspended suspension contains a small amount of ferrite, and can be cleaned by sand filtration or membrane filtration. The heavy metal removal effect is shown in Table 3.

The results show that compared with the simple use of zero-valent iron to remove heavy metals, the removal effect of four heavy metals such as As, Sb, Cd and Hg is significantly improved by adding KMnO ₄ . Among them, As can be completely removed within 10min, Hg also reaches 100% removal within 30min, and the average removal rates of Sb and Cd are also more than 80%, which is much higher than the pure zero-valent iron system. With the increase of the number of uses, the removal effect of zero-valent iron on As, Sb and Hg is relatively stable, and there is no significant decrease, but the removal of Cd decreases slightly with the increase of reaction batch, which may be caused by partial loss of iron. . Similarly, KMnO ₄ significantly increases the rate and efficiency of zero-valent iron removal of heavy metals.

Table 3: Zero-valent iron/KMnO ₄ removal of multiple batches of heavy metal containing water results

Example 7

The raw water containing heavy metal was the same as in Example 4. The H ₂ O ₂ concentration in the system was 0.5 mM, and the zero-valent iron was repeatedly used ten times. The heavy metal removal effect is shown in Table 4.

With the addition of H ₂ O ₂ , the removal effect of zero-valent iron on As, Sb, Cd and Hg heavy metals was significantly improved. As was completely removed within 10 min, Hg was completely removed within 30 min, and Sb removal reached 86-90. %, Cd is 95-100%. The results of Tables 1, 2, 3, and 4 show that the zero-valent iron/oxidant synergy system has high removal efficiency for various heavy metals.

Table 4: Zero-valent iron/H ₂ O ₂ removal of multiple batches of heavy metal containing water results

Although the present invention has been described in detail above with the aid of the general description, the specific embodiments and the examples of the invention, it may be obvious to those skilled in the art . Therefore, such modifications or improvements made without departing from the spirit of the invention are intended to be within the scope of the invention.

Claims

A method for removing water body weight metal, characterized in that: the surface of the zero-valent iron is activated by an oxidizing agent, and the fresh iron (III) / (II) (hydrogen) oxide active component is continuously produced, by adsorption, precipitation, redox mode, A method for quickly and efficiently removing heavy metals from water.
The method according to claim 1, wherein said oxidizing agent is a commonly used oxidizing agent for water treatment, preferably potassium permanganate, hydrogen peroxide/sodium/potassium, ozone, chlorine, chlorine dioxide, hypochlorous acid, sodium hypochlorite. / Calcium, perchlorate, chlorate (ClO 3 - ), high-iron (VI) acid salt; the above oxidizing agents are used singly or in combination of two or more.
The method according to claim 1, wherein the zero-valent iron is a zero-valent iron powder or a zero-valent iron particle, and the type of zero-valent iron is not limited, and the size range of the zero-valent iron is not limited.
The method according to claim 1, wherein the concentration of the oxidizing agent in the reaction system ranges from 0.001 mM to 10 M; and the activation temperature ranges from -20 to 100 °C.
The method according to claim 1, wherein the oxidizing agent is pre-added before the water treatment, intermittently or continuously added during the water treatment, or a combination of two or two of the above-mentioned activation modes, and a combination of several; the oxidizing agent is added to the water to be purified, or Join the zero-valent iron system directly.
The method of claim 1 wherein the method of embodiment is in a batch mode or in the form of a stabilized bed, a fluidized bed, a filter column or a filter wall.
The method according to claim 1, wherein the treatable water body comprises sewage, industrial and agricultural wastewater, drinking water, ground water, and heavy metals in the water body are removed, including As, Hg, Cd, Pb, Cr, Se, Sb, Cu, Zn.
The method according to claim 6, wherein the concentration of iron powder or iron particles in the batch mode ranges from 1 mg/L to 1000 g/L, and the concentration of the oxidant in the reactor ranges from 0.001 mM to 10 M, and the temperature range is - 20-100 ° C; material dosing method, sequence, mixing and agitation mode, stirring rate is not limited; zero-valent iron, oxidant, water to be purified, the order of addition is not limited.
The method according to claim 6, wherein the concentration of the oxidizing agent in the reaction system of the stabilized bed, the fluidized bed, the filter column or the filter wall is in the range of 0.001 mM to 10 M, and the temperature is in the range of -20 to 100 ° C; In the water to be purified, or directly added to the zero-valent iron bed system.
Process according to claim 6, characterized in that other auxiliary medium, adsorption and filter medium are added, preferably activated carbon, magnesia, bauxite, clay, montmorillonite, zeolite, kaolin, sand, ore, ceramsite .
The method according to claim 8, wherein the batch processing method further comprises a subsequent solid-liquid separation; the subsequent solid-liquid separation is gravity sedimentation, centrifugation, magnetic separation, sand filtration, granulation or membrane filtration; The iron (III)/(II) (hydrogen) oxide iron produced by iron and oxidation is continuously used multiple times, and the lost iron is added.
The method according to claim 9, wherein the method of stabilizing the bed, flowing the bed, filtering column or filtering wall further comprises adding an alkaline solution to stabilize the ferrous iron, preventing the ferrous iron from leaking, or removing residual ferrous iron in the water by subsequent oxidation; The alkaline solution includes sodium hydroxide, potassium hydroxide, ammonia water, calcium hydroxide, magnesium hydroxide; the concentration ranges from 1 mM to 10 M; the alkaline solution is pre-added, intermittently added in water treatment or continuously added; the subsequent oxidation The residual ferrous iron in the water is removed, and the oxidizing agent is a commonly used water treatment oxidizing agent, preferably air, chlorine, chlorine dioxide, sodium hypochlorite/calcium, potassium permanganate, ozone, hydrogen peroxide.
The method according to claim 5, wherein air or oxygen is introduced while the oxidant is added.
The method of claim 2 wherein the oxidizing agent is sodium hypochlorite or potassium permanganate.
The method according to any one of claims 1 to 14, characterized in that the method comprises the steps of: filling zero-valent iron particles in a filter column, and introducing a solution containing an oxidizing agent from the top of the filter column to activate zero-valent The iron, and then the water body containing the heavy metal and the oxidant, collects the water body flowing out from the bottom end of the filter column, that is, the water body which removes the heavy metal.
The method according to any one of claims 1 to 14, wherein the method comprises the steps of: adding a zero-valent iron powder to a water body containing a heavy metal and an oxidizing agent, stirring, and fully reacting to obtain a suspension, solid-liquid separation After that, the water of the heavy metal is removed; the residual iron powder is reused.