CN113754040A

CN113754040A - Method for oxidizing trivalent arsenic in water body by using micro/nano activated carbon powder

Info

Publication number: CN113754040A
Application number: CN202111116000.4A
Authority: CN
Inventors: 朱长银; 薛晨言; 王镝翔; 周东美
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2021-09-23
Filing date: 2021-09-23
Publication date: 2021-12-07

Abstract

The invention discloses a method for oxidizing trivalent arsenic in a water body by using micro/nano activated carbon powder, which comprises the steps of adding the micro/nano activated carbon powder into a solution containing the trivalent arsenic, adjusting the pH of the solution to be slightly alkaline (the pH is about 7-9.5) by using an alkali solution, introducing air/oxygen, stirring and reacting for 1-3 days, and oxidizing the trivalent arsenic in a polluted water body into pentavalent arsenic. The method is suitable for treating the trivalent arsenic polluted water body or soil, has the advantages of high oxidation efficiency, wide application range, low cost, simple operation and the like, and provides a new idea for oxidizing the trivalent arsenic in the water body.

Description

Method for oxidizing trivalent arsenic in water body by using micro/nano activated carbon powder

Technical Field

The invention belongs to the field of polluted water body/soil remediation, and particularly relates to a method for oxidizing trivalent arsenic in a water body by using micro/nano activated carbon powder and application thereof.

Background

Arsenic (As) contamination As a speciesThe common heavy metal pollution problem causes serious threat to human health. The arsenic limit value is 10 mug/L according to the sanitary Standard for Drinking Water (GB 5749-2006) in China. China is polluted by high arsenic, and water bodies are widely distributed, and arsenic pollution phenomena exist in river delta areas such as Yangtze river, yellow river, Zhujiang river and the like and areas such as river sleeve basins, great congruent basins, Pascal basins and the like. Arsenic pollution in water is mainly inorganic arsenic, and inorganic arsenic comprises trivalent arsenic (As (III)) and pentavalent arsenic (As (V)), wherein trivalent arsenic has higher toxicity and fluidity than pentavalent arsenic. Trivalent arsenic is mainly in nonionic state H in water body₃AsO₃There is difficulty in being removed by adsorption, while pentavalent arsenic is relatively easy to be removed by adsorption. Therefore, the preoxidation of trivalent arsenic into pentavalent arsenic is a key strategy and means in the process of removing arsenic pollution in water bodies.

There are various methods for oxidizing trivalent arsenic, among which chemical oxidation is mainly performed by adding an oxidizing agent such as ozone, liquid chlorine, hypochlorous acid, fenton's reagent, hydrogen peroxide, trivalent iron, potassium permanganate, etc. to a contaminated water body (sewage, underground water) containing trivalent arsenic, and trivalent arsenic in a water body can also be oxidized by electrochemical oxidation, biological oxidation, etc. However, the method has many problems, such as high cost of adding strong oxidant, easy secondary pollution and increased subsequent treatment cost; the electrochemical oxidation method has the advantages of complex assembly of the electrode device, high cost and high energy consumption; the biofilm reactor is green and environment-friendly in oxidation, but the microbial species and activity are greatly influenced by the environment and are difficult to regulate.

Based on the analysis, the key point of treating the trivalent arsenic pollution in the water body is to develop a green and environment-friendly trivalent arsenic oxidation method with high oxidation efficiency and low cost, and is simple to operate. In recent years, researchers found biochar (pyrolysis temperature of 300-^oC) The high-activity durable free radical or active functional group (reductive hydroquinone and the like) contained in the arsenic trioxide can react with oxygen to generate high-activity species (hydrogen peroxide and hydroxyl free radical) and can efficiently oxidize trivalent arsenic in water. For example, patent CN201910435744.9 discloses a method for oxidizing trivalent arsenic in groundwater by using charcoal, which uses agricultural and forestry waste as raw material and passes through high temperature (400)-500^oC) The biochar is obtained after pyrolysis and washing by ionized water, and the trivalent arsenic is oxidized by the active oxygen (hydrogen peroxide and singlet oxygen) generated by the reaction of the biochar and oxygen under the acidic condition. Patent CN202010294238.5 discloses a bone char capable of oxidizing trivalent arsenic, which is prepared by using calcium-containing minerals in bovine bone meal as a natural template, and has high arsenic oxidation efficiency after acid treatment, and the main mechanism is similar to that of conventional biochar, and generates active species for the reaction of bone char and oxygen, thereby realizing rapid oxidation of trivalent arsenic. Although the method for generating active species can rapidly oxidize trivalent arsenic, the active species generation process needs reducing substances, the reducing substances on the surface of the biochar cannot continuously react with oxygen to generate active species after being consumed, and catalytic materials are frequently replaced in the reaction process. Therefore, it is necessary to develop an arsenic oxidizing material having a low cost and a high oxidation efficiency.

Activated carbon is an important carbon material, and organic raw materials (fruit shell, coal, wood and the like) are heated under the condition of isolating air (the pyrolysis temperature is generally more than 800 DEG)^oC) To reduce non-carbon components such as hydrogen, oxygen, etc., and then activated by air, carbon dioxide, water vapor, alkali, etc. Compared with biological carbon, the activated carbon has high pyrolysis temperature, the content of surface persistent free radicals and oxygen-containing functional groups is very low, and in addition, the activated carbon has larger specific surface area and can efficiently adsorb heavy metals and organic pollutants in polluted water. Currently, in the field of water treatment, activated carbon is generally used as an adsorbent and a supported oxidant for arsenic adsorption and oxidation removal, for example, in patent CN201210394589.9, activated carbon fiber is supported by titanium dioxide for photoelectrocatalysis oxidation to remove arsenic, and in patent CN202010993519.x, manganese dioxide is used to modify activated carbon to prepare a composite adsorbent for removing arsenic in water. It is generally believed that activated carbon is chemically inert, and that the persistent radical strength and reduced species content of the activated carbon surface is extremely low and cannot react with oxygen to form active species. Research reports that carbon materials can be used as conductors to promote the degradation of organic pollutants by strong oxidants such as persulfate and peroxymonosulfate through electron transfer (chem. Eng. J., 2015, 266, 28-33, j, hazard. mater, 2016, 320, 571-. Oxygen is an important oxidant in the environment, but no research or patent reports that trivalent arsenic in a water body is directly oxidized by oxygen through the electron-mediated action of activated carbon at present.

Disclosure of Invention

The technical problem to be solved is as follows: the invention provides a method for repairing trivalent arsenic pollution in a water body by oxidizing trivalent arsenic with micro-nano activated carbon powder, aiming at solving the problem of trivalent arsenic pollution in the polluted water body.

The technical scheme is as follows: the application of micron/nanometer activated carbon in oxidizing trivalent arsenic in underground water.

The application of micron/nanometer active carbon in preparing trivalent arsenic product in oxidizing underground water.

The method comprises the following specific steps: adding micro/nano activated carbon into the water solution containing trivalent arsenic, adjusting the pH of the solution to 7-9.5 by using alkali liquor, and stirring for reaction for 1-3 days to complete oxidation.

The particle size of the micro/nano activated carbon is 200 nanometers to 5 micrometers.

The micro/nano activated carbon is prepared by ball milling common activated carbon.

The oxidation reaction process needs to be carried out by introducing air or oxygen.

Specifically, the method for oxidizing trivalent arsenic in water comprises the following steps of using micron/nanometer activated carbon powder as an active ingredient: adjusting pH of the solution to be slightly basic (pH 7-9.5), and introducing air or oxygen. The method comprises the following specific steps: adding micro/nano activated carbon powder (0.5 g/L) into water containing trivalent arsenic (750 ppb-37.5 ppm), adding sodium hydroxide to adjust the pH value of the solution to 7-9.5, introducing air or oxygen, and reacting for 1-3 days at normal temperature in a shaking box with 200 rpm. The micro/nano activated carbon powder is obtained by ball milling purchased common activated carbon, and the specific steps are as follows: adding 5 g of activated carbon into a zirconia ball milling tank, adding 60 g of 7 mm balls and 50 g of 3 mm balls, carrying out ball milling for 10 min, pausing for 5 min, rotating at 400 rpm, and separating the balls after ball milling for one day. Compared with the conventional activated carbon, the micro/nano activated carbon powder has higher specific surface area and activity and can provide more reactive active sites for arsenic oxidation.

The reaction mechanism is as follows: under slightly alkaline conditions, the oxidation-reduction potential of As (V)/As (III) is-0.397V, O₂/O₂ ^•−Oxidation reduction potential of-0.127V, O₂/O₂ ^•−Is higher than As (V)/As (III), oxygen can oxidize trivalent arsenic theoretically, but because the redox potential difference between the two is small, the reaction is extremely slow in kinetics (the oxidation rate of trivalent arsenic is lower than 5% in one day of reaction). After micro/nano activated carbon powder is added into the system, oxygen and trivalent arsenic can be adsorbed on activated carbon graphite microcrystals and carbon defects. The activated carbon has very good conductivity due to few functional groups, and can transfer electrons from trivalent arsenic to oxygen, so that oxidation of the trivalent arsenic is promoted. Compared with the direct reaction of the trivalent arsenic and the oxygen in the water solution, the reaction rate of the trivalent arsenic and the oxygen adsorbed on the micro/nano activated carbon is higher, the feasibility on dynamics is realized, and the method can be used for oxidizing the trivalent arsenic in the practical water body. In the reaction process, the activated carbon is only used as an electronic mediator and does not change, so that the activated carbon can permanently catalyze the oxidation of trivalent arsenic by oxygen.

Has the advantages that: (1) the method utilizes the micron/nano activated carbon powder as a catalyst to be directly put into water for oxidation of trivalent arsenic, compared with the prior art, the method has simple operation, does not need complex preparation and pretreatment processes, adopts activated carbon and oxygen as reaction agents, and has low cost and environmental protection. (2) The micro/nano activated carbon powder has larger specific surface area (>800m²And/g), the common active carbon raw material is simple and can be directly purchased in the market, and the micro/nano active carbon powder can be obtained in batches by ball milling. (3) The mechanism of the invention mainly utilizes oxygen to indirectly oxidize the trivalent arsenic, the micro/nano activated carbon powder only provides oxidation sites of the trivalent arsenic, the oxidant consumed by the reaction is oxygen, and the reaction is maintained simply. (4) The process of oxidizing trivalent arsenic by the micro/nano activated carbon can be carried out under the condition of alkaline pH, the limitation on the water environment is small, and in-situ remediation is easy to carry out.

Drawings

FIG. 1 is a scanning electron microscope spectrogram of micro/nano activated carbon powder;

FIG. 2 is an X-ray photoelectron spectrum of carbon and oxygen on the surface of the micro/nano activated carbon powder;

FIG. 3 micro-nano activated carbon and biochar (pyrolysis temperature 500)^oC) Persistent radical signal strength of;

FIG. 4 shows the oxidation efficiency of micro/nano activated carbon to As (III) under different pH conditions;

FIG. 5 Effect of micro/nano activated carbon pre-oxidation treatment on As (III) oxidation;

FIG. 6 is a graph showing the effect of different initial trivalent arsenic concentrations on As (III) oxidation efficiency of activated carbon under aerobic conditions;

FIG. 7 is a graph showing the cyclic oxidation of As (III) by activated carbon powder under aerobic conditions (wherein the As (III) is added in an amount of 200. mu. mol in a single oxidation);

FIG. 8 shows the oxidation of As (III) by conventional activated carbon (two other activated carbon arsenic oxides are shown and labeled activated carbon 1 and activated carbon 2).

Detailed Description

Example 1

Adding 5 g of activated carbon into a zirconia ball milling tank, adding 60 g of 7 mm balls and 50 g of 3 mm balls, carrying out ball milling for 10 min, pausing for 5 min, rotating at 400 rpm, and separating the balls after ball milling for one day to obtain the micron/nanometer activated carbon. FIG. 1 is the scanning electron microscope spectrogram of micron/nanometer activated carbon nanometer powder with a diameter of hundreds of nanometers to several micrometers and a specific surface area of 820 m² g^-1. The X-ray photoelectron spectrum shows that the carbon content of the active carbon is very high (up to 90 percent), and the active carbon has very good conductivity (the conductivity is 0.71S mm)^-1). The micro/nano activated carbon obtained by ball milling is used for oxidizing As (III), the concentration of the micro/nano activated carbon is 0.5 g/L, the concentration of As (III) is 750 ppb, and the influence of different pH values (7, 8 and 9.5) on the effect of oxidizing the As (III) by the micro/nano activated carbon is compared.

Taking 8 mL of brown bottle with a polytetrafluoroethylene gasket as a reaction vessel, firstly adding 0.2 g of activated carbon powder and 40 mL of ultrapure water into a centrifuge tube to prepare 5 g/L suspension, taking part of the suspension into the reaction vessel, adjusting the pH value of the solution to 7, 8 and 9.5, and adding As (III) mother liquor to ensure that the initial concentration of As (III) in the system is 750 ppb and the volume of the solution is 5 mL. The reaction flask was placed in a 200 rpm reciprocating shaking chamber for 3 days.

As shown in FIG. 4, the As (III) oxidation rates at pH 7, 8 and 9.5 after 18 h reaction were 28%, 45% and 97%, respectively, and it can be seen that increasing the pH significantly promoted the oxidation of As (III), mainly because the higher the pH, the more easily As (III) is oxidized by oxygen and the faster the rate of electron transfer through activated carbon. Under the condition of pH =9.5, the oxidation rate of As (III) is extremely high, and the oxidation rate of As (III) reaches 97% when the reaction is carried out for 8 h. At pH =9.5, no hydrogen peroxide and hydroxyl radicals were detected during the reaction, demonstrating that under alkaline conditions, mainly carbon mediates the oxidation of as (iii) by oxygen.

To further prove the oxidation mechanism of As (III) under slightly alkaline conditions, the As (III) is subjected to oxygen oxidation treatment on micro/nano activated carbon for 2 days in advance and then is subjected to oxidation to remove active oxygen substances such as hydrogen peroxide and hydroxyl radicals. The results show that as shown in fig. 5, the pre-oxidation treatment has little influence on the oxidation of as (iii), which indicates that active substances such as hydrogen peroxide and hydroxyl radicals are not the main power for oxidizing as (iii), and further proves the oxidation of as (iii) by oxygen through micro/nano activated carbon.

Example 2

The micro/nano activated carbon obtained by ball milling is used for oxidizing As (III), the concentration of the micro/nano activated carbon is 0.5 g/L, the initial aerobic condition is adopted, and the influence of different initial As (III) concentrations on the As (III) oxidizing effect is compared.

An 8 mL brown bottle with a polytetrafluoroethylene gasket is used as a reaction container, 0.2 g of activated carbon powder and 40 mL of ultrapure water are added into a centrifuge tube to prepare 5 g/L suspension, part of the suspension is taken out to be placed into a reaction solution with a pH value of 9.5, arsenic mother liquor with different volumes is added to ensure that the initial concentration of As (III) in the system is 750 ppb, 1.5 ppm, 3.75 ppm, 7.5 ppm and 37.5 ppm respectively, and the volume of the solution is 5 mL. The reaction flask was placed in a 200 rpm reciprocating shaking chamber for 3 days. The reaction was carried out in air.

As a result, as shown in FIG. 6, the As (III) oxidation efficiency decreased with increasing initial As (III) concentration. At pH =9.5, the initial as (iii) concentrations at 750 ppb, 1.5 ppm, 3.75 ppm, 7.5 ppm, 37.5 ppm after 8 h of reaction correspond to as (iii) oxidation rates of 100%, 100%, 100%, 100%, 45%, respectively. At an As (III) concentration of 750 ppb to 7.5 ppm, increasing the As (III) concentration has less influence on the As (III) oxidation rate at pH =9.5, and further proves the strong oxidizing capability of the micro/nano activated carbon on the As (III) at pH = 9.5.

Example 3

The micro/nano activated carbon obtained by ball milling is used for oxidizing As (III), the concentration of the micro/nano activated carbon is 0.5 g/L, the concentration of As (III) is 15 ppm, and the oxidation limit of the micro/nano activated carbon powder under the alkaline pH (9.5) is inspected by utilizing a cycling reaction experiment.

Taking 8 mL of brown bottle with a polytetrafluoroethylene gasket as a reaction container, firstly adding 0.2 g of activated carbon powder and 40 mL of ultrapure water into a centrifuge tube to prepare 5 g/L suspension, taking part of the suspension to be put into a reaction solution with the pH value of 9.5, and adding arsenic mother solution to ensure that the initial concentration of As (III) in the system is 15 ppm and the volume of the solution is 5 mL. The reaction was carried out in air. Placing the reaction bottle in a reciprocating oscillation box at 200 rpm for reaction, centrifuging the reaction liquid after half a day, pouring out supernatant, adding the activated carbon suspension and the arsenic mother liquor again to ensure that the concentration of the activated carbon is 0.5 g/L and the concentration of As (III) is 15 ppm, then placing the reaction bottle in the oscillation box for reaction for half a day, and performing four groups of cycles every 12 hours.

As shown in figure 7, the activated carbon has excellent reaction activity on As (III) under the aerobic condition at pH =9.5, the oxidation efficiency of As (III) at the end of each cycle respectively reaches 78.55%, 71.8%, 67.59% and 65.96%, and the results show that the micro/nano activated carbon mediates the oxidation of As (III) to have good sustainability, and further prove that the micro/nano activated carbon has a main action in the oxidation process of As (III), and the reaction process has little influence on the catalytic capability.

Example 4

Selecting another two common commercial grade micron activated carbon powders (specific surface areas of 110 m and 95 m respectively)² g^-1) For the oxidation of As (III), the concentration of the active carbon is 0.5 g/L, As(III) the concentration was 750 ppb and the pH of the solution was 9.5.

Taking 8 mL of brown bottle with a polytetrafluoroethylene gasket as a reaction container, firstly adding 0.2 g of activated carbon powder and 40 mL of ultrapure water into a centrifuge tube to prepare 5 g/L suspension, taking part of the suspension to be put into a reaction solution with a pH value of 9.5, and adding arsenic mother solution to ensure that the initial concentration of As (III) in the system is 750 ppb respectively and the volume of the solution is 5 mL. The reaction flask was placed in a 200 rpm reciprocating shaking chamber for 3 days.

As shown in FIG. 8, the oxidizing ability of two kinds of conventional micron activated carbon powders to As (III) is very limited, and after 32 hours of reaction, the oxidizing rate of As (III) is only 27% and 18%. The result shows that the common micron activated carbon has poor oxidation capacity on As (III), and the micron/nanometer activated carbon has better oxidation effect on As (III), which is mainly because the micron/nanometer activated carbon has larger specific surface area and can provide more reaction sites for the reaction, thereby promoting the oxidation of As (III).

Finally, the above preferred embodiments are only for illustrating the technical solutions of the present invention, and it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims

1. The application of micron/nanometer activated carbon in oxidizing trivalent arsenic in underground water.

2. The application of micron/nanometer active carbon in preparing trivalent arsenic product in oxidizing underground water.

3. The application of claim 1, comprising the following steps: adding micro/nano activated carbon into the water solution containing trivalent arsenic, adjusting the pH of the solution to 7-9.5 by using alkali liquor, and stirring for reaction for 1-3 days to complete oxidation.

4. Use according to claim 1, wherein the micro/nano activated carbon has a particle size of 200 nm to 5 μm.

5. The use according to claim 1, wherein the micro/nano activated carbon is prepared by ball milling of ordinary activated carbon.

6. The use of claim 1, wherein the oxidation reaction is carried out by introducing air or oxygen.