CN107555554B - Capacitance deionization technology for absorbing oxyacid radical of arsenic by using layered metal oxide - Google Patents

Abstract

A capacitance deionization technology for absorbing oxyacid radicals of arsenic by using layered metal oxides belongs to the technical field of water treatment science. The desalting method is a capacitance deionization method, the anode material is a compound of calcined graphene and layered double-metal oxide, and the cathode material is activated carbon acidified by nitric acid. After the assembly is finished, a voltage of 0.4-1.2V is applied to adsorb the aqueous solution containing the oxygen acid radicals of arsenic, the adsorption efficiency can reach 97%, and the maximum theoretical adsorption value of the lang-miracle reaches 849 mg/g. The invention aims to provide a method for adsorbing arsenic with high efficiency, low energy consumption and no secondary pollution, which can effectively reduce the concentration of arsenic in water.

Description

Capacitance deionization technology for absorbing oxyacid radical of arsenic by using layered metal oxide

Technical Field

The invention relates to a capacitive deionization technology for absorbing oxyacid radicals of arsenic by using a layered metal oxide, belonging to the technical field of water treatment science.

Background

Water, one of the most common substances on earth, is an important resource on which all lives and living things are based, and is also an important component of living things. In general, the quality of life is determined by the quality of water, and the importance of water quality to human health can be seen. Arsenic is an element with strong biological toxicity, and chronic poisoning of arsenic is caused by long-time contact with inorganic arsenic mainly through drinking underground water with high arsenic content, food processed by the underground water and irrigated grains. Mainly manifested as cancer, skin injury, cardiovascular and cerebrovascular diseases, etc. In most northern groundwater in China, the content of arsenic is far beyond the standard arsenic concentration of 10ug/L specified by the world drinking water health organization. People are exposed to excessive levels of arsenic, a natural groundwater contaminant. In 2001 to 2005, the ministry of health in china implemented a "sampling and screening plan for arsenic pollution in water in china", and screened 20517 villages in 292 counties (12% of the country), and arsenic pollution of about 445000 wells. Investigation shows that more than 5 percent of water wells have arsenic concentration higher than 50ug/L which is the national standard before China, and about 10000 individuals are affected by the local arsenic poisoning in the known and suspicious local arsenic poisoning areas. After the wells were further screened, it was estimated that 560 thousands of people were drinking water containing high arsenic concentration (> 50 ug/L), and approximately 1470 thousands of people were drinking water containing arsenic concentration higher than 10 ug/L. Therefore, the method is a work which benefits the nation and the people and has important significance for solving the problem of arsenic pollution of underground water.

The traditional arsenic adsorption method comprises an oxidation precipitation method, flocculation/co-precipitation, ion exchange and adsorption, a membrane technology, a biotechnology and the like. Compared with the method, the capacitive deionization method has the characteristics of low energy consumption, low cost, high efficiency, safety, reliability, no secondary pollution and the like. Effectively reduces the concentration of arsenic in the water body.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a capacitive deionization technology for adsorbing the oxyacid radical of arsenic by using a layered metal oxide so as to adsorb the arsenic in water.

The technical scheme adopted by the invention is as follows: a capacitance deionization technology for adsorbing oxygen-containing acid radicals of arsenic by utilizing layered metal oxides adopts a closed loop formed by a deionization capacitance module and a direct-current voltage circuit, and oxygen-containing acid radical water with arsenic flows through the deionization capacitance module and then the oxygen-containing acid radicals of arsenic are adsorbed; the closed loop adsorbs the oxygen-containing acid radicals of arsenic under the constant current voltage of 0.4-1.2V; the oxygen-containing acid radical of the arsenic is arsenite radical, arsenate hydrogen radical and arsenate dihydrogen radical;

the deionization capacitor module comprises an anode, a cathode, an organic glass plate, a titanium strip, a cation exchange membrane and a silica gel gasket; the anode material is a composite of layered Mg/Al, Ca/Ti or Ni/Co bimetallic oxide and graphene oxide; the cathode material is activated carbon treated by nitric acid solution.

The preparation method of the anode material comprises the following steps: weighing two inorganic metal salts according to a molar ratio of 2:1-4:1, dissolving the two inorganic metal salts in 200ml of deionized water, carrying out ultrasonic treatment for 30 minutes, adding alkali source urea, putting the mixture into a reaction kettle, putting the reaction kettle into an oven to react for 24 hours at 120 ℃, washing the material to be neutral after the reaction is finished, drying the material at 80 ℃, and grinding the material to be small particles. Roasting the sample at 400-600 ℃ for 5 hours in an argon atmosphere at the heating rate of 2-5 ℃ per minute; the two inorganic metal salts are inorganic metal salts of Mg/Al, Ca/Ti or Ni/Co;

the preparation method of the cathode material comprises the steps of weighing 5g of activated carbon, adding the activated carbon into a nitric acid solution with the volume fraction of 20-50%, and carrying out heat treatment at 50-70 ℃ for 5 hours; and cooling to room temperature after the reaction is finished, washing the material to be neutral, and drying at the temperature of 80 ℃ to obtain the cathode material.

The preparation method of the anode or the cathode comprises the following steps: mixing an anode material or a cathode material, polyvinylpyrrolidone/polyvinyl butyral and acetylene black according to a mass ratio of 82.5:10:7.5, controlling the total mass to be 0.1-0.2g, putting the materials into a mortar, adding ethanol for grinding, and uniformly coating the mixture in the mortar on 5 x 7cm of graphite paper when no obvious particles are ground; standing and air-drying, and drying in an oven at 80 ℃ for 30 minutes to obtain the anode or the cathode.

The invention has the beneficial effects that: the core of the arsenic adsorption method lies in the selection of electrode materials. The layered double hydroxide is a hydrotalcite compound, and the product of roasting after the layered double hydroxide is compounded with graphene is used as an anode material of an electrode. In recent years, hydrotalcite has attracted much attention as an adsorbent having selective properties for removing anionic pollutants from water. The hydrotalcite after high-temperature thermal decomposition is a bimetallic oxide, has a uniform structure, a small particle size and a large specific surface area, and has strong adsorption capacity on various anions. The bimetallic oxide recovers the original structure by adsorbing anions in the solution, and toxic anions in the water body are removed. To suppress the homonymous ion rejection effect and effectively improve the stability of the desalination module, nitric acid treated negatively charged activated carbon was chosen as the cathode material. 1.2V voltage is applied to the module, the flow rate of a peristaltic pump is 3ml/min, the adsorption efficiency can reach 99.7% through different concentration determination, and the maximum theoretical adsorption value of the lang-miracle reaches 849 mg/g. This shows that the method of the invention has excellent adsorption performance on the oxyacid radicals of arsenic, and effectively reduces the concentration of arsenic in the water body. Therefore, the method is a technology for removing the oxyacid radicals of the arsenic in the water body with high efficiency and low energy consumption, which is different from the traditional arsenic adsorption technology.

Drawings

FIG. 1 is a cold field and TEM image of calcined graphene/Mg-Al layered double hydroxide (a-b) and reacted graphene/Mg-Al layered double hydroxide (c-d)

FIG. 2 is a process flow diagram of the embodiment: wherein 1 is a constant current direct voltage power supply, 2 is a silicone tube, 3 is a peristaltic pump, and 4 is a reservoir

FIG. 3 is an assembly structure diagram of the asymmetric desalination module, wherein a-h are an organic glass plate, an electrode plate, a titanium strip, a non-woven fabric, a silica gel gasket, a non-woven fabric, an electrode plate and a titanium strip in sequence

FIG. 4 is an adsorption rate curve of the asymmetric module under the conditions that the voltage is 1.2V and the mass concentration of the sodium arsenite solution is 68.74ppm in the embodiment

FIG. 5 is the adsorption curves of the asymmetric module under the conditions of voltage of 0, 0.4, 0.8 and 1.2V and the mass concentration of the sodium arsenite solution of 50ppm in the embodiment

FIG. 6 is an adsorption curve of the asymmetric module in the embodiment under the voltage of 1.2V in the sodium arsenite solution with the mass concentration of 68 ppm, 177 ppm, 327 ppm and 648ppm respectively

FIG. 7 is a Langery-Dawler curve fitted to the asymmetry module on the basis of FIG. 6 in the embodiment.

Detailed Description

(1) Preparation of anode material: dispersing 40ml of 5mg/ml graphite oxide in 100ml deionized water, performing ultrasonic treatment for 30min, and adding 0.02mol Mg (NO)₃)₂·6H₂O and 0.01mol Al (NO)₃)₃·9H₂And O, continuing ultrasonic treatment for 30min, and then adding 7.3g of urea. And (3) putting the mixed solution into a reaction kettle, reacting for 24 hours at 120 ℃, washing and centrifuging the obtained product to be neutral, and drying for 12 hours at 80 ℃. And roasting the obtained sample for 5 hours at the temperature rise rate of 2 ℃ per minute to 400 ℃ under the protection of argon gas to obtain the graphene/magnesium-aluminum layered metal oxide compound.

(2) Preparing a cathode material: 5g of activated carbon is weighed and added into a nitric acid solution with the volume fraction of 50 percent, and the mixture is subjected to heat treatment at 60 ℃ for 5 hours. And cooling to room temperature after finishing, washing the material to be neutral, and drying at 80 ℃ for later use.

(3) Preparing an electrode slice: mixing the solid powder prepared in the step (1), polyvinylpyrrolidone/polyvinyl butyral and acetylene black according to a mass ratio of 82.5:10:7.5, adding ethanol, grinding, and uniformly coating the mixed solution on 5 x 7cm of graphite paper, wherein the mass of the material is controlled to be 0.1-0.2 g. Standing and air-drying, and drying in a drying oven at 80 ℃ for 30 minutes to obtain the prepared anode electrode plate for later use. The preparation method of the cathode electrode plate is similar to that of the anode click plate, and only the solid powder prepared in the step (1) needs to be replaced by the solid powder prepared in the step (2).

(4) Assembling the modules: the asymmetric CDI module is composed of an organic glass plate, a double faced adhesive tape, a titanium strip, an electrode plate, a non-woven fabric, a silica gel sheet, a non-woven fabric, an electrode plate, a titanium strip, a double faced adhesive tape and an organic glass plate in sequence.

(5) And (3) forming a closed loop by the asymmetric module and the direct-current voltage circuit, feeding the sodium arsenite solution with the mass concentration of 68.74ppm into the module from the water reservoir through a silicon tube by using a peristaltic pump, and feeding the sodium arsenite solution back to the water reservoir after adsorption. A voltage of 1.2V was applied to the module and the peristaltic pump flow rate was 3 ml/min. After the reaction was started, 100. mu.l of the solution in the reservoir was taken at 0, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 23.5 hours, respectively, and then the concentration of As in the solution was measured by an atomic fluorescence spectrometer and the amount of arsenite adsorbed was calculated. The adsorption efficiency can reach 99.7%.

(6) The module was tested for changes in the concentration of arsenite at voltages of 0, 0.4, 0.8, 1.2V, respectively, and an initial mass concentration of 50ppm of sodium arsenite solution, according to the method described in (5).

The adsorption amount of the module to arsenite in a sodium arsenite solution with initial mass concentrations of 68, 177, 327 and 648ppm was tested according to the method described in (5). The maximum theoretical adsorption value of the langevir reaches 849mg/g determined by different concentrations. This shows that the method of the invention has excellent adsorption performance on the oxyacid radicals of arsenic, and effectively reduces the concentration of arsenic in the water body.

Claims (1)

1. A capacitance deionization technology for adsorbing the oxyacid radical of arsenic by using a layered metal oxide is characterized in that: the technology adopts a closed loop formed by a de-ionization capacitor module and a direct-current voltage circuit, and the oxyacid radical water with arsenic flows through the de-ionization capacitor module and then the oxyacid radical of arsenic is adsorbed; the closed loop adsorbs the oxygen-containing acid radicals of arsenic under the constant current voltage of 1.2V; the oxygen acid radical of the arsenic is arsenite;

the incoming capacitor module comprises an anode, a cathode, an organic glass plate, a titanium strip, a cation exchange membrane and a silica gel gasket; the anode material is a composite of layered Mg/Al bimetallic oxide and graphene oxide; the cathode material is activated carbon treated by nitric acid solution;

the preparation method of the anode material comprises the following steps:

weighing magnesium nitrate hexahydrate and aluminum nitrate nonahydrate according to a molar ratio of 2:1, dissolving in 200ml deionized water, carrying out ultrasonic treatment for 30 minutes, adding alkali source urea, putting the mixture into a reaction kettle, putting the reaction kettle into an oven, reacting for 24 hours at 120 ℃, washing the material to be neutral after the reaction is finished, drying at 80 ℃, and grinding the material to be small particles;

roasting the sample at 400 ℃ for 5 hours in an argon atmosphere, wherein the heating rate is 2 ℃ per minute;

the preparation method of the cathode material comprises the following steps:

weighing 5g of activated carbon, adding the activated carbon into a nitric acid solution with the volume fraction of 50%, and carrying out heat treatment at 60 ℃ for 5 hours; cooling to room temperature after the reaction is finished, washing the material to be neutral, and drying at 80 ℃ to obtain a cathode material;

the preparation method of the anode or the cathode comprises the following steps: mixing an anode material or a cathode material, polyvinylpyrrolidone/polyvinyl butyral and acetylene black according to a mass ratio of 82.5:10:7.5, controlling the total mass to be 0.1-0.2g, putting the materials into a mortar, adding ethanol for grinding, and uniformly coating the mixture in the mortar on 5 x 7cm of graphite paper when no obvious particles are ground; standing and air-drying, and drying in an oven at 80 ℃ for 30 minutes to obtain the anode or the cathode.

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