RU2840972C1 - Method of producing modified carbon sorbent - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of producing modified carbon sorbents. Proposed method comprises electrochemical treatment of carbon sorbent in cell with cation-exchange membrane that separates anode and cathode spaces. Insoluble oxide ruthenium-titanium electrodes are used. Method is carried out with superimposition of cathode polarization and current density of 1 A⋅g^-1 for 15 minutes in solution of 5% NaCl. Volume ratio of the carbon sorbent to the catholyte solution is equal to 1:5.

EFFECT: reducing energy costs for implementing the method, increasing the environmental friendliness of the method while maintaining the sorption capacity of the sorbent without reducing the efficiency of wastewater treatment from metal ions.

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Description

The invention relates to methods for producing modified carbon sorbents by applying polarization from an external current source, which makes it possible to increase their sorption capacity in the purification of wastewater from chemical industry enterprises containing metal ions.

The most important indicator of carbon sorbents is their sorption capacity, which depends on the specific surface, surface condition and the presence of functional groups on the surface of the sorbent. To increase the sorption capacity of carbon sorbents, they are subject to modification.

A method for producing modified activated carbon is known, which includes preparing a modifier solution, impregnating the carbon and drying it. Quercetin, alginic acid or its alkali metal salts are used as a modifier, and activated carbon with a ratio of the volume of micropores to the total pore volume of 0.3÷0.4 is used, and impregnation is carried out with an aqueous solution of the modifier with a ratio of the volumes of impregnation and carbon of 0.8÷1.0 [Patent No. 2104927 C1, Russian Federation, IPC C01B 31/16, B01J 20/20. Method for producing modified activated carbon: No. 96124758/25: declared 31.12.1996: published 20.02.1998].

The disadvantage of this method is the low efficiency of sorption of heavy metal cations, the use of special modifiers for impregnating sorbents, and the labor intensity of the method.

A method is known for the electrosorption of cesium ions from an aqueous solution on activated carbon of the DAK brand with simultaneous cathodic polarization of the carbon [Sveshnikova D.A., Khamizov R.Kh., Atayev M.B., Amirov A.M. et al. Study of the patterns of electrosorption of cesium ions by activated carbon DAK // Sorption and chromatographic processes. 2016. Vol. 16. No. 3. Pp. 270-280].

The disadvantage of this method is the energy intensity of the electrosorption process, which does not allow the extraction of heavy metal ions from large volumes of wastewater.

A method for modifying carbon sorbents is known [Gimaeva A.R., Valinurova E.R., Igdavletova D.K., Petrova O.P., Kudasheva F.Kh. Study of the processes of sorption of lead and zinc ions from water by activated carbon adsorbents // Sorption and chromatographic processes. 2012. Vol. 12. No. 2. Pp. 267-273], in which hydrochloric and sulfuric acids are widely used as oxidizing agents. Carbon sorbents modified in this way are cation exchangers, have sorption activity with respect to metal ions due to the fact that they contain carboxyl, lactone, phenolic groups on the surface.

The disadvantages of the method are associated with the high consumption of highly concentrated reagents, energy costs for heat treatment, and are also characterized by the duration of the modification process and the toxicity of the reagents used, and the presence of hazardous waste.

The closest to the claimed method in terms of the technical essence of modification of the carbon sorbent is the method for obtaining oxidized carbon from plant materials for the purification of waste water from copper ions (prototype) [Patent No. 2329948 C1 Russian Federation, IPC C01B 31/08, B01J 20/20. Method for obtaining oxidized carbon from plant materials for the purification of waste water from copper ions: No. 2007103696/15: declared. 30.01.2007: published. [27.07.2008], which includes the treatment of carbon sorbent with nitric acid for 3 hours at a temperature of 75-85 °C or hydrogen peroxide by a chemical method using a 15% solution or electrochemically in a cell with a platinum mesh anode, an electrolyte of 5 M sulfuric acid solution at a current density of 14±1 mA/ ^cm2 for 20 min. The efficiency of modification of the carbon sorbent, i.e. the degree of its oxidation, is noticeably affected by the conditions of the oxidation reaction, namely: the concentration of the reagent, the temperature and the time of treatment. This method was chosen as a prototype.

The disadvantages of this method are the energy consumption for heating the electrolyte solution, the use of expensive platinum electrodes and aggressive concentrated acids, and the need to wash the coal after modification, which results in the formation of waste water.

The technical task of the proposed invention is to develop a method for modifying a carbon sorbent, reducing energy costs for its implementation, increasing the environmental friendliness of the method while maintaining the sorption capacity of the sorbent without reducing the efficiency of wastewater treatment from metal ions.

The set task is achieved by developing a method for obtaining a modified carbon sorbent, which consists of electrochemical treatment of the carbon sorbent in a cell with a cation-exchange membrane separating the anode and cathode spaces, using insoluble ORTA electrodes (oxide ruthenium-titanium electrode) with the imposition of cathode polarization and a current density of 1 A⋅g ^-1 for 15 minutes in a 5% NaCl solution at a volume ratio of carbon sorbent: catholyte solution equal to 1:5.

The imposition of cathodic polarization leads to a shift in the electrokinetic potential of the carbon sorbent into the negative potential region, which leads to an increase in the sorption capacity of carbon with respect to metal cations.

The proposed method eliminates the use of aggressive reagents - concentrated acids, which leads to an increase in the environmental friendliness of the method. The costs of the process are reduced due to the use of less expensive insoluble ORTA electrodes.

The method is confirmed by the following examples.

Example 1. The carbon sorbent is wetted in a 5% NaCl solution (catholyte) in a volume ratio of 1:5 and placed in a cell with a cation-exchange membrane and an ORTA cathode. The cell and cathode are lowered into a 5% NaCl solution. The carbon sorbent is modified in the cell by applying cathodic polarization at a current density of 1 A⋅g ^-1 for 15, 20 and 40 minutes. After modification, the carbon sorbent is dried at 100 °C. Then, Cu ²⁺ ions are sorbed on the modified sorbent in a static mode for 60 min at a carbon sorbent: 50 mg/l Cu ²⁺ solution ratio of 1:125. The results are presented in Table 1.

Table 1 - Effect of the duration of the carbon sorbent modification process on the efficiency of sorption purification of the solution from Cu ²⁺ ions

Modification duration, min Electrokinetic potential of carbon sorbent after modification, mV Degree of solution purification from Cu ²⁺ , % Electrokinetic potential of carbon sorbent after sorption, mV 0 -5 10 +5.7 15 -19 … -20 66 +5 … +5.5 20 66 40 67

The results show that cathodic treatment increases the sorption capacity of coal sixfold. Increasing the duration of cathodic treatment practically does not increase the efficiency of solution purification; treatment for 15 minutes is optimal.

Example 2. The modification of the carbon sorbent is carried out in the sequence and under the conditions described in Example 1, with the difference that the modification process is carried out at a current density of 1-3 A⋅g ^-1 for 15 min.

Next, the sorption of Cu ²⁺ ions from the solution was carried out as described in Example 1. The results are presented in Table 2.

Table 2 - Effect of current density of the carbon sorbent modification process on the efficiency of sorption purification

Current density, A⋅g ^-1 Degree of solution purification from Cu ²⁺ , % 0 10 1 66 2 69 3 73

The results show that increasing the current density during cathodic treatment from 1 to 3 A⋅g ^-1 does not lead to a significant increase in the efficiency of solution purification; treatment at a current density of 1 A⋅g ^-1 is optimal.

Table 3 presents comparative conditions for the process of modifying a carbon sorbent using the claimed method and the prototype, as well as subsequent purification of wastewater using the example of sorption of Cu ²⁺ ions.

Table 3 - Comparative data on the modification of the carbon sorbent and subsequent sorption of Cu ²⁺ ions on it using the claimed method and the prototype

Parameter Prototype Claimed Modification: Installation Without separation, electrochemical modification in the bulk of the solution With separation of the cathode space by a cation exchange membrane Method of modification Electrochemical Electrochemical, superposition of cathodic polarization Electrode material Platinum Ruthenium titanium oxide electrode Solution for modification 5 _{M H2SO4} 5% NaCl Modification duration, min 20 15 Sorption T:F 1:20 1:125 Initial concentration of Cu ²⁺ ions, mg/l 0,041 50 Cleaning efficiency, % 51 66 (pH = 4)
89 (pH = 6 - 7)

Thus, the claimed method allows to reduce the duration of modification of carbon sorbent from 20 to 15 minutes, to refuse aggressive reagents (sulfuric acid), thereby increasing the environmental friendliness of the process, while increasing the sorption capacity of carbon sorbent (efficiency of wastewater treatment from metal cations).

Claims (1)

A method for modifying a carbon sorbent, which consists of electrochemically treating the carbon sorbent in a cell with a cation-exchange membrane separating the anode and cathode spaces, using insoluble ruthenium-titanium oxide electrodes with the application of cathode polarization and a current density of 1 A⋅g ^-1 for 15 minutes in a 5% NaCl solution at a volume ratio of carbon sorbent: catholyte solution equal to 1:5.