RU2625466C1 - Method for removing nitrite-ions from water solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves electrochemical treatment of aqueous solutions containing 0.10-0.20 g/l of nitrite ions and 0.30-0.45 g/l of sodium sulfate or sodium chloride, in a cell of a non-current type with a diaphragm, a cathode of stainless steel, an ORTA-type anode at current strength of 0.25-0.40 A, current density of 0.25-0.40 A/cm², voltage of 38-42 V, temperature of 22-30°C, a duration of 40-45 minutes.

EFFECT: method allows to increase the removal degree of nitrite ions, to reduce the consumption of electroconductive additive, to expand the range of solutions used.

2 ex

Description

The invention relates to a method for purifying water and wastewater from nitrite ions.

содержатся в природных водах, в сточных водах, в промывных водах животноводства, в пищевых продуктах в концентрациях от 100 до 1000 мг/л [1].It is known that nitrite ions

contained in natural waters, in wastewater, in flushing waters of animal husbandry, in food products in concentrations from 100 to 1000 mg / l [1].

Nitrite ions are harmful substances, so they must be removed from aqueous solutions to maintain the environmental safety of the country.

Various methods for removing nitrite ions from aqueous solutions are described.

In the patent of Germany [2] a catalytic method for purifying water from nitrites and nitrates is proposed, which consists in introducing hydrogen, which is a reducing agent, into the contaminated water, followed by reduction of nitrites and nitrates on catalysts consisting of a porous carrier impregnated with metal components (palladium, rhodium, etc. .).

The method is characterized by the complexity of the technology, the use of catalysts, the need for their processing.

A method for purifying water from nitrates and nitrites is described, combining electrochemical and catalytic purification methods, including introducing water into the cathode space of the electrolyzer, where hydrogen, ammonia and nitrogen oxides are formed as a result of cathodic reduction, after which water is supplied to the catalyst, where the reaction with the formation of molecular nitrogen and nitrogen oxides [3].

The method is associated with the complexity of the technology, the high cost of equipment.

A method is described for removing nitrite ions from aqueous solutions by oxidizing them with sodium hypochlorite to nitrates [4].

The disadvantages of the method: solutions of sodium hypochlorite decompose over time, lose their activity.

The closest in essence is a method of removing nitrite ions from aqueous solutions by treatment in an electrochemical cell with an inert (carbon or graphite) electrodes with an undivided anode and cathode space [5].

The interelectrode space was filled with an aqueous solution of sodium chloride at a concentration of 1.5-2.0 g / l, the concentration of nitrite ions was 0.17-0.19 mg / l. The electric treatment was carried out at a voltage of 19.0-19.5 V per cell, current density 0.4-0.6 A / cm ² , and an electrolysis time of 20-40 minutes. The degree of removal of nitrite ions is, according to our estimates, 8.6-61.7%, an average of 35.2%. The disadvantages of the method:

- low efficiency (degree of removal of nitrite ions 35.2%);

- high consumption of sodium chloride (electrolyte) 1.5-2.0 g / l in relation to the content of nitrite ions (ratio of more than 8000);

- incompleteness of data on electrical processing (there are no indicators of current strength, which does not allow to calculate the indicator of the specific consumption of the amount of electricity (ampere-hours per 1 liter of aqueous solution)).

The technical result is an increase in the efficiency of the method, a decrease in the electrolyte consumption, and an increase in the electric processing indices.

This is achieved by the fact that nitrite ions were introduced into the aqueous solution as electrolytes in the form of sodium sulfate or sodium chloride at their mass ratio of electrolyte: nitrite ion (1.5: 1 - 4.5: 1). Electrochemical treatment (ECHO) is carried out in an electrolyzer with a diaphragm of an installation (device) of the MELESTA type, a non-flow type with a stainless steel cathode and an OPTA anode (oxide-ruthenium-titanium anode). The total volume of the solution is about 1 liter (660 ml of catholyte and 330 ml of anolyte). The electrolyzer is equipped with a new cover and rectifier type VSA-5k. Interelectrode gap of 30 mm. ECHO was carried out at a temperature of 18-30 ° C, at a current strength of 0.25-0.40 A, voltage 38-42 V (current density at the electrodes 0.25-0.40 A / cm ² ). The initial concentration of nitrite ions was 0.1-0.2 g / l, electrolyte Na ₂ SO ₄ or NaCl 0.3-0.45 g / l. The duration of the ECHO is 40-45 minutes. In the anode space during ECHO, oxidizing agents formed - chlorine, active chlorine - in the case of using NaCl; oxygen, persulfates, OH ^⋅ radical - in the case of using Na ₂ SO ₄ . The reduction of nitrites in catholyte was hydrogen to N ₂ and NO. The degree of removal of nitrite ions ranged from 65 to 90% in the anolyte, 31-54% in catholyte.

Examples of the method.

-ионов), загружали в катодную камеру 660 мл раствора, в анодную камеру 330 мл раствора, проводили ЭХО при силе тока 0,25-0,40 А, напряжении 42 В, при температуре 22-30°С в течение 40 мин.Example 1. In a volumetric flask with a capacity of 1 l was dissolved in distilled water 0.3 g of sodium sulfate and 0.3 g / l of sodium nitrite (0.25 g / l

-ions), 660 ml of solution were loaded into the cathode chamber, 330 ml of solution into the anode chamber, ECHO was performed at a current strength of 0.25-0.40 A, voltage of 42 V, at a temperature of 22-30 ° C for 40 minutes.

The method of chemical analysis determined the content of nitrite ions: in catholyte 0.138 g / l, the degree of removal of nitrite to the original 31%; in anolyte, 0.062 g / l, removal rate 69%, average 50%.

Example 2. Prepared 1 l of a solution containing 0.45 g / l NaCl and 0.15 g / l NaNO ₂ (NO ₂ 0.1 g / l). ECHO was performed with 660 ml of a solution in catholyte and 330 ml in anolyte at a current strength of 0.20-0.30 A, voltage 38-41 V, temperature 19-26 ° C, for 45 minutes.

The chemical analysis determined the content of nitrite ions: in catholyte 0.046 g / l, the degree of removal of nitrite to the original 54%; in anolyte 0.010 g / l, removal rate 90%, average 72%.

Thus, the proposed method allows you to:

- increase efficiency (degree of removal of nitrite ions);

- reduce the consumption of conductive additives (Na ₂ SO ₄ and NaCl);

- bring a more complete set of technological indicators, expand the range of solutions used.

Changes in process performance may result in poor processing performance.

The list of sources of information taken into account during the examination:

1. Khalemsky A.M. et al. Solving the problems of water purification // Non-ferrous metallurgy, 2014, No. 2. - from. 60.

2. German patent No. 3830850 op 1990, C02F 1/46.

3. The patent of Germany No. 3933206 op 1990, C02F 1/46.

4. Volynets MP, Volynets V.F. Analytical Chemistry of Nitrogen, Moscow: Nauka, 1977, p. 128.

5. Patent RU No. 2471718 op 2013, C02F 1/46.

Claims (1)

A method for removing nitrite ions from aqueous solutions containing nitrite ions in an electrochemical cell, characterized in that the aqueous solution contains nitrite ions and an electrolyte in the form of sodium sulfate or sodium chloride at a concentration of 0.10-0.20 g / l, and 0.30-0.45 g / l, respectively, the electrochemical treatment is carried out in a cell with a diaphragm, a stainless steel cathode, an ORTA type anode, with a current strength of 0.25-0.40 A, voltage 38-42 V, current density 0.25-0.40 A / cm ² , temperature 22-30 ° C, duration 40-45 min.