RU2404930C1 - Method of purifying waste water from dyes - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: method is realised through purification from azo dyes in a cell with nanodispersed photocatalyst Fe2O3 with exposure to daylight and oxygen pressure of 0.3 MPa without applying additional voltage across the cell. The method intensifies the process of neutralising azo dyes owing to faster reduction of oxygen and active particles and reduction power consumption. ^ EFFECT: cost-effectiveness of the process is achieved by using daylight and cheap, readily available nano-sized photocatalysts when treating waste water containing dyes. ^ 2 ex

Description

The invention relates to methods for wastewater treatment from dyes by photocatalytic oxidation under oxygen pressure and can be used in wastewater treatment in the textile industry.

A known method of wastewater treatment [1], the essence of which is that the electrolysis of wastewater is carried out using an insoluble titanium anode coated with ruthenium and titanium oxides (ORTA) as an anode in the presence of chlorine ions, where active chlorine and oxygen are formed , which are the main oxidizing agents in the destruction of organic dyes. At the same time, UV irradiation is simultaneously carried out, which leads to an increase in the completeness of oxidation due to the activation of gaseous substances formed during electrolysis.

The disadvantage of this method is that during electrolysis, active chlorine is formed, which in some cases can lead to the formation of more toxic organochlorine compounds.

There is also known a method of treating wastewater containing dyes, described in [2], the essence of which is as follows. The solution containing dyes is subjected to treatment in an electrolyzer with an anode made of titanium dioxide, at a current of 0.5 mA, while UV irradiation and sparging into an electrolyte solution containing purified wastewater, oxygen under pressure up to 1.0 MPa.

The disadvantage of this method is the use of UV radiation, which can lead to increased energy consumption.

As a prototype, you can give a method of decolorizing wastewater from dyes using a photocatalytic system [3]. As a catalyst, a titanium grid was used, the wire diameter of which is 0.23 mm, in addition, titanium dioxide powder was dosed into the working solution. The process was carried out in a laboratory reactor, which is an electrolyzer, while the anode was a grid of titanium, and the cathode was a platinum grid, which was previously treated with sulfuric acid. The glass container was irradiated with UV radiation.

The disadvantage is the use of UV radiation, which leads to increased energy costs.

The task of the invention is the intensification of the process of neutralizing dyes and reducing energy costs.

The technical result - the efficiency of the process is achieved using daylight and cheap, affordable nanoscale photocatalysts in the treatment of wastewater containing dyes. The neutralization of dyes occurs due to the photocatalytic process during irradiation with daylight.

The essence of the proposed method of wastewater treatment from dyes is that a solution of azo dye is poured into the cell and 0.5 is poured; 1.0 or 2.0 g of Fe ₂ O ₃ catalyst per 200 ml of solution and treated for 1 hour with daylight at an oxygen pressure of up to 0.6 MPa without applying additional voltage to the cell. An autoclave lined with fluoroplastic with a volume of 200 ml is used as a cell. To irradiate the dye solution with visible light, one side of the cell is made of 10 mm thick silica glass.

Wastewater containing dyes is irradiated with daylight in the presence of a photocatalyst at an excess oxygen pressure of up to 0.6 MPa. Nanodispersed metal oxides, in particular Fe ₂ O _3, serve as the photocatalyst. When treating wastewater containing dyes in the presence of a non-sized catalyst, an increase in the redox potential between the electron and hole conduction zones of the photocatalyst occurs. The presence of oxygen dissolved under pressure leads to the formation of active particles also involved in the oxidation process, which also contributes to the intensification of the process of degradation of dyes. The optimal pressure is 0.3 MPa. At pressures below 0.3 MPa, the performance of the process is insufficient. A further increase in pressure does not increase the efficiency of the process.

The difference of the proposed method from its analogue is that when the process is carried out, a nanosized metal oxide powder (in particular, Fe ₂ O ₃ ) is used as a catalyst, irradiation is performed by visible light under oxygen pressure without applying additional voltage to the cell.

Example 1. Preparing a model solution of direct black dye 2 C, with a concentration of 0.1 g / l. The solution is poured into a cell with a bulk nanodispersed photocatalyst and placed on a laboratory magnetic stirrer. The solution is irradiated with daylight under an oxygen pressure of 0.1 MPa for 1 hour. The degree of discoloration of the solution is 68%.

Example 2. The process is carried out as in the previous case, with the difference that photocatalytic oxidation proceeds at a pressure of 0.3 MPa. The degree of discoloration of the solution is ~ 80%.

With an increase in O ₂ pressure from 0.1 to 0.3 MPa, a 2.1-fold increase in the rate of the photocatalytic oxidation process occurs, associated with the formation of active oxygen-containing particles, such as O ₂ , HO ₂ and HO, participating in the oxidation reaction.

An increase in the reaction rate with an increase in O ₂ pressure leads to an increase in the degree of discoloration of the solution. The drawing shows the dependence of the degree of discoloration of the dye solution on the pressure of O ₂ when exposed to daylight (C (Fe ₂ O ₃ ) = 5 g / l, C _cr = 100 mg / l). In this case, an almost linear dependence of the degree of discoloration on the pressure of O ₂ is observed, and the degree of discoloration with increasing pressure from 0.1-0.3 MPa increases by 18%.

The method can be implemented both on a laboratory and on an industrial scale in local wastewater treatment plants for textile and knitwear dyeing shops.

The proposed method has several advantages:

- reduced energy costs through the use of energy of daylight;

- increases the degree of purification of the solution from the dye by increasing the rate of oxygen reduction of the active particles.

Literature

1. SU 709568 (Leningrad Civil Engineering Institute), 11/20/1980.

2. RU 2337885 Method for photoelectrochemical wastewater treatment from dyes (Dagestan State University) / Adamadzieva N.A., Aliev Z.M., Isaev A.B., Shapieva M.A. / from 10.11.08. Application No. 2006144015 dated 12/11/2006.

3. Lix Z., Liu H.L., Yue P.T., Sun Y.P. Photoelectrocatalytic oxidation of rose Bengal in aqueous solution using a Ti / TiO mesh electrode // Environ. Sci. and Technol. - 2000 - V.34 - No. 20 - p. 4401-4406.

Claims (1)

A method of photocatalytic wastewater treatment from dyes, characterized in that the azo dyes are cleaned in a cell with a Fe ₂ O ₃ nanodispersed photocatalyst when exposed to daylight and an oxygen pressure of 0.3 MPa without additional voltage being applied to the cell.

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