SU1110754A1 - Method for purifying waste liquors from hexavalent chromium ions - Google Patents

Abstract

A METHOD FOR CLEANING WASTE WATER FROM SIXIVALENT CHROMIUM IONS, including electrolysis using a porous cathode and filtering through the cathode in the direction from the anode to the cathode, characterized in that, to reduce power consumption, a cathode made of copper powder with a particle size of 0 is used, 05-0.50 mm, and electrolysis is carried out at a cathode current density of 0.050, 30 A / dm and a pH of 2-5.

Description

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The invention relates to the treatment of waste water containing hexavalent chromium, and can be used in the disposal of electroplating. A known method of purification of wastewater containing hexavalent chromium, including pumping wastewater through volume-porous lead cathodes, while the anodes are dissolved.

The disadvantage of this method is that, in addition to the consumption of expensive (GO) material, it is possible to contaminate the sticks with toxic lead.

The closest to the technical essence and achievable. / The result to the proposed is a method of cleaning sewage from ions of generous chromium, including their electrolysis using a porous cathode and filtration through the cathode in the direction of the 1T anode to the cathode. Porous cathodes are made of graphite or activated carbon 2.

The disadvantage of this method is the high power consumption due to the physicochemical properties of the cathode made of carbon material.

The purpose of the invention is to reduce power consumption.

The goal is achieved by the fact that according to the method of wastewater purification from hexavalent chromium ions, including electrolysis using a porous cathode and filtration through the cathode in the direction from the anode to the cathode, the cathode is made of copper powder with a particle size of 0.05-0.50 mm and electrolysis is carried out at a cathode current density of 05050, 30 A / dm and a pH of 2-5

The method is carried out as follows.

Waste water containing hexavalent chromium ions is fed into a flow cell with a porous copper cathode and a lead anode. At the cathode, a current density of 0.05-0.30 A / dm and a pH of 2-5 are maintained. Depending on the concentration of chromium ions, the specific flow rate is 1.6-2.0 l. The particle size of the copper powder for the manufacture of the cathode is chosen in the range of 0.05-0.50 mm.

The particle size of the copper powder of 0.0 0.50 mm allows the process to be carried out without diffusion limitations with a high filtration rate and to prevent the copper from being carried away from the electrolyzer. The resistance of the electrode is significantly lower than coal, which contributes to a reduction in energy consumption {p coal 820 μΩ-M; f copper 0.017 µOhm1m).

During the electrolysis of dilute chromic solutions, the following reactions take place at the cathode:

Cr ,, of + 14H + 6eT52 Cr + 7H20 (1) OjHH- + Ae- -2H20. (2) Oj.-i-2H20 + 4e-40H (3)

. 2H- -2- (4)

2H20 + 2- H2H20H (5)

Of these reactions, the most likely are (1), (4), (5), since the solubility of oxygen in wastewater is limited. The use of copper powder as a porous cathode contributes to a shift in the current balance towards the target reaction (1). As follows from equation (1), hydrogen ions are involved in the reduction reaction of chromium. However, they can be consumed according to equation (4) to release gaseous hydrogen. The copper powder cathode reduces the consumption of protons for a side process and they are spent mainly on the flow of the hexavalent chromium reduction. This makes it possible to carry out the reaction in a weakly acidic medium () with a high current output.

During the electrochemical treatment of chromium-containing drains, the cathode is not reduced. The resulting trivalent chromium ions, depending on the pH value, are hydrolyzed directly in the cathode bulk, where they accumulate as chromium hydroxide. B. Depending on the flow rate, the hydroxide zone shifts deep into the cathode. The copper porous cathode is periodically washed with an acidified or alkalized solution to remove trivalent chromium, or, in the accumulation mode, disposed of the cathode mass in the form of a copper-chromium catalyst.

Example. The reduction of hexavalent chromium to trivalent is carried out by the method of electrochemical treatment of wastewater in a Tlectrolyzer with a strong porous copper cathode with a grain size of 0.05-0.5 mm and an insoluble lead anode. Concentration of the initial solution of 10, 50, 100 mg / l. Depending on the performance of the installation, the specific flow rate of the duct is 1.6-2 l / dm / h.

Directional filtering solution from the anode to the cathode. A constant voltage is applied to the apparatus, which provides the overall current density at the cathode within the claimed limits. After 2 h of operation of the electrolyzer, the mode is considered established, a sample is taken for chromium at the outlet. The results obtained are presented in the table.

As follows from the table, the specific energy consumption decreases with decreasing water pH. The current outputs in the case of the copper cathode remain constant and depend on the current density and the specific flow rate, while the current outputs at the angle decrease with increasing pH. The lower limit of the acidity () is determined by the technological parameters of chromium-containing wastewater, which is available for treatment. The upper limit follows. assume that, at large values, the hydrolysis of trivalent chromium occurs directly in the active zone of the cathode and the precipitated chromium hydroxide shields the surface of the cathode.

With an increase in current density, the energy consumption for the recovery of hexavalent chromium increases, and at currents exceeding 0.3 A / dm, there is abundant gassing at the cathode. At current densities lower than 0.05 A / dm, the stability of the cathode is disturbed and the overall dimensions of the equipment increase.

Thus, the optimum current density range is 0.050, 3 A / dm. The specific energy consumption for the recovery of hexavalent chromium by the proposed method, and 2-3 times, is lower than the known.

The proposed wastewater treatment method, in comparison with the known reagent methods, is characterized by almost reagent-free treatment, which does not lead to salinization of the wastewater; the possibility of creating low-waste closed production due to the return of treated effluents to the technology; compactness and simplicity of technological design, its automation.

The economic effect from the use of the proposed method only due to the saving of hüteats is 0.16 rub. per 1 m of treated except containing waste.

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Claims (1)

METHOD FOR WASTE WATER CLEANING FROM IONS OF HEXVALENT CHROME, including electrolysis using a porous cathode and filtering through the cathode in the direction from the anode to the cathode, characterized in that, in order to reduce energy consumption, a cathode made of copper powder with a particle size of 0 is used. 05-0.50 mm, and electrolysis is carried out at a cathodic current density of 0.050.30 A / dm ² and a solution pH of 2-5. > 1110754 1 'koi ’filtration rate and prevention1