SK82994A3 - Method of electro-chemical reduction of nitrates - Google Patents

Abstract

The invention relates to a process for the catalytic electrochemical reduction of nitrate, principally to give elemental nitrogen in aqueous solutions at a cathode. The aim of the invention is to denitrify even concentrated salt-containing aqueous solutions by these nitrate reductions. The aqueous solution is introduced into the cathode compartment of an electrolysis cell, in which the cathode compartment and anode compartment are separated from each other by a cation exchange membrane, and is subjected to a voltage in the same.

Description

METHOD OF ELECTROCHEMICAL REDUCTION OF NITRATES

Technical field

The invention relates to a method of catalytic electrochemical reduction of nitrates, in particular to elemental nitrogen in an aqueous solution on the cathode.

BACKGROUND OF THE INVENTION

Aqueous solutions containing nitrates are, for example, ion exchange regenerates, which are used to eliminate nitrates from drinking water, or waste solutions from industry.

Conventional enzymatic biological denitrification, known hitherto, often works unreliable, especially at higher salt concentrations. So far, for example, it has not been possible to process nitrate-containing ion exchange regenerates so that the regeneration medium can be circulated.

SUMMARY OF THE INVENTION

It is an object of the invention to denitrify concentrated aqueous salt solutions by catalytic, cathodic reduction of nitrates.

SUMMARY OF THE INVENTION The object of the present invention is to provide a combination of electrolysis with concentration-increasing methods such as ion exchange, reverse osmosis, electrodialysis, the prerequisites for creating process combinations of beneficial nitrate elimination from water and aqueous solutions for environmental protection.

This object is solved by the teachings of the claims by placing an aqueous solution containing nitrates in the cathode space of the electrolyzer and introducing a suitable electrical voltage.

In the electrolyser, the cathode and anode compartments are separated from each other by a cation exchange membrane, the cathode is doped with a catalyst, and in the anode compartment there is another aqueous solution, such as sulfuric acid, that circulates.

At the cathode there is a chemical reduction of nitrates according to the first of the above equations, whereby at

one mole of nitrate consumes moles of protons.

NO 2 + 6H ⁺ + 5e <--> 0.5 N ₂ + 3H ₂ O

2.5H ₂ O - 5e <----> 1.25 O ₂ + 5H ⁺

At the anode, according to the second equation, water breaks down to form 5 moles of protons that pass from the anode space through the cation exchange membrane to the cathode space. Water decay is associated with increasing the concentration of the solution in the anode compartment, so water must be added. A deficiency of at least 1 mole of protons per mole of nitrates remaining in the cathode compartment must be compensated by the addition of an acid, for example hydrochloric acid, to the nitrate-treated solution.

Due to the fact that the electrochemical reduction of nitrates is strongly kinetic and can be disturbed by side reactions accompanying the whole process, such as the formation of ammonium, in addition to the composition of the nitrate-containing solution and potential, electrode.

According to the invention, the catalytic cathode reduction of nitrates according to the above-mentioned equation allows an electrode of, for example, activated carbon particles doped with various heavy metals, for example copper with palladium. By varying the carrier material and also the heavy metal content of the carrier material, it is possible to influence the nitrate reduction kinetics and thereby the formation of by-products.

Examples of CLS / M / vite / iOs of the invention

The following is an example of an embodiment of the process according to the invention.

In an electrolyzer in which the cathode and anode compartments are separated by a cation exchange membrane, there is a nitrate solution in the cathode compartment, about 10 g of a nitrate vial of solution and about 5% sulfuric acid in the anode compartment. The electrode made of activated carbon particles doped with copper with palladium serves as a cathode, the copper content being less than 10% and the palladium content being less than 1%. At a potential of 1,000 to 1,400 mV, about 90% of the nitrate is converted to nitrogen. The pH is kept constant by the addition of hydrochloric acid in the cathode space. Full reduction of nitrate is not desirable because the solution treated in the cathode space serves as a regenerating agent for the anion exchanger contaminated with nitrate.

Claims (4)

PATENT CLAIMS A method for the electrochemical reduction of nitrates by catalysis, in particular elemental nitrogen in an aqueous solution, characterized in that an aqueous nitrate solution located in the cathode compartment is subjected to an electrical voltage, the cathode compartment and the anode compartment being separated from each other by a cation exchange membrane. Method according to claim 1, characterized in that the cathode consists of a support material which is doped with a catalyst. Method according to claim 1 or 2, characterized in that the support material is a catalytic mixture of heavy metals. Method according to one of Claims 1 to 3, characterized in that, after treatment, the nitrate-containing solution electrolytically treated in the cathode space is treated with an ion exchanger.