EP0245279B1 - Method for the electrochemical oxidation of sulphuric acid chromium iii solutions into chromium vi solutions - Google Patents

Method for the electrochemical oxidation of sulphuric acid chromium iii solutions into chromium vi solutions Download PDF

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Publication number
EP0245279B1
EP0245279B1 EP86901730A EP86901730A EP0245279B1 EP 0245279 B1 EP0245279 B1 EP 0245279B1 EP 86901730 A EP86901730 A EP 86901730A EP 86901730 A EP86901730 A EP 86901730A EP 0245279 B1 EP0245279 B1 EP 0245279B1
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EP
European Patent Office
Prior art keywords
chromium
nitric acid
solutions
litre
sulphuric acid
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Expired
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EP86901730A
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German (de)
French (fr)
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EP0245279A1 (en
Inventor
Richard Vytlacil
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Andritz Hydro GmbH Austria
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Andritz Hydro GmbH Austria
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals

Definitions

  • the invention relates to a process for the electrochemical oxidation of sulfuric acid chromium III solutions to chromium VI solutions, in a cell divided by means of a diaphragm, while flushing air into the electrolyte in the cathode compartment.
  • nitric acid-containing, sulfuric acid chromium III solutions such as those that occur in the oxidative purification of flue gases
  • nitric acid remains in the electrolyte during the processing of the oxidizing agent, up to 30% ammonium ions are formed on the cathode in the presence of chromium III ions, in addition to the hydrogen.
  • the discharge of these ammonium salts is only possible by complex processes.
  • the cell voltages that can be achieved in practice in this arrangement lie between 4.8 and 6.4 volts and can be increased even further due to the poorer conductivity of chrome-plated cathodes.
  • the object of the invention is to provide a method of the type mentioned at the outset which on the one hand avoids the disadvantages of the known methods and in which on the other hand the electricity costs for the electrolysis are lower.
  • the process according to the invention is characterized in that the electrolyte contains nitric acid, sulfuric acid and chromium III and the nitric acid is used as a redox carrier for the oxygen electrode serving as the cathode and that the nitric acid is regenerated by flushing in oxygen or air.
  • the method according to the invention allows a considerable reduction in the electricity costs during electrolysis.
  • the most positive cathode fraction is the cathodic oxygen reduction.
  • the reduction of oxygen in acidic solutions is, however, kinetically strongly inhibited.
  • Usable oxygen electrodes require either expensive catalysts based on precious metals or suitable redox carriers in an acidic environment.
  • the reduced species of the redox transmitter must have such a high reactivity that it can be oxidized again by the oxygen dissolved in the electrolyte.
  • the reduction of nitric acid was chosen as the cathode reaction for the process according to the invention, since its reversible potential of +940 mV is close to that of the oxygen electrode.
  • the cell voltages that can be achieved under these conditions are between 0.9 volts and approximately 2 volts. This means that the electricity costs for electrolysis can be reduced to about 1/3.
  • the electrolysis is preferably operated with an electrolyte composition of 20 g / l to 300 g / IH 2 SO 4 , 20 g / l to 200 g / l HN0 3 and 20 g / l to 30 g / l chromium .
  • activated carbon and / or graphite are preferably used as the cathode material.
  • electrodes with high oxygen overvoltage such as, for. B. lead dioxide, manganese dioxide, tin dioxide and / or combinations thereof.
  • the electrolytic cell consists of the usual arrangement of several anode and cathode spaces, which are separated by diaphragms and are connected in series, anodes and cathodes working as bipolar electrodes.
  • the electrolyte is supplied to the individual cathode compartments and then to the anode compartments via appropriate supply lines and is drawn off via a collecting line. Air and / or oxygen is blown in, for example, through perforated tubes which are arranged in the bottom of the cathode compartments.
  • Either porous gas diffusion electrodes made of activated carbon or graphite or shaking electrodes made of the same material are used as cathodes. This consumes residual gas, with traces of nitrogen oxides, which can arise as intermediates in the cathode reaction and are carried away with the gas flow, is returned to the oxidative flue gas scrubber.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Treating Waste Gases (AREA)
  • Water Treatment By Electricity Or Magnetism (AREA)

Abstract

The treatment of nitric acid-containing sulphuric acid chromium III solutions, as they are produced during the oxidizing purification of combustion gases, presents great difficulties or is very costly. The aim of the invention is to provide a method wherein the current expenses for the electrolysis are low. The method, according to the invention, for the electrochemical oxidation of sulphuric acid chromium III solutions into chromium VI lies essentially in that the nitric acid, the sulphuric acid and the chromium are contained in the electrolyte, the nitric acid being used as redox carrier for the oxygen electrode acting as cathode and the nitric acid being regenerated by the oxygen. Carbon or graphite are used as cathode material. For the anode, electrodes are used which present a higher oxygen overvoltage such as for example lead dioxide. The cell voltages which may be obtained in these conditions are comprised between 0.9 and 2 volts. This means that the current expenses for the electrolysis are reduced by 1/3 approximately.

Description

Die Erfindung betrifft ein verfahren zur elektrochemischen Oxidation von schwefelsauren Chrom-III-Lösungen zu Chrom-VI-Lösungen, in einer mittels Diaphragma unterteilten Zelle unter Einspülen von Luft in den im Kathodenraum befindlichen Elektrolyten.The invention relates to a process for the electrochemical oxidation of sulfuric acid chromium III solutions to chromium VI solutions, in a cell divided by means of a diaphragm, while flushing air into the electrolyte in the cathode compartment.

Nach einem betriebsinternem Stand der Technik bereitet die Aufbereitung von salpetersäurehältigen, schwefelsauren Chrom-III-Lösungen, wie sie bei der oxidativen Reinigung von Rauchgasen anfallen, grobe Schwierigkeiten. Bleibt bei der Aufarbeitung des oxidationsmittels Salpetersäure im Elektrolyt zurück, so entstehen an der Kathode in Gegenwart von Chrom-III-Ionen, neben dem Wasserstoff bis zu 30 % Ammoniumionen. Der Austrag dieser Ammoniumsalze ist nur durch aufwendige Verfahren möglich.According to an in-house state of the art, the preparation of nitric acid-containing, sulfuric acid chromium III solutions, such as those that occur in the oxidative purification of flue gases, presents great difficulties. If nitric acid remains in the electrolyte during the processing of the oxidizing agent, up to 30% ammonium ions are formed on the cathode in the presence of chromium III ions, in addition to the hydrogen. The discharge of these ammonium salts is only possible by complex processes.

Wird die Salpetersäure vollständig aus dem Systementfernt, so bleibt als Kathodenreaktion die Wasserstoffentwicklung; doch besteht dabei die Gefahr, daß aus der schwefelsauren Lösung Chrom an der Kathode abgeschieden wird, welches der Lösung wieder zugesetzt werden muß.If the nitric acid is completely removed from the system, the evolution of hydrogen remains as the cathode reaction; however, there is a risk that chromium is deposited on the cathode from the sulfuric acid solution, which must be added to the solution again.

Ein verfahren der eingangs genannten Art ist aus der Druckschrift "Chemical Abstracts", Band 90, Nr. 24, 11.Juni 1979, Columbus, Ohio (US), Seite 531, Spalte 1, Zusammenfassung 194736 w SU, A, 583202 (Letskitch), 5. Dezember 1977 bekannt.A method of the type mentioned at the beginning is described in the publication "Chemical Abstracts", Volume 90, No. 24, June 11, 1979, Columbus, Ohio (US), page 531, column 1, abstract 194736 w SU, A, 583202 (Letskitch ), December 5, 1977.

Die in der Praxis erreichbaren Zellenspannungen liegen bei dieser Anordnung zwischen 4,8 und 6,4 Volt und können aufgrund der schlechteren Leitfähigkeit chromüberzogener Kathoden noch weiter erhöht werden.The cell voltages that can be achieved in practice in this arrangement lie between 4.8 and 6.4 volts and can be increased even further due to the poorer conductivity of chrome-plated cathodes.

Aufgabe der Erfindung ist es, ein Verfahren der eingangs genannten Art zu schaffen, das einerseits die Nachteile der bekannten Verfahren vermeidet und bei dem andererseits die Stromkosten für die Elektrolyse geringer sind.The object of the invention is to provide a method of the type mentioned at the outset which on the one hand avoids the disadvantages of the known methods and in which on the other hand the electricity costs for the electrolysis are lower.

Das erfindungsgemäße Verfahren ist dadurch gekennzeichnet, daß der Elektrolyt Salpetersäure, Schwefelsäure und Chrom-lll enthält und die Salpetersäure als Redoxträger für die als Kathode dienende Sauerstoffelektrode vervendet wird und daß durch Einspülen von Sauerstoff bzw. Luft die Salpetersäure regeneriert wird.The process according to the invention is characterized in that the electrolyte contains nitric acid, sulfuric acid and chromium III and the nitric acid is used as a redox carrier for the oxygen electrode serving as the cathode and that the nitric acid is regenerated by flushing in oxygen or air.

Das Verfahren gemäß der Erfindung erlaubt durch den Ersatz der Wasserstoffelektrode gegen eine Elektrodenreaktion mit bedeutend positiverem Elektrodenpotential eine beträchtliche Senkung der Stromkosten bei der Elektrolyse.By replacing the hydrogen electrode with an electrode reaction with a significantly more positive electrode potential, the method according to the invention allows a considerable reduction in the electricity costs during electrolysis.

Als positivste Kathodenraktion bietet sich die kathodische Sauerstoffreduktion an. Die Reduktion von Sauerstoff in sauren Lösungen ist jedoch kinetisch stark gehemmt. Brauchbare Sauerstoffelektroden erfordern in saurem Milieu entweder teure Katalysatoren auf Edelmetallbasis oder geeignete Redoxüberträger. Die reduzierte Spezies des Redoxüberträgers muß eine so hohe Reaktivität aufweisen, daß sie durch den im Elektrolyt gelösten Sauerstoff wieder oxidiert werden kann. Als Kathodenreaktion für das erfindungsgemäße Verfahren, wurde die Reduktion von Salpetersäure gewählt, da ihr reversibles Potential mit +940 mV nahe dem der Sauerstoffelektrode liegt. Die unter diesen Bedingungen erreichbaren zellspannungen liegen zwischen 0,9 Volt und etwa 2 Volt. Das bedeutet, daß die Stromkosten für die Elektrolyse auf etwa 1/3 gesenkt werden können.The most positive cathode fraction is the cathodic oxygen reduction. The reduction of oxygen in acidic solutions is, however, kinetically strongly inhibited. Usable oxygen electrodes require either expensive catalysts based on precious metals or suitable redox carriers in an acidic environment. The reduced species of the redox transmitter must have such a high reactivity that it can be oxidized again by the oxygen dissolved in the electrolyte. The reduction of nitric acid was chosen as the cathode reaction for the process according to the invention, since its reversible potential of +940 mV is close to that of the oxygen electrode. The cell voltages that can be achieved under these conditions are between 0.9 volts and approximately 2 volts. This means that the electricity costs for electrolysis can be reduced to about 1/3.

Weitere Vorteile liegen darin, daß bei Prozessen bei denen ausschließlich Nitrosegase zu Salpetersäure oxidiert werden, die aufwendige quantitative Entfernung der Salpetersäure aus der Chromschwefelsäure entfällt und daß unter Reaktionsbedingungen, d. h. bei Potentialen positiver +840 mV/NWE die Salpetersäure nicht bis zum Ammoniak reduziert werden kann.Further advantages are that in processes in which only nitrous gases are oxidized to nitric acid, the elaborate quantitative removal of the nitric acid from the chromosulfuric acid is eliminated and that under reaction conditions, i. H. at potentials positive +840 mV / NWE the nitric acid cannot be reduced to ammonia.

Gemäß einem besonderen Merkmal der Erfindung wird die Elektrolyse bevorzugt mit einer Elektrolytzusammensetzung von 20 g/I bis 300 g/I H2S04, 20 g/I bis 200 g/I HN03 und 20 g/I bis 30 g/I Chrom betrieben.According to a special feature of the invention, the electrolysis is preferably operated with an electrolyte composition of 20 g / l to 300 g / IH 2 SO 4 , 20 g / l to 200 g / l HN0 3 and 20 g / l to 30 g / l chromium .

Nach einem weiteren Merkmal der Erfindung werden als Kathodenmaterial bevorzugt aktivierte Kohle und/oder Graphit eingesetzt.According to a further feature of the invention, activated carbon and / or graphite are preferably used as the cathode material.

Gemäß einer Ausgestaltung der Erfindung werden als Anodenmaterial Elektroden mit hoher Sauerstoffüberspannung wie z. B. Bleidioxid, Mangandioxid, Zinndioxid und/oder deren Kombinationen verwendet.According to one embodiment of the invention, electrodes with high oxygen overvoltage such as, for. B. lead dioxide, manganese dioxide, tin dioxide and / or combinations thereof.

Die Elektrolysezelle besteht aus der üblichen Anordnung von mehreren durch Diaphragmen getrennten, hintereinander geschalteten Anodenund Kathodenräumen, wobei Anodenund Kathoden als bipolare Elektroden arbeiten. Der Elektrolyt wird über entsprechende Zuleitungen den einzelnen Kathodenräumen und anschließend den Anodenräumen zugeführt und über eine Sammelleitung abgezogen. Luft und /oder Sauerstoff wird beispielsweise über gelochte Rohre, die im Boden der Kathodenräume angeordnet sind, eingeblasen.The electrolytic cell consists of the usual arrangement of several anode and cathode spaces, which are separated by diaphragms and are connected in series, anodes and cathodes working as bipolar electrodes. The electrolyte is supplied to the individual cathode compartments and then to the anode compartments via appropriate supply lines and is drawn off via a collecting line. Air and / or oxygen is blown in, for example, through perforated tubes which are arranged in the bottom of the cathode compartments.

Die austretenden überschüssigen Gase werden abgesaugt und den Zellen wieder zugeführt. Abreagierter Sauerstoff wird kontinuierlich ersetzt.The escaping excess gases are suctioned off and returned to the cells. Reacted oxygen is continuously replaced.

Als Kathoden werden entweder poröse Gasdiffusionselektrodenaus aktivierter Kohle oder Graphit, oder Schüttelelektroden aus gleichem Material eingesetzt. Das verbraucht Restgas, mit Spuren von Stickoxiden, welche bei der Kathodenreaktion als Zwischenprodukte entstehen können und mit dem Gasstrom mitgerissen werden, wird der oxidativen Rauchgaswäsche wieder zugeführt.Either porous gas diffusion electrodes made of activated carbon or graphite or shaking electrodes made of the same material are used as cathodes. This consumes residual gas, with traces of nitrogen oxides, which can arise as intermediates in the cathode reaction and are carried away with the gas flow, is returned to the oxidative flue gas scrubber.

Claims (4)

1. Process for the electrochemical oxidation of chromium (III) sulphate solutions to chromium (VI) solutions, characterised in that the electcrolyte contains nitric acid, sulphuric acid and chromium, the nitric acid being used as the redox agent for the oxygen electrode acting as the cathode, and in that the nitric acid is regenerated by flushing oxygen or air into the electrolyte situated in the cathode chamber.
2. Process according to claim 1, characterised in that electrolysis preferably operates at an electrolyte composition of 20 g/litre to 300 g/litre H2S04, 20 g/litre to 200 g/litre HN03 and 20 g/litre to 30 g/litre chromium.
3. Process according to claim 1 or 2, characterised in that active carbon and/or graphite is preferably employed as the cathode material.
4. Process according to one of claims 1 to 3, characterised in that electrodes having high oxygen overvoltage, such as, for example lead dioxide, manganese dioxide, tin dioxide and/or combinations thereof are used as the anode material.
EP86901730A 1985-02-27 1986-02-27 Method for the electrochemical oxidation of sulphuric acid chromium iii solutions into chromium vi solutions Expired EP0245279B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT577/85 1985-02-27
AT0057785A AT382894B (en) 1985-02-27 1985-02-27 METHOD FOR THE ELECTROCHEMICAL OXIDATION OF SULFURIC ACID CHROME III SOLUTIONS TO CHROME VIL SOLUTIONS

Publications (2)

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EP0245279A1 EP0245279A1 (en) 1987-11-19
EP0245279B1 true EP0245279B1 (en) 1989-07-12

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EP86901730A Expired EP0245279B1 (en) 1985-02-27 1986-02-27 Method for the electrochemical oxidation of sulphuric acid chromium iii solutions into chromium vi solutions

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US (1) US4859294A (en)
EP (1) EP0245279B1 (en)
JP (1) JPS62501979A (en)
AT (1) AT382894B (en)
AU (1) AU5580786A (en)
DD (1) DD243300A5 (en)
DE (1) DE3664341D1 (en)
FI (1) FI80075C (en)
HU (1) HU201361B (en)
WO (1) WO1986005215A1 (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3940978A1 (en) * 1989-12-12 1991-06-13 Hoechst Ag METHOD FOR THE ELECTROCHEMICAL REGENERATION OF CHROMIUM ACIDIC ACID
US6468414B1 (en) 2001-02-16 2002-10-22 Hydro-Quebec Method of purification of a redox mediator before electrolytic regeneration thereof
GB2399349A (en) * 2003-03-13 2004-09-15 Kurion Technologies Ltd Regeneration of chromic acid etching and pickling baths
JP6206382B2 (en) * 2014-11-28 2017-10-04 住友金属鉱山株式会社 Method for producing indium hydroxide powder
IL273018B2 (en) * 2017-09-08 2023-11-01 Haskoli Islands Electrolytic ammonia production using transition metal oxide catalysts

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE103860C (en) *
US1739107A (en) * 1925-11-05 1929-12-10 Marvin J Udy Process of making chromic acid
DE2310622A1 (en) * 1973-03-02 1974-09-12 Basf Ag DIAPHRAGM CELL FOR THE PRODUCTION OF SULFURIC ACID CHROMIC ACID SOLUTIONS
US4006067A (en) * 1973-03-05 1977-02-01 Gussack Mark C Oxidation-reduction process
US4273628A (en) * 1979-05-29 1981-06-16 Diamond Shamrock Corp. Production of chromic acid using two-compartment and three-compartment cells

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Publication number Publication date
HUT46081A (en) 1988-09-28
EP0245279A1 (en) 1987-11-19
FI80075B (en) 1989-12-29
AT382894B (en) 1987-04-27
WO1986005215A1 (en) 1986-09-12
FI80075C (en) 1990-04-10
FI873678A0 (en) 1987-08-25
HU201361B (en) 1990-10-28
AU5580786A (en) 1986-09-24
DD243300A5 (en) 1987-02-25
FI873678A (en) 1987-08-25
DE3664341D1 (en) 1989-08-17
US4859294A (en) 1989-08-22
JPS62501979A (en) 1987-08-06
ATA57785A (en) 1986-09-15

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