EP0245279A1 - 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.

Info

Publication number
EP0245279A1
EP0245279A1 EP86901730A EP86901730A EP0245279A1 EP 0245279 A1 EP0245279 A1 EP 0245279A1 EP 86901730 A EP86901730 A EP 86901730A EP 86901730 A EP86901730 A EP 86901730A EP 0245279 A1 EP0245279 A1 EP 0245279A1
Authority
EP
European Patent Office
Prior art keywords
chromium
solutions
nitric acid
oxygen
cathode
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP86901730A
Other languages
German (de)
French (fr)
Other versions
EP0245279B1 (en
Inventor
Richard Vytlacil
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Andritz Hydro GmbH Austria
Original Assignee
Andritz Hydro GmbH Austria
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Andritz Hydro GmbH Austria filed Critical Andritz Hydro GmbH Austria
Publication of EP0245279A1 publication Critical patent/EP0245279A1/en
Application granted granted Critical
Publication of EP0245279B1 publication Critical patent/EP0245279B1/en
Expired legal-status Critical Current

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Classifications

    • 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.
  • nitric acid-containing, sulfuric, chromium-III solutions such as are produced in the oxidative purification of flue gases, is very difficult. If nitric acid remains in the electrolyte when the oxidant is worked up, 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 are 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 process of the type mentioned at the outset which on the one hand avoids the disadvantages of the known processes and 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, the nitric acid being Redox transmitter is used for the oxygen electrode serving as the cathode and that the nitric acid is regenerated by flushing oxygen or air into the electrolyte in the cathode compartment.
  • the method according to the invention allows a considerable reduction in the electricity costs in 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 / 1 to 300 g / 1 H2SO4, 20 g / 1 to 200 g / 1 HNO3 and 20 g / 1 to 30 g / 1 chromium.
  • 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 a plurality of 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 spaces.
  • Either porous gas diffusion electrodes made of activated carbon or graphite or shaking electrodes made of the same material are used as cathodes. That consumes residual gas, with traces of nitrogen oxides, which can arise as intermediates in the cathode reaction and are entrained with the gas flow, is returned to the oxidative flue gas scrubbing.

Landscapes

  • 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

Le traitement de solutions de chrome III dans l'acide sulfurique contenant de l'acide nitrique, comme elles se produisent lors de la purification oxydante des gaz de combustion, présente de grosses difficultés ou est très coûteux. Le but de l'invention est de créer un procédé dans lequel les frais de courant pour l'électrolyse sont faibles. Le procédé selon l'invention pour l'oxydation électrochimique de solutions de chrome III dans l'acide sulfurique en solutions de chrome VI réside, pour l'essentiel, en ce que l'acide nitrique, l'acide sulfurique et le chrome sont contenus dans l'électrolyte, l'acide nitrique étant utilisé comme transporteur rédox pour l'électrode d'oxygène servant de cathode et l'acide nitrique étant régénéré par l'oxygène. Le carbone ou le graphite sont utilisés comme matière de la cathode. Pour l'anode, on utilise des électrodes présentant une surtension d'oxygène élevée comme, par exemple, le dioxyde de plomb. Les tensions de la cellule que l'on peut obtenir dans ces conditions sont comprises entre 0,9 et 2 volts. Cela signifie que les dépenses de courant pour l'électrolyse sont abaissées d'environ 1/3.The treatment of solutions of chromium III in sulfuric acid containing nitric acid, as occurs during oxidative purification of flue gases, presents great difficulties or is very expensive. The aim of the invention is to create a process in which the current costs for electrolysis are low. The process according to the invention for the electrochemical oxidation of chromium III solutions in sulfuric acid into chromium VI solutions consists essentially in the fact that nitric acid, sulfuric acid and chromium are contained in the electrolyte, the nitric acid being used as a redox carrier for the oxygen electrode serving as the cathode and the nitric acid being regenerated by the oxygen. Carbon or graphite are used as the cathode material. Electrodes with a high oxygen overvoltage, such as lead dioxide, are used for the anode. The cell voltages that can be obtained under these conditions are between 0.9 and 2 volts. This means that the current costs for electrolysis are lowered by approximately 1/3.

Description

Verfahren zur elektrochemischen Oxidation von schwefel¬ sauren Chrom-m-Lösungen zu Chro -VI-Lösungen Die Erfindung betrifft ein Verfahren zur elektroche¬ mischen Oxidation von schwefelsauren Chrom-III-Lösungen zu Chrom-VI-Lösungen.The invention relates to a process for the electrochemical oxidation of sulfuric acid chromium III solutions to chromium VI solutions.
Die Aufbereitung von salpetersäurehältigen, schwefel¬ sauren Chrom-III-Lösungen, wie sie bei der oxidativen Reinigung von Rauchgasen anfallen, bereiten große 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 % Ammonium- ionen. Der Austrag dieser Ammoniumsalze ist nur durch aufwendige Verfahren möglich.The preparation of nitric acid-containing, sulfuric, chromium-III solutions, such as are produced in the oxidative purification of flue gases, is very difficult. If nitric acid remains in the electrolyte when the oxidant is worked up, 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 System entfernt, so 'bleibt als Kathodenreaktion die Wasser- stoffentwicklung; 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, so 'remains as a cathode reaction material development the water; 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.
Die in der Praxis erreichbaren Zellenspannungen liegen bei dieser Anordnung zwischen 4,8 und 6,4 Volt und können aufgrund der schlechteren Leitfähigkeit chrom- überzogener Kathoden noch weiter erhöht werden.The cell voltages that can be achieved in practice in this arrangement are 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 anderer- seits die Stromkosten für die Elektrolyse geringer sind.The object of the invention is to provide a process of the type mentioned at the outset which on the one hand avoids the disadvantages of the known processes and on the other hand the electricity costs for the electrolysis are lower.
Das erfindungsgemäße Verfahren ist dadurch gekennzeich¬ net, daß im Elektrolyten Salpetersäure, Schwefelsäure und Chrom enthalten sind, wobei die Salpetersäure als Redoxüberträger für die als Kathode dienende Sauer¬ stoffelektrode verwendet wird und daß durch Einspülen von Sauerstoff bzw. Luft in den im Kathodenraum be¬ findlichen Elektrolyten die Salpetersäure regeneriert wird. i IThe process according to the invention is characterized in that the electrolyte contains nitric acid, sulfuric acid and chromium, the nitric acid being Redox transmitter is used for the oxygen electrode serving as the cathode and that the nitric acid is regenerated by flushing oxygen or air into the electrolyte in the cathode compartment. i I
Das Verfahren gemäß der Erfindung erlaubt durch den Ersatz der Wasserstoffelektrode gegen eine Elektroden¬ reaktion-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 in electrolysis.
Als positivste Kathodenraktion bietet sich die katho¬ dische Sauerstoffreduktion an. Die Reduktion von Sauerstoff in sauren Lösungen ist jedoch kinetisch stark gehemmt. Brauchbare Sauerstoffelektroden erfor¬ dern 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 erfindungs- gemäße Verfahren, wurde die Reduktion von Salpeter¬ säure 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 lie in the fact that in processes in which only nitrous gases are oxidized to nitric acid, the complex quantitative removal of the nitric acid from the chromosulfuric acid is dispensed with and that under reaction conditions, ie at potentials of positive +840 mV / NWE, the nitric acid does not reach can be reduced to ammonia.
Gemäß einem besonderen Merkmal der Erfindung wird die Elektrolyse bevorzugt mit einer Elektrolytzusammen¬ setzung von 20 g/1 bis 300 g/1 H2SO4, 20 g/1 bis 200 g/1 HNO3 und 20 g/1 bis 30 g/1 Chrom betrieben.According to a special feature of the invention, the electrolysis is preferably operated with an electrolyte composition of 20 g / 1 to 300 g / 1 H2SO4, 20 g / 1 to 200 g / 1 HNO3 and 20 g / 1 to 30 g / 1 chromium.
Nach einem weiteren Merkmal der Erfindung werden als Kathodenmaterial bevorzugt aktivierte Kohle und/oderAccording to a further feature of the invention, activated carbon and / or are preferably used as the cathode material
Graphit eingesetzt.Graphite used.
Gemäß einer Ausgestaltung der Erfindung werden als Anodenmaterial Elektroden mit hoher Sauerstoffüber¬ spannung 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, hinterein¬ ander geschalteten Anoden- und Kathodenräumen, wobei Anoden und 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 beispiels¬ weise über gelochte Rohre, die im Boden der Kathoden- räume angeordnet sind, eingeblasen.The electrolytic cell consists of the usual arrangement of a plurality of 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 spaces.
Die austretenden überschüssigen Gase werden abgesaugt und den Zellen wieder zugeführt. Abreagierter Sauer¬ stoff 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 Gasdiffusionselek¬ troden aus aktivierter Kohle oder Graphit, oder Schüttel¬ elektroden 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. That consumes residual gas, with traces of nitrogen oxides, which can arise as intermediates in the cathode reaction and are entrained with the gas flow, is returned to the oxidative flue gas scrubbing.

Claims

Patentansprüche Claims
Verfahren zur elektrochemischen Oxidation von schwefelsauren Chrom-III-Lösungen zu Chrom-VI- Lösungen, dadurch gekennzeichnet, daß im Elektro¬ lyten Salpetersäure, Schwefelsäure und Chrom ent¬ halten sind, wobei die Salpetersäure als Redox- träger für die als Kathode dienende Sauerstoff¬ elektrode verwendet wird und'daß durch Einspülen von Sauerstoff bzw. Luft in den im Kathodenraum befindlichen Elektrolyten die Salpetersäure re¬ generiert wird.Process for the electrochemical oxidation of sulfuric acid chromium III solutions to chromium VI solutions, characterized in that nitric acid, sulfuric acid and chromium are contained in the electrolyte, the nitric acid as redox carrier for the oxygen serving as cathode Electrode is used and that the nitric acid is regenerated by flushing oxygen or air into the electrolyte in the cathode compartment.
1010
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Elektrolyse bevorzugt mit einer Elektro-2. The method according to claim 1, characterized in that the electrolysis preferably with an electrical
- lytzusammeiitsetzung von 20 g/1 bis 300 g/1 H2SO., 20 g/1 bis 200 g/1 HN03 und 20 g/1 bis 30 g/1 15 Chrom betrieben wird.- lyt composition of 20 g / 1 to 300 g / 1 H 2 SO., 20 g / 1 to 200 g / 1 HN0 3 and 20 g / 1 to 30 g / 1 15 chromium is operated.
3. Verfahren nach Anspruch 1 oder 2, dadurch- gekenn¬ zeichnet, daß als Kathodenmaterial bevorzugt aktivierte Kohle und/oder Graphit eingesetzt wer-3. The method according to claim 1 or 2, characterized- gekenn¬ characterized in that activated carbon and / or graphite are preferably used as the cathode material
20 den.20 den.
4. Verfahren nach einem der Ansprüche 1 bis 3, da¬ durch gekennzeichnet, daß als Anodenmaterial Elektroden mit hoher Sauerstoffüberspannung wie4. The method according to any one of claims 1 to 3, da¬ characterized in that electrodes with a high oxygen overvoltage such as
25 z. B. Bleidioxid, Mangandioxid, Zinndioxid und/25 z. B. lead dioxide, manganese dioxide, tin dioxide and /
\ oder deren Kombination verwendet werden. \ or their combination can be used.
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)

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

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
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

Country Status (10)

Country Link
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

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8605215A1 *

Also Published As

Publication number Publication date
HUT46081A (en) 1988-09-28
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
EP0245279B1 (en) 1989-07-12
JPS62501979A (en) 1987-08-06
ATA57785A (en) 1986-09-15

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