EP1044167A1 - Removal of heavy metal ions from aqueous media - Google Patents

Removal of heavy metal ions from aqueous media

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Publication number
EP1044167A1
EP1044167A1 EP98966413A EP98966413A EP1044167A1 EP 1044167 A1 EP1044167 A1 EP 1044167A1 EP 98966413 A EP98966413 A EP 98966413A EP 98966413 A EP98966413 A EP 98966413A EP 1044167 A1 EP1044167 A1 EP 1044167A1
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EP
European Patent Office
Prior art keywords
sulfide
heavy metal
mercury
metal ions
wet oxidation
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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.)
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EP98966413A
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German (de)
French (fr)
Inventor
Holger Heidenreich
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Bayer AG
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Bayer AG
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Publication date
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Publication of EP1044167A1 publication Critical patent/EP1044167A1/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/58—Treatment of water, waste water, or sewage by removing specified dissolved compounds
    • C02F1/62—Heavy metal compounds
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/02—Treatment of water, waste water, or sewage by heating
    • C02F1/025—Thermal hydrolysis
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S210/00—Liquid purification or separation
    • Y10S210/902—Materials removed
    • Y10S210/911—Cumulative poison
    • Y10S210/912—Heavy metal
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S210/00—Liquid purification or separation
    • Y10S210/902—Materials removed
    • Y10S210/911—Cumulative poison
    • Y10S210/912—Heavy metal
    • Y10S210/914—Mercury

Definitions

  • the invention relates to a method for removing heavy metal ions, in particular mercury and silver ions, from aqueous media.
  • Waste water containing organic compounds can be cleaned in various ways.
  • One possibility is that the waste water is concentrated and then the residue is burned.
  • Another possibility is to subject the wastewater to an oxidative treatment (so-called wet oxidation) (H. Perkow, R. Steiner, H. Vollmüller, Chem.-Ing.-Tech. 52
  • the present invention was therefore based on the object of providing an improved process for removing heavy metal ions from aqueous media.
  • a process has now been found for removing heavy metal ions, in particular mercury and silver ions from aqueous media, which is characterized in that sulfide precipitation is carried out in the presence of iron oxide to precipitate the heavy metal ions.
  • the heavy metal ions to be precipitated are dissolved heavy metal salts which are precipitated in the form of their sulfides during sulfide precipitation.
  • a water-soluble sulfide is preferably used for the sulfide precipitation, water-soluble preferably being understood to mean a solubility in water at 20 ° C. of greater than or equal to 100 g / 1, in particular greater than 300 g / 1.
  • particularly preferred sulfides are hydrogen sulfide, alkali sulfide, in particular sodium sulfide, alkali hydrogen sulfide, in particular sodium hydrogen sulfide or mixtures thereof.
  • the sulfide used for the sulfide precipitation is preferably used stoichiometrically or in a stoichiometric excess, based on the heavy metal cation to be precipitated.
  • the sulfide precipitation is preferably carried out at a temperature of 20 to 155 ° C. It can be carried out at normal pressure or at elevated pressure, preferably at 1 to 6 bar.
  • the process according to the invention is preferably carried out in the presence of an iron oxide compound from the group FeO, Fe 2 ⁇ 3 and Fe 2 ⁇ 4 or mixtures thereof.
  • the amount by weight of iron oxide is preferably 5 to 500, in particular 5 to 100 mg / l of waste water.
  • the wet oxidation product of iron and heavy metal is used as the aqueous medium.
  • the content of inorganic salts is preferably 0 to 15% by weight, based on the iron-containing water.
  • the iron content of the water supplied to the wet oxidation is preferably - the iron is preferably in the form of iron sulfate - 5 to 500 mg / 1, particularly preferably 10 to 100 mg / 1.
  • the aqueous medium generally has a pH of 0.5 to 2.5.
  • the waste water is preferably pumped with a high-pressure pump through a heat exchanger, in which it is preheated by the cleaned waste water in countercurrent.
  • the temperature should be sufficiently high that the oxidation, which is preferably carried out with air, starts. From a TOC content of 10,000 to 20,000 mg / 1, the oxidation can proceed autothermally without the use of additional energy. Since oxidation in the gas phase generally proceeds very slowly under the temperature conditions of the wet oxidation, it is preferably ensured by setting a pressure which is above the saturated steam pressure at the corresponding temperature that at least part of the water in the reactor is preferably present in liquid form.
  • a catalyst is preferably added to accelerate the reaction.
  • Metals from the subgroups are used in particular as catalysts.
  • preferred catalysts are understood to be divalent catalytic copper ions, copper sulfate or copper sulfide being preferably used.
  • the copper catalyst is preferably used in an amount of 100 to 1000 mg / 1, particularly preferably from 200 to 700 mg / 1.
  • the wet oxidation is carried out at a temperature of 240 to 280 ° C., it being advantageous to set a pressure of 100 to 200 bar.
  • the cleaned waste water and the low-oxygen exhaust gas are preferably separated from one another in a liquid separator.
  • the catalyst is preferably precipitated as sulfide, separated and returned to the wet oxidation process, where it is in turn oxidized to copper sulfate.
  • reaction products of the wet oxidation are carbon dioxide and water with small proportions of anoxidized, low molecular weight fragments of poorly degradable organic compounds.
  • the nitrogen content of organic compounds is largely converted into ammonia, which is stripped from the cleaned, acidic wastewater after pH adjustment.
  • iron oxide required for sulfide precipitation comes from the wet oxidation stage of an iron-containing aqueous medium, it may be advantageous to remove this solution or suspension after the wet oxidation, i.e. Add polyelectrolytes before or preferably after sulfide precipitation.
  • salts are, for example
  • Polyphosphoric acid, polyvinylsulfuric acid, polyvinylsulfonic acid, polyvinylphosphonic acid, polyacrylic acid, polyethyleneimines, polyvinylamines, polyvinylpyridines etc. are to be mentioned.
  • the polyelectrolytes can be used, for example, in an amount of 0.0001 to 0.1% by weight, based on the suspension or solution.
  • the aqueous medium used for the wet oxidation has, in particular, a pH of 5.5 to 8.0.
  • Heavy metal ion-reduced wastewater obtained by the process according to the invention preferably has a residual heavy metal content of less than 1 mg / kg copper or silver and less than 0.005 mg / kg mercury.
  • mercury ions are separated off in the presence of copper ions by sulfide precipitation, characterized in that the water-soluble sulfide is present in a stoichiometric amount or in excess, preferably from 1.0 to 2.0 molar equivalents, preferably 1.0 to 1.5 molar equivalents per equivalent of mercury ions.
  • Mercury sulfide is preferably precipitated, with the large amount of copper ions remaining in solution.
  • the precipitated mercury sulfide can then be separated off together with the iron oxide.
  • the separated copper sulfide can then, for example, be used again as a catalyst in the wet oxidation process, where it is then oxidized to the soluble copper sulfate.
  • composition 15,000 mg / 1 TOC
  • the waste water purified to a residual TOC content of 350 mg / l (degree of purification of 97.6%) is cooled while preheating the reaction feed, depressurized under high pressure - separation of the purified waste water and the low-oxygen exhaust gas - and the finely divided Iron oxide continuously separated using a sand filter and filter press.
  • the acidic wastewater pH approx. 2.0
  • a 30% sodium hydrogen sulfide solution approximatelyx. 37 1 / h; end point detection via redox potential measurement
  • Copper is decanted to return it as a catalyst suspension for the wet oxidation process before the reactor.
  • Partially distributed mercury sulfide that co-precipitates under these conditions is thus partly returned to the catalyst cycle and concentrated therein without being able to be discharged, and partly remains finely divided in the waste water (concentration of mercury in the purified waste water 0.2 mg / kg ).
  • Example 2 30 m 3 / h of neutralized wastewater of the following composition are continuously oxidized with air in a high-pressure wet oxidation reactor at 250 ° C. and 150 bar pressure.
  • composition 15,000 mg / 1 TOC
  • the wastewater (pH 2.0), which has been cleaned to a residual TOC content of 350 mg / l (degree of purification of 97.6%), is cooled with preheating of the reactor feed, depressurized - separation of the cleaned wastewater and of the low-oxygen exhaust gas - and continuously via one
  • Fine flow metering pump with 14 ml / h of a 30% sodium hydrogen sulfide solution. After a residence time of approx. 1 hour, the precipitated mercury sulfide is continuously separated off together with the finely divided iron oxide using a sand filter and filter press. Then the filtrate, largely cleaned of mercury, is removed with a 30% solution for the purpose of separating the copper catalyst
  • the waste water from Example 2 is wet-oxidized as described above and a 30% sodium hydrogen sulfide solution is added to precipitate the mercury.
  • the water with 30 1 / h of an aqueous 0.1% mixture of a cationic high molecular weight polyacrylamide copolymer.
  • the iron oxide which can now be readily filtered, is separated off together with the precipitated mercury sulfide, as described above.
  • the catalyst removal is then continued, as set out in Example 2. After the HgS / CuS separation, the cleaned wastewater contains ⁇ 1 mg / kg copper and ⁇ 0.002 mg / kg mercury.

Abstract

A method for removing heavy metal ions from aqueous media, characterised in that a sulphide precipitation is carried out in the presence of ferric oxide.

Description

Entfernung von Schwermetallionen aus wäßrigen MedienRemoval of heavy metal ions from aqueous media
Die Erfindung betrifft ein Verfahren zum Entfernen von Schwermetallionen, insbesondere Quecksilber- und Silberionen, aus wäßrigen Medien.The invention relates to a method for removing heavy metal ions, in particular mercury and silver ions, from aqueous media.
Organisch belastete, d.h. organische Verbindungen enthaltende Abwässer, lassen sich auf verschiedene Art und Weise reinigen. Eine Möglichkeit ist die, daß das Abwasser eingeengt und anschließend der Rückstand verbrannt wird. Eine andere Möglichkeit besteht darin, daß man das Abwasser einer oxidativen Behandlung (sogenannte Naß- oxidation) unterzieht (H. Perkow, R. Steiner, H. Vollmüller, Chem.-Ing.-Tech. 52Organically contaminated, i.e. Waste water containing organic compounds can be cleaned in various ways. One possibility is that the waste water is concentrated and then the residue is burned. Another possibility is to subject the wastewater to an oxidative treatment (so-called wet oxidation) (H. Perkow, R. Steiner, H. Vollmüller, Chem.-Ing.-Tech. 52
(1980) Nr. 12, S. 943-951). Letztere Verfahrensweise eignet sich besonders für das Reinigen salzhaltiger Abwässer, da das Salz auf verschiedene Weise der wäßrigen Phase vorher entzogen werden kann.(1980) No. 12, pp. 943-951). The latter procedure is particularly suitable for the purification of saline wastewater, since the salt can be removed from the aqueous phase beforehand in various ways.
Neben der organischen Fracht sind auch Schwermetallionen, insbesondere Quecksilber- und Silberionen, in Abwässern häufig enthalten, wobei diese praktisch restlos entfernt werden müssen.In addition to the organic load, heavy metal ions, in particular mercury and silver ions, are also frequently present in wastewater, and these have to be removed practically completely.
So ist das Entfernen von Quecksilberionen aus Abgasströmen beispielsweise in EP-A-550 967 mit Hilfe von Ionenaustauschern beschrieben. Nachteilig hierbei ist allerdings der Einsatz von teuren Betriebsmitteln. Daneben wird gemäß DE-A- 4 229 662 auch die Quecksilberionenentfernung über die Sulfidfällung bei relativ großen Quecksilbermengen erwähnt. Dabei ist jedoch die relativ schlechte Filtrierbarkeit der dabei entstehenden Quecksilbersulfide problematisch, zumal dann, wenn die Schwermetallmengen sehr klein sind, insbesondere im Bereich wenigerThe removal of mercury ions from exhaust gas streams is described for example in EP-A-550 967 with the aid of ion exchangers. The disadvantage here, however, is the use of expensive equipment. In addition, according to DE-A-4 229 662, the removal of mercury by sulfide precipitation with relatively large amounts of mercury is also mentioned. However, the relatively poor filterability of the resulting mercury sulfides is problematic, especially when the amounts of heavy metals are very small, especially in the range less
Milligramm pro Liter liegen.Milligrams per liter.
Der vorliegenden Erfindung lag daher die Aufgabe zugrunde, ein verbessertes Verfahren zur Entfernung von Schwermetallionen aus wäßrigen Medien bereitzustellen. Es wurde nun ein Verfahren zur Entfernung von Schwermetallionen, insbesondere Quecksilber- und Silberionen aus wäßrigen Medien gefunden, das dadurch gekennzeichnet ist, daß zum Ausfällen der Schwermetallionen eine Sulfidfällung in Gegenwart von Eisenoxid durchgeführt wird.The present invention was therefore based on the object of providing an improved process for removing heavy metal ions from aqueous media. A process has now been found for removing heavy metal ions, in particular mercury and silver ions from aqueous media, which is characterized in that sulfide precipitation is carried out in the presence of iron oxide to precipitate the heavy metal ions.
Bei den auszufällenden Schwermetallionen handelt es sich dabei um gelöste Schwermetallsalze, die bei der Sulfidfällung in Form ihrer Sulfide ausgefällt werden.The heavy metal ions to be precipitated are dissolved heavy metal salts which are precipitated in the form of their sulfides during sulfide precipitation.
Bevorzugt wird für die Sulfidfällung ein wasserlösliches Sulfid verwendet, wobei unter wasserlöslich vorzugsweise eine Löslichkeit in Wasser bei 20°C von größer oder gleich 100 g/1, insbesondere größer 300 g/1 verstanden wird. Als besonders bevorzugte Sulfide werden beispielsweise Schwefelwasserstoff, Alkalisulfid, insbesondere Natriumsulfid, Alkalihydrogensulfid, insbesondere Natriumhydrogensulfid oder deren Gemische eingesetzt.A water-soluble sulfide is preferably used for the sulfide precipitation, water-soluble preferably being understood to mean a solubility in water at 20 ° C. of greater than or equal to 100 g / 1, in particular greater than 300 g / 1. For example, particularly preferred sulfides are hydrogen sulfide, alkali sulfide, in particular sodium sulfide, alkali hydrogen sulfide, in particular sodium hydrogen sulfide or mixtures thereof.
Das für die Sulfidfällung eingesetzte Sulfid wird vorzugsweise stöchiometrisch oder im stöchiometrischen Überschuß, bezogen auf das zu fällende Schwermetallkation eingesetzt. Die Sulfidfällung erfolgt vorzugsweise bei einer Temperatur von 20 bis 155°C Sie kann bei Normaldruck oder bei erhöhtem Druck, vorzugsweise bei 1 bis 6 bar erfolgen.The sulfide used for the sulfide precipitation is preferably used stoichiometrically or in a stoichiometric excess, based on the heavy metal cation to be precipitated. The sulfide precipitation is preferably carried out at a temperature of 20 to 155 ° C. It can be carried out at normal pressure or at elevated pressure, preferably at 1 to 6 bar.
Ebenfalls bevorzugt ist es, die Sulfidfällung im Sauren, insbesondere bei einem pH- Wert von 0,5 bis 2,5 durchzuführen.It is also preferred to carry out the sulfide precipitation in acid, in particular at a pH of 0.5 to 2.5.
Das erfϊndungsgemäße Verfahren wird vorzugsweise in Gegenwart von einer Eisenoxidverbindung aus der Gruppe FeO, Fe2θ3 und Fe2θ4 oder deren Gemischen durchgeführt. Die Gewichtsmenge des Eisenoxids beträgt vorzugsweise 5 bis 500, insbesondere 5 bis 100 mg/1 Abwasser.The process according to the invention is preferably carried out in the presence of an iron oxide compound from the group FeO, Fe 2 θ3 and Fe 2 θ 4 or mixtures thereof. The amount by weight of iron oxide is preferably 5 to 500, in particular 5 to 100 mg / l of waste water.
In einer besonders bevorzugten Aus ührungsform des erfindungsgemäßen Verfahrens wird als wäßriges Medium das Naßoxidationsprodukt von eisen- und schwermetall- haltigem Wasser mit einem Gehalt an organischen Verbindungen, ausgedrückt in TOC (total organic carbon) von bis zu 50 g/1, vorzugsweise 15 bis 20 g/1 verwendet, wobei dieses der Naßoxidation zugeführte Wasser gegebenenfalls anorganische Salze enthält und einen pH- Wert von insbesondere 5,5 bis 8,0 besitzt. Der Gehalt an anorganischen Salzen liegt vorzugsweise bei 0 bis 15 Gew.-%, bezogen auf das eisenhaltige Wasser. Der Eisengehalt des der Naßoxidation zugeführten Wassers beträgt vorzugsweise - das Eisen liegt bevorzugt als Eisensulfat vor - 5 bis 500 mg/1, besonders bevorzugt 10 bis 100 mg/1. Nach der Naßoxidation besitzt das wäßrige Medium im allgemeinen einen pH- Wert von 0,5 bis 2,5.In a particularly preferred embodiment of the process according to the invention, the wet oxidation product of iron and heavy metal is used as the aqueous medium. containing water with an organic compound content, expressed in TOC (total organic carbon) of up to 50 g / 1, preferably 15 to 20 g / 1, this water optionally supplied to the wet oxidation containing inorganic salts and a pH of in particular 5.5 to 8.0. The content of inorganic salts is preferably 0 to 15% by weight, based on the iron-containing water. The iron content of the water supplied to the wet oxidation is preferably - the iron is preferably in the form of iron sulfate - 5 to 500 mg / 1, particularly preferably 10 to 100 mg / 1. After the wet oxidation, the aqueous medium generally has a pH of 0.5 to 2.5.
Bei der Naßoxidation wird vorzugsweise das Abwasser mit einer Hochdruckpumpe durch einen Wärmetauscher gepumpt, in dem es im Gegenstrom vom gereinigten Abwasser vorgeheizt wird. Beim Eintritt in den Reaktor sollte die Temperatur ausreichend hoch sein, so daß die vorzugsweise mit Luft durchgeführte Oxidation anläuft. Ab einem TOC-Gehalt von 10 000 bis 20 000 mg/1 kann die Oxidation ohne Einsatz von Zusatzenergie autotherm verlaufen. Da eine Oxidation in der Gasphase unter den Temperaturbedingungen der Naßoxidation in der Regel sehr langsam verläuft, wird vorzugsweise durch Einstellung eines Druckes, der oberhalb des Sattdampfdruckes bei der entsprechenden Temperatur liegt, dafür gesorgt, daß vorzugsweise wenigstens ein Teil des Wassers im Reaktor flüssig vorliegt.In wet oxidation, the waste water is preferably pumped with a high-pressure pump through a heat exchanger, in which it is preheated by the cleaned waste water in countercurrent. When entering the reactor, the temperature should be sufficiently high that the oxidation, which is preferably carried out with air, starts. From a TOC content of 10,000 to 20,000 mg / 1, the oxidation can proceed autothermally without the use of additional energy. Since oxidation in the gas phase generally proceeds very slowly under the temperature conditions of the wet oxidation, it is preferably ensured by setting a pressure which is above the saturated steam pressure at the corresponding temperature that at least part of the water in the reactor is preferably present in liquid form.
Zur Verminderung von Korrosionsproblemen und der damit verbundenen erheblichen Apparatekosten durch Senkung der Reaktionstemperatur wird zur Beschleunigung der Reaktion vorzugsweise ein Katalysator zugesetzt. Als Katalysator finden insbesondere Metalle der Nebengruppen Verwendung.To reduce corrosion problems and the associated considerable equipment costs by lowering the reaction temperature, a catalyst is preferably added to accelerate the reaction. Metals from the subgroups are used in particular as catalysts.
Als bevorzugte Katalysatoren werden im Rahmen dieser Erfindung zweiwertige kata- lytisch wirkende Kupferionen verstanden, wobei bevorzugt Kupfersulfat oder Kupfersulfid eingesetzt wird. Der Kupferkatalysator wird vorzugsweise in einer Menge von 100 bis 1000 mg/1, besonders bevorzugt von 200 bis 700 mg/1 eingesetzt. Bevor- zugt wird die Naßoxidation bei einer Temperatur von 240 bis 280°C durchgeführt, wobei es vorteilhaft ist, einen Druck von 100 bis 200 bar einzustellen.In the context of this invention, preferred catalysts are understood to be divalent catalytic copper ions, copper sulfate or copper sulfide being preferably used. The copper catalyst is preferably used in an amount of 100 to 1000 mg / 1, particularly preferably from 200 to 700 mg / 1. Before- in addition, the wet oxidation is carried out at a temperature of 240 to 280 ° C., it being advantageous to set a pressure of 100 to 200 bar.
In einem Flüssigkeitsabscheider werden das gereinigte Abwasser und das sauerstoff- arme Abgas vorzugsweise voneinander getrennt.The cleaned waste water and the low-oxygen exhaust gas are preferably separated from one another in a liquid separator.
Wegen der starken fungiziden, algiziden und bakteriziden Wirkung von Kupferionen wird der Katalysator vorzugsweise als Sulfid gefällt, abgetrennt und in den Naßoxi- dationsprozeß zurückgeführt, wo er wiederum zu Kupfersulfat oxidiert wird.Because of the strong fungicidal, algicidal and bactericidal effects of copper ions, the catalyst is preferably precipitated as sulfide, separated and returned to the wet oxidation process, where it is in turn oxidized to copper sulfate.
Die Reaktionsprodukte der Naßoxidation sind je nach Reaktionsbedingungen Kohlendioxid und Wasser mit geringen Anteilen an anoxidierten, niedermolekularen Bruchstücken schwer abbaubarer organischer Verbindungen. Der Stickstoffgehalt organischer Verbindungen wird weitestgehend in Ammoniak umgewandelt, das aus dem gereinigten, sauren Abwasser nach pH-Stellung gestrippt wird.Depending on the reaction conditions, the reaction products of the wet oxidation are carbon dioxide and water with small proportions of anoxidized, low molecular weight fragments of poorly degradable organic compounds. The nitrogen content of organic compounds is largely converted into ammonia, which is stripped from the cleaned, acidic wastewater after pH adjustment.
Sofern das für die Sulfidfällung benötigte Eisenoxid aus der Stufe der Naßoxidation eines eisenhaltigen wäßrigen Mediums stammt, kann es vorteilhaft sein, dieser Lösung bzw. Suspension nach der Naßoxidation d.h. vor oder vorzugsweise nach der Sulfidfällung Polyelektrolyte zuzusetzen. Als solche sind beispielsweise Salze derIf the iron oxide required for sulfide precipitation comes from the wet oxidation stage of an iron-containing aqueous medium, it may be advantageous to remove this solution or suspension after the wet oxidation, i.e. Add polyelectrolytes before or preferably after sulfide precipitation. As such, salts are, for example
Polyphosphorsäure, Polyvinylschwefelsäure, Polyvinylsulfonsäure, Polyvinylphos- phonsäure, Polyacrylsäure, Polyethylenimine, Polyvinylamine, Polyvinylpyridine usw. zu nennen. Die Polyelektrolyte können beispielsweise in einer Menge von 0,0001 bis 0,1 Gew.-%, bezogen auf die Suspension bzw. Lösung, eingesetzt werden. Das für die Naßoxidation eingesetzte wäßrige Medium, hat insbesondere einen pH-Wert von 5,5 bis 8,0. Die gebildeten Schwermetallsulfide, insbesondere Quecksilbersulfid, Silbersulfid aber auch Kupfersulfid, beispielsweise wenn es als Katalysator in einer vorgeschalteten Naßoxidationsreaktion eingesetzt worden war, können dann gemeinsam abgetrennt werden. Nach dem erfindungsgemäßen Verfahren erhaltene schwermetallionenreduzierte Abwässer besitzen vorzugsweise einen Restgehalt an Schwermetallen von kleiner 1 mg/kg Kupfer oder Silber und kleiner 0,005 mg/kg Quecksilber.Polyphosphoric acid, polyvinylsulfuric acid, polyvinylsulfonic acid, polyvinylphosphonic acid, polyacrylic acid, polyethyleneimines, polyvinylamines, polyvinylpyridines etc. are to be mentioned. The polyelectrolytes can be used, for example, in an amount of 0.0001 to 0.1% by weight, based on the suspension or solution. The aqueous medium used for the wet oxidation has, in particular, a pH of 5.5 to 8.0. The heavy metal sulfides formed, in particular mercury sulfide, silver sulfide but also copper sulfide, for example if it had been used as a catalyst in an upstream wet oxidation reaction, can then be separated off together. Heavy metal ion-reduced wastewater obtained by the process according to the invention preferably has a residual heavy metal content of less than 1 mg / kg copper or silver and less than 0.005 mg / kg mercury.
In einer ganz besonders bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens erfolgt die Abtrennung von Quecksilberionen in Gegenwart von Kupferionen durch Sulfidfällung, dadurch gekennzeichnet, daß man das wasserlösliche Sulfid in einer stöchiometrischen Menge oder im Überschuß, vorzugsweise von 1,0 bis 2,0 Mol-Äquivalenten, bevorzugt 1,0 bis 1,5 Mol-Äquivalenten pro Äquivalent Quecksilberionen, einsetzt.In a very particularly preferred embodiment of the process according to the invention, mercury ions are separated off in the presence of copper ions by sulfide precipitation, characterized in that the water-soluble sulfide is present in a stoichiometric amount or in excess, preferably from 1.0 to 2.0 molar equivalents, preferably 1.0 to 1.5 molar equivalents per equivalent of mercury ions.
Dabei erfolgt vorzugsweise die Fällung von Quecksilbersulfid, wobei die große Menge der Kupferionen in Lösung bleiben. Das ausgefallene Quecksilbersulfid kann dann zusammen mit dem Eisenoxid abgetrennt werden.Mercury sulfide is preferably precipitated, with the large amount of copper ions remaining in solution. The precipitated mercury sulfide can then be separated off together with the iron oxide.
Im Anschluß daran ist es bevorzugt, die gelösten Kupferionen, die vorzugsweise demFollowing this, it is preferred to use the dissolved copper ions, preferably the
Kupferkatalysator eines vorgeschalteten Naßoxidationsschrittes entsprechen, durch Sulfidfällung abzutrennen. Das abgetrennte Kupfersulfid kann dann beispielsweise wieder als Katalysator in den Naßoxidationsprozeß eingesetzt werden, wo es dann zum löslichen Kupfersulfat oxidiert wird. Correspond to copper catalyst of an upstream wet oxidation step, separated by sulfide precipitation. The separated copper sulfide can then, for example, be used again as a catalyst in the wet oxidation process, where it is then oxidized to the soluble copper sulfate.
Beispiel 1example 1
30 m3/h eines neutralisierten Abwassers folgender Zusammensetzung werden in einem Hochdruck-Naßoxidationsreaktor bei 250°C und 150 bar Druck mit Luft kontinuierlich oxidiert.30 m 3 / h of neutralized wastewater of the following composition are continuously oxidized with air in a high-pressure wet oxidation reactor at 250 ° C. and 150 bar pressure.
Zusammensetzung: 15 000 mg/1 TOCComposition: 15,000 mg / 1 TOC
9,9 % Natriumsulfat 410 mg/kg Kupfer 29 mg/kg Eisen9.9% sodium sulfate 410 mg / kg copper 29 mg / kg iron
0,28 mg/kg Quecksilber Dichte 1,18 to/m3 0.28 mg / kg mercury density 1.18 to / m 3
Nach der Naßoxidation wird das auf einen Rest-TOC-Gehalt von 350 mg/1 (Abreini- gungsgrad von 97,6 %) abgereinigte Abwasser unter Vorwärmung des Reaktionszulaufs abgekühlt, hochdruckentspannt - Trennung des gereinigten Abwassers und des sauerstoffarmen Abgases - und das fein verteilte Eisenoxid über Sandfilter und Filterpresse kontinuierlich abgetrennt. Das saure Abwasser (pH- Wert ca. 2,0) wird mit einer 30 %igen Natriumhydrogensulfid-Lösung (ca. 37 1/h; Endpunktserkennung über Redoxpotentialmessung) kontinuierlich versetzt, worauf das gefällte Sulfid desAfter the wet oxidation, the waste water purified to a residual TOC content of 350 mg / l (degree of purification of 97.6%) is cooled while preheating the reaction feed, depressurized under high pressure - separation of the purified waste water and the low-oxygen exhaust gas - and the finely divided Iron oxide continuously separated using a sand filter and filter press. The acidic wastewater (pH approx. 2.0) is continuously mixed with a 30% sodium hydrogen sulfide solution (approx. 37 1 / h; end point detection via redox potential measurement), whereupon the precipitated sulfide from the
Kupfers abdekantiert wird, um es als Katalysator-Suspension für den Naßoxidationsprozeß vor den Reaktor zurückzuführen. Unter diesen Bedingungen mitgefälltes fein verteiltes Quecksilbersulfid wird somit teils ebenfalls in den Katalysator-Kreislauf zurückgegeben und konzentriert sich darin auf, ohne daß es ausgeschleust werden kann, teils verbleibt es fein verteilt im Abwasser (Konzentration an Quecksilber im gereinigten Abwasser 0,2 mg/kg).Copper is decanted to return it as a catalyst suspension for the wet oxidation process before the reactor. Partially distributed mercury sulfide that co-precipitates under these conditions is thus partly returned to the catalyst cycle and concentrated therein without being able to be discharged, and partly remains finely divided in the waste water (concentration of mercury in the purified waste water 0.2 mg / kg ).
Beispiel 2 30 m3/h eines neutralisierten Abwassers folgender Zusammensetzung werden in einem Hochdruck-Naßoxidationsreaktor bei 250°C und 150 bar Druck mit Luft kontinuierlich oxidiert.Example 2 30 m 3 / h of neutralized wastewater of the following composition are continuously oxidized with air in a high-pressure wet oxidation reactor at 250 ° C. and 150 bar pressure.
Zusammensetzung: 15 000 mg/1 TOCComposition: 15,000 mg / 1 TOC
9,9 % Natriumsulfat 410 mg/kg Kupfer 29 mg/kg Eisen 0,36 mg/kg Quecksilber Dichte 1,18 to/m3 9.9% sodium sulfate 410 mg / kg copper 29 mg / kg iron 0.36 mg / kg mercury density 1.18 to / m 3
Nach der Naßoxidation wird das auf einen Rest-TOC-Gehalt von 350 mg/1 (Abreini- gungsgrad von 97,6 %) abgereinigte Abwasser (pH- Wert 2,0) unter Vorwärmung des Reaktorzulaufs abgekühlt, hochdruckentspannt - Trennung des gereinigten Abwassers und des sauerstoffarmen Abgases - und kontinuierlich über eineAfter the wet oxidation, the wastewater (pH 2.0), which has been cleaned to a residual TOC content of 350 mg / l (degree of purification of 97.6%), is cooled with preheating of the reactor feed, depressurized - separation of the cleaned wastewater and of the low-oxygen exhaust gas - and continuously via one
Feinstromdosierpumpe mit 14 ml/h einer 30 %-igen Natgriumhydrogensulfid-Lösung versetzt. Nach ca. 1 Stunde Verweilzeit wird das gefällte Quecksilbersulfid zusammen mit dem fein verteilten Eisenoxid über Sandfilter und Filterpresse kontinuierlich abgetrennt. Anschließend wird das von Quecksilber weitgehend gereinigte Filtrat zwecks Abtrennung des Kupferkatalysators mit einer 30 %-igenFine flow metering pump with 14 ml / h of a 30% sodium hydrogen sulfide solution. After a residence time of approx. 1 hour, the precipitated mercury sulfide is continuously separated off together with the finely divided iron oxide using a sand filter and filter press. Then the filtrate, largely cleaned of mercury, is removed with a 30% solution for the purpose of separating the copper catalyst
Natriumhydrogensulfid-Lösung (ca. 37 1/h; Endpunktserkennung über Redoxpotentialmessung) kontinuierlich versetzt, worauf das gefällte Sulfid des Kupfer abdekantiert wird, um es als Katalysator-Suspension für den Naßoxidationsprozeß vor den Reaktor zurückzuführen. Nach der HgS/CuS-Abtrennung sind in dem gereinigten Abwasser <0,005 mg/kg Quecksilber.Sodium hydrogen sulfide solution (approx. 37 l / h; end point detection via redox potential measurement) is added continuously, whereupon the precipitated sulfide of the copper is decanted in order to return it as a catalyst suspension for the wet oxidation process upstream of the reactor. After the HgS / CuS separation there are <0.005 mg / kg mercury in the cleaned wastewater.
Beispiel 3Example 3
Das Abwasser aus Beispiel 2 wird, wie oben beschrieben, naßoxidiert und zwecks Fällung des Quecksilbers mit einer 30 %-igen Natriumhydrogensulfid-Lösung versetzt. Zur Beschleunigung und Komplettierung der Eisenoxid-Fällung wird das Ab- wasser mit 30 1/h einer wässrigen 0,1 %igen Mischung eines kationischen hochmolekularen Polyacrylamidcopolymers beaufschlagt. Das nunmehr gut filtrierbare Eisenoxid wird, wie oben beschrieben, zusammen mit dem gefällten Quecksilbersulfid abgetrennt. Anschließend wird, wie in Beispiel 2 dargelegt, mit der Katalysator- Abtrennung fortgefahren. Das gereinigte Abwasser enthält nach der HgS/CuS-Abtrennung <1 mg/kg Kupfer und <0,002 mg/kg Quecksilber. The waste water from Example 2 is wet-oxidized as described above and a 30% sodium hydrogen sulfide solution is added to precipitate the mercury. To accelerate and complete the iron oxide precipitation, the water with 30 1 / h of an aqueous 0.1% mixture of a cationic high molecular weight polyacrylamide copolymer. The iron oxide, which can now be readily filtered, is separated off together with the precipitated mercury sulfide, as described above. The catalyst removal is then continued, as set out in Example 2. After the HgS / CuS separation, the cleaned wastewater contains <1 mg / kg copper and <0.002 mg / kg mercury.

Claims

Patentansprüche claims
1. Verfahren zur Entfernung von Schwermetallionen aus wäßrigen Medien, dadurch gekennzeichnet, daß zum Ausfallen der Schwermetallionen eine Sulfid- fällung in Gegenwart von Eisenoxid durchgeführt wird.1. A method for removing heavy metal ions from aqueous media, characterized in that a sulfide precipitation is carried out in the presence of iron oxide to precipitate the heavy metal ions.
2. Verfahren gemäß Anspruch 1 zur Entfernung von Quecksilberionen aus wäßrigen Medien.2. The method according to claim 1 for the removal of mercury ions from aqueous media.
3. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß man für die Sulfidfällung ein Sulfid mit einer Wasserlöslichkeit von größer oder gleich 100 g/1, bei 20°C, einsetzt.3. The method according to claim 1, characterized in that a sulfide with a water solubility of greater than or equal to 100 g / 1, at 20 ° C, is used for the sulfide precipitation.
4. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß man als Sulfid Schwefelwasserstoff, Alkalisulfid, Alkalihydrogensulfid oder Gemische davon einsetzt.4. The method according to claim 1, characterized in that the sulfide used is hydrogen sulfide, alkali sulfide, alkali hydrogen sulfide or mixtures thereof.
5. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß man die Sulfidfällung in Gegenwart von 5 bis 500 mg/1, insbesondere 5 bis 100 mg/1 an Eisenoxid durchführt.5. The method according to claim 1, characterized in that one carries out the sulfide precipitation in the presence of 5 to 500 mg / 1, in particular 5 to 100 mg / 1 of iron oxide.
6. Verfahren gemäß Anspruch 1, dadurch gekennzeichnet, daß man die Sulfidfällung bei einem pH- Wert von 0,5 bis 2,5 durchfuhrt.6. The method according to claim 1, characterized in that one carries out the sulfide precipitation at a pH of 0.5 to 2.5.
7. Verfahren gemäß Anspruch 1 , dadurch gekennzeichnet, daß als wäßriges Medium das Naßoxidationsprodukt von eisen- und schwermetallhaltigem Wasser mit einem TOC-Gehalt von bis zu 50 g/1 eingesetzt wird. 7. The method according to claim 1, characterized in that the wet oxidation product of water containing iron and heavy metals with a TOC content of up to 50 g / 1 is used as the aqueous medium.
EP98966413A 1998-01-10 1998-12-29 Removal of heavy metal ions from aqueous media Withdrawn EP1044167A1 (en)

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