CA2160123A1 - Method of treating process water - Google Patents
Method of treating process waterInfo
- Publication number
- CA2160123A1 CA2160123A1 CA002160123A CA2160123A CA2160123A1 CA 2160123 A1 CA2160123 A1 CA 2160123A1 CA 002160123 A CA002160123 A CA 002160123A CA 2160123 A CA2160123 A CA 2160123A CA 2160123 A1 CA2160123 A1 CA 2160123A1
- Authority
- CA
- Canada
- Prior art keywords
- process water
- metal ions
- pulp
- alkaline liquid
- bleaching
- 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.)
- Abandoned
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C11/00—Regeneration of pulp liquors or effluent waste waters
- D21C11/0021—Introduction of various effluents, e.g. waste waters, into the pulping, recovery and regeneration cycle (closed-cycle)
- D21C11/0028—Effluents derived from the washing or bleaching plants
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1026—Other features in bleaching processes
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Removal Of Specific Substances (AREA)
- Paper (AREA)
- Treatment Of Water By Oxidation Or Reduction (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
- Physical Water Treatments (AREA)
Abstract
A method of treating process water con-taining metal ions in connection with bleach-ing pulp of ligno-cellulose-containing material.
The process water is brought into contact with an alkaline liquid, which preferably also con-tains sulphide, whereby metal ions precipitate in the form of difficultly soluble metal compounds.
The precipitated metal compounds thereafter are separated from the process water.
The process water is brought into contact with an alkaline liquid, which preferably also con-tains sulphide, whereby metal ions precipitate in the form of difficultly soluble metal compounds.
The precipitated metal compounds thereafter are separated from the process water.
Description
`~WO94/23L~ 21 6 0 1 23 PCT/SE94/00130 Method of treating process water This invention relates to a method of treating process water containing metal ions, in connection with the bleaching of pulp of lignocellulose-containing material.
In order to minimize the effect by various emissions, such as BOD, COD,colour etc. on the environment, there is a strong interest to substantially restrict the emissions by closing the wastewater system of the bleach plants.
This implies, that the wastewater should be recycled to the process instead of being emitted. As a result of closing the system, however, the content of metal ions, such as manganese, copper, iron etc. in the system can increase to a level giving rise to problems at bleaching with hydroperoxide and, respectively, ozone.
The metal ions enter the system via the wood raw material and, therefore, the affluent of metal ions cannot be eliminated as would be desirable for process reasons.
The content of these metal ions in the pulp, however, is very low and, therefore, they do not cause any environmental problem, not in the local working environment and not in the recipient, either.
In future, the bleaching of papermaking pulp will be based to a high degree on hydroperoxide bleaching and ozone bleaching. For achieving high ISO-brightness, this type of bleaching requires the unbleached pulp and process water to be free, or substantially free, of certain metal ions, because otherwise a considerable deco~position of charged hydroperoxide to water and oxygen and, respectively, of charged ozone to oxygen will take place, without any simultaneous bleaching effect.
W094/~1~ ~6~ PCT/SEg4/00130'~
In order to remove the metal ions prior to bleaching, the pulp must be pretreated with chemicals, for example chelating agents such as EDTA or DTPA, which selectively bind the undesired metal ions and thereby render it possible to wash them out prior to the bleaching. For process reasons, the resulting washing water must be eliminated from the system, and at the same time environmental reasons require that the washing water is not emitted.
The present invention offers a solution for the aforesaid problems. The invention, thus, has the object to remove these metal ions from the process water in the bleach plant and thereby render it possible to close the wastewater system of the bleach plant without causing problems at the bleaching.
The invention is described in greater detail in the following, with reference to the accompanying Figure 1 showing by way of a flow sheet an application of the method according to the invention.
Fig. 2 is a diagram showing the manganese content as a function of the reaction time at one embodiment.
Unbleached pulp is supplied through a duct 1 to a pretreatment step 2 where the pulp is treated with chelating agentsof the type EDTA or DTPA. Metals such as manganese are here solved out of the fiber material.
The pulp is directed from here to a first washing step 3, for example in the form of a washing press or washing filter where wastewater containing the critical metal ions is removed through a duct 4.The pulp free of critical metal ions is directed to a bleaching step 5 for being bleached with hydroperoxide or ozone.
~Og4/231~ 216 D 1 2~ PCT/SE94/00130 After the bleaching step 5 the pulp is directed to a second washing step 6, from where the washed pulp is removed through a duct 7. The wastewater removed through the duct 4 is directed to a vessel 8 where the wastewater is brought into contact with an alkaline liquid, which preferably also contains sulphide, for example green liquor or white liquor from a sulphate pulp mill. In this vessel 8 the metal ions are precipitated mainly as compounds difficult to solve in the form of hydroxides and sulphides. These difficultly soluble compounds thereafter can be separated from the liquid phase in a suitable way, for example by sedimentation, filtering or the like. The wastewater free of metal ions thereby can be used as washing water in positions where a low content of metals is of importance, for example in a bleach plant entirely free of chlorine. The waste-water from the vessel 8 is removed through a duct 9 and can be used again as washing water in other process steps.
The precipitated metal compounds can be recycled through a duct lO to the chemical recovery plant of the pulp mill, where they gradually will be ejected, for example into the green liquor slime. This eject passage exists already previously and, therefore, does not additionally harm the environment. As an alternative method, the precipitated metal compounds are ejected directly out of the system without passing through the chemical recovery plant. The undesired metals, thus, are in both cases transported out of the bleach plant, and the accumulation effect in the bleach plant thereby can be avoided when the drain system is closed. As the method does not include an evaporation process, the energy balance of the mill is not deteriorated~ either.
WOg4/23122 ~ PCT/SEg4/00130--~6~ 4 It was found that suitable conditions for achieving an effective elimination of the metal ions in the reaction vessel 8 shall be an alkaline pH, preferably higher than pH 11 at room or higher temperature.The reaction time can be very short, less than 1 minute.
A longer reaction time, 1-~0 minutes, however, has no detrimental effect on the precipitation reaction.
The amount of charged hydroxide and sulphide shall exceed the stoichiometric demand in order to bind the undesired metals.
Example 50 ml wastewater from a complex former step was treated with 25 and, respectively, 50 ml green liquor from a pulp mill. Final pH was 12.~-12.9.The result is shown in Fig. 1 where the manganese content is shown as a function of the reaction time; As appears from the diagram, the manganese content decreases rapidly, in less than 1 minute, at both green liquor charges from 1.4 mg/l to below 0.2 mg/l. Thereafter an insignificant additional decrease of the manganese content at longer reaction times is observed.
The invention-, of course, is not restricted to the embodiment described above, but can be varied within the scope of the invention idea.
In order to minimize the effect by various emissions, such as BOD, COD,colour etc. on the environment, there is a strong interest to substantially restrict the emissions by closing the wastewater system of the bleach plants.
This implies, that the wastewater should be recycled to the process instead of being emitted. As a result of closing the system, however, the content of metal ions, such as manganese, copper, iron etc. in the system can increase to a level giving rise to problems at bleaching with hydroperoxide and, respectively, ozone.
The metal ions enter the system via the wood raw material and, therefore, the affluent of metal ions cannot be eliminated as would be desirable for process reasons.
The content of these metal ions in the pulp, however, is very low and, therefore, they do not cause any environmental problem, not in the local working environment and not in the recipient, either.
In future, the bleaching of papermaking pulp will be based to a high degree on hydroperoxide bleaching and ozone bleaching. For achieving high ISO-brightness, this type of bleaching requires the unbleached pulp and process water to be free, or substantially free, of certain metal ions, because otherwise a considerable deco~position of charged hydroperoxide to water and oxygen and, respectively, of charged ozone to oxygen will take place, without any simultaneous bleaching effect.
W094/~1~ ~6~ PCT/SEg4/00130'~
In order to remove the metal ions prior to bleaching, the pulp must be pretreated with chemicals, for example chelating agents such as EDTA or DTPA, which selectively bind the undesired metal ions and thereby render it possible to wash them out prior to the bleaching. For process reasons, the resulting washing water must be eliminated from the system, and at the same time environmental reasons require that the washing water is not emitted.
The present invention offers a solution for the aforesaid problems. The invention, thus, has the object to remove these metal ions from the process water in the bleach plant and thereby render it possible to close the wastewater system of the bleach plant without causing problems at the bleaching.
The invention is described in greater detail in the following, with reference to the accompanying Figure 1 showing by way of a flow sheet an application of the method according to the invention.
Fig. 2 is a diagram showing the manganese content as a function of the reaction time at one embodiment.
Unbleached pulp is supplied through a duct 1 to a pretreatment step 2 where the pulp is treated with chelating agentsof the type EDTA or DTPA. Metals such as manganese are here solved out of the fiber material.
The pulp is directed from here to a first washing step 3, for example in the form of a washing press or washing filter where wastewater containing the critical metal ions is removed through a duct 4.The pulp free of critical metal ions is directed to a bleaching step 5 for being bleached with hydroperoxide or ozone.
~Og4/231~ 216 D 1 2~ PCT/SE94/00130 After the bleaching step 5 the pulp is directed to a second washing step 6, from where the washed pulp is removed through a duct 7. The wastewater removed through the duct 4 is directed to a vessel 8 where the wastewater is brought into contact with an alkaline liquid, which preferably also contains sulphide, for example green liquor or white liquor from a sulphate pulp mill. In this vessel 8 the metal ions are precipitated mainly as compounds difficult to solve in the form of hydroxides and sulphides. These difficultly soluble compounds thereafter can be separated from the liquid phase in a suitable way, for example by sedimentation, filtering or the like. The wastewater free of metal ions thereby can be used as washing water in positions where a low content of metals is of importance, for example in a bleach plant entirely free of chlorine. The waste-water from the vessel 8 is removed through a duct 9 and can be used again as washing water in other process steps.
The precipitated metal compounds can be recycled through a duct lO to the chemical recovery plant of the pulp mill, where they gradually will be ejected, for example into the green liquor slime. This eject passage exists already previously and, therefore, does not additionally harm the environment. As an alternative method, the precipitated metal compounds are ejected directly out of the system without passing through the chemical recovery plant. The undesired metals, thus, are in both cases transported out of the bleach plant, and the accumulation effect in the bleach plant thereby can be avoided when the drain system is closed. As the method does not include an evaporation process, the energy balance of the mill is not deteriorated~ either.
WOg4/23122 ~ PCT/SEg4/00130--~6~ 4 It was found that suitable conditions for achieving an effective elimination of the metal ions in the reaction vessel 8 shall be an alkaline pH, preferably higher than pH 11 at room or higher temperature.The reaction time can be very short, less than 1 minute.
A longer reaction time, 1-~0 minutes, however, has no detrimental effect on the precipitation reaction.
The amount of charged hydroxide and sulphide shall exceed the stoichiometric demand in order to bind the undesired metals.
Example 50 ml wastewater from a complex former step was treated with 25 and, respectively, 50 ml green liquor from a pulp mill. Final pH was 12.~-12.9.The result is shown in Fig. 1 where the manganese content is shown as a function of the reaction time; As appears from the diagram, the manganese content decreases rapidly, in less than 1 minute, at both green liquor charges from 1.4 mg/l to below 0.2 mg/l. Thereafter an insignificant additional decrease of the manganese content at longer reaction times is observed.
The invention-, of course, is not restricted to the embodiment described above, but can be varied within the scope of the invention idea.
Claims (5)
1. A method of treating process water containing metal ions, in connection with bleaching pulp of lignocellulose--containing material, c h a r a c t e r i z e d i n that the process water is brought into contact with an alkaline liquid, whereby metal ions precipitate in the form of difficultly soluble metal compounds, whereafter the precipitated metal compounds are separated from the process water.
2. A method as defined in claim 1, c h a r a c t e r -i z e d i n that the alkaline liquid also contains sulphide.
3. A method as defined in claim 2, c h a r a c t e r -i z e d i n that the alkaline liquid consists of green liquor and/or white liquor from a sulphate pulp mill.
4. A method as defined in any one of the claims 1-3, c h a r a c t e r i z e d i n that the amount of charged hydroxide and sulphide shall exceed the stoichiometric demand in order to bind the metal ions.
5. A method as defined in any one of the claims 1-4, c h a r a c t e r i z e d i n that the reaction time is less than 1 minute and the pH value higher than 11.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE9301161-7 | 1993-04-07 | ||
| SE9301161A SE9301161L (en) | 1993-04-07 | 1993-04-07 | Process for treating process water |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2160123A1 true CA2160123A1 (en) | 1994-10-13 |
Family
ID=20389509
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002160123A Abandoned CA2160123A1 (en) | 1993-04-07 | 1994-02-17 | Method of treating process water |
Country Status (12)
| Country | Link |
|---|---|
| EP (1) | EP0693144A1 (en) |
| JP (1) | JPH08508546A (en) |
| CN (1) | CN1120358A (en) |
| AU (1) | AU672501B2 (en) |
| BR (1) | BR9406105A (en) |
| CA (1) | CA2160123A1 (en) |
| FI (1) | FI954766A (en) |
| NO (1) | NO953993L (en) |
| NZ (1) | NZ263264A (en) |
| SE (1) | SE9301161L (en) |
| WO (1) | WO1994023122A1 (en) |
| ZA (1) | ZA941235B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE9301160L (en) * | 1992-08-28 | 1994-03-01 | Sunds Defibrator Ind Ab | Process for treating process water |
| SE504424C2 (en) * | 1994-11-04 | 1997-02-10 | Kvaerner Pulping Tech | Ways to precipitate transition metals and alkaline earth metals from bleaching liquids by adding alkaline liquid |
| SE9500732L (en) * | 1995-02-27 | 1996-08-28 | Eka Chemicals Ab | Procedure for the treatment of liquids |
| US5792315A (en) * | 1995-02-27 | 1998-08-11 | Eka Chemicals Ab | Purifying aqueous effluent from a pulp mill using electro chemical membrane device |
| SE9803384L (en) * | 1998-03-02 | 1999-09-03 | Kemira Kemi Ab | Process for treating process water |
| AP3994A (en) * | 2008-12-19 | 2017-01-11 | Xyleco Inc | Processing biomass |
| US20100263813A1 (en) * | 2009-04-21 | 2010-10-21 | Andritz Inc. | Green liquor pretreatment of lignocellulosic material |
| WO2013040747A1 (en) * | 2011-09-19 | 2013-03-28 | 北京沃特玛德环境技术股份有限公司 | Method for comprehensively utilizing solid waste during soda recovery in papermaking industry |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4684472A (en) * | 1985-12-26 | 1987-08-04 | Phillips Petroleum Company | Precipitation of waste chromium compounds utilizing an aqueous sulfide solution |
| ES2053858T3 (en) * | 1989-04-28 | 1994-08-01 | Siemens Ag | PROCEDURE FOR THE ELIMINATION OF COPPER FROM WASTE WATER. |
| US5120448A (en) * | 1990-09-19 | 1992-06-09 | Dorica Josesph G | Removal of aox frm bleach plant mill effluents by ph shift using the alkalinity/acidity sources available at the mill |
| EP0564443A1 (en) * | 1992-03-15 | 1993-10-06 | Kamyr, Inc. | Treatment of bleach plant filtrates |
-
1993
- 1993-04-07 SE SE9301161A patent/SE9301161L/en not_active Application Discontinuation
-
1994
- 1994-02-17 CA CA002160123A patent/CA2160123A1/en not_active Abandoned
- 1994-02-17 EP EP94911328A patent/EP0693144A1/en not_active Ceased
- 1994-02-17 NZ NZ263264A patent/NZ263264A/en unknown
- 1994-02-17 JP JP6521969A patent/JPH08508546A/en active Pending
- 1994-02-17 CN CN94191676A patent/CN1120358A/en active Pending
- 1994-02-17 AU AU63876/94A patent/AU672501B2/en not_active Ceased
- 1994-02-17 BR BR9406105A patent/BR9406105A/en not_active Application Discontinuation
- 1994-02-17 WO PCT/SE1994/000130 patent/WO1994023122A1/en not_active Application Discontinuation
- 1994-02-23 ZA ZA941235A patent/ZA941235B/en unknown
-
1995
- 1995-10-06 FI FI954766A patent/FI954766A/en unknown
- 1995-10-06 NO NO953993A patent/NO953993L/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JPH08508546A (en) | 1996-09-10 |
| NZ263264A (en) | 1996-08-27 |
| AU6387694A (en) | 1994-10-24 |
| WO1994023122A1 (en) | 1994-10-13 |
| AU672501B2 (en) | 1996-10-03 |
| NO953993D0 (en) | 1995-10-06 |
| ZA941235B (en) | 1994-09-20 |
| NO953993L (en) | 1995-10-06 |
| CN1120358A (en) | 1996-04-10 |
| SE9301161D0 (en) | 1993-04-07 |
| SE9301161L (en) | 1994-10-08 |
| FI954766A0 (en) | 1995-10-06 |
| FI954766A (en) | 1995-10-06 |
| EP0693144A1 (en) | 1996-01-24 |
| BR9406105A (en) | 1995-12-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |