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

Definitions

• This invention relates to a method of treating process water containing metal ions, in connection with the bleaching of pulp of lignocellulose-containing material.
• 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 is very low and, therefore, they do not cause any environmental problem, not in the local working environment and not in the recipient, either.
• the bleaching of papermaking pulp will be based to a high degree on hydroperoxide bleaching and ozone bleaching.
• 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 decomposition of charged hydroperoxide to water and oxygen and, respectively, of charged ozone to oxygen will take place, without any simultaneous bleaching effect .
• the pulp 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.
• 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 agents of 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.
• 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.
• an alkaline liquid which preferably also contains sulphide, for example green liquor or white liquor from a sulphate pulp mill.
• 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 10 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.
• the precipitated metal compounds are ejected directly out of the system without passing through the chemical recovery plant.
• the undesired metals thus, are i-n 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.
• the method does not include an evaporation process, the energy balance of the mill is not deteriorated, either.
• 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--60 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.
• 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/1 to below 0.2 mg/1. Thereafter an insignificant additional decrease of the manganese content at longer reaction times is observed.

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)
• Physical Water Treatments (AREA)
• Separation Using Semi-Permeable Membranes (AREA)

Priority Applications (6)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20389509

Family Applications (1)

Country Status (12)

Cited By (4)

Families Citing this family (4)

Citations (4)

• 1993
  • 1993-04-07 SE SE9301161A patent/SE9301161L/ not_active Application Discontinuation
• 1994
  • 1994-02-17 AU AU63876/94A patent/AU672501B2/en not_active Ceased
  • 1994-02-17 WO PCT/SE1994/000130 patent/WO1994023122A1/en not_active Application Discontinuation
  • 1994-02-17 BR BR9406105A patent/BR9406105A/pt not_active Application Discontinuation
  • 1994-02-17 CN CN94191676A patent/CN1120358A/zh active Pending
  • 1994-02-17 JP JP6521969A patent/JPH08508546A/ja active Pending
  • 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
  • 1994-02-23 ZA ZA941235A patent/ZA941235B/xx unknown
• 1995
  • 1995-10-06 NO NO953993A patent/NO953993D0/no unknown
  • 1995-10-06 FI FI954766A patent/FI954766A0/fi unknown

Patent Citations (4)

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