WO2001073195A1 - Traitement de filtrats d'usines de blanchiment - Google Patents

Traitement de filtrats d'usines de blanchiment Download PDF

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Publication number
WO2001073195A1
WO2001073195A1 PCT/SE2001/000318 SE0100318W WO0173195A1 WO 2001073195 A1 WO2001073195 A1 WO 2001073195A1 SE 0100318 W SE0100318 W SE 0100318W WO 0173195 A1 WO0173195 A1 WO 0173195A1
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WO
WIPO (PCT)
Prior art keywords
filtrate
aluminium
bleaching
pulp
magnesium
Prior art date
Application number
PCT/SE2001/000318
Other languages
English (en)
Inventor
Christos Rampotas
Original Assignee
Kemira Kemi Ab
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 Kemira Kemi Ab filed Critical Kemira Kemi Ab
Priority to AU2001232590A priority Critical patent/AU2001232590A1/en
Publication of WO2001073195A1 publication Critical patent/WO2001073195A1/fr

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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
    • D21C11/00—Regeneration of pulp liquors or effluent waste waters
    • D21C11/0064—Aspects concerning the production and the treatment of green and white liquors, e.g. causticizing green liquor
    • 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
    • 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
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds
    • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

  • the present invention relates to a method m bleaching of pulp and, more specifically, the invention relates to a method, m which the pulp is washed m connection with the bleaching, and the washing liquid from the washing is separated from the pulp m the form of a filtrate, which is treated with an aluminium compound for precipitation of interfering substances, whereupon the precipitated material is removed from the purified filtrate, which is recirculated to the bleaching process.
  • Pulp which here relates to cellulose-containing pulp for making paper, is normally subjected to bleaching m order to dissolve lignm and/or increase the brightness of the pulp.
  • the bleaching of pulp is usually carried out m a plurality of steps, such as 4-5 steps when bleaching sulphate pulp or 1-2 steps when bleaching mechanical pulp, and m peroxide bleaching the bleaching is carried out m at least one of these steps with hydro- gen peroxide under alkaline conditions.
  • An increasing amount of papermakmg pulp is currently bleached by means of hydrogen peroxide.
  • the hydrogen peroxide bleaching can be carried out at atmospheric pressure and a temperature of about 70-100°C or be pressurised, for instance to a pressure of 5 bar with oxygen, and be carried out at a temperature above 100°C, such as 100-120°C.
  • a conventional peroxide bleaching method for sulphate pulp can comprise, for instance, the following steps: an oxygen step, m which the pulp is treated with oxygen, followed by washing of the pulp before treating it with a complex- mg agent, such as ethylene diamme tetraacetic acid (EDTA) to complex interfering metal ions, such as iron, magnesium, copper, zinc and chromium.
  • EDTA ethylene diamme tetraacetic acid
  • the treatment with a complexmg agent can be carried out m one or more steps.
  • the pulp is washed and then fed to a peroxide bleaching step, where the pulp is bleached with hydrogen peroxide .
  • a peroxide bleaching step the pulp is washed and after separation of the fil- trate, this can at least partly be recirculated to the peroxide bleaching step as washing liquid.
  • the various washing steps that occur m connection with the bleaching are generally carried out with a washing liquid (water) which is fed countercurrently to the process flow, i.e. clean washing water is added at the end of the bleaching and is supplied m the direction of the beginning of the bleaching, the washing liquid being successively used to wash more and more contaminated (unbleached) pulp. In this manner, the washing liquid can be utilised opti- mally.
  • the efficiency of the hydrogen peroxide m the peroxide bleaching is impaired by interfering substances, such as oxygen-demanding organic material (below referred to as COD material, i.e. chemically oxygen-demand- ing material) and metal ions, such as manganese, iron, chromium, copper, nickel and zinc.
  • COD material oxygen-demanding organic material
  • metal ions such as manganese, iron, chromium, copper, nickel and zinc.
  • the negative effect of interfering substances m the peroxide bleaching step increases by recirculation of the filtrate from the washing of the pulp after the peroxide bleaching step by the filtrate containing interfering substances from the peroxide bleaching step, and m continued recirculation of the filtrate an increasing amount of interfering substances is accumulated m the filtrate.
  • hydrogen peroxide must normally be added to the bleaching step m a great excess, and it is as a rule estimated that about 40% of the added hydrogen peroxide is consumed for bleaching while about 40% decom- poses owing to the presence of interfering substances.
  • the filtrate which is obtained after washing and dewate ⁇ ng of the pulp after the peroxide bleaching step contains only about 20% of remaining hydrogen peroxide together with oxygen-demanding organic material .
  • the bleaching process is also desirable for the bleaching process to be closed to a greater extent than has been possible till now by recirculating waste water flows from the bleaching process m order to achieve a reduced need for fresh water and also to provide a less environmentally harmful bleaching process.
  • a purified waste water flow such as a washing liquid filtrate
  • the object of the present invention is to provide, by means of an after-treatment of a filtrate that has been treated according to the above-mentioned WO 99/53133, a reduction of the aluminium content of the filtrate, preferably to less than 5 ppm, more preferred less than 1 ppm.
  • a further object of the invention is to provide a further purification of the filtrate such that it can be recirculated to the bleaching process, preferably to the peroxide bleaching step, thereby achieving a reduced need for fresh water in the bleaching process and a more closed bleaching process .
  • the filtrate is first treated according to the method disclosed in WO 99/53133, and reference is therefore made to the description of this method contained in WO 99/53133, which in its entirety is incorporated herewith by reference.
  • the inventive after-treatment of the filtrate is carried out by adding a magnesium compound to the filtrate and by adjusting the pH of the filtrate to above 7 for precipitation of an aluminium-containing precipi- tate, which is removed, whereupon the thus further purified filtrate can be recirculated to the bleaching process, preferably to the peroxide bleaching step.
  • the invention provides a method m bleaching of pulp, m which the pulp is washed m connection with the bleaching, and the washing liquid from the washing is separated from the pulp m the form of a filtrate, which is treated with an aluminium compound for precipitation of interfering substances, whereupon the precipitated material is removed from the puri- fied filtrate, which is recirculated to the bleaching process, characterised m that the purified filtrate, prior to the recirculation to the bleaching method, is treated by adding a magnesium compund and adjusting the pH of the purified filtrate to above 7 for precipitation of an aluminium-containing precipitate, which is removed, whereupon the remaining filtrate is recirculated to the bleaching process.
  • pulp used in the context is meant a cellulose-containing pulp for making paper, said pulp comprising mechanical pulp as well as semi-chemical and chemical pulp, such as sulphate pulp and sulphite pulp.
  • peroxide bleaching which is used m the context is meant bleaching with an alkali peroxide or, preferably, hydrogen peroxide as the bleaching chemi- cal.
  • the filtrate obtained from washing the pulp from the bleaching process is first treated according to the method disclosed in WO 99/53133 by precipitating interfering substances using an aluminium compound .
  • aluminium compound which is used for treatment of the filtrate is not particularly critical and can be selected among a large number of different aluminium compounds, such as those known as flocculating or precipitating agents in connection with the purification of drinking water and waste water.
  • aluminium chloride aluminium nitrate, aluminium sulphate
  • polyaluminium compounds such as polyaluminium chloride, polyaluminium nitrate and polyaluminium sulphate.
  • aluminium chloride is less pre- ferred since it may cause corrosion.
  • Particularly preferred aluminium compounds are aluminium sulphate, polyaluminium nitrate and polyaluminium sulphate.
  • the amount of aluminium compound which is added to the filtrate should at least be sufficient to reduce and, if possible, essentially minimise interfering substances, such as oxygen-demanding organic material (COD material) as well as metals, by precipitation from the filtrate.
  • COD material oxygen-demanding organic material
  • the aluminium compound used for precipitation should, especially if it contains aluminium in loosely bound/dissociable form, not be added in such an excess that considerable amounts of non-reacted aluminium com- pound, after removal of precipitated material from the filtrate, accompany the filtrate to the bleaching process, preferably the peroxide bleaching step. It has, m fact, been established m the invention that the aluminium compound used for the precipitation can have a negative effect, for instance on the peroxide bleaching so that the consumption of peroxide increases.
  • the temperature m the treatment of the filtrate with the aluminium compound is not particularly critical, and the treatment is normally carried out at the temperature that the filtrate has after washing of the pulp. This temperature is usually m the range 60-100°C, pre- ferably 70-90°C.
  • the treatment of the filtrate with the aluminium compound can be carried out within a wide pH range.
  • the pH should be m the range 3.5-11, preferably 4-6 with regard to good precipitation and flocculation of interfering substances, such as organic oxygen-demanding material (COD) .
  • the pH of the filtrate can be adjusted, the adjustment suitably being effected by using an alkali, such as sodium hydroxide, or an acid, such as sulphuric acid.
  • the treatment of the filtrate with the aluminium compound is suitably carried out m such manner that the desired amount of aluminium compound is added to the filtrate under agitation so that the aluminium compound is distributed uniformly m the filtrate for precipitation and flocculation of interfering substances.
  • the aluminium compound should be given sufficient time to act before the formed precipitate is separated from the filtrate, for instance by flotation.
  • a time from about 1 s to about 30 mm, preferably about 1-5 mm, should be allowed to pass from the addition of the aluminium compound to the separation of the precipitate.
  • a flocculating aid the form of a polymer can be added.
  • flocculating aids are well known to those skilled m the art and comprise, for instance, polyacrylamide .
  • the purified filtrate is treated according to the invention by adding a magnesium compound to the filtrate and by adjusting the pH of the filtrate to above 7.
  • a precipitate is thus formed containing aluminium from the filtrate and, accordingly, by separating the precipitate from the filtrate more aluminium can be removed from the filtrate.
  • the filtrate, thus further purified can then be recirculated to the bleaching process, pre- ferably to the peroxide bleaching step.
  • the magnesium compound added to the filtrate can be selected from a number of different magnesium compounds, for instance magnesium oxide, magnesium sulphate and magnesium chloride. Of these, magnesium oxide and magne- sium sulphate are preferred to magnesium chloride since magnesium chloride may cause corrosion. Magnesium oxide is particularly preferred for use in the invention.
  • the amount of magnesium compound added to the filtrate is not critical as long as it, in combination with the adjustment of the pH, results in precipitation of aluminium-containing material from the filtrate.
  • the amount of magnesium compound added be at least equal to the amount of aluminium in the filtrate, in terms of moles, i.e. the molar ratio Mg:Al should be at least 1:1.
  • the magnesium compound be added in excess in terms of moles in proportion to the aluminium content of the filtrate.
  • the molar ratio is at most 9:1.
  • the molar ratio to be from 3:1 to 6:1, and particularly preferred is for the molar ratio Mg:Al to be about 5:1.
  • the pH of the filtrate need to be above 7.
  • the pH of the filtrate can be as high as 14.
  • the pH of the filtrate it is preferred for the pH of the filtrate to be 8.5-11, and it is particularly preferred for the pH of the filtrate to be about 9.5. Since the pH of the filtrate is low following the preceding treatment with the aluminium compound, for instance the range of 4-6 and possibly, some cases, as high as 7, the adjustment of the pH of the filtrate according to the invention is done by using an alkali.
  • This alkali can be selected from a number of different alkaline agents, such as alkaline metal hydroxides, preferably sodium hydroxide, potassium hydroxide etc.
  • alkaline metal hydroxides preferably sodium hydroxide, potassium hydroxide etc.
  • a particularly preferred alkaline agent for adjusting the pH of the filtrate is white liquor, which normally is avail- able a sulphate process.
  • white liquor pulping liquor for the manufacture of sulphate pulp containing about 10 % sodium hydroxide and traces of sodium carbonate.
  • the white liquor used m the method according to the present mven- tion is preferably oxidised.
  • the amount of alkaline agent, for instance white liquor, added to the filtrate according to the present invention must be sufficient to adjust the pH of the filtrate to above 7, preferably to 8.5-11, most preferred to about 9.5.
  • an aluminium- and magnesium-containing precipitate is formed, which is removed from the filtrate.
  • the precipitate formed is flocculent and easy to separate from the filtrate.
  • the separation of the precipitate may be carried out using centricleaner or flotation.
  • the relative order is not critical as far as the addition of magnesium compound and the adjustment of the pH is concern- ed, it is preferred to add the magnesium compound first and then adjust the pH, whereas the inverse order is less preferred.
  • the temperature in the treatment of the filtrate according to the invention is not critical, but suitably the same as the preceding precipitation treatment with the aluminium compound, i.e. 50-100 C C, preferably 60-85°C.
  • magnesium has a positive effect m peroxide bleaching and, therefore, a special addition of magnesium is usually made prior to the peroxide bleaching step.
  • This special addition of magnesium can be eliminated the invention, since the filtrate already contains magnesium from the precipitation treatment.
  • the addition of the mag- nesium compound thus serves the two purposes of on the one hand acting as precipitant for the aluminium content of the filtrate and, on the other, having a favourable effect on the peroxide bleaching and eliminating the conventional magnesium charge.
  • the magnesium is present m the peroxide bleaching step combination with aluminium, preferably with a molar ratio Mg:Al from 3:1 to 6:1.
  • a particularly prefer- red example of such a compound i s hydrotalcite which has the general formula
  • hydrotalcite is composed of infinite layers, on the one hand Mg (OH) 2 layers where a certain part of Mg 2+ has been replaced with Al 3+ and, on the other hand, intermediate layers with C0 3 2" and H 2 0.
  • the amount of carbonate ions corresponds to half the amount of aluminium (in moles) since they constitute a charge equali- sation when 2-valent magnesium ions are substituted with 3-valent aluminium ions.
  • the carbonate ions can be replaced with other anions of the type S0 4 2" .
  • the magnesium compound is added in excess in terms of moles, particularly preferred in a molar ratio Mg:Al from 3:1 to 6:1, provides conditions for forming a combination compound consisting of magnesium and aluminium as above, and particularly hydrotalcite provided that carbonate ions are present at the same time.
  • white liquor as described above, contains carbonate
  • an adjustment of the pH of the filtrate using white liquor means that carbonate ions are added at the same time, which facilitates the formation of hydrotalcite.
  • a con- siderable reduction of the aluminium content of the filtrate is achieved, but also the positive effect of magnesium and aluminium in the form of hydrotalcite being added to the peroxide bleaching step.
  • Example 1 With a view to further facilitating the understand- ing of the invention, it will elucidated below by way of some non-limiting examples.
  • Example 1
  • the remaining filtrate was then divided into two parts, called Sample 1 and Sample 2, and these were subjected to treatment according to the invention by adding MgO, and then adjusting the pH to be above 7. Accordingly, MgO an amount corresponding to 432 mg Mg/1 was added to Sample 1 and the pH of the Sample was adjusted by means of NaOH to 9.15, while MgO in an amount corresponding to 1350 mg Mg/1 was added to Sample 2 and the pH adjusted to 9.7. The temperature during treatment was 70°C. In the adjustment of the pH, a precipitate was formed, which was removed by way of flotation. The remaining purified filtrate of Samples 1 and 2 was analysed with regard to Al, Fe, Mn, Mg, Na, S, pH and the molar ratio Mg/Al . The results are shown m Table 1.
  • Samples 3, 4, 5 and 6 These samples were treated according to the invention by adding a mag- nesium compound, followed by adjustment of the pH to above 7.
  • MgO was added in an amount corresponding to 1932 mg Mg/1
  • MgS0 4 was added to Samples 4, 5 and 6.
  • MgS0 4 was added to Samples 4, 5 and 6 in the amounts of 80, 160 and 240 Mg/1 respec- tively.
  • the pH of the Samples was then adjusted by way of NaOH to the values indicated in Table 2.
  • the temperature during treatment was 70°C in Sample 3 and 71°C in Samples 4, 5 and 6. In the adjustment of the pH, a precipitate was formed, which was removed by way of flota- tion.
  • the remaining purified filtrates of Samples 3, 4, 5 and 6 were analysed with regard to Al , Fe, Mn, Mg, Na, S, pH and the molar ratio Mg/Al . The results are shown in Table 2.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Coloring Foods And Improving Nutritive Qualities (AREA)

Abstract

L'invention concerne un procédé de blanchiment de pâte selon lequel la pâte est lavée en liaison avec le blanchiment et le liquide de lavage issu du lavage est séparé de la pâte sous la forme d'un filtrat qui est traité avec un composé d'aluminium pour la précipitation des substances indésirables. Ensuite, le matière précipitée est retirée du filtrat épuré qui est renvoyé au procédé de blanchiment. Le procédé est caractérisé en ce que le filtrat épuré, avant d'être renvoyé au processus de blanchiment, est traité par addition d'un composé de magnésium, tel que de l'oxyde de magnésium, et par ajustement du pH du filtrat épuré à plus de 7, de préférence, 8,5 à 11, pour la précipitation d'un précipité contenant de l'aluminium, qui est retiré. Ensuite, le filtrat restant est renvoyé au processus de blanchiment, de préférence, à une opération de blanchiment au peroxyde. Ce traitement permet de réduire davantage la teneur en aluminium du filtrat, ce qui permet d'obtenir des niveaux de teneur en aluminium inférieurs à 5 ppm. Lors du renvoi du filtrat à une opération de blanchiment au péroxyde, une quantité avantageuse de magnésium accompagné d'aluminium, de préférence, sous forme d'hydrotalcite, est cédée à l'opération de blanchiment au péroxyde grâce au fait que le filtrat recyclé contient de petites quantités de magnésium et d'aluminium, et de préférence aussi du carbonate.
PCT/SE2001/000318 2000-03-24 2001-02-15 Traitement de filtrats d'usines de blanchiment WO2001073195A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001232590A AU2001232590A1 (en) 2000-03-24 2001-02-15 Treatment of bleach plant filtrates

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0001037A SE516037C2 (sv) 2000-03-24 2000-03-24 Rening av blekningsfiltrat före återföring till blekningsförfarandet
SE0001037-1 2000-03-24

Publications (1)

Publication Number Publication Date
WO2001073195A1 true WO2001073195A1 (fr) 2001-10-04

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SE (1) SE516037C2 (fr)
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102007022752A1 (de) * 2007-05-11 2008-11-13 Voith Patent Gmbh Bleichen von lignocellulosischen Primärfasern
WO2021232133A1 (fr) * 2020-05-22 2021-11-25 Suzano S.A. Procédés de traitement d'un circuit de récupération de procédé kraft pour réduire la teneur en métaux dans un procédé kraft

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1354455A (en) * 1971-11-03 1974-06-05 Degremont Methods of purifying effluents from the manufacture and bleaching of wood pulp
EP0564443A1 (fr) * 1992-03-15 1993-10-06 Kamyr, Inc. Traitement d'éffluents de blanchiment
WO1999053133A1 (fr) * 1998-04-08 1999-10-21 Kemira Kemi Ab Traitement des filtrats provenant du blanchiment de la pate au peroxyde

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1354455A (en) * 1971-11-03 1974-06-05 Degremont Methods of purifying effluents from the manufacture and bleaching of wood pulp
EP0564443A1 (fr) * 1992-03-15 1993-10-06 Kamyr, Inc. Traitement d'éffluents de blanchiment
WO1999053133A1 (fr) * 1998-04-08 1999-10-21 Kemira Kemi Ab Traitement des filtrats provenant du blanchiment de la pate au peroxyde

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102007022752A1 (de) * 2007-05-11 2008-11-13 Voith Patent Gmbh Bleichen von lignocellulosischen Primärfasern
WO2021232133A1 (fr) * 2020-05-22 2021-11-25 Suzano S.A. Procédés de traitement d'un circuit de récupération de procédé kraft pour réduire la teneur en métaux dans un procédé kraft
CN115667622A (zh) * 2020-05-22 2023-01-31 苏扎诺公司 处理牛皮纸工艺回收循环以降低牛皮纸工艺中的金属水平的方法

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Publication number Publication date
SE516037C2 (sv) 2001-11-12
SE0001037L (sv) 2001-09-25
SE0001037D0 (sv) 2000-03-24
AU2001232590A1 (en) 2001-10-08

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