SE500052C2

SE500052C2 - Treatment of process water to remove metal ions - by bringing the process water into contact with pulp not intended for bleaching by hydroperoxide or ozone

Info

Publication number: SE500052C2
Application number: SE9202464A
Authority: SE
Inventors: Ulf Germgaard; Solveig Norden
Original assignee: Sunds Defibrator Ind Ab
Priority date: 1992-08-28
Filing date: 1992-08-28
Publication date: 1994-03-28
Also published as: ZA935691B; SE9202464L; SE9202464D0

Abstract

Treating process water contg. metal ions washed out from pulp of lignocellulose contg. material, prior to bleaching of the pulp with hydroperoxide or ozone, comprises contacting the process water with pulp not intended to be bleached by hydroperoxide or ozone at a pH above 7 at 50-120 deg. C whereby the metal ion content is partially or entirely removed from the process water. Pref. the process water is brought into contact with pulp at pH 11.0-12.0. The process water is waste water from the washing of pulp after treatment with complex former. The metal ions are sepd. at the washing of the pulp prior to bleaching with hydroperoxide or ozone and are returned entirely or partially to at least a partial flow of the pulp after the bleaching. The pulp used for the sepn. consists of bleached pulp, unbleached pulp or reject pulp.

Description

2 Oblekt massa tillföres genom en ledning 1 till ett förbehandlingssteg 2 där massan behandlas med komplexbildare av typ EDTA eller DTPA. Metaller såsom mangan löses där ut ur fibermaterialet. Därifrån förs massan till ett första tvättsteg 3, företrädesvis i form av en tvättpress, där avloppsvatten innehållande de kritiska metalljonerna dras av genom en ledning 4. Den från kritiska metalljoner befriade massan förs till ett bleksteg 5 för blekning med väteperoxid eller ozon. Efter blek- steget 5 förs massan till ett andra tvättsteg 6 där avloppsvatt- net från det första tvâttsteget 3 via ledningen 4 äter bringas i kontakt med massan och där massan ånyo binder de ursprungliga metalljonerna. Avloppsvattnet från det andra tvâttsteget avleds genom en ledning 7 och den tvättade massan tas ut genom en ledning 8. Det från metalljoner befriade avloppsvattnet kan áterföras till tidigare steg i processen. Unbleached pulp is supplied through a line 1 to a pretreatment step 2 where the pulp is treated with complexing agents of the EDTA or DTPA type. Metals such as manganese are dissolved there from the fibrous material. From there the pulp is passed to a first washing step 3, preferably in the form of a washing press, where wastewater containing the critical metal ions is drawn off through a line 4. The pulp freed from critical metal ions is passed to a bleaching step 5 for bleaching with hydrogen peroxide or ozone. After the bleaching step 5, the pulp is taken to a second washing step 6 where the waste water from the first washing step 3 via the line 4 eats is brought into contact with the pulp and where the pulp again binds the original metal ions. The wastewater from the second washing stage is diverted through a line 7 and the washed mass is taken out through a line 8. The wastewater freed from metal ions can be returned to earlier stages in the process.

Massan kommer således att transportera metallerna ut ur blekeriet och ackumulationseffekten i blekeriet kan därmed undvikas vid slutning av avloppssystemet.The pulp will thus transport the metals out of the bleaching plant and the accumulation effect in the bleaching plant can thus be avoided when closing the drainage system.

Det har visat sig att lämpliga betingelser för att uppnå en god eliminering av metalljonerna i det andra tvâttsteget 6 skall vara pH över 7, företrädesvis pH 11 eller högre och en temperatur av 50-120°C, företrädesvis 70-100°C. Tiden som pro- cessvattnet och massan skall vara i kontakt med varandra bör vara 0,1-60 minuter, företrädesvis 1-5 minuter.It has been found that suitable conditions for achieving a good elimination of the metal ions in the second washing step 6 should be pH above 7, preferably pH 11 or higher and a temperature of 50-120 ° C, preferably 70-100 ° C. The time that the process water and the pulp should be in contact with each other should be 0.1-60 minutes, preferably 1-5 minutes.

Ett alternativt förfaringssätt är att enbart en delström av massan utnyttjas för att avskilja metalljonerna från avlopps- vattnet från det första tvâttsteget. Det är naturligtvis även möjligt att använda en oblekt massa som inte skall blekas eller ett rejektmassaflöde för att avskilja metalljonerna.An alternative method is that only a partial stream of the pulp is used to separate the metal ions from the wastewater from the first washing step. Of course, it is also possible to use an unbleached pulp that is not to be bleached or a reject pulp stream to separate the metal ions.

Vidare är det också tänkbart att utnyttja metallavskilj- ningen enligt uppfinningen som komplement till annan typ av avskiljning av metaller.Furthermore, it is also conceivable to use the metal separation according to the invention as a complement to another type of metal separation.

Exempel 1 Manganhalten i en ligninfri vattenlösning som behandlades med väteperoxidblekt massa visade sig minska betydligt när behandlingen gjordes vid pH 12 jämfört med pH 10-11. Behandling under 10 min vid 80°C. 3 Vätska 1 Initial halt (mg/1) 6,5 Behandling vid pH 10 6,4 Behandling vid pH ll 6,5 Behandling vid pH 12 1,2 Exempel 2 Manganhalten uppmättes i ett laboratorietillverkat blekeriavlopp efter behandling med väteperoxidblekt massa.Example 1 The manganese content of a lignin-free aqueous solution treated with hydrogen peroxide bleached pulp was found to decrease significantly when the treatment was done at pH 12 compared to pH 10-11. Treatment for 10 minutes at 80 ° C. 3 Liquid 1 Initial content (mg / l) 6.5 Treatment at pH 6.4 Treatment at pH 11 6.5 Treatment at pH 12 1.2 Example 2 The manganese content was measured in a laboratory-made bleaching effluent after treatment with hydrogen peroxide bleached pulp.

Behandlingen gjordes vid olika pH. Vid pH 12 och i tvâ fall även vid pH 11, noteras en kraftig reduktion av manganhalten.The treatment was done at different pH. At pH 12 and in two cases also at pH 11, a sharp reduction in the manganese content is noted.

Vätska 2 Vätska 3 Vätska 4 Initial halt (mg/1) 3,3 3,5 3,6 Behandling vid pH 10 - - 3,4 Behandling vid pH 11 0,7 resp 0,4 2,7 0,3 Behandling vid pH 12 - 1,3 0,03 Exempel 3 Manganhalten uppmättes i ett laboratorietillverkat blekeriavlopp efter behandling med väteperoxidblekt massa där behandlingen gjordes vid olika pH och temperatur. Resultaten visar att behandlingstider över 2 minuter ej inverkar nämnvärt pä resultatet. Ökat pH tycks också vara viktigare än ökad tempe- ratur.Liquid 2 Liquid 3 Liquid 4 Initial content (mg / l) 3.3 3.5 3.6 Treatment at pH 10 - - 3.4 Treatment at pH 11 0.7 and 0.4 2.7 0.3 Treatment at pH 12 - 1.3 0.03 Example 3 The manganese content was measured in a laboratory-produced bleaching effluent after treatment with hydrogen peroxide bleached pulp where the treatment was carried out at different pH and temperature. The results show that treatment times over 2 minutes do not significantly affect the result. Increased pH also seems to be more important than increased temperature.

H11 80°§ H12 80°_C_ H11 90°Q Initial halt (mg/l) 3,5 3,5 3,5 Behandlingstid 2 min 2,3 1,9 2,6 Behandlingstid 10 min 2,6 1,3 2,5 Behandlingstid 60 min - - 2,3 .f Vï -\ _.- CD CÜ U1 BO I-h Exempel 4 Manganhalten uppmättes i laboratorietillverkade blekeri- avlopp frán vâteperoxidblekning av massor med olika ligninhalt.H11 80 ° § H12 80 ° _C_ H11 90 ° Q Initial content (mg / l) 3.5 3.5 3.5 Treatment time 2 min 2.3 1.9 2.6 Treatment time 10 min 2.6 1.3 2 Treatment time 60 min - - 2,3 .f Vï - \ _.- CD CÜ U1 BO Ih Example 4 The manganese content was measured in laboratory-produced bleaching effluents from wet peroxide bleaching of pulps with different lignin contents.

Behandling under 10 minuter vid 80%L Massans ligninhalt uppmätt som kappatal har ingen avgörande inverkan på uppnàdd manganhalt.Treatment for 10 minutes at 80% L The lignin content of the pulp measured as kappa has no decisive effect on the manganese content reached.

Massa 1 Massa 2 (kappatal 5) (kappatal 9) Initialhalt (mg/1) 3,6 3,6 Behandling vid pH 10 3,4 - Behandling vid pH 11 0,3 1,1 Behandling vid pH 12 0,03 <0,01 Uppfinningen är givetvis inte begränsad av dessa utför- ingsformer utan kan varieras inom ramen för uppfinningstanken.Mass 1 Mass 2 (kappa number 5) (kappa number 9) Initial content (mg / l) 3.6 3.6 Treatment at pH 10 3.4 - Treatment at pH 11 0.3 1.1 Treatment at pH 12 0.03 < 0.01 The invention is of course not limited by these embodiments but can be varied within the scope of the inventive concept.

Claims

500 052 5 Patent claims

Process for treating process water containing metal ions washed from pulp of lignocellulosic material before bleaching the pulp with hydrogen peroxide or ozone, characterized in that the process water is brought into contact with pulp which is not to be bleached with hydrogen peroxide or ozone at pH above 7 and a temperature of 50-12G%, whereby the process water is completely or partially freed from the metal ion content.

Process according to Claim 1, characterized in that the process water is brought into contact with the pulp at pH 11 or higher.

Process according to Claim 1 or 2, characterized in that the process water consists of waste water from washing of pulp after treatment with complexing agents.

4. A method according to any one of claims 1-3, characterized in that the metal ions are separated during washing of the pulp before bleaching with hydrogen peroxide or ozone and are returned in whole or in part to at least a partial stream of the pulp after said bleaching.

Process according to one of Claims 1 to 3, characterized in that the pulp used for separating the metal ions from the process water consists of bleached pulp, unbleached pulp or reject pulp.