FI127857B

FI127857B - Method for producing a product comprising phosphorus and use of the product

Info

Publication number: FI127857B
Application number: FI20146078A
Authority: FI
Inventors: Macarena Crampet; Matti Ristolainen; Jussi Penttilä; Mats Backman; Bruno Vuan; Maria Jose Aguerrebere; Dayana Travers
Original assignee: Upm Kymmene Corp
Priority date: 2014-12-09
Filing date: 2014-12-09
Publication date: 2019-04-15
Also published as: UY36424A; FI20146078A

Abstract

A method for producing a product comprising phosphorus is disclosed, wherein the method comprises obtaining an effluent or filtrate from a chemical pulping process; adjusting the pH of at least a portion of the effluent or filtrate to alkaline with an alkaline agent; allowing phosphorus to be precipitated in the form of a phosphate salt; and separating the precipitate to produce purified effluent or filtrate and a sludge comprising the precipitate. Further, a product obtainable by the method and use of the product are described.

Description

METHOD FOR PRODUCING A PRODUCT COMPRISING PHOSPHORUS

AND USE OF THE PRODUCT

20146078 prh 29 -10- 2015

FIELD OF THE INVENTION

The invention relates to a method for producing a product comprising phosphorus. The invention further relates to the product obtainable by the method and the use of the product.

BACKGROUND OF THE INVENTION

Phosphorus is an essential nutrient for plants, and modern agriculture is dependent on input of phosphorus fertilizers. As the phosphorus in most phosphorus fertilizers is obtained from non-renewable 15 rock phosphate, there is a need for providing other, cost-effective and renewable sources of phosphorus for applications such as fertilization.

Effluents produced in pulp or paper mills and other effluent-producing plants are typically treated 20 in waste water treatment plants to reduce the amount of compounds which may be harmful to the environment, such as phosphorus. Phosphorus must be removed from effluents that are discharged from the mill to the environment, e.g. to a water system, to prevent pollu25 tion. As environmental regulations restricting phosphorus emissions tend to become stricter, there is a need to reduce the amount of phosphorus in effluents that are conveyed from the mill to a waste water treatment plant and ultimately to the environment.

There is therefore also a need for a method that is capable of recovering phosphorus from effluents obtained from processes such as chemical pulping processes .

Ledung L & Jonsson T, Effects of new separa35 tion technologies on the mass balances in closed cycle

20146078 prh 29 -10- 2015 kraft pulp mills, International chemical recovery conference, Whistler, BC, Canada, 11-14 June 2011, oral presentations, pp. 109-114 [Montreal, QC, Canada: Pulp and Paper Technical Association of Canada, 2001], ab5 stract, describes a process simulation of a softwood kraft pulp mill, in which a separation technique based on pre-evaporation of neutral/acidic bleach plant filtrates followed by precipitation of non-process elements, e.g. phosphorus, by raising the pH value is in10 tegrated.

WO 2014072584 describes a method for treating liquid flows at a chemical pulp mill comprising dosing first acidification chemical to unbleached pulp flow in order to dissolve at least a part of the phosphorus 15 compounds in the unbleached pulp flow, forming a phosphorus compounds containing filtrate, and removing at least a portion of said phosphorus containing filtrate from the unbleached pulp flow in a phosphorus removal step .

WO 2014044905 discloses a method of processing waste and side flows of pulp and paper industry comprising at least bark and other wood based waste flows and at least one fibrous waste flow.

WO 2011151511 describes a method of pro25 cessing organic side flows and waste slurries in connection with a biorefinery.

WO 2014118441 discloses a method to be used in connection with the recovery of pulping chemicals from spent pulping liquor.

PURPOSE OF THE INVENTION

The purpose of the invention is to provide a new type of method for producing a product comprising phosphorus. Further, the purpose of the invention is 35 to provide a product obtainable by the method and a use for the product.

20146078 prh 29 -10- 2015

SUMMARY

The method according to the present invention is characterized by what is presented in claim 1.

The product according to the present inven5 tion is characterized by what is presented in claim 13.

The use according to the present invention is characterized by what is presented in claim 17.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with 15 the description help to explain the principles of the invention. In the drawings:

Fig. 1 is a flow chart illustration of a method for producing a product comprising phosphorus; and

Fig. 2 is a schematic illustration of a system for producing a product comprising phosphorus.

DETAILED DESCRIPTION OF THE INVENTION

A method according to the present invention 25 for producing a product comprising phosphorus comprises obtaining an effluent or filtrate from a chemical pulping process;

adjusting the pH of at least a portion of the 30 effluent or filtrate to alkaline with an alkaline agent;

allowing phosphorus to be precipitated in the form of a phosphate salt; and separating the precipitate to produce puri35 fied effluent or filtrate and a sludge comprising the precipitate .

20146078 prh 29 -10- 2015

In this context, the term effluent or filtrate should be understood as referring to an aqueous liquid that contains phosphorus, which is to be removed either completely or in part.

In this context, the term effluent should also be understood as referring to a waste liquid which is obtained from the process and which is to be discharged from the process. The effluent is usually treated for purifying purposes by waste water treat10 ment before discharging. The waste water treatment may take place at a waste water treatment plant of a chemical pulping mill. The effluent may also refer e.g. a bleaching effluent or a filtrate which is to be discharged or to be treated for purifying purposes by 15 waste water treatment before discharging. The effluent may be obtainable or derived from any process, system or structure associated with a chemical pulping process that has not been subjected to a waste water treatment in a waste water treatment plant. For in20 stance, the effluent or filtrate may be a leachate containing phosphorus, such as landfill run-off water, run-off water from a lime storage area or from a hydrated lime storage area, or ash leaching purge solution .

In this context, the term filtrate should also be understood as referring to an effluent from which solid suspended matter is removed by a filtration treatment, a flotation treatment or any other treatment. Thus the term filtrate does not neces30 sarily imply that the solid suspended matter, such as fibers, have been removed by filtration.

The effluent or filtrate may be selected from the group consisting of an effluent or filtrate issued from fiberline operations of a chemical pulping pro35 cess; a leachate containing phosphorus, such as landfill run-off water or run-off water from lime or hy

20146078 prh 29 -10- 2015 drated lime storage area; ash leaching purge solution; and any mixtures thereof.

The method may be used in a chemical pulping mill, in which chemical pulp is produced using the so5 called sulphate or kraft process or the soda pulping process .

In this context, the term pulp should be understood as referring to a lignocellulosic fibrous material prepared by chemically or mechanically sepa10 rating cellulose fibres from a natural fibre based material. So-called kraft or sulphate processes can be used for producing pulp. The chemical pulping process may be a kraft pulping process or a soda pulping process .

The operations of a kraft pulp mill are conventionally divided in a fiber line, a chemical recovery system and waste water treatment. The fiber line operations typically include cooking, brownstock washing (washing away spent cooking chemicals from the 20 pulp), oxygen delignification, bleaching and pulp drying. In many conventional kraft pulp mills, the pH in the cooking, brownstock washing, oxygen delignification and knotting and screening stages is alkaline. Any effluents or filtrates obtained from such stages 25 are typically alkaline. Often the pH in one or more bleaching stages is acidic. Thus effluents or filtrates obtained from bleaching stages may be acidic or alkaline, depending on the specific stage and the chemicals used therein.

The effluent or filtrate may be obtained from the first stage of the process in which the conditions are acidic.

When the effluent or filtrate is an effluent or filtrate issued from fiberline operations of a 35 chemical pulping process, it may be an acidic bleaching filtrate or an acidic bleaching effluent. The acidic bleaching filtrate or acidic bleaching effluent

20146078 prh 29 -10- 2015 may be obtainable from the first acidic bleaching stage .

The present inventors have found that typically very high phosphorus content may be found in ef5 fluents or filtrates obtainable from a chemical pulping process, in particular from the first stage of the process in which the conditions are acidic. As an example, the concentration of phosphorus of the effluent or filtrate may be 5 - 20 mg/1, or 9 - 16 mg/1. Thus 10 it may be very useful to obtain the effluent or filtrate from the first stage of the process in which the conditions are acidic. A significant amount of phosphorus in effluents or filtrates from the process may thus be recovered, even if only the effluent or fil15 trate from the first stage of the process in which the conditions are acidic, or a portion thereof, is processed according to one or more embodiments of the method.

In this context, the term bleaching stage 20 may refer to any stage after brown stock stages, and should be understood as also including oxygen delignification stage(s), which selectively removes lignin, hexenuronic acid and/or metals. In this context, the term bleaching stage may also refer to any stages 25 immediately following the oxygen stage. First bleaching stage can be an alkaline or an acidic one. Commonly it is an acidic A stage followed by a D stage without a washing stage between them. This is the so called A/Dl bleaching stage.

The filtrate may be an A, D, DI, A/D or A/Dl bleaching filtrate or any other acidic bleaching filtrate. A should be understood as referring to an acidic bleaching stage. D should be understood as referring to a chlorine dioxide bleaching stage. A, D 35 and DI stages may be stages separate from each other;

each of A, D and DI stages should however in this context be understood as being bleaching stages.

20146078 prh 29 -10- 2015

The acidic effluent may also be obtainable from the acidification treatment of unbleached pulp, which is performed before the bleaching, after brownstock washing and oxygen treatment of the oxygen 5 delignification unit. This acidic effluent also typically contains dissolved phosphorus compounds.

The filtrate may also be an acidic filtrate obtainable from the acidification treatment of the unbleached pulp after brownstock washing, which treat10 ment is performed to dissolve acid-dissolving phosphorus compounds contained in the pulp before bleaching.

The pH of the effluent or filtrate obtainable from a chemical pulping process may be below 7; or below 6; or below 3. The pH of the effluent or filtrate 15 obtainable from a chemical pulping process may also be 1 - 7; or 2 - 7; or 1 - 6; or 2 - 6; or 1 - 3; or 2 3.

In an embodiment, the method comprises obtaining a first portion of an effluent or filtrate from a chemical pulping process;

obtaining a second portion of an effluent or filtrate from the same or different stage of the chemical pulping process;

adjusting pH of the first portion of the ef25 fluent or filtrate to alkaline with an alkaline agent;

allowing phosphorus to be precipitated in the form of a phosphate salt;

separating the precipitate to produce purified effluent or filtrate and a sludge comprising the 30 precipitate; and combining the purified effluent or filtrate with the second portion of the effluent or filtrate.

The first portion of the effluent or filtrate and the second portion of the effluent or filtrate may 35 be obtained from the same stage of the chemical pulping process. They may also be obtained from two or more different stages of the chemical pulping process.

20146078 prh 29 -10- 2015

For instance, the first portion of effluent or filtrate may be obtained from a first stage in which conditions are acidic; and the second portion of the effluent or filtrate may be obtained from a second 5 and/or later stage in which conditions are acidic.

The first portion of the effluent or filtrate may be obtained from the first stage of the process in which conditions are acidic.

The first and/or second portion of effluent 10 or filtrate comprises an effluent or filtrate may be obtained from a stage in which conditions are acidic, to which effluent or filtrate an alkaline effluent or filtrate has been added. In such an embodiment, the pH of said second portion of effluent or filtrate may not 15 be alkaline prior to combining the purified effluent or filtrate with the second portion of the effluent or filtrate. The pH of the first portion of effluent or filtrate may already be made alkaline by the addition or mixing of alkaline effluent or filtrate therein 20 prior to adjusting the pH of the first portion to alkaline, as the pH will in any case be adjusted to alkaline. The alkaline effluent or filtrate may be obtained from a stage of the process in which conditions are alkaline. The alkaline effluent may be added or 25 mixed to an effluent or filtrate obtained from a stage in which conditions are acidic prior to obtaining the first and second portion and/or adjusting the pH of the first portion of the effluent or filtrate to alkaline. The alkaline effluent or filtrate may also be 30 added or mixed to the second portion prior to combining the purified effluent or filtrate with the second portion of the effluent or filtrate, provided the pH of said second portion of effluent or filtrate is not alkaline prior to combining the purified effluent or 35 filtrate with the second portion of the effluent or filtrate .

In an embodiment, the method comprises

20146078 prh 29 -10- 2015 obtaining an effluent or filtrate from a chemical pulping process;

dividing the effluent or filtrate into a first portion and a second portion;

adjusting the pH of the first portion of the effluent or filtrate to alkaline with an alkaline agent;

allowing phosphorus to be precipitated in the form of a phosphate salt;

separating the precipitate to produce purified effluent or filtrate and a sludge comprising the precipitate; and combining the purified effluent or filtrate with the second portion of the effluent or filtrate.

The effluent or filtrate may be divided e.g.

by dividing a flow of the effluent or filtrate into two separate flows. The first flow may be conveyed to the subsequent adjusting the pH of the first portion of the effluent or filtrate to alkaline with an alka20 line agent, allowing phosphorus to be precipitatted in the form of a phosphate salt, and separating the precipitate to produce purified effluent or filtrate and a sludge comprising the precipitate to obtain a flow of purified effluent or filtrate. The second flow of 25 the effluent or filtrate may then be combined with the flow of purified effluent or filtrate.

The pH of the first portion of the effluent or filtrate obtained by dividing the effluent or filtrate may be below 7; or below 6; or below 3. The pH 30 of the first portion of the effluent or filtrate obtained by dividing the effluent or filtrate may be 1 7; or 2 - 7; or 1 - 6; or 2 - 6; or 1 - 3; or 2 - 3.

The method may comprise adjusting the pH of the at least a portion or of the first portion of the effluent or filtrate with the alkaline agent to a pH in the range of 8 - 14; or 8 - 11; or 9 - 10; or 9.2 9.8.

20146078 prh 29 -10- 2015

When pH of the at least a portion or the first portion of the effluent or filtrate is adjusted to alkaline, phosphorus precipitates, typically as calcium phosphate. The source of calcium in the calci5 um phosphate precipitated may be calcium originally contained in the effluent or filtrate and/or calcium that is introduced to the first portion of the effluent or filtrate as a component of the alkaline agent. Thus the precipitate typically contains calcium phos10 phate. The precipitate may further comprise other phosphate salts, such as calcium hydrogen phosphate; calcium carbonate; calcium sulphate; organic phosphorus compounds; and/or other precipitated/coprecipitated components.

The alkaline agent may be any agent that is capable of raising the pH of the at least a portion ot the first portion of the effluent or filtrate to a pH at which phosphorus can precipitate. The alkaline agent may be a solution, such as an aqueous solution, 20 a solid, or a mixture thereof.

The alkaline agent may be selected from the group consisting of

CaO;

an alkali metal hydroxide, such as NaOH;

Ca(OH)₂;

NH₄OH;

an alkaline effluent or filtrate;

an alkaline bleaching effluent or filtrate; a powder or an aqueous solution thereof;

and any mixtures thereof.

The alkaline agent may be solid CaO. The alkaline agent may also be an aqueous solution of CaO, an aqueous solution of an alkali metal hydroxide such as NaOH, an aqueous solution of Ca(OH)₂, an aqueous 35 solution of NH₄OH, or any mixture thereof.

The alkaline agent may also be a mixture of a solid and an aqueous solution.

If the alkaline agent is Ca(OH)₂, CaO, a powder or an aqueous solution of Ca(OH)₂ or CaO, or any mixture thereof, at least some of the calcium ions contained therein may precipitate with the phosphorus 5 contained in the first portion of the effluent or filtrate .

The alkaline agent may be an alkaline agent that is used for adjusting pH of waste water, such as an aqueous solution of Ca(OH)₂.

The concentration of the alkaline agent may vary. A relatively strong alkaline agent, or an aqueous solution containing a high concentration of an alkaline agent, may however have the added utility that a small volume of the alkaline agent is needed to ad15 just the pH to alkaline. Thus an increase in volume and dissolution of the precipitate can be avoided. For instance, if an aqueous solution of Ca(OH)₂ is used as the alkaline agent, the concentration of the aqueous solution of Ca(OH)₂ is preferably at least 2 g/1, or 20 more preferably at least 20 g/1. Even more preferably the alkaline agent is solid CaO.

When adjusting the pH of the at least a portion or the first portion of the effluent or filtrate, it may be mixed with the alkaline agent. The mixing typically 25 accelerates the precipitation of phosphorus. The mixing

20146078 prh 29 -10- 2015 may be effected e.g. be effected using an alkaline effluent agent with by agitation. The mixing may also apparatus suitable the first portion or filtrate. Such apparatus a piping comprising means for mixing may be e.g. a a stirrer. Such apparatus may tank or for of mixing the the acidic be e.g. a

The may means for mixing, mixer, a mixing arm or also be e.g. a piping fitted with one or more nozzles for injecting the alkaline agent into the piping in which the first por35 tion of the acidic effluent or filtrate may flow.

The temperature may be e.g. between 25 - 90°C when adjusting the pH of the at least a portion or the

20146078 prh 29 -10- 2015 first portion of the effluent or filtrate and/or allowing the phosphorus to precipitated. Increasing the temperature may enhance precipitation.

Separating the precipitate may be effected 5 e.g. by flotation, flocculation, filtration, decantation, clarification, sedimentation, centrifugation or by any combination thereof.

When separating the precipitate, a flocculation reagent or coagulation reagent may be used. Suit10 able flocculation/coagulation reagents may be e.g. anionic polymers such as polyacrylamide (PAM), nonionic or cationic polymers. However, in principle any flocculation reagent capable of assisting the contact and adhesion of particles of the precipitate may be used. 15 The flocculation or coagulation reagent may be mixed with the at least a portion or the first portion of the effluent or filtrate prior to, during or after adjusting the pH of the same to alkaline or during or after allowing phosphorus to be precipitated in the 20 form of a phosphate salt. A flocculation or coagulation reagent may expedite the precipitating and separating of the precipitate.

Chemical pulping processes typically comprise a stage in which green liquor dregs are filtered using 25 a green liquor dregs filter. A filtration of the precipitate may also be effected by filtration using a green liquor dregs filter. The phosphorus-containing precipitate may thus be conveniently filtered using existing green dregs filtration equipment, and the re30 moval of the precipitate may therefore require minimal equipment investments.

Thus the sludge comprising the phosphoruscontaining precipitate may be conveyed to and filtered using the green liquor dregs filter. As the conditions 35 at the green liquor dregs filter are alkaline, the phosphorus remains in the precipitate during the filtration. Furthermore, if a method such as decantation,

20146078 prh 29 -10- 2015 clarification, flotation, sedimentation or filtration is first used to separate the precipitate, a sludge comprising the precipitate (and an amount of effluent or filtrate) is obtained. As the volume of the sludge is 5 smaller, typically much smaller, than the volume of the purified effluent or filtrate, the green liquor dregs filter does not become overloaded with the sludge. A product comprising the precipitate and green liquor dregs may thus be obtained. If a green liquor dregs 10 filter pre-coated with a layer of lime mud is used, a product comprising the precipitate, green liquor dregs and lime mud may be obtained.

The sludge or the product comprising the precipitate, green liquor dregs and optionally lime mud 15 may be recovered and, if desired, processed further for use e.g. as described below.

After the precipitate is separated from the at least a portion or the first portion of the effluent or filtrate, the purified effluent or filtrate thus ob20 tained has substantially reduced phosphorus content. The removal of phosphorus may be so efficient that substantially all phosphorus present in the at least a portion or the first portion of the effluent or filtrate is recovered.

It may not always be desirable to completely eliminate phosphorus from the effluent or filtrate, in particular in cases when the effluent or filtrate is subseguently conveyed to a waste water treatment plant. Many waste water treatment plants utilize bacterial 30 processes for waste water treatment, for which a low amount of phosphorus in the effluent or filtrate is preferable or even necessary. Further, it may be sufficient to treat only a portion of the effluent or filtrate in order to significantly reduce phosphorus 35 content in the effluent or filtrate. For instance, a treatment of all acidic effluents or filtrates obtainable from a process is not necessary to significantly

20146078 prh 29 -10- 2015 reduce phosphorus in the total volume of effluents and filtrates obtainable from the whole process.

The at least a portion or the first portion of the effluent or filtrate may consist of 2 - 95 % (v/v) ; 5 - 95 % (v/v) ; 5 - 50 % (v/v) ; or 10 - 40 % (v/v) of the total volume of the effluent or filtrate. In this context, the total volume of the effluent or filtrate may be understood as consisting of the total volume of both the first and second portion.

A significant recovery of phosphorus in effluent or filtrate may be obtained even if the at least a portion or the first portion of the effluent or filtrate is a relatively small portion as compared to the whole volume of the effluent or filtrate.

The first and second portion of the effluent or filtrate or their volume ratios may be selected so that e.g. the concentration of phosphorus, the pH of said portions and/or the pH of the combined purified effluent or filtrate and the second portion of the ef20 fluent or filtrate is optimal.

The first portion of the effluent or filtrate may have a higher content or concentration of phosphorus than the second portion. The first portion of the effluent or filtrate may have e.g. a phosphorus con25 centration of 5 - 20 mg/1; or 9 - 16 mg/1.

The first portion of the effluent or filtrate may also be obtainable from the stage in which conditions are acidic and in which the content or concentration of phosphorus is highest.

Combining the purified effluent or filtrate with the second portion of the effluent or filtrate may be performed at any stage of the process before post-neutralization of the combination (i.e. the combination of the purified effluent or filtrate with the second portion of the effluent or filtrate) in a waste water treatment plant, wherein the post-neutralization is performed for adjusting the pH suitable for aerobic

20146078 prh 29 -10- 2015 treatment. The post-neutralization is typically performed before the aeration basin. It may, for instance, be performed at the fiberline, before preliminary clarifier treatment or at any other stage before aeration.

The method may further comprise conveying the combination of the purified effluent or filtrate and the second portion of the effluent or filtrate to waste water treatment or discharge.

The combination of the purified effluent or filtrate and the second portion of the effluent or filtrate may be directly conveyed to waste water treatment, e.g. to a waste water treatment plant, or discharge. The pH of the combination of the purified 15 effluent or filtrate and the second portion of the effluent or filtrate may also be further adjusted, e.g.

to a neutral pH, if necessary. The pH of the combination of the purified effluent or filtrate and the second portion of the effluent or filtrate may be neutral 20 or near neutral, for instance in the range of 6 to 8, or in the range of 6.5 to 7.5. The pH of the combination of the purified effluent or filtrate and the second portion of the effluent or filtrate may also be adjusted to neutral or near neutral, for instance to a 25 pH in the range of 6 to 8, or in the range of 6.5 to

7.5.

If the purified effluent or filtrate is combined with the second portion of the effluent or filtrate, the second portion of the effluent or filtrate 30 is often capable of adjusting the pH to a lower level.

The pH of the resulting combination may thus be neutral or close to a neutral pH. Depending e.g. on the ratio of the volume of the purified effluent or filtrate to the volume of the second portion of the ef35 fluent or filtrate, pH of the combination of the purified effluent or filtrate and the second portion of the effluent or filtrate obtainable may be further ad

20146078 prh 29 -10- 2015 justed. A suitable neutralising agent may be used to adjust the pH of the effluent. The neutralising agent may be an alkaline agent or an acidic agent. It may also be the same alkaline agent with which pH of the 5 at least a portion or the first portion of the effluent or filtrate is adjusted to alkaline.

The method may further comprise processing the sludge into a form that is more suitable for use e.g. as a fertilizer product.

The method may comprise drying the sludge.

The sludge may be dried e.g. using an oven or a mechanical cyclone, such as a Tornado cyclone. Such cyclones may operate by creating a high velocity airstream, for instance with a powerful fan or impellers, which is guided into an air channel where it is mixed with the sludge to be processed. The sludge may be fed into the channel by a feeder or a conveyor or sprayed, if it contains sufficient moisture (e.g. over 50%). As the air-sludge mixture flows in a cyclone device, changes in radial velocity and pressure may cause heavy vibrations or shear forces in the sludge particles and disintegrate them. A light fraction containing fine dried sludge may be recovered from one end of the cyclone during the process. The mechanical cy25 clone, such as a Tornado cyclone, may also utilize waste heat, such as waste heat produced in the chemical pulping process. The product obtainable by drying may be e.g. in the form of flakes or small particles.

The method may comprise mixing the sludge with a suitable material, such as a material selected from the group consisting of fiber sludge, biosludge, lime kiln dust, lime mud, waste lime, green liquor dregs, and any mixtures thereof. It is also possible to mix a first portion of the sludge with a material (one or more materials) and a second portion of the sludge with another material (one or more other materials) . Such materials may contain components, such as

20146078 prh 29 -10- 2015 calcium carbonate, which may have beneficial effects in the mixture or in a product obtainable from the mixture when used e.g. as a fertilizer.

The material may be selected from the group 5 consisting of lime kiln dust, lime mud and waste lime.

Lime kiln dust, lime mud and waste lime contain calcium (CaO) which may react with water when mixed with the sludge so that Ca(OH)₂ is formed. They may thus be capable of removing water from the sludge.

The fiber sludge or biosludge may be dried prior to mixing the sludge with it.

The sludge mixed with a suitable material may subsequently be dried, pelletized and/or granulated.

The method may comprise pelletizing or granu15 lating the sludge and optionally drying the pelletized or granulated sludge by heating. The pelletizing or granulating may also be done after drying the sludge. Granulating may, in principle, be performed either by wet granulation or by dry granulation. Various suita20 ble pelletizing and granulation techniques are known.

The product obtainable by pelletizing or granulation is in a convenient form (pellets or granules) that may exhibit little or no dusting and may have a much lower weight than raw sludge. Transportation and storage of 25 such a product may therefore be easy and economical.

In an embodiment, the method comprises separating the precipitate by flotation, flocculation, filtration, decantation, clarification, sedimentation, and/or centrifugation to produce puri30 fied effluent or filtrate and a sludge comprising the precipitate;

mixing the sludge with a material selected from the group consisting of fiber sludge, biosludge, lime kiln dust, lime mud, waste lime, green liquor 35 dregs, and any mixtures thereof;

drying the sludge or a mixture of the sludge and the material, optionally using a mechanical cyclone; and pelletizing or granulating the sludge or the 5 mixture of the sludge and the material and optionally drying the pelletized or granulated sludge or the mixture of the sludge and the material by heating.

In an embodiment, the method comprises separating the precipitate by flotation, 10 flocculation, filtration, decantation, clarification, sedimentation, and/or centrifugation to produce purified effluent or filtrate and a sludge comprising the precipitate;

mixing the sludge with a material selected 15 from the group consisting of fiber sludge, biosludge, lime kiln dust, lime mud, waste lime, green liquor dregs, and any mixtures thereof; and pelletizing or granulating the sludge or a mixture of the sludge and the material, and optionally 20 drying the pelletized or granulated sludge or mixture of the sludge and the material by heating.

The method may also comprise removing or reducing the amount of one or more components, such as heavy metals, from the sludge or from a product ob25 tainable from it.

20146078 prh 29 -10- 2015

The present invention also relates to a product obtainable by the method according to one or more embodiments of the invention.

The product may comprise or consist of the sludge, or it may be derived or obtainable from the sludge as described in this specification. For instance, the product may comprise or consist of the sludge obtainable after filtration or centrifugation. Such sludge typically contains water, and may contain approx. 10 - 50 % (w/w) of dry material based on the total weight of the sludge. The product may comprise or consist of e.g. dried sludge or dried sludge mixed,

20146078 prh 29 -10- 2015 before or after drying, with one or more other materials as described above. The product comprises phosphorus, i.e. phosphorus in the form of a phosphate salt.

The product may be a fertilizer product. Such a fertilizer product may be e.g. in the form of pellets, fertilizer or soil improvement mixture, or fertilizer sticks or cups or in other form known in the art.

The product may be a dry product. The product 10 may also be in the form of pellets or granules. Such products may exhibit little or no dusting and may have a lower weight than the sludge. Transportation of such a product may therefore be easy and economical.

The sludge and a product obtainable from it 15 typically contains Ca, Mg, Μη, P, Al and Fe as the main inorganic components. It may also contain e.g.

Na, Zn, Cu, Cr, Pb, Ni, As, Co, Cd and Hg. The components and their amounts may vary e.g. depending on the source of the material used for pulping in the chemi20 cal pulping process. Different countries may place restrictions on the amount of certain components, for instance minimum levels of B, Mo, Se and S or maximum levels of Cd in fertilizer products. The sludge appears well suited for fertilizer use e.g. according to 25 the Finnish regulations for fertilizer products.

The product may comprise e.g. at least 8 g/kg of phosphorus by dry weight of the product.

The product may comprise e.g. 30 - 98 % (w/w) , or 50 - 95 % (w/w) , or 70 - 90 % (w/w) of or30 ganic material by dry weight of the product.

The present invention also relates to the use of the product obtainable by one or more embodiments of the method as a fertilizer.

The embodiments of the invention described 35 hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment of the invention.

20146078 prh 29 -10- 2015

A method, a product or a use, to which the invention is related, may comprise at least one of the embodiments of the invention described hereinbefore.

A technical effect of one or more embodiments disclosed herein is that the sludge and the product obtainable from the sludge contains a large amount of phosphorus, calcium, sulphates and other components that are beneficial e.g. in fertilizer use. Some of the components may function as nutrients or prevent 10 nutrient migration to run-off water. Further, it typically contains a relatively large amount of organic material, which is also beneficial in fertilizer use, as it may function as a carbon source and expedite uptake of nitrogen from the atmosphere. On the other 15 hand, it typically does not contain high amounts of components having adverse effects. A product according to one or more embodiments may be used as a fertilizer e.g. in nurseries, in forestry, in agriculture, in horticulture and in greenhouses.

A technical effect of one or more embodiments disclosed herein is that the sludge and the product obtainable from the sludge may be provided in a form that is relatively light and has a reduced volume. It may also be provided in a form that is essentially 25 dust-free or dusts little.

A technical effect of one or more embodiments disclosed herein is that the sludge and the product obtainable from the sludge is essentially a renewable source of phosphorus, as it is for the most part de30 rived from a material used in a chemical pulping process, such as wood or waste paper.

A technical effect of one or more embodiments disclosed herein is that the method is a low cost process, which does not require significant investments 35 for equipment. It also does not require significant investments for reagents; reagents such as alkaline

20146078 prh 29 -10- 2015 agents which would in any case be used to adjust the pH of effluent or filtrate may be utilized.

A technical effect of one or more embodiments disclosed herein is that the need to adjust the pH of 5 effluent or filtrate is reduced.

A technical effect of one or more embodiments disclosed herein is that a significant reduction and recovery in phosphorus in effluent or filtrate may be obtained even if the volume of the first portion of 10 the effluent or filtrate is relatively small as compared to the whole volume of the effluent or filtrate.

A technical effect of one or more embodiments disclosed herein is that small amounts of phosphorus may be retained in the effluent or filtrate that is 15 conveyed to waste water treatment; this may be advantageous e.g. when the subsequent waste water treatment utilizes bacterial processes, for which an amount of phosphorus in the effluent or filtrate is preferable.

A technical effect of one or more embodiments 20 disclosed herein is that it can be performed e.g. at the fiber line of a chemical pulping mill. Thus it can be used to reduce phosphorus in effluent or filtrate already at the chemical pulping mill.

EXAMPLES

Reference will now be made in detail to the embodiments of the present invention, an example of which is illustrated in the accompanying drawing.

The description below discloses some embodi30 ments of the invention in such a detail that a person skilled in the art is able to utilize the invention based on the disclosure. Not all steps of the embodiments are discussed in detail, as many of the steps will be obvious for the person skilled in the art 35 based on this specification.

20146078 prh 29 -10- 2015

For reasons of simplicity, item numbers will be maintained in the following exemplary embodiments in the case of repeating components.

Figure 1 illustrates a method according to one embodiment of the present invention for producing a product comprising phosphorus. The chemical pulping process comprises in this embodiment at least two separate process stages in which conditions are acidic.

At a) , a first portion of an effluent or filtrate is 10 obtained from one such stage. A second portion of an effluent or filtrate is obtained either from a separate stage at b), or the effluent or filtrate which is obtained from a single stage is divided at bl) into a first portion and a second portion. The first portion 15 thus obtained is conveyed to c) . Alkaline agent is added to adjust the pH of the first portion of the effluent or filtrate to alkaline at c). At d), phosphorus is allowed to be precipitated, and the precipitate is separated at e) so that a sludge containing the 20 precipitate is obtained. The purified effluent or filtrate from which the precipitate has been separated at e) is conveyed to f) , in which the purified effluent or filtrate and the second portion of the effluent or filtrate are combined. The combination thus obtained 25 may be conveyed to discharge or waste water treatment.

The sludge obtained may be dried at g) . The dried sludge may be mixed with another material at h) , such as fiber sludge, biosludge, lime kiln dust, lime mud, waste lime, or green liquor dregs, which may also be 30 dried prior to mixing at h) . However, it is also possible to mix the sludge with one or more of such materials prior to drying. The mixture may be pelletized or granulated at i).

Figure 2 illustrates a system according to 35 one embodiment of the present invention for reducing phosphorus in effluent or filtrate from a chemical pulping process which comprises at least one stage in

20146078 prh 29 -10- 2015 which conditions are acidic. Various components that may be a part of the system have not been included in this schematic illustration for simplicity.

In this exemplary embodiment, the system com5 prises a digestion apparatus 1 for cooking pulp from lignocellulosic material. From the digestion apparatus

1, the pulp (often called brownstock) is conveyed to a washing apparatus 2 for washing the pulp. The washing apparatus 2 may contain e.g. one or more 10 brownstock washers, typically using countercurrent flow. The washed pulp is conveyed to a bleaching apparatus 3. In this embodiment, the bleaching apparatus contains three bleaching stages denoted 3' , 3'' and

3'''. Stage 3', in this embodiment the first bleaching 15 stage, is a bleaching stage in which conditions are acidic, for instance a A/Dl stage; stages 3'' and 3''' may be acidic or alkaline. The system also comprises apparatus 11 for drying pulp. The bleaching apparatus comprises an apparatus 4 for separating effluent or 20 filtrate from pulp obtainable from bleaching stage 3'.

The system further comprises a first conduit 5 for conveying a first portion of the acidic effluent or filtrate obtainable using the apparatus 4 for separating effluent or filtrate from pulp to the purification 25 apparatus 6. The first conduit 5 is thus connected to the apparatus 4 for separating effluent or filtrate from pulp and to the purification apparatus 6. The purification apparatus 6 comprises an apparatus 8 adapted for mixing an alkaline agent with the first 30 portion of the acidic effluent or filtrate and for allowing phosphorus to be precipitated. The apparatus 8 may contain e.g. a tank for allowing phosphorus to be precipitated. Such a tank may be e.g. a cone bottom tank. The apparatus 8 further comprises a separation 35 apparatus 9 for separating the precipitate to produce purified effluent or filtrate, such as a filtration or flocculation apparatus.

20146078 prh 29 -10- 2015

The system also comprises a second conduit 7 for conveying a second portion of the acidic effluent or filtrate obtainable from the apparatus 4 for separating effluent or filtrate from pulp; and a third 5 conduit 10 for conveying the purified effluent or filtrate from the separation apparatus 9. The second conduit 7 is connected to the apparatus 4 for separating effluent or filtrate from pulp. The third conduit 10 is connected to the separation apparatus 9 for sepa10 rating the precipitate to produce purified effluent or filtrate. The second conduit 7 and third conduit 10 are connected directly or indirectly for combining the purified effluent or filtrate with the second portion of the acidic effluent or filtrate. The second conduit 15 7 and the third conduit 10 may be connected e.g. so that they form a conduit for conveying the combination of the purified effluent or filtrate and the second portion of the acidic effluent or filtrate to a waste water treatment plant 12 and further to discharge.

The system further comprises an apparatus 13 for drying the sludge obtained from the separation apparatus 9 and an apparatus 14 for pelletizing the sludge. The apparatus 14 may also be an apparatus for granulating the sludge.

EXAMPLE 1 - Phosphorus removal from acidic bleaching filtrate

Acidic bleaching filtrates (A/Dl filtrates) 30 were obtained from a kraft pulp mill. A 9 m³/ADt flow of filtrate was divided into two portions, a first portion of 2 m³/ADt and a second portion of 7 m³/ADt.

The first portion was treated using an aqueous solution of calcium hydroxide (Ca(OH)₂) . Calcium hydrox35 ide was used in a concentration of 1.84 g/1 or 20 g/1. pH of the first portion was adjusted to 9.0, 9.2, 9.5,

9.8 or 10.0 by adding the aqueous solution of calcium

20146078 prh 29 -10- 2015 hydroxide. Precipitate was removed by decantation after 2 hours or by filtration using a fiberglass filter after 2 min of adjusting the pH to alkaline. After precipitate removal, the purified filtrate obtained from the first 5 portion was combined with the second portion and conveyed to the waste water treatment plant.

Samples were obtained from the first portion of the filtrate prior to addition of the solution of calcium hydroxide and after removal of precipitate. Total 10 phosphorus content of the samples were determined using the analysis method ICP (Inductive Coupled Plasma) metals with microwave digestion SFS-ΕΝ ISO 11885.

A reduction of approx. 87-99 % in phosphorus content was measured in the purified filtrate obtained 15 from the first portion as compared to the untreated acidic bleaching filtrate. Adjusting the pH of the first portion to a pH above 9.2 did not improve the reduction obtained.

A clearly better reduction was provided by fil20 tration (approx. 90-99 %) as compared to decantation (approx. 60-88 %). Thus decantation provided a reduction of 7-16 percentage units lower than filtration.

The solution with the higher Ca(OH)₂ concentration (20 g/1) gave a better reduction than the more di25 lute Ca(OH)₂ solution (1.84 g/1). This was likely due to higher sample dilution with 1.84 g/1 which nearly double filtrate amount after treatment compared to 20 g/1 (dilution factor was only 1.06).

0 EXAMPLE 2

Sludge was generated from 15 litres of A/Dl filtrate essentially as described in Example 1 and dried in an oven. The dry content and the content of various inorganic elements of the sludge were determined.

Product obtained from A/Dl filtrate treated

g/i

20146078 prh 29 -10- 2015

Filtrated sludge	3.1
Oven dry sludge	1.0
Inorganic content, 550 °C	0.2
Inorganic content, 950 °C	0.1
Organic content, oven dry	0.8
Dry content, %
Filter cake, oven cake	32
Ash content 550 °C	18
Ash content 950 °C	13
Element	mg/kg DS
Ca	210 000
Mg	43 000
Mn	23 000
P	9 000
Al	5 000
Fe	4 800
Na	1 400
Zn	22
Cu	17
Cr	14
Pb	8
Ni	8
As	<5
Co	<1.5
Cd	<1.5
Hg	<0.020

It is obvious to a person skilled in the art that with the advancement of technology, the basic 5 idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

A process for the preparation of a product comprising phosphorus, the process comprising obtaining a chemical or effluent filtrate

5 pulping processes;

adjusting the pH of at least a portion of the effluent or filtrate to an alkaline alkaline agent;

allowing the precipitation of phosphorus in the form of a phosphate salt; and

Separating the precipitate by flotation, flocculation, filtration, decantation, clarification, sedimentation and / or centrifugation to produce purified wastewater or slurry comprising filtrate and precipitate;

Wherein the effluent or filtrate is an aqueous liquid containing phosphorus that is wholly or partially removed and wherein the effluent or filtrate is effluent or filtrate from fiber line operations in a chemical pulping process; phosphorus-containing leachate; ash leaching solution; or any mixture thereof; and the method further comprising processing the slurry into a form suitable for use as a fertilizer product.

The method of claim 1, wherein the wastewater or filtrate is selected from the group consisting of wastewater or filtrate derived from the chemical fiber pulping process fiber line.

30 radios; phosphorus-containing leachate, such as landfill or leachate from the lime or slaked lime storage area; ash leaching solution; and any mixtures thereof.

35

The process according to claim 1 or 2, wherein the effluent or filtrate is an acid bleaching fluid

20146078 prh 25 -01-20199 dos or acid bleach wastewater optionally available from the first acid bleaching step.

The method of any one of claims 1 to 3, wherein the chemical pulping process is

5 the pH of the effluent or filtrate from the process is less than 7; or less than 6; or less than 3.

The process of any one of claims 1 to 4, wherein the process comprises obtaining the first 10 parts of the waste water or filtrate from a chemical pulping process;

obtaining another portion of the waste water or filtrate from the same or a different step of the chemical pulping process;

adjusting the pH of the first 15 parts of the effluent or filtrate to an alkaline alkaline agent;

allowing the precipitation of phosphorus in the form of a phosphate salt;

separating the precipitate to produce purified wastewater or filtrate and a slurry comprising the precipitate; and combining the purified waste water or filtrate with the waste water or other portion of the filtrate.

The method of any one of claims 1 to 5, wherein the method comprises

25 providing a waste water or filtrate from a chemical pulping process;

dividing the waste water or filtrate into a first portion and a second portion;

adjusting the pH of the first 30 parts of the effluent or filtrate to an alkaline agent;

allowing the precipitation of phosphorus in the form of a phosphate salt;

separating the precipitate to produce purified sewage or filtrate and a slurry comprising the precipitate; and

20146078 prh 25 -01-20199 Combine purified waste water or filtrate with waste water or other portion of filtrate.

The method of any one of claims 1 to 6, wherein the method comprises at least

Adjusting the pH of a portion of the water or filtrate, or a portion thereof, with an alkaline agent to a pH of 8 to 14; a value of 8-11; or 9-10; or 9.2 to 9.8.

The process of any one of claims 1 to 7, wherein the alkaline agent is selected from the group consisting of

10 which consists of the following

CaO;

an alkali metal hydroxide such as NaOH;

Ca (OH) ₂ ;

NH ₄ OH;

15 alkaline wastewater or filtrate;

alkaline bleaching water or filtrate;

a powder or an aqueous solution thereof;

and any mixtures thereof.

The process of any one of claims 1 to 8, wherein the process comprises separating the precipitate by filtration and optionally filtration using a filter of green liquor precipitate.

The process according to any one of claims 1 to 9, wherein the process comprises a slurry

25 optionally using a mechanical cyclone.

The method of any one of claims 1 to 10, wherein the method comprises mixing the slurry with a material selected from the group consisting of fiber slurry, bio slurry, lime slurry.

30 n dust, lime, waste lime, green liquor and any mixture thereof.

The process according to any one of claims 1 to 11, wherein the process comprises pelleting or granulating a slurry and optionally reducing

35 drying of the slurried or granulated slurry by heating.

A product obtainable by the process of any one of claims 1-12.

The product of claim 13, wherein the product is a fertilizer product.

5

The product of claim 13 or 14, wherein the product is in the form of pellets or granules.

The product of any one of claims 13 to 15, wherein the product comprises at least 8 g / kg

10 phosphorus based on the dry weight of the product.

Use of a product obtainable by a process according to any one of claims 1 to 12 as a fertilizer.