The invention also relates to a method for using the extraction agents for extraction of cations, preferably metal ions, as well as anions, from a solid phase to a liquid phase or from one liquid phase to another. A special and important application of the invention relates to extraction of metal ions from lignocellulose, especially while simultaneously attaining delignification and bleaching of the lignocellu- lose. In a preferred method for simultaneous metal ion extraction, delignification and bleaching of the ligno- cellulose an extraction agent based on oil of turpentine including an organophilic chelating agent in the presence of an oxidation agent is used.

A special application is to remove incrust forming and bleaching hampering metal ions with simultaneous deligni- fication in closed systems under EFM (Effluent Free Mill) conditions.

STATE OF THE ART Chlorine based bleaching Within the pulp industry traditionally for decades elementary chlorine and chlorine based compounds such as sodium hypo- chlorite and chlorine dioxide have been used for bleaching - delignification of chemical pulps. However, this causes discharge to the recipients of organochlorine compounds, which are defined and quantified as adsorbable organic halogens (AOX). Among said bleaching chemicals chlorine dioxide gives the least AOX under the same premise and the allowed levels of AOX in discharges from bleach plants gradually have been reduced to such an extent and are now at such a low level that the pulp mills in at least Scandinavia and the rest of Europe have changed to only chlorine dioxide in ECF (Elementally Chlorine Free) bleaching-delignification in order to fulfil the aims. However, also the use of chlorine dioxide has been questioned by the pressure from different consumer organizations which require paper products completely bleached without chlorine based chemicals and, furthermore, the restrictions against discharges of organo- chlorine compounds have been so severe in certain countries that the requirements as to low AOX levels in the discharges hardly could be fulfilled even if only chlorine dioxide was used.

ECF (Elementally Chlorine Free) and TCF (Totally Chlorine Free) bleaching The increasing environmental hesitations against discharges containing these organic chlorine compounds, AOX, accordingly during the latest decade have accelerated a rapid development of chlorine free process steps including oxygen (0), ozone (Z) and hydrogen peroxide (P) as a complement to chlorine dioxide step (D) in so-called ECF bleaching-delignification of sulphate pulps in for instance the sequence [ODQPD], where Q is a step for treatment with chelating agents but also to a certain extent has become a complete replacement for the chlorine dioxide in TCF bleaching-delignification, for reducing of AOX to nearly zero in for instance the sequence [OQPPP] The Q step has been introduced since the chlorine free alter- natives require a very good control of metal ions. By intro- duction of also new cooking methods, for instance so-called "Modified Continuous Cooking" (MCC), "Iso Thermal Cooking" (ITC) and "Superbatch Cooking", and applying sequential bleaching with oxygen, ozone and hydrogen peroxide in for instance the sequence [OZQ(EOP)P] in TCF bleaching/deligni- fication brightness levels comparable with oxygen and chlorine dioxide [ODD] in ECF bleaching/delignification have been obtainable, i.e. about 90% ISO without any essential impairment of the CED (cupriethylene diamine) viscosity of the pulp, usually according to TAPPI or SCAN, by means of which the degree of degradation of the cellulose in the different process steps can be determined.

Transition metals A key factor for attaining this in TCF production is that the levels of transition metal ions in the pulp in the above- mentioned chlorine free bleaching steps are low, preferably near zero level in at least the peroxide step (P) since especially manganese gives serious disturbances in bleaching with peroxide by catalysing certain side reactions wherein free radicals are involved, which attack the hydrocarbon chains. This means that one has to remove manganese before the P step, usually by the addition of chelating agents in a so-called Q step before one or several P steps in the bleach plant. An often used method is the so-called Lignox method (EKA Nobel) which is described in SE-A-8902058. By our introduction of a new method, which is described in the U.S. patent 5 571 378, the so-called Hampox-Q process (Hampshire Chemical AB), additional advantages as regards brightness and viscosity have been obtained and confirmed in full-scale production at Munksj AB Aspa Bruk for more than two years.

Discharge of metal ion complexes What is common for all Q steps is that complexes of manganese washed out from the pulp must be removed from the white water system in order to prevent that too high levels are built up in the bleach plant. Thus, this must be more or less open and includes the addition of water free from manganese complex to the wash filter in the Q step since it is the wash water which sets the limit as to how low manganese level can be achieved in the pulp into the bleaching step. Thus, the white water must be discharged from the bleach plant and replaced with water free from manganese complex, usually fresh water and condensed water. Discharge of the complexes to the recipient of course gives rise to environmental problems since the chelating agents are restrictively biodegradable and are regarded as being able to release heavy metals from the bottom sediment. Accordingly, by changing to TCF technique and thereby solving the problems with discharge of AOX to the recipient, the discharge of chelating agents to the recipient introduces a new problem, though not so big, it is still of a great concern.

Destruction of metal ion complexes Thus, it should be desirable to get rid of the manganese complexes in an environmentally suitable way. One way, the introduce of which has started, is to close the system and destruct the complexes in the chemical recovery system of the mill with EFM (Effluent Free Mill) production as a goal. This means that the effluent from the white water system of the bleach plant instead of being passed directly to external purification and then discharged into the recipient either is directly integrated counter-current with the brown side and then later indirectly reaches the chemical recovery or that it is integrated directly with the chemical recovery by transfer to the weak liquor to evaporator and the soda recovery unit together with the filtrates from the brown side.

Incrusts Closing of the system in pulp mill in EFM production in order to eliminate discharge of metal complexes, AOX, COD (i.e. oxygen consuming organic substance expressed as chemical oxygen demand) and other environmentally harmful substances from the white water of the bleach plant and instead transfer this directly to the so-called brown side of the fibre line or directly to the chemical recovery process for destruction according to the present knowledge in the art gives rise to incrust problems since the white water in addition to transition metals also carries high levels of other so-called non-process metal ions, commonly named non-process elements (NPE), especially Ca, Mg, Al, Ba and K, which have been desorbed from the pulp by the acidic pH value in the Q step of the bleach plant and in optional acidic Z steps, and which together with different anions, such as sulphate, phosphate, oxalate, silicate and carbonate, can form sparingly soluble salts and form problematic incrusts in the form of barium sulphate and calcium oxalate in the bleach plant, calcium carbonate in digesters, while in the chemical recovery sodium aluminum silicate can be formed in black liquor evaporators and calcium carbonate in the surrounding equip- ment of the green liquor preparation, such as in pumps and pipelines. The pH lowering in the Q step must be carried out in order that the manganese ions shall be able to form complexes effectively but at the same time it causes an undesirable release of fibre adsorbed calcium and magnesium ions. By means of the previously mentioned Hampox-Q process, which uses a higher pH level and thus releases less calcium and magnesium ions, the situation can be improved but incrust problems cannot be excluded.

To pass the filtrate from the bleach plant to the weak liquor in the above described manner and then let them pass to the soda recovery unit in the same manner as the filtrate from the brown side thus results in increased incrust formation in the evaporators since the acidic filtrates from the Q steps and the optional Z steps in the bleach plant contain high levels of NPE in the form of ions such as Ca, Mg, Al, K and Ba and different anions, such as silicate, phosphate, oxalate, carbonate and sulphate, which can form sparingly soluble salts and be included in the incrusts. The incrust formation can be reduced in the evaporators by passing the filtrates not to the weak liquor, but to the wash liquor, which goes to the melt dissolver and then to the green liquor clarification where the transition metal ions can be expelled but then incompletely since the ligand instead of a complete degradation such as in the soda recovery unit is subjected to a gradually splitting with a certain degree of retained complex forming ability in the green liquor preparation (melt solution, green liquor clarification), white liquor preparation (causticizing, white liquor clarification), impregnation, cooking, discharging, etc., by means of which optionally some non-process metal ions can be returned and built up in the system to a balance level which depends on the ratio in rapidity between addition and degradation of the complexes in soda recovery unit and other parts of the system.

In summary according to the present state of the art, if in TCF-EFM production one wishes to avoid accumulation of high levels of non-process metal ions in the bleach plant (in order to prevent disturbances from manganese ions in the bleaching process and reduce calcium and magnesium incrusts in washing filters and other equipment) one can choose one of the following alternatives, all of which, however, give rise to other disadvantages.

(a) From the bleach plant discharge part of the collected wash filtrates in the white water system of the bleach plant to the recipient, whereby chelating agents in the white water are discharged as well, or to avoid discharge of chelating agents: (b) transfer of the wash filtrates to the brown side by integration of the bleach plant and thereby destruction of the metal complexes in the soda recovery unit, which gives rise to incrust problems, or (c) transfer of the wash filtrates directly to the melt dissolver in the chemical recovery process which also gives rise to incrust problems.

Thus, in all the alternatives there are problems. In case (a) environmental problems owing to chelating agents in the recipient, in cases (b) and (c) severe incrust problems on the brown side and in the chemical recovery system. Thus, it is desirable that the white water has such a low level of chelating agents which are controversial from an environ- mental point of view that the white water can be passed directly to the external purification of the mill and then be discharged in the recipient.

Proposed solutions of the incrust problem In the literature different methods are described concerning internal purification and recirculation of spent liquors from the bleach plant in order to manage the NPE problems and thus the incrust problem but all have in common that they are not cost effective for different reasons. One method is the use of ion exchanger and another membrane filtration but both have in common that ion exchangers and membrane filters easily are contaminated and must be cleaned and require large maintainance costs and frequently must be replaced. Thus, said methods have not obtained any widespread use in pulp production.

Other methods for carrying out metal ion extractions have been described in our previous Swedish patent applications Nos. 9603858-3 and 9603859-1 with the title "Process in the production of cellulose pulp" and "Process in the production of lignocellulose" respectively. These include metal ion extraction of lignocellulose with an organophilic chelating agent dissolved in an organic solvent, preferably turpentine, under reductive conditions. The requirement for reductive conditions according to these previous patent applications is based on the fact that it has been found that metal ion complexes of transition metals in the higher valence stages at pH values above about 8.5 have a tendency to precipitate in aqueous media, the precipitation preferably occurring on the pulp fibres if such are present.

This problem has been dealt with and been discussed also in our U.S. patent US 5 571 378 but in said case chiefly on the bleaching side in a new and more effective Q step in connection with peroxide bleaching.

Summarizing our previous Swedish patent applications Nos. 9603858-3 and 9603859-1 the problem was solved due to the high stability and solubility of the organophilic complexes in the organic solvent; NPE in the form of transition metal ions, but also incrust forming metal ions, such as Ca and Mg, could effectively be extracted.

THE SOLUTION OF THE PROBLEM The invention The problems in the processes according to the prior art now according to the present invention have been solved by metal ion extraction with turpentine oil related extraction agents in the presence of an oxidation agent, with or without an organophilic chelating agent. When applied to lignocellulose, more closely to sulphate pulp, a delignification and a bleaching are obtained together with the metal ion extraction. The present invention comprises the following causes of events: complex binding, ion exchange, metal ion extraction and delignification. The turpentine oil related extraction agents, with or without organophilic chelating agent, are fundamental to the invention. In addition to this there is the surprising discovery that the complexes of the transition metal ions in the organic phase under oxidative conditions are stable at essentially higher pH values than what previously have been regarded as possible.

Our theoretical explanation model to the stability is that the oxidation of the transition metal ions to at least one stage above their lowest valence stages increases the complex constants with several powers of ten as compared to the corresponding complex constants of the metal ions in the lowest valence stages. However, in aqueous medium this increased stability is surpassed by the fact that the solubility of the hydroxides of said metal ions at the same time decreases and thus the hydroxides are precipitated already at pH values above about 8. This interplay between solubility product of the hydroxides and the complex constants is expressed as the conditional complex constants of the respective metal ion. According to the theoretical explanation model these decrease dramatically in aqueous medium at pH above about 8 contrary to in the organic medium wherein the hydroxyl ion concentration is low. The theoretical explanation model will be further developed later in this specification.

Within the scope of the concept there is also extraction of anions, i.e. counterions to the above-mentioned metal ions, which together with the metal ions can form sparingly soluble salts which cause incrust problems. The extraction takes place in the same manner as in the extraction of metal ions but through ion pair extraction with an organophilic onium compound, which will be described more closely later, instead of through complex formation extraction with an organophilic chelating agent. Anions which cause incrust problems are inter alia carbonate, oxalate and sulphate ions but to the category anions also the metal ion complexes of conventional chelating agents, such as NTA, EDTA and DTPA, belong and also these complexes turn out to be extractable over to the orga- nic phase. This means that an organophilic onium compound, which is cationic, can extract metal ions, which also are cationic, said organophilic conventional chelating agents functioning as carriers for the metal ions in an unexpectedly well functioning concept. In this manner merely the anionic extraktion offers a complete concept for extraction and control of incrust forming anions and cations (metal ions).

The invention in the sulphate process With the use of the sulphate process as an example it is described below what takes place and what can be attained in a metal ion extraction with a turpentine oil related extraction agent in the presence of an oxidation agent, with or without an organophilic chelating agent on the brown side in alkaline environment. With the oxidation agent is meant that the trasition metals are oxidized up at least one stage above their lowest valence stages, which gives stable organo- philic complexes, which in its turn catalyze a deligni- fication of the lignocellulose. The exact mechanisms for this are not known but probable such will be described later in the specification where it is also explained more closely why the oxidation of the transition metals gives more stable complexes. In this context reference is also made to our U.S. patent 5 571 378 and to: Nordgren, A. and Elofson, A., "New Process for Metal Ion Chelation at elevated pH in Pulp Production", 1994 Pulping Conference, TAPPI PRESS, Proceedings Book 3, page 1321 (1994).

Complex bonding/metal ion extraction of the transition metals (for instance Fe and Mn) and in proper sense the incrust forming metal ions (for instance Ca, Mg and Ba), in other words NPE already on the brown side means that NPE to a substantially less extent, through the pulp flow, are transferred to the complex forming (pretreatment) step (Q) and the peroxide step (P) in the bleach plant. Since a substantially less amount of NPE reaches the Q step the need of chelating agents (EDTA or DTPA) becomes less there and the washing out of the complexes formed at a given dilution factor will be more effective in the wash filter of the Q step before the P step. The delignification which simultaneously takes place releases a substantial amount of lignin from the lignocellulose which lignin in the form of molecular fragments (COD) is removed already during the metal ion extraction on the brown side, which favours a low peroxide consumption in the P step of the bleach plant.

When considering and including an oxygen step (0) and a (occurring less frequently) ozone step (Z) in addition to the Q and P steps described in the review above, the complex bonding/metal ion extraction/delignification are carried out as early as possible on the brown side in a position already before the oxygen step so that NPE, especially Fe, will not reach this in higher extent and affect the selectivity negatively. At the same time the lignocellulose, as previously mentioned, by the combination of complex bonding, metal ion extraction and delignification, is freed from a substantial amount of COD. When in this manner more NPE and COD have been extracted out and removed from the ligno- cellulose there will be less left in the oxygen step (0) , to the ozone step (Z), if any, and, which previously has been described, to the peroxide step (P) in the bleach plant, which in its turn reduces the consumption of oxygen, optionally ozone, and hydrogen peroxide. Since a substan- tially less amount of NPE reaches the Q step the need of complexing agent, EDTA or DTPA becomes substantially less in this step as previously mentioned. Thereby advantages are obtained, both since the need of chelating agents in the Q step and delignification in the P step will be less, which saves both chelating agents and hydrogen peroxide and at the same time environmental advantages are obtained since a substantially less amount of oxygen consuming organic substance (COD) and chelating agent (in form of complex bonded NPE) passes out in the recipient. Essentially only a smaller amount of oxygen consuming organic substances (released lignin and carbohydrates) which are formed in the bleach plant then load the external purification in form of COD. If also this load is to be eliminated even the white water system of the bleach plant must be integrated with the chemical recovery, either directly or in counter-current through the brown side. The invention offers by means of what has been stated above large possibilities for a closing of the system under EFM conditions.

It will be understood that the invention is not restricted only to the process line for pulp production, to which the brown side belongs, but also includes other sectors. Thus, in summary the invention applies to: (1) the process line for pulp production; (2) the chemical recovery cycle; (3) the cooking liquor preparation; in which sectors the extractions can be carried out in at least one position, in at least one of the following steps or moments: (1) (a) chips handling before digester, (b) preimpregnation to digester, (c) digester, (d) the washing zone of the digester (continuous technique) or the displacement moment of the digester (superbatch technique), (e) stripping before black liquor evaporation, (f) after digester on the brown side on pulp and on white water flows, (g) in the bleach plant on pulp and on white water flows, (h) after the bleach plant, for instance in combination with paper making or board machines; (2) black liquor evaporation; (3) (a) green liquor clarification, or (b) white liquor clarification.

Extraction experiments According to the present invention NPE are extracted from lignocellulose by metal ion extraction with or without organophilic chelating agent dissolved in turpentine in the presence of an oxidation agent whereby at the same time a delignification occurs. By the extraction incrust forming NPE and oxygen consuming organic species (COD) are removed from the lignocellulose, which, as pointed out previously, makes possible a closure of the system under EFM conditions. On the basis of the periodic table of elements the following elements are the most important as regards NPE: group I: Na, K and Cu group II: Ca, Mg, Zn and Ba group III: Al group VI: Cr and Mo group VII: Mn groups VIII, IX and X: Fe, Co and Ni To our surprise it was found that turpentine as an extraction agent, without organophilic chelating agent, had a substan- tial ion exchange capacity for the above-mentioned NPE. Thus, for instance it was found possible in a one step extraction with balm turpentine of Chinese origin to extract out substantial amounts of fibre adsorbed and water dissolved metal ions from sulphate pulp. Certainly considerably more could be extracted over to the organic phase in the presence of an organophilic chelating agent, but the pure turpentine in certain cases can be an alternative or supplement to the combination of organic extraction agent with organophilic chelating agent. The aim here has been to extract metal ions but obviously all types of cations can be extracted, for instance ammonium ions.

Oils of turpentine are a subgroup of plant and wood saps which are comprehended under the term ethereal (essential) oils, in most cases consisting of mixtures of terpene and sesquiterpene compounds with a smaller portion of compounds from other classes of compounds. A second larger group consists to a large extent of aromatic compounds including phenols. Under the term essential oils also eucalyptus oils, sassafras oil and camphor oil are included of which especially eucalyptus oils are interesting as extraction agent in the pulp industry since eucalyptus wood is an important raw material for pulp production.

Oil of turpentine is the common name of the volatile compo- nents designated as "turpentine" or "balsam" in crude rosins from especially species of pine trees of different conifers.

According to the starting material and method of preparation one distinguishes according to DIN 53248 (April, 1977) between for instance: gum spirits of turpentine; by extraction and/or steam distillation purified wood tur- pentine; crude and purified sulphate turpentine; sulphite turpentine; purified (distilled) wood tar, etc.

The main components in turpentine oils are mono and bicyclic monoterpenes CloHl6; furthermore, there are smaller amounts of terpene-oxygen compounds (for instance terpene alcohols) sesquiterpenes C15H24 and other compounds; the composition depends on from which species of the pinus the turpentine oil has been recovered; however, the main component in most cases is alpha-pinene with in the cited order decreasing amounts of beta-pinene, camphene, 3-carene and limonene.

Thus, for instance Swedish sulphate turpentine can contain: 50-75% alpha-pinene; 4-7% beta-pinene; 1% camphene; 15-40% 3-carene; 1-3% limonene and with a boiling range of 150-175"C at 1013 mbar. Turpentine oil of Chinese origin, which has been used in the experiments, can consist of: 60-92% alpha- pinene; 4-9% beta-pinene; 1-2% camphene; 0-10% 3-carene; 1-3% limonene and with a boiling range of 150-1600C at 1013 mbar.

In addition to the above stated components turpentine oil can contain alpha- and gamma-terpinene, alpha- and beta- phellandrene, terpinolene, myrcene, p-cymene, bornyl acetate, anethole, sesquiterpene, heptane, nonane and several other compounds such as abietic acids, pimaric acids and palustric acids, which are derivatives of tricyclic terpenes. They belong to the group natural rosin acids and are the main component of different colophony rosins. Such are obtained as a distillation residue in distillation of gum turpentine recovered from different species of pinus, and in the distillation of tall oil, wherein also a smaller amount of fatty acids is included in the pine resin, while a third type of colophony rosin is obtained by solvent extraction of root parts and is called root rosins. To the group synthetic resin acids belong compounds such as modified hydrocarbon, aceto- phenone and polyamide resins.

Sulphite turpentine essentially differs from the other tur- pentine oils by containing as much as 70-90% p-cymene and smaller amounts of borneol, dipentene and sesquiterpene.

The higher fraction of distilled wood tar, so-called natural "pine oil", can have the following composition: 50-70% alpha- terpineol; 5-10% borneol (and isoborneol); 5-10% fenchol; 5-15% other turpentine alcohols (p-menthanol-8, beta-ter- pineol, terpene, etc.); 0-10% terpinyl and bornyl acetate; 0-3% monoterpenes (pinene, dipentene, terpinols, etc.); 5-10% of other components (cineols, campher, anethole, estragole, sesquiterpenes, etc.).

Synthetic "pine oil", prepared by hydration of alpha-pinene rich turpentine oil fractions, can have the following compo- sition: 50-95% alpha- and gamma-terpineol; 3-20% of other terpene alcohols (beta-terpineol, terpinene-l-ol, fenchol, etc.); 0-30% terpenes (3-carene, terpinene, dipentene, ter- pinols, etc.); 1-10% 1,4- and 1,8-cineol.

The chemical properties of turpentine oils depend on the components included of which for instance pinene is reactive in the presence of acids, acidic salts, surfactants or Friedel-Crafts catalysts and they can form hydrates in the presence of water. It is quite plausible that certain reactions take place during the extraction which change the chemical and physical properties of the extraction agent but then also the reaction products and the novel properties of the extraction agent are included in the inventive concept and the application of the invention.

General test methods for characterizing turpentine oils are summarized in DIN 53248 (April, 1977) and to a large extent correspond with international standards of ISO 412-1976. The determination of separate components can be made by gas chromatography according to DIN 51405 or ASTM E 260-69.

Quantitative analysis of resin acids in colophony rosin can be made according to ASTM D 1585-63 and ASTM D 1240-54.

It is implied that the above stated turpentine oils or deri- vatives of these included in the term etherial oils only are examples and that also other compounds or derivatives thereof included by the same term can be used separately or be included as components. The same is true as regards turpen- tine replacements such as decal in and tetralin; the hydro- genation product hydroterpine (monocyclic monoterpenes; boiling range 180-1950C) closely related with turpentine oil; distillation and rearranged products from turpentine oil, or other synthetic turpentine oils or their derivatives prepared in different ways.

Further, compounds having dissociable hydrogen ions of for instance phenolic character, such as for instance p-cymene, can be included. Others can be of thiophenol character, such as for instance lignothiols formed in the cooking step of the sulphate process while others can be of carboxylic acid character, for instance tall oil fatty acids containing inter alia fatty acids and resin acids which can be taken up and dissolve in the turpentine. Other acids, such as ligno- sulphonic acids and lignocarboxylic acids, can be formed in the oxygen step of the sulphate process by oxidation of lignothiol and lignine fragments respectively. In the sulphite process lignosulphonic acids can be formed directly in the cooking step by sulphonation of lignine fragments.

Preferred extraction agents according to the invention are gum turpentine, sulphate and sulphite turpentine, which need not be present in purified form but can be raw turpentines.

The steam which is relieved from the head of the boiler during the sulphate and sulphite cook contains the raw tur- pentine. The steams are condensed and the condensate is passed to a decanter and the raw turpentine is separated as a supernate. By oxidative treatment and distillation the raw turpentine can be purified.

The above data for turpentine oils and resin acids are derived mainly from Ullmanns Encyklopädie der technischen Chemie, 4th Edition, Volume 22, the chapters Terpene and Terpentinöl, and Volume 20, the chapter Riech und Aroma- stoffe, and Volume 12, the chapters Hartze, naturliche und syntetische, respectively.

The following Table 1 reports extraktion experiments on lignocellulose, more particularly sulphate pulp in the presence of air at a pulp consistency of 5% based on the aqueous phase, at the weight ratio water/turpentine - 1/1 and at a temperature of 60-700C. Comparative studies have been made between turpentine in combination with an organophilic chelating agent, the aromatic hydrocarbon toluene in com- bination with an organophilic chelating agent and only tur- pentine respectively. All extractions are one stage extractions. The sulphate pulp contained 7 mg Fe, 251 mg Mn, 203 mg Mg and 1596 mg Ca / kg dry calculated pulp at 12% pulp consistency. As organophilic chelating agent N,N-bis(2- hydroxy-5-nonylbenzyl) glycine is used in a stoichiometric amount. The gum turpentine used in our experiments had the following main components: 84% alpha-pinene; 8% beta-pinene; 1.5% limonene; 1.5% bicyclic sesquiterpene; less than 1% menthyl acetate.

Table 1. Metal ion extraction of sulphate pulp Extracted to organic phase (%) pH Fe Mn Mg Ca Turpentine + organophilic 7.5 82 93 70 88 chelating agent 8.5 81 89 85 81 9.5 83 80 73 80 Toluene + organophilic 7.5 81 18 88 91 chelating agent 8.5 85 17 85 84 9.5 83 25 89 84 Turpentine 7.5 75 75 17 53 8.5 84 80 46 60 9.5 80 81 55 80 According to the state of the art lignocellulose in its capacity as an ion exchanger in the sulphate process competes so much with the water soluble chelating agents EDTA and DTPA in aqueous medium at higher pH that normally it is not in practice possible to carry out a complex binding at pH above 6. Thus, it was surprising when, as shown in the Table, we found that with turpentine, with or without an organophilic chelating agent, it worked extremely well to extract the metal ions effectively over the whole pH range. As can be seen from the Table also toluene functioned well in combina- tion with an organophilic chelating agent with a high per- centage of extracted metal ions. The extraction process could easily be followed by development of the colour of the complexes with transition metal ions, which will be described more closely later in the following text.

A reason for the strong competition from the lignocellulose is regarded to be 4-O-methyl glucuronic acid substituents on the hemicellulose xylan, which substituents in the cooking process by elimination of a methoxy group and rearrangement are converted to 4-deoxyhex-4-euronic acid substituents (Hex-A), which in the capacity of a strong chelating agent can bind metal ions and in this manner can serve as ion exchangers. [T. Vuorinen, J. Buchert, J. Teleman, M. Tenkanen, P. Fagerström, "Selective hydrolysis of hexen- uronic acid groups and its application in ECF and TCF bleaching of kraft pulps", International Pulp Bleaching Conference Proceedings, Washington, USA (1996), page 43].

Another reason to a strong competition from the lignocellu- lose can be that transition metal ions are bound to thiol groups formed by substitution on the lignin component at the high sulphidity in the cook stage; this according to a hypothesis we have presented in our U.S. Patent 5,571,378 (U.S. Patent Application Serial No. 08/327,919), "Process for high-pH metal ion chelation in pulps" (Hampox-Q) for control of metal ions on the bleaching side. According to the patent and as a support for the hypothesis zero levels of manganese can be obtained by oxidation in the presence of DTPA, wherein as a part of the explanation model it was stated that ligno- thiol groups are oxidized to lignosulphonic acid groups causing weaker bonds to transition metal ions whereby DTPA is capable to complex bind the metal ions. The hypothesis is also supported by the experience that fibre adsorbed manganese substantially decreases after oxidation and delignification in an oxygen stage where the explanation model can be that lignothiol groups are oxidized to ligno- sulphonic acid groups and that lignothiol fragments and lignosulphonic acid fragments respectively in the form of manganese complexes or manganese salts, which previously were a part of the lignocellulose, are split off and dissolve in the delignification.

In addition to the ions reported in the Table also Al (80%), Si (50%), K (10%) and others. It is surprising that Si and Al were extracted since they are present as silicate and alumi- nate ions respectively in the actual pH range. The reason is not made clear but organophilic ammonium ions can play an important part as a support to organic phase. This will be further discussed later in the text.

The following Table 2 illustrates one stage extraction experiments with turpentine and toluene respectively on only an aqueous phase without lignocellulose. The Table shows the results both with and without organophilic chelating agent in the organic phases. In these cases no pulp has been included in the experiments but the extractions have been made only between the aqueous phase and the organic phase consisting of the respective organic extraction agents. The weight ratio between aqueous phase and organic phase was 1/1 and the temperature in the experiments 60-700C. Before the extraction 139 mg Fe, 137 mg Mn, 61 mg Mg and 501 mg Ca / 1 in the form of metal salts were dissolved in the aqueous phase.

Table 2. Metal ion extraction of an aqueous phase Extracted to organic phase (%) pH Fe Mn Mg Ca Turpentine + organophilic 7.5 85 100 11 49 chelating agent 8.5 85 100 61 86 9.5 78 95 72 90 Toluene + organophilic 7.5 78 63 4 22 chelating agent 8.5 85 88 6 33 9.5 85 88 18 53 Turpentine 7.5 53 80 5 10 8.5 40 80 9 20 9.5 55 80 26 63 Toluene 7.5 1 0 2 1 8.5 1 0 2 1 9.5 1 0 2 1 From Table 2 it can be seen that toluene alone practically did not at all extract the metal ions while turpentine served well as an organic solvent for the metal ions. Together with an organophilic chelating agent toluene served relatively well compared with turpentine as solvent for the complexes of Fe and Mn but did not at all reach the level of turpentine for Mg and Ca. By the absence of lignocellulose, in compari- son with Table 1, a clear increase of extracted Mg and Ca at increased pH in all cases except for toluene alone, in which the solubility is too low for a judgment, can be clearly seen. There is also the same tendency for Fe and Mn but less pronounced.

In similar experiments as in Table 2 but in the presence of a stoichiometric amount of DTPA the organophilic chelating agent in turpentine overmatched DTPA so that the major part of the metal ions were extracted to the organic phase in the high pH range as in the experiments according to Table 2.

This was unexpected and surprising since DTPA is the most effective chelating agent in its type and it can be inter- preted as a synergism between turpentine and organophilic chelating agent since the organophilic chelating agent in toluene as well as turpentine alone only gave an insignifi- cant metal ion extraction in the presence of DTPA. Thus, as regards turpentine alone the result differs from that in Table 2 where the metal ion extraction was significant; a difference which thus is an effect of DTPA. The metal ion extraction with toluene alone was barely demonstrable in the presence as well as in the absence of DTPA.

During the extraction, as previously mentioned, the organic phases passed through a characteristic colour shift from colourless to pale orange via purple to finally a brownish nuance, indicating an oxidation by oxygen of the air of the organophilic Fe(II) and Mn(II) complex to higher valencies; to Fe(III) and at least Mn(III), perhaps Mn(IV). These complexes have shown to be stable in the organic medium, which is demonstrated by the presence of their characteristic colour even at as high pH as 11.5-12. It can be presumed that it is the specific chemical - physical surrounding in the organic medium which conditions the stability, since for instance the EDTA or DTPA complexes with manganese in their higher valencies are not stable in aqueous medium at so high pH but, as previously mentioned, are overmatched by ligno- cellulose modified in the cooking process or are precipitated as oxide hydrates already at pH above 6.

Thus, it was surprising when we found that the complexes of the transition metals in the organic phase under oxidative conditions were stable at considerably higher pH values than what previously had been regarded as possible. The oxidation of the transition metal ions to valencies one stage above their lowest increases the complex constants with several ten powers. According to what we have found in our studies this can be utilized up to pH 11.5-12 when otherwise so weak complexes are formed that oxide hydrates begin to precipitate or the competition from the fibre phase present, which as previously mentioned also functions as ion exchanger, gives rise to fibre adsorption. At pH above 11.5-12 the advantages of reductive conditions are present according to our two pre- vious patent applications in which extraction under reductive conditions in order to bring the transition metal ions to the lower valence stages is emphasized.

Thus, by means of the present invention a well-known problem in sulphate pulp production has been solved, viz. to be able to effectively complex bind transition metals such as Mn(III) and Fe(III) in the form of stable complexes at high pH, as stated up to pH 11.5-12. The problem of not being able to effectively complex bind and remove these metal ions in an oxidative environment, i.e. on the brown side after the screen room, as from the oxygen stage where high pH values prevail thus have obtained a surprising solution. The basic principle is, as can be seen from what has been stated previously, the extraction with organic solvents, preferably turpentine oils, in which owing to the high stability and solubility of the complexes, NPE in the form of transition metal ions, but also incrust forming metal ions, such as for instance Ca and Mg, can be extracted effectively. Organic solvents in general, but terpenes especially, in combination with organophilic chelating agents further increase these possibilities.

The logical but surprising conclusion of what has been stated above is, as previously mentioned, that the complexes in the organic solvent are more stable and overmatch chelating agents such as EDTA and DTPA, but also the hexenuronic acid and/or the lignothiols in the lignocellulose modified in the cooking process up to pH 11.5-12; as regards the hexenuronic acid in that this by oxidative hydrolysis is split off and rearranged to other species during the extraction, and/or in that the complexes in the organic solvent are more stable than even the hexenuronic acid; as regards the lignothiols in that these are oxidized to lignosulphonic acids and/or in that lignothiols and lignosulphonic acids respectively are split off as a stage in the delignification process during the extraction and/or in that the complexes in the organic solvent are more stable than the complexes of the lignothiols and lignosulphonates respectively. Irrespective of the explanation this is innovative since the problem with metal ions affinity to lignocellulose according to the prior art so far only has been possible to solve by hydrolysis at a low pH (about 3) and a high temperature (about 900C) or by strongly acidic oxidative bleaching/delignification with ozone or chlorine dioxide.

The present invention supplements our previous Swedish Patent Applications 9603858-3 and 9603859-1 as regards the use of organophilic chelating agents. In the present invention the dosage of complexing agent in the borderline case can approach zero, while in the two previous applications this never could be the case since the organic solvent was not expected to have any chelating agent capacity and thus, the dosage always must have a value larger than zero. This was before the chelating agent capacity of turpentine was detected and the difference between turpentine and for instance toluene in this respect had been clarified. Thus, the present invention and our two previous ones supplement each other in a covering manner and together give large possibilities to solve the metal ion control in the pulp production under ECF conditions. Complex binding during oxidative conditions has been discussed in our U.S. Patent 5,571,378 but mainly on the bleach plant side in a new and more effective Q step in connection with peroxide bleaching.

In summary the experiments presented in Table 1 show the capacity of turpentine, with or without organophilic chelating agent, to extract metal ions from a solid phase to a liquid phase, i.e. in this case extraction of strongly fibre adsorbed metal ions from a sulphate pulp to an organic phase. Here turpentine together with an organophilic chelating agent is best but only turpentine has a potential which is not insignificant.

In Table 2 toluene is compared with turpentine. The table shows the capacity of these organic solvents, with and without organophilic chelating agent, to extract metal ions from one liquid phase to another, i.e. in the illustrated cases from an aqueous phase to an organic phase. Without organophilic chelating agent turpentine is completely superior to toluene, which without an organophilic chelating agent practically does not dissolve any metal ions at all, while turpentine manages relatively well without the organo- philic chelating agent. The extractions in the examples have been made in one step but it is implied that an optional number of steps can be used.

The explanation of the ion exchange properties of the tur- pentine can be its content of organic compounds with substi- tuents in the form of functional groups such as for instance carboxylic acid groups, phenolic groups and hydroxyl groups manifested in a considerable buffer capacity for alkalis.

Thus, in titration with sodium hydroxide in an aqueous medium a buffer capacity corresponding to 8 meq/kg up to pH 8.5 and 30 meq/kg up to pH 11, with maximum buffer capacities, i.e.

PKa values, at about 7 and 10 respectively and values there- between, corresponding to the presence of functional groups of acid character, as for instance the above-mentioned.

Possible compounds with functional groups of acid character could be natural or synthetic resin acids, fatty acids and monohydric, dihydric and trihydric phenols. A hypothesis is that said groups can form complexes by bonds to metal ions of covalent and/or electrostatic character but also can form salts, for instance carboxylic acid salts, by ion bonds. The pre-requisite for complex binding is that the atom of the functional group which atom provides the bond has a free electron pair.

Such atoms can be for instance 0, N or S. Possibly also certain components containing double bonds can form stable so-called pi-complexes with transition metals which if aromatic properties are present also should be able to give pi-complexes of sandwich type.

There can be other explanations but without being bond to these and irrespective of responsible mechanisms turpentine functions as ion exchanger with high capacity. The great advantages as compared to conventional ion exchangers in the form of granules as regards pulp production resides in the possibility to extract not only the liquid phase, for instance filtrate on a fibre line, but also solid phase, for instance pulp fibres in a washing device. From this follows that they also, as distinguished from ion exchangers in the form of granules, function without disturbances in the presence of particulate impurities. However, the liquid ion exchangers are not restricted only to pulp production but they generally can be used in applications where there is a need to transfer metal ions from one system to another.

Such applications can be recovery of metal ions from diffe- rent waste waters, for instance from surface treatments such as in cleaning, pickling, corrosion protection treatment or from baths for plating of metal surfaces such as electrolytic or chemical baths for for instance copper, nickel, chromium, silver, gold, platinum or other platings, film developing baths in photo laboratories, or generally when valuable metal ions shall be recovered or ions of for instance heavy metals shall be prevented from entering the recipient. Together with the metal ions also organic substances are extracted, which can be undesirable to discharge in a recipient owing to toxicity or consumption of oxygen; it can be within the industry but it can also be municipal activities, for instance municipal purification.

The composition of the extraction agents In experiments with vacuum distilled turpentine the distillate did not show any cation activity while the distillation residue (3.5%) showed a high such activity, which has been shown experimentally in experiments analogous to those described above, cf. Table 2. This supports the above described hypthesis that it is smaller amounts of specific components of the turpentine which cause the cation activity. These components can consist of resin acids, fatty acids and monohydric, dihydric or trihydric phenols which have been mentioned and described above. By dissolving the distillation residue or one or more of its components in an optional organic solvent in an optional concentration, suitably strongly concentrated, it is possible to formulate an extraction agent for each specific purpose.

After identification of the components it is also possible to synthesize these and then in the same manner to formulate an extraction agent for each specific purpose. In doing this it is possible to start from different natural or synthetic resins, such as colophony and modified synthetic resins respectively. This offers large possibilities to improve the above shown probable synergism between an organophilic chelating agent and the extraction agent.

Described in a more exact way the extraction agent can be turpentine or a compound or a mixture of different compounds at least one of these compounds having properties like tur- pentine while the others can be inactive or less active as ion exchanger and principally function as organic solvent for organic substances present in the system. By definition the extraction agent shall have a restricted solubility in water and vice versa, which thus means that the inactive organic solvent does not need to be insoluble in water but can consist of for instance butanol or other alcohols, which, however, must not be included in such an amount that the extraction is prevented owing to the fact that the extraction agent obtains a too high solubility in the aqueous phase or in the medium constituting the other phase. Further- more, in the extraction agent such substances which are present in the white water system of the pulp mills as a result of the treatment of the wood in the manufacturing process can be included, such as alcohols including fatty alcohols, carboxylic acids including fatty acids, mono- or polyfunctional phenols and their derivatives, thiols, thio- phenols, sulphonic acids, hydrolysis products of hemicellu- lose such as glucuronic acid and hexenuronic acid, hydrolysis products of lignin such as hydroxy phenyl propane derivatives and hydrolysis fragments of lignin and derivatives thereof such as lignothiols, turpentine oils specific for the wood and the manufacturing process, etc., which have been described previously in more detail. In order to obtain the desired properties of the extraction agent and in order to increase for instance its cation exchange capacity it is possible to dissolve one or more cation active (anionic) organic compounds in an organic solvent with restricted water solubility. The cation active organic compounds for instance can be one or more of the above-mentioned substances present in the white water system of the pulp mill or optionally other cation active compounds such as different resin acids of the origin stated above.

As a working hypothesis it was supposed that if on the other side an extraction agent is formulated by dissolving an organophilic anion active (cationic) compound in an organic solvent essentially insoluble in water anions could be extracted with the extraction agent formulated in this manner. Among the anions inter alia oxalate, sulphate, aluminate, silicate, phosphate and carbonate ions conduce to the incrust problems by being counter ions to for instance Ca, Mg, Al and Ba ions while chloride ions increase the corrosion problems when closing a pulp mill under so-called EFM (effluent free mill) conditions. Thus, under these conditions, but also generally, it is desirable for instance in the sulphate or sulphite process to reduce the dis- advantage of these ions. Since hydrophilic (water soluble) conventional chelating agents, such as for instance EDTA or DTPA, also are anions both as free ligands (which as a matter of fact they cannot exist as in the presence of metal ions in a pulp mill) and as metal ion complexes, it was even supposed that it should be possible to extract these complexes in the form of ion pairs to the organic phase by means of the organophilic anion active (cationic) compound. This could be experimentally confirmed which will be described later in the following specification.

Such an extraction according to the invention means increased possibilities to take care of also water soluble chelating agents of conventional type and the complex bonded metal ions from especially a white water system of a peroxide bleach plant for treatment in a separate system different from the recovery system for cooking chemicals of the mill. Thanks to this white water with metal ion complexes from the Q step of the peroxide bleach plant does not need to be returned to the recovery system for cooking chemicals of the mill where incrust forming metal ions in a known manner can cause problems, or alternatively it is not necessary to discharge metal complexes to the recipient where the metal ion complexes can cause environmental problems.

The organophilic anion active (cat ionic) compounds can be organophilic homologues of different onium salts such as ammonium, sulphonium, oxonium, phosphonium salts, etc. with organic substituents on the respective functional onium atom (N, S, O, P respective, etc.) which with a complete number of substituents are stable and act as cat ionic (positive) onium ions over the whole pH range, as well as corresponding homologues of amines, sulphines, oxines and phosphines which can be converted to onium salts by proton transfer.

Preferred onium salts are organophilic quarternary alkyl ammonium salts among which quarternary homologues such as N,N,N,N-tetraalkyl ammonium bases (R1R2R3R4NOH) are preferred and among which those with 4-22 carbon atoms in at least one alkyl substituent and 1-4 each in the other three substi- tuents are most preferred, one example being N-dodecyl-N,N,N- trimethyl ammonium hydroxide, which has twelve carbon atoms in an alkyl substituent and one carbon atom each in the other three substituents, another example being tetrabutyl ammonium hydroxide which has 4 carbon atoms in all alkyl substituents.

The counter ion (the anion) to the different onium salts must be different from the anion which shall be extracted and preferably is an hydroxyl ion. Regeneration to hydroxy form can be made analogously with what is described for the organophilic chelating agents under the heading "Detailed description of the invention" but with extraction with an alkaline instead of an acidic aqueous solution.

Unlike the quarternary ammonium compounds the primary, secondary and tertiary amines are neutral and become cat ionic ammonium ions only when protonized in some protic medium, for instance in the protolyte or ampholyte water or in a protic organic medium which, like. water, can function as a proton donator (acid) such as for instance components of turpentine.

The pKa value of said amine corresponds to the point at the pH scale when half the amount of the amine has been pro- tonized while a complete protonization corresponds to the neutralization point of the amine, which is lower than the pKa value; how much depends on the concentration of said amine in said medium. The pKa value of the amine is dependent inter alia on the protolytic properties of the medium such as its protolysis or acid constant, which for water is 14.00 at 250C. Other media have other protolysis constants, higher or lower than 14. As guideline values concerning pKa values of aliphatic amines in water about 10-11 can be stated, i.e. in aqueous medium pH must be lower in order that a cat ionic ammonium compound shall be present.

Many aminocarboxylic acids have also similar pKa values.

Thus, also the oligomeric organophilic chelating agent used in our experiments in its capacity of aminocarboxylic acid can be converted to ammonium carboxylic acid by protonization and in the form of an anion active (cationic) ammonium com- pound can extract the above-mentioned chloride and sulphate ions as well as hydrophilic (water soluble) chelating agents, such as EDTA and DTPA, in the form of ion pair to the organic phase. The condition is that the pH value of this is lower than the pKa value of the ammonium form of the organophilic chelating agent in the organic phase, for instance a tur- pentine with mainly alpha-pinene. This pH value is dependent on the pH value of the aqueous phase.

In addition to the previously mentioned organophilic anion active (cationic) onium ions (for instance R1,R2,R3,R4N+) the extraction agent at the same time can be allowed to contain organophilic cation active (anionic) species (for instance R5Coo-) and/or organophilic chelating agents (anionic, for instance R6L-) and/or their metal ion complexes (also anionic, for instance RLMm-) (where R1, R2, R3, R4, R5, R6 and R7 are alkyl groups, L is a ligand and M is a complex bonded metal ion) but then it must be taken into account that organophilic anion active (cationic ammonium ions) (Rl,R2,R3R4N+) will form ion pairs with cation active (anionic) species (R5Coo-) wherein anion active and cation active species between themselves inactivate each other and prevent that cations and anions respectively in the aqueous phase are extracted over to the organic phase, which means that this is not a preferred embodiment.

This also applies to the organophilic chelating agents (anionic, R6L-) and/or their metal ion complexes (also anionic, R7LMm-) but since they can be present and are present respectively as metal ion complexes and not as metal salts they are not inactivated when forming ion pairs. The same applies to chelating agent components belonging to the organic solvent.

As regards the conventional hydrophilic (water soluble) chelating agents, such as EDTA or DTPA which also are anionic, the formation of ion pairs with an organophilic anion active (cationic) onium compound (Rl,R2,R3,R4N+) can even be desirable; thereby they can bring over metal ion complexes (anionic) from the aqueous phase to the organic phase and function as carrier and free the aqueous phase from both metal ions and chelating agents. That this really takes place has been shown experimentally in experiments analogous with those described above but with the use of N-octadecyl-N,N,N- trimethyl ammonium chloride.

The water soluble chelating agents can be selected among glycine, iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylene diamine tetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), hydroxyethyl ethylene diamine triacetic acid (HEEDTA), diethylene triamine penta- methylene phosphonic acid (DTPMPA), monomeric or oligomeric forms of N,N-bis(2-hydroxy-5-sulphobenzyl) glycine, N,N-bis- (2-hydroxy-5-alkylbenzyl) glycine, N,N-bis(2-hydroxy-5- carboxybenzyl) glycine or mixtures thereof.

Delignification in connection with metal ion extraction In connection with the extraction of sulphate pulp with addition of atmospheric oxygen to our surprise a considerable delignification of the pulp measured as kappa number reduction was obtained. This was also the case in the presence of hydrogen peroxide. It is to be supposed that certain metal ion complexes can function as catalysts for oxidation of lignin and it is understood that an oxidation and thereby a delignification can be effected also with several oxidation agents, such as for instance oxygen, ozone, hydrogen peroxide or peroxy acids, such as peroxyacetic acid, peroxyoxalic acid, peroxybenzoic acid, peroxysulphuric acid and their salts and other peroxides, such as benzoyl per- oxide. Preferred oxidation agents are atmospheric oxygen, oxygen, hydrogen peroxide and peroxyacetic acid. Perhaps a part of the kappa number reduction can be ascribed to oxida- tive hydrolysis of hexenuronic acid groups on the hemicellu- lose. Such a hypothesis can be strengthen by the fact that the organophilic chelating agents in turpentine easily sur- pass the lignocellulose in the property of strong ion exchanger as described and discussed above.

The characteristic colour of the organophilic metal ion complexes in the organic solvent indicates the presence of transition metals, for instance Fe and Mn, in their higher valencies which can indicate a catalytic activity of these.

Optionally they can also be present as organophilic salts in the form of catalytically active ion pairs. The high degree of delignification under the prevailing mild conditions of low temperature and low pH perhaps can be explained by the fact that the reactions take place and are catalyzed in the organic solvent phase and/or in its boundary layer. There might be other explanations but without being bond to these and irrespective of mechanisms behind a substantial kappa number reduction is obtained according to the invention and at the same time the metal ions in the pulp are extracted therefrom in an effective way and removed from the system which prevents incrust formation.

Table 3 shows delignification, viscosity and brightness in extraction of sulphate pulp in the presence of hydrogen peroxide. By means of said analytical data an illustration of what occurs with the pulp after the metal ion extraction with organophilic chelating agent in turpentine is obtained, in comparison with extraction with only turpentine and before extraction.

The sulphate pulp contained 7 mg Fe, 160 mg Mn, 237 mg Mg and 1574 mg Ca/kg dry calculated pulp at 12% pulp concentration.

As organophilic chelating agent N,N-bis(2-hydroxy-5-nonyl- benzyl) glycine was used in a stoichiometric amount. The conditions were the same as in the experiments described in Table 1.

Table 3. pH Kappa a) Viscosity b) Brightness c, ml 0,1N mPa.s (cp) % ISO KMnO4 Turp. + organophilic 7.5 19.2 50.3 33.6 chelating agent 8.5 18.4 49.9 36.2 9.5 17.5 42.6 36.9 10.5 17.6 46.8 36.9 11.5 18.3 41.8 36.7 Turpentine 7.5 18.4 38.6 33.1 8.5 17.4 27.9 36.3 9.5 15.7 34.0 37.7 10.5 16.4 34.7 36.8 11.5 15.7 28.5 36.9 Before extraction 20.0 56.0 25.5 a) TAPPI T 236 cm-85. b) TAPPI T 230 om-82 (viscosimeters: Haake; n=64 and Cannon-Fenske). c) SCAN P 3:75.

The kappa number is a measure of the delignification degree and the table shows a kappa number reduction which increases with pH as expected. It is possible that a part of the kappa number reduction as compared with the reference shall be attributed to turpentine extraction of water insoluble fibre adsorbed organic substance. An interesting point and which is important to note is that the viscosity losses were con- siderably lower in the presence of an organophilic chelating agent. The brightness values have also been included in the table. Also here a pH dependence can be seen as an increase as a function of pH.

Table 4 shows extraction experiments without hydrogen peroxide but in the presence of atmospheric oxygen. From the kappa number reduction it can be seen that also with air oxygen a delignification is effected. In this case the same starting pulp has been used as in the experiments presented in Table 1 and the other conditions were the same except that the weight ratio water/turpentine was 2/1.

Table 4. pH Kappa a) Viscosity b) Brightness C) ml 0,1N mPa.s (cp) % ISO KMnO4 Turp. + organophilic 8.5 17.8 53.3 29.1 chelating agent 9.5 18.8 54.2 30.6 10.5 19.9 51.1 28.8 Turpentine 8.5 22.1 38.0 34.6 9.5 18.9 47.9 29.3 10.5 18.9 48.3 28.7 Before extraction 22.3 56.9 27.0 a) TAPPI T 236 cm-85. b) TAPPI T 230 om-82 (viscosimeters: Haake; n=64 and Cannon-Fenske). c) SCAN P 3:75.

Delignification according to the invention can be a comple- ment to a conventional oxygen delignification and can make it possible to increase the kappa number reduction without losing viscosity in the oxygen step, i.e. increase the selectivity of this. It could even increase the flexibility of the cooking process. These possibilities could make it more cost effective to prepare TCF pulps in competition with ECF pulps. As can be seen from the tables the extraction conditions are decisive for the selectivity, i.e. the viscosity losses, and lowest losses are obtained in the presence of an organophilic chelating agent.

It is implied that these examples only are presented for illustrative purpose and that modifications can be made as regards for instance oxidation agent, consistency, solvent, amount of solvent, temperature, reaction time, pH, etc. without departing from the idea and scope of application of the invention. Thus, there is wide scope for influencing the result in a desired direction and in this way it is possible to vary the selectivity and the degree of delignification within wide limits.

Thus, for instance reaction time, temperature and pressure can be varied within wide limits by selection of equipment for extraction and reactors. It is even conceivable to carry out the reaction (delignification) in a separate reactor different from the extraction, as an augmentation or a correspondence to an oxygen or a peroxide step, or as an oxidizing process in organic solvent directly on the wood (chips) for delignification of lignocellulose, as an augmentation to, or even in capacity of the primary delignification step corresponding to existing cooking processes, for instance the sulphate or sulphite process.

If the aim only is metal ion extraction and influence on the chromophores in the lignin for obtaining increased bright- ness, which is desirable as regards mechanical pulps, there is room for selection of suitable conditions also for this.

If the oxidation agent for instance is atmospheric oxygen it can be the air oxygen present in the process or it can have been added in a controlled manner.

Reductive conditions As regards mechanical, chemimechanical or semi-chemical pulps in conventional bleaching of these according to the state of the art both oxidative and reductive methods are used, for instance with hydrogen peroxide and with sodium dithionite respectively, with only the one or the other method or with both methods in combination. The bleaching method according to the invention can be combined with the methods according to the state of the art in order to obtain an improved bleaching in this manner and make it more selective by extraction of NPE, especially Mn.

In this connection, but also generally speaking, it is according to the present invention possible to use a reduction agent instead of an oxidation agent in metal ion extraction with only turpentine oils, in the same manner as described in our two previous Swedish patent applications Nos. 9603858-3 and 9603859-1 which related to metal ion extraction with an optional organic solvent in combination with an organophilic chelating agent. In the metal ion extraction in the presence of a reduction agent the complexes of transition metal ions, for instance iron and manganese, are reduced to their lower valence levels and are extracted together with other categories of metal ions, for instance calcium, magnesium and barium. The reduction agent, or a combination of reduction agents, can be selected among hydrogen sulphide, sulphide, sulphur dioxide, hydrogen sulphite, sulphite borohydride, dithionite, tetrathionite, thiosulphate, hypophosphite, orthophosphite, etc. where the counter ion to the anions of said examples can belong to the groups alkali or alkaline earth metals, generally sodium, magnesium and calcium; sodium dithionite is for instance an especially suitable reduction agent.

Orqanophilic chelatinq agents The organophilic chelating agent, i.e. a chelating agent with one or several lipophilic groups or substituents, can be selected for instance from organophilic derivatives of amino carboxylic acids, hydroxy alkylamino carboxylic acids, hydroxy carboxylic acids, amino phosphonic acids, phosphonic acids, hydroxy benzylamino carboxylic acids, hydroxy alkyl- benzylamino carboxylic acids, hydroxy sulphobensylamino carboxylic acids, hydroxy carboxy benzylamino carboxylic acids or mixtures thereof, where the substituents can consist of such groups as for instance: saturated or unsaturated fatty acid groups (acyl groups); saturated or unsaturated sulphonyl groups; saturated or unsaturated aliphatic hydro- carbon groups, such as for instance alkyl, alkenyl or alkynyl groups; substituted or unsubstituted, saturated or unsatu- rated alicyclic hydrocarbon groups, such as for instance cyclohexyl and alkylcyclohexyl groups; substituted or unsubstituted aromatic hydrocarbon groups, such as for instance nonylphenol groups including their nonyl group isomers, etc., wherein the bonds between substituents and substrates can be for instance of the types C-N, C-O; C-C, C-S, S-N, S-O, S-C, S-S.

Examples of suitable organophilic chelating agents are organophilic derivatives of glycine, iminodiacetic acid (IDA) , nitrilotriacetic acid (NTA) , ethylene diamine tetra- acetic acid (EDTA) , diethylene triamine pentaacetic acid (DTPA), hydroxy ethyl ethylene diamine triacetic acid (HEEDTA), diethylene triamine pentamethylene phosphonic acid (DTPMPA), monomeric or oligomeric forms of N,N-bis(2-hydroxy- 5-sulphobenzyl) glycine, N,N-bis(2-hydroxy-5-alkylbenzyl) glycine, N,N-bis(2-hydroxy-5-carboxybenzyl) glycine or mixtures thereof.

In the borderline case in extraction with only turpentine related ion exchangers according to the invention the lower limit as regards the dosage of organophilic chelating agent by definition will be zero. The upper limit is calculated based on the amount of metal ions in the pulp and based on the requirement for low metal ion levels. Thus, at the levels of NPE which can be present in sulphate pulp for instance a one stage extraction in laboratory scale with a stoichio- metric amount of organophilic chelating agent resulted in a reduction of the amount of fibre adsorbed Mn, Ca and Mg according to Table 1. However, since the chelating agent is recovered and recirculated after "make up" for losses of chelating agents this amount is not the same as the con- sumption of organophilic chelating agent but the consumption can be one tenth of the dosage.

DETAILED DESCRIPTION OF THE INVENTION Preferably applied in the sulphate process the extraction is carried out in at least one position in at least one stage preferably on the brown side in alkaline environment by means of a turpentine oil related ion exchanger in the presence of an oxidation agent if also delignification/bleaching is to be included, wherein fibre adsorbed and water dissolved NPE pass over into the organic phase. In addition to NPE also resinous substances, COD and AOX, soluble in organic solvents, are extracted.

In the enclosed drawings: Figure 1 shows a block diagram over the brown line with an example of integrated two phase extraction in the pulp flow with only an organic solvent, alternatively in combination with an organophilic chelating agent.

Figure 2 shows a block diagram over the brown line with an example of differentiated extraction on the white water system in an extractor with only an organic solvent, alter- natively in combination with an organophilic chelating agent.

According to one embodiment of the invention the extraction can be carried out in for instance a diffuser as is shown in Fig. 1. It can then be carried out with or without a reduction agent as has been described in our previous patent applications Nos. 9603858-3 and 9603959-1, or in the presence of an oxidation agent according to the present invention when also a delignification/bleaching of the lignocellulose can be effected wherein a separate reactor before the diffuser can be used in order to be able to increase the reaction time or other parameters such as temperature and pressure. The oxida- tion agent can be atmospheric oxygen present in the process or it can be added in some controlled manner. The organic phase with dissolved metal ion complexes/organic metal salts together with the wash liquor pass out from the diffuser to the white water system from which the organic phase is sepa- rated in a separator. The organic phase is extracted with a diluted acid, for instance sulphuric acid, the metal ions being released and being passed over to the acid phase. The organic phase (with the organophilic chelating agent, if any) is recirculated after "make up" to the diffuser and the pro- cedure is repeated in a circle process. The acid phase is neutralized with for instance sodium hydroxide and any remaining organic solvent in the neutralized acid phase is separated in the turpentine decanting before it goes to the external purification or to the chemical recovery cycle for separation of the metal ions in the green liquor filtration.

By vacuum distillation or steam distillation with or without vacuum the organic phase (together with organophilic chela- ting agents, if any) can be converted to higher purity when there is such a need. Organophilic chelating agents, if any, can be recovered and be freed from oxygen consuming organic substance (COD) by recrystallization of the distillation residue in an organic solvent, for instance turpentine.

Alternatively the organic phase before the distillation is extracted with an alcohol-water mixture for recovery of the organophilic chelating agent. Preferred alcohols are the lower homologues, such a methanol and ethanol.

According to a further embodiment the extraction can be carried out differentiated in an extractor on the white water system, i.e. alongside of the pulp flow, as is illustrated in Fig. 2, and then the white water after having been freed from NPE can be recirculated to the extractor. This embodiment of the invention means a process which is simpler from a process technical point of view since the organic solvent will not enter the main flow of the pulp. On the other hand the extraction of the resinous substances soluble in organic solvent and NPE will be inferior since the organic solvent and the dissolved organophilic chelating agent respectively will not be in direct contact with the fibre. Thus, this process in its basic structure is more suitable for the removal of NPE in the form of alkaline earth metals Ca, Mg and Ba than for fibre adsorbed Mn, which must be reduced to zero level in order not to disturb the bleaching process even if the main part of Mn would be possible to extract out into the organic phase.

However, Mn on the fibre phase still can be complex bonded and extracted in an indirect manner by the use of water soluble chelating agents in interaction with the organophilic chelating agents. As can be seen from what has been stated above we found to our surprise that the organophilic chelating agents in the interface between the organic phase and the aqueous phase overmatched the water soluble metal ion complexes of EDTA or DTPA. Thus, if EDTA or DTPA are added to the aqueous phase they can be used for collecting and trans- porting Mn from the fibre phase over to the organic phase and then they can be recirculated without Mn back to the fibre phase and collect more Mn and so on in a circle process. The same discussion is valid also for other NPE. In this manner an effective extraction of metal ions from the fibre phase can be effected without the need of bringing the organic phase in direct contact with the fibre phase which means the advantages of the integrated system in effectivity combined with the simplicity of the differentiated system in equipment and method of function.

The extraction can be carried out in the presence of an oxidating agent for the oxidation of oxygen consuming organic compounds (COD) but no delignification is effected since the extraction agent will not come into direct contact with the pulp. It can also be carried out with or without a reduction agent as has been described in our previous patent applica- tions Nos. SE 9603858-3 and SE 9603859-1.

The different forms of extraction according to the invention can be carried out batchwise in one or several stages or continuously in counter-current. For batchwise differential extraction/separation according to the gravitation principle stainless tanks with agitators can be used, which are used alternately while continuous differential counter-current extraction, also according to the gravitation principle, consists of a tower or a column with a zone for mechanical dispersing of the liquid phases and another zone where the separation takes place. More advanced continuous apparatuses for differential counter-current extraction are based on the centrifugal principle. Suitable such are for instance Podbielniak, Quadronics, (Liquid Dynamics), Luwestra (Centriwestra) or De Laval extractors.

The amount of extraction agent, preferably turpentine, can be selected within wide limits, the lower limit being determined by the amount of metal ions which shall be extracted but also by the type of extraction equipment, and can amount to the order five to ten times the amount of pulp which shall be extracted in the extraction zone in integrated extraction in some washing apparatus, for instance in a diffuser, while the amount in differentiated extraction of the white water flow in an extraction apparatus alongside the flow of pulp can be put lower, how much depends on the type of extraction appa- ratus. The upper limit should for practical and economical reasons not be put higher than what is necessary for an effective extraction. With the levels of NPE which can be present in sulphate pulp for instance a one stage extraction in laboratory scale gave a reduction of the amount of fibre adsorbed Mn, Ca and Mg according to Table 1.

By combining the metal ion extraction with a Q step for treatment of water soluble chelating agents, for instance DTPA according to our U.S. Patent 5,571,378 (U.S. Patent Application Serial No. 08/327,919), "Process for high-pH metal ion chelation in pulps" (Hampox-Q) for metal ion control on the bleaching plant side, low manganese levels for a good stabilization of the peroxide steps in ECF and TCF production can be obtained with a small amount of DTPA. If the extraction is carried out with anion active (cationic) ammonium bases, for instance N-dodecyl-N,N,N-trimethyl ammonium hydroxide, dissolved in an organic solvent, the metal ion complexes of the water soluble chelating agents can be extracted over to the organic phase. Simultaneously also incrust forming anions, such as sulphate and chloride ions, are extracted over to the organic phase.

By combination with water soluble chelating agents in accordance with the concepts in our previous Swedish patent applications Nos. SE 9603858-3 and SE 9603859-1, relating to "A process in making cellulose pulp", also the anionic complexes of these can be extracted over to the organic phase. In this manner a covering system for metal ion control can be drawn up and adjusted to different special characters of existing production units.