Method for separating lignosulfonate

Abstract

The invention relates to a method for separating lignosulfonate (LS) from wastewater. In order to reduce the refractory COD load of the wastewater, for alkaline water (F) having a pH value of 8 to 14, a method is carried out, comprising the steps of: adding a magnesium compound which forms magnesium hydroxide in situ in the alkaline wastewater (F), or an aqueous, chlorine-free magnesium hydroxide solution; forming a lignosulfonate product (P) via reaction with magnesium hydroxide; separating lignosulfonate product (P) and alkaline wastewater (F).

Description

[0001] (20165.0)

[0002] Description of a process for separating lignosulfonate

[0003] The invention relates to a method for separating lignosulfonate from wastewater.

[0004] Refractory chemical oxygen demand (COD) is difficult to degrade in biological wastewater treatment plants, making it challenging to comply with limit values. Lignosulfonate, usually ammonium, sodium, calcium, or magnesium lignosulfonate, is also considered a refractory, i.e., non-degradable, COD component. Lignosulfonate is formed from lignin during the production of pulp, which, along with cellulose and hemicelluloses, is a natural component of wood. Lignosulfonate is used, for example, in connection with crude oil production, in the construction industry, and for soil improvement. To reduce the proportion of refractory COD in wastewater, it has been suggested that lye, followed by magnesium chloride, be added to the lignosulfonate-containing wastewater to precipitate the lignosulfonate (LanlanYe et al., Rapid and effective removal of sodium lignosulfonate from aqueous solutions by in-situ formed magnesium hydroxide; Korean J. Chem.).Eng. 33 (12), 3541-3549 (2016)). These experiments were conducted using purified, powdered sodium lignosulfonate (SLSN) in aqueous solution. However, additional chlorine or chloride ions are undesirable in wastewater. The treatment of pulp production wastewater by concentrating the wastewater and using magnesium hydroxide is taught in CA 799877.

[0005] The present invention relates to the removal of lignosulfonate, in particular sodium lignosulfonate, from alkaline wastewater, such as that generated during pulp production and bleaching. The majority of the lignosulfonate is dissolved during pulping, e.g., a magnesium bisulfite pulping process, or other, mostly acidic, pulping processes. The wastewater from the pulping process is completely collected, evaporated, and incinerated, firstly for closed-loop recycling and recovery of the pulping chemicals, and secondly for energy recovery. However, the unbleached pulp still contains lignosulfonate after pulping, which is generally largely extracted from the pulp in an alkaline extraction with the addition of oxygen and / or peroxide (EOP stage). The wastewater from this EOP stage therefore contains a high concentration of lignosulfonate, which is collected as a COD load. This load has a high proportion of a refractory, i.e.,, non-degradable COD load. The challenge is to provide a process for reducing the chemical oxygen demand of alkaline wastewater that does not require the addition of chloride ions.

[0006] This problem is solved by a method according to claim 1.

[0007] According to the invention, a process for separating lignosulfonate from alkaline wastewater with a pH value of 8 to 14 is proposed, comprising the following steps:

[0008] Addition of a chlorine-free magnesium compound that forms magnesium hydroxide in situ in the alkaline wastewater or an aqueous, chlorine-free solution containing magnesium hydroxide,

[0009] Formation of a lignosulfonate product by reaction with magnesium hydroxide,

[0010] Separation of lignosulfonate product and alkaline wastewater.

[0011] The magnesium compound added is, according to the invention, free of chlorine or chloride ions. Typically, magnesium oxide or, preferably, a water-soluble magnesium compound is added, for example, a chlorine-free magnesium salt, e.g., magnesium sulfite or magnesium bisulfite, or an organic magnesium compound, e.g., magnesium acetate. The magnesium compound can be added in solid or liquid form.

[0012] Alternatively, an aqueous solution of magnesium hydroxide can be added to the alkaline wastewater.

[0013] The magnesium compound is preferably added directly to the alkaline wastewater, i.e., without prior concentration of the water.

[0014] The alkaline wastewater, e.g., the wastewater from an end-of-process (EOP) stage of pulp production, has an alkaline pH value, usually above a pH of at least 8, typically between pH 9.5 and 12. The pH of the wastewater is a maximum of pH 14. The inventors recognized that this wastewater thus offers good conditions for the separation of lignosulfonate. If necessary, the pH of the alkaline wastewater is adjusted by adding sodium hydroxide (NaOH) or calcium hydroxide (Ca(OH)₂), e.g., to a value of pH 10.5 to pH 12, preferably from pH 11.0 to 12.0. Adjusting or maintaining a constant pH of pH 8 or higher is also advantageous during and after the reaction of lignosulfonate and magnesium hydroxide, since the magnesium compound is often added as an acidic aqueous solution, which lowers the pH.Accordingly, it is preferred to adjust the pH value of the alkaline wastewater to suit the magnesium compound to be added either at the beginning of the process to a sufficiently high level or to maintain it above a minimum pH value of at least pH 8, advantageously at least pH 9.5, by adding, for example, NaOH or Ca(0H)2 during the reaction.

[0015] The lignosulfonate is separated by adding a chlorine-free magnesium compound, which forms magnesium hydroxide in situ in the alkaline wastewater, to the wastewater. The bond between the in-situ formed magnesium hydroxide and the lignosulfonate readily forms in less than 15 minutes, advantageously in less than 5 minutes. A process temperature of 10 °C to 90 °C promotes the reaction. After separating the lignosulfonate product from the alkaline wastewater, at least 25%, advantageously at least 50%, and preferably at least 90% of the refractory COD load of the alkaline wastewater is removed. This reduction of the refractory, i.e., non-biodegradable, COD load is advantageous because, although refractory COD components in wastewater degrade very slowly in the receiving water body, they hardly lead to direct oxygen depletion in flowing waters.They are therefore biodegradable in the long term; however, the at least partial removal of the refractory COD load opens up various possibilities. If less refractory COD load is discharged into the receiving water body and the COD load is used for energy recovery, this is doubly advantageous. Additionally, it opens up the possibility of producing other types of pulp and increasing production volumes while maintaining the same COD load. In a simple embodiment of the process according to the invention, magnesium oxide is added as a solid, preferably in powder form. The particle size of the magnesium oxide is advantageously between 1 pm and 500 pm. The magnesium oxide is converted in situ to magnesium hydroxide in the alkaline wastewater, which binds lignosulfonate to form a lignosulfonate product that then precipitates from the wastewater and can be separated.A disadvantage of using magnesium oxide is that only the surface of the magnesium oxide particles reacts to form magnesium hydroxide (Mg(OH)₂). Therefore, large quantities of magnesium oxide (MgO) are required to precipitate the lignosulfonate. Typically, at least 1 kg MgO / m is used. 3 Wastewater up to 10 kg MgO / m 3 Wastewater, preferably 3 kg MgO / m 3 Wastewater up to 8 kg MgO / m 3 Wastewater is used to precipitate the lignosulfonate it contains as completely as possible. Since magnesium oxide is used as a solid, it is recommended to distribute the magnesium oxide as evenly as possible in the wastewater, for example by dynamic or static homogenization.

[0016] It is preferred to use a water-soluble magnesium compound, in particular a water-soluble magnesium salt, for carrying out the process according to the invention. As will be explained in more detail below, magnesium acetate and magnesium sulfite or magnesium bisulfite are particularly preferred salts. The use of an aqueous magnesium hydroxide solution is also advantageous. Since the salts are used in dissolved form, a small quantity of up to 1 kg / m³ is sufficient, just as with the direct use of magnesium hydroxide. 3 with regard to alkaline wastewater, advantageously 50 g / m³ 3 up to 700 g / m² 3 , preferably 100 g / m² 3 up to 500 g / m² 3, in order to generate enough magnesium hydroxide in situ so that the refractory lignosulfonate contained in the wastewater can be bound as completely as possible with the magnesium hydroxide to form a lignosulfonate product and subsequently precipitated or separated from the wastewater.

[0017] It has been surprisingly found that lignosulfonate can be precipitated from wastewater particularly completely and rapidly when, in addition to the magnesium compound, a chlorine-free ammonium, sodium, potassium, or calcium compound, preferably water-soluble, is added. Salts or oxides of the ammonium, sodium, potassium, or calcium compound are particularly preferred, e.g., ammonia solution, sodium, potassium, or calcium hydroxide, calcium oxide, and / or an ammonium, sodium, potassium, and / or calcium salt mixed with the magnesium compound. Here, too, the addition of chlorine-free salts, preferably a water-soluble salt of an acid available in pulp production, e.g., a sulfite, bisulfite, or acetate, is preferred. Mixtures of ammonium, sodium, potassium, or calcium compounds are also advantageously used.The water-soluble ammonium, sodium, potassium or calcium compound is advantageous in a quantity of 0.01 kg / m³. 3 up to 10 kg / m² 3 , advantageously from 0.1 kg / m 3 up to 6 kg / m 3 , preferably of 0.05 kg / m² 3 up to 0.3 kg / m² 3 This applies to the amount of wastewater to be treated. The amount of ammonium, sodium, potassium and / or calcium compound used is advantageously lower than the amount of magnesium compound used.

[0018] The product of magnesium hydroxide and lignosulfonate, formed by adding a chlorine-free magnesium compound, optionally supplemented by a chlorine-free ammonium, sodium, potassium, or calcium compound, to alkaline wastewater, precipitates from the wastewater and is separated from it. The separation of the lignosulfonate product and the wastewater can be carried out in any number of ways. Separation in a settling tank is particularly simple and cost-effective. However, a filtration system, a decanter, a centrifuge, or other separation methods, especially solid-liquid separation processes, can also be used. The required residence time in a settling tank is at least 30 minutes and at most 5 hours, preferably between 1 and 3 hours.

[0019] It has been found that the lignosulfonate product obtained by precipitation has a solids content of over 40%, and usually over 55%, based on the total weight of the precipitated material. The inventors have discovered that the lignosulfonate bound to magnesium hydroxide in the product may still contain components that can be utilized separately. Accordingly, in an advantageous embodiment of the process according to the invention, the precipitated lignosulfonate product is washed to remove soluble, particularly water-soluble, impurities or to separate components. It is important to ensure that the water used to wash the lignosulfonate product has a neutral or alkaline pH, since the lignosulfonate product is soluble in acidic aqueous media.

[0020] The lignosulfonate product can then be used industrially, for example, as an aid in oil drilling. Alternatively, due to its considerable energy content of 6,000 kJ / kg to 17,000 kJ / kg (anhydrous), the lignosulfonate product can be used as a fuel to generate energy through combustion, particularly process energy, for example, for pulping or, alternatively, if an energy surplus is generated by burning the lignosulfonate product, for electricity generation. A particular advantage of combustion is that the magnesium used to bind the lignosulfonate is oxidized during combustion and can be reused for precipitating lignosulfonate from alkaline wastewater. Combustion of the lignosulfonate product thus enables a largely closed-loop system for the magnesium oxide.Sulfur contained in the lignosulfonate product can also be recovered from the combustion residue after combustion and, if necessary, reused, e.g., in the pulping of cellulose.

[0021] The process steps described above can be used in a variety of applications wherever alkaline, lignosulfonate-containing wastewater is available. However, the process for precipitating lignosulfonate from alkaline wastewater is particularly suitable for pulp production, especially pulp bleaching. During pulping, the majority of the lignin is usually dissolved from the wood matrix by sulfur-containing compounds in aqueous solution; lignin and cellulose or pulp are separated. The resulting lye or acid, along with the lignosulfonate it contains, is evaporated and then combusted; the combustion of the lignosulfonate provides process energy and enables the recovery of the pulping chemicals. During pulping, the lignin or lignosulfonate is not completely removed from the pulp. The degradation of the lignin or lignosulfonate...The extraction of lignosulfonate from the pulp is completed in an alkaline extraction stage with the addition of oxygen and peroxide (EOP stage). The alkaline wastewater from the EOP stage typically has a pH value of 8 to 14, mostly 9.5 to 12, and contains 1.5 kg / m³. 3 up to 5 kg / m 3 Lignosulfonate, often 1.5 to 4.5 kg / m 3 , based on the wastewater volume. The lignosulfonate can be easily precipitated from the alkaline wastewater of the EOP stage using the inventive process by adding a chlorine-free magnesium compound that forms magnesium hydroxide in situ in aqueous alkaline solution, or by adding a magnesium hydroxide-containing solution.

[0022] The inventors have discovered that the inventive process can be used particularly efficiently in connection with pulp production because a recovery of the chlorine-free magnesium compound used in the invention has been developed.

[0023] When the lignosulfonate product obtained by precipitation is burned, the magnesium hydroxide is oxidized to magnesium oxide, which is then contained in the combustion residues of the lignosulfonate product.

[0024] The magnesium oxide can be reused directly, possibly after comminution, to precipitate lignosulfonate from alkaline wastewater. This closed-loop process makes the use of the chlorine-free magnesium compound economical, despite the high application rates.

[0025] Preferably, however, magnesium oxide, in particular the combustion product from the combustion of the lignosulfonate product containing magnesium oxide, is introduced into an acidic liquid, especially an acidic aqueous liquid, to form a magnesium salt that is then at least partially in solution. In the context of pulp production, both acetic acid and vapor condensate containing sulfurous acid and acetic acid, respectively, are available. It has proven advantageous to utilize a partial stream of these aqueous, acidic solutions to provide a sufficient quantity of magnesium salts, and optionally ammonium, sodium, potassium, and / or calcium salts, dissolved in water, which is then introduced into the alkaline wastewater of the EOP stage. Since the salts are in dissolved form, the magnesium compound undergoes extensive conversion to magnesium hydroxide formed in situ.Accordingly, especially in closed-loop systems, only a very small amount of magnesium compound and optionally ammonium, sodium, potassium and / or calcium compound is required to bind and separate a maximum amount of lignosulfonate from the alkaline wastewater.

[0026] For this embodiment of the process according to the invention, the cycle closure is carried out as described above. After precipitation and, if necessary, washing of the lignosulfonate, the lignosulfonate with a solids content between 40% and 70% based on the mass dried to constant weight at 105 °C is combusted, and the magnesium oxide contained in the combustion residue is dissolved in an acidic aqueous solution.

[0027] Details of the method according to the invention are explained in more detail in the following exemplary embodiments. These show:

[0028] Fig. 1 Pulp pulping and EOP stage according to the prior art. Fig. 2 Pulp pulping and EOP stage with precipitation of lignosulfonate.

[0029] Pulp production based on magnesium sulfite or bisulfite, which takes place at an acidic pH, is designed as a closed-loop process, as shown in Fig. 1. Wood chips W are pulped in an acidic, aqueous magnesium sulfite or bisulfite solution under pressure and heat according to step C in Fig. 1. After pulping C, washing and sorting S follow, during which the pulp is separated from the cooking liquor containing lignosulfonate and the pulping chemicals in aqueous solution. The collected cooking liquor is evaporated E until the solids content reaches more than 50% (based on the dry matter dried to constant weight at 105 °C). The lignosulfonate has a calorific value of approximately 6,000 kJ / kg to 17,000 kJ / kg (anhydrous). The combustion I of the lignosulfonate, which follows the evaporation E, contributes to covering the energy consumption of the digestion C.Furthermore, the chemicals used for digestion are recovered from the combustion product of combustion I in the recovery process R.

[0030] The unbleached pulp U, obtained by washing and sorting S, still contains significant amounts of lignosulfonate LS, which could not be washed out. The amount of lignosulfonate in the pulp ranges from 6 g / kg to 50 g / kg, based on pulp dried at 105 °C to constant weight. To obtain pulp that is as free as possible from lignin and lignosulfonate, the pulp is bleached. The first bleaching stage B after pulping C is typically an alkaline extraction stage with oxygen and peroxide (EOP stage). At the end of the EOP stage B, the bleached pulp BP is separated from the wastewater or filtrate F. The wastewater F from this EOP stage is alkaline with a typical pH of 8 to 14, typically 9.5 to 12.It essentially contains lignosulfonate, which was extracted from the pulp during the EOP stage, lignin and cellulose degradation products, which were extracted from the pulp by oxygen and peroxide, as well as sodium ions or sodium hydroxide. The resulting solution is therefore a complex mixture of substances in an aqueous, alkaline solution. The bleached pulp (BP) may then be subjected to further processing or bleaching.

[0031] The alkaline wastewater F has a high organic load, thus exhibiting a high COD value. Where possible, this organic load is broken down during wastewater treatment (WW). However, it has been shown that the known biological wastewater treatment processes are unable to break down a large proportion of the organic load. This refractory portion of the organic load passes through wastewater treatment (WW) without further action and remains in the wastewater that is discharged into the receiving water body. Since emission limits also include upper limits for COD loads, the refractory, i.e., non-biodegradable, COD of lignosulfonate in the wastewater occasionally restricts production volume.

[0032] Fig. 2 shows the solution according to the invention by the process for precipitating lignosulfonate from alkaline wastewater F, which has a pH value of 9.5 to 12. If necessary, the pH value can be adjusted to the desired or required pH value by adding an alkali, e.g., sodium hydroxide solution. An aqueous solution L of a water-soluble, chlorine-free magnesium compound, typically magnesium sulfite or bisulfite, or magnesium acetate, is added to the alkaline wastewater F. The magnesium compound is advantageously present in dissolved form in the aqueous solution. Alternatively, an aqueous solution of magnesium hydroxide can be added. The addition of 50 g / m³ is common. 3 up to 1 kg / m² 3 of the water-soluble magnesium compound to alkaline wastewater F, preferably of 100 g / m³ 3 up to 700 g / m² 3The amount of water-soluble magnesium compound added can be dosed depending on the lignosulfonate load. The aqueous magnesium hydroxide solution is mixed in, for example, using a static or dynamic mixing device. When this aqueous solution L is added to the alkaline wastewater F, magnesium hydroxide forms in situ, unless magnesium hydroxide solution is already being added. This magnesium hydroxide reacts with the lignosulfonate contained in the alkaline wastewater F to form a lignosulfonate product P, which then precipitates from the wastewater F. The separation SP from the wastewater F and the lignosulfonate product P can be carried out in any desired manner. A settling tank can be used, which the wastewater passes through in approximately 0.5 to 3 hours. A decanter, filtration system, centrifuge, or other suitable separation equipment, in particular solid / liquid separators, can also be used.The lignosulfonate product P has a magnesium hydroxide content of 10 wt.% to 50 wt.% based on the total weight of the lignosulfonate product P, preferably from 10 wt.% to 30 wt.%.

[0033] After SP is separated from the alkaline wastewater F, the product P, consisting of lignosulfonate and magnesium hydroxide, has a solids content of 40% or more, preferably over 60%. In addition to the aforementioned components, product P often contains impurities from bleach B. If this is the case, these impurities can be washed out of product P in a washing process WP.

[0034] The product P, which may be washed, is then dried further to increase the solids content and subsequently incinerated, preferably in the incineration unit I, in which, as shown in Fig. 2, the evaporated black liquor from the pulping process is also incinerated, or alternatively in a separate incineration unit. Thanks to its high calorific value of approximately 6,000 kJ / kg to 17,000 kJ / kg (anhydrous), the lignosulfonate LS again contributes to the provision of process energy or energy for power generation. The magnesium oxide from the combustion residue A, which contains magnesium oxide formed during combustion by oxidation, can be advantageously recovered or used again to bind the lignosulfonate LS. In this way, only a small amount of additional magnesium compound is required for the formation of the lignosulfonate product P in each subsequent separation cycle.

[0035] The combustion residue A, or the magnesium oxide obtained from it, is advantageously introduced into an aqueous, acidic liquid, such as cooking acid or vapor condensate, whereupon magnesium salts are formed in aqueous liquid L. Cooking acid typically contains sulfurous acid, so that magnesium sulfite or bisulfite is formed. Vapor condensate from pulp production typically contains acetic acid, so that magnesium acetate is formed in aqueous liquid L. However, other organic acids may also be present, which form organic magnesium compounds, in particular salts, and are therefore suitable for binding lignosulfonate within the framework of the process according to the invention.In most cases, it is sufficient to divert a partial stream of the respective aqueous, acidic liquid, with which sufficient magnesium salt dissolved in aqueous liquid L can be provided to remove a maximum of lignosulfonate LS from the alkaline wastewater F by forming the lignosulfonate product P.

[0036] An alternative, but preferred, embodiment of a process for precipitating lignosulfonate from alkaline wastewater F involves the use of a chlorine-free magnesium compound that forms magnesium hydroxide in situ, as well as a chlorine-free, preferably water-soluble, ammonium, sodium, potassium, and / or calcium compound. Salts of these compounds are preferred, particularly those of acids available in the pulp and paper production process, such as sulfurous acid or acetic acid. Where possible, oxides or hydroxides may also be used. Typical amounts of the ammonium, sodium, potassium, and / or calcium compounds are 0.01 kg / m³. 3 up to 10 kg / m 3 , advantageously from 0.1 kg / m 3 up to 6 kg / m 3 , preferably of 0.05 kg / m² 3 up to 0.3 kg / m² 3, each based on the wastewater volume. The chlorine-free ammonium, sodium, potassium, and / or calcium compound can typically be used in a mixture with the magnesium compound and undergo the same cycle described above: addition to the alkaline wastewater F, formation of the lignosulfonate product P and separation SP, optional scrubbing WP, optional evaporation E and combustion I, and addition of the combustion product A to an aqueous, acidic liquid L. It has been shown that when magnesium and ammonium, sodium, potassium, and / or calcium compounds are used in combination, more lignosulfonate can be separated from the alkaline wastewater by precipitation.The yield of lignosulfonate product P can be increased to at least 35%, preferably at least 55%, and particularly at least 95%, by adding a chlorine-free ammonium, sodium, potassium, and / or calcium compound, in each case based on the lignosulfonate content in the alkaline wastewater. The yield of precipitated lignosulfonate product P improves by more than 5%, and advantageously by more than 10%, compared to the separation of lignosulfonate using only a chlorine-free magnesium compound, by the additional addition of a chlorine-free, preferably water-soluble ammonium, sodium, potassium, and / or calcium compound, based on the separation of lignosulfonate using only a chlorine-free magnesium compound.

[0037] Finally, in a particularly simple embodiment of the process according to the invention, chlorine-free magnesium oxide can be added as a solid to the alkaline wastewater F. The magnesium oxide is advantageously added as a finely divided solid, as dust or powder. Upon contact with the alkaline wastewater F, magnesium hydroxide ions form in situ on the surface of the solid particles, which then react with the lignosulfonate to form a product P. The magnesium oxide must be intensively mixed, preferably stirred, over a period of preferably 2 minutes to 8 hours, as otherwise the solid will not come into sufficient contact with the lignosulfonate to form a product. Typically, at least 1 kg / m³ is used. 3 up to 10 kg / m² 3 Magnesium oxide, preferably at least 3 kg / m³ 3 up to 8 kg / m 3 Magnesium oxide added, each based on the amount of alkaline wastewater F.

[0038] Here, too, a cycle for the repeated use of the magnesium compound can be established. The product P is precipitated SP, optionally washed WP, ​​and optionally subjected to further evaporation E and combustion I. Subsequently, the combustion product A, optionally after comminution, is returned to the alkaline wastewater F, which contains undesirable amounts of lignosulfonate. Since magnesium oxide is used as a solid, this simple embodiment of the process according to the invention requires larger quantities of the magnesium compound than a process using a magnesium compound dissolved in water. Between 1 kg / m³ is used. 3 of alkaline wastewater F and 10 kg / m³ 3 , advantageously between 3 kg / m 3 and 8 kg / m² 3 of alkaline wastewater F. The optimization of the amount of MgO used depends on the lignosulfonate LS content in the alkaline wastewater F.

[0039]

Claims

(20165.0) Claims 1. Method for separating lignosulfonate (LS) from alkaline wastewater (F) having a pH of 8 to 14, comprising the following steps: Addition of a chlorine-free magnesium compound, which is present in the alkaline solution. Wastewater (F) in situ forms magnesium hydroxide or an aqueous, chlorine-free solution containing magnesium hydroxide, Formation of a lignosulfonate product (P) by reaction with magnesium hydroxide, Separation of the lignosulfonate product (P) from the alkaline wastewater (F).

2. Method according to claim 1, characterized in that magnesium oxide or a magnesium salt, in particular magnesium acetate, magnesium sulfite or magnesium bisulfite, is added to the alkaline wastewater (F).

3. Method according to claim 1 or 2, characterized in that an ammonium, sodium, potassium and / or calcium compound, in particular as a salt of acetic acid or sulfurous acid, is added to the alkaline wastewater (F).

4. The method according to claim 3, characterized in that the ammonium, sodium, potassium and / or calcium compound is present in an amount of 0.01 kg / m³ 3 up to 10 kg / m² 3 , is used in relation to the wastewater to be treated.

5. Method according to one of the preceding claims, characterized in that the separation of lignosulfonate product (P) and alkaline wastewater (F) is carried out by filtration, in a settling tank, a decanter or a centrifuge.

6. Method according to one of the preceding claims, characterized in that the lignosulfonate product (P) is added to a washing process (WK) to remove impurities. 7- Method according to one of the preceding claims, characterized in that the lignosulfonate product (P) is subjected to combustion (I).

8. Method according to claim 7, characterized in that at least one magnesium compound, optionally one sulfur compound, is recovered from a combustion residue (A).

9. Method according to claim 7, characterized in that the energy obtained by burning (I) the lignosulfonate product (P) is used as process energy or for electricity generation.

10. Method according to claim 8, characterized in that magnesium oxide from a combustion residue (A) is used to precipitate lignosulfonate (LS).

11. Method according to claim 8 or 10, characterized in that magnesium oxide is added to an acidic liquid obtained during pulp production (C), and that the acidic liquid (L), containing a preferably dissolved magnesium salt, is then used to precipitate lignosulfonate (LS) from an alkaline wastewater (F) by forming a lignosulfonate product (P).

12. The method according to claim 11, characterized in that magnesium oxide is reacted with at least a partial stream of an acidic liquid containing acetic acid to form magnesium acetate, wherein the magnesium acetate is then used to separate lignosulfonate (LS) from the alkaline wastewater.

13. The method according to claim 11, characterized in that magnesium oxide is reacted with at least a partial stream of an acidic liquid containing sulfurous acid to form magnesium sulfite and / or magnesium bisulfite, wherein the magnesium sulfite or magnesium bisulfite is then used to separate lignosulfonate (LS). - 17 - 14- Method according to claim 7, characterized in that the ammonium, sodium, potassium and / or calcium compound is added to an acidic liquid obtained during pulp production (C), and that the acidic aqueous liquid (L) containing a dissolved salt of the ammonium, sodium, potassium and / or calcium compound is then used to improve the separation of lignosulfonate (LS) by forming a lignosulfonate product (P) from an alkaline wastewater (F).

15. Method according to one of claims 10 or 14, characterized in that magnesium oxide and an ammonium, sodium, potassium and / or calcium compound are added together to an acidic liquid obtained during pulp production (C).

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