Method for removing silicon from green liquor in papermaking

Abstract

This invention relates to a method for desiliconizing green liquor in papermaking, belonging to the field of papermaking pulping chemical regeneration technology. This method aims to solve the technical problem in existing technologies where direct carbon dioxide is introduced into green liquor for desiliconization, resulting in the formation of colloids from the generated silicic acid, making subsequent solid-liquid separation difficult. The key points of the technical solution are: first, solid-liquid separation of the green liquor is performed to obtain a clear green liquor; then, white mud slurry is added to the clear liquor as seed crystals, and carbon dioxide gas is introduced to carry out a carbonization reaction, generating an easily separable silicon-containing suspension; next, solid-liquid separation is performed on the silicon-containing suspension to obtain a silicon-containing filter cake and a causticizing mother liquor; finally, calcium hydroxide is added to the causticizing mother liquor to carry out a causticizing reaction, obtaining white liquor and recyclable white mud slurry. This method is mainly applied to the desiliconization and purification of green liquor during the alkali recovery process in papermaking, and can utilize carbon dioxide in industrial flue gas to achieve carbon resource utilization; the separated silicon-containing filter cake can be further processed into activated calcium silicate products.

Description

Technical Field

[0001] This invention belongs to the field of papermaking pulping liquor regeneration, specifically relating to a method for removing silicon from papermaking green liquor. Background Technology

[0002] Pulp made from herbaceous plants such as bamboo, reeds, bagasse, and wheat straw using chemical methods such as the caustic soda process and the sulfate process is called straw pulp. During the pulping process, black liquor is produced. This black liquor is burned in an alkali recovery boiler to form a molten substance. Dissolving this molten substance forms green liquor, whose main components are sodium carbonate, sodium silicate, and sodium sulfate. Currently, lime is usually added to the green liquor, and after solid-liquid separation, white mud and white liquor are obtained.

[0003] However, green liquor made from herbaceous plants contains more silicon compounds than green liquor made from wood. If the green liquor from straw pulp papermaking is not desiliconized to remove the silicon compounds, it is easy for the white mud and white liquor to be difficult to separate, and the separated white liquor has low clarity, making it difficult to recycle the white mud.

[0004] To solve the above-mentioned technical problems, Zhao Qi applied for a Chinese invention patent on February 12, 2014, entitled "Method for producing sodium metasilicate and light calcium carbonate by recovering green liquor from straw pulp papermaking alkali", with authorization announcement number CN103771430B. The patent adopts a technical solution of introducing carbon dioxide gas into the green liquor to generate a silica suspension, thereby removing silicides from the green liquor.

[0005] However, in practical applications, when carbon dioxide is directly introduced into the green liquor filtrate, the generated silicic acid is easily dispersed in the liquid phase in a colloidal form. This colloidal silicic acid easily clogs the filtration device during subsequent solid-liquid separation, significantly reducing separation efficiency and even making it difficult to continue the separation operation. Summary of the Invention

[0006] The purpose of this invention is to provide a method for removing silicon from green liquor used in papermaking. This method involves adding white mud slurry as seed crystals to the clear green liquor and then introducing carbon dioxide gas to carry out a carbonization reaction to generate a silicon-containing suspension that is easy to separate. This solves the technical problem in the prior art where the generated silicic acid easily forms colloids, clogs the filter device, and leads to difficulties in subsequent solid-liquid separation when carbon dioxide is directly introduced into the green liquor for silicon removal. This method improves the efficiency of solid-liquid separation, ensures stable production, and enables the resource utilization of carbon dioxide in industrial flue gas.

[0007] To achieve the aforementioned objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for removing silicon from papermaking green liquor includes the following steps:

[0009] S1: Perform solid-liquid separation on the green liquor to separate the solid impurities contained in the green liquor and obtain clear green liquor;

[0010] S2: Add white mud slurry to the green liquor and introduce carbon dioxide gas to produce a silicon-containing suspension through carbonization reaction;

[0011] S3: Perform solid-liquid separation on the silica-containing suspension to obtain silica-containing filter cake and causticizing mother liquor;

[0012] S4: Add calcium hydroxide to the causticizing mother liquor to carry out the causticizing reaction. After the reaction, solid-liquid separation is performed to obtain white liquor and white mud slurry.

[0013] Preferably, in step S2, 0.5 wt% to 3 wt% of white mud slurry is added to the clear green liquor; and / or,

[0014] In S2, the volume fraction of carbon dioxide in the carbon dioxide-containing gas is 20%–95%; and / or,

[0015] In S2, carbon dioxide gas is introduced into the clear green liquor according to a molar ratio of silicon in the clear green liquor to carbon dioxide in the carbon dioxide-containing gas of 1:1.5–3.5; and / or,

[0016] In S2, the carbonization reaction temperature is 70℃~85℃; and / or,

[0017] In S2, the carbonization reaction time is 1 h to 4 h; and / or,

[0018] In S2, the silica-containing suspension generated by the carbonization reaction has a pH value of 9.5–11.

[0019] Preferably, in step S2, 1 wt% to 2 wt% of white mud slurry is added to the clear green liquor; and / or,

[0020] In S2, the volume fraction of carbon dioxide in the carbon dioxide-containing gas is 24%–28%; and / or,

[0021] In S2, carbon dioxide gas is introduced into the clear green liquor according to a molar ratio of silicon in the clear green liquor to carbon dioxide in the carbon dioxide-containing gas of 1:2.1–3.5; and / or,

[0022] In S2, the carbonization reaction temperature is 80℃~85℃; and / or,

[0023] In S2, the carbonization reaction takes 3 to 3.5 hours; and / or,

[0024] In S2, the silica-containing suspension generated by the carbonization reaction has a pH value of 10 to 10.5.

[0025] Preferably, in S2, the carbon dioxide-containing gas introduced into the green liquid includes purified gas obtained by purifying industrial flue gas.

[0026] Industrial flue gas includes flue gas from coal-fired boilers and / or flue gas from alkali recovery boilers.

[0027] Preferably, the method for purifying industrial flue gas includes the following steps:

[0028] Industrial flue gas is passed into a gas scrubber for dust removal to obtain purified gas.

[0029] Preferably, the method for purifying industrial flue gas includes the following steps:

[0030] Industrial flue gas is passed into a dust removal device for dust removal treatment;

[0031] The industrial flue gas that has undergone dust removal is passed into a desulfurization device for desulfurization treatment;

[0032] The desulfurized industrial flue gas is passed into the absorption tower, so that the carbon dioxide in the flue gas is absorbed by the carbon dioxide absorption liquid in the absorption tower to obtain carbon dioxide-rich absorption liquid.

[0033] The obtained carbon dioxide-rich absorbent is passed into a regeneration tower for regeneration treatment to obtain purified gas and carbon dioxide absorbent.

[0034] Preferably, the method further includes the following steps:

[0035] S5.1: Wash the silica-containing filter cake to obtain a washed filter cake, and then dry the washed filter cake;

[0036] S5.2: The dried washed filter cake is pre-calcined at a temperature of 650℃~750℃ to obtain the pre-calcined product;

[0037] S5.3: The pre-calcined material is subjected to a high-temperature solid-phase reaction at a temperature of 900℃~1100℃ to obtain calcium silicate clinker, which is then cooled to obtain active calcium silicate.

[0038] Preferably, the dried washing filter cake is pulverized, and then pre-calcined at a temperature of 650℃~750℃ to obtain the pre-calcined product.

[0039] Preferably, step S5.1 further includes: adding a calcium source regulator or a silicon source regulator to the washing filter cake to adjust the molar ratio of calcium to silicon in the washing filter cake to 1.5 to 2.2.

[0040] Preferably, the calcium source regulator is one or more of calcium oxide, calcium hydroxide, calcium carbonate, or limestone; and / or,

[0041] The silicon source regulator is one or more of silicon dioxide, quartz powder, silica powder, or diatomaceous earth.

[0042] The beneficial effects of this invention are:

[0043] By adding white mud slurry as seed crystals to the green liquor, effective nucleation sites are provided for calcium silicate precipitation during the carbonization reaction with carbon dioxide gas. This promotes the precipitation of silicon in the form of easily filtered and separated solid particles, rather than forming difficult-to-handle colloidal silica. Furthermore, the white mud slurry can be the product of subsequent causticizing reactions, thus achieving material recycling, improving resource utilization, and reducing production costs.

[0044] The carbon dioxide-containing gas introduced can be derived from purified industrial flue gas. This technological feature transforms greenhouse gases that would otherwise be emitted into valuable chemical raw materials for use in the desiliconization process of green liquor. This not only reduces the raw material cost of the desiliconization process but also achieves carbon capture and utilization, thereby reducing carbon emissions from the paper industry.

[0045] Silica-containing filter cake can be converted into high-value-added activated calcium silicate by washing, drying, and heat treatment within a specific temperature range. Because activated calcium silicate has a porous structure, it can be used as a functional filler in the paper industry to improve paper opacity, whiteness, and stiffness, as well as enhance its printability and dimensional stability. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some examples or embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort, and this application can be applied to other similar scenarios based on the provided drawings. Unless obvious from the linguistic context or otherwise stated, the same reference numerals in the drawings represent the same structure or operation.

[0047] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0048] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for explaining the relevant application and are not intended to limit the application. The described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.

[0049] Example 1

[0050] See Figure 1 This embodiment provides a basic method for removing silicon from papermaking green liquor, specifically including the following steps:

[0051] S1: Perform solid-liquid separation on the green liquor to separate the solid impurities contained in the green liquor and obtain clear green liquor.

[0052] Solid-liquid separation of papermaking green liquor can be performed using conventional filtration or centrifugal separation equipment in the field, such as green liquor clarifiers, plate and frame filter presses, vacuum drum filters, or centrifuges, to remove unburned carbon particles, ash, and other solid impurities entrained in the green liquor and obtain a clearer green liquor.

[0053] S2: Add white mud slurry to the green liquor and introduce carbon dioxide gas to produce a silicon-containing suspension through carbonization reaction.

[0054] The clear green liquor obtained from S1 is transferred to a carbonization reactor, where white mud slurry is added and carbon dioxide gas is introduced. The order of adding the white mud slurry and introducing the carbon dioxide gas is not restricted. The white mud slurry is generated by adding calcium hydroxide to the causticizing mother liquor for a causticizing reaction, thus achieving material recycling.

[0055] Sodium silicate in the green liquid reacts with carbon dioxide to produce silicic acid. The main component of the white mud slurry is calcium carbonate. The white mud slurry can act as a seed crystal, providing an effective heterogeneous nucleation site for the precipitation of calcium silicate. This promotes the combination of silicic acid with calcium ions in the system and precipitates out in the form of solid calcium silicate particles, rather than forming colloidal silicic acid that is difficult to filter, thus obtaining a silicon-containing suspension.

[0056] S3: Perform solid-liquid separation on the silica-containing suspension to obtain silica-containing filter cake and causticizing mother liquor.

[0057] The silicon-containing suspension generated by S2 undergoes solid-liquid separation. Since silicon mostly exists in the form of solid particles, this separation process is easy to carry out and highly efficient. The solid residue obtained after separation is the silicon-containing filter cake, and the liquid portion is the causticizing mother liquor.

[0058] S4: Add calcium hydroxide to the causticizing mother liquor to carry out the causticizing reaction. After the reaction, solid-liquid separation is performed to obtain white liquor and white mud slurry.

[0059] The causticizing mother liquor obtained in S3 is transferred to a causticizing reactor, where calcium hydroxide is added to initiate a causticizing reaction. The calcium hydroxide reacts with the causticizing mother liquor. After the reaction is complete, the reaction products are separated into solid and liquid components. A clear liquid, i.e., white liquor, is obtained, whose main component is sodium hydroxide, and can be reused in the pulping process. Simultaneously, a solid residue, i.e., white mud slurry, is obtained, whose main component is calcium carbonate. This white mud slurry can be used as a seed crystal in S2, forming a material cycle.

[0060] Example 2

[0061] Based on Example 1 above, this example further optimizes the carbonization reaction conditions in S2 to improve the silicon removal effect.

[0062] In step S2, the amount of white mud slurry added to the clear green liquor can be from 0.5 wt% to 3 wt% of the mass of the clear green liquor. Within this range, sufficient crystal nuclei can be provided to ensure effective precipitation of calcium silicate. More preferably, the amount of white mud slurry added is from 1 wt% to 2 wt% of the mass of the clear green liquor. Within this range, the amount of white mud slurry introduced can be reduced while ensuring the seed crystal effect.

[0063] In S2, the volume fraction of carbon dioxide in the introduced carbon dioxide gas can be from 20% to 95%. More preferably, the volume fraction of carbon dioxide is from 24% to 28%.

[0064] In step S2, the amount of carbon dioxide gas introduced is controlled according to the molar ratio of silicon in the clear green liquid to carbon dioxide in the carbon dioxide gas, which can be from 1:1.5 to 1:3.5. This ratio ensures sufficient carbon dioxide for complete reaction of sodium silicate. More preferably, the molar ratio is from 1:2.1 to 1:3.5, at which the reaction is more thorough and the silicon removal rate is higher.

[0065] In S2, the carbonization reaction temperature is controlled between 70°C and 85°C. This temperature range is beneficial for accelerating the reaction rate and promoting the formation of easily filterable crystal morphologies. More preferably, the reaction temperature is between 80°C and 85°C, where the reaction kinetics are even better.

[0066] In S2, the carbonization reaction can take 1 to 4 hours. More preferably, the reaction time is 3 to 3.5 hours to ensure that the reaction reaches equilibrium.

[0067] In S2, the silica-containing suspension generated by the carbonization reaction has a pH value of 9.5 to 11, more preferably 10 to 10.5.

[0068] Example 3

[0069] This embodiment, based on the above embodiment 1 or embodiment 2, specifically describes the source of the carbon dioxide-containing gas introduced into the green liquid.

[0070] The carbon dioxide-containing gas introduced into the green liquor includes purified gas obtained from the purification treatment of industrial flue gas. More specifically, the carbon dioxide-containing gas introduced into the green liquor can be entirely or partially purified gas obtained from the purification treatment of industrial flue gas. The industrial flue gas includes flue gas from coal-fired boilers and / or flue gas from alkali recovery boilers.

[0071] There are various methods for purifying industrial flue gas. This embodiment describes two typical methods:

[0072] Method 1: Industrial flue gas is passed through a gas scrubber for dust removal and cooling. After removing most of the dust, purified gas is obtained, which can be directly or after pressure regulation and then passed into the carbonization reactor. This method is suitable for scenarios where the purity requirements for carbon dioxide are not high.

[0073] Method 2: Industrial flue gas is passed through dust removal equipment such as an electrostatic precipitator or bag filter for dust removal. Then, the dust-treated flue gas is passed through desulfurization equipment such as a wet desulfurization tower for desulfurization to remove sulfur dioxide. Next, the desulfurized flue gas is passed through an absorption tower, where carbon dioxide in the flue gas is absorbed by the carbon dioxide absorbent liquid, resulting in a carbon dioxide-rich absorbent liquid. Amine liquid is commonly used as the absorbent liquid. Finally, the carbon dioxide-rich absorbent liquid is passed through a regeneration tower for heating and regeneration, desorbing high-concentration carbon dioxide gas to obtain purified gas. Simultaneously, the regenerated absorbent liquid is returned to the absorption tower for recycling. This method can obtain high-purity carbon dioxide gas.

[0074] Example 4

[0075] Based on any one of the above embodiments 1 to 3, this embodiment further provides a method for resource utilization of the silica-containing filter cake obtained in S3, specifically including the following steps:

[0076] S5.1: Wash the silica-containing filter cake to obtain a washed filter cake, and then dry the washed filter cake.

[0077] The silica-containing filter cake obtained in step S3 is washed to remove soluble impurities such as sodium salts, resulting in a washed filter cake. The washed filter cake is then dried using methods such as oven drying or airflow drying.

[0078] Furthermore, step S5.1 may also include adding a calcium source regulator or a silicon source regulator to the washing filter cake to adjust the molar ratio of calcium to silicon in the washing filter cake to 1.5–2.2, a ratio suitable for the synthesis of calcium silicate. The calcium source regulator may be selected from one or more of calcium oxide, calcium hydroxide, calcium carbonate, or limestone. The silicon source regulator may be selected from one or more of silica, quartz powder, silica powder, or diatomaceous earth.

[0079] S5.2: The dried washed filter cake is pre-calcined at a temperature of 650℃~750℃ to obtain the pre-calcined product.

[0080] The washed filter cake, after drying and optional component adjustment, is pre-calcined. Preferably, it can be pulverized first to increase the specific surface area and make the calcination more uniform. Then, the material is pre-calcined at a temperature of 650°C to 750°C. This process can remove bound water and preliminarily activate the material to obtain the pre-calcined product.

[0081] S5.3: The pre-calcined material is subjected to a high-temperature solid-phase reaction at a temperature of 900℃~1100℃ to obtain calcium silicate clinker, which is then cooled to obtain active calcium silicate.

[0082] The pre-calcined material is subjected to a high-temperature solid-state reaction at 900℃ to 1100℃ to allow the calcium and silicon sources to fully react and form calcium silicate clinker. After the reaction is complete, cooling yields the activated calcium silicate product. This activated calcium silicate has a porous structure and can be used as a functional filler in papermaking, plastics, coatings, and other fields, for example, to improve the opacity and stiffness of paper.

[0083] Example 5

[0084] This embodiment provides a method for removing silicon from and recycling papermaking green liquor, with the following specific steps:

[0085] S1: Take 15 cubic meters of green liquor from the bamboo pulp alkali recovery system. Its main components are sodium carbonate, sodium silicate, and sodium sulfate. Filter the green liquor using a plate and frame filter press to remove unburned carbon particles and ash, etc., to obtain a clear green liquor. The silica content in the clear green liquor is 5.0 g / L (calculated as silicon element).

[0086] S2: The clear green liquor is pumped into a carbonization reactor equipped with a stirrer and a heater. White mud slurry, measured at 2 wt% of the clear green liquor mass from subsequent steps, is added to the carbonization reactor. Stirring is started, and the reaction system temperature is maintained at 80°C using the heater. Subsequently, alkali recovery boiler flue gas (approximately 25% carbon dioxide volume fraction) treated according to Method 1 of Example 3 is introduced into the reaction system. The flow rate of the introduced carbon dioxide gas is controlled by a flow meter to ensure that the ratio of the total moles of introduced carbon dioxide to the total moles of silicon in the clear green liquor is 2.5:1, at which point the introduction of carbon dioxide gas is stopped. After 3 hours of reaction, due to the reaction of sodium silicate in the clear green liquor with carbon dioxide and under the seed induction provided by the white mud slurry, calcium silicate in the form of solid particles is generated, resulting in an easily filterable silicon-containing suspension with a pH of 10.3.

[0087] S3: The entire silica-containing suspension in the carbonization reactor was pumped into another plate and frame filter press for filtration. After solid-liquid separation, a blocky silica-containing filter cake with a water content of approximately 45% and a clear causticizing mother liquor were obtained. This separation process was smooth, and no filter cloth clogging occurred. By measuring the silicon content in the causticizing mother liquor and the clear green liquor, the silicon removal rate was found to be 80%.

[0088] S4: Transfer the causticizing mother liquor to the causticizing reactor. Under stirring conditions, add the calculated amount of calcium hydroxide to carry out the causticizing reaction. After the reaction is complete, pump the causticizing product into a centrifuge for centrifugal separation. A clear white liquor, mainly composed of sodium hydroxide, is obtained after separation and can be returned to the pulping section for use. Simultaneously, white mud slurry, mainly composed of calcium carbonate, is obtained. A portion of this white mud slurry can be used as seed crystals and recycled in the above steps; the remainder can be disposed of separately.

[0089] S5: The silica-containing filter cake was washed three times with water in a washing tank to remove residual soluble sodium salts, resulting in a washed filter cake. The washed filter cake was dried in an oven at 105°C to constant weight. Testing showed that the molar ratio of calcium to silicon in the dried filter cake was approximately 1.8. The dried filter cake was then pulverized and passed through a 100-mesh sieve. The sieved material was placed in a muffle furnace and pre-calcined at 700°C for 2 hours to obtain a pre-calcined material. Finally, the pre-calcined material was calcined at 1000°C for 1.5 hours, and after natural cooling, it was ground to obtain the activated calcium silicate product.

[0090] This embodiment effectively solves the filter clogging problem caused by the direct carbonization of colloidal silica in the prior art by pre-adding white mud slurry as seed crystals. The solid-liquid separation efficiency of the silica-containing suspension is high, and production is continuous and stable. Simultaneously, this method enables the recycling of white mud slurry within the system and converts the silica-containing filter cake into high-value-added activated calcium silicate, achieving resource utilization of waste.

[0091] Example 6

[0092] Based on Example 5 above, this example provides another method for desiliconization and resource recovery of papermaking green liquor. Steps S1, S3, S4, and S5 in this example are the same as those in Example 5. The step S2, which differs from that in Example 5, is as follows:

[0093] The clarified green liquor was pumped into carbonization reactor 2, and white mud slurry, accounting for 2.0 wt% of the clarified green liquor mass, was added. The reaction temperature was controlled at 75°C. Alkali recovery boiler flue gas (with a carbon dioxide volume fraction of approximately 25%) treated according to method one in Example 3 was introduced. The carbon dioxide flow rate was controlled to maintain a silicon to carbon dioxide molar ratio of 1:2.5. Under these conditions, the reaction was carried out for 3.2 hours, and the pH of the silicon-containing suspension was 10. By measuring the silicon content in the causticizing mother liquor and the clarified green liquor, a silicon removal rate of 85% was obtained.

[0094] Example 7

[0095] Based on Example 5 above, this example provides another method for desiliconization and resource recovery of papermaking green liquor. Steps S1, S3, S4, and S5 in this example are the same as those in Example 5. The step S2, which differs from that in Example 5, is as follows:

[0096] The clarified green liquor was pumped into carbonization reactor 2, and white mud slurry, accounting for 2.0 wt% of the clarified green liquor mass, was added. The reaction temperature was controlled at 75°C. Flue gas from a coal-fired boiler treated according to method one in Example 3 (with a carbon dioxide volume fraction of approximately 20%) was introduced. The carbon dioxide flow rate was controlled to maintain a silicon to carbon dioxide molar ratio of 1:2.5. Under these conditions, the reaction was carried out for 3.2 hours, and the pH of the silicon-containing suspension was 10.5. By measuring the silicon content in the causticizing mother liquor and the clarified green liquor, a silicon removal rate of 78% was obtained.

[0097] Example 8

[0098] Based on Example 5 above, this example provides another method for desiliconization and resource recovery of papermaking green liquor. Steps S1, S3, S4, and S5 in this example are the same as those in Example 5. The step S2, which differs from that in Example 5, is as follows:

[0099] The clear green liquor was pumped into carbonization reactor 2, and white mud slurry 8, accounting for 3 wt% of the clear green liquor mass, was added. The reaction temperature was controlled at 85℃. In this embodiment, unpurified flue gas from an alkali recovery boiler (with a carbon dioxide volume fraction of approximately 25%) was directly used as the carbon dioxide-containing gas. The carbon dioxide flow rate was controlled to maintain a silicon to carbon dioxide molar ratio of 1:2.5. Under these conditions, the reaction lasted for 3.2 hours, and the pH of the silicon-containing suspension was 10.5. By measuring the silicon content in the causticizing mother liquor and the clear green liquor, a silicon removal rate of 78% was obtained.

[0100] In the description of the embodiments of this application, unless otherwise stated, "、" means "or". For example, A and B can mean A or B. "And" and "or" in this article are merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and or B can mean: A exists alone, A and B exist simultaneously, and B exists alone.

[0101] It should be noted that, for ease of description, only the parts relevant to the application are shown in the accompanying drawings; unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0102] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed, and is not intended to limit this application. For those skilled in the art, this application can have various modifications and variations; the scope of this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described application concept; for example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for removing silicon from papermaking green liquor, characterized in that, Includes the following steps: S1: Perform solid-liquid separation on the green liquor to separate the solid impurities contained in the green liquor and obtain clear green liquor; S2: Add white mud slurry to the green liquor and introduce carbon dioxide gas to produce a silicon-containing suspension through carbonization reaction; S3: Perform solid-liquid separation on the silica-containing suspension to obtain silica-containing filter cake and causticizing mother liquor; S4: Add calcium hydroxide to the causticizing mother liquor to carry out the causticizing reaction. After the reaction, solid-liquid separation is performed to obtain white liquor and white mud slurry.

2. The method for removing silicon from papermaking green liquor as described in claim 1, characterized in that: In S2, 0.5wt%–3wt% of white mud slurry is added to the clear green liquor; and / or, In S2, the volume fraction of carbon dioxide in the carbon dioxide-containing gas is 20%–95%; and / or, In S2, carbon dioxide gas is introduced into the clear green liquor according to a molar ratio of silicon in the clear green liquor to carbon dioxide in the carbon dioxide-containing gas of 1:1.5–3.5; and / or, In S2, the carbonization reaction temperature is 70℃~85℃; and / or, In S2, the carbonization reaction time is 1 h to 4 h; and / or, In S2, the silica-containing suspension generated by the carbonization reaction has a pH value of 9.5–11.

3. The method for removing silicon from papermaking green liquor as described in claim 1, characterized in that: In S2, 1wt%–2wt% of white mud slurry is added to the clear green liquor; and / or, In S2, the volume fraction of carbon dioxide in the carbon dioxide-containing gas is 24%–28%; and / or, In S2, carbon dioxide gas is introduced into the clear green liquor according to a molar ratio of silicon in the clear green liquor to carbon dioxide in the carbon dioxide-containing gas of 1:2.1–3.5; and / or, In S2, the carbonization reaction temperature is 80℃~85℃; and / or, In S2, the carbonization reaction takes 3 to 3.5 hours; and / or, In S2, the silica-containing suspension generated by the carbonization reaction has a pH value of 10 to 10.

5.

4. The method for removing silicon from papermaking green liquor as described in claim 1, characterized in that: In S2, the carbon dioxide-containing gas introduced into the green liquid includes purified gas obtained by purifying industrial flue gas. Industrial flue gas includes flue gas from coal-fired boilers and / or flue gas from alkali recovery boilers.

5. The method for removing silicon from papermaking green liquor as described in claim 4, characterized in that: Methods for purifying industrial flue gas include the following steps: Industrial flue gas is passed into a gas scrubber for dust removal to obtain purified gas.

6. The method for removing silicon from papermaking green liquor as described in claim 4, characterized in that: Methods for purifying industrial flue gas include the following steps: Industrial flue gas is passed into a dust removal device for dust removal treatment; The industrial flue gas that has undergone dust removal is passed into a desulfurization device for desulfurization treatment; The desulfurized industrial flue gas is passed into the absorption tower, so that the carbon dioxide in the flue gas is absorbed by the carbon dioxide absorption liquid in the absorption tower to obtain carbon dioxide-rich absorption liquid. The obtained carbon dioxide-rich absorbent is passed into a regeneration tower for regeneration treatment to obtain purified gas and carbon dioxide absorbent.

7. The method for removing silicon from papermaking green liquor as described in claim 1, characterized in that, It also includes the following steps: S5.1: Wash the silica-containing filter cake to obtain a washed filter cake, and then dry the washed filter cake; S5.2: The dried washed filter cake is pre-calcined at a temperature of 650℃~750℃ to obtain the pre-calcined product; S5.3: The pre-calcined material is subjected to a high-temperature solid-phase reaction at a temperature of 900℃~1100℃ to obtain calcium silicate clinker, which is then cooled to obtain active calcium silicate.

8. The method for removing silicon from papermaking green liquor as described in claim 7, characterized in that: S5.1 also includes: adding a calcium source regulator or a silicon source regulator to the washing filter cake to adjust the molar ratio of calcium to silicon in the washing filter cake to 1.5 to 2.

2.

9. The method for removing silicon from papermaking green liquor as described in claim 8, characterized in that: The calcium source regulator is one or more of calcium oxide, calcium hydroxide, calcium carbonate, or limestone; and / or, The silicon source regulator is one or more of silicon dioxide, quartz powder, silica powder, or diatomaceous earth.

10. The method for removing silicon from papermaking green liquor as described in claim 7, characterized in that: In S5.2, the dried washing filter cake is crushed and then pre-calcined at a temperature of 650℃~750℃ to obtain the pre-calcined product.

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