CN115092950A - Method for recycling papermaking white mud - Google Patents
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Abstract
The invention particularly relates to a recycling method of papermaking white mud, belonging to the technical field of recycling, and the method comprises the step of calcining the papermaking white mud under the condition of set temperature to obtain CaO and CO 2 A gas; digesting and aging the CaO to form Ca (OH) 2 An emulsion; according to the set demarcation point value to the Ca (OH) 2 Classifying the emulsion to obtain a fine-grain emulsion and a coarse-grain emulsion with set grain sizes; carrying out carbonization reaction on the fine-fraction emulsion with the set particle size at the set carbon-containing gas flow rate to obtain nano calcium carbonate; the nano calcium carbonate product with higher added value is obtained by calcining, digesting, aging, grading, carbonizing and curing the papermaking white mud, so that the method has good social benefit, solves the problem that the existing recovery method of the papermaking white mud stays in the refining of the white mud and the preparation of common light calcium carbonate, and also solves the problems of white mud stockpiling, low utilization rate and the like.
Description
Technical Field
The invention belongs to the technical field of recycling, and particularly relates to a recycling method of papermaking white mud.
Background
Paper mills produce large quantities of causticized white mud (also known as papermaking white mud) during the black liquor soda recovery process, and it is reported that nearly 0.8t of white mud is produced per 1t of brown stock produced, and that over 300 million tons of white mud are produced annually by paper mills throughout the country. The pH value of the white mud is generally 10-12, the white mud belongs to a high-alkalinity substance, and harmful components (particularly alkali components) in the white mud are easy to permeate into underground water and soil through weathering rain and erosion of surface runoff due to random stacking of the white mud, so that water bodies and soil are polluted.
At present, a great deal of research work is carried out at home and abroad aiming at the comprehensive utilization aspect of the papermaking white mud, for example, the Kolliang indicates that the papermaking white mud can be used as a flue gas desulfurizer in the current situation of comprehensive utilization of the alkali-making white mud and the papermaking white mud, the environmental protection problem exists in the use process, and the use cost is high. Maobu introduces a method for preparing light calcium carbonate by using causticized white mud in 'research on producing light calcium carbonate by causticizing alkali-making method', but the obtained light calcium carbonate is low in white mud recovery rate. Haohozin introduces a method for preparing nano calcium carbonate from papermaking white mud in research on a method for preparing calcium carbonate from papermaking white mud, and the method uses ammonium chloride to treat caustic soda, so that water pollution is caused and the cost is high. The royal jade dragon introduces a method for preparing light calcium carbonate filler in white mud recovered from straw pulp alkali in the optimization of the use process of white mud light calcium carbonate recovered from straw pulp alkali. Li Zhong Ming introduced the method for preparing light calcium carbonate from alkali-recovered white mud in the 'preparation of light calcium carbonate from alkali-recovered white mud', the method adds a flocculating agent in the process, needs a dissociation process in the later period, has complex steps, and the product is light calcium carbonate with low additional value. The Chinese patent application CN 104803405A introduces a process for preparing calcium carbonate from white mud by carbonizing reaction in a high-pressure upflow reaction kettle, and the method does not dehydrate or remove impurities from the white mud, and the produced calcium carbonate is common light calcium carbonate, and has complex steps and low product added value.
At present, a lot of researches on comprehensive utilization of resources of papermaking white mud are carried out, but most researches stay in refining and preparing common light calcium carbonate from white mud, so that the production cost is high, the added value of products is low, and the market prospect is poor.
Disclosure of Invention
The application aims to provide a recycling method of papermaking white mud so as to provide a brand-new utilization way of the papermaking white mud.
The embodiment of the invention provides a method for recycling papermaking white mud, which comprises the following steps:
calcining the papermaking white mud under the condition of set temperature to obtain CaO and CO 2 A gas;
digesting and aging the CaO to form Ca (OH) 2 An emulsion;
according to the set demarcation point value, Ca (OH) 2 Classifying the emulsion to obtain a fine-grain emulsion and a coarse-grain emulsion with set grain sizes;
and carrying out carbonization reaction on the fine-fraction emulsion with the set particle size according to the set carbon-containing gas flow to obtain the nano calcium carbonate.
Optionally, the set air amount is 0.28-0.32m 3 /g-CaCO 3
Optionally, the temperature of the carbonization reaction is 15-25 ℃.
Optionally, the pH value at the end of the carbonization reaction is 6-8.
Optionally, the carbonizing reaction of the fine-fraction emulsion to form a nano calcium carbonate slurry specifically includes:
carrying out carbonization reaction on the fine-fraction emulsion by adopting a three-phase jet carbonization reactor to form nano calcium carbonate slurry;
wherein the diameter of a gas micropore pipe of the three-phase jet flow carbonization reactor is 1-3 μm; and/or
The gas pressure of the carbonization reaction is 0.15MPa-0.25 MPa; and/or
The pressure of the slurry of the carbonization reaction is 0.10MPa-0.20 MPa; and/or
The injection speed of the gas-solid-liquid three-phase mixed slurry of the carbonization reaction is 2-6 m/s.
Optionally, calcining the papermaking white mud under the condition of set temperature to obtain CaO and CO 2 The gas specifically comprises:
calcining the papermaking white mud by adopting a suspension roaster under the condition of set temperature to obtain CaO and CO 2 A gas;
wherein the set temperature is 860 ℃ and 950 ℃; and/or
The calcining time is 2-4 h.
Optionally, the digested CaO and H 2 The mass ratio of O is 1: 4-6; and/or
The temperature of the digestion treatment is 70-85 ℃; and/or
The digestion treatment time is 2-3 h; and/or
The stirring speed of the digestion treatment is 250-350 r/min; and/or
The aging time is 10-12 h; and/or
The curing time is 1.5-2.5 h.
Optionally, the set demarcation point value is 0.35-0.40 mm.
Optionally, the fine-fraction emulsion with a set particle size is carbonized at a set carbon-containing gas flow rate to obtain nano calcium carbonate, and the method specifically includes:
carrying out carbonization reaction on the fine-fraction emulsion with the set particle size to form nano calcium carbonate slurry, and then curing to obtain cured slurry;
concentrating the cured slurry to obtain supernatant and underflow slurry;
recycling the supernatant to digestion treatment;
washing the underflow slurry, and then carrying out solid-liquid separation and drying to obtain nano calcium carbonate;
wherein the washing detergent is absolute ethyl alcohol, and the dosage of the absolute ethyl alcohol is 18-22 kg/t; and/or
The drying temperature is 85-90 ℃, and the drying time is 10-12 h.
Optionally, the method further includes:
reacting the CO with 2 And recycling the gas to the carbonization reaction.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
according to the recycling method of the papermaking white mud provided by the embodiment of the invention, the papermaking white mud is calcined, digested, aged, graded, carbonized and cured, and especially the particle size of the nano calcium carbonate is controlled by controlling the gas amount of carbonization reaction, so that a nano calcium carbonate product with a high added value is obtained, good social benefits are achieved, the problem that the existing recovery method of the papermaking white mud stays in the refining of the white mud and the preparation of common light calcium carbonate is solved, and the problems of white mud stacking, low utilization rate and the like are solved.
The above description is only an overview of the technical solutions of the present invention, and the present invention can be implemented in accordance with the content of the description so as to make the technical means of the present invention more clearly understood, and the above and other objects, features, and advantages of the present invention will be more clearly understood.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a process flow diagram provided by an embodiment of the present invention;
FIG. 2 is a scanning electron microscope image of a nano calcium carbonate product provided by an embodiment of the present invention;
fig. 3 is a flow chart of a method provided by an embodiment of the invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the general idea of the embodiment of the application is as follows:
the applicant found that: the nano calcium carbonate has quantum size effect, small size effect, surface effect and macroscopic quantum effect, is widely applied to the fields of rubber, plastic, papermaking, chemical building materials, printing ink, coating, sealant, adhesive and the like, has wider application field along with the rapid development of industry and the continuous improvement of the living standard of people, and can gradually replace the traditional light calcium carbonate, kaolin and the like. At present, the nano calcium carbonate in domestic market has the defects of large particle size, unstable product and the like, and most of the nano calcium carbonate used in the market is light calcium carbonate or submicron calcium carbonate.
A great deal of research work is carried out at home and abroad aiming at the preparation of the nano calcium carbonate, and the main work is as follows:
(1) in the research on preparing flaky calcium carbonate by a carbonization method, the wenyan introduces a batch carbonization method to prepare flaky nano calcium carbonate, the method has low carbonization concentration (< 0.4%), large water consumption and serious lamination.
(2) Wang nong studied the influence of different additives on the particle size and the appearance of the nano calcium carbonate in 'the influence of the additives on the appearance and the particle size of the nano calcium carbonate' and other people, and prepared the nano calcium carbonate with different appearances and different sizes.
(3) The research of synthesizing nano calcium carbonate by a hypergravity method in Zhu Keming introduces that the hypergravity method is used for preparing the nano calcium carbonate to produce the calcium carbonate with the particle size of 15-40nm, but the equipment investment is large, the equipment is easy to scale after long-time running, and the equipment is difficult to clean due to the particularity, short in period and high in production cost.
(4) In 'preparation of nano calcium carbonate and research on adsorption performance', Liqiong adopts calcium chloride and sodium carbonate as raw materials to prepare nano calcium carbonate by a double decomposition method, wherein the nano calcium carbonate has a non-unique shape and a particle size of more than 100 nm.
(5) Wangjiangfei uses calcium oxide as raw material in the research on preparation process of nano calcium carbonate, and prepares nano calcium carbonate in circulating water pump, and said method can directly introduce gas into the water pump, and can produce cavitation phenomenon, and its equipment is easy to damage, and can raise production cost.
(6) A preparation method of nano calcium carbonate and application thereof (CN 112374518A) have the advantages of strict production environment, long reaction time and high cost of ammonium bicarbonate as a raw material, and the method needs to be carried out under a vacuum condition.
(7) A method for preparing nano calcium carbonate with the particle size less than 20nm (CN 112479242A) needs a plurality of times of carbonization to prepare the nano calcium carbonate. The process has complex steps and needs to add the organic dissociation reagent for many times, which leads to high production cost.
(8) A device and a method for preparing high-dispersion nano calcium carbonate (CN 110484023B) are introduced, and the method and the device for preparing the nano calcium carbonate not only need high-speed stirring but also need to add an organic mixed catalyst in the carbonization process, thereby increasing the energy consumption and the production cost.
(9) A method (CN 109650430B) for preparing nano calcium carbonate from high-magnesium limestone introduces a method for preparing nano calcium carbonate from low-grade high-magnesium limestone by conventional high-temperature calcination, and the process has the defects of high energy consumption, complex flow, various medicament types and the like.
(10) A method for preparing hollow nano calcium carbonate by using ultrasonic aerosol (CN 111017973B) introduces a method for generating calcium hydroxide solution aerosol by using calcium hydroxide emulsion liquid drops in an ultrasonic aerosol generating device in dry heat and excessive carbon dioxide atmosphere, and forming central control nano calcium carbonate after water evaporation.
(11) A method for preparing nano calcium carbonate (CN 114212814A) introduces a method for preparing nano calcium carbonate by using calcium carbonate ore, and the method has high cost of raw materials and easy agglomeration of products.
The traditional preparation method of the nano calcium carbonate mainly has the defects of unstable product performance, non-unique appearance, uneven and larger granularity, high equipment maintenance cost, need of adding an organic catalyst and the like.
The preparation method has the advantages that the papermaking white mud is used for preparing the nano calcium carbonate, the novel energy-saving roasting process and the novel energy-saving roasting equipment are adopted, the energy consumption in the firing process can be effectively reduced, the low-consumption and high-efficiency three-phase jet flow reactor is adopted in the carbonization process, stirring is not required to be increased, any additive is not required to be added, the process is simple, and the production cost is low.
According to an exemplary embodiment of the present invention, there is provided a method for recycling papermaking white mud, the method comprising:
s1, calcining the papermaking white mud to obtain CaO and CO 2 A gas;
in some embodiments, the calcining is low temperature calcining at a temperature of 860 ℃ to 950 ℃;
in some embodiments, the papermaking white mud is calcined to obtain CaO and CO 2 The gas specifically comprises:
calcining the papermaking white mud by adopting a suspension roaster to obtain CaO and CO 2 A gas;
wherein the low-temperature calcination time is 2-4 h.
Specifically, in the embodiment, the novel energy-saving calcining equipment is adopted to calcine and decompose the white mud into CaO and CO at low temperature 2 Gas, optionally, clean-up to collect CO 2 Gas (with concentration of 40% -50%) is used for carbonization process.
S2, digesting the CaO to form Ca (OH) 2 Aging and grading the slurry to obtain fine-fraction emulsion and coarse-fraction emulsion;
in some embodiments, the digested CaO and H 2 The mass ratio of O is 1: 4-6; the temperature of the digestion treatment is 70-85 ℃; the digestion treatment time is 2-3 h; the stirring speed of the digestion treatment is 250-350 r/min; the aging time is 10-12 h.
CaO dissolved in H 2 O is an exothermic reaction, CaO and H are controlled 2 The mass ratio of O is 1: 4-6, the calorific value is just suitable for the temperature required by the digestion reaction, and the concentration is lower than 1: 4-6, the calorific value is too small, the temperature cannot reach the reaction temperature, and the concentration is higher than 1: 4-6, CaO digestion to Ca (OH) 2 The increase in volume concentration is detrimental to the reaction stirring.
The temperature of the digestion treatment is controlled to be 70-85 ℃, when the temperature is too low, the digestion is not complete, and the digestion of the large-particle CaO is not complete.
The time of the digestion treatment is controlled to be 2-3h to ensure the complete digestion of CaO.
The stirring speed is controlled to be 250-350r/min to accelerate the digestion of CaO, when the rotation speed is lower than 250-350r/min, the solid-liquid contact surface of the digestion system is too little to be beneficial to the reaction, and when the rotation speed is higher than 250-350r/min, the slurry is easy to splash.
The aging time is controlled to be 10-12h so as to ensure that CaO is digested more completely, and Ca (OH) is generated 2 The emulsion is more uniform and smooth, the size fraction classification is facilitated, and the digestion time is too short Ca (OH) 2 The emulsion can agglomerate, and local large block volume is generated, which is not beneficial to grading the particle size.
In some embodiments, the fine fraction emulsion and the coarse fraction emulsion have a cut point value of 0.35 to 0.40 mm. Optionally, the fine fraction emulsion and the coarse fraction emulsion have a cut point value of 0.38 mm.
Specifically, the classified particle size is 0.038mm, the-0.038 mm is returned to the calcination process, and the +0.038mm is fed to the carbonization process.
Specifically, in this example, CaO and H are mixed 2 Mixing and digesting the O according to the proportion; aging the digested slurry; aged Ca (OH) 2 The emulsion is classified to obtain fine fraction of refined Ca (OH) 2 The emulsion, optionally, the coarse fraction, is returned to the calcination process.
S3, carrying out carbonization reaction on the fine-grained emulsion to form nano calcium carbonate slurry, and then curing to obtain nano calcium carbonate;
specifically, in this example, Ca (OH) was purified 2 Diluting the emulsion and then carrying out carbonization reaction; curing the carbonized nano calcium carbonate slurry; optionally, concentrating the aged slurry, returning the supernatant to the digestion process, washing the underflow slurry with absolute ethyl alcohol, and performing solid-liquid separation, wherein the ethyl alcohol washing liquid is recycled; and drying the washed materials to obtain the final product of nano calcium carbonate.
Furthermore, the washing liquid can be recycled, and the filter cake enters a drying process.
In some embodiments, the carbonizing the fine-fraction emulsion to form a nano calcium carbonate slurry specifically comprises:
carrying out carbonization reaction on the fine-fraction emulsion by adopting a three-phase jet carbonization reactor to form nano calcium carbonate slurry;
wherein the temperature of the carbonization reaction is 15-25 ℃; and/or
The gas amount of the carbonization reaction is 0.28-0.32m 3 /g-CaCO 3 (ii) a And/or
The pH value of the carbonization reaction end point is 6-8; and/or
The diameter of a gas micropore pipe of the three-phase jet flow carbonization reactor is 1-3 mu m; and/or
The gas pressure of the carbonization reaction is 0.15-0.25 Mpa, preferably 0.2 Mpa; and/or
The slurry pressure of the carbonization reaction is 0.10MPa-0.20MPa, preferably, the slurry pressure is 0.15 MPa; and/or
The injection speed of the gas-solid-liquid three-phase mixed slurry of the carbonization reaction is 2-6 m/s.
In some embodiments, the time for maturation is 1.5-2.5 hours.
Ca(OH) 2 Emulsion with CO 2 The gas reaction is exothermic, the reaction is favored by reducing the temperature, and theoretically, the reaction is favored by the lower temperature, but the temperature of the carbonization reaction is controlled to be 15-25 ℃ in consideration of the production cost.
The gas velocity of the carbonization reaction is a key factor influencing the particle size of the nano calcium carbonate, the larger the gas velocity is, the smaller the particle size is, but the particle size increases with the increase of the gas velocity after the gas velocity is higher than a certain velocity, the gas velocity is too low, and CO is generated 2 Gas and Ca (OH) 2 The contact surface between emulsions is small, the reaction time is prolonged, and the generated nano calcium carbonate particles generate secondary growth, so that the particle size is enlarged. So the gas amount of the carbonization reaction is controlled to be 0.28-0.32m 3 /g-CaCO 3 。
Controlling the pH value at the end point of the carbonization reaction to be 6-8, and generating calcium bicarbonate when the pH value is more than 8 and less than 6.
The diameter of a gas micropore pipe of the three-phase jet flow carbonization reactor is controlled to be 1-3 mu m, when the aperture is larger than 3 mu m, the gas is not uniformly distributed, so that the contact between a gas phase and a solid phase is not uniform, the particle size distribution of a product is influenced, and the aperture is smaller than 1 mu m, so that the gas passing performance is poor.
The gas pressure of the carbonization reaction is controlled to be 0.15-0.25 Mpa, the slurry pressure of the carbonization reaction is controlled to be 0.10-0.20 Mpa, and when the gas pressure is greater than the slurry pressure, gas phase, liquid phase and solid phase can be better subjected to mass transfer, so that the reaction is facilitated.
The control of the injection speed of the gas-solid-liquid three-phase mixed slurry of the carbonization reaction to be 2-6m/s is beneficial to uniformly mixing the gas-solid-liquid three phases for reaction, the three-phase reaction contact time is too short when the speed is too high, the gas utilization rate is not high, the reaction time is increased when the speed is too low, and the reaction is not beneficial to the reaction.
The nano calcium carbonate can be crystallized better by curing, the curing time is controlled to be 1.5-2.5h, and if the curing time is too short, the crystallinity is influenced.
In some embodiments, the fine fraction emulsion is subjected to a carbonization reaction to form a nano calcium carbonate slurry, and then is subjected to aging to obtain nano calcium carbonate, specifically comprising:
carrying out carbonization reaction on the fine-fraction emulsion to form nano calcium carbonate slurry, and then curing to obtain cured slurry;
concentrating the cured slurry to obtain supernatant and underflow slurry;
recycling the supernatant to a digestion treatment;
and washing the underflow slurry, and then carrying out solid-liquid separation and drying to obtain the nano calcium carbonate.
In some embodiments, the detergent used for washing is absolute ethyl alcohol, and the amount of the absolute ethyl alcohol is 18-22 kg/t; and/or
The drying temperature is 85-90 ℃, and the drying time is 10-12 h.
The nano calcium carbonate is washed by absolute ethyl alcohol to prevent the nano calcium carbonate from caking after drying, fluffy nano calcium carbonate powder can be obtained after washing and drying, the absolute ethyl alcohol can be recycled, and the consumption of the absolute ethyl alcohol is controlled to be 18-22 kg/t.
The drying temperature is controlled to be 85-90 ℃ and the drying time is 10-12h, so that the water content of the nano calcium carbonate is required to be less than or equal to 0.5 percent.
In some embodiments, the method further comprises:
reacting the CO with 2 And recycling the gas to the carbonization reaction.
The recycling method of the papermaking white mud of the present application will be described in detail with reference to examples, comparative examples and experimental data.
Example 1
A method for recycling papermaking white mud comprises the following steps:
calcining the white mud at 950 ℃ for 4 hours by adopting novel energy-saving calcining equipment to decompose the white mud into CaO and CO 2 Gas, purification and CO Collection 2 A gas; CaO and H are reacted 2 O is according to1: 5, the digestion temperature is 85 ℃, the digestion stirring speed is 350r/min, and the digestion time is 2 hours; after digestion, the slurry is aged for 12 hours; aged Ca (OH) 2 Classifying the emulsion by 0.038mm size fraction, returning the product of +0.038mm size fraction to the calcining process, and refining Ca (OH) in-0.038 mm size fraction 2 An emulsion; -0.038mm size fraction refined Ca (OH) 2 Diluting the emulsion to 4%, and performing carbonization reaction in a three-phase jet flow reactor at 25 deg.C with CO 2 The gas amount is 0.3m 3 /g-CaCO 3 The carbonization reaction end point is that the pH value of the slurry is 7; curing the carbonized nano calcium carbonate slurry for 2 hours; concentrating the cured slurry, returning the supernatant to the digestion process, washing the underflow slurry with absolute ethyl alcohol, and then carrying out solid-liquid separation, wherein the ethyl alcohol washing liquid is recycled; and drying the washed materials at 85 ℃ for 10 hours to obtain the final product of nano calcium carbonate.
Example 2
A recycling method of papermaking white mud comprises the following steps:
calcining the white mud at 900 ℃ for 3 hours by adopting novel energy-saving calcining equipment to decompose the white mud into CaO and CO 2 Gas, purification and CO Collection 2 A gas; reacting CaO with H 2 O is as follows 1: 5, the digestion temperature is 80 ℃, the digestion stirring speed is 380r/min, and the digestion time is 3 hours; aging the digested slurry for 10 hours; aged Ca (OH) 2 Classifying the emulsion by 0.038mm size fraction, returning the product of +0.038mm size fraction to the calcining process, and refining Ca (OH) in-0.038 mm size fraction 2 An emulsion; -0.038mm size fraction refined Ca (OH) 2 Diluting the emulsion to 4.5%, and performing carbonization reaction in a three-phase jet flow reactor at 20 deg.C with CO 2 The gas amount is 0.31m 3 /g-CaCO 3 The carbonization reaction end point is that the pH value of the slurry is 6; curing the carbonized nano calcium carbonate slurry for 2 hours; concentrating the cured slurry, returning the supernatant to the digestion process, washing the underflow slurry with absolute ethyl alcohol, and performing solid-liquid separationSeparating, and recycling the ethanol washing solution; and drying the washed materials at 88 ℃ for 12 hours to obtain the final product of nano calcium carbonate.
Example 3
A recycling method of papermaking white mud comprises the following steps:
calcining the white mud at 870 ℃ for 2 hours by adopting novel energy-saving calcining equipment to decompose the white mud into CaO and CO 2 Gas purification and CO collection 2 A gas; reacting CaO with H 2 O is as follows 1: 5, the digestion temperature is 75 ℃, the digestion stirring speed is 340r/min, and the digestion time is 2 hours; after digestion, the slurry is aged for 11 hours; aged Ca (OH) 2 The emulsion is classified by 0.038mm size fraction, the product of +0.038mm size fraction is returned to the calcination process, and the product of-0.038 mm size fraction is refined Ca (OH) 2 An emulsion; -0.038mm size fraction refined Ca (OH) 2 Diluting the emulsion to 5%, and performing carbonization reaction in a three-phase jet flow reactor at 28 deg.C with CO introduced 2 The gas amount is 0.29m 3 /g-CaCO 3 The carbonization reaction end point is that the pH value of the slurry is 8; curing the carbonized nano calcium carbonate slurry for 2 hours; concentrating the cured slurry, returning the supernatant to the digestion process, washing the underflow slurry with absolute ethyl alcohol, and then carrying out solid-liquid separation, wherein the ethyl alcohol washing liquid is recycled; and drying the washed material at 90 ℃ for 11 hours to obtain the final product of nano calcium carbonate.
Comparative example 1
A method for recycling papermaking white mud comprises the following steps:
calcining the white mud at 850 ℃ for 4 hours by adopting novel energy-saving calcining equipment to decompose the white mud into CaO and CO 2 Gas, purification and CO Collection 2 A gas; reacting CaO with H 2 O is as follows 1: 5, the digestion temperature is 85 ℃, the digestion stirring speed is 350r/min, and the digestion time is 2 hours; aging the digested slurry for 12 hours; aged Ca (OH) 2 Classifying the emulsion by 0.038mm size fraction, returning the product of +0.038mm size fraction to the calcining process,-0.038mm size fraction of refined Ca (OH) 2 An emulsion; -0.038mm size fraction refined Ca (OH) 2 Diluting the emulsion to 4%, and performing carbonization reaction in a three-phase jet flow reactor at 25 deg.C with CO 2 The gas amount is 0.3m 3 /g-CaCO 3 The carbonization reaction end point is that the pH value of the slurry is 7; curing the carbonized nano calcium carbonate slurry for 2 hours; concentrating the cured slurry, returning the supernatant to the digestion process, washing the underflow slurry with absolute ethyl alcohol, and then carrying out solid-liquid separation, wherein the ethyl alcohol washing liquid is recycled; and drying the washed materials at 85 ℃ for 10 hours to obtain the final product of nano calcium carbonate.
Comparative example 2
A method for recycling papermaking white mud comprises the following steps:
calcining the white mud at 950 ℃ for 4 hours by adopting novel energy-saving calcining equipment to decompose the white mud into CaO and CO 2 Gas, purification and CO Collection 2 A gas; reacting CaO with H 2 O is as follows 1: 5, the digestion temperature is 65 ℃, the digestion stirring speed is 350r/min, and the digestion time is 2 hours; after digestion, the slurry is aged for 12 hours; aged Ca (OH) 2 Classifying the emulsion by 0.038mm size fraction, returning the product of +0.038mm size fraction to the calcining process, and refining Ca (OH) in-0.038 mm size fraction 2 An emulsion; -0.038mm size fraction refined Ca (OH) 2 Diluting the emulsion to 4%, and performing carbonization reaction in a three-phase jet flow reactor at 25 deg.C with CO 2 The gas amount is 0.3m 3 /g-CaCO 3 The carbonization reaction end point is that the pH value of the slurry is 7; curing the carbonized nano calcium carbonate slurry for 2 hours; concentrating the cured slurry, returning the supernatant to the digestion process, washing the underflow slurry with absolute ethyl alcohol, and then carrying out solid-liquid separation, wherein the ethyl alcohol washing liquid is recycled; and drying the washed materials at 85 ℃ for 10 hours to obtain the final product of nano calcium carbonate.
Comparative example 3
A method for recycling papermaking white mud comprises the following steps:
calcining the white mud at 950 ℃ for 4 hours by adopting novel energy-saving calcining equipment to decompose the white mud into CaO and CO 2 Gas, purification and CO Collection 2 A gas; reacting CaO with H 2 O is as follows 1: 5, the digestion temperature is 85 ℃, the digestion stirring speed is 350r/min, and the digestion time is 2 hours; after digestion, the slurry is aged for 12 hours; aged Ca (OH) 2 Classifying the emulsion by 0.038mm size fraction, returning the product of +0.038mm size fraction to the calcining process, and refining Ca (OH) in-0.038 mm size fraction 2 An emulsion; -0.038mm size fraction refined Ca (OH) 2 Diluting the emulsion to 6%, and performing carbonization reaction in a three-phase jet flow reactor at 25 deg.C with CO introduced 2 The gas amount is 0.3m 3 /g-CaCO 3 The carbonization reaction end point is that the pH value of the slurry is 7; curing the carbonized nano calcium carbonate slurry for 2 hours; concentrating the cured slurry, returning the supernatant to the digestion process, washing the underflow slurry with absolute ethyl alcohol, and then carrying out solid-liquid separation, wherein the ethyl alcohol washing liquid is recycled; and drying the washed materials at 85 ℃ for 10 hours to obtain the final product of nano calcium carbonate.
Examples of the experiments
Comparative analysis was carried out on the products obtained in examples 1 to 3 and comparative examples 1 to 3, and the results are shown in the following table:
| average particle diameter of nm | Whiteness degree | Specific surface area m 2 /g | |
| Example 1 | 75.56 | 95.54 | 20.28 |
| Example 2 | 74.35 | 94.36 | 19.89 |
| Example 3 | 76.47 | 96.31 | 21.84 |
| Comparative example 1 | 160.53 | 75.26 | 12.03 |
| Comparative example 2 | 110.32 | 80.26 | 17.56 |
| Comparative example 3 | 103.56 | 94.97 | 17.42 |
As can be seen from the comparison of the data in example 1 and comparative example 1, the calcination temperature has an influence on the particle size, whiteness and specific surface of the product, mainly because the calcination temperature is not up to 860 ℃, calcium carbonate in the white mud is not sufficiently calcined, and the crystal growth of the nano calcium carbonate is induced by the crystal seed in the carbonization process, so that the particle size of the nano calcium carbonate is enlarged, the specific surface area is reduced, and the whiteness of the nano calcium carbonate is reduced because the white mud is gray.
As is clear from the comparison of the data in example 1 and comparative example 2, the digestion temperature has an influence on the particle size, whiteness and specific surface area, mainly because the digestion temperature does not reach 70 ℃, CaO is not completely digested, and Ca (OH) is generated 2 The slurry has high viscosity, the coating part does not contain completely digested CaO particles, and the CaO is low in solubility due to low temperature in the carbonization process and is coated by the generated nano calcium carbonate, so that the nano calcium carbonate has large particle size, small specific surface area and low whiteness.
As can be seen from the comparison of the data in example 1 and comparative example 3, the carbonization concentration has an influence on the particle diameter and the specific surface area, mainly because the carbonization concentration is increased and CO is present 2 With Ca (OH) 2 The reaction contact surface of the particles is gradually reduced, and the generated nano calcium carbonate particles have secondary growth because of overhigh concentration, so that the particle size of the particles is increased and the specific surface area of the particles is reduced.
One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:
(1) the method provided by the embodiment of the invention adopts a novel energy-saving roasting process and equipment to carry out calcination, digestion, aging, grading, carbonization, curing, filtration, washing and drying to obtain the nano calcium carbonate, and has the advantages of low cost, less investment and simple process flow;
(2) the method provided by the embodiment of the invention can effectively solve the problem of economic and efficient utilization of the papermaking white mud, increases the reserve amount of raw materials required by the preparation of the nano calcium carbonate, and provides powerful technical support for the sustainable and healthy development of the nano calcium carbonate market;
(3) the method provided by the embodiment of the invention solves the problems of white mud stockpiling, low utilization rate and the like, changes the white mud into valuable, obtains the nano calcium carbonate product with higher added value, and has good social benefit.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A recycling method of papermaking white mud is characterized by comprising the following steps:
calcining the papermaking white mud under the condition of set temperature to obtain CaO and CO 2 A gas;
digesting and aging the CaO to form Ca (OH) 2 An emulsion;
according to the set demarcation point value to the Ca (OH) 2 Classifying the emulsion to obtain a fine-grain emulsion and a coarse-grain emulsion with set grain sizes;
and carrying out carbonization reaction on the fine-grained emulsion with the set grain size according to the set carbon-containing gas flow to obtain the nano calcium carbonate.
2. The recycling method of papermaking white mud according to claim 1, characterized in that the flow rate of the carbon-containing gas is set to be 0.28-0.32m 3 /g-CaCO 3 。
3. The method for recycling papermaking white mud according to claim 1, characterized in that the temperature of the carbonization reaction is 15-25 ℃.
4. The method for recycling papermaking white mud according to claim 1, characterized in that the pH value at the end point of the carbonization reaction is 6-8.
5. The recycling method of papermaking white mud according to claim 1, wherein the fine fraction emulsion is carbonized to form nano calcium carbonate slurry, and the method specifically comprises the following steps:
carrying out carbonization reaction on the fine-fraction emulsion by adopting a three-phase jet carbonization reactor to form nano calcium carbonate slurry;
wherein the diameter of a gas micropore pipe of the three-phase jet carbonization reactor is 1-3 mu m; and/or
The gas pressure of the carbonization reaction is 0.15MPa-0.25 MPa; and/or
The pressure of the slurry of the carbonization reaction is 0.10MPa-0.20 MPa; and/or
The injection speed of the gas-solid-liquid three-phase mixed slurry of the carbonization reaction is 2-6 m/s.
6. The recycling method of papermaking white mud according to claim 1, characterized in that the papermaking white mud is calcined under the set temperature condition to obtain CaO and CO 2 The gas specifically comprises:
calcining the papermaking white mud by adopting a suspension roaster under the condition of set temperature to obtain CaO and CO 2 A gas;
wherein the set temperature is 860 ℃ and 950 ℃; and/or
The calcining time is 2-4 h.
7. The method for recycling papermaking white mud according to claim 1, characterized in that the digested CaO and H 2 The mass ratio of O is 1:4-6; and/or
The temperature of the digestion treatment is 70-85 ℃; and/or
The digestion treatment time is 2-3 h; and/or
The stirring speed of the digestion treatment is 250-350 r/min; and/or
The aging time is 10-12 h; and/or
The curing time is 1.5-2.5 h.
8. The recycling method of papermaking white mud according to claim 1, characterized in that the set cut-off point value is 0.35-0.40 mm.
9. The recycling method of papermaking white mud according to claim 1, wherein the fine fraction emulsion with a set particle size is carbonized at a set carbon-containing gas flow rate to obtain nano calcium carbonate, and the method specifically comprises the following steps:
carrying out carbonization reaction on the fine-fraction emulsion with the set particle size at the set carbon-containing gas flow rate to form nano calcium carbonate slurry, and then curing to obtain cured slurry;
concentrating the cured slurry to obtain supernatant and underflow slurry;
recycling the supernatant to digestion treatment;
washing the underflow slurry, and then carrying out solid-liquid separation and drying to obtain nano calcium carbonate;
wherein the washing detergent is absolute ethyl alcohol, and the dosage of the absolute ethyl alcohol is 18-22 kg/t; and/or
The drying temperature is 85-90 ℃, and the drying time is 10-12 h.
10. The method for recycling papermaking white mud according to claim 8, characterized in that the method further comprises:
reacting the CO with 2 And recycling the gas to the carbonization reaction.
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|---|---|---|---|---|
| CN1438279A (en) * | 2002-03-27 | 2003-08-27 | 东北大学 | Method for preparing high-white ness nano calcium carbide |
| CN102718373A (en) * | 2011-11-01 | 2012-10-10 | 山东大学 | Method for treating white mud produced by papermaking and use of the white mud treated by the method in removal of CO2 in tail flue gas from coal-fired boiler |
| CN103861532A (en) * | 2014-03-03 | 2014-06-18 | 北京旭荣工程设计有限公司 | Homogeneous three-phase reactor for jet aeration |
| CN205676168U (en) * | 2016-05-24 | 2016-11-09 | 广西平南县恒祥钙业有限公司 | A kind of carburizing reagent system of injection reactor and nano-calcium carbonate |
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- 2022-08-01 CN CN202210918420.2A patent/CN115092950A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1438279A (en) * | 2002-03-27 | 2003-08-27 | 东北大学 | Method for preparing high-white ness nano calcium carbide |
| CN102718373A (en) * | 2011-11-01 | 2012-10-10 | 山东大学 | Method for treating white mud produced by papermaking and use of the white mud treated by the method in removal of CO2 in tail flue gas from coal-fired boiler |
| CN103861532A (en) * | 2014-03-03 | 2014-06-18 | 北京旭荣工程设计有限公司 | Homogeneous three-phase reactor for jet aeration |
| CN205676168U (en) * | 2016-05-24 | 2016-11-09 | 广西平南县恒祥钙业有限公司 | A kind of carburizing reagent system of injection reactor and nano-calcium carbonate |
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