Controllable pH regulation and stable dispersion method for coal gangue-based powder

Abstract

The invention discloses a controllable pH regulation and stable dispersion method of coal gangue-based powder. The method comprises the following steps: pretreating coal gangue powder, establishing a buffer system in a water medium, keeping the pH value of the system in a suitable range, and inhibiting ion-induced agglomeration by combining a dispersing agent and an anti-calcium bridging agent; the coupling agent is added to improve the interface bonding between the powder and the polymer, and the stabilizing agent is added to prolong the storage stability of the slurry. The particles can be further depolymerized by adopting wet ball milling or ultrasonic dispersion, and the slurry which still has low viscosity and good fluidity under the condition of high solid content is obtained. The slurry can be directly coated on a stone paper base material to form a functional layer which is firm in adhesion and excellent in ink affinity, and can also be converted into a pre-coated master batch to participate in sheet extrusion after being dried. The method is mild in process, and stable application of the coal gangue powder in the rich mineral paper is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of stone paper raw material processing technology, specifically a method for controllable pH adjustment and stable dispersion of coal gangue-based powder. Background Technology

[0002] Coal gangue is a large amount of solid waste generated during coal mining and washing. It is abundant and mainly composed of silicon dioxide, alumina, carbonates, and small amounts of metal oxides. For a long time, coal gangue has been disposed of primarily through dumping, which not only occupies land but also poses environmental risks. With the development of resource recycling and green materials, how to stably apply coal gangue to new material systems has gradually become a focus of industry attention.

[0003] In the production of highly filled polymer composites such as stone paper, the dispersion stability of powder fillers directly determines the forming quality and performance of the sheets. While coal gangue possesses potential resource value, the complex hydroxyl groups, metal ions, and heterogeneous mineral structure on the particle surface make it prone to agglomeration, sedimentation, and pH drift in aqueous systems, limiting its stability in coating and extrusion processes. Common dispersion methods in the industry mostly involve simple mechanical grinding or reliance on conventional dispersants, which often fail to maintain a uniform state for extended periods under medium-to-high solids content conditions.

[0004] In view of the above problems, a method for controllable pH adjustment and stable dispersion of coal gangue-based powder is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for controllable pH adjustment and stable dispersion of coal gangue-based powders, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for controllable pH adjustment and stable dispersion of coal gangue-based powder, comprising the following steps:

[0007] S1: After pretreatment, coal gangue powder is dispersed in an aqueous medium. Under a set buffer system, the pH of the system is controlled to be on the side away from the isoelectric point of the powder. Anionic dispersant and stabilizer are added to achieve uniform deagglomeration of the powder.

[0008] S2: Further modification measures selected from one or more of the following are implemented during the dispersion process:

[0009] Introducing an organophosphonic acid anti-calcium bridging agent and combining it with a silane coupling agent under alkaline buffer conditions modifies the powder surface and enhances its binding force with aqueous emulsions or polymers.

[0010] The dispersed powder is wet-coated and dried and granulated to form a pre-coated dry powder masterbatch with a coupling layer, so as to maintain uniform dispersion when blended and extruded with polyolefins or grafted modified polyolefins.

[0011] Adding a decomposable microporous agent and an ink-loving resin under weakly alkaline conditions creates a micro-roughened structure on the surface of the base coating and gives it ink affinity.

[0012] S3: The dispersed and modified powder is applied to the base coating, extrusion filler layer or printing coating of stone paper sheet to improve the stability, ink affinity and bonding strength of the coating with the substrate.

[0013] Preferably, the modification measures include: adding an organophosphonic acid anti-calcium bridging agent under buffer conditions of pH 8.8–9.4, wherein the anti-calcium bridging agent is selected from hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylene phosphonic acid (ATMP), or a combination thereof, and the total addition amount is 0.05–0.20% of the inorganic powder mass; and simultaneously or subsequently introducing a silane coupling agent under the pH conditions, so that it reacts with the powder surface after hydrolysis aging for 15–30 minutes, wherein the addition amount of the coupling agent is 0.20–0.80% of the inorganic powder mass.

[0014] Preferably, the modification measures include: dispersing and surface-modified coal gangue powder, reacting it with a dispersant and a coupling agent under pH 9.0-9.5 conditions, then wet-processing it with a solid content of 55-65%, followed by hot air drying or spray drying at ≤90℃ to obtain a pre-coated dry powder masterbatch with a moisture content of no more than 0.2%; when the masterbatch is used for co-extrusion with polyolefin or graft-modified polyolefin, the mass ratio of the pre-coated dry powder to calcium carbonate, graft-modified polyolefin and polyolefin resin is (10-30):(30-50):(2-5):(20-40).

[0015] Preferably, the modification measures include: adding 0.05-0.30% of a decomposable microporous agent to the dispersion system under weakly alkaline conditions of pH 8.8-9.2, so that the resulting coating releases gas during drying at 70-90°C to form a micro-coarsened structure with a surface roughness Ra of 0.8-2.5 μm; and simultaneously introducing 3-10% of an ink-loving resin into the dispersion system, wherein the ink-loving resin is selected from one or more of polyvinyl alcohol, cationic modified chitosan, or carboxyl-containing acrylic emulsion, to improve the ink adsorption and printability of the stone paper surface.

[0016] Preferably, during the dispersion process, changes in zeta potential and pH value are detected online, and acid or alkali is added in real time to form a closed-loop control, so that the absolute value of the zeta potential of the system is stabilized at 35-45mV, and the pH fluctuation range is controlled within ±0.2.

[0017] Preferably, the solid content of the dispersion system is controlled at 40-60%, and the conductivity of the system is limited to no more than 0.8 mS / cm by online conductivity monitoring to ensure dispersion stability and long-term storage performance of the slurry.

[0018] Preferably, the particle size distribution of the dispersed powder slurry satisfies the following: the median particle size D50 is 1.5 to 3.0 μm, and the D90 does not exceed 5.0 μm.

[0019] Preferably, the dispersion slurry is prepared at 25°C and a shear rate of 100s. -1 The viscosity under the specified conditions is controlled within the range of 200–1200 mPa·s to balance high solids content dispersion stability and construction fluidity.

[0020] Preferably, the dispersion slurry has a supernatant liquid fraction of no more than 5% after standing for 24 hours and exhibits no hard sedimentation within 7 days of storage at room temperature.

[0021] Preferably, 0.05-0.30% of a non-adsorbent rheology stabilizer is further added to the dispersion system. The stabilizer is selected from one or more of xanthan gum, hydroxypropyl cellulose, or hydrophobically modified polyether to enhance long-term anti-settling properties without significantly increasing the viscosity of the system.

[0022] Compared with existing technologies, the beneficial effects of this invention are as follows: The method for controllable pH adjustment and stable dispersion of coal gangue-based powder provided by this invention establishes a buffer environment in an aqueous system, far from the isoelectric point of the powder, thereby stabilizing the surface charge of the particles and preventing agglomeration and sedimentation. Simultaneously, the introduction of an anti-calcium bridging agent chelates dissolved ions, eliminating the bridging effect caused by calcium and magnesium ions and ensuring the long-term stability of the dispersion system. The synergistic effect of the dispersant and stabilizer allows the slurry to maintain suitable viscosity and good flowability even under high solids content conditions, facilitating pumping and coating while preventing hard settling and stratification during storage. Through modification with coupling agents or ink-loving resins, the bonding force between the powder and the polyolefin matrix and surface coating is significantly enhanced, improving coating adhesion and ink affinity. The slurry prepared by this method can be used directly as a surface coating layer for stone paper or, after drying, converted into a pre-coated masterbatch for extrusion, taking into account adaptability to different process paths. Compared with traditional methods relying on a single dispersant or strong acid / alkali conditions, this invention demonstrates superior stability, applicability, and material properties. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] This invention provides a technical solution: a method for controllable pH adjustment and stable dispersion of coal gangue-based powder, comprising the following steps:

[0026] S1: After pretreatment, coal gangue powder is dispersed in an aqueous medium. Under a set buffer system, the pH of the system is controlled to be on the side away from the isoelectric point of the powder. Anionic dispersant and stabilizer are added to achieve uniform deagglomeration of the powder.

[0027] S2: Further modification measures selected from one or more of the following are implemented during the dispersion process:

[0028] Introducing an organophosphonic acid anti-calcium bridging agent and combining it with a silane coupling agent under alkaline buffer conditions modifies the powder surface and enhances its binding force with aqueous emulsions or polymers.

[0029] The dispersed powder is wet-coated and dried and granulated to form a pre-coated dry powder masterbatch with a coupling layer, so as to maintain uniform dispersion when blended and extruded with polyolefins or grafted modified polyolefins.

[0030] Adding a decomposable microporous agent and an ink-loving resin under weakly alkaline conditions creates a micro-roughened structure on the surface of the base coating and gives it ink affinity.

[0031] S3: The dispersed and modified powder is applied to the base coating, extrusion filler layer or printing coating of stone paper sheet to improve the stability, ink affinity and bonding strength of the coating with the substrate.

[0032] Based on the above method, the specific operation process of the method will be described in detail below with reference to the embodiments.

[0033] Powder pretreatment (S1): Coal gangue raw material can be initially crushed by a jaw crusher, and then ground by a ball mill to a particle size distribution with D90 ≤ 1000 μm. To avoid agglomeration caused by iron impurities, a magnetic separator is preferred for iron removal. Washing is done with deionized water until the conductivity of the filtrate is ≤ 200 μS / cm. Drying can be done in a forced-air drying oven at a temperature controlled at 105℃ ± 5℃ for 12 hours. For powders requiring surface activation, calcination can be performed in a muffle furnace at 500–750℃ for 0.5–2 hours to increase the number of surface hydroxyl groups, which is beneficial for subsequent dispersion.

[0034] The buffer system (S2) is constructed using deionized water with a conductivity ≤10 μS / cm. 0.05–0.20% sodium bicarbonate or 0.02–0.10 M acetate / sodium acetate buffer is added, and the mixture is thoroughly mixed using a magnetic stirrer. The conductivity is monitored in real-time using a conductivity meter to ensure the solution conductivity is ≤500 μS / cm.

[0035] pH adjustment (S3) involves adjusting the system pH to 8.8–9.4 or 4.5 ± 0.5 using an acid (citric acid, acetic acid) or a base (sodium hydroxide, ammonia, triethanolamine). It is preferable to use a titration pump (accuracy 0.01 mL / s) to add the solution dropwise, and to use an online pH electrode (accuracy ± 0.05) to record the pH curve, avoiding overshoot.

[0036] Adding dispersants and stabilizers (S4): Under the action of a stirrer (200-400 rpm), add polycarboxylate superplasticizer (PCE, 40% solids content, 0.3-0.6% of powder) and sodium hexametaphosphate (SHMP, 0.05-0.15% of powder) sequentially to the buffer solution. If stronger complexing is required, sodium polyacrylate (PAA) can be added. The preferred order of adding dispersants is small molecule SHMP first, followed by large molecule PCE, to avoid premature aggregation of chains.

[0037] Implementation of modification measures (S4)

[0038] Route A: Add HEDP (0.05-0.20%, solids) under buffer conditions, then introduce silane coupling agents (KH-570, APTES, etc.) at pH 9.0±0.3, maintain at 25±1℃ using a constant temperature water bath, and complete hydrolysis aging by magnetic stirring for 20 minutes.

[0039] Route B: Under wet conditions, the solid content is controlled at 55-65%. After grinding in a ball mill (planetary type, 300 rpm) for 60 minutes, the dry powder masterbatch with a moisture content of ≤0.2% is obtained by spray drying in a spray drying tower (inlet air 160℃, outlet air 90℃).

[0040] Route C: Under weakly alkaline conditions, add 0.05-0.30% NH4HCO3, and simultaneously add a graphitizing resin such as PVOH (polyvinyl alcohol, 6%), chitosan, or acrylic emulsion. Drying is performed in two stages in a hot air circulating oven: 60℃ for 2 minutes and 80℃ for 3 minutes to ensure uniform micropore release, with the Ra value controlled between 0.8 and 2.5 μm.

[0041] Depolymerization and Stabilization (S5): The pretreated powder is slowly added to the medium at a solid content of 40-60%, and ground using a planetary ball mill (300 rpm, 60 min). Simultaneously, an ultrasonic disperser (400 W, 10 min) is activated for synergistic depolymerization. The zeta potential is monitored online during this process to ensure an absolute value ≥35 mV. Subsequently, 0.05-0.30% of a non-adsorbent rheology stabilizer (xanthan gum, hydroxypropyl cellulose) is added, followed by 0.01-0.05% of an organosilicon defoamer.

[0042] Filtration and Storage (S6): The mixture is filtered through a 120-mesh sieve to remove coarse particles and air bubbles. The dispersed slurry is then placed in a sealed container and purged with nitrogen headspace to prevent CO2 intrusion and pH drift. The storage temperature is controlled at 25±2℃.

[0043] After processing, the powder particles in the dispersion slurry system are:

[0044] Zeta potential: This is an indicator of the surface charge state of particles (coal gangue powder, calcium carbonate, etc.) in a dispersion system. It is usually tested using electrophoretic light scattering (ELSZ and other equipment) and can reflect the electrostatic stability of powders in an aqueous medium. When tested with an ELSZ-2000 at 25℃, |ζ|=38~42mV;

[0045] Particle size: Measured by a laser particle size analyzer, the particle size in the wet dispersion state is D50 = 2.2 μm and D90 = 4.8 μm;

[0046] Viscosity refers to the rheological properties of the entire powder slurry. It is affected by the degree of powder dispersion, interparticle interactions, and solid content. Essentially, it is a system parameter of powder dispersed in a liquid. It is measured using a rotational rheometer (shear rate 100s). -1 The viscosity was measured to be 650 mPa·s.

[0047] Stability: After standing for 24 hours, the supernatant liquid fraction was 3.5%; no hard sediment was observed after 7 days of storage.

[0048] Stone paper sheet application: The cross-cut adhesion of the base coating reaches 5B, and the ink absorption time of printing is reduced by 28%.

[0049] Specifically, the modification measures include: adding an organophosphonic acid anti-calcium bridging agent under buffer conditions of pH 8.8–9.4, wherein the anti-calcium bridging agent is selected from hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylene phosphonic acid (ATMP), or a combination thereof, and the total addition amount is 0.05–0.20% of the inorganic powder mass; and simultaneously or subsequently introducing a silane coupling agent under the pH conditions, so that it reacts with the powder surface after hydrolysis aging for 15–30 minutes, wherein the addition amount of the coupling agent is 0.20–0.80% of the inorganic powder mass.

[0050] Under buffer conditions of pH 8.8–9.4, organophosphonic acid anti-calcium bridging agents are added in combination with silane coupling agents to inhibit calcium bridging. 2+ This method bridges and enhances the bonding force between powder and polymer. The specific operation, equipment selection, and effect verification of this method are described below.

[0051] 1. Establishing buffer conditions

[0052] Sodium bicarbonate (0.12%, m / m) was added to deionized water (conductivity ≤10 μS / cm), and the solution was stirred magnetically until dissolved. The conductivity was monitored using a conductivity meter and found to be ≤0.6 mS / cm. The pH of the system was then adjusted to 9.0±0.2 by titration with 0.5 mol / L NaOH.

[0053] 2. Addition of anti-calcium bridging agents

[0054] Hydroxyethylidene diphosphonic acid (HEDP) solution was added to the buffer solution using a metering pump (flow rate 0.5 mL / min) to ensure uniform distribution at an addition amount of 0.10% of the powder mass. HEDP selectively chelates Ca... 2+ This effectively reduced the concentration of free calcium ions. The detection method used was EDTA titration. Results showed that free Ca... 2+ It should be controlled within the range of 0.5 to 0.8 mM.

[0055] 3. Powder addition and dispersion

[0056] Pretreated coal gangue powder (D90 = 15 μm, activation temperature 650℃, time 1 h) and light calcium carbonate powder were slowly added. The solid content was set at 50%. The depolymerization process was completed using a planetary ball mill (280 rpm, time 45 min) combined with an ultrasonic disperser (400 W, time 10 min). During this process, the anti-calcium bridging agent reacted with the dissolved calcium carbonate in the system. 2+ This reduces the occurrence of flocculation and aggregation.

[0057] 4. Introduction of silane coupling agents

[0058] Methacryloxypropyltrimethoxysilane (KH-570) was added at pH 9.0 ± 0.3, at a concentration of 0.40% of the powder mass. To promote the hydrolysis reaction, the mixture was first magnetically stirred at 25°C for 20 min to partially hydrolyze it in water to generate silanol. The system was then aged in a constant-temperature water bath (25 ± 1°C) for 25 min, during which the silane molecules condensed with the hydroxyl groups on the powder surface via Si–OH, forming strong chemical bonds.

[0059] 5. Auxiliary stabilizers and defoaming treatment

[0060] After the coupling reaction is complete, 0.15% xanthan gum is added as a non-adsorption stabilizer, and 0.02% silicone defoamer is added. The mixture is then stirred at low speed (100 rpm, 3 min) to distribute it evenly.

[0061] 6. Effect Detection

[0062] · Potential: The ζ potential detected by the electrophoretic light scattering instrument is -39.5mV.

[0063] · Particle size distribution: Detected by laser particle size analyzer, D50 = 2.3 μm, D90 = 4.6 μm.

[0064] · Stability: After standing for 24 hours, the volume fraction of the supernatant was 2.8%, and no hard sediment was observed within 7 days.

[0065] · Application performance: A 10μm dry film thickness coating was prepared on a stone paper substrate, and the adhesion grade was 5B according to the GB / T9286 cross-cut test; it did not peel off after boiling in water for 2 hours.

[0066] 7. Comparative Experiment

[0067] The control system was prepared without HEDP and silane coupling agent, using only PCE dispersion. Results showed a zeta potential of -26 mV, a supernatant liquid fraction of 12% after 24 hours, and a coating adhesion of only 2B, demonstrating the significant synergistic effect of the anti-calcium bridging agent and silane.

[0068] Specifically, the modification measures include: dispersing and surface-modified coal gangue powder, reacting it with a dispersant and a coupling agent under pH 9.0–9.5 conditions, then wet-processing it with a solid content of 55–65%, followed by hot air drying or spray drying at ≤90℃ to obtain a pre-coated dry powder masterbatch with a moisture content of no more than 0.2%; when the masterbatch is used for co-extrusion with polyolefin or graft-modified polyolefin, the mass ratio of the pre-coated dry powder to calcium carbonate, graft-modified polyolefin, and polyolefin resin is (10–30):(30–50):(2–5):(20–40).

[0069] A method for pre-coating and drying dispersed powder to form a pre-coated dry powder masterbatch with a coupling layer is used to ensure uniform dispersion during subsequent co-extrusion with polyolefins or graft-modified polyolefins. The specific operation steps are as follows.

[0070] 1. Construction of wet dispersion system

[0071] Pretreated coal gangue powder (D90≈12μm, activation temperature 650℃, 1h) was mixed with light calcium carbonate powder at a mass ratio of 2:6. Deionized water was used as the dispersion medium, and PCE dispersant (0.5%, based on inorganic powder), SHMP (0.1%), and HEDP (0.1%) were added. The solid content was controlled to be 60% under stirring conditions.

[0072] 2. pH control and coupling agent reaction

[0073] The initial conductivity of the system was 0.6 mS / cm, and the pH was adjusted to 9.3 using NaOH solution. Then, a titanate coupling agent (0.5%, based on powder) was added dropwise, and the system was milled for 60 minutes using a planetary ball mill (300 rpm) to ensure complete adsorption and reaction of the coupling agent. To ensure uniform dispersion, ultrasonic dispersion (500 W, 15 minutes) was simultaneously employed during the milling process.

[0074] 3. Drying and Granulation

[0075] After wet dispersion, the slurry is processed through a spray drying tower: inlet air temperature 160℃, outlet air temperature 85-90℃, atomization pressure 0.5MPa, to obtain spherical dry powder particles with an average particle size of approximately 50μm. The moisture content (dried at 105℃ to constant weight) is 0.18%, which meets the standard of ≤0.2% in the claims.

[0076] 4. Characterization of pre-coated powder

[0077] Scanning electron microscopy (SEM) revealed a uniform and dense coupling agent film on the particle surface; Fourier transform infrared spectroscopy (FTIR) measurements were performed at 1100 cm⁻¹. -1 The presence of Ti–O–C stretching vibration peaks nearby indicates that the titanate ester reacted successfully with the powder surface.

[0078] 5. Blending and extrusion with polyolefins

[0079] The pre-coated dry powder was mixed with calcium carbonate, MAH-grafted polyethylene (MAPE), and HDPE in a mass ratio of 20:30:3:47, and then processed into stone paper sheets using a twin-screw extruder (temperature 185-205℃, speed 60rpm).

[0080] 6. Performance Effect

[0081] · Melt torque: reduced by approximately 9.5% compared to the uncoated powder system;

[0082] · Mechanical properties: Elongation at break increased by 12%; tensile strength increased by 8%;

[0083] · Surface chalking: Taber abrasion test (500g, 500 rpm), the chalking grade decreased from grade 2 in the control to grade 0–1;

[0084] · Dispersion uniformity: When the cross-section of the sheet is observed under an optical microscope, the particles are evenly distributed and there is no obvious agglomeration.

[0085] 7. Controlled experiment

[0086] The system without pre-coated powder exhibits significantly higher melt torque under the same extrusion conditions (approximately...).

[0087] The elongation decreased by 10%, and the surface powdering was severe, which verified the actual effect of pre-coated dry powder masterbatch in improving the processing performance of stone paper.

[0088] Specifically, the modification measures include: adding 0.05-0.30% of a decomposable microporous agent to the dispersion system under weakly alkaline conditions of pH 8.8-9.2, so that the resulting coating releases gas during drying at 70-90°C to form a micro-coarsened structure with a surface roughness Ra of 0.8-2.5 μm; and simultaneously introducing 3-10% of an ink-loving resin into the dispersion system, wherein the ink-loving resin is selected from one or more of polyvinyl alcohol, cationic modified chitosan, or carboxyl-containing acrylic emulsion, to improve the ink adsorption and printability of the stone paper surface.

[0089] Under weakly alkaline conditions, a biodegradable microporous agent and an ink-loving resin are added to the dispersion system. Through a drying process, a slightly roughened surface is formed, enhancing the printability of stone paper. The specific operation is as follows:

[0090] 1. Preparation of distributed systems

[0091] An acetate / sodium acetate buffer pair was established in deionized water to achieve a system pH of 8.9 ± 0.1 and a conductivity of [missing value].

[0092] ≤0.7mS / cm. Add PCE dispersant (0.4%, powder basis) and SHMP (0.1%, powder basis), stir evenly, and then slowly add coal gangue powder (D90≈10μm, activated at 600℃ for 1h) and light calcium carbonate (D50≈2μm). The solid content is set at 45%.

[0093] 2. Addition of microporous agents

[0094] Ammonium carbamate (NH4HCO3) was used as a decomposable microporous agent, added at 0.18% of the total powder mass. The mixture was stirred for 5 minutes (200 rpm) to ensure uniform dispersion of the microporous agent. During the drying stage, NH4HCO3 decomposes to produce CO2 and NH3 gases, forming uniform micropores.

[0095] 3. Introduction of graphitic resins

[0096] Polyvinyl alcohol (PVOH, 88% hydrolysis degree, molecular weight approximately 30k) was added to the system at a concentration of 6% of the total dry matter. To enhance adhesion and ink affinity, cationic modified chitosan can also be used.

[0097] (3%) or carboxylated acrylic emulsion (35% solids, 5% additives). The preferred combination is...

[0098] The combination of PVOH and chitosan provides both film-forming and ink-attracting properties.

[0099] 4. Slurry film formation and drying process

[0100] The prepared dispersion slurry was coated onto the surface of a stone paper substrate, with the coating amount controlled at 8–10 g / m². 2

[0101] (Dry film meter). The drying process uses a hot air circulating oven and is carried out in two stages:

[0102] · Stage 1: Keep warm at 60℃ for 2 minutes to slowly remove some moisture;

[0103] · Stage 2: Heat to 85℃ for 3 minutes to decompose NH4HCO3 and form uniform micropores. After drying, the whiteness of the coating surface did not decrease significantly, and the surface roughness (Ra value) was measured to be...

[0104] 1.4 μm, which is within the range defined by the claims (0.8–2.5 μm).

[0105] 5. Performance Testing

[0106] · Ink affinity for printing: Using an ink absorber, the absorption time is shortened by approximately 27% compared to the untreated primer;

[0107] · Adhesion: GB / T9286 cross-cutting method, grade 4B–5B;

[0108] · Abrasion resistance: Taber test (CS-10 wheel, 500g, 100 rpm), the area of ​​ink layer peeling off was reduced by 35% compared with the control;

[0109] · Surface condition: Scanning electron microscopy revealed uniformly distributed micropores with diameters of 0.5–2 μm, and no through-hole macropores were observed.

[0110] 6. Comparative Experiment

[0111] · Control 1: Without NH4HCO3, only PVOH was added, the Ra value was only 0.3μm, the ink absorption time was prolonged, and the ink spreadability was poor;

[0112] · Control 2: When NH4HCO3 was added directly to the unbuffered system, local calcium carbonate corrosion spots appeared during the drying process, the Ra value was too large and uneven, and the coating adhesion decreased.

[0113] The results show that the synergistic effect of the buffer system, the control of the amount of microporous agent added, and the ink-loving resin is the key to obtaining uniform micro-coarsening and high ink affinity.

[0114] Specifically, during the dispersion process, changes in zeta potential and pH value are detected online, and acid or alkali is added in real time to form a closed-loop control, so that the absolute value of the zeta potential of the system is stabilized at 35-45mV, and the pH fluctuation range is controlled within ±0.2.

[0115] During the dispersion process, changes in zeta potential and pH value are monitored online, and acid or alkali is added in real time to form a closed-loop control, thereby maintaining the stability of the system. This embodiment details its specific implementation steps, equipment configuration, and effects.

[0116] 1. Equipment Configuration

[0117] · Online pH electrode: accuracy ±0.01, real-time monitoring of the acidity and alkalinity of the dispersion system;

[0118] · Zeta potential online detection module: It adopts a flow electrophoretic light scattering instrument (ELS-F type) to continuously sample and measure zeta potential in the slurry circulation path;

[0119] · Metering pump system: Two lines, connected to dilute NaOH (0.5 mol / L) and dilute citric acid (0.5 mol / L) solutions respectively, with a flow rate accuracy of 0.1 mL / min;

[0120] · Central control unit (PLC or microcontroller system): Sets the threshold ranges for ζ potential and pH, and automatically controls the start and stop of the metering pump based on feedback signals.

[0121] 2. Operating Procedures

[0122] In the dispersion step of claim 1, as the powder is gradually added to the system, the pH value and ζ...

[0123] The potential is monitored in real time.

[0124] · Control objectives: Maintain the absolute value of the zeta potential within 35–45 mV; control pH fluctuations within...

[0125] Within ±0.2.

[0126] · When a decreasing trend in the absolute value of the ζ potential is detected (e.g., below 34mV), the control unit triggers the pumping of a trace amount of NaOH or citric acid solution for compensation, causing the ζ potential to rise back to the set range.

[0127] ·If a pH deviation exceeding ±0.2 is detected, the system will automatically adjust the dosage by adding a small amount of medication.

[0128] 3. Supporting measures

[0129] To ensure accuracy, the slurry was tested via a bypass flow cell using a circulating pump (flow rate 5 L / min). The temperature of the test cell was kept constant at 25 ± 1℃ to avoid the influence of temperature drift on the zeta potential.

[0130] 4. Experimental Results

[0131] · Unclosed-loop control: The initial zeta potential of the system was -38mV, which gradually decreased to -28mV after stirring for 60 min. The pH drifted from 9.0 to 8.5, and the supernatant liquid fraction reached 10% after 24 h.

[0132] · Closed-loop control system: the zeta potential was maintained between -37 and -41 mV, the pH fluctuation was within 9.0 ± 0.1, the supernatant liquid fraction was only 3.1% after 24 hours, and there was no hard sedimentation within 7 days.

[0133] 5. Practical Application Results

[0134] After preparing the stone paper base coating using a closed-loop controlled dispersion powder slurry, the ink absorption time was shortened by 25%, and the coating cross-cut adhesion grade was improved to 5B; while the control sample without closed-loop control only reached 3B, and local peeling occurred.

[0135] Specifically, the solid content of the dispersion system is controlled at 40-60%, and the conductivity of the system is limited to no more than 0.8 mS / cm by online conductivity monitoring to ensure dispersion stability and long-term storage performance of the slurry.

[0136] The solid content of the dispersion system is controlled between 40% and 60%, and the conductivity of the system is limited to no more than 0.8 mS / cm through online conductivity monitoring to ensure the dispersion stability and long-term storage performance of the slurry. The specific implementation method is as follows.

[0137] 1. Raw material preparation and dispersion

[0138] · Coal gangue powder: activated at 650℃ for 1 hour, D90≈12μm.

[0139] · Light calcium carbonate: D50≈2μm, whiteness≥90.

[0140] · Dispersants: PCE 0.45%, SHMP 0.10%.

[0141] ·Stabilizer: Xanthan gum 0.15%.

[0142] A sodium bicarbonate buffer system was established in deionized water (conductivity ≤ 10 μS / cm), and the initial conditions were adjusted.

[0143] pH = 9.0 ± 0.1.

[0144] 2. Solid content control

[0145] The powder was slowly added to the medium, with a target solids content set at 50%. Stirring conditions: high-speed disperser 1000 rpm for 15 min; followed by ball milling (280 rpm for 45 min) for further deagglomeration. The solids content of the system was confirmed by weighing, with an error controlled within ±0.5%.

[0146] 3. Conductivity monitoring and control

[0147] · Conductivity meter: online quadrupole probe, measurement range 0–2 mS / cm, accuracy

[0148] ±0.01mS / cm.

[0149] · During the powder dispersion process, the system conductivity increased from the initial 0.15 mS / cm to

[0150] 0.65 mS / cm, and kept within the range of no more than 0.8 mS / cm.

[0151] · If an increasing trend in conductivity occurs (e.g., >0.8 mS / cm), the ion concentration in the system can be reduced by adding deionized water or by using a dialysis membrane (with a molecular weight cutoff of 500 Da).

[0152] 4. Experimental Results

[0153] · Control system (35% solids content, conductivity 1.2 mS / cm): ζ-potential after dispersion –

[0154] 29mV, 24h supernatant liquid fraction 12%, slurry hardened after 7d of storage.

[0155] · Optimized system (50% solids content, conductivity 0.65 mS / cm): ζ-potential –39 mV,

[0156] D50 = 2.5 μm, D90 = 4.8 μm, supernatant liquid fraction of 3.4% after 24 h, and no hard sedimentation after 7 days of storage.

[0157] 5. Application Results

[0158] The stone paper primer was prepared using an optimized system, with a dry film thickness of 10 μm, a cross-cut adhesion rating of 5B, and resistance to boiling in water for 2 hours without peeling off; while the control sample only had a rating of 3B and was accompanied by local peeling.

[0159] Specifically, the particle size distribution of the dispersed powder slurry meets the following requirements: the median particle size D50 is 1.5 to 3.0 μm, and the D90 does not exceed 5.0 μm.

[0160] The particle size distribution of the dispersed powder slurry meets the following requirements: median particle size D50 is 1.5–3.0 μm, and D90 does not exceed 5.0 μm. The following explains the results under the following production conditions:

[0161] 1. Raw material processing and feeding

[0162] Coal gangue raw material is crushed and activated (temperature 600-700℃, time 1 hour), then sieved and set aside. After being premixed with light calcium carbonate powder in a certain proportion, it is evenly added to the dispersion tank via a screw conveyor.

[0163] 2. Dispersion tank and buffer medium

[0164] The dispersion tank is equipped with an online stirrer (variable frequency speed control, speed range 200-1500 rpm) and contains deionized water and bicarbonate buffer. The initial solid content of the system is controlled at 45-55%, the conductivity is not higher than 0.8 mS / cm, and the pH is adjusted to 9.0±0.1.

[0165] 3. Addition of dispersants and stabilizers

[0166] Polycarboxylate dispersant (0.3–0.6%, powder basis) and sodium hexametaphosphate (0.05–0.15%, powder basis) are continuously added to the dispersion tank via a metering pump. To maintain uniform dispersion over a long period, a non-adsorbent stabilizer (0.1–0.3%) may be added. All additives are monitored by an online flow meter.

[0167] 4. Depolymerization and particle size control

[0168] The slurry is circulated through a wet ball mill (cylinder speed 250–300 rpm, grinding media filling rate 60%) for 30–60 minutes. An ultrasonic dispersion module (power 300–500W) can be connected in series in the pipeline to assist deagglomeration. This process combination ensures that coal gangue and calcium carbonate particles are uniformly deagglomerated to the monomer scale.

[0169] 5. Online monitoring and control

[0170] A laser particle size online detection unit is installed on the discharge pipeline to monitor D50 and D90 in real time. The control system links the feedback signal with the process parameters. If the detection result exceeds the target range (D50>3.0μm or D90>5.0μm), the ball milling time is automatically extended or the ultrasonic power is increased until the particle size meets the standard.

[0171] 6. Characteristics of the product slurry

[0172] The slurry obtained under production line conditions has a stable particle size distribution: D50 1.8–2.5μm, D90 4.0–4.8μm, with a narrow distribution and good repeatability. This slurry can be directly used for stone paper primer or filling processes, ensuring coating uniformity and sheet mechanical properties.

[0173] By strictly controlling the particle size distribution within the aforementioned range, we can avoid both the roughness and powdering of the coating caused by excessively large particles, and the excessively fine particles that lead to excessively high viscosity and increased energy consumption. This control strategy achieves a balance between efficient dispersion and stable production, making it suitable for continuous industrial production.

[0174] Specifically, the dispersion slurry is at 25°C and a shear rate of 100s. -1 The viscosity under the specified conditions is controlled within the range of 200–1200 mPa·s to balance high solids content dispersion stability and construction fluidity.

[0175] Dispersion slurry at 25℃ and shear rate 100s -1 Under ideal conditions, the viscosity should be controlled between 200 and 1200 mPa·s to balance high solids content dispersion stability with workability. In industrial production, this viscosity range is achieved through the coordinated control of dispersant dosage, solids content ratio, and energy input. In the production process, coal gangue and calcium carbonate powder are pretreated and added to the dispersion tank in proportion, maintaining a solids content of 45-55%, while the pH is stabilized at 9.0±0.1 using a bicarbonate buffer system. The dispersant consists of 0.3-0.6% polycarboxylate superplasticizer and 0.05-0.15% sodium hexametaphosphate, continuously added by a metering pump and monitored by an online flow meter. The depolymerization process uses a wet ball mill at 250-300 rpm for 40-60 min, with an ultrasonic module (300-500W) connected in series for auxiliary dispersion. Under these conditions, the slurry viscosity remains at 600-800 mPa·s, exhibiting good flowability, which is beneficial for pumping and coating.

[0176] If the viscosity is higher than 1200 mPa·s, it is usually caused by excessive solids content or insufficient dispersant, which can be corrected by adding a small amount of dispersant or diluting with deionized water. If it is lower than 200 mPa·s, the slurry system is too thin, which will lead to particle sedimentation and uneven film formation. The solids content can be appropriately increased or the amount of dispersant reduced. Online viscosity detection uses a rotational rheometer in conjunction with an automatic sampling device, and the data is fed back to the control system in real time to achieve closed-loop control of viscosity. This process reduces energy consumption while ensuring slurry stability, thus balancing production continuity and coating quality. Compared with the traditional process that relies on high-energy ball milling but does not control viscosity, this method significantly reduces the risk of slurry sedimentation and improves the application adaptability and final surface uniformity of stone paper primer or filler processes.

[0177] Specifically, the dispersion slurry has a supernatant liquid fraction of no more than 5% after standing for 24 hours and no hard sedimentation phenomenon after being stored at room temperature for 7 days.

[0178] To achieve this requirement, the production process relies not only on dispersants but also on the comprehensive control of potential regulation, solid content ratio, and stabilizers. In actual production, after the coal gangue and calcium carbonate powder are dispersed and deagglomerated, the pH of the system is controlled at 9.0±0.1, and the absolute value of the zeta potential is maintained at 35-45mV to ensure sufficient electrostatic repulsion between particles. Simultaneously, a small amount of non-adsorbent rheology stabilizer (such as xanthan gum 0.1-0.3% and hydroxypropyl cellulose 0.05-0.2%) is introduced to inhibit particle sedimentation by forming a weak physical network structure without significantly increasing the system viscosity.

[0179] The slurry is stored in a sealed container with headspace nitrogen purging to prevent pH drift caused by CO2 intrusion. The storage tank is equipped with a slow-speed paddle agitator (20 rpm), which is automatically activated for 5 minutes daily to prevent slight settling caused by prolonged standing. Industrial-scale testing shows that after continuous standing at 25°C for 24 hours, the supernatant liquid fraction is controlled at 3-4%, which meets the scope of the claims; further extended to 7 days, no significant hard settling is observed, and the slurry can be restored to uniform dispersion through simple stirring.

[0180] The advantage of this process lies in its ability to fundamentally reduce particle agglomeration through stable control of zeta potential and conductivity. Furthermore, the microstructure support provided by a non-adsorbent stabilizer gives the slurry excellent static tolerance, eliminating the need for excessively high viscosity to maintain suspension. This ensures both application fluidity and long-term storage stability. This measure allows the production line to supply materials in large batches while avoiding frequent stirring or rework, improving the continuity and economy of the stone paper primer and filling processes.

[0181] Specifically, 0.05–0.30% of a non-adsorbent rheology stabilizer is further added to the dispersion system. The stabilizer is selected from one or more of xanthan gum, hydroxypropyl cellulose, or hydrophobically modified polyether to enhance long-term anti-settling properties without significantly increasing the viscosity of the system.

[0182] Adding 0.05–0.30% of a non-adsorbent rheology stabilizer to the dispersion system enhances long-term anti-settling properties without significantly increasing the system viscosity. This measure is particularly crucial in industrial production because both coal gangue and calcium carbonate powder have high densities, and relying solely on the charge repulsion of the dispersant may still result in slow settling during long-term storage.

[0183] In the production process, after dispersion is complete and the zeta potential is confirmed to have reached a stable value, a stabilizing agent is uniformly added to the dispersion tank via a metering pump. Suitable stabilizing agents include xanthan gum, hydroxypropyl cellulose (HPC), or hydrophobically modified polyether (HEUR), with xanthan gum being the most commonly used at an addition rate of 0.1%. The stabilizing agent does not strongly adsorb onto the powder surface but forms a low-concentration three-dimensional network structure in the aqueous phase, damping particle movement and effectively inhibiting sedimentation.

[0184] To ensure effective addition, the stabilizer is diluted with deionized water and dissolved under high shear in a separate premix tank before being pumped to the main dispersion tank. After addition, the viscosity of the system increases only slightly (approximately 50–80 mPa·s), remaining within the range of 200–1200 mPa·s specified in claim 8, and will not affect pumping and coating.

[0185] Application results show that the slurry modified with the stabilizer showed no significant hardening after 14 days of storage at room temperature, and the supernatant liquid fraction after 24 hours of settling further decreased to 2–3%. Compared with the system without the stabilizer, the sedimentation delay effect was significant. The advantage of this measure is that it achieves long-term storage stability at extremely low cost and dosage, avoiding rework or blockage caused by sedimentation, and is particularly suitable for continuous feeding and large-scale applications in stone paper production lines.

[0186] The core of this invention lies in preparing a stable dispersion slurry with high solids content and controllable pH of coal gangue-based powder. Depending on subsequent processes, the slurry can be applied in two ways:

[0187] One type is direct coating application. After dispersion and stabilization, the slurry can be directly used as a base coating, surface coating, or ink-receptive coating in the stone paper production process. In this type of process, after the stone paper sheet is extruded, the slurry is evenly coated onto the surface of the substrate using a coating machine, and then dried and cured by hot air or infrared drying to form a functional layer with strong adhesion, a smooth surface, and good printability.

[0188] Another type is extrusion filling applications. When the slurry is used as the main filler for stone paper sheets, it needs to be spray-dried or cryogenically dried to transform it into a pre-coated dry powder masterbatch with a coupling layer. This masterbatch is then blended with polyolefins (PE / PP) and graft-modified polyolefins (such as MAPE) in a specific ratio and plasticized into sheets using a twin-screw extruder. Through dispersion and surface modification treatments in the slurry stage, the final dry powder filler is uniformly distributed in the molten system, thereby reducing extrusion energy consumption and improving the mechanical properties and surface uniformity of the sheet.

[0189] Therefore, although the embodiments of the present invention all take the preparation of slurry as the basic step, the slurry obtained can be used directly as a functional coating or dried and converted into a masterbatch for extrusion, which has process flexibility and wide application.

[0190] Example 2

[0191] First, regarding the powder raw materials, coal gangue, after crushing and screening, is fed into a muffle furnace and calcined at 700℃ for 0.5 hours to remove some organic impurities and activate its surface hydroxyl groups. The calcined coal gangue powder is then sieved to obtain particles with a D90 of approximately 15 μm. Unlike commonly used light calcium carbonate, this embodiment uses kaolin as an auxiliary filler, with a D50 of approximately 1.5 μm and a whiteness of not less than 85. Coal gangue and kaolin are mixed at a mass ratio of 1:3 and fed as the main powder raw material. This combination provides superior hiding power and mechanical strength in stone paper coatings or filler layers, while avoiding the Ca content issues found in single calcium carbonate systems. 2+ Excessive release of bridges can cause bridging issues.

[0192] For the dispersion medium, deionized water (conductivity ≤10 μS / cm) was used, and a boric acid / borax buffer was added to form a buffer system. The concentration of the buffer system was controlled at 0.02 mol / L, the pH was maintained in the range of 8.7–9.2, and the conductivity was maintained in the range of 0.5–0.7 mS / cm. Compared with the bicarbonate buffer system, the boric acid / borax buffer is more resistant to the intrusion of carbon dioxide from the environment, avoids long-term pH drift, and is suitable for continuous production and storage conditions.

[0193] The dispersant system uses sodium polyacrylate (PAA, molecular weight 5000, added at 0.4% of powder mass) and sodium metasilicate (Na2SiO3, added at 0.1% of powder mass). Sodium polyacrylate provides strong anionic charge repulsion through its carboxyl groups, while sodium metasilicate hydrolyzes in water to generate polysilicate ions, which can form a silica sol protective layer on the particle surface, further enhancing the steric hindrance effect. The synergistic effect of the two can significantly reduce the risk of powder agglomeration.

[0194] To further stabilize the system and avoid Ca 2+ Mg 2+To prevent plasma-induced agglomeration, this embodiment uses ethylenediaminetetramethylenephosphonic acid (EDTMP) as the anti-calcium bridging agent, added at 0.12% of the powder mass. The polyphosphonic acid groups and multidentate complexation of EDTMP enhance its chelating ability for divalent ions, thus more effectively reducing the concentration of free calcium ions in the slurry. Tests show that after adding EDTMP, the concentration of free calcium ions in the system is significantly reduced. 2+ The concentration can be stably controlled at 0.5–0.7 mM.

[0195] For the coupling agent, γ-aminopropyltriethoxysilane (APTES) was used at an addition amount of 0.5% of the powder mass. Under conditions of pH ≈ 8.9, this silane was first hydrolyzed in water for 20 minutes to generate –Si–OH groups, which then condensed with hydroxyl groups on the surface of coal gangue and kaolin to form strong Si–O–Si bonds, thereby introducing amino functional groups onto the surface of the inorganic powder. This modification not only improved the compatibility of the powder with organic polymers but also enhanced the adhesion between the subsequent stone paper substrate and the base coating.

[0196] The deagglomeration process employs a horizontal sand mill with a circulation flow rate of 10 L / min, a rotor linear velocity of 10 m / s, and a grinding time of approximately 40 minutes. A 400W online ultrasonic device is connected in series at the mill outlet to perform high-frequency cavitation dispersion of the slurry. The combination of mechanical impact and ultrasonic cavitation effectively breaks down secondary aggregates of powder, ensuring narrower and more uniform particle size distribution.

[0197] To further improve anti-settling performance, a hydrophobically modified polyether (HEUR-type thickener) was added at the end of the slurry, at a dosage of 0.2% of the powder mass. HEUR molecules form a physical network structure in the aqueous phase through hydrophobic association, effectively inhibiting particle settling while having limited effect on viscosity improvement. Online rotational rheometer testing showed that the slurry at 25℃ and a shear rate of 100s⁻¹ exhibited good viscosity. -1 The viscosity is maintained at 700–850 mPa·s, which is within the suitable range for construction.

[0198] The final slurry had a zeta potential of -36mV, and laser particle size analyzer results showed D50≈2.1μm and D90≈4.6μm. After standing at room temperature for 24 hours, the supernatant liquid fraction was approximately 3.5%, and no hard settling was observed after 7 days of storage. This slurry was used for coating stone paper sheets, and according to the GB / T9286 cross-cutting test, it achieved an adhesion grade of 4B, and the ink absorption time was reduced by approximately 22%.

[0199] By changing the buffer system, dispersant, and coupling system, it was demonstrated that this method does not rely on a single formulation to achieve stable dispersion. In particular, the strong chelating effect of EDTMP and the surface protective layer formation mechanism of Na2SiO3 significantly enhance the system's anti-agglomeration ability. Simultaneously, the introduction of the HEUR stabilizer enables the system to possess excellent anti-settling properties under suitable viscosity conditions. This example fully demonstrates that this dispersion method has strong formulation compatibility and process flexibility, and can be adjusted according to different powder raw materials and production conditions to maintain stable performance.

[0200] Example 3

[0201] Firstly, regarding the powder raw materials, coal gangue was calcined at 650℃ for 1 hour and then sieved to a D90≈12μm. In this embodiment, calcium carbonate or kaolin is no longer used; instead, talc powder is selected as an auxiliary filler. Talc powder has a distinct flaky structure, D50≈2.5μm, a Mohs hardness of 1, and exhibits good lubricity and lamellar orientation. Coal gangue and talc powder are mixed and fed at a mass ratio of 2:5. This combination not only improves the flexibility of the stone paper coating but also reduces frictional resistance and improves surface smoothness during extrusion.

[0202] Deionized water was used as the dispersion medium, and a sodium bisulfate / sodium sulfate buffer system was introduced to control the pH of the system at 8.5–8.9. This type of buffer has a high buffering capacity in the slightly acidic–weakly alkaline range, making it suitable for talc surface treatment. This is because talc surfaces contain magnesium hydroxyl groups, and excessively high pH levels can easily lead to the dissolution of magnesium ions. This buffer system effectively inhibits the release of magnesium ions, maintaining the stability of the talc layer structure.

[0203] The dispersant system was changed to sodium lignosulfonate (0.4% added, based on powder) and sodium polyaspartate (0.2% added, based on powder). Sodium lignosulfonate, as a macromolecular anionic dispersant, can form an adsorption layer on the particle surface; sodium polyaspartate has excellent metal ion complexing ability and can prevent magnesium and calcium ion-induced flocculation. The synergistic effect of the two allows the system to maintain stable dispersion even at high solid content.

[0204] To further improve the adhesion between the powder and the polyolefin substrate, this embodiment uses a titanate coupling agent (NDZ-201) at an addition amount of 0.6% of the powder mass. In the system, the titanate binds to the hydroxyl groups on the surface of talc and coal gangue via transesterification, forming an organic long-chain structure on the particle surface, thus enhancing the affinity of the powder in the polymer matrix. The anti-calcium bridging agent is phosphorous acid (H3PO3) at an addition amount of 0.15% (based on powder mass), which, under weakly alkaline conditions, inhibits calcium bridging. 2+ Mg 2+ It has a good complexing effect, avoiding the problem of "magnesium salt bridging" in talc slurry.

[0205] The deagglomeration equipment used was a continuous stirred ball mill with a rotation speed of 260 rpm, a grinding media filling rate of 65%, and a grinding time of 50 minutes. To prevent over-grinding from causing the flake talc powder to break, the internal temperature of the ball mill was controlled below 35℃. To enhance the dispersion effect, a 300W ultrasonic vibration module was connected in parallel in the pipeline to perform intermittent cavitation dispersion of the slurry (2 minutes on, 3 minutes off, cycling).

[0206] Hydroxypropyl methylcellulose (HPMC) was added as a stabilizer at the end of the slurry, at an addition amount of 0.25% of the powder mass. HPMC forms a weak gel structure in the aqueous phase, which does not significantly increase the viscosity of the system, but effectively prevents particle settling. The viscosity was measured using an online rheometer at 25°C and a shear rate of 100 s⁻¹. -1 The viscosity of the slurry was approximately 650 mPa·s, and it had good fluidity.

[0207] Testing revealed that the system had a zeta potential of -34 mV, and laser particle size analyzer measurements showed D50≈2.4 μm and D90≈4.9 μm. After standing at 25°C for 24 hours, the supernatant liquid fraction was 4%, and no hardening or settling was observed after 7 days of storage. When used to make stone paper-filled sheets, the surface smoothness was significantly improved, the bending performance was superior to traditional calcium carbonate systems, and ink transfer was excellent under high-speed printing conditions.

[0208] By introducing talc instead of calcium carbonate, stone paper gains better flexibility and smoothness; a sulfate buffer system effectively controls the release of magnesium ions from the talc surface; sodium lignosulfonate and sodium polyaspartate are selected as dispersants, providing both electrostatic steric stabilization and metal ion complexation; titanate coupling agents improve the compatibility of the powder with polyolefins, while HPMC stabilizers ensure long-term storage stability. This example demonstrates that this method is not only applicable to calcium carbonate or kaolin systems but can also be successfully applied to talc systems, exhibiting broader raw material compatibility and industrial application potential.

[0209] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for controllable pH adjustment and stable dispersion of coal gangue-based powder, characterized in that, Includes the following steps: S1: After pretreatment, coal gangue powder is dispersed in an aqueous medium. Under a set buffer system, the pH of the system is controlled to be on the side away from the isoelectric point of the powder. Anionic dispersant and stabilizer are added to achieve uniform deagglomeration of the powder. S2: Further modification measures selected from one or more of the following are implemented during the dispersion process: Introducing an organophosphonic acid anti-calcium bridging agent and combining it with a silane coupling agent under alkaline buffer conditions modifies the powder surface and enhances its binding force with aqueous emulsions or polymers. The dispersed powder is wet-coated and dried and granulated to form a pre-coated dry powder masterbatch with a coupling layer, so as to maintain uniform dispersion when blended and extruded with polyolefins or grafted modified polyolefins. Adding a decomposable microporous agent and an ink-loving resin under weakly alkaline conditions creates a micro-roughened structure on the surface of the base coating and gives it ink affinity. S3: The dispersed and modified powder is applied to the base coating, extrusion filler layer or printing coating of stone paper sheet to improve the stability, ink affinity and bonding strength of the coating with the substrate.

2. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 1, characterized in that: The modification measures include: adding an organophosphonic acid anti-calcium bridging agent under buffer conditions of pH 8.8–9.4, wherein the anti-calcium bridging agent is selected from hydroxyethylidene diphosphonic acid (HEDP), aminotrimethylene phosphonic acid (ATMP) or a combination thereof, and the total addition amount is 0.05–0.20% of the inorganic powder mass; and simultaneously or subsequently introducing a silane coupling agent under the pH conditions, so that it reacts with the powder surface after hydrolysis aging for 15–30 minutes, wherein the addition amount of the coupling agent is 0.20–0.80% of the inorganic powder mass.

3. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 1, characterized in that: The modification measures include: dispersing and surface-modified coal gangue powder, reacting it with a dispersant and a coupling agent under pH 9.0-9.5 conditions, then wet-processing it with a solid content of 55-65%, followed by hot air drying or spray drying at ≤90℃ to obtain a pre-coated dry powder masterbatch with a moisture content of no more than 0.2%; when the masterbatch is used for co-extrusion with polyolefin or graft-modified polyolefin, the mass ratio of the pre-coated dry powder to calcium carbonate, graft-modified polyolefin and polyolefin resin is (10-30):(30-50):(2-5):(20-40).

4. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 1, characterized in that: The modification measures include: adding 0.05-0.30% of a decomposable microporous agent to the dispersion system under weakly alkaline conditions of pH 8.8-9.2, so that the resulting coating releases gas during drying at 70-90°C to form a micro-coarsened structure with a surface roughness Ra of 0.8-2.5 μm; and simultaneously introducing 3-10% of an ink-loving resin into the dispersion system, wherein the ink-loving resin is selected from one or more of polyvinyl alcohol, cationic modified chitosan, or carboxyl-containing acrylic emulsion, to improve the ink adsorption and printability of the stone paper surface.

5. A method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to any one of claims 1-4, characterized in that: During the dispersion process, changes in zeta potential and pH value are detected online, and acid or alkali is added in real time to form a closed-loop control, so that the absolute value of the zeta potential of the system is stabilized at 35-45mV, and the pH fluctuation range is controlled within ±0.

2.

6. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 5, characterized in that: The solid content of the dispersion system is controlled at 40-60%, and the conductivity of the system is limited to no more than 0.8 mS / cm by online conductivity monitoring to ensure dispersion stability and long-term storage performance of the slurry.

7. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 6, characterized in that: The particle size distribution of the dispersed powder slurry meets the following requirements: the median particle size D50 is 1.5 to 3.0 μm, and the D90 does not exceed 5.0 μm.

8. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 7, characterized in that: The dispersion slurry was subjected to a shear rate of 100s at 25°C. -1 The viscosity under the specified conditions is controlled within the range of 200–1200 mPa·s to balance high solids content dispersion stability and construction fluidity.

9. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 8, characterized in that: The dispersion slurry, after standing for 24 hours, has a supernatant liquid fraction of no more than 5%, and shows no hard sedimentation within 7 days of storage at room temperature.

10. The method for controllable pH adjustment and stable dispersion of coal gangue-based powder according to claim 8, characterized in that: 0.05–0.30% of a non-adsorbent rheology stabilizer, selected from one or more of xanthan gum, hydroxypropyl cellulose, or hydrophobically modified polyether, is further added to the dispersion system to enhance long-term anti-settling properties without significantly increasing the viscosity of the system.