Resin carbonization separation and recovery process of coated sand waste

Abstract

The application discloses a resin carbonization separation and recovery process for coated sand waste, and relates to the technical field of separation and recovery, which comprises the following steps: pretreating coated sand waste to obtain pretreated particles comprising sand particle matrix and a coated resin layer coated on the surface of the sand particle matrix; performing interface-oriented limited oxygen carbonization treatment on the pretreated particles, so that the coated resin layer preferentially carbonizes along the contact interface between the sand particle matrix and the coated resin layer, and primary carbonized particles with a continuous interface carbonized shell layer formed on the surface are obtained; performing outward migration and enrichment treatment on the primary carbonized particles to form an outward migration and enrichment shell; and then performing selective brittle fracture and peeling treatment and grading separation to obtain regenerated sand and resin carbonization recovery products, which can promote the outward migration and enrichment of residual components and the overall peeling, reduce the acid consumption value of the regenerated sand, reduce the damage to the sand particle matrix, and improve the separation efficiency and resource utilization level of the resin carbonization recovery products.

Description

Technical Field

[0001] This invention relates to the field of separation and recycling technology, specifically to a resin carbonization separation and recycling process for coated sand waste. Background Technology

[0002] As the foundry industry continues to demand higher precision, dimensional stability, and production efficiency in complex core forming, coated sand, due to its excellent fluidity, shell-forming properties, and surface quality control capabilities, has been widely used in engine blocks, cylinder heads, water jacket cores, and thin-walled precision castings.

[0003] While existing technologies can recover some coated sand waste, most solutions still remove the resin layer through high-temperature roasting, mechanical scrubbing, or a combination of both. The focus is mainly on removing the resin film from the surface of the sand grains and then reusing the recycled sand. These technologies typically do not control the interfacial changes of the resin layer on the sand grain surface, nor do they treat the migration, enrichment, and separation of alkaline residues, inorganic ash, and carbonization products as a complete process. As a result, problems such as damage to the sand grain matrix, high acid consumption, poor compatibility with recoating, unstable core performance, and difficulty in recycling carbonaceous components are likely to occur. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the technical solution of this invention is as follows: The resin carbonization separation and recycling process for coated sand waste includes the following steps: Pre-treatment of coated sand waste yields pre-treated particles, which consist of a sand matrix and a coating resin layer covering the surface of the sand matrix. The pretreated particles are subjected to interface-guided oxygen-limited carbonization treatment, which causes the coated resin layer to preferentially carbonize along the contact interface between the sand matrix and the coated resin layer, resulting in primary carbonized particles with a continuous interface carbonized shell on the surface. The primary carbonized particles are subjected to an external migration enrichment treatment, which causes the alkaline residue and inorganic ash on the surface of the sand matrix to migrate and accumulate outward along the continuous interface carbonized shell layer, forming enriched carbonized particles with an external migration enrichment shell on the outside of the primary carbonized particles. Selective brittle exfoliation treatment is performed on enriched carbonized particles to allow the continuous interface carbonized shell and the external enriched shell to be separated from the surface of the sand matrix as an integrated shell structure, resulting in an exfoliation mixture, which includes the exposed sand matrix and the exfoliated shell. The stripping mixture is graded and separated to obtain recycled sand and resin carbonization recovery.

[0005] Furthermore, the interface-guided oxygen-limited carbonization treatment was carried out under conditions of oxygen volume fraction of 0.8%–2.5% and heating rate of 8℃ / min–25℃ / min. After the particle temperature rises to 430℃~620℃, it is kept at that temperature for 2min~15min. The carbonization of the resin coating begins at the interface between the sand matrix and the resin coating. The continuous interface carbonized shell grows outward along the normal direction of the sand grain matrix surface, and after treatment, primary carbonized particles are obtained.

[0006] Furthermore, the continuous interfacial carbonized shell forms a continuous coating area on the surface of the sand grain matrix; The continuous coating area corresponds to the area where the coating resin layer was originally attached to the surface of the sand matrix; The continuous interface carbonized shell contains migration channels extending along the thickness direction.

[0007] Furthermore, the migration enrichment treatment was carried out at a particle temperature of 450℃~580℃; The duration of the relocation enrichment treatment is 1 min to 8 min; Alkaline residues and inorganic ash migrate to the outer side of the continuous interface carbonized shell through migration channels; Alkaline residues and inorganic ash accumulate on the outer surface of the continuous interface carbonized shell, forming an externally enriched shell. Based on the external enrichment shell and the continuous interface carbonization shell, the continuous interface carbonization shell and the external enrichment shell together form a double-layer separation shell structure on the surface of the enriched carbonization particles. Among them, alkaline residues include at least one of potassium salts, sodium salts, and calcium salts.

[0008] Furthermore, the double-layered separated shell structure includes a continuous interfacial carbonized shell and an externally enriched cladding shell; In the double-layer separated shell structure, the continuous interface carbonized shell layer constitutes the inner layer close to the sand grain matrix, and the outward migration enrichment shell layer constitutes the outer layer located outside the continuous interface carbonized shell layer. The exogenous enrichment shell and the continuous interface carbonized shell maintain a layered bonding state that allows for synchronous cracking.

[0009] Furthermore, the endpoints of the interface-guided oxygen-limited carbonization treatment and the migration enrichment treatment are determined by combining the exhaust gas detection signal and the particle surface state detection signal, respectively. The sampling period was 15s to 60s; within 2 to 5 consecutive sampling periods, the total hydrocarbon release rate decreased to 5% to 20% of the peak value of the migration and enrichment stage and remained stable; the change rate of the comprehensive color value of the particle surface remained stable; based on this, it was determined that the migration and enrichment process was completed.

[0010] Furthermore, the selective brittle fracture peeling process employs self-friction disturbance; The frictional linear velocity of the self-friction disturbance is 1.0 m / s to 4.0 m / s; the action time is 0.5 min to 5 min. The double-layered shell structure preferentially undergoes brittle fracture under self-friction disturbance and detaches from the surface of the sand matrix, while the sand matrix remains intact.

[0011] Furthermore, the self-friction disturbance is carried out at a temperature of 120℃~280℃ when the enriched carbonized particles are concentrated; The double-layered separation shell structure becomes brittle and detaches within the temperature range of 120℃ to 280℃ when enriched carbonized particles; The sand matrix remains largely intact within this temperature range.

[0012] Furthermore, the hierarchical separation includes first separation and second separation; The first separation process strips the mixture to obtain a first stream rich in exposed sand grain matrix and a second stream rich in stripped shells; The second separation process treats the second stream to obtain resin carbonization recovery material; The first separation method uses air separation, with an air velocity of 6 m / s to 15 m / s. The second separation method uses electrostatic separation, with an electric field strength of 1.0 kV / cm to 3.0 kV / cm.

[0013] The beneficial effects of this invention are as follows: 1. By using interface-guided oxygen-limited carbonization treatment, the coated resin layer preferentially starts carbonization from the contact interface between the sand matrix and the coated resin layer, and forms a continuous interface carbonization shell on the surface of the sand matrix. This avoids the direct and disorderly burning away of the resin layer, and is conducive to establishing a continuous coating area and migration channel on the surface of the sand matrix. This provides a stable basis for the subsequent migration of residual components and shell peeling, while also helping to reduce the risk of thermal damage and breakage of the sand matrix.

[0014] 2. Through the external enrichment treatment, alkaline residues and inorganic ash migrate outward along the continuous interface carbonized shell layer, forming an external enrichment shell on the outer surface. Combined with self-friction disturbance, the double-layer separation shell structure composed of the continuous interface carbonized shell layer and the external enrichment shell preferentially undergoes brittle fracture and detaches as a whole. This can transform the residues originally attached to the surface of the sand matrix into a shell structure that can be separated as a whole, which is beneficial to reduce the acid consumption value of the regenerated sand and improve the separation efficiency and purity of the resin carbonized recovery.

[0015] 3. Combining interface-guided oxygen-limited carbonization treatment with external migration enrichment treatment can not only form a continuous interface carbonization shell with migration channels, but also further form a double-layer separation shell structure that can crack synchronously. Combined with graded separation, high-quality recycled sand and resin carbonization recovery products can be obtained at the same time. This not only improves the resource utilization of coated sand waste, but also takes into account the integrity of the sand matrix, residue control and by-product recovery. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process steps of the present invention; Figure 2 This is a schematic diagram of the evolution of the particle surface structure in this invention; Figure 3 This is a schematic diagram of the peeling and grading separation process of the present invention; Figure 4 This is a schematic diagram of the morphology after selective brittle fracture and peeling according to the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 Please see Figure 1 , Figure 3 and Figure 4 This invention provides a resin carbonization separation and recycling process for coated sand waste, comprising the following steps: Pre-treatment of coated sand waste yields pre-treated particles, which consist of a sand matrix and a coating resin layer covering the surface of the sand matrix. The pretreated particles are subjected to interface-guided oxygen-limited carbonization treatment, which causes the coated resin layer to preferentially carbonize along the contact interface between the sand matrix and the coated resin layer, resulting in primary carbonized particles with a continuous interface carbonized shell on the surface. The primary carbonized particles are subjected to an external migration enrichment treatment, which causes the alkaline residues and inorganic ash on the surface of the sand matrix to migrate and accumulate to the outside along the continuous interface carbonized shell, resulting in enriched carbonized particles with an external migration enrichment shell on the outside. Selective brittle exfoliation treatment is performed on enriched carbonized particles to allow the continuous interface carbonized shell and the external enriched shell to be separated from the surface of the sand matrix as an integrated shell structure, resulting in an exfoliation mixture, which includes the exposed sand matrix and the exfoliated shell. The stripping mixture is graded and separated to obtain recycled sand and resin carbonization recovery.

[0019] In this embodiment, coated sand waste generated during the production of a cast iron water jacket core was selected as the test material.

[0020] The coated sand waste uses quartz sand as the sand particle matrix, and the surface of the sand particle matrix is ​​coated with a phenolic resin coating layer, and contains a small amount of alkaline residues and inorganic ash from raw materials and production processes.

[0021] Pre-treatment of coated sand waste aims to reduce agglomeration, remove metallic impurities, narrow particle size distribution, and make the exposed state of the outer surface of the coated resin layer more uniform, thereby providing uniform starting conditions for subsequent interface-guided oxygen-limited carbonization treatment.

[0022] Specifically, the coated sand waste is first lightly crushed to dissociate the agglomerated material into single particles and small aggregates; then ferromagnetic impurities are removed by magnetic separation; the target particle size is then retained by sieving; finally, free water is removed under low-temperature drying conditions to obtain pretreated particles.

[0023] After the above treatment, the pretreated particles include a sand matrix and a coating resin layer on the surface of the sand matrix, and the degree of agglomeration between particles is significantly reduced, which facilitates uniform heating during the heat treatment process.

[0024] The resulting pretreated particles are fed into a heat treatment unit with oxygen-limited atmosphere control capability for interface-guided oxygen-limited carbonization treatment.

[0025] During the process, the oxygen volume fraction in the reaction atmosphere is controlled at 0.8% to 2.5%, preferably 1.4%. The heating rate is controlled at 8℃ / min to 25℃ / min, preferably 12℃ / min; The particle temperature is raised to 430℃~620℃, preferably to 520℃ and then held for 2min~15min, preferably 6min.

[0026] Under the above conditions, the coated resin layer does not undergo disordered ablation from the outer surface inward, but rather preferential carbonization occurs along the contact interface between the sand matrix and the coated resin layer.

[0027] As the interface carbonization progresses, a continuous interface carbonization shell layer gradually forms on the inner side of the coated resin layer, closely adhering to the surface of the sand grain matrix.

[0028] The continuous interface carbonized shell has a continuous coating characteristic, and its distribution area on the surface of the sand grain matrix corresponds to the area where the coating resin layer was originally attached to the surface of the sand grain matrix. After this step, primary carbonized particles with a continuous interface carbonized shell on the surface are obtained.

[0029] Compared with the traditional high-temperature integral calcination method, the beneficial effects of this step are: on the one hand, it preserves the intermediate state of the carbonized shell layer that can be peeled off later, and on the other hand, it avoids the over-burning and fine powdering of the sand matrix surface caused by the direct integral burning away of the coating resin layer.

[0030] After obtaining the primary carbonized particles, the primary carbonized particles are subjected to external migration and enrichment treatment.

[0031] The migration enrichment process is carried out at a particle temperature of 450℃ to 580℃, preferably around 520℃, for a duration of 1 min to 8 min, preferably 3 min.

[0032] During this process, the alkaline residues and inorganic ash on the surface of the sand matrix no longer remain on the surface of the sand matrix, but migrate outward along the migration path formed by the micropores and cracking inside the continuous interface carbonized shell, and gradually accumulate on the outer surface of the continuous interface carbonized shell.

[0033] As migration and aggregation continue, an external enrichment shell forms on the outer side of the continuous interface carbonized shell. The external enrichment shell enriches alkaline residues and inorganic ash from the original coating system and production process. The alkaline residues may include at least one of potassium salts, sodium salts and calcium salts.

[0034] After relocation and enrichment treatment, enriched carbonized particles are obtained.

[0035] At this point, the continuous interface carbonized shell and the outward enrichment shell together form an integrated shell structure that can be detached as a whole on the surface of the enriched carbonized particles.

[0036] The beneficial effect of this step is that it transforms the residual components that were originally close to the surface of the sand matrix and difficult to remove directly into an enriched layer located on the outside of the shell, thereby creating conditions for subsequent overall stripping and helping to reduce the acid consumption value and surface residue of the final recycled sand.

[0037] After cooling the enriched carbonized particles to a state window suitable for brittle exfoliation, selective brittle exfoliation is performed.

[0038] Preferably, the temperature for enriching carbonized particles is controlled at 120°C to 280°C, and more preferably at about 190°C.

[0039] Within this temperature range, the integrated shell structure consisting of the continuous interface carbonized shell and the outward enrichment shell maintains high brittleness, while the sand grain matrix can still maintain its main integrity.

[0040] Selective brittle fracture stripping is preferably achieved by particle-to-particle self-grinding friction, where the enriched carbonized particles are in contact friction while tumbling and sliding against each other. The apparent linear velocity of the particle group is controlled to be 1.0 m / s to 4.0 m / s, preferably 2.2 m / s, and the processing time is controlled to be 0.5 min to 5 min, preferably 2.5 min.

[0041] Through the above treatment, the integrated shell structure preferentially undergoes brittle fracture and detaches from the surface of the sand matrix as a whole, while the main body of the sand matrix does not undergo significant breakage.

[0042] After this step, a stripping mixture is obtained, which includes the exposed sand grain matrix and the stripping shell layer.

[0043] The beneficial effect of this step is that the object being peeled is transformed from the residual film and surface dirt in the traditional recycling process into a shell with structural integrity. Therefore, selective detachment can be achieved with lower mechanical strength, thus balancing peeling efficiency and sand matrix protection.

[0044] Subsequently, the stripping mixture is graded and separated to achieve dual-product recovery of recycled sand and resin carbonization recyclables.

[0045] First, the stripped mixture is separated by air classification, with the air velocity controlled at 6 m / s to 15 m / s, preferably 10 m / s. By utilizing the differences in apparent density, morphology and aerodynamic behavior between the exposed sand matrix and the stripped shell, a first stream rich in exposed sand matrix and a second stream rich in stripped shell are obtained.

[0046] The second material is then subjected to electrostatic separation, with the electric field strength controlled at 1.0 kV / cm to 3.0 kV / cm, preferably 1.8 kV / cm, to further separate the components with higher carbon content from the entrained non-target inorganic fine powder, thereby obtaining the resin carbonization recovery material.

[0047] After necessary cooling and granulation, the first batch of material can be used as recycled sand, while the resin carbonization recyclables can be collected separately as recycled carbonaceous materials.

[0048] The beneficial effect of this step is that, in this embodiment, the coating resin is no longer simply regarded as an impurity to be eliminated, but is transformed into a stream of carbonaceous products that can be independently recycled through the aforementioned shelling and overall peeling process, thereby simultaneously realizing the regeneration of sand matrix and the recovery of resin carbides.

[0049] When using the process route of this embodiment, the pretreatment step creates uniform incoming material conditions for subsequent heat treatment; the interface-guided oxygen-limited carbonization treatment causes the coated resin layer to preferentially carbonize along the interface and form a continuous interface carbonized shell layer; the outward migration enrichment treatment causes alkaline residues and inorganic ash to migrate to the outer surface of the shell layer and form an outward migration enrichment shell; the selective brittle peeling treatment causes the integrated shell structure to detach as a whole; and the graded separation step recovers the exposed sand grain matrix and the peeled shell layer separately.

[0050] Therefore, this embodiment can achieve resin carbonization separation and recycling of coated sand waste under low damage conditions, taking into account the quality of recycled sand, acid consumption control and carbonization recovery output, and is suitable for casting production scenarios that need to improve the recycling rate of coated sand and reduce the secondary pollution burden.

[0051] Example 2 Please refer to Figure 1 , Figure 3 and Figure 4Specifically: the interface-guided oxygen-limited carbonization treatment is carried out under the conditions of an oxygen volume fraction of 0.8% to 2.5% and a heating rate of 8℃ / min to 25℃ / min; After the particle temperature rises to 430℃~620℃, it is kept at that temperature for 2min~15min. The carbonization of the resin coating begins at the interface between the sand matrix and the resin coating. The continuous interface carbonized shell grows outward along the normal direction of the sand grain matrix surface, and after treatment, primary carbonized particles are obtained.

[0052] A continuous interface carbonized shell forms a continuous coating zone on the surface of the sand grain matrix; The continuous coating area corresponds to the area where the coating resin layer was originally attached to the surface of the sand matrix; The continuous interface carbonized shell contains migration channels extending along the thickness direction.

[0053] In this embodiment, the same application scenario as in Embodiment 1 is used, namely, the coated sand waste generated by a cast iron water jacket core production line is selected as the test raw material, and the verification is carried out with the same raw material baseline.

[0054] The coated sand waste uses quartz sand as the sand matrix, with an average particle size of 0.28 mm, an original loss on ignition of 2.48%, an original acid consumption value of 7.5 mL / 50 g, and a coating resin mass fraction of 2.8%. The raw material contains a small amount of potassium salt, sodium salt, and calcium salt residues brought in by the coating system and production aids, and also shows localized agglomerated particles and attached ash.

[0055] First, the raw materials were pretreated in the same way as in Example 1, that is, a low-pressure roller pressing method was used to gently deagglomerate the large agglomerates without breaking the main sand particle matrix. Then, a permanent magnet roller was used to remove ferromagnetic impurities. Next, the particles were sieved to retain the 0.15mm to 0.60mm particle size. Finally, the particles were dried at 105°C for 35 minutes to reduce the free water content to below 0.20% to obtain pretreated particles.

[0056] The pretreated particles were fed into a rotary heat treatment device with oxygen-limited atmosphere control capability, and the interface-guided oxygen-limited carbonization treatment window in this embodiment was verified.

[0057] In the experimental group, the oxygen volume fraction was controlled at 1.4%, the heating rate was 12℃ / min, and the particle temperature was held at 520℃ for 6 minutes.

[0058] To avoid deviations caused by furnace temperature replacing particle temperature, thermocouples are installed inside the material layer, and infrared temperature measurement results are used for verification.

[0059] During the process, the coated resin layer was not directly oxidized and ablated from the outer surface. Instead, a carbonization initiation zone was first formed at the interface between the sand matrix and the coated resin layer. Then, it was pushed outward along the normal direction of the sand matrix surface, and finally a continuous interface carbonization shell was formed on the sand matrix surface.

[0060] The continuous interface carbonized shell forms a continuous coating area on the surface of the sand grain matrix, which corresponds to the area where the coating resin layer was originally attached to the surface of the sand grain matrix.

[0061] To verify the existence of continuous coating zones and migration channels, processed particles were sampled, embedded, and polished, and their cross-sections were observed using optical and scanning electron microscopes. Simultaneously, image analysis software was used to calculate the coverage of the continuous coating zone, and micropores and fractured microchannels extending along the thickness direction were identified in combination with the cross-sectional morphology, which were then used as migration channels.

[0062] The results show that under the in-window processing conditions, the continuous interface carbonized shell has high integrity, and a relatively continuous thickness direction migration path can be observed inside the shell.

[0063] Compared to conditions where oxygen content, heating rate, holding temperature, or holding time deviate from the range, conditions within the window are more conducive to preferential carbonization of the coating resin layer from the contact interface, and the formation of a continuous coating area and migration channel without causing significant surface overheating.

[0064] The purpose of this step is to provide a stable structural basis for subsequent relocation and enrichment treatment, enabling alkaline residues and inorganic ash to migrate outward along the continuous interface carbonized shell. Its beneficial effect is to transform the "disordered pyrolysis" in traditional thermal regeneration into "interface preferential carbonization", thereby improving the repeatability of subsequent shell construction and overall stripping.

[0065] Table 1: Comparison of the effects of interface-guided oxygen-limited carbonization treatment parameters on the formation of continuous interface carbonized shells. Parameter name Example 2 of the present invention - within the window Comparative Example A - Below Range Group Comparative example B - higher than the range group Comparative Example C - Existing Thermal Method Group Raw material batch (kg) 50 50 50 50 Average particle size (mm) 0.28 0.28 0.28 0.28 Original ignition reduction (%) 2.48 2.48 2.48 2.48 Original acid consumption value (mL / 50g) 7.5 7.5 7.5 7.5 Resin mass fraction (%) 2.8 2.8 2.8 2.8 Oxygen volume fraction (%) 1.4 0.4 3 20.9 Heating rate (°C / min) 12 6 28 12 Particle insulation temperature (°C) 520 420 640 760 Insulation time (min) 6 1 18 10 Initial carbonization percentage at the interface (%) 89 41 64 29 Continuous coverage area (%) 92 52 67 35 Migration channel identification rate (%) 85 37 55 24 Primary carbonized particle integrity rate (%) 95 96 79 71 Particle surface overheating index 0.11 0.04 0.43 0.81 Subsequent Relocation and Accumulation Potential Index 8.8 3.6 5.7 2.8 Energy consumption per unit (kWh / t) 147 141 166 238 As can be seen from Table 1, Example 2 of the present invention is significantly better than the lower range group, the higher range group and the existing thermal method group in terms of the three core indicators directly corresponding to this embodiment: “interface initial carbonization ratio, continuous coating area coverage rate and migration channel identification rate”.

[0066] Under the conditions within the window, the initial carbonization rate of the interface reached 89%, indicating that the coated resin layer can preferentially initiate carbonization from the sand matrix-coated resin layer contact interface; the coverage rate of the continuous coating area reached 92%, indicating that the continuous interface carbonized shell layer and the original attachment area of ​​the coated resin layer have a high degree of correspondence; the identifiability rate of the migration channel reached 85%, indicating that a high proportion of thickness-direction pathways were formed inside the shell layer, providing a structural basis for subsequent external migration and enrichment.

[0067] In contrast, in Comparative Example A, the oxygen content, heating rate, holding temperature, and holding time were all below the range. Although the surface overburning index was the lowest, the initial carbonization ratio at the interface was only 41%, and the coverage of the continuous coating area was only 52%. This indicates that when the parameters are generally low, although the resin layer is not easily over-oxidized, it is difficult to form a sufficiently complete continuous carbonized shell at the interface.

[0068] In Comparative Example B, the parameters were generally higher than the range. Although the initial carbonization ratio at the interface increased to 64%, the surface overheating index increased significantly, and the integrity rate of primary carbonized particles decreased. This indicates that excessively high parameters can disrupt the continuity of the shell and introduce thermal damage.

[0069] Comparative Example C represents the conventional high-temperature thermal method of air roasting. Its initial carbonization rate at the interface is only 29%, the coverage rate of the continuous coating area is only 35%, and the identifiability of the migration channel is only 24%. This indicates that the dominant mechanism of the existing conventional thermal method is overall oxidation burn-off, rather than interface-guided oxygen-limited carbonization.

[0070] This demonstrates that the oxygen volume fraction of 0.8% to 2.5%, the heating rate of 8°C / min to 25°C / min, the particle temperature of 430°C to 620°C, and the holding time of 2 min to 15 min in this embodiment are not arbitrarily set, but rather serve as a synergistic window for the stable construction of a continuous interface carbonized shell, a continuous coating region, and a migration channel.

[0071] The beneficial effect of this window is that it distinguishes itself from "insufficient carbonization" below the range and "excessive oxidation" above the range or from existing thermal methods, thus providing a feasible structural basis for subsequent relocation enrichment treatment and overall stripping treatment.

[0072] Example 3 Please refer to Figure 1 , Figure 3 and Figure 4 Specifically: the migration and enrichment treatment is carried out at a particle temperature of 450℃~580℃; The duration of the relocation enrichment treatment is 1 min to 8 min; Alkaline residues and inorganic ash migrate to the outer side of the continuous interface carbonized shell through migration channels; Alkaline residues and inorganic ash accumulate on the outer surface of the continuous interface carbonized shell, forming an externally enriched shell. Among them, alkaline residues include at least one of potassium salts, sodium salts, and calcium salts.

[0073] The dual-layer separated shell structure includes a continuous interfacial carbonized shell and an external migration and enrichment cladding shell; In the double-layer separated shell structure, the continuous interface carbonized shell layer constitutes the inner layer close to the sand grain matrix, and the outward migration enrichment shell layer constitutes the outer layer located outside the continuous interface carbonized shell layer. The exogenous enrichment shell and the continuous interface carbonized shell maintain a layered bonding state that allows for synchronous cracking.

[0074] The endpoints of interface-guided oxygen-limited carbonization treatment and migration enrichment treatment are determined by a combination of exhaust gas detection signals and particle surface state detection signals, respectively.

[0075] The sampling period was 15s to 60s; within 2 to 5 consecutive sampling periods, the total hydrocarbon release rate decreased to 5% to 20% of the peak value of the migration and enrichment stage and remained stable; the change rate of the comprehensive color value of the particle surface remained stable; based on this, it was determined that the migration and enrichment process was completed.

[0076] In this embodiment, the same application scenario as in Embodiment 1 is used, namely, the coated sand waste generated by a cast iron water jacket core production line is selected as the test raw material.

[0077] The coated sand waste uses quartz sand as the sand matrix, with an average particle size of 0.28 mm, an original loss on ignition of 2.48%, an original acid consumption value of 7.5 mL / 50 g, a coating resin mass fraction of 2.8%, and contains potassium, sodium and calcium salt residues from the coating system and production aids, as well as a small amount of inorganic ash and locally agglomerated particles.

[0078] To ensure comparability between the examples, the pretreatment method was consistent with that of Example 1: first, the agglomerated material was deagglomerated using a low-pressure roller pressing method to dissociate the agglomerates without causing the main body of the sand particle matrix to break; then, ferromagnetic impurities were removed by a permanent magnet roller; subsequently, the particles were screened to retain the 0.15mm to 0.60mm particle size; finally, the particles were dried at 105℃ for 35 minutes to reduce the free water content to below 0.20% to obtain pretreated particles.

[0079] The obtained pretreated particles were fed into a rotary heat treatment device with oxygen-limited atmosphere control capability. First, interface-guided oxygen-limited carbonization treatment was carried out according to the window conditions of Example 2, that is, the oxygen volume fraction was controlled at 1.4%, the heating rate was 12℃ / min, and the particle temperature was raised to 520℃ and held for 6min.

[0080] Primary carbonized particles are obtained after the process.

[0081] In this embodiment, this step serves as the foundation for the external migration enrichment process. Its purpose is not to burn off the entire coating resin layer, but to pre-form a continuous interfacial carbonized shell on the surface of the sand matrix and establish migration channels extending along the thickness direction inside the shell, thereby providing structural conditions for the subsequent migration of alkaline residues and inorganic ash to the outside.

[0082] After obtaining the primary carbonized particles, an external migration enrichment treatment is carried out. This treatment is conducted at a particle temperature of 520℃ for 3 minutes. During the treatment, potassium salts, sodium salts, calcium salts, and inorganic ash located on the surface of the sand matrix no longer remain on the surface. Instead, they migrate outwards along the migration channels within the continuous interface carbonized shell and accumulate on the outer surface, gradually forming an externally migrated enriched coating. The endpoint of the external migration enrichment treatment is not determined by a single time control, but rather by a combination of exhaust gas detection signals and particle surface condition detection signals.

[0083] The exhaust gas detection uses an online total hydrocarbon analyzer. The sampling probe is set in the straight pipe section between the exhaust gas outlet of the external enrichment treatment device and the cooling section to reduce the measurement deviation caused by condensation and retention. The sampling cycle is set to 30 seconds.

[0084] The peak total hydrocarbon release rate is defined as the maximum total hydrocarbon release rate recorded during a single migration enrichment treatment stage. In this embodiment, when the total hydrocarbon release rate drops to less than 10% of the peak value of the migration enrichment treatment stage within three consecutive sampling periods, and the fluctuation between adjacent sampling points does not exceed ±5% of the value measured at the previous sampling point, the total hydrocarbon release rate is considered to remain stable.

[0085] The particle surface condition detection uses an industrial camera for image acquisition, with the light source color temperature fixed at 6500K, the camera resolution fixed at 2448×2048 pixels, the shooting height fixed at 180mm, and the background board using a black non-reflective matte board.

[0086] In each sampling cycle, no fewer than 50 particles are taken from the sampling port, spread out evenly, and photographed. The comprehensive colorimetric values ​​of the particle surface are then statistically analyzed using image analysis software.

[0087] The rate of change of the overall chromaticity value is calculated as the ratio of the difference between the average overall chromaticity values ​​of two consecutive sampling periods to the average overall chromaticity value of the previous sampling period.

[0088] In this embodiment, when the rate of change of the comprehensive colorimetric value is not higher than 1.5% / min in three consecutive sampling periods, the surface state of the particles is considered to be stable.

[0089] The migration enrichment process is considered complete only when both the total hydrocarbon release rate and the rate of change in the overall color value simultaneously meet the above conditions. The advantage of this endpoint determination method is that it avoids relying solely on experience or single-time control to determine the treatment endpoint, thereby improving the repeatability and industrial implementation stability of the migration enrichment process.

[0090] To verify the formation of the exogenous enrichment shell and the double-layered separation shell structure, cross-sectional samples and morphological analysis were performed on the enriched carbonized particles after the exogenous enrichment treatment.

[0091] Two hundred enriched carbonized particles were randomly selected from each sample group, encapsulated in thermosetting resin, and then subjected to coarse grinding, fine grinding, and polishing to obtain the particle cross-section.

[0092] Cross-sectional observations were performed using scanning electron microscopy, and elemental distribution was determined using energy dispersive spectroscopy (EDS). To avoid subjectivity in sampling areas, the inner baseline region was uniformly selected as the inner 1 / 3 thickness of the continuous interfacial carbonized shell adjacent to the outer surface of the sand grain matrix; the outer enrichment region was uniformly selected as the area from the outer surface of the continuous interfacial carbonized shell to the outer surface of the outward enrichment cladding.

[0093] The enrichment factor of K+Na+Ca on the outer side is calculated as the ratio of the total content of potassium, sodium and calcium in the outer region to the total content of the corresponding elements in the inner baseline region.

[0094] In this embodiment, the enrichment factor of K+Na+Ca on the outer side is 2.9, indicating that the alkaline residue has significantly migrated from the surface of the sand matrix to the outer surface of the continuous interface carbonized shell.

[0095] The migration enrichment shell coverage rate is obtained through cross-sectional statistics. That is, when the continuous coverage length of the enrichment layer on the outer periphery of the particle is not less than 70% of the outer periphery length of the continuous interface carbonized shell, the particle is considered to have formed a migration enrichment shell. In this embodiment, the migration enrichment shell coverage rate is 88%.

[0096] If a continuous interfacial carbonized shell, an outward-migrating enrichment shell, and a clear interlayer boundary are observed simultaneously in the same batch of cross-sectional particles, then the particles are considered to have formed a double-layer separated shell structure. In this embodiment, the formation rate of the double-layer separated shell structure is 86%.

[0097] To further verify whether a layered bonding state capable of synchronous cracking has been formed between the exogenous enriched shell and the continuous interfacial carbonized shell, the enriched carbonized particles were cooled to 190℃, and a verification peeling test was conducted using a particle-to-particle self-grinding friction method. The apparent linear velocity of the particle group was 2.2 m / s, and the action time was 2.5 min.

[0098] After peeling, 200 particles were randomly selected to observe the fracture morphology of the shell. If the continuous interface carbonized shell and the outward enriched shell cracked together on the same particle and detached as a whole, it was identified as a synchronously cracked particle.

[0099] The synchronous cracking rate in this embodiment is 82%.

[0100] The integrity rate of the sand particles after stripping is calculated as the ratio of the mass of intact sand particles to the total mass of the exposed sand particle matrix. In this embodiment, it reaches 94%.

[0101] After complete processing, the acid consumption value of the regenerated sand decreased to 2.3 mL / 50 g, and the purity of the resin carbonization recovery reached 73%. This indicates that the double-layer separation shell structure formed by the external migration and enrichment process can not only migrate alkaline residues and inorganic ash from the surface of the sand matrix and enrich them in the outer layer, but also allow them to crack and detach as a whole under subsequent mechanical action, thereby simultaneously achieving residue migration, reduced acid consumption value, protection of the sand matrix, and high-purity separation of the carbonization recovery.

[0102] Unlike existing high-temperature thermal scrubbing methods, the core of this embodiment is not to enhance the cleaning power, but to transform the problem of "difficult-to-remove surface residues" into "easily peelable overall shell" through the construction of an intermediate structure. This is also the core creative basis of this embodiment.

[0103] Table 2: Verification Table of Parameters for Migration Enrichment Treatment and Endpoint Determination Parameter name Example 3 of the present invention - within the window Comparative Example A-1 - Below the Range Group Comparative Example B-1 - Higher Range Group Comparative Example C-1 - Existing Thermal Direct Scrubbing Group Raw material batch (kg) 50 50 50 50 Average particle size (mm) 0.28 0.28 0.28 0.28 Original ignition reduction (%) 2.48 2.48 2.48 2.48 Original acid consumption value (mL / 50g) 7.5 7.5 7.5 7.5 Resin mass fraction (%) 2.8 2.8 2.8 2.8 Interface-guided oxygen-limited carbonization treatment conditions 1.4% oxygen / 12℃ / min / 520℃ / 6min 1.4% oxygen / 12℃ / min / 520℃ / 6min 1.4% oxygen / 12℃ / min / 520℃ / 6min Air / 12°C / min / 760°C / min Temperature for relocation and enrichment treatment (°C) 520 430 600 none Relocation enrichment processing time (min) 3 0.5 10 0 Sampling period (s) 30 10 75 not applicable Number of consecutive sampling periods (times) 3 1 6 not applicable Total hydrocarbon release rate threshold (% peak value) 10 3 25 not applicable Overall chromaticity value change rate stability threshold (% / min) 1.5 3.8 2.9 not applicable Outward enrichment shell coverage rate (%) 88 39 57 14 External enrichment factor of K+Na+Ca 2.9 1.1 1.7 1 Double-layer separated shell structure formation rate (%) 86 33 51 11 Synchronous cracking rate (%) 82 28 41 9 Sand grain integrity rate after peeling (%) 94 95 78 72 Acid consumption value of regenerated sand (mL / 50g) 2.3 5 4.1 5.6 Purity (%) of resin carbonization recycled material 73 35 47 15 Energy consumption per unit (kWh / t) 156 148 173 233 As can be seen from Table 2, the core advantage of Example 3 of the present invention is not just that a certain parameter is in the middle value, but that the migration enrichment treatment temperature, treatment time, sampling cycle, number of consecutive sampling cycles and total hydrocarbon release rate determination threshold together constitute a collaborative window.

[0104] Within this window, alkaline residues and inorganic ash can migrate outward along the continuous interface carbonized shell, forming a well-covered, significantly enriched outer shell suitable for overall cracking on the outer surface of the shell.

[0105] In Example 3 of this invention, the coverage rate of the outer enrichment shell reached 88%, the enrichment factor of K+Na+Ca on the outside reached 2.9, the formation rate of the double-layer separated shell structure reached 86%, and the synchronous cracking rate reached 82%. This indicates that under the conditions of 520℃, 3min, 30s sampling cycle, 3 consecutive sampling cycles, and the total hydrocarbon release rate dropping to below 10% of the peak value, an ideal interlayer relationship was established between the outer enrichment shell and the continuous interface carbonized shell.

[0106] The results are directly reflected in the reduction of acid consumption value of regenerated sand to 2.3 mL / 50 g and the increase of purity of resin carbonization recovery to 73%, proving that this embodiment is not only superior to the comparative example in terms of intermediate structure, but also has obvious advantages in final process effect.

[0107] In Comparative Example A-1, the migration enrichment treatment temperature of 430℃, the treatment time of 0.5 min, the sampling cycle of 10 s, the continuous sampling cycle of 1, and the total hydrocarbon threshold of 3% peak value were all lower than the ranges defined in this embodiment.

[0108] The integrity rate of the sand particles after stripping reached 95%, indicating that the thermal damage was small. However, the coverage rate of the outer enrichment shell was only 39%, the enrichment multiple of K+Na+Ca on the outside was only 1.1, the formation rate of the double-layer separation shell structure was only 33%, the synchronous cracking rate was only 28%, and the acid consumption value of the regenerated sand was still as high as 5.0mL / 50g.

[0109] The results indicate that when the overall parameters are too low, the alkaline residues and inorganic ash migrate outwards insufficiently, making it difficult for the outer layer of the outward enrichment shell to form a complete outer layer. At the same time, too short a sampling period, insufficient number of consecutive sampling periods, and too low a total hydrocarbon threshold setting will cause the treatment to terminate prematurely, thereby further weakening the outward enrichment process.

[0110] Therefore, being below the range does not mean "milder and safer," but rather results in "the process being terminated before the double-layered shell structure is established," which fails to support the core technical effect of the present invention.

[0111] In Comparative Example B-1, the migration enrichment treatment temperature of 600℃, treatment time of 10 min, sampling cycle of 75 s, continuous sampling cycles of 6, and total hydrocarbon threshold peak of 25% were all higher than the specified range. The migration enrichment shell coverage rate increased to 57% in this group, and the enrichment factor for K+Na+Ca on the outer surface reached 1.7, indicating that high temperature and long-term treatment do indeed promote a certain degree of migration enrichment. However, the formation rate of the double-layer separation shell structure was only 51%, the synchronous cracking rate was only 41%, and the integrity rate of sand particles after peeling decreased to 78%, indicating that excessively high parameters can introduce significant side effects.

[0112] The reasons are as follows: on the one hand, excessively high temperatures and excessively long durations can cause local densification or sintering of the outer layer, destroying the "interlayer bonding state that can crack synchronously"; on the other hand, excessively long sampling periods and excessively large number of consecutive periods can delay the determination of the endpoint, causing the outward enrichment process that should have stopped to continue, thereby causing excessive thermal damage to the shell.

[0113] Therefore, an overall high parameter will not naturally lead to a better double-layer separation shell structure. Instead, it will cause the outer enrichment shell to change from a "peelable outer layer" to a "locally over-bound outer layer", ultimately weakening the subsequent peeling and separation effect.

[0114] Comparative Example C-1 uses the existing thermal direct scrubbing route, without external enrichment treatment, and there is no endpoint determination based on the total hydrocarbon release rate and the overall color value change rate.

[0115] The group had an external enrichment shell coverage rate of only 14%, a double-layer separation shell structure formation rate of only 11%, a synchronous cracking rate of only 9%, a regenerated sand acid consumption value as high as 5.6 mL / 50 g, and a resin carbonization recovery purity of only 15%.

[0116] This indicates that the main mechanism of the traditional route is still "overall oxidation + surface scrubbing," which cannot establish a double-layer separation shell structure composed of a continuous interfacial carbonized shell and an externally migrated enriched shell, let alone achieve overall deshelling through intermediate structure control. Therefore, the difference between Example 3 of this invention and existing thermal methods lies not in whether heat treatment was performed, but in whether a double-layer separation shell structure suitable for overall cracking was constructed through controlled external migration enrichment treatment and objective endpoint determination.

[0117] Based on the structural characterization results in Table 2 and Example 3 of this invention, two conclusions can be drawn.

[0118] First, the boundary parameters in this embodiment are not arbitrarily selected, but rather a collaborative window formed around the core concept of "formation of an outer shell for migration and enrichment - establishment of a double-layer separation shell structure - formation of an interlayer bonding state that can be cracked simultaneously"; the conditions within the window can take into account the degree of residual migration, the stability of interlayer relationships, and the feasibility of subsequent stripping.

[0119] Secondly, the process logic of this invention differs from the traditional "high-temperature burning + mechanical scrubbing" route. Instead of obtaining clean sand by increasing the decontamination intensity, it transforms the surface residue problem into an overall shell peeling problem by constructing an intermediate structure. It is precisely this structure-oriented process route that enables Example 3 of this invention to simultaneously outperform the comparative example in terms of acid consumption value, sand particle integrity rate after peeling, and purity of the resin carbonization recovery product.

[0120] Example 4 Please refer to Figure 1 , Figure 3 and Figure 4 Specifically: the selective brittle fracture peeling treatment employs self-friction disturbance; The frictional linear velocity of the self-friction disturbance is 1.0 m / s to 4.0 m / s; the action time is 0.5 min to 5 min. The double-layered shell structure preferentially undergoes brittle fracture under self-friction disturbance and detaches from the surface of the sand matrix, while the sand matrix remains intact.

[0121] Self-friction disturbance is carried out when the temperature of enriched carbide particles is 120℃~280℃; The double-layered separation shell structure becomes brittle and detaches within the temperature range of 120℃ to 280℃ when enriched carbonized particles; The sand matrix remains largely intact within this temperature range.

[0122] In this embodiment, the same application scenario as in Embodiments 1, 2, and 3 is adopted, namely, the coated sand waste generated by a cast iron water jacket core production line is selected as the test raw material, and the verification is carried out with the same raw material baseline.

[0123] This embodiment focuses on verifying the self-friction disturbance and temperature window in this embodiment.

[0124] "Self-friction disturbance" refers to the process of frictional peeling formed by the interaction of enriched carbonized particles under external driving, including tumbling, sliding, rubbing, and slight shearing between particles. It does not rely on rigid friction elements to directly apply strong impact to the particles.

[0125] This method differs from traditional high-intensity mechanical scrubbing. Its core lies in utilizing the higher brittleness and lower interlayer crack resistance threshold of the double-layer separation shell structure compared to the sand matrix, causing the shell to preferentially fracture and detach.

[0126] In this embodiment, "friction linear velocity" is defined as the apparent velocity of the particle group along the main direction of motion within the self-friction disturbance device, which is calculated from the linear velocity of the rotating drum and the slip velocity of the particle layer.

[0127] "Maintaining the integrity of the sand matrix" means that after self-friction disturbance, the proportion of sand particles without obvious fractures, chipping, and pulverization is maintained at a high level after sieving and microscopic analysis.

[0128] "Preferential brittle fracture in double-layered shell structures" means that, within the same processing time, the proportion of overall shell cracking and detachment is significantly higher than the proportion of sand particles breaking apart.

[0129] In this embodiment, a particle-to-particle self-friction disturbance device is used to selectively fracture and peel off the enriched carbonized particles.

[0130] Preferably, the temperature for enriching carbonized particles is controlled at 190°C, which is located in the middle of the 120°C to 280°C window.

[0131] The particle filling rate inside the device is controlled at 45%, so that the particles continuously undergo self-friction contact while tumbling and sliding; the apparent friction linear velocity is controlled at 2.2 m / s, and the action time is controlled at 2.5 min.

[0132] No additional hard abrasive media is introduced during the process, nor are rigid impact blades installed, in order to reduce the direct impact on the sand particle matrix.

[0133] After the stripping process, the samples were graded and statistically analyzed.

[0134] "Synchronous cracking rate" is defined as the proportion of particles in a randomly selected sample of 200 particles in which the continuous interface carbonized shell and the external enriched shell crack together and detach as a whole; "sand grain integrity rate after peeling" is defined as the proportion of sand grains in the exposed sand grain matrix after peeling that have not undergone obvious fracture, chipping, or pulverization; "shell detachment rate" is defined as the proportion of particles whose shells detach from the particle surface after peeling.

[0135] The results showed that under the conditions of 190℃, 2.2m / s and 2.5min, the double-layered shell structure preferentially underwent brittle fracture and detached from the surface of the sand matrix, with a synchronous cracking rate of 84%, a shell detachment rate of 89%, and a sand grain integrity rate of 94% after peeling.

[0136] Compared to temperature ranges below and above the specified range, as well as existing high-intensity scrubbing methods using thermal methods, the self-friction disturbance in this embodiment better reflects the process characteristics of "low-damage overall desquamation." Its beneficial effects are: First, the object being peeled away changes from dispersed residues to a complete double-layered shell structure, making shell fragmentation more concentrated and peeling more thorough; Second, self-friction disturbance avoids strong scouring of the sand matrix by rigid components, significantly reducing the sand breakage rate. Third, within the temperature window of 120℃ to 280℃, the double-layered shell structure maintains high brittleness, while the sand grain matrix still has sufficient integrity. Therefore, it is more conducive to achieving the selective separation objective of "preferential brittle fracture of the shell and preservation of the matrix".

[0137] Table 3: Verification Table of Self-Friction Disturbance and Temperature Window Parameter name Example 4 of the present invention - Self-friction assembly within the window Comparative Example A-2 - Below the Range Group Comparative example B-2 - higher than the range group Comparative Example C-2 - Existing Thermal High-Intensity Scrubbing Set Temperature for enrichment of carbonized particles (°C) 190 95 320 380 Self-friction linear velocity (m / s) 2.2 0.6 4.8 not applicable Duration of action (min) 2.5 0.3 6.5 3 Shell detachment rate (%) 89 31 62 55 Synchronous cracking rate (%) 84 24 39 18 Sand grain integrity rate after peeling (%) 94 97 73 69 Sand breakage rate (%) 4.9 1.8 16.2 18.7 Acid consumption value of regenerated sand (mL / 50g) 2.2 4.6 3.8 5.3 Purity (%) of resin carbonization recycled materials 74 29 46 21 Energy consumption per unit (kWh / t) 163 151 178 236 Table 3 shows that the advantages of Example 4 of the present invention are mainly reflected in the synergistic improvement of five indicators: "shell separation rate, synchronous cracking rate, sand grain integrity rate after peeling, acid consumption value of regenerated sand and purity of resin carbonization recovery product".

[0138] In the self-friction group within the window, the temperature for enriching carbonized particles was controlled at 190℃, the self-friction linear velocity was controlled at 2.2m / s, and the action time was 2.5min. The resulting shell detachment rate reached 89%, the synchronous cracking rate reached 84%, the sand particle integrity rate after peeling reached 94%, the acid consumption value of the regenerated sand was reduced to 2.2mL / 50g, and the purity of the resin carbonized recycled material reached 74%.

[0139] This indicates that within a temperature window of 120℃ to 280℃, and under self-friction disturbance conditions of 1.0 m / s to 4.0 m / s and 0.5 min to 5 min, the double-layered separation shell structure can preferentially undergo brittle fracture and detach as a whole, while the sand grain matrix remains intact. This result directly supports the technical effectiveness of "self-friction disturbance" and "temperature window" in this embodiment, and demonstrates that this parameter combination is not arbitrarily assembled, but rather collaboratively set around the core objective of "preferential shell fracture."

[0140] In Comparative Example A-2, the self-friction linear velocity was only 0.6 m / s, the action time was only 0.3 min, and the enrichment temperature of carbonized particles was 95°C, all of which are lower than the limits of this embodiment.

[0141] After peeling, the integrity rate of the sand particles reached 97%, which seemed to be more "mild" on the surface. However, the shell detachment rate was only 31%, the synchronous cracking rate was only 24%, the acid consumption value of the regenerated sand was still as high as 4.6mL / 50g, and the purity of the resin carbonization recovery product was only 29%.

[0142] This indicates that below the specified range, the double-layered separation shell structure did not obtain sufficient pyrolysis driving force, and the self-friction disturbance was insufficient to overcome the interlayer bonding and the integrity of the shell itself, resulting in a large amount of the stripped object remaining on the surface of the sand matrix, making it difficult to reduce the subsequent acid consumption value.

[0143] In other words, while lower parameters reduce the risk of sand breakage, they also prevent the "selective brittle fracture peeling" sought in this embodiment from occurring fully, thus failing to achieve the goal of overall desquamation.

[0144] In Comparative Example B-2, the temperature for enriching carbonized particles was increased to 320°C, the self-friction linear velocity was increased to 4.8 m / s, and the action time was extended to 6.5 min, all of which are higher than the ranges defined in this embodiment.

[0145] The shell detachment rate of this group increased to 62%, which was significantly higher than that of the group below the range. However, the synchronous cracking rate was only 39%, and the integrity rate of sand particles after peeling decreased to 73%, while the sand particle breakage rate was as high as 16.2%. This indicates that although the excessively high parameters enhanced the tendency of shell fracture and detachment, they also caused the sand particle matrix to bear excessive mechanical and thermal stress, resulting in the loss of selectivity.

[0146] In other words, excessively high temperatures and speeds do not make "overall shell removal" better; instead, they transform the "preferential shell cracking" of this invention into "damage to both the shell and the substrate."

[0147] Therefore, the higher range group verifies the necessity of the upper bound boundary.

[0148] Comparative Example C-2 adopts the existing thermal high-intensity scrubbing route. Its pretreatment basis is different from Example 4 of the present invention. Instead of establishing the double-layer separation shell structure formed in Example 4 of the present invention, the material directly enters the high-intensity mechanical scrubbing after air roasting.

[0149] Although the shell detachment rate of this group was 55%, the synchronous cracking rate was only 18%, the integrity rate of sand particles after peeling was only 69%, the sand particle breakage rate reached 18.7%, the acid consumption value of regenerated sand was still as high as 5.3mL / 50g, and the purity of resin carbonization recovery product was only 21%.

[0150] This indicates that the main mechanism of the traditional approach is still "high-temperature burn-off + strong mechanical removal of residues". The target of its treatment is not a double-layered separation shell structure with a clear hierarchical relationship. Therefore, it cannot effectively achieve the overall separation of the shell layers, nor can it protect the main body of the sand grain matrix.

[0151] Compared with Example 4 of this invention, the shortcomings of the existing thermal high-intensity scrubbing route precisely highlight the inventiveness of this invention: This invention does not simply increase mechanical action, but utilizes the double-layer separation shell structure constructed by the external migration enrichment treatment, and under specific temperature windows and specific self-friction disturbance conditions, causes the shell layer to crack and detach before the matrix, thereby obtaining the comprehensive effect of low acid consumption value, high integrity rate and high purity resin carbonization recovery product.

[0152] As can be seen from Table 3, the three boundaries in this embodiment—enriched carbonized particle temperature of 120℃~280℃, self-friction linear velocity of 1.0m / s~4.0m / s, and action time of 0.5min~5min—together constitute the synergistic window for selective brittle fracture peeling.

[0153] Inside the window, the double-layered shell structure is in a brittle state suitable for pyrolysis, but has not entered the range where the main body of the matrix would be damaged due to high temperature and strong friction; outside the window, whether the temperature is too low or too high, this balance will be disrupted.

[0154] Below the range, the driving force for pyrolysis is insufficient, and the shell does not detach completely; above the range, although the shell can rupture, the main body of the sand particles will also be significantly damaged.

[0155] Therefore, the technical significance of this window lies in unifying the "peeling effect" and the "abrasive grain protection effect," distinguishing this invention from the traditional strong grinding decontamination route. This conclusion not only supports the process boundary setting in this embodiment but also proves from the results that this invention has a clear inventive basis in the peeling stage: that is, using a double-layer separation shell structure as the object, low-damage overall peeling is achieved under controlled temperature and controlled self-friction disturbance, rather than relying on high temperature and high-intensity mechanical scrubbing to forcibly remove surface residues.

[0156] Example 5 Please refer to Figure 1 , Figure 3 and Figure 4 Specifically: hierarchical separation includes first separation and second separation; The first separation process strips the mixture to obtain a first stream rich in exposed sand grain matrix and a second stream rich in stripped shells; The second separation process treats the second stream to obtain resin carbonization recovery material; The first separation method uses air separation, with an air velocity of 6 m / s to 15 m / s. The second separation method uses electrostatic separation, with an electric field strength of 1.0 kV / cm to 3.0 kV / cm.

[0157] In this embodiment, the same application scenario as in Embodiments 1-4 is used, that is, coated sand waste generated by a cast iron water jacket core production line is selected as the test raw material, and the same raw material baseline and pretreatment conditions are maintained.

[0158] This embodiment focuses on verifying the hierarchical separation.

[0159] "First separation" refers to the preliminary pneumatic separation step of the stripping mixture. Its purpose is to take advantage of the differences in apparent density, morphology, specific surface area and suspension behavior between the exposed sand matrix and the stripped shell, so that the exposed sand matrix with higher density and more complete particle shape is preferentially enriched as the first stream, and the flaky, shaving and porous carbonaceous stripped shell is preferentially enriched as the second stream.

[0160] "Second separation" refers to the step of fine separation of the second stream. Its purpose is to further improve the purity of the resin carbonized recovery by taking advantage of the differences in charged behavior, conductivity and polarization response between the resin carbides and the entrained inorganic fine powder and sand particles.

[0161] "First logistics" refers to the logistics obtained after the first separation, which is rich in exposed sand grain matrix; "Second logistics" refers to the logistics obtained after the first separation, which is rich in the peeled-off shell layer; "Resin carbonization recovery material" refers to the carbonaceous recovery product obtained from the second stream after the second separation.

[0162] In this embodiment, the first separation and fixation adopts air separation, and the second separation and fixation adopts electrostatic separation.

[0163] The air separation stage uses a vertical airflow separation device with an air separation velocity set at 10 m / s, which causes the stripped mixture to form a stable material curtain and be separated under the action of airflow.

[0164] To ensure repeatability of air separation, the feeding rate is controlled at 120 kg / h, the material curtain thickness is controlled at 8 mm to 15 mm, the wind speed measuring point is set at the middle of the sorting section, and the measured value is the average value of 30 consecutive seconds.

[0165] After air separation, the heavier portion at the bottom is collected as the first material, while the lighter portion that floats and deflects more is collected as the second material.

[0166] The first and second logistics materials were weighed separately, and samples were taken to analyze their composition.

[0167] The purity of the exposed sand matrix in the first stream was determined by microscopic screening combined with the ignition subtraction method, and was defined as the proportion of the mass of the exposed sand matrix in the first stream to the total mass of the first stream. The enrichment of the peeled shell layer in the second stream was determined by ash correction method and microscopic morphology statistical method, and was defined as the proportion of the mass of the peeled shell layer in the second stream to the total mass of the second stream.

[0168] After the first separation is completed, the second material is introduced into the electrostatic separation device. The electric field strength is set to 1.8kV / cm, the electrode spacing is fixed at 20mm, and the feed layer thickness is controlled to be less than 3mm, so that the difference in response between the carbonaceous shell component and the entrained inorganic fine powder in the electric field can be stably expressed.

[0169] After electrostatic separation, the stream from the side with the more pronounced electrical response was collected as the resin carbonization recovery material, and its purity and recovery rate were determined.

[0170] The purity of the resin carbonization recovery material was determined by a combination of ash correction method and thermogravimetric analysis, and was defined as the proportion of the mass of carbonaceous components in the resin carbonization recovery material to its total mass; the recovery rate of the resin carbonization recovery material was defined as the proportion of the mass of the resin carbonization recovery material to the mass of the theoretically recoverable carbonaceous components in the stripping mixture.

[0171] Meanwhile, the acid consumption value and loss on ignition of the recycled sand obtained from the first material granulation were measured to evaluate the impact of graded separation on the quality of the recycled sand.

[0172] Under the above conditions, the purity of the exposed sand matrix in the first stream of this embodiment reaches 94%, the enrichment of the peeled shell layer in the second stream reaches 87%, the purity of the resin carbonization recovery reaches 76%, the recovery rate of the resin carbonization recovery reaches 71%, the acid consumption value of the regenerated sand is reduced to 2.1 mL / 50 g, and the loss on ignition of the regenerated sand is reduced to 0.31%.

[0173] Mechanistic analysis shows that air separation does not simply remove light impurities, but rather utilizes the difference in aerodynamic behavior between the peeled shell and the exposed sand matrix to achieve coarse separation; electrostatic separation is not simply powder separation, but further utilizes the difference in electrical response between carbonaceous and inorganic components in the second stream to achieve fine purification.

[0174] Therefore, the two-stage route of "first separation using air separation and second separation using electrostatic separation" in this embodiment is not a series combination of equipment in the general sense, but a graded separation logic designed around the different phase characteristics of the stripped mixture and the second stream.

[0175] The first separation is responsible for dividing the stripped material into "first stream suitable for direct use as a source of recycled sand" and "second stream suitable for further carbonaceous purification"; the second separation further divides the second stream into "resin carbonization recovery" and entrained residual components.

[0176] The beneficial effects of this route are that, on the one hand, it can simultaneously improve the purity of the exposed sand matrix in the first logistics and the enrichment of the peeled shell layer in the second logistics, and on the other hand, it can significantly improve the purity and recovery rate of the resin carbonization recyclables and reduce the acid consumption value and ignition loss of the recycled sand, thereby forming a dual-product recycling mode of "recycled sand" and "resin carbonization recyclables".

[0177] Table 4: Comparison of Graded Separation Parameter Window and Dual Logistics Recycling Effect Parameter name Example 5 of the present invention - Window-based air-separation electrostatic group Comparative Example A-5 - Below Range Group Comparative Example B-5 - Higher Range Group Comparative Example C-5 - Existing Single-Stage Air Separator First separation method Wind Selection Wind Selection Wind Selection Wind Selection Wind-separated wind speed (m / s) 10 4 18 10 Second separation method electrostatic separation electrostatic separation electrostatic separation none Electrostatic field strength (kV / cm) 1.8 0.6 3.5 0 Purity (%) of exposed sand particles in the first logistics process 94 78 81 83 Secondary logistics shell enrichment (%) 87 62 69 74 Purity (%) of resin carbonization recycled materials 76 41 55 0 Resin carbonization recovery rate (%) 71 38 52 0 Acid consumption value of regenerated sand (mL / 50g) 2.1 4 3.5 3.7 Regenerated sand ignition loss (%) 0.31 0.58 0.47 0.49 Overall recovery rate after separation (%) 89 83 84 82 Energy consumption per unit (kWh / t) 169 158 181 151 As can be seen from Table 4, Example 5 of the present invention is superior to the lower range group, the higher range group and the existing single-stage air classifier group in key indicators such as the purity of the first material, the enrichment of the second material, the purity of the resin carbonization recovery product, the recovery rate of the resin carbonization recovery product and the acid consumption value of the regenerated sand.

[0178] In the electrostatic air separation unit within the window, the air separation velocity was controlled at 10 m / s and the electrostatic field strength was controlled at 1.8 kV / cm. The purity of the exposed sand matrix in the first stream reached 94%, indicating that the air separation could effectively separate the exposed sand matrix with higher density and more complete particle shape from the stripping mixture. The enrichment of the stripped shell layer in the second stream reached 87%, indicating that the first separation not only achieved preliminary diversion but also significantly enriched the carbonaceous shell layer in the second stream.

[0179] After electrostatic separation, the purity of the resin carbonization recovery material reached 76%, the recovery rate reached 71%, the acid consumption value of the regenerated sand decreased to 2.1 mL / 50 g, and the loss on ignition of the regenerated sand decreased to 0.31%. This indicates that the second separation further amplified the difference in electrical response between the carbonaceous components and the entrained inorganic components in the second stream, significantly improving the quality of both products.

[0180] This demonstrates that the fixed route in this embodiment can simultaneously take into account both the quality of the recycled sand and the quality of the carbonized reclaimed materials.

[0181] In Comparative Example A-5, the air separation velocity and electrostatic field strength were both below the ranges specified in this embodiment, at 4 m / s and 0.6 kV / cm, respectively. In this group, the purity of the exposed sand matrix in the first stream was only 78%, the enrichment of the peeled shell in the second stream was only 62%, the purity of the resin carbonization recovery was only 41%, the recovery rate was only 38%, and the acid consumption value of the regenerated sand was still as high as 4.0 mL / 50 g.

[0182] It can be seen that when the air separation velocity is too low, the density and morphology differences in the stripping mixture are not enough to be fully converted into a separation effect, resulting in some shell layers and fine sand particles still being mixed between the first and second streams; when the electrostatic field strength is too low, the response difference between the carbonaceous shell layer and the inorganic entrainment in the second stream is not enough to be effectively amplified, so the purification effect of the second separation is also poor.

[0183] The explanation below the range group indicates that the first and second separations are not formally connected, but rather each undertakes a separation task at a different level. If the intensity of either stage is insufficient, the final dual-logistics recovery effect will be significantly reduced.

[0184] In Comparative Example B-5, the wind speed and electrostatic field strength were both higher than the ranges specified in this embodiment, at 18 m / s and 3.5 kV / cm, respectively.

[0185] The purity of the exposed sand matrix in the first stream of this group was 81%, which was slightly higher than that in the lower range group, but significantly lower than that in Example 5 of this invention; the enrichment of the peeled shell in the second stream was 69%, the purity of the resin carbonization recovery was 55%, the recovery rate was 52%, and the acid consumption of the regenerated sand was 3.5 mL / 50 g.

[0186] The reason for this result is that when the wind speed is too high, some finer but denser sand particles will be excessively entrained into the second stream, reducing the purity of the first stream. At the same time, when the electrostatic field strength is too high, some inorganic fine powder and broken sand particles in the second stream will also be mistakenly adsorbed or deflected, affecting the purity of the resin carbonization recovery product.

[0187] Therefore, exceeding the range does not necessarily mean a stronger separation effect; on the contrary, it introduces new entrainment and false separation phenomena, indicating that there is a reasonable window for both air separation velocity and electrostatic field strength.

[0188] Comparative example C-5 adopts the existing single-stage air separation route, that is, only one air separation is performed at a wind speed of 10m / s, and electrostatic separation is no longer performed.

[0189] The purity of the exposed sand matrix in the first stream of this group is 83%, and the enrichment of the peeled shell layer in the second stream is 74%. This indicates that single-stage air separation can only achieve coarse separation and cannot further form high-purity resin carbonized reclaimed material. Therefore, the purity and recovery rate of the resin carbonized reclaimed material are both recorded as 0.

[0190] The acid consumption value of the regenerated sand in this group was still 3.7 mL / 50 g, and the reduction on ignition of the regenerated sand was 0.49%, which was significantly worse than that of Example 5 of the present invention.

[0191] This indicates that while a single air separation route can separate light and heavy components to a certain extent, it cannot meet the technical objective of "further separation of the second material" emphasized in this embodiment, nor can it achieve stable recovery of high-purity resin carbonization recyclables.

[0192] Compared with Example 5 of the present invention, the existing single-stage air separation route lacks the crucial second separation step, making it difficult to simultaneously obtain high-quality recycled sand and high-purity carbonized reclaimed material.

[0193] As can be seen from Table 4, the first separation in this embodiment uses wind separation with a wind speed of 6m / s to 15m / s, and the second separation uses electrostatic separation with an electric field strength of 1.0kV / cm to 3.0kV / cm. These settings are not arbitrary, but rather form a synergistic window for graded separation based on the different phase characteristics of the stripped mixture and the second stream.

[0194] Under the conditions within the window, the first separation utilizes the difference in aerodynamic behavior to establish an initial purity difference between the first and second streams. The second separation then utilizes the difference in electrical response to further improve the purity and recovery rate of the resin carbonization recyclables, thus forming a dual-product recovery route of "regenerated sand - resin carbonization recyclables".

[0195] Compared with parameters below the range, parameters above the range, and existing single-stage air separation routes, the beneficial effects of this invention are: it can simultaneously improve the purity of the exposed sand matrix in the first stream, the enrichment of the peeled shell layer in the second stream, and the purity of the resin carbonized recycled material, and significantly reduce the acid consumption value and ignition loss of the regenerated sand.

[0196] This demonstrates that the ingenuity of this embodiment lies not in simply connecting two devices in series, but in designing a two-stage fixed separation route that matches the state of the stripping mixture and the second material based on the differences in their physical properties, thereby achieving a synergistic improvement in subsequent recycling efficiency and product quality.

[0197] 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.

Claims

1. A resin carbonization separation and recycling process for coated sand waste, characterized in that, Includes the following steps: Pre-treatment of coated sand waste yields pre-treated particles, wherein the pre-treated particles comprise a sand matrix and a coated resin layer covering the surface of the sand matrix. The pretreated particles are subjected to interface-guided oxygen-limited carbonization treatment, which causes the coated resin layer to preferentially carbonize along the contact interface between the sand matrix and the coated resin layer, resulting in primary carbonized particles with a continuous interface carbonized shell on the surface. The primary carbonized particles are subjected to an external migration enrichment treatment, which causes the alkaline residue and inorganic ash on the surface of the sand matrix to migrate and accumulate outward along the continuous interface carbonized shell layer, forming enriched carbonized particles with an external migration enrichment shell on the outside of the primary carbonized particles. Selective brittle exfoliation treatment is performed on enriched carbonized particles to allow the continuous interface carbonized shell and the external enriched shell to be separated from the surface of the sand particle matrix as an integrated shell structure, resulting in an exfoliation mixture, which includes the exposed sand particle matrix and the exfoliated shell. The stripping mixture is graded and separated to obtain recycled sand and resin carbonization recovery.

2. The resin carbonization separation and recycling process for coated sand waste according to claim 1, characterized in that, The interface-guided oxygen-limited carbonization treatment is carried out under conditions of oxygen volume fraction of 0.8% to 2.5% and heating rate of 8℃ / min to 25℃ / min. After the particle temperature rises to 430℃~620℃, it is kept at that temperature for 2min~15min. The coating resin layer begins to carbonize from the contact interface between the sand grain matrix and the coating resin layer. The continuous interface carbonized shell grows outward along the normal direction of the sand grain matrix surface, and after processing, primary carbonized particles are obtained.

3. The resin carbonization separation and recycling process for coated sand waste according to claim 2, characterized in that, The continuous interface carbonized shell layer forms a continuous coating area on the surface of the sand grain matrix; The continuous coating area corresponds to the area where the coating resin layer was originally attached to the surface of the sand matrix; The continuous interface carbonized shell has migration channels extending along the thickness direction.

4. The resin carbonization separation and recycling process for coated sand waste according to claim 3, characterized in that, The migration and enrichment treatment is carried out at a particle temperature of 450℃~580℃; The duration of the migration enrichment treatment is 1 min to 8 min; Alkaline residues and inorganic ash migrate to the outer side of the continuous interface carbonized shell through migration channels; Alkaline residues and inorganic ash accumulate on the outer surface of the continuous interface carbonized shell, forming an externally enriched shell. Based on the external enrichment shell and the continuous interface carbonization shell, the continuous interface carbonization shell and the external enrichment shell together form a double-layer separation shell structure on the surface of the enriched carbonization particles. Among them, alkaline residues include at least one of potassium salts, sodium salts, and calcium salts.

5. The resin carbonization separation and recycling process for coated sand waste according to claim 4, characterized in that, The dual-layer separated shell structure includes a continuous interface carbonized shell layer and an external migration enrichment shell. In the double-layer separated shell structure, the continuous interface carbonized shell layer constitutes the inner layer close to the sand grain matrix, and the outward migration enrichment shell layer constitutes the outer layer located outside the continuous interface carbonized shell layer. The exogenous enrichment shell and the continuous interface carbonized shell maintain a layered bonding state that allows for synchronous cracking.

6. The resin carbonization separation and recycling process for coated sand waste according to claim 5, characterized in that, The endpoints of the interface-guided oxygen-limited carbonization treatment and the migration enrichment treatment are determined by a combination of exhaust gas detection signals and particle surface state detection signals, respectively. The sampling period was 15s to 60s; within 2 to 5 consecutive sampling periods, the total hydrocarbon release rate decreased to 5% to 20% of the peak value of the migration and enrichment treatment stage and remained stable; the change rate of the comprehensive color value of the particle surface remained stable; based on this, it was determined that the migration and enrichment treatment was completed.

7. The resin carbonization separation and recycling process for coated sand waste according to claim 5, characterized in that, The selective brittle fracture peeling process employs self-friction disturbance; The frictional linear velocity of the self-friction disturbance is 1.0 m / s to 4.0 m / s; The action time is 0.5 min to 5 min; The double-layered separation shell structure preferentially undergoes brittle fracture under self-friction disturbance and detaches from the surface of the sand matrix, while the sand matrix remains intact.

8. The resin carbonization separation and recycling process for coated sand waste according to claim 6, characterized in that, The self-friction disturbance is implemented when the temperature of enriched carbonized particles is 120℃~280℃; The double-layered separation shell structure brittlely cracks and detaches within a temperature range of 120℃ to 280℃ when enriched carbonized particles. The sand matrix remains largely intact within this temperature range.

9. The resin carbonization separation and recycling process for coated sand waste according to claim 7, characterized in that, The hierarchical separation includes a first separation and a second separation; The first separation process strips the mixture to obtain a first stream rich in exposed sand grain matrix and a second stream rich in stripped shell layer; The second separation process treats the second stream to obtain resin carbonization recovery material; The first separation is carried out by air separation, and the wind speed of the air separation is 6m / s to 15m / s; The second separation is electrostatic separation, and the electric field strength of the electrostatic separation is 1.0kV / cm to 3.0kV / cm.

Images