Separation Of Ash Research Articles

Carbon-ash separation of coal gasification fine slag by flocculation-flotation process

ABSTRACT Coal gasification slag (CGFS), which was a bulk solid waste in coal chemical industry, shows great application potential in the preparation of silica microspheres, zeolites ceramic materials, etc. However, its high residual carbon characteristics hinder to its development. Decarburization is a necessary precondition for the effective utilization of CGFS. The efficient separation of carbon or ash from CGFS remains a challenge due to its ultra-fine particle size. This work provides a novel flocculation-flotation process to achieve the complete carbon-ash separation of CGFS. The addition of anionic polyacrylamide (APAM) or polyethylene oxide (PEO) had positive effect on the flotation of CGFS, especially for APAM. With APAM dosage of 50 g/t, the ash content of carbon slag and ash slag were 59.04% and 97.11%, respectively. In this process, the zeta potential of carbon slag and ash slag decreased from −17.43 and −11.77 mV to −23.45 and −29.80 mV, respectively. The greater change of zeta potential of ash slag indicates its stronger adsorption of APAM, leading to the higher flocculation trend of ash particles than that of carbon slag. APAM has selective flocculation effect on ash slag, which contributed to reduce the mechanical entrainment during flotation, thereby achieving complete carbon-ash separation of CGFS.

Investigation of high internal phase water-in-oil emulsion on coal gasification fine slag flotation decarburization and its oil saving mechanism

Froth flotation stands as the preferred technique for the separation of charcoal and ash from coal gasification fine slag (CGFS). However, the presence of a well-developed pore structure and an abundance of oxygen-containing functional groups on the surface of residual charcoal necessitates the use of substantial dosage of collectors during the flotation of CGFS. To address this, a high internal phase water-in-oil (HIP W/O) emulsion, with an internal phase water volume fraction of 85 %, was formulated for the flotation decarburization of CGFS, with the objective of reducing the collector dosage. The outcomes of flotation tests demonstrated that at dosages of 50 kg/t for kerosene and 15.04 kg/t for the organic liquid of the HIP W/O emulsion, both were capable of yielding tailings with an ash content exceeding 95 %. The results from Cryo-SEM and viscosity tests suggest that the high viscosity characteristics of the HIP W/O emulsion are primarily attributed to the compact arrangement of emulsion droplets and the active influence of emulsifiers at the oil–water interface. High-speed camera observations revealed that the HIP W/O emulsion droplets exhibited a tendency to disperse into bar-shaped flocs with larger particle sizes in water. This particular dispersion morphology is advantageous for enhancing the oil agglomeration flotation mechanism within the flotation decarburization process of CGFS. LF-NMR tests have further substantiated that the emulsion droplets are not readily absorbed by the microporous structure of the residual charcoal within the CGFS. Wettability tests and FTIR analyses have demonstrated that the hydrophobic modification of the residual charcoal surface, achieved through the HIP W/O emulsion, markedly surpasses that of conventional kerosene. The combination of these results indicates that the use of HIP W/O emulsion in the flotation decarbonization process of CGFS offers multiple benefits. It not only significantly reduces the dosage of organic collectors required, but also enhances the economic efficiency and effectiveness of the flotation process, presenting a novel reagent option for the decarbonization of CGFS.

The influence of selected grain size fractions of coal fly ash on properties of clay-cement mortars used for the flood levees construction

This study examines the influence of different grain size fractions of coal fly ash on the properties of clay-cement mortars used in flood levee construction. Dry aerodynamic separation and mesh sieving were used to obtain ultrafine, fine, and medium fractions of high-calcium and silica fly ash. The experimental results reveal that the rheological properties of fresh mortars are significantly influenced by these fractions. High-calcium fly ash mortars exhibit high reactivity and rapid increase in viscosity, with finer fractions showing the highest reactivity. Silica ashes show increased reactivity in the later stages of suspension hardening. Their spherical shape contributes to reducing internal friction during flow in initial technological operations. Furthermore, the compressive strength of hardened mortars improves as the particle size decreases for both ashes, resulting in a dense and uniform microstructure. The separation and fractionation of fly ashes contribute to the obtaining of fractions that influence the parameters of clay-cement suspension application on different scales. The results show the potential benefits of ash separation, which can bring advantages in terms of economic viability, engineering performance, and ecological sustainability.

Effect of ultrasonic-hydraulic coupling cavitation pretreatment on carbon extraction from coal gasification coarse slag by flotation

Coal gasification coarse slag represents a type of low-value solid waste produced in coal gasification. This study investigated how the pretreatment of the pulp obtained from coal gasification coarse slag affects carbon extraction by flotation. Ultrasonic treatment can promote carbon ash separation. Flotation results revealed that at an ultrasonic action time of 15 min, the ultrasonic power was 90 W and the microbubble generator flow rate was 300 ml/min. Moreover, the best flotation effect was observed under these conditions. Compared with the results obtained for conventional flotation, the concentrate ash content decreased from 36.88 % to 25.51 % and the combustible substance recovery index increased from 79.84 % to 92.91 %. After coupled cavitation treatment, coal gasification coarse slag exhibited a reduced particle size, an increased specific surface area, a smooth and clean surface, a reduced number of surface inorganic elements, an increased number of pores and a remarkable carbon ash separation effect. This study can provide a reference for special methods such as ultrasonic-hydraulic coupling cavitation to strengthen the flotation of coal gasification coarse slag.

Physicochemical Characteristics of Residual Carbon and Inorganic Minerals in Coal Gasification Fine Slag.

Investigating the physicochemical properties and embedding forms of residual carbon (RC) and slag particles (SPs) in coal gasification fine slag (FS) is the basis for achieving its separation and utilization. An in-depth understanding of their compositional characteristics allows for targeted treatment and utilization programs for different components. In this work, the physicochemical properties and embedding forms of RC and SPs in FS were systematically investigated. An innovative calculation method is proposed to determine the mass fraction of dispersed carbon particles, dispersed mineral-rich particles, and carbon-ash combined particles by using a high-temperature heating stage coupled with an optical microscope. The unburned RC with a rough, loose surface and a well-developed pore structure acted as a framework in which the smaller spherical SPs with a smooth surface were embedded. In addition, the sieving pretreatment process facilitated the enrichment of the RC. Moreover, the RC content showed significant dependencies according to the FS particle size. For FS with a particle size of 0.075-0.150 mm, the mass proportions of dispersed carbon, ash particles, and the carbon-ash combination were 15.19%, 38.72%, and 46.09%, respectively. These findings provide basic data and reliable technical support for the subsequent carbon and ash separation process and the comprehensive utilization of coal gasification slag.

Composition and Structural Characteristics of Coal Gasification Slag from Jinhua Furnace and Its Thermochemical Conversion Performance

Gasification technology enables the clean and efficient utilization of coal. However, the process generates a significant amount of solid waste—coal gasification slag. This paper focuses on the Jinhua furnace coal gasification slag (fine slag, FS; coarse slag, CS) as the research subject, analyzing its composition and structural characteristics, and discussing the thermochemical conversion performance of both under different atmospheres (N2 and air). The results show that the fixed carbon content in FS is as high as 35.82%, while it is only 1% in CS. FS has a large number of fluffy porous carbon on its surface, which wraps around or embeds into smooth and variously sized spherical inorganic components, with a specific surface area as high as 353 m2/g, and the pore structure is mainly mesoporous. Compared to the raw coal (TYC), the types of organic functional groups in FS and CS are significantly reduced, and the graphitization degree of the carbon elements in FS is higher. The ash in FS is mainly amorphous and glassy, while in CS, it mainly has crystalline structures. The weight loss rates of TYC and FS under an inert atmosphere are 27.49% and 10.38%, respectively; under an air atmosphere, the weight loss rates of TYC and FS are 81.69% and 44.40%, respectively. Based on the analysis of the thermal stability of FS and its high specific surface area, this paper suggests that FS can be used to prepare high-value-added products such as porous carbon or high-temperature-resistant carbon materials through the method of carbon–ash separation.

Ultrasonication Improves the Flotation of Coal Gasification Fine Slag Residue

Coal gasification fine slag (CGFS) is a significant source of solid waste requiring improved treatment methods. This study primarily investigates the mechanism of ultrasonic treatment in optimising flotation-based decarbonization of CGFS and its impact on CGFS modified with surfactants. The objective is to maximise the carbon ash separation effect to support the clean and efficient utilisation of CGFS. Flotation experiments revealed optimal conditions at an ultrasonication power of 180 W for 2 min and a slurry concentration of 60 g/L, resulting in a residual ash content of 82.59%. Particle size analysis, scanning electron microscopy (SEM), and Brunner−Emmet−Teller (BET) measurements demonstrate the efficacy of ultrasound in extracting inorganic minerals from the surface and pores of residual carbon, consequently reducing both pore and particle sizes. Fourier transform infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses indicate alterations in the surface chemistry of CGFS induced by ultrasound treatment. The content of hydrophilic groups decreased from 31.64% to 29.88%, whereas the COO- group content decreased from 13.13% to 8.43%, consequently enhancing hydrophobicity. Adsorption experiments demonstrate an increase in surfactant adsorption capacity following ultrasonic treatment. Furthermore, ultrasonic treatment facilitates the desorption of surfactants previously adsorbed onto the surfaces of CGFS residue. Therefore, optimal flotation is obtained by applying ultrasonic pretreatment to CGFS before adding flotation chemicals. Upon the addition of Polysorbate (Tween-80), the residual ash content increased 90.17%.

Enrichment of Iron-containing Concentrate with Ammonium Hydrofluoride

The rationality of using ash and slag waste from coal-fired TPP to obtain high-quality iron-containing concentrate (FC) is demonstrated. Using the method of wet magnetic separation of ash and slag waste from TPP, FC is extracted with Fe2O3 content of 59.2 %. It has been established that the method of chemical enrichment with ammonium hydrofluoride can increase the Fe2O3 content in FC to 79 %; a by-product of the reaction between FC and NH4F•HF is high-quality amorphous silica (white soot). The effect of process temperature on the composition of the resulting FC has been studied, at that the phase composition of iron oxides remains virtually unchanged. Optimal modes of the process are proposed.

Resources recovery from coal gasification residue by combined hydrocyclone and vibrating screen and characterization of separated products

Coal gasification fine slag (CGFS) is a solid waste rich in residual carbon and various inorganic elements produced in the process of coal gasification, and components separation is a prerequisite for its resourceful utilization and harmless disposal. In this paper, a CGFS sample was separated by a combined process of hydrocyclone and high-frequency vibrating screen (HFVS), and three products were obtained by optimizing separation parameters. The properties of each product were analyzed by XRD, XRF, SEM, BET, and TG-DSC. The results showed that the effective separation of residual carbon and ash in CGFS could be achieved at the hydrocyclone feeding pressure of 0.04 MPa and the HFVS aperture size of 0.074 mm, and LOI of the obtained concentrate, middling, and tailing products were 78.57%, 38.17%, and 20.42%, respectively, with a total recovery of residual carbon in concentrate and middling reaching 88.19%. Concentrate particles are mainly irregular or flocculent carbon with well-developed and comprehensive types of pores, as well as high calorific value and good combustion characteristics, which can be used to prepare porous adsorbent materials or as high-quality fuel. Middling is rich in aluminum and silicon elements, and it contains certain mesoporosity, calorific value and moderate combustibility, which suitable for preparing carbon-silicon composites or firing porous ceramics. Tailings have little residual carbon content but mainly consist of tiny spherical particles rich in inorganic element species and content, and it have fewer internal pores and low calorific value, which are suitable for the preparation of building materials, aluminum/silicon-based materials, or ecological restoration materials. This study provides important guidance for resource recovery and utilization of CGFS.

Facile Route for Effective Separation and Full-Scale Recycling of Fly Ash and Unburned Carbon.

The synchronous production of high-quality unburned carbon concentrate and cleaned ash from high LOI (loss on ignition) fly ash without yielding secondary solid waste is a dilemma issue. In this study, a viable flotation process with one rougher and two cleaners is developed for simultaneously obtaining carbon concentrate with a yield of 18.00% and an ash content of 17.49% and cleaned ash with a yield of 82.00% and a LOI of 4.63% from fly ash, reaching 84.72% of combustible substance recovery and 80.66% of flotation perfection index. The characteristic analyses of the stage by stage releasing products using laser particle size analysis, XRF, XRD, and SEM-EDS demonstrate that the inevitable factors that lead to a remaining higher ash content in the one-step flotation carbon concentrate are the random entrainment of mineral particles in the size range of 0-20 μm, especially the quasi-colloidal parts within 0-12.5 μm and the weak selective collection of fine-grained conjoined granules in the size range of 0-40 μm. Consequently, at least two cleaning steps are required for the effective separation of unburned carbon and ash. Furthermore, batch flotation test results show that diesel is superior to kerosene in the collection of unburned carbon, with an optimum dosage of 800 g/t; no. 2 oil acts more positively than MIBC for the separation of unburned carbon and ash, with an optimal dosing amount of 600 g/t; the optimum pulp concentration and flotation time are as follows: 100 g/L and 3.5 min for the rougher, 45 g/L and 2 min for the first cleaning, and 30 g/L and 3 min for the second cleaning. This study provides an economically feasible technological solution for the full-scale recovery of high-LOI fly ash in one step and avoids the problem of secondary solid waste that would have been generated in previous studies.

Effect of moisture content on charging and triboelectrostatic separation of coal gasification fine ash

Resource utilization of coal gasification fine ash is restricted by moisture content. Drying and dewatering are indispensable in triboelectrostatic separation. The study aims to determine the minimum required moisture content for effective gasification fine ash separation. Thereinto, experiments reveal a profound influence of moisture content on the electrical properties of gasification fine ash, subsequently impacting the separation process. With higher moisture content, the resistivity and relative dielectric constant of gasification fine ash decrease and increase, respectively. The electrical conductivity of gasification fine ash is enhanced by moisture, but the ability to retain charge is reduced, resulting in a decline in the charge-to-mass ratio. Additionally, severely agglomerated particles and poor separation will be generated by a high moisture content. Comprehensive triboelectrostatic separation experiments demonstrate that gasification fine ash with an additional moisture content of 10% could still be effectively separated yielding carbon-enriched and ash-enriched products with a LOI of 37.17% and 12.47%, respectively. Remarkably, the carbon recovery rate reaches a high of 78.44%. To a certain extent, the drying energy consumption is reduced. This paper provides significant inspiration for resource utilization of coal gasification fine ash.

Optimization of Technological Parameters of Complex Chlorinating Ash Processing Technology

Today, the problem of ash processing is not in the absence of rational technology, but in solving the problem of complex extraction of valuable components (metals) from it. A new method has been developed for calculating and optimizing the technological parameters of key processes of magnetic separation of ash, chlorinating firing of non-magnetic fraction and leaching of the stub with hydrochloric acid (30%) to obtain pure silica. Based on new approaches and solutions using the latest achievements of IT technologies, models have been developed that allow predicting the outputs of the products of the main processes depending on the initial parameters and the consumption of the reagents used. For ease of use in practice, nomograms have been constructed using mathematical models that allow determining the final technological parameters of processes depending on various parameters (productivity, iron content, reagent consumption, etc.) without complex technological calculations. Nomograms are the necessary tools for the selection and justification of the main and auxiliary equipment of the integrated ash processing technology developed by the authors of this work.

Investigation of fluidization characteristics and separation performance of trapezoidal gas-solid fluidized bed

ABSTRACT A trapezoidal gas-solid fluidized bed separation system was designed to improve the separation space and processing capability of the gas-solid separation fluidized bed by combining inclined air distribution plates with horizontal air distribution plates. The distribution pattern of bed density was investigated under different operational conditions. The results showed that the operational conditions significantly influenced the standard deviation of bed density fluctuation and the skewness of bed density. When the fluidization number of the horizontal section and inclined section are 1.4 and 1.2 respectively, the aperture of the distributor plate is 6–2 mm, and the static bed height is 150 mm, the minimum standard deviation of bed density fluctuation (Sρ) is 0.07 g/cm3, and the skewness of density fluctuation (SKρ) was less than 0, indicating good fluidization quality of the bed under these conditions. Experimental separation tests of 13 ~ 6 mm raw coal were conducted in both the horizontal section of the bed and the overall trapezoidal fluidized bed, and the results showed that under the operational conditions with the best stability of bed density, ash separation was most prominent, with a possible minimum deviation (E) value of 0.120 g/cm3. Furthermore, under the same operational conditions, the maximum processing capacity of the horizontal bed section was 300 g, while the trapezoidal gas-solid fluidized bed with inclined air distribution plates could achieve a maximum processing capacity of 400 g, indicating that the trapezoidal gas-solid fluidized bed effectively expanded the separation space.

Cyclic catalytic Fe-N doped composite particle electrodes derived from gasification fine slag for non-selective mineralization of organic wastewater

As a typical coal-based solid waste, coal gasification fine slag (GFS) will have an annual discharge of more than 50 million tons in 2025 in China alone. However, the difficulty of its resource utilization lies in the precise separation of carbon and ash due to their complex distribution pattern. There is an urgent need to develop GFS-based materials for comprehensive utilization of carbon and ash. In this study, a combined process of acid leaching and pyrolysis was designed, in which active metal iron was leached from ash and immobilized on the surface of residual carbon in the form of Fe-N-C. The unique structure of Fe-N doped carbon/ash synergistically improved the efficiency of electrocatalytic degradation of organic wastewater by 72.78 ± 1.37%. The hierarchical porous structure of residual carbon considerably enhanced the accessibility of ash catalytic sites. Abundant ash defects and Fe-N active sites promoted the conversion of free radical precursors to reactive oxygen species (ROS). The removal rate of various organic wastewater within 35 min reached more than 100 ± 1.83% %, with excellent electrocatalytic performance and pH adaptability. Fe-NCPE had a high specific surface area (318.36 m2·g−1), orderly graphite phase (002 crystal surface size 1.3 nm), and abundant catalytic sites. We also proposed the catalytic mechanism by combining molecular simulation with experiments. The high adsorption capacity above 24.07 ± 0.12 mg·g−1 ensured the continuous and rapid supply of pollutants and H2O2 near the catalytic site·H2O2 was converted into ROS mainly composed of hydroxyl groups through the valence state change of aluminum or Fenton-like reaction of nitrogen-linked iron. The ROS then attacked organic molecules to degrade pollutants. The above two processes corresponded to two cyclic catalytic reactions. Therefore, this study provides an innovative and promising approach for comprehensive utilization of carbon and ash in GFS.

Triboelectrostatic separation of coal gasification fine ash based on different mineralogical characteristics

Unburned carbon particles in coal gasification fine ash can be recycled as fuel for further combustion and ash particles are highly valuable for utilization, which can only be of secondary utilization if the two are separated. Due to the small size of gasification fine ash particles, triboelectrostatic separation has more technological advantages than traditional flotation. In this study, a first attempt has been made to separate carbon and ash particles from coal gasification fine ash by triboelectrostatic separation. It aims to investigate the feasibility of the method and to study how different mineralogical characteristics affect triboelectrostatic separation. Herein, proximate analysis, X-ray fluorescence spectroscopy analysis and X-ray diffraction analysis were adopted to investigate the fundamental nature of raw ash. The triboelectrostatic separation experiments under single conditions were conducted. Carbon enriched products with loss on ignition of 37.45% and ash enriched products with that of 10.32% were obtained whose yield was 29.81% and 32.98%, respectively. Results demonstrated the feasibility of the dry technology to separate residual carbon and ash particles in coal gasification fine ash. Furthermore, triboelectrostatic separation of coal gasification fine ash was significantly affected by differences in particle size and microtopography. Particles of small size were firstly adsorbed by plates in the high voltage electric field. The charge capacity of flake and blocky carbon particles was stronger than that of bonded and flocculated carbon particles allowing them easier to be separated.

Study on recovery of residual carbon from coal gasification fine slag and the influence of oxidation on its characteristics

Coal gasification fine slag (CGFS) is a kind of solid waste that is difficult to separate and utilize. In this work, ultrasonic-assisted flotation was used to recover residual carbon (RC) from CGFS. The ultrasonic treatment not only promotes the separation of RC and ash, but also improves the surface hydrophobicity of CGFS. Compared with conventional flotation, the loss on ignition (LOI) of concentrates and flotation perfect index obtained by ultrasonic-assisted flotation were increased by 12.21% and 4.57%, respectively. In addition, the RC was modified by air and steam. The characterization results of the samples show that air oxidation can significantly improve the oxygen-containing groups on the RC surface, especially the CO groups, and steam treatment is more conducive to increase the disorder of carbon microstructure. Furthermore, the textural properties of the RC were developed by air-steam treatment, and the highest specific surface area and pore volume of the oxidized RC were increased by 27.25 times and 6 times than the raw RC, respectively. RC-A2S2 obtained by air-steam alternating treatment had a high CO2 storage capacity of 2.00 mmol/g at 25 °C. The above research results have important reference value for strengthening of CGFS flotation and utilization of RC.

Dry Magnetic Separation of Ash from a Coal Power Station

The purpose was to expand the applicaation area of dry ash in power plants. It was shown that using ash with a low content of Fe2O3 (~7%) allows to obtain a high-iron concentrate with a Fe2O3 content of 70%. The Fe2O3 extraction from ash is dependent on the magnetic induction and fractional ash composition. The conclusion was made about the possibility of using the obtained magnetite concentrate in ferrous metallurgy in the manufacture of basic iron and steel.

Improving flotation decarbonization efficiency of coal gasification fly ash by mechanically breaking pore: An experimental and molecular dynamics simulation study

The high unburned carbon content of solid waste coal gasification fly ash is the main reason that it cannot be used in the construction material industry, which leads to serious waste of resources and environmental pollution. Currently, decarburization flotation has been a dominating method for coal gasification fly ash resource utilization. However, the flotation process has low efficiency and high reagent consumption because of the rich surface porosity of unburned carbon. Herein, we innovatively developed a mechanical grinding strategy to break the pore distribution on the surface of unburned carbon, significantly reducing the pore size, increasing hydrophobic functional groups and improving the flotation efficiency. The removal rate of unburned carbon is more than 95% in flotation tailings with a mechanical grinding intensity of 120 rpm and grinding time of 30 min. Furthermore, the adsorption of water on porous unburned carbon surface was studied by molecular dynamics simulation for the first time, and the results show that decreasing the particle surface porosity of unburned carbon can accelerate the diffusion rate of water molecules on the unburned carbon surface, improve the wettability of the particle surface and increase the adhesion probability between the unburned carbon particles and bubbles and remarkably improve the its floatability. This work is the first application of mechanically breaking pore to the flotation separation of unburned carbon and ash from coal gasification fly ash and provides valuable inspiration for the design of porous particles flotation, not limited to the separation of gasification fly ash.

An all-in-one strategy for municipal solid waste incineration fly ash full resource utilization by heat treatment with added kaolin

Resourcization has become a popular research topic for the final disposal of municipal solid waste incineration fly ash (MSWI FA). However, the current research is limited to building material preparation or valuable chloride recovery, which may cause resource waste and secondary pollution. A unique process, heat treatment with the addition of kaolin (KL), was presented to achieve complete resource utilization of MSWI FA. The physical properties of ceramsite could be improved by adding KL, and dioxin removal, heavy metals, and valuable chloride separation could be achieved via sintering at 1150 °C. The separation and purification of dust carried by the flue gas during thermal treatment (secondary fly ash) was achieved via wet separation. A building ceramsite with a compressive strength of 24.8 MPa was obtained, whereas dioxin and heavy metal toxicity were far below the standard limits. Heavy metal content was enriched by 12 times, approximately 59.6%, achieved after secondary fly ash separation and purification. A heavy metal product containing 39.5% Zn, 19.1% Pb, and chloride salt containing 41.8% KCl were obtained. This showed a high potential for the developed process to separate multiple valuable elements from ashes. This novel process will further promote the development and application of harmless and resourceful technologies for MSWI FA.

Insight into the mechanism of gasification fine slag enhanced flotation with selective dispersion flocculation

Coal gasification fine slag (CGFS) produced in the coal chemical industry has caused severe environmental pollution and resource waste. To realize the utilization of CGFS, we have to efficiently separate unburned carbon (UC) in CGFS. In this work, based on the discovery of the covering between CGFS particles, the selective dispersion flocculation flotation method is proposed to improve the efficient separation of UC from CGFS. The mechanism of selective dispersion flocculation is revealed through adsorption mode, interaction force between particles, and the particle size distribution of floc under different reagent conditions. Results show that a hydrophilic layer is formed on the surface of ash particles, which hinders the adsorption of PAM and ash particles due to the chemical adsorption of SHMP with ash particles. However, carbon particles are not affected by SHMP and can be directly adsorbed with PAM. This selective adsorption dominates the interaction force of adsorbed particles, and then controls the agglomeration of particles. After selective dispersion flocculation, the original carbon-ash selective agglomeration state is changed to the carbon–carbon selective agglomeration state. D90 of fine carbon particles changed from 110.21 μm to 356.84 μm. Compared with the traditional flotation process, the combustible recovery rate of foam products is increased by 10.4 % and loss on ignition (LOI) is increased by approximately 5 %. This work is conducive to fundamentally understanding the mechanism of selective dispersion flocculation. It is helpful to guide the separation of carbon and ash from gasification slag in industry.