Utilization Of Solid Waste Research Articles

Synchronous recycling of multi-source solid wastes for low-carbon geopolymer preparation: Primary factors identification and feasibility assessment

Exploring efficient utilization technology for solid wastes is important for the sustainable development, and the geopolymer preparation is a potential strategy for the utilization of multi-source solid wastes. However, the complex components in wastes disturbed the actual compositions in raw materials, which limited the strengthening of geopolymer and simultaneous utilizing of multi-source solid wastes. This study aims to determine the primary factors and preparation feasibility of multi-source solid waste-based geopolymer (MSWG). In this study, the geopolymer with multi-source wastes showed significant advantages in mechanical property and emission/cost reduction than that of geopolymer with unitary waste. The mechanical strength of MSWG can reach 115.77 MPa, which increased by 481.76% and 20.88% than that of unitary fly ash-based geopolymer (19.90 MPa) and blast furnace slag-based geopolymer (95.77 MPa), respectively. Meanwhile, the silicon species, aluminum species, and their connectivity forms in different MSWG were characterized and quantitatively calculated by deconvolution, which provided a feasible method for identifying the primary factors (Si–O–Al bond, Q4(3Al), Q4(4Al), and [AlO4]-Q4(4Si)) for mechanical strength. Furthermore, the composite of wastes provided more significant advantage for geopolymer preparation in emission/cost reduction, and the carbon emissions (0.261–0.315 t-CO2/t) of MSWG were reduced by 62.55%–68.90% than that of ordinary Portland cement. These results demonstrated the potential of MSWG in preparation feasibility, strength enhancement, and emission/cost reduction, and provided a feasible and cost-effective method for the simultaneously resourceful treatment of different solid wastes.

Steel slag source-derived FeOOH for enhanced BiVO4 photoelectrochemical water splitting

Green, healthy, and sustainable energy development has always been the cornerstone of global energy development. In this study, industrial waste steel slag was utilized as the raw material, and FeOOH was loaded onto a BiVO4 surface using the impregnation method. The optimized photoanode exhibited a lower onset potential and higher surface activity, achieving a current density of 3.08 mA/cm2 at 1.23 V vs. RHE, and dramatically enhancing the oxygen and hydrogen production efficiencies of the entire system. The incorporation of FeOOH from a steel slag source improves the photoelectrochemical (PEC) water splitting capacity and broadens the steel slag utilization pathways for more economical and green energy use. This study combines the high value-added utilization of solid waste with the field of PEC, presenting a novel approach.

Simulation test study on filling flow law of gangue slurry in goaf

The disposal and utilization of solid waste of coal gangue is one of the main problems in coal mining in China. Injecting coal gangue into goaf in the form of slurry can effectively solve the problems of ground stacking and environmental pollution prevention. In order to obtain the flow law of gangue slurry in the void of the accumulated rock in the goaf, a visualization simulation test device for gangue slurry permeation grouting in the goaf was independently designed. The flow and diffusion characteristics, flow and diffusion velocity changes, void pressure changes, and viscosity changes of three mass concentrations (76%, 78%, 80%) of gangue slurry in the void between caved rock blocks in goaf were studied by visual grouting simulation test. The results show that: (1) The seepage process of gangue slurry in the goaf simulation test is divided into three diffusion forms, namely radial diffusion, axial diffusion, and bidirectional diffusion. The three diffusion forms are interrelated and inseparable. (2) The initial flow velocity of the slurry with different concentrations is different under the same permeation grouting pressure, and the higher the slurry concentration, the smaller the initial flow velocity of the slurry. The velocity of the slurry has a nonlinear relationship with the diffusion distance of the slurry. (3) With the permeation and diffusion of slurry, pressure sensors at different positions are subjected to pressure from bottom to top and enter the pressure boost stage, gradually forming stress peaks. When the slurry exceeds the position of the pressure sensor, the pressure on the pressure sensor is weakened and begins to enter the pressure relief stage, and the stress decline trend gradually becomes gentle with time. (4) The water loss effect occurs during slurry flow interaction with rock mass, resulting in slurry viscosity increasing. The viscosity of the slurry affects the difference in the amount of viscosity change. The research results can provide a certain theoretical basis for the goaf gangue slurry filling project.

Study on the Mechanical Properties and Mechanism of a Nickel-Iron Slag Cement-Based Composite under the Action of Sodium Sulfate.

The accumulated amount of nickel-iron slag has increased with the rapid development of the nickel-iron industry. To determine a method for comprehensively utilizing nickel-iron slag, triaxial compression tests of nickel-iron slag cement-based composite materials under the action of sodium sulfate were conducted, and the effects of the sodium sulfate concentration on the stress-strain relation, shear strength, cohesion, and internal friction angle of the composite materials were analyzed. In addition, the influence mechanism of the nickel-iron slag content and sodium sulfate concentration on the composite was examined. The results revealed that the stress-strain curve of the nickel-iron slag cement-based composites reflected softening. With the increase in the sodium sulfate concentration, the brittleness increased, while the shear strength, cohesion, and internal friction angle decreased; the addition of nickel-iron slag slowed down the rate at which these parameters decrease. Scanning electron microscopy images revealed that nickel-iron slag can improve the internal structure of the cement composite soil, enhance its compactness, and improve its corrosion resistance. The optimum nickel-iron slag content of 14% can improve the cementitious composites' resistance to sodium sulfate erosion in terms of solid waste utilization and cementitious soil performance. The results obtained can provide technical parameters for preparing and designing cement-based composite materials as well as certain theoretical significance and engineering reference value.

Study on mechanical properties and microstructure of steel-polypropylene fiber coal gangue concrete

Incorporating coal gangue into the concrete matrix can realize the utilization of solid waste and reduce the use of natural aggregate. To improve the mechanical properties of coal gangue concrete, this paper designs four-level and four-factor orthogonal tests with coal gangue ceramide substitution rate, coal gangue ceramide sand substitution rate, steel fiber content, and polypropylene fiber content as independent variables. Through multidimensional data analysis of the test results, The main and secondary factors of compressive strength of hybrid fiber coal gangue concrete from strong to weak are the replacement rate of coal gangue ceramic sand, the replacement rate of coal gangue ceramic grain, the content of steel fiber and the content of polypropylene fiber. The optimal content is 30% coal gangue ceramic particle, 25∼30% coal gangue ceramic sand, 0.75∼1% steel fiber, and 0.2% polypropylene fiber. The grey prediction model GM (1, 5) is obtained, which can predict the concrete strength well within the range selected in this paper. The influence of fiber and coal gangue on the microstructure was studied by scanning electron microscopy, and the influence law of interfacial transition zone on the strength of concrete was explored, which provided a theoretical basis for the study of solid waste utilization of coal gangue.

A strategy for reutilization of solid waste by using industrial soda residue to construct calcium vanadate nanomaterials for high-performance aqueous Zn-ion batteries

Here, efficient recycling of waste is incorporated into designing energy storage materials to satisfy the pressing demand of sustainable energy storage technologies. CaV4O9 nanomaterials were firstly synthesized by a hydrothermal route using industrial waste soda residue as raw material, which were used us cathode material for high-performance aqueous Zn-ion batteries. The prepared CaV4O9 nanomaterials display a relatively higher discharge capacity of 292 mAh g−1 at 0.1 A g−1 in combination with a better cycling performance (capacity retention of 82.8% after 1000 cycles at 5.0 A g−1) and an enhanced rate performance, its electrochemical performance is obviously superior to that of calcium vanadate obtained by analytical purity calcium carbonate as raw material. The superior electrochemical performance should be ascribed to the doping effect of metal ions in the CaV4O9 coming from soda residue. This strategy provides a new idea for the high-value and fine utilization of solid waste in energy storage field.

Valorization of olive mill solid waste-derived biochar: An efficient approach for simultaneous adsorption and oxidation of micropollutant in surface water

This study explores the utilization of olive mill solid waste (OMSW) as a source of biochar (BC) for effective removal of micropollutants during surface water treatment. The conversion of OMSW into BC was accomplished via pyrolysis conducted at varying temperatures ranging from 400 to 600 °C. To improve its performance, BC was subjected to activation through either physical-thermal or chemical techniques. BC samples were characterized by SEM microscopy revealing a porous structure, surface area analysis showed an increase in surface area for biochar samples subjected to physical-thermal activation (BC-T) (20 m2/g) and chemical activation using potassium hydroxide (BC-KOH) (70 m2/g) or zinc/iron (BC-Zn/Fe) (456 m2/g). The zero point of charge range from <3 to 4.2 for the different BC samples whereas FTIR measurements showed that physical activation at 900 °C favors a graphitic structure in BC.The catalytic properties of the biochar samples were investigated in the activation of sodium persulfate (PSF) for the oxidation of micropollutants (MPS), including ciprofloxacin (CPX), sulfamethoxazole (SMZ), and paracetamol (PCM), in natural Lake Kinneret water. BC-KOH exhibited the highest removal efficiency, and the removal of MPS increased with higher dosages of BC and PSF. Under optimized conditions ([biochar]: 500 mg/L and [PSF]: 200 mg/L), significant removal efficiencies were achieved for PCM (88.2 % ± 0.7), CPX (80.8 % ± 1.9), and SMZ (64.1 % ± 3.2) after a 5-hour treatment. Finally, MPS adsorbed on BC experienced significant surface oxidation, resulting in removal efficiencies for PCM (97.9 %), CPX (92 %), and SMZ (77.9 %). This oxidation process is expected to enhance the treatment effectiveness prior to regeneration.

The influence of carbon imperfections on the physicochemical characteristics of coal gangue aggregates

In order to promote the development of coal gangue aggregate concrete and the resource utilization of coal gangue solid waste, the coal gangue samples were crushed into aggregates, and then the macroscopic characteristics and microscopic structures of the aggregates were characterized through methods such as calcination, sulfuric acid solution dry-wet cycle, XRD, TG-DTG, and SEM-EDS, based on the Chinese national aggregate standard, the key influencing factors of the physicochemical properties of coal gangue aggregates were analyzed. The results show that coal gangue with lower loss on ignition and carbon content has smaller crushing value, lower water absorption rate, and stronger soundness. The carbon content and carbon distribution significantly affect the macroscopic physicochemical properties of coal gangue aggregates. Carbon, as a defect, is uniformly distributed in coal gangue, which increases the crushing value of coal gangue aggregates and greatly reduces their soundness, leading to the “second-order adverse effect” and “opening window effect”, which are detrimental to the durability of coal gangue aggregate concrete. The composition and physicochemical properties of a large number of coal gangue samples were determined, and the correlation between composition overlay effects on physicochemical properties were analyzed using a “three-dimensional surface”. This analysis confirms the adverse effects of carbon defects on the physicochemical properties of coal gangue aggregates. Carbon content can be used as the primary control index for coal gangue in resource utilization.

Reusing the steel slag to design a gradient-doped high-entropy oxide for high-performance sodium ion batteries

Herein, a high-entropy layered oxide (HEO) is proposed as an outstanding cathode material for long-life sodium-ion batteries. Based on the self-segregation of elements from surface to bulk phase, a multi-element gradient doped high-entropy cathode material is prepared by doping steel slag with available elements (Mg, Al, Si, Fe, Ca). The surface high-entropy region vastly improves the air stability of materials and reduces surface impurities and side reactions. The Na-O-Mg configuration of near-surface high-entropy region continuously stimulates the anionic redox activity, and the DEMS shows the high-strength Al-O bonding achieves zero oxygen release. Therefore, the LNSM-0.01 reveals a stable capacity of ∼24 mA h g−1 in the range of 4.0–4.5 V. The Ca2+ in bulk phase high-entropy region disrupts the Na+/vacancy ordering transition and enhances the kinetic performance (90 mA h g−1 at 1000 mA g−1), while Fe2+/3+ provides a large amount number of charge compensation. Further, DFT calculations prove that the entropy stability based on synergistic effect immeasurably reinforce the layered oxide configuration, building a more robust structural framework during cycling. This work deepens the understanding on multi-element gradient doping to prepare HEOs, and provides a novel pathway for resource utilization of solid waste.

An intelligent design method for new binder material activated by solid wastes by integrating attention-based tree model and heuristic optimization algorithm

To promote the utilization of industrial solid waste, a new green binder system namely SCGF for sustainable concrete is developed, in which slag-fly ash is activated by soda residue-carbide slag. However, the mix design of the SCGF is challenging due to heavy workload and the lack of theoretical basis. The relationship between mix proportion and mechanical properties of SCGF needs to be accurately expressed. In this paper, an intelligent design method of SCGF is proposed by coupling the attention mechanism, machine learning and multi-objective heuristic optimization algorithm. After training with experimental data, the prediction performance of attention-based tree model is evaluated. Multiple Pareto optimal solutions can be obtained by the proposed intelligent mix proportion design method. The results show that attention-based tree models perform higher accuracy (accuracy > 95 %) and better measures than that of classical tree models. Compared the strength and cost of SCGF to cement mortar, the mix proportion designed in this study has obvious advantages in environmental protection and economy (>50 % cost saving). Therefore, the proposed method can provide a theoretical basis for the recycling and utilization of industrial solid wastes.

Aromatics production from relay catalytic pyrolysis of cow manure using Ru/C and ZSM-5 dual catalysts synthesized from coal gasification fine slag

Resource utilization of solid waste can aid in gradual substitution of fossil fuels while achieving waste recycling. In this study, residual carbon and ash slag from the coal gasification fine slag were separated by froth flotation, and then was used to prepare Ru/C and ZSM-5 dual catalysts with carbon-rich and ash-rich components as raw materials, respectively. The performance of two catalysts for catalytic upgrading of volatiles from pyrolysis of cow manure (CM) to produce light aromatic hydrocarbons was systematically investigated. The direct pyrolysis products of CM mainly included alcohols, ketones, ethers, and other oxygen-containing compounds. When ZSM-5 was used as the catalyst, the yield of monocyclic aromatic hydrocarbons (MAHs) increased significantly due to the better catalytic cracking and aromatization abilities of ZSM-5 catalyst. However, the yield of phenols in the pyrolysis products improved when Ru/C was used as the catalyst due to the cleavage effect of Ru/C on the C–O bond. When Ru/C and ZSM-5 were used as dual catalysts in relay catalytic pyrolysis of volatiles, the increase in MAHs yield in the pyrolysis product was higher than the total increase obtained under Ru/C and ZSM-5 single catalysis. The possible pathways for the generation of MAHs from CM under Ru/C and ZSM-5 relay catalytic pyrolysis were revealed by the pyrolysis experiment performed on model compounds.

A Preliminary Study on the Improvement of Gangue/Tailing Cemented Fill by Bentonite: Flow Properties, Mechanical Properties and Permeability.

Backfill mining has significant advantages in safe mining, solid waste utilization and ecological environmental protection, but solid waste materials (tailings, gangue and coal gasification slag, etc.), as derivative residues of the chemical and metallurgical industries, contain a large number of heavy metal elements, which is posing great challenges to the underground environment after backfill. In order to study the feasibility of bentonite for reducing the permeability of gangue/tailing sand cemented backfill body, relevant tests were carried out from the basic performance index, flow performance and mechanical properties of paste backfill materials. The test results show that bentonite has a significant effect on the water secretion rate of cemented fillers, and also promotes the improvement of slump and diffusion diameter of backfill slurry. The enhancement effect of mechanical properties in the early stage is not obvious, mainly concentrated in the middle and late stages of specimen curing. With the increase of bentonite content, the 28-day uniaxial compressive strength increased from 7.1 MPa and 7.9 MPa to 8.7 MPa and 9.0 MPa, respectively. Bentonite is filled between the pores of the cemented backfill with its fine particles and water swelling, which can reduce the porosity and permeability of the gangue and tailings cemented backfill. Therefore, on the premise of satisfying the flow and mechanical properties of paste backfill, bentonite can be used to improve the permeability of cemented backfill and reduce the leaching and migration of heavy metal ions.

The design of ternary all-solid-waste binder for solidified soil and the mechanical properties, mechanism and environmental benefits of CGF solidified soil

Utilization of industrial solid waste to develop binder and solidified waste soil, which can achieve ‘waste control by waste’. Based on the alkali-activated mechanism and interaction mechanism of the binder-soil particles-water, the component distribution ratio design method of ternary all-solid-waste binder for solidified soil was constructed. The CGF all-solid-waste alkali-activated binders (CGF binders) are composed of general industrial solid waste, with which calcium carbide slag (CCR) as alkali activator, ground granulated blast furnace slag (GGBS) and fly ash (FA) as high and low-activity pozzolanic material respectively. Macro and microscopic tests were performed to reveal the mechanical properties and solidification mechanism as well as quantitatively evaluate the environmental and economic benefits of CGF solidified pure clay, pure silt, and pure sand (CGF solidified soils). The results revealed that the strength of CGF solidified soils was significantly affected by the alkali activator content and the activity of pozzolanic materials, and the strength of partially CGF solidified soils were higher than cement solidified soils under the same conditions. The relationship between binder-soil particles-water, viz., the alkali-activated reaction between binder and water, along with the pozzolanic reaction between the alkali activator and the clay particles jointly determined the strength and strength growth rate of the solidified soil. The strength of the optimal CGF solidified soils were 1.38–2.30 times higher than cement solidified soils, however, the carbon emission per unit strength and cost per unit strength of the cement solidified soil were 71.43–125.02 times and 3.53–5.88 times higher than the optimal CGF solidified soils, respectively. The findings can provide a reference for the design and development of solid waste-based binders suitable for solidified soils.

Utilization of solid mine waste in the building materials for 3D printing.

3D printing technology is gradually considered to be a rapid development of a green revolution in the field of architecture. Recently, utilizing solid mine waste to replace natural sand not only greatly reduces the 3D printing costs, but also contributes to an environmental sustainability development. However, most solid waste inevitably has an impact on the inherent mechanical strength and printability of concrete materials. It is an urgent requirement to expand the alternative materials and improve the overall property of 3D concrete materials. This paper reported an innovative concrete material that replaced natural sand with fine limestone powders for 3D concrete printing applications. The experimental measurements were performed including microstructures characteristics, flowability, buildability, shrinkability, layer-interface properties, mechanical properties and interlayer bonding strength. Besides, an effective method was proposed to characterize the printable properties of concrete materials and then the reasonable limestone powder replacement ratio was determined. Based on the investigation results, appropriate substituting limestone powder (40%) can effectively improve the grading of the concrete, thus promoting its printability and buildability. Moreover, the microstructures of the 3D printing concrete materials after curing were denser and their mechanical property improved by approximately 45%. With the further increase of replacement ratio, the reduction in the flowability led to a decrease of the printability. A large number of fine particles increased the shrinkage of the curing process and some bubbles were stranded inside the materials due to its increase in the viscosity, thereby reducing the mechanical properties of the hardened material. The produced concrete for 3D printing can be treated as an eco-friendly building material that contributes to the rational development and resource utilization of solid water, thus promoting the sustainable development of construction field.

Construction of Testing Standards System for Comprehensive Utilization of Bulk Industrial Solid Waste

According to the general steps of comprehensive utilization of each type of bulk industrial solid waste, including fly ash, coal gangue, tailings, smelting slag, industrial by-product gypsum, and red mud, we construct the testing standards system for comprehensive utilization of bulk industrial solid waste in China. The standards system, according to the lifecycle stage of "raw materials - pre-treatment - processing - forming products - using products", can be divided into 5 standard subsystems, namely a subsystem of physical property testing standards for raw materials, a subsystem of chemical property testing standards, a subsystem of process testing standards, a subsystem of the product quality performance testing standards and a subsystem of the environmental impact testing standards. The standards system provide top-level guidance for the implementation and development of comprehensive utilization testing methods for bulk industrial solid waste.

Microwave-enhanced selective leaching calcium from steelmaking slag to fix CO2 and produce high value-added CaCO3

The abundant resources of steel slag make it an intriguing prospect for long-term CO2 storage by mineral carbonation. Herein, the dissolution of steel slag in an acetic acid (HAc) solution and the fixation of CO2 in the leachate of steel slag to synthesize high-value CaCO3 were investigated. Results show that the microwave water bath condition is beneficial for improving the leaching rate of Ca and Mg elements in steel slag, while the low-concentration HAc solution displays high selectivity for Ca + Mg. In a water bath reaction enhanced by microwave, the leaching rate and selectivity of Ca + Mg can be increased by elevating the reaction temperature, extending the leaching time, lowering the concentration of HAc solution, and increasing the stirring rate. The kinetic parameters of the calcium element, including the apparent activation energy, were determined to be 14.51 kJ·mol−1, suggesting control by surface chemical reactions. Finally, high-purity CaCO3 crystal whiskers can be synthesized under 400 W ultrasonic conditions with a reaction temperature of 70 ℃, reaction time of 15 min, and a solution pH at 9.1 by introducing 20 % CO2 into the leachate. This strategy facilitates the concurrent utilization of dilute CO2 flue gas and voluminous solid steel slag waste, thereby improving the economic and environmental performance of the steel industry.

Case Study on the Performance of High-Flowing Steel-Fiber-Reinforced Mixed-Sand Concrete

To promote the efficient utilization of bulk solid wastes, including superfine river sand and fly ash, high-flowing steel-fiber-reinforced mixed-sand concrete (SFRMC) was developed in this study. Superfine river sand and coarse manufactured sand were mixed in a proportion of 4:6 to make the mixed sand. Fly ash, with a content of 30~75%, was blended with 0~12% silica fume on the premise of equivalent activity. The water dosage and sand ratio were adjusted with the volume fraction of steel fiber, which varied from 0.4 to 1.6%, to ensure the high flowability of fresh SFRMC. The mechanical properties, including cubic and axial compressive strengths, modulus of elasticity, splitting tensile strength, and flexural strength and toughness of the SFRMC, were analyzed, accounting for the influences of the contents of fly ash and steel fiber. The predictive formulas for the splitting tensile strength, modulus of elasticity, and flexural strength were proposed by introducing the influencing factors of steel fiber. The SFRMC showed an increased modulus of elasticity with increases in the steel fiber factor, and flexural toughness was enhanced with increased contents of both steel fiber and fly ash.

Research of the workability, mechanical and hydration mechanism of coal gangue-construction solid waste backfilling materials

In order to effectively address the issues of coal gangue emissions and the accumulation of construction solid waste, a combined treatment of coal gangue and construction solid waste can be implemented. In this study, a composite backfilling material was designed, with coal gangue and construction solid waste as the main aggregates. Through laboratory experiments, the time-dependent flow performance, mechanical properties, and microstructure of the material were analyzed under different proportions of factors including fly ash content, substitution rate of construction solid waste, mass concentration, and water reducing agent content. The research results indicate the following: The effects of reducing agent content, mass concentration, fly ash content, and substitution rate of construction solid waste on flow performance increased in that order. The addition of construction solid waste is negatively correlated with the strength of filling materials. The appropriate substitution ratios for FA, construction solid waste, mass concentration, and reducing agent were determined to be 21 %, 50 %, 80 %, and 0.6 %, respectively. The CH component in the material exhibited a trend of initially increasing and then decreasing, providing a large amount of reactants for secondary hydration reactions and strengthening the internal structure of the material. In the middle stage of hydration, FA and activators played an important role in the later stage by providing raw materials for secondary hydration, enriching the internal composition of the structure, and enhancing the backfilling performance of the backfilling material. This study can achieve the recycling and utilization of coal gangue and construction solid waste, and enhance the stability and bearing capacity of backfilling materials.

Comprehensive utilization of blast furnace slag, municipal sludge and kaolin clay in building brick manufacture: Crystalline transformation, morphology observation and property assessment

At present, the comprehensive utilization of bulk industrial solid waste has attracted wide attention. The recycling of industrial solid waste in building materials not only provides valuable insights for the management of solid waste, but also alleviates the over-exploitation of natural clay resources in the construction industry. In this study, municipal sludge (MS) and blast furnace slag (BFS) were incorporated into kaolin clay (KC) to synthesize sustainable composite bricks, and the sintering effects and engineering properties of bricks were adjusted by changing BFS dosages. The results indicated that the addition of BFS would promote liquid glassy phase production in bricks due to the higher content of alkali/alkaline-earth metal oxides, and the ingredient, viscosity and content of liquid glassy phases could also be regulated through varying the dosage of BFS (0-15%), thereby affecting the pore structure, particle arrangement/consolidation and performance of bricks. Among all synthesized bricks, the optimum dosages of BFS, MS and KC for satisfying the building standard thresholds were 10%, 40% and 50%, with corresponding linear shrinkage, porosity, density, water absorption, compressive and flexure strengths of 12.97%, 18.15%, 1.83 g/cm3, 0.82%, 15 MPa and 38 Mpa, respectively. Finally, mechanism analysis further demonstrated that the formation and evolution of liquid glassy phases were the key responsibility for adjusting the brick micromorphology and performance. Based on this study, using MS and BFS in brick manufacturing benefited the value-added utilization of industrial solid wastes, clean protection of environments and sustainable production of building materials, providing a reference for the process optimization and potential application of MS and BFS wastes in masonry construction.

Precipitation of silica by CO2 bubbles/microbubbles and kinetics research

In China, the production of silica is mainly achieved through its precipitation process. Carbonization of precipitated silica makes full use of carbon-containing flue gases, such as lime kiln gas, thereby reducing the cost of silica production and making it an effective way of CO2 resource utilization. It is an important research field of cleaner production. The research in this study focuses on the production of precipitated silica through carbonation. This study evaluated the impact of Na2O·3.45SiO2 concentration and carbonization temperature during the process. The pH and temperature of the suspension were observed in order to evaluate the proposed process and contrast it with the traditional bubble generator process. The optimization of carbonization mass transfer by microbubbles was preliminarily studied by experiments and computational analysis methods. The results demonstrated that when the Na2O·3.45SiO2 concentration was at 0.2 mol/L and the temperature was 60 °C, the microbubbles could improve the efficiency of CO2 utilization by 1.9 times. The research on the specific surface area (BET) of the prepared silica powder revealed that BET decreased with the increase of Na2O·3.45SiO2 concentration when bubbling was present. Under bubbling/microbubble conditions, when the temperature was 60 °C, with the Na2O·3.45SiO2 concentration increased from 0.1 M to 0.5 M, the BET decreased by 29.2% and 16.8%, respectively. However, when the concentration of Na2O·3.45SiO2 increased to 0.5 M, the introduction of microbubbles made the BET higher than the bubble by 13.3%. Under bubbling/microbubble conditions, when the temperature increased from 25 °C to 60 °C, BET decreased with the increase of temperature, with the BET decreased by 13.5% and 12.8%, respectively. Furthermore, the kinetics of carbonation at room temperature and 0.2 mol/L Na2O·3.45SiO2 with bubbling were calculated. The results showed that carbonation was pseudo second-order reaction process. The process realized the solid waste utilization of CO2, and had important guiding significance for the preparation of high-performance silica.