Effective Diffusion Coefficient Research Articles

Low cost and sustainable biochar-based nanocomposite for the effective remediation of persistent Alizarin Red S

ABSTRACT Huge volumes of wastewater including dyes are occasionally released to the environment lacking any treatment or landfilled as waste that are challenging to manage and remove regardless of the treatment technique employed. Therefore, this work focused on removal of Alizarin Red S (ARS) as an anionic dye from aqueous solutions. To achieve this goal, bovine bone was employed as a source of hydroxyapatite which was modified by Fe(II) to produce a new biosorbent material with magnetic properties. Comparative studies between the hydroxyapatite (HA) and the magnetic hydroxyapatite (HA – Fe) have been executed to remove ARS dye. The Zero Point Charge (pHZPC) was estimated to be 8.4 and 10.8 for HA and HA – Fe, respectively. Hence the best pH for the sorption was desired at 5.0 which is less than pHZPC. The kinetic investigations demonstrated that the values of qt steadily reached equilibrium after 60 min to be 173 and 142.6 mg/g by HA and HA – Fe, respectively. The sorption obeys pseudo-second-order theory and the most likely nature of ARS sorption by both HA and HA – Fe is chemisorption since the effective diffusion coefficient was in the order of 10−15 m2/s. The maximum sorption capacity of ARS by HA and HA – Fe was computed from Langmuir theory to be 250 and 370.2 mg/g, respectively. Also, using the Dubinin-Radushkevich isotherm, the mean free energy was identified to be between 8 and 16 kJ/mol, this indicates that the sorption follows chemical ion exchange. Based on the thermodynamics, the sorption has endothermic nature and is spontaneous. Overall, magnetic hydroxyapatite is thought to be a good option for wastewater treatment because it is an eco-friendly material.

Αn Experimental and Numerical Study on the Drying of Celery (Apium Graveolens L.) Growing in Southern Tunisia

The present work experimentally investigates the curves of the drying kinetics of celery leaves (Apium Graveolens L.) in a drying convective oven. These curves were determined at 50°C, 60°C, and 70°C. For the fitting of the experimental results, the Lewis, Handerson, and Pabis, Page, Midilli &Kucuk, Logarithmic, Modified Page, Wang, and Singh and Two Terms models were used. The Midilli & Kucuk model provided the best fit for the experimental results. The effective water diffusion coefficient (Deff) varied from 3.65×10-10 m2/s to 7.29×10-10 m2/s in the considered temperature range. The higher temperature gave a higher effective water diffusion coefficient and Drying Rate (DR). The activation energy calculated using an exponential expression based on the Arrhenius equation was 31.72 kJ/mol. The Characteristic Drying Curve (CDC) was also determined as a three-degree polynomial.

Extraction of High Stearic High Oleic Sunflower Oil Using Eco-Friendly Solvents

The present work aimed to evaluate the extractive p erformance of three green solvents—absolute ethanol, hydrated ethanol (96%), and absolute isopropanol (AIP)—in high stearic high oleic sunflower seeds, comparing them with the conventional solvent hexane. The oil yield from exhaustive Soxhlet extraction with hydrated ethanol was significantly lower, with no significant differences being observed among the other solvents. Extraction with AIP produced the extract with the lowest non-lipid material content and the oil with the lowest concentration of crystallizable waxes, showing a 53% reduction compared to hexane. Since AIP showed a higher extraction efficiency than absolute ethanol after 4 h of processing, its oil extraction kinetics when used as a solvent were further studied. A modified Fick’s diffusion model revealed that, for hexane extraction at 50 °C, the effective diffusion coefficient and the washing fraction were higher than those for AIP extraction (26% and 5.4% higher, respectively). No clear dependence of the oil extraction kinetics on the temperature was observed between the studied temperatures (50 °C and 70 °C). The results showed the feasibility of using absolute ethanol and AIP as alternatives to hexane. Additionally, isopropanol presented operational advantages, producing oil that required less dewaxing during refining than that extracted with hexane or ethanol and showing higher oil selectivity than ethanol.

Transportation behaviour of OH and H2O2 in plasma-treated water

Abstract The transportation of plasma-generated species through a liquid environment is a key step within the plasma-driven biocatalysis process, but is also of great importance for other systems with plasma-liquid interfaces. The aim of this study is to explore the transportation processes and lifetime of plasma-generated species in an aqueous solution. Therefore, a combination of experimental methods, reactive molecular dynamics simulations, and reaction-diffusion modelling was used. Experimentally, an atmospheric pressure plasma jet was used to treat an aqueous sample. Convective transport was visualized by particle image velocimetry in the plasma-treated water. Chemiluminescence measurements of OH were conducted by the use of luminol and 2D-UV-absorption spectroscopy was used to detect H2O2 in the plasma-treated water. The strength of convective transport was found to decrease with the gas flow rate through the jet, and at low gas flows, an effective diffusion coefficient for H2O2 could be calculated. OH was mainly present at the liquid surface under all treatments investigated.
The reactive molecular dynamics simulations form the basic model of an ideal system, where all transportation is purely diffusion-driven, and molecular diffusion coefficients can be calculated. The results of the MD simulations were compared with the experimental studies to gain a deeper understanding of the differences between the ideal and the real system. To bridge the gap between the time scales of the MD simulations and the experiments, a kinetic model was used to understand the spatio-temporal changes and the influence of transport mechanisms and reaction chemistry. For low flow rate cases good agreement between experimental measurements and kinetic modelling could be obtained when the experimentally measured effective diffusion coefficient was used as input to the model. The differences in the H2O2 concentration profiles in the liquid when using the molecular diffusion coefficient derived from MD and the effective diffusion coefficient from the experimental measurements are highlighted.

Drying kinetics and thermodynamic properties of peanut seeds (Arachis hypogaea L.)

The aim of this study was to evaluate the drying process and determine the activation energy, effective diffusion coefficient, and thermodynamic properties of peanut seeds. The peanut seeds (variety “Amena 018”), harvested with an initial moisture content of 0.36 ± 0.003 kg kg-1 db, were dried in a forced circulation oven at temperatures of 40, 45, 50, 55, and 60°C until they reached a final moisture content of 0.11 ± 0.001 kg kg-1 db. The mathematical models were adjusted by nonlinear regression using the Gauss-Newton method, Akaike's information criterion (AIC), and Schwarz’s Bayesian information criterion (BIC). The two-term model showed the best fit for the temperatures of 40, 45, 50, and 55°C, and the two-term exponential for 60°C; the drying rate increased with increasing temperature and decreased with increasing drying time, the effective diffusion coefficient varied from 7.5097 × 10-11 to 11.5741 × 10-11 m2 s-1 for the 40-60°C range, and the activation energy was 18.54 kJ mol-1. The enthalpy, entropy, and Gibbs free energy values ranged from 15.931 to 15.765 kJ mol-1, -0.110401 to -0.110916 kJ mol-1 K-1, and 50.504-52.718 kJ mol-1, respectively, for temperatures from 40 to 60°C.

Heat and Mass Transfer in Shrimp Hot-Air Drying: Experimental Evaluation and Numerical Simulation

Shrimp is one of the most popular and widely consumed seafood products worldwide. It is highly perishable due to its high moisture content. Thus, dehydration is commonly used to extend its shelf life, mostly via air drying, leading to a temperature increase, moisture removal, and matrix shrinkage. In this study, a mathematical model was developed to describe the changes in moisture and temperature distribution in shrimp during hot-air drying. The model considered the heat and mass transfer in an irregular-shaped computational domain and was solved using the finite element method. Convective heat and mass transfer coefficients (57.0–62.9 W/m2∙K and 0.007–0.008 m/s, respectively) and the moisture effective diffusion coefficient (6.5 × 10−10–8.5 × 10−10 m2/s) were determined experimentally and numerically. The shrimp temperature and moisture numerical solution were validated using a cabinet dryer with a forced air circulation at 60 and 70 °C. The model predictions demonstrated close agreement with the experimental data (R2≥ 0.95 for all conditions) and revealed three distinct drying stages: initial warming up, constant drying rate, and falling drying rate at the end. Initially, the shrimp temperature increased from 25 °C to around 46 °C and 53 °C for the process at 60 °C and 70 °C. Thus, it presented a constant drying rate, around 0.04 kg/kg min at 60 °C and 0.05 kg/kg min at 70 °C. During this stage, the process is controlled by the heat transferred from the surroundings. Subsequently, the internal resistance to mass transfer becomes the dominant factor, leading to a decrease in the drying rate and an increase in temperatures. A numerical analysis indicated that considering the irregular shape of the shrimp provides more realistic moisture and temperature profiles compared to the simplified finite cylinder geometry. Furthermore, a sensitivity analysis was performed using the validated model to assess the impact of the mass and heat transfer parameters and relative humidity inside the cavity on the drying process. The proposed model accurately described the drying, allowing the further evaluation of the quality and safety aspects and optimizing the process.

The Pore Structure Characteristics of Mortar and Its Application in the Study of Chloride Ion Transport Performance

The cement-based materials widely used in infrastructure construction, such as bridges and ports, are subjected to seawater erosion and medium erosion during their service life, and their durability has always been a concern. The diffusion coefficient of chloride ions is an important indicator in the research of cement-based materials’ durability, and the pore structure is one of the most fundamental reasons affecting the diffusion behavior of chloride ions. In this paper, Mercury intrusion porosimetry (MIP), Nuclear magnetic resonance (NMR), and Nitrogen adsorption method (NAD) were used to analyze the pore structures of mortars with different volume fractions of sands. The relationship between mortar pore structure and chloride ion diffusion coefficient was established to predict its chloride ion diffusion coefficient. It may provide a new idea for studying the durability of cement-based materials. Results indicated that similar to cement paste, the pore structure of mortar satisfied the fractal characteristics of solid phase within a certain range of pores. The most probable gel pore diameter of mortars with different sand volume fractions was about 4 nm, while the most probable capillary pore diameter was approximately 46 nm, and the critical pore diameter was ranging from 50 to 60 nm. MIP results indicated that with the increase in sand volume fraction (ϕagg), the total porosity (fmip) of the mortar decreased, satisfying the relationship of fmip = 0.1859 − 0.0789ϕagg. However, the porosity of the matrix (fbase) increased with the increase in sand volume fraction, which was due to the introduction of more interfaces by the addition of aggregates. The effective chloride ion diffusion coefficient (Dcp,base) of the matrix can be obtained by fitting. Based on this, the interface transition zone (ITZ) and the cement matrix were comprehensively considered as a whole fractal phase. The predicted value of the chloride ion diffusion coefficient obtained by the Mori–Tanaka homogenization method was in good agreement with the results obtained from rapid chloride migration (RCM) experiments, and the maximum error between the simulated and experimental values did not exceed 11%. This finding can provide new ideas for accurately predicting the chloride ion diffusion coefficient of mortar and even concrete.

Effects of temperature and humidity on drying kinetics, final quality and cell wall pectin content of wolfberry (Lycium barbarum)

The effects of four groups of hot-air drying methods, including constant temperature (50 °C) and constant humidity (10%) (CTCH), constant temperature (50 °C) and variable humidity (60%-47%-35%-23%-10%) (CTVH), variable temperature (40 °C-46 °C-52 °C-58 °C-64 °C) and constant humidity (10%) (VTCH), variable temperature (40 °C-46 °C-52 °C-58 °C-64 °C) and variable humidity (60%-47%-35%-23%-10%) (VTVH), on the drying kinetics, product quality and the content of pectin polysaccharides in cell wall of wolfberry were studied. Among them, VTVH showed the highest drying efficiency with the shortest drying time of 13 h, which was 9.52% shorter than that of CTCH, and the highest effective water diffusion coefficient for wolfberries (9.356 × 10−9 m2·min−1). After VTVH drying, samples showed the highest polysaccharides content (46.48%) and rehydration rate (52.24%), as well as the lowest color difference (6.07) and shrinkage rate (66.38%). The content of water-soluble pectin (WSP) in wolfberry was the highest under VTCH drying condition, which was 48.67% higher than that of CTVH drying condition.

All-optical mapping of Ca2+ transport and homeostasis in dendrites

Calcium mediates many important signals in dendrites. However, the basic transport properties of calcium in dendrites have been difficult to measure: how far and how fast does a local influx of calcium propagate? We developed an all-optical system for simultaneous targeted Ca2+ import and Ca2+ concentration mapping. We co-expressed a blue light-activated calcium selective channelrhodopsin, CapChR2, with a far-red calcium sensor, FR-GECO1c, in cultured rat hippocampal neurons, and used patterned optogenetic stimulation to introduce calcium into cells with user-defined patterns of space and time. We determined a mean steady-state length constant for Ca2+ transport ϕ ∼ 5.8 μm, a half-life for return to baseline t1/2 ∼ 1.7 s, and an effective diffusion coefficient D ∼ 20 μm2/s, though there were substantial differences in Ca2+ dynamics between proximal and distal dendrites. At high Ca2+ concentration, distal dendrites showed nonlinear activation of Ca2+ efflux, which we pharmacologically ascribed to the NCX1 antiporter. Genetically encoded tools for all-optical mapping of Ca2+ transport and handling provide a powerful capability for studying this important messenger.

Investigation of the effective diffusion coefficient of nitrogen gas using high-resolution 3D X-ray computed tomography images of nuclear-grade graphite IG-110

Investigation of the effective diffusion coefficient of nitrogen gas using high-resolution 3D X-ray computed tomography images of nuclear-grade graphite IG-110

Thermo-kinetic behavior of closed-loop heat pump dryer with different drying chambers for holy basil leaves drying application: an experiment approach

ABSTRACT A closed-loop heat pump drier was designed and constructed with three different drying chambers (tray, fluidized bed, and integrated) to investigate the drying kinetics (drying rate and specific moisture evaporation rate) of holy basil leaves in this research work. The significance of drying temperature, air velocity, and mass of leaves on the performance of the dryer chambers was explored and compared through an experimental investigation. In addition, the present research focuses on analyzing the significance of drying air temperature (45, 50, and 55°C), air velocity (1.5, 2.0, and 2.5 m/s), and mass of holy basil leaves (5, 6, and 7 kg) on the performance of the dryer chambers. In tested combinations, the specific moisture evaporation rate and drying rate are higher in the integrated drying chamber. Notably, the effective moisture diffusivity coefficient exhibited a range of values from 2.68166 × 10−10 to 6.10243 × 10−10 m2/s. The design of the experiment approach is applied to optimize the number of experiments, and an analysis of variance was conducted to identify the most influential parameter. The results showed that temperature had a greater effect, accounting for 32% of the variation in the moisture evaporation rate.

Elucidating the impact of gas transport on high-performing air electrodes: a 1D physically based model unveiling the correlation between microstructure and impedance response

Abstract A 1D physically-based model on high performing air electrodes for Solid Oxide Cells is used to unravel the physical mechanisms lying behind the resistive peaks observed in experimental impedance data, posing particular attention to the low frequency contribution. In particular, the latter is commonly observed when analyzing the impedance response of high performing air electrode materials but its physical interpretation is still questioned. The model construction is grounded on the microstructural characteristics of conventional screen-printed electrodes. These properties were extracted by combining the statistical analysis of experimental 2D images taken with a scanning electron microscope and a validated microstructural model able to generate the synthetic 3D reconstructions of homogeneous electrode architectures. The implemented electrochemical model was tailored on the specific characteristics of a reference high performing SmBa0.8Ca0.2Co2O5+δ electrode material. Specifically, the model was used to reproduce its stationary and dynamic behavior between 650-750 °C, with an inlet oxygen partial pressure between 0.1-1 atm. The performed simulations unraveled the physical mechanisms lying behind the resistive contributions emerging from the impedance data. In particular, the effect of gas transport was analyzed in detail to understand the impact of the electrode microstructure on its electrochemical behavior. A sensitivity analysis on the effective gas diffusion coefficient highlighted that, in the investigated operating conditions, the electrochemical performance of classic screen-printed air electrodes is not limited by the gas diffusion. On the contrary, the low frequency contribution evidenced in the Nyquist plots was addressed to the impact of gas conversion. The developed electrochemical model successfully completed the correlation between microstructural and electrochemical properties and the results included in this work can be extended to different electrode materials tested in similar operating conditions.

Effect of various novel pre-treatments on drying and rehydration behaviour of ginger and quality attributes of dried ginger

Abstract The present study focused on the influence of different solution-based osmo-sonic pre-treatments on the drying, rehydration, and quality attributes of ginger cubes. Osmo-sonic pre-treated drying followed the empirical page model, and rehydration was better explained by the exponential model. All the pre-treatments increased the effective moisture diffusivity and mass transfer coefficient, which increased the drying rate from 22.34 to 79.78 %. Pre-treatment led to an increase in appearance by an increase in L* and a* and a decrease in b*. The FTIR spectra showed the absence of a new functional group, but a change was observed in the characteristics band upon pre-treatment. The comparison of different pre-treatment showed that the CA + US pre-treatment had a better drying profile, whereas DW + US had a better antioxidant profile with the highest TPC (22.31 mg GAE/g), TFC (58.37 mg QE/g), DPPH inhibition (89.01 %), and ABTS assay (13.27 mg TE/g).

Optimization of the Drying Process for Gamma-Irradiated Mushroom Slices Using Mathematical Models and Machine Learning Algorithms

Concerns over dried product quality and energy consumption have prompted researchers to explore integrated techniques for improving quality and reducing energy use. This study investigates the effect of gamma irradiation pretreatment (0, 1.2, 2.4, and 3.6 kGy) on button mushroom slices, followed by thin-layer drying at 50, 60, and 70 °C. The results indicated that increasing irradiation dose and drying temperature significantly reduced drying time. The Midilli model provided the best fıt to the drying data (R2 = 0.9969–0.9998). Artificial neural networks (ANN) accurately predicted moisture variations, achieving R2 = 0.9975 and RMSE = 0.0220. The Support Vector Machine (SVM) algorithm, employing the Pearson universal kernel in normalized mode, also performed well, with R2 = 0.9939 and RMSE = 0.0344. Similarly, in the k-nearest neighbors (kNN) algorithm with three neighbors (k = 3), the R2 and RMSE values were 0.9888 and 0.0458, respectively. Gamma irradiation enhanced the effective diffusion coefficient (Deff) to 10.796 × 10−8 m2/s, and reduced activation energy (Ea) to 11.09 kJ/mol. The highest heat utilization efficiency (41.1%) was observed at 3.6 kGy and 50 °C. These findings highlight the potential of integrating gamma irradiation pretreatment and advanced drying techniques to optimize energy use and improve the quality of dried mushroom slices.

Drying Kinetics of Leucaena esculenta Seeds Using a Solar Dryer

The drying kinetics and physical and chemical characteristics of Leucaena esculenta seed drying using a forced convection solar dryer are described. The drying kinetics behavior is examined for three experiments under climate conditions of three different winter days in central Mexico, observing significant effects related to the reported pH levels of the seeds with values of 6.34, 5.98, 5.97, 5.82, and 6.07. The airflow measurements inside the drying chamber were observed, including the geometric dimensions, color, appearance, weight, and moisture loss, and the effective diffusivity coefficient Deff of Leucaena esculenta with values between 1.23 × 10−7 and 8.09 × 10−9 m2s. Solar drying, with the technology used in this study, is a viable alternative to give added value to Leucaena esculenta. This study can be the basis for developing alternatives to preserve seeds for animal and human consumption.

Optimal diffusion of chiral active particles with strategic reorientations.

We investigate the competing effects of the simultaneous presence of chirality and generalized tumbles in the dynamics of an active Brownian particle. Chiral active particles perform circular motions that give rise to slow transport at late times. By interrupting these circular trajectories at the right time by performing a tumble at the correct angle, we show that particles can enhance their diffusion. After deriving exact expressions for the orientational propagator and correlations, we use this to calculate the first two moments of displacement. For the effective diffusion coefficient, we study various optimal tumbling strategies. We show that under optimization of the tumbling rate, the case of symmetrically distributed tumbles always gives rise to enhanced diffusion, with an effective diffusion coefficient taking a universal value. Next, two cases are considered in detail, namely, directional reversal and tumbles at an arbitrary but fixed angle. We discuss how asymmetric tumbles can enhance diffusion beyond that of symmetric tumbles. Finally, we discuss a situation where the reorientations are realized dynamically in finite time.

Investigation of the Kinetic Dynamics in the Intermittent Microwave–Hot-Air Combined Drying of Peanut Pods

The drying process is crucial for maintaining the quality of peanut pods and mitigating the risk of mold proliferation. The aim of this study was to investigate the kinetic characteristics of a synergistic intermittent microwave and a hot-air-drying technique, with an emphasis on enhancing efficiency and reducing energy consumption. A comprehensive analysis was performed on key parameters—including moisture content, moisture ratio, drying rate, and effective moisture diffusion coefficient—to elucidate moisture migration during the drying process. The findings indicated that higher microwave power significantly accelerates the drying rate while substantially shortening the drying time for peanut pods. The effective moisture diffusion coefficient was found to range from 0.987 × 10−9 to 1.227 × 10−9 m2/s, with the Verma model demonstrating superior accuracy in predicting drying behavior. The experiment achieved a minimum specific energy consumption of 12,535 kJ/kg and a maximum thermal efficiency of 18.1% at a microwave power density of 0.8 W/g combined with a temperature of 40 °C. However, the observed thermal efficiency was lower than that in previous studies, mainly due to the suboptimal regulation of experimental parameters. Future research should focus on optimizing these parameters and further exploring the impact of this drying method on energy consumption to achieve more efficient and sustainable peanut drying.

Characterization of Guest DNA Transport and Adsorption within Host Porous Protein Crystals.

Nucleic acid transport through protein-based pores is a well-characterized phenomenon due in part to advancements in nanopore sequencing. A less studied area is nucleic acid transport through extended protein-based channels, where the additional surface area and increased contact time allow for the study of prolonged binding interactions. Porous protein crystals composed of "CJ", a putative polyisoprenoid-binding protein from Campylobacter jejuni, represent a favorable, highly ordered material for studying DNA transport and binding/unbinding along protein-based channels. These crystals adopt a hexagonal prism habit and contain a densely packed hexagonal array of 13 nm diameter axial nanopores that run from the top to the bottom of the crystal. After cross-linking, the crystals are easily manipulated for experimentation. An adsorption isotherm between host crystals and guest double-stranded 8 base pair DNA (8mer) revealed a high equilibrium adsorption constant of 206 ± 30 L/g. Fluorescence confocal microscopy tracked the loading of guest DNA into host crystals predominately along the major axial crystal nanopores. Four different computational models based on the finite volume (FV) method were assessed to model the transport process for guest 8mer and 15mer dsDNA loading into empty host crystals in terms of fundamental parameters, such as the intrapore diffusion constant. Fitting the models to the data revealed that the most basic FV model sufficed to describe the observed loading behavior, characterized by a single effective diffusion coefficient. Leveraging Fick's first law, we more directly fit a numerical range for the observed intrapore diffusion coefficient as a function of time, position within the crystal, and relative guest concentration. This new transport analysis strategy was applied to both out-of-equilibrium loading and fluorescence recovery after photobleaching (FRAP) experiments. The intrapore diffusion constants are comparable between 8mer and 15mer dsDNA and were found to be 2 orders of magnitude faster for DNA loading into empty crystals than that observed in FRAP experiments, which averaged (10 ± 4) × 10-11 cm2/s.

Effect of hot air temperature and slice thickness on the drying kinetics and quality of Hami melon (Cantaloupe) slices

The effects of hot air temperature and slice thickness on the drying kinetics and quality of Hami melon slices (HMS) were studied. HMS (3 mm and 5 mm) were carried out in a forced convection drying oven at temperatures ranging from 60 ~ 90 °C. The increase in hot air temperature and the decrease in slice thickness led to shorter drying times and higher drying rates. The drying rate curves indicated that the drying process of HMS did not exhibit a constant drying rate period. In the drying kinetics modeling process, the Explinear model was suited for describing the drying curves with higher accuracy. According to Fick’s second law, the moisture effective diffusion coefficient of 3 mm and 5 mm HMS ranged from 4.72 ~ 15.96 × 10-11m2/s at temperatures of 60, 70, 80, and 90 °C. When the thickness of HMS were 3 mm and 5 mm, the activation energies were 30.13 and 43.75 kJ/mol, respectively. When dried at low temperatures, the color of HMS was closer to fresh Hami melon. With the increase of hot air temperature, the hardness of HMS decreases and the rehydration increases. When the thickness of the HMS decreases, the hardness of the slices decreases and the rehydration increases.

Corrosion induced by industrial coal-fired flue gas: deterioration mechanism of an existing concrete structure

This article investigated the corrosion deterioration behavior of concrete structures exposed to industrial coal-fired flue gas for 12 years. The concrete’s macro-mechanical properties, pore structure characteristics, and micro-properties were tested by in-situ and laboratory tests along the height and depth. The test results indicated that different corrosion mechanisms were occurred inside the concrete along the corrosion depth direction. In the shallow concrete zone (0–8 mm), sulfation is predominant, with gypsum (Gyp) as the primary product. O 4 2 − In the coexistence concrete zone (8 ∼ 14 mm), both sulfation and carbonation are present, with the pH increasing from 8.0 to 11.0. Beyond 14 mm, S O 4 2 − and Gyp are no longer detected. In the deep concrete zone (14–18 mm), carbonation is the dominant process, with CaCO3 as the main product. Considering the impact of the effective diffusion coefficient and SO2 concentration gradient distribution, a prediction model for the neutralization depth of concrete in industrial coal-fired flue gas has been proposed.