Initial Water Content Research Articles

Effects of initial water and salt content on permeability and microstructure of sodic-saline loessal soils

Effects of initial water and salt content on permeability and microstructure of sodic-saline loessal soils

Formation of giant copper deposits driven by rapid uplift and sudden depressurization

Abstract Porphyry Cu deposits (PCDs) in collisional orogens are new targets for modern mineral exploration. A series of post-collisional (Miocene; 22-12Ma) porphyry copper deposit (PCDs) with Cu reserve over 45 Mt have been discovered in the Gangdese magmatic belt, southern Tibet. These magmas derived from partial melting of sulfide-bearing Tibetan juvenile lower crust are fertile for porphyry Cu in many aspects, such as high oxidation state, and rich volatiles such as water, S, and Cl, but some of individual plutons ended up with economic concentrations. The fundamental question remains what accounts for the significant Cu endowments. We measured the igneous zircon water contents of ore-related and barren high Sr/Y magmas in the Gangdese belt, southern Tibet and found that magmas that produce giant PCDs have lower zircon water contents than barren and small-deposit related magmas. Combined with previous fluid inclusions, magmatic breccias, apatite geochemistry, and thermal histories, which demonstrated higher initial water content in causative porphyries such as giant deposits of Qulong and Jiama, we believe that the lower zircon water content may be attributed to these magmas experiencing of faster cooling and sudden depressurization of a large, primed, volatile-saturated or supersaturated mid-upper crustal magma chamber, which could lead to rapid and voluminous volatile exsolution and fluid discharge. These processes caused intense hydrothermal alteration and large ore deposition. In contrast, magmas that experienced slow cooling and deep emplacement would undergo steady state degassing and weak alteration. The variable intrusive and thermal histories across Gangdese reflects interplay between surface and lithospheric dynamics within the Himalaya—Tibet orogen. Our findings suggest the difference of zircon water content reflects the emplacement rate and depth of granitic body, and therefore may serve as an indicator for tectonics and potential for mineralization.

Study on the redistribution mechanism and secondary purge strategy of proton exchange membrane fuel cells

Effective control of membrane water content is essential for increasing the space for ice formation during the cold start stage and enhancing the success rate of start-up. Shutdown purge can effectively lower the membrane water content following fuel cell operation. However, during the cooling and standing process after purge, the rapid change in saturated vapor pressure can result in the redistribution of membrane dissolved water, leading to an increase in its content and a reduction in the success rate of cold start. Therefore, this study establishes a multidimensional, multiphase simulation model to comprehensively and thoroughly analyze the redistribution mechanism after purging and investigates the relationship between membrane water content and cold start. This is achieved by identifying the maximum membrane water content boundary during the cold start process and ultimately improving the success rate of cold start through a secondary purge strategy. The research results indicate that the membrane water content of the fuel cell increases from 2.31 to 8.31 after redistribution. During the cold start stage, the cold start success of the fuel cell under different environmental temperatures exhibits relatively specific boundary conditions, with the cold start process being closely related to the load current density and initial membrane water content. After implementing the secondary purging strategy, the membrane water content of the fuel cell decreases again, displaying favorable cold start characteristics in the cold start stage and successfully starting at −10 °C. This study can provide a reliable basis for the development of purging strategies during shutdown and offer a theoretical foundation for the boundary identification process of cold start.

Global and Local Shear Behavior of the Frozen Soil–Concrete Interface: Effects of Temperature, Water Content, Normal Stress, and Shear Rate

The interface between soil and concrete in cold climates has a significant effect on the structural integrity of embedded structures, including piles, liners, and others. In this study, a novel temperature control system was employed to conduct direct shear tests on this interface. The test conditions included normal stress (25 to 100 kPa), temperature (ranging from 20 to −6 °C), water content (from 10 to 19%), and shear rates (0.1 to 1.2 mm/min). Simultaneously, the deformation process of the interface was continuously photographed using a modified visual shear box, and the non-uniform deformation mechanism of the interface was analyzed by combining digital image correlation (DIC) technology with the photographic data. The findings revealed that the shear stress–shear displacement curves did not exhibit a discernible peak strength at elevated temperatures, indicating deformation behavior characterized by strain hardening. In the frozen state, however, the deformation softened, and the interfacial ice bonding strength exhibited a positive correlation with decreasing temperature. When the initial water content was 16% and the normal stress was 100 kPa, the peak shear strength increased significantly from 99.9 kPa to 182.9 kPa as the test temperature dropped from 20 °C to −6 °C. Both shear rate and temperature were found to have a marked effect on the peak shear strength, with interface cohesion being the principal factor contributing to this phenomenon. At a shear rate of 0.1 mm/min, the curve showed hardening characteristics, but at other shear rates, the curves exhibited strain-softening behavior, with the softening becoming more pronounced as shear rates increased and temperatures decreased. Due to the refreezing of interfacial ice, the residual shear strength increased in proportion to the reduction in shear rate. On a mesoscopic level, it was evident that the displacement of soil particles near the interface exhibited more pronounced changes. At lower shear rates, the phenomenon of interfacial refreezing became apparent, as evidenced by the periodic changes in interfacial granular displacement at the interface.

Exploring Soil–Water Characteristic Curves in Transitional Oil Sands Tailings

Soil–water characteristics curves (SWCC) have proved useful in estimating parameters used in modeling unsaturated geotechnical properties of soils including permeability and strength. Either saturation, gravimetric, and instantaneous and initial volumetric water content designation can be used to develop SWCCs. Studies have shown that any of the designations will give good estimates for soils that do not undergo volume change with suction change whereas, for soils that undergo substantial volume change, only saturation and instantaneous volumetric water content designation obtained by incorporating shrinkage curves can give correct estimates. Transition oil sands tailings have fines content that cannot be categorized as sandy or fine materials, and research on volume change with suction change in these materials is limited. In this study, HyProps, Tempe cells, and a chilled-mirror water potential meter were used to measure suction and corresponding water contents for samples that were prepared by mixing coarse sand and Fluid Tailing by ratios that mimic transition zone tailings. Shrinkage tests were also performed to observe the extent of volume change with suction increase. Air Entry Values (AEV) estimated from SWCCs based on gravimetric water content were found to be lower than those estimated from saturation-based SWCCs due to substantial volume changes in these materials with suction increase. The use of saturation water content designation is recommended in estimating AEV for transitional oil sands tailings. This is useful information in predicting the long term unsaturated geotechnical behavior of these materials for environmental management and safety purposes.

Performance evaluation of waste phosphogypsum-based solidified sludge: From laboratory test to field application

Massive dredged sludge is being landfilled without effective use due to its high-water content and poor engineering properties, which not only leads to soil resources waste, but also occupies a large amounts of land sources. In this study, ternary stabilizer, including waste phosphogypsum (PG), ground granulated blast-furnace slag (GGBS), and lime (LM) with a mixing proportion of PG: GGBS: LM = 35:60:5, was adopted to improve the mechanical and environmental behaviors of sludge for subgrade filling purpose. The initial water content of sludge was controlled using two different dehydration methods for comparison. A series of laboratory tests, including unconfined compressive strength (UCS), organic matter content, and pH value were tested to understand its physical-mechanical properties. Thereafter, field application model equipped with a mini weather monitoring station was constructed to monitor the influence of solidified matrix on the surrounding water and soil environment. Time -dependent parameters such as plant growth, temperature, humidity, total nitrogen, phosphorus/potassium content, electrical conductivity, and pH value were monitored. Results indicate that the incorporation of PG-GGBS-LM ternary stabilizer significantly improves the mechanical and environmental properties of dredged sludge. The optimal dosage of the ternary stabilizer is 36%, which can result in a UCS value of the 2.0 MPa (slightly higher than ordinary Portland cement) after 28 days of curing. Field application reveals that plants could grow normally in solidified sludge. The environmental related parameters (i.e., total nitrogen, phosphorus/potassium content, electrical conductivity, and pH value) were similar with those in conventional planting soil, suggesting the advantage of the proposed PG-GGBS-LM ternary stabilizer in mechanical, economic and environmental aspects.

Estimating radial attenuation of vacuum pressure for dredged clays

The radial attenuation of vacuum pressure in dredged clays limits the effectiveness of vacuum consolidation. In this study, a series of model tests were conducted on five dredged clays with varying initial water contents to investigate this radial attenuation. The significant radial attenuation can be divided into two stages: the increasing and stabilization stages. In the stabilization stage, exponential radial attenuation is observed. Lower initial void ratio (e 0) and higher void ratio at liquid limit (e L) lead to a decrease in radial attenuation. Additionally, higher applied vacuum pressure (p v) results in a greater reduction in the magnitude of the radial vacuum pressure. In the increasing stage, the radial vacuum pressure increases exponentially to a stable state after start-up. The radial attenuation is attributed to the differential start-up time (i.e., initial time-point at which the increase begins) and varying increase rates. Lower e 0, higher e L, and higher p v values reduce the start-up time and raise the increase rate. A changing pattern is proposed to describe the exponential radial attenuation using three parameters: radial attenuation coefficient (k 2), increasing coefficient (k 3), and time-delay coefficient (D t). Furthermore, an empirical estimation for the radial attenuation is also suggested without relying on time-consuming tests

Study on the Consolidation Characteristics of Slurry-like Mud Treated by Flocculation-Solidification-High-Pressure Filtration Combined Method.

The disposal and reutilization of the enormous amounts of slurry-like mud (MS) dredged from navigation channel construction, ecological dredging, and other construction activities have been receiving increasing attention. In this paper, a flocculation-solidification-high-pressure filtration combined method (FSHCM) is used to treat MS, and the consolidation characteristics of The SHCM-treated MS are studied by conducting a series of one-dimensional consolidation compression tests. Various parameters, including the dosage of the curing agent, initial water content, and dry weight of the MS, are systematically analyzed to evaluate their influence on the consolidation behavior. The experimental results demonstrate that higher curing agent and initial water contents enhance the structural yield stress and compressive resistance, while increased dry weight decreases the structural yield stress but increases the compressive strain and void ratio. As the curing age increases, the ability of the FSHCM-treated MS to resist compressive deformation is further enhanced. In addition, the compressibility of the mud cake samples changes significantly at the yield point. This study has practical guiding significance for the optimal design and long-term application of FSHCM-treated MS.

Effective removal of Calcium and Magnesium Ions from boiler feed Water using Polyacrylonitrile supported titanium tungstovanadate composite ion exchange nanofiber

<p><em><strong>​​​​​​</strong></em><span style="font-family:"Times New Roman","serif";font-size:12.0pt;line-height:150%;">The challenge posed by the presence of calcium ions (Ca<sup>2+</sup>) in process streams is attributed to its adverse effects on the heat transfer efficiency of process equipment. In this study, a novel electrospun nanofibrous composite was synthesized by combining polyacrylonitrile (PAN) with well-dispersed Titanium tungestovanadate (TWV) cation exchanger. Homogeneous precipitation technique was employed to synthesize nano-titanium (IV) tungstovanadate (TWV) cation exchanger. Various synthesis parameters, including reactant volume ratio, amount of precipitating agent and reaction temperature, were optimized to achieve the highest ion exchange capacity (IEC). The prepared ion exchange material exhibited an ion exchange capacity (IEC) of 2.39 meq.g<sup>-1</sup> for Na<sup>+</sup> ions. The incorporation of the prepared nanoparticles into nanofibers conferred the sorption capabilities of the composite. The nanofibers' morphologies and structures were analyzed using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Batch sorption experiments were carried out to investigate the sorption properties. Controlled experiments were conducted to investigate the impact of various factors, including solution pH, temperature, dosage, contact time, and the initial concentration of the hard water. The results indicated that the optimum adsorption conditions that gave the highest percentage of removal 99%, 98% for Ca<sup>2+</sup> and Mg<sup>2+</sup>  ions respectively were 50 mg of adsorbent dosage, 500 ppm of Ca<sup>2+</sup> and Mg<sup>2+</sup>  solution =7, and a contact time of 30 min at room temperature .The  kinetic data were fitted to pseudo second order model. Furthermore, the thermodynamic study suggested that the adsorption on PAN/TWV NF was endothermic and spontaneous.</span></p>

Mechanistic insights into pore water conversion to gas hydrates in clay minerals

The conversion of pore water to gas hydrates is an important prerequisite for natural gas hydrates (NGHs) accumulation and hydrate-based CO2 sequestration. However, the mechanism of water-to-hydrate conversion in clays, which are prevalent in hydrate reservoirs or marine sediments serving as potential hosts for CO2 hydrates, still remains poorly understood, impeding further advancements in exploiting NGHs and developing CO2 sequestration strategies. In this paper, the characteristics of pore water conversion to hydrates in montmorillonite and kaolin were comprehensively examined through quantitative measurements and NMR analysis, and compared with those in silt and coarse sand. It revealed that the water-to-hydrate conversion was more restricted in clays than in sands. Especially in montmorillonite, since almost all pore water was detected as bound water, the final water conversion was extremely low and sensitive to the subcooling degree. Additionally, as the initial water content increased from 15 wt% to 35 wt%, the final water conversion in kaolin, silt, and coarse sand decreased exponentially due to intensified kinetic limitation, whereas that in montmorillonite initially rose and then fell, attaining the maximum at a threshold of 20 wt%. It is found that the competition between thermodynamic and kinetic limitations controls water-to-hydrate conversion in clays. Specifically, in kaolin, silt and coarse sand, the main controlling factor of water-to-hydrate conversion is the kinetic limitation, as their unconverted equilibrium water is negligible. However, in montmorillonite, the thermodynamic limitation dominates at low water contents, transitioning to kinetic limitation at high water contents. This study provides direct evidence and mechanistic insights into how clays affect water-to-hydrate conversion in porous media, which has significant implications for the geological accumulation of NGHs and the site selection for hydrate-based CO2 sequestration.

Contrast Experiments on Breaching Characteristics of Landslide Dams and Debris-flow Dams

Abstract: The difference in soil properties determines the different breaching characteristics exhibited by landslide dams (LD) and debris-flow dams (DFD). In this study, two types of soil were prepared by controlling the initial water content and the mixing time of the soil to construct the LD and DFD. Based on observations of breach in dams with six different grain size distributions: 1) the erosion resistance within the soil leads to a slower failure speed for DFD under the same grain size distribution and particle density. However, both types of dams exhibit a non-uniform downcutting process in the longitudinal direction, induced by uneven velocities. 2) Laterally, DFD are characterized by the creep slide of the breach bank, distinct from the intermittent slide observed in LD. 3) For the range of conditions tested, the peak discharge of LD significantly exceeds that of DFD. Additionally, the flood curve of LD exhibits a bimodal characteristic, attributed to the slide of the bank slope and the non-uniform distribution of particles within the dam. Finally, a prediction formula for the downcutting coefficient of the breach was established and validated by past studies. This study provides a basis for predicting outburst floods of LD and DFD.

Water‒soil-air‒plant mutual feedback mechanism under the application of red bed composite polymers.

Red bed composite polymers composed of weathered red bed soil, adhesive materials, and water-retaining materials have been applied as a new type of material for environmental restoration. However, the promotion and application of this material has been limited by a lack of understanding of its action mechanism in environmental restoration. The objective of this study is to innovatively propose a water‒soil-air‒plant mutual feedback mechanism based on this material. Therefore, water‒soil-air‒plant mutual feedback tests were conducted in this study under 3 initial water contents and 10 red bed composite polymers ratios. Key parameters, namely, water content, soil conductivity, pH, temperature, O2 and CO2 contents, pigeon pea (Cajanus cajan) germination number and plant height were monitored and analyzed. As the results, a mutual feedback mechanism driving water retention, soil consolidation, air retention, and plant rooting was revealed under the application of red bed composite polymers. And, suitable environments and optimal compositions for this material are proposed. The study results provide a theoretical basis for the large-scale application of red bed composite polymers.

Reducing drought vulnerability of forest soils using Xanthan gum-based soil conditioners

Climate change increases the frequency and severity of droughts in many parts of Europe, thereby affecting the availability of water resources. Therefore, preserving the soil water content is essential for maintaining forest diversity and plant vitality. To improve soil hydraulic properties and reduce drought vulnerability, three xanthan-gum-based soil conditioners (SC_R, SC_CG, and SC_ZZC) were developed under the European ONEforest project. These soil conditioners (SCs), including oxide ash and cellulose fibres of different lengths, differ in their filler properties. This study evaluated the performance of these soil conditioners in forest soils in Slovenia (S1), Spain (S2), and Germany (S3). Water absorption, water retention, hydraulic conductivity, seed germination, and plant growth in the untreated soils and mixtures were analysed.The results showed a 53% to 100% increase in water absorption with high dosage of SCs (1.7% of dry SC per dry soil mass). The addition of SCs also significantly improved the water retention capacity of the treated soils within a suction range of 0-100 kPa, which is advantageous for maintaining adequate water availability for plant growth. The effect of SCs on unsaturated hydraulic conductivity varies depending on the soil type. For example, at a similar suction, the unsaturated hydraulic conductivity of mixtures with soils S2 and S3 can be more than an order of magnitude lower than that of untreated soils S2 and S3. In contrast, mixtures with soil S1 showed unsaturated hydraulic conductivity similar to that of the untreated soil. In the seeding experiment, plants in treated soils survived for up to 8 d without watering compared to those in untreated soils, with survival linked to the initial water content of the mixtures. These findings suggest that soil conditioners reduce drought vulnerability by improving water retention and regulating water loss. However, the optimal dosage should be adjusted according to different soil types and local environmental conditions.

The Effect of Chicken Bones Powder Adsorbent Mass and its Contact Time on Reducing Color Concentration in Peat Water Treatment

Peat water is surface water or ground water which is found abundantly in tidal, swampy and lowland areas. It has a reddish-brown color, with an acerbic taste (high acidity), and has a high organic content. Peat water can be treated using the adsorption method. Adsorption is a physical phenomenon in which the molecules of the adsorbed material are attracted to a solid surface, which acts as an adsorbent. In this study, the authors used the adsorption method to reduce the color concentration of peat water using activated chicken bones powder as an adsorbent and observing the changes that occur when mass of powder to the amount of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5 and 2.0 grams were added to 50 ml of peat water with contact time that varied from 20, 30, 40, 50 and 60 minutes. From this study, we conclude that the optimum yield was obtained when the mass and contact time were at 0.5 grams and 40 minutes, which yield a percentage of reduction of 95.59%, wherein the initial color concentration of peat water at 337.816 was reduced to 14.89 Pt-Co, which is in line with the standard color for clean water as specified in a Regulation by the Minister of Health of the Republic of Indonesia No. 492/MENKES/PER/IV/2010, which state the standard color for clean water is 15 Pt-Co.

A novel test set up to study three-dimensional electrokinetic dewatering of dredged soil

The dredged soil obtained from maintenance activities of water bodies has emerged as a potential alternate fill material for infrastructure development. However, dredged soil requires stabilization due to high initial water content, low shear strength and high compressibility. Among several methods, stabilization of dredged soil by using electrokinetics is one of the effective ground improvement techniques that uses electric field to dewater and strengthen the soil. In this context, a series of experiments were conducted on dredged soil by using a combination of electrokinetic treatment with and without 6 kPa seating pressure (viz., low surcharge). A customized and patented electrokinetic dewatering (EKD) test set up was used for the three-dimensional electrokinetic treatment of soil. The potential difference (in the range of 6 V–48 V) within the soil was achieved by inserting stainless steel pipes of 21.4 mm outer diameter, 1.2 mm thickness, and 170 mm length. Two control tests (with and without seating pressure of 6 kPa) also were performed to understand the effectiveness of EKD. From the study, up to 1057% and 427% increase in dewatering was noted in EKD tests due to application of 24 V (optimum voltage noted in EKD tests) as compared to control tests, without and with seating pressure, respectively. Further, seating pressure with EKD resulted in effective control of crack formation in the dredged soil and uniform improvement in shear strength along the depth (up to 95 kPa). The combination of low surcharge with EKD, adopted in the study, is also expected to yield lower differential settlement, and hence better performance of geotechnical structures built on improved dredged soil. The novel 3-dimensional patented EKD test setup with Arduino-programmed automatic water pumping enables collecting and accurately measuring dewatered effluent volume, performing cone penetration tests on undisturbed soil, and collecting soil samples for determination of water content/physiochemical properties from different locations. Overall, the developed EKD setup can be utilized for evaluating the effectiveness and adopting real-time progress management for EKD or other ground improvement methods, and remediation of sludge, mine tailings, dredged sediments, and contaminated soils.

Experimental investigations of the shear strength and deformation behavior of a frozen unsaturated silt

There are limited studies in literature with respect to the deformation and shear strength behavior of frozen unsaturated soils that consider sensitive changes in temperatures below 0 °C. For this reason, the focus of the present study is directed towards investigating the shear strength and deformation behavior of a frozen unsaturated silt. As a part of the study, one-dimensional freezing tests were performed on compacted silt samples with various initial water contents and dry densities. The pulsed nuclear magnetic resonance (P-NMR) method was used to obtain distribution of unfrozen water content of silt samples; this information was used to explain the deformation behavior during freezing. The volume change behavior in unsaturated soils due to freezing can be associated to three primary factors: expansion caused by the ice-water phase transition and shrinkage induced by ice-cementation and dehydration. A critical water saturation was also observed at which the frost heave is minimum, or no volume change occurs. In addition, conventional direct shear tests were performed on compacted unsaturated silt samples both in frozen and unfrozen conditions to determine and quantify the shear strength contribution arising from the different cohesion components. The investigations in this study provide valuable information that can be used in rational explanation of the strength and deformation behavior of unsaturated frozen soils.

Accelerated removal of solvent residuals from PLGA microparticles by alcohol vapor-assisted fluidized bed drying

The removal of residual solvents from biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microparticles by fluidized bed drying was investigated. Microparticles were prepared by the O/W solvent extraction/evaporation method and the influence of various process and formulation parameters on the secondary drying was studied. PLGA microparticles and films were characterized for residual organic solvent and water content, recrystallisation, surface morphology, drug loading and in-vitro release of the drugs dexamethasone and risperidone. While alcohol-free fluidized bed drying decreased the residual dichloromethane content only from about 7 % (w/w) to 6.4 % (w/w) (18 °C) or 3.2 % (w/w) (35 °C) within 24 h, 140 mg/L methanol vapor in purge gas facilitated almost complete removal of dichloromethane or ethyl acetate from microparticles (0–0.11 % (w/w) after 6 h). By controlling the alcohol concentration and temperature of the purge gas, the alcohol absorption and complete removal was controlled. Risperidone increased the methanol absorption enhancing the plasticization. A high initial residual water content was identified to promote aggregation and was eliminated by starting fluidized bed drying without alcohol. Alcohol vapor-assisted fluidized bed drying accelerated microparticle manufacturing without affecting the redispersibility, the drug loading and the in-vitro release of risperidone and dexamethasone.

Permeability characteristics, structural failure characteristics, and triggering process of loess landslides in two typical strata structures

Landslides occurring at the interface of strata are among the most common forms of loess landslides in China. Statistics indicate that significant loess-red silty clay interface landslides induced by irrigation in the Heifangtai Platform than loess-paleosol interface landslides in the South Jingyang Platform. To uncover the permeability characteristics, structural failure patterns, and triggering processes of two typical strata structures. This study employs Nuclear Magnetic Resonance (NMR) and Scanning Electron Microscopy (SEM) techniques to investigate the permeability and structural failure of two soil combination types: loess-red silty clay and loess-paleosol. The results revealed a positive correlation between the stagnant water effect and flow rate, but a negative correlation with the initial water content. Notably, these two typical strata exhibited distinct differences in the stagnant water effect. In loess-red silty clay, continuous filling of mesopores and macropores by fine clay particles, while at the same time the agglomerates disintegration at the interface, thereby enhancing the stagnant water effect. In contrast, loess-paleosol exhibited good connectivity between the mosaic pores at the interface. This facilitated the formation of several elongated microcracks, which acted as dominant channels for infiltration and weakened the stagnant water effect. However, the macroscopic triggering mechanism for loess landslides in both loess-red silty clay and loess-paleosol combination strata remains similar. Irrigation water stagnates within the relatively impermeable layers, saturating and structurally damaging the bottom of loess layer, ultimately inducing landslides. These findings provide a scientific basis for the future study of loess landslide hazards in different strata structures, which is of great significance.

Effects of accelerated carbonation on fine incineration bottom ash: CO2 uptake, strength improvement, densification, and heavy metal immobilization

Incinerating municipal solid waste (MSW) can effectively reduce its mass and volume while producing electricity. However, this process generates incineration bottom ash (IBA), which is an aggregate-like waste containing heavy metals. Due to the higher heavy metal contents, fine IBA can be removed from total IBA and treated separately to promote the use of IBA. Furthermore, MSW incineration generates carbon dioxide (CO2), which is another concern. In this context, it is beneficial to use accelerated carbonation to treat fine IBA, because it can not only contribute to carbon capture but also provide carbonated IBA that may be utilized as aggregates in civil engineering. The accelerated carbonation process of fine IBA is affected by many parameters. Therefore, this study investigated the effects of CO2 pressure (PCO2), initial water content (wi), and carbonation time on the properties of carbonated IBA, including CO2 uptake, unconfined compressive strength (UCS), density, and leaching of heavy metals. The evolution of mineralogy and microstructure of carbonated IBA was also analyzed. The results showed that IBA with wi of 15% and PCO2 of 200 kPa could achieve a CO2 uptake of 6% of IBA mass. The carbonation time significantly affected UCS and dry density of carbonated IBA. As the carbonation time increased from 0 h to 120 h, the UCS increased from 67 kPa to 691 kPa while the dry density increased from 1.38 g/cm3 to 1.51 g/cm3. Compared with untreated IBA, the leaching concentrations of Cu, Cr, Zn, and Pb from carbonated IBA were reduced significantly. As the carbonation time increased, the microstructure of carbonated IBA became denser. This densified structure was one of the reasons for the strength improvement and dry density increment of carbonated IBA.

Insight into the mechanisms and in-plane reaction heterogeneity of the dynamic response of proton exchange membrane fuel cells

The voltage undershoot is one of the main dynamic problems of proton exchange membrane fuel cells (PEMFCs) under dynamic loadings. However, its mechanisms remain poorly understood due to its complex and coupled influencing factors. Besides, PEMFCs with a large active area are more prone to local dynamic failures for their pronounced in-plane (I-P) heterogeneity, while few studies have focused on the I-P heterogeneity of the dynamic response of large-area fuel cells. In this work, the mechanisms and the I-P heterogeneity of the voltage undershoot of a 320 cm2 PEMFC are thoroughly studied based on an in-situ monitoring method and a voltage loss decoupling method. Results show that the voltage overshoot is primarily driven by the ohmic loss (OL) overshoot and the concentration polarization (CP) overshoot. Results also prove that the OL overshoot is mainly caused by the instantaneous water shortage in the proton exchange membrane (PEM) which depends on the initial water content in the PEM. Besides, the CP overshoot is due to the instantaneous reactant shortage at the catalyst, and it is much sensitive to the change in the oxygen diffusion coefficient of the ionomer caused by the change in its water content. Meanwhile, both OL overshoot and CP overshoot demonstrate significant I-P heterogeneities under poor dynamic operating conditions, especially in cases of high load step and low inlet air humidity. Finally, the influences of operating conditions on the voltage undershoot and its I-P heterogeneity are discussed, and suggestions for improving the dynamic performance of PEMFCs are proposed.