Reactive Media Research Articles

Removal of Mn(II) from Acidic Wastewater on the Red Mud– Loess Mixture: Fixed–Bed Column Tests

In this study, the purification effect of red mud–loess mixture (RM–L) as a reactive medium in a permeable reactive barrier (PRB) for groundwater contaminated by acidic wastewater (AW) containing Mn(II) was explored considering removal capacity and pH value, and the safety of Mn(II) on RM–L after purification was evaluated. The breakthrough parameters of the Mn(II) were determined and the purifying performances of RM–L toward AW were evaluated by fixed-bed column tests at various initial concentrations of Mn(II), flow rates, and packing heights. The speciation of Mn(II) loaded on the RM–L was evaluated by the Tessier method. Results show the RM–L with a removal capacity of 17.30 mg·g−1 at 100 mg·L−1 initial concentration, 1 mL·min−1 flow rate and 7 cm packing height. The reduction in initial concentration and flow rate and the increase in packing height improve the total removal percentage of Mn(II) and the removal capacity of the RM–L. Moreover, the RM–L has a long-term effective acid buffer capacity for AW containing Mn(II), ensuring the pH values of effluent could be maintained at a neutral value. Furthermore, the Mn(II) could be loaded on the RM–L after the purification in stable forms that are dominated by the iron-manganese oxidate form.

Synthesis of Metal Chalcogenide Semiconductors by Thermal Decomposition of Organosulfur and Organoselenium Compounds.

Metal chalcogenides - because of their excellent optical and electrical properties - are important semiconductor materials for optical devices, such as solar cells, sensors, and photocatalysts. The challenges associated with metal chalcogenides are the complexity of the conventional synthesis methods and the stringent synthesis conditions. In this study, the synthesis conditions were simplified in a solvent-free synthesis method using cadmium precursor, thiourea and selenium to synthesize metal chalcogenides, such as CdS and CdSe, which have particularly suitable band gaps for the optical devices. CdSx Se1-x solid solution was successfully synthesized under molten thiourea as the reactive reaction medium at relatively low temperatures, even at 180 °C, with residual melamine derivatives in the solid phase. The luminescence properties of CdSx Se1-x and the products in the gas and solid phases were investigated. Optimization of the synthesis conditions for solid solutions of CdSx Se1-x and the role of organic compounds in the formation of metal chalcogenides are discussed.

Actinides in complex reactive media: A combined ab initio molecular dynamics and machine learning analytics study of transuranic ions in molten salts

The predominant ionic chemistry and the similarity in ionic radius of actinides make it very difficult to structurally distinguish them in liquids. To tackle this problem, we investigate actinides in molten salts using ab initio molecular dynamics and machine learning analytics. Ab initio simulations show that the f-states clearly affects the electronic properties while their impact on structural properties is not obvious. For the series of trivalent actinides U3+, Pu3+, Cm3+, Cf3+, and Fm3+ in molten NaCl and FLiBe, actinide-ligand bonds have a higher degree of covalency in NaCl (than in FLiBe), and a higher degree of ionicity in FLiBe. Furthermore, a machine learned classification model can distinguish atomic environments of chemically similar actinides with more than 80% confidence, as long as atoms beyond the first solvation shells are considered. Our work shows that only two types of descriptors are necessary to account for all the fluctuations in heavy metal/molten salt mixtures: The first descriptor represents the electronic state of the heavy metal, while the second encompasses the local coordination environment.

Numerical Solution of Problem for Forest Fire Initiation and Spread

The theoretical study of the problems of forest fire initiation and spread were carried out in this paper. Mathematical model of forest fire was based on an analysis of experimental data and using concept and methods from reactive media mechanics. The research was based on numerical solution of three-dimensional Reynolds equations for boundary layer of atmosphere and forest vegetation. The boundary-value problem is solved numerically using the method of splitting according to physical processes.

Generalized kinetic model for the photocatalytic degradation processes: Validation for dye wastewater treatment in a visible-LED tubular reactor

A novel generalized kinetic model was developed to predict the photocatalytic degradation of methylene blue and synthetic blue wastewater. The kinetic model was validated using nitrogen-crosslinking, ZnO-incorporated, and chlorophyll-sensitized phenolic resins as photocatalysts. The model considers the generation of reactive oxygen species (ROS), rate of electron-hole pair generation (Rg), and the attack of ROS on the pollutant. The six-flux model was used to elucidate the absorption and scattering of photons in a visible-LED tubular reactor, while the extended effective quantum yield model helped to calculate the harnessed energy by the photocatalyst; both parameters were employed for the calculation of Rg. The model showed robustness and high accuracy (R2 >0.85) under several operational conditions for dye-containing water. When the physical-chemical characteristics of the semiconductor and the reactive media are added to the kinetic model, it represents a major step in the process engineering of heterogeneous photocatalysis systems.

Synchronization of detonations: Arnold tongues and devil's staircases

We report on the phenomenon of detonation synchronization and demonstrate the existence of the Arnold tongues and devil's staircases in the problem of gaseous detonation in a periodically inhomogeneous reactive medium. Universal properties of these dynamical structures – the Farey tree, fractal dimension and period-doubling bifurcations – are revealed.

Cork‐based permeable reactive barriers coupled to electrokinetic processes for interrupting pollutants reaching groundwater: a case study of lead‐contaminated soil

AbstractBACKGROUNDA novel, original and green technology for the remediation of lead‐contaminated soil is proposed. The treatment strategy integrates two well‐known technologies: electrokinetic (EK) remediation and permeable reactive barriers (PRBs). The novelty of the present work is based on the use of cork granules, as reactive media, in the PRBs for interrupting Pb reaching groundwater. The cork barrier (treatment zone) was emplaced near the anodic compartment to favor the retention and sorption of Pb due to the migration/diffusion effects promoted from soil to the anode during EK remediation. For this purpose, NaNO3 (0.1 mol L−1) and citric acid (0.1 mol L−1) were tested as supporting electrolytes in the cathodic reservoir, while in the anodic compartment a solution of 0.1 mol L−1 NaNO3 was used. Additionally, the influence of direct current and reverse polarity approaches on EK efficiency was evaluated.RESULTSResults clearly indicated that the novel cork‐based PRBs concept was efficient when coupled with EK. Nevertheless, pH conditions played a significant role in Pb sorption by cork granules as well as in the physical–chemical properties of cork under an electrical field. The transportation of Pb by EK, towards the PRB with cork granules, was favored through the use of citric acid in the catholyte and reverse polarity strategy.CONCLUSIONSThese approaches promote a better pH control in the soil and electrode wells, being able to reach near 80% Pb removal from soil, after 14 days of experiment. Therefore, this technology can be used for in situ remediation of Pb‐contaminated groundwater. © 2022 Society of Chemical Industry (SCI).

Hydrodynamic Boundary Layer Flow of Chemically Reactive Fluid over Exponentially Stretching Vertical Surface with Transverse Magnetic Field in Unsteady Porous Medium

This article addresses the hydrodynamic boundary layer flow of a chemically reactive fluid over an exponentially stretching vertical surface with transverse magnetic field in an unsteady porous medium. The flow problem is modelled as time depended dimensional partial differential equations which are transformed to dimensionless equations and solved by means of approximate analytic method. The results are illustrated graphically and numerically and compared with previously published results which shown a good agreement. Physically increasing Eckert number of a fluid amplifies the kinetic energy of the fluid, and as a novelty, the Eckert number under the influence of chemically reactive magnetic field is effective in controlling the kinematics of hydrodynamic boundary layer flow in porous medium. Interestingly, whilst the Eckert number amplifies the thermal boundary layer thickness and velocity as well as the concentration of the fluid, the presence of the magnetic field and the strength of the chemical reaction have a retarding effect on the flow. Also, the chemical reaction parameter and permeability of porous medium are effective in reducing skin friction in chemically reactive magnetic porous medium and are relevant in practice because reduced skin friction enhances the efficiency of a system. The results of the current study are useful in solar energy collector systems and materials processing.

Low-cost Treatment Method for Organic Matter and Nutrients in Landfill Leachate-Batch Sorption Experiments

In this study, the ability of a low-cost composite adsorbent prepared using Washed Sea Sand (WSS), Dewatered Alum Sludge (DAS), Zero Valent Iron (ZVI), and Granular Activated Carbon (GAC), to treat Organic Compounds in terms of COD, Total Nitrogen (TN) and Total Phosphorus (TP) was investigated. The percentages of the materials used for the composite are DAS 40%, WSS 40%, ZVI 10%, and GAC 10%. The results of the study indicated that the removal efficiency of COD in landfillleachate by the composite adsorbent was 79.93±1.95%, which was followed by DAS (10.1%), WSS (51.3%), ZVI (42.0%), and GAC (100.0%). The corresponding adsorption capacity was 8.5 mg/g by the composite adsorbent and adsorption capacities of GAC, ZVI, WSS, and DAS were 24.39 mg/g, 2.27 mg/g, 7.01 mg/g, and 1.70 mg/g, respectively. Further, the maximum removal efficiencies of the composite adsorbent for TN and TP were 84.9% and 97.4%, respectively, and the respective adsorption capacities were 1.85 mg/g and 0.55 mg/g. A study on the behaviour of the equilibrium data of COD and nutrient adsorption revealed that Elovich and Langmuir isotherm models provided the best fits. Further, batch studies on the composite adsorbent media indicated that the optimum COD removal took place at a temperature of 35° C, an initial concentration of 398 mg/L, and pH of 5.55. The importance of the composite lies in the fact that it can treat more than one contaminant simultaneously. In addition, the application of used materials is sustainable as proper disposal sites are highly limited. According to the results of the study, 200 times diluted leachate having a COD value of 380 mg/L can be treated up to a percentage efficiency of 80%, by the composite adsorbent. The data were statistically analyzed. The result showed the ability of the composite adsorbent to be used as packing media in any landfill-leachate treatment system or any treatment system targeting COD of any given wastewater of the same characteristics as landfill-leachate. Packing media can be either filtration media in pump-and-treat treatment systems or reactive media in permeable reactive barriers. This research was based on a mass range of 3-18 g within 180 minutes. However, further research on a widened mass range within a longer time period is needed. 
 Keywords: Adsorption, Batch sorption experiments, Composite adsorbent, Landfill-leachate, Organic matter

Resin based 3D printing for fabricating reactive porous media

Resin based three-dimensional (3D) printing is popular for many applications including replicating geologic porous media samples. This study is the first to explore resin-based 3D printing of reactive porous media. Here, digital light projection (DLP) 3D printing of sandstone replicates was performed using photosensitive resin mixed with calcite of varying amounts. Printed samples were imaged in 3D using X-ray micro computed tomography (μCT). Printed sample porosities are consistent and close to the original mesh porosity. Calcite volume fractions are generally in agreement with the calcite content in the resin mixture. Calcite accessible surface areas are similar to published values for real sandstones and calcite dissolution was observed in acidic batch experiments, evidence of its surface reactivity. DLP printing is thereby promising for fabricating reactive porous media samples.

Interpreting Self-Potential Signal during Reactive Transport: Application to Calcite Dissolution and Precipitation

Geochemistry and reactive transport play a critical role in many fields. In particular, calcite dissolution and precipitation are chemical processes occurring ubiquitously in the Earth’s subsurface. Therefore, understanding and quantifying them are necessary for various applications (e.g., water resources, reservoirs, geo-engineering). These fundamental geochemical processes can be monitored using the self-potential (SP) method, which is sensitive to pore space changes, water mineralization, and mineral–solution interactions. However, there is a lack of physics-based models linking geochemical processes to the SP response. Thus, in this study, we develop the first geochemical–geophysical fully coupled multi-species numerical workflow to predict the SP electrochemical response. This workflow is based on reactive transport simulation and the computation of a new expression for the electro-diffusive coupling for multiple ionic species. We apply this workflow to calcite dissolution and precipitation experiments, performed for this study and focused on SP monitoring alternating with sample electrical conductivity (EC) measurements. We carried out this experimental part on a column packed with calcite grains, equipped for multichannel SP and EC monitoring and subjected to alternating dissolution or precipitation conditions. From this combined experimental investigation and numerical analysis, the SP method shows clear responses related to ionic concentration gradients, well reproduced with electro-diffusive simulation, and no measurable electrokinetic coupling. This novel coupled approach allows us to determine and predict the location of the reactive zone. The workflow developed for this study opens new perspectives for SP applications to characterize biogeochemical processes in reactive porous media.

Epoxidation of used cooking oils: Kinetic modeling and reaction optimization

This work developed a kinetic model for the epoxidation of used cooking oils (UCOs) via Prileschajew reaction with peracetic acid formed in situ. Such models, that have been not reported, are required for process design to assess feasibility of exploitation of UCOs as feedstock in the production of value-added oleochemical epoxides. The study evaluated the impact of reaction temperature and H2O2 loading on the oxirane yield, under constant loading of acetic acid (5% wt.), using H2SO4 as catalyst (2% wt.). Experiments were monitored by quantifying oxirane oxygen content along reaction, and the assessed conditions were defined based upon a factorial design. Considering a two-phase reactive media, two kinetic models were proposed and the corresponding kinetic parameters were adjusted by regression of the experimental data. It was found that the model that included two oxirane ring opening reactions pathways better described the experimental results, and that it can be further used for process design and scale up. Finally, the validated model was used to optimize a batch UCOs epoxidation by mean of a multi-objective optimization approach. Results indicate that conversions below 88% are required to avoid oxirane ring opening reaction, obtaining a product with an oxirane oxygen content of 4.4% wt.

Enhanced solute transport in porous media due to pH-dependent adsorption and transverse dispersion

The process of pH-dependent adsorption/desorption controls the transport of solutes in reactive porous media, the greater the adsorption the slower the solute migration. Earlier works show that in the presence of longitudinal hydrodynamic dispersion and pH-dependent adsorption, a fast solute transport phenomenon may arise. However, the effect of transverse dispersion on this fast transport phenomenon has not been investigated, yet.In this paper, we report an experimental and modeling work on the fast transport of strontium (Sr2+) through a reactive porous medium made of sand and hydrous ferric oxide (HFO) coated sand, where both longitudinal and transverse dispersion were important. A reactive transport model for an incompressible fluid was developed combining surface complexation with mass conservation equations for a solute and the acidity (difference between the concentration of total proton and hydroxide ions). The model was used to design and describe experiments run in a column-flood system and in a two-dimensional (2D) bead-pack. Results show that when an alkaline solution containing Sr2+ is injected into a 2D bead-pack containing HFO-coated sand and equilibrated with an acidic solution, a Sr2+ plume forms which comprises: (i) a retarded front due to the adsorption of Sr2+ onto the porous medium; (ii) a fast wave (or pulse) ahead of the retarded front due to longitudinal dispersion and traveling at the average fluid velocity; and (iii) a continuous leakage from the retarded front due to transverse dispersion.The results of this work confirm that pH-dependent adsorption/desorption process in conjunction with longitudinal dispersion causes fast wave, i.e., a solute migration which is faster than expected if the interplay between pH and dispersion is neglected. Furthermore, transverse dispersion in the presence of a pH gradient gives rise to a plume composed of a leakage from the retarded front connected to the fast wave.

Green approach for the synthesis of graphene glass hybrid as a reactive barrier for remediation of groundwater contaminated with lead and tetracycline

In this work, Graphene Glass Hybrid (GGH) was fabricated through pyrolysis by adopting a green method in which the sustainable carbon source used was low-quality-dates and the supporting material was glass waste (GW). The GGH was identified as a cost-effective and functional reactive material, suitable for use in permeable barrier technology to remediate (Pb) lead-and (TC) tetracycline-contaminated groundwater, via batch and continuous experiments. The GGH prepared showed macroporous structures that resembled 2-D graphene sheets, stacked on the inorganic glass support, capable of eliminating the Pb and TC from the aqueous medium. The GGH composite thus prepared was characterized using Fourier Transform Infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) analysis, Raman spectroscopy, electron diffraction measurements, X-ray photoelectron spectroscopy, Energy-Dispersive X-ray (EDX), and measurements of the surface area. From the results, the Langmuir model was proven to give a better fit than the Freundlich model, for the sorption data; from the perspective of kinetics, the pseudo-second-order model fitted the experimental data better than the pseudo-first-order model. In order to assess the performance of the GGH reactive medium, in continuous mode, a series of column experiments were performed. To simulate the conduction of Pb and TC through the GGH reactive medium in one-dimensional equilibrium transport, a numerical model solved using the COMSOL Multiphysics 3.5a software was advanced. From the findings, the GGH was proven to be effective, eco-friendly, and economically reactive in PRB, for the remediation of Pb- and TC-contaminated groundwater.

Mathematical Modeling of Large Forest Fires Initiation and Spread

It is presented mathematical model for description of heat and mass transfer processes at crown and large forest fires initiation and spread, taking into account their mutual influences. Mathematical model of forest fire was based on an analysis of experimental data and using concepts and methods from reactive media mechanics. The paper suggested in the context of the general mathematical model of forest fires give a new mathematical setting and method of numerical solution of a problem of a forest fire modeling. The boundary-value problem is solved numerically using the control volume methods and method of splitting according to physical processes. In this context, a study - mathematical modeling - of the conditions of forest fire initiation and spreading that would make it possible to obtain a detailed picture of the change in the velocity, temperature and component concentration fields with time, and determine as well as the conditions of forest fires initiation and spread is of interest.

Removal of Phosphorus from Hypolimnetic Lake Water by Reactive Filter Material in a Recirculating System—Laboratory Trial

A toolbox of methods must be available for the remediation of lakes and water bodies suffering from eutrophication. One method suggested is hypolimnetic withdrawal based on a closed-circuit system. Prior to the start of a pilot-scale test at Lake Hönsan, Sweden, a laboratory trial with containers filled with water and bottom sediment from this lake was performed. A peristaltic pump distributed equal bottom water volume to four columns, two filled with glass beads and two with the filter material Polonite, and then back to the surface of the containers. The reactive filter medium (RFM) removed phosphate (PO4-P) efficiently (98.6%), despite the relatively low influent concentration (390 µg L−1). The control column filled with glass beads, removed 2.9% of the PO4-P. The anoxic sediment, containing 2.47 mg P g−1, released PO4-P, which was indicated by the increased concentration in near-bottom water. The redirected water after RFM filtration had high pH (x¯=11.1); however, an equalization took place in the water mass to a lower but still increased pH value (x¯=8.7) compared to the control (x¯=7.02). This article reports the pros and cons of a full-scale system using the proposed method.

Studies on Cement Pastes Exposed to Water and Solutions of Biological Waste

The paper presents studies on the early stages of biological corrosion of ordinary Portland cements (OPC) subjected to the reactive media from the agricultural industry. For ten months, cement pastes of CEM I type with various chemical compositions were exposed to pig slurry, and water was used as a reference. The phase composition and structure of hydrating cement pastes were characterized by X-ray diffraction (XRD), thermal analysis (DTA/TG/DTG/EGA), and infrared spectroscopy (FT-IR). The mechanical strength of the cement pastes was examined. A 10 to 16% decrease in the mechanical strength of the samples subjected to pig slurry was observed. The results indicated the presence of thaumasite (C3S·CO2·SO3·15H2O) as a biological corrosion product, likely formed by the reaction of cement components with living matter resulting from the presence of bacteria in pig slurry. Apart from thaumasite, portlandite (Ca(OH)2)—the product of hydration—as well as ettringite (C3A·3CaSO4·32H2O) were also observed. The study showed the increase in the calcium carbonate (CaCO3) phase. The occurrence of unreacted phases of cement clinker, i.e., dicalcium silicate (C2S) and tricalcium aluminate (C3A), in the samples was confirmed. The presence of thaumasite phase and the exposure condition-dependent disappearance of CSH phase (calcium silicate hydrate), resulting from the hydration of the cements, were demonstrated.

Double diffusive convective motion in a reactive porous medium layer saturated by a non-Newtonian Kuvshiniski fluid

The impact of chemical reactions on the double-diffusive convective motion in a non-Newtonian viscoelastic fluid (Kuvshiniski type) saturated porous layer is examined applying both linear and nonlinear stability techniques. The Darcy model that includes the Kuvshiniski type viscoelastic effect of viscoelastic fluid and the Boussinesq estimation is employed as the momentum equation. The conditions for the occurrence of the stationary and oscillatory style of convective motions are determined by applying linear stability theory in terms of a critical thermal Rayleigh–Darcy number. Using the weakly nonlinear stability analysis, the convective heat and mass transfers are calculated. It is observed that the occurrence of oscillatory convection is possible only if the value of the solute Rayleigh–Darcy number is negative and also depends on other involved physical parameters. With rising values of the Kuvshiniski parameter and the heat capacity ratio, the range of the solute Rayleigh–Darcy number in which oscillatory convection is privileged diminishes, whereas it grows with the chemical reacting parameter and the Lewis number. The critical thermal Rayleigh–Darcy number at which the convective motion occurs increased nearly 3% with a 15% increase in the value of the Kuvshiniski parameter. Furthermore, the convective heat and mass transfers are reduced by growing the Kuvshiniski parameter and the heat capacity ratio, while both are enhanced by increasing the thermal Rayleigh–Darcy number and the solute Rayleigh–Darcy number.

Simultaneous removal of Pb and MTBE by mixed zeolites in fixed-bed column tests

The co-contamination of metals and organic pollutants, such as Pb and methyl tert-butyl ether (MTBE), in groundwater, has become a common and major phenomenon in many contaminated sites. This study evaluated the feasibility of their simultaneous removal with permeable reactive barrier (PRB) packed with mixed zeolites (clinoptilolite and ZSM-5) using fixed-bed column tests and breakthrough curve modeling. The effect of grain size on the permeability of PRB and removal efficacy was also assessed by granular and power clinoptilolite. The replacement of granular clinoptilolite by powder clinoptilolite largely reduced the breakthrough time but increased the saturation time nearly fourfold. The column adsorption capacity of clinoptilolite powders almost tripled that of clinoptilolite granules (130.6 mg/g versus 45.3 mg/g) due to higher specific surface areas. The minimum thickness and corresponding longevity of PRB were calculated as 7.12 cm and 321.5 min when 5% of granular clinoptilolite was mixed with 5% ZSM-5 and 90% sand as mixed PRB reactive media compared with 10.86 cm and 1230.2 min for the application of powder clinoptilolite. This study is expected to provide theoretical support and guidance for the practical application of mixed adsorbents in PRBs.

Hydrothermal carbonization of cellulose in aqueous phase of bio-oil: The significant impacts on properties of hydrochar

Aqueous phase of bio-oil (APBO) is a major fraction of bio-oil deriving from pyrolysis of biomass. APBO mostly contains water, carboxylic acids and different kinds of organics, which can afford a potential reactive medium for hydrothermal carbonization (HTC) of biomass. In this study, the HTC of cellulose in APBO was conducted, aiming to probe the effects of the APBO organics on the properties of the hydrochar. The results showed that the organics such as sugars, sugar-derivatives and phenolics in APBO could adsorb on the surface of cellulose and suppress the hydrolysis at lower temperature (i.e. 180 °C), while they could cross-polymerize with cellulose derivatives at higher temperatures (i.e. 220 or 260 °C). Compared with the hydrochar obtained in water, the APBO remarkably enhanced hydrochar yield by 11.3% and resulted in the abundant formation of aliphatic structures, making the hydrochar carbon and hydrogen-rich but with a lower thermal stability. In addition, the involvement of the APBO organics within the cross-polymerization interfered with the nucleation of the sugars/furans and inhibited the formation of the spheres with a hydrophilic shell and a hydrophobic core, resulting in the formation of an irregularly shaped hydrochar. Such a process also made the hydrochar rather hydrophobic, while the combustion performance was highly improved, exhibiting a lower ignition temperature (170 °C in APBO vs 306 °C in water).