Instantaneous Concentration Research Articles

Entrainment and adaptation processes in the evolution of collisional bedload layers

We performed laboratory experiments which describe the evolution, from triggering until full formation, of a bedload layer. The phenomenon is driven by a turbulent open-channel flow at about constant discharge since the very initiation of the process. The flow stays uniform and the slope constant during the transient phase, during which we measured the instantaneous velocity and concentration profiles of the solid phase within the bedload layer. The timing of the process is governed by inertia and resistance forces. The bedload layer progressively thickens, fed by sediments entrained from the bed, which is progressively eroded, until the final steady uniform condition (i.e., equilibrium) is reached. We then applied a recent numerical model, able to cope with collisional suspensions using extended kinetic theories, to replicate the experimental results. The model results are used to further analyze and discuss the physical processes within the flow.

Surf Zone Turbulence and Suspended Sediment Dynamics—A Review

The existence of sandy beaches relies on the onshore transport of sand by waves during post-storm conditions. Most operational sediment transport models employ wave-averaged terms, and/or the instantaneous cross-shore velocity signal, but the models often fail in predictions of the onshore-directed transport rates. An important reason is that they rarely consider the phase relationships between wave orbital velocity and the suspended sediment concentration. This relationship depends on the intra-wave structure of the bed shear stress and hence on the timing and magnitude of turbulence production in the water column. This paper provides an up-to-date review of recent experimental advances on intra-wave turbulence characteristics, sediment mobilization, and suspended sediment transport in laboratory and natural surf zones. Experimental results generally show that peaks in the suspended sediment concentration are shifted forward on the wave phase with increasing turbulence levels and instantaneous near-bed sediment concentration scales with instantaneous turbulent kinetic energy. The magnitude and intra-wave phase of turbulence production and sediment concentration are shown to depend on wave (breaker) type, seabed configuration, and relative wave height, which opens up the possibility of more robust predictions of transport rates for different wave and beach conditions.

Stream Suspended Mud as an Indicator of Post-Mining Landform Stability in Tropical Northern Australia

Mining can cause environmental disturbances and thus mined lands must be managed properly to avoid detrimental impacts in the future. They should be rehabilitated in such a way that post mining landforms behave similarly as the surrounding stable undisturbed areas. A challenge for government regulators and mine operators is setting closure criteria for assessment of the stability of the elevated post-mining landforms. Stability of a landform is often measured by the number and incision depth of gullies. This can assess mass stability and bulk movement of coarse material. However, there is a need for a more sensitive approach to assess catchment disturbances using the concept of waves of fine suspended sediment and thus determine the dynamics of recovery of a post mining landform. A more environmentally meaningful approach would be to assess the fine suspended sediment (FSS, silt + clay (0.45 µm < diameter < 63 µm)) leaving the system and entering downstream waterways. We propose assessing stability through relationships between rainfall event loads of FSS and event discharge (Q) in receiving streams. This study used an innovative approach where, instead of using instantaneous FSS concentration, it used total FSS load in waves of sediment driven through the system by rainfall runoff events. High resolution stream monitoring data from 2004 to 2015 in Gulungul and Magela Creeks, Northern Territory, Australia, were used to develop a relationship between sediment wave and event discharge, ∑FSS α f(Q). These creeks are adjacent to and receive runoff from Ranger Mine. In 2008, a 10 ha elevated waste rock landform was constructed and instrumented in the Gulungul Creek catchment. The earthworks required to build the landform created a considerable disturbance in the catchment, making a large volume of disturbed soil and substrate material available for erosion. Between 2008 and 2010, in the first two wet seasons immediately after construction, the downstream monitoring site on Gulungul Creek showed elevated FSS wave loads relative to discharge, compared with the upstream site. From 2010 onwards, the FSS loads relative to Q were no longer elevated. This was due to the establishment of vegetation on the site and loose fine sediment being trapped by vegetation. Large scale disturbance associated with mining and rehabilitation of elevated landforms causes elevated FSS loads in receiving streams. The predicted FSS loads for the stream as per the relationships between FSS and event discharge may not show a 1:1 relation with the observed loads for respective gauging stations. When downstream monitoring shows that FSS wave loads relative to rainfall runoff event discharge reduce back to pre-construction catchment levels, it will indicate that the landform is approaching equilibrium. This approach to assess landform stability will increase the sensitivity of assessing post-mining landform recovery and assist rehabilitation engineers to heal the land and benefit owners of the land to whom it is bestowed after rehabilitation.

Simultaneous measurements of time-resolved velocity and concentration fields behind a sand dune-inspired jet in crossflow

The flow field and scalar concentration behind a sand dune-inspired jet-in-crossflow were measured to quantify the characteristics of flow and scalar mixing. The velocity was resolved from particle image velocimetry measurements, and the time-resolved concentration was simultaneously captured by planar laser-induced fluorescence. During the experiments, the velocity ratio was set to 0.4, 0.6, 0.8, 1.0, and 1.2. The corresponding jet flow statistics, concentration statistics, and flow-concentration dynamics were comparatively analyzed. Aided by the dune, all jets were found to discharge tangentially into the mainstream, forming an energetic shear layer in the dune upper region that not only affects the jet attachment but also influences the flow mixing dynamics. The measured turbulent flow statistics (vorticity, turbulent kinetic energy, and Reynolds stress), concentration statistics (scalar standard deviation and turbulent scalar flux), and dynamics of the flow-concentration fields (instantaneous evolutions, scalar dissipation, and strain rate) revealed not only the complex nature of the generated shear layer but also the significant correlations between the shear flow and scalar mixing. Proper orthogonal decomposition (POD) analysis successfully decomposed the instantaneous velocity and concentration fields into a series of energetic POD modes, vividly demonstrating the modulating effect of the energetic shear layer on the flow and scalar mixing.

Effect of sex and food on the pharmacokinetics of different classes of BCS drugs in rats after cassette administration

The cassette dosing technique is employed in the drug discovery stage of non-clinical studies to obtain pharmacokinetic data from multiple drug candidates in a single experiment. The objective of the current investigation was to evaluate the effect of sex and food on the selected pharmacokinetic parameters of four biopharmaceutical classification system (BCS) drugs (BCS-I: propranolol, BCS-II: diclofenac, BCS-III: atenolol, and BCS-IV: acetazolamide) utilizing cassette dosing in male and female rats under fed and fasting conditions. Different animal groups were dosed intravenous (i.v) and oral at 1 and 10 mg/kg, respectively, in the form of cassette at a dose of 5 mL/kg. Blood samples were analyzed by liquid chromatography-tandem mass spectrometry. Pharmacokinetics parameters were calculated using Phoenix software version 8.1. A significant increase (p < 0.05) of the area under the plasma concentration–time (AUC0-last) was observed for diclofenac and acetazolamide in females over males after i.v dosing. Additionally, acetazolamide showed greater instantaneous concentration at the time of dosing, and clearance in females (p < 0.05) compared to males after i.v administration. After oral dosing, propranolol exhibited significant variations (p < 0.05) in the maximum drug concentration (Cmax), AUC0-last, the volume of distribution (Vd), and bioavailability in females as compared to males under fed state. Diclofenac showed significant changes (p < 0.05) in AUC0-last, and clearance (Cl) in females as compared to males under fasting and fed state. However, acetazolamide exhibited a significant enhancement (p < 0.05) in AUC0-last, Vd, and Cl in fasting females than the males. The data here illustrates that there is an appreciable difference in AUC and Cmax values exist in male and female rats under fed and fasting conditions administered with the cassette dosing of tested BCS class drugs.

Description of Dust Emission Parameterization in CAS‐ESM2 and Its Simulation of Global Dust Cycle and East Asian Dust Events

AbstractThe dust emission parameterization in the Chinese Academy of Sciences Earth System Model version 2 (CAS‐ESM2) is described with emphasis on the implementation process and simulations of global dust cycle and East Asia dust event statistics. The parameterization is based on the scheme of Shao (2004; http://doi.org/10.1029/2003JD004372) which considers two major dust emission mechanisms, namely, saltation bombardment and aggregation disintegration. Shao (2004; http://doi.org/10.1029/2003JD004372) scheme was well tested against field observations and has been widely used in regional dust modeling. Here this scheme is implemented into a global climate model for the first time and thus provides an independent solution for simulating global dust emissions. With this scheme, CAS‐ESM2 reasonably simulates the main dust emission regions in the Earth and reproduces the observations of dust deposition flux and surface dust concentrations at most stations. Compared to the synoptic records of dust events, the model also captures the general patterns and seasonal variations of dust activities in East Asia. However, the model underestimates the frequency of strong dust events (instantaneous surface dust concentrations &gt;1,000 μg m−3) due to the weaker surface winds simulated by the model. The model tends to simulate much weaker and longer‐lasting dust events in Eastern Sources (35–49°N, 94–126.5°E) of northern China, suggesting the weaker and slower‐moving synoptic weather systems associated with dust events in the model. Overall CAS‐ESM2 performs well in simulating the key aspects of global dust distribution and East Asian dust events, yet some biases remain to be improved.

Analysis and Forecasting of PM2.5, PM4, and PM10 Dust Concentrations, Based on In Situ Tests in Hard Coal Mines

The method of analyzing the results of dust concentration measurements in mine workings that was conducted within the ROCD (Reducing risks from Occupational exposure to Coal Dust) European project using the developed dust prediction algorithm is presented. The analysis was based on the measurements of average dust concentration with the use of the CIP-10R gravimetric dust meters, for the respirable PM4 dust concentration, and IPSQ analyzer for instantaneous concentration measurements (including PM2.5 dust) and with the use of Pł-2 optical dust meters for instantaneous concentration measurements of PM10 dust. Based on the analyses of the measurement results, the characteristics of the distribution of PM10, PM4, and PM2.5 dust particles were developed for the tested dust sources. Then, functional models based on power functions were developed. The determined models (functions) allow predicting the dust distribution in such conditions (and places) for which we do not have empirical data. The developed models were implemented in a specially developed online tool, which enables predicting the concentration of PM10, PM4, and PM2.5 dust (on the basis of dust concentration of one source) at any distance from the dust source.

Simulations of reactive supersonic/subsonic flow interactions for space launcher applications

Purpose The design of a space launcher requires some considerations about the unsteady loads and heat transfer occurring at the base of the structure. In particular, these phenomena are predominant during the early stage of the flight. This paper aims to evaluate the ability of the unstructured, high order finite-volume CFD solver FLUSEPA, developed by Airbus Safran Launchers, to accurately describe these phenomena. Design/methodology/approach This paper first performs a steady simulation on a base flow around a four-clustered rocket configuration. Results are compared with NASA experiments and Loci-CHEM simulations. Then, unsteady simulations of supersonic H2/air reacting mixing layer based on the experiment of Miller, Bowman and Mungal are performed. Three meshes with different cells number are used to study the impact of spatial resolution. Instantaneous and time-averaged concentrations are compared with the combined OH/acetone planar laser-induced fluorescence imaging from the experiment. Findings FLUSEPA satisfactorily predicts the base heat flux at the base of a four-clustered rocket configuration. NASA Loci-CHEM reactive simulations indicate that afterburning plays an important role and should not be neglected. The unsteady reactive computation of a supersonic mixing layer shows that FLUSEPA is also able to accurately predict flow structures and interactions. However, the complexity of the experiment and the lack of details concerning the facility prevents from obtaining satisfactory converged results. Originality/value This study is the first step on the development of a cost-effective method aiming at predicting unsteady loads and heat transfer on space launchers using an unsteady and reactive model for the CDF calculations. It uses original techniques such as conservative CHIMERA-like overset grids, local re-centering of fluxes and local adaptive time-stepping to reduce computational cost while being robust and accurate.

Influence of monomer structure and dose rate on kinetic elements in electron-beam polymerizations

In electron-beam (EB) polymerizations, altering the dose rate can cause property changes in the cured polymer, such as conversion, glass transition temperature (Tg), and physical or mechanical properties. These dose rate effects (DREs) complicate scale-up of EB polymerizations in industrial processes. A predictive relationship between DRE and changes in Tg was used to determine that DREs correlate to the number and lability of available bonds, not monomer size. Furthermore, the relationship between the primary radicals produced during EB irradiation and dose rate was explored via measurement of primary radical radiation chemical yield, G(R•). Namely, G(R•) is independent of dose rate, and instantaneous primary radical concentration is directly proportional to dose rate. Moreover, it was shown that non-reciprocity between dose rate and the rate of polymerization results in DREs. Future developments in radiation chemical yield measurements will aid in determining whether this disproportionality is due to the impact of dose rate on the concentration of propagating radicals or on the kinetic mechanism itself.

Experimental study on the vapor-liquid two-phase explosion of n-heptane under high-temperature source ignition

The combustion and explosion characteristics of vapor-liquid two-phase (aerosol) under high-temperature sources ignition are an essential subject in fuel utilization and prevention of chain explosion accidents. In this study, a series of experiments were carried out in a 20 L vessel to observe instantaneous concentration and droplet size distribution of n-heptane aerosol and analyze the energy characteristics of n-heptane aerosol explosion under high-temperature source ignition. Tests were conducted for n-hexane/air mixtures of mass concentrations from 50.19 g/m3 to 317.87 g/m3, the ignition temperature of 1373.15 K, and the initial temperature and pressure of 22 ℃ and 0.10 MPa, respectively. The influence of the instantaneous concentration and droplet size of n-heptane aerosol on the explosive characteristics under high-temperature source ignition was examined. The results show that the explosion pressure-time history of the n-heptane aerosol at the high-temperature ignition was found to have a “double peak” structure produced in the first and second explosion respectively. The second peak of the pressure in an explosion time history of the n-heptane aerosol ignited at the high-temperature source is 2–5 times the first. The liquid n-heptane was driven by pressure to form aerosol in the vessel. The aerosol flows from the nozzle on the vessel wall to the center of the vessel (high-temperature source). The first explosion formed when the mist contacts a high-temperature source will generate outward radiation pressure waves, which are opposite to the initial converging flow direction of the aerosol, forming a reverse flow, and then causing a transient negative pressure. When the high-temperature product of the first explosion swells and meets the droplets of unburned n-heptane, a second explosion occurs, forming the second explosion peak. Compared with premixed aerosol explosion under electric spark ignition, the explosion process under high-temperature source ignition is more complicated. The explosion is coupled with the flow, and the explosion energy output is significantly increased. The latter is about 1.6 times the former. At the moment when the first explosion was initiated by the high-temperature source, the concentration of 301.14 g/m3 at which the first explosion pressure reached maximum was greater than the stoichiometric concentration of 83.65 g/m3 due to energy consumption caused by heat absorption of the droplets.

Measurement of Lagrangian Trajectories in a 3 L Stirred Tank Reactor using 4D Particle Tracking Velocimetry with Shake-the-Box

Stirred tank reactors are widely used in the chemical industry and bioprocess engineering and, consequently, a large number of scientific publications deal with the characterization of those apparatuses. However, there is very little information about the flow conditions. This is mostly due to the fact that these apparatuses are generally made of stainless steel, which restricts optical access. Furthermore, three-dimensional flow field measurements are still not trivial and involve costly equipment, therefore, investigations often reduce to two-dimensional PIV measurements. Nevertheless, recent works (Rosseburg et al., 2018; Taghavi and Moghaddas, 2020; Kuschel et al., 2021) impressively show the formation of compartments which hinder and delay mixing. However, these measurements are based either on instantaneous concentration profiles by means of pLIF measurements or on a two-dimensional projection of the system and thus do not allow conclusions about the development of the three dimensional compartments and the exchange rates between the compartments. In this work, for the first time, instantaneous flow field measurements with high spatial and temporal resolution are performed in the entire volume of a 3L stirred tank reactor based on 4D particle tracking velocimetry. The highly resolved particle trajectories further allow detailed Lagrangian analysis of the mixing dynamics inside the reactor, data that was previously inaccessible.

Air Quality Studies at Ukrainian Airports

Sustainability of aviation must be provided to limit the harmful influence and protect public health and the environment. As a rule, national and international regulations aim to reduce ambient air pollution from the aviation sector. Ukraine and other countries have historically adopted international regulations concerning air quality to protect public health and the natural environment. Local regulations also regulate it. However, these documents cover mainly stationary emission sources. In contrast, mobile sources, especially aircraft, are not considered, although, unlike most transportation modes, aircraft travel great distances at various altitudes, generating emissions that potentially impact air quality. This paper was aimed to study the principles and methods to monitor air pollution from aircraft engines at main airports of Europe, north America, and Asia. Based on measurement campaign analysis at some airports of the world and modelling results by complex model PolEmiCa (Pollution and Emission Calculation), the method and technical characteristics for measurement system detect the aircraft engine emissions. The developed practical recommendations were realised at Ukrainian airports and used for validation of model PolEmiCa. Thus, the modelling results for each engine are in good agreement with the results of measurements by the AC32M Nitrogen Oxides (NOX) analyser system due to considering the jet and plume-regime during an experimental investigation at Boryspol airport. Analysis of measured instantaneous concentration demonstrates a high correlation with the runway movements and take-off at Zhulyany airport.

Coherent structure characteristics of the swirling flow during turbulent mixing in a multi-inlet vortex reactor

Improving the efficiency of the production of uniformly sized functional nanoparticles for pharmaceutical and agricultural applications has been a problem of great interest. The macroscale multi-inlet vortex Reactor (macro-MIVR) could potentially be used for this purpose due to its ability to achieve the rapid mixing necessary for the flash nanoprecipitation nanoparticle fabrication technique. In the presented work, the coherent structures, a key contributor to the turbulent mixing, were investigated for the turbulent swirling flow within the MIVR. The two-point spatial correlations of velocity and concentration fluctuations at various basepoints were measured from instantaneous velocity and concentration fields obtained using simultaneous stereoscopic particle image velocimetry and planar laser-induced fluorescence. The basepoint locations were chosen as the middle and at the edge of the partially mixed concentration spiral arms. The correlations were found to be elliptical in shape, inclined, and peaked at the basepoints. A region near the basepoint was positively correlated and was surrounded by negatively correlated regions. Autocorrelations of concentration were also elliptical and curved toward the center of the reactor. The linear stochastic estimation was used to interpret the coherent structure features that would result in the observed spatial correlations. The linear stochastic estimates of the velocity fields were computed directly from the cross correlations of the tangential velocity fluctuations with the concentration fluctuations. The estimated conditional velocity fields revealed obliquely oriented counter-rotating vortical structures that stir the fluid from high-concentration regions to low-concentration regions, and the orientation of these vortical structures depended on the local concentration gradient.

N, P, and COD conveyed by urban runoff: a comparative research between a city and a town in the Taihu Basin, China.

Stormwater runoff containing various pollutants exerts adverse effects on receiving water bodies and deteriorates the urban aquatic environment. Although numerous studies have been conducted on runoff pollution, research comparing its characteristics in cities with those in towns is rare in the literature. To close this gap, the present study was conducted. The instantaneous concentrations of ammonia-N, TN, TP, and COD during the rainfall events in the town were higher than those in the city in most conditions. The outfall concentrations increased with the increase of rainfall intensity. EMCs (the average value of EMC) and CV (coefficient of variation) of TN and DTN in the town were higher than those in the city, which may lie in the differences of urban environment planning and management, road cleaning methods, garbage disposal methods, industrial enterprise, etc. On the one hand, EMCs and CV of TP in the city's industrial areas were lowest among three functional areas, while on the other hand, in the town it was in the commercial areas rather than the industrial areas that EMCs and CV were the lowest, which may be caused by the low level of economic development of small towns in China. The concentrations of COD in the town were generally higher than that in the city. Compared with the city, the correlation among COD and various forms of N was stronger in the town, which may illustrate a stronger similarity of pollutant sources in the town. According to the results, road runoff in the town contributed more to urban aquatic pollution; thus, further research should concentrate on this particular type of runoff.

Estimation the dielectric properties of solvation shells and nano-cavities by solvatochromic shift of organic dye

We investigated the preferential solvation effect of pyridinium-N-phenolate betaine (organic dye) taken as a molecular probe in two binary solvents (water-BuOH and water-BuNH2) in concentration range 0-100%. The Onsager-Liptay model was used to connect the spectral solvatochromic shift in solvation shell of the dye with the dielectric permittivity of the environment around its chromophore. That makes it possible to estimate the effective dielectric constant in the microscopic region of the probe, based on the values of the experimentally measured solvatochromic shifts. It was shown that the solvation shell of the dye is significantly depleted with the second component of binary solvent in water solution. It is true both for the water-BuOH and water-BuNH2 solvents. The absolute spectral shift in case of water-BuNH2 solvent is greater than in the second case. However, the relative depletion is stronger in case of water-BuOH. The innovative potential of the method is in the development the nanoprobe devices to measure the dielectric constant of small objects and nano-regions, to control instantaneous solvent concentration into evaporating sessile droplet of binary solvent in different zones of the droplet.

Product Control and Insight into Conversion of C6 Aldose Toward C2, C4 and C6 Alditols in One‐Pot Retro‐Aldol Condensation and Hydrogenation Processes

Alcohols have a wide range of applicability, and their functions vary with the carbon numbers. C6 and C4 alditols are alternative of sweetener, as well as significant pharmaceutical and chemical intermediates, which are mainly obtained through the fermentation of microorganism currently. Similarly, as a bulk chemical, C2 alditol plays a decisive role in chemical synthesis. However, among them, few works have been focused on the chemical production of C4 alditol yet due to its difficult accumulation. In this paper, under a static and semi‐flowing procedure, we have achieved the product control during the conversion of C6 aldose toward C6 alditol, C4 alditol and C2 alditol, respectively. About C4 alditol yield of 20 % and C4 plus C6 alditols yield of 60 % are acquired in the one‐pot conversion via a cascade retro‐aldol condensation and hydrogenation process. Furthermore, in the semi‐flowing condition, the yield of ethylene glycol is up to 73 % thanks to its low instantaneous concentration.

Assessment of home care aides’ respiratory exposure to total volatile organic compounds and chlorine during simulated bathroom cleaning: An experimental design with conventional and “green” products

Home care (HC) aide visits to clients’ homes often involve cleaning and disinfecting (C&D) bathrooms. Some ingredients in C&D household products are associated with respiratory illness, including sodium hypochlorite (bleach) and quaternary ammonium compounds (quats). “Green” products may be safer for the environment, however there are limited quantitative evaluations of their respiratory risks. This study assessed airborne concentrations and time profiles of total volatile organic compounds (TVOC) and chlorine generated during typical bathroom cleaning performed by aides using conventional and green products. Aides performed cleaning tasks in a simulated residential bathroom constructed in an environmental air sampling laboratory. A balanced experimental design involved each aide coming to the lab for four visits during which she performed two 20-min cleaning sessions using one of three C&D products (bleach-based, 1–5% sodium hypochlorite by weight; quats-based, 0.1–1% by weight quaternary ammonium compounds; and “green,” 0.05% by weight thymol, a component of botanical thyme oil) or distilled water as a control. TVOC and chlorine direct reading instruments were attached to aides with sample inlets located in the breathing zone. Ten-second averages of TVOC and chlorine gas concentrations and instantaneous peak concentrations were recorded for the sessions’ duration. TVOC concentrations by methods of C&D application (spraying, streaming, wiping) also were evaluated. The study completed 169 air sampling sessions with 22 aides. The quats-based product generated more than twice the average TVOC concentrations (mean = 1,210 ppb) than the bleach-based (mean = 593 ppb) or green (mean = 498 ppb) products. Each product generated TVOC concentrations that rose rapidly within the first few minutes of application. Spraying produced the highest TVOC exposures, wiping the lowest. Thirteen aides (65%) experienced peak chlorine exposures above the OSHA PEL ceiling limit (1 ppm) when using the bleach-based product. HC aides may experience respiratory hazards from use of conventional or green C&D products formulated with bleach or other respiratory irritants and sprayed in small, poorly ventilated spaces typical of bathrooms. Spraying should be avoided.

Development and Evaluation of a Fluctuating Plume Model for Odor Impact Assessment

For environmental odor nuisance, it is extremely important to identify the instantaneous concentration statistics. In this work, a Fluctuating Plume Model for different statistical moments is proposed. It provides data in terms of mean concentrations, variance, and intensity of concentration. The 90th percentile peak-to-mean factor, R90, was tested here by comparing it with the experimental results (Uttenweiler field experiment), considering different Probability Distribution Functions (PDFs): Gamma and the Modified Weibull. Seventy-two percent of the simulated mean concentration values fell within a factor 2 compared to the experimental ones: the model was judged acceptable. Both the modelled results for standard deviation, σC, and concentration intensity, Ic, overestimate the experimental data. This evidence can be due to the non-ideality of the measurement system. The propagation of those errors to the estimation of R90 is complex, but the ranges covered are quite repeatable: the obtained values are 1–3 for the Gamma, 1.5–4 for Modified Weibull PDF, and experimental ones from 1.4 to 3.6.

Fractional diffusion models for radionuclide anomalous transport in geological repository systems

Abstract Using the new derivatives of fractional order, alluded to the Atangana-Baleanu (AB) derivative and Caputo-Fabrizio (CF) derivative, three fractional diffusion models are proposed to describe radionuclide anomalous transport in geological repository systems. The analytical solutions of the Atangana-Baleanu fractional diffusion (ABFD) models and Caputo-Fabrizio fractional diffusion (CFFD) model in the context of instantaneous and constant concentration source are presented. The mean square displacements (MSDs) for the ABFD and CFFD models in terms of instantaneous source are investigated. Based on the fitting analysis of experimental data of radionuclide diffusion, parameters related to the ABFD and CFFD models are determined. The good agreement between the theoretical and experimental results indicates that the proposed fractional diffusion models are more effective and flexible to characterize the radionuclide anomalous migration. Furthermore, the comparison of the proposed ABFD and CFFD models is also discussed.

Geochemical behaviour of benign desulphurised waste rocks for mine drainage control and sustainable management

Large volumes of waste rock (WR) are generated in open-pit mines. WR is characterised by high anisotropy in its physical, chemical, mineralogical, and hydrogeological properties. WR is often deposited in unsaturated piles on the mine surface. Mineralogical investigations defined the diameter of physical locking of sulphides (DPLS) allowing the WR to be separated into two fractions: i) a reactive fine fraction (<2.4 mm), and ii) an inert coarse fraction (>2.4 mm). Environmental desulphurisation carried out on the reactive fine fraction decreased the risk of contamination caused by WR oxidation. The geochemical behaviour of three benign desulphurised lithologies (altered greywacke (AGR), carbonated greywacke (CGR) and carbonated porphyry (CPO)) and their corresponding fine fractions (<2.4 mm) were assessed using kinetic weathering cells (WCs). These tests confirmed the effectiveness of environmental desulphurisation to prevent acid mine drainage formation. In fact, geochemical analyses of the leachates from WCs showed that pH values ranged between 7.4 and 8.9. Moreover, instantaneous concentrations of iron and zinc were below 0.5 mg/L and 3 mg/L, respectively. Pyrite oxidation rates, which represent sample reactivity, were higher for head samples (3.01, 4.86, and 2.54 μmol/kg/day for AGR, CGR, and CPO lithologies, respectively) in comparison to the benign desulphurised materials (2.32, 2.4, and 2.25 μmol/kg/day for AGR, CGR, and CPO lithologies, respectively). Pyrite in the dismantled material was only partially liberated or almost encapsulated, making it mineralogically unavailable for oxidation. The benign desulphurised material with low initial sulphide content was potentially non-acid generating at the long-term scale. Upstream environmental desulphurisation has been confirmed as an effective strategy for WR management and valorisation.