The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Jean-louis Morel - One of the best experts on this subject based on the ideXlab platform.
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Short-term effects of biochar on soil heavy metal mobility are controlled by intra-Particle Diffusion and soil pH increase
European Journal of Soil Science, 2014Co-Authors: F. Rees, Marie-odile Simonnot, Jean-louis MorelAbstract:Biochar, the solid product of biomass pyrolysis, can be used as a soil amendment to stabilize metals in contaminated soils. The effects of biochar on the mobility of metals in soils are, however, poorly understood. To identify the predominant processes, we focused on (i) a possible kinetic limitation by transport in biochar Particles, (ii) the evolution of biochar mineral phases and (iii) the effect of biochar on soil pH. Batch experiments were conducted to measure the sorption kinetics of copper (Cu), cadmium (Cd) and nickel (Ni) and the sorption-desorption isotherms for lead (Pb), Cu, Cd, zinc (Zn) and Ni in a wood-derived biochar. Sorption data were then compared with extraction test results using biochar with one acidic and one basic soil contaminated by Zn, Cd and Pb. Kinetic results showed that biochar Particle sizes controlled metal sorption rate despite a similar specific surface area, which indicated a limitation by intra-Particle Diffusion. Isotherms showed a partially reversible sorption to biochar following the order Pb>Cu>Cd≥Zn>Ni, which we explained primarily by the (co)precipitation of metals or their adsorption on specific biochar mineral phases. Effective metal immobilization was observed with biochar in both contaminated soils but could not be predicted from the sorption isotherms. This immobilization appeared to be governed by the soil pH increase, which induced a greater retention of metals on soil Particles. Short-term effects of biochar on contaminated soils may therefore be controlled by Diffusion in biochar Particles and by soil alkalinization processes.
F. Rees - One of the best experts on this subject based on the ideXlab platform.
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Short-term effects of biochar on soil heavy metal mobility are controlled by intra-Particle Diffusion and soil pH increase
European Journal of Soil Science, 2014Co-Authors: F. Rees, Marie-odile Simonnot, Jean-louis MorelAbstract:Biochar, the solid product of biomass pyrolysis, can be used as a soil amendment to stabilize metals in contaminated soils. The effects of biochar on the mobility of metals in soils are, however, poorly understood. To identify the predominant processes, we focused on (i) a possible kinetic limitation by transport in biochar Particles, (ii) the evolution of biochar mineral phases and (iii) the effect of biochar on soil pH. Batch experiments were conducted to measure the sorption kinetics of copper (Cu), cadmium (Cd) and nickel (Ni) and the sorption-desorption isotherms for lead (Pb), Cu, Cd, zinc (Zn) and Ni in a wood-derived biochar. Sorption data were then compared with extraction test results using biochar with one acidic and one basic soil contaminated by Zn, Cd and Pb. Kinetic results showed that biochar Particle sizes controlled metal sorption rate despite a similar specific surface area, which indicated a limitation by intra-Particle Diffusion. Isotherms showed a partially reversible sorption to biochar following the order Pb>Cu>Cd≥Zn>Ni, which we explained primarily by the (co)precipitation of metals or their adsorption on specific biochar mineral phases. Effective metal immobilization was observed with biochar in both contaminated soils but could not be predicted from the sorption isotherms. This immobilization appeared to be governed by the soil pH increase, which induced a greater retention of metals on soil Particles. Short-term effects of biochar on contaminated soils may therefore be controlled by Diffusion in biochar Particles and by soil alkalinization processes.
Marie-odile Simonnot - One of the best experts on this subject based on the ideXlab platform.
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Short-term effects of biochar on soil heavy metal mobility are controlled by intra-Particle Diffusion and soil pH increase
European Journal of Soil Science, 2014Co-Authors: F. Rees, Marie-odile Simonnot, Jean-louis MorelAbstract:Biochar, the solid product of biomass pyrolysis, can be used as a soil amendment to stabilize metals in contaminated soils. The effects of biochar on the mobility of metals in soils are, however, poorly understood. To identify the predominant processes, we focused on (i) a possible kinetic limitation by transport in biochar Particles, (ii) the evolution of biochar mineral phases and (iii) the effect of biochar on soil pH. Batch experiments were conducted to measure the sorption kinetics of copper (Cu), cadmium (Cd) and nickel (Ni) and the sorption-desorption isotherms for lead (Pb), Cu, Cd, zinc (Zn) and Ni in a wood-derived biochar. Sorption data were then compared with extraction test results using biochar with one acidic and one basic soil contaminated by Zn, Cd and Pb. Kinetic results showed that biochar Particle sizes controlled metal sorption rate despite a similar specific surface area, which indicated a limitation by intra-Particle Diffusion. Isotherms showed a partially reversible sorption to biochar following the order Pb>Cu>Cd≥Zn>Ni, which we explained primarily by the (co)precipitation of metals or their adsorption on specific biochar mineral phases. Effective metal immobilization was observed with biochar in both contaminated soils but could not be predicted from the sorption isotherms. This immobilization appeared to be governed by the soil pH increase, which induced a greater retention of metals on soil Particles. Short-term effects of biochar on contaminated soils may therefore be controlled by Diffusion in biochar Particles and by soil alkalinization processes.
Anatoly Spitkovsky - One of the best experts on this subject based on the ideXlab platform.
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simulations of ion acceleration at non relativistic shocks iii Particle Diffusion
The Astrophysical Journal, 2014Co-Authors: Damiano Caprioli, Anatoly SpitkovskyAbstract:We use large hybrid (kinetic-protons-fluid-electrons) simulations to investigate the transport of energetic Particles in self-consistent electromagnetic configurations of collisionless shocks. In previous papers of this series, we showed that ion acceleration may be very efficient (up to 10%-20% in energy), and outlined how the streaming of energetic Particles amplifies the upstream magnetic field. Here, we measure Particle Diffusion around shocks with different strengths, finding that the mean free path for pitch-angle scattering of energetic ions is comparable with their gyroradii calculated in the self-generated turbulence. For moderately strong shocks, magnetic field amplification proceeds in the quasi-linear regime, and Particles diffuse according to the self-generated Diffusion coefficient, i.e., the scattering rate depends only on the amount of energy in modes with wavelengths comparable with the Particle gyroradius. For very strong shocks, instead, the magnetic field is amplified up to non-linear levels, with most of the energy in modes with wavelengths comparable to the gyroradii of highest-energy ions, and energetic Particles experience Bohm-like Diffusion in the amplified field. We also show how enhanced Diffusion facilitates the return of energetic Particles to the shock, thereby determining the maximum energy that can be achieved in a given time via diffusive shock acceleration. The parameterizationmore » of the Diffusion coefficient that we derive can be used to introduce self-consistent microphysics into large-scale models of cosmic ray acceleration in astrophysical sources, such as supernova remnants and clusters of galaxies.« less
Eric Loth - One of the best experts on this subject based on the ideXlab platform.
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Random Walk Models for Particle Diffusion in Free-Shear Flows
AIAA Journal, 2020Co-Authors: Todd L. Bocksell, Eric LothAbstract:The main objectives were to establish and investigate discontinuous and continuous random walk models appropriate for free-shear e ows with regard to turbulent Particle Diffusion. The models were designed to capture the crossing trajectories effect, the continuity effect, and the inertial-limit effect, all for the case of heavy Particles whose densities are much greater than that of the surrounding e uid. In addition, both techniques included an isotropic drift velocity to account for inhomogeneous turbulence. The computational efe ciency of the continuous random walk models is improved by utilizing local time stepping, which effectively e lters out high-frequency velocity e uctuations that do not have a signie cant ine uence on Particle Diffusion. The predictive performances of these two random walk models were examined through comparison with experimental data and idealized test conditions. The results indicate that both models agree well with experimental data for a nearly homogeneous turbulent wake and an inhomogeneous turbulent axisymmetric jet (although the continuous random walk model performs somewhat better for the inhomogeneous e ows ). It was also found that the proposed drift velocity models are important to ensure continuity when simulating Particle Diffusion with inhomogeneous turbulence.
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stochastic modeling of Particle Diffusion in a turbulent boundary layer
International Journal of Multiphase Flow, 2006Co-Authors: T L Bocksell, Eric LothAbstract:Abstract Several Continuous Random Walk (CRW) models were constructed to predict turbulent Particle Diffusion based on Eulerian statistics that can be obtained with Reynolds-Averaged Navier Stokes (RANS) solutions. The test conditions included a wide range of Particle inertias (Stokes numbers) with a near-wall injection (y+ = 4) in a turbulent boundary layer that is strongly anisotropic and inhomogeneous. To assess the performance of the models, the CRW results were compared to Particle Diffusion statistics gathered from a Direct Numerical Simulation (DNS). In particular, comparisons were made with transverse concentration profiles, root-mean-square of Particle trajectory coordinates, and mean transverse Particle velocity away from the wall. The results showed that accurate simulation required a modified (non-dimensionalized) Markov chain to handle the large gradients in turbulence near the wall as shown by simulations with fluid-tracer Particles. For finite-inertia Particles, an incremental drift correction for the Markov chain developed herein to account for Stokes number effects was critical to avoiding non-physical Particle collection in low-turbulence regions. In both cases, inclusion of anisotropy in the turbulence model was found to be important, but the influence of off-diagonal terms was found to be weak. The results were generally good, especially for long-time and large inertia Particles.