scholarly journals Leaching of trace metals (Pb, Zn) from contaminated tailings: New insight from a modelling approach

2021 ◽  
Author(s):  
Samuel Mertz ◽  
Lydie Le Forestier ◽  
Philippe Bataillard ◽  
Nicolas Devau
Keyword(s):  
Pore Solution ◽  
Biogeochemical Processes ◽  
Metal Pollutants ◽  
Sufficient Energy ◽  
Gas Interactions ◽  
Complexation Reactions ◽  
The Impact ◽  
Water Gas ◽  
Pb Concentration ◽  
Modelling Approach

<p>Reclamation measurements are commonly applied to mitigate the leaching of metal pollutants in order to reduce the risk for humans and the environment. Organic and/or inorganic amendments are often recommended to stabilize tailings and to reduce leaching of contaminants. In a recent microcosm percolation experiment (Thouin et al., 2019), the addition of a mining slurry called ochre and manure, either alone or in combination, drastically reduced the leaching of several metal pollutants, notably Pb. Nevertheless, the biogeochemical processes involved in the immobilization of metal pollutants remain unknown, preventing the management of this remediation technique from being optimized and its extension to other sites.  To fill this gap, a multicomponent reactive model was developed to simulate and forecast the impact of amendments on the leaching of metal pollutants. This model accounts for the following biogeochemical processes: kinetically-controlled dissolution and precipitation reactions, sorption reactions (i.e. surface complexation reactions), water-gas interactions and microbially-driven redox reactions with an explicit microbial growth. For all treatments, simulations revealed that Pb reactivity followed dynamic patterns driven by watering steps. The decrease in Pb concentration in the leachates of amended tailings compared to untreated tailings was also accurately reproduced. In untreated tailings, Pb reactivity is mainly controlled by the dissolution of Pb-bearing mineral phases. These reactions were maintained in thermodynamic disequilibrium due to the renewal of pore solution at each watering step. In amended tailings, this pattern was strengthened as the iron oxides contributed by ochre maintained a low Pb concentration in pore solution by sorbing released Pb. Sorption reactions were enhanced by the increase in pH induced by the dissolution of calcium carbonate initially present in ochre. The latter reaction was partially counterbalanced in tailings amended with manure as organic matter provided sufficient energy to fuel microbial aerobic respiration, leading to the release of protons. Pb desorption was promoted by this pH drop. By providing a better understanding of the effect of amendment, this multicomponent reactive model is a powerful tool to optimize the reclamation of tailings, in order to limit contaminant transfer to the environment.</p><p>Thouin H. et al. (2019), Appl. Geochem. 111, 104438</p>

scholarly journals Simulations of the Impact of Co-injected Gases on CO2 Storage, the SIGARRR Project: First Results on Water-gas Interactions Modeling

2014 ◽  
Vol 63 ◽  
pp. 3160-3171 ◽  
Author(s):  
J. Corvisier ◽  
E. El Ahmar ◽  
C. Coquelet ◽  
J. Sterpenich ◽  
R. Privat ◽  
...  
Keyword(s):  
Co2 Storage ◽  
First Results ◽  
Gas Interactions ◽  
The Impact ◽  
Water Gas

scholarly journals Selecting pH cut-offs for the safe verification of nasogastric feeding tube placement: a decision analytical modelling approach

BMJ Open ◽  
2017 ◽  
Vol 7 (11) ◽  
pp. e018128 ◽  
Author(s):  
Melody Zhifang Ni ◽  
Jeremy R Huddy ◽  
Oliver H Priest ◽  
Sisse Olsen ◽  
Lawrence D Phillips ◽  
...  
Keyword(s):  
Care Pathway ◽  
Feeding Tube ◽  
Tube Placement ◽  
X Rays ◽  
Clinical Environment ◽  
Nasogastric Feeding ◽  
Relative Safety ◽  
Checking Procedure ◽  
The Impact ◽  
Modelling Approach

ObjectivesThe existing British National Patient Safety Agency (NPSA) safety guideline recommends testing the pH of nasogastric (NG) tube aspirates. Feeding is considered safe if a pH of 5.5 or lower has been observed; otherwise chest X-rays are recommended. Our previous research found that at 5.5, the pH test lacks sensitivity towards oesophageal placements, a major risk identified by feeding experts. The aim of this research is to use a decision analytic modelling approach to systematically assess the safety of the pH test under cut-offs 1–9.Materials and methodsWe mapped out the care pathway according to the existing safety guideline where the pH test is used as a first-line test, followed by chest x-rays. Decision outcomes were scored on a 0–100 scale in terms of safety. Sensitivities and specificities of the pH test at each cut-off were extracted from our previous research. Aggregating outcome scores and probabilities resulted in weighted scores which enabled an analysis of the relative safety of the checking procedure under various pH cut-offs.ResultsThe pH test was the safest under cut-off 5 when there was ≥30% of NG tube misplacements. Under cut-off 5, respiratory feeding was excluded; oesophageal feeding was kept to a minimum to balance the need of chest X-rays for patients with a pH higher than 5. Routine chest X-rays were less safe than the pH test while to feed all without safety checks was the most risky.DiscussionThe safety of the current checking procedure is sensitive to the choice of pH cut-offs, the impact of feeding delays, the accuracy of the pH in the oesophagus, as well as the extent of tube misplacements.ConclusionsThe pH test with 5 as the cut-off was the safest overall. It is important to understand the local clinical environment so that appropriate choice of pH cut-offs can be made to maximise safety and to minimise the use of chest X-rays.Trial registration numberISRCTN11170249; Pre-results.

Gas Turbine Combined Cycle With CO2-Capture Using Auto-Thermal Reforming of Natural Gas

2000 ◽  
Author(s):  
Thormod Andersen ◽  
Hanne M. Kvamsdal ◽  
Olav Bolland
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Process Integration ◽  
Combined Cycle ◽  
Co2 Removal ◽  
Gas Turbine Combustor ◽  
Chemical Absorption ◽  
Fuel Gas ◽  
The Impact ◽  
Water Gas

A concept for capturing and sequestering CO2 from a natural gas fired combined cycle power plant is presented. The present approach is to decarbonise the fuel prior to combustion by reforming natural gas, producing a hydrogen-rich fuel. The reforming process consists of an air-blown pressurised auto-thermal reformer that produces a gas containing H2, CO and a small fraction of CH4 as combustible components. The gas is then led through a water gas shift reactor, where the equilibrium of CO and H2O is shifted towards CO2 and H2. The CO2 is then captured from the resulting gas by chemical absorption. The gas turbine of this system is then fed with a fuel gas containing approximately 50% H2. In order to achieve acceptable level of fuel-to-electricity conversion efficiency, this kind of process is attractive because of the possibility of process integration between the combined cycle and the reforming process. A comparison is made between a “standard” combined cycle and the current process with CO2-removal. This study also comprise an investigation of using a lower pressure level in the reforming section than in the gas turbine combustor and the impact of reduced steam/carbon ratio in the main reformer. The impact on gas turbine operation because of massive air bleed and the use of a hydrogen rich fuel is discussed.

scholarly journals Lanthanoid Complexes Supported by Retro-Claisen Condensation Products of β-Triketonates

2018 ◽  
Author(s):  
Laura Abad Galán ◽  
Alexandre N. Sobolev ◽  
Eli Zysman-Colman ◽  
Mark Ogden ◽  
Massimiliano Massi
Keyword(s):  
Chelating Ligands ◽  
X Ray Diffraction ◽  
Reaction Conditions ◽  
Claisen Condensation ◽  
X Ray ◽  
Condensation Products ◽  
Complexation Reactions ◽  
The Impact ◽  
Low Solubility

<i>β</i>-Triketonates have been recently used as chelating ligands for lanthanoid ions, presenting unique structures varying from polynuclear assemblies to polymers. In an effort to overcome low solubility of the complexes of tribenzoylmethane, four <i>β</i>-triketones with higher lipophilicity were synthesised. Complexation reactions were performed for each of these molecules using different alkaline bases in alcoholic media. X-ray diffraction studies suggested that the ligands were undergoing decomposition under the reaction conditions. This is proposed to be caused by <i>in situ</i>retro-Claisen condensation reactions, consistent with two examples that have been reported previously. The lability of the lanthanoid cations in the presence of a varying set of potential ligands gave rise to structures where one, two, or three of the molecules involved in the retro-Claisen condensationreaction were linked to the lanthanoid centres. These results, along with measurements of ligand decomposition in the presence of base alone, suggest that using solvents of lower polarity will mimimise the impact of the retro-Claisen condensation in these complexes. <br>

scholarly journals Key Factors for Activated Carbon Adsorption of Pharmaceutical Compounds from Wastewaters: A Multivariate Modelling Approach

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 166
Author(s):  
Rui M. C. Viegas ◽  
Ana S. Mestre ◽  
Elsa Mesquita ◽  
Miguel Machuqueiro ◽  
Marta A. Andrade ◽  
...  
Keyword(s):  
Adsorption Capacity ◽  
Activated Carbons ◽  
Univariate Analysis ◽  
Pharmaceutical Compounds ◽  
Pls Regression ◽  
Short Term ◽  
Latent Structures ◽  
The Impact ◽  
Inorganic Matrix ◽  
Modelling Approach

Projection to Latent Structures (PLS) regression, a generalization of multiple linear regression, is used to model two datasets (40 observed data points each) of adsorption removal of three pharmaceutical compounds (PhCs), of different therapeutic classes and physical–chemical properties (carbamazepine, diclofenac, and sulfamethoxazole), from six real secondary effluents collected from wastewater treatment plants onto different powdered activated carbons (PACs). For the PLS regression, 25 descriptors were considered: 7 descriptors related to the PhCs properties, 10 descriptors related to the wastewaters properties (8 related to the organic matrix and 2 to the inorganic matrix), and 8 descriptors related to the PACs properties. This modelling approach showed good descriptive capability, showing that hydrophobic PhC-PAC interactions play the major role in the adsorption process, with the solvation energy and log Kow being the most suitable descriptors. The results also stress the importance of the competition effects of water dissolved organic matter (DOM), namely of its slightly hydrophobic compounds impacting the adsorption capacity or its charged hydrophilic compounds impacting the short-term adsorption, while the water inorganic matrix only appears to impact PAC adsorption capacity and not the short-term adsorption. For the pool of PACs tested, the results point to the BET area as a good descriptor of the PAC capacity, while the short-term adsorption kinetics appears to be better related to its supermicropore volume and density. The improvement in these PAC properties should be regarded as a way of refining their performance. The correlations obtained, involving the impact of water, PhC and PAC-related descriptors, show the existence of complex interactions that a univariate analysis is not sufficient to describe.

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