Complejación de metales por sustancias húmicas acuáticas como proceso natural, tomando como caso de estudio el Lago de Xochimilco

22 This work discusses the importance of organic matter, specifically Aquatic Humic Substances (SHA) 23 within the speciation and distribution of metals within an aquatic system, in this case Xochimilco 24 Lake, a site with great ecological importance. This lake is the natural habitat of the endemic species 25 “axolotl” (ajolote). In this research, complexation reactions between SHA and metals (Cu, Mn, Pb 26 and Zn) were carried out under different reaction conditions, the source of AHS was water samples 27 taken in Xochimilco Lake in presence and absence of pH buffer dissolution and varying the 28 concentration of metals. The results show that there is a direct competition between the major 29 elements and trace elements to react with the AHS. Under the pH conditions of Xochimilco Lake 30 complexes formation is possible. 31

New Insights into Surfactant Adsorption Estimation During ASP Flooding in Carbonates Under Harsh Conditions Using Surface Complexation Modeling

Several laboratory experiments demonstrated that the use of sodium hydroxide could increase the solution pH and reduce the adsorption of anionic surfactants. However, a better understanding of rock-oil-brine interactions and their effect on surfactant adsorption during alkaline-surfactant-polymer (ASP) flooding is needed for realistic and representative estimations of surfactant adsorption levels. Therefore, this study presents a novel approach to capture these interactions and better predict their effect on surfactant adsorption as well as effluent concentrations of surfactant and various aqueous species. Currently, surface complexation models (SCM) consider rock-brine, oil-brine, and surfactant-brine reactions. In this work, four new surface complexation reactions with intrinsic stability constants that honor oil-surfactant interactions have been proposed for the first time and then validated against experimental data reported in the literature. In addition, we analyzed the effect of various parameters on surface adsorption under harsh conditions of high-temperature and high-salinity using the proposed surface complexation model (SCM). The results showed that the developed surfactant-based SCM is robust and accurate for estimating surfactant adsorption and its concentration in the effluent during chemical floods. The model was validated against two sets of ASP corefloods from the literature including single-phase and two-phase dynamic surfactant adsorption studies. The findings highlighted that oil-surfactant surface complexation reactions are important and should be captured for more representative and accurate estimation of surfactant adsorption during chemical flooding. Moreover, the detail and comprehensive analysis showed that surfactant adsorption increases and its concentration in the effluent decreases with the increase in temperature of the chemical flood, which could be due to the increase in kinetic energy of the species. It was also showed that a decrease in water total salinity decreases the surfactant adsorption on the rock surface, which is related to the increase in the repulsive forces between the adsorbed species. Additionally, with the increase in surfactant concentration in the chemical flood, the effluent surfactant concertation increases, with a slight increase in surfactant adsorption. This slight increase in adsorption can be neglected compared to the injected and produced masses of the surfactant that are proportional. Moreover, the effect of sulfate spiking is significant where the increase in sulfate concentration reduces the surfactant adsorption. Furthermore, it is worth highlighting that the lowest surfactant adsorption levels were achieved through injected water dilution; less than 0.1 mg/g of rock. This is the first study to test a novel formulation of surface complexation modeling considering oil-surfactant effect on surfactant adsorption properties. The proposed framework to estimate surfactant adsorption is conducted for high-temperature and high-salinity reservoir condition. Thus, it could be used in numerical reservoir simulators to estimate oil recovery due to wettability alteration by chemical flooding in carbonates, which will be investigated in our future work. The surfactant adsorption mechanisms during chemical flooding is very case-dependent and hence, the findings of this study cannot be generalized.

The Effect of Exogenous Oxytetracycline on High-Temperature Anaerobic Digestion of Elements in Swine Wastewater

Tetracycline antibiotics (TCs) are a common type of antibiotic found in swine wastewater. Oxytetracycline (OTC) is a significant type of TC. This study mainly examined the influence of OTC on high-temperature anaerobic digestion by adding OTC to collections of swine wastewater at different times during the digestion process. The results showed that high-temperature anaerobic digestion was suitable for the removal of TCs, with an 87% OTC removal efficiency achieved by day 20. Additionally, OTC added from external sources was found to inhibit the chlortetracycline degradation process and affect the first-order degradation kinetic model of TCs. Complexation reactions were the main ways in which OTC affected the heavy metal content of the water. The exogenous addition of OTC was found to inhibit the activity of some digester microbial strains, reduce the proportion of dominant strains, such as MBA03, and kill certain specific strains. This performance alteration was most obvious when OTC was added in the middle of the reaction.

A Comprehensive Numerical Model for One-Dimensional Pit Growth of 316L SS under a Salt Film

A comprehensive mathematical model, including electrode kinetics, hydrolysis and complexation reactions, salt film precipitation and pit interface movement, was developed to investigate pit growth of stainless steels 316L under a salt film. The new mathematical framework incorporates activity coefficients into the hydrolysis and complexation reaction calculations for the first time, using experimental results to parametrize the electrode kinetics in a saturated pit solution. The model was validated by 1D pit experiments and results documented in the literature. It can successfully estimate the transition potentials, salt film thickness, pit stability product, saturated pit concentration, and the pH at the pit base during pit propagation under the presence of a salt film. Moreover, the model can predict the Cr enrichment and Fe depletion in the saturated solution at the pit base, attributed to the higher diffusion coefficient of Fe and the lower Cr diffusivity.

Reactive Transport Modelling of the Long-Term Interaction between Carbon Steel and MX-80 Bentonite at 25 ∘C

The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste (HLW). In some of these concepts, carbon steel is considered as a potential canister material and bentonites are planned as backfill material to protect metallic waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron-bentonite interaction. The numerical model accounts for diffusion, aqueous complexation reactions, mineral dissolution/precipitation and cation exchange at a constant temperature of 25 ∘C under anoxic conditions. Our results suggest that Fe is sorbed at the montmorillonite surface via cation exchange in the short-term, and it is consumed by formation of the secondary phases in the long-term. The numerical model predicts precipitation of nontronite, magnetite and greenalite as corrosion products. Calcite precipitates due to cation exchange in the short-term and due to montmorillonite dissolution in the long-term. Results further reveal a significant increase in pH in the long-term, while dissolution/precipitation reactions result in limited variations of the porosity. A sensitivity analysis has also been performed to test the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the bentonite porewater, on the corrosion processes. Overall, outcomes suggest that the predicted main corrosion products in the long-term are Fe-silicate minerals, such phases thus should deserve further attention as a chemical barrier in the diffusion of radionuclides to the repository far field.

Reactive transport modelling of long-term interactions between iron and MX-80 bentonite

The geological disposal in deep bedrock repositories is the preferred option for the management of high-level radioactive waste. In some of these concepts, carbon steel is considered as potential canister material and bentonites are planned as backfill material to protect metal waste containers. Therefore, a 1D radial reactive transport model has been developed in order to better understand the processes occurring during the long-term iron–bentonite interaction. The conceptual model accounts for diffusion, chemistry of the porewater and aqueous complexation reactions, mineral dissolution/precipitation and absorption, at a constant temperature of 25 ∘C under anoxic conditions. The geometry of the axisymmetric model reflects the canister–bentonite interface and the bentonite. The primary phases considered are montmorillonitic smectite, quartz, muscovite, albite, illite, pyrite and calcite. We assume that carbon steel is composed only of iron. The potential secondary phases considered are from reported experiments, such as magnetite, nontronitic smectite, greenalite, cronstedtite and siderite. The numerical model results suggest that at the iron–bentonite interface, Fe is adsorbed at the smectite surface via ion exchange in the short term and it is consumed by formation of the secondary phases in the long term. Furthermore, calcite precipitates are due to cation exchange in the short term and due to montmorillonitic smectite dissolution in the long term. The numerical model predicts the precipitation of nontronitic smectite, magnetite and greenalite as corrosion products. Results further reveal a significant increase in pH in the long term, whereas dissolution/precipitation reactions result in limited variations of the porosity. Progressing bentonite dissolution owing to the rising pH and concomitantly increasing silicate concentrations in the porewater induce formation of Fe-silicates as corrosion products at the expense of magnetite. A sensitivity analysis has also been performed to study the effect of selected parameters, such as corrosion rate, diffusion coefficient and composition of the porewater, on the corrosion products. Overall, outcomes suggest that pH and concentration of dissolved Si play an important role in corrosion mechanisms. The predicted main secondary phases in the long term are Fe-silicate minerals. Thus, such phases deserve further attention as possible chemical barriers for radionuclide migration in the repository near-field.

New methods of cleaning soil from heavy metals

The purpose of the work was to study new methods of cleaning soil from heavy metals. In this work, it was proposed to extract heavy metals Cd, Zn, Fe, Cu, Mn, Pb from soils using the method of biological purification. For this, we recommended to carry out preliminary treatment of soils with complexones and to carry out additional introduction of biophilic elements into complex compounds. The possibility of using electromechanical treatment for removing heavy metals from soils after a preliminary increase in the mobility of ions by acidification and the use of complexation reactions is shown. The experiments were carried out on the plants of sowing oat Avena sativa L. variety Yakov when grown in laboratory conditions on sod-podzolic soil with the introduction of soluble salts of heavy metals into the soil. It was noted that the largest amount of heavy metals is concentrated in the root system of plants. When growing oats in the field, the concentration of metals in the grain was assessed: Mn - 30-35 ppm, Fe - 55-65 ppm, Cu - 4-5 ppm, Zn - 30-35 ppm, Cd, Pb < 3 ppm.

Analytical Solutions for the Injection of Wettability Modifiers in Carbonate Reservoirs Based on a Reduced Surface Complexation Model

The potential of tuned-composition waterflooding to enhance oil recovery from carbonate reservoirs has been widely investigated in the literature. The consensus is that wettability alteration occurs because of the electrostatic interactions between the carbonate rock surface and the potential determining ions, Ca2+, Mg2+, CO32−, and SO42−. Recently, glycine, the simplest amino acid, has also been investigated as a wettability modifier for carbonates that acts similarly as the sulfate ions in brine. The impact of wettability modifiers like glycine and calcite's potential determining ions has been described by surface complexation models (SCM) and the wetting-state of the rock has been related to change of the surface potential. However, determining the relevance of the geochemical reactions is obstructed by the complexity of the SCM. Moreover, the surface potential as a surrogate of the wetting-state of the rock does not correlate with the experimental results with glycine reported in the literature. The present research analyzed the results of single-phase displacement using a SCM for calcite to determine the important surface complexation reactions. Then, wettability alteration is modeled as a set of anion exchange reactions between wettability modifiers, like SO42− and Gly−, and adsorbed carboxylic acids. Finally, analytical solutions are presented for the coupled two-phase and multicomponent reactive-transport model with anion exchange reactions.