1,720,974 research outputs found
A guideline for the identification of environmentally relevant, ionizable organic molecule species
No full textAn increasing number of organic compounds detected today in the aquatic environment are ionizable and, therefore, partially or permanently charged (ionic) under the pH conditions encountered in these systems. For evaluating their environmental behavior, which strongly depends on the charge state, the identification of functional groups together with their correct assignment of the respective acidic or basic dissociation constants (plc) is essential. Despite the growing concern and increasing awareness for ionizable compounds, contradicting and/or confusing information regarding their acid/base properties can be regularly found in the literature, especially when complex structures are encountered. Therefore, we provide a simplified, general, and comprehensive guideline for the identification of ionizable functional groups in organic compounds combined with the correct assignment of their respective pK(a) values. Beside the explicit definition of basic terms, several tables with more than 30 of the most frequently encountered ionizable compound classes, including their typical pK(a) value ranges are the centerpiece of the proposed procedure. The straight forward application of the guideline is successfully shown for several environmentally relevant compounds as example. (C) 2013 Elsevier Ltd. All rights reserved
A framework for assessing the retardation of organic molecules in groundwater: Implications of the species distribution for the sorption-influenced transport
No full textThe pH-dependent molecule speciation (charge state) in solution strongly influences the transport of ionizable organic compounds in the aquatic environment. Therefore, the sorption behavior is complex and reliable predictions only based on physico-chemical sorbate, sorbent and solution properties are challenging. A short overview of underlying sorption processes causing retardation during the solute transport in aquifers is completed by a description of approaches for estimating respective sorption coefficients/retardation factors and discussed together with their limitations. Based on these initial considerations, a systematic framework is proposed, which allows the assessment of transport properties of organic molecule species by their chemical nature (neutral, acidic, basic, ampholytic). As a result, the transport properties of many (ionizable) organic molecules of interest- can be assessed and even first presumptions for the sorption behavior of new and not yet investigated molecules can be derived. (C) 2015 Elsevier B.V. All rights reserved.German Research Foundation (DFG) [LI 1314/3-1, LI 1314/3-2
Temperature determination using thermo-sensitive tracers: Experimental validation in an isothermal column heat exchanger
No full textThe estimation of thermal drawdown and its spatial and temporal evolution is a major challenge in the context of geothermal reservoir management. Column experiments were performed with the aim of assessing the potential of thermo-sensitive tracers to measure prevailing in situ temperatures of the flowed-through medium, The results from 40 isothermal experiments with different residence times and temperatures using thermo-sensitive tracers are presented. The resulting precise temperature estimates were independent of the residence time and measured concentration. Considering pH, an accuracy of up to 1 K was achieved. The underlying theory was successfully verified and the general applicability proven. (C) 2014 Elsevier Ltd. All rights reserved.German Ministry for Environment (BMU) [0325417
Determination of temperatures and cooled fractions by means of hydrolyzable thermo-sensitive tracers
No full textThis work presents the development of improved tracer techniques for monitoring internal temperatures and cooled fractions in water saturated porous media. The analysis is based on reactive chemical compounds whose hydrolysis reactions allow for accurate temperature measurements. The tracers are designed to improve geothermal reservoir management procedures. Thermo-sensitive tracers will provide valuable information about the thermal state of the examined permeable media. This is demonstrated by means of laboratory experiments with sand-packed columns. The special heating/cooling setup provides a defined internal temperature distribution. In 70 independent experiments, tracer sensitivity was examined. Practical limitations in three different experimental schemes, flow-through, moving thermal front and push pull, were investigated. The results show that thermo-sensitive tracers can be used to measure temperatures and cooled fractions with high precision and accuracy. (C) 2015 Elsevier Ltd. All rights reserved.German Ministry for Environment (BMU) [0325417
Sorption of the organic cation metoprolol on silica gel from its aqueous solution considering the competition of inorganic cations
No full textSystematic batch experiments with the organic monovalent cation metoprolol as sorbate and the synthetic material silica gel as sorbent were conducted with the aim of characterizing the sorption of organic cations onto charged surfaces. Sorption isotherms for metoprolol (>99% protonated in the tested pH of around 6) in competition with mono- and divalent inorganic cations (Na+, NH4+, Ca2+, and Mg2+) were determined in order to assess their influence on cation exchange processes and to identify the role of further sorptive interactions. The obtained sorption isotherms could be described well by an exponential function (Freundlich isotherm model) with consistent exponents (about 0.8). In general, a decreasing sorption of metoprolol with increasing concentrations in inorganic cations was observed. Competing ions of the same valence showed similar effects. A significant sorption affinity of metoprolol with ion type dependent Freundlich coefficients K-F,K-0.77 between 234.42 and 426.58 (L/kg)(0.77) could still be observed even at very high concentrations of competing inorganic cations. Additional column experiments confirm this behavior, which suggests the existence of further relevant interactions beside cation exchange. In subsequent batch experiments, the influence of mixtures with more than one competing ion and the effect of a reduced negative surface charge at a pH below the point of zero charge (pH(PZC) approximate to 2.5) were also investigated. Finally, the study demonstrates that cation exchange is the most relevant but not the sole mechanism for the sorption of metoprolol on silica gel. (C) 2014 Elsevier Ltd. All rights reserved
Sorption influenced transport of ionizable pharmaceuticals onto a natural sandy aquifer sediment at different pH
No full textThe pH-dependent transport of eight selected ionizable pharmaceuticals was investigated by using saturated column experiments. Seventy-eight different breakthrough curves on a natural sandy aquifer material were produced and compared for three different pH levels at otherwise constant conditions. The experimentally obtained K-OC data were compared with calculated K-OC values derived from two different log K-OW-log K-OC correlation approaches. A significant pH-dependence on sorption was observed for all compounds with pK(a) in the considered pH range. Strong retardation was measured for several compounds despite their hydrophilic character. Besides an overall underestimation of K-OC, the comparison between calculated and measured values only yields meaningful results for the acidic and neutral compounds. Basic compounds retarded much stronger than expected, particularly at low pH when their cationic species dominated. This is caused by additional ionic interactions, such as cation exchange processes, which are insufficiently considered in the applied K-OC correlations. (C) 2011 Elsevier Ltd. All rights reserved.European Commission [518118-1
Role of cation exchange processes on the sorption influenced transport of cationic beta-blockers in aquifer sediments
No full textThe influence of cation exchange processes on the transport behavior of the cationic beta-blockers atenolol and metoprolol was investigated by applying saturated laboratory column experiments. Breakthrough curves using natural sediments under different competitive conditions were generated and resulting sorption coefficients were compared. For the cationic species of atenolol (at pH = 8), the existence and dominating role of cation exchange processes were demonstrated by varying calcium concentrations. No effect of atenolol concentration on its retardation was observed within a wide concentration range. The breakthrough curve comparison of atenolol and the more hydrophobic metoprolol under constant conditions showed a significantly stronger retardation for metoprolol than for atenolol. However, additional non-polar interactions cannot explain the observed differences as they are determined to be negligible for both compounds. Due to the dominating role of cation exchange processes for the cationic species on overall sorption, a simple prediction of beta-blocker transport in the subsurface by using K-OC values derived from log K-OW-log K-OC correlations is not feasible. (C) 2012 Elsevier Ltd. All rights reserved
A new generation of tracers for the characterization of interfacial areas during supercritical carbon dioxide injections into deep saline aquifers: Kinetic interface-sensitive tracers (KIS tracer)
No full textThe storage of supercritical carbon dioxide in deep saline aquifers requires new techniques to assess plume spreading, storage efficiencies and operational strategies after and during injections. In this work, a new class of reactive tracers (KIS tracers) planned to be used for the characterization of interfacial areas between supercritical CO2 and formation brine is presented. The implementation of a time-dependent hydrolysis reaction at the interface enables to investigate the development of the CO2/brine interface. Besides the basic concept for these novel tracers and the methodology for a suitable target molecular design, the desired tracer properties as well as the exemplary synthesis of first promising compounds are presented here. Additionally, the first experimental results of an analog study in a static two-phase batch system are shown and evaluated with a newly developed macroscopic model. Subsequently, the numerical forward modeling of different functions for the interfacial area change is described. The first results are promising and show the potential for new applications of KIS tracers after further research
Sorption of cationic organic substances onto synthetic oxides: Evaluation of sorbent parameters as possible predictors
No full textSorption of organic cations onto silica surfaces over a wide concentration range of competing electrolytes
No full textThe fundamental understanding of organic cation-solid phase interactions is essential for improved predictions of the transport and ultimate environmental fates of widely used substances (e.g., pharmaceutical compounds) in the aquatic environment. We report sorption experiments of two cationic model compounds using two silica gels and a natural aquifer sediment. The sorbents were extensively characterized and the results of surface titrations under various background electrolyte concentrations were discussed. The salt dependency of sorption was systematically studied in batch experiments over a wide concentration range (five orders of magnitude) of inorganic ions in order to examine the influence of increasing competition on the sorption of organic cations. The organic cation uptake followed the Freundlich isotherm model and the sorption capacity decreases with an increase in the electrolyte concentration due to the underlying cation exchange processes. However, the sorption recovers considerably at high ionic strength (I> 1 M). To our knowledge, this effect has not been observed before and appears to be independent from the sorbent characteristics and sorbate structure. Furthermore, the recovery of sorption was attributed to specific, non-ionic interactions and a connection between the sorption coefficient and activity coefficient of the medium is presumed. Eventually, the reasons for the differing sorption affinities of both sorbates are discussed. (C) 2016 Elsevier Inc. All rights reserved
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