Sorption processes, contaminated

Manganese (IV) oxide enjoys numerous applications in modem technologies. The most widely known areas of its usage are sorption processes one could recall that co-precipitation of contaminating cations with manganese oxide is still employed as part of the in-tank precipitation in processes of treatment of supernatant wastes at high concentration. Furthermore, co-precipitation data are usually used as benchmark results in studies of novel sorbents for strontium [4],... 

LDHs are also promising materials as sorbents for anionic organic contaminants via both ion-exchange and reconstruction reactions. There have been a large number of reports of the use of LDHs for removal of species such as aromatic carboxylic acids, phenols, pesticides, and humic or fulvic acids. Recently, Cardoso et al. [152] found that the sorption process of terephthalate anions from aqueous solutions by calcined Mg/Al - CO3 LDHs takes place by reconstruction of the LDHs and involves the intercalation and adsorption of terephthalate anions. Calcined Mg/Al - CO3 LDHs were found to be capable of removing 40 to 85 % of the benzoate from solutions in the concentration... 

The sorption process generally is studied by plotting the equilibrium concentration of a compound on the adsorbent, as a function of equilibrium concentration in the gas or solution at a given temperature. Adsorption isotherms are graphs obtained by plotting measured adsorption data against the concentration value of the adsorbate. Several mechanisms may be involved in the retention of contaminants on... 

We begin with a discussion of the most common minerals present in Earth s crust, soils, and troposphere, as well as some less common minerals that contain common environmental contaminants. Following this is (1) a discussion of the nature of environmentally important solid surfaces before and after reaction with aqueous solutions, including their charging behavior as a function of solution pH (2) the nature of the electrical double layer and how it is altered by changes in the type of solid present and the ionic strength and pH of the solution in contact with the solid and (3) dissolution, precipitation, and sorption processes relevant to environmental interfacial chemistry. We finish with a discussion of some of the factors affecting chemical reactivity at mineral/aqueous solution interfaces. 

Many processes are operative in the environment that contribute to the regional elimination of a contaminant by altering its distribution. Contaminants with sufficiently high vapor pressure can evaporate from contaminated terrestrial or aquatic compartments and be transferred through the atmosphere to new locations. Such processes of global distillation are considered largely responsible for the worldwide distribution of relatively volatile organochlorine pesticides such as lindane and hexachlorobenzene. Entrainment by wind and upper atmospheric currents of contaminant particles or dust onto which the contaminants are sorbed also contribute to contaminant redistribution. Sorption of contaminant to suspended solids in an aquatic environment with commensurate sedimentation can result with the removal of contaminants from the water... 

Sorption is the process where a sorbate binds to a sorbent. In this discussion, the sorbate is the organic contaminant and the sorbent is the aquifer solid. Sorption has a large impact on the rate at which a contaminant is transported, as well as on its ultimate fate. Since sorbed contaminant is immobile, the sorption process retards contaminant transport. Also, since sorbed contaminant is frequently assumed to be unavailable for microbial degradation [5-7], sorption slows the rate at which a contaminant is biodegraded in the subsurface. 

Sometimes propane from natural gas and refinery operations becomes contaminated with carbonyl sulphide (COS) which is not removed in acid gas plants. Alternative approaches to removing COS from liquid propane by sorption processes have been compared by Wilson et al ... 

A modular pilot size plant involving coagulation/flocculation, centrifugation, ultrafiltration, and sorption processes was designed and constmeted by Benito et al. [13] for the treatment of oily wastewaters. Empirical equations developed by Shaalan [65] predict the impact of water contaminants on flux decline. These formulae enable decision-making concerning a suitable water pretreatment scheme and also selection of the most appropriate cleaning cycle. 

Composite Sorption Magnitude and Isotherm Nonlinearity. Accurate assessment of the extent to which the global isotherm for a system is nonlinear is important for accurate portrayal of sorption processes in that system. From a practical point of view, the extrapolation of linear approximations of weakly nonlinear or near-linear sorption isotherms to concentration ranges beyond which they are valid can result in significant errors in projections of contaminant fate and transport (1). From a conceptual point of view, observations of isotherm nonlinearity over specific concentration ranges may be employed in conjunction with models such as the DRM to probe and evaluate the extent to which multiple sorption mechanisms are operative in a particular system. 

Sorption in natural systems may result from a variety of local processes involving different reaction mechanisms. The extent to which such individual reactions must be considered depends on the accuracy with which the overall sorption process must be characterized, particularly with respect to whether alternative sorption mechanisms will be important determinants of the environmental behavior, transport, and fate of contaminants in a given system. 

Specific adsorption on well defined materials has been the subject of many reviews [8-13]. Specific adsorption plays a key role in transport of nutrients and contaminants in the natural environment, and many studies with natural, complex, and ill defined materials have been carried out. Specific adsorption of ions by soils and other materials was reviewed by Barrow [14,15]. The components of complex mineral assemblies can differ in specific surface area and in affinity to certain solutes by many orders of magnitude. For example, in soils and rocks, (hydr)oxides of Fe(IH) and Mn(IV) are the main scavengers of metal cations and certain anions, even when their concentration expressed as mass fraction is very low. Traces of Ti02 present as impurities are responsible for the enhanced uptake of U by some natural kaolinites. In general, complex materials whose chemical composition seems very similar can substantially differ in their sorption properties due to different nature and concentration of impurities , which are dispersed in a relatively inert matrix, and which play a crucial role in the sorption process. In this respect the significance of parameters characterizing overall sorption properties of complex materials is limited. On the other hand the assessment of the contributions of particular components of a complex material to the overall sorption properties would be very tedious. 

Therefore, microbial degradation contributed only to a minor extent to the concentration profile of 1-chloronaphthalene observed in the aquifer. Consequently, the significant attenuation of 1-chloronaphthalene levels observed within a few meters from the point source has to be attributed mainly to sorption processes. For the polycyclic aromatic contaminants a similar environmental behaviour can be assumed (Stupp and Puttmann, 2001). 

Eor most organic pollutants the key mechanism of NA is mass reduction by microbial decomposition. Most inorganic pollutants cannot be reduced in mass and are mainly attenuated by sorption processes. For this group of contaminants, NA aims at a reten-... 

Phosphates — if of organic origin — have an important indicator value as the soil complex retains them strongly by both sorption processes and chemical reactions. Phosphates of inorganic origin (e.g. industrial fertilizers, corrosion inhibitors), or those which were formed by plant degradation are not significant as indicators of faecal contamination [27-32]. 

The paper summarizes eiforts started to deliver a profound chemical base for risk assessment, namely to properly take into account the physico-chemical phenomena governing the contamination source term development in time and space. One major aspect there is the substitution of conventional distribution coefficients (IQ values) for the empirical description of sorption processes by surface complexation models, in combination with other thermodynamic concepts. Thus, the framework of a Smart Kd is developed for complex scenarios with a detailed explanation of the underl3dng assumptions and theories. It helps to identify essential processes and the associated most critical parameters, easing further refinement studies. The presented case studies cover a broad spectrum of contamination cases and successfully demonstrate the applicability of the methodology. The necessity to create a mineral-specific sorption database to support the Smart IQ approach is derived and a first prototype for such a digital database introduced, combining numeric data with a knowledge base about the relevant theories, experimental methods, and structural information. 

Sorption processes are the general category of heterogeneous reactions whereby free chemical species become associated in some manner with a surface. The field of sorptive geochemistry has mushroomed in the last several years largely because of the desire of scientists and engineers to study the mobility and fate of contaminants in the environment. 

Sorption processes appear to be of only minor significance in the attenuation of organics, where adsorption of organic compounds occurs primarily on particulate organic matter in sediments (Cherry et al, 1984). The structure and effective surface area of the organic matter are therefore significant variables in the retardation of organic contaminants. Of equal importance is the hydrophobicity of the contaminant. 

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