Adsorption precipitation

Flux Decline Plugging, Fouling, Polarization Membranes operated in NFF mode tend to show a steady flux decline while those operated in TFF mode tend to show a more stable flux after a short initial decline. Irreversible flux decline can occur by membrane compression or retentate channel spacers blinding off the membrane. Flux decline by fouling mechanisms (molecular adsorption, precipitation on the membrane surface, entrapment within the membrane structure) are amenable to chemical cleaning between batches. Flux decline amenable to mechanical disturbance (such as TFF operation) includes the formation of a secondary structure on the membrane surface such as a static cake or a fluid region of high component concentration called a polarization layer. 

Table 20.5 also indicates whether a process is biotic (mediated or initiated by organisms in the environment), abiotic (not involving biological mediation), or both. Biotic processes are limited to environmental conditions that favor growth of mediating organisms. Abiotic processes occur under a wide range of conditions. Adsorption, precipitation, complexation, and neutralization are abiotic all other processes in Table 20.5 may be either. 

The coefficient actually measures multiple processes (reversible and irreversible adsorption, precipitation, and coprecipitation). Consequently, it is a purely empirical number with no theoretical basis on which to predict adsorption under differing environmental conditions or to give information on the types of bonding mechanisms involved. 

Another full-scale process combines catalytic oxidation including biodegradation, adsorption, precipitation/flocculation, and reverse osmosis [120]. 

In some cases (particularly reactive dyes) dyes can pass the aerobic, anaerobic degradation step and colored water is observed at the end of the treatment. In such cases a special treatment of the colored wastewater (reduction, adsorption, precipitation) has to be introduced [105,134-137]. In the presence of low concentrations of organic compounds, ozonation can be used as a final polishing step. 

The fate of heavy metals in aquatic systems depends on partitioning between soluble and partieulate solid phases. Adsorption, precipitation, coprecipitation, and complexation are processes that affect partitioning. These same processes, which are influenced by pH, redox potential, the ionic strength of the water, the concentration of complexing ions, and the metal concentration and type, affect the adsorption of heavy metals to soil (Richter and Theis 1980). 

The effect of using mixtures of surfactants on micelle formation, monolayer formation, solubilization, adsorption, precipitation, and cloud point phenomena is discussed. Mechanisms of surfactant interaction and some models useful in describing these phenomena are outlined. The use of surfactant mixtures to solve technological problems is also considered. 

Preparation of stabilized highly dispersed colloidal platinum, that is, Pt particles of from 1 to 10 nm size in aqueous solution by chemical reduction followed by adsorptive precipitation of the dispersed Pt particles on the outer and inner surface of soot particles. 

Flocculation Adsorption, precipitation, formation of complexes Decolorization, elimination of organic carbon... 

The last term (Sq/dt) is an implicit reaction term expressing the unknown rate law. This term is written so that it is applicable to ion exchange, specific adsorption, precipitation or an enzyme-catalyzed reaction. This is possible since Eq. (3.2) represents a single equation in two unknowns (Skopp and McAllister, 1986). 

The processes of adsorption, precipitation and coprecipitation are difficult to distinguish on that basis from the analysis of the diminution of the ions from the solution, changes of pH and kinetics. Only the spectroscopic investigations of the molecular interactions between adsorbent and adsorbate may help to distinguish a type of the process [146,147]. As an adsorption of the ions, is assumed process of the two-dimensional structure formation, whereas for three-dimensional structures precipitation or surface precipitation takes place. From this reason an AFM method may be useful at investigations of the morphology changes of the adsorbate surface [147]. 

Heterogeneous or homogeneous immunoassays Certain assays require an additional method to remove unbound label (also termed free label) leaving bound label, and for a given assay these labelled components are either antibody or antigen, but not both. These assays are called heterogeneous assays, and common methods of separation include adsorption, precipitation, or commonly the use of a solid phase. In contrast, homogeneous assays do not require the removal of... 

Sorption refers to the acquisition of a chemical species from the aqueous phase by a contiguous solid phase. The three principal sorption mechanisms are adsorption, precipitation, and absorption (or incorporation). 

Radiochemical purification of the induced activity in the presence of carrier involves chemical operations such as precipitation, distillation, solvent extraction, chromatography, and ion exchange. While the chemistry performed on the carrier and sample should be designed to isolate the material in a pure state, a useful operation frequently carried out is scavenging. Strongly adsorptive precipitates such as ferric hydroxide, lanthanum fluoride, and antimony sulfide may be formed in the solution. These precipitates, by coprecipitation, occlusion, and surface adsorption can be used to remove unwanted traces of activity. A scavenging agent should be chosen that wdll not carry down appreciable amounts of the carrier from solution. An alternative method is to add hold-back carriers for the unwanted traces of activity and precipitate the required element in their presence. 

The techniques that have been used to determine the approximate molecular weights of humic materials are often those used to study biological macromolecules. Such techniques are often prone to artifacts arising from adsorption, precipitation, and degradation. Many of the methods suffer from one common problem, the lack of appropriate standards. Only colligative properties are free of this problem however, they yield number-averaged molecular weight, with no indication of the polydispersity of the humic material. 

Figure 7. A log-log plot of a sorption isotherm, with an inflection indicating the transition from adsorption to surface precipitation processes. On the right, illustrative Fourier transformed EXAFS spectra for the adsorbate (solid curve) are compared with that for a precipitate (dotted curve) to show the adsorption — precipitation transition. Data are from Charlet and Manceau (48) for Cr(III) sorbed on hydrous ferric oxide.

A preparation method of highly effective methane to formaldehyde selective oxidation (MPO) FeOx/SiOa catalysts, based on "adsorption-precipitation" of Fe" ions under controlled conditions (ADS/PRC), is reported. The performance of ADS/PRC catalysts in the MPO reaction at 650°C has been compared with that of conventional systems prepared by the "incipient wetness" of silica carriers with aqueous solutions of Fe (INC/WET). The ADS/PRC method, enabling a higher dispersion of the active phase, provides very effective MPO catalysts featuring CH4 turnover frequency (TOF) and HCHO productivity (STYhcho) values larger than those of the counterpart INC/WET systems. 

Therefore, this contribution is aimed at providing basic evidences into the suitability of the preparation method based on the adsorption-precipitation of Fe" precursors to attain highly dispersed FeOx/SiOa systems featuring a superior catalytic performance in MPO. 

Theoretical basis to Fe" adsorption-precipitation" preparation route... 

Then, the "adsorption-precipitation" of Fe ions (ADS/PRC) in aqueous solutions, under N2 atmosphere and controlled pH conditions [13], has been exploited to attain a higher dispersion of MPO FeOx/Si02 catalysts [7,11], Such a preparation route, preventing the formation of insoluble hydroxides (Kps Fe(OH)2, 1.8-10 ) also at high pH values (pH>6), allows for a progressive interaction of the negatively polarised silica support surface with... 

A versatile preparation method of effective FeOx/SiOz catalysts via the adsorption-precipitation (ADS/PRC) of Fe precursors from aqueous solution is outlined. 

Internal pore fouling This is caused by the deposition of material inside the porous structure which often leads to significant flux decline and irreversible fouling. Internal pore fouling can be due to adsorption, precipitation, pore plugging or particle adhesion. 

Ion Exchange Sites Surface adsorption Precipitated (CO3, S. OH) Co.ppted. amorphous hydrous oxides) Co-ordinated to organics Occluded (crystalline hydrous oxides) Lattice component (mineral)... 

Biologically treated water contains considerable quantities of mineral nutrients which, because of ever increasing eutrophization will have to be disposed in the future as well. At present, the third stage is not much applied (particularly because the costs increases by 50%), but from the experimental viewpoint it has already been quite well elaborated. From industrial waters, first of all phosphorus has to be eliminated, and then, to a lesser extent, the nitrogenous compounds [1-3]. Physico-chemical methods of treatment have been successfully developed, for example, by adsorption, precipitation or the use of ion exchangers studies involving the biological elimination of nutrients are so far rather scarce. 

The oxidation of Cr(lll) to Cr(Vl) has been reported in the water column overlying reduced sediment by Masscheleyn et al. (1992). Adsorption/precipitation reaction was slow enough to deter increase in Cr(Vl) in the water column spiked with 1 and 10 mg L Cr(lll). In this study, the majority of the Cr(lll) initially added to the water column was precipitated, but some remained in solution as Cr(lll)-organic ligand complex. The observed oxidation was as rapid with 12 and 57% of the 1 and 10 mg L added Cr(lll) being oxidized within 24 h. After 1 day, the Cr oxidation rate was exceeded by Cr(Vl) removal (adsorptive difference). Table 12.4 depicts the quantities of Cr(Vl) measured with time. 

The S system is one of the main systems for regulating sedimentary redox processes. It participates in a series of diagenesis such as complexation, exchange adsorption, precipitation. The existing forms of S are regulated by environmental pE and pH. S in the East China Sea sediment interstitial waters mainly exists in the form of SO , it amounts to 99% of total S, HS amounts to only 1% of total S, the others are a little H2S, S , etc. Sulfate is reduced to sulfide through microbial processes in anoxic circumstances. SO / HS (S°) is one of the main redox electrode pairs which regulate marine environments. 

Methods of coacervation, physical adsorption, precipitation by a nonsolvent or solvent evaporation are used for microencapsulation. A developed surface may be prepared by removing solvent from a vitrified polymer by sublimation at low temperature under vacuum. 

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