Purification coefficient

The effectiveness of the solution purification from impurities is characterised by the purification coefficient (factor) [20,23,49]... 

Eqs. (10.45) and (10.46) are of little use for determining the limiting values of the purification coefficient, since at low surfactant concentrations foam stability dramatically decreases, and the foam layers containing the adsorbed product have no time to separate from the solution. For this reason determination of the minimum residual surfactant concentration, necessary to obtain a stable foam provides precise information on the purification coefficient. The minimum residual concentration is closed to that for the formation of black spots (cbi) in microscopic foam films, in case they form (cLR = cs,r = cbi) [24]... 

The module operation efficiency is determined on the one hand, by selectivity of membrane elements and sorption characteristics of ion-exchangers and on the other hand, by physico-chemical and radionuclide composition, concentration of suspended particles, salts and radionuclide activity levels. The integral decontamination-purification coefficients Kpurj t, depending on LRW radionuclide, physical and chemical composition, vary within 10 - 10 . Depending on composition of initial LRW and in compliance with on-line control data, MMSF can operate either imder the full-cycle mode involving all basic modules or imder reduced-cycle mode using only some of modules. 

Refractories. Its low coefficient of expansion, high thermal conductivity, and general chemical and physical stabihty make sihcon carbide a valuable material for refractory use. Suitable apphcations for sihcon carbide refractory shapes include boiler furnace walls, checker bricks, mufflers, kiln furniture, furnace skid rails, trays for zinc purification plants, etc (see Refractories). 

FIG. 23-27 CO, in potassium carbonate solutions (<2) equilibrium in 20% solution, (h) mass-transfer coefficients in 40% solutions. (Data cited hy Kohl and Riesenfeld, Gas Purification, Gulf Fuhlishing, 1985.)... 

The most common method of purification of inorganic species is by recrystallisation, usually from water. However, especially with salts of weak acids or of cations other than the alkaline and alkaline earth metals, care must be taken to minimise the effect of hydrolysis. This can be achieved, for example, by recrystallising acetates in the presence of dilute acetic acid. Nevertheless, there are many inorganic chemicals that are too insoluble or are hydrolysed by water so that no general purification method can be given. It is convenient that many inorganic substances have large temperature coefficients for their solubility in water, but in other cases recrystallisation is still possible by partial solvent evaporation. 

The development and adaptation of procedures for the separation, isolation, purification, identification, and analysis of the components of the pyrethrum mixture have been studied and evaluated. Results of studies to determine the molar extinction coefficient of pyrethrin I as well as a gas chromatographic procedure for the determination of pyrethrins are reported. The use of chromatographic separation procedures (including partition, adsorption, gas, and thin-layer chromatography), colorimetry, and infrared spectrophotometry are discussed. 

Atmospheric sensitivity renders the preparation of ultrapure samples difficult. Nevertheless, vacuum distillation ", ultra-high-vacuum reactive distillation " and crystal growth purification methods " are described zone-refining methods have been applied on a limited scale only - , presumably because of the high volatility of the metals and the unfavorable distribution coefficients. 

When a melt-zone is moved through a long crystal, an impurity concentration builds up in the melt zone due to rejection by the crystal as it resolidifies. We can also say that the distribution coefficient favors a purification process, i.e.- k 1. Another reason (at least where metals are concerned) is that a solid-solution between impurity and host ions exists. It has been observed that the following situation, as shown in the following diagram, occurs ... 

Here, we show two cases for impurity segregation between melt and crystal as it grows in time. Note that an initial purification occurs in both cases but the distribution coefficient for the case on the right is such that the amount of impurity actually incorporated into the crystal, ki Cq. 

This illustrates the fact that impurity segregation and purification processes are dependent upon the type of impurity involved and its individual segregation coeffleient. As we illustrated above in 6.8.1., the problem is that the impurity is initially rejected from the solid, but its concentration builds up in front of the growing OTStal. The segregation coefficient, k,, then operates on that increased concentration and the product, ki Co. increases. 

The effect of irradiation on the extractability of sulfoxides towards plutonium, uranium and some fission products were studied by Subramanian and coworkers . They studied mainly the effect of irradiation on dihexyl sulfoxide (DHSO) and found that irradiation did not change the distribution coefficient for Ru, Eu and Ce but increases the distribution coefficient for Zr and Pu. When comparing DHSO and tributyl phosphate (TBP), the usual solvent for the recovery and purification of plutonium and uranium from spent nuclear fuels, the effect of irradiation to deteriorate the extraction capability is much larger in TBP. Lan and coworkers studied diphenyl sulfoxides as protectors for the gamma radiolysis of TBP. It was found that diphenyl sulfoxide can accept energy from two different kinds of excited TBP and thus inhibits the decomposition of the latter. 

One of the first bed materials was based on the extractant diamyl amylphosphonate (DAAP marketed under the name U-TEVA-Spec ) and was designed for purification of the tetravalent actinides (U (IV), Th (IV), Pu (IV)) and hexavalent uranium (U(VI)). This material is characterized by high (>10-100) distribution coefficients for U and Th in significant (>3 M) concentrations of both nitric and hydrochloric acids, and so is useful for both U and Th purification (Horwitz et al. 1992 Goldstein et al. 1997 Eikenberg et al. 2001a). 

The reaction solution was diluted with 36 mL of water. The unreacted free drug and other low molecular weight materials were removed by a Centriprep-10 concentrator. Purification was repeated until HPLC analysis (Bio-Sil TSK-250) of the product indicated the absence of free drug. The final purified product was lyophilized to afford 483 mg of a yellow solid. This solid product was readily soluble in water or aqueous buffer. The amount of drug covalently bound to MVE was estimated by the absorbance at 303 nm using a molar extinction coefficient of 17.03 x 103. The MVE-y-hy-MTX contains 26% methotrexate-y-hydrazide by weight. 

The achievement of the corresponding monocrystals of sufficient optical and crystalline quality is made possible only after very thorough purification. Chemical impurities are known to disturb the crystal lattice through the occurence of twins, veils dislocations, rounding-off of faces ultimately quenching further growth. Any crystalline defect dramatically increases the residual absorption coefficient and lowers the optical damage threshold. 

Mass transfer coefficients have been obtained in a packed tower with 40% K2C03 (6.8 mols/liter of water) (Kohl Riesenfeld, Gas Purification, p 227, 1985). 

Other references in Table in discuss applications in precipitation of metal.compounds, gaseous reduction of metals from solution, equilibrium of copper in solvent extraction, electrolyte purification and solid-liquid equilibria in concentrated salt solutions. The papers by Cognet and Renon (25) and Vega and Funk (59) stand out as recent studies in which rational approaches have been used for estimating ionic activity coefficients. In general, however, few of the studies are based on the more recent developments in ionic activity coefficients. 

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