Batch equilibration

Although SPE can be done in a batch equilibration similar to that used in LLE, it is much more common to use a small tube (minicolumn) or cartridge packed with the solid particles. SPE is often referred to as LSE, bonded phase or sorbent extraction SPE is a refinement of open-column chromatography. The mechanisms of retention include reversed phase, normal phase, and ion exchange. 

We have found that similar behavior occurs when the column is packed with other salts of Group I elements, such as NaSbF Na AlF, or NiF, or with Nafion ion-exchange resins (H or K forms). In batch equilibration experiments, using 1 g amounts of solids stirred with 5-15 ml volumes of solutions, we have found that the radon ions can also be collected on the compounds CsBrF, Ca(BrF )2, and Ba(BrF )2. Thus it is apparent that, in its oxidized state, radon can displace H, Na, K, Cs, Caz, and Baz ions from a number of solid materials. 

A review of the commonly used experimental methods for solubility determinations is presented in Table 1. Briefly, batch equilibration is the conventional method of preparing saturated solutions for solubility determinations, where an excess amount of solute chemical is added to water and equilibrium is achieved... 

Table II. Activities of Principal Radionuclides Remaining in High-Level Waste After One Batch Equilibration...

The general procedure for the batch equilibration experiments was as follows. About 0.25 to 0.55 grams of clay and 45 to 70 ml of 0.68 N NaCl solution were added to a 125-ml polyethylene bottle, Next 2.5 ml of a 0.68 N NaCl solution, buffered with predetermined amounts of sodium bicarbonate and/or boric acid, were added, (in order to obtain data at low values of the solution pH, addition... 

Distribution Coefficient. Distribution coefficients were determined using conventional batch equilibrations, in which a known amount of clay is contacted with a known volume of solution and shaken until equilibrium is essentially reached, at least overnight at room temperature. In tests with several ions and montmorillonite, equilibrium was reached in less than two hours. 

Procedures. Batch equilibrations of interbed solids (Mabton Interbed, Rattlesnake Ridge sandstone, or tuff), tracers, and groundwaters were used to measure radionuclide distributions between solid and liquid phases. Triplicate measurements were made for each combination of temperature, redox condition, tracer concentration, tracer type, groundwater composition, and interbed sample. Constant temperatures were maintained by placing the... 

Batch equilibration with exchanger resin Collects ion of interest over an extended time... 

Under this umbrella, a number of different applications lie, amongst others the batch equilibration and equilibrium soil solution methods. According to the USEPA (1999), the former represents the most common laboratory method for determining partition coefficients—normally defined as Kd—both for contaminated sites studies and for predictions of chemicals behaviour in soils (OECD, 2002). The batch equilibration method consists of mixing a soil with a known amount of liquid (background electrolyte), which is then shaken into a slurry and allowed to equilibrate for an adequate time. The solution will be separated from the solids by centrifuging the slurry, resulting in a supernatant and a separated solid phase. The supernatant will, therefore, be removed, filtered and analysed. 

As was mentioned before, Arey et al. [19] conducted batch equilibration experiments to evaluate the ability of hydroxyapatite to remove uranium from contaminated sediments at the Savannah River Site of DOE and showed that removal of U was due to secondary phosphate minerals that had solubility even lower than autunite (Ca(U02)2(P04)2- IOH2O). The authors suggest formation of Al/Fe secondary phosphate. A similar conclusion was reached by Fuller et al. [20], who showed that uranyl ions can be removed by using hydroxyapatite. 

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