Liquid elutriator

A bed, containing particles of different sizes, behaves in a similar manner to a mixture of liquids of different volatilities. Thus the finer particles, when associated with the fluidising medium, correspond to the lower boiling liquid and are more readily elutriated and the rate of their removal from the system and the degree of separation are affected by the height of the reflux column. A law analogous to Henry s Law for the solubility of gases... 

Measurements of binary vapor-liquid equilibria can be expressed in terms of activity coefficients, and then correlated by the Wilson or other suitable equation. Data on all possible pairs of components can be combined to represent the vapor-liquid behavior of the complete mixture. For exploratory purposes, several rapid experimental techniques are applicable. For example, differential ebulliometry can obtain data for several systems in one laboratory day, from which infinite dilution activity coefficients can be calculated and then used to evaluate the parameters of correlating equations. Chromatography also is a well-developed rapid technique for vapor-liquid equilibrium measurement of extractive distillation systems. The low-boiling solvent is deposited on an inert carrier to serve as the adsorbent. The mathematics is known from which the relative volatility of a pair of substances can be calculated from the effluent trace of the elutriated stream. Some of the literature of these two techniques is cited by Walas (1985, pp. 216-217). 

ELUTRIATION. The separation of solids hy the action of water or other liquids hence, also the washing of a solid by decantation or a related process. 

Although this chapter focuses on applications with effluent wastewaters, all types of aquatic environmental media (freshwater, brackish, marine) can be appraised with the pT-scale procedure. Testing of liquid samples is virtually unlimited and can include untreated and treated wastewater, surface water, ground water, porewater, elutriates and organic extracts of sediments. Applications could also be extended to assess toxicity of particle-bound substances in suspended matter and sediments. In this case, sample dilutions can be made with reference sediment material (Hoss and Krebs, 2003). The pT-method can also capture the effects of both soluble and particulate toxicity in a sample, provided that appropriate bioassays are employed. 

The general objective, principle, and scope of application of the pT-method are succinctly described in Section 1 and also reported elsewhere in this book (see Chapter 3 of this volume, Section 5.1), where readers will appreciate that this hazard assessment scheme is adaptable to both liquid and solid media. Briefly recalled here in the context of solid-media samples such as dredged material, the pT-value, which relates to a single bioassay, and the pT-index, derived from the most sensitive organism in a test battery, permit a numerical classification of environmental samples on the basis of ecotoxicological principles. Sediment from any aquatic ecosystem (freshwater, brackish, marine) and from any of its phases (whole sediment, porewaters, elutriates or organic extracts) can be appraised provided that the proper standardized toxicity tests are available. There are whole-sediment test protocols standardized for many agencies (e.g., Environment Canada, ASTM). 

As more bioassays for assessment of the liquid (porewater, elutriate) and solid (whole sediment) compartments of sediments reach standardization, future investigations will, however, have to determine their performance and adequacy. While the present battery employed in the work presented herein is undeniably useful, it may yet be optimized with other liquid-phase tests and likely be supplemented with direct-contact bioassays capable of estimating the toxic potential of contaminants more closely bound to sediments. 

Bioassay using a biological system which measures toxic effects of the liquid/aquatic phase of a test material (e.g., porewater, elutriate, leachate) and determines a response (e.g., acute and/or chronic toxicity). See also Solid-phase (toxicity) test. Volume 1(2), Volume 2(9). 

These methods fall into two general classifications those using a liquid sedimentation technique, and those employing an air elutriation system. 

The third, (c), is clear liquid overflow recycling to an elutriating leg which prevents undersized particles from escaping prematurely. Draft tube baffle (DTB) crystallizers contain elutriation legs, but DTB units are more commonly evaporative rather than cooling crystallizers. 

Evidence that most of the soil organic matter occurs in association with clay has come from studies where unbound organic matter, consisting of free humic and nonhumic substances plus undecayed or partially modified plant remains, is removed by flotation in a liquid of density intermediate between the free material and the clay-organic complex (see Greenland, 1965b). Solutions of density between 1.8 and 2.0 have been used, such as a benzene-bromoform mixture. Elutriation and sieving methods have also been applied. 

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